Our financial instruments consist primarily of cash and cash equivalents, certificates of deposit, accounts receivable, commodity contracts, accounts payable, debt, and interest rate swaps. The carrying amount of cash and cash equivalents, certificates of deposit, accounts receivable, accounts payable, and current debt approximates their fair value because of the short-term maturity of these instruments.  Included in accounts receivable is $31.8$46.2 million and $31.9 million of factoring receivables we have purchased under factoring arrangements at March 31,September 30, 2018 and December 31, 2017, respectively, net of a $0.4 million and $0.2 million allowance for bad debt for each respective date. We advance approximately 85% to 95% of each receivable factored and retain the remainder as collateral for collection issues that might arise.  The retained amounts are returned to the clients after the related receivable has been collected, net of accrued interest. At March 31,September 30, 2018 and December 31, 2017, the retained amounts related to factored receivables totaled $0.5$2.4 million and $0.6 million, respectively, and were included in accounts payable in the condensed consolidated balance sheets.  Our clients are smaller trucking companies that factor their receivables to us for a fee to facilitate faster cash flow.  We evaluate each client's customer base under predefined criteria.  The carrying value of the factored receivables approximates the fair value, as the receivables are generally repaid directly to us by the client's customer within 30-40 days due to the combination of the short-term nature of the financing transaction and the underlying quality of the receivables.

Interest rates that are currently available to us for issuance of long-term debt with similar terms and remaining maturities are used to estimate the fair value of our long-term debt, which primarily consists of revenue equipment installment notes.  The fair value of our revenue equipment installment notes approximated the carrying value at March 31,September 30, 2018, as the weighted average interest rate on these notes approximates the market rate for similar debt. Borrowings under our revolving Credit Facility (as defined herein) approximate fair value due to the variable interest rate on that facility.  Additionally, commodity contracts, which are accounted for as hedge derivatives, as discussed in Note 6, are valued based on the forward rate of the specific indices upon which the contract is being settled and adjusted for counterparty credit risk using available market information and valuation methodologies. The fair value of our interest rate swap agreements is determined using the market-standard methodology of netting the discounted future fixed-cash payments and the discounted expected variable-cash receipts. The variable-cash receipts are based on an expectation of future interest rates (forward curves) derived from observable market interest rate curves. These analyses reflect the contractual terms of the swap, including the period to maturity and use observable market-based inputs, including interest rate curves and implied volatilities. The fair value calculation also includes an amount for risk of non-performance of our counterparties using "significant unobservable inputs" such as estimates of current credit spreads to evaluate the likelihood of default, which we have determined to be insignificant to the overall fair value of our interest rate swap agreements.

We engage in activities that expose us to market risks, including the effects of changes in fuel prices and in interest rates.  Financial exposures are evaluated as an integral part of our risk management program, which seeks, from time-to-time, to reduce the potentially adverse effects that the volatility of fuel markets and interest rate risk may have on operating results.

In an effort to seek to reduce the variability of the ultimate cash flows associated with fluctuations in diesel fuel prices, we periodically enter into various derivative instruments, including forward futures swap contracts.  Specifically, we enter into hedging contracts with respect to ultra-low sulfur diesel ("ULSD"). Under these contracts, we pay a fixed rate per gallon of ULSD and receive the monthly average price of Gulf Coast ULSD. The retrospective and prospective regression analyses provided that changes in the prices of diesel fuel and ULSD were deemed to be highly effective based on the relevant authoritative guidance. We do not engage in speculative transactions, nor do we hold or issue financial instruments for trading purposes.

In August 2015, we entered into an interest rate swap agreement with a notional amount of $28.0 million, which was designated as a hedge against the variability in future interest payments due on the debt associated with the purchase of our corporate headquarters as described in Note 7. The terms of the swap agreement effectively convert the variable rate interest payments on this note to a fixed rate of 4.2% through maturity on August 1, 2035.  In 2016 and 2017, we also entered into several interest rate swaps, which were designated to hedge against the variability in future interest rate payments associated with the purchase of certain trailers.  Because the critical terms of the swaps and hedged items coincide, in accordance with the requirements of ASC 815, the change in the fair value of the derivative is expected to exactly offset changes in the expected cash flows due to fluctuations in the LIBOR rate over the term of the debt instrument, and therefore no ongoing assessment of effectiveness is required. The fair value of all interest rate swap agreements that were in effect at March 31,September 30, 2018, of approximately $0.5$1.2 million, is included in other short and long-term assets in the condensed consolidated balance sheet and is included in accumulated other comprehensive income, net of tax. Additionally, less than $0.1 million was reclassified from accumulated other comprehensive income into our results of operations as additional interest expense for the three months ended March 31,September 30, 2018, related to changes in interest rates during such period. Based on the amounts in accumulated other comprehensive income as of March 31,September 30, 2018, we expect to reclassify gains of approximately $0.1 million, net of tax, on derivative instruments from accumulated other comprehensive income into our results of operations during the next twelve months due to changes in interest rates. The amounts actually realized will depend on the fair values as of the date of settlement.

We recognize all derivative instruments at fair value on our condensed consolidated balance sheets.  Our derivative instruments are designated as cash flow hedges, thus the gain or loss on the derivatives is reported as a component of accumulated other comprehensive income and will be reclassified into earnings in the same period during which the hedged transaction affects earnings.  The change in fair value of the hedge offsets the change in fair value of the hedged item.

At March 31,September 30, 2018, we had fuel hedge contracts on approximately 5.71.9 million gallons for the remainder of 2018, or approximately 16.1%17.1% of our projected remaining 2018 fuel requirements.

The fair value of the fuel hedge contracts that were in effect at March 31,September 30, 2018, of approximately $0.8$0.9 million is included in other short-term assets in the consolidated balance sheet and is included in accumulated other comprehensive income, net of tax.  Changes in the fair values of these instruments can vary dramatically based on changes in the underlying commodity prices. For example, during the firstthird quarter in 2018, market "spot" prices for ULSD peaked at a high of approximately $2.08$2.31 per gallon and hit a low price of approximately $1.80$2.02 per gallon. During the same 2017 quarter, market "spot" prices ranged from a high of $1.63$1.83 per gallon to a low of $1.46$1.41 per gallon. Market price changes can be driven by factors such as supply and demand, inventory levels, weather events, refinery capacity, political agendas, the value of the U.S. dollar, geopolitical events, and general economic conditions, among other items.

Additionally, $0.2$0.6 million wasand $1.3 million were reclassified from accumulated other comprehensive income into our results of operations as a reduction to fuel expense for the three and nine months ended March 31,September 30, 2018, respectively, related to gains on contracts that expired.  Based on the amounts in accumulated other comprehensive income as of March 31,September 30, 2018, and the expected timing of the purchases of the diesel hedged, we expect to reclassify gains of approximately $0.6 million, net of tax, on derivative instruments from accumulated other comprehensive income into our results of operations during the next twelve months due to the actual prices paid for diesel fuel purchases.  The amounts actually realized will be dependent on the fair values as of the date of settlement.

We perform both a prospective and retrospective assessment of the effectiveness of our fuel hedge contracts at inception and quarterly, including assessing the possibility of counterparty default.  If we determine that a derivative is no longer expected to be highly effective, we discontinue hedge accounting prospectively and recognize subsequent changes in the fair value of the hedge in earnings.  As a result of our effectiveness assessment at inception and at March 31,September 30, 2018, we believe our hedge contracts have been and will continue to be highly effective in offsetting changes in cash flows attributable to the hedged risk.

Outstanding financial derivative instruments expose us to credit loss in the event of nonperformance by the counterparties to the agreements. We do not expect any of the counterparties to fail to meet their obligations.  Our credit exposure related to these financial instruments is represented by the fair value of contracts reported as assets.  To manage credit risk, we review each counterparty's audited financial statements, credit ratings, and obtain references as we deem necessary.

We and substantially all of our subsidiaries are parties to a Third Amended and Restated Credit Facility (the "Credit Facility") with Bank of America, N.A., as agent (the "Agent") and JPMorgan Chase Bank, N.A. (together with the Agent, the "Lenders").

The Credit Facility is a $95.0 million revolving credit facility, with an uncommitted accordion feature that, so long as no event of default exists, allows us to request an increase in the revolving credit facility of up to $50.0 million subject to Lender acceptance of the additional funding commitment.  The Credit Facility includes, within our $95.0 million revolving credit facility, a letter of credit sub facility in an aggregate amount of $95.0 million and a swing line sub facility in an aggregate amount equal to the greater of $10.0 million or 10% of the Lenders' aggregate commitments under the Credit Facility from time-to-time.  The Credit Facility matures in September 2021.

Borrowings under the Credit Facility are classified as either "base rate loans" or "LIBOR loans."  Base rate loans accrue interest at a base rate equal to the greater of the Agent's prime rate, the federal funds rate plus 0.5%, or LIBOR plus 1.0%, plus an applicable margin ranging from 0.5% to 1.0%; while LIBOR loans accrue interest at LIBOR, plus an applicable margin ranging from 1.5% to 2.0%.  The applicable rates are adjusted quarterly based on average pricing availability.  The unused line fee is the product of 0.25% times the average daily amount by which the Lenders' aggregate revolving commitments under the Credit Facility exceed the outstanding principal amount of revolver loans and the aggregate undrawn amount of all outstanding letters of credit issued under the Credit Facility.  The obligations under the Credit Facility are guaranteed by us and secured by a pledge of substantially all of our assets, with the notable exclusion of any real estate or revenue equipment pledged under other financing agreements, including revenue equipment installment notes and capital leases.

Borrowings under the Credit Facility are subject to a borrowing base limited to the lesser of (A) $95.0 million, minus the sum of the stated amount of all outstanding letters of credit; or (B) the sum of (i) 85% of eligible accounts receivable, plus (ii) the lesser of (a) 85% of the appraised net orderly liquidation value of eligible revenue equipment, (b) 95% of the net book value of eligible revenue equipment, or (c) 35% of the Lenders' aggregate revolving commitments under the Credit Facility, plus (iii) the lesser of (a) $25.0 million or (b) 75% of the appraised fair market value of eligible real estate, as reduced by a periodic amortization amount.  We had $4.0 million outstanding under the Credit Facility asAs of March 31,September 30, 2018, there were undrawn letters of credit outstanding of approximately $32.8$35.1 million, and available borrowing capacity of $57.9 million.was $59.9 million, and $6.2 million in outstanding borrowings under the Credit Facility. The interest rate on outstanding borrowings under the Credit Facility as of March 31,September 30, 2018, was 5.3%5.8% on $4.0$6.2 million of base rate loans, and there were no outstanding LIBOR loans.loans. Based on availability as of March 31,September 30, 2018 and December 31, 2017, there was no fixed charge coverage requirement.

The Credit Facility includes usual and customary events of default for a facility of this nature and provides that, upon the occurrence and continuation of an event of default, payment of all amounts payable under the Credit Facility may be accelerated, and the Lenders' commitments may be terminated.  If an event of default occurs under the Credit Facility and the Lenders cause or have the ability to cause all of the outstanding debt obligations under the Credit Facility to become due and payable, this could result in a default under other debt instruments that contain acceleration or cross-default provisions. The Credit Facility contains certain restrictions and covenants relating to, among other things, debt, dividends, liens, acquisitions and dispositions outside of the ordinary course of business, and affiliate transactions.  Failure to comply with the covenants and restrictions set forth in the Credit Facility could result in an event of default.

Capital lease obligations are utilized to finance a portion of our revenue equipment and are entered into with certain finance companies who are not parties to our Credit Facility.  The leases in effect at March 31,September 30, 2018 terminate in AprilOctober 2018 through September 2023 and contain guarantees of the residual value of the related equipment by us. As such, the residual guarantees are included in the related debt balance as a balloon payment at the end of the related term as well as included in the future minimum capital lease payments. These lease agreements require us to pay personal property taxes, maintenance, and operating expenses.

Pricing for the revenue equipment installment notes is quoted by the respective financial affiliates of our primary revenue equipment suppliers and other lenders at the funding of each group of equipment acquired and include fixed annual rates for new equipment under retail installment contracts. The notes included in the funding are due in monthly installments with final maturities at various dates ranging from AprilOctober 2018 to June 2023.July 2023. The notes contain certain requirements regarding payment, insuring of collateral, and other matters, but do not have any financial or other material covenants or events of default except certain notes totaling $128.0$133.0 million are cross-defaulted with the Credit Facility. Additionally, the abovementioned fuel hedge contracts totaling $0.8$0.9 million at March 31,September 30, 2018, are cross-defaulted with the Credit Facility.  Additional borrowings from the financial affiliates of our primary revenue equipment suppliers and other lenders are expected to be available to fund new tractors expected to be delivered for the remainder of 2018, while any other property and equipment purchases, including trailers, are expected to be funded with a combination of available cash, notes, operating leases, capital leases, and/or from the Credit Facility.

Our 2006 Omnibus Incentive Plan, as amended (the "Incentive Plan") governs the issuance of equity awards and other incentive compensation to management and members of the board of directors.  In February 2013, the Compensation Committee re-approved, subject to stockholder re-approval, the material terms of the performance-based goals under the Incentive Plan so that certain incentive awards granted thereunder would continue to qualify as exempt "performance-based compensation" under Internal Revenue Code Section 162(m).  Our stockholders re-approved the material terms of the performance-based goals under the Incentive Plan at our 2013 Annual Meeting held on May 29, 2013.

The Incentive Plan permits annual awards of shares of our Class A common stock to executives, other key employees, consultants, non-employee directors, and eligible participants under various types of options, restricted stock awards, or other equity instruments.  At March 31,September 30, 2018, 193,18649,405 of the abovementioned 1,550,000 shares were available for award under the Incentive Plan.  No participant in the Incentive Plan may receive awards of any type of equity instruments in any calendar yearcalendar-year that relates to more than 200,000 shares of our Class A common stock.  No awards may be made under the Incentive Plan after March 31, 2023. To the extent available, we have issued treasury stock to satisfy all share-based incentive plans.

Included in salaries, wages, and related expenses within the condensed consolidated statements of operations is $1.1 million and $0.3 million of stock-based compensation expense for the three months ended March 31,September 30, 2018 and 2017, isand $2.9 million and $0.6 million of stock-based compensation expense of approximately $0.8 millionfor the nine months ended September 30, 2018 and $0.2 million,2017, respectively. All stock compensation expense recorded in 2018 and 2017 relates to restricted shares,shares.  An additional $0.4 million and $0.3 million of stock-based compensation was recorded in general supplies and expenses in the condensed consolidated statements of operations for each of the three- and nine-month periods ended September 30, 2018 and 2017, respectively, as no options were granted during these periods.this amount relates to the issuance of restricted stock to non-employee directors.

The Incentive Plan allows participants to pay the federal and state minimum statutory tax withholding requirements related to awards that vest or allows participants to deliver to us shares of Class A common stock having a fair market value equal to the minimum amount of such required withholding taxes. To satisfy withholding requirements for shares that vested through March 31,September 30, 2018, certain participants elected to forfeit receipt of an aggregate of 6552,753 shares of Class A common stock at a weighted average per share price of $27.16$29.57 based on the closing price of our Class A common stock on the dates the shares vested in 2018, in lieu of the federal and state minimum statutory tax withholding requirements. We remitted less than $0.1 million to the proper taxing authorities in satisfaction of the employees' minimum statutory withholding requirements.

We own a minority investment in Transport Enterprise Leasing, LLC ("TEL"). TEL is a tractor and trailer equipment leasing company and used equipment reseller. We have not guaranteed any of TEL's debt and have no obligation to provide funding, services, or assets. In May 2016, the operating agreement with TEL was amended to, among other things, remove the previously agreed to fixed date purchase options.  TEL’s majority owners are generally restricted from transferring their interests in TEL, other than to certain permitted transferees, without our consent. We sold less thanapproximately $0.1 million of tractors or trailers to TEL during each of the quarternine months ended March 31,September 30, 2018 and 2017, and we sold none to TEL during the same 2017 quarter. We received $2.1$5.9 million and $0.1$4.2 million respectively, for providing various maintenance services, certain back-office functions, and for miscellaneous equipment.  We recognized a net reversal of previously deferred gains totaling approximately $0.2 million and less than $0.1 million for each of the threenine months ended March 31,September 30, 2018 and 2017, respectively, representing 49% of the gains on units sold to TEL less any gains previously deferred and recognized when the equipment was subsequently sold to a third party.  Deferred gains, totaling $0.2 million at March 31,September 30, 2018, are being carried as a reduction in our investment in TEL.  At March 31,September 30, 2018 and December 31, 2017, we had accounts receivable from TEL of $5.3$5.7 million and $8.6$7.8 million, respectively, related to cash disbursements made pursuant to our performance of certain back-office and maintenance functions on TEL’s behalf.

We have accounted for our investment in TEL using the equity method of accounting and thus our financial results include our proportionate share of TEL's 2018 net income through March 31,September 30, 2018, or $1.5$5.4 million. Our investment in TEL, totaling $21.8$25.7 million and $20.1 million at March 31,September 30, 2018 and December 31, 2017, respectively, is included in other assets in the accompanying condensed consolidated balance sheets.

See TEL'sTEL’s summarized financial information below:

From time-to-time, we are a party to ordinary, routine litigation arising in the ordinary course of business, most of which involves claims for personal injury and property damage incurred in connection with the transportation of freight.

We maintain insurance to cover liabilities arising from the transportation of freight for amounts in excess of certain self-insured retentions. In management's opinion, our potential exposure under pending legal proceedings is adequately provided for in the accompanying condensed consolidated financial statements.

On May 8, 2017, the U.S. District Court for the Southern District of Ohio issued a pre-trial decision against our Southern Refrigerated Transport, Inc. ("SRT") subsidiary relating to a cargo claim incurred in 2008. The court had previously ruled in favor of the plaintiff in 2014, and the prior decision was reversed in part by the Sixth Circuit Court of Appeals and remanded for further proceedings in 2015.  As a result of this decision, we increased the reserve in respect of this case by $0.9 million in the first quarter of 2017 in order to accrue additional legal fees and pre-judgment interest since the time of the previously noted appeal.  We are appealingOn September 25, 2018, the District Court’s decision on damagesSixth Circuit Court of Appeals ruled in favor of the plaintiff and against SRT.  While considering its further appeal to the Sixth Circuit.U.S. Supreme Court, SRT will likely pay this claim, related accrued interest and legal fees totaling approximately $6.8 million within the next six months.

Our SRT subsidiary is a defendant in a lawsuit filed on December 16, 2016 in the Superior Court of San Bernardino County, California.  The lawsuit was filed on behalf of David Bass (a California resident and former driver), who is seeking to have the lawsuit certified as a class action case wherein he alleges violation of multiple California wage and hour statutes over a four year period of time, including failure to pay wages for all hours worked, failure to provide meal periods and paid rest breaks, failure to pay for rest and recovery periods, failure to reimburse certain business expenses, failure to pay vested vacation, unlawful deduction of wages, failure to timely pay final wages, failure to provide accurate itemized wage statements, and unfair and unlawful competition as well as various state claims.  The case was removed from state court in February, 2017 to the U.S. District Court in the Central District of California, and subsequently, SRT moved the District Court to transfer venue of the case to the U.S. District Court sitting in the Western District of Arkansas.  The motion to transfer was approved by the California District Court in July, 2017, and the case will now be heard in the U.S. District court in the Western District of Arkansas.

Based on our present knowledge of the facts and, in certain cases, advice of outside counsel, management believes the resolution of open claims and pending litigation, taking into account existing reserves, is not likelyreasonably possible to have a materially adverse effect on our consolidated financial statements.

We had $32.8$35.1 million and $32.9 million of outstanding and undrawn letters of credit as of March 31,September 30, 2018 and December 31, 2017, respectively. The letters of credit are maintained primarily to support our insurance programs.

OCI is comprised of net income and other adjustments, including changes in the fair value of certain derivative financial instruments qualifying as cash flow hedges.

The following table summarizes the change in the components of our OCI balance for the periods presented (in thousands; presented net of tax):