We have no capital lease obligations. Debt at December 31, 2017 and 2016 is summarized in the following table (in thousands):



	December 31, 2017			December 31, 2016
Senior Notes	$	150,000		$	150,000
Credit Facility	78,000			68,000
Total debt	228,000			218,000
Less: Debt issuance costs	(1,011		)	(1,512		)
Long-term debt, net	$	226,989		$	216,488

In 2011, we issued two series of senior notes with an aggregate principal amount of $150 million ("Senior Notes") in a private placement transaction. Series A consists of $75 million in aggregate principal amount of notes that bear interest at a fixed rate of 4.01% and are due in full on September 30, 2021. Series B consists of $75 million in aggregate principal amount of notes that bear interest at a fixed rate of 4.11% and are due in full on September 30, 2023. Interest on each series of the Senior Notes is payable semi-annually on March 30 and September 30.

The terms of our Credit Facility allow an aggregate borrowing capacity of $400 million and to increase the uncommitted availability by an additional $50 million to bring the total borrowings available from $400 million to $450 million if certain prescribed conditions are met by the Company. The Credit Facility bears interest at variable rates from LIBOR plus 1.25% to a maximum of LIBOR plus 2.0%.

Any outstanding balance under the Credit Facility is due August 29, 2019, when the Credit Facility matures. Interest payment terms are variable depending upon the specific type of borrowing under this facility. Our available capacity at any point in time is subject to all terms of the agreements, and is reduced by borrowings outstanding at the time and outstanding letters of credit which totaled $14.3 million at December 31, 2017, resulting in an available borrowing capacity under the Credit Facility of $307.7 million. In addition to those items under the Credit Facility, we had $14.0 million of outstanding letters of credit and performance guarantees and bonds from other sources as of December 31, 2017.

The terms of the Credit Facility and Senior Notes require us to meet certain covenants, including, but not limited to, an interest coverage ratio (consolidated EBITDA divided by interest expense) and a leverage ratio (consolidated net indebtedness divided by consolidated EBITDA), where consolidated EBITDA (as defined in each agreement) and interest expense are calculated using the most recent four fiscal quarters. The Credit Facility has the more restrictive covenants with a minimum interest coverage ratio of 3.0 to 1.0 and a maximum leverage ratio of 2.5 to 1.0. We believe that we are in compliance with all such covenants contained in our credit agreements. Certain of our material, wholly-owned subsidiaries are guarantors or co-borrowers under the Credit Facility and Senior Notes.

In 2014, we entered into two interest rate swap agreements to hedge changes in the variable interest rate on our LIBOR-priced debt. See Note 14 - Derivative Instruments and Hedging Activities for discussion of our derivative instruments.

The estimated fair value of total debt at December 31, 2017 and 2016 approximated the book value of total debt. The fair value was estimated using Level 2 inputs by calculating the sum of the discounted future interest and principal payments through the date of maturity.