	March 31, 2020			December 31, 2019
Senior Notes	$	150,000		$	150,000
Credit Facility		154,000			157,000
Total long-term debt		304,000			307,000
Less: Debt issuance costs		(1,580	)		(1,717	)
Long-term debt, net	$	302,420		$	305,283

We have two series of senior notes outstanding with an aggregate principal amount of $150 million ("Senior Notes") issued 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 aggregate borrowing commitment under our revolving credit facility (the “Credit Facility”) is $300 million. The Credit Facility provides an option to increase the commitment under the Credit Facility by an additional $100 million to bring the total borrowings available to $400 million if certain prescribed conditions are met by the Company. The Credit Facility bears interest at variable rates from LIBOR plus 1.375% to a maximum of LIBOR plus 2.00%. Any outstanding balance under the Credit Facility is due June 19, 2023, when the Credit Facility matures. Our available capacity at any point in time is reduced by borrowings outstanding at the time and outstanding letters of credit which totaled $14.6 million at March 31, 2020, resulting in an available borrowing capacity under the Credit Facility of $131.4 million. In addition to those items under the Credit Facility, we had $6.6 million of outstanding letters of credit and performance guarantees and bonds from other sources as of March 31, 2020.

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 and Senior Notes include a cross-default provision, which means that a default under one agreement may result in the default of the other agreement. 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. The Credit Facility agreement allows non-cash charges such as impairment of assets, stock compensation and other non-cash charges to be added back in the calculation of EBITDA. The terms of our Credit Facility also allow us to negotiate in good faith to amend any ratio or requirement to preserve the original intent of the agreement if any change in accounting principle would affect the computation of any financial ratio or requirement of the Credit Facility. Pursuant to the terms of our Credit Facility, we have calculated our leverage ratio to be 1.93, and our interest coverage ratio to be 8.59 for the period ending March 31, 2020. 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.

We entered into two interest rate swap agreements for a total notional amount of $50 million, including one of which was entered during the three months ended March 31, 2020. See Note 17 - Derivative Instruments and Hedging Activities.

The estimated fair value of total debt at March 31, 2020 and December 31, 2019 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.