(6)Debt

The Company’s outstanding debt is as follows (in thousands):



	June 30, 2018		December 31, 2017
	Long-term		Long-term
Senior unsecured notes due September 2024	$	500,000	$	500,000
Senior unsecured notes due December 2021		800,000		800,000
Total debt, gross		1,300,000		1,300,000
Unamortized debt issuance costs		(18,855)		(20,229)
Total debt, net	$	1,281,145	$	1,279,771

Credit Facility

The Company has a $300 million asset-based revolving credit facility which matures in October 2022. The borrowing base under the credit facility is calculated based on a formula referencing the borrower’s and the subsidiary guarantors’ eligible accounts receivable, eligible inventory and eligible premium rental drill pipe less reserves. Availability under the credit facility is the lesser of (i) the commitments, (ii) the borrowing base and (iii) the highest principal amount permitted to be secured under the indenture governing the 7 1/8% senior unsecured notes due 2021. At June 30, 2018, the borrowing base was $263.0 million and the Company had $37.9 million of letters of credit outstanding that reduced its borrowing availability under the revolving credit facility. The credit agreement contains various covenants, including, but not limited to, limitations on the incurrence of indebtedness, permitted investments, liens on assets, making distributions, transactions with affiliates, merger, consolidations, dispositions of assets and other provisions customary in similar types of agreements.

Senior Unsecured Notes

The Company has outstanding $500 million of 7 3/4% senior unsecured notes due September 2024. The indenture governing the 7 3/4% senior unsecured notes due 2024 requires semi-annual interest payments on March 15th and September 15th of each year, beginning on March 15, 2018, through the maturity date of September 15, 2024.

The Company also has outstanding $800 million of 7 1/8% senior unsecured notes due December 2021. The indenture governing the 7 1/8% senior unsecured notes due 2021 requires semi-annual interest payments on June 15th and December 15th of each year through the maturity date of December 15, 2021.