Long-Term Debt (Tables)

12 Months Ended

Dec. 31, 2018

Debt Disclosure [Abstract]

Borrowing Base Utilization Grid, Credit Facility [Table Text Block]

The borrowing base utilization grid as set forth in the Credit Agreement is as follows:

Borrowing Base Utilization Percentage	<25%		≥25% <50%		≥50% <75%		≥75% <90%		≥90%
Eurodollar Loans	1.500	%	1.750	%	2.000	%	2.250	%	2.500	%
ABR Loans or Swingline Loans	0.500	%	0.750	%	1.000	%	1.250	%	1.500	%
Commitment Fee Rate	0.375	%	0.375	%	0.500	%	0.500	%	0.500	%

Schedule of Credit Agreement Facilities [Table Text Block]

The following table presents the outstanding balance, total amount of letters of credit outstanding, and available borrowing capacity under the Credit Agreement as of February 7, 2019, and December 31, 2018, and under the Company’s Fifth Amended and Restated Credit Agreement as of December 31, 2017:

	As of February 7, 2019		As of December 31, 2018		As of December 31, 2017
	(in thousands)
Credit facility balance (1)	$	—	$	—	$	—
Letters of credit (2)	—		200		200
Available borrowing capacity	1,000,000		999,800		924,800
Total aggregate lender commitment amount	$	1,000,000	$	1,000,000	$	925,000

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⁽¹⁾  Unamortized deferred financing costs attributable to the credit facility are presented as a component of other noncurrent assets on the accompanying balance sheets and totaled $6.4 million and $3.1 million as of December 31, 2018, and 2017, respectively. These costs are being amortized over the term of the credit facility on a straight-line basis.

⁽²⁾  Letters of credit outstanding reduce the amount available under the credit facility on a dollar-for-dollar basis. The letter of credit outstanding as of December 31, 2018, was released effective January 8, 2019.

Schedule of Senior Notes [Table Text Block]

The Senior Notes, net of unamortized deferred financing costs line on the accompanying balance sheets as of December 31, 2018, and 2017, consisted of the following:

	As of December 31,
	2018						2017
	Principal Amount		Unamortized Deferred Financing Costs		Principal Amount, Net of Unamortized Deferred Financing Costs		Principal Amount		Unamortized Deferred Financing Costs		Principal Amount, Net of Unamortized Deferred Financing Costs
	(in thousands)
6.50% Senior Notes due 2021	$	—	$	—	$	—	$	344,611	$	2,656	$	341,955
6.125% Senior Notes due 2022	476,796		3,921		472,875		561,796		5,800		555,996
6.50% Senior Notes due 2023	—		—		—		394,985		3,707		391,278
5.0% Senior Notes due 2024	500,000		4,688		495,312		500,000		5,610		494,390
5.625% Senior Notes due 2025	500,000		5,808		494,192		500,000		6,714		493,286
6.75% Senior Notes due 2026	500,000		6,407		493,593		500,000		7,242		492,758
6.625% Senior Notes due 2027	500,000		7,533		492,467		—		—		—
Total	$	2,476,796	$	28,357	$	2,448,439	$	2,801,392	$	31,729	$	2,769,663

Schedule of Senior Convertible Notes [Table Text Block]

The net carrying amount of the liability component of the Senior Convertible Notes, as reflected on the accompanying balance sheets, consisted of the following as of December 31, 2018 and 2017:

	As of December 31,
	2018			2017
	(in thousands)
Principal amount of Senior Convertible Notes	$	172,500		$	172,500
Unamortized debt discount	(22,313		)	(30,183		)
Unamortized deferred financing costs	(2,293		)	(3,210		)
Net carrying amount	$	147,894		$	139,107

The net carrying amount of the equity component of the Senior Convertible Notes recorded in additional paid-in capital on the accompanying balance sheets consisted of the following as of December 31, 2018 and 2017:

	As of December 31,
	2018			2017
	(in thousands)
Equity component due to allocation of proceeds to equity	$	40,217		$	40,217
Related issuance costs	(1,375		)	(1,375		)
Deferred tax liability	(5,267		)	(5,267		)
Net carrying amount	$	33,575		$	33,575