Long-Term Debt (Tables)

12 Months Ended

Dec. 31, 2016

Debt Disclosure [Abstract]

Schedule of Borrowing Base Utilization, Credit Facility [Table Text Block]

The borrowing base utilization grid under the Credit Agreement is as follows:

Borrowing Base Utilization Percentage	<25%		≥25% <50%		≥50% <75%		≥75% <90%		≥90%
Eurodollar Loans	1.750	%	2.000	%	2.250	%	2.500	%	2.750	%
ABR Loans or Swingline Loans	0.750	%	1.000	%	1.250	%	1.500	%	1.750	%
Commitment Fee Rate	0.300	%	0.300	%	0.350	%	0.375	%	0.375	%

Schedule of Line of Credit Facilities [Table Text Block]

The following table presents the outstanding balance, total amount of letters of credit, and available borrowing capacity under the Credit Agreement as of February 15, 2017, December 31, 2016, and December 31, 2015:

	As of February 15, 2017		As of December 31, 2016		As of December 31, 2015
	(in thousands)
Credit facility balance (1)	$	103,500	$	—	$	202,000
Letters of credit (2)	200		200		200
Available borrowing capacity	1,061,300		1,164,800		1,297,800
Total aggregate lender commitment amount	$	1,165,000	$	1,165,000	$	1,500,000

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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 $5.9 million and $4.9 million as of December 31, 2016, and 2015, respectively.

⁽²⁾  Letters of credit reduce the amount available under the credit facility on a dollar-for-dollar basis.

Schedule of Long-term Debt Instruments [Table Text Block]

The Senior Notes, net of unamortized deferred financing costs line on the accompanying balance sheets as of December 31, 2016, and 2015, consisted of the following:

	As of December 31,
	2016						2015
	Principal Amount		Unamortized Deferred Financing Costs		Senior Notes, Net of Unamortized Deferred Financing Costs		Principal Amount		Unamortized Deferred Financing Costs		Senior Notes, Net of Unamortized Deferred Financing Costs
	(in thousands)
6.50% Senior Notes due 2021	$	346,955	$	3,372	$	343,583	$	350,000	$	4,106	$	345,894
6.125% Senior Notes due 2022	561,796		6,979		554,817		600,000		8,714		591,286
6.50% Senior Notes due 2023	394,985		4,436		390,549		400,000		5,231		394,769
5.0% Senior Notes due 2024	500,000		6,533		493,467		500,000		7,455		492,545
5.625% Senior Notes due 2025	500,000		7,619		492,381		500,000		8,524		491,476
6.75% Senior Notes due 2026	500,000		8,078		491,922		—		—		—
Total	$	2,803,736	$	37,017	$	2,766,719	$	2,350,000	$	34,030	$	2,315,970

Convertible Debt [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, 2016:

	As of December 31, 2016
	(in thousands)
Principal amount of Senior Convertible Notes	$	172,500
Unamortized debt discount	(37,513		)
Unamortized deferred financing costs	(4,131		)
Net carrying amount	$	130,856

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, 2016:

	As of December 31, 2016
	(in thousands)
Equity component due to allocation of proceeds to equity	$	40,217
Less: related issuance costs	(1,375		)
Less: deferred tax liability	(5,267		)
Net carrying amount	$	33,575