Long-Term Debt (Tables)

12 Months Ended

Dec. 31, 2013

Debt Disclosure [Abstract]

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

Interest and commitment fees are accrued based on the borrowing base utilization grid below.  Eurodollar loans accrue interest at the London Interbank Offered Rate plus the applicable margin from the utilization table below, and Alternate Base Rate (“ABR”) and swingline loans accrue interest at Prime plus the applicable margin from the utilization table below.  Commitment fees are accrued on the unused portion of the aggregate commitment amount and are included in interest expense in the accompanying statements of operations.

Borrowing Base Utilization Grid

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 Long-term Debt Instruments [Table Text Block]

The following table presents the outstanding balance, total amount of letters of credit, and available borrowing capacity under the Company's credit facility as of February 12, 2014, December 31, 2013, and December 31, 2012:

	As of February 12, 2014		As of December 31, 2013		As of December 31, 2012
	(in millions)
Credit facility balance	$	—	$	—	$	340.0
Letters of credit (1)	$	0.8	$	0.8	$	0.8
Available borrowing capacity	$	1,299.2	$	1,299.2	$	659.2

⁽¹⁾ Letters of credit reduce the amount available under the credit facility on a dollar-for-dollar basis.

Schedule of Long-Term Debt [Table Text Block]

The Senior Notes line on the accompanying balance sheets, as of December 31, 2013, and 2012, consisted of the following:

	As of December 31,
	2013		2012
	(in thousands)
6.625% Senior Notes due 2019	$	350,000	$	350,000
6.50% Senior Notes due 2021	350,000		350,000
6.50% Senior Notes due 2023	400,000		400,000
5.0% Senior Notes due 2024	500,000		—
Total long-term debt	$	1,600,000	$	1,100,000

Schedule of Debt Instrument Redemption Price, 5% Senior Notes Due 2024 [Table Text Block]

On or after July 15, 2018, the Company may also redeem all or, from time to time, a portion of the 2024 Notes at the redemption prices set forth below, during the twelve-month period beginning on July 15 of each applicable year, expressed as a percentage of the principal amount redeemed, plus accrued and unpaid interest:

2018	102.500	%
2019	101.677	%
2020	100.833	%
2021 and thereafter	100.000	%

Schedule of Debt Instrument Redemption Price, 6.50% Senior Notes Due 2023 [Table Text Block]

On or after July 1, 2017, the Company may also redeem all or, from time to time, a portion of the 2023 Notes at the redemption prices set forth below, during the twelve-month period beginning on July 1 of each applicable year, expressed as a percentage of the principal amount redeemed, plus accrued and unpaid interest:

2017	103.250	%
2018	102.167	%
2019	101.083	%
2020 and thereafter	100.000	%

Schedule of Debt Instrument, Redemption Price, 6.50% Senior Notes Due 2021 [Table Text Block]

The Company may also redeem all or, from time to time, a portion of the 2021 Notes on or after November 15, 2016, at the prices set forth below, during the twelve-month period beginning on November 15 of the applicable year, expressed as a percentage of the principal amount redeemed, plus accrued and unpaid interest:

2016	103.250	%
2017	102.167	%
2018	101.083	%
2019 and thereafter	100.000	%

Schedule of Debt Instrument, Redemption Price, 6.625% Senior Notes Due 2019 [Table Text Block]

The Company may also redeem all or, from time to time, a portion of the 2019 Notes on or after February 15, 2015, at the prices set forth below, during the twelve-month period beginning on February 15 of the applicable year, expressed as a percentage of the principal amount redeemed, plus accrued and unpaid interest:

2015	103.313	%
2016	101.656	%
2017 and thereafter	100.000	%