Debt (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013		Dec. 16, 2013
Debt Instruments [Abstract]
Senior notes	$ 914,680		$ 1,127,986
Net unamortized premiums	15,547		22,729
Total debt, net	2,087,855		2,301,161
Less current maturities	0		(211,558)
Total long-term debt, net	2,087,855		2,089,603
Credit Facility
Debt Instruments [Abstract]
Credit facility	1,173,175	[1]	1,173,175	[1]
June 2014 Senior Notes
Debt Instruments [Abstract]
Senior notes	0		205,257
November 2020 Senior Notes
Debt Instruments [Abstract]
Senior notes	299,970		300,000
Net unamortized premiums					10,000
September 2022 Senior Notes
Debt Instruments [Abstract]
Senior notes	599,163		600,000
Net unamortized premiums					$ 7,000
Credit Facility
Debt Instruments [Abstract]
Debt Instrument, Interest Rate at Period End	2.66%		2.67%

[1] (1) Variable interest rates of 2.66% and 2.67% at June 30, 2014, and December 31, 2013, respectively.