Fair Value Measurement (Details 2) (USD $) In Thousands, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2013		Dec. 31, 2012
Senior secured revolving credit facility
Fair value and carrying value of financial instruments
Interest Rate Generally Fixed (Number of Days)	30 days		30 days
10.25% Senior notes due 2014, net of unamortized discount
Fair value and carrying value of financial instruments
Interest rate on debt instrument (as a percent)	10.25%		10.25%
Unamortized discount	$ 1,553		$ 2,340
6.75% Senior notes due 2020
Fair value and carrying value of financial instruments
Interest rate on debt instrument (as a percent)	6.75%		6.75%
6.375% Senior notes due 2022
Fair value and carrying value of financial instruments
Interest rate on debt instrument (as a percent)	6.375%		6.375%
Level 1
Fair value and carrying value of financial instruments
Debt Instrument, Fair Value Disclosure	1,140,000		1,179,000
Level 2
Fair value and carrying value of financial instruments
Debt Instrument, Fair Value Disclosure	646,000		563,000
Carrying Amount
Fair value and carrying value of financial instruments
Debt Instrument, Fair Value Disclosure	1,760,000		1,668,000
Carrying Amount | Senior secured revolving credit facility
Fair value and carrying value of financial instruments
Debt Instrument, Fair Value Disclosure	646,000	[1]	562,900	[1]
Carrying Amount | 10.25% Senior notes due 2014, net of unamortized discount
Fair value and carrying value of financial instruments
Debt Instrument, Fair Value Disclosure	205,257	[2]	205,257	[3]
Carrying Amount | 6.75% Senior notes due 2020
Fair value and carrying value of financial instruments
Debt Instrument, Fair Value Disclosure	300,000		300,000
Carrying Amount | 6.375% Senior notes due 2022
Fair value and carrying value of financial instruments
Debt Instrument, Fair Value Disclosure	600,000		600,000
Carrying Amount | Cash and cash equivalents
Fair value and carrying value of financial instruments
Cash and Cash Equivalents, Fair Value Disclosure	8,914		312
Estimated Fair Value
Fair value and carrying value of financial instruments
Debt Instrument, Fair Value Disclosure	1,786,000		1,742,000
Estimated Fair Value | Senior secured revolving credit facility
Fair value and carrying value of financial instruments
Debt Instrument, Fair Value Disclosure	646,000	[1]	563,000	[1]
Estimated Fair Value | 10.25% Senior notes due 2014, net of unamortized discount
Fair value and carrying value of financial instruments
Debt Instrument, Fair Value Disclosure	221,000		229,000
Estimated Fair Value | 6.75% Senior notes due 2020
Fair value and carrying value of financial instruments
Debt Instrument, Fair Value Disclosure	311,000		323,000
Estimated Fair Value | 6.375% Senior notes due 2022
Fair value and carrying value of financial instruments
Debt Instrument, Fair Value Disclosure	599,000		627,000
Estimated Fair Value | Cash and cash equivalents
Fair value and carrying value of financial instruments
Cash and Cash Equivalents, Fair Value Disclosure	8,914		312
Estimated Fair Value | Level 1 | 10.25% Senior notes due 2014, net of unamortized discount
Fair value and carrying value of financial instruments
Debt Instrument, Fair Value Disclosure	221,000		229,000
Estimated Fair Value | Level 1 | 6.75% Senior notes due 2020
Fair value and carrying value of financial instruments
Debt Instrument, Fair Value Disclosure	311,000		323,000
Estimated Fair Value | Level 1 | 6.375% Senior notes due 2022
Fair value and carrying value of financial instruments
Debt Instrument, Fair Value Disclosure	599,000		627,000
Estimated Fair Value | Level 1 | Cash and cash equivalents
Fair value and carrying value of financial instruments
Cash and Cash Equivalents, Fair Value Disclosure	8,914		312
Estimated Fair Value | Level 2 | Senior secured revolving credit facility
Fair value and carrying value of financial instruments
Debt Instrument, Fair Value Disclosure	$ 646,000	[1]	$ 563,000	[1]

[1] The Company's credit facility can be repaid at any time without penalty. Interest is generally fixed for 30-day increments at the prime rate or LIBOR plus a stipulated margin for the amount utilized and at a stipulated percentage as a commitment fee for the portion not utilized. The carrying amount of the credit facility approximated fair value due to the short-term maturities of the borrowings and because the borrowings bear interest at variable market rates.

[2] Carrying amount does not include unamortized discount of $1.6 million.

[3] Carrying amount does not include unamortized discount of $2.3 million.