Subsequent Events (Details Textuals) (USD $)	1 Months Ended	12 Months Ended			15 Months Ended	1 Months Ended		1 Months Ended	12 Months Ended			1 Months Ended										1 Months Ended						0 Months Ended	1 Months Ended		12 Months Ended		12 Months Ended	0 Months Ended	12 Months Ended		12 Months Ended				2 Months Ended	17 Months Ended
	Jan. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012	Jan. 31, 2013 Restricted Stock 2004 Plan [Member]	Jan. 04, 2013 Restricted Stock 2004 Plan [Member]	Jan. 31, 2013 SARs [Member]	Dec. 31, 2012 SARs [Member]	Dec. 31, 2011 SARs [Member]	Dec. 31, 2010 SARs [Member]	Jan. 31, 2013 SARs [Member] Minimum [Member]	Jan. 31, 2013 SARs [Member] Maximum [Member]	Feb. 27, 2013 4 5/8% Senior Subordinated Notes due 2023 [Member]	Feb. 27, 2013 4 5/8% Senior Subordinated Notes due 2023 [Member] Debt Instrument, Redemption, Period One [Member]	Feb. 27, 2013 4 5/8% Senior Subordinated Notes due 2023 [Member] Debt Instrument, Redemption, Period Two [Member]	Feb. 27, 2013 4 5/8% Senior Subordinated Notes due 2023 [Member] Debt Instrument, Redemption, Period Three [Member]	Feb. 27, 2013 4 5/8% Senior Subordinated Notes due 2023 [Member] Debt Instrument, Redemption, Period Four [Member]	Feb. 27, 2013 4 5/8% Senior Subordinated Notes due 2023 [Member]	Feb. 05, 2013 4 5/8% Senior Subordinated Notes due 2023 [Member]	Feb. 05, 2013 4 5/8% Senior Subordinated Notes due 2023 [Member]	Feb. 27, 2013 4 5/8% Senior Subordinated Notes due 2023 [Member] Debt Instrument, Redemption, Period One [Member]	Feb. 27, 2013 4 5/8% Senior Subordinated Notes due 2023 [Member] Debt Instrument, Redemption, Period Two [Member]	Feb. 27, 2013 4 5/8% Senior Subordinated Notes due 2023 [Member] Debt Instrument, Redemption, Period Three [Member]	Feb. 27, 2013 4 5/8% Senior Subordinated Notes due 2023 [Member] Debt Instrument, Redemption, Period Four [Member]	Feb. 27, 2013 4 5/8% Senior Subordinated Notes due 2023 [Member] Initial Redemption Period with Proceeds from Equity Offering [Member]	Feb. 27, 2013 4 5/8% Senior Subordinated Notes due 2023 [Member] Initial Redemption Period with Make-Whole Premium [Member]	Feb. 19, 2013 9.75% Senior Subordinated Notes due 2016 [Member]	Feb. 27, 2013 9.75% Senior Subordinated Notes due 2016 [Member]	Feb. 28, 2009 9.75% Senior Subordinated Notes due 2016 [Member]	Dec. 31, 2012 9.75% Senior Subordinated Notes due 2016 [Member]	Jun. 30, 2009 9.75% Senior Subordinated Notes due 2016 [Member]	Dec. 31, 2012 9.75% Senior Subordinated Notes due 2016 [Member] Debt Instrument, Redemption, Period One [Member]	Feb. 19, 2013 9.5% Senior Subordinated Notes due 2016 [Member]	Dec. 31, 2012 9.5% Senior Subordinated Notes due 2016 [Member]	Mar. 08, 2010 9.5% Senior Subordinated Notes due 2016 [Member]	Dec. 31, 2012 9.5% Senior Subordinated Notes due 2016 [Member] Debt Instrument, Redemption, Period One [Member]	Dec. 31, 2012 9.5% Senior Subordinated Notes due 2016 [Member] Debt Instrument, Redemption, Period Two [Member]	Dec. 31, 2012 9.5% Senior Subordinated Notes due 2016 [Member] Debt Instrument, Redemption, Period Three [Member]	Dec. 31, 2012 9.5% Senior Subordinated Notes due 2016 [Member] Initial Redemption Period with Make-Whole Premium [Member]	Feb. 21, 2013 Treasury Stock Repurchase Program [Member]	Feb. 21, 2013 Treasury Stock Repurchase Program [Member]
Subsequent Event [Line Items]
Selling price of debt instrument as a percentage of par																			100.00%											92.816%
Anticipated Pre Adjusted Cash Paid For Purchase Of Oil And Natural Gas Properties		$ 1,050,000,000
Debt Instrument, Interest Rate, Stated Percentage																				4.625%	4.625%										9.75%				9.50%
Proceeds From Issuance of Subordinated Long Term Debt Net of Commissions and Fees																			1,180,000,000
Debt Instrument, Frequency of Periodic Payment														January 15 and July 15 of each year, commencing July 15, 2013																	March 1 and September 1 of each year				semi-annually, on May 1 and November 1, at a rate of 9½%
Debt Instrument, Restrictive Covenants														The indenture contains certain restrictions on our ability to: (1) incur additional debt; (2) pay dividends on our common stock or redeem, repurchase or retire such capital stock or subordinated debt unless certain leverage ratios are met; (3) make investments; (4) create liens on our assets; (5) create restrictions on the ability of our restricted subsidiaries to pay dividends or make other payments to the Company; (6) engage in transactions with our affiliates; (7) transfer or sell assets; and (8) consolidate, merge or transfer all or substantially all of our assets and the assets of our subsidiaries.
Debt Instrument, Collateral														All of our significant subsidiaries fully and unconditionally guaranteed this debt.																	All of our subsidiaries, other than minor subsidiaries, guarantee this debt jointly and severally.				All of our subsidiaries, other than minor subsidiaries, guarantee this debt jointly and severally.
Debt Instrument, Face Amount																					1,200,000,000									420,000,000	426,400,000	6,400,000			224,900,000	225,000,000
Debt Instrument, Repurchased Face Amount																												191,700,000						186,700,000
Maturity date																			Jul. 15, 2023												Mar. 01, 2016				May 01, 2016
Debt Instrument, Redemption Price, Percentage															102.313%	101.542%	100.771%	100.00%								104.625%	100.00%	105.425%	104.875%					106.87%			104.75%	102.375%	100.00%	100.00%
Debt Instrument, Redemption Period, Start Date																						on or after January 15, 2018	on or after January 15, 2019	on or after January 15, 2020	on or after January 15, 2021	Prior to July 15, 2016							after May 1, 2013					after May 1, 2014	after May 1, 2015	prior to May 1, 2013
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed																										35.00%	100.00%													100.00%
Treasury Stock, Shares, Acquired					31,100,000																																				3,500,000
Treasury Stock, Value, Acquired, Cost Method		(8,125,000)	(9,683,000)	(6,729,000)	(461,900,000)																																				(59,100,000)	(521,000,000)
Treasury Stock Acquired, Average Cost Per Share																																									$ 16.73
Stock Repurchase Program, Remaining Authorized Repurchase Amount		$ 309,300,000																																							$ 250,200,000
Equity Award Grant
Value (per share) of restricted stock grant							$ 16.77
Awards Granted						1,545,077		605,802
Exercise price of SARs granted								$ 16.77
Weighted average grant-date fair value, granted									$ 8.90	$ 9.68	$ 8.45	$ 5.42	$ 8.72
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights	The awards generally vest 33% per year over a three-year period.