Long-Term Debt - Additional Information (Detail) (USD $)	12 Months Ended	1 Months Ended		12 Months Ended				12 Months Ended					12 Months Ended					12 Months Ended				1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2011	Aug. 31, 2011 Maximum	Aug. 31, 2011 Revolving credit facility	Dec. 31, 2011 Revolving credit facility	Dec. 31, 2011 Revolving credit facility Minimum	Dec. 31, 2011 Revolving credit facility Maximum	Dec. 31, 2011 Revolving credit facility After June 30, 2013	Dec. 31, 2011 Revolving credit facility Group Twelve	Dec. 31, 2011 Revolving credit facility Group Thirteen	Aug. 31, 2011 Revolving credit facility Letter of Credit	Dec. 31, 2011 Previous Revolving Credit Facility	Dec. 31, 2011 10.375% Senior Unsecured Notes due 2016	Dec. 31, 2011 10.375% Senior Unsecured Notes due 2016 Semi Annual Payment, First Payment	Dec. 31, 2011 10.375% Senior Unsecured Notes due 2016 Semi Annual Payment, Second Payment	Dec. 31, 2011 10.375% Senior Unsecured Notes due 2016 Group One	Dec. 31, 2011 10.375% Senior Unsecured Notes due 2016 Group Two	Dec. 31, 2011 7.25% Senior Unsecured Notes due 2019	Dec. 31, 2011 7.25% Senior Unsecured Notes due 2019 Semi Annual Payment, First Payment	Dec. 31, 2011 7.25% Senior Unsecured Notes due 2019 Semi Annual Payment, Second Payment	Dec. 31, 2011 7.25% Senior Unsecured Notes due 2019 Group One	Dec. 31, 2011 7.25% Senior Unsecured Notes due 2019 Group Two	Apr. 30, 2011 4.50% Convertible Notes due 2012	Jun. 30, 2011 4.50% Convertible Notes due 2012	Dec. 31, 2011 4.50% Convertible Notes due 2012	Dec. 31, 2011 4.50% Convertible Notes due 2012 Semi Annual Payment, First Payment	Dec. 31, 2011 4.50% Convertible Notes due 2012 Semi Annual Payment, Second Payment
Debt Disclosure [Line Items]
Maximum borrowing capacity			$ 300,000,000							$ 20,000,000
Credit facility maturity period			5 years
Credit facility expiration			August 2016
Letter of credit initial borrowing base			380,000,000
Optional additional borrowing			600,000,000
Borrowing Base Commitment Description			The borrowing base is redetermined semi-annually. There is an accordion feature that allows us to increase the commitment up to the lower of the borrowing base or $600 million upon receiving additional commitments from one or more lenders.
Letter of credit amount outstanding											1,400,000
Available borrowing capacity											199,600,000
Credit facility interest rate description				Borrowings under the Revolver bear interest, at our option, at either (i) a rate derived from the London Interbank Offered Rate, as adjusted for statutory reserve requirements for Eurocurrency liabilities (the "Adjusted LIBOR"), plus an applicable margin ranging from 1.500% to 2.500% or (ii) the greater of (a) the prime rate, (b) the federal funds effective rate plus 0.5% or (c) the one-month Adjusted LIBOR plus 1.0%, and, in each case, plus an applicable margin (ranging from 0.500% to 1.500%). The applicable margin is determined based on the ratio of our outstanding borrowings to the available Revolver capacity.
Credit facility interest rate option two, base rate over federal funds effective rate				0.50%
Credit facility interest rate option two, base rate over one-month Adjusted LIBOR				1.00%
Credit facility interest rate option one, applicable margin rate over Adjusted LIBOR					1.50%	2.50%
Credit facility interest rate option two, applicable margin rate					0.50%	1.50%
Commitment fees for undrawn credit facility								0.375%	0.50%
Effective interest rate				2.0625%																				8.50%
Current ratio					1.0
Debt to EBITDAX ratio				4.5			4.0
Original sale amount, percentage of par												97.00%
Effective yield to maturity												11.00%
Annual interest rate												10.375%					7.25%							4.50%
Interest payment date													June 15	December 15				April 15	October 15						May 15	November 15
Redemption period start															June 2013	June 2015				April 2015	June 2017
Redemption option, percent of principal															105.188%	100.00%				103.625%	100.00%
Debt maturity																								November 2012
Conversion rate, numerator																								17.316
Conversion rate, denominator																								1,000
Initial conversion price																								$ 57.75
Principal amount of Convertible notes tendered																						225,085,000	225,085,000
Cash paid to repurchase principal																						232,963,000	232,963,000
Tender premium per principal amount																						35
Tender offer, principal amount																						1,000
Percentage of outstanding debt extinguished																						98.00%
Loss on extinguishment of debt																							(25,900,000)
Loss on extinguishment of debt charged to earnings	(25,421,000)																						(24,238,000)
Loss on extinguishment of debt charged directly to shareholders' equity																							(1,700,000)
Outstanding warrants to acquire shares of common stock	3,982,680
Warrants exercise price	74.25
Cash proceeds from sale of Note Hedges		$ 100,000