Long-Term Debt - Additional Information (Detail) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2011
Debt Disclosure [Line Items]
Loss on extinguishment of debt	$ (25,900,000)
Loss on extinguishment of debt charged to earnings	(24,238,000)	(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	3,982,680
Warrants exercise price		74.25
Subsequent Event | Revolving credit facility | After December 31, 2012
Debt Disclosure [Line Items]
Debt to EBITDAX ratio	4	4
Revolving credit facility
Debt Disclosure [Line Items]
Maximum borrowing capacity	300,000,000	300,000,000
Credit facility expiration		August 2016
Optional additional borrowing	300,000,000	300,000,000
letter of credit initial borrowing base	400,000,000	400,000,000
Credit facility interest rate description		Borrowings under the Revolver bear interest, at our option, at either (i) a rate derived from LIBOR, 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% and (c) the one-month Adjusted LIBOR plus 1.0%, and in each case, plus an applicable margin (ranging from 0.500% to 1.500%). In each case, the applicable margin is determined based on the ratio of our outstanding borrowings to the available Revolver capacity. Commitment fees will be charged at 0.375% on the undrawn portion of the facility.
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%
Percentage basis of the borrowing base for increasing the commitment fee percentage for utilization levels	50.00%	50.00%
Debt to EBITDAX ratio	4.5	4.5
Available borrowing capacity	264,000,000	264,000,000
Revolving credit facility | Commitment Fee Percentage on the Undrawn Portion of the Facility at Current Utilization Levels
Debt Disclosure [Line Items]
Commitment fees for undrawn credit facility		0.375%
Revolving credit facility | Commitment Fee Percentage Based upon Utilization Levels in Excess of 50% of the Borrowing Base
Debt Disclosure [Line Items]
Commitment fees for undrawn credit facility		0.50%
Revolving credit facility | Minimum
Debt Disclosure [Line Items]
Credit facility interest rate option one, applicable margin rate over Adjusted LIBOR		1.50%
Credit facility interest rate option two, applicable margin rate	0.50%	0.50%
Current ratio	1	1
Revolving credit facility | Maximum
Debt Disclosure [Line Items]
Credit facility interest rate option one, applicable margin rate over Adjusted LIBOR		2.50%
Credit facility interest rate option two, applicable margin rate	1.50%	1.50%
Previous Revolving Credit Facility
Debt Disclosure [Line Items]
Letter of credit amount outstanding	1,400,000	1,400,000
Available borrowing capacity	160,000,000	160,000,000
10.375% Senior Unsecured Notes due 2016
Debt Disclosure [Line Items]
Original sale amount, percentage of par	97.00%	97.00%
Effective yield to maturity	11.00%	11.00%
Annual interest rate	10.375%	10.375%
10.375% Senior Unsecured Notes due 2016 | Semi Annual Payment, First Payment
Debt Disclosure [Line Items]
Interest payment date		June 15
10.375% Senior Unsecured Notes due 2016 | Semi Annual Payment, Second Payment
Debt Disclosure [Line Items]
Interest payment date		December 15
10.375% Senior Unsecured Notes due 2016 | Group one
Debt Disclosure [Line Items]
Redemption period start	June 2013	June 2013
Redemption option, percent of principal	105.188%	105.188%
10.375% Senior Unsecured Notes due 2016 | Group Two
Debt Disclosure [Line Items]
Redemption period start	June 2015	June 2015
Redemption option, percent of principal	100.00%	100.00%
7.25% Senior Unsecured Notes due 2019
Debt Disclosure [Line Items]
Annual interest rate	7.25%	7.25%
7.25% Senior Unsecured Notes due 2019 | Semi Annual Payment, First Payment
Debt Disclosure [Line Items]
Interest payment date		April 15
7.25% Senior Unsecured Notes due 2019 | Semi Annual Payment, Second Payment
Debt Disclosure [Line Items]
Interest payment date		October 15
7.25% Senior Unsecured Notes due 2019 | Group one
Debt Disclosure [Line Items]
Redemption period start	April 2015	April 2015
Redemption option, percent of principal	103.625%	103.625%
7.25% Senior Unsecured Notes due 2019 | Group Two
Debt Disclosure [Line Items]
Redemption period start	June 2017	June 2017
Redemption option, percent of principal	100.00%	100.00%
4.5% Convertible Notes due 2012
Debt Disclosure [Line Items]
Annual interest rate	4.50%	4.50%
Debt maturity		November 2012
Conversion rate, numerator		17.3160
Conversion rate, denominator	1,000	1,000
Initial conversion price	$ 57.75	$ 57.75
Effective interest rate		8.50%
Principal amount of Convertible Notes tendered	225,085,000
Cash paid to repurchase principal	232,963,000
Tender premium per principal amount	35
Tender offer, princpipal amount	1,000	1,000
Percentage of outstanding debt extinguished	98.00%
Loss on extinguishment of debt charged to earnings	$ (24,238,000)
4.5% Convertible Notes due 2012 | Semi Annual Payment, First Payment
Debt Disclosure [Line Items]
Interest payment date		May 15
4.5% Convertible Notes due 2012 | Semi Annual Payment, Second Payment
Debt Disclosure [Line Items]
Interest payment date		November 15