Long-Term Debt - Additional Information (Detail) (USD $)	12 Months Ended			1 Months Ended	12 Months Ended		12 Months Ended		12 Months Ended				1 Months Ended			12 Months Ended		1 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Senior Convertible Notes due 2017	Dec. 31, 2012 Senior Convertible Notes due 2017	Mar. 06, 2012 Senior Convertible Notes due 2017	Dec. 31, 2012 Bank Debt	Apr. 26, 2011 Bank Debt	Dec. 31, 2012 Bank Credit Facility	Feb. 21, 2013 Bank Credit Facility Subsequent Event	Dec. 31, 2012 Letter of Credit	Feb. 21, 2013 Letter of Credit Subsequent Event	Nov. 08, 2012 7.5% Senior Notes due 2022	Nov. 17, 2010 8.625% Senior Notes due 2017	Jan. 26, 2010 8.625% Senior Notes due 2017	Dec. 31, 2012 6.75% Senior Subordinated Notes due 2014	Dec. 15, 2004 6.75% Senior Subordinated Notes due 2014	Feb. 28, 2010 8.25 % Senior Subordinated Notes due 2011	Dec. 31, 2010 8.25 % Senior Subordinated Notes due 2011	Dec. 05, 2001 8.25 % Senior Subordinated Notes due 2011
Debt Instrument [Line Items]
Credit facility initial date							Apr. 26, 2011
Redetermined base borrowing and credit facility								$ 700,000,000
Maturity of new credit facility if note issue under 2004 indenture are retired on or before April 15, 2014									Apr. 26, 2015
Initial bank and availability under facility							400,000,000		379,046,000	379,046,000
Outstanding borrowing under bank credit facility									0	0	20,954,000	20,954,000
Period in which outstanding amount has to be repaid to cure deficiency							10 days
Period in which bank has to add new properties to borrowing base and has to grant mortgage to banks							30 days
Oil and gas reserve as proportion of discounted present value of future net cash flow, for mortgage							80.00%
Debt to EBITDA ratio, as defined in credit agreement							not greater than 3.25 for preceding four quarter
EBITDA to consolidated net interest, as defined in credit agreement							not less than 3.0 for preceding four quarter
Debt to EBITDA ratio							1.55 to 1
EBITDA to consolidated net interest ratio							21.56 to 1
Aggregate principal amount of senior notes						300,000,000							300,000,000	100,000,000	275,000,000		200,000,000			200,000,000
Proceeds from issuance of senior notes	300,000,000		375,000,000		291,145,000								293,203,000	98,227,000	265,299,000
Interest rate due on convertible note due 2017						1.75%
Initial conversion rate of convertible note 2017					Initial conversion rate of 23.4449 shares of our common stock per $1 principal amount of 2017 Convertible Notes
Initial conversion price of convertible note 2017				$ 42.65	$ 42.65
Closing share price				$ 20.52
Convertible notes principal amount				1,000	1,000
Percentage of current conversion price lower than closing sale price					130.00%
Maximum trading day					20 days
Consecutive trading days ending on last trading day					30 days
Period in which distribution is made to all holders of common stock rights, option or warrants					45 days
Consecutive trading days immediately preceding, but excluding, declaration date					10 days
Percentage in which distribution has per share value exceeding closing sale price of common stock					10.00%
Percentage in which closing sale price of common stock is excess of convertible notes					98.00%
Number of consecutive business day					5 days
Number of consecutive trading day				25 days	25 days
Percentage of convertible notes principal amount					100.00%
Payment for call option					70,830,000
Anti-dilution adjustments for purchases of call option					7,033,470
Strike price per share					$ 55.91
Proceeds from sale of warrants					40,170,000
Carrying amount of liability component				229,170,000	229,170,000
Effective market interest rate					7.51%
Carrying amount of equity component				70,830,000	70,830,000
Transaction costs allocated to liability and equity components					8,855,000
Proceeds from warrant transaction				40,170,000	40,170,000
Liability component of convertible note				239,126,000	239,126,000
Interest cost related to amortization of discount					9,956,000
Amortization of deferred financing cost					951,000
Interest cost related to contractual interest coupon of convertible notes					4,302,000
Accrued interest payment				1,750,000	1,750,000
Redemption of senior notes													35.00%	35.00%
Equity offerings redemption price													107.50%
Accrued interest payment	18,546,000	14,059,000											3,313,000	13,477,000
Total cost of the redemption																204,355,000		202,382,000
Cost of redemption excluding accrued and unpaid interest																200,681,000		200,483,000
Accrued and unpaid interest																3,674,000		1,899,000
Redemption resulted in a charge to earnings	1,972,000	607,000	1,820,000													1,972,000			1,820,000
Deferred financing costs, net of accumulated amortization	27,753,000	14,437,000		6,764,000	6,764,000
Effective interest rates	7.51%	7.75%	8.08%
Total interest cost incurred	$ 68,031,000	$ 51,322,000	$ 42,975,000