Long-Term Debt - Additional Information (Detail) (USD $)	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Nov. 27, 2013	Nov. 08, 2012	Feb. 24, 2015	Oct. 31, 2014	Jun. 24, 2014	Mar. 06, 2012
Debt Instrument [Line Items]
Proceeds from sale of warrants			$ 40,170,000
Liability component of convertible note	1,041,035,000	1,027,084,000
Proceeds from issuance of senior notes		489,250,000	300,000,000
Effective interest rates	7.51%	7.75%	7.04%
Accrued interest payment	9,022,000	9,022,000
Deferred financing costs, net of accumulated amortization	12,415,000	11,754,000
Total interest cost incurred	84,577,000	79,697,000	68,031,000
Letter of Credit [Member]
Debt Instrument [Line Items]
Outstanding borrowing under bank credit facility	480,779,000
Subsequent Event [Member] | Letter of Credit [Member]
Debt Instrument [Line Items]
Outstanding borrowing under bank credit facility						480,779,000
Minimum [Member]
Debt Instrument [Line Items]
Percentage of borrowing base utilization	1.50%
Maximum [Member]
Debt Instrument [Line Items]
Percentage of borrowing base utilization	2.50%
Bank debt [Member]
Debt Instrument [Line Items]
Credit facility initial date	Jun. 24, 2014
Redetermined base borrowing and credit facility								900,000,000
Maturity of new credit facility if note issue under 2004 indenture are retired on or before April 15, 2014	Jul. 01, 2019
Initial bank and availability under facility	0						500,000,000	500,000,000
Outstanding borrowing under bank credit facility	19,221,000
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
Debt to EBITDA ratio, as defined in credit agreement	not greater than 3.75 for preceding four quarter
EBITDA to consolidated net interest, as defined in credit agreement	not less than 2.5 for preceding four quarter
Debt to EBITDA ratio	2.26 to 1
EBITDA to consolidated net interest ratio	12.03 to 1
Liability component of convertible note	0
Bank debt [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Initial bank and availability under facility						0
Outstanding borrowing under bank credit facility						480,779,000
1.75% Senior Convertible Notes due 2017 [Member]
Debt Instrument [Line Items]
Aggregate principal amount of senior notes			300,000,000						300,000,000
Initial conversion rate of convertible note 2017	An initial conversion rate of 23.4449 shares of our common stock per $1 principal amount of 2017 Convertible Notes,
Initial conversion rate of common stock	0.0234449
Principal amount of 2017 convertible notes	$ 1
Initial conversion price of convertible note 2017	$ 42.65
Closing share price	$ 16.88
Convertible notes principal amount	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
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
Liability component of convertible note	266,035,000	252,084,000
Accrued interest payment	1,750,000
Interest expense related to amortization of discount	13,951,000	12,959,000
Amortization of deferred financing costs	1,332,000	1,238,000
Interest expense related to contractual interest coupon of convertible notes	5,250,000	5,250,000
7.5% Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Aggregate principal amount of senior notes				475,000,000	300,000,000
Liability component of convertible note	775,000,000	775,000,000
Proceeds from issuance of senior notes				480,195,000	293,203,000
Effective interest rates				3.00%
Redemption of senior notes					35.00%
Equity offerings redemption price					107.50%
Accrued interest payment	$ 7,266,000