Long-Term Debt - Additional Information (Detail)				12 Months Ended
	Nov. 20, 2015 USD ($) instalment	Nov. 27, 2013 USD ($)	Nov. 08, 2012 USD ($)	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Feb. 22, 2016 USD ($)	Oct. 31, 2015 USD ($)	Jun. 24, 2014 USD ($)	Dec. 31, 2012 USD ($)	Mar. 06, 2012 USD ($)
Debt Instrument [Line Items]
Base borrowing and credit facility				$ 0	$ 0
Line of Credit Facility, Fair Value of Amount Outstanding				$ 0
Consolidated Funded Debt to consolidated EBITDA financial ratio covenant				3.09
Consolidated EBITDA To Consolidated Net Interest Expense				7.91
Liability component of convertible note				$ 1,060,955,000	1,032,281,000
Proceeds from issuance of senior notes				0	0	$ 489,250,000
Accrued interest payment				9,022,000	9,022,000
Total interest cost incurred				$ 85,267,000	84,577,000	79,697,000
Subsequent Event [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Fair Value of Amount Outstanding							$ 50,000,000
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
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				$ 480,779,000				$ 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				80.00%
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				3.09 to 1
EBITDA to consolidated net interest ratio				7.91 to 1
Bank debt [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Initial bank and availability under facility							430,779,000
Outstanding borrowing under bank credit facility							$ 19,221,000
Building Loan [Member]
Debt Instrument [Line Items]
Aggregate principal amount of senior notes	$ 11,802,000
Senior convertible note, stated interest rate	4.20%
Number of monthly installments | instalment	180
Monthly installment payment	$ 73,000
EBITDA to Net Interest Expense ratio	2.00			7.91
Liability component of convertible note				$ 11,702,000	$ 0
4.20% Term Loan due 2030 [Member]
Debt Instrument [Line Items]
Senior convertible note, stated interest rate				4.20%	4.20%
1.75% Senior Convertible Notes due 2017 [Member]
Debt Instrument [Line Items]
Interest Expense, Debt				$ 5,250,000	$ 5,250,000	5,250,000
Aggregate principal amount of senior notes										$ 300,000,000	$ 300,000,000
Senior convertible note, stated interest rate				1.75%	1.75%					1.75%
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				0.023445
Initial conversion price of convertible note 2017 | $ / shares				$ 42.65
Closing share price | $ / shares				$ 4.29
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
Cash share holders receive for each dollar in principle				1
Payment for call option				$ 70,830,000
Anti-dilution adjustments for purchases of call option (in shares) | shares				7,033,470
Strike price per share | $ / shares				$ 55.91
Proceeds from sale of warrants				$ 40,170,000
Liability component of convertible note				279,244,000	$ 262,791,000
Accrued interest payment				1,750,000
Interest expense related to amortization of discount				15,019,000	13,951,000	12,599,000
Amortization of deferred financing costs				1,434,000	$ 1,332,000	$ 1,238,000
Interest expense related to contractual interest coupon of convertible notes				$ 5,250,000
Effective interest rates				7.51%	7.75%	7.04%
Senior Convertible Notes Due Two Thousand Seventeen And Two Thousand And Twenty Two [Member]
Debt Instrument [Line Items]
Deferred Finance Costs, Net				$ 6,869,000	$ 8,754,000
7.5% Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Aggregate principal amount of senior notes		$ 475,000,000	$ 300,000,000
Senior convertible note, stated interest rate				7.50%	7.50%
Liability component of convertible note				$ 770,009,000	$ 769,490,000
Proceeds from issuance of senior notes		$ 480,195,000	$ 293,203,000
Effective interest rates		3.00%
Accrued interest payment				7,266,000
Other Assets [Member] | 1.75% Senior Convertible Notes due 2017 [Member]
Debt Instrument [Line Items]
Deferred Finance Costs, Net				$ 2,845,000	$ 3,661,000
Covenant Compliance [Member]
Debt Instrument [Line Items]
Consolidated Funded Debt to consolidated EBITDA financial ratio covenant				3.75
Consolidated EBITDA To Consolidated Net Interest Expense				2.5