Long-Term Debt - Additional Information (Detail) (USD $)					3 Months Ended					3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Letter of Credit [Member]	May 05, 2014 Subsequent Event [Member] Letter of Credit [Member]	Mar. 31, 2014 Bank debt [Member]	Dec. 31, 2013 Bank debt [Member]	Apr. 26, 2011 Bank debt [Member]	May 05, 2014 Bank debt [Member] Subsequent Event [Member]	Apr. 30, 2014 Bank debt [Member] Subsequent Event [Member]	Mar. 31, 2014 1.75% Senior Convertible Notes due 2017 [Member]	Dec. 31, 2013 1.75% Senior Convertible Notes due 2017 [Member]	Mar. 06, 2012 1.75% Senior Convertible Notes due 2017 [Member]
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					378,600,000			378,600,000	400,000,000
Outstanding borrowing under bank credit facility			21,400,000	21,400,000	0			0
Oil and gas reserve as proportion of discounted present value of future net cash flow, for mortgage					80
Aggregate principal amount of Senior Subordinated Notes												300,000,000
Initial conversion rate of convertible note 2017										An initial conversion rate of 23.4449 shares of our common stock per $1,000 principal amount of 2017 Convertible Notes
Initial conversion rate of common stock										23.4449
Principal amount of 2017 convertible notes										$ 1,000
Initial conversion price of convertible note 2017										$ 42.65
Closing share price										$ 41.97
Payment for call option										70,800,000
Anti-dilution adjustments for purchases of call option										7,033,470
Strike price per share										$ 55.91
Proceeds from sale of warrants										40,100,000
Liability component of convertible note	1,030,466,000	1,027,084,000								255,500,000	252,100,000
Interest expense related to amortization of discount										3,400,000
Amortization of deferred financing costs										300,000
Interest expense related to contractual interest coupon of convertible notes										$ 1,300,000