Earnings Per Share - Calculation of Basic and Diluted Weighted Average Shares Outstanding and Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended											12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Basic:
Net income (loss)	$ (190,515)	[1]	$ (29,415)	[2]	$ 4,444	$ 25,943	$ 1,752	[3],[4]	$ 36,102	$ 39,022	$ 40,758	$ (189,543)	$ 117,634	$ 149,426
Net income attributable to participating securities													(2,817)	(2,984)
Net income (loss) attributable to common stock - basic												(189,543)	114,817	146,422
Diluted:
Net income (loss)	(190,515)	[1]	(29,415)	[2]	4,444	25,943	1,752	[3],[4]	36,102	39,022	40,758	(189,543)	117,634	149,426
Net income attributable to participating securities													(2,815)	(2,982)
Net income (loss) attributable to common stock - diluted												$ (189,543)	$ 114,819	$ 146,444
Weighted average shares (denominator):
Weighted average shares - basic												52,721	48,693	48,319
Dilutive effect of stock options													42	42
Weighted average shares - diluted												52,721	48,735	48,361
Basic earnings (loss) per share	$ (3.47)		$ (0.54)		$ 0.08	$ 0.52	$ 0.04		$ 0.72	$ 0.78	$ 0.82	$ (3.60)	$ 2.36	$ 3.03
Diluted earnings (loss) per share	$ (3.47)		$ (0.54)		$ 0.08	$ 0.52	$ 0.04		$ 0.72	$ 0.78	$ 0.82	$ (3.60)	$ 2.36	$ 3.03

[1] Includes a write-down of oil and gas properties of $304,062 before income tax effect ($194,600 net of income tax effect).

[2] Includes a write-down of oil and gas properties of $47,130 before income tax effect ($30,163 net of income tax effect).

[3] Includes franchise tax settlement of $12,590 before income tax effect ($8,058 net of income tax effect).

[4] Includes loss on early extinguishment of debt of $27,279 before income tax effect ($17,459 net of income tax effect).