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		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Basic:
Net income (loss)	$ (29,415)	$ 36,102	$ 972	$ 115,882
Net income attributable to participating securities		(924)	(22)	(2,728)
Net income (loss) attributable to common stock-basic	(29,415)	35,178	950	113,154
Diluted:
Net income (loss)	(29,415)	36,102	972	115,882
Net income attributable to participating securities		(923)	(22)	(2,726)
Net income (loss) attributable to common stock-diluted	$ (29,415)	$ 35,179	$ 950	$ 113,156
Weighted average shares (denominator):
Weighted average shares-basic	54,866	48,732	51,998	48,680
Dilutive effect of stock options		44	53	40
Dilutive effect of convertible notes			88
Weighted average shares-diluted	54,866	48,776	52,139	48,720
Basic earnings (loss) per share	$ (0.54)	$ 0.72	$ 0.02	$ 2.32
Diluted earnings (loss) per share	$ (0.54)	$ 0.72	$ 0.02	$ 2.32