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		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Basic:
Net income	$ 4,444	$ 39,022	$ 30,387	$ 79,780
Net income attributable to participating securities	(111)	(1,015)	(698)	(1,794)
Net income attributable to common stock - basic	4,333	38,007	29,689	77,986
Diluted:
Net income	4,444	39,022	30,387	79,780
Net income attributable to participating securities	(111)	(1,015)	(697)	(1,793)
Net income attributable to common stock - diluted	$ 4,333	$ 38,007	$ 29,690	$ 77,987
Weighted average shares (denominator):
Weighted average shares - basic	52,050	48,687	50,540	48,653
Dilutive effect of stock options	58	38	54	38
Dilutive effect of convertible notes	265		133
Weighted average shares - diluted	52,373	48,725	50,727	48,691
Basic earnings per share	$ 0.08	$ 0.78	$ 0.59	$ 1.60
Diluted earnings per share	$ 0.08	$ 0.78	$ 0.59	$ 1.60