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
	Mar. 31, 2014	Mar. 31, 2013
Basic:
Net income	$ 25,943	$ 40,758
Net income attributable to participating securities	(537)	(770)
Net income attributable to common stock - basic	25,406	39,988
Diluted:
Net income	25,943	40,758
Net income attributable to participating securities	(537)	(770)
Net income attributable to common stock - diluted	$ 25,406	$ 39,988
Weighted average shares (denominator):
Weighted average shares - basic	49,013	48,619
Dilutive effect of stock options	49	38
Weighted average shares - diluted	49,062	48,657
Basic earnings per share	$ 0.52	$ 0.82
Diluted earnings per share	$ 0.52	$ 0.82