Earnings Per Share - Reconciliation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Net income	$ 19,374	$ 12,219	$ 39,709	$ 66,258
Weighted average common shares outstanding – basic	22,107	22,488	22,151	22,573
Weighted average common stock equivalents	485	487	465	479
Weighted average common shares outstanding – diluted	22,592	22,975	22,616	23,052
Earnings per share:
Basic (USD per share)	$ 0.88	$ 0.54	$ 1.79	$ 2.94
Diluted (USD per share)	$ 0.86	$ 0.53	$ 1.76	$ 2.87