Earnings Per Share - Details of Basic and Diluted Earnings Per Share (EPS) (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	$ 13,504	$ 30,372	$ 30,277	$ 49,689
Weighted average common shares outstanding used in basic EPS	43,457	43,049	43,363	43,233
Common shares issuable upon exercise of dilutive stock options and PSAs / RSUs	408	792	586	878
Weighted average common shares outstanding and common share equivalents used in diluted EPS	43,865	43,841	43,949	44,111
Earnings per share
Basic	$ 0.31	$ 0.71	$ 0.70	$ 1.15
Diluted	$ 0.31	$ 0.69	$ 0.69	$ 1.13