Summary of Significant Accounting Policies - Reconciliation of Basic and Diluted Income (Loss) Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share Basic And Diluted [Abstract]
Net income	$ 5,807	$ 9,293	$ 5,241	$ 5,284	$ 5,942	$ 8,057	$ 8,735	$ 4,388	$ 25,625	$ 27,122	$ 133,825
Denominator:
Weighted average common shares outstanding, basic									87,920,230	88,680,322	87,401,123
Basic earnings per share:
Net income per share, basic	$ 0.07	$ 0.11	$ 0.06	$ 0.06	$ 0.07	$ 0.09	$ 0.10	$ 0.05	$ 0.29	$ 0.31	$ 1.53
Net income	$ 5,807	$ 9,293	$ 5,241	$ 5,284	$ 5,942	$ 8,057	$ 8,735	$ 4,388	$ 25,625	$ 27,122	$ 133,825
Denominator:
Weighted average common shares outstanding, basic									87,920,230	88,680,322	87,401,123
Dilutive securities:
Stock options									1,815,489	1,856,707	1,625,668
Restricted stock units									559,466	406,705	311,905
Weighted average common shares outstanding, diluted									90,295,185	90,943,734	89,338,696
Diluted earnings per share:
Net income per share, diluted	$ 0.06	$ 0.10	$ 0.06	$ 0.06	$ 0.07	$ 0.09	$ 0.10	$ 0.05	$ 0.28	$ 0.30	$ 1.50