Summary of Significant Accounting Policies - Reconciliation of Basic and Diluted Income (Loss) Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share Basic And Diluted [Abstract]
Net income (loss)	$ 5,942	$ 8,057	$ 8,735	$ 4,388	$ 151,093	$ (21,384)	$ 5,073	$ (957)	$ 27,122	$ 133,825	$ 13,601
Denominator:
Weighted average common shares outstanding, basic									88,680,322	87,401,123	85,882,646
Basic earnings per share:
Net income (loss) per share, basic	$ 0.07	$ 0.09	$ 0.10	$ 0.05	$ 1.72	$ (0.24)	$ 0.06	$ (0.01)	$ 0.31	$ 1.53	$ 0.16
Net income (loss)	$ 5,942	$ 8,057	$ 8,735	$ 4,388	$ 151,093	$ (21,384)	$ 5,073	$ (957)	$ 27,122	$ 133,825	$ 13,601
Denominator:
Weighted average common shares outstanding, basic									88,680,322	87,401,123	85,882,646
Dilutive securities:
Stock options									1,856,707	1,625,668	89,418
Restricted stock units									406,705	311,905	342,142
Weighted average common shares outstanding, diluted									90,943,734	89,338,696	86,314,206
Diluted earnings per share:
Net income (loss) per share, diluted	$ 0.07	$ 0.09	$ 0.10	$ 0.05	$ 1.67	$ (0.24)	$ 0.06	$ (0.01)	$ 0.30	$ 1.50	$ 0.16