Net Income Per Share - Schedule of Earnings Per Share, Basic and Diluted (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Numerator:        
Net income, as reported $ 2,425 $ 8,039 $ 14,436 $ 21,300
Less: net income attributable to participating securities (84) (202) (454) (501)
Net income available to common shareholders-basic $ 2,341 $ 7,837 $ 13,982 $ 20,799
Basic:        
Weighted-average shares of common stock outstanding 41,687,590 39,797,638 40,730,524 39,771,986
Less: weighted-average shares of unvested restricted common stock outstanding (1,710,470) (1,027,012) (1,382,087) (963,540)
Weighted-average number of common shares used in computing basic net income per common share 39,977,120 38,770,626 39,348,437 38,808,446
Net income per share applicable to common shareholders-basic $ 0.06 $ 0.20 $ 0.36 $ 0.54
Net income available to common shareholders-basic $ 2,341 $ 7,837 $ 13,982 $ 20,799
Add-back: undistributed earnings allocated to unvested shareholders (88) 105 33 227
Less: undistributed earnings reallocated to unvested shareholders 87 (104) (32) (224)
Net income available to common shareholders-diluted $ 2,340 $ 7,838 $ 13,983 $ 20,802
Weighted-average shares of common stock outstanding 41,687,590 39,797,638 40,730,524 39,771,986
Less: weighted-average shares of unvested restricted common stock outstanding (1,710,470) (1,027,012) (1,382,087) (963,540)
Weighted-average number of common shares used in computing diluted net income per common share 40,261,247 39,230,783 39,699,790 39,382,558
Net income per share applicable to common shareholders-diluted $ 0.06 $ 0.20 $ 0.35 $ 0.53
Weighted Average [Member]        
Basic:        
Weighted-average number of common shares issuable upon exercise of outstanding stock options, based on the treasury stock method 284,127 460,157 351,353 574,112