Net Income per Share - Reconciliation of Basic to Diluted Net Income per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net income	$ 13,277	$ 5,313	$ 38,987	$ 23,472
Shares used in net income per common share - basic (in shares)	29,008	25,726	28,912	25,684
Dilutive effect of the equity premium on Convertible Notes at the average price of common stock (in shares)		295		123
Incremental shares of unvested restricted common stock (in shares)	66		89	6
Shares used in net income per common share - diluted (in shares)	29,074	26,021	29,001	25,813
Earnings per share:
Basic net income	$ 0.46	$ 0.21	$ 1.35	$ 0.91
Diluted net income	$ 0.46	$ 0.20	$ 1.34	$ 0.91