Net Income (Loss) Per Share - Calculation of Basic and Diluted Weighted-Average Number of Shares of Common Stock and EPS (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Basic:
Net income (loss), basic	$ 27,512	$ (19,036)	$ 13,414	$ (21,660)
Net income (loss), shares, basic	35,678	20,129	30,645	19,848
Net income (loss), per share, basic	$ 0.77	$ (0.95)	$ 0.44	$ (1.09)
Weighted-average number of shares of common stock-diluted:
Restricted stock and performance unit awards	148		185
Diluted:
Net income (loss), diluted	$ 27,512	$ (19,036)	$ 13,414	$ (21,660)
Net income (loss), shares, diluted	35,826	20,129	30,830	19,848
Net income (loss), per share, diluted	$ 0.77	$ (0.95)	$ 0.44	$ (1.09)