Net Income (Loss) Per Share - Calculations of Net Income (Loss) Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Basic:
Net loss	$ (698)	$ (2,497)	$ 36,093	$ 21,663	$ (16,623)	$ 32,060	$ (24,896)	$ (6,170)	$ 54,561	$ (15,629)
Basic (in shares)									20,636	20,544
Net income (loss) per share (in dollars per share)	$ (0.03)	$ (0.12)	$ 1.75	$ 1.05	$ (0.81)	$ 1.56	$ (1.21)	$ (0.30)	$ 2.64	$ (0.76)
Diluted:
Net loss	$ (698)	$ (2,497)	$ 36,093	$ 21,663	$ (16,623)	$ 32,060	$ (24,896)	$ (6,170)	$ 54,561	$ (15,629)
Diluted (in shares)									20,636	20,544
Net income (loss) per share (in dollars per share)	$ (0.03)	$ (0.12)	$ 1.75	$ 1.05	$ (0.81)	$ 1.56	$ (1.21)	$ (0.30)	$ 2.64	$ (0.76)