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						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Basic:
Net income (loss)	$ (2,497)	$ 36,093	$ 21,663	$ 32,060	$ (24,896)	$ (6,170)	$ 55,259	$ 994
Weighted average common shares outstanding (in shares)	20,657			20,561			20,623	20,535
Net income (loss) per share (in dollars per share)	$ (0.12)			$ 1.56			$ 2.68	$ 0.05
Diluted:
Unvested restricted stock and DSU's	0			0			0	0
Employee stock options	0			0			0	0
Weighted average common shares outstanding	$ 20,657			$ 20,561			$ 20,623	$ 20,535
Net income (loss) per dilutive share	$ 0			$ 0			$ 0	$ 0