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				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Basic:
Net income (loss)	$ 36,093	$ 21,663	$ (24,896)	$ (6,170)	$ 57,756	$ (31,066)
Weighted average common shares outstanding (in shares)	20,628		20,539		20,606	20,523
Net income (loss) per share (in dollars per share)	$ 1.75		$ (1.21)		$ 2.80	$ (1.51)
Diluted:
Unvested restricted stock and DSU's	30		0		0	0
Employee stock options	0		0		0	0
Weighted average common shares outstanding	$ 20,658		$ 20,539		$ 20,606	$ 20,523
Net income (loss) per dilutive share	$ 0		$ 0		$ 0	$ 0