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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Basic:
Net income (loss)	$ (29,097)	$ 38,976	$ (51,194)	$ 23,524
Weighted average common shares outstanding (in shares)	20,411	20,333	20,395	20,391
Net income (loss) per share (in dollars per share)	$ (1.43)	$ 1.92	$ (2.51)	$ 1.15
Diluted:
Interest on convertible senior debentures	$ 0	$ 1,119	$ 0	$ 2,229
Net income (loss) for dilutive share computation	$ (29,097)	$ 40,095	$ (51,194)	$ 25,753
Convertible senior debentures (in shares)	0	3,034	0	3,034
Unvested restricted stock and DSUs (in shares)	0	148	0	155
Employee stock options (in shares)	0	24	0	22
Weighted average common shares outstanding (in shares)	20,411	23,539	20,395	23,602
Net income (loss) per share (in dollars per share)	$ (1.43)	$ 1.70	$ (2.51)	$ 1.09