Earnings (Loss) per Share - Schedule of Computation of Basic and Diluted Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income (loss)	$ (21,505)	$ (8,059)	$ (18,742)	$ 35,679
Basic weighted average common stock outstanding	34,420,654	33,952,574	34,337,345	33,808,237
Basic earnings (loss) per share	$ (0.62)	$ (0.24)	$ (0.55)	$ 1.06
Basic and diluted loss per share	$ (0.62)	$ (0.24)
Diluted Earnings (Loss) per Share
Net income (loss)	$ (21,505)	$ (8,059)	$ (18,742)	$ 35,679
Add back: Interest expense on Exchangeable Notes				2,542
Net income (loss) allocated to common stockholders			$ (18,742)	$ 38,221
Basic weighted average common stock outstanding	34,420,654	33,952,574	34,337,345	33,808,237
Net effect of dilutive equity awards				439,264
Net effect of assumed conversion of 5.0% Exchangeable Notes to common stock				9,524,614
Diluted weighted average common stock outstanding	34,420,654	33,952,574	34,337,345	43,772,115
Diluted earnings (loss) per share	$ (0.62)	$ (0.24)	$ (0.55)	$ 0.87