(Loss) Income Per Common Share - Computations of Basic and Diluted Loss Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share Reconciliation [Abstract]
Net (loss) income, as reported		$ (127,700)	$ (41,971)	$ 111,961	$ (360,679)
Participating earnings	[1]	(58)	(56)	(1,251)	(167)
Basic net (loss) income attributed to common shareholders		(127,758)	(42,027)	110,710	(360,846)
Reallocation of participating earnings	[1]	0	0	1	0
Diluted net (loss) income attributed to common shareholders		$ (127,758)	$ (42,027)	$ 110,711	$ (360,846)
Net (loss) income per common share:
Basic		$ (0.52)	$ (0.23)	$ 0.45	$ (2.10)
Diluted		$ (0.52)	$ (0.23)	$ 0.45	$ (2.10)

[1] Restricted Stock Awards represent participating securities because they participate in nonforfeitable dividends or distributions with common equity owners. Income allocable to participating securities represents the distributed and undistributed earnings attributable to the participating securities. Participating securities, however, do not participate in undistributed net losses.