Income (Loss) Per Common Share - Computations of Basic and Diluted Income (Loss) Per Common Share (Detail) - USD ($) $ / shares in Units, $ 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
Earnings Per Share Reconciliation [Abstract]
Net income (loss)		$ 115,185	$ 1,419	$ (79,836)	$ 49,238	$ 116,604	$ (30,598)
Participating earnings	[1]	(1,592)		(69)		(1,400)	(126)
Basic net income (loss) attributed to common shareholders		113,593		(79,905)		115,204	(30,724)
Reallocation of participating earnings	[1]	4				6
Diluted net income (loss) attributed to common shareholders		$ 113,597		$ (79,905)		$ 115,210	$ (30,724)
Net loss per common share:
Basic		$ 0.46		$ (0.32)		$ 0.46	$ (0.13)
Diluted		$ 0.46		$ (0.32)		$ 0.46	$ (0.13)

[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.