Summary of Significant Accounting Policies - Calculation of Basic and Diluted Earnings (Loss) Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Accounting Policies [Abstract]
Net Income (Loss)	$ (1,910)	$ (96,229)	$ 222,423	$ (29,360)	$ (46,906)	$ (24,937)	$ (98,139)	$ (71,843)
Basic weighted-average common shares outstanding in period (in shares)	210,377,152				209,393,002		210,155,678	166,731,287
Diluted weighted-average common shares outstanding in period (in shares)	210,377,152				209,393,002		210,155,678	166,731,287
Net Income (Loss) Per Common Share, Basic (in dollars per share)	$ (0.01)				$ (0.22)		$ (0.47)	$ (0.43)
Net Income (Loss) Per Common Share, Diluted (in dollars per share)	$ (0.01)				$ (0.22)		$ (0.47)	$ (0.43)