Income Taxes - Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Current federal income tax (provision) benefit	$ 7,781	$ 7,781	$ 22,941
Current tax (provision), various states	(5)	0	(2)
Total current income tax benefit	7,776	7,781	22,939
Deferred federal income tax (provision) benefit	(282,947)	(81,054)	182,422
Tax benefit from US tax reform legislation	0	713,655	0
Deferred tax (provision) benefit, various states	(31,931)	(7,002)	27,414
Total deferred income tax (provision) benefit	(314,878)	625,599	209,836
(Provision) benefit for income taxes	$ (307,102)	$ 633,380	$ 232,775