Income Taxes - Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Current federal income tax (provision) benefit	$ 0	$ (7,781)	$ (7,781)
Current tax (provision), various states	0	5	0
Total current income tax (benefit)	0	(7,776)	(7,781)
Deferred federal income tax (provision) benefit	191,328	282,947	81,054
Tax benefit from US tax reform legislation	0	0	(713,655)
Deferred tax (provision) benefit, various states	21,361	31,931	7,002
Total deferred income tax provision (benefit)	212,689	314,878	(625,599)
Provision (benefit) for income taxes	$ 212,689	$ 307,102	$ (633,380)
Effective tax rate	21.50%	23.70%	(405.80%)