Income Taxes Components of current and deferred income tax expense (benefit) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current provision (benefit)
Federal									$ (44,462)	$ 81,101	$ 9,464
State and other									7,202	(11,801)	(13,104)
Current Income Tax Expense (Benefit)									(37,260)	69,300	(3,640)
Deferred provision (benefit)
Federal									271,544	444,695	312,288
State and other									91,233	(22,388)	22,499
Deferred Income Tax Expense (Benefit)									362,777	422,307	334,787
Income tax expense (benefit)	$ 91,842	$ 95,153	$ 85,081	$ 53,440	$ 331,352	$ 90,710	$ 21,798	$ 47,747	$ 325,517	$ 491,607	$ 331,147