Income Taxes (Income Tax Provision (Benefit)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current income tax expense (benefit)
Federal	$ (17,885)	$ (19,485)	$ 0
State	1,884	(1,388)	(785)
Total current income tax benefit	(16,001)	(20,873)	(785)
Deferred income tax expense (benefit)
Federal	93,395	(113,863)	(521,519)
State	9,839	18,084	(21,866)
Total deferred income tax expense (benefit)	103,234	(95,779)	(543,385)
Total income tax expense (benefit)	$ 87,233	$ (116,652)	$ (544,170)