Income Taxes - Income Tax (Benefit) Expense Attributable to (Loss) Income Before Income Taxes (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
Components Of Income Tax Expense Benefit Continuing Operations [Abstract]
U.S. federal, Current									$ 0	$ 0	$ 0
U.S. state and local, Current									0	17	98
Total, Current	$ 0	$ 0	$ 0	$ 0	$ 17	$ 0	$ 0	$ 0	0	17	98
U.S. federal, Deferred									(25,322)	(302,507)	(266,105)
U.S. state and local, Deferred									(5,167)	51,464	(14,743)
Total, Deferred	(68,784)	24,137	(28,518)	42,676	(349,097)	(71,992)	57,651	112,395	(30,489)	(251,043)	(280,848)
U.S. federal, Total									(25,322)	(302,507)	(266,105)
U.S. state and local, Total									(5,167)	51,481	(14,645)
Total (benefit) expense for income taxes	$ (68,784)	$ 24,137	$ (28,518)	$ 42,676	$ (349,080)	$ (71,992)	$ 57,651	$ 112,395	$ (30,489)	$ (251,026)	$ (280,750)