Income Taxes (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current income tax provision
State income tax	$ 21	$ 108	$ 371
Federal alternative minimum tax	(8,178)	(1,144)	2,588
Net current income tax (benefit) provision	(8,157)	(1,036)	2,959
Deferred income tax provision (benefit)
Federal tax (benefit) expense at statutory rate	45,447	(34,333)	(289,412)
State income tax	368	539	(13,215)
Permanent differences	(4,740)	(499)	698
AMT credit refundable (net of sequestration)	0	1,144	(2,588)
AMT credit refundable (net of sequestration)	8,178	0	0
Tax Cuts and Jobs Act rate change	51,525	0	0
Change in federal valuation allowance	(101,917)	33,688	145,777
Change in state valuation allowance	1,139	(539)	8,413
Net deferred income tax benefit	0	0	(150,327)
Total income tax benefit	$ (8,157)	$ (1,036)	$ (147,368)
Federal statutory rate	35.00%	35.00%	35.00%