Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets:
Basis difference – investments	$ 8,015	$ 17,261
Federal NOL carryforwards	145,608	239,942
State NOL carryforwards	8,301	35,896
Other	2,756	2,816
Gross deferred tax asset	164,680	295,915
Valuation allowance	(162,708)	(292,214)
Deferred tax asset	1,972	3,701
Deferred tax liabilities:
Other	1,972	3,701
Deferred tax liability	1,972	3,701
Net deferred tax asset	$ 0	$ 0