Income Taxes (Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Abstract]
Expected federal statutory income tax					$ (27,821)	$ (72,945)	$ (51,480)
State income taxes, net of federal benefits					(8,314)	(9,485)	(4,544)
Change in federal tax rate used for deferred purposes					112,611	200	972
Adjustment to deferred tax assets					15,210		(6,492)
Change in valuation allowance					(91,807)	82,572	61,541
Income tax expense (benefit)	$ (437)	$ 316	$ 27	$ 315	$ (121)	$ 342	$ (3)
Expected federal statutory income tax, Percent					(35.00%)	(35.00%)	(35.00%)
State income taxes, net of federal benefits, Percent					(10.50%)	(4.60%)	(3.10%)
Change in federal tax rate used for deferred purposes, Percent					141.70%	0.10%	0.70%
Adjustment to deferred tax assets, Percent					19.10%	0.00%	(4.40%)
Change in valuation allowance, Percent					(115.50%)	39.60%	41.80%
Income tax expense (benefit) , Percent					(0.20%)	0.10%	0.00%