Income Taxes (Narrative) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Federal statutory income tax rate, percent			35.00%
Tax benefit from change in enacted tax rate	[1]	$ (81,307)	$ 0	$ 0
Income tax benefit		(57,678)	$ (71,194)	$ (626,948)
Operating loss carryforwards		587,900
Unrecognized tax benefits		$ 0
Start
Operating Loss Carryforwards [Line Items]
Operating loss expiration period		Jan. 01, 2021
End
Operating Loss Carryforwards [Line Items]
Operating loss expiration period		Jan. 01, 2037
Effective starting 2018 [Member]
Operating Loss Carryforwards [Line Items]
Federal statutory income tax rate, percent		21.00%

[1] In 2017, the revaluation from the Tax Act.