Income Taxes (Deferred Tax Assets and Liabilities by Balance Sheet Classification (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets and Liabilities by Balance Sheet Classification [Abstract]
Deferred tax assets	$ 152,362	$ 233,900
Deferred tax liabilities	(237)	(1,472)
Total net deferred tax assets	$ 152,125	$ 232,428