Income Taxes - Schedule of Significant Components of the Income Tax Expense (benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Current
U.S. federal	$ 5,966	$ 1,001
U.S. state & local	598
Total current income tax expense	6,564	1,001
Deferred
U.S. federal	(110,361)	(538)
U.S. state & local	1,516	125
Total deferred income tax expense	(108,845)	(413)
Income tax expense (benefit)	$ (102,281)	$ 588