Income Taxes - Components of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Current	$ 3,813	$ 26,359	$ 29,885
Deferred	(84,585)	4,108	6,085
Total income tax expense	$ (80,772)	$ 30,467	$ 35,970