Income Taxes - Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Increase (decrease) in valuation allowance before consideration of the Tax Act	$ (5,713)	$ 246,037
Increase (decrease) in valuation allowance before consideration of the Tax Act	0	48,531
Total increase (decrease) in valuation allowance	(5,713)	294,568
Tax Act rate change - decrease in valuation allowance	0	(172,235)
Impact on net operating loss usage	6,042	(50,551)
Total increase (decrease) in valuation allowance due to Tax Act	6,042	(222,786)
Total increase (decrease) in valuation allowance	$ 329	$ 71,782