Income Taxes - Deferred Tax Valuation Allowance (Details) - Valuation Allowance of Deferred Tax Assets - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Valuation Allowance [Line Items]
Beginning balance	$ 59,349	$ 76,395	$ 62,605
Additions	25,193	5,332	13,790
Reduction in valuation allowance due to rate change from Tax Act	(22,378)
Increase in valuation allowance due to rate change from Tax Act	5,824
Ending balance	$ 90,366	$ 59,349	$ 76,395