Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of beginning of period	$ 8,478	$ 12,596	$ 12,004
Additions for prior year tax positions	0	0	0
Reductions for prior year tax positions	0	(1,849)	0
Additions for current year tax positions	0	0	592
Reductions for current year tax positions	0	0	0
Reductions related to closed years/settlements with tax authorities	(4,585)	(2,269)	0
Balance as of end of period	$ 3,893	$ 8,478	$ 12,596