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 the beginning of the year	$ 1,790	$ 1,594	$ 1,039
Increases related to prior year tax positions	0	101	348
Decreases related to prior year tax positions	(152)	0	0
Increases related to current year tax positions	96	422	283
Settlements	0	0	0
Lapse of statute	0	(327)	(76)
Balance as of the end of the year	$ 1,734	$ 1,790	$ 1,594