Income Taxes - Income Tax Benefit Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of unrecognized tax benefits
Balance at January 1	$ 1,606	$ 1,510	$ 1,485
Additions based on positions related to current period	313	467	25
Reductions due to lapse of statute of limitations	0	(371)	0
Balance at December 31	$ 1,919	$ 1,606	$ 1,510