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
Balance at January 1	$ 2,476	$ 2,286	$ 2,897
Additions (reductions) based on tax positions related to prior years	142	190	(611)
Balance at December 31	$ 2,618	$ 2,476	$ 2,286