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 the beginning and ending unrecognized tax benefit
Balance at beginning of year	$ 3,163	$ 3,892	$ 3,981
Additions based on tax positions related to the current year	470	441	400
Decreases resulting from a lapse in the applicable statute of limitations	(369)	(351)	(489)
Remeasurement due to enactment of federal tax reform	0	(819)	0
Balance at end of year	$ 3,264	$ 3,163	$ 3,892