Income Taxes - Uncertain tax positions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
A reconciliation of the beginning and ending liability for uncertain tax positions
Balance at beginning of year	$ 3,531	$ 2,361	$ 490
Increase Resulting from Current Period Tax Positions	21	97	73
Increases for tax position taken in prior years	146	1,602	1,809
Decreases due to settlements with taxing authorities	(693)	(8)	(11)
Decreases due to lapses in the statute of limitations	(1,210)	(521)
Balance at the end of year	1,795	3,531	$ 2,361
Unrecognized tax benefits that would affect the effective tax rate, if recognized	1,174
Accrued interest and penalties reported as income tax liability	$ 502	$ 804
U.S. corporate income tax rate	21.00%	35.00%
Net deferred tax liability		$ 22,452