Income Taxes - Unrecognized tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes
Recognized tax benefit				$ 700
Unrecognized tax benefits	$ 1,836	$ 1,476	$ 1,476	1,836	$ 4,314	$ 1,476
Accrued interest and penalties on unrecognized tax benefits				2,100	2,100	$ 2,300
Interest and penalties recorded on unrecognized tax benefits	(0)	(200)	(400)
Uncertain tax position	2,600
Reconciliation of total amounts of unrecognized tax benefits
Balance at beginning of the period	4,314	1,476	1,047
Gross increases - tax positions in current period	151	1,470	128
Balance at end of the period	1,836	4,314	1,476
Deferred taxes provided for withholding or other taxes for repatriation of foreign earnings	0
Undistributed earnings from foreign subsidiaries				106,300
Foreign withholding taxes on the undistributed earnings				$ 6,000	$ 6,300
Undistributed Foreign Earnings	300	1,600	4,700
Prior tax period 1
Reconciliation of total amounts of unrecognized tax benefits
Gross increases - tax positions in prior period		1,378	$ 301
Gross decreases - tax positions in prior period	(21)
Prior tax period 2
Reconciliation of total amounts of unrecognized tax benefits
Gross decreases - tax positions in prior period	$ (2,608)	$ (10)