Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of unrecognized tax benefits
Balance at January 1	$ 5,080	$ 2,618	$ 2,476
Additions based on tax position taken in current year	(4,625)	2,758
Additions based on tax positions related to prior years	(218)	226	142
Reductions as a result of a lapse of the applicable statutes	4,203	(522)
Balance at December 31	$ 4,440	$ 5,080	$ 2,618