Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income
Period Start Balance	$ 94,026	$ 124,060	$ 236,369
Period End Balance	209,357	94,026	124,060
Amounts reclassified from AOCI	0	0	0
Unrealized Gain/(Loss) on Marketable Securities
Accumulated Other Comprehensive Income
Period Start Balance	23
Other comprehensive loss	(30)
Period End Balance	(7)	23
Foreign Currency Items
Accumulated Other Comprehensive Income
Period Start Balance	2,596
Period End Balance	2,596	2,596
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income
Period Start Balance	2,619	2,583	2,564
Other comprehensive loss	(30)
Period End Balance	$ 2,589	$ 2,619	$ 2,583