Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income
Period Start Balance	$ 124,060	$ 236,369	$ 265,431
Period End Balance	94,026	124,060	236,369
Amounts reclassified from AOCI	0	0	0
Unrealized Gain/(Loss) on Marketable Securities
Accumulated Other Comprehensive Income
Period Start Balance	(13)
Other comprehensive gain	36
Period End Balance	23	(13)
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	2,583	2,564	2,541
Other comprehensive gain	36
Period End Balance	$ 2,619	$ 2,583	$ 2,564