Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income
Period Start Balance	$ 236,369	$ 265,431	$ 290,105
Period End Balance	124,060	236,369	265,431
Amounts reclassified from AOCI	0	0	0
Unrealized Gain/(Loss) on Marketable Securities
Accumulated Other Comprehensive Income
Period Start Balance	(32)
Other comprehensive gain	19
Period End Balance	(13)	(32)
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	2,564	2,541	2,307
Other comprehensive gain	19
Period End Balance	$ 2,583	$ 2,564	$ 2,541