Intangible Assets and Goodwill Changes In Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Amortization of purchased intangibles	$ 943	$ 1,212	$ 1,928
Original cost	15,385	15,195
Accumulated amortization	(13,242)	(12,120)
Net identifiable intangible assets	2,143	3,075
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Original cost	4,945	4,878
Accumulated amortization	(3,861)	(3,293)
Net identifiable intangible assets	1,084	1,585
Developed technology
Finite-Lived Intangible Assets [Line Items]
Original cost	8,256	8,135
Accumulated amortization	(8,151)	(7,741)
Net identifiable intangible assets	105	394
Trademarks / trade names
Finite-Lived Intangible Assets [Line Items]
Original cost	2,184	2,182
Accumulated amortization	(1,230)	(1,086)
Net identifiable intangible assets	$ 954	$ 1,096