Intangible Assets and Goodwill Amortization expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Amortization of purchased intangibles	$ 1,928	$ 2,101	$ 2,142
Cost of revenues
Finite-Lived Intangible Assets [Line Items]
Amortization of purchased intangibles	1,024	1,197	1,251
Operating expenses
Finite-Lived Intangible Assets [Line Items]
Amortization of purchased intangibles	$ 904	$ 904	$ 891