Purchased Intangible Assets and Goodwill (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization	$ 1,073	$ 1,039	$ 1,000
Definite life intangible assets, weighted average remaining life	2 years 4 months 15 days
Minimum
Acquired Finite-Lived Intangible Assets [Line Items]
Definite life intangible assets, amortization period	13 years
Maximum
Acquired Finite-Lived Intangible Assets [Line Items]
Definite life intangible assets, amortization period	20 years