Acquisitions (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Contingent consideration liability		$ 2,211
Goodwill	$ 15,794	15,794
Challenger And Hybrid [Member]
Business Acquisition [Line Items]
Acquisition purchase price		22,800
Contingent consideration liability		6,000
Cash		1,200
Intangible assets		9,900
Net liabilities assumed		1,200
Goodwill		12,900
Challenger And Hybrid [Member] | Other Long-Term Liabilities [Member]
Business Acquisition [Line Items]
Contingent consideration liability		2,100
Challenger And Hybrid [Member] | Accrued Expenses And Other Current Liabilities [Member]
Business Acquisition [Line Items]
Contingent consideration liability		$ 100