Geographic And Group Information (Geographic Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Apr. 01, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 71,429	$ 68,778
North America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	58,620	59,517
International (Primarily European Countries) [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 12,809	$ 9,261

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Name:	us-gaap_Revenues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration