Geographic and Group Information (Geographic Revenue before Reimbursements) (Details) - USD ($) $ in Thousands	3 Months Ended
	Apr. 02, 2021	Mar. 27, 2020
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from continuing operations before reimbursements	$ 63,486	$ 69,533
Revenue from Continuing Operations Before Reimbursement [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from continuing operations before reimbursements	63,410	65,186
Revenue from Continuing Operations Before Reimbursement [Member] | North America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from continuing operations before reimbursements	57,138	57,054
Revenue from Continuing Operations Before Reimbursement [Member] | International (Primarily European Countries) [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from continuing operations before reimbursements	$ 6,272	$ 8,132