Geographic and Group Information (Geographic Revenue before Reimbursements) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 28, 2019	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue before reimbursements from continuing operations	$ 73,521	$ 74,527	$ 140,676	$ 145,634
Revenue Before Reimbursements [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue before reimbursements from continuing operations	67,976	68,706	130,346	134,745
Revenue Before Reimbursements [Member] | North America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue before reimbursements from continuing operations	56,750	57,245	109,287	110,770
Revenue Before Reimbursements [Member] | International (Primarily European Countries) [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue before reimbursements from continuing operations	$ 11,226	$ 11,461	$ 21,059	$ 23,975