Geographic and Group Information (Geographic Revenue before Reimbursements) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue before reimbursements from continuing operations	$ 72,690	$ 73,718	$ 213,366	$ 219,352
Revenue Before Reimbursements [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue before reimbursements from continuing operations	66,755	68,183	197,101	202,928
Revenue Before Reimbursements [Member] | North America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue before reimbursements from continuing operations	56,014	55,321	165,301	166,092
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	$ 10,741	$ 12,862	$ 31,800	$ 36,836