Identified Intangible Assets and Goodwill, Net (Details) - USD ($) $ in Thousands	Sep. 26, 2020	Dec. 31, 2019	Sep. 28, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Identified intangible assets, gross	$ 46,116	$ 44,094
Accumulated amortization	35,270	33,160
Identified intangible assets, net	10,846	10,934
Goodwill	45,152	42,285	$ 39,898	$ 37,971
Customer lists/relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Identified intangible assets, gross	29,803	28,301
Accumulated amortization	21,528	20,024
Employment-related [Member]
Finite-Lived Intangible Assets [Line Items]
Identified intangible assets, gross	8,684	8,391
Accumulated amortization	7,651	7,348
Tradenames [Member]
Finite-Lived Intangible Assets [Line Items]
Identified intangible assets, gross	7,629	7,402
Accumulated amortization	$ 6,091	$ 5,788