GOODWILL AND INTANGIBLE ASSETS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2017	Dec. 31, 2016	Dec. 26, 2015
Components of amortized intangible assets
Gross Carrying Amount	$ 216,035	$ 205,079
Accumulated Amortization	142,289	121,486
Amortization expense for intangible assets	15,911	15,935	$ 18,339
Estimated amortization expense
2016	14,537
2017	13,761
2018	12,647
2019	10,525
2020	7,550
Customer Relationships
Components of amortized intangible assets
Gross Carrying Amount	200,810	191,316
Accumulated Amortization	$ 131,062	$ 111,342
Weighted Average Life	13 years	13 years
Proprietary Software And Database
Components of amortized intangible assets
Gross Carrying Amount	$ 3,671	$ 3,616
Accumulated Amortization	$ 3,107	$ 3,056
Weighted Average Life	8 years	8 years
Patents & Proprietary Technology
Components of amortized intangible assets
Gross Carrying Amount	$ 6,693	$ 6,434
Accumulated Amortization	$ 3,999	$ 3,420
Weighted Average Life	11 years	11 years
Other
Components of amortized intangible assets
Gross Carrying Amount	$ 4,861	$ 3,713
Accumulated Amortization	$ 4,121	$ 3,668
Weighted Average Life	3 years	3 years