GOODWILL AND INTANGIBLE ASSETS - Amortized Intangible Assets - (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 01, 2017	Jun. 25, 2016	Jul. 01, 2017	Jun. 25, 2016	Dec. 31, 2016
Components of amortized intangible assets
Gross Carrying Amount	$ 210,383		$ 210,383		$ 205,079
Accumulated Amortization	132,097		132,097		121,486
Amortization expense for intangible assets	3,903	$ 4,078	7,767	$ 8,073
Estimated amortization expense
2015	15,498		15,498
2016	13,840		13,840
2017	13,079		13,079
2018	11,989		11,989
2019	9,903		9,903
Customer Relationships
Components of amortized intangible assets
Gross Carrying Amount	196,201		196,201		191,316
Accumulated Amortization	121,382		$ 121,382		$ 111,342
Weighted Average Life			13 years		13 years
Proprietary Software & Database
Components of amortized intangible assets
Gross Carrying Amount	3,659		$ 3,659		$ 3,616
Accumulated Amortization	3,083		$ 3,083		$ 3,056
Weighted Average Life			8 years		8 years
Patents & Proprietary Technology
Components of amortized intangible assets
Gross Carrying Amount	6,581		$ 6,581		$ 6,434
Accumulated Amortization	3,720		$ 3,720		$ 3,420
Weighted Average Life			11 years		11 years
Other
Components of amortized intangible assets
Gross Carrying Amount	3,942		$ 3,942		$ 3,713
Accumulated Amortization	$ 3,912		$ 3,912		$ 3,668
Weighted Average Life			3 years		3 years