GOODWILL AND INTANGIBLE ASSETS - Amortized Intangible Assets - (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 30, 2017	Sep. 24, 2016	Dec. 31, 2016
Components of amortized intangible assets
Gross Carrying Amount	$ 215,396		$ 215,396		$ 205,079
Accumulated Amortization	137,847		137,847		121,486
Amortization expense for intangible assets	4,025	$ 3,964	11,792	$ 12,037
Estimated amortization expense
2015	15,823		15,823
2016	14,492		14,492
2017	13,718		13,718
2018	12,608		12,608
2019	10,474		10,474
Customer Relationships
Components of amortized intangible assets
Gross Carrying Amount	200,269		200,269		191,316
Accumulated Amortization	126,845		$ 126,845		$ 111,342
Weighted Average Life			13 years		13 years
Proprietary Software & Database
Components of amortized intangible assets
Gross Carrying Amount	3,687		$ 3,687		$ 3,616
Accumulated Amortization	3,111		$ 3,111		$ 3,056
Weighted Average Life			8 years		8 years
Patents & Proprietary Technology
Components of amortized intangible assets
Gross Carrying Amount	6,633		$ 6,633		$ 6,434
Accumulated Amortization	3,859		$ 3,859		$ 3,420
Weighted Average Life			11 years		11 years
Other
Components of amortized intangible assets
Gross Carrying Amount	4,807		$ 4,807		$ 3,713
Accumulated Amortization	$ 4,032		$ 4,032		$ 3,668
Weighted Average Life			3 years		3 years