GOODWILL AND INTANGIBLE ASSETS - Amortized Intangible Assets - (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 24, 2016	Sep. 26, 2015	Sep. 24, 2016	Sep. 26, 2015	Dec. 27, 2014	Dec. 26, 2015
Components of amortized intangible assets
Gross Carrying Amount	$ 209,913		$ 209,913			$ 215,939
Accumulated Amortization	120,311		120,311			111,672
Amortization expense for intangible assets	3,964	$ 4,507	12,037	$ 14,157
Estimated amortization expense
2015	15,895		15,895
2016	15,390		15,390
2017	13,764		13,764
2018	12,994		12,994
2019	11,945		11,945
Customer Relationships
Components of amortized intangible assets
Gross Carrying Amount	195,371		195,371			201,801
Accumulated Amortization	109,595		$ 109,595			101,614
Weighted Average Life			13 years		13 years
Proprietary Software & Database
Components of amortized intangible assets
Gross Carrying Amount	3,658		$ 3,658			3,571
Accumulated Amortization	3,056		$ 3,056			2,966
Weighted Average Life			8 years		8 years
Patents & Proprietary Technology
Components of amortized intangible assets
Gross Carrying Amount	6,998		$ 6,998			6,815
Accumulated Amortization	3,831		$ 3,831			3,421
Weighted Average Life			11 years		11 years
Other
Components of amortized intangible assets
Gross Carrying Amount	3,886		$ 3,886			3,752
Accumulated Amortization	$ 3,829		$ 3,829			$ 3,671
Weighted Average Life			3 years		3 years