GOODWILL AND INTANGIBLE ASSETS - Amortized Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Dec. 26, 2020	Dec. 28, 2019	Dec. 26, 2020	Dec. 28, 2019	Dec. 29, 2018
Components of amortized intangible assets
Gross Carrying Amount	$ 271,042	$ 269,748	$ 271,042	$ 269,748
Accumulated Amortization	170,847	163,113	170,847	163,113
Amortization expense for intangible assets	18,147	18,087			$ 15,328
Estimated Amortization Expense
2021	15,435		15,435
2022	13,270		13,270
2023	11,571		11,571
2024	9,656		9,656
2025	8,222		8,222
Customer Relationships
Components of amortized intangible assets
Gross Carrying Amount	237,232	237,626	237,232	237,626
Accumulated Amortization	155,760	149,720	$ 155,760	$ 149,720
Weighted Average Life			13 years	13 years
Patents & Proprietary Technology
Components of amortized intangible assets
Gross Carrying Amount	26,208	24,068	$ 26,208	$ 24,068
Accumulated Amortization	8,301	6,358	$ 8,301	$ 6,358
Weighted Average Life			14 years	14 years
Other
Components of amortized intangible assets
Gross Carrying Amount	7,602	8,054	$ 7,602	$ 8,054
Accumulated Amortization	$ 6,786	$ 7,035	$ 6,786	$ 7,035
Weighted Average Life			4 years	5 years

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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