GOODWILL AND INTANGIBLE ASSETS - Amortized Intangible Assets - (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 27, 2021	Mar. 28, 2020	Dec. 26, 2020
Components of amortized intangible assets
Gross Carrying Amount	$ 270,695		$ 271,042
Accumulated Amortization	175,941		170,847
Amortization expense for intangible assets	4,232	$ 4,593
Estimated amortization expense
2021	15,976
2022	13,337
2023	11,503
2024	9,587
2025	8,153
Customer Relationships
Components of amortized intangible assets
Gross Carrying Amount	237,388		237,232
Accumulated Amortization	$ 160,088		$ 155,760
Weighted Average Life	13 years		13 years
Patents & Proprietary Technology
Components of amortized intangible assets
Gross Carrying Amount	$ 25,823		$ 26,208
Accumulated Amortization	$ 8,642		$ 8,301
Weighted Average Life	14 years		14 years
Other
Components of amortized intangible assets
Gross Carrying Amount	$ 7,484		$ 7,602
Accumulated Amortization	$ 7,211		$ 6,786
Weighted Average Life	4 years		4 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 remainder of current fiscal year.

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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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