SUPPLEMENTAL BALANCE SHEET INFORMATION - Allowance for credit losses (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 26, 2021	Sep. 27, 2020	Dec. 27, 2020	Dec. 29, 2019
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 3,964	$ 5,447	$ 2,921	$ 4,288
Provision for credit losses	2,881	6,582
Write-offs	(1,827)	(5,925)
Foreign currency translation	(11)	(22)
Ending balance	$ 3,964	$ 5,447
Cumulative-effect adjustment
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance				$ 524

Amount of allowance for credit loss on accounts receivable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5074-111524

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121599878&loc=SL82895884-210446

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Balance Type:	credit
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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of direct write-downs of accounts receivable charged against the allowance.

+ References

+ Details

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Balance Type:	debit
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- Definition

Amount of foreign currency translation gain (loss) which (increases) decreases allowance for credit loss on financing receivable.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

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Balance Type:	credit
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- Definition

Amount of expense (reversal of expense) for expected credit loss on accounts receivable.

+ References

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