Debt - Schedule of debt (Details) - USD ($) $ in Thousands	Sep. 26, 2021	Dec. 31, 2020	Dec. 31, 2019
Line of Credit Facility [Line Items]
Long-term Debt, Gross	$ 575,922	$ 674,986	$ 526,635
Other	4,320	4,701
Less unamortized debt issuance costs	(12,600)	(16,684)	(15,065)
Less current portion of long-term debt	(5,528)	(5,528)	(3,800)
Long Term Debt Including Related Parties Noncurrent	570,394	669,458	522,835
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Long-term Debt, Gross		0	20,500
First Lien Note [Member]
Line of Credit Facility [Line Items]
Long-term Debt, Gross	539,202	541,969	376,200
Second Lien Note [Member]
Line of Credit Facility [Line Items]
Long-term Debt, Gross	$ 45,000	$ 145,000	$ 145,000

Long Term Debt Including Related Parties Noncurrent.

No definition available.

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Balance Type:	credit
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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
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-Section 50
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+ Details

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- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
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Balance Type:	debit
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- Definition

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.

+ References

No definition available.

+ Details

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

+ Details

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- Definition

Amount of long-term debt classified as other.

+ References

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- Details

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- Details

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- Details

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