Goodwill and Intangible Assets - Gross Amount, Accumulated Amortization and Estimated Amortization (Details) - USD ($) $ in Thousands	3 Months Ended
Dec. 27, 2020	Sep. 27, 2020
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 84,471	$ 106,421
Accumulated Amortization	(73,578)	(92,478)
Estimated amortization expense
2021	5,600
2022	2,741
2023	1,962
2024	590
Total	$ 10,893	13,943
Client relations
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Life (in Years)	2 years 9 months 18 days
Gross Amount	$ 47,222	60,775
Accumulated Amortization	$ (40,497)	(53,392)
Backlog
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Life (in Years)	7 months 6 days
Gross Amount	$ 30,085	37,682
Accumulated Amortization	$ (27,329)	(32,761)
Trade names
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Life (in Years)	1 year 10 months 24 days
Gross Amount	$ 7,164	7,964
Accumulated Amortization	$ (5,752)	$ (6,325)

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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-Publisher FASB
-Name Accounting Standards Codification
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Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
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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).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
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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 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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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 340
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Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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