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Franchise Rights Acquired, Goodwill and Other Intangible Assets - Additional Information (Detail)				3 Months Ended			9 Months Ended		12 Months Ended
	May 05, 2024 USD ($)	Mar. 30, 2024 USD ($)	May 07, 2023 USD ($)	Sep. 28, 2024 USD ($)	Mar. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 28, 2024 USD ($) Segment	Sep. 30, 2023 USD ($)	Dec. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Goodwill And Intangible Assets Disclosure [Line Items]
Number of reportable segments \| Segment							1
Number of operating segments \| Segment							1
Finite-lived intangible assets, aggregate amortization expense				$ 8,124,000		$ 13,628,000	$ 25,886,000	$ 32,590,000
Goodwill impairment	$ 0	$ 0	$ 0						$ 3,586,000
Net book value of goodwill				242,754,000			$ 242,754,000		$ 243,441,000	$ 155,998,000
Franchise right maturity period							7 years
Behavioral Reporting Unit
Goodwill And Intangible Assets Disclosure [Line Items]
Goodwill impairment				0
Net book value of goodwill				$ 153,012,000			$ 153,012,000
Percentage of goodwill held				63.00%			63.00%
Behavioral Reporting Unit \| Minimum
Goodwill And Intangible Assets Disclosure [Line Items]
Percentage of estimated fair value in excess of carrying amount				100.00%			100.00%
Clinical Reporting Unit
Goodwill And Intangible Assets Disclosure [Line Items]
Goodwill impairment				$ 0
Net book value of goodwill				$ 89,742,000			$ 89,742,000
Percentage of goodwill held				37.00%			37.00%
Clinical Reporting Unit \| Minimum
Goodwill And Intangible Assets Disclosure [Line Items]
Percentage of estimated fair value in excess of carrying amount				20.00%			20.00%
All Reporting Units \| Minimum
Goodwill And Intangible Assets Disclosure [Line Items]
Percentage of estimated fair value in excess of carrying amount	30.00%	25.00%			25.00%
Franchise rights acquired
Goodwill And Intangible Assets Disclosure [Line Items]
Indefinite-lived intangible assets, impairment charges	$ 0		$ 0
Franchise rights acquired \| Maximum
Goodwill And Intangible Assets Disclosure [Line Items]
Finite-lived intangible assets, estimated useful life (in years)				1 year			1 year
Franchise rights acquired \| United States
Goodwill And Intangible Assets Disclosure [Line Items]
Net book value of franchise rights acquired				$ 68,627,000			$ 68,627,000
Indefinite-lived intangible assets, impairment charges	$ 0			$ 54,295,000	$ 251,431,000
Impairment, Intangible Asset, Indefinite-Lived (Excluding Goodwill), Statement of Income or Comprehensive Income [Extensible Enumeration]	Asset Impairment Charges			Asset Impairment Charges	Asset Impairment Charges
Percentage of franchise rights acquired held				100.00%			100.00%
Franchise rights acquired \| United States \| Minimum
Goodwill And Intangible Assets Disclosure [Line Items]
Percentage of estimated fair value in excess of carrying amount	5.00%
Franchise rights acquired \| United Kingdom
Goodwill And Intangible Assets Disclosure [Line Items]
Indefinite-lived intangible assets, impairment charges	$ 0			$ 2,750,000	$ 155,000
Impairment, Intangible Asset, Indefinite-Lived (Excluding Goodwill), Statement of Income or Comprehensive Income [Extensible Enumeration]	Asset Impairment Charges			Asset Impairment Charges	Asset Impairment Charges
Franchise rights acquired \| United Kingdom \| Minimum
Goodwill And Intangible Assets Disclosure [Line Items]
Percentage of estimated fair value in excess of carrying amount	5.00%
Franchise rights acquired \| Australia
Goodwill And Intangible Assets Disclosure [Line Items]
Indefinite-lived intangible assets, impairment charges					$ 4,074,000
Impairment, Intangible Asset, Indefinite-Lived (Excluding Goodwill), Statement of Income or Comprehensive Income [Extensible Enumeration]					Asset Impairment Charges
Franchise rights acquired \| New Zealand
Goodwill And Intangible Assets Disclosure [Line Items]
Indefinite-lived intangible assets, impairment charges					$ 2,328,000
Impairment, Intangible Asset, Indefinite-Lived (Excluding Goodwill), Statement of Income or Comprehensive Income [Extensible Enumeration]					Asset Impairment Charges