Franchise Rights Acquired, Goodwill and Other Intangible Assets - Additional Information (Detail)	3 Months Ended
	Mar. 29, 2025 USD ($) Segment	Mar. 30, 2024 USD ($)	Dec. 28, 2024 USD ($)	Dec. 30, 2023 USD ($)
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	$ 5,950,000	$ 9,290,000
Goodwill impairment		$ 0
Net book value of goodwill	$ 240,283,000		$ 239,583,000	$ 243,441,000
Franchise right maturity period	7 years
Behavioral Reporting Unit
Goodwill And Intangible Assets Disclosure [Line Items]
Goodwill impairment	$ 0
Net book value of goodwill	$ 150,541,000
Percentage of goodwill held	62.70%
Behavioral Reporting Unit | Minimum
Goodwill And Intangible Assets Disclosure [Line Items]
Percentage of estimated fair value in excess of carrying amount	55.00%
Clinical Reporting Unit
Goodwill And Intangible Assets Disclosure [Line Items]
Goodwill impairment	$ 0
Net book value of goodwill	$ 89,742,000
Percentage of goodwill held	37.30%
Clinical Reporting Unit | Minimum
Goodwill And Intangible Assets Disclosure [Line Items]
Percentage of estimated fair value in excess of carrying amount	60.00%
All Reporting Units | Minimum
Goodwill And Intangible Assets Disclosure [Line Items]
Percentage of estimated fair value in excess of carrying amount		25.00%
Franchise Rights Acquired | Maximum
Goodwill And Intangible Assets Disclosure [Line Items]
Finite-lived intangible assets, estimated useful life (in years)	1 year
Franchise Rights Acquired | United States
Goodwill And Intangible Assets Disclosure [Line Items]
Net book value of franchise rights acquired	$ 41,078,000
Indefinite-lived intangible assets, impairment charges	$ 27,549,000	$ 251,431,000
Impairment, Intangible Asset, Indefinite-Lived (Excluding Goodwill), Statement of Income or Comprehensive Income [Extensible Enumeration]	Asset Impairment Charges	Asset Impairment Charges
Percentage of franchise rights acquired held	100.00%
Franchise Rights Acquired | United Kingdom
Goodwill And Intangible Assets Disclosure [Line Items]
Indefinite-lived intangible assets, impairment charges		$ 155,000
Impairment, Intangible Asset, Indefinite-Lived (Excluding Goodwill), Statement of Income or Comprehensive Income [Extensible Enumeration]		Asset Impairment Charges
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