Commitments and Contingencies - Additional Information (Detail) £ in Millions	Jan. 19, 2021 GBP (£) Extension	Dec. 30, 2020 GBP (£) Health_Center	Jan. 15, 2021 USD ($)	Jan. 15, 2021 GBP (£)	Dec. 31, 2020	Feb. 01, 2017 USD ($)
Commitment And Contingencies [Line Items]
Term of lease					15 years
Aggregate committed amount of credit facility | $						$ 500,000,000
Waterland Private Equity Fund VII C.V [Member]
Commitment And Contingencies [Line Items]
Purchase price of acquisition		£ 800
Date of acquisition agreement		Dec. 30, 2020
Waterland Private Equity Fund VII C.V [Member] | Subsequent Event
Commitment And Contingencies [Line Items]
Payment for acquisition	£ 800
Lease extension options, description	two 10-year
Term of lease	25 years
Number of lease extension options | Extension	2
Extension term of lease	10 years
Purchase price of acquisition with 364-day acquisition loan	£ 250
Ownership interest in joint venture under the equity method	9.90%
Waterland Private Equity Fund VII C.V [Member] | Subsequent Event | Interim Credit Facility [Member]
Commitment And Contingencies [Line Items]
Aggregate committed amount of credit facility | $			$ 900,000,000
Amount utilized from credit facility				£ 500
Waterland Private Equity Fund VII C.V [Member] | Subsequent Event | Revolving Credit Facility [Member]
Commitment And Contingencies [Line Items]
Credit facilities, amount outstanding				£ 350
Behavioral Health Care Facilities [Member] | Waterland Private Equity Fund VII C.V [Member] | Minimum [Member]
Commitment And Contingencies [Line Items]
Number of facilities acquired | Health_Center		35
Behavioral Health Care Facilities [Member] | Waterland Private Equity Fund VII C.V [Member] | Maximum [Member]
Commitment And Contingencies [Line Items]
Number of facilities acquired | Health_Center		40