Real Estate and Other Activities - Net Assets Acquired (Parenthetical) (Detail) $ in Thousands, £ in Millions		9 Months Ended
		Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($) Hospital	Jun. 30, 2021 Property	Jun. 25, 2021 GBP (£)	Mar. 31, 2021 GBP (£)
Business Acquisition [Line Items]
Advanced to the mortgage loan | $	[1]	$ 1,090,400	$ 737,242
Priory Group [Member]
Business Acquisition [Line Items]
Number of real estate assets acquired | Property				35
Deferred income tax liabilities, incurred | £					£ 47.1
Steward Health Care System LLC [Member]
Business Acquisition [Line Items]
Number of facilities acquired | Hospital			2
Mortgage Loans [Member] | Priory Group [Member]
Business Acquisition [Line Items]
Advanced to the mortgage loan | £						£ 800.0
Mortgage Loans [Member] | Steward Health Care System LLC [Member]
Business Acquisition [Line Items]
Advanced to the mortgage loan | $			$ 737,000
Intangible Lease Assets
Business Acquisition [Line Items]
Weighted-average useful life of acquired intangible lease assets (in years)		36 years 1 month 6 days	27 years 7 months 6 days

[1] The 2021 column includes an £800 million mortgage loan advanced to the Priory Group (“Priory”) in the first quarter of 2021 and converted to fee simple ownership in a portfolio of 35 properties in the second quarter of 2021 as described below. The 2020 column includes $737 million of loans advanced to Steward Health Care, Inc. (“Steward”) in 2017 and exchanged for the fee simple real estate of two hospitals as described below