Real Estate and Other Activities - Net Assets Acquired (Detail) - USD ($) $ in Thousands		Sep. 30, 2021	Sep. 30, 2020
Business Acquisition [Line Items]
Total assets acquired		$ 4,301,739	$ 3,524,910
Liabilities assumed		(65,525)	(134,203)
Loans repaid	[1]	(1,090,400)	(737,242)
Total net assets acquired		3,211,339	2,787,668
Land and Land Improvements [Member]
Business Acquisition [Line Items]
Total assets acquired		562,742	330,941
Building [Member]
Business Acquisition [Line Items]
Total assets acquired		1,670,741	2,610,197
Intangible Lease Assets
Business Acquisition [Line Items]
Total assets acquired		197,735	364,006
Mortgage Loans [Member]
Business Acquisition [Line Items]
Total assets acquired		1,090,400	47,641
Equity Investments [Member]
Business Acquisition [Line Items]
Total assets acquired		108,710
Other Loans and Assets [Member]
Business Acquisition [Line Items]
Total assets acquired		$ 736,936	$ 306,328

[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