Rent and Tenant Receivables and Other Assets, Net (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Straight-line rent receivable, net	$ 289,312,000		$ 289,312,000		$ 278,831,000
Accounts receivable, net	49,328,000		49,328,000		53,051,000
Deferred costs, net	2,662,000		2,662,000		5,185,000
Investment in direct financing leases, net	5,422,000		5,422,000		6,547,000
Investment in Retained REITs	7,948,000		7,948,000		7,255,000
Prepaid expenses	6,223,000		6,223,000		3,850,000
Leasehold improvements, property and equipment, net	3,081,000		3,081,000		3,991,000
Other assets, net	7,935,000		7,935,000		7,910,000
Total	371,911,000		371,911,000		366,620,000
Unrealized gain (loss) included in consolidated statement of operations			700,000	$ (600,000)
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Amortization expense	100,000	$ 100,000	400,000	400,000
Write off of leasehold	0	0	0	0
Accumulated amortization	3,800,000		3,800,000		3,400,000
Property and Equipment [Member]
Property, Plant and Equipment [Line Items]
Accumulated amortization	7,300,000		7,300,000		6,500,000
Depreciation	200,000	300,000	800,000	800,000
Write off of depreciation	0	0	0	0
Line of Credit [Member]
Property, Plant and Equipment [Line Items]
Amortization expense	800,000	$ 800,000	2,500,000	$ 2,300,000
Accumulated amortization for deferred costs	$ 55,400,000		$ 55,400,000		$ 52,900,000