Rent and Tenant Receivables and Other Assets, Net (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Straight-line rent receivable, net	$ 278,831,000	$ 266,195,000
Accounts receivable, net	53,051,000	41,556,000
Deferred costs, net	5,185,000	7,208,000
Investment in direct financing leases, net	6,547,000	9,341,000
Investment in Retained REITs	7,255,000	7,552,000
Prepaid expenses	3,850,000	3,453,000
Leasehold improvements, property and equipment, net	3,991,000	4,809,000
Other assets, net	7,910,000	8,281,000
Total	366,620,000	348,395,000
Unrealized gain (loss) included in consolidated statement of operations	(300,000)
Write off of depreciation			$ 800,000
Maximum [Member]
Property, Plant and Equipment [Line Items]
Write off of depreciation		100,000
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Amortization expense	500,000	700,000	1,200,000
Write off of leasehold	0	0	0
Accumulated amortization	3,400,000	2,800,000
Property and Equipment [Member]
Property, Plant and Equipment [Line Items]
Accumulated amortization	6,500,000	5,400,000
Depreciation expense	1,100,000	1,300,000	2,300,000
Line of Credit [Member]
Property, Plant and Equipment [Line Items]
Amortization expense	6,300,000	2,100,000	7,300,000
Debt write off	3,200,000	1,800,000	$ 0
Accumulated amortization for deferred costs	$ 52,900,000	$ 49,800,000