Rent and Tenant Receivables and Other Assets, Net (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Straight-line rent receivable, net	$ 255,336,000		$ 255,336,000		$ 230,529,000
Accounts receivable, net	35,908,000		35,908,000		36,921,000
Investment securities, at fair value	26,282,000		26,282,000		40,974,000
Deferred costs, net	20,324,000		20,324,000		5,746,000
Mortgage notes receivable, net	18,757,000		18,757,000		20,294,000
Investment in direct financing leases, net	14,082,000		14,082,000		19,539,000
Leasehold improvements, property and equipment, net	10,604,000		10,604,000		12,089,000
Restricted escrow deposits	8,400,000		8,400,000		4,995,000
Prepaid expenses	8,398,000		8,398,000		6,493,000
Investment in Cole REITs	7,844,000		7,844,000		3,264,000
Other assets, net	3,971,000		3,971,000		5,003,000
Income tax receivable	2,147,000		2,147,000		3,213,000
Total	412,053,000		412,053,000		389,060,000
Interest receivable reserves	0		0		1,800,000
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Amortization expense	300,000	$ 300,000	900,000	$ 900,000
Accumulated amortization	5,600,000		5,600,000		4,700,000
Property and Equipment [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	300,000	500,000	1,200,000	1,300,000
Line of Credit [Member]
Property, Plant and Equipment [Line Items]
Amortization expense	1,300,000	$ 2,600,000	6,000,000	$ 7,800,000
Accumulated amortization for deferred costs	46,300,000		46,300,000		40,300,000
Accounts Receivable [Member]
Property, Plant and Equipment [Line Items]
Allowance for doubtful accounts	5,400,000		5,400,000		6,300,000
Allowance for suspended revenue recognition	9,400,000		9,400,000		12,600,000
Rent Receivables [Member]
Property, Plant and Equipment [Line Items]
Allowance for doubtful accounts	$ 1,200,000		$ 1,200,000		$ 2,000,000