Rent and Tenant Receivables and Other Assets, Net (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) commercial_mortgage_backed_securities mortgage_note	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Property, Plant and Equipment [Line Items]
Straight-line rent receivable, net	$ 259,106,000	$ 230,529,000
Accounts receivable, net	36,939,000	36,921,000
Deferred costs, net	17,515,000	5,746,000
Investment in direct financing leases, net	13,254,000	19,539,000
Mortgage notes receivable, net	10,164,000	20,294,000
Leasehold improvements, property and equipment, net	9,754,000	12,089,000
Investment in Cole REITs	7,844,000	3,264,000
Prepaid expenses	5,022,000	6,493,000
Other assets, net	3,594,000	5,003,000
Income tax receivable	1,760,000	3,213,000
Restricted escrow deposits	1,140,000	4,995,000
Investment securities, at fair value	0	40,974,000
Total	366,092,000	389,060,000
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Amortization expense	1,200,000	1,200,000	$ 2,300,000
Write off of leasehold	0	0	1,000,000
Accumulated amortization	5,900,000	4,700,000
Property and Equipment [Member]
Property, Plant and Equipment [Line Items]
Write off of leasehold	800,000	600,000	1,200,000
Accumulated amortization	7,000,000	5,700,000
Depreciation expense	2,300,000	1,800,000	3,400,000
Line of Credit [Member]
Property, Plant and Equipment [Line Items]
Amortization expense	7,300,000	10,400,000	$ 10,400,000
Accumulated amortization for deferred costs	47,600,000	40,300,000
Accounts Receivable [Member]
Property, Plant and Equipment [Line Items]
Allowance for doubtful accounts	5,300,000	6,300,000
Allowance for suspended revenue recognition	9,100,000	12,600,000
Rent Receivables [Member]
Property, Plant and Equipment [Line Items]
Allowance for doubtful accounts	1,000,000	2,000,000
Allowance for suspended revenue recognition	$ 100,000	$ 0
Mortgage notes receivable [Member]
Property, Plant and Equipment [Line Items]
Number of mortgage notes receivable | mortgage_note	5
Weighted-average interest rate	6.40%
Number of notes receivable held for sale | mortgage_note	3
Notes receivable held for sale	$ 8,800,000
Commercial Mortgage Backed Securities [Member]
Property, Plant and Equipment [Line Items]
Number of securities matured | commercial_mortgage_backed_securities	2
Number of securities sold | commercial_mortgage_backed_securities	6
Proceeds from sale and maturity of securities	$ 36,000,000
Weighted Average [Member] | Mortgage notes receivable [Member]
Property, Plant and Equipment [Line Items]
Weighted-average years to maturity	12 years 1 month 6 days
Other Income [Member] | Mortgage notes receivable [Member]
Property, Plant and Equipment [Line Items]
Gain on sale of mortgage notes receivable	$ 1,700,000
Other Income [Member] | Commercial Mortgage Backed Securities [Member]
Property, Plant and Equipment [Line Items]
Loss on sale and maturity of CMBS	$ 2,200,000