Fair Value Measures - Reconciliations of the changes in assets and liabilities with Level 3 inputs (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
CMBS [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 40,974	$ 47,215
Total gains and losses
Unrealized loss included in other comprehensive income, net	(71)	(547)
Realized loss included in other income, net	(34)
Valuation Allowance	0
Unrealized gain included in other income, net	0
Purchases, issuance, settlements
Return of principal received	(4,864)	(4,077)
Amortization included in net income, net	157	(914)
Sale of investments	(9,880)
Transfers out of Level 3 into Level 1	(12,756)
Ending balance	13,526	$ 41,677
Cole Real Estate Investments, Inc. [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	3,264
Total gains and losses
Unrealized loss included in other comprehensive income, net	0
Realized loss included in other income, net	0
Valuation Allowance	0
Unrealized gain included in other income, net	5,102
Purchases, issuance, settlements
Return of principal received	0
Amortization included in net income, net	0
Sale of investments	(522)
Transfers out of Level 3 into Level 1	0
Ending balance	$ 7,844