Fair Value Measures - Reconciliations of the changes in assets and liabilities with Level 3 inputs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 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 gain (loss) included in other comprehensive income (loss), net	(837)	(194)
Realized loss included in other income, net	(34)
Unrealized gain included in other income, net	0
Purchases, issuance, settlements
Return of principal received	(4,402)	(3,469)
Amortization included in net income, net	40	(922)
Sale of investments	0
Ending balance	35,741	$ 42,630
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 gain (loss) included in other comprehensive income (loss), net	0
Realized loss included in other income, net	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)
Ending balance	$ 7,844