Fair Value Measures - Reconciliations of the changes in assets and liabilities with Level 3 inputs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 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 loss included in other comprehensive income, net	(205)	(951)
Realized loss included in other income, net	(34)
Unrealized gain included in other income, net	0
Purchases, issuance, settlements
Return of principal received	(4,864)	(4,388)
Amortization included in net income, net	157	(902)
Sale of investments	(36,028)
Ending balance	0	40,974
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
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	$ 3,264