Fair Value Measures - Reconciliations of the changes in assets and liabilities with Level 3 inputs (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Commercial Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		$ 40,974
Total gains and losses
Unrealized loss included in other income, net		(899)
Realized loss included in other income, net		(34)
Unrealized gain included in other income, net		0
Purchases, issuance, settlements
Return of principal received		(4,632)
Amortization included in net income, net		80
Sale of investments		0
Ending balance		35,489
Cole Real Estate Investments, Inc. [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 7,844	3,264
Total gains and losses
Unrealized loss included in other income, net	(292)	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	$ 7,552	$ 7,844