Fair Value Measures - Impairment Charges by Asset Class (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($) property	Sep. 30, 2016 USD ($) property
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Properties impaired | property	53	139
Total impairment loss	$ 30,857	$ 176,200
Number of real estate properties disposed | property	6
Investment in Real Estate Assets, Net [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impairment loss	$ 30,327
Investment in Direct Financing Leases, Net [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impairment loss	553
Below-Market Lease Liabilities, Net [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impairment loss	$ (23)