Fair Value Measures - Impairment Charges by Asset Class (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) property	Dec. 31, 2017 USD ($) property	Dec. 31, 2016 USD ($) property
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Properties impaired | property	70	69	153
Below-market lease liabilities, net	$ (296)	$ (92)	$ (421)
Total impairment loss	54,647	50,548	182,800
Real Estate Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impairment loss	53,562	50,087	183,240
Direct Financing Leases [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impairment loss	$ 1,381	$ 553	$ 0