Fair Value of Assets and Liabilities - Narrative (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) debt_security property	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) debt_security property	Jun. 30, 2018 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of assets	$ 2,213	$ 548	$ 8,419	$ 548
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement, number of debt securities | debt_security	2		2
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement, number of debt securities | debt_security	4		4
Discontinued Operations, Held-for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of real estate properties held for sale | property	22		22
Discontinued Operations, Held-for-sale | Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of assets	$ 2,117		$ 8,323
Number of real estate properties held for sale | property	15		15
Sale price less estimated cost to sell	$ 7,613		$ 7,613