Fair Value of Assets and Liabilities - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) debt_security property	Mar. 31, 2018 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of assets	$ 6,206	$ 0
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
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	5
Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Sale price less estimated cost to sell	$ 7,489
Nonrecurring | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Sale price less estimated cost to sell	0
Nonrecurring | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Sale price less estimated cost to sell	$ 7,489
Discontinued Operations, Held-for-sale | Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of properties acquired | property	15
Sale price less estimated cost to sell	$ 7,489
Impairment of assets	$ 6,206