Summary of Significant Accounting Policies (Real Estate Assets) (Details)	3 Months Ended
	Mar. 31, 2019 USD ($) property	Mar. 31, 2018 USD ($) property	Dec. 31, 2018 USD ($) property
Real Estate Properties [Line Items]
Impairment | $	$ 20,073,000	$ 0
Number of properties impaired | property	7	0
Number of real estate property held for sale | property	2	10	1
Assets held for sale | $	$ 20,749,000	$ 11,300,000	$ 6,780,000
Buildings
Real Estate Properties [Line Items]
Acquired real estate asset, useful life	40 years
Site improvements
Real Estate Properties [Line Items]
Acquired real estate asset, useful life	15 years