Investments - Activity in Real Estate Investments and Intangible Lease Liabilities Held for Sale (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) Property	Mar. 31, 2018 USD ($) Property
Investments [Abstract]
Number of Properties, Held for sale balance | Property		3
Number of Properties, Transfers to held for sale classification | Property	2	4
Number of Properties, Sales | Property		(3)
Number of Properties, Held for sale balance | Property	2	4
Real Estate Investments, Held for sale balance		$ 4,173
Real Estate Investments, Transfers to held for sale classification	$ 3,765	5,885
Real Estate Investments, Sales		(4,173)
Real Estate Investments, Held for sale balance	3,765	5,885
Intangible Lease Liabilities, Held for sale balance		(129)
Intangible Lease Liabilities, Sales		129
Net Carrying Value, Held for sale balance,		4,044
Net Carrying Value, Transfers to held for sale classification	3,765	5,885
Net Carrying Value, Sales		(4,044)
Net Carrying Value, Held for sale balance	$ 3,765	$ 5,885