Real Estate Investments and Related Intangibles - Property Acquisitions (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($) property	Sep. 30, 2018 USD ($) property
Acquisition, 2019 [Member]
Business Acquisition [Line Items]
Number of properties acquired | property	40
Total purchase price of assets acquired	$ 260,715
Capitalized acquisition costs	1,400
Acquisitions 2018 [Member]
Business Acquisition [Line Items]
Number of properties acquired | property		42
Total purchase price of assets acquired		$ 280,427
Outstanding tenant improvements		2,100
Capitalized acquisition costs		$ 1,600
Build-to-suit Development Project [Member] | Acquisition, 2019 [Member]
Business Acquisition [Line Items]
Capitalized acquisition costs	700
Development in process	$ 27,600
Number of real estate properties acquired | property	1