Real Estate Investments and Related Intangibles - Property Acquisitions (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) property building	Dec. 31, 2018 USD ($) property	Dec. 31, 2017 USD ($) property land_parcels
Acquisition, 2019 [Member]
Business Acquisition [Line Items]
Number of properties acquired | property	66
Total purchase price of assets acquired	$ 403,573	$ 502,652	$ 748,784
Capitalized acquisition costs	2,300
Acquisitions 2018 [Member]
Business Acquisition [Line Items]
Number of properties acquired | property		52
Total purchase price of assets acquired		$ 502,700
Capitalized acquisition costs		2,600
Outstanding tenant improvements		$ 2,100
Acquisitions, 2017 [Member]
Business Acquisition [Line Items]
Number of properties acquired | property			88
Total purchase price of assets acquired			$ 748,800
Capitalized acquisition costs			$ 3,300
Number of land parcels acquired | land_parcels			3
Number of real estate properties acquired in non-monetary exchange | property			22
Build-to-suit Development Project [Member] | Acquisition, 2019 [Member]
Business Acquisition [Line Items]
Capitalized acquisition costs	$ 700
Number of real estate properties acquired | building	1
Development in process	$ 27,600