Real Estate Investments and Related Intangibles - Property Acquisitions (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) land_parcels property	Dec. 31, 2017 USD ($) land_parcels property	Dec. 31, 2016 USD ($)
Acquisitions 2018 [Member]
Business Acquisition [Line Items]
Number of properties acquired | property	52
Total purchase price of assets acquired	$ 502,652
Number of land parcels acquired | land_parcels	1
Allowance for tenant improvements	$ 2,100
Capitalized acquisition costs	2,600
Acquisitions 2017 [Member]
Business Acquisition [Line Items]
Number of properties acquired | property		88
Total purchase price of assets acquired		$ 748,784
Number of land parcels acquired | land_parcels		3
Number of properties acquired in non-monetary exchange | property		22
Capitalized acquisition costs		$ 3,300
Acquisitions 2016 [Member]
Business Acquisition [Line Items]
Number of properties acquired | property		8
Total purchase price of assets acquired			$ 100,194
Build-to-suit Development Project [Member] | Acquisitions 2018 [Member]
Business Acquisition [Line Items]
Development in process	3,500
Capitalized acquisition costs	$ 500
Number of real estate properties acquired | property	1
Remaining investment	$ 24,900
Development in progress expected period of completion	12 months