Investment in Real Estate Inestment in Real Estate - Summary of Industrial Property Dispositions (Details) $ in Thousands, ft² in Millions		12 Months Ended
		Dec. 31, 2018 USD ($) ft² Property	Dec. 31, 2017 USD ($) ft² Property	Dec. 31, 2016 USD ($) ft² Property
Real Estate Properties [Line Items]
Number of industrial properties | Property		458
Gross leasable area (GLA) of industrial properties | ft²		63.1
Proceeds from sale of industrial properties | $	[1]	$ 192,047	$ 236,059	$ 169,911
Gain on sale of real estate | $	[1]	$ 81,600	$ 131,269	$ 68,202
Disposition Activity
Real Estate Properties [Line Items]
Number of industrial properties | Property		53	60	63
Gross leasable area (GLA) of industrial properties | ft²		2.6	4.6	3.9

[1] (B) Gross proceeds and gain on sale of real estate include the sale of several land parcels for the years ended December 31, 2018, 2017 and 2016.