Commitments and Contingencies - Additional Information (Details) $ in Thousands, ft² in Millions	Sep. 30, 2018 USD ($) ft² Property
Other Commitments [Line Items]
Number of industrial properties | Property	468
Gross leasable area (GLA) of industrial properties | ft²	61.0
Development Activity
Other Commitments [Line Items]
Number of industrial properties | Property	9
Gross leasable area (GLA) of industrial properties | ft²	3.7
Estimated total investment | $	$ 261,300
Estimated total investment remaining to be funded | $	$ 127,500