Investments in Unconsolidated Joint Ventures (Liberty Venture I, LP) (Details) ft² in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) ft² bldg	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Schedule of Equity Method Investments [Line Items]
Number of buildings (in buildings) | bldg	60
Gross proceeds	$ 849,528	$ 379,139	$ 1,192,918
Management fee income	$ 73,224	82,673	12,941
New Jersey | Liberty Venture I, LP
Schedule of Equity Method Investments [Line Items]
Ownership percentage	25.00%
Leaseable square feet (in sqft) | ft²	4,800
Construction in Progress | New Jersey | Liberty Venture I, LP
Schedule of Equity Method Investments [Line Items]
Number of buildings (in buildings) | bldg	1
Leaseable square feet (in sqft) | ft²	302
Total anticipated development cost	$ 21,000
Industrial Property | Building and Building Improvements | New Jersey | Liberty Venture I, LP
Schedule of Equity Method Investments [Line Items]
Number of buildings (in buildings) | bldg	29
Equity Method Investee | Liberty Venture I, LP | New Jersey
Schedule of Equity Method Investments [Line Items]
Management fee income	$ 1,300	1,600	$ 2,300
Prepaid Expenses and Other Current Assets | Equity Method Investee | Liberty Venture I, LP | New Jersey
Schedule of Equity Method Investments [Line Items]
Due from related parties	$ 1	$ 223