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Net rentable area for properties owned.

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Unconsolidated Joint Ventures - Liberty Property 18th & Arch LP and Liberty Property 18th & Arch, Hotel, LP (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) ft² investment	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Jun. 30, 2014 ft² room story investment
Schedule of Equity Method Investments [Line Items]
Investments in and advances to unconsolidated joint ventures	$ 353,215		$ 350,981
Building and Building Improvements
Schedule of Equity Method Investments [Line Items]
Leaseable square feet (in sqft) \| ft²	1,069,670
Philadelphia \| Liberty Property 18th & Arch
Schedule of Equity Method Investments [Line Items]
Number of equity method investments (in investments) \| investment	2			2
Anticipated Aggregate Investment	$ 962,000
Investments in and advances to unconsolidated joint ventures	193,000
Philadelphia \| Construction in Progress \| Liberty Property 18th & Arch
Schedule of Equity Method Investments [Line Items]
Number of stories in a high-rise building (in stories) \| story				60
Number of hotel rooms (in rooms) \| room				219
Leaseable square feet (in sqft) \| ft²				1,300,000
Philadelphia \| Building and Building Improvements \| Liberty Property 18th & Arch
Schedule of Equity Method Investments [Line Items]
Anticipated Aggregate Investment	226,100
Other Liabilities \| Philadelphia \| Liberty Property 18th & Arch \| Guarantee Obligations
Schedule of Equity Method Investments [Line Items]
Loss contingency accrual	44,500		$ 67,300
Equity Method Investee \| Liberty Property 18th & Arch \| Philadelphia
Schedule of Equity Method Investments [Line Items]
Net operating income	$ 0	$ (1,800)