Investments in Unconsolidated Joint Ventures (Liberty Property 18th & Arch LP and Liberty Property 18th & Arch Hotel, LP) (Details) ft² in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) ft²	Dec. 31, 2016 USD ($) ft² condominium_unit	Dec. 31, 2015 USD ($)	Jun. 30, 2014 USD ($) ft² room story investment
Schedule of Equity Method Investments [Line Items]
Operating Income (Loss)	$ 236,644,000	$ 240,466,000	$ 244,368,000
Maximum exposure to loss	288,456,000	245,078,000
Development in progress	378,472,000	267,450,000
Gain (loss) on sale of properties	114,965,000	$ 219,270,000	100,314,000
Liberty Property 18th & Arch [Member]
Schedule of Equity Method Investments [Line Items]
Maximum exposure to loss	$ 177,800,000
Philadelphia [Member] | Liberty Property 18th & Arch [Member]
Schedule of Equity Method Investments [Line Items]
Number of equity method investments | investment				2
Anticipated investment in joint ventures				$ 190,700,000
Ownership percentage				20.00%
Philadelphia [Member] | Construction in Progress [Member] | Liberty Property 18th & Arch [Member]
Schedule of Equity Method Investments [Line Items]
Number of stories in a high-rise building | story				60
Leaseable square feet | ft²	300			1,300
Number of hotel rooms | room				217
Anticipated aggregate investment	$ 354,100,000			$ 953,700,000
Philadelphia [Member] | Building and Building Improvements [Member] | Liberty Property 18th & Arch [Member]
Schedule of Equity Method Investments [Line Items]
Leaseable square feet | ft²	1,100
Anticipated aggregate investment	$ 599,600,000
Liberty Property 18th & Arch [Member]
Schedule of Equity Method Investments [Line Items]
Leaseable square feet | ft²		15
Number of Residential Condominium Units | condominium_unit		3
Proceeds from sale of property		$ 14,300,000
Gain (loss) on sale of properties		300,000
Liberty Property 18th & Arch [Member] | Equity Method Investee [Member] | Philadelphia [Member]
Schedule of Equity Method Investments [Line Items]
Management fees revenue	200,000	100,000	100,000
Liberty Property 18th & Arch [Member] | Equity Method Investee [Member] | Prepaid Expenses and Other Current Assets [Member] | Philadelphia [Member]
Schedule of Equity Method Investments [Line Items]
Due from related parties	466,000	1,300,000
Liberty Property 18th & Arch [Member] | Equity Method Investee [Member] | Operating Income (Loss) [Member] | Philadelphia [Member]
Schedule of Equity Method Investments [Line Items]
Operating Income (Loss)	$ (3,500,000)
Liberty Property 18th & Arch [Member] | Equity Method Investee [Member] | Other Income [Member] | Philadelphia [Member]
Schedule of Equity Method Investments [Line Items]
Operating Income (Loss)		$ 600,000	$ 1,600,000