Investments in Unconsolidated Joint Ventures (Liberty Property 18th & Arch LP and Liberty Property 18th & Arch Hotel, LP) (Details) ft² in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) ft²	Dec. 31, 2017 USD ($) ft²	Dec. 31, 2016 USD ($) ft² condominium_unit	Jun. 30, 2014 USD ($) ft² room story investment
Schedule of Equity Method Investments [Line Items]
Maximum exposure to loss	$ 350,981	$ 288,456
Gain (loss) on sale of properties	384,673	114,965	$ 219,270
Management fee income	73,224	$ 82,673	$ 12,941
Liberty Property 18th & Arch
Schedule of Equity Method Investments [Line Items]
Maximum exposure to loss	191,400
Philadelphia | Liberty Property 18th & Arch
Schedule of Equity Method Investments [Line Items]
Number of equity method investments (in investments) | investment				2
Anticipated investment in joint ventures				$ 192,200
Ownership percentage				20.00%
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
Leaseable square feet (in sqft) | ft²				1,300
Number of hotel rooms (in rooms) | room				217
Total anticipated development cost	$ 225,500			$ 961,200
Philadelphia | Building and Building Improvements | Liberty Property 18th & Arch
Schedule of Equity Method Investments [Line Items]
Leaseable square feet (in sqft) | ft²	250	1,100
Total anticipated development cost	$ 136,100	$ 599,600
Liberty Property 18th & Arch
Schedule of Equity Method Investments [Line Items]
Leaseable square feet (in sqft) | ft²			15
Number of residential condominium units (in condominium) | condominium_unit			3
Proceeds from sale of property			$ 14,300
Gain (loss) on sale of properties			300
Liberty Property 18th & Arch | Equity Method Investee | Philadelphia
Schedule of Equity Method Investments [Line Items]
Accrual of development cost guarantee accrual	67,100	5,600
Net operating income (loss)	(61,800)	(3,500)	600
Management fee income	2,200	230	$ 75
Liberty Property 18th & Arch | Equity Method Investee | Prepaid Expenses and Other Current Assets | Philadelphia
Schedule of Equity Method Investments [Line Items]
Due from related parties	$ 1,300	$ 466