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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