Recent Transactions (Schedule Of Properties Acquired) (Details)
 6 Months Ended
Jun. 30, 2017
USD ($)
ft²
item
Dec. 31, 2016
USD ($)
Business Acquisition [Line Items]    
Number of Buildings, Acquired | item 9  
Rentable Square Feet, Acquired | ft² 1,392,500  
Acquisition Cost $ 394,589,000  
Cash consideration 2,000,000  
Loan balance $ 2,950,219,000 $ 2,340,009,000
Red Bank Portfolio [Member]    
Business Acquisition [Line Items]    
Number of Buildings, Acquired | item [1] 3  
Rentable Square Feet, Acquired | ft² [1] 279,472  
Acquisition Cost [1] $ 27,228,000  
Short Hills / Madison Portfolio [Member]    
Business Acquisition [Line Items]    
Number of Buildings, Acquired | item [2] 6  
Rentable Square Feet, Acquired | ft² [2] 1,113,028  
Acquisition Cost [2] $ 367,361,000  
Unsecured Revolving Credit Facility [Member] | Short Hills / Madison Portfolio [Member]    
Business Acquisition [Line Items]    
Loan balance $ 124,500,000  
[1] This acquisition was funded through borrowings under the Company's unsecured revolving credit facility.
[2] This acquisition was funded through borrowings under the Company's unsecured revolving credit facility and a new $124.5 million loan secured by three of the properties.