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Equity - Common Stock Offering Narrative (Details) - USD ($)
 12 Months Ended
Apr. 10, 2015
Apr. 01, 2015
Jan. 20, 2015
Feb. 12, 2013
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Class of Stock [Line Items]              
Shares of stock sold (in shares) 6,037,500   11,000,000        
Share price     $ 31.75        
Proceeds from issuance of common stock     $ 385,600,000   $ 385,589,000 $ 197,468,000 $ 202,542,000
Shares sold under program to date         14,500,000    
Minimum              
Class of Stock [Line Items]              
Share price           $ 21.92 $ 20.55
Maximum              
Class of Stock [Line Items]              
Share price           $ 22.07 $ 22.27
At-the-Market              
Class of Stock [Line Items]              
Shares of stock sold (in shares)           76,000 612,644
Maximum shares authorized, value           $ 125,000,000.0  
Common Stock              
Class of Stock [Line Items]              
Shares of stock sold (in shares)         12,650,000 9,563,500 9,812,644
Proceeds from issuance of common stock       $ 189,900,000      
Public Offering | Common Stock              
Class of Stock [Line Items]              
Shares of stock sold (in shares)       8,000,000      
Exercise of Over-allotment Option              
Class of Stock [Line Items]              
Shares of stock sold (in shares)     1,650,000        
Exercise of Over-allotment Option | Common Stock              
Class of Stock [Line Items]              
Shares of stock sold (in shares)       1,200,000      
Public offering price (dollars per share)       $ 21.50      
EOP Northern California Portfolio              
Class of Stock [Line Items]              
Shares issued as consideration for business combination   63,474,791          
EOP Northern California Portfolio | Common Stock              
Class of Stock [Line Items]              
Shares issued as consideration for business combination   8,626,311