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Investment in Real Estate - Narrative (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Feb. 14, 2017
Real Estate [Abstract]        
Revenue of acquiree since acquisition date $ 14.0      
Pro forma, earnings (loss) since acquisition date, actual (3.5)      
Gains on sales 22.9 $ 30.5 $ 5.5  
Gain related to sale of an option to purchase land $ 7.5      
Subsequent Event | 222 Kearny Street        
Business Acquisition [Line Items]        
Proceeds from disposition of real estate held-for-sale       $ 51.8