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Shareholders' Equity - Participating Preferred Shares (Details)
$ in Millions
 3 Months Ended
Mar. 31, 2017
USD ($)
market
Mar. 31, 2016
Class of Stock [Line Items]    
Cumulative change in value of index based on purchase prices 50.00%  
Number of top markets used for purchase price index | market 20  
Liquidation preference value | $ $ 476.7  
5.0% Series A Participating Preferred Shares    
Class of Stock [Line Items]    
Preferred stock, dividend rate, percentage 5.00% 5.00%
5.0% Series B Participating Preferred Shares    
Class of Stock [Line Items]    
Preferred stock, dividend rate, percentage 5.00% 5.00%
5.5% Series C Participating Preferred Shares    
Class of Stock [Line Items]    
Preferred stock, dividend rate, percentage 5.50% 5.50%