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Shareholders' Equity - At the Market Common Share Offering Program (Details) - USD ($)
$ / shares in Units, shares in Millions
 3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Nov. 30, 2016
Class of Stock [Line Items]      
Proceeds from issuance of shares $ 350,612,000 $ 1,000  
Stock issuance costs 236,000 $ 0  
At the Market - Common Share Offering Program | Class A common shares      
Class of Stock [Line Items]      
Shares available for future issuance $ 281,700,000   $ 400,000,000
Shares issued during period (in shares) 0.6    
Proceeds from issuance of shares $ 14,300,000    
Shares issued, price per share (in USD per share) $ 22.72    
Proceeds from issuance of common stock, net of issuance costs $ 14,100,000    
Stock issuance costs $ 200,000