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Shareholders' Equity - Share Repurchase (Details) - Class A common shares - USD ($)
 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Sep. 30, 2015
Class of Stock [Line Items]      
Repurchase of Class A common stock, authorized amount     $ 300,000,000
Average price per share of Class A common shares (in dollars per share)   $ 15.44  
Total price from repurchase of common shares   $ 96,000,000  
Remaining repurchase authorization $ 146,700,000    
Common Stock      
Class of Stock [Line Items]      
Repurchases of Class A common shares (in shares) 0 6,200,000