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Shareholders' Equity - Valuation Inputs (Details) - Class A common shares - $ / shares
6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award    
Weighted-average fair value (in dollars per share) $ 3.82 $ 2.81
Expected term (in years) 7 years 7 years
Dividend yield (as a percent) 3.00% 3.00%
Volatility (as a percent) 21.30% 27.40%
Risk-free interest rate (as a percent) 2.20% 1.50%