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Shareholders' Equity / Partners' Capital - Share Repurchase Program (Details) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Mar. 31, 2018
Feb. 28, 2018
Sep. 30, 2015
Class A common shares/units            
Class of Stock [Line Items]            
Repurchase of Class A common stock, authorized amount       $ 300,000,000   $ 300,000,000
Weighted-average price of shares (in dollars per share) $ 19.36   $ 15.44      
Total cost of Class A common shares $ 34,900,000   $ 96,000,000      
Remaining repurchase authorization amount $ 265,100,000          
Class A common shares/units | Common Stock            
Class of Stock [Line Items]            
Repurchases and retire of Class A common shares (in shares) 1,800,000 0 6,200,000      
Preferred shares            
Class of Stock [Line Items]            
Repurchase of Class A common stock, authorized amount $ 250,000,000       $ 250,000,000