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Net Income Per Common Unit - Additional Information (Detail) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2019
Jun. 30, 2018
Jul. 16, 2019
Apr. 16, 2018
Unit Repurchase Program [Line Items]          
Amount remaining available for repurchases $ 115,400,000 $ 115,400,000      
Common stock repurchased, units 7,000,000.0 8,500,000 2,200,000    
Common stock repurchased, cost $ 290,900,000 $ 343,100,000 $ 71,700,000    
Common Class A          
Unit Repurchase Program [Line Items]          
Amount authorized to repurchase under unit repurchase program       $ 1,000,000,000.0  
Blackstone          
Unit Repurchase Program [Line Items]          
Amount authorized to repurchase under unit repurchase program         $ 1,000,000,000.0