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Common Unit Repurchase Plans and Retirement - Company's Repurchase Activities (Parenthetical) (Detail) - shares
shares in Millions
1 Months Ended 3 Months Ended
Sep. 30, 2019
Mar. 31, 2019
Nov. 30, 2019
Aug. 31, 2019
Jul. 31, 2019
Capital Unit [Line Items]          
Company's common units authorized for repurchase       2.3 1.3
Private Transaction          
Capital Unit [Line Items]          
Company's common units repurchased 1.2 1.2      
Repurchase Plan          
Capital Unit [Line Items]          
Company's common units authorized for repurchase       2.3 1.3
Common Stock Available for Repurchase Under Open Market Transactions          
Capital Unit [Line Items]          
Company's common units authorized for repurchase       1.0  
Common Stock Available for Repurchase Under Open Market Transactions | Subsequent Event          
Capital Unit [Line Items]          
Company's common units authorized for repurchase     0.4    
Common Stock Available for Repurchase Under Privately Negotiated Transactions          
Capital Unit [Line Items]          
Company's common units authorized for repurchase       1.3  
Common Stock Available for Repurchase Under Privately Negotiated Transactions | Subsequent Event          
Capital Unit [Line Items]          
Company's common units authorized for repurchase     0.1