Company's Repurchase Activities (Parenthetical) (Detail) - shares shares in Millions	Jul. 31, 2018	Feb. 28, 2018	Jan. 31, 2018
Capital Unit [Line Items]
Company's common units authorized for repurchase		5.5	2.2
Plan III Common Units Repurchase Program
Capital Unit [Line Items]
Company's common units authorized for repurchase		5.5	2.2
Common Stock Available for Repurchase Under Open Market Transactions
Capital Unit [Line Items]
Company's common units authorized for repurchase		3.0
Common Stock Available for Repurchase Under Open Market Transactions | Subsequent Event
Capital Unit [Line Items]
Company's common units authorized for repurchase	0.5
Common Stock Available for Repurchase Under Privately Negotiated Transactions
Capital Unit [Line Items]
Company's common units authorized for repurchase		2.5
Common Stock Available for Repurchase Under Privately Negotiated Transactions | Subsequent Event
Capital Unit [Line Items]
Company's common units authorized for repurchase	2.5