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Derivative Activities - Additional Information (Detail)
$ in Millions
Sep. 30, 2019
USD ($)
t_per_M
MMBTU
bbl
Derivatives Excluding Basis Swaps and Freight Swaps  
Derivative [Line Items]  
Derivative assets liabilities at fair value net $ 152.3
Commodity | Natural Gas Basis Swaps  
Derivative [Line Items]  
Derivative assets liabilities at fair value net $ 4.6
Volume Hedged | MMBTU 129,765,000
Commodity | Propane Spread Swaps  
Derivative [Line Items]  
Derivative assets liabilities at fair value net $ (3.3)
Volume Hedged | bbl 1,875,000
Freight | Swaps | Level 2  
Derivative [Line Items]  
Derivative assets liabilities at fair value net $ 1.4
Freight | Swaps | Contracts Settle Through December 2019 | Level 2  
Derivative [Line Items]  
Volume Hedged | t_per_M 10,000
Freight | Swaps | Contracts Settle in 2020 | Level 2  
Derivative [Line Items]  
Volume Hedged | t_per_M 4,000
Freight | Swaps | Contracts Settle in 2021 | Level 2  
Derivative [Line Items]  
Volume Hedged | t_per_M 5,000