Derivative Activities - Additional Information (Detail)	Dec. 31, 2018 USD ($) t_per_M MMBTU
Derivatives Excluding Basis Swaps and Freight Swaps
Derivative [Line Items]
Derivative assets liabilities at fair value net	$ 80,900,000
Commodity | Natural Gas Basis Swaps
Derivative [Line Items]
Derivative assets liabilities at fair value net	$ 4,800,000
Volume Hedged | MMBTU	70,940,000
Commodity | Propane Spread Swaps
Derivative [Line Items]
Derivative assets liabilities at fair value net	$ 117,000
Commodity | Swaps | Freight | Level 2
Derivative [Line Items]
Derivative assets liabilities at fair value net	$ (561,000)
Volume Hedged | t_per_M	10,000