Other Commitments and Contingencies - Additional Information (Detail) gal in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) gal
Commitments and Contingencies Disclosure [Abstract]
Number of Years for Asset Management Agreement	3 years
Number of years to purchase propane under contract	6 years
Estimated current annual commitment | gal	2.5
Debt Service Coverage Ratio	1.25
Ratio based on average number of prior quarters	6
Number of Propane Price Indices	2
Ratios based on average of the prior quarters	1 year 6 months
Funds from operations interest coverage ratio minimum times	2
Total debt to capital maximum	0.65
Number Of Years For Power Purchase Agreement	20 years
Contract Duration	20 years
Aggregate guaranteed amount	$ 72.7
Draws on letters of credit	$ 5.0