Other Commitments and Contingencies - Additional Information (Detail) gal in Millions, $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2017 USD ($) gal	Sep. 30, 2017 USD ($) 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	2.8	2.8
Number of Propane Price Indices		2
Total liabilities to tangible net worth minimum times	3.75	3.75
Fixed charge coverage ratio minimum times	1.5	1.5
Time to cure ratio		30 days
Ratios based on average of the prior quarters	1 year 6 months
Funds from operations interest coverage ratio minimum times	2	2
Total debt to capital maximum	0.65	0.65
Number Of Years For Power Purchase Agreement		20 years
Contract Duration		20 years
Aggregate guaranteed amount	$ 71.9	$ 71.9
Draws on letters of credit		$ 5.8