Other Commitments and Contingencies - Additional Information (Detail) gal in Millions, $ in Millions	3 Months Ended
	Mar. 31, 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	3.1
Total liabilities to tangible net worth minimum times	3.75
Fixed charge coverage ratio minimum times	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
Total debt to capital maximum	0.65
Number Of Years For Power Purchase Agreement	20 years
Contract Duration	20 years
Maximum authorized liability under such guarantees and letters of credit	$ 85.0
Aggregate guaranteed amount	56.6
Draws on letters of credit	$ 7.0