Other Commitments and Contingencies - Additional Information (Detail) gal in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) gal
Other Commitments [Line Items]
Number of Years for Asset Management Agreement	3 years
Debt Service Coverage Ratio	1.25
Debt Service Coverage Ratio Measurement Period	12
Maximum Days To Make Default Good	5 days
Ratio based on average number of prior quarters	6
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 | $	$ 77.3
Draws on letters of credit | $	$ 7.0
Sandpiper [Member]
Other Commitments [Line Items]
Annual Estimate Of Volume Of Propane To Be Purchased | gal	288
Sharp Energy Inc [Member]
Other Commitments [Line Items]
Annual Estimate Of Volume Of Propane To Be Purchased | gal	288