Rates and Other Regulatory Activities - Additional Information (Detail) (USD $)	0 Months Ended					9 Months Ended	12 Months Ended			6 Months Ended	9 Months Ended	0 Months Ended		6 Months Ended		0 Months Ended
	Jun. 13, 2013 mi MW in	May 31, 2013	Oct. 12, 2012 compressor_station	Oct. 09, 2012	Jan. 02, 2012	Sep. 30, 2013	Mar. 31, 2013	Sep. 28, 2012	May 25, 2012 Customer	Jun. 30, 2013 Florida [Member]	Sep. 30, 2013 Florida [Member]	Oct. 12, 2012 Eastern Shore [Member]	May 14, 2012 Eastern Shore [Member]	Jun. 30, 2013 Natural Gas Operations [Member]	Jun. 30, 2013 Electric Operations [Member]	May 14, 2012 Mainline Expansion Project [Member]
Investment In Affiliates [Line Items]
Duration of right to give notice to FPU										180 days	180 days
Duration of closing of the purchase											12 months
Period of extension granted by court				60 days
Number of compressors			3
Period of current agreement exceeds											2 years
Amortization period of regulatory asset											Five years
Period to file case		2 years 6 months
Additional lateral capacity													15,040
Estimated capital cost	$ 11,200,000											$ 12,100,000				$ 16,300,000
Number of Customers Filing Motion									2
Legal fees						1,900,000
FranchiseDisputeLitigationExpensesThatRecoveryIsAllowed						1,800,000
RefundAmountToBeAppliedToRecoverLitigationExpenses						1,800,000
RegulatoryAssetAmountApprovedForFranchiseDispute						2,000,000
Litigation Expenses Recognized in Prior Periods Deferred As Regulatory Asset						1,500,000
Litigation Expenses Recognized in Current Period Deferred As Regulatory Asset						376,000
Regulatory Liability Related To Fuel Cost Refund						(2,000,000)
Acquisition adjustments goodwill amount requested to be reclassified as regulatory assets								745,800
Net periodic benefit curtailment gain					892,000
Defined benefit plan recognized net gain loss due to curtailments recorded as regulatory liability					722,000									464,000	258,000
Amortization period for the curtailment gain regulatory liability					34 months
White Oak lateral capacity of firm transportation service	55,200
White Oak lateral length of pipeline to be installed	5.5
Lateral diamater of pipeline to be installed	16
Filing period for fuel retention percentage and cash out surcharge							12 months
Cycle power of the Calpine Project proposed power plant	309
New plant capacity volume			17,500
Proposed fuel retention percentage rate							0.24%
Cash-Our Surcharge							0.00%
Deferred gas required for operations underrecovery regulatory balance							285,000
Deferred cash out costs overrecovery regulatory balance							$ 146,000