Regulatory Assets and Liabilities and Regulatory Matters (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Apr. 30, 2013
Regulatory Assets
Amortization period for remediation and investigation costs expected to be recovered	5 years
Unrealized gains (losses) on derivative financial instruments contracts	$ (1,363)	$ (1,743)
Fair value of electric utility electricity supply contracts	345	(4,759)
Net book value of TL-96 line transferred			2,650
Deferred income taxes on TL-96 line transferred			$ 384
Minimum
Regulatory Assets
Average remaining depreciable lives of the associated property	1 year
Minimum | Other Regulatory Assets
Regulatory Assets
Period to recover costs related to regulatory assets	1 year
Maximum
Regulatory Assets
Average remaining depreciable lives of the associated property	65 years
Maximum | Removal Costs
Regulatory Assets
Period to recover costs related to regulatory assets	5 years
Maximum | Other Regulatory Assets
Regulatory Assets
Period to recover costs related to regulatory assets	20 years