Risk Management Activities and Financial Instruments (Details) (USD $)	12 Months Ended						12 Months Ended					12 Months Ended
	Mar. 31, 2014 item	Mar. 31, 2013 item	Mar. 31, 2012	Mar. 31, 2014 Revolving credit facility	Jun. 29, 2013 Revolving credit facility	Mar. 31, 2013 Revolving credit facility	Mar. 31, 2014 Minimum Natural gas retail contracts	Mar. 31, 2013 Minimum Natural gas retail contracts	Mar. 31, 2014 Maximum Natural gas retail contracts	Mar. 31, 2013 Maximum Natural gas retail contracts	Mar. 31, 2014 Exchange traded futures and options	Mar. 31, 2014 Commodity derivatives MMcf	Mar. 31, 2013 Commodity derivatives MMcf	Mar. 31, 2014 Commodity derivatives Natural gas retail contracts	Mar. 31, 2013 Commodity derivatives Natural gas retail contracts	Mar. 31, 2014 Commodity derivatives Forward contracts MMcf	Mar. 31, 2013 Commodity derivatives Forward contracts MMcf	Mar. 31, 2014 Commodity derivatives Futures MMcf	Mar. 31, 2013 Commodity derivatives Futures MMcf	Mar. 31, 2014 Commodity derivatives Swaps MMcf	Mar. 31, 2013 Commodity derivatives Swaps MMcf	Mar. 31, 2014 Currency contracts Currency swap	Mar. 31, 2013 Currency contracts Currency swap
Risk management activities and financial instruments
Aggregate overall exposure limit of unmatched volumes of proprietary current natural gas inventory (in million cubic feet)												8,000
Volume of current natural gas inventory offset with derivative contracts (in million cubic feet)												18,400	25,700			(1,400)	1,600	20,100	14,100	(300)	10,000
Percentage of the total current inventory of natural gas offset with derivative contracts												97.20%
Volume of natural gas inventory (in million cubic feet)												18,400
Doubtful accounts expense	$ 400,000	$ 0
Number of significant counterparties	1
Percentage of total revenue from one counterparty	56.00%	28.00%	40.00%
Exchange-traded derivative instruments as percentage of commodity risk management assets											68.60%
Period of energy contracts to customers in retail markets							1 year	1 year	5 years	5 years
Reduction in value of energy contracts														0	1,000,000
Maximum borrowing capacity				400,000,000	400,000,000
Borrowings outstanding	119,500,000	65,000,000		119,500,000		65,000,000
Number of interest rate swap or swaption agreements	0	0
Notional value of currency swaps																						$ 13,000,000	$ 84,000,000