Changes in Non-Cash Working Capital (Details) (USD $)	3 Months Ended
Jun. 30, 2013	Jun. 30, 2012
Changes in Non-Cash Working Capital
Margin deposits	$ 11,551,000	$ (22,321,000)
Trade receivables	960,000	2,110,000
Accrued receivables	77,427,000	22,920,000
Natural gas inventory	(45,693,000)	7,216,000
Prepaid expenses and other current assets	1,538,000	(954,000)
Other assets	(63,000)
Trade payables	336,000	(489,000)
Accrued liabilities	32,428,000	8,306,000
Deferred revenue	6,261,000	(11,235,000)
Other long-term liabilities	(79,000)
Total	84,666,000	5,553,000
Proceeds from sales of cushion gas		$ 14,200,000

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The proceeds from sale of cushion gas during the period.

+ References

No definition available.

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- Definition

Change in recurring obligations of a business that arise from the acquisition of merchandise, materials, supplies and services used in the production and sale of goods and services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 28

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585

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- Definition

The increase (decrease) during the reporting period in amount due within one year (or one business cycle) from customers for the credit sale of goods and services.

+ References

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The increase (decrease) during the reporting period in the aggregate amount of expenses incurred but not yet paid.

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The increase (decrease) during the reporting period, excluding the portion taken into income, in the liability reflecting revenue yet to be earned for which cash or other forms of consideration was received or recorded as a receivable.

+ References

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- Definition

The increase (decrease) during the reporting period in the aggregate value of all inventory held by the reporting entity, associated with underlying transactions that are classified as operating activities.

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The increase (decrease) during the reporting period in money or securities placed with a broker or counterparty as security for a trading or derivative position.

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The increase (decrease) during the reporting period of all assets and liabilities used in operating activities.

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- Definition

The increase (decrease) during the reporting period in other noncurrent operating liabilities not separately disclosed in the statement of cash flows.

+ References

No definition available.

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The increase (decrease) during the reporting period in other assets used in operating activities not separately disclosed in the statement of cash flows. May include changes in other current assets, other noncurrent assets, or a combination of other current and noncurrent assets.

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The increase (decrease) during the reporting period in the amount of outstanding money paid in advance for goods or services that bring economic benefits for future periods.

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- Definition

The increase (decrease) during the reporting period of the amount of revenue for work performed for which billing has not occurred, net of uncollectible accounts.

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