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v3.8.0.1

Divestitures and Acquisitions (Details) - USD ($) $ / shares in Units, $ in Thousands |  | 3 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Apr. 03, 2018 | Mar. 31, 2018 | Mar. 31, 2017 | Mar. 31, 2018 | Mar. 31, 2017 | Sep. 30, 2017 | Jan. 01, 2017
Disposal Group, Including Discontinued Operation, Additional Disclosures [Abstract] |  |  |  |  |  |  |
Disposal Group, Including Discontinued Operation, Cash Purchase Price |  |  |  |  |  |  | $ 38,300
Disposal Group, Including Discontinued Operation, Working Capital Adjustment |  |  |  |  |  |  | 109,000
Disposal Group, Including Discontinued Operation, Consideration |  |  |  |  |  |  | 147,300
Disposal Group, Including Discontinued Operation, Consideration Placed in Escrow |  |  |  |  |  |  | $ 7,000
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax, Per Diluted Share |  |  |  |  |  | $ 0.03 |
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract] |  |  |  |  |  |  |
Income tax expense |  |  |  | $ 0 | $ 6,841 |  |
Income from discontinued operations, net of tax |  |  |  | 0 | 10,994 |  |
Gain on sale of discontinued operations, net of tax |  | $ 0 | $ 2,716 | 0 | 2,716 |  |
Net income from discontinued operations |  | 0 | 2,716 | 0 | 13,710 |  |
Summary of Cash Flow Hedge Activity [Abstract] |  |  |  |  |  |  |
Gain (Loss) on Discontinuation of Cash Flow Hedge |  |  |  | 0 | 10,579 |  |
Discontinued Operation, Tax Effect of Gain (Loss) from Disposal of Discontinued Operation |  | 0 |  | $ 0 | 10,215 |  |
Subsequent Event [Member] |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |
Subsequent Event, Description | On April 3, 2018, we filed formula rate mechanisms in our Mid-Tex and West Texas service areas, seeking increases in operating income |  |  |  |  |  |
Natural Gas Marketing Segment [Member] | Discontinued Operations, Held-for-sale or Disposed of by Sale [Member] |  |  |  |  |  |  |
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract] |  |  |  |  |  |  |
Operating revenues |  |  |  |  | 303,474 |  |
Purchased gas cost |  |  |  |  | 277,554 |  |
Operating expenses |  |  |  |  | 7,874 |  |
Operating income |  |  |  |  | 18,046 |  |
Other nonoperating expense |  |  |  |  | (211) |  |
Income from discontinued operations before income taxes |  |  |  |  | 17,835 |  |
Income tax expense |  |  |  |  | 6,841 |  |
Income from discontinued operations, net of tax |  |  |  |  | 10,994 |  |
Gain on sale of discontinued operations, net of tax |  |  | 2,716 |  | 2,716 |  |
Net income from discontinued operations |  |  |  |  | 13,710 |  |
Discontinued Operation, Alternative Cash Flow Information [Abstract] |  |  |  |  |  |  |
Depreciation and Amortization, Discontinued Operations |  |  |  |  | 185 |  |
Capital Expenditure, Discontinued Operations |  |  |  |  | 0 |  |
Noncash Change in Commodity Contract Cash Flow Hedges |  |  |  |  | (8,165) |  |
Discontinued Operation, Additional Disclosures [Abstract] |  |  |  |  |  |  |
Gain on Discontinuation of Cash Flow Hedge |  |  |  |  | 10,600 |  |
Gain (Loss) On Hedge Ineffectiveness |  |  |  |  | 3,400 |  |
Disposal Group, Including Discontinued Operation, Consideration Placed in Escrow Released |  | $ 3,000 |  |  |  |  |
Effect of Fair Value Hedges on Results of Operations [Abstract] |  |  |  |  |  |  |
Commodity contracts |  |  |  |  | (9,567) |  |
Fair value adjustment for natural gas inventory designated as the hedged item |  |  |  |  | 12,858 |  |
Total (increase) decrease to purchased gas cost |  |  |  |  | 3,291 |  |
Basis ineffectiveness |  |  |  |  | (597) |  |
Timing ineffectiveness |  |  |  |  | 3,888 |  |
Summary of Cash Flow Hedge Activity [Abstract] |  |  |  |  |  |  |
Gain (loss) reclassified from AOCI into purchased gas cost for effective portion of commodity contracts |  |  |  |  | (2,612) |  |
Gain (loss) arising from ineffective portion of commodity contracts |  |  |  |  | 111 |  |
Gain (Loss) on Discontinuation of Cash Flow Hedge |  |  |  |  | 10,579 |  |
Total impact on purchased gas cost |  |  |  |  | 8,078 |  |
Gain (Loss) On Derivative Instruments Not Designated Hedges Net Pretax |  |  |  |  | $ 6,800 |  |
Discontinued Operation, Tax Effect of Gain (Loss) from Disposal of Discontinued Operation |  |  | $ 10,215 |  |  |  |

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- Definition The amount of net gain (loss) reclassified into earnings in the period when cash flow hedge is discontinued because it is probable that the original forecasted transactions will not occur by the end of the original period or an additional two month time period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994 + Details
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- Definition Total amount of gain (loss) derived from fair value hedges recognized in earnings in the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959 + Details
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- Definition The amount of gain reclassified into earnings in the period when cash flow hedge is discontinued because it is probable that the original forecasted transactions will not occur by the end of the original period or an additional two month time period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994 + Details
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