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CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Mar. 31, 2018 | Mar. 31, 2017
Statement of Comprehensive Income [Abstract] |  |  |  |  |  |
Net income | $ 178,992 | $ 164,728 |  | $ 493,124 | $ 289,760 |
Other comprehensive income (loss), net of tax |  |  |  |  |  |
Net unrealized holding gains (losses) on available-for-sale securities, net of tax | (939) | 1,530 |  | (1,046) | 702 |
Schedule of Other Comprehensive Income (Loss), Cash Flow Hedges [Line Items] |  |  |  |  |  |
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax | 22,244 | 4,230 | [1] | 21,289 | 100,426 | [1]
Total other comprehensive income (loss) | 21,305 | 5,760 |  | 20,243 | 101,128 |
Total comprehensive income (loss) | 200,297 | 170,488 |  | 513,367 | 390,888 |
Interest Rate Contract [Member] |  |  |  |  |  |
Schedule of Other Comprehensive Income (Loss), Cash Flow Hedges [Line Items] |  |  |  |  |  |
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax | 22,244 | 4,230 |  | 21,289 | 95,444 |
Commodity Contract [Member] |  |  |  |  |  |
Schedule of Other Comprehensive Income (Loss), Cash Flow Hedges [Line Items] |  |  |  |  |  |
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax | $ 0 | $ 0 |  | $ 0 | $ 4,982 |
[1] | Utilizing an income tax rate ranging from 37 percent to 39 percent based on the effective rates in each taxing jurisdiction for the three and six-month period ended March 31, 2017.

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