Shareholders' Equity - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	$ 3,898,666	$ 3,463,059	$ 3,194,797
Net current-period other comprehensive income (loss)	44,541	82,768	(78,692)
Cumulative effect of accounting change	22,900		14,527
Shareholders' equity, ending balance	4,769,951	3,898,666	3,463,059
Available- for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	7,048	4,484
Other comprehensive income (loss) before reclassifications	1,426	2,502
Amounts reclassified from accumulated other comprehensive income	(1,821)	62
Net current-period other comprehensive income (loss)	(395)	2,564
Cumulative effect of accounting change	1,471
Shareholders' equity, ending balance	8,124	7,048	4,484
Cash Flow Hedges \| Interest rate agreements
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	(112,302)	(187,524)
Other comprehensive income (loss) before reclassifications	43,184	74,560
Amounts reclassified from accumulated other comprehensive income	1,752	662
Net current-period other comprehensive income (loss)	44,936	75,222
Cumulative effect of accounting change	(24,405)
Shareholders' equity, ending balance	(91,771)	(112,302)	(187,524)
Cash Flow Hedges \| Commodity contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	0	(4,982)
Other comprehensive income (loss) before reclassifications		9,847
Amounts reclassified from accumulated other comprehensive income		(4,865)
Net current-period other comprehensive income (loss)		4,982
Shareholders' equity, ending balance		0	(4,982)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	(105,254)	(188,022)	(109,330)
Other comprehensive income (loss) before reclassifications	44,610	86,909
Amounts reclassified from accumulated other comprehensive income	(69)	(4,141)
Net current-period other comprehensive income (loss)	44,541	82,768	(78,692)
Cumulative effect of accounting change	(22,934)
Shareholders' equity, ending balance	$ (83,647)	$ (105,254)	$ (188,022)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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