Shareholders' Equity - Components of Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Oct. 01, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock outstanding (in shares)	119,338,925
Shareholders' equity, beginning balance	$ 5,750,223	$ 4,769,951
Net income	178,673	157,646
Other comprehensive income	1,052	(22,258)
Cash dividends	$ (69,557)	(58,722)
Cumulative effect of accounting change		(8,210)
Public and other stock offerings (in shares)	2,720,060
Public and other stock offerings	$ 263,272	498,975
Stock-based compensation plans	$ 4,112	2,603
Common stock outstanding (in shares)	122,262,403
Shareholders' equity, ending balance	$ 6,127,775	$ 5,348,195
Cash dividends per share (USD per share)	$ 0.575	$ 0.525
Common stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock outstanding (in shares)	119,338,925	111,273,683
Shareholders' equity, beginning balance	$ 597	$ 556
Public and other stock offerings (in shares)	2,758,929	5,434,812
Public and other stock offerings	$ 13	$ 27
Stock-based compensation plans (in shares)	164,549	184,464
Stock-based compensation plans	$ 1	$ 1
Common stock outstanding (in shares)	122,262,403	116,892,959
Shareholders' equity, ending balance	$ 611	$ 584
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' equity, beginning balance	3,712,194	2,974,926
Public and other stock offerings	263,259	498,948
Stock-based compensation plans	4,111	2,602
Shareholders' equity, ending balance	3,979,564	3,476,476
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' equity, beginning balance	(114,583)	(83,647)
Other comprehensive income	1,052	(22,258)
Cumulative effect of accounting change			$ (8,210)
Shareholders' equity, ending balance	(113,531)	(114,115)
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' equity, beginning balance	2,152,015	1,878,116
Net income	178,673	157,646
Cash dividends	(69,557)	(58,722)
Cumulative effect of accounting change			$ 8,210
Shareholders' equity, ending balance	$ 2,261,131	$ 1,985,250

Aggregate dividends paid during the period for each share of common stock outstanding.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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

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Number of new stock issued during the period.

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Number, after forfeiture, of shares or units issued under share-based payment arrangement. Excludes shares or units issued under employee stock ownership plan (ESOP).

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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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