Shareholders' Equity - Components of Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock outstanding, beginning balance (in shares)	132,419,754
Shareholders' equity, beginning balance	$ 7,906,889	$ 6,791,203
Net income	249,209	217,678
Other comprehensive income (loss)	(45,947)	60,121
Cash dividends	(90,411)	(79,023)
Public and other stock offerings	265,861	220,009
Stock-based compensation plans	$ 3,944	3,168
Common stock outstanding, ending balance (in shares)	135,425,081
Shareholders' equity, ending balance	$ 8,289,545	$ 7,213,156
Cash dividends per share (USD per share)	$ 0.680	$ 0.625
Common stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock outstanding, beginning balance (in shares)	132,419,754	125,882,477
Shareholders' equity, beginning balance	$ 662	$ 629
Public and other stock offerings (in shares)	2,730,115	2,126,118
Public and other stock offerings	$ 13	$ 11
Stock-based compensation plans (in shares)	275,212	144,366
Stock-based compensation plans	$ 2	$ 1
Common stock outstanding, ending balance (in shares)	135,425,081	128,152,961
Shareholders' equity, ending balance	$ 677	$ 641
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' equity, beginning balance	5,023,751	4,377,149
Public and other stock offerings	265,848	219,998
Stock-based compensation plans	3,942	3,167
Shareholders' equity, ending balance	5,293,541	4,600,314
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' equity, beginning balance	69,803	(57,589)
Other comprehensive income (loss)	(45,947)	60,121
Shareholders' equity, ending balance	23,856	2,532
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' equity, beginning balance	2,812,673	2,471,014
Net income	249,209	217,678
Cash dividends	(90,411)	(79,023)
Shareholders' equity, ending balance	$ 2,971,471	$ 2,609,669