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Shareholders' Equity Statement of Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock outstanding (in shares)	116,892,959		111,273,683
Shareholders' equity, beginning balance	$ 4,769,951	$ 3,898,666
Net Income	157,646	314,132
Other Comprehensive Loss, Net of Tax	(22,258)	(1,062)
Cash dividends	(58,722)	(51,837)
Stock Issued or Granted During Period, Share-based Compensation [Abstract]
Public and other stock offerings	498,975	400,759
Stock-based compensation plans	2,603	2,962
Shareholders' equity, ending balance	$ 5,348,195	$ 4,563,620
Cash dividends per share	$ 0.525	$ 0.485
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock outstanding (in shares)	116,892,959	110,962,112	111,273,683	106,104,634
Shareholders' equity, beginning balance	$ 556	$ 531
Stock Issued or Granted During Period, Share-based Compensation [Abstract]
Public and other stock offerings (in shares)	5,434,812	4,621,518
Public and other stock offerings	$ 27	$ 22
Stock-based compensation plans (in shares)	184,464	235,960
Stock-based compensation plans	$ 1	$ 2
Shareholders' equity, ending balance	584	555
Additional Paid-in Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' equity, beginning balance	2,974,926	2,536,365
Stock Issued or Granted During Period, Share-based Compensation [Abstract]
Public and other stock offerings	498,948	400,737
Stock-based compensation plans	2,602	2,960
Shareholders' equity, ending balance	3,476,476	2,940,062
Accumulated Other Comprehensive Income
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' equity, beginning balance	(83,647)	(105,254)
Other Comprehensive Loss, Net of Tax	(22,258)	(1,062)
Cumulative Effect of New Accounting Principle in Period of Adoption	(8,210)
Stock Issued or Granted During Period, Share-based Compensation [Abstract]
Shareholders' equity, ending balance	(114,115)	(106,316)
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' equity, beginning balance	1,878,116	1,467,024
Net Income	157,646	314,132
Cash dividends	(58,722)	(51,837)
Cumulative Effect of New Accounting Principle in Period of Adoption	8,210
Stock Issued or Granted During Period, Share-based Compensation [Abstract]
Shareholders' equity, ending balance	$ 1,985,250	$ 1,729,319