Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($)		Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock Outstanding	Common Stock	Value of Shares Held in Rabbi Trust at Cost	Deferred Compensation and Other Retirement Benefit Obligations	Additional Paid in Capital	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income/(Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding				34,377,388
Net income		$ 86,526,000							$ 86,526,000
Other comprehensive income		30,463,000									$ 30,463,000
Cash dividends declared per common share (in dollars per share)									$ 1.38
Common dividend declared		(45,715,000)							$ (45,715,000)
Proceeds from exercise of stock options, net of cash paid				5,873
Proceeds from exercise of stock options, net of cash paid		114,000			$ 0			$ 114,000
Stock based compensation		3,297,000						3,297,000
Restricted stock awards issued, net of awards surrendered				49,249
Restricted stock awards issued, net of awards surrendered		(1,186,000)			1,000			(1,187,000)
Shares issued under direct stock purchase plan				23,037
Shares issued under direct stock purchase plan		1,620,000			0			1,620,000
Stock Repurchased During Period, Shares				(1,500,000)
Stock Repurchased During Period, Value		(95,091,000)			(15,000)			(95,076,000)
Increase (Decrease) in Deferred Compensation and Other Retirement Benefits						$ 23,000	$ (23,000)
Increase (Decrease) in Deferred Compensation		0
Period End Balance at Sep. 30, 2020		1,689,724,000			328,000	(4,712,000)	4,712,000	944,218,000	696,546,000		48,632,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method, net of tax.		817,000
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	[1]	(1,137,000)
Off-Balance Sheet, Credit Loss, Liability, Change in Method, Credit Loss Expense (Reversal)		(1,000,000)
Off-Balance Sheet, Credit Loss, Liability, Change in Method, Credit Loss Expense (Reversal), net of tax.		736,000
Common Stock, Shares, Outstanding				32,942,110
Net income		34,873,000							$ 34,873,000
Other comprehensive income		(3,213,000)									(3,213,000)
Cash dividends declared per common share (in dollars per share)									$ 0.46
Common dividend declared		(15,161,000)							$ (15,161,000)
Proceeds from exercise of stock options, net of cash paid				5,000
Stock Repurchased During Period, Value, as a result of Stock Options Exercised		140,000						140,000
Stock based compensation		868,000						868,000
Restricted stock awards issued, net of awards surrendered				(43)
Restricted stock awards issued, net of awards surrendered		(3,000)						(3,000)
Shares issued under direct stock purchase plan				8,480
Shares issued under direct stock purchase plan		528,000						528,000
Increase (Decrease) in Deferred Compensation and Other Retirement Benefits						(63,000)	63,000
Increase (Decrease) in Deferred Compensation		0
Period End Balance at Sep. 30, 2020		$ 1,689,724,000			328,000	(4,712,000)	4,712,000	944,218,000	696,546,000		48,632,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding				32,955,547
Common Stock, Shares, Outstanding		32,965,692		32,965,692
Cumulative Effect of New Accounting Principle in Period of Adoption (Deprecated 2020-01-31)	[2]		$ 1,553,000							$ 1,553,000
Net income		$ 119,290,000							$ 119,290,000
Other comprehensive income		(22,128,000)									(22,128,000)
Cash dividends declared per common share (in dollars per share)									$ 1.44
Common dividend declared		(47,572,000)							$ (47,572,000)
Proceeds from exercise of stock options, net of cash paid				4,744
Stock Repurchased During Period, Value, as a result of Stock Options Exercised		57,000						57,000
Stock based compensation		3,467,000						3,467,000
Restricted stock awards issued, net of awards surrendered				53,795
Restricted stock awards issued, net of awards surrendered		(1,246,000)			1,000			(1,247,000)
Shares issued under direct stock purchase plan				19,581
Shares issued under direct stock purchase plan		1,515,000						1,515,000
Increase (Decrease) in Deferred Compensation and Other Retirement Benefits						(91,000)	91,000
Increase (Decrease) in Deferred Compensation		0
Period End Balance at Sep. 30, 2021		1,755,954,000			329,000	(3,157,000)	3,157,000	949,316,000	787,742,000		18,567,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding				33,037,859
Net income		40,007,000							$ 40,007,000
Other comprehensive income		(11,000,000)									(11,000,000)
Cash dividends declared per common share (in dollars per share)									$ 0.48
Common dividend declared		(15,861,000)							$ (15,861,000)
Stock based compensation		707,000						707,000
Restricted stock awards issued, net of awards surrendered				(763)
Restricted stock awards issued, net of awards surrendered		(3,000)						(3,000)
Shares issued under direct stock purchase plan				6,716
Shares issued under direct stock purchase plan		482,000						482,000
Increase (Decrease) in Deferred Compensation and Other Retirement Benefits						(41,000)	41,000
Increase (Decrease) in Deferred Compensation		0
Period End Balance at Sep. 30, 2021		$ 1,755,954,000			$ 329,000	$ (3,157,000)	$ 3,157,000	$ 949,316,000	$ 787,742,000		$ 18,567,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding		33,043,812		33,043,812

[1] Represents adjustment needed to reflect the cumulative day one impact pursuant to the Company's adoption of Accounting Standards Update 2016-13. The adjustment represents a $1.1 million decrease to the allowance attributable to the change in accounting methodology for estimating the allowance for credit losses resulting from the Company's adoption of the standard.

[2] Represents adjustment needed to reflect the cumulative impact on retained earnings pursuant to the Company's adoption of Accounting Standards Update 2016-13. The adjustment presented includes $1.1 million ($817,000, net of tax) attributable to the change in accounting methodology for estimating the allowance for credit losses and $1.0 million ($736,000, net of tax) related to the reserve for unfunded commitments resulting from the Company's adoption of the standard. Amount shown in the table above is presented net of tax.