Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	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	Accumulated Other Comprehensive Income/(Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding		32,965,692
Net income	$ 119,290						$ 119,290
Other comprehensive income	(22,128)							$ (22,128)
Cash dividends declared per common share (in dollars per share)							$ 1.44
Common dividend declared	(47,572)						$ (47,572)
Proceeds from exercise of stock options, net of cash paid		4,744
Proceeds from exercise of stock options, net of cash paid			$ 0
Stock Repurchased During Period, Value, as a result of Stock Options Exercised	(57)					$ (57)
Stock based compensation	3,467					3,467
Restricted stock awards issued, net of awards surrendered		53,795
Restricted stock awards issued, net of awards surrendered	(1,246)		1			(1,247)
Shares issued under direct stock purchase plan		19,581
Shares issued under direct stock purchase plan	1,515		0			1,515
Increase (Decrease) in Deferred Compensation and Other Retirement Benefits				$ (91)	$ 91
Increase (Decrease) in Deferred Compensation	0
Period End Balance at Sep. 30, 2021	1,755,954		329	(3,157)	3,157	949,316	787,742	18,567
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding		33,037,859
Net income	40,007						$ 40,007
Other comprehensive income	(11,000)							(11,000)
Cash dividends declared per common share (in dollars per share)							$ 0.48
Common dividend declared	(15,861)						$ (15,861)
Stock based compensation	707					707
Restricted stock awards issued, net of awards surrendered		(763)
Restricted stock awards issued, net of awards surrendered	(3)					(3)
Shares issued under direct stock purchase plan		6,716
Shares issued under direct stock purchase plan	482					482
Increase (Decrease) in Deferred Compensation and Other Retirement Benefits				(41)	41
Increase (Decrease) in Deferred Compensation	0
Period End Balance at Sep. 30, 2021	$ 1,755,954		329	(3,157)	3,157	949,316	787,742	18,567
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding		33,043,812
Common Stock, Shares, Outstanding	47,349,778	47,349,778
Net income	$ 186,770						$ 186,770
Other comprehensive income	(181,252)							(181,252)
Cash dividends declared per common share (in dollars per share)							$ 1.53
Common dividend declared	(70,983)						$ (70,983)
Stock based compensation	3,483					3,483
Restricted stock awards issued, net of awards surrendered		50,096
Restricted stock awards issued, net of awards surrendered	(1,085)					(1,085)
Shares issued under direct stock purchase plan		21,717
Shares issued under direct stock purchase plan	1,765					1,765
Stock Repurchased During Period, Shares		(1,786,965)
Stock Repurchased During Period, Value	(139,946)		(18)			(139,928)
Increase (Decrease) in Deferred Compensation and Other Retirement Benefits				(93)	93
Increase (Decrease) in Deferred Compensation	0
Period End Balance at Sep. 30, 2022	2,817,201		454	(3,239)	3,239	2,113,313	882,503	(179,069)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding		46,069,761
Net income	71,897						$ 71,897
Other comprehensive income	(69,605)							(69,605)
Cash dividends declared per common share (in dollars per share)							$ 0.51
Common dividend declared	(23,251)						$ (23,251)
Stock based compensation	1,017					1,017
Restricted stock awards issued, net of awards surrendered		296
Restricted stock awards issued, net of awards surrendered	0
Shares issued under direct stock purchase plan		7,541
Shares issued under direct stock purchase plan	606					606
Stock Repurchased During Period, Shares		(442,972)
Stock Repurchased During Period, Value	(34,648)		(5)			(34,643)
Increase (Decrease) in Deferred Compensation and Other Retirement Benefits				(43)	43
Increase (Decrease) in Deferred Compensation	0
Period End Balance at Sep. 30, 2022	$ 2,817,201		$ 454	$ (3,239)	$ 3,239	$ 2,113,313	$ 882,503	$ (179,069)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding	45,634,626	45,634,626