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		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)		$ 0			(1,085)
Shares issued under direct stock purchase plan		21,717
Shares issued under direct stock purchase plan	1,765		0			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
Common Stock, Shares, Outstanding	45,641,238	45,641,238
Net income	$ 184,699							$ 184,699
Other comprehensive income	2,338								2,338
Cash dividends declared per common share (in dollars per share)								$ 1.65
Common dividend declared	(72,875)							$ (72,875)
Proceeds from exercise of stock options, net of cash paid		3,238
Stock Repurchased During Period, Value, as a result of Stock Options Exercised	81					81
Stock based compensation	4,721					4,721
Restricted stock awards issued, net of awards surrendered		81,721
Restricted stock awards issued, net of awards surrendered	(1,136)		1			(1,137)
Shares issued under direct stock purchase plan		32,809
Shares issued under direct stock purchase plan	1,990					1,990
Stock Repurchased During Period, Shares		(1,617,033)
Stock Repurchased During Period, Value	(121,111)		(16)			(121,095)	[1]
Increase (Decrease) in Deferred Compensation and Other Retirement Benefits				(108)	108
Increase (Decrease) in Deferred Compensation	0
Period End Balance at Sep. 30, 2023	2,885,408		440	(3,335)	3,335	1,999,448		1,046,266	(160,746)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding		44,130,901
Net income	60,808							$ 60,808
Other comprehensive income	(7,811)								(7,811)
Cash dividends declared per common share (in dollars per share)								$ 0.55
Common dividend declared	(24,277)							$ (24,277)
Proceeds from exercise of stock options, net of cash paid		1,572
Stock Repurchased During Period, Value, as a result of Stock Options Exercised	1					1
Stock based compensation	1,128					1,128
Restricted stock awards issued, net of awards surrendered		(4,838)
Restricted stock awards issued, net of awards surrendered	(26)					(26)
Shares issued under direct stock purchase plan		14,338
Shares issued under direct stock purchase plan	671					671
Increase (Decrease) in Deferred Compensation and Other Retirement Benefits				(46)	46
Increase (Decrease) in Deferred Compensation	0
Period End Balance at Sep. 30, 2023	$ 2,885,408		$ 440	$ (3,335)	$ 3,335	$ 1,999,448		$ 1,046,266	$ (160,746)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding	44,141,973	44,141,973
Sales and Excise Tax Payable	$ 1,200

[1] Inclusive of $1.2 million impact of excise tax attributable to shares repurchased under the share repurchase program during the nine months ended September 30, 2023