Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Balance at Dec. 31, 2022	$ 3,342,628	$ 309,513	$ 1,716,884	$ 2,088,413	$ (772,182)
Balance, Shares Issued at Dec. 31, 2022		92,947
Net income	341,999			341,999
Other comprehensive income (loss)	(122,812)				(122,812)
Comprehensive income (loss)	219,187
Cash dividends declared	(79,169)			(79,169)
Common stock activity, long-term incentive plans	15,499		15,356	143
Issuance of stock from dividend reinvestment and stock purchase plans	2,858		2,858
Balance at Sep. 30, 2023	3,501,003	$ 309,513	1,735,098	2,351,386	(894,994)
Balance, Shares Issued at Sep. 30, 2023		92,947
Balance at Jun. 30, 2023	3,554,476	$ 309,513	1,727,745	2,280,004	(762,786)
Balance, Shares Issued at Jun. 30, 2023		92,947
Net income	97,738			97,738
Other comprehensive income (loss)	(132,208)				(132,208)
Comprehensive income (loss)	(34,470)
Cash dividends declared	(26,390)			(26,390)
Common stock activity, long-term incentive plans	6,463		6,429	34
Issuance of stock from dividend reinvestment and stock purchase plans	924		924
Balance at Sep. 30, 2023	3,501,003	$ 309,513	1,735,098	2,351,386	(894,994)
Balance, Shares Issued at Sep. 30, 2023		92,947
Balance at Dec. 31, 2023	$ 3,803,661	$ 309,513	1,739,671	2,375,604	(621,127)
Balance, Shares Issued at Dec. 31, 2023	92,947	92,947
Net income	$ 338,741			338,741
Other comprehensive income (loss)	145,631				145,631
Comprehensive income (loss)	484,372
Cash dividends declared	(96,890)			(96,890)
Common stock activity, long-term incentive plans	10,422	$ 10,293		129
Issuance of stock from dividend reinvestment and stock purchase plans	3,095		3,095
Repurchase of common stock	(29,973)		(29,973)
Balance at Sep. 30, 2024	$ 4,174,687	$ 309,513	1,723,086	2,617,584	(475,496)
Balance, Shares Issued at Sep. 30, 2024	92,947	92,947
Balance at Jun. 30, 2024	$ 3,920,718	$ 309,513	1,732,084	2,537,057	(657,936)
Balance, Shares Issued at Jun. 30, 2024		92,947
Net income	115,572			115,572
Other comprehensive income (loss)	182,440				182,440
Comprehensive income (loss)	298,012
Cash dividends declared	(35,089)			(35,089)
Common stock activity, long-term incentive plans	5,320		5,276	44
Issuance of stock from dividend reinvestment and stock purchase plans	1,077		1,077
Repurchase of common stock	(15,351)		(15,351)
Balance at Sep. 30, 2024	$ 4,174,687	$ 309,513	$ 1,723,086	$ 2,617,584	$ (475,496)
Balance, Shares Issued at Sep. 30, 2024	92,947	92,947