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	244,261			244,261
Other comprehensive income (loss)	9,396				9,396
Comprehensive income	253,657
Cash dividends declared	(52,779)			(52,779)
Common stock activity, long-term incentive plans	9,036		8,927	109
Issuance of stock from dividend reinvestment and stock purchase plans	1,934		1,934
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
Balance at Mar. 31, 2023	3,531,232	$ 309,513	1,720,623	2,188,561	(687,465)
Balance, Shares Issued at Mar. 31, 2023		92,947
Net income	117,794			117,794
Other comprehensive income (loss)	(75,321)				(75,321)
Comprehensive income	42,473
Cash dividends declared	(26,392)			(26,392)
Common stock activity, long-term incentive plans	6,164		6,123	41
Issuance of stock from dividend reinvestment and stock purchase plans	999		999
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
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	$ 223,169			223,169
Other comprehensive income (loss)	(36,809)				(36,809)
Comprehensive income	186,360
Cash dividends declared	(61,801)			(61,801)
Common stock activity, long-term incentive plans	5,102		5,017	85
Issuance of stock from dividend reinvestment and stock purchase plans	2,018		2,018
Repurchase of common stock	(14,622)		(14,622)
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	92,947
Balance at Mar. 31, 2024	$ 3,853,436	$ 309,513	1,739,702	2,457,736	(653,515)
Balance, Shares Issued at Mar. 31, 2024		92,947
Net income	114,557			114,557
Other comprehensive income (loss)	(4,421)				(4,421)
Comprehensive income	110,136
Cash dividends declared	(35,274)			(35,274)
Common stock activity, long-term incentive plans	5,921		5,883	38
Issuance of stock from dividend reinvestment and stock purchase plans	1,121		1,121
Repurchase of common stock	(14,622)		(14,622)
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	92,947