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, 2021	$ 3,670,352	$ 309,513	$ 1,755,701	$ 1,659,073	$ (53,935)
Balance, Shares Issued at Dec. 31, 2021		92,947
Net income	380,302			380,302
Other comprehensive loss	(758,846)				(758,846)
Comprehensive income (loss)	(378,544)			380,302	(758,846)
Cash dividends declared	(71,249)			(71,249)
Common stock activity, long-term incentive plans	16,101		15,967	134
Issuance of stock from dividend reinvestment and stock purchase plans	2,671		2,671
Repurchase of common stock	(58,892)		(58,892)
Balance at Sep. 30, 2022	3,180,439	$ 309,513	1,715,447	1,968,260	(812,781)
Balance, Shares Issued at Sep. 30, 2022		92,947
Balance at Jun. 30, 2022	3,349,723	$ 309,513	1,710,898	1,856,489	(527,177)
Balance, Shares Issued at Jun. 30, 2022		92,947
Net income	135,389			135,389
Other comprehensive loss	(285,604)				(285,604)
Comprehensive income (loss)	(150,215)			135,389	(285,604)
Cash dividends declared	(23,668)			(23,668)
Common stock activity, long-term incentive plans	6,131		6,081	50
Issuance of stock from dividend reinvestment and stock purchase plans	871		871
Repurchase of common stock	(2,403)		(2,403)
Balance at Sep. 30, 2022	3,180,439	$ 309,513	1,715,447	1,968,260	(812,781)
Balance, Shares Issued at Sep. 30, 2022		92,947
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	92,947
Net income	$ 341,999			341,999
Other comprehensive loss	(122,812)				(122,812)
Comprehensive income (loss)	219,187			341,999	(122,812)
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	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 loss	(132,208)				(132,208)
Comprehensive income (loss)	(34,470)			97,738	(132,208)
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	92,947