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 Income (Loss) [Member]
Balance at Dec. 31, 2020	$ 3,439,025	$ 309,513	$ 1,757,937	$ 1,291,506	$ 80,069
Balance, Shares Issued at Dec. 31, 2020		92,947
Net income	325,472			325,472
Other comprehensive income (loss)	(79,871)				(79,871)
Comprehensive income (loss)	245,601			325,472	(79,871)
Cash dividends declared	(72,046)			(72,046)
Common stock activity, long-term incentive plans	16,755		16,506	249
Issuance of stock from dividend reinvestment and stock purchase plans	2,940		2,940
Repurchase of common stock	(2,509)		(2,509)
Balance at Sep. 30, 2021	3,629,766	$ 309,513	1,774,874	1,545,181	198
Balance, Shares Issued at Sep. 30, 2021		92,947
Balance at Jun. 30, 2021	3,562,901	$ 309,513	1,770,973	1,439,553	42,862
Balance, Shares Issued at Jun. 30, 2021		92,947
Net income	129,582			129,582
Other comprehensive income (loss)	(42,664)				(42,664)
Comprehensive income (loss)	86,918			129,582	(42,664)
Cash dividends declared	(24,002)			(24,002)
Common stock activity, long-term incentive plans	5,480		5,432	48
Issuance of stock from dividend reinvestment and stock purchase plans	978		978
Repurchase of common stock	(2,509)		(2,509)
Balance at Sep. 30, 2021	3,629,766	$ 309,513	1,774,874	1,545,181	198
Balance, Shares Issued at Sep. 30, 2021		92,947
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	92,947
Net income	$ 380,302			380,302
Other comprehensive income (loss)	(758,846)				(758,846)
Comprehensive income (loss)	(378,544)			380,302	(758,846)
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	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 income (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	92,947