Consolidated Statements of Changes in Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), Net [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	463,215			463,215
Other comprehensive income (loss)	(134,004)				(134,004)
Comprehensive income (loss)	329,211			463,215	(134,004)
Cash dividends declared	(95,927)			(95,927)
Common stock activity, long-term incentive plans	15,967		15,688	279
Issuance of stock from dividend reinvestment and stock purchase plans	3,872		3,872
Repurchase of common stock	(21,796)		(21,796)
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	524,089			524,089
Other comprehensive income (loss)	(718,247)				(718,247)
Comprehensive income (loss)	(194,158)			524,089	(718,247)
Cash dividends declared	(94,891)			(94,891)
Common stock activity, long-term incentive plans	16,640		16,498	142
Issuance of stock from dividend reinvestment and stock purchase plans	3,577		3,577
Repurchase of common stock	(58,892)		(58,892)
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	$ 392,602			392,602
Other comprehensive income (loss)	151,055				151,055
Comprehensive income (loss)	543,657			392,602	151,055
Cash dividends declared	(105,557)			(105,557)
Common stock activity, long-term incentive plans	19,118		18,972	146
Issuance of stock from dividend reinvestment and stock purchase plans	3,815		3,815
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