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	244,913			244,913
Other comprehensive income (loss)	(473,242)				(473,242)
Comprehensive income (loss)	(228,329)			244,913	(473,242)
Cash dividends declared	(47,581)			(47,581)
Common stock activity, long-term incentive plans	9,970		9,886	84
Repurchase of common stock	(56,489)		(56,489)
Issuance of stock from dividend reinvestment and stock purchase plans	1,800		1,800
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
Balance at Mar. 31, 2022	3,450,951	$ 309,513	1,742,021	1,758,693	(359,276)
Balance, Shares Issued at Mar. 31, 2022		92,947
Net income	121,435			121,435
Other comprehensive income (loss)	(167,901)				(167,901)
Comprehensive income (loss)	(46,466)			121,435	(167,901)
Cash dividends declared	(23,672)			(23,672)
Common stock activity, long-term incentive plans	5,990		5,957	33
Repurchase of common stock	(37,999)		(37,999)
Issuance of stock from dividend reinvestment and stock purchase plans	919		919
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
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	$ 244,261			244,261
Other comprehensive income (loss)	9,396				9,396
Comprehensive income (loss)	253,657			244,261	9,396
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	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 (loss)	42,473			117,794	(75,321)
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	92,947