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	195,890			195,890
Other comprehensive income (loss)	(37,207)				(37,207)
Comprehensive income (loss)	158,683			195,890	(37,207)
Cash dividends declared	(48,044)			(48,044)
Common stock activity, long-term incentive plans	11,275		11,074	201
Issuance of stock from dividend reinvestment and stock purchase plans	1,962		1,962
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
Balance at Mar. 31, 2021	3,416,903	$ 309,513	1,764,145	1,374,688	(31,443)
Balance, Shares Issued at Mar. 31, 2021		92,947
Net income	88,718			88,718
Other comprehensive income (loss)	74,305				74,305
Comprehensive income (loss)	163,023			88,718	74,305
Cash dividends declared	(24,023)			(24,023)
Common stock activity, long-term incentive plans	6,040		5,870	170
Issuance of stock from dividend reinvestment and stock purchase plans	958		958
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
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)
Dividends declared	47,581			47,581
Common stock activity, long-term incentive plans	9,970		9,886	84
Issuance of stock from dividend reinvestment and stock purchase plans	1,800		1,800
Repurchase of common stock	(56,489)		(56,489)
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	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
Issuance of stock from dividend reinvestment and stock purchase plans	919		919
Repurchase of common stock	(37,999)		(37,999)
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	92,947