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	107,172			107,172
Other comprehensive loss	(111,512)				(111,512)
Comprehensive loss	(4,340)			107,172	(111,512)
Dividends declared	(24,021)			(24,021)
Common stock activity, long-term incentive plans	5,235		5,204	31
Issuance of stock from dividend reinvestment and stock purchase plans	1,004		1,004
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
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	$ 123,478			123,478
Other comprehensive loss	(305,341)				(305,341)
Comprehensive loss	(181,863)			123,478	(305,341)
Dividends declared	(23,909)			(23,909)
Common stock activity, long-term incentive plans	3,980		3,929	51
Repurchase of common stock	(18,490)		(18,490)
Issuance of stock from dividend reinvestment and stock purchase plans	881		881
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	92,947