Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Total
Balance at Dec. 31, 2020	$ 96,241	$ 149,334	$ 2,289,626	$ 20,825	$ (378,028)	$ 2,177,998
Balance (in shares) at Dec. 31, 2020	96,241
Increase (decrease) in shareholders' equity
Net income			50,771			50,771
Dividends:
Cash			(34,813)			(34,813)
Purchase of treasury stock					(48)	(48)
Exercise of stock options	$ 71	1,479				1,550
Exercise of stock options (in shares)	71
Stock compensation expense recognized in earnings		159				159
Other comprehensive loss, net of tax:
Net change in unrealized gains and losses on available for sale securities, net of reclassification adjustments				(3,012)		(3,012)
Balance at Mar. 31, 2021	$ 96,312	150,972	2,305,584	17,813	(378,076)	2,192,605
Balance (in shares) at Mar. 31, 2021	96,312
Balance at Dec. 31, 2021	$ 96,351	152,144	2,470,710	(31,980)	(378,744)	2,308,481
Balance (in shares) at Dec. 31, 2021	96,351
Increase (decrease) in shareholders' equity
Net income			53,493			53,493
Dividends:
Cash			(38,026)			(38,026)
Purchase of treasury stock					(3,380)	(3,380)
Exercise of stock options	$ 6	140				146
Exercise of stock options (in shares)	6
Stock compensation expense recognized in earnings		121				121
Other comprehensive loss, net of tax:
Net change in unrealized gains and losses on available for sale securities, net of reclassification adjustments				(173,156)		(173,156)
Balance at Mar. 31, 2022	$ 96,357	$ 152,405	$ 2,486,177	$ (205,136)	$ (382,124)	$ 2,147,679
Balance (in shares) at Mar. 31, 2022	96,357