Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive (Loss) Income, Net of Taxes	Retained Earnings	Treasury Stock	Total
Balance at Dec. 31, 2019	$ 177	$ 202,321	$ 28,190	$ 661,553	$ (83,835)	$ 808,406
Net income				138,211		138,211
Unrealized gains (losses) on securities available for sale, net of deferred federal income taxes			25,337			25,337
Restricted share awards issued	1	528				529
Recognition of employee share-based compensation		6,930				6,930
Dividends paid and accrued				(54,735)		(54,735)
Acquisition of treasury stock					(39,999)	(39,999)
Balance at Dec. 31, 2020	178	209,779	53,527	745,029	(123,834)	884,679
Net income				130,710		130,710
Unrealized gains (losses) on securities available for sale, net of deferred federal income taxes			(28,948)			(28,948)
Restricted share awards issued		475				475
Recognition of employee share-based compensation		5,816				5,816
Dividends paid and accrued				(53,996)		(53,996)
Acquisition of treasury stock					(11,563)	(11,563)
Balance at Dec. 31, 2021	178	216,070	24,579	821,743	(135,397)	927,173
Net income				46,561		46,561
Unrealized gains (losses) on securities available for sale, net of deferred federal income taxes			(105,117)			(105,117)
Restricted share awards issued	1					1
Recognition of employee share-based compensation		5,979				5,979
Dividends paid and accrued				(52,995)		(52,995)
Reissuance of treasury stock					5,000	5,000
Acquisition of treasury stock					(14,603)	(14,603)
Balance at Dec. 31, 2022	$ 179	$ 222,049	$ (80,538)	$ 815,309	$ (145,000)	$ 811,999