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 Revision of Prior Period, Accounting Standards Update, Adjustment	Retained Earnings	Treasury Stock	Revision of Prior Period, Accounting Standards Update, Adjustment	Total
Balance at Dec. 31, 2018	$ 176	$ 196,292	$ (10,706)	$ (2,373)	$ 616,717	$ (83,835)	$ (2,373)	$ 718,644
Net income					99,601			99,601
Unrealized gains on securities available for sale, net of deferred federal income taxes			38,896					38,896
Restricted share awards issued	1	462						463
Recognition of employee share-based compensation, net of deferred federal income taxes		5,567						5,567
Dividends paid and accrued					(52,392)			(52,392)
Balance at Dec. 31, 2019	177	202,321	28,190		661,553	(83,835)		808,406
Net income					138,211			138,211
Unrealized gains 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, net of deferred federal income taxes		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 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, net of deferred federal income taxes		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