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, 2018	$ 176	$ 196,292	$ (10,706)	$ 616,717	$ (83,835)	$ 718,644
Net (loss) income				29,946		29,946
Unrealized gains (losses) on securities available for sale, net of deferred federal income taxes			20,053			20,053
Restricted share awards issued	1	462				463
Recognition of employee share-based compensation, net of deferred federal income taxes		1,260				1,260
Dividends paid and accrued				(12,300)		(12,300)
Balance at Mar. 31, 2019	177	198,014	9,347	631,990	(83,835)	755,693
Cumulative effect of adoption of updated accounting guidance for callable debt securities at January 1, 2019				(2,373)		(2,373)
Balance at Dec. 31, 2019	177	202,321	28,190	661,553	(83,835)	808,406
Net (loss) income				(1,990)		(1,990)
Unrealized gains (losses) on securities available for sale, net of deferred federal income taxes			(21,786)			(21,786)
Restricted share awards issued		528				528
Recognition of employee share-based compensation, net of deferred federal income taxes		1,215				1,215
Dividends paid and accrued				(13,872)		(13,872)
Acquisition of treasury stock					(10,392)	(10,392)
Balance at Mar. 31, 2020	$ 177	$ 204,064	$ 6,404	$ 645,691	$ (94,227)	$ 762,109