Consolidated Statements of Changes in Shareholders' Equity - USD ($)	Cumulative Effect, Period of Adoption, Adjustment [Member] Retained Earnings [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] AOCI Attributable to Parent [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member]	Preferred Stock [Member]	Common Stock Including Additional Paid in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balances at Dec. 31, 2017	$ (42,000)	$ 42,000	$ 0	$ 0	$ 309,772,000	$ 61,001,000	$ (4,903,000)	$ 365,870,000
Employee stock purchase plan					52,000			52,000
Dividend reinvestment plan					1,165,000			1,165,000
Stock option exercises					108,000			108,000
Stock grants to directors for retainer fees					441,000			441,000
Stock-based compensation expense					2,410,000			2,410,000
Share repurchase program					(5,943,000)			(5,943,000)
Cash dividends						(27,500,000)		(27,500,000)
Net income						42,024,000		42,024,000
Change in net unrealized gain/(loss) on securities available for sale, net of tax effect							(3,379,000)	(3,379,000)
Change in fair value of interest rate swap, net of tax effect							1,000	1,000
Balances at Dec. 31, 2018				0	308,005,000	75,483,000	(8,239,000)	375,249,000
Employee stock purchase plan					50,000			50,000
Dividend reinvestment plan					729,000			729,000
Stock option exercises					128,000			128,000
Stock grants to directors for retainer fees					375,000			375,000
Stock-based compensation expense					2,931,000			2,931,000
Share repurchase program					(7,183,000)			(7,183,000)
Cash dividends						(17,108,000)		(17,108,000)
Net income						49,456,000		49,456,000
Change in net unrealized gain/(loss) on securities available for sale, net of tax effect							11,934,000	11,934,000
Balances at Dec. 31, 2019				0	305,035,000	107,831,000	3,695,000	416,561,000
Employee stock purchase plan					49,000			49,000
Dividend reinvestment plan					814,000			814,000
Stock option exercises					3,000			3,000
Stock grants to directors for retainer fees							394,000	394,000
Stock-based compensation expense					2,325,000			2,325,000
Share repurchase program					(6,591,000)			(6,591,000)
Cash dividends						(17,930,000)		(17,930,000)
Net income						44,138,000		44,138,000
Change in net unrealized gain/(loss) on securities available for sale, net of tax effect							1,791,000	1,791,000
Balances at Dec. 31, 2020				$ 0	$ 302,029,000	$ 134,039,000	$ 5,486,000	$ 441,554,000