Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($)	Preferred Stock [Member]	Common Stock Including Additional Paid in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balances at Dec. 31, 2018	$ 0	$ 308,005,000	$ 75,483,000	$ (8,239,000)	$ 375,249,000
Employee stock purchase plan		39,000			39,000
Dividend reinvestment plan		541,000			541,000
Stock grants to directors for retainer fees		375,000			375,000
Stock-based compensation expense		2,199,000			2,199,000
Cash dividends			(12,746,000)		(12,746,000)
Net income			36,139,000		36,139,000
Change in net unrealized holding gain/(loss) on securities available for sale, net of tax effect				12,498,000	12,498,000
Share repurchase program		(7,110,000)			(7,110,000)
Stock option exercises		16,000			16,000
Balances at Sep. 30, 2019	0	304,065,000	98,876,000	4,259,000	407,200,000
Balances at Jun. 30, 2019	0	306,669,000	90,618,000	2,830,000	400,117,000
Employee stock purchase plan		13,000			13,000
Dividend reinvestment plan		180,000			180,000
Stock-based compensation expense		711,000			711,000
Cash dividends			(4,342,000)		(4,342,000)
Net income			12,600,000		12,600,000
Change in net unrealized holding gain/(loss) on securities available for sale, net of tax effect				1,429,000	1,429,000
Share repurchase program		(3,508,000)			(3,508,000)
Balances at Sep. 30, 2019	0	304,065,000	98,876,000	4,259,000	407,200,000
Balances at Dec. 31, 2019	0	305,035,000	107,831,000	3,695,000	416,561,000
Employee stock purchase plan		37,000			37,000
Dividend reinvestment plan		610,000			610,000
Stock grants to directors for retainer fees		394,000			394,000
Stock-based compensation expense		2,102,000			2,102,000
Cash dividends			(13,436,000)		(13,436,000)
Net income			30,056,000		30,056,000
Change in net unrealized holding gain/(loss) on securities available for sale, net of tax effect				1,858,000	1,858,000
Share repurchase program		(6,282,000)			(6,282,000)
Balances at Sep. 30, 2020	0	301,896,000	124,451,000	5,553,000	431,900,000
Balances at Jun. 30, 2020	0	300,897,000	118,239,000	6,085,000	425,221,000
Employee stock purchase plan		12,000			12,000
Dividend reinvestment plan		206,000			206,000
Stock grants to directors for retainer fees		45,000			45,000
Stock-based compensation expense		736,000			736,000
Cash dividends			(4,474,000)		(4,474,000)
Net income			10,686,000		10,686,000
Change in net unrealized holding gain/(loss) on securities available for sale, net of tax effect				(532,000)	(532,000)
Balances at Sep. 30, 2020	$ 0	$ 301,896,000	$ 124,451,000	$ 5,553,000	$ 431,900,000