Consolidated Statements of Changes in Shareholders' Equity - 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, 2016	$ 0	$ 305,488,000	$ 40,904,000	$ (5,581,000)	$ 340,811,000
Employee stock purchase plan		46,000			46,000
Dividend reinvestment plan		1,576,000			1,576,000
Stock option exercises		318,000			318,000
Stock grants to directors for retainer fees		363,000			363,000
Stock-based compensation expense		1,981,000			1,981,000
Cash dividends			(12,046,000)		(12,046,000)
Net income			31,274,000		31,274,000
Change in net unrealized gain/(loss) on securities available for sale, net of tax effect				1,493,000	1,493,000
Reclassification of stranded tax effect related to available for sale securities resulting from Tax Cuts and Jobs Act			869,000	(869,000)	0
Change in fair value of interest rate swap, net of tax effect				54,000	54,000
Balances at Dec. 31, 2017	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
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
Reclassification of equity securities related to ASU 2016-01 adoption			(42,000)	42,000	0
Share repurchase program		(5,943,000)			(5,943,000)
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
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
Share repurchase program		(7,183,000)			(7,183,000)
Balances at Dec. 31, 2019	$ 0	$ 305,035,000	$ 107,831,000	$ 3,695,000	$ 416,561,000