Condensed 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, 2017	$ 0	$ 309,772,000	$ 61,001,000	$ (4,903,000)	$ 365,870,000
Employee stock purchase plan		26,000			26,000
Dividend reinvestment plan		328,000			328,000
Stock option exercises		55,000			55,000
Stock grants to directors for retainer fees		403,000			403,000
Stock-based compensation expense		1,136,000			1,136,000
Cash dividends			(7,202,000)		(7,202,000)
Net income			20,327,000		20,327,000
Change in net unrealized holding gain/(loss) on securities available for sale, net of tax effect				(6,025,000)	(6,025,000)
Reclassification of equity securities related to ASU 2016-01 adoption			(42,000)	42,000	0
Change in fair value of interest rate swap, net of tax effect				1,000	1,000
Balances at Jun. 30, 2018	0	311,720,000	74,084,000	(10,885,000)	374,919,000
Balances at Mar. 31, 2018	0	310,601,000	68,241,000	(10,502,000)	368,340,000
Employee stock purchase plan		12,000			12,000
Dividend reinvestment plan		164,000			164,000
Stock grants to directors for retainer fees		403,000			403,000
Stock-based compensation expense		540,000			540,000
Cash dividends			(3,603,000)		(3,603,000)
Net income			9,446,000		9,446,000
Change in net unrealized holding gain/(loss) on securities available for sale, net of tax effect				(383,000)	(383,000)
Balances at Jun. 30, 2018	0	311,720,000	74,084,000	(10,885,000)	374,919,000
Balances at Dec. 31, 2018	0	308,005,000	75,483,000	(8,239,000)	375,249,000
Employee stock purchase plan		26,000			26,000
Dividend reinvestment plan		361,000			361,000
Stock option exercises		16,000			16,000
Stock grants to directors for retainer fees		374,000			374,000
Stock-based compensation expense		1,488,000			1,488,000
Cash dividends			(8,404,000)		(8,404,000)
Net income			23,539,000		23,539,000
Change in net unrealized holding gain/(loss) on securities available for sale, net of tax effect				11,069,000	11,069,000
Share repurchase program		(3,601,000)			(3,601,000)
Balances at Jun. 30, 2019	0	306,669,000	90,618,000	2,830,000	400,117,000
Balances at Mar. 31, 2019	0	305,346,000	83,107,000	(4,724,000)	383,729,000
Employee stock purchase plan		12,000			12,000
Dividend reinvestment plan		179,000			179,000
Stock option exercises		14,000			14,000
Stock grants to directors for retainer fees		374,000			374,000
Stock-based compensation expense		744,000			744,000
Cash dividends			(4,204,000)		(4,204,000)
Net income			11,715,000		11,715,000
Change in net unrealized holding gain/(loss) on securities available for sale, net of tax effect				7,554,000	7,554,000
Balances at Jun. 30, 2019	$ 0	$ 306,669,000	$ 90,618,000	$ 2,830,000	$ 400,117,000