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		40,000			40,000
Dividend reinvestment plan		500,000			500,000
Stock-based compensation expense		1,763,000			1,763,000
Cash dividends			(11,134,000)		(11,134,000)
Net income			30,450,000		30,450,000
Change in net unrealized holding gain/(loss) on securities available for sale, net of tax effect				(8,494,000)	(8,494,000)
Stock option exercises		66,000			66,000
Stock grants to directors for retainer fees		403,000			403,000
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 Sep. 30, 2018	0	312,544,000	80,275,000	(13,354,000)	379,465,000
Balances at Jun. 30, 2018	0	311,720,000	74,084,000	(10,885,000)	374,919,000
Employee stock purchase plan		14,000			14,000
Dividend reinvestment plan		172,000			172,000
Stock-based compensation expense		627,000			627,000
Cash dividends			(3,932,000)		(3,932,000)
Net income			10,123,000		10,123,000
Change in net unrealized holding gain/(loss) on securities available for sale, net of tax effect				(2,469,000)	(2,469,000)
Stock option exercises		11,000			11,000
Balances at Sep. 30, 2018	0	312,544,000	80,275,000	(13,354,000)	379,465,000
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-based compensation expense		2,199,000			2,199,000
Share repurchase program		(7,110,000)			(7,110,000)
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
Stock option exercises		16,000			16,000
Stock grants to directors for retainer fees		375,000			375,000
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
Share repurchase program		(3,508,000)			(3,508,000)
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
Balances at Sep. 30, 2019	$ 0	$ 304,065,000	$ 98,876,000	$ 4,259,000	$ 407,200,000