Condensed Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($)	Preferred Stock [Member]	Common Stock [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balances at Dec. 31, 2015	$ 0	$ 304,819,000	$ 27,722,000	$ 1,263,000	$ 333,804,000
Employee stock purchase plan		27,000			27,000
Dividend reinvestment plan		1,079,000			1,079,000
Stock option exercises		606,000			606,000
Stock grants to directors for retainer fees		327,000			327,000
Stock-based compensation expense		901,000			901,000
Cash dividends			(7,895,000)		(7,895,000)
Net income			23,828,000		23,828,000
Change in net unrealized holding gain/(loss) on securities available for sale, net of tax effect				469,000	469,000
Change in fair value of interest rate swap, net of tax effect				57,000	57,000
Share repurchase program		(3,732,000)			(3,732,000)
Balances at Sep. 30, 2016	0	304,027,000	43,655,000	1,789,000	349,471,000
Balances at Dec. 31, 2016	0	305,488,000	40,904,000	(5,581,000)	340,811,000
Employee stock purchase plan		36,000			36,000
Dividend reinvestment plan		1,426,000			1,426,000
Stock option exercises		289,000			289,000
Stock grants to directors for retainer fees		363,000			363,000
Stock-based compensation expense		1,431,000			1,431,000
Cash dividends			(8,941,000)		(8,941,000)
Net income			23,295,000		23,295,000
Change in net unrealized holding gain/(loss) on securities available for sale, net of tax effect				3,791,000	3,791,000
Change in fair value of interest rate swap, net of tax effect				45,000	45,000
Balances at Sep. 30, 2017	$ 0	$ 309,033,000	$ 55,258,000	$ (1,745,000)	$ 362,546,000