INVESTMENT SECURITIES (Details) - USD ($)		Sep. 30, 2017	Dec. 31, 2016
Available-for-sale
Amortized Cost		$ 511,009,000	$ 523,412,000
Unrealized Gains		1,050,000	898,000
Unrealized Losses		1,213,000	1,576,000
Market Value		510,846,000	522,734,000
Held to Maturity
Amortized Cost		184,262,000	177,365,000
Unrealized Gains		88,000	137,000
Unrealized Losses		827,000	756,000
Market Value		183,523,000	176,746,000
Total
Amortized Cost		695,271,000	700,777,000
Unrealized Gain		1,138,000	1,035,000
Unrealized Loss		2,040,000	2,332,000
Fair Value		694,369,000	699,480,000
U.S. Government Treasury [Member]
Available-for-sale
Amortized Cost		257,635,000	286,867,000
Unrealized Gains		32,000	262,000
Unrealized Losses		869,000	851,000
Market Value		256,798,000	286,278,000
U.S. Government Agency [Member]
Available-for-sale
Amortized Cost		147,550,000	131,489,000
Unrealized Gains		729,000	495,000
Unrealized Losses		290,000	344,000
Market Value		147,989,000	131,640,000
States and Political Subdivisions [Member]
Available-for-sale
Amortized Cost		95,869,000	95,197,000
Unrealized Gains		175,000	23,000
Unrealized Losses		54,000	381,000
Market Value		95,990,000	94,839,000
Mortgage-Backed Securities [Member]
Available-for-sale
Amortized Cost		1,218,000	1,312,000
Unrealized Gains		114,000	118,000
Unrealized Losses		0	0
Market Value		1,332,000	1,430,000
Equity Securities [Member]
Available-for-sale
Amortized Cost	[1]	8,737,000	8,547,000
Unrealized Gains		0	0
Unrealized Losses		0	0
Market Value	[1]	8,737,000	8,547,000
Federal Home Loan Bank		3,200,000	3,300,000
Federal Reserve Bank stock		4,800,000	4,800,000
FNBB, Inc. stock		800,000	500,000
U.S. Government Treasury [Member]
Held to Maturity
Amortized Cost		93,309,000	119,131,000
Unrealized Gains		2,000	107,000
Unrealized Losses		183,000	81,000
Market Value		93,128,000	119,157,000
U.S. Government Agency [Member]
Held to Maturity
Amortized Cost		0	0
Unrealized Gains		0	0
Unrealized Losses		0	0
Market Value		0	0
States and Political Subdivisions [Member]
Held to Maturity
Amortized Cost		7,051,000	8,175,000
Unrealized Gains		31,000	1,000
Unrealized Losses		2,000	38,000
Market Value		7,080,000	8,138,000
Mortgage-Backed Securities [Member]
Held to Maturity
Amortized Cost		83,902,000	50,059,000
Unrealized Gains		55,000	29,000
Unrealized Losses		642,000	637,000
Market Value		$ 83,315,000	$ 49,451,000

[1] Includes Federal Home Loan Bank, Federal Reserve Bank, and FNBB, Inc . stock recorded at cost of $3. 2 million, $4.8 million, and $0. 8 million, respectively, at September 30, 2017 and $3 .3 million, $4.8 million, and $0. 5 million, respectively, at December 31, 2016 .