SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 59,870,000	$ 60,228,000	$ 59,016,000	$ 56,429,000	$ 54,827,000	$ 54,368,000	$ 54,285,000	$ 52,980,000	$ 235,545,000	$ 216,459,000	$ 205,914,000
Interest expense	4,985,000	5,183,000	5,269,000	5,180,000	5,007,000	4,805,000	5,232,000	5,374,000	20,617,000	20,417,000	23,336,000
Net interest income	54,885,000	55,045,000	53,747,000	51,249,000	49,820,000	49,563,000	49,053,000	47,606,000	214,928,000	196,042,000	182,578,000
Provision (benefit)	500,000	800,000	700,000	(500,000)	1,750,000	1,901,000	2,250,000	4,502,000	1,500,000	10,403,000	10,200,000
Total noninterest income	19,824,000	19,247,000	20,261,000	16,557,000	18,473,000	17,098,000	16,857,000	17,516,000	75,888,000	69,943,000	68,009,000
Total noninterest expenses	46,486,000	47,031,000	48,644,000	54,977,000	44,364,000	42,607,000	42,980,000	41,887,000	197,138,000	171,838,000	173,649,000
Provision for income taxes	8,268,000	7,867,000	7,213,000	3,869,000	6,201,000	6,415,000	5,934,000	5,350,000	27,218,000	23,899,000	16,484,000
Net Income	$ 19,455,000	$ 18,594,000	$ 17,451,000	$ 9,460,000	$ 15,978,000	$ 15,738,000	$ 14,746,000	$ 13,383,000	$ 64,960,000	$ 59,845,000	$ 50,254,000
Basic earnings per share (in dollars per share)	$ 0.74	$ 0.71	$ 0.67	$ 0.38	$ 0.67	$ 0.66	$ 0.62	$ 0.56	$ 2.51	$ 2.50	$ 2.18
Diluted earnings per share (in dollars per share)	$ 0.74	$ 0.71	$ 0.67	$ 0.38	$ 0.66	$ 0.66	$ 0.61	$ 0.56	$ 2.50	$ 2.49	$ 2.18
Weighted average common shares (basic) (in shares)	26,238,004	26,200,621	26,149,593	24,959,865	23,968,320	23,911,678	23,897,413	23,819,065	25,891,382	23,899,562	23,011,814
Common share equivalents (in shares)	52,772	63,493	71,819	80,215	86,812	90,685	94,560	100,173	68,566	93,815	76,764
Weighted average common shares (diluted) (in shares)	26,290,776	26,264,114	26,221,412	25,040,080	24,055,132	24,002,363	23,991,973	23,919,238	25,959,948	23,993,377.000	23,088,578
Gain on life insurance benefits	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 337,000	$ 1,627,000	$ 0	$ 1,964,000	$ 227,000
Available-For-Sale Securities - Fixed Income Gross Realized Gains	0	0	798,000	0	121,000	0	0	0	798,000	121,000	258,000
Total Unusual or infrequent Income Items	0	0	798,000	0	121,000	0	337,000	1,627,000
Utilities Operating Expense, Impairments	0	0	109,000	0	0	21,000	0	503,000
Gains (Losses) on Extinguishment of Debt	0	0	0	122,000	0	0	0	0	0	0	(763,000)
Available-for-Sale Securities - Fixed Income Gross Realized Losses	0	0	1,124,000	0	21,000	0	0	0	1,124,000	21,000	0
Loss on termination of derivatives	0	0	0	0	0	0	1,122,000	0		1,100,000
Acquisition Related Costs	0	0	271,000	10,230,000	586,000	677,000		77,000	$ 10,501,000	$ 1,339,000	$ 8,685,000
Total unusual or infrequent expense items	$ 0	$ 0	$ 1,504,000	$ 10,352,000	$ 607,000	$ 698,000	$ 1,122,000	$ 580,000