SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 54,827	$ 54,368	$ 54,285	$ 52,980	$ 52,571	$ 51,027	$ 51,495	$ 50,820	$ 216,459	$ 205,914	$ 196,192
Interest expense	5,007	4,805	5,232	5,374	5,666	5,831	5,880	5,958	20,417	23,336	23,393
Net interest income	49,820	49,563	49,053	47,606	46,905	45,196	45,615	44,862	196,042	182,578	172,799
Provision	1,750	1,901	2,250	4,502	3,150	2,650	3,100	1,300	10,403	10,200	18,056
Total noninterest income	18,473	17,098	16,857	17,516	17,464	18,130	16,692	15,724	69,943	68,009	62,016
Total noninterest expenses	44,364	42,607	42,980	41,887	47,845	40,722	42,164	42,920	171,838	173,649	159,459
Provision for income taxes	6,201	6,415	5,934	5,350	2,786	5,299	4,285	4,114	23,899	16,484	14,673
Net Income	15,978	15,738	14,746	13,383	10,588	14,655	12,758	12,252	59,845	50,254	42,627
Basic earnings per share (in dollars per share)	$ 0.67	$ 0.66	$ 0.62	$ 0.56	$ 0.45	$ 0.64	$ 0.56	$ 0.54	$ 2.50	$ 2.18	$ 1.96
Diluted earnings per share (in dollars per share)	$ 0.66	$ 0.66	$ 0.61	$ 0.56	$ 0.45	$ 0.64	$ 0.56	$ 0.54	$ 2.49	$ 2.18	$ 1.95
Weighted average common shares (basic) (in shares)	23,968,320	23,911,678	23,897,413	23,819,065	23,383,608	22,946,308	22,888,155	22,823,753	23,899,562	23,011,814	21,782,499
Common share equivalents (in shares)	86,812	90,685	94,560	100,173	97,445	100,806	52,144	46,040	93,815	76,764	29,817
Weighted average common shares (diluted) (in shares)	24,055,132	24,002,363	23,991,973	23,919,238	23,481,053	23,047,114	22,940,299	22,869,793	23,993,377	23,088,578	21,812,316
Gains (Losses) on Extinguishment of Debt	0	0	0	0	0	763	0	0	0	763	0
Gain on life insurance benefits	0	0	337	1,627	227	0	0	0	1,964	227	1,307
Available-for-sale Securities, Gross Realized Gains	121	0	0	0	258	0	0	0	121	258	5
Total Unusual or infrequent Income Items	121	0	337	1,627	485	763	0	0
Utilities Operating Expense, Impairments	0	21	0	503	0	0	0	0
Available-for-sale Securities, Gross Realized Losses	21	0	0	0	0	0	0	0	21	0	0
Loss on termination of derivatives	0	0	1,122	0	0	0	0	0	1,100
Acquisition Related Costs	586	677		77	6,219	366	754	1,345	1,339	8,685	6,741
Severance Costs	0	0	0	0	0	0	0	325
Total unusual or infrequent expense items	$ 607	$ 698	$ 1,122	$ 580	$ 6,219	$ 366	$ 754	$ 1,670