SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 63,428,000	$ 62,308,000	$ 61,160,000	$ 59,741,000	$ 59,870,000	$ 60,228,000	$ 59,016,000	$ 56,429,000	$ 246,637,000	$ 235,545,000	$ 216,459,000
Interest expense	4,676,000	4,640,000	4,627,000	4,850,000	4,985,000	5,183,000	5,269,000	5,180,000	18,793,000	20,617,000	20,417,000
Net interest income	58,752,000	57,668,000	56,533,000	54,891,000	54,885,000	55,045,000	53,747,000	51,249,000	227,844,000	214,928,000	196,042,000
Provision (benefit)	4,000,000	950,000	600,000	525,000	500,000	800,000	700,000	(500,000)	6,075,000	1,500,000	10,403,000
Total noninterest income	21,762,000	20,416,000	21,095,000	19,155,000	19,824,000	19,247,000	20,261,000	16,557,000	82,428,000	75,888,000	69,943,000
Total noninterest expenses	51,637,000	46,857,000	47,146,000	46,482,000	46,486,000	47,031,000	48,644,000	54,977,000	192,122,000	197,138,000	171,838,000
Provision for income taxes	7,698,000	9,793,000	9,508,000	8,428,000	8,268,000	7,867,000	7,213,000	3,869,000	35,427,000	27,218,000	23,899,000
Net Income	$ 17,179,000	$ 20,484,000	$ 20,374,000	$ 18,611,000	$ 19,455,000	$ 18,594,000	$ 17,451,000	$ 9,460,000	$ 76,648,000	$ 64,960,000	$ 59,845,000
Basic earnings per share (in dollars per share)	$ 0.64	$ 0.78	$ 0.77	$ 0.71	$ 0.74	$ 0.71	$ 0.67	$ 0.38	$ 2.90	$ 2.51	$ 2.50
Diluted earnings per share (in dollars per share)	$ 0.64	$ 0.78	$ 0.77	$ 0.71	$ 0.74	$ 0.71	$ 0.67	$ 0.38	$ 2.90	$ 2.50	$ 2.49
Weighted average common shares (basic) (in shares)	26,710,029	26,324,316.000	26,304,129.000	26,275,323	26,238,004.000	26,200,621.000	26,149,593.000	24,959,865	26,404,071	25,891,382	23,899,562
Common share equivalents (in shares)	60,022	53,072.000	47,885.000	43,409	52,772.000	63,493.000	71,819.000	80,215	51,847	68,566	93,815
Weighted average common shares (diluted) (in shares)	26,770,051	26,377,388	26,352,014	26,318,732	26,290,776.000	26,264,114.000	26,221,412.000	25,040,080	26,455,918	25,959,948	23,993,377.000
Available-For-Sale Securities - Fixed Income Gross Realized Gains	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 798,000	$ 0	$ 0	$ 798,000	$ 121,000
Total Unusual or infrequent Income Items	0	0	0	0	0	0	798,000	0
Utilities Operating Expense, Impairments	0	0	0	0	0	0	109,000	0
Gains (Losses) on Extinguishment of Debt	0	0	0	437,000	0	0	0	122,000	437,000	122,000	0
Available-for-Sale Securities - Fixed Income Gross Realized Losses	0	0	0	0	0	0	1,124,000	0	0	1,124,000	21,000
Acquisition Related Costs	4,764,000	151,000	206,000	334,000		0	271,000	10,230,000	$ 5,455,000	$ 10,501,000	$ 1,339,000
Total unusual or infrequent expense items	$ 4,764,000	$ 151,000	$ 206,000	$ 771,000	$ 0	$ 0	$ 1,504,000	$ 10,352,000