SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest income	$ 72,876,000	$ 71,778,000	$ 68,133,000	$ 64,407,000	$ 63,428,000	$ 62,308,000	$ 61,160,000	$ 59,741,000	$ 277,194,000	$ 246,637,000	$ 235,545,000
Interest expense	5,044,000	4,705,000	4,378,000	4,207,000	4,676,000	4,640,000	4,627,000	4,850,000	18,334,000	18,793,000	20,617,000
Net interest income	67,832,000	67,073,000	63,755,000	60,200,000	58,752,000	57,668,000	56,533,000	54,891,000	258,860,000	227,844,000	214,928,000
Provision (benefit)	1,300,000	0	1,050,000	600,000	4,000,000	950,000	600,000	525,000	2,950,000	6,075,000	1,500,000
Total noninterest income	21,914,000	20,770,000	21,398,000	18,912,000	21,762,000	20,416,000	21,095,000	19,155,000	82,994,000	82,428,000	75,888,000
Total noninterest expenses	51,467,000	51,310,000	52,809,000	48,773,000	51,637,000	46,857,000	47,146,000	46,482,000	204,359,000	192,122,000	197,138,000
Provision for income taxes	14,915,000	12,681,000	10,731,000	9,014,000	7,698,000	9,793,000	9,508,000	8,428,000	47,341,000	35,427,000	27,218,000
Net Income	$ 22,064,000	$ 23,852,000	$ 20,563,000	$ 20,725,000	$ 17,179,000	$ 20,484,000	$ 20,374,000	$ 18,611,000	$ 87,204,000	$ 76,648,000	$ 64,960,000
Basic earnings per share (in dollars per share)	$ 0.80	$ 0.87	$ 0.75	$ 0.77	$ 0.64	$ 0.78	$ 0.77	$ 0.71	$ 3.19	$ 2.90	$ 2.51
Weighted average common shares (basic) (in shares)	27,445,739	27,436,792.000	27,257,799.000	27,029,640	26,710,029.000	26,324,316.000	26,304,129.000	26,275,323	27,294,028	26,404,071	25,891,382
Diluted earnings per share (in dollars per share)	$ 0.80	$ 0.87	$ 0.75	$ 0.76	$ 0.64	$ 0.78	$ 0.77	$ 0.71	$ 3.19	$ 2.90	$ 2.50
Common share equivalents (in shares)	77,615	76,307.000	74,497.000	81,283	60,022.000	53,072.000	47,885.000	43,409	78,076	51,847	68,566
Weighted average common shares (diluted) (in shares)	27,523,354	27,513,099	27,332,296	27,110,923	26,770,051.000	26,377,388.000	26,352,014.000	26,318,732	27,372,104	26,455,918	25,959,948
Gains (Losses) on Extinguishment of Debt	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 437,000	$ 0	$ 437,000	$ 122,000
Acquisition Related Costs	0	0	2,909,000	484,000	4,764,000	151,000	206,000	334,000	3,393,000	5,455,000	10,501,000
Total unusual or infrequent expense items	0	0	2,909,000	484,000	4,764,000	151,000	206,000	771,000
Tax Expense related to a change in tax law	2,361,000	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	466,000	$ 0	$ 0
Investments in Low Income Housing Projects [Member]
Tax Expense related to a change in tax law	466,000								466,000
Net Deferred Tax Asset [Member]
Tax Expense related to a change in tax law	$ 1,895,000								$ 1,900,000