SUPPLEMENTARY FINANCIAL INFORMATION (Details) - USD ($) $ / shares in Units, $ in Thousands	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
Supplemental Income Statement Elements [Abstract]
Fee revenue and other income	$ 22,025	$ 22,149	$ 21,457	$ 20,505	$ 20,184	$ 21,514	$ 20,838	$ 20,832	$ 86,136	$ 83,368	$ 79,907
Interest income	10,158	9,985	10,010	9,777	9,774	9,581	9,803	9,552	39,930	38,710	39,759
Interest expense	507	505	504	513	501	498	521	591	2,029	2,111	2,460
Net interest income	9,651	9,480	9,506	9,264	9,273	9,083	9,282	8,961	37,901	36,599	37,299
Provision for loan losses	(500)			(1,000)	(850)				(1,500)	(850)
Operating expense	23,946	23,552	23,059	22,916	22,201	22,634	22,640	22,308	93,473	89,783	85,414
Income tax expense	1,806	1,855	2,035	2,020	2,017	2,083	1,932	1,946	7,716	7,978	7,759
Net income	$ 6,424	$ 6,222	$ 5,869	$ 5,833	$ 6,089	$ 5,880	$ 5,548	$ 5,539	$ 24,348	$ 23,056	$ 24,033
Net income per share:
Basic earnings per share	$ 0.58	$ 0.56	$ 0.53	$ 0.52	$ 0.54	$ 0.52	$ 0.49	$ 0.48	$ 2.18	$ 2.03	$ 2.09
Diluted earnings per share	$ 0.57	$ 0.55	$ 0.52	$ 0.51	$ 0.53	$ 0.51	$ 0.48	$ 0.48	$ 2.15	$ 2.00	$ 2.06