UNAUDITED QUARTERLY FINANCIAL INFORMATION (Details) - USD ($) $ / shares in Units, $ in Thousands	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
UNAUDITED QUARTERLY FINANCIAL INFORMATION [Abstract]
Net interest income	$ 33,586		$ 31,814		$ 33,070		$ 30,094		$ 31,728		$ 31,959		$ 30,594		$ 30,255		$ 128,564	$ 124,536	$ 128,487
Provision (credit) for loan losses	(439)		416		(1,135)		(172)		(522)		(501)		(1,130)		281		(1,330)	(1,872)	369
Net interest income after provision for loan losses	34,025		31,398		34,205		30,266		32,250		32,460		31,724		29,974		129,894	126,408	128,118
Non-interest income	1,739		1,899		1,677		3,301		2,596		1,817		1,565		3,060		8,616	9,038	7,463
Non-interest expense	16,139		16,124		16,366		13,864		15,231		14,724		15,298		15,823		62,493	61,076	62,692
Income before income taxes	19,625		17,173		19,516		19,703		19,615		19,553		17,991		17,211		76,017	74,370	72,889
Tax expense (benefit)	8,241		7,092		7,987		7,925		7,628		7,788		7,531		7,177		31,245	30,124	29,341
Net income	$ 11,384		$ 10,081		$ 11,529		$ 11,778		$ 11,987		$ 11,765		$ 10,460		$ 10,034		$ 44,772	$ 44,246	$ 43,548
Earnings per share:
Basic (in dollars per share)	$ 0.31	[1]	$ 0.28	[1]	$ 0.32	[1]	$ 0.33	[1]	$ 0.33	[1]	$ 0.33	[1]	$ 0.29	[1]	$ 0.28	[1]	$ 1.24	$ 1.23	$ 1.24
Diluted (in dollars per share)	$ 0.31	[1]	$ 0.28	[1]	$ 0.32	[1]	$ 0.33	[1]	$ 0.33	[1]	$ 0.33	[1]	$ 0.29	[1]	$ 0.28	[1]	$ 1.23	$ 1.23	$ 1.23
Net gain on the the disposal of other assets																	$ 0	$ 649	$ (21)

[1] The quarterly EPS amounts, when added, may not coincide with the full fiscal year EPS reported on the Consolidated Statements of Operations due to differences in the computed weighted average shares outstanding as well as rounding differences.