UNAUDITED QUARTERLY FINANCIAL INFORMATION (Details) (USD $) In Thousands, except Per 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
UNAUDITED QUARTERLY FINANCIAL INFORMATION [Abstract]
Net interest income	$ 31,728		$ 31,959		$ 30,594		$ 30,255		$ 30,767		$ 31,653		$ 33,752		$ 32,314		$ 124,536	$ 128,487	$ 109,842
Provision (credit) for loan losses	(522)		(501)		(1,130)		281		(56)		240		28		157		(1,872)	369	3,921
Net interest income after provision for loan losses	32,250		32,460		31,724		29,974		30,823		31,413		33,724		32,157		126,408	128,118	105,921
Non-interest income	2,596		1,817		1,565		3,060		1,837		2,008		1,721		1,898		9,038	7,463	23,849
Non-interest expense	15,231		14,724		15,298		15,823		15,461		15,575		15,347		16,309		61,076	62,692	62,572
Income before income taxes	19,615		19,553		17,991		17,211		17,199		17,846		20,098		17,746		74,370	72,889	67,198
Tax expense (benefit)	7,628		7,788		7,531		7,177		6,891		7,215		8,059		7,176		30,124	29,341	26,890
Net income	11,987		11,765		10,460		10,034		10,308		10,631		12,039		10,570		44,246	43,548	40,308
Earnings per share:
Basic (in dollars per share)	$ 0.33	[1]	$ 0.33	[1]	$ 0.29	[1]	$ 0.28	[1]	$ 0.29	[1]	$ 0.30	[1]	$ 0.34	[1]	$ 0.30	[1]	$ 1.23	$ 1.24	$ 1.18
Diluted (in dollars per share)	$ 0.33	[1]	$ 0.33	[1]	$ 0.29	[1]	$ 0.28	[1]	$ 0.29	[1]	$ 0.30	[1]	$ 0.34	[1]	$ 0.30	[1]	$ 1.23	$ 1.23	$ 1.17
Net gain on the the disposal of other assets																	$ 649	$ (21)	$ 13,726

[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.