NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2014 RetailBranch		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014 Segment RetailBranch	Dec. 31, 2013	Dec. 31, 2012
Nature of Operations [Abstract]
Trust Preferred securities payable	$ 70,680								$ 70,680								$ 70,680	$ 70,680
Number of retail branches	25																25
Loans [Abstract]
Minimum performance period before a non-accrual loan is classified current																	6 months
Accounting for Goodwill and Other Intangible Assets [Abstract]
Goodwill	55,638								55,638								55,638	55,638
Earnings Per Share Reconciliation [Abstract]
Net income	11,987		11,765		10,460		10,034		10,308		10,631		12,039		10,570		44,246	43,548	40,308
Less: Dividends paid on earnings allocated to participating securities																	(168)	(180)	(184)
Income attributable to common stock																	44,078	43,368	40,124
Weighted average common shares outstanding, including participating securities (in shares)																	36,174,962	35,507,765	34,623,287
Less: weighted average participating securities																	(301,785)	(320,566)	(327,326)
Weighted average common shares outstanding (in shares)																	35,873,177	35,187,199	34,295,961
Basic earnings per common share (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
Income attributable to common stock																	$ 44,078	$ 43,368	$ 40,124
Weighted average common shares outstanding																	35,873,177	35,187,199	34,295,961
Weighted average common equivalent shares outstanding (in shares)																	75,339	119,073	68,492
Weighted average common equivalent shares outstanding (in shares)																	35,948,516	35,306,272	34,364,453
Diluted earnings per common share (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
Disclosure About Segments of an Enterprise and Related Information [Abstract]
Number of reportable segments																	1
Number of operating segments																	1
Customer measurement threshold to revenue, Minimum (in hundredths)																	10.00%
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average shares excluded from earnings per share calculation (in shares)																	293,272	901,037	1,279,708
Building [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Depreciation (in hundredths)																	2.22%
Building [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Depreciation (in hundredths)																	2.50%
Furniture, Fixtures, Equipment [Member]
Property, Plant and Equipment [Line Items]
Depreciation (in hundredths)																	10.00%

[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.