NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2015 USD ($) RetailBranch $ / shares		Sep. 30, 2015 USD ($) $ / shares		Jun. 30, 2015 USD ($) $ / shares		Mar. 31, 2015 USD ($) $ / shares		Dec. 31, 2014 USD ($) $ / shares		Sep. 30, 2014 USD ($) $ / shares		Jun. 30, 2014 USD ($) $ / shares		Mar. 31, 2014 USD ($) $ / shares		Dec. 31, 2015 USD ($) RetailBranch Segment $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares
Nature of Operations [Abstract]
Trust Preferred securities payable | $	$ 70,680								$ 70,680								$ 70,680	$ 70,680
Number of retail branches | RetailBranch	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 | $	$ 11,384		$ 10,081		$ 11,529		$ 11,778		$ 11,987		$ 11,765		$ 10,460		$ 10,034		44,772	44,246	$ 43,548
Less: Dividends paid on earnings allocated to participating securities | $																	(136)	(168)	(180)
Income attributable to common stock | $																	$ 44,636	$ 44,078	$ 43,368
Weighted average common shares outstanding, including participating securities (in shares)																	36,477,854	36,174,962	35,507,765
Less: weighted average participating securities																	(245,037)	(301,785)	(320,566)
Weighted average common shares outstanding (in shares)																	36,232,817	35,873,177	35,187,199
Basic earnings per common share (in dollars per share) | $ / shares	$ 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
Income attributable to common stock | $																	$ 44,636	$ 44,078	$ 43,368
Weighted average common shares outstanding																	36,232,817	35,873,177	35,187,199
Weighted average common equivalent shares outstanding (in shares)																	89,516	75,339	119,073
Weighted average common equivalent shares outstanding (in shares)																	36,322,333	35,948,516	35,306,272
Diluted earnings per common share (in dollars per share) | $ / shares	$ 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
Disclosure About Segments of an Enterprise and Related Information [Abstract]
Number of reportable segments | Segment																	1
Number of operating segments | Segment																	1
Customer measurement threshold to revenue, Minimum (in hundredths)																	10.00%
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%
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)																	126,172	293,272	901,037

[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.