ACCOUNTING POLICIES (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) Component Calculation Segment Factor $ / shares	Mar. 31, 2016 USD ($) $ / shares
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of broad components used in allowance methodology | Component	2
Number of calculations used for general loan loss allocation | Calculation	2
Number of main loan segments | Segment	5
Period of historical net charge-off data for each loan class used in determining allowance level	36 months
Number of qualitative environmental factors used in qualitative calculation for loan loss allocation | Factor	8
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income	$ 26,257	$ 24,403
Net income per diluted common share (in dollars per share) | $ / shares	$ 0.57	$ 0.55
Core Deposits [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset useful life (amortization period)	7 years
Core Deposits [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset useful life (amortization period)	20 years
Customer Relationships [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset useful life (amortization period)	7 years
Customer Relationships [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset useful life (amortization period)	20 years
Commercial Portfolio Segment [Member] | Minimum [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Threshold balance of loans individually evaluated for impairment	$ 500
ASU 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income	$ 2,200
Net income per diluted common share (in dollars per share) | $ / shares	$ 0.05