ACCOUNTING POLICIES (Details) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) $ / shares	Sep. 30, 2016 USD ($) $ / shares	Sep. 30, 2017 USD ($) Component Calculation Segment Factor $ / shares	Sep. 30, 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 | $	$ 35,243	$ 27,160	$ 78,691	$ 77,420
Net income per diluted common share (in dollars per share) | $ / shares	$ 0.68	$ 0.61	$ 1.60	$ 1.74
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		$ 500
ASU 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income | $	$ 300		$ 2,900
Net income per diluted common share (in dollars per share) | $ / shares			$ 0.05
ASU 2016-09 [Member] | Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income per diluted common share (in dollars per share) | $ / shares	$ 0.01