ACQUISITIONS (Details) shares in Thousands, $ in Thousands			3 Months Ended
	Oct. 24, 2016 USD ($) Branch	Dec. 04, 2015 USD ($) Branch shares	Mar. 31, 2016 USD ($)
Merchants Bancshares, Inc. [Member]
Business Acquisition [Line Items]
Purchase price of acquisition	$ 362,000
Deposits to be acquired	1,500,000
Assets acquired	$ 2,100,000
Merchants Bancshares, Inc. [Member] | VERMONT [Member]
Business Acquisition [Line Items]
Number of branch locations to be added upon merger | Branch	31
Merchants Bancshares, Inc. [Member] | MASSACHUSETTS [Member]
Business Acquisition [Line Items]
Number of branch locations to be added upon merger | Branch	1
Oneida Financial Corp [Member]
Business Acquisition [Line Items]
Purchase price of acquisition		$ 158,468
Deposits to be acquired		$ 699,241
Issuance of common shares (in shares) | shares		2,380
Number of new branch locations included in acquisition or purchase agreement | Branch		12
Assets acquired		$ 769,000
Decrease in other assets as a result of fair value adjustment			$ (900)
Increase in other liabilities as a result of fair value adjustment			700
Increase in goodwill as a result of fair value adjustment			$ 1,600