ACQUISITIONS, Summary of Loans Acquired (Details) - Merchants Bancshares, Inc. [Member] $ in Thousands	May 12, 2017 USD ($)
Summary of loans acquired [Abstract]
Contractually required principal and interest at acquisition	$ 1,888,925
Contractual cash flows not expected to be collected	(20,547)
Expected cash flows at acquisition	1,868,378
Interest component of expected cash flows	(379,698)
Fair value of acquired loans	1,488,680
Acquired Impaired Loans [Member]
Summary of loans acquired [Abstract]
Contractually required principal and interest at acquisition	16,351
Contractual cash flows not expected to be collected	(5,794)
Expected cash flows at acquisition	10,557
Interest component of expected cash flows	(758)
Fair value of acquired loans	9,799
Acquired Non-impaired Loans [Member]
Summary of loans acquired [Abstract]
Contractually required principal and interest at acquisition	1,872,574
Contractual cash flows not expected to be collected	(14,753)
Expected cash flows at acquisition	1,857,821
Interest component of expected cash flows	(378,940)
Fair value of acquired loans	$ 1,478,881