BUSINESS COMBINATIONS (Details)			1 Months Ended	9 Months Ended
	Jun. 07, 2018 USD ($) item	May 18, 2018 USD ($)	May 31, 2018 USD ($) item $ / shares shares	Sep. 30, 2019 USD ($) shares	Sep. 30, 2018 USD ($) shares	Dec. 31, 2018 USD ($) shares	Oct. 01, 2018 USD ($)	Aug. 31, 2016 USD ($)	Apr. 29, 2016 USD ($)
Business Acquisition [Line Items]
Assets				$ 1,355,383,000		$ 1,318,040,000
FFNM acquisition					$ 34,101,000
Purchase Price:
FFNM shares outstanding | shares				10,740,712		10,712,745
Net assets acquired:
Goodwill				$ 19,574,000		$ 22,024,000	$ 19,574,000
Eagle River
Net assets acquired:
Goodwill									$ 1,839,000
Niagara Bancorporation
Net assets acquired:
Goodwill								$ 50,000
FFNM
Business Acquisition [Line Items]
Number of banking offices | item			7
Increase deferred tax asset				1,950,000
Decrease Goodwill				2,450,000
FFNM acquisition (in shares) | shares			2,146,378
Purchase Price:
FFNM shares outstanding | shares			3,726,925
Price per share / Cash Price | $ / shares			$ 9.15
Total purchase price			$ 34,101,000
Net assets acquired:
Cash and cash equivalents			13,267,000
Securities available for sale			96,297,000
FHLB Stock			1,748,000
Total loans		$ 192,000,000	185,444,000
Premises and equipment			5,134,000
Other real estate owned			194,000
Deposit based intangible			2,894,000
Mortgage service rights			886,000
Deferred tax assets			4,631,000
Bank owned life insurance			5,170,000
Other assets			1,775,000
Total assets			317,440,000
Non-interest bearing deposits			60,616,000
Interest bearing deposits			193,099,000
Total deposits		254,000,000	253,715,000
FHLB Borrowings			40,722,000
Deferred tax liability			133,000
Other liabilities			1,397,000
Total liabilities			295,967,000
Net assets acquired			21,473,000
Goodwill		12,628,000	$ 12,628,000
Increase to MSRs		500,000
FFNM | Minimum
Business Acquisition [Line Items]
Assets		$ 318,000,000
Lincoln Community Bank
Business Acquisition [Line Items]
Number of banking centers | item	2
Cash consideration	$ 8,500,000
Decrease deferred tax liability				163,000
Decrease Goodwill				$ 163,000
Net assets acquired:
Cash and cash equivalents	10,971,000
Securities available for sale	6,947,000
Total loans	38,001,000				39,000,000
Premises and equipment	1,249,000
Other real estate owned	69,000
Deposit based intangible	1,353,000
Bank owned life insurance	1,653,000
Other assets	339,000
Total assets	60,582,000
Non-interest bearing deposits	15,559,000
Interest bearing deposits	37,654,000
Total deposits	53,213,000				53,000,000
Deferred tax liability	68,000
Other liabilities	53,000
Total liabilities	53,334,000
Net assets acquired	7,248,000
Goodwill	$ 1,252,000						$ 1,252,000
Lincoln Community Bank | Minimum
Business Acquisition [Line Items]
Assets					$ 59,000,000
Shares of Common Stock
Business Acquisition [Line Items]
FFNM acquisition (in shares) | shares					2,146,378
Common Stock and Additional Paid in Capital
Business Acquisition [Line Items]
FFNM acquisition					$ 34,101,000