LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES - Summary of recorded investment amount and related allowance for losses of impaired loans (Details)	9 Months Ended
	Sep. 30, 2018 USD ($) borrower loan	Sep. 30, 2018 USD ($) loan	Sep. 30, 2017 borrower	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Financing Receivable, Impaired [Line Items]
Allowance for loan loss	$ 2,455,000	$ 2,455,000		$ 2,589,000	$ 2,484,000
Loans outstanding included in current and 30 - 89 days past due	1,000,000	1,000,000
Amount of troubled debt restructured loans, outstanding	44,401	44,401
Amount of troubled debt restructured loans, specific reserve	$ 15,953	$ 15,953
Number of borrowers	43	1	48
Specific Reserve	$ 223,000	$ 223,000
Home Equity
Financing Receivable, Impaired [Line Items]
Loans outstanding included in current and 30 - 89 days past due	158,000	158,000
Consumer
Financing Receivable, Impaired [Line Items]
Allowance for loan loss	$ 204,000	$ 204,000		214,000	182,000
Number of loans | loan	3	3
Amount of consumer and indirect loans, outstanding	$ 230,677	$ 230,677
Amount of consumer and indirect loans, specific reserves	$ 74,149	74,149
Number of borrowers | borrower	3
Commercial
Financing Receivable, Impaired [Line Items]
Allowance for loan loss	$ 242,000	242,000		237,000	284,000
Loans outstanding included in current and 30 - 89 days past due	208,000	208,000
Specific Reserve	208,000	208,000
Commercial Real Estate
Financing Receivable, Impaired [Line Items]
Allowance for loan loss	256,000	256,000		$ 291,000	$ 259,000
Loans outstanding included in current and 30 - 89 days past due	$ 626,000	$ 626,000