LOANS AND SERVICING - Allowance for loan losses (Details) - USD ($) $ in Thousands	3 Months Ended						12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Allowance for loan losses
Beginning Balance			$ 2,408			$ 2,229	$ 2,408	$ 2,229
Charge-offs							(3)	(26)
Recoveries							6	5
(Benefit) provision	$ 53	$ 67	74	$ 62	$ 111	27	194	200
Ending Balance	2,605			2,408			2,605	2,408
Ending balance: Individually evaluated for impairment	7			14			7	14
Ending balance: Collectively evaluated for impairment	2,598			2,394			2,598	2,394
Loans
Ending Balance: Individually evaluated for impairment	2,052			2,046			2,052	2,046
Ending Balance: Collectively evaluated for impairment	277,440			253,968			277,440	253,968
Total Loans	279,492			256,014			279,492	256,014
Residential loans:
Loans
Total Loans	106,069			104,735			106,069	104,735
One- to four- family, residential loans
Allowance for loan losses
Beginning Balance			197			273	197	273
(Benefit) provision							(26)	(76)
Ending Balance	171			197			171	197
Ending balance: Individually evaluated for impairment				7				7
Ending balance: Collectively evaluated for impairment	171			190			171	190
Loans
Ending Balance: Individually evaluated for impairment	1,543			1,567			1,543	1,567
Ending Balance: Collectively evaluated for impairment	88,647			84,905			88,647	84,905
Total Loans	90,190			86,472			90,190	86,472
Home equity loans and lines of credit
Allowance for loan losses
Beginning Balance			276			249	276	249
Recoveries							2	1
(Benefit) provision							(40)	26
Ending Balance	238			276			238	276
Ending balance: Collectively evaluated for impairment	238			276			238	276
Loans
Ending Balance: Individually evaluated for impairment	143			104			143	104
Ending Balance: Collectively evaluated for impairment	15,736			18,159			15,736	18,159
Total Loans	15,879			18,263			15,879	18,263
Commercial loans:
Loans
Total Loans	148,087			130,664			148,087	130,664
One-to-four family investment property
Allowance for loan losses
Beginning Balance			90			46	90	46
(Benefit) provision							(11)	44
Ending Balance	79			90			79	90
Ending balance: Individually evaluated for impairment	7			7			7	7
Ending balance: Collectively evaluated for impairment	72			83			72	83
Loans
Ending Balance: Individually evaluated for impairment	85			88			85	88
Ending Balance: Collectively evaluated for impairment	12,996			15,167			12,996	15,167
Total Loans	13,081			15,255			13,081	15,255
Multi-family real estate
Allowance for loan losses
Beginning Balance			233			113	233	113
(Benefit) provision							1	120
Ending Balance	234			233			234	233
Ending balance: Collectively evaluated for impairment	234			233			234	233
Loans
Ending Balance: Collectively evaluated for impairment	30,748			30,709			30,748	30,709
Total Loans	30,748			30,709			30,748	30,709
Commercial real estate
Allowance for loan losses
Beginning Balance			1,021			943	1,021	943
(Benefit) provision							241	78
Ending Balance	1,262			1,021			1,262	1,021
Ending balance: Collectively evaluated for impairment	1,262			1,021			1,262	1,021
Loans
Ending Balance: Individually evaluated for impairment	281			287			281	287
Ending Balance: Collectively evaluated for impairment	83,302			66,865			83,302	66,865
Total Loans	83,583			67,152			83,583	67,152
Commercial business loan
Allowance for loan losses
Beginning Balance			305			311	305	311
Charge-offs								(22)
(Benefit) provision							59	16
Ending Balance	364			305			364	305
Ending balance: Collectively evaluated for impairment	364			305			364	305
Loans
Ending Balance: Collectively evaluated for impairment	20,675			17,548			20,675	17,548
Total Loans	20,675			17,548			20,675	17,548
Construction loans
Loans
Total Loans	25,154			20,378			25,154	20,378
One-to-four family, construction loans
Allowance for loan losses
Beginning Balance			113			117	113	117
(Benefit) provision							(9)	(4)
Ending Balance	104			113			104	113
Ending balance: Collectively evaluated for impairment	104			113			104	113
Loans
Ending Balance: Collectively evaluated for impairment	12,599			12,967			12,599	12,967
Total Loans	12,599			12,967			12,599	12,967
Multi-family
Allowance for loan losses
Beginning Balance			12			97	12	97
(Benefit) provision							35	(85)
Ending Balance	47			12			47	12
Ending balance: Collectively evaluated for impairment	47			12			47	12
Loans
Ending Balance: Collectively evaluated for impairment	5,725			1,486			5,725	1,486
Total Loans	5,725			1,486			5,725	1,486
Non-residential
Allowance for loan losses
Beginning Balance			91			77	91	77
(Benefit) provision							13	14
Ending Balance	104			91			104	91
Ending balance: Collectively evaluated for impairment	104			91			104	91
Loans
Ending Balance: Collectively evaluated for impairment	6,830			5,925			6,830	5,925
Total Loans	6,830			5,925			6,830	5,925
Consumer
Allowance for loan losses
Beginning Balance			2			$ 3	2	3
Charge-offs							(3)	(4)
Recoveries							4	4
(Benefit) provision							(1)	(1)
Ending Balance	2			2			2	2
Ending balance: Collectively evaluated for impairment	2			2			2	2
Loans
Ending Balance: Collectively evaluated for impairment	182			237			182	237
Total Loans	$ 182			237			182	237
Unallocated
Allowance for loan losses
Beginning Balance			$ 68				68
(Benefit) provision							$ (68)	68
Ending Balance				68				68
Ending balance: Collectively evaluated for impairment				$ 68				$ 68