Note 4 - Investment Securities Available for Sale (Details Textual) - USD ($)	3 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2018
Proceeds from Sale of Debt Securities, Available-for-sale	$ 0	$ 0
Debt Securities, Available-for-sale, Amortized Cost, Total	75,761,501		$ 78,267,079
Debt Securities, Available-for-sale, Total	72,638,697		75,404,136
Pledged Financial Instruments, Not Separately Reported, Securities, Total	744,186		744,186
Collateral Pledged [Member]
Debt Securities, Available-for-sale, Restricted	719,728		$ 723,023
Fraternity Community Bancorp, Inc. [Member] \| Mortgage-backed Securities, Issued by Private Enterprises [Member]
Debt Securities, Available-for-sale, Amortized Cost, Total	53,850
Debt Securities, Available-for-sale, Total	$ 54,709

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Section 50
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-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Amount of restricted investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

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Sum of the carrying amounts as of the date of the latest financial statement presented of securities which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
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-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

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Amount of cash inflow from sale of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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