Note 4 - Securities Available for Sale - Summary of Securities Available for Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Amortized cost	$ 78,801	$ 79,839
Gross unrealized gains	104	92
Gross unrealized losses	(1,433)	(1,454)
Fair value	77,472	78,477
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] \| Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Amortized cost	91	327
Gross unrealized gains	2	10
Gross unrealized losses	0	0
Fair value	93	337
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] \| Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Amortized cost	4,834	295
Gross unrealized gains	1	7
Gross unrealized losses	(78)	0
Fair value	4,757	302
Collateralized Mortgage Obligations [Member] \| Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Amortized cost	223	371
Gross unrealized gains	0	0
Gross unrealized losses	(5)	(5)
Fair value	218	366
Collateralized Mortgage Backed Securities [Member]
Amortized cost	5,148	993
Gross unrealized gains	3	17
Gross unrealized losses	(83)	(5)
Fair value	5,068	1,005
Other Marketable Securities [Member]
Amortized cost	73,653	78,846
Gross unrealized gains	101	75
Gross unrealized losses	(1,350)	(1,449)
Fair value	72,404	77,472
Other Marketable Securities [Member] \| US Government Agencies Debt Securities [Member]
Amortized cost	69,962	74,979
Gross unrealized gains	0	16
Gross unrealized losses	(1,201)	(1,079)
Fair value	68,761	73,916
Other Marketable Securities [Member] \| US States and Political Subdivisions Debt Securities [Member]
Amortized cost	2,699	2,819
Gross unrealized gains	2	0
Gross unrealized losses	(8)	(20)
Fair value	2,693	2,799
Other Marketable Securities [Member] \| Corporate Debt Securities [Member]
Amortized cost	234	290
Gross unrealized gains	0	2
Gross unrealized losses	(1)	0
Fair value	233	292
Other Marketable Securities [Member] \| Preferred Stock [Member]
Amortized cost	700	700
Gross unrealized gains	0	0
Gross unrealized losses	(140)	(350)
Fair value	560	350
Other Marketable Securities [Member] \| Equity Securities [Member]
Amortized cost	58	58
Gross unrealized gains	99	57
Gross unrealized losses	0	0
Fair value	$ 157	$ 115

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

+ Details

Name:	us-gaap_AvailableForSaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAmortizedCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CollateralizedMortgageObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=hmnf_OtherMarketableSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_PreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: