Securities - Amortized Cost and Approximate Fair Value of Securities, Together with Gross Unrealized Gains and Losses of Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 154,486	$ 155,588
Gross Unrealized Gains	6,936	7,029
Gross Unrealized Losses	(130)	(223)
Fair Value	161,292	162,394
U.S. Government and Federal Agency and Government Sponsored Enterprises (GSEs) [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,526	7,528
Gross Unrealized Gains	709	708
Fair Value	8,235	8,236
Mortgage-backed Securities - GSE Residential [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	142,008	143,033
Gross Unrealized Gains	6,075	6,044
Gross Unrealized Losses	(129)	(222)
Fair Value	147,954	148,855
Small Business Administration [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,502	3,578
Gross Unrealized Gains	152	62
Fair Value	3,654	3,640
State and Political Subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,450	1,449
Gross Unrealized Gains		215
Gross Unrealized Losses	(1)	(1)
Fair Value	$ 1,449	$ 1,663

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

No definition available.

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121645371&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

No definition available.

+ 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

No definition available.

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USTreasuryAndGovernmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=iroq_SmallBusinessAdministrationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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