Line of Credit Facility, Maximum Borrowing Capacity, Increase Amount

No definition available.

Name:	iaa_LineofCreditFacilityMaximumBorrowingCapacityIncreaseAmount
Namespace Prefix:	iaa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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+ Details

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

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
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

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

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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

- Definition

The cash outflow for loan and debt issuance costs.

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+ Details

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Balance Type:	credit
Period Type:	duration

- Details

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Period Type:

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

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- Details

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- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

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- Details

Name:	us-gaap_VariableRateAxis=us-gaap_EurodollarMember
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Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=iaa_SeniorNotesdue20175.500Member
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Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
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Period Type:

- Details

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Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
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Balance Type:
Period Type:

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

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- Details

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Long-Term Debt - Narrative (Details)			6 Months Ended
Long-Term Debt - Narrative (Details)	Apr. 30, 2021 USD ($)	Jun. 28, 2019 USD ($)	Jun. 27, 2021 USD ($)	Jun. 28, 2020 USD ($)	Dec. 27, 2020 USD ($)	Dec. 27, 2020 CAD ($)	Jul. 07, 2020 CAD ($)	May 01, 2020 USD ($)	Jun. 06, 2019 USD ($)
Long-Term Debt
Amount outstanding						$ 0
Payments of Financing Costs			$ (4,600,000)	$ (2,700,000)
Loss on extinguishment of debt			10,300,000	$ 0
Outstanding letters of credit			5,600,000		$ 6,100,000
Estimated fair value of long-term debt			$ 523,200,000		532,500,000
2019 Term Loan
Long-Term Debt
Estimated fair value of long-term debt					$ 770,100,000
New Credit Agreement \| Base Rate
Long-Term Debt
Interest rate	0.75%
New Credit Agreement \| Base Rate \| Minimum
Long-Term Debt
Interest rate	0.375%
New Credit Agreement \| Base Rate \| Maximum
Long-Term Debt
Interest rate	1.25%
New Credit Agreement \| Federal Funds Rate
Long-Term Debt
Interest rate	0.50%
New Credit Agreement \| LIBOR
Long-Term Debt
Interest rate	1.00%
New Credit Agreement \| Eurodollar
Long-Term Debt
Interest rate	1.75%
New Credit Agreement \| Eurodollar \| Minimum
Long-Term Debt
Interest rate	1.375%
New Credit Agreement \| Eurodollar \| Maximum
Long-Term Debt
Interest rate	2.25%
Notes \| Senior Notes
Long-Term Debt
Aggregate principal amount, senior notes									$ 500,000,000.0
Senior notes stated interest rate, percentage									5.50%
Secured Debt \| Term Loan Facility
Long-Term Debt
Credit facility, term		7 years
Aggregate principal amount, line of credit		$ 800,000,000
Secured Debt \| Term Loan Facility \| Base Rate
Long-Term Debt
Interest rate, per annum			1.84%		2.44%	2.44%
Revolving Credit Facility \| Revolving Credit Facility
Long-Term Debt
Credit facility, term		5 years
Aggregate principal amount, line of credit		$ 225,000,000
Amount outstanding			$ 0
Revolving Credit Facility \| Credit Agreement Amendment
Long-Term Debt
Aggregate principal amount, line of credit								$ 361,000,000.0
Increase in aggregate principal amount								$ 136,000,000.0
Revolving Credit Facility \| New Credit Agreement \| Minimum
Long-Term Debt
Commitment fee	0.175%
Revolving Credit Facility \| New Credit Agreement \| Maximum
Long-Term Debt
Commitment fee	0.30%
Revolving Credit Facility \| New Credit Agreement \| JPMORGAN CHASE BANK N.A.
Long-Term Debt
Aggregate principal amount, line of credit	$ 525,000,000
Revolving Credit Facility \| Canadian Credit Facility
Long-Term Debt
Aggregate principal amount, line of credit							$ 10,000,000.0
2021 Term Loan \| New Credit Agreement \| JPMORGAN CHASE BANK N.A.
Long-Term Debt
Aggregate principal amount, line of credit	$ 650,000,000