Increased present value of lessee's discounted obligation for lease payments from operating lease.

No definition available.

Name:	amba_IncreasedOperatingLeaseLiabilities
Namespace Prefix:	amba_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Increased amount of lessee's right to use underlying asset under operating lease.

+ References

No definition available.

+ Details

Name:	amba_IncreasedOperatingLeaseRightOfUseAsset
Namespace Prefix:	amba_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Lease commencement date.

+ References

No definition available.

+ Details

Name:	amba_LeaseCommencementDate
Namespace Prefix:	amba_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Lease liability payments over the remainder of lease term.

+ References

No definition available.

+ Details

Name:	amba_LeaseLiabilityPaymentsOverRemainderOfLeaseTerm
Namespace Prefix:	amba_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Leased property, construction completion period, after lease inception date.

+ References

No definition available.

+ Details

Name:	amba_LeasedPropertyConstructionCompletionPeriodAfterLeaseInceptionDate
Namespace Prefix:	amba_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Lessee construction costs paid in construction phase.

+ References

No definition available.

+ Details

Name:	amba_LesseeConstructionCostsPaidInConstructionPhase
Namespace Prefix:	amba_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Term of lessee's lease.

+ References

No definition available.

+ Details

Name:	amba_LesseeLeaseTermOfContract
Namespace Prefix:	amba_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Lessee operating lease number of renewed contracts.

+ References

No definition available.

+ Details

Name:	amba_LesseeOperatingLeaseNumberOfRenewedContracts
Namespace Prefix:	amba_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Lessee undiscounted cash payments for lease liabilities.

+ References

No definition available.

+ Details

Name:	amba_LesseeUndiscountedCashPaymentsForLeaseLiabilities
Namespace Prefix:	amba_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Date which lease or group of leases is set to expire, in CCYY-MM-DD format.

+ References

No definition available.

+ Details

Name:	us-gaap_LeaseExpirationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

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

- Definition

Indicates (true false) whether lessee has option to extend operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918673-209980

+ Details

Name:	us-gaap_LesseeOperatingLeaseExistenceOfOptionToExtend
Namespace Prefix:	us-gaap_
Data Type:	xbrli:booleanItemType
Balance Type:	na
Period Type:	duration

- Definition

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918673-209980

+ Details

Name:	us-gaap_LesseeOperatingLeaseTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of operating lease expense. Excludes sublease income.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918638-209977

+ Details

Name:	us-gaap_OperatingLeaseExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Weighted average discount rate for operating lease calculated at point in time.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (g)(4)
-URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918686-209980

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 55
-Paragraph 53
-URI http://asc.fasb.org/extlink&oid=121568110&loc=SL77918982-209971

+ Details

Name:	us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average remaining lease term for operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 55
-Paragraph 53
-URI http://asc.fasb.org/extlink&oid=121568110&loc=SL77918982-209971

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (g)(3)
-URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918686-209980

+ Details

Name:	us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121573735&loc=d3e41499-112717

+ Details

Name:	us-gaap_OperatingLeasesRentExpenseNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=amba_ParmaLeaseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=amba_RenewedContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=country_US
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=amba_AdditionalOfficeSpaceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=amba_ShanghaiMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=country_IT
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_BuildingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Leases - Additional Information (Detail)	1 Months Ended	3 Months Ended	12 Months Ended			15 Months Ended
Leases - Additional Information (Detail)	Aug. 31, 2019 USD ($)	Jan. 31, 2021 USD ($)	Jan. 31, 2021 USD ($)	Jan. 31, 2020 USD ($) Contract	Jan. 31, 2019 USD ($)	Oct. 31, 2020
Lessee Lease Description [Line Items]
Operating leases, existence of options to extend			true	true
Operating lease expense under ASC 842			$ 3,000,000.0	$ 3,000,000.0
Operating lease expense under ASC 840					$ 4,600,000
Weighted-average remaining lease term – operating leases		4 years 3 months 25 days	4 years 3 months 25 days
Weighted-average discount rate – operating leases		4.11%	4.11%
Parma Lease [Member]
Lessee Lease Description [Line Items]
Future undiscounted cash payments		$ 0	$ 0
Renewed Contract [Member]
Lessee Lease Description [Line Items]
Operating lease number of renewed contracts \| Contract				2
An increase to operating lease right-of-use assets				$ 4,000,000.0
An increase to operating lease liabilities				$ 4,000,000.0
U.S. [Member] \| Additional Office Space [Member]
Lessee Lease Description [Line Items]
Lease term		56 months	56 months
Commencement date		Dec. 01, 2020				Jan. 01, 2021
Expiration date			Aug. 31, 2025
An increase to operating lease right-of-use assets			$ 1,600,000
An increase to operating lease liabilities			$ 1,600,000
U.S. [Member] \| Renewed Contract [Member]
Lessee Lease Description [Line Items]
Lease term				63 months
Commencement date				Jun. 01, 2020
Expiration date				Aug. 31, 2025
Shanghai [Member] \| Renewed Contract [Member]
Lessee Lease Description [Line Items]
Lease term				2 years
Commencement date				Dec. 01, 2019
Expiration date				Nov. 30, 2021
Italy [Member] \| Building [Member]
Lessee Lease Description [Line Items]
Lease term	35 years
Construction completion period	2 years
Italy [Member] \| Parma Lease [Member] \| Building [Member]
Lessee Lease Description [Line Items]
Future undiscounted cash payments	$ 2,200,000
Future undiscounted cash payments in construction phase	1,800,000
Future undiscounted cash payments, paid in remainder of lease term	$ 400,000