Commitments and contingencies disclosure.

No definition available.

Name:	nptn_CommitmentsAndContingenciesDisclosureLineItems
Namespace Prefix:	nptn_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Litigation, Pre-Trial Preservation Order, Assets Ordered To Be Preserved

+ References

No definition available.

+ Details

Name:	nptn_LitigationPreTrialPreservationOrderAssetsOrderedToBePreserved
Namespace Prefix:	nptn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Loss Contingency, Number of Lawsuits

+ References

No definition available.

+ Details

Name:	nptn_LossContingencyNumberofLawsuits
Namespace Prefix:	nptn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of expense provided in the period for legal costs incurred on or before the balance sheet date pertaining to resolved, pending or threatened litigation, including arbitration and mediation proceedings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.3)
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

+ Details

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

- Definition

Amount awarded to other party in judgment or settlement of litigation.

+ References

No definition available.

+ Details

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

- Definition

The value (monetary amount) of the award the plaintiff seeks in the legal matter.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118942415&loc=d3e14557-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118942415&loc=d3e14435-108349

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942415&loc=d3e14326-108349

+ Details

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

- Definition

The total number of new claims filed pertaining to a loss contingency during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118942415&loc=d3e14435-108349

+ Details

Name:	us-gaap_LossContingencyNewClaimsFiledNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of pending claims pertaining to a loss contingency.

+ References

+ Details

Name:	us-gaap_LossContingencyPendingClaimsNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of cash paid for the settlement of litigation or for other legal issues during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3536-108585

+ Details

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

- Definition

Cash received for the settlement of litigation during the current period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3536-108585

+ Details

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

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_IndemnificationGuaranteeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=nptn_FinisarCorpMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=nptn_LestinaInternationalLtd.LitigationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=nptn_LawsuitFiledByLestinaInternationalLtd.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=nptn_NeoPhotonicsDongguanCo.LtdMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=nptn_LestinaInternationalLtd.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=nptn_APATOELegalDisputeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=nptn_APATOEMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=nptn_APATOEAndNeoChinaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=nptn_ClaimAgainstAPATOEAndZheijiangMerchantsPropertyInsuranceCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=nptn_NeoChinaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=nptn_ApatOptoelectronicsComponentsCoArbitrationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Commitments and contingencies (Details)							1 Months Ended											3 Months Ended	12 Months Ended
Commitments and contingencies (Details)	Mar. 31, 2020 CNY (¥)	Mar. 31, 2020 USD ($)	Oct. 25, 2017 CNY (¥)	Oct. 25, 2017 USD ($)	Jun. 16, 2017 USD ($)	Dec. 27, 2016 USD ($)	Aug. 31, 2019 USD ($)	Mar. 31, 2019 CNY (¥)	Mar. 31, 2019 USD ($)	Feb. 28, 2019 CNY (¥)	Feb. 28, 2019 USD ($)	Jan. 31, 2019 USD ($)	Dec. 31, 2018 CNY (¥) lawsuit	Dec. 31, 2018 USD ($) lawsuit	Nov. 30, 2018 USD ($)	Jul. 31, 2018 USD ($)	Apr. 30, 2018 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2010 claim lawsuit
Commitments And Contingencies Disclosure [Line Items]
Number of defendants \| lawsuit																			4
Indemnification Agreement
Commitments And Contingencies Disclosure [Line Items]
Payment for legal settlement																		$ 0
Finisar Corp
Commitments And Contingencies Disclosure [Line Items]
Pending claims \| claim																			2
Lestina International Ltd. litigation
Commitments And Contingencies Disclosure [Line Items]
Damages sought, value						$ 3,000,000.0
Lawsuit Filed by Lestina International Ltd. \| NeoPhotonics Dongguan Co., Ltd \| Lestina International Ltd.
Commitments And Contingencies Disclosure [Line Items]
Loss contingency, damages awarded, value												$ 2,200,000
APAT OE Legal Dispute
Commitments And Contingencies Disclosure [Line Items]
Damages sought, value																	$ 20,000,000.0
APAT OE Legal Dispute \| APAT OE
Commitments And Contingencies Disclosure [Line Items]
New claims filed, number \| lawsuit													2	2
APAT OE and NeoChina
Commitments And Contingencies Disclosure [Line Items]
Damages sought, value													¥ 50,900,000	$ 7,600,000
Assets ordered to be preserved												$ 3,800,000		$ 29,000,000.0
Claim Against APAT OE and Zheijiang Merchants Property Insurance Company \| NeoChina
Commitments And Contingencies Disclosure [Line Items]
Damages sought, value										¥ 350,000	$ 52,000
APAT Arbitration
Commitments And Contingencies Disclosure [Line Items]
Damages sought, value					$ 1,500,000		$ 8,100,000				$ 7,100,000				$ 7,800,000	$ 12,000,000.0
Damages awarded to company			¥ 700,000	$ 110,000
Attorney fees	¥ 846,000	$ 119,000						¥ 810,000	$ 121,000
APAT Arbitration \| NeoChina
Commitments And Contingencies Disclosure [Line Items]
Loss contingency, damages awarded, value	¥ 54,607,000	$ 7,700,000