Debt, lump sum payment on the maturity date.

No definition available.

Name:	nptn_DebtLumpSumPaymentOnMaturityDate
Namespace Prefix:	nptn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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

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

- Definition

Amount of the required periodic payments applied to principal.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

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

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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+ Details

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

- Definition

Amount of cash outflow for payment of an obligation from a lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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+ Details

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- Details

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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

Name:	us-gaap_DebtInstrumentAxis=nptn_MitsubishiBankLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=nptn_TokyoInterbankOfferRateMember
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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Balance Type:
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- Details

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Balance Type:
Period Type:

- Details

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Debt - Mitsubishi Bank Loans (Details) - Mitsubishi Bank - Notes payable to banks $ in Millions			1 Months Ended
	Feb. 25, 2015 JPY (¥)	Feb. 25, 2015 USD ($)	Jan. 31, 2018 JPY (¥)	Jan. 31, 2018 USD ($)	Mar. 31, 2017 JPY (¥)	Mar. 31, 2022 JPY (¥)	Mar. 31, 2022 USD ($)	Mar. 31, 2017 USD ($)	Feb. 25, 2015 USD ($)
Mitsubishi Bank loans
Debt Instrument [Line Items]
Debt issuance costs	¥ 40,500,000								$ 0.4
Mitsubishi Bank loans \| TIBOR
Debt Instrument [Line Items]
Variable rate	1.40%	1.40%
Mitsubishi Bank Term Loan A
Debt Instrument [Line Items]
Debt, aggregate principal amount	¥ 500,000,000								4.4
Repayments of lines of credit			¥ 500,000,000	$ 4.4
Mitsubishi Bank Term Loan B
Debt Instrument [Line Items]
Debt, aggregate principal amount	1,000,000,000								$ 8.2
Debt, periodic principal payments	8,300,000	$ 0.1
Debt, lump sum payment on the maturity date	¥ 8,400,000	$ 0.1
Mitsubishi Bank Term Loan B \| TIBOR
Debt Instrument [Line Items]
Variable rate	1.40%	1.40%
2015 Mitsubishi Bank Loan
Debt Instrument [Line Items]
Long-term debt						¥ 291,700,000	$ 2.4
2017 Mitsubishi Bank Loan
Debt Instrument [Line Items]
Debt, aggregate principal amount					¥ 690,000,000			$ 5.7
Long-term debt						¥ 230,000,000	$ 1.9
Debt term					72 months
Line of credit facility, outstanding					¥ 690,000,000			$ 5.7
2017 Mitsubishi Bank Loan \| TIBOR
Debt Instrument [Line Items]
Variable rate					1.00%