Credit Facility and Debt - Narrative (Details)		12 Months Ended
May 06, 2020 USD ($)	Sep. 30, 2021 USD ($) credit
Paycheck Protection Program
Line of Credit Facility [Line Items]
Proceeds from Paycheck Protection Program - CARES Act	$ 6,500,000
PPP loan balance - CARES Act		$ 0
Revolving Credit Facility
Line of Credit Facility [Line Items]
Liquidity requirement, minimum after specific uses		25,000,000
Liquidity requirement, minimum		10,000,000
Excess availability requirement, minimum		1,000,000
Long-term line of credit		0
Standby letters of credit, total amount outstanding		500,000
Line of credit facility, remaining borrowing capacity		13,400,000
Revolving Credit Facility \| Tenth Amendment
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity		$ 15,000,000
Revolving Credit Facility \| Tenth Amendment \| London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Basis spread on variable rate		1.75%
Revolving Credit Facility \| LIBOR Rate Loan
Line of Credit Facility [Line Items]
Number of standby letters of credit outstanding \| credit		1

Line Of Credit Facility, Covenant Terms, Excess Availability Requirement, Minimum.

No definition available.

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- Definition

Line Of Credit Facility, Covenant Terms, Liquidity Requirement, Minimum.

+ References

No definition available.

+ Details

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- Definition

Line Of Credit Facility, Covenant Terms, Minimum Liquidity Requirement, Following Specific Uses.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Notes Payable, CARES Act

+ References

No definition available.

+ Details

Name:	emkr_NotesPayableCARESAct
Namespace Prefix:	emkr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Standby Letters of Credit, Number of Letters of Credit Outstanding

+ References

No definition available.

+ Details

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Namespace Prefix:	emkr_
Data Type:	xbrli:integerItemType
Balance Type:	na
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:	num:percentItemType
Balance Type:	na
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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

Name:	us-gaap_LineOfCredit
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_LineOfCreditFacilityLineItems
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Data Type:	xbrli:stringItemType
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

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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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

- Definition

The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3255-108585

+ Details

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Period Type:	duration

- Details

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- Details

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- Details

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- Details

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- Details

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