Trade Payables and Other Liabilities - Summary of Trade Payables and Other Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Mar. 31, 2025
Trade and other payables [abstract]
Trade payables	$ 18,086	$ 5,670
Non-trade payables	896	612
Accruals	6,981	6,731
Goods and services tax payable, net	124	0
Warrant liabilities	88	0
Others	1,180	2,057
Total trade payables and other liabilities	$ 27,355	$ 15,070

The amount of liabilities to pay for goods or services that have been received or supplied but have not been paid, invoiced or formally agreed with the supplier, including amounts due to employees.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Note Expiry date 2027-01-01
-Name IAS
-Number 1
-IssueDate 2025-01-01
-Paragraph 78
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2025-en-b&anchor=para_78&doctype=Standard
-URIDate 2025-03-27

+ Details

Name:	ifrs-full_Accruals
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The non-current amount of payment due to suppliers for goods and services used in the entity's business. [Refer: Trade payables]

+ References

+ Details

Name:	ifrs-full_NoncurrentPayablesToTradeSuppliers
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of current payables that the entity does not separately disclose in the same statement or note.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Note Expiry date 2027-01-01
-Name IAS
-Number 1
-IssueDate 2025-01-01
-Paragraph 55
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2025-en-b&anchor=para_55&doctype=Standard
-URIDate 2025-03-27

+ Details

Name:	ifrs-full_OtherCurrentPayables
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of trade payables and other payables. [Refer: Trade payables; Other payables]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2027-01-01
-Name IAS
-Number 1
-IssueDate 2025-01-01
-Paragraph 54
-Subparagraph k
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2025-en-b&anchor=para_54_k&doctype=Standard
-URIDate 2025-03-27

+ Details

Name:	ifrs-full_TradeAndOtherPayables
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	ifrs-full_TradeAndOtherPayablesAbstract
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of payment due to suppliers for goods and services used in the entity's business.

+ References

+ Details

Name:	ifrs-full_TradeAndOtherPayablesToTradeSuppliers
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of warrant liabilities.

+ References

+ Details

Name:	ifrs-full_WarrantLiability
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Goods and services tax payable net.

+ References

No definition available.

+ Details

Name:	omse_GoodsAndServicesTaxPayableNet
Namespace Prefix:	omse_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant