Commitments and related party transactions - Additional Information (Detail) $ in Thousands, $ in Thousands	12 Months Ended
Apr. 30, 2018 CAD ($)	Apr. 30, 2018 USD ($)
Disclosure of transactions between related parties [line items]
Lease commitments	$ 144
Term expiration date	Apr. 30, 2018	Apr. 30, 2018
Lease agreement commitment	$ 132
Exploration and evaluation	220
Management contract expiring in January 2020 [member]
Disclosure of transactions between related parties [line items]
Directors remuneration	$ 600
Management contract expiration team	January 2020	January 2020
Management contract expiring in August 2021 [member]
Disclosure of transactions between related parties [line items]
Directors remuneration		$ 315
Management contract expiration team	August 2021	August 2021

The amount of current lease liabilities. [Refer: Lease liabilities]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2019-01-01
-Name IFRS
-Number 16
-IssueDate 2017-01-01
-Paragraph 47
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=16&date=2017-03-01&anchor=para_47_b&doctype=Standard
-URIDate 2017-03-09

+ Details

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

- Definition

The amount of remuneration paid or payable to the entity's directors.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2017-01-01
-Paragraph 112
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_112_c&doctype=Standard
-URIDate 2017-03-09

+ Details

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

+ References

No definition available.

+ Details

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

- Definition

The amount of the lease commitments for short-term leases accounted for applying paragraph 6 of IFRS 16. Short-term lease is a lease that, at the commencement date, has a lease term of 12 months or less. A lease that contains a purchase option is not a short-term lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2019-01-01
-Name IFRS
-Number 16
-IssueDate 2017-01-01
-Paragraph 55
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=16&date=2017-03-01&anchor=para_55&doctype=Standard
-URIDate 2017-03-09

+ Details

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

- Definition

The amount of exploration and evaluation assets recognised as tangible assets in accordance with the entity's accounting policy. [Refer: Exploration and evaluation assets [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 6
-IssueDate 2017-01-01
-Paragraph 25
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=6&date=2017-03-01&anchor=para_25&doctype=Standard
-URIDate 2017-03-09

+ Details

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Lease term expiration date.

+ References

No definition available.

+ Details

Name:	sam_LeaseTermExpirationDate
Namespace Prefix:	sam_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Management contract expiration team.

+ References

No definition available.

+ Details

Name:	sam_ManagementContractExpirationTeam
Namespace Prefix:	sam_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	ifrs-full_MaturityAxis=sam_ManagementContractExpiringInJanuary2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_MaturityAxis=sam_ManagementContractExpiringInAugust2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: