Amount of contributions made by an employer to a defined contribution plan regarding severances.

No definition available.

Name:	sigm_DefinedContributionPlanEmployerContributionRelatedToSeverancesAmount
Namespace Prefix:	sigm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount employees over age 50 may contribute to a defined contribution plan over the maximum.

+ References

No definition available.

+ Details

Name:	sigm_DefinedContributionPlanMaximumAnnualContributionsPerEmployeeAdditionalAmountForEmployeesOverAge50
Namespace Prefix:	sigm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the amount of severance employee funds.

+ References

No definition available.

+ Details

Name:	sigm_SeveranceEmployeeFunds
Namespace Prefix:	sigm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Information about the number of shares issued to participants in the specified Purchase Plan that continued to be held by the original purchasers of such shares which may be subject to the rescission rights.

+ References

No definition available.

+ Details

Name:	sigm_ShareIssuedUnderEmployeeStockPurchasePlanSubjectToRescissionRights
Namespace Prefix:	sigm_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

+ Details

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

- Definition

Amount of discretionary contributions made by an employer to a defined contribution plan.

+ References

No definition available.

+ Details

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

- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum amount the employee may contribute to a defined contribution plan.

+ References

No definition available.

+ Details

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

- Definition

Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 5.P.3)
-URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140864-122747

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 5.P.4(b))
-URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747

+ Details

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

- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

+ Details

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Liability for amount due employees, in addition to wages and any other money that employers owe employees, when their employment ends through a layoff or other termination. For example, a company may provide involuntarily terminated employees with a lump sum payment equal to one week's salary for every year of employment.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_PlanNameAxis=sigm_PurchasePlan2010Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RestructuringPlanAxis=sigm_Fiscal2018PlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RestructuringCostAndReserveAxis=us-gaap_OneTimeTerminationBenefitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanNameAxis=sigm_SeverancePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanSponsorLocationAxis=us-gaap_DomesticPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanNameAxis=sigm_EndowmentInsurancePensionPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanSponsorLocationAxis=sigm_DenmarkTaiwanTheNetherlandsAndGermanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanNameAxis=sigm_RetirementPensionPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Note 9 - Employee Benefits (Details Textual)	3 Months Ended			6 Months Ended			12 Months Ended
Note 9 - Employee Benefits (Details Textual)	Jul. 29, 2017 USD ($) $ / shares shares	Apr. 29, 2017 USD ($)	Jul. 30, 2016 USD ($)	Jul. 29, 2017 USD ($) $ / shares shares	Jul. 30, 2016 USD ($)	Jul. 30, 2016 USD ($)	Mar. 31, 2018 CNY (¥)	Mar. 31, 2017 CNY (¥)
Restructuring Charges	$ 1,723,000			$ 1,966,000
Purchase Plan 2010 [Member]
Share Issued Under Employee Stock Purchase Plan, Subject to Rescission Rights \| shares	38,374			38,374
Share Price \| $ / shares	$ 3.89			$ 3.89
Fiscal 2018 Plan [Member]
Restructuring Charges	$ 1,723,000	$ 243,000
Fiscal 2018 Plan [Member] \| One-time Termination Benefits [Member]
Restructuring Charges	1,700,000			$ 1,900,000
Severance Plan [Member]
Supplemental Unemployment Benefits, Severance Benefits	900,000			900,000
Severance Employee Funds	800,000			800,000
Defined Contribution Plan, Employer Contribution Related to Severances, Amount	100,000		100,000	100,000		100,000
Domestic Plan [Member] \| Endowment Insurance Pension Plan [Member]
Defined Contribution Plan, Employer Discretionary Contribution Amount	500,000		600,000	$ 1,100,000		1,200,000
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent				8.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay				20.00%
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount \| ¥								¥ 17,817
Domestic Plan [Member] \| Endowment Insurance Pension Plan [Member] \| Scenario, Forecast [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount \| ¥							¥ 19,512
Denmark, Taiwan, The Netherlands and Germany [Member] \| Retirement Pension Plan [Member]
Defined Contribution Plan, Cost	200,000
Defined Contribution Plan, Employer Discretionary Contribution Amount			200,000	$ 400,000	$ 400,000
Pension Plan [Member] \| Domestic Plan [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Additional Amount for Employees Over Age 50				6,000
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 200,000		$ 100,000	400,000		$ 300,000
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount				$ 18,000