Number of shares subscribed by qualified employees.

No definition available.

Name:	gigm_NumberOfSharesSubscribedByQualifiedEmployees
Namespace Prefix:	gigm_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Share based compensation arrangement by share based payment award equity instruments other than options granted fair value.

+ References

No definition available.

+ Details

Name:	gigm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantedFairValue
Namespace Prefix:	gigm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from share-based compensation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 25
-Paragraph 20
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=115928272&loc=d3e28680-109314

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32632-109319

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32621-109319

+ Details

Name:	us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

+ References

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Unrecognized cost of unvested options awarded to employees as compensation.

+ References

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The cash inflow associated with the amount received from the stock plan during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3255-108585

+ Details

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

- Definition

The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

+ Details

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

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

- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Gross number of share options (or share units) granted during the period.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of share instruments newly issued under a share-based compensation plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of share options (or share units) exercised during the current period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(2)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 3: 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(28))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: 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(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644

+ Details

Name:	us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	gigm_ShareBasedCompensationAxis=gigm_CapitalizedCostMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_GeneralAndAdministrativeExpenseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Share-Based Compensation - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 3,000	$ (7,000)	$ 9,000
Stock-based compensation tax benefit recognized	$ 292,000	$ 299,000
Share-based compensation, number of shares reserved for issuance, contractual terms		6 years 3 days
Share-based compensation, number of options exercised	0	0	0
Options granted to employees on grant date	0		0
Unrecognized compensation cost related to nonvested options	$ 1,000
Unrecognized compensation cost related to nonvested options, expected recognition period	1 year 6 months
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of RSUs granted	$ 0	$ 0	$ 0
Unrecognized compensation cost related to nonvested RSUs	0	0
Cash received from employee stock award vesting and the forfeiture of RSUs	$ 0	0	0
2004 Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of shares reserved for issuance	1,400,000
Share-based compensation, number of shares reserved for issuance, contractual terms	10 years
2006 Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of shares reserved for issuance	200,000
Share-based compensation, number of shares reserved for issuance, contractual terms	10 years
2007 Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of shares reserved for issuance	400,000
Share-based compensation, number of shares reserved for issuance, contractual terms	10 years
2008 Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of shares reserved for issuance	200,000
Share-based compensation, number of shares reserved for issuance, contractual terms	10 years
2008 Employee Share Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares subscribed by qualified employees	0
2008 Employee Share Purchase Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of shares reserved for issuance	40,000
2009 Equity Incentive Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of shares reserved for issuance	300,000
Share-based compensation, number of shares reserved for issuance, contractual terms	10 years
2009 Employee Share Purchase Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of shares reserved for issuance	40,000
Share-based compensation, number of shares issued	0
2010 Equity Incentive Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of shares reserved for issuance	200,000
Share-based compensation, number of shares reserved for issuance, contractual terms	10 years
2010 Employee Share Purchase Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of shares reserved for issuance	40,000
Share-based compensation, number of shares issued	0
Capitalized stock-based compensation
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 0	0
Stock-based compensation tax benefit recognized	0	0	0
General and Administrative Expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 3,000	$ (7,000)	$ 9,000