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Reconciliation of Beginning and Ending Amounts of Valuation Allowance on Deferred Tax Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Valuation Allowance [Abstract]
Balance at beginning of year	$ 12,732	$ 11,765	$ 9,928
Subsequent reversal and utilization of valuation allowance	(87)	(17)
Changes to valuation allowance	1,585	723	2,107
Expirations	(1,720)
Exchange differences	536	261	(270)
Balance at end of year	$ 13,046	$ 12,732	$ 11,765

X

- Definition

Deferred tax assets expirations.

+ References

No definition available.

+ Details

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Namespace Prefix:	gigm_
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Balance Type:	credit
Period Type:	duration

X

- Definition

Deferred Tax Assets Valuation Allowances Currency Translation Increase Decrease

+ References

No definition available.

+ Details

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Namespace Prefix:	gigm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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X

- Definition

Reversal of deferred tax asset valuation allowance.

+ References

No definition available.

+ Details

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

X

- Definition

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	credit
Period Type:	instant

X

- References

No definition available.

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Namespace Prefix:	us-gaap_
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Balance Type:	na
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X

- Definition

Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319

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