Stock-Based Compensation - Outstanding and Exercisable Options under Stock Based Compensation Plans (Details)	12 Months Ended
Dec. 31, 2025 $ / shares shares
Stock-Based Compensation [Abstract]
Options Outstanding, Number of Shares (in Shares) \| shares	6,572,509
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 6 months 29 days
Options Outstanding, Weighted Average Exercise Price (in Dollars per share)	$ 2.39
Options Exercisable, Number of Shares (in Shares) \| shares	6,138,254
Options Exercisable, Weighted Average Exercise Price (in Dollars per share)	$ 2.45
$0.89-1.50 [Member]
Stock-Based Compensation [Abstract]
Options Outstanding, Number of Shares (in Shares) \| shares	1,771,541
Options Outstanding, Weighted Average Remaining Contractual Life	7 years 1 month 6 days
Options Outstanding, Weighted Average Exercise Price (in Dollars per share)	$ 1.19
Options Exercisable, Number of Shares (in Shares) \| shares	1,536,540
Options Exercisable, Weighted Average Exercise Price (in Dollars per share)	$ 1.19
$1.51-2.50 [Member]
Stock-Based Compensation [Abstract]
Options Outstanding, Number of Shares (in Shares) \| shares	3,022,227
Options Outstanding, Weighted Average Remaining Contractual Life	5 years 10 months 6 days
Options Outstanding, Weighted Average Exercise Price (in Dollars per share)	$ 2
Options Exercisable, Number of Shares (in Shares) \| shares	2,922,227
Options Exercisable, Weighted Average Exercise Price (in Dollars per share)	$ 2
$2.51-5.00 [Member]
Stock-Based Compensation [Abstract]
Options Outstanding, Number of Shares (in Shares) \| shares	1,558,741
Options Outstanding, Weighted Average Remaining Contractual Life	3 years 9 months 25 days
Options Outstanding, Weighted Average Exercise Price (in Dollars per share)	$ 3.47
Options Exercisable, Number of Shares (in Shares) \| shares	1,558,741
Options Exercisable, Weighted Average Exercise Price (in Dollars per share)	$ 3.47
$5.01-6.71 [Member]
Stock-Based Compensation [Abstract]
Options Outstanding, Number of Shares (in Shares) \| shares	220,000
Options Outstanding, Weighted Average Remaining Contractual Life	2 years 1 month 6 days
Options Outstanding, Weighted Average Exercise Price (in Dollars per share)	$ 5.92
Options Exercisable, Number of Shares (in Shares) \| shares	220,000
Options Exercisable, Weighted Average Exercise Price (in Dollars per share)	$ 5.92
Minimum [Member] \| $0.89-1.50 [Member]
Stock-Based Compensation [Abstract]
Minimum Exercise Price (in Dollars per share)	0.89
Minimum [Member] \| $1.51-2.50 [Member]
Stock-Based Compensation [Abstract]
Minimum Exercise Price (in Dollars per share)	1.51
Minimum [Member] \| $2.51-5.00 [Member]
Stock-Based Compensation [Abstract]
Minimum Exercise Price (in Dollars per share)	2.51
Minimum [Member] \| $5.01-6.71 [Member]
Stock-Based Compensation [Abstract]
Minimum Exercise Price (in Dollars per share)	5.01
Maximum [Member] \| $0.89-1.50 [Member]
Stock-Based Compensation [Abstract]
Maximum Exercise Price (in Dollars per share)	1.5
Maximum [Member] \| $1.51-2.50 [Member]
Stock-Based Compensation [Abstract]
Maximum Exercise Price (in Dollars per share)	2.5
Maximum [Member] \| $2.51-5.00 [Member]
Stock-Based Compensation [Abstract]
Maximum Exercise Price (in Dollars per share)	5
Maximum [Member] \| $5.01-6.71 [Member]
Stock-Based Compensation [Abstract]
Maximum Exercise Price (in Dollars per share)	$ 6.71

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.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (h)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

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

- Definition

The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of shares reserved for issuance pertaining to the outstanding exercisable stock options as of the balance sheet date in the customized range of exercise prices for which the market and performance vesting condition has been satisfied.

+ References

+ Details

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

- Definition

The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(ii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

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

- Definition

The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average exercise price as of the balance sheet date for those equity-based payment arrangements exercisable and outstanding.

+ References

+ Details

Name:	us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

The weighted average price as of the balance sheet date at which grantees could acquire the underlying shares with respect to all outstanding stock options which are in the customized range of exercise prices.

+ References

+ Details

Name:	us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average remaining contractual term of outstanding stock options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 718
-SubTopic 10
-Subparagraph (e)(1)
-Name Accounting Standards Codification
-Paragraph 2
-Section 50
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis=galt_ExercisePriceRangeOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis=galt_ExercisePriceRangeTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis=galt_ExercisePriceRangeThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis=galt_ExercisePriceRangeFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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