v3.25.3

Stock-Based Compensation - Schedule of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2025 USD ($) $ / shares shares	Dec. 31, 2024 USD ($) $ / shares shares
Share-Based Payment Arrangement [Abstract]
Number of Shares, Beginning Balance \| shares	4,499,702
Number of Shares, Granted \| shares	2,368,800
Number of Shares, Exercised \| shares	(258,621)
Number of Shares, Forfeited \| shares	(258,581)
Number of Shares, Ending Balance \| shares	6,351,300	4,499,702
Number of Shares, Options exercisable at September 30 2025 \| shares	2,330,390
Number of Shares, options unvested at September 30, 2025 \| shares	4,020,910
Weighted-Average Exercise Price, Outstanding, Beginning balance \| $ / shares	$ 17.19
Weighted-Average Exercise Price, Granted \| $ / shares	23.45
Weighted-Average Exercise Price, Exercised \| $ / shares	11.07
Weighted-Average Exercise Price, Forfeited \| $ / shares	19.15
Weighted-Average Exercise Price, Outstanding, Ending balance \| $ / shares	19.69	$ 17.19
Weighted-Average Exercise Price, Options exercisable as of June 30 2025 \| $ / shares	15.99
Weighted-Average Exercise Price, Options unvested as of June 30, 2025 \| $ / shares	$ 21.84
Weighted Average Remaining Contractual Term	8 years 6 months	8 years 8 months 12 days
Weighted Average Remaining Contractual Term, Options exercisable as of June 30, 2025	7 years 8 months 12 days
Weighted Average Remaining Contractual Term, Options unvested as of June 30, 2025	9 years
Aggregate Intrinsic Value, Beginning Balance \| $	$ 24,867
Aggregate Intrinsic Value, Granted \| $	37,735
Aggregate Intrinsic Value, Exercised \| $	5,465
Aggregate Intrinsic Value, Forfeited \| $	1,051
Aggregate Intrinsic Value, Ending Balance \| $	126,224	$ 24,867
Aggregate Intrinsic Value, Options exercisable at September 30, 2025 \| $	55,736
Aggregate Intrinsic Value, Options unvested at September 30, 2025 \| $	$ 70,488

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Share based compensation arrangement by share based payment award options nonvested weighted average remaining contractual term1.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Intrinsic value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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

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Number of non-vested options outstanding.

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

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

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Dianthus Therapeutics, Inc. /DE/ 10-Q