The Company and Basis of Presentation (Details) $ / shares in Units, $ in Thousands									3 Months Ended		12 Months Ended	121 Months Ended
	Nov. 29, 2024 shares	Nov. 20, 2024 USD ($) $ / shares shares	May 14, 2024 shares	Apr. 23, 2024 shares	Mar. 20, 2024 USD ($) $ / shares shares	Mar. 18, 2024 shares	Dec. 11, 2023 $ / shares shares	Jun. 22, 2023 $ / shares	Mar. 31, 2025 USD ($) segment $ / shares shares	Mar. 31, 2024 shares	Dec. 31, 2024 USD ($) $ / shares shares	Mar. 31, 2025 USD ($) $ / shares shares	Sep. 06, 2024 USD ($)	Apr. 25, 2024 shares	Apr. 24, 2024 shares	Dec. 31, 2023 shares
Company and Basis of Presentation [Line Items]
Number of operating segments | segment									1
Proceeds from raising capital | $												$ 1,300,000
Accumulated deficit | $									$ (1,017,205)		$ (972,432)	(1,017,205)
Marketable securities | $									$ 564,800			$ 564,800
Conversion Of Series B Non-Voting Convertible Preferred Stock | Common Stock
Company and Basis of Presentation [Line Items]
Shares converted (in shares)			10,198,320						10,198,320
At-The-Market Offering
Company and Basis of Presentation [Line Items]
Sale of stock, authorized amount | $													$ 500,000
Common Stock and Series B Non Voting Convertible Preferred Stock
Company and Basis of Presentation [Line Items]
Series B non-voting convertible preferred stock, par value (in dollars per share) | $ / shares							$ 0.0001
Conversion basis					40
Series B Non Voting Convertible Preferred Stock
Company and Basis of Presentation [Line Items]
Conversion basis					40
Issuance of non-voting convertible preferred stock (in shares)					121,625	271,625	150,000
Preferred stock, par value (in dollars per share) | $ / shares									$ 0.0001		$ 0.0001	$ 0.0001
Preferred stock, outstanding (in shares)									16,667		16,667	16,667
Preferred stock, not automatically converted, outstanding (in shares)									16,667			16,667
Series B Non Voting Convertible Preferred Stock | Preferred Stock
Company and Basis of Presentation [Line Items]
Issuance of non-voting convertible preferred stock (in shares)										122,000
Preferred stock, outstanding (in shares)									17,000		17,000	17,000
Series B Non Voting Convertible Preferred Stock | Conversion Of Series B Non-Voting Convertible Preferred Stock | Preferred Stock
Company and Basis of Presentation [Line Items]
Shares converted (in shares)			254,958						254,958
Series B Non Voting Convertible Preferred Stock | Private Placement
Company and Basis of Presentation [Line Items]
Sale of stock, price per share (in dollars per share) | $ / shares					$ 1,480
Sale of stock, proceeds received | $					$ 168,900
Placement agent and other offering costs | $					$ 11,200
Series A Non Voting Convertible Preferred Stock
Company and Basis of Presentation [Line Items]
Preferred stock, par value (in dollars per share) | $ / shares									$ 0.0001		$ 0.0001	$ 0.0001
Exchange of Series A non-voting convertible preferred stock into common stock (in shares)				90,992
Preferred stock, outstanding (in shares)									346,045		346,045	346,045		346,045	346,045
Series A Non Voting Convertible Preferred Stock | Preferred Stock
Company and Basis of Presentation [Line Items]
Preferred stock, outstanding (in shares)									346,000	437,000	346,000	346,000				437,000
Series A Non Voting Convertible Preferred Stock | Conversion Of Series A Non-Voting Convertible Preferred Stock | Preferred Stock
Company and Basis of Presentation [Line Items]
Shares converted (in shares)				90,992
Common Stock
Company and Basis of Presentation [Line Items]
Exchange of Series A non-voting convertible preferred stock into common stock (in shares)				3,639,680
Common Stock | At-The-Market Offering
Company and Basis of Presentation [Line Items]
Sale of stock, price per share (in dollars per share) | $ / shares											$ 26.935
Sale of stock, proceeds received | $											$ 20,500
Placement agent and other offering costs | $											$ 400
Sale of stock, aggregate offering price | $													200,000
Number of shares of common stock sold (in shares)									0		777,432
Sale of stock, remaining authorized amount | $									$ 179,100			$ 179,100
Common Stock | At-The-Market Offering | Maximum
Company and Basis of Presentation [Line Items]
Sale of stock, aggregate offering price | $													$ 179,100
Common Stock | Underwritten Offering
Company and Basis of Presentation [Line Items]
Sale of stock, price per share (in dollars per share) | $ / shares		$ 27.50
Sale of stock, proceeds received | $		$ 215,900
Placement agent and other offering costs | $		$ 14,200
Number of shares of common stock sold (in shares)		8,366,250
Common Stock | Over-Allotment Option
Company and Basis of Presentation [Line Items]
Number of shares of common stock sold (in shares)	1,091,250
Spyre Therapeutics, Inc.
Company and Basis of Presentation [Line Items]
Asset acquisition, stockholder payment period								3 years
Asset acquisition, cash payment, threshold period								1 year
Asset Acquisition | Series A Non Voting Convertible Preferred Stock
Company and Basis of Presentation [Line Items]
Preferred stock, par value (in dollars per share) | $ / shares								$ 0.0001