The Company and Basis of Presentation (Details) $ / shares in Units, $ in Thousands				3 Months Ended	12 Months Ended	133 Months Ended
	Apr. 16, 2026 USD ($) $ / shares shares	Oct. 15, 2025 USD ($) $ / shares shares	Jun. 22, 2023	Mar. 31, 2026 USD ($) segment $ / shares shares	Dec. 31, 2025 USD ($) $ / shares shares	Mar. 31, 2026 USD ($) $ / shares	Sep. 06, 2024 USD ($)
Company and Basis of Presentation [Line Items]
Number of operating segments | segment				1
Proceeds from raising capital						$ 1,700,000
Accumulated deficit				$ 1,196,640	$ 1,127,635	1,196,640
Cash, cash equivalents, and marketable securities				$ 741,500		$ 741,500
At-The-Market Offering
Company and Basis of Presentation [Line Items]
Sale of stock, authorized amount							$ 200,000
At-The-Market Offering | Common Stock
Company and Basis of Presentation [Line Items]
Number of shares of common stock sold (in shares) | shares				296,396	445,668
Sale of stock, price per share (in dollars per share) | $ / shares				$ 33.566	$ 33.772	$ 33.566
Sale of stock, proceeds received				$ 9,700	$ 14,800
Placement agent and other offering costs				200	$ 300
Sale of stock, remaining authorized amount				$ 154,100		$ 154,100
October 2025 Underwritten Offering | Common Stock
Company and Basis of Presentation [Line Items]
Number of shares of common stock sold (in shares) | shares		17,094,594
Sale of stock, price per share (in dollars per share) | $ / shares		$ 18.50
Sale of stock, proceeds received		$ 296,400
Placement agent and other offering costs		$ 19,900
Over-Allotment Option | Common Stock
Company and Basis of Presentation [Line Items]
Number of shares of common stock sold (in shares) | shares		2,229,729
Over-Allotment Option | Common Stock | Subsequent Events
Company and Basis of Presentation [Line Items]
Number of shares of common stock sold (in shares) | shares	975,000
April 2026 Underwriting Agreement | Common Stock | Subsequent Events
Company and Basis of Presentation [Line Items]
Number of shares of common stock sold (in shares) | shares	7,475,000
Sale of stock, price per share (in dollars per share) | $ / shares	$ 62.00
Sale of stock, proceeds received	$ 435,300
Placement agent and other offering costs	$ 28,100
Spyre Therapeutics, Inc.
Company and Basis of Presentation [Line Items]
Asset acquisition, cash payment, threshold period (in years)			1 year