Stock-Based Compensation - Narrative (Details)		1 Months Ended							12 Months Ended
	Sep. 29, 2023 grant	Jan. 31, 2024 shares	Nov. 30, 2023 USD ($) shares	Feb. 28, 2023 shares	Oct. 31, 2018 shares	Jun. 30, 2018	Feb. 28, 2018 shares	Apr. 30, 2016 USD ($) shares	Dec. 31, 2025 USD ($) $ / shares shares	Dec. 31, 2024 USD ($) $ / shares shares	Dec. 31, 2023 USD ($) $ / shares shares	Jan. 01, 2025 shares	Jan. 01, 2024 shares	Jun. 22, 2023 shares	Jan. 01, 2023 shares	May 31, 2022 $ / shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding option awards (in shares)									11,370,247	9,253,158
Exercise price per warrant (in dollars per share) | $ / shares																$ 0.0025
Stock-based compensation | $									$ 37,614,000	$ 44,833,000	$ 25,675,000
Tax benefits recognized | $									$ 0	$ 0	$ 0
Dividend yield									0.00%	0.00%	0.00%
Non- Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense | $									$ 1,026,000	$ 15,888,000	$ 11,438,000
Parapyre Option Obligation
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of annual grant of common stock outstanding for warrants														1.00%
Warrants term	10 years
Number of separate grants | grant	2
Stock-based compensation | $									$ 0
Parapyre Warrants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Warrants to purchase shares (in shares)										848,184	684,407
Exercise price per warrant (in dollars per share) | $ / shares										$ 23.28	$ 21.52
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average grant date fair value (in dollars per share) | $ / shares									$ 19.98	$ 28.39	$ 9.67
Intrinsic value of options exercised | $									$ 4,000,000.0	$ 22,700,000	$ 400,000
Unrecognized stock-based compensation expense for options | $									$ 81,300,000
Weighted average period over which unrecognized compensation is expected to be recognized									2 years 3 months 18 days
Stock Options | Non- Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option issued (in shares)									0	10,000	477,000
Stock option vested (in shares)									119,250	139,187	0
Unvested restricted stock units | Non- Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted (in shares)									0
2016 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Initial reserves of common stock (in shares)								44,000
Increase in common stock reserved for issuance (in shares)					70,384
Annual percentage of additional shares			5.00%		4.00%
Additional shares authorized (in shares)			4,481,152
Annual limit for non-employee director compensation (in shares)								4,000
Annual limit for non-employee director compensation | $			$ 750,000
Non-employee director compensation | $			$ 1,000,000
Additional common stock available for issuance (in shares)												3,814,905	3,023,650		104,561
Shares reserved for issuance (in shares)									10,810,714
Outstanding option awards (in shares)									4,827,082
Dividend yield									0.00%	0.00%	0.00%
2015 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Available for issuance (in shares)								20,395
2018 Equity Inducement Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Initial reserves of common stock (in shares)							44,000
Additional shares authorized (in shares)									750,000	1,000,000
Shares reserved for issuance (in shares)									7,460,440
Outstanding option awards (in shares)									6,620,097
2018 Plan, 2016 Plan and 2015 Plan | Service Based Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Awards granted, vesting period							4 years
Awards granted, expiration period							10 years
Spyre 2023 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding option awards (in shares)									0					2,734
2016 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional common stock available for issuance (in shares)												602,570	360,571		26,140
Shares reserved for issuance (in shares)								6,600	972,775
Awards granted, expiration period								10 years
Percentage of fair market value of common stock								85.00%
Percentage of discount through payroll deductions to eligible employees to purchase common stock								15.00%
Maximum purchase value per employee under employee stock purchase plan | $								$ 25,000
Additional annual percentage increase of common stock						1.00%
Maximum shares purchased under employee stock purchase plan (in shares)		2,000		400				80
Stock-based compensation expense | $									$ 300,000	$ 300,000	$ 100,000
Dividend yield									0.00%	0.00%	0.00%