Stock-Based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		12 Months Ended
	Jun. 22, 2023	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2016	Dec. 31, 2024	Sep. 30, 2024	Jan. 01, 2024	Jan. 01, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation		$ 8,859	$ 13,835
2015 and 2016 and 2018 Equity Inducement Plan | Service Based Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vest period grant date		4 years
Share-based payment award, term		10 years
2015 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares subject to options outstanding (in shares)		952
2016 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Annual percentage of additional shares				5.00%
Additional number of shares available for issuance (in shares)							3,814,905	3,023,650
Common stock available for future issuance (in shares)		11,007,869
Outstanding option awards (in shares)		4,817,317
2018 Equity Inducement Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock available for future issuance (in shares)		6,856,811
Outstanding option awards (in shares)		6,300,368
2018 Equity Inducement Plan, Amended
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock available for future issuance, additional amount authorized (in shares)						1,000,000
Spyre 2023 Equity Incentive Plan | Asset Acquisition
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of outstanding and unexercised stock options to purchase (in shares)	2,734
Parapyre Option Obligation
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation		$ 0	$ 5,400
2024 Parapyre Option Obligation | Outstanding Parapyre warrants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Warrants to purchase shares (in shares)		1,532,591			848,184
Exercise price per warrant (in dollars per share)		$ 22.49			$ 23.28
2016 Employee Stock Purchase Plan | Employee Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares issued (in shares)		16,877
2016 Employee Stock Purchase Plan | 2016 ESPP | Employee Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares sold (in shares)		16,877	2,330
Sale of stock, proceeds received		$ 300	$ 0