Fair Value of Financial Instruments - Fair Value of Financial Instruments (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Carrying Amount | MidCap Credit Facility
Financial liabilities:
Total financial liabilities fair value	$ 28.1	$ 33.0
Carrying Amount | Senior Convertible Notes
Financial liabilities:
Total financial liabilities fair value	227.2	226.9
Carrying Amount | Mann Group Convertible Note
Financial liabilities:
Total financial liabilities fair value	8.8	8.8
Carrying Amount | Milestone Rights
Financial liabilities:
Total financial liabilities fair value	3.9	3.9
Carrying Amount | Contingent Milestone Liability
Financial liabilities:
Total financial liabilities fair value	0.3	0.3
Carrying Amount | Financing Liability
Financial liabilities:
Total financial liabilities fair value	104.1	104.1
Carrying Amount | Liability for Sale of Future Royalties
Financial liabilities:
Total financial liabilities fair value	148.0
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3 | MidCap Credit Facility
Financial liabilities:
Total financial liabilities fair value	30.2	35.5
Estimate of Fair Value Measurement | Senior Convertible Notes | Fair Value, Inputs, Level 3
Financial liabilities:
Total financial liabilities fair value	246.4	231.3
Estimate of Fair Value Measurement | Mann Group Convertible Note | Fair Value, Inputs, Level 3
Financial liabilities:
Total financial liabilities fair value	17.1	14.4
Estimate of Fair Value Measurement | Milestone Rights | Fair Value, Inputs, Level 3
Financial liabilities:
Total financial liabilities fair value	12.8	11.9
Estimate of Fair Value Measurement | Contingent Milestone Liability | Fair Value, Inputs, Level 3
Financial liabilities:
Total financial liabilities fair value	0.3	0.3
Estimate of Fair Value Measurement | Financing Liability | Fair Value, Inputs, Level 3
Financial liabilities:
Total financial liabilities fair value	106.7	$ 106.8
Estimate of Fair Value Measurement | Liability for Sale of Future Royalties | Fair Value, Inputs, Level 3
Financial liabilities:
Total financial liabilities fair value	$ 159.6