Fair Value of Financial Instruments - Fair Value of Financial Instruments (Detail) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
MidCap Credit Facility
Financial liabilities:
Financial liabilities fair value	$ 40.5	$ 55.4
Senior Convertible Notes
Financial liabilities:
Financial liabilities fair value	257.0
Mann Group Convertible Notes
Financial liabilities:
Financial liabilities fair value	44.9	52.2
PPP Loan
Financial liabilities:
Financial liabilities fair value	4.8	4.7
Milestone Rights Liability
Financial liabilities:
Financial liabilities fair value	15.0	19.8
2024 Convertible Notes
Financial liabilities:
Financial liabilities fair value		7.0
Mann Group Promissory Notes
Financial liabilities:
Financial liabilities fair value		78.9
Carrying Value | MidCap Credit Facility
Financial liabilities:
Financial liabilities fair value	38.6	49.3
Carrying Value | Senior Convertible Notes
Financial liabilities:
Financial liabilities fair value	223.2
Carrying Value | Mann Group Convertible Notes
Financial liabilities:
Financial liabilities fair value	18.4	28.0
Carrying Value | PPP Loan
Financial liabilities:
Financial liabilities fair value	4.9	4.9
Carrying Value | Milestone Rights Liability
Financial liabilities:
Financial liabilities fair value	5.9	7.3
Carrying Value | 2024 Convertible Notes
Financial liabilities:
Financial liabilities fair value		5.0
Carrying Value | Mann Group Promissory Notes
Financial liabilities:
Financial liabilities fair value		63.0
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3 | MidCap Credit Facility
Financial liabilities:
Financial liabilities fair value	40.5	55.4
Estimate of Fair Value Measurement | Senior Convertible Notes | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value	257.0
Estimate of Fair Value Measurement | Mann Group Convertible Notes | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value	44.9
Estimate of Fair Value Measurement | PPP Loan | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value	4.8	4.7
Estimate of Fair Value Measurement | Milestone Rights Liability | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value	$ 15.0	19.8
Estimate of Fair Value Measurement | 2024 Convertible Notes | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value		7.0
Estimate of Fair Value Measurement | Mann Group Promissory Notes | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value		$ 78.9