Fair Value of Financial Instruments - Fair Value of Financial Instruments (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financial liabilities:
Financial liabilities fair value	$ 95.7	$ 110.6
MidCap Credit Facility
Financial liabilities:
Financial liabilities fair value	35.8	40.0
2024 Convertible Notes
Financial liabilities:
Financial liabilities fair value	3.1	3.7
June 2020 Note
Financial liabilities:
Financial liabilities fair value	2.4	2.3
December 2020 Note
Financial liabilities:
Financial liabilities fair value	2.1	2.0
Mann Group Promissory Notes
Financial liabilities:
Financial liabilities fair value	38.0	46.2
Milestone Rights Liability
Financial liabilities:
Financial liabilities fair value	14.3	16.4
Carrying Value
Financial liabilities:
Financial liabilities fair value	126.3	126.2
Carrying Value | MidCap Credit Facility
Financial liabilities:
Financial liabilities fair value	38.9	38.9
Carrying Value | 2024 Convertible Notes
Financial liabilities:
Financial liabilities fair value	5.0	5.0
Carrying Value | June 2020 Note
Financial liabilities:
Financial liabilities fair value	2.6	2.5
Carrying Value | December 2020 Note
Financial liabilities:
Financial liabilities fair value	2.5	2.5
Carrying Value | Mann Group Promissory Notes
Financial liabilities:
Financial liabilities fair value	70.0	70.0
Carrying Value | Milestone Rights Liability
Financial liabilities:
Financial liabilities fair value	7.3	7.3
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value	95.7	110.6
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3 | MidCap Credit Facility
Financial liabilities:
Financial liabilities fair value	35.8	40.0
Estimate of Fair Value Measurement | 2024 Convertible Notes | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value	3.1	3.7
Estimate of Fair Value Measurement | June 2020 Note | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value	2.4	2.3
Estimate of Fair Value Measurement | December 2020 Note | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value	2.1	2.0
Estimate of Fair Value Measurement | Mann Group Promissory Notes | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value	38.0	46.2
Estimate of Fair Value Measurement | Milestone Rights Liability | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value	$ 14.3	$ 16.4