Fair Value of Financial Instruments - Fair Value of Financial Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Financial liabilities:
Financial liabilities fair value	$ 110.6	$ 102.0
MidCap Credit Facility
Financial liabilities:
Financial liabilities fair value	40.0
Deerfield Credit Facility
Financial liabilities:
Financial liabilities fair value		11.4
June 2020 Note
Financial liabilities:
Financial liabilities fair value	2.3
2024 Convertible Notes
Financial liabilities:
Financial liabilities fair value	3.7
December 2020 Note
Financial liabilities:
Financial liabilities fair value	2.0
Mann Group Promissory Notes
Financial liabilities:
Financial liabilities fair value	46.2	55.0
Milestone Rights Liability
Financial liabilities:
Financial liabilities fair value	16.4	18.1
Senior Convertible Notes
Financial liabilities:
Financial liabilities fair value		17.5
Carrying Value
Financial liabilities:
Financial liabilities fair value	126.2	111.4
Carrying Value | MidCap Credit Facility
Financial liabilities:
Financial liabilities fair value	38.9
Carrying Value | Deerfield Credit Facility
Financial liabilities:
Financial liabilities fair value		11.3
Carrying Value | June 2020 Note
Financial liabilities:
Financial liabilities fair value	2.5
Carrying Value | 2024 Convertible Notes
Financial liabilities:
Financial liabilities fair value	5.0
Carrying Value | December 2020 Note
Financial liabilities:
Financial liabilities fair value	2.5
Carrying Value | Mann Group Promissory Notes
Financial liabilities:
Financial liabilities fair value	70.0	72.1
Carrying Value | Milestone Rights Liability
Financial liabilities:
Financial liabilities fair value	7.3	8.9
Carrying Value | Senior Convertible Notes
Financial liabilities:
Financial liabilities fair value		19.1
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value	110.6	102.0
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3 | MidCap Credit Facility
Financial liabilities:
Financial liabilities fair value	40.0
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3 | Deerfield Credit Facility
Financial liabilities:
Financial liabilities fair value		11.4
Estimate of Fair Value Measurement | June 2020 Note | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value	2.3
Estimate of Fair Value Measurement | 2024 Convertible Notes | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value	3.7
Estimate of Fair Value Measurement | December 2020 Note | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value	2.0
Estimate of Fair Value Measurement | Mann Group Promissory Notes | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value	46.2	55.0
Estimate of Fair Value Measurement | Milestone Rights Liability | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value	$ 16.4	18.1
Estimate of Fair Value Measurement | Senior Convertible Notes | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value		$ 17.5