Fair Value of Financial Instruments (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Financial liabilities:
Financial liabilities fair value	$ 103.4	$ 123.2
Warrant Liability
Financial liabilities:
Financial liabilities fair value	0.0	7.4
Milestone Rights Liability
Financial liabilities:
Financial liabilities fair value	18.7	18.4
Senior Convertible Notes | Senior Convertible Notes
Financial liabilities:
Financial liabilities fair value	24.7	22.9
Facility Financing Obligation
Financial liabilities:
Financial liabilities fair value	60.0	74.5
Carrying Value
Financial liabilities:
Financial liabilities fair value	94.5	115.2
Carrying Value | Warrant Liability
Financial liabilities:
Financial liabilities fair value		7.4
Carrying Value | Milestone Rights Liability
Financial liabilities:
Financial liabilities fair value	8.9	8.9
Carrying Value | Senior Convertible Notes | Senior Convertible Notes
Financial liabilities:
Financial liabilities fair value	27.7	27.6
Carrying Value | Facility Financing Obligation
Financial liabilities:
Financial liabilities fair value	57.9	71.3
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value	103.4	123.2
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3 | Warrant Liability
Financial liabilities:
Financial liabilities fair value		7.4
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 3 | Milestone Rights Liability
Financial liabilities:
Financial liabilities fair value	18.7	18.4
Estimate of Fair Value Measurement | Senior Convertible Notes | Fair Value, Inputs, Level 3 | Senior Convertible Notes
Financial liabilities:
Financial liabilities fair value	24.7	22.9
Estimate of Fair Value Measurement | Facility Financing Obligation | Fair Value, Inputs, Level 3
Financial liabilities:
Financial liabilities fair value	$ 60.0	$ 74.5