Changes in Level 3 Liabilities Measured at Fair Value (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Payment to Takeda	$ (15,000,000)
Change in fair value of liability (recognized in Net loss)		$ 0
Contingent Consideration
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of Liabilities - Beginning Balance	21,800,000
Change in fair value of liability (recognized in Net loss)	1,600,000
Fair Value of Liabilities - Beginning Balance	8,400,000	21,800,000
2017 Exchange Notes
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfer from Level 2 to Level 3 - April 1, 2017	21,866,000
Exchange Notes conversions (recognized in equity)	(894,000)
Change in fair value of liability (recognized in Net loss)	(3,938,000)
Fair Value of Liabilities - Beginning Balance	17,034,000
Convertible debt - 2016 Notes
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of Liabilities - Beginning Balance	101,900,000
Change in fair value of liability (recognized in Net loss)	27,300,000
Fair Value of Liabilities - Beginning Balance	$ 129,200,000	$ 101,900,000