Concentrations of Credit Risk and Major Customers - Percentages of Total Revenues (Detail) - Sales Revenue, Net	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Concentration Risk [Line Items]
Percentage of revenues	100.00%	100.00%
Eisai Agreement
Concentration Risk [Line Items]
Percentage of revenues	57.70%	53.60%
Boehringer Ingelheim Agreement
Concentration Risk [Line Items]
Percentage of revenues	13.60%	0.00%
Ildong Agreement
Concentration Risk [Line Items]
Percentage of revenues	11.60%	43.00%
Toll manufacturing agreements
Concentration Risk [Line Items]
Percentage of revenues	10.40%	2.80%
Axovant Agreement
Concentration Risk [Line Items]
Percentage of revenues	6.00%	0.00%
Other collaborative agreements
Concentration Risk [Line Items]
Percentage of revenues	0.70%	0.60%