Collaborations - Additional Information (Detail)		1 Months Ended			3 Months Ended			12 Months Ended
	Dec. 28, 2016 USD ($)	Oct. 31, 2016 USD ($)	Jan. 31, 2016 USD ($)	May 31, 2015 USD ($)	Mar. 31, 2017 USD ($) Milestone	Mar. 31, 2017 CHF (SFr) Milestone	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total arrangement consideration					$ 115,600,000
Payment received from Eisai	$ 10,000,000
Cost of product sales					2,532,000		$ 2,428,000
Net product sales					2,711,000		3,518,000
Inventory					$ 7,055,000			$ 6,708,000
Eisai | 9.5% Royalty Rate
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty rate on annual net sales					9.50%	9.50%
Eisai | 9.5% Royalty Rate | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty portion of annual net sales amount					$ 175,000,000
Eisai | 13.5% Royalty Rate
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty rate on annual net sales					13.50%	13.50%
Eisai | 13.5% Royalty Rate | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty portion of annual net sales amount					$ 500,000,000
Eisai | 13.5% Royalty Rate | Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty portion of annual net sales amount					$ 175,000,000
Eisai | 18.5% Royalty Rate
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty rate on annual net sales					18.50%	18.50%
Eisai | 18.5% Royalty Rate | Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty portion of annual net sales amount					$ 500,000,000
Axovant
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative agreement upfront payments				$ 4,000,000
Collaborative agreement revenue recognition period				5 years
Additional milestone payments on achievement					$ 41,500,000
Number of development milestone | Milestone					2	2
Number of regulatory milestone | Milestone					4	4
Revenue recorded					$ 400,000		600,000
Boehringer Ingelheim
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative agreement upfront payments			$ 7,500,000
Collaborative agreement revenue recognition period			2 years
Additional milestone payments on achievement					$ 251,000,000
Number of development milestone | Milestone					3	3
Number of regulatory milestone | Milestone					9	9
Revenue recorded					$ 1,200,000		$ 1,300,000
Refund of withholding taxes		$ 1,200,000
Number of commercial milestone | Milestone					4	4
Eisai First Amended Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative agreement initiation date					2012-05	2012-05
Eisai Second Amended Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative agreement initiation date					2013-11	2013-11
Manufacturing and supply commitment period					2 years	2 years
Eisai Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement initial term					2 years	2 years
Collaboration agreement extended initial term					6 months	6 months
Collaboration agreement extension fee | SFr						SFr 2,000,000
Proceeds from sale of inventory	$ 10,000,000
Eisai Agreement | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional manufacturing support payments | SFr						13,000,000
Manufacturing support payments to be received | SFr						SFr 6,000,000
License Deliverable
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Estimated selling price of the deliverables for revenue recognition								64,000,000
Inventory Deliverable
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Estimated selling price of the deliverables for revenue recognition					$ 30,800,000
Consideration allocated to deliverable revenue								0
Carrying value of inventory recognized in cost of product sales								$ 0
Recognized revenues on net product sales					2,200,000
Cost of product sales					300,000
Deferred revenues					29,400,000
Inventory					4,100,000
Manufacturing and Supply Commitment Deliverable
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Estimated selling price of the deliverables for revenue recognition					20,800,000
Consideration allocated to deliverable revenue					2,100,000
Net product sales					500,000
Manufacturing and Supply Commitment Deliverable | Other Eisai Collaboration Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Management support payment recognized					1,600,000
Development Milestones | Axovant
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional milestone payments on achievement					4,000,000
Development Milestones | Boehringer Ingelheim
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional milestone payments on achievement					7,000,000
Development Milestones | Boehringer Ingelheim | Non-substantive
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional milestone payments on achievement					30,000,000
Regulatory Milestones | Axovant
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional milestone payments on achievement					37,500,000
Regulatory Milestones | Boehringer Ingelheim | Non-substantive
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional milestone payments on achievement					84,000,000
Commercial Milestones | Boehringer Ingelheim | Non-substantive
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional milestone payments on achievement					$ 130,000,000