Collaboration Revenue - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended		12 Months Ended
	Feb. 29, 2016	Jan. 31, 2016	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Period of performance identifiable deliverables		10 years
Collaboration revenue - related party			$ 3,015	$ 2,710
Nestlé Health Science [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront cash payment	$ 120,000		120,000
Development milestone payments		$ 285,000
Regulatory payments		375,000
Sales based milestones		$ 1,125,000
Reimbursement of development services			580
Proceeds on achievement of development milestone					$ 10,000
Collaboration revenue associated with substantive milestones - related party					$ 10,000
Collaboration revenue - related party			3,015	$ 2,710
Deferred revenue			$ 105,799