Commitments and Contingencies - Additional Information (Detail)	1 Months Ended		12 Months Ended
	Dec. 31, 2015	Mar. 31, 2014 ft²	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Loss Contingencies [Line Items]
Rent expense			$ 1,290,000	$ 763,000	$ 520,000
Aggregate noncancelable purchase commitments			7,100,000
Other potential commitments			10,000,000
Pending or threatened legal proceedings			0
Maximum [Member]
Loss Contingencies [Line Items]
Commitment to make development and sales-related milestone payments			$ 30,000,000
Boehringer Ingelheim Commercial Supply Agreement [Member]
Loss Contingencies [Line Items]
Initial term of agreement period			8 years
Automatic renewal period of agreement			3 years
Termination period of agreement			3 years
Menlo Park, California [Member]
Loss Contingencies [Line Items]
Operating facility lease area | ft²		12,900
Operating facility lease term		39 months
Total obligation under lease			$ 500,000
Menlo Park, California [Member] | Sublease Agreement [Member]
Loss Contingencies [Line Items]
Operating facility lease term	24 months
Total obligation under lease			$ 600,000