Commitments and Contingencies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016 USD ($) Lawsuits	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jul. 20, 2015 ft²	Nov. 21, 2014 ft²	Sep. 15, 2014 ft²
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Operating lease | ft²					113,200	74,500
Lease agreement tenant incentive	$ 20,500,000
Stand by letter of credit	2,900,000
Tenant improvement allowance	3,100,000	$ 3,400,000
Rent expense	6,000,000	7,100,000	$ 3,700,000
Accruals from milestones achieved	220,163,000	141,827,000	100,371,000
License agreements amount	$ 70,000	135,000	83,000
Royalty payment		0
Milestone payment period	5 years
Contract term	5 years
Number of days for election	30 days
Period under contract term to declare development candidate for milestone Payments forgo	3 years
Legal proceedings | Lawsuits	0
Minimum [Member]
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Range related to royalties amount	0.50%
Range related to non royalties amount	7.00%
Maximum [Member]
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Range related to royalties amount	2.50%
Range related to non royalties amount	25.00%
Accrued Income Receivable [Member]
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Accruals from milestones achieved	$ 4,100,000
License Agreement Terms [Member]
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Accruals from milestones achieved	70,000	53,000
Payment of patent related to licensor	100,000
Payment of clinical development related to licensor	1,600,000
Regulatory payment related to licensor	5,400,000
Sales based payment related to licensor	$ 3,700,000
Patent-related milestone expense		$ 0	$ 50,000
Option to renew licenses	Option to renew these licenses on an annual basis in exchange for payments approximating $70,000 for 2017
License Agreement Terms [Member] | Clinical Milestones [Member]
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Accruals from milestones achieved	$ 500,000
License Agreement Terms [Member] | Patent Milestones [Member]
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Accruals from milestones achieved	$ 75,000
Preexisting Leases [Member]
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Operating lease | ft²						38,500
38 Sidney Street Lease Arrangement [Member]
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Lease termination date	Jun. 15, 2015
88 Sidney Street Lease Arrangement [Member]
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Operating lease | ft²				146,030
Lease termination date	May 15, 2022