Commitments and Contingencies - Additional Information (Detail) $ in Millions	1 Months Ended	6 Months Ended
	Apr. 30, 2015 USD ($) ft² RenewalOptions	Jun. 30, 2015 USD ($) ft² RenewalOptions $ / ft²
BMR Lease
Commitments and Contingencies [Line Items]
Area of office and laboratory space held under operating lease | ft²	295,000
Lease term	15 years
Number of lease renewal options | RenewalOptions	2
Lease renewal options period	5 years
Facility lease annual rent for the first year	$ 19.8
Facility lease percentage of annual rent increase after first year	3.00%
Cost of base building and tenant improvement	$ 56.1
Leased and occupied rentable area percentage	70.00%
BMR Lease | Minimum
Commitments and Contingencies [Line Items]
Remaining lease term	10 years
101 Main Street Leases
Commitments and Contingencies [Line Items]
Area of office and laboratory space held under operating lease | ft²		72,000
Operating lease annual rent increase per square foot | $ / ft²		1
101 Main Street Leases | 10th Floor Lease
Commitments and Contingencies [Line Items]
Number of lease renewal options | RenewalOptions		1
Operating lease term		4 years
Operating lease renewal options period		5 years
Operating lease annual rent for the first year		$ 1.7
101 Main Street Leases | Additional Lease
Commitments and Contingencies [Line Items]
Number of lease renewal options | RenewalOptions		1
Operating lease term		5 years 6 months
Operating lease renewal options period		5 years
Operating lease annual rent for the first year		$ 3.5
BMR Lease and 101 Main Street Leases
Commitments and Contingencies [Line Items]
Lease obligation through 2034		$ 409.3