Commitments and Contingencies - Additional Information (Detail) (Subsequent Event, USD $) In Millions, unless otherwise specified	1 Months Ended	0 Months Ended
	Apr. 30, 2015 RenewalOptions sqft	May 08, 2015 sqft
BMR Lease
Commitments and Contingencies [Line Items]
Area of office and laboratory space held under operating lease	295,000
Operating lease term	15 years
Number of lease renewal options	2
Lease renewal options period	5 years
Operating lease annual rent for the first year	$ 19.8
Operating 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		72,000
Operating lease annual rent increase per square foot		1
101 Main Street Leases | 10th Floor Lease
Commitments and Contingencies [Line Items]
Operating lease term		4 years
Number of lease renewal options		1
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]
Operating lease term		5 years 6 months
Number of lease renewal options		1
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]
Operating lease obligation through 2034		$ 409