Property and Equipment (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Property and equipment
Property and equipment, gross	$ 79,065,000	$ 74,517,000
Less accumulated depreciation and amortization	(41,689,000)	(36,980,000)
Property and equipment, net	37,376,000	37,537,000
Depreciation and amortization expense	11,729,000	11,325,000	9,999,000
Assets under capital lease	5,500,000	1,400,000
Accumulated amortization balances related to assets under capital lease	1,200,000	900,000
301 Binney Street, Cambridge, Massachusetts
Property and equipment
Additional term of the lease	24 months
Manufacturing equipment
Property and equipment
Property and equipment, gross	2,812,000
Laboratory equipment
Property and equipment
Property and equipment, gross	14,039,000	16,315,000
Computer and office equipment
Property and equipment
Property and equipment, gross	5,202,000	6,476,000
Furniture and fixtures
Property and equipment
Property and equipment, gross	2,365,000	2,449,000
Software
Property and equipment
Property and equipment, gross	12,352,000	11,047,000
Construction in process
Property and equipment
Property and equipment, gross	996,000	1,460,000
Leased vehicles
Property and equipment
Property and equipment, gross	4,472,000
Leasehold improvements
Property and equipment
Property and equipment, gross	$ 36,827,000	$ 36,770,000