Leases and Facility Lease Obligation - Additional Information (Detail) (Lease Agreements, USD $)	1 Months Ended		6 Months Ended	1 Months Ended	6 Months Ended	1 Months Ended	3 Months Ended		6 Months Ended
	Sep. 30, 2013 Binney Street, Cambridge, Massachusetts sqft	Jan. 31, 2013 Binney Street, Cambridge, Massachusetts sqft	Jun. 30, 2014 Binney Street, Cambridge, Massachusetts RenewalOptions	May 31, 2012 Landsdowne and Sidney Streets, Cambridge Massachusetts sqft	Jun. 30, 2014 Landsdowne and Sidney Streets, Cambridge Massachusetts RenewalOptions sqft	Jan. 31, 2013 Lausanne Switzerland sqft	Jun. 30, 2014 Lausanne Switzerland	Jun. 30, 2013 Lausanne Switzerland	Jun. 30, 2014 Lausanne Switzerland	Jun. 30, 2013 Lausanne Switzerland
Operating Lease Obligations [Line Items]
Area of office and laboratory in square foot					100,000
Extended lease expiration date					2019-07
Number of consecutive renewal options					2
Operating lease renewal options, lease term in years					5 years
Operating lease, letters of credit outstanding			$ 9,200,000		$ 1,400,000
Operating lease term			15 years	3 years		10 years
Additional square feet of office space	142,000			26,000
Future minimum annual rental payments under operating lease due, remainder of year			5,300,000		3,600,000		4,200,000	576,000	4,200,000	576,000
Future minimum annual rental payments under operating lease due, year two			8,400,000		6,700,000		13,100,000	1,100,000	13,100,000	1,100,000
Future minimum annual rental payments under operating lease due, year three			26,600,000		5,900,000		15,500,000	1,200,000	15,500,000	1,200,000
Future minimum annual rental payments under operating lease due, year four			30,400,000		6,000,000		33,800,000	1,200,000	33,800,000	1,200,000
Future minimum annual rental payments under operating lease due, year five			30,900,000		6,100,000		37,700,000	1,200,000	37,700,000	1,200,000
Future minimum annual rental payments under operating lease due, thereafter			347,100,000		3,600,000		387,600,000	6,000,000	387,600,000	6,000,000
Area of laboratory and office space under lease agreement	386,000	244,000				22,000
Year in which leased facility will be available for occupancy		2015				2014
Construction in progress and facility lease obligation			144,300,000
Number of renewal options			3
Number of lease years after optional extension			5 years
Number of lease years before optional extension and early termination can be exercised						5 years
Operating lease rent expense							1,900,000	1,500,000	3,800,000	2,900,000
Contingent rent expense							$ 158,000	$ 170,000	$ 338,000	$ 341,000