Lease, Licensed Technology and Other Commitments - Additional Information (Detail) (USD $)	12 Months Ended			1 Months Ended
	Dec. 31, 2014 Employee	Dec. 31, 2013	Dec. 31, 2012	May 31, 2012 sqft	Sep. 30, 2013 sqft	Jan. 31, 2013 sqft
Operating Lease Obligations [Line Items]
Construction in progress and facility lease obligation	$ 196,000,000	$ 99,400,000
Current portion of long-term facility lease obligation	6,707,000
Number of officers under employment agreements	20
Aggregate base salaries payable to officers, due next year	7,700,000
Aggregate base salaries payable to officers, due next two years	7,700,000
Licensed Technology
Operating Lease Obligations [Line Items]
License fees paid	470,000	145,000	145,000
Licensed Technology | Year 2015
Operating Lease Obligations [Line Items]
Future expected annual license fees	485,000
Licensed Technology | Year 2016
Operating Lease Obligations [Line Items]
Future expected annual license fees	110,000
Licensed Technology | Year 2017
Operating Lease Obligations [Line Items]
Future expected annual license fees	105,000
Licensed Technology | Year 2018
Operating Lease Obligations [Line Items]
Future expected annual license fees	100,000
Licensed Technology | Year 2019
Operating Lease Obligations [Line Items]
Future expected annual license fees	85,000
Lease Agreements
Operating Lease Obligations [Line Items]
Future minimum annual rental payments under operating lease due, year one	13,900,000
Future minimum annual rental payments under operating lease due, year two	15,500,000
Future minimum annual rental payments under operating lease due, year three	33,700,000
Future minimum annual rental payments under operating lease due, year four	37,500,000
Future minimum annual rental payments under operating lease due, year five	35,600,000
Future minimum annual rental payments under operating lease due, thereafter	351,400,000
Operating lease rent expense	7,600,000	6,100,000	5,900,000
Contingent rent expense	700,000	700,000	600,000
Lease Agreements | Landsdowne and Sidney Streets, Cambridge Massachusetts
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	1,400,000
Operating lease term				3 years
Additional square feet of office space				26,000
Future minimum annual rental payments under operating lease due, year one	6,700,000
Future minimum annual rental payments under operating lease due, year two	5,900,000
Future minimum annual rental payments under operating lease due, year three	6,000,000
Future minimum annual rental payments under operating lease due, year four	6,100,000
Future minimum annual rental payments under operating lease due, year five	3,600,000
Lease Agreements | Binney Street, Cambridge, Massachusetts
Operating Lease Obligations [Line Items]
Operating lease, letters of credit outstanding	9,200,000
Operating lease term	15 years
Additional square feet of office space					142,000
Future minimum annual rental payments under operating lease due, year two	8,400,000
Future minimum annual rental payments under operating lease due, year three	26,600,000
Future minimum annual rental payments under operating lease due, year four	30,400,000
Future minimum annual rental payments under operating lease due, year five	30,900,000
Area of laboratory and office space under lease agreement					386,000	244,000
Year in which leased facility will be available for occupancy						2015
Construction of tenant improvement expected completion date	In the first half of 2016
Construction in progress and facility lease obligation	196,000,000
Current portion of long-term facility lease obligation	6,700,000
Number of renewal options	3
Number of lease years after optional extension	5 years
Future minimum annual rental payments under operating lease due, remainder of year	5,300,000
Future minimum annual rental payments under operating lease due, thereafter	347,100,000
Area expected to be subleased	170,000
Lease Agreements | Lausanne Switzerland
Operating Lease Obligations [Line Items]
Operating lease term						10 years
Future minimum annual rental payments under operating lease due, year one	1,000,000
Future minimum annual rental payments under operating lease due, year two	1,000,000
Future minimum annual rental payments under operating lease due, year three	1,000,000
Future minimum annual rental payments under operating lease due, year four	1,000,000
Future minimum annual rental payments under operating lease due, year five	1,100,000
Area of laboratory and office space under lease agreement						22,000
Year in which leased facility will be available for occupancy						2014
Future minimum annual rental payments under operating lease due, thereafter	$ 4,300,000
Number of lease years before optional extension and early termination can be exercised						5 years