Major Customers, Partnerships and Strategic Alliances - Additional Information (Detail)	1 Months Ended			3 Months Ended		12 Months Ended
	Jan. 31, 2014 USD ($) Program	Jun. 30, 2012 Targets	Jan. 31, 2012 USD ($) Targets	Mar. 31, 2017 USD ($) Product	Mar. 31, 2016 USD ($)	Dec. 31, 2014 USD ($)
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Number of research programs | Program	2
Research and development				$ 12,942,000	$ 15,266,000
Bioverativ Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues under agreement	$ 20,000,000
Potential amount eligible to receive for certain milestones	115,800,000
Potential amount to be funded for achievement of specified commercialized and sales milestones	160,500,000
Milestone revenue receivable	276,300,000
Milestone payments received				$ 0
Number of products approved | Product				0
Royalty revenues				$ 0
Research program to develop laboratory research reagents				44 months
Deferred revenue				$ 6,000,000
Bioverativ Inc [Member] | Sickle cell disease [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone revenue receivable	7,500,000
Bioverativ Inc [Member] | Beta-thalassemia Project [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone revenue receivable	$ 6,000,000
Research and development				$ 1,600,000	2,000,000
Shire AG [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues under agreement			$ 13,000,000
Research program to develop laboratory research reagents				6 years
Deferred revenue				$ 1,800,000
Research and development				$ 100,000	$ 400,000
Aggregate number of gene targets | Targets			7
Number of initial gene targets | Targets			4
Number of gene targets | Targets		5
Number of additional gene targets | Targets		2
Recognition of milestone						$ 1,000,000