Major Customers, Partnerships and Strategic Alliances - Agreement with Sigma-Aldrich Corporation - Additional Information (Detail) (USD $)	3 Months Ended		1 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Oct. 31, 2009	Jul. 31, 2007
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development	$ 14,980,000	$ 12,083,000
Sigma-Aldrich Corporation [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research program to develop laboratory research reagents				3 years
Upfront license fee			20,000,000
Public offering, common stock shares issued			636,133
Amount received on commercial license fees	5,000,000
Reduced royalty rate	10.50%
Funding available under the amended agreement	25,000,000
Milestone payments received	0
Sigma-Aldrich Corporation [Member] | Upfront license fee [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Upfront license fee			15,100,000
Common stock issued under license agreement			4,900,000
Sigma-Aldrich Corporation [Member] | License agreement terms [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Royalty revenues expected to be received			5,000,000
Research and development	$ 200,000	$ 0