Major Customers, Partnerships and Strategic Alliances - Revenues Recognized under Agreement (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Biogen Inc [Member]
Revenues:
Recognition of upfront fee	$ 608,000	$ 1,523,000
Royalty revenues	0
Research services	2,031,000	1,533,000
Total	2,639,000	3,056,000
Shire AG [Member]
Revenues:
Recognition of upfront fee	542,000	542,000
Research services	429,000	4,522,000
Total	971,000	5,064,000
Sigma-Aldrich Corporation [Member]
Revenues:
Royalty revenues	12,000	264,000
License fee revenues	7,000	4,256,000
Total	$ 19,000	$ 4,520,000