Major Customers, Partnerships and Strategic Alliances - Revenues Recognized under Agreement (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Biogen Inc [Member]
Revenues:
Recognition of upfront fee	$ 6,176,000	$ 5,313,000
Royalty revenues	0
Research services	7,769,000	7,751,000
Total	13,945,000	13,064,000
Shire AG [Member]
Revenues:
Recognition of upfront fee	2,167,000	2,167,000	$ 2,167,000
Recognition of milestone		1,000,000
Research services	13,584,000	22,765,000	14,286,000
Total	15,751,000	25,932,000	16,453,000
Sigma-Aldrich Corporation [Member]
Revenues:
Royalty revenues	390,000	344,000	824,000
License fee and milestone revenues	4,463,000	448,000	1,351,000
Total	$ 4,853,000	$ 792,000	$ 2,175,000