Investment in Variable Interest Entity - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Variable Interest Entity [Line Items]
Common stock, shares issued		37,771,459	36,184,912
Acquired in-process research and development		$ 12,000	$ 209	$ 1,905
Research And development expense		$ 31,343	$ 23,983	$ 9,017
LA Cell Inc [Member]
Variable Interest Entity [Line Items]
Upfront payment	$ 2,000
Additional upfront payment	$ 3,000
License maintenance fees payment period	6 years
Ownership of outstanding shares, voting rights percentage		48.00%
Acquired in-process research and development		$ 2,000
Non compete consulting expense		6,000
Research And development expense		$ 125
LA Cell Inc [Member] | Class C Common Stock [Member]
Variable Interest Entity [Line Items]
Common stock, shares issued	2,648,948