Loan Payable - Summary of Changes in Carrying Value of Loan Payable (Detail) (USD $)	3 Months Ended		3 Months Ended	1 Months Ended	3 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 CIRM [Member]	Apr. 30, 2013 Silicon Valley Bank [Member]	Jun. 30, 2014 Silicon Valley Bank [Member]
Debt Instrument [Line Items]
Carrying value of loan payable (current and non-current) Beginning Balance	$ 15,843,919		$ 7,640,528		$ 8,203,391
Loan proceeds				(9,900,000)
Repayment of principal	(956,035)				(956,035)
Accretion of discount	51,651				51,651
Carrying value of loan payable (current and non-current) Ending Balance	14,939,535		7,640,528		7,299,007
Carrying value of loan payable, current portion	3,832,630	3,664,370			3,832,630
Carrying value of loan payable, non-current portion	11,106,905	9,244,874	7,640,528		3,466,377
Total loan payable	$ 14,939,535		$ 7,640,528		$ 7,299,007