Loan Payable - Additional Information (Detail) (USD $)	1 Months Ended				3 Months Ended	6 Months Ended
	Jan. 31, 2014	Jul. 31, 2013	Apr. 30, 2013	Sep. 30, 2012	Jun. 30, 2014	Jun. 30, 2014
Debt Instrument [Line Items]
Proceeds from loan
Loan term						3 years
Annual interest rate on loan					6.00%	6.00%
Period of loan subject to interest payments only						6 months
Period of loan subject to principal and interest payments						30 months
Final fee payment at the end of loan term						1,000,000
Proceeds received under loan agreement						9,900,000
Initial carrying amount assigned to loan, net of discount					9,512,000	9,512,000
Fair value allocated to warrant					388,000	388,000
Cash discount					100,000	100,000
Note issuance costs						117,000
Deferred financing costs, discount and accretion percentage						9.00%
CIRM [Member]
Debt Instrument [Line Items]
Proceeds from loan
Loan term				10 years
Approval of fund by California Institute for Regenerative Medicine (CIRM)			19,300,000
Approval of fund by California Institute for Regenerative Medicine (CIRM) maximum period				4 years
Loan interest rate description						One year LIBOR rate plus two percent
LIBOR rate plus percentage						2.00%
LIBOR rate plus percentage increase						1.00%
Proceeds from initial disbursement of the loan	3,800,000	3,800,000
Silicon Valley Bank Loan Agreement Warrant [Member]
Debt Instrument [Line Items]
Term of warrant expiration						10 years
Exercise price of warrant					1.7034	1.7034
Warrant expiration period						April 2023
Silicon Valley Bank Loan Agreement Warrant [Member] | Common Stock [Member]
Debt Instrument [Line Items]
Number of shares of common stock acquired using warrant					293,531	293,531
Silicon Valley Bank [Member]
Debt Instrument [Line Items]
Proceeds from loan			$ 9,900,000