Equipment Loan Payable - Additional Information (Detail) - Silicon Valley Bank [Member] - USD ($)	1 Months Ended	9 Months Ended
Jul. 31, 2014	Sep. 30, 2018
Class of Warrant or Right [Line Items]
Amount of loan to purchase equipment	$ 1,800,000
Line of credit facility, interest rate, stated percentage	3.25%
Bank loan and security agreement, repayment period	36 months
Debt instrument, maturity date		May 31, 2018
Warrants Outstanding	6,566
Exercise Price	$ 7.99
Prime Rate [Member]
Class of Warrant or Right [Line Items]
Amount of loan bears interest basis spread on variable rate	2.75%

Exercise price per share or per unit of warrants or rights outstanding.

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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