Loans Payable - Additional Information (Detail)	1 Months Ended		12 Months Ended
	May 31, 2016 USD ($) $ / shares shares	Sep. 30, 2014 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) Installment shares	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($)
Debt Instrument [Line Items]
Loan payable, end-of-term payment due			$ 690,000
Warrants issued to lenders as part of new loan agreement, shares of common stock to purchase | shares	1,202,117	608,696	259,067
Warrants issued to lenders as part of new loan agreement, exercise price | $ / shares	$ 0.87	$ 1.15
Warrants issued to lenders as part of new loan agreement, fair value	$ 700,000	$ 400,000	$ 667,000	$ 413,000
Warrants exercised | shares			0
Unamortized discount recognized			$ 997,000		$ 500,000
Maximum amount of debt conversion			2,000,000
Cash proceeds from issue of units			200,000
Loans Payable | Minimum
Debt Instrument [Line Items]
Option to purchase equity, net cash proceeds of equity securities			$ 10,000,000
Loans Payable | Hercules Amended Loan Agreement
Debt Instrument [Line Items]
Proceeds from additional borrowing capacity		$ 10,000,000
Loan payable, Commencement date		May 01, 2016
Loan payable, due date			Jan. 01, 2018
Loan payable, end-of-term payment due			$ 500,000
Loan issuance costs paid			$ 200,000
Loan payable, description of interest rate terms			Per annum interest is payable on the principal balance of the loan each month it remains outstanding at the greater of 11.9% and an amount equal to 11.9% plus the prime rate minus 4.75% as determined daily, provided however, that the per annum interest rate shall not exceed 15.0% (11.9% as of December 31, 2016).
Loan payable, interest rate, base rate			11.90%
Loan payable, interest rate, additional rate deducted from base rate			4.75%
Loan payable, interest rate			11.90%
Debt instrument convertible beneficial conversion feature			$ 0
Loans Payable | Hercules Amended Loan Agreement | Minimum
Debt Instrument [Line Items]
Loan payable, interest rate			11.90%
Loans Payable | Hercules Amended Loan Agreement | Maximum
Debt Instrument [Line Items]
Loan payable, interest rate			15.00%
Loans Payable | Hercules May 2016 Loan Agreement
Debt Instrument [Line Items]
Proceeds from additional borrowing capacity	5,000,000
Loan payable, Commencement date			Jul. 01, 2017
Loan payable, due date			Dec. 01, 2019
Loan payable, end-of-term payment due			$ 200,000
Loan issuance costs paid			100,000
Loan outstanding principal amount	$ 15,000,000		$ 20,000,000
Loan payable, number of installments of principal and interest | Installment			30
Loan payable, frequency of installments of principal and interest			Monthly payments of principal and interest
Unrestricted and unencumbered cash and cash equivalents			$ 25,000,000
Additional borrowing capacity			$ 5,000,000
Loan payable, Commencement date deferred by six months			Jan. 01, 2018
Loans Payable | Hercules May 2016 Loan Agreement | Financial covenant | Minimum
Debt Instrument [Line Items]
Unrestricted and unencumbered cash and cash equivalents			$ 10,000,000