Balance Sheet Details - Accrued Expenses (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accrued clinical trial costs	$ 330	$ 1,112
Accrued other	2,315	2,769
Total	$ 2,645	$ 3,881

Amount of expenses incurred but not yet paid classified as other, due within one year or the normal operating cycle, if longer.

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