Balance Sheet Components - Summary of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Payables and Accruals [Abstract]
Accrued offering costs	$ 615
Accrued employee related costs	572	$ 759
Accrued research and development costs	686	526
Accrued professional fees	408	140
Other	23	48
Total accrued liabilities	$ 2,304	$ 1,473