Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Operating Loss Carryforwards [Line Items]
Provision or benefit for income taxes	$ 0	$ 0
Statutory Federal income tax rate	34.00%	34.00%
Cumulative change in ownership percentage description	more than 50%
Income tax holiday, testing period	3 years
Cumulative change in ownership percentage	50.00%
Impact on income tax, tax attribute carry forwards	$ 0
Operating loss expiration year	2031
R&D/orphan drug tax credit carry forwards	$ 19,369,000	$ 8,109,000
Uncertain income tax position	50.00%
Unrecognized tax benefits	$ 0
Period of change in unrecognized tax benefits	12 months
Tax liability, penalties or interest	$ 0	$ 0
Federal [Member]
Operating Loss Carryforwards [Line Items]
Tax loss carry forwards	80,300,000
R&D/orphan drug tax credit carry forwards	$ 18,800,000
Aforementioned tax credit expiration beginning year	2031
State and Local Jurisdiction [Member] | CALIFORNIA
Operating Loss Carryforwards [Line Items]
Tax loss carry forwards	$ 74,400,000
R&D/orphan drug tax credit carry forwards	$ 900,000