Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax [Line Items]
Total provision (benefit) for income taxes	$ (365,000)	$ 0	$ 0
Increase (Decrease) in valuation allowance	67,000,000	64,000,000
Unrecognized income tax benefits that, if recognized, would affect effective tax rate	0	365,000,000
Unrecognized income tax benefits	3,228,000	$ 2,906,000	$ 2,048,000	$ 1,435,000
California Franchise Tax Board
Income Tax [Line Items]
Written off related to net operating losses	$ 194,000,000
Minimum
Income Tax [Line Items]
Federal research tax credits, expiration year	2024
Maximum
Income Tax [Line Items]
Federal research tax credits, expiration year	2035
Federal
Income Tax [Line Items]
Net operating loss carryforwards	$ 612,000,000
Federal | Research Tax Credit Carryforward
Income Tax [Line Items]
Tax credits carryforwards	18,000,000
California
Income Tax [Line Items]
Net operating loss carryforwards	$ 223,000,000
California | Minimum
Income Tax [Line Items]
Net operating loss carryforwards, expiration year	2017
California | Maximum
Income Tax [Line Items]
Net operating loss carryforwards, expiration year	2035
California | Research Tax Credit Carryforward
Income Tax [Line Items]
Tax credits carryforwards	$ 5,000,000