Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax [Line Items]
Increase (Decrease) in valuation allowance	$ 63,500,000	$ 30,700,000
Unrecognized income tax benefits that, if recognized, would affect effective tax rate	365,000	365,000
Unrecognized income tax benefits	2,906,000	2,048,000	1,435,000	1,344,000
Unrecognized Tax Benefits, Period Increase (Decrease)	(365,000)
Minimum
Income Tax [Line Items]
Federal research tax credits, expiration year	2024
Maximum
Income Tax [Line Items]
Federal research tax credits, expiration year	2034
Earliest Tax Year
Income Tax [Line Items]
Tax years remain open to examinations	2003
Latest Tax Year
Income Tax [Line Items]
Tax years remain open to examinations	2013
Federal
Income Tax [Line Items]
Net operating loss carryforwards	364,400,000
Federal | Research Tax Credit Carryforward
Income Tax [Line Items]
Tax credits carryforwards	15,200,000
California
Income Tax [Line Items]
Net operating loss carryforwards	449,600,000
California | Minimum
Income Tax [Line Items]
Net operating loss carryforwards, expiration year	2018
California | Maximum
Income Tax [Line Items]
Net operating loss carryforwards, expiration year	2034
California | Research Tax Credit Carryforward
Income Tax [Line Items]
Tax credits carryforwards	$ 3,800,000