Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Line Items]
Percentage of uncertain tax positions likelihood of being sustained	50.00%
Accrual interest or penalties	$ 0	$ 0
Deferred tax assets	382,400,000	367,100,000
Research and development tax credit carry forwards	33,500,000	29,000,000
Net operating loss carry forwards related to stock option exercises	77,000,000
Deferred tax assets, valuation allowance	382,400,000	367,100,000
Increases related to prior year tax positions	6,636,000	47,000	$ 543,000
Increases related to current year tax positions	2,584,000	$ 676,000	$ 916,000
Unrecognized tax benefits that would affect effective tax rate	26,200,000
Federal
Income Taxes [Line Items]
Operating loss carry forward, net	$ 736,000,000
Operating loss carry forward beginning expiration year	2021
Research and development tax credit carry forwards	$ 38,200,000
Alternative Minimum Tax credit carry forwards	$ 213,000
Federal | R&D
Income Taxes [Line Items]
Tax credit carry forwards beginning expiration year	2018
California
Income Taxes [Line Items]
Operating loss carry forward, net	$ 567,300,000
Research and development tax credit carry forwards	$ 27,200,000