Income Taxes -Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Aug. 31, 2004	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Provision for income taxes		$ 240,000	$ 51,000	$ 0
Valuation allowance of deferred tax asset		665,365,000	654,298,000
Change in the valuation allowance		11,100,000	(260,200,000)
Federal operating loss carryforwards		2,100,000,000
State operating loss carryforwards		2,400,000,000
Federal operation loss carryforwards, not subject to expiration		$ 77,000,000
Operating loss carryforwards, limitations on use		Pursuant to Internal Revenue Code (“IRC”) Sections 382 and 383, annual use of the Company’s federal and California net operating loss and research and development credit carryforwards may be limited in the event a cumulative change in ownership of more than 50% occurs within a three-year period.
Net operating loss carryforwards	$ 216,000,000
Net operating loss and credit carryforwards, annual use limitation	$ 13,000,000
Research and development credits		$ 81,583,000	$ 83,461,000
Undistributed earnings from its foreign subsidiaries		$ 0
Effective income tax rate		21.00%	35.00%	35.00%
Decrease of deferred tax assets		$ 301,000,000
Decrease in valuation allowance		301,000,000
Additional income tax expense or benefit		0
Change in tax rate deferred tax asset and liability provisional amount			$ 301,000,000
Federal
Income Taxes [Line Items]
Research and development credits		$ 54,200,000
Federal research and development credits begin to expire		2024
State
Income Taxes [Line Items]
Research and development credits		$ 27,400,000
Topic 606
Income Taxes [Line Items]
Adjustment of deferred tax liability due to adoption of new revenue guidance		$ 400,000