Gross Amounts and Dates of Expiration of Tax Credits and Carryovers (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Line Items]
Federal losses carryovers	$ 616,915
California loss carryovers	67,781
Research credits	28,291	$ 26,705
Federal foreign tax credits	610
Federal
Income Tax Disclosure [Line Items]
Research credits	19,397
California
Income Tax Disclosure [Line Items]
Research credits	11,259
Expires 2020-2022
Income Tax Disclosure [Line Items]
Federal losses carryovers	64,730
Expires 2020-2022 | Federal
Income Tax Disclosure [Line Items]
Research credits	6,928
Expires 2023-2029
Income Tax Disclosure [Line Items]
Federal losses carryovers	186,421
California loss carryovers	14,732
Federal foreign tax credits	610
Expires 2023-2029 | Federal
Income Tax Disclosure [Line Items]
Research credits	4,875
Expires 2030-2039
Income Tax Disclosure [Line Items]
Federal losses carryovers	239,731
California loss carryovers	53,049
Expires 2030-2039 | Federal
Income Tax Disclosure [Line Items]
Research credits	7,594
No Expiration
Income Tax Disclosure [Line Items]
Federal losses carryovers	126,033
No Expiration | California
Income Tax Disclosure [Line Items]
Research credits	$ 11,259