Gross Amounts and Dates of Expiration of Tax Credits and Carryovers (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Line Items]
Federal losses carryovers	$ 638,103
California loss carryovers	75,407
Research credits	28,892	$ 28,291
Federal foreign tax credits	610
Federal
Income Tax Disclosure [Line Items]
Research credits	19,249
California
Income Tax Disclosure [Line Items]
Research credits	12,207
Expires 2021-2023
Income Tax Disclosure [Line Items]
Federal losses carryovers	55,587
Expires 2021-2023 | Federal
Income Tax Disclosure [Line Items]
Research credits	7,786
Expires 2024-2030
Income Tax Disclosure [Line Items]
Federal losses carryovers	190,581
California loss carryovers	28,779
Federal foreign tax credits	610
Expires 2024-2030 | Federal
Income Tax Disclosure [Line Items]
Research credits	2,248
Expires 2031-2040
Income Tax Disclosure [Line Items]
Federal losses carryovers	209,368
California loss carryovers	46,628
Expires 2031-2040 | Federal
Income Tax Disclosure [Line Items]
Research credits	9,215
No Expiration
Income Tax Disclosure [Line Items]
Federal losses carryovers	182,567
No Expiration | California
Income Tax Disclosure [Line Items]
Research credits	$ 12,207