Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Benefit for income taxes from release of valuation allowance				$ 1,411
Percentage of corporate tax rate		35.00%
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Provisional Income Tax Expense (Benefit)		$ 38,000
Net operating loss carry-forwards for federal income tax, expiration period		2023
Net operating loss carry-forwards for state income tax, expiration period		2021
Limitations in use of net operating losses		Events which may cause limitations in the amount of the net operating losses that the Company may use in any one year include, but are not limited to, a cumulative ownership change of more than 50% over a three-year period.
Period for cumulative ownership change		3 years
Valuation allowances, deferred tax asset, increase		$ 9,900	$ 7,800	$ 11,100
Federal
Income Taxes [Line Items]
Net operating loss carry-forwards		$ 276,300	197,600
Research credit carry-forwards for tax purposes, expiration period		2028
California
Income Taxes [Line Items]
Net operating loss carry-forwards		$ 230,800	137,600
Minimum
Income Taxes [Line Items]
Cumulative ownership change percentage		50.00%
Research credit carry-forward | Federal
Income Taxes [Line Items]
Research credit carry-forwards for tax purposes		$ 5,600	4,700
Research credit carry-forward | California
Income Taxes [Line Items]
Research credit carry-forwards for tax purposes		6,400	$ 5,200
ASU 2016-09
Income Taxes [Line Items]
Increase in deferred tax assets		$ 18,000
Scenario Forecast
Income Taxes [Line Items]
Percentage of corporate tax rate	21.00%