Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Effective income tax rate and tax provision from continuing operations	0.00%	0.00%	0.00%
Deferred tax assets, relates to net operating loss carryforwards	$ 98,445,000	$ 49,689,000
Deferred tax assets, operating loss foreign	351,100,000
Deferred tax assets, operating loss state	$ 354,000,000.0
Operating loss expiration date	2032
Research and development tax credit	$ 23,061,000	12,908,000
Increase in valuation allowance	$ 85,800,000	25,700,000	$ 13,700,000
Time period over percentage change of ownership	3 years
Unrecognized tax benefits related to liability	$ 0	0
Unrecognized tax benefits related to penalties or interest accrued	0	0
Unrecognized tax benefits that would impact effective tax rate	$ 0
Minimum percentage of likelihood of realization of tax benefits	50.00%
Reserve for unrecognized tax benefits	$ 7,504,000	$ 3,810,000	$ 2,471,000	$ 1,474,000
Internal Revenue Service
Income Taxes [Line Items]
Operating loss carryforwards adjustments period	3 years
California Franchise Tax Board
Income Taxes [Line Items]
Operating loss carryforwards adjustments period	4 years
Australia
Income Taxes [Line Items]
Uncertain tax positions statute of limitation	4 years
Minimum
Income Taxes [Line Items]
Change of ownership percentage in equity ownership	50.00%
Federal
Income Taxes [Line Items]
Research and development tax credit	$ 7,200,000
Research and development tax credit carryforward, expiration year	2032
Orphan tax credit carryovers, expiration beginning year	2036
Orphan tax credit carryovers	$ 18,200,000
State
Income Taxes [Line Items]
Research and development tax credit	$ 5,900,000