Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation Of Income Taxes [Line Items]
Federal statutory income tax rate	21.00%	21.00%	35.00%
Increase in valuation allowance	$ 47,300,000	$ 36,100,000	$ 5,500,000
Valuation allowance changes, description	The Company does not expect any significant changes in its valuation allowance positions within the next 12 months.
Federal and state net operating loss carryforwards	$ 947,000,000	781,000,000
International net operating loss carryforwards	6,000,000
Research and development tax credits	$ 35,285,000	11,154,000
Minimum percentage chances of tax benefit to be realized on examination	50.00%
Unrecognized tax benefits affect the Company's effective tax rate	$ 0
Interest or penalties recorded	$ 0
Expected significant change in unrecognized tax benefits, description	The Company does not expect any significant change in its unrecognized tax benefits within the next 12 months
Federal [Member]
Reconciliation Of Income Taxes [Line Items]
Net operating loss, carryforwards, period	20 years
Net operating loss carryforwards, expiration year	Dec. 31, 2037
Interest expense carryforward	$ 13,000,000.0	$ 10,000,000.0
Research and development tax credits	$ 23,000,000.0
Research and development tax credit carryforwards, expiration year	Dec. 31, 2039
State [Member]
Reconciliation Of Income Taxes [Line Items]
Net operating loss carryforwards, expiration year	Dec. 31, 2039
Research and development tax credits	$ 12,200,000
Research and development tax credit carryforwards, expiration year	Dec. 31, 2034