Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Income Taxes [Line Items]
Federal statutory rate on loss before provision for income taxes		34.00%
Cumulative ownership percentage		50.00%
Cumulative ownership period		3 years
Increase (decrease) in valuation allowance		$ (8,158,000)	$ 469,000	$ 5,467,000
Interest or penalties related to uncertain tax positions		0	0	0
Uncertain tax positions that would impact effective tax rate		1,610,000	1,049,000
Re-measurement of deferred tax assets change in tax rate reduced amount		18,696,000
Re-measurement of deferred tax liabilities change in tax rate reduced amount		4,394,000
Adjustment to valuation allowance due to impact of tax cuts and jobs act		14,302,000	$ 0	$ 0
Scenario Forecast
Schedule Of Income Taxes [Line Items]
Federal statutory rate on loss before provision for income taxes	21.00%
Federal [Member]
Schedule Of Income Taxes [Line Items]
Net operating loss carryforwards		$ 110,087,000
Net operating loss carryforwards expiration date		2026
State [Member]
Schedule Of Income Taxes [Line Items]
Net operating loss carryforwards		$ 91,585,000
Net operating loss carryforwards expiration date		2022
Federal Research and Development [Member]
Schedule Of Income Taxes [Line Items]
Research and development credits		$ 6,139,000
Research and development credits expiration year		2026
State Research and Development [Member]
Schedule Of Income Taxes [Line Items]
Research and development credits		$ 6,451,000
Foreign Tax Authority [Member] | French Tax Authority [Member] | Minimum [Member]
Schedule Of Income Taxes [Line Items]
Income tax examination year		2012
Foreign Tax Authority [Member] | French Tax Authority [Member] | Maximum [Member]
Schedule Of Income Taxes [Line Items]
Income tax examination year		2016