Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Provisional tax benefit recognized for Tax Act	$ 0.4
Tax benefit for remeasurement of deferred tax assets and liabilities	0.2
Provisional tax benefit for release of valuation allowance	0.2
Deferred tax provision			$ 0.1	$ 0.1
Net operating loss carryforwards, federal	171.2	$ 171.2	$ 50.3
Net operating loss carryforwards, state	118.7	118.7
Net operating loss carryforwards, foreign	93.1	93.1
Deferred Tax Assets Operating Loss Carryforwards [Member]
Operating Loss Carryforwards [Line Items]
Increase in valuation allowance		2.8
Domestic Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Research and development credit carryforwards	2.2	2.2
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Research and development credit carryforwards	1.1	1.1
Foreign Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Research and development credit carryforwards	$ 0.1	$ 0.1