Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Federal statutory tax rate		34.00%	34.00%	34.00%
Change in deferred tax assets due to tax cuts and jobs act of 2017		$ (38.7)
Change in valuation allowance due to tax cuts and jobs act of 2017		(38.7)
Deferred Tax Valuation allowance increase (decrease)		(11.0)	$ 17.4
Federal [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		$ 266.3
Operating loss carryforwards, expiration date		Dec. 31, 2024
Federal [Member] | Research Tax Credit Carryforward
Income Taxes [Line Items]
Tax credit carryforwards		$ 3.8
Tax credit carryforwards, expiration date		Dec. 31, 2024
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		$ 144.8
Operating loss carryforwards, expiration date		Dec. 31, 2019
State and Local Jurisdiction [Member] | Research Tax Credit Carryforward
Income Taxes [Line Items]
Tax credit carryforwards		$ 1.3
Tax credit carryforwards, expiration date		Dec. 31, 2024
Maximum
Income Taxes [Line Items]
Federal statutory tax rate		35.00%
Scenario Plan [Member]
Income Taxes [Line Items]
Federal statutory tax rate	21.00%