Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Federal statutory tax rate	21.00%	34.00%	34.00%
Decrease to federal deferred tax assets	$ 38.7
Deferred Tax Valuation allowance increase (decrease)	19.4	$ (11.0)
Federal [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	$ 330.8
Operating loss carryforwards, expiration date	Dec. 31, 2024
Federal [Member] | Research Tax Credit Carryforward
Income Taxes [Line Items]
Tax credit carryforwards	$ 4.6
Tax credit carryforwards, expiration date	Dec. 31, 2024
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	$ 198.1
Operating loss carryforwards, expiration date	Dec. 31, 2019
State and Local Jurisdiction [Member] | Research Tax Credit Carryforward
Income Taxes [Line Items]
Tax credit carryforwards	$ 2.0
Tax credit carryforwards, expiration date	Dec. 31, 2024