Income Tax - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income tax expense	$ 0	$ 0
Federal and state effective tax rate before valuation allowance	24.00%
Unrecognized tax benefits	$ 2,100,000		$ 1,600,000
Accrued interest and penalties related to uncertain tax positions	$ 0		$ 0

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of unrecognized tax benefits.

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Amount of expense for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

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