Income Taxes - Summary of Reconciliation of Income Tax Expense (Benefit) Computed at Statutory Federal and State Income Tax Rate (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Income Tax Disclosure [Abstract]
Federal income tax expense (benefit) at statutory rate	$ (2,693)
Change in valuation allowance	2,164
Impact of US tax reform	1,022
State income tax expense net of federal benefit	(514)
Other non-deductible expenses	21
Total tax expense (benefit)	$ 0