Income Taxes - Schedule of Deferred Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Components of Deferred Tax Assets and Liabilities [Abstract]
Net operating loss	$ 9,252	$ 8,974
Stock-based compensation	2,691
Financing lease obligation	2,131
Credits	735	592
Accrued Expenses	576	574
Other	8	81
Total deferred tax assets	15,393	10,221
Property and equipment	(2,600)	(53)
Deferred Revenue	(1)	9
Total deferred tax liabilities	(2,601)	(44)
Less valuation allowance	(12,792)	(10,177)
Total	$ 0	$ 0