Income Taxes - Components of Tax Provision (Benefit) Allocated to Continuing Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 8	$ 0	$ (2)
State	30	(11)	49
Foreign	9	21	19
Sub-total	47	10	66
Deferred:
Federal	(253)	0	0
State	0	0	0
Foreign	0	0	0
Sub-total	(253)	0	0
Total tax provision (benefit)	$ (206)	$ 10	$ 66