Income Taxes - Components of Income Tax Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current provision (benefit):
Federal	$ 0	$ 0	$ 0
State	54	(26)	69
Current provision (benefit), Total	54	(26)	69
Deferred provision:
Federal	(10)	7	6
State	(2)	1	1
Deferred provision, Total	(12)	8	7
Total	$ 42	$ (18)	$ 76