Income Taxes - Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefit, beginning of period	$ 1,135	$ 940
Gross increases — current year tax positions	422	327
Gross increases — prior year tax positions	38	73
Gross decreases — prior year tax positions	0	(205)
Unrecognized tax benefit, end of period	$ 1,595	$ 1,135