Segment Information - Summary of Long-Lived Assets by Geographical Area (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting, Asset Reconciling Item [Line Items]
Long-lived assets, net of accumulated depreciation	$ 4,390	$ 2,905
U.S.
Segment Reporting, Asset Reconciling Item [Line Items]
Long-lived assets, net of accumulated depreciation	4,342	2,842
Global
Segment Reporting, Asset Reconciling Item [Line Items]
Long-lived assets, net of accumulated depreciation	$ 48	$ 63