Segment Information - Geographical Segment Revenue (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue		$ 6,417	$ 5,751	$ 19,395	$ 18,437
Domestic [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue		1,678	1,836	5,040	5,451
International [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	[1]	$ 4,739	$ 3,915	$ 14,355	$ 12,986

[1] Revenue from the Central Banks, consisting of a consortium of central banks around the world, is classified as international revenue. Reporting revenue by country for this customer is not practicable.