Significant Accounting Policies - Summary of Revenue Recognized from Contract Liabilities and Remaining Balance (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2021 USD ($)
Significant Accounting Policies [Line Items]
Deferred revenues, beginning balance	$ 4,248
Payments received in advance of services to be performed	19,874
Revenue recognized for services performed during the period	(19,354)
Foreign Currency Translation	(15)
Deferred revenues, ending balance	4,753
Information Services [Member]
Significant Accounting Policies [Line Items]
Deferred revenues, beginning balance	3,203
Payments received in advance of services to be performed	8,064
Revenue recognized for services performed during the period	(7,614)
Deferred revenues, ending balance	3,653
Post-trade Services [Member]
Significant Accounting Policies [Line Items]
Deferred revenues, beginning balance	1,045
Payments received in advance of services to be performed	11,810
Revenue recognized for services performed during the period	(11,740)
Foreign Currency Translation	(15)
Deferred revenues, ending balance	$ 1,100