Significant Accounting Policies - Summary of Revenue Recognized from Contract Liabilities and Remaining Balance (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2020 USD ($)
Significant Accounting Policies [Line Items]
Deferred revenues, beginning balance	$ 3,499
Payments received in advance of services to be performed	18,957
Revenue recognized for services performed during the period	(17,327)
Foreign Currency Translation	(37)
Deferred revenues, ending balance	5,092
Information Services [Member]
Significant Accounting Policies [Line Items]
Deferred revenues, beginning balance	2,138
Payments received in advance of services to be performed	7,467
Revenue recognized for services performed during the period	(6,093)
Deferred revenues, ending balance	3,512
Post-trade Services [Member]
Significant Accounting Policies [Line Items]
Deferred revenues, beginning balance	1,361
Payments received in advance of services to be performed	11,490
Revenue recognized for services performed during the period	(11,234)
Foreign Currency Translation	(37)
Deferred revenues, ending balance	$ 1,580