Significant Accounting Policies - Summary of Revenue Recognized from Contract Liabilities and Remaining Balance (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($)
Significant Accounting Policies [Line Items]
Deferred revenues, beginning balance	$ 2,810
Payments received in advance of services to be performed	15,568
Revenue recognized for services performed during the period	(14,617)
Foreign Currency Translation	(30)
Deferred revenues, ending balance	3,731
Information Services [Member]
Significant Accounting Policies [Line Items]
Deferred revenues, beginning balance	1,959
Payments received in advance of services to be performed	6,030
Revenue recognized for services performed during the period	(5,437)
Deferred revenues, ending balance	2,552
Post-trade Services [Member]
Significant Accounting Policies [Line Items]
Deferred revenues, beginning balance	851
Payments received in advance of services to be performed	9,538
Revenue recognized for services performed during the period	(9,180)
Foreign Currency Translation	(30)
Deferred revenues, ending balance	$ 1,179