Significant Accounting Policies - Summary of Revenue Recognized from Contract Liabilities and Remaining Balance (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Significant Accounting Policies [Line Items]
Deferred revenues, beginning balance	$ 2,660
Payments received in advance of services to be performed	18,675
Revenue recognized for services performed during the period	(18,474)
Foreign Currency Translation	(51)
Deferred revenues, ending balance	2,810
Information Services [Member]
Significant Accounting Policies [Line Items]
Deferred revenues, beginning balance	1,763
Payments received in advance of services to be performed	7,109
Revenue recognized for services performed during the period	(6,913)
Deferred revenues, ending balance	1,959
Post-trade Services [Member]
Significant Accounting Policies [Line Items]
Deferred revenues, beginning balance	897
Payments received in advance of services to be performed	11,566
Revenue recognized for services performed during the period	(11,561)
Foreign Currency Translation	(51)
Deferred revenues, ending balance	$ 851