Significant Accounting Policies - Summary of Revenue Recognized from Contract Liabilities and Remaining Balance (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Significant Accounting Policies [Line Items]
Deferred revenues, beginning balance	$ 2,810
Payments received in advance of services to be performed	5,666
Revenue recognized for services performed during the period	(4,951)
Foreign Currency Translation	20
Deferred revenues, ending balance	3,545
Information Services [Member]
Significant Accounting Policies [Line Items]
Deferred revenues, beginning balance	1,959
Payments received in advance of services to be performed	1,957
Revenue recognized for services performed during the period	(1,799)
Deferred revenues, ending balance	2,117
Post-trade Services [Member]
Significant Accounting Policies [Line Items]
Deferred revenues, beginning balance	851
Payments received in advance of services to be performed	3,709
Revenue recognized for services performed during the period	(3,152)
Foreign Currency Translation	20
Deferred revenues, ending balance	$ 1,428