Segment Information - Operating Revenue by Reportable Segment (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Segment Reporting, Revenue Reconciling Item [Line Items]
Total	$ 301,207	$ 278,828
Index [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total	163,435	144,613
Analytics [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total	112,420	110,263
All Other [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total	$ 25,352	$ 23,952

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Name:	us-gaap_Revenues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration