Segment Information - Operating Revenues by Reportable Segment (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating revenues	$ 549,842	$ 517,099	$ 498,180	$ 478,423	$ 443,661	$ 425,333	$ 409,616	$ 416,780	$ 2,043,544	$ 1,695,390	$ 1,557,796
Index [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating revenues									1,251,764	1,016,495	920,937
Analytics [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating revenues									544,299	513,808	496,925
ESG and Climate [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating revenues									166,192	111,364	90,659
All Other - Private Assets [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating revenues									$ 81,289	$ 53,723	$ 49,275