Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenues:
Total revenues	$ 1,104,038	$ 1,018,891
Costs and expenses:
Cost of services and product development	334,467	341,278
Selling, general and administrative	487,255	496,639
Depreciation	25,750	22,517
Amortization of intangibles	30,514	32,179
Acquisition and integration charges	640	1,560
Total costs and expenses	878,626	894,173
Operating income	225,412	124,718
Interest expense, net	(26,149)	(26,349)
Other income (expense), net	15,490	(1,515)
Income before income taxes	214,753	96,854
Provision for income taxes	50,653	21,757
Net income	$ 164,100	$ 75,097
Net income per share:
Basic (in dollars per share)	$ 1.86	$ 0.84
Diluted (in dollars per share)	$ 1.84	$ 0.83
Weighted average shares outstanding:
Basic (in shares)	88,352	89,219
Diluted (in shares)	89,139	90,066
Research
Revenues:
Total revenues	$ 979,732	$ 909,291
Conferences
Revenues:
Total revenues	24,802	13,870
Consulting
Revenues:
Total revenues	$ 99,504	$ 95,730