Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue	$ 1,179.0	$ 1,019.9	$ 911.7
Operating expense:
Cost of revenue	483.1	411.1	386.6
Sales and marketing	177.9	148.5	134.3
General and administrative	210.7	147.8	129.8
Depreciation and amortization	117.7	96.7	91.2
Total operating expense	989.4	804.1	741.9
Operating income	189.6	215.8	169.8
Non-operating income:
Interest expense, net	(8.7)	(1.8)	(3.6)
Gain on sale of investments, reclassified from other comprehensive income	1.2	1.0	3.2
Gain on sale of business	0.0	0.0	16.7
Gain on sale of a product line	0.0	10.5	0.0
Gain on sale of equity investments	19.5	5.6	0.0
Other income (expense), net	(3.1)	1.8	(5.0)
Non-operating income, net	8.9	17.1	11.3
Income before income taxes and equity in net loss of unconsolidated entities	198.5	232.9	181.1
Equity in net loss of unconsolidated entities	(0.9)	(2.1)	(1.3)
Income tax expense	45.6	47.8	42.9
Consolidated net income	$ 152.0	183.0	136.9
Net Income (Loss) Available to Common Stockholders, Basic		$ 183.0	$ 136.9
Net income per share:
Basic net income per share (in dollars per share)	$ 3.56	$ 4.30	$ 3.21
Diluted net income per share (in dollars per share)	3.52	4.25	3.18
Dividends per common share:
Dividends declared per common share (in dollars per share)	1.14	1.03	0.94
Dividends paid per common share (in dollars per share)	$ 1.12	$ 1.00	$ 0.92
Weighted average shares outstanding:
Basic (in shares)	42.7	42.6	42.7
Diluted (in shares)	43.2	43.0	43.0