Condensed Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Statement [Abstract]
Revenue	$ 324.0	$ 258.9
Operating expense:
Cost of revenue	137.0	105.1
Sales and marketing	50.9	40.0
General and administrative	57.4	40.8
Depreciation and amortization	34.2	23.5
Total operating expense	279.5	209.4
Operating income	44.5	49.5
Non-operating expense, net:
Interest expense, net	(3.2)	(0.7)
Gain on sale of investments, reclassified from other comprehensive income	(0.4)	0.6
Other expense, net	(7.7)	(3.2)
Non-operating expense, net	(11.3)	(3.3)
Income before income taxes and equity in net loss of unconsolidated entities	33.2	46.2
Equity in net loss of unconsolidated entities	(0.8)	(1.5)
Income tax expense	8.5	11.5
Consolidated net income	$ 23.9	$ 33.2
Net income per share:
Basic (in dollars per share)	$ 0.56	$ 0.78
Diluted (in dollars per share)	0.55	0.77
Dividends declared (in dollars per share)	0.30	0.28
Dividends paid per common share (in dollars per share)	$ 0.30	$ 0.28
Weighted average shares outstanding:
Basic (in shares)	42.9	42.6
Diluted (in shares)	43.3	43.0