Acquisitions - Aggregate Disclosure Related to Business Acquisitions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Cash paid, net of cash acquired	$ 0.0	$ 297.0	$ 58.0
Contingent acquisition consideration	14.0	45.0
Excess purchase price allocated to goodwill	3,280.0	3,280.0	2,956.0
Spicerack Media [Member]
Business Acquisition [Line Items]
Goodwill deductible for income tax purposes	$ 13.0
Aggregate total 2018
Business Acquisition [Line Items]
Total consideration		46.0
Cash paid, net of cash acquired		34.0
Contingent acquisition consideration		9.0
Allocation of purchase price to intangible assets, net		$ 42.0
Weighted average useful life of acquired intangible assets		9 years 4 months 24 days
Excess purchase price allocated to goodwill		$ 11.0
Aggregate total 2017
Business Acquisition [Line Items]
Total consideration			66.0
Cash paid, net of cash acquired			$ 58.0
Contingent acquisition consideration		8.0
Allocation of purchase price to intangible assets, net		56.0
Weighted average useful life of acquired intangible assets			8 years 3 months 18 days
Excess purchase price allocated to goodwill		$ 13.0
Minimum
Business Acquisition [Line Items]
Discount rate		9.00%
Royalty rate		1.00%
Maximum
Business Acquisition [Line Items]
Discount rate		20.00%
Royalty rate		16.00%