Discontinued Operations - Income (Loss) From Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of Big Fish Games			$ 970.7
Big Fish Games
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net revenue	$ 0.0	$ 0.0		$ 0.0	$ 13.2
Operating expenses	0.0	0.0		0.0	8.4
Selling, general and administrative expense	0.8	0.7		2.8	5.6
Research and development	0.0	0.0		0.0	0.9
Total operating expense	0.8	0.7		2.8	14.9
Operating loss	(0.8)	(0.7)		(2.8)	(1.7)
Other expense	0.0	0.0		0.0	(0.1)
Total other income	0.0	0.0		0.0	219.4
(Loss) income from discontinued operations before provision for income taxes	(0.8)	(0.7)		(2.8)	217.7
Income tax benefit (provision)	0.4	(1.0)		0.9	(51.6)
(Loss) income from discontinued operations, net of tax	$ (0.4)	$ (1.7)		$ (1.9)	$ 166.1