Discontinued Operations (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Jan. 09, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Aug. 31, 2018	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax				$ 219.5
Proceeds from sale of Big Fish Games				970.7	$ 0.0
Disposal Group, Including Discontinued Operation, Cash and Cash Equivalents	$ 0.3
Stock-based compensation		$ 3.9	$ 3.9	16.5	17.5
Disposal Group, Including Discontinued Operations, Transaction Expense				14.1
Gain (Loss) on Disposition of Business				219.5	0.0
Disposal Group, Including Discontinued Operation, Accounts, Notes and Loans Receivable, Net	34.7
Disposal Group, Including Discontinued Operation, Game Software Development, Net, Current	6.7
Disposal Group, Including Discontinued Operation, Other Assets, Current	17.0
Disposal Group, Including Discontinued Operation, Property, Plant and Equipment, Noncurrent	17.8
Disposal Group, Including Discontinued Operation, Game Software Development, Net, Noncurrent	13.8
Disposal Group, Including Discontinued Operation, Goodwill, Noncurrent	530.7
Disposal Group, Including Discontinued Operation, Intangible Assets, Noncurrent	238.4
Disposal Group, Including Discontinued Operation, Other Assets, Noncurrent	24.0
Disposal Group, Including Discontinued Operation, Accounts Payable, Current	(8.5)
Disposal Group, Including Discontinued Operation, Accrued Liabilities, Current	(22.6)
Disposal Group, Including Discontinued Operation, Deferred Revenue, Current	(44.2)
Disposal Group, Including Discontinued Operation, Deferred Tax Liabilities	(52.0)
Disposal Group, Including Discontinued Operation, Other Liabilities, Noncurrent	(4.9)
Carrying Value of Disposal Group	751.2
Earnout Payment, Financing Activity						$ 5.2	$ 34.2
Discontinued Operation, Tax Effect of Discontinued Operation				51.2
Other Adjustments to Income, Discontinued Operations				5.2
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent							$ 168.3
Big Fish Games [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of Big Fish Games	$ 990.0
Stock-based compensation				3.4
Disposal Group, Including Discontinued Operation, Revenue		0.0	118.0	13.2	342.5
Disposal Group, Including Discontinued Operation, Operating Expense		0.0	95.3	8.4	271.5
Disposal Group, Including Discontinued Operation, General and Administrative Expense		0.7	6.7	5.6	18.9
Disposal Group, Including Discontinued Operations, Research And Development Expense		0.0	9.8	0.9	30.0
Disposal Group, Including Discontinued Operations, Transaction Expense		0.0	0.2	0.0	0.6
Disposal Group, Including Discontinued Operations, Total Operating Expense		0.7	112.0	14.9	321.0
Disposal Group, Including Discontinued Operation, Operating Income (Loss)		(0.7)	6.0	(1.7)	21.5
Disposal Group, Including Discontinued Operation, Other Expense		0.0	(1.2)	(0.1)	(1.6)
Disposal Group, Including Discontinued Operation, Other Income		0.0	(1.2)	219.4	(1.6)
Gain (Loss) on Disposition of Business		0.0	0.0	219.5	0.0
Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, before Income Tax		(0.7)	4.8	217.7	19.9
Discontinued Operation, Tax Effect of Income (Loss) from Discontinued Operation During Phase-out Period		(1.0)	(1.2)	(51.6)	(5.6)
Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, Net of Tax		$ (1.7)	$ 3.6	$ 166.1	$ 14.3