Discontinued Operations - Income (Loss) From Discontinued Operations (Details) - Big Fish Games - Discontinued Operations, Held-for-sale - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net revenue	$ 466.0	$ 486.2	$ 413.7
Operating expenses	369.0	398.9	340.1
Selling, general and administrative expense	27.8	20.9	15.2
Research and development	39.6	39.0	39.4
Transaction expense, net	4.7	5.8	21.7
Total operating expense	441.1	464.6	416.4
Operating income (loss)	24.9	21.6	(2.7)
Other expense	(1.7)	(0.9)	(0.6)
Income (loss) from discontinued operations before provision for income taxes	23.2	20.7	(3.3)
Income tax provision	(5.1)	(9.3)	(2.3)
Income (loss) from discontinued operations, net of tax	$ 18.1	$ 11.4	$ (5.6)