Income Taxes - Deferred Taxes (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 25, 2016
Deferred tax assets:
Allowance for doubtful accounts	$ 0.2	$ 0.4
Sundry accruals	1.5	2.2
Vacation accrual	3.2	4.7
Stock-based compensation	3.1	5.2
Payroll related accruals	2.1	2.9
Lease accruals	2.5	4.5
Investments	1.3	2.0
Net operating loss carryforwards	95.7	124.8
Tax credit carryforwards	9.5	9.4
Deferred revenue	1.9	2.5
Reserves and other	6.1	11.9
Gross deferred tax assets	127.1	170.5
Valuation allowance	(87.5)	(133.1)
Total deferred tax assets, net of valuation allowance	39.6	37.4
Deferred tax liabilities:
Unearned revenue	(38.8)	(43.0)
Other intangibles	(5.4)	(7.0)
Property and equipment, principally due to differences in depreciation	(0.7)	(2.0)
Other	(1.7)	(2.7)
Total deferred tax liabilities	(46.6)	(54.7)
Net deferred tax liability	$ (7.0)	$ (17.3)