Income Taxes - Deferred Taxes (Details) - USD ($) $ in Millions	Dec. 25, 2016	Dec. 27, 2015
Deferred tax assets:
Allowance for doubtful accounts	$ 0.4	$ 0.5
Sundry accruals	2.2	2.2
Vacation accrual	4.7	4.5
Stock-based compensation	5.2	5.1
Payroll related accruals	2.9	3.6
Lease accruals	4.5	5.1
Investments	2.0	2.0
Net operating loss carryforwards	124.8	98.4
Tax credit carryforwards	9.4	9.2
Deferred revenue	2.5	3.1
Reserves and other	11.9	7.0
Gross deferred tax assets	170.5	140.7
Valuation allowance	(133.1)	(102.1)
Total deferred tax assets, net of valuation allowance	37.4	38.6
Deferred tax liabilities:
Unearned revenue	(43.0)	(39.1)
Other intangibles	(7.0)	(3.2)
Property and equipment, principally due to differences in depreciation	(2.0)	(4.5)
Other	(2.7)	(2.3)
Total deferred tax liabilities	(54.7)	(49.1)
Net deferred tax asset (liability)	$ (17.3)	$ (10.5)