Income taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 30, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Allowance for Doubtful Accounts	$ 2,013	$ 2,685
Deferred tax assets, Capital leases	2,158	3,295
Deferred tax assets, Rent, Noncurrent	9,452	11,905
Deferred Tax Assets, Property, Plant and Equipment	375	0
Deferred tax liabilities, Property and equipment	0	1,977
Deferred tax assets, Deferred compensation and long-term incentive accrual	15,033	19,900
Deferred Tax Assets, Tax Deferred Expense, Other	16,676	27,874
Deferred tax assets, Deferred revenue, Noncurrent	9,049	12,609
Deferred tax assets, Real estate rserves, Noncurrent	1,153	1,264
Deferred tax liabilities, Franchise rights and other intangibles	372,988	551,679
Deferred tax assets, Unused foreign tax credits	1,912	11,457
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Accrued Liabilities	4,697	5,368
Deferred tax assets, Other, Noncurrent	224	1,758
Deferred tax liabilities, Other, Noncurrent	0	0
Deferred tax assets, Gross, Noncurrent	62,742	98,115
Deferred tax liabilities, Net, Noncurrent	372,988	553,656
Deferred tax assets, Valuation allowance, Noncurrent	(899)	(1,131)
Deferred tax assets, Total noncurrent	$ 61,843	$ 96,984