Income taxes (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 29, 2013	Dec. 29, 2013
Income Taxes (Textual) [Abstract]
Unrecognized tax benefits that, if recognized, would impact effective tax rate	$ 44.8		$ 44.8		$ 46.5
Net benefit from the reversal of interest and penalty expense	1.4	1.6	3.8	19.0
Accrued interest and penalties payable related to unrecognized tax benefits	7.7		7.7		11.5
Estimated decrease in gross unrecognized tax positions within the next 12 months, maximum	$ 6.0		$ 6.0
Federal [Member]
Income Tax Examination [Line Items]
Tax years subject to examination			2011 through 2013 tax years remain subject to IRS examination
State [Member]
Income Tax Examination [Line Items]
Tax years subject to examination			The 2010 through 2013 tax years generally remain subject to examination by state authorities
UNITED KINGDOM
Income Tax Examination [Line Items]
Tax years subject to examination			the 2012 and 2013 tax years are subject to examination in the U.K