Commitments and contingencies (Details) - Belgium - Foreign tax authority - EUR (€) € in Thousands		1 Months Ended		3 Months Ended
	Dec. 28, 2012	Dec. 31, 2013	Jan. 31, 2012	Jun. 28, 2014	Sep. 29, 2012
Commitments And Contingencies [Line Items]
Interest income earned on deposits related to tax assessment (in euros)					€ 1,583
2008
Commitments And Contingencies [Line Items]
Assessment received from Belgian tax authority (in euros)			€ 23,789	€ 30,131
2005
Commitments And Contingencies [Line Items]
Assessment received from Belgian tax authority (in euros)	€ 46,135
2009
Commitments And Contingencies [Line Items]
Assessment received from Belgian tax authority (in euros)	€ 35,567
2006
Commitments And Contingencies [Line Items]
Assessment received from Belgian tax authority (in euros)		€ 38,817
2007
Commitments And Contingencies [Line Items]
Assessment received from Belgian tax authority (in euros)		39,635
2010
Commitments And Contingencies [Line Items]
Assessment received from Belgian tax authority (in euros)		€ 43,117