Financial instruments Aggregate accounts receivable, net of allowance for doubtful accounts (Details) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 27, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Doubtful Accounts Receivable		$ 8,900	$ 8,800
Spain, Italy, Portugal, and Greece
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Doubtful Accounts Receivable		7,900	8,100
Current and long-term accounts receivable (net of allowances of $7.9 million and $8.1 million at September 27, 2015 and December 31, 2014, respectively) in Greece, Italy, Spain and Portugal	[1]	$ 72,128	$ 76,190
Percentage of total net current and long-term accounts receivable - Greece, Italy, Spain and Portugal		26.10%	27.30%
Long-term portion of accounts receivable, net		$ 16,200	$ 11,300

[1] (1) The long-term portion of accounts receivable, net from customers in Greece, Italy, Spain and Portugal at September 27, 2015 and December 31, 2014 was $16.2 million and $11.3 million, respectively, and is reported on the condensed consolidated balance sheet in other assets.