Financial instruments Aggregate accounts receivable, net of allowance for doubtful accounts (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 29, 2015		Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current and long term accounts receivable, allowances	$ 2,300,000		$ 2,400,000
Spain, Italy, Portugal, and Greece
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current and long-term accounts receivable (net of allowances of $7.1 million and $8.1 million at March 29, 2015 and December 31, 2014, respectively) in Greece, Italy, Spain and Portugal (1)	76,322,000	[1]	76,190,000	[1]
Percentage of total net current and long-term accounts receivable	26.60%		27.30%
Current and long term accounts receivable, allowances	7,100,000		8,100,000
Long-term portion of accounts receivable, net	$ 10,300,000		$ 11,300,000

[1] The long-term portion of accounts receivable, net from customers in Greece, Italy, Spain and Portugal at March 29, 2015 and December 31, 2014 was $10.3 million and $11.3 million, respectively, and is reported on the condensed consolidated balance sheet in other assets