Segment Information - Sales to External Customers and Gross Profit (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 30, 2014	Mar. 31, 2013
Segment Reporting Information [Line Items]
Sales to external customers	$ 226,264	$ 221,189
Gross profit	106,324	102,551
Industry [Member]
Segment Reporting Information [Line Items]
Sales to external customers	106,437	99,064
Gross profit	56,132	50,514
Science [Member]
Segment Reporting Information [Line Items]
Sales to external customers	119,827	122,125
Gross profit	$ 50,192	$ 52,037