Segment Information - Goodwill and Total Assets (Details) (USD $) In Thousands, unless otherwise specified	Mar. 29, 2015	Dec. 31, 2014	Mar. 30, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Goodwill	$ 166,923	$ 170,773	$ 184,260	$ 136,152
Total Assets	1,359,840	1,417,818
Industry [Member]
Segment Reporting Information [Line Items]
Goodwill	78,867	76,858
Total Assets	458,780	444,168
Science [Member]
Segment Reporting Information [Line Items]
Goodwill	88,056	93,915
Total Assets	416,403	470,899
Corporate Eliminations [Member]
Segment Reporting Information [Line Items]
Total Assets	$ 484,657	$ 502,751