SUPPLEMENTAL BALANCE SHEET INFORMATION (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 29, 2014	Mar. 30, 2013	Dec. 28, 2013
Accrued Warranty Obligations
Balance at beginning of year	$ 3,285	$ 3,528
Additions charged to cost of sales	906	596
Warranty claims	(781)	(742)
Balance at end of period	3,410	3,382
Accrued Expenses and Other Current Liabilities
Deferred revenue	14,252		13,609
Deferred lease liability	5,365		5,448
Accrued and deferred taxes	5,309		3,130
Short-term accrued warranty obligations	3,229		3,093
Other	9,367		10,061
Accrued expenses and other current liabilities, total	37,522		35,341
Accumulated Other Comprehensive Loss
Cumulative foreign currency translation losses	(1,849)		(2,296)
Unrecognized net pension losses, net of tax	(2,356)		(2,399)
Unrealized gains on marketable securities, net of tax	1,096		1,076
Accumulated other comprehensive loss	$ (3,109)		$ (3,619)
Photonics and Optics | All products other than filters, gratings, laser beam profilers and dental CAD/CAM scanners
Warranty
Product warranty period	1 year
Photonics and Optics | Original equipment manufacturer | Minimum
Warranty
Product warranty period	15 months
Photonics and Optics | Original equipment manufacturer | Maximum
Warranty
Product warranty period	19 months
Optics | Filters and gratings products
Warranty
Product warranty period	90 days
Photonics | Laser beam profilers and dental CAD/CAM scanners
Warranty
Product warranty period	2 years
Lasers Division | Minimum
Warranty
Product warranty period	90 days
Lasers Division | Maximum
Warranty
Product warranty period	2 years