Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jul. 01, 2012	Jul. 03, 2011	Jul. 01, 2012	Jul. 03, 2011
Earnings Per Share Reconciliation
Basic EPS - net income	$ 30,293	$ 26,060	$ 55,960	$ 48,372
Basic EPS - shares	37,993	38,883	37,939	38,686
Basic EPS - per share amount	$ 0.80	$ 0.67	$ 1.48	$ 1.25
Dilutive effect of 2.875% convertible debt - net income	455	451	910	902
Dilutive effect of 2.875% convertible debt - shares	3,033	3,033	3,033	3,033
Dilutive effect of 2.875% convertible debt - per share amount	$ (0.05)	$ (0.04)	$ (0.09)	$ (0.07)
Dilutive effect of stock options, restricted stock units, and shares issuable to Philips - net income	0	0	0	0
Dilutive effect of stock options, restricted stock units, and shares issuable to Philips - shares	588	650	607	640
Dilutive effect of stock options, restricted stock units, and shares issuable to Philips - per share amount	$ (0.01)	$ (0.01)	$ (0.02)	$ (0.02)
Diluted EPS - net income	$ 30,748	$ 26,511	$ 56,870	$ 49,274
Diluted EPS - shares	41,614	42,566	41,579	42,359
Diluted EPS - per share amount	$ 0.74	$ 0.62	$ 1.37	$ 1.16