Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jul. 01, 2012	Jun. 30, 2013	Jul. 01, 2012
Earnings Per Share Reconciliation
Basic EPS - net income	$ 29,993	$ 30,293	$ 56,794	$ 55,960
Basic EPS - shares	39,496	37,993	39,012	37,939
Basic EPS - per share amount	$ 0.76	$ 0.80	$ 1.46	$ 1.48
Dilutive effect of 2.875% convertible debt - net income	325	455	780	910
Dilutive effect of 2.875% convertible debt - shares	2,164	3,033	2,595	3,033
Dilutive effect of 2.875% convertible debt - per share amount	$ (0.03)	$ (0.05)	$ (0.08)	$ (0.09)
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	621	588	620	607
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	$ 30,318	$ 30,748	$ 57,574	$ 56,870
Diluted EPS - shares	42,281	41,614	42,227	41,579
Diluted EPS - per share amount	$ 0.72	$ 0.74	$ 1.36	$ 1.37