Changes in shareholders' equity Reconciliation of basic to diluted weighted average common shares outstanding (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2015	Sep. 28, 2014	Sep. 27, 2015	Sep. 28, 2014
Equity [Abstract]
Basic (in shares)	41,597	41,399	41,542	41,347
Dilutive effect of share-based awards (in shares)	511	440	483	441
Dilutive effect of 3.875% Convertible Notes and warrants (in shares)	6,424	4,789	5,944	4,468
Diluted (in shares)	48,532	46,628	47,969	46,256