Changes in shareholders' equity Reconciliation of basic to diluted weighted average common shares outstanding (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 28, 2015	Jun. 29, 2014	Jun. 28, 2015	Jun. 29, 2014
Equity [Abstract]
Basic (in shares)	41,560	41,380	41,514	41,321
Dilutive effect of share-based awards (in shares)	473	413	470	442
Dilutive effect of 3.875% Convertible Notes and warrants (in shares)	6,048	4,599	5,704	4,308
Diluted (in shares)	48,081	46,392	47,688	46,071