XML 68 R57.htm IDEA: XBRL DOCUMENT v3.7.0.1
Shareholders' equity - Additional Information (Details) - USD ($)
$ / shares in Units, $ in Thousands, shares in Millions
3 Months Ended 6 Months Ended
Jul. 02, 2017
Apr. 02, 2017
Jun. 26, 2016
Jul. 02, 2017
Jun. 26, 2016
Dec. 31, 2016
Shareholders Equity [Line Items]            
Investment warrants, exercise price (in dollars per share)   $ 74.65        
Conversion of convertible notes, shares issued upon conversion 0.5   1.5 0.4 2.2  
Convertible notes - redeemable equity component $ 0     $ 0   $ 1,824
Equity Option            
Shareholders Equity [Line Items]            
Weighted average antidilutive shares which were not included in the calculation of earnings per share 0.7   5.0 0.6 5.1  
Convertible Note            
Shareholders Equity [Line Items]            
Weighted average antidilutive shares which were not included in the calculation of earnings per share 0.5   1.7 0.5 2.6