XML 52 R41.htm IDEA: XBRL DOCUMENT v3.8.0.1
Debt - Carrying amount of notes and interest expense (Details) - 1.375% Convertible Senior Notes - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Apr. 01, 2017
Dec. 30, 2017
Mar. 06, 2017
Debt        
Total Debt issuance costs       $ 10,600
Liability component        
Principal $ 400,000   $ 400,000 $ 400,000
Unamortized debt discount (47,745)   (50,499)  
Unamortized debt issuance costs (7,206)   (7,622)  
Net carrying amount 345,049   341,879  
Equity component        
Net carrying amount $ 57,735   $ 57,735  
Effective interest rate 4.75%      
Amortization of debt discount and debt issuance costs 3 years 10 months 24 days      
Interest expense related to the Notes        
Contractual interest expense $ 1,390 $ 382    
Amortization of debt discount 2,753 754    
Amortization of debt issuance costs 416 115    
Interest Expense, Total $ 4,559 $ 1,251