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Summary of Significant Accounting Policies - Concentration of Credit Risk (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 30, 2017
Dec. 31, 2016
Roll forward of the accounts receivable allowances    
Balance at beginning of period $ 4,253 $ 3,648
Increases to reserves 6,774 2,761
Amounts written off (3,660) (2,156)
Effects of foreign currency translation 11  
Balance at end of period 7,378 4,253
Roll forward of the unbilled receivables allowances    
Balance at beginning of period 1,720 2,354
Increases to reserves 2,255 2,102
Amounts written off (2,235) (2,736)
Effects of foreign currency translation 6  
Balance at end of period $ 1,746 $ 1,720