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Contractual Obligations and Other Contingencies (Details)
12 Months Ended
Dec. 31, 2017
USD ($)
financial_covenant
Jan. 02, 2018
USD ($)
Dec. 31, 2016
USD ($)
Short-term Debt [Line Items]      
Bank line of credit $ 300,000,000    
Borrowings under line of credit $ 35,382,000   $ 0
Number of financial covenants | financial_covenant 1    
Change in bank line of credit $ 77,600,000    
Remaining borrowing capacity 187,000,000    
Standby Letter of Credit      
Short-term Debt [Line Items]      
Irrevocable standby letter of credit, outstanding $ 77,600,000    
Standby Letter of Credit | Subsequent Event      
Short-term Debt [Line Items]      
Irrevocable standby letter of credit, outstanding   $ 65,900,000  
LIBOR      
Short-term Debt [Line Items]      
Basis spread on variable rate 0.75%    
Prime Rate or Overnight Bank Funding Rate      
Short-term Debt [Line Items]      
Basis spread on variable rate 0.50%