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Convertible Senior Notes - Components of Convertible Senior Notes (Details) - 1.75% Convertible Senior Notes Due June 1, 2018 - USD ($)
Dec. 30, 2017
Dec. 31, 2016
May 30, 2013
Debt Instrument [Line Items]      
Principal $ 150,000,000 $ 150,000,000 $ 150,000,000.0
Unamortized discount (4,670,000) (15,114,000)  
Debt issuance costs (402,000) (1,300,000)  
Net carrying amount $ 144,928,000 $ 133,586,000