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Components of Convertible Senior Notes (Detail) - USD ($)
$ in Thousands
Oct. 01, 2017
Dec. 31, 2016
Dec. 12, 2016
Debt Instrument      
Net carrying amount of convertible debt $ 362,595 $ 352,669  
1.25% Convertible Senior Unsecured Notes Due December 15, 2023      
Debt Instrument      
Debt principal 460,000 460,000 $ 460,000
Unamortized discount 97,405 107,331  
Net carrying amount of convertible debt $ 362,595 $ 352,669