Convertible Senior Notes - Interest Expense Recognized Related to Notes Prior to Capitalization of Interest (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 28, 2015	Mar. 29, 2014
Debt Disclosure [Abstract]
Contractual interest expense	$ 656infn_ContractualInterestExpense	$ 657infn_ContractualInterestExpense
Amortization of debt issuance costs	177us-gaap_AmortizationOfFinancingCosts	160us-gaap_AmortizationOfFinancingCosts
Amortization of debt discount	2,057	1,860
Total interest expense	$ 2,890us-gaap_InterestExpenseDebt	$ 2,677us-gaap_InterestExpenseDebt

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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