Debt - Carrying amount of notes and interest expense (Details) - 1.375% Convertible Senior Notes - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2017	Mar. 06, 2017
Debt
Total Debt issuance costs		$ 10,600
Liability component
Principal	$ 400,000	$ 400,000
Unamortized debt discount	(50,499)
Unamortized debt issuance costs	(7,622)
Net carrying amount	341,879
Equity component
Net carrying amount	$ 57,735
Effective interest rate	4.75%
Amortization of debt discount and debt issuance costs	4 years 2 months 12 days
Interest expense related to the Notes
Contractual interest expense	$ 4,492
Amortization of debt discount	8,816
Amortization of debt issuance costs	1,330
Interest Expense, Total	$ 14,638