Debt - Carrying amount and interest expense of notes (Details) - 1.375% Convertible Senior Notes - USD ($) $ in Thousands	12 Months Ended
	Dec. 29, 2018	Dec. 30, 2017
Liability component
Principal	$ 400,000	$ 400,000
Unamortized debt discount	(39,298)	(50,499)
Unamortized debt issuance costs	(5,931)	(7,622)
Net carrying amount	354,771	341,879
Equity component
Net carrying amount	$ 57,735	57,735
Effective interest rate	4.75%
Amortization period of debt discount and debt issuance costs	3 years 2 months 12 days
Interest expense related to the Notes
Contractual interest expense	$ 5,500	4,492
Amortization of debt discount	11,202	8,816
Amortization of debt issuance costs	1,690	1,330
Interest Expense, Total	$ 18,392	$ 14,638