Convertible Notes, Other Debts And Capital Leases - Convertible Note Roll Forward (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 28, 2018	Dec. 31, 2017	Dec. 31, 2015
Debt Instrument [Line Items]
Principal amount	$ 128,250	$ 128,250	$ 128,250
Less: Debt discount, net of amortization	(13,404)	(17,404)
Less: Debt issuance costs, net of amortization	(1,616)	(2,098)
Carrying amount	$ 113,230	$ 108,748
Remaining amortization period (years)	2 years 2 months 12 days	2 years 10 months 28 days
Effective interest rate on liability component	9.94%	9.94%
Carrying amount of equity component	$ 26,062	$ 26,062