Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017	Dec. 29, 2018	Dec. 30, 2017
Income Taxes
Provision (benefit) for income taxes	$ (442)	$ (1,261)	$ 3,929	$ 709
Effective income tax rate (as a percent)	3.00%	7.10%	(10.70%)	(2.30%)
Federal statutory rate (as a percent)			21.00%			35.00%
Gross unrecognized tax benefits	$ 2,600		$ 2,600
Gross unrecognized tax benefits which would affect the effective tax rate if recognized	2,000		2,000
Unrecognized tax benefits as a result of a lapse in the statute of limitations			1,500
Amount of estimated decrease in unrecognized tax benefits	$ 400		400
2013 | Norwegian
Income Taxes
Adjustments to taxable income excluding interest and penalties			$ 30,000
Forecast | Norwegian
Income Taxes
Taxes payable during appeal process					$ 15,000