Income Taxes (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jul. 01, 2017	Jul. 02, 2016	Jul. 01, 2017	Jul. 02, 2016
Income Taxes
Income tax benefit (provision)		$ (1,261)	$ (1,710)	$ 709	$ (1,975)
Effective income tax rate reconciliation
Effective income tax rate (as a percent)		7.10%	9.90%	(2.30%)	8.50%
Components of deferred taxes
Gross unrecognized tax benefits		$ 3,700		$ 3,700
Gross unrecognized tax benefits which would affect the effective tax rate if recognized		2,300		2,300
Amount of estimated decrease in unrecognized tax benefits		$ 1,900		$ 1,900
Norwegian | 2013
Income Taxes
Adjustments to taxable income excluding interest and penalties	$ 33,000