Revenue Recognition - Contract Balances (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jul. 01, 2018	Jul. 01, 2018	Jan. 01, 2018
Revenue, Major Customer [Line Items]
Revenue recognized related to deferred revenue and customer loyalty program	$ 3,100	$ 7,000
Contract liabilities	33,555	33,555	$ 30,574
Change		2,981
Deferred revenue.
Revenue, Major Customer [Line Items]
Contract liabilities	17,755	17,755	15,850
Change		1,905
Customer loyalty program
Revenue, Major Customer [Line Items]
Contract liabilities	$ 15,800	15,800	$ 14,724
Change		$ 1,076