Revenue Recognition - Contract Balances (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Major Customer [Line Items]
Revenue recognized related to deferred revenue and customer loyalty program	$ 3,500,000	$ 10,500,000
Contract liabilities	34,320,000	34,320,000	$ 30,574,000
Change		3,746,000
Contract assets	1,800,000	1,800,000		$ 400,000
Deferred revenue.
Revenue, Major Customer [Line Items]
Contract liabilities	17,335,000	17,335,000	15,850,000
Change		1,485,000
Customer loyalty program
Revenue, Major Customer [Line Items]
Contract liabilities	$ 16,985,000	16,985,000	$ 14,724,000
Change		$ 2,261,000
Divested stores located in China and Minnesota
Revenue, Major Customer [Line Items]
Amortization term of contract assets	10 years	10 years