ACCOUNTING POLICIES (Details 6)	3 Months Ended
	Mar. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)
Revenue recognition
Number of principal segments (in segment) | segment	2
Product delivery period from date of shipment, minimum	1 day
Product delivery period from date of shipment, maximum	8 days
Advertising revenue as a percentage of total revenues	2.00%		2.00%
Allowance for returns	$ 15,423,000	$ 17,391,000
Deferred revenue	41,712,000	46,468,000
Deferred revenue, revenue recognized			$ 35,000,000
Cost of goods sold
Total revenue, net	$ 445,331,000		$ 432,435,000
Total revenue, net (as a percent)	100.00%		100.00%
Cost of goods sold
Product costs and other cost of goods sold	$ 333,521,000		$ 326,803,000
Fulfillment and related costs	17,941,000		18,725,000
Total cost of goods sold	$ 351,462,000		$ 345,528,000
Product costs and other cost of goods sold (as a percent)	75.00%		76.00%
Fulfillment and related costs (as a percent)	4.00%		4.00%
Total cost of goods sold (as a percent)	79.00%		80.00%
Gross profit	$ 93,869,000		$ 86,907,000
Gross profit (as a percent)	21.00%		20.00%
Advertising expense
Advertising expense	$ 68,900,000		$ 33,800,000
Prepaid advertising expense	834,000	987,000
Self-funded health insurance
Self-funded health insurance reserve	$ 1,600,000	1,000,000
Income taxes
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Transition Tax For Accumulated Foreign Earnings, Provisional Income Tax Expense		25,300,000
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Change In Tax Rate, Deferred Tax Asset, Provisional Income Tax Expense		25,200,000
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Transition Tax For Accumulated Foreign Earnings, Provisional Liability		41,000
Club O loyalty program, gold
Club O loyalty program
Expiration period of Club O reward dollars after expiration of the customer's membership	90 days
Club O Membership Fees and Reward Points [Member]
Revenue recognition
Deferred revenue	$ 5,933,000	$ 6,503,000