Basis of Presentation (Details) $ in Thousands	3 Months Ended								9 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($) segment	Dec. 31, 2015 USD ($)
Class of Stock [Line Items]
Number of reportable segments | segment										1	1
Allowance for doubtful accounts receivable	$ 800				$ 400					$ 800	$ 400
Net sales	336,963	$ 340,845	$ 294,831	$ 301,951	295,096	$ 287,996	$ 286,850	$ 279,836		$ 1,274,589	$ 1,149,778	$ 1,027,447
Vendor concentration										43.00%	41.00%	44.00%
Advertising expense										$ 132,300	$ 101,200	$ 83,600
Research and development expense										11,300	9,800	9,500
Interest paid										14,300	15,000
Income taxes paid										105,100	54,500	54,900
Excess tax benefit from stock options									$ 1,400	1,500		1,500
Trade receivables, net	139,165				110,873					139,165	110,873
Other receivables	11,095				4,573					11,095	4,573
Total	150,260				115,446					$ 150,260	115,446
Common stock
Class of Stock [Line Items]
Stock split, conversion ratio										4.2
Reimbursement Receivable [Member]
Class of Stock [Line Items]
Reimbursement receivables	4,100				3,800					$ 4,100	3,800
Taxes Receivable [Member]
Class of Stock [Line Items]
Reimbursement receivables	$ 5,000				$ 500					5,000	500
Geographic Distribution, Domestic [Member]
Class of Stock [Line Items]
Net sales										1,229,000	1,109,300	990,500
Geographic Distribution, Foreign [Member]
Class of Stock [Line Items]
Net sales										$ 45,600	$ 40,500	$ 36,900
Computer Equipment [Member] | Maximum [Member]
Class of Stock [Line Items]
Property, plant and equipment, useful life										3 years
Furniture and Fixtures [Member] | Maximum [Member]
Class of Stock [Line Items]
Property, plant and equipment, useful life										10 years
Machinery and Equipment [Member] | Maximum [Member]
Class of Stock [Line Items]
Property, plant and equipment, useful life										15 years
Machinery and Equipment [Member] | Minimum
Class of Stock [Line Items]
Property, plant and equipment, useful life										7 years
Land, Buildings and Improvements [Member] | Maximum [Member]
Class of Stock [Line Items]
Property, plant and equipment, useful life										40 years
Computer Software, Intangible Asset [Member] | Maximum [Member]
Class of Stock [Line Items]
Finite-lived intangible asset, useful life										5 years
Top Two Customers [Member] | Credit Concentration Risk [Member]
Class of Stock [Line Items]
Concentration risk, percentage										60.00%
Top Two Customers [Member] | Customer Concentration Risk [Member]
Class of Stock [Line Items]
Concentration risk, percentage										59.00%	63.00%	69.00%