Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Provisional tax benefit recognized for remeasurement of deferred tax liability		$ 12,000
United States	$ 278,311	259,436	$ 234,646
Foreign	14,682	9,746	6,732
Total	292,993	269,182	241,378
Current [Abstract]
Federal	39,504	71,329	77,000
State and other	14,609	11,289	12,182
Current tax	54,113	82,618	89,182
Deferred [Abstract]
Federal	4,676	(6,643)	4,079
State and other	(15)	2,007	(330)
Deferred tax	4,661	(4,636)	3,749
Total	$ 58,774	$ 77,982	$ 92,931
Reconciliation of U.S. federal statutory tax rate to effective tax rate [Abstract]
Federal statutory rate (in hundredths)	21.00%	35.00%	35.00%
Change in valuation allowance (in hundredths)	(0.13%)	(0.06%)	0.10%
Stock-based compensation (as a percent)	(5.23%)	(4.67%)	(0.00%)
Federal tax reform (as a percent)	0.00%	(4.46%)	0.00%
Other, primarily state income tax rate (in hundredths)	4.42%	3.16%	3.40%
Total effective tax rate (in hundredths)	20.06%	28.97%	38.50%
Deferred tax assets [Abstract]
Product inventories	$ 5,413	$ 4,287
Accrued expenses	776	1,804
Leases	1,189	1,188
Share-based compensation	9,427	8,884
Uncertain tax positions	2,558	2,087
Net operating losses	5,058	5,441
Other	2,080	1,629
Total noncurrent	26,501	25,320
Less: Valuation allowance, non-current	(5,058)	(5,440)
Component reclassified for net presentation	(20,897)	(19,071)
Total non-current, net	546	809
Total deferred tax assets	546	809
Deferred tax liabilities [Abstract]
Trade discounts on purchases	2,094	1,520
Prepaid expenses	1,804	1,857
Intangible assets, primarily goodwill	30,988	29,348
Depreciation	14,924	10,870
Interest rate swaps	486	61
Total non-current	50,296	43,656
Component reclassified for net presentation	(20,897)	(19,071)
Deferred income taxes	29,399	24,585
Total deferred tax liabilities	29,399	24,585
Net deferred tax liability	28,853	23,776
Loss Carryforwards [Line Items]
Excess Tax Benefit (Tax Deficiency) from Share-based Compensation, Financing Activities	0	0	$ 7,370
Uncertain tax positions activity [Roll Forward]
Beginning balance	9,937	7,846	5,978
Increases for tax positions taken during a prior period	76	129	10
Increases for tax positions taken during the current period	3,809	3,260	2,819
Decreases resulting from the expiration of the statute of limitations	1,603	869	961
Decreases relating to settlements	40	429	0
Ending balance	12,179	9,937	7,846
Unrecognized tax benefits that, if recognized, would decrease the effective tax rate	9,622	7,900
Interest expense related to unrecognized tax benefits	207	249	$ 156
Accrued interest on unrecognized tax benefits	1,081	866
International Subsidiaries [Member]
Loss Carryforwards [Line Items]
Tax loss carry-forwards	18,972
Deferred tax asset, valuation allowance	5,058	5,441
Adjustments for New Accounting Pronouncement [Member]
Loss Carryforwards [Line Items]
Excess tax benefits recognized as a result of the adoption	$ 15,300	$ 12,600