Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities
Net income	$ 148,603	$ 128,224	$ 111,030
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	20,338	16,373	14,495
Amortization	1,639	1,015	1,387
Share-based compensation	9,902	9,543	9,065
Excess tax benefits from share-based compensation	(7,370)	(7,706)	(5,524)
Provision for doubtful accounts receivable, net of write-offs	(155)	197	(539)
Provision for inventory obsolescence, net of write-offs	(448)	576	(687)
Provision for deferred income taxes	3,749	4,198	6,986
(Gains) losses on sale of property and equipment	(320)	230	179
Equity earnings in unconsolidated investments, net	(156)	(211)	(204)
Net losses on foreign currency transactions	679	774	277
Impairment of goodwill and other non-operating assets	4,113	500	0
Other	923	(869)	206
Changes in operating assets and liabilities, net of effects of acquisitions:
Receivables	(5,666)	(16,656)	(12,751)
Product inventories	(8,050)	(10,848)	(30,409)
Prepaid expenses and other assets	(3,077)	(434)	(2,265)
Accounts payable	(17,896)	9,956	20,090
Accrued expenses and other current liabilities	18,570	11,188	10,479
Net cash provided by operating activities	165,378	146,050	121,815
Investing activities
Acquisition of businesses, net of cash acquired	(19,730)	(4,483)	(10,648)
Purchases of property and equipment, net of sale proceeds	(34,352)	(29,095)	(17,328)
Payments to fund credit agreement	(5,322)	(8,860)	0
Collections from credit agreement	3,737	4,557	0
Other investments, net	24	88	165
Net cash used in investing activities	(55,643)	(37,793)	(27,811)
Financing activities
Proceeds from revolving line of credit	1,154,090	911,712	820,720
Payments on revolving line of credit	(1,072,557)	(890,406)	(763,429)
Proceeds from asset-backed financing	155,000	143,400	121,600
Payments on asset-backed financing	(126,500)	(156,000)	(106,000)
Proceeds from short-term borrowings, long-term debt and other long-term liabilities	18,442	8,119	3,607
Payments on short-term borrowings, long-term debt and other long-term liabilities	(19,037)	(7,948)	(3,075)
Payments of deferred financing costs	(69)	(320)	(394)
Excess tax benefits from share-based compensation	7,370	7,706	5,524
Proceeds from stock issued under share-based compensation plans	11,752	18,269	13,530
Payments of cash dividends	(49,749)	(43,117)	(37,600)
Purchases of treasury stock	(178,414)	(99,219)	(136,466)
Net cash used in financing activities	(99,672)	(107,804)	(81,983)
Effect of exchange rate changes on cash and cash equivalents	(1,344)	(2,046)	(5,197)
Change in cash and cash equivalents	8,719	(1,593)	6,824
Cash and cash equivalents at beginning of year	13,237	14,830	8,006
Cash and cash equivalents at end of year	$ 21,956	$ 13,237	$ 14,830