Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities
Net income	$ 128,224	$ 111,030	$ 97,330
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	16,373	14,495	13,359
Amortization	1,015	1,387	1,237
Share-based compensation	9,543	9,065	8,150
Excess tax benefits from share-based compensation	(7,706)	(5,524)	(4,611)
Provision for doubtful accounts receivable, net of write-offs	197	(539)	(930)
Provision for inventory obsolescence, net of write-offs	576	(687)	(416)
Provision for deferred income taxes	4,198	6,986	4,679
Losses on sales of property and equipment	230	179	97
Equity earnings in unconsolidated investments, net	(211)	(204)	(182)
Losses on foreign currency transactions	774	277	220
Other	(369)	206	108
Changes in operating assets and liabilities, net of effects of acquisitions:
Receivables	(16,656)	(12,751)	(10,085)
Product inventories	(10,848)	(30,409)	(27,291)
Prepaid expenses and other assets	(434)	(2,265)	504
Accounts payable	9,956	20,090	14,007
Accrued expenses and other current liabilities	11,188	10,479	8,912
Net cash provided by operating activities	146,050	121,815	105,088
Investing activities
Acquisition of businesses, net of cash acquired	(4,483)	(10,648)	(1,244)
Purchases of property and equipment, net of sale proceeds	(29,095)	(17,328)	(18,742)
Payments to fund credit agreement	(8,860)	0	0
Collections from credit agreement	4,557	0	0
Other investments, net	88	165	125
Net cash used in investing activities	(37,793)	(27,811)	(19,861)
Financing activities
Proceeds from revolving line of credit	911,712	820,720	678,936
Payments on revolving line of credit	(890,406)	(763,429)	(715,400)
Proceeds from asset-backed financing	143,400	121,600	70,000
Payments on asset-backed financing	(156,000)	(106,000)	(18,000)
Proceeds from short-term borrowings, long-term debt and other long-term liabilities	8,119	3,607	0
Payments on short-term borrowings, long-term debt and other long-term liabilities	(7,948)	(3,075)	(10)
Payments of deferred financing costs	(320)	(394)	(1,044)
Excess tax benefits from share-based compensation	7,706	5,524	4,611
Proceeds from stock issued under share-based compensation plans	18,269	13,530	21,409
Payments of cash dividends	(43,117)	(37,600)	(33,808)
Purchases of treasury stock	(99,219)	(136,466)	(96,179)
Net cash used in financing activities	(107,804)	(81,983)	(89,485)
Effect of exchange rate changes on cash and cash equivalents	(2,046)	(5,197)	(199)
Change in cash and cash equivalents	(1,593)	6,824	(4,457)
Cash and cash equivalents at beginning of year	14,830	8,006	12,463
Cash and cash equivalents at end of year	$ 13,237	$ 14,830	$ 8,006