Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating activities
Net income	$ 165,674	$ 146,031
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	17,947	15,020
Amortization	1,132	1,288
Share-based compensation	9,496	7,373
Excess tax benefits from share-based compensation	0	(6,582)
Equity earnings in unconsolidated investments, net	(121)	(113)
Other	1,074	3,799
Changes in operating assets and liabilities, net of effects of acquisitions:
Receivables	(90,204)	(71,936)
Product inventories	9,057	23,624
Prepaid expenses and other assets	(1,523)	(1,094)
Accounts payable	(27,328)	(49,479)
Accrued expenses and other current liabilities	26,816	75,239
Net cash provided by operating activities	112,020	143,170
Investing activities
Acquisition of businesses, net of cash acquired	(6,879)	(19,314)
Purchase of property and equipment, net of sale proceeds	(37,709)	(30,388)
Payments to fund credit agreement	0	(3,852)
Collections from credit agreement	0	3,300
Other investments, net	4	21
Net cash used in investing activities	(44,584)	(50,233)
Financing activities
Proceeds from revolving line of credit	918,338	873,854
Payments on revolving line of credit	(857,609)	(866,801)
Proceeds from asset-backed financing	156,600	145,000
Payments on asset-backed financing	(97,800)	(90,000)
Proceeds from short-term borrowings, long-term debt and other long-term liabilities	25,001	15,705
Payments on short-term borrowings, long-term debt and other long term liabilities	(17,497)	(16,107)
Payments of deferred and contingent acquisition consideration	(199)	0
Payments of deferred financing costs	(909)	0
Purchase of redeemable noncontrolling interest	(2,573)	0
Excess tax benefits from share-based compensation	0	6,582
Proceeds from stock issued under share-based compensation plans	8,647	10,978
Payments of cash dividends	(43,165)	(37,007)
Purchases of treasury stock	(141,580)	(117,901)
Net cash used in financing activities	(52,746)	(75,697)
Effect of exchange rate changes on cash and cash equivalents	(248)	(185)
Change in cash and cash equivalents	14,442	17,055
Cash and cash equivalents at beginning of period	21,956	13,237
Cash and cash equivalents at end of period	$ 36,398	$ 30,292