Consolidated Statements of Cash Flows $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares
Proceeds from Term Facility	$ 0	$ 0	$ 185,000
Common stock, outstanding (in shares) | shares	40,192,901	40,232,210
Stockholders' Equity Attributable to Parent	$ 1,071,393	$ 639,470	410,180
Net income	650,624	366,738	261,575
Operating activities
Net income	650,624	366,738	261,575
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	28,287	27,967	27,885
Amortization	1,739	1,431	1,389
Share-based compensation	15,187	14,516	13,472
Provision (benefit) for doubtful accounts receivable, net of write-offs	1,134	(664)	(710)
Provision for inventory obsolescence, net of write-offs	3,798	2,362	1,310
(Benefit) provision for deferred income taxes	4,650	(2,542)	3,723
Losses (gains) on sales of property and equipment	(93)	38	(85)
Equity earnings in unconsolidated investments, net	(291)	(295)	(262)
Net losses on foreign currency transactions	325	1,748	1,347
(Recovery) impairment of goodwill and other assets	0	6,944	0
Other	473	410	3,313
Changes in operating assets and liabilities, net of effects of acquisitions:
Receivables	(79,940)	(38,688)	(15,691)
Product inventories	(525,207)	(42,447)	(14,165)
Prepaid expenses and other assets	(51,199)	(13,744)	(4,218)
Accounts payable	114,893	(9,212)	16,860
Accrued expenses and other current liabilities	149,110	83,019	3,033
Net cash provided by operating activities	313,490	397,581	298,776
Investing activities
Acquisition of businesses, net of cash acquired	(811,956)	(124,587)	(8,901)
Purchases of property and equipment, net of sale proceeds	(37,658)	(21,702)	(33,362)
Net cash used in investing activities	(849,614)	(146,289)	(42,263)
Financing activities
Proceeds from revolving line of credit	1,438,408	1,053,968	1,066,529
Payments on revolving line of credit	(974,506)	(1,145,616)	(1,415,988)
Proceeds from Long-term Lines of Credit	250,000	0	0
Proceeds from asset-backed financing	495,000	326,700	189,000
Payments on asset-backed financing	(430,000)	(321,700)	(182,500)
Proceeds from Term Facility	0	0	185,000
Payments on Term Facility	(9,250)	(9,250)	0
Proceeds from short-term borrowings and current portion of long-term debt	9,279	13,822	30,863
Payments on short-term borrowings and current portion of long-term debt	(9,377)	(13,698)	(28,286)
Payments on deferred and contingent acquisition consideration	(362)	(281)	(312)
Payments of deferred financing costs	(2,638)	(12)	(406)
Proceeds from stock issued under share-based compensation plans	17,197	19,824	18,574
Payments of cash dividends	(119,581)	(91,929)	(83,772)
Purchases of treasury stock	(138,039)	(76,199)	(23,188)
Net cash provided by (used in) financing activities	526,131	(244,371)	(244,486)
Effect of exchange rate changes on cash and cash equivalents	186	(1,376)	198
Change in cash and cash equivalents	(9,807)	5,545	12,225
Cash and cash equivalents at beginning of year	34,128	28,583	16,358
Cash and cash equivalents at end of year	$ 24,321	$ 34,128	$ 28,583
Common Stock [Member]
Common stock, outstanding (in shares) | shares	40,193,000	40,232,000	40,074,000
Stockholders' Equity Attributable to Parent	$ 40	$ 40	$ 40
Net income	0	0	0
Operating activities
Net income	0	0	0
Additional Paid-in Capital [Member]
Stockholders' Equity Attributable to Parent	551,963	519,579	485,239
Net income	0	0	0
Operating activities
Net income	0	0	0
Retained Deficit [Member]
Stockholders' Equity Attributable to Parent	526,874	133,870	(64,740)
Net income	650,624	366,738	261,575
Operating activities
Net income	650,624	366,738	261,575
Accumulated Other Comprehensive Income (Loss) [Member]
Stockholders' Equity Attributable to Parent	(7,484)	(14,019)	(10,359)
Net income	0	0	0
Operating activities
Net income	$ 0	$ 0	$ 0