Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash Flows from Operating Activities
Net income	$ 268,550	$ 319,466	$ 219,923
Adjustments to reconcile net income to net cash provided by operations:
Depreciation and amortization	59,051	56,583	45,205
Stock option expense	22,502	18,422	14,831
Deferred payroll taxes	(18,175)	36,350
(Payments) Litigation settlements	(9,440)
Proceeds Litigation settlements		2,684	6,000
Noncash portion of long-term incentive compensation	7,745	7,208	5,740
Provision/(benefit) for deferred income taxes (Note 11)	2,400	1,433	(2,770)
Noncash directors' compensation	1,173	1,171	767
Amortization of debt issuance costs	306	306	306
Loss on sale of transportation equipment (Note 19)			2,266
Changes in operating assets and liabilities:
(Increase)/decrease in accounts receivable	(8,431)	12,773	(19,247)
(Increase)/decrease in inventories	(3,014)	367	(1,757)
Increase in prepaid expenses	(6,511)	(3,027)	(3,491)
Increase in accounts payable and other current liabilities	9,832	19,096	28,417
Change in current income taxes	(20,401)	13,525	161
Net change in lease assets and liabilities	(44)	1,206	3,108
Increase in other assets	(10,305)	(11,834)	(11,963)
Increase in other liabilities	12,074	12,323	12,354
Other sources	1,285	1,237	1,399
Net cash provided by operating activities	308,597	489,289	301,249
Cash Flows from Investing Activities
Capital expenditures	(58,675)	(58,831)	(53,022)
Business combinations, net of cash acquired (Note 7)		(3,600)	(138,010)
Other sources	918	871	272
Net cash used by investing activities	(57,757)	(61,560)	(190,760)
Cash Flows from Financing Activities
Purchases of treasury stock	(576,042)	(175,594)	(92,631)
Proceeds from revolving line of credit	210,300	174,900	482,900
Payments on revolving line of credit	(25,300)	(264,900)	(482,100)
Proceeds from exercise of stock options	35,848	50,382	34,380
Dividends paid	(22,016)	(21,079)	(19,788)
Capital stock surrendered to pay taxes on stock-based compensation	(15,129)	(25,328)	(28,474)
Change in cash overdraft payable	11,884	(9,849)	(3,927)
Other (uses)/sources	(165)	256	478
Net cash used by financing activities	(380,620)	(271,212)	(109,162)
(Decrease)/Increase in Cash and Cash Equivalents	(129,780)	156,517	1,327
Cash and cash equivalents at beginning of year	162,675	6,158	4,831
Cash and cash equivalents at end of period	$ 32,895	$ 162,675	$ 6,158