Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
OPERATING ACTIVITIES
Net income	$ 614,147	$ 358,614
Adjustments to reconcile net income to net cash provided by (used for) operating activities:
Depreciation and amortization	68,621	77,067
Provision for credit losses	3,979	12,701
Stock-based compensation	93,962	33,127
Deferred income taxes	(11,683)	(9,468)
Excess tax benefit on stock-based compensation	(10,830)	(17,127)
Other operating activities	1,384	13,104
Changes in operating elements, net of acquisitions:
Receivables	(1,290,485)	(367,538)
Contract assets	(220,889)	(56,131)
Prepaid expenses and other	(38,525)	12,331
Accounts payable and outstanding checks	595,036	186,755
Accrued compensation	35,413	16,458
Accrued transportation expense	165,580	46,396
Accrued income taxes	6,400	17,125
Other accrued liabilities	4,947	8,907
Other assets and liabilities	2,043	4,728
Net cash provided by operating activities	19,100	337,049
INVESTING ACTIVITIES
Purchases of property and equipment	(26,503)	(17,446)
Purchases and development of software	(26,062)	(22,815)
Acquisitions, net of cash acquired	(14,749)	(223,230)
Other investing activities	0	5,525
Net cash used for investing activities	(67,314)	(257,966)
FINANCING ACTIVITIES
Proceeds from stock issued for employee benefit plans	43,183	100,542
Stock tendered for payment of withholding taxes	(25,246)	(16,535)
Repurchase of common stock	(428,801)	(68,563)
Cash dividends	(208,926)	(207,428)
Payments on long-term borrowings	(2,048)	0
Proceeds from short-term borrowings	2,768,000	1,043,600
Payments on short-term borrowings	(2,136,251)	(1,126,600)
Net cash provided by (used for) financing activities	9,911	(274,984)
Effect of exchange rates on cash and cash equivalents	(2,844)	612
Net change in cash and cash equivalents	(41,147)	(195,289)
Cash and cash equivalents, beginning of period	243,796	447,858
Cash and cash equivalents, end of period	$ 202,649	$ 252,569