Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
OPERATING ACTIVITIES
Net income	$ 270,348	$ 173,305
Adjustments to reconcile net income to net cash used for operating activities:
Depreciation and amortization	22,486	23,278
Provision for credit losses	1,672	(1,250)
Stock-based compensation	24,606	23,989
Deferred income taxes	(2,916)	3,869
Excess tax benefit on stock-based compensation	(4,965)	(7,853)
Other operating activities	42	488
Changes in operating elements, net of acquisitions:
Receivables	(424,025)	(437,862)
Contract assets	(51,439)	(43,495)
Prepaid expenses and other	(11,924)	(26,692)
Accounts payable and outstanding checks	143,980	206,237
Accrued compensation	(79,885)	(27,977)
Accrued transportation expense	42,825	24,044
Accrued income taxes	48,502	34,087
Other accrued liabilities	8,099	(1,959)
Other assets and liabilities	(1,334)	1,099
Net cash used for operating activities	(13,928)	(56,692)
INVESTING ACTIVITIES
Purchases of property and equipment	(10,046)	(5,435)
Purchases and development of software	(16,183)	(8,071)
Other investing activities	2,250	0
Net cash used for investing activities	(23,979)	(13,506)
FINANCING ACTIVITIES
Proceeds from stock issued for employee benefit plans	25,366	17,709
Stock tendered for payment of withholding taxes	(16,462)	(20,712)
Repurchase of common stock	(161,279)	(130,204)
Cash dividends	(72,855)	(70,030)
Proceeds from long-term borrowings	200,000	0
Proceeds from short-term borrowings	1,062,000	816,000
Payments on short-term borrowings	(1,015,000)	(566,000)
Net cash provided by financing activities	21,770	46,763
Effect of exchange rates on cash and cash equivalents	1,533	(2,750)
Net change in cash and cash equivalents	(14,604)	(26,185)
Cash and cash equivalents, beginning of period	257,413	243,796
Cash and cash equivalents, end of period	$ 242,809	$ 217,611