Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
OPERATING ACTIVITIES
Net income	$ 173,305	$ 78,146
Adjustments to reconcile net income to net cash (used for) provided by operating activities:
Depreciation and amortization	23,278	24,393
Provision for credit losses	(1,250)	5,675
Stock-based compensation	23,989	11,397
Deferred income taxes	3,869	1,622
Excess tax benefit on stock-based compensation	(7,853)	(3,737)
Other operating activities	488	788
Changes in operating elements, net of acquisitions:
Receivables	(437,862)	(133,142)
Contract assets	(43,495)	8,713
Prepaid expenses and other	(26,692)	(11,038)
Accounts payable and outstanding checks	206,237	98,946
Accrued compensation	(27,977)	(23,879)
Accrued transportation expense	24,044	(7,294)
Accrued income taxes	34,087	5,196
Other accrued liabilities	(1,959)	1,829
Other assets and liabilities	1,099	884
Net cash (used for) provided by operating activities	(56,692)	58,499
INVESTING ACTIVITIES
Purchases of property and equipment	(5,435)	(7,841)
Purchases and development of software	(8,071)	(6,862)
Acquisitions, net of cash acquired	0	(223,617)
Net cash used for investing activities	(13,506)	(238,320)
FINANCING ACTIVITIES
Proceeds from stock issued for employee benefit plans	17,709	11,269
Stock tendered for payment of withholding taxes	(20,712)	(13,795)
Repurchase of common stock	(130,204)	(68,563)
Cash dividends	(70,030)	(69,871)
Proceeds from short-term borrowings	816,000	765,600
Payments on short-term borrowings	(566,000)	(587,600)
Net cash provided by financing activities	46,763	37,040
Effect of exchange rates on cash and cash equivalents	(2,750)	(10,505)
Net change in cash and cash equivalents	(26,185)	(153,286)
Cash and cash equivalents, beginning of period	243,796	447,858
Cash and cash equivalents, end of period	$ 217,611	$ 294,572