Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
OPERATING ACTIVITIES
Net income	$ 358,614	$ 477,862
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	77,067	75,122
Provision for credit losses	12,701	642
Stock-based compensation	33,127	40,657
Deferred income taxes	(9,468)	(3,360)
Excess tax benefit on stock-based compensation	(17,127)	(6,908)
Other operating activities	13,104	(4,471)
Changes in operating elements, net of acquisitions:
Receivables	(367,538)	104,108
Contract assets	(56,131)	9,067
Prepaid expenses and other	12,331	(18,940)
Accounts payable and outstanding checks	186,755	3,871
Accrued compensation	16,458	(45,319)
Accrued transportation expense	46,396	(5,323)
Accrued income taxes	17,125	(7,042)
Other accrued liabilities	8,907	5,210
Other assets and liabilities	4,728	(1,318)
Net cash provided by operating activities	337,049	623,858
INVESTING ACTIVITIES
Purchases of property and equipment	(17,446)	(26,661)
Purchases and development of software	(22,815)	(24,282)
Acquisitions, net of cash acquired	(223,230)	(59,188)
Other investing activities	5,525	16,625
Net cash used for investing activities	(257,966)	(93,506)
FINANCING ACTIVITIES
Proceeds from stock issued for employee benefit plans	100,542	40,442
Stock tendered for payment of withholding taxes	(16,535)	(14,352)
Repurchase of common stock	(68,563)	(241,303)
Cash dividends	(207,428)	(207,865)
Proceeds from long-term borrowings	0	929,000
Payments on long-term borrowings	0	(1,018,000)
Proceeds from short-term borrowings	1,043,600	14,000
Payments on short-term borrowings	(1,126,600)	(19,000)
Net cash used for financing activities	(274,984)	(517,078)
Effect of exchange rates on cash and cash equivalents	612	(7,465)
Net change in cash and cash equivalents	(195,289)	5,809
Cash and cash equivalents, beginning of period	447,858	378,615
Cash and cash equivalents, end of period	$ 252,569	$ 384,424