Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating Activities:
Net earnings	$ 184,188	$ 153,530	$ 306,970	$ 293,641
Adjustments to reconcile net earnings to net cash from operating activities:
Provisions for losses (recoveries) on accounts receivable	2,389	1,584	4,209	(304)
Deferred income tax expense	9,287	3,697	4,148	5,805
Stock compensation expense	21,638	23,824	32,794	37,206
Depreciation and amortization	14,109	12,677	26,769	26,070
Other, net	118	(29)	551	160
Changes in operating assets and liabilities:
(Increase) decrease in accounts receivable	(185,055)	(28,187)	(168,375)	202,290
Increase (decrease) in accounts payable and accrued expenses	106,760	39,900	107,677	(82,383)
(Increase) decrease in deferred contract costs	(2,333)	(13,010)	(18,401)	18,249
(Decrease) increase in contract liabilities	(595)	13,003	20,606	(23,722)
Increase (decrease) in income taxes payable, net	20,154	(49,606)	30,642	(32,613)
Decrease (increase) in other, net	16,061	(1,676)	4,131	791
Net cash from operating activities	186,721	155,707	351,721	445,190
Investing Activities:
Purchase of property and equipment	(22,114)	(12,987)	(28,241)	(22,422)
Other, net	(68)	1,038	(211)	1,293
Net cash from investing activities	(22,182)	(11,949)	(28,452)	(21,129)
Financing Activities:
Proceeds from issuance of common stock	29,187	32,287	52,586	59,477
Repurchases of common stock	(30,985)	(190,589)	(314,225)	(234,923)
Dividends Paid	(86,815)	(85,184)	(86,815)	(85,184)
Payments for taxes related to net share settlement of equity awards	(9,170)	(6,674)	(10,566)	(6,674)
Net cash from financing activities	(97,783)	(250,160)	(359,020)	(267,304)
Effect of exchange rate changes on cash and cash equivalents	1,726	(377)	(14,285)	2,158
Change in cash and cash equivalents	68,482	(106,779)	(50,036)	158,915
Cash and cash equivalents at beginning of period	1,111,973	1,189,429	1,230,491	923,735
Cash and cash equivalents at end of period	1,180,455	1,082,650	1,180,455	1,082,650
Taxes Paid:
Income taxes	$ 38,504	$ 97,715	$ 73,808	$ 134,968