Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Operating Activities:
Net earnings	$ 160,627	$ 163,067	$ 454,268	$ 440,213
Adjustments to reconcile net earnings to net cash from operating activities:
Provisions for losses on accounts receivable	757	1,969	453	2,232
Deferred income tax benefit	(5,822)	(23,610)	(17)	(17,522)
Stock compensation expense	12,155	13,902	49,361	43,171
Depreciation and amortization	12,386	13,335	38,456	40,833
Other, net	652	666	812	770
Changes in operating assets and liabilities:
Decrease (increase) in accounts receivable	43,885	(210,092)	246,175	(156,321)
(Decrease) increase in accounts payable and accrued expenses	(58,816)	115,629	(141,199)	127,860
Decrease (increase) in deferred contract costs	10,301	(34,623)	28,550	(51,235)
(Decrease) increase in contract liabilities	(13,211)	36,256	(36,933)	49,149
(Decrease) increase in income taxes payable, net	(671)	9,292	(33,284)	(9,258)
(Decrease) increase in other, net	(744)	930	47	862
Net cash from operating activities	161,499	86,721	606,689	470,754
Investing Activities:
Purchase of property and equipment	(15,521)	(11,733)	(37,943)	(37,642)
Other, net	232	1,109	1,525	(886)
Net cash from investing activities	(15,289)	(10,624)	(36,418)	(38,528)
Financing Activities:
Proceeds from issuance of common stock	60,713	47,806	120,190	169,566
Repurchases of common stock	(61,999)	(147,828)	(296,922)	(555,760)
Dividends Paid			(85,184)	(79,180)
Payments for taxes related to net share settlement of equity awards			(6,674)	(3,215)
Distributions to noncontrolling interest		(633)		(633)
Purchase of noncontrolling interest		(613)		(613)
Net cash from financing activities	(1,286)	(101,268)	(268,590)	(469,835)
Effect of exchange rate changes on cash and cash equivalents	(11,604)	(5,071)	(9,446)	(22,878)
Change in cash and cash equivalents	133,320	(30,242)	292,235	(60,487)
Cash and cash equivalents at beginning of period	1,082,650	1,020,854	923,735	1,051,099
Cash and cash equivalents at end of period	1,215,970	990,612	1,215,970	990,612
Taxes Paid:
Income taxes	$ 61,201	$ 59,313	$ 196,169	$ 183,444