Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating Activities:
Net earnings	$ 153,530	$ 140,946	$ 293,641	$ 277,146
Adjustments to reconcile net earnings to net cash from operating activities:
Provisions for losses (recoveries) on accounts receivable	1,584	528	(304)	263
Deferred income tax expense	3,697	3,235	5,805	6,088
Stock compensation expense	23,824	18,002	37,206	29,269
Depreciation and amortization	12,677	13,576	26,070	27,498
Other, net	(29)	56	160	104
Changes in operating assets and liabilities:
(Increase) decrease in accounts receivable	(28,187)	(46,876)	202,290	53,771
Increase (decrease) in accounts payable and accrued expenses	39,900	58,075	(82,383)	12,231
(Increase) decrease in deferred contract costs	(13,010)	(20,019)	18,249	(16,612)
Increase (decrease) in contract liabilities	13,003	20,294	(23,722)	12,893
(Decrease) increase in income taxes payable, net	(49,606)	(38,059)	(32,613)	(18,550)
(Decrease) increase in other, net	(1,676)	(1,202)	791	(68)
Net cash from operating activities	155,707	148,556	445,190	384,033
Investing Activities:
Purchase of property and equipment	(12,987)	(12,113)	(22,422)	(25,909)
Other, net	1,038	(1,564)	1,293	(1,995)
Net cash from investing activities	(11,949)	(13,677)	(21,129)	(27,904)
Financing Activities:
Proceeds from issuance of common stock	32,287	95,363	59,477	121,760
Repurchases of common stock	(190,589)	(235,572)	(234,923)	(407,932)
Dividends Paid	(85,184)	(79,180)	(85,184)	(79,180)
Payments for taxes related to net share settlement of equity awards	(6,674)	(3,215)	(6,674)	(3,215)
Net cash from financing activities	(250,160)	(222,604)	(267,304)	(368,567)
Effect of exchange rate changes on cash and cash equivalents	(377)	(24,322)	2,158	(17,807)
Change in cash and cash equivalents	(106,779)	(112,047)	158,915	(30,245)
Cash and cash equivalents at beginning of period	1,189,429	1,132,901	923,735	1,051,099
Cash and cash equivalents at end of period	1,082,650	1,020,854	1,082,650	1,020,854
Taxes Paid:
Income taxes	$ 97,715	$ 85,612	$ 134,968	$ 124,131