Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating Activities:
Net earnings	$ 108,755	$ 116,439	$ 202,322	$ 213,486
Adjustments to reconcile net earnings to net cash from operating activities:
Provision for losses on accounts receivable	515	562	1,446	1,140
Deferred income tax expense (benefit)	7,261	(6,115)	12,854	3,781
Stock compensation expense	17,203	12,957	27,826	23,788
Depreciation and amortization	12,042	11,642	23,969	22,971
Other, net	(174)	(6)	(525)	30
Changes in operating assets and liabilities:
(Increase) decrease in accounts receivable	(73,142)	(48,344)	2,312	64,366
Increase in accounts payable and accrued expenses	52,623	51,422	34,299	36,078
Decrease in income taxes payable, net	(47,159)	(34,734)	(27,335)	(23,809)
Increase (decrease) in other current assets	3,290	1,361	(275)	(694)
Net cash from operating activities	81,214	105,184	276,893	341,137
Investing Activities:
Purchase of property and equipment	(20,380)	(13,279)	(33,141)	(27,314)
Other, net	40	4,414	(631)	3,855
Net cash from investing activities	(20,340)	(8,865)	(33,772)	(23,459)
Financing Activities:
Proceeds from issuance of common stock	51,501	48,488	96,866	90,123
Repurchases of common stock	(84,052)	(96,115)	(137,960)	(166,407)
Dividends paid	(75,726)	(73,000)	(75,726)	(73,000)
Net cash from financing activities	(108,277)	(120,627)	(116,820)	(149,284)
Effect of exchange rate changes on cash and cash equivalents	6,270	(9,345)	14,174	4,074
(Decrease) increase in cash and cash equivalents	(41,133)	(33,653)	140,475	172,468
Cash and cash equivalents at beginning of period	1,156,043	1,013,917	974,435	807,796
Cash and cash equivalents at end of period	1,114,910	980,264	1,114,910	980,264
Taxes Paid:
Income taxes	$ 103,508	$ 108,369	$ 132,654	$ 146,353