Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Operating Activities:
Net earnings	$ 120,606	$ 107,949	$ 322,928	$ 321,435
Adjustments to reconcile net earnings to net cash from operating activities:
Provision for losses on accounts receivable	1,741	1,321	3,187	2,461
Deferred income tax (benefit) expense	(28,854)	(1,439)	(16,000)	2,342
Stock compensation expense	11,210	10,476	39,036	34,264
Depreciation and amortization	12,272	11,882	36,241	34,853
Other, net	377	11	(148)	41
Changes in operating assets and liabilities:
(Increase) decrease in accounts receivable	(126,102)	(58,279)	(123,790)	6,087
Increase in accounts payable and accrued expenses	61,833	38,070	96,132	74,148
Increase (decrease) in income taxes payable, net	38,149	7,197	10,814	(16,612)
Increase in other current assets	(5,872)	(1,395)	(6,147)	(2,089)
Net cash from operating activities	85,360	115,793	362,253	456,930
Investing Activities:
Purchase of property and equipment	(34,462)	(12,659)	(67,603)	(39,973)
Other, net	(261)	1,617	(892)	5,472
Net cash from investing activities	(34,723)	(11,042)	(68,495)	(34,501)
Financing Activities:
Proceeds from issuance of common stock	65,915	57,522	162,781	147,645
Repurchases of common stock	(202,776)	(101,690)	(340,736)	(268,097)
Dividends paid	0	0	(75,726)	(73,000)
Net cash from financing activities	(136,861)	(44,168)	(253,681)	(193,452)
Effect of exchange rate changes on cash and cash equivalents	4,758	1,853	18,932	5,927
(Decrease) increase in cash and cash equivalents	(81,466)	62,436	59,009	234,904
Cash and cash equivalents at beginning of period	1,114,910	980,264	974,435	807,796
Cash and cash equivalents at end of period	1,033,444	1,042,700	1,033,444	1,042,700
Taxes Paid:
Income taxes	$ 58,257	$ 58,696	$ 190,911	$ 205,049