Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Activities:
Net earnings	$ 490,383	$ 432,533	$ 459,497
Adjustments to reconcile net earnings to net cash from operating activities:
Provision for losses on accounts receivable	5,356	2,607	2,173
Deferred income tax (benefit) expense	(43,695)	15,835	17,999
Stock compensation expense	50,908	45,217	43,415
Depreciation and amortization	49,310	46,796	46,012
Other	(4,382)	(3,540)	(24)
Changes in operating assets and liabilities:
(Increase) decrease in accounts receivable	(184,771)	(102,297)	62,619
Increase (decrease) in accounts payable and accrued expenses	114,631	102,716	(84,164)
Increase (decrease) in income taxes payable, net	16,264	(12,370)	18,382
(Increase) decrease in other current assets	(5,365)	1,988	653
Net cash from operating activities	488,639	529,485	566,562
Investing Activities:
Purchase of short-term investments	(12)	(54)	(47,026)
Proceeds from maturities of short-term investments	12	17	87,320
Purchase of property and equipment	(95,016)	(59,316)	(44,383)
Proceeds from sale of property and equipment	84,405	229	258
Other, net	(1,074)	5,928	(3,595)
Net cash from investing activities	(11,685)	(53,196)	(7,426)
Financing Activities:
Proceeds from issuance of common stock	205,092	185,313	130,964
Repurchases of common stock	(478,258)	(337,658)	(629,991)
Dividends paid	(150,495)	(145,123)	(135,673)
Distributions to noncontrolling interest	(904)	(1,335)	(2,122)
Net cash from financing activities	(424,565)	(298,803)	(636,822)
Effect of exchange rate changes on cash and cash equivalents	24,275	(10,847)	(41,625)
Increase (decrease) in cash and cash equivalents	76,664	166,639	(119,311)
Cash and cash equivalents at beginning of year	974,435	807,796	927,107
Cash and cash equivalents at end of year	1,051,099	974,435	807,796
Supplemental Cash Flow Information:
Cash paid for income taxes	$ 249,704	$ 254,312	$ 239,367