Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Activities:
Net earnings	$ 592,016	$ 619,790	$ 490,383
Adjustments to reconcile net earnings to net cash from operating activities:
(Recoveries) provisions for losses on accounts receivable	(1)	3,808	5,356
Deferred income tax expense (benefit)	4,482	(12,031)	(43,695)
Stock compensation expense	61,543	56,147	50,908
Depreciation and amortization	50,950	54,019	49,310
Other, net	941	647	(4,382)
Changes in operating assets and liabilities:
Decrease (increase) in accounts receivable	265,919	(214,971)	(184,771)
(Decrease) increase in accounts payable and accrued expenses	(181,987)	86,036	114,631
Decrease (increase) in deferred contract costs	28,811	(42,097)
(Decrease) increase in contract liabilities	(37,097)	43,928
(Decrease) increase in income taxes payable, net	(18,472)	(19,691)	16,264
Decrease (increase) in other, net	4,830	(2,781)	(5,365)
Net cash from operating activities	771,935	572,804	488,639
Investing Activities:
Purchase of property and equipment	(47,022)	(47,474)	(95,016)
Proceeds from sale of property and equipment	579	215	84,405
Other, net	428	(1,140)	(1,074)
Net cash from investing activities	(46,015)	(48,399)	(11,685)
Financing Activities:
Proceeds from issuance of common stock	148,245	182,732	205,092
Repurchases of common stock	(389,060)	(647,898)	(478,258)
Dividends Paid	(170,553)	(156,840)	(150,495)
Payments for taxes related to net share settlement of equity awards	(6,674)	(3,248)
Purchase of noncontrolling interest		(688)
Distributions to noncontrolling interest		(1,796)	(904)
Net cash from financing activities	(418,042)	(627,738)	(424,565)
Effect of exchange rate changes on cash and cash equivalents	(1,122)	(24,031)	24,275
Change in cash and cash equivalents	306,756	(127,364)	76,664
Cash and cash equivalents at beginning of period	923,735	1,051,099	974,435
Cash and cash equivalents at end of period	1,230,491	923,735	1,051,099
Supplemental Cash Flow Information:
Cash paid for income taxes	$ 222,083	$ 239,255	$ 249,704