Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Cash received from customers	$ 569,001	$ 550,291
Cash paid to suppliers and employees	(509,683)	(507,160)
Interest paid, net	(231)	(459)
Income tax payments, net	(4,528)	(4,567)
Investment proceeds and miscellaneous receipts, net	3,912	4,496
Proceeds from forward foreign exchange contracts, net	4,337	342
Net cash provided by operating activities	62,808	42,943
Cash flows from investing activities:
Capital expenditures	(21,591)	(23,629)
Proceeds from dispositions of property, plant and equipment	38	74
Payments for purchases of marketable securities and investments	(98,151)	(95,375)
Proceeds from maturities of marketable securities and investments	67,710	82,573
Proceeds from Sale of Debt Securities, Available-for-sale	39,672	22,324
Payments for Previous Acquisition	0	(16,083)
(Payments for) proceeds from Other Investing Activities	(100)	7,403
Net cash used in investing activities	(12,422)	(22,713)
Cash flows from financing activities:
Payments on long-term borrowings	(1,415)	(237)
Payments of contingent consideration	(1,265)	(1,433)
Proceeds from Issuance of Common Stock	4,068	0
Proceeds from Sale of Treasury Stock	0	3,831
Payments for purchases of treasury stock	(100,005)	0
Net cash (used in) provided by financing activities	(98,617)	2,161
Effect of Exchange Rate on Cash and Cash Equivalents	(5,977)	1,982
Beginning Cash, Cash Equivalents, and Restricted Cash	662,651	434,164
Cash and cash equivalents	603,551	455,890
Restricted Cash, Current	3,110	113
Restricted Cash, Noncurrent	1,782	2,534
Ending Cash, Cash Equivalents, and Restricted Cash	608,443	458,537
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	$ (54,208)	$ 24,373