Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 89,915	$ 109,798
Adjustments to reconcile net income to net cash provided by operating activities:
Allowance for credit losses	4,690	2,325
Depreciation	15,913	15,652
Amortization of cloud computing implementation costs	3,288	0
Amortization of intangible assets	338	342
Stock-based compensation	13,525	11,244
Deferred income taxes	12,022	5,736
Changes in assets and liabilities:
Accounts receivable	(36,700)	(35,294)
Capitalized cloud computing implementation costs	(10,379)	(4,751)
Accounts payable and accrued expenses	18,193	(11,910)
Accrued payroll and benefit cost	(4,396)	13,308
Income taxes payable	20,124	17,470
Other assets and liabilities, net	(1,607)	3,159
Net cash flows provided by operating activities	124,926	127,079
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures	(14,276)	(12,670)
Payments for employee deferred compensation plans	(37,061)	(27,376)
Redemptions from employee deferred compensation plans	22,987	16,966
Net cash flows used in investing activities	(28,350)	(23,080)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repayment of notes payable	(53)	(49)
Repurchases of common stock	(69,968)	(72,343)
Dividends paid	(40,476)	(37,887)
Net cash flows used in financing activities	(110,497)	(110,279)
Effect of exchange rate fluctuations	(6,643)	(654)
Change in cash and cash equivalents	(20,564)	(6,934)
Cash and cash equivalents at beginning of period	270,478	276,579
Cash and cash equivalents at end of period	249,914	269,645
Non-cash items:
Stock repurchases awaiting settlement	$ 0	$ 7,332