Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 110,598	$ 89,915
Adjustments to reconcile net income to net cash provided by operating activities:
Allowance for credit losses	3,157	4,690
Depreciation	13,962	15,913
Amortization of cloud computing implementation costs	9,957	3,288
Amortization of intangible assets	576	338
Realized and unrealized (gains) losses from investments held in employee deferred compensation trusts	(11,694)	40,781
Stock-based compensation	14,182	13,525
Deferred income taxes	2,584	12,022
Changes in operating assets and liabilities:
Accounts receivable	(95,024)	(36,700)
Capitalized cloud computing implementation costs	(8,488)	(10,379)
Accounts payable and accrued expenses	(6,603)	18,193
Accrued payroll and benefit cost	13,009	2,978
Employee deferred compensation plan obligations	2,586	(48,155)
Income taxes payable	25,409	20,124
Other assets and liabilities, net	(6,155)	(1,607)
Net cash flows provided by operating activities	68,056	124,926
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures	(9,739)	(14,276)
Investments in employee deferred compensation trusts	(28,509)	(37,061)
Proceeds from employee deferred compensation trust redemptions	22,799	22,987
Net cash flows used in investing activities	(15,449)	(28,350)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repayment of notes payable	(58)	(53)
Repurchases of common stock	(79,465)	(69,968)
Dividends paid	(44,277)	(40,476)
Net cash flows used in financing activities	(123,800)	(110,497)
Effect of exchange rate fluctuations	(5,303)	(6,643)
Change in cash and cash equivalents	(76,496)	(20,564)
Cash and cash equivalents at beginning of period	574,426	270,478
Cash and cash equivalents at end of period	497,930	249,914
Non-cash items:
Stock repurchases awaiting settlement	3,912	0
Fund exchanges within employee deferred compensation trusts	$ 37,661	$ 138,633