Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 598,626	$ 306,276	$ 454,433
Adjustments to reconcile net income to net cash provided by operating activities:
Allowance for credit losses	9,464	4,200	9,868
Depreciation	52,210	62,281	64,264
Amortization of cloud computing implementation costs	28,023	18,399	3,624
Amortization of intangible assets	2,241	1,219	1,361
Realized and unrealized gains	(37,359)	(66,866)	(44,492)
Stock-based compensation	55,932	52,486	48,300
Deferred income taxes	(21,133)	(13,146)	(9,473)
Changes in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	(292,628)	127,740	(48,461)
Capitalized cloud computing implementation costs	(31,240)	(33,178)	(30,338)
Accounts payable and accrued expenses	52,610	1,098	(9,204)
Accrued payroll and benefit cost	99,005	119,231	17,705
Employee deferred compensation plan obligations	100,058	13,923	87,670
Income taxes payable	3,587	182	(18,798)
Other assets and liabilities, net	(16,260)	2,683	(6,830)
Net cash flows provided by operating activities	603,136	596,528	519,629
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures	(36,611)	(33,377)	(59,464)
Investments in employee deferred compensation trusts	(85,432)	(64,351)	(71,432)
Proceeds from employee deferred compensation trust redemptions	34,434	123,025	28,758
Payments for acquisitions, net of cash acquired	0	(15,836)	0
Net cash flows (used in) provided by investing activities	(87,609)	9,461	(102,138)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from (Repayments of) Debt	(239)	(218)	(200)
Repurchases of common stock	(287,738)	(159,172)	(277,535)
Dividends paid	(170,612)	(155,935)	(145,631)
Net cash flows used in financing activities	(458,589)	(315,325)	(423,366)
Effect of exchange rate fluctuations	(12,363)	13,284	(226)
Change in cash and cash equivalents	44,575	303,948	(6,101)
Cash and cash equivalents at beginning of period	574,426	270,478	276,579
Cash and cash equivalents at end of period	619,001	574,426	270,478
Cash paid during the year for:
Interest	548	577	232
Income taxes, net of refunds	219,726	128,321	191,522
Non-cash items:
Stock repurchases awaiting settlement	5,593	3,104	6,469
Fund exchanges within employee deferred compensation trusts	$ 116,815	$ 208,055	$ 41,648