Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities:
Net income	$ 514,982	$ 367,010
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred sales commissions	16,135	12,148
Non-cash long-term incentive compensation expense	27,666	15,068
Depreciation and other amortization	64,505	72,034
Unrealized losses on investments	4,269	13,637
Other, net	10,064	154
Changes in assets and liabilities:
Decrease (increase) in securities, segregated	680,396	(787,322)
(Increase) in receivables	(222,721)	(145,247)
Decrease (increase) in investments	19,963	(42,626)
(Increase) in deferred sales commissions	(20,483)	(34,435)
(Increase) decrease in right-of-use assets	(33,369)	5,278
Increase (decrease) in other assets	(80,455)	(9,909)
(Decrease) increase in payables	(513,344)	851,419
(Decrease) in lease liabilities	(18,415)	(49,946)
Increase (decrease) in accounts payable and accrued expenses	13,617	(3,895)
Increase in accrued compensation and benefits	265,557	202,893
Net cash provided by operating activities	848,662	820,487
Cash flows from investing activities:
Purchases of furniture, equipment and leasehold improvements	(25,914)	(6,531)
Acquisition of business, net of cash acquired	(3,793)	(13,552)
Net cash used in investing activities	(29,707)	(20,083)
Cash flows from financing activities:
(Repayment) borrowings of debt, net	(85,000)
(Repayment) borrowings of debt, net		125,000
Increase in overdrafts payable	8,315	16,570
Distributions to General Partner and Unitholders	(531,810)	(446,624)
Capital contributions to affiliates	(408)	(971)
Additional investments by AB Holding with proceeds from exercise of compensatory options to buy AB Holding Units	3,402	147
Purchases of AB Holding Units to fund long-term incentive compensation plan awards, net	(75,468)	(47,415)
Other	721	642
Net cash used in financing activities	(768,085)	(622,500)
Effect of exchange rate changes on cash and cash equivalents	(1,223)	(11,162)
Net increase in cash and cash equivalents	49,647	166,742
Cash and cash equivalents as of beginning of the period	1,073,906	691,171
Cash and cash equivalents as of end of the period	1,123,553	857,913
Non-cash investing activities:
Fair value of assets acquired (less cash acquired of $2.8 million and $0.6 million, respectively)	13,235	18,389
Fair value of liabilities assumed	1,642	437
Non-cash financing activities:
Payables recorded under contingent payment arrangements	7,800	4,400
Company-sponsored investment funds
Adjustments to reconcile net income to net cash provided by operating activities:
Unrealized losses on investments	(936)	11,938
Changes in assets and liabilities:
Decrease (increase) in investments	136,578	334,970
Increase (decrease) in other assets	(15,347)	7,318
Cash flows from financing activities:
(Redemptions) of non-controlling interest in consolidated company-sponsored investment funds, net	$ (87,837)	$ (269,849)