Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income	$ 861,783	$ 781,683	$ 779,498
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred sales commissions	27,355	15,029	21,343
Non-cash long-term incentive compensation expense	195,642	208,182	187,514
Depreciation and other amortization	138,240	166,542	70,000
Unrealized losses (gains) on investments	10,405	(13,431)	23,164
Other, net	(2,914)	10,281	(6,446)
Changes in assets and liabilities:
(Increase) decrease in securities, segregated	(658,612)	74,688	(353,204)
(Increase) decrease in receivables	(182,684)	223,137	(207,000)
Decrease (increase) in investments	7,597	460,347	(294,383)
(Increase) in deferred sales commissions	(55,125)	(34,177)	(8,365)
(Increase) in right-of-use assets	(131,765)	(11,141)
Decrease (increase) in other assets	69,160	(23,140)	(152,726)
Increase (decrease) in payables	861,502	(641,369)	1,024,317
Increase (decrease) in lease liabilities	37,695	(107,276)
Increase (decrease) in accounts payable and accrued expenses	10,666	(56,518)	(11,225)
Increase (decrease) in accrued compensation and benefits	46,885	(7,486)	4,341
Net cash provided by operating activities	1,521,421	827,480	1,308,481
Cash flows from investing activities:
Purchases of equity method investments	(4,079)	0	0
Purchases of furniture, equipment and leasehold improvements	(41,504)	(28,303)	(32,789)
Acquisition of businesses, net of cash acquired	(13,552)	5,255	0
Net cash used in investing activities	(59,135)	(23,048)	(32,789)
Cash flows from financing activities:
Proceeds (repayment) of debt	115,000	2,105
Proceeds (repayment) of debt			(25,454)
(Decrease) increase in overdrafts payable	(12,633)	(59,924)	3,273
Distributions to General Partner and Unitholders	(836,879)	(703,512)	(858,193)
(Redemptions) subscriptions of non-controlling interests of consolidated company-sponsored investment funds, net	0	0	(638)
Capital contributions (to) from affiliates	(867)		(1,421)
Capital contributions (to) from affiliates		269
Interest accretion, net of (payments) on contingent payment arrangements	1,921
Interest accretion, net of (payments) on contingent payment arrangements		(1,991)	(1,093)
Additional investments by AB Holding with proceeds from exercise of compensatory options to buy AB Holding Units	147	11,511	16,589
Purchases of AB Holding Units to fund long-term incentive compensation plan awards, net	(148,624)	(171,930)	(267,427)
Other	(1,615)	(1,580)	(2,151)
Net cash used in financing activities	(1,102,583)	(774,961)	(1,608,658)
Effect of exchange rate changes on cash and cash equivalents	23,032	8,376	(12,158)
Net increase (decrease) in cash and cash equivalents	382,735	37,847	(345,124)
Cash and cash equivalents as of beginning of the period	691,171	653,324	998,448
Cash and cash equivalents as of end of the period	1,073,906	691,171	653,324
Cash paid:
Interest paid	18,858	66,002	60,286
Income taxes paid	59,791	52,444	41,946
Non-cash investing activities:
Fair value of assets acquired (excluding cash acquired of $0.6 million and $11.8 million)	18,389	28,966	0
Fair value of liabilities assumed	437	16,837	0
Non-cash financing activities:
Payables recorded under contingent payment arrangements	4,400	17,384	0
Consolidated company-sponsored investment funds
Adjustments to reconcile net income to net cash provided by operating activities:
Unrealized losses (gains) on investments	(854)	(36,150)	(14,217)
Changes in assets and liabilities:
Decrease (increase) in investments	279,276	(193,158)	908,804
Decrease (increase) in other assets	7,169	11,437	(662,934)
Cash flows from financing activities:
(Redemptions) subscriptions of non-controlling interests of consolidated company-sponsored investment funds, net	$ (219,033)	$ 150,091	$ (472,143)