Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Cash flows from operating activities:
Net income	$ 308,636	$ 221,694
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred sales commissions	21,495	20,161
Non-cash long-term incentive compensation expense	8,807	7,554
Depreciation and other amortization	22,036	21,440
Non-cash lease expense	20,169	17,305
Retirement plan loss	0	20,756
Retirement plan funding	0	(1,700)
Other, net	10,528	(4,227)
Changes in assets and liabilities:
Decrease (increase) in securities, segregated	147,677	(272,256)
(Increase) decrease in receivables	(21,232)	104,484
(Increase) in deferred sales commissions	(11,082)	(28,361)
Increase in other liabilities of consolidated company-sponsored investment funds	8,168	17,182
Increase in payables	13,843	224,090
(Decrease) in accounts payable and accrued expenses	(86,412)	(12,042)
Increase in accrued compensation and benefits	33,570	3,877
Cash payments to relieve operating lease liabilities	(17,315)	(15,892)
Net cash provided by operating activities	460,631	148,816
Cash flows from investing activities:
Purchases of furniture, equipment and leasehold improvements	(10,319)	(7,478)
Net cash (used in) investing activities	(10,319)	(7,478)
Cash flows from financing activities:
Repayment of debt, net	(105,000)
Proceeds from debt, net		30,000
Distributions to General Partner and Unitholders	(311,714)	(339,628)
Capital contributions (to) AB Holding	(493)	(1,109)
Purchases of AB Holding Units for long-term incentive compensation plan awards, net	(7,411)	(29,475)
Other, net	(3,266)	(2,730)
Net cash (used in) financing activities	(364,351)	(190,670)
Effect of exchange rate changes on cash and cash equivalents	(5,341)	12,823
Net increase (decrease) in cash and cash equivalents	80,620	(36,509)
Cash and cash equivalents as of beginning of the period	796,573	834,033	$ 834,033
Cash and cash equivalents as of end of the period	877,193	797,524	$ 796,573
Excluding Company-Sponsored Investment Funds
Adjustments to reconcile net income to net cash provided by operating activities:
Unrealized (gains) losses on investments	(6,279)	4,758
(Gains) losses on equity method investments	(41,098)	6,073
Changes in assets and liabilities:
Decrease (increase) in investments	144,895	(29,238)
(Increase) decrease in other assets	(23,230)	41,034
Company-Sponsored Investment Funds
Adjustments to reconcile net income to net cash provided by operating activities:
Unrealized (gains) losses on investments	11,275	1,744
Changes in assets and liabilities:
Decrease (increase) in investments	(80,266)	(202,080)
(Increase) decrease in other assets of consolidated company-sponsored investment funds	(3,554)	2,460
Cash flows from financing activities:
Terminations of non-controlling interest in consolidated company-sponsored investment funds, net	$ 63,533	$ 152,272