Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income	$ 593,172	$ 466,007
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred sales commissions	17,362	25,015
Non-cash long-term incentive compensation expense	13,051	26,947
Depreciation and other amortization	52,599	49,995
Unrealized (gains) losses on investments	(5,226)	3,323
Other, net	585	10,195
Changes in assets and liabilities:
(Increase) decrease in segregated cash and securities	(446,556)	161,531
(Increase) decrease in receivables	(179,020)	8,079
Decrease (increase) in investments	(30,130)	(76,780)
(Increase) decrease in deferred sales commissions	(3,974)	1,871
(Increase) decrease in other assets	(134,259)	(33,003)
Increase (decrease) in payables	584,282	(58,126)
(Decrease) increase in accounts payable and accrued expenses	(22,908)	23,982
Increase in accrued compensation and benefits	395,643	358,586
Net cash provided by operating activities	1,114,383	1,080,878
Cash flows from investing activities:
Purchases of investments	0	(11)
Proceeds from sales of investments	0	10
Purchases of furniture, equipment and leasehold improvements	(26,993)	(24,952)
Proceeds from sales of furniture, equipment and leasehold improvements	0	39
Net cash used in investing activities	(26,993)	(24,914)
Cash flows from financing activities:
Repayment of commercial paper, net	(97,303)	(220,363)
(Repayment) proceeds of bank loans	(75,000)	0
(Decrease) increase in overdrafts payable	(39,025)	66,134
Distributions to General Partner and Unitholders	(652,991)	(489,049)
Redemptions of investments in consolidated company-sponsored investment funds, net	0	(43,217)
Purchase of non-controlling interest	0	(1,833)
Capital contributions (to) from affiliates	(1,344)	79
Payments of contingent payment arrangements	(1,146)	(6,344)
Additional investments by AB Holding with proceeds from exercise of compensatory options to buy AB Holding Units	10,802	17,672
Purchases of AB Holding Units to fund long-term incentive compensation plan awards, net	(82,710)	(134,186)
Purchases of AB Units	(129)	(993)
Debt issuance costs	(1,705)	0
Net cash used in financing activities	(1,459,152)	(820,473)
Effect of exchange rate changes on cash and cash equivalents	(9,139)	17,458
Net (decrease) increase in cash and cash equivalents	(380,901)	252,949
Cash and cash equivalents as of beginning of the period	998,448	994,510
Cash and cash equivalents as of end of the period	617,547	1,247,459
Company-sponsored investment funds
Adjustments to reconcile net income to net cash provided by operating activities:
Unrealized (gains) losses on investments	(23,755)	(33,062)
Changes in assets and liabilities:
Decrease (increase) in investments	966,737	(180,966)
(Increase) decrease in other assets	(663,220)	327,284
Cash flows from financing activities:
Redemptions of investments in consolidated company-sponsored investment funds, net	(518,601)	$ (8,373)
Cash and cash equivalents as of beginning of the period	326,518
Cash and cash equivalents as of end of the period	$ 10,438