Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net income	$ 388,772	$ 308,527
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred sales commissions	12,711	17,386
Non-cash long-term incentive compensation expense	14,825	21,337
Depreciation and other amortization	35,626	33,313
Unrealized (gains) losses on investments	(3,257)	2,636
Other, net	(1,907)	5,712
Changes in assets and liabilities:
(Increase) in segregated cash and securities	(472,517)	(131,552)
(Increase) in receivables	(213,529)	(50,545)
Decrease (increase) in investments	(59,219)	(37,978)
Decrease in deferred sales commissions	653	1,923
(Increase) decrease in other assets	(116,890)	(68,430)
Increase in payables	682,703	70,082
(Decrease) in accounts payable and accrued expenses	(8,816)	(11,189)
Increase in accrued compensation and benefits	225,571	201,417
Net cash provided by operating activities	765,474	448,239
Cash flows from investing activities:
Purchases of investments	0	(11)
Proceeds from sales of investments	0	10
Purchases of furniture, equipment and leasehold improvements	(11,458)	(14,023)
Proceeds from sales of furniture, equipment and leasehold improvements	0	39
Net cash used in investing activities	(11,458)	(13,985)
Cash flows from financing activities:
Issuance (repayment) of commercial paper, net	20,058	(33,709)
(Repayment) proceeds of bank loans	(75,000)	30,000
(Decrease) increase in overdrafts payable	(28,952)	68,504
Distributions to General Partner and Unitholders	(466,522)	(339,139)
(Redemptions) of investments in consolidated company-sponsored investment funds, net	0	(7,869)
Purchase of non-controlling interest	0	(1,833)
Capital contributions to affiliates	(1,178)	(280)
Additional investments by AB Holding with proceeds from exercise of compensatory options to buy AB Holding Units	8,340	9,246
Purchases of AB Holding Units to fund long-term incentive compensation plan awards, net	(34,864)	(127,472)
Purchases of AB Units	(105)	(684)
Other	105	(807)
Net cash used in financing activities	(1,093,974)	(476,775)
Effect of exchange rate changes on cash and cash equivalents	(6,039)	11,179
Net (decrease) in cash and cash equivalents	(345,997)	(31,342)
Cash and cash equivalents as of beginning of the period	998,448	994,510
Cash and cash equivalents as of end of the period	652,451	963,168
Company-sponsored investment funds
Adjustments to reconcile net income to net cash provided by operating activities:
Unrealized (gains) losses on investments	(20,463)	(18,550)
Changes in assets and liabilities:
Decrease (increase) in investments	965,121	(57,045)
(Increase) decrease in other assets	(663,910)	161,195
Cash flows from financing activities:
(Redemptions) of investments in consolidated company-sponsored investment funds, net	(515,856)	$ (72,732)
Cash and cash equivalents as of beginning of the period	326,518
Cash and cash equivalents as of end of the period	$ 23,693