Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 720,800	$ 694,846	$ 586,302
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred sales commissions	31,886	41,066	49,145
Non-cash long-term incentive compensation expense	185,234	152,162	176,160
Depreciation and other amortization	66,999	59,026	56,426
Unrealized losses (gains) on investments	3,554	(28,204)	29,281
Losses on real estate asset write-offs	8,161	5,456	0
Other, net	5,028	3,629	(2,888)
Changes in assets and liabilities:
Decrease (increase) in segregated cash and securities	129,747	(380,823)	(88,997)
Decrease (increase) in receivables	65,982	(295,677)	(121,985)
Decrease in investments	293	187,752	58,053
Decrease (increase) in deferred sales commissions	1,878	(5,886)	(29,925)
(Increase) decrease in other assets	(13,131)	12,961	(42,690)
(Decrease) increase in payables	(338,523)	886,520	65,309
Increase (decrease) in accounts payable and accrued expenses	23,090	2,459	(32,372)
Increase (decrease) in accrued compensation and benefits	12,187	(3,238)	(34,645)
Net cash provided by operating activities	645,452	1,548,048	667,174
Cash flows from investing activities:
Purchases of investments	(12)	0	(168)
Proceeds from sales of investments	11	372	4,240
Purchases of furniture, equipment and leasehold improvements	(39,417)	(36,728)	(30,217)
Proceeds from sales of furniture, equipment and leasehold improvements	75	15	2
Purchase of intangible asset	0	(2,500)	0
Purchase of businesses, net of cash acquired	0	(20,541)	0
Net cash used in investing activities	(39,343)	(59,382)	(26,143)
Cash flows from financing activities:
(Repayment) issuance of commercial paper, net	(28,553)	(72,003)	93,867
Proceeds from bank loans	75,000	0	0
Increase (decrease) in overdrafts payable	63,393	(84,512)	79,540
Distributions to General Partner and Unitholders	(644,139)	(537,564)	(597,872)
Purchases (redemptions) of non-controlling interests of consolidated company-sponsored investment funds, net	(43,217)	364	(12,165)
Purchase of non-controlling interest	(1,833)	0	0
Capital contributions from affiliates	366	1,000	2,041
Payments of contingent payment arrangements/purchase of shares	(7,592)	(5,545)	(5,027)
Additional investments by AB Holding with proceeds from exercise of compensatory options to buy AB Holding Units	20,110	6,108	9,233
Purchases of AB Holding Units to fund long-term incentive compensation plan awards, net	(219,627)	(235,893)	(213,484)
Purchases of AB Units	(1,003)	(374)	(805)
Other	0	(22)	(26)
Net cash used in financing activities	(623,931)	(1,061,278)	(644,698)
Effect of exchange rate changes on cash and cash equivalents	21,760	(10,178)	(10,353)
Net increase (decrease) in cash and cash equivalents	3,938	417,210	(14,020)
Cash and cash equivalents as of beginning of the period	994,510	541,483	555,503
Cash and cash equivalents as of beginning of the period			577,300
Cash and cash equivalents as of end of the period	998,448	994,510	541,483
Cash paid:
Interest paid	30,975	11,148	3,984
Income taxes paid	67,421	27,387	25,999
Non-cash investing activities:
Fair value of assets acquired	0	33,583	0
Fair value of liabilities assumed	0	1,149	0
Fair value of redeemable non-controlling interest recorded	0	0	0
Non-cash financing activities:
Payables recorded under contingent payment arrangements	0	11,893	0
VIEs Consolidated [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Unrealized losses (gains) on investments	(36,340)	(29,121)	0
Changes in assets and liabilities:
Consolidation of cash and cash equivalents of consolidated company-sponsored investment funds	0	358,534	0
Decrease in investments	(639,067)	(342,938)	0
(Increase) decrease in other assets	417,674	229,524	0
Cash flows from financing activities:
Purchases (redemptions) of non-controlling interests of consolidated company-sponsored investment funds, net	163,164	(132,837)	$ 0
Cash and cash equivalents as of beginning of the period	337,525
Cash and cash equivalents as of end of the period	$ 326,518	$ 337,525