Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues:
Commissions	$ 352,027	$ 409,765	$ 1,190,522	$ 1,262,921
Principal transactions	65,182	75,536	277,946	250,198
Fees from related parties	8,814	8,208	20,897	21,224
Data, software and post-trade	21,523	18,364	61,060	55,015
Interest and dividend income	2,418	3,976	13,115	15,454
Other revenues	5,075	5,288	13,754	12,263
Total revenues	455,039	521,137	1,577,294	1,617,075
Expenses:
Compensation and employee benefits	244,240	278,544	872,426	856,615
Equity-based compensation and allocations of net income to limited partnership units and FPUs	33,007	40,330	103,030	96,223
Total compensation and employee benefits	277,247	318,874	975,456	952,838
Occupancy and equipment	45,224	44,709	143,545	135,820
Fees to related parties	7,610	7,123	18,239	16,507
Professional and consulting fees	15,637	21,262	55,398	64,614
Communications	30,088	29,882	91,133	90,267
Selling and promotion	5,943	20,320	31,276	60,213
Commissions and floor brokerage	12,933	15,831	45,730	47,240
Interest expense	19,488	15,258	54,279	43,441
Other expenses	18,458	42,757	59,145	88,537
Total expenses	432,628	516,016	1,474,201	1,499,477
Other income (losses) , net:
Gain (loss) on divestitures and sale of investments	(9)		(9)	18,435
Gains (losses) on equity method investments	1,527	1,530	3,669	3,051
Other income (loss)	4,779	2,095	(107)	23,491
Total other income (losses), net	6,297	3,625	3,553	44,977
Income (loss) from operations before income taxes	28,708	8,746	106,646	162,575
Provision (benefit) for income taxes	3,778	6,186	21,125	51,076
Consolidated net income (loss)	24,930	2,560	85,521	111,499
Less: Net income (loss) attributable to noncontrolling interest in subsidiaries	5,549	6,089	23,727	39,549
Net income (loss) available to common stockholders	19,381	(3,529)	61,794	71,950
Basic earnings (loss) per share
Net income (loss) available to common stockholders	$ 19,381	$ (3,529)	$ 61,794	$ 71,950
Basic earnings (loss) per share	$ 0.05	$ (0.01)	$ 0.17	$ 0.21
Basic weighted-average shares of common stock outstanding	363,244	346,060	360,629	341,940
Fully diluted earnings (loss) per share
Net income (loss) for fully diluted shares	$ 29,575	$ (3,529)	$ 90,270	$ 108,378
Fully diluted earnings (loss) per share	$ 0.05	$ (0.01)	$ 0.17	$ 0.21
Fully diluted weighted-average shares of common stock outstanding	549,244	346,060	544,475	523,218