Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenues:
Commissions	$ 382,640	$ 422,974	$ 838,495	$ 853,156
Principal transactions	99,453	90,432	212,764	174,662
Fees from related parties	6,562	7,221	12,083	13,016
Data, software and post-trade	20,139	18,741	39,537	36,651
Interest and dividend income	6,536	7,813	10,697	11,478
Other revenues	3,758	4,006	8,679	6,975
Total revenues	519,088	551,187	1,122,255	1,095,938
Expenses:
Compensation and employee benefits	283,437	290,071	628,186	578,071
Equity-based compensation and allocations of net income to limited partnership units and FPUs	27,819	43,752	70,023	55,893
Total compensation and employee benefits	311,256	333,823	698,209	633,964
Occupancy and equipment	47,247	45,109	98,321	91,111
Fees to related parties	5,194	6,457	10,629	9,384
Professional and consulting fees	19,805	23,347	39,761	43,352
Communications	30,524	29,974	61,045	60,385
Selling and promotion	6,634	21,491	25,333	39,893
Commissions and floor brokerage	13,520	16,791	32,797	31,409
Interest expense	17,457	14,985	34,791	28,183
Other expenses	21,499	21,765	40,687	45,780
Total expenses	473,136	513,742	1,041,573	983,461
Other income (losses) , net:
Gain (loss) on divestitures and sale of investments		(1,619)		18,435
Gains (losses) on equity method investments	1,119	738	2,142	1,521
Other income (loss)	1,129	194	(4,886)	21,396
Total other income (losses), net	2,248	(687)	(2,744)	41,352
Income (loss) from operations before income taxes	48,200	36,758	77,938	153,829
Provision (benefit) for income taxes	8,641	14,993	17,347	44,890
Consolidated net income (loss)	39,559	21,765	60,591	108,939
Less: Net income (loss) attributable to noncontrolling interest in subsidiaries	11,460	8,154	18,178	33,460
Net income (loss) available to common stockholders	28,099	13,611	42,413	75,479
Basic earnings (loss) per share
Net income (loss) available to common stockholders	$ 28,099	$ 13,611	$ 42,413	$ 75,479
Basic earnings (loss) per share	$ 0.08	$ 0.04	$ 0.12	$ 0.22
Basic weighted-average shares of common stock outstanding	360,614	341,272	359,308	339,845
Fully diluted earnings (loss) per share
Net income (loss) for fully diluted shares	$ 40,436	$ 21,010	$ 60,695	$ 100,195
Fully diluted earnings (loss) per share	$ 0.07	$ 0.04	$ 0.11	$ 0.21
Fully diluted weighted-average shares of common stock outstanding	546,123	522,984	542,390	467,232