Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Trading income, net	$ 912,316	$ 1,266,682	$ 766,027
Interest and dividends income	108,778	87,508	50,407
Commissions, net and technology services	498,544	184,339	116,503
Other, net	10,444	340,189	95,045
Total revenue	1,530,082	1,878,718	1,027,982
Operating Expenses:
Brokerage, exchange and clearance fees, net	284,768	301,779	256,926
Communication and data processing	209,393	176,120	131,506
Employee compensation and payroll taxes	383,713	215,556	177,489
Payments for order flow	102,120	74,645	27,727
Interest and dividends expense	158,039	141,814	91,993
Operations and administrative	116,232	66,769	62,123
Depreciation and amortization	65,644	61,154	47,327
Amortization of purchased intangibles and acquired capitalized software	70,595	26,123	15,447
Termination of office leases	66,452	23,357	3,671
Debt issue cost related to debt refinancing and prepayment	41,132	11,727	10,460
Transaction advisory fees and expenses	26,117	11,487	25,270
Charges related to share based compensation at IPO	0	24	772
Financing interest expense on long-term borrowings	121,859	71,800	64,107
Total operating expenses	1,646,064	1,182,355	914,818
Income (loss) before income taxes and noncontrolling interest	(115,982)	696,363	113,164
Provision for (benefit from) income taxes	(12,277)	76,171	94,266
Net income (loss)	(103,705)	620,192	18,898
Noncontrolling interest	45,110	(330,751)	(15,959)
Net income (loss) available for common stockholders	$ (58,595)	$ 289,441	$ 2,939
Earnings (loss) per share
Basic (in dollars per share)	$ (0.53)	$ 2.82	$ 0.03
Diluted (in dollars per share)	$ (0.53)	$ 2.78	$ 0.03
Weighted average common shares outstanding
Basic (in shares)	113,918,103	100,875,793	62,579,147
Diluted (in shares)	113,918,103	102,089,139	62,579,147
Net income (loss)	$ (103,705)	$ 620,192	$ 18,898
Other comprehensive income (loss)
Foreign exchange translation adjustment, net of taxes	(1,475)	(5,127)	9,117
Comprehensive income (loss)	(105,180)	615,065	28,015
Less: Comprehensive income (loss) attributable to noncontrolling interest	45,668	(328,697)	(21,833)
Comprehensive income (loss) attributable to common stockholders	$ (59,512)	$ 286,368	$ 6,182