Interest Income and Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Interest Income Expense Net [Abstract]
Loans held for investment, net	$ 95,075	$ 76,281	$ 274,693	$ 250,565
Investment securities	34,247	31,966	95,738	121,630
Margin balances	6,624	5,803	19,001	22,298
Financial instruments owned	3,581	2,924	9,019	10,357
Other	2,317	(2,563)	4,524	(894)
Total interest income	141,844	114,411	402,975	403,956
Senior notes	11,850	15,411	35,924	39,677
Bank deposits	1,111	1,478	3,608	13,324
Other	(2,938)	(3,067)	(891)	(1,738)
Total interest expense	$ 10,023	$ 13,822	$ 38,641	$ 51,263