Other Liabilities and Accrued Expenses - Schedule of Other Liabilities and Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Jan. 01, 2019
Other Liabilities Disclosure [Abstract]
Accounts payable and accrued expenses	$ 99,260	$ 68,829
Operating lease liability	26,233	29,491	$ 33,558
Deferred tax liabilities, net	15,403	32,306
Securities sold, not yet purchased	67,099	0
Due to brokers	41,856	1,140
Assets Sold under Agreements to Repurchase, Repurchase Liability	63,676	6,733
Commissions payable	17,920	9,179
Other	19,787	24,462
Total other liabilities and accrued expenses	$ 351,234	$ 172,140