Assets and Liabilities Held For Sale - Schedule of Major Classes of Assets and Liabilities Classified as Held-for-Sale (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accrued commissions and other receivables, net	$ 322,250	$ 739,009
Cash segregated under regulatory requirements	19,059	257,115
Goodwill	486,885	556,211
Other intangible assets, net	212,048	287,157
Other assets	452,841	480,427
Cash and cash equivalents	450,830	596,291
Loans, forgivable loans and other receivables from employees and partners, net	375,982	408,142
Fixed assets, net	199,349	216,024
Assets held for sale	1,002,786	0
Accounts payable, accrued and other liabilities	627,994	1,364,119
Accrued compensation	169,183	220,726
Liabilities held for sale	799,366	$ 0
Disposal Group, Held-for-sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other intangible assets, net	55,600
Fixed assets, net	9,200
Disposal Group, Held-for-sale, Not Discontinued Operations | Brokerage Insurance
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accrued commissions and other receivables, net	497,845
Cash segregated under regulatory requirements	278,785
Goodwill	68,978
Other intangible assets, net	55,562
Other assets	38,903
Cash and cash equivalents	36,574
Loans, forgivable loans and other receivables from employees and partners, net	13,931
Fixed assets, net	9,179
Other	3,029
Assets held for sale	1,002,786
Accounts payable, accrued and other liabilities	784,456
Accrued compensation	14,910
Liabilities held for sale	$ 799,366