Fair Value Measurements - Financial Assets and Liabilities Measured on a Recurring and Nonrecurring Basis (Details) - USD ($) $ in Thousands | Jun. 30, 2022 | Dec. 31, 2021 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | $ 35,377 | $ 39,274 |
Fair Value, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents | 72,316 | 12,056 |
Securities owned — trading | 35,377 | 39,274 |
Other assets | 549,286 | 623,288 |
Total assets at fair value | 656,979 | 674,618 |
Accounts payable and accrued liabilities | 3,690 | 3,530 |
Other Liabilities, Fair Value Disclosure | 103,645 | 115,146 |
Total liabilities at fair value | 107,335 | 118,676 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents | 72,316 | 12,056 |
Securities owned — trading | 35,365 | 39,274 |
Other assets | 540,828 | 614,122 |
Total assets at fair value | 648,509 | 665,452 |
Accounts payable and accrued liabilities | 0 | 0 |
Other Liabilities, Fair Value Disclosure | 103,583 | 115,041 |
Total liabilities at fair value | 103,583 | 115,041 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents | 0 | 0 |
Securities owned — trading | 12 | 0 |
Other assets | 8,458 | 9,166 |
Total assets at fair value | 8,470 | 9,166 |
Securities sold, but not yet purchased | | 0 |
Accounts payable and accrued liabilities | 0 | 0 |
Other Liabilities, Fair Value Disclosure | 62 | 105 |
Total liabilities at fair value | 62 | 105 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents | 0 | 0 |
Securities owned — trading | 0 | 0 |
Other assets | 0 | 0 |
Total assets at fair value | 0 | 0 |
Securities sold, but not yet purchased | 0 | 0 |
Accounts payable and accrued liabilities | 3,690 | 3,530 |
Other Liabilities, Fair Value Disclosure | 0 | 0 |
Total liabilities at fair value | 3,690 | 3,530 |
Equity Securities [Member] | Fair Value, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 208 | 467 |
Equity Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 208 | 467 |
Equity Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 0 | |
Equity Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 0 | 0 |
Debt Securities [Member] | Fair Value, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 62 | 105 |
Debt Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 0 | 0 |
Debt Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 62 | 105 |
Debt Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 0 | 0 |
Mutual Funds [Member] | Fair Value, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 541 | |
Mutual Funds [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 541 | |
Mutual Funds [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 0 | 0 |
Mutual Funds [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 0 | 0 |
Securities Sold, Not yet Purchased | Fair Value, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 811 | 572 |
Securities Sold, Not yet Purchased | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 749 | 467 |
Securities Sold, Not yet Purchased | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 62 | 105 |
Money Market Funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 126 | 123 |
Money Market Funds [Member] | Fair Value, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 126 | 123 |
Money Market Funds [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 126 | 123 |
Money Market Funds [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 0 | 0 |
Money Market Funds [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 0 | 0 |
Other Security Investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 62 | 0 |
Other Security Investments | Fair Value, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 62 | |
Other Security Investments | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 50 | |
Other Security Investments | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 12 | |
Other Security Investments | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 0 | |
Mutual Funds [Member] | Fair Value, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 9,820 | 19,112 |
Mutual Funds [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 9,820 | 19,112 |
Mutual Funds [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 0 | 0 |
Mutual Funds [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 0 | 0 |
Equity Securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 876 | 440 |
Equity Securities [Member] | Fair Value, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 876 | 440 |
Equity Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 876 | 440 |
Equity Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 0 | 0 |
Equity Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 0 | 0 |
U.S. treasury obligations [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 24,493 | 19,599 |
U.S. treasury obligations [Member] | Fair Value, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 24,493 | 19,599 |
U.S. treasury obligations [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 24,493 | 19,599 |
U.S. treasury obligations [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 0 | 0 |
U.S. treasury obligations [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 0 | 0 |
Deferred Compensation Plan | Fair Value, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets | 437,994 | 499,548 |
Deferred Compensation Plan | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets | 437,994 | 499,548 |
Deferred Compensation Plan | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets | 0 | 0 |
Deferred Compensation Plan | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets | 0 | 0 |
Other Investments | Fair Value, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets | 8,458 | 9,166 |
Other Investments | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets | 0 | 0 |
Other Investments | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets | 8,458 | 9,166 |
Other Investments | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets | 0 | 0 |
Fractional Shares | Fair Value, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets | 102,834 | 114,574 |
Securities sold, but not yet purchased | | 114,574 |
Other Liabilities, Fair Value Disclosure | 102,834 | |
Fractional Shares | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets | 102,834 | 114,574 |
Other Liabilities, Fair Value Disclosure | 102,834 | 114,574 |
Fractional Shares | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets | 0 | 0 |
Other Liabilities, Fair Value Disclosure | 0 | |
Fractional Shares | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets | 0 | $ 0 |
Other Liabilities, Fair Value Disclosure | $ 0 | |