XML 67 R57.htm IDEA: XBRL DOCUMENT v3.20.2
Fair Value Measurements - Additional Information (Narrative) (Details) - USD ($)
$ in Thousands
6 Months Ended
Jun. 30, 2020
Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Auction Rate Securities Purchased as a Result of Settlements with Regulators $ 141,400  
Securities owned, at fair value $ 502,029 $ 799,719
Forward or delayed delivery of the underlying instrument with settlement 180 days  
Total amount of ARS the firm purchased and hold $ 29,600  
Auction Rate Securities Committed To Purchase related to settlements with regulators 2,400  
Auction Rate Securities Purchased as a result of Legal Settlements and Awards 106,100  
Equity Securities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Securities owned, at fair value 30,734 32,215
Auction rate securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Securities owned, at fair value $ 29,566 $ 25,314
Hedge Funds [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investment Redemption Notice Period Minimum 30 days  
Investment Redemption Notice Period Maximum 120 days