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Revenue - Additional Information (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2018
Revenue from Contracts with Customers [Line Items]    
Contract with Customer, Liability, Revenue Recognized $ 3,740 $ 8,984
Period in Which Performance Obligations Under Client Arrangements Settled   1 year
Underwriting Fees [Member]    
Revenue from Contracts with Customers [Line Items]    
Reimbursement Revenue 116 $ 3,913
Professional Fees [Member]    
Revenue from Contracts with Customers [Line Items]    
Cost of Reimbursable Expense 34 1,957
Travel and Related Expenses [Member]    
Revenue from Contracts with Customers [Line Items]    
Cost of Reimbursable Expense 16 391
Communications and Information Services [Member]    
Revenue from Contracts with Customers [Line Items]    
Cost of Reimbursable Expense 16 391
Other Operating Expenses [Member]    
Revenue from Contracts with Customers [Line Items]    
Cost of Reimbursable Expense 50 1,174
Investment Banking [Member] | Advisory Fees [Member]    
Revenue from Contracts with Customers [Line Items]    
Revenue, Variable Consideration Recognized $ 50,829 $ 50,829