Revenue - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Revenue from Contracts with Customers [Line Items]
Contract with Customer, Liability, Revenue Recognized	$ 16,468
Period in Which Performance Obligations Under Client Arrangements Settled	1 year
Underwriting Fees [Member]
Revenue from Contracts with Customers [Line Items]
Reimbursement Revenue	$ 4,680
Professional Fees [Member]
Revenue from Contracts with Customers [Line Items]
Reimbursable Expense	2,340
Travel and Related Expenses [Member]
Revenue from Contracts with Customers [Line Items]
Reimbursable Expense	460
Communications and Information Services [Member]
Revenue from Contracts with Customers [Line Items]
Reimbursable Expense	476
Other Operating Expenses [Member]
Revenue from Contracts with Customers [Line Items]
Reimbursable Expense	1,404
Investment Banking [Member] | Advisory Fees [Member]
Revenue from Contracts with Customers [Line Items]
Revenue, Variable Consideration Recognized	$ 3,374