New Accounting Pronouncements (Policies)	3 Months Ended
Mar. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Recently Adopted Accounting Guidance	Recently Adopted Accounting Guidance Fair Value Measurement In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement. The objective of this guidance is to improve the effectiveness of disclosure requirements on fair value measurement by eliminating certain disclosure requirements for fair value measurements for all entities, requiring public entities to disclose certain new information and modifying some disclosure requirements. The accounting update is effective for the fiscal year beginning after December 15, 2019 (January 1, 2020 for our company) and early adoption is permitted. We early adopted the guidance in the update on January 1, 2019. The adoption of the accounting update did not have a material impact on our consolidated financial statements. See Note 4 for further information. Derivatives and Hedging In August 2017, the FASB issued ASU 2017-12, “Targeted Improvements to Accounting for Hedging Activities,” which amends the hedge accounting recognition and presentation requirements. The accounting update improves the transparency and understandability of information conveyed to financial statement users by better aligning companies’ hedging relationship to their existing risk management strategies, simplifies the application of hedge accounting and increases transparency regarding the scope and results of hedging program. The accounting update is effective for the fiscal year beginning after December 15, 2018 (January 1, 2019 for our company). The adoption of the accounting update did not have a material impact on our consolidated financial statements. See Note 12 for further information. Callable Debt Securities In March 2017, the FASB issued ASU 2017-08, “Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities,” which shortens the amortization period for the premium on certain callable debt securities to the earliest call date. The amendments are applicable to any purchased individual debt security with an explicit and non-contingent call feature that is callable at a fixed price on a preset date. The accounting update is effective for fiscal years beginning after December 15, 2018 (January 1, 2019 for our company) under a modified retrospective approach. The change was applied prospectively from January 1, 2019 and there is no impact to our previously presented results. The adoption of the accounting update resulted in a reduction of beginning retained earnings of $4.4 million after-tax as a cumulative effect of adoption of an accounting change. Leases In February 2016, the FASB issued ASU 2016-02 that requires for leases longer than one year, a lessee recognize in the statements of financial condition a right-of-use asset, representing the right to use the underlying asset for the lease term, and a lease liability, representing the liability to make lease payments. The accounting update also requires that for finance leases, a lessee recognize interest expense on the lease liability, separately from the amortization of the right-of-use asset in the statements of earnings, while for operating leases, such amounts should be recognized as a combined expense. In addition, this accounting update requires expanded disclosures about the nature and terms of lease agreements. This change was applied prospectively from January 1, 2019 and there is no impact on our previously presented results. Upon adoption, in accordance with the new lease standard, we elected to not reassess the lease classification or initial direct costs of existing leases, and to not reassess whether existing contracts contain a lease. In addition, we have elected to account for each contract’s lease and non-lease components as a single lease component. The adoption of the new lease standard resulted in a reduction of beginning retained earnings of $2.4 million after-tax as a cumulative effect of adoption of an accounting change. Upon adoption, the company recorded a gross up of approximately $670 million on its consolidated statements of financial condition to recognize the right-of-use assets, included in fixed assets, net and lease liabilities, included in accounts payable and accrued expenses.
Recently Issued Accounting Guidance	Recently Issued Accounting Guidance Goodwill Impairment Testing In January 2017, the FASB issued ASU 2017-04, “Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment,” which simplifies the subsequent measurement of goodwill and eliminates Step 2 from the goodwill impairment test. Under the accounting update, the annual, or interim, goodwill impairment test is performed by comparing the fair value of a reporting unit with its carrying amount, and an impairment charge should be recognized for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. The accounting update is effective for annual or any interim impairment tests in fiscal years beginning after December 15, 2019 (January 1, 2020 for our company) and early adoption is permitted. We are currently evaluating the impact of the accounting update, but the adoption is not expected to have a material impact on our consolidated financial statements. Financial Instruments – Credit Losses In June 2016, the FASB issued ASU 2016-13, “Financial Instruments − Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments.” This accounting update impacts the impairment model for certain financial assets measured at amortized cost by requiring a current expected credit loss (“CECL”) methodology to estimate expected credit losses over the entire life of the financial asset, recorded at inception or purchase. CECL will replace the loss model currently applicable to bank loans, held-to-maturity securities, and other receivables carried at amortized cost. The accounting update also eliminates the concept of other-than-temporary impairment for available-for-sale securities. Impairments on available-for-sale securities will be required to be recognized in earnings through an allowance, when the fair value is less than amortized cost and a credit loss exists or the securities are expected to be sold before recovery of amortized cost. Under the accounting update, there may be an ability to determine there are no expected credit losses in certain circumstances, e.g., based on collateral arrangements for lending and financing transactions or based on the credit quality of the borrower or issuer. Overall, the amendments in this accounting update are expected to accelerate the recognition of credit losses for portfolios where CECL models will be applied. The accounting update is effective for fiscal years beginning after December 15, 2019 (January 1, 2020 for our company) with early adoption permitted as of January 1, 2019. We are currently evaluating the impact of the accounting update, but the adoption is not expected to have a material impact on our consolidated financial statements.
Revenue Recognition	Commissions. We earn commission revenue by executing, settling, and clearing transactions for clients primarily in OTC and listed equity securities, insurance products, and options. Trade execution and clearing and custody services, when provided together, represent a single performance obligation as the services are not separately identifiable in the context of the contract. Commission revenues associated with combined trade execution and clearing and custody services, as well as trade execution services on a standalone basis, are recognized at a point in time on trade-date. Commission revenues are generally paid on settlement date and we record a receivable between trade-date and payment on settlement date. Investment Banking. We provide our clients with a full range of capital markets and financial advisory services. Capital markets services include underwriting and placement agent services in both the equity and debt capital markets, including private equity placements, initial public offerings, follow-on offerings, underwriting and distributing public and private debt. Capital raising revenues are recognized at a point in time on trade-date, as the client obtains the control and benefit of the capital markets offering at that point. Costs associated with capital raising transactions are deferred until the related revenue is recognized or the engagement is otherwise concluded, and are recorded on a gross basis within other operating expenses in the consolidated statements of operations as we are acting as a principal in the arrangement. Any expenses reimbursed by our clients are recognized as investment banking revenues. Revenues from financial advisory services primarily consist of fees generated in connection with merger, acquisition and restructuring transactions. Advisory fees from mergers and acquisitions engagements are recognized at a point in time when the related transaction is completed, as the performance obligation is to successfully broker a specific transaction. Fees received prior to the completion of the transaction are deferred within accounts payable and accrued expenses on the consolidated statements of financial condition. Advisory fees from restructuring engagements are recognized over time using a time elapsed measure of progress as our clients simultaneously receive and consume the benefits of those services as they are provided. A significant portion of the fees we receive for our advisory services are considered variable as they are contingent upon a future event (e.g., completion of a transaction or third party emergence from bankruptcy) and are excluded from the transaction price until the uncertainty associated with the variable consideration is subsequently resolved, which is expected to occur upon achievement of the specified milestone. Payment for advisory services are generally due promptly upon completion of a specified milestone or, for retainer fees, periodically over the course of the engagement. We recognize a receivable between the date of completion of the milestone and payment by the customer. Expenses associated with investment banking advisory engagements are deferred only to the extent they are explicitly reimbursable by the client and the related revenue is recognized at the same time as the associated revenues. All other investment banking advisory related expenses, including expenses incurred related to restructuring assignments, are expensed as incurred. All investment banking advisory expenses are recognized within other operating expenses on the consolidated statements of operations and any expenses reimbursed by our clients are recognized as investment banking revenues. Asset Management Fees. We earn management and performance fees in connection with investment advisory services provided to institutional and individual clients. Investment advisory fees are charged based on the value of assets in fee-based accounts and are affected by changes in the balances of client assets due to market fluctuations and levels of net new client assets. Fees are charged either in advance based on fixed rates applied to the value of the customers’ account at the beginning of the period or periodically based on contracted rates and account performance. Contracts can be terminated at any time with no incremental payments due to our company upon termination. If the contract is terminated by the customer fees are prorated for the period and fees charged for the post termination period are refundable to the customer.

New Accounting Pronouncements (Policies)

3 Months Ended

Mar. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Fair Value Measurement

In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement. The objective of this guidance is to improve the effectiveness of disclosure requirements on fair value measurement by eliminating certain disclosure requirements for fair value measurements for all entities, requiring public entities to disclose certain new information and modifying some disclosure requirements. The accounting update is effective for the fiscal year beginning after December 15, 2019 (January 1, 2020 for our company) and early adoption is permitted. We early adopted the guidance in the update on January 1, 2019. The adoption of the accounting update did not have a material impact on our consolidated financial statements. See Note 4 for further information.

Derivatives and Hedging

In August 2017, the FASB issued ASU 2017-12, “Targeted Improvements to Accounting for Hedging Activities,” which amends the hedge accounting recognition and presentation requirements. The accounting update improves the transparency and understandability of information conveyed to financial statement users by better aligning companies’ hedging relationship to their existing risk management strategies, simplifies the application of hedge accounting and increases transparency regarding the scope and results of hedging program. The accounting update is effective for the fiscal year beginning after December 15, 2018 (January 1, 2019 for our company). The adoption of the accounting update did not have a material impact on our consolidated financial statements. See Note 12 for further information.

Callable Debt Securities

In March 2017, the FASB issued ASU 2017-08, “Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities,” which shortens the amortization period for the premium on certain callable debt securities to the earliest call date. The amendments are applicable to any purchased individual debt security with an explicit and non-contingent call feature that is callable at a fixed price on a preset date. The accounting update is effective for fiscal years beginning after December 15, 2018 (January 1, 2019 for our company) under a modified retrospective approach. The change was applied prospectively from January 1, 2019 and there is no impact to our previously presented results. The adoption of the accounting update resulted in a reduction of beginning retained earnings of $4.4 million after-tax as a cumulative effect of adoption of an accounting change.

Leases

In February 2016, the FASB issued ASU 2016-02 that requires for leases longer than one year, a lessee recognize in the statements of financial condition a right-of-use asset, representing the right to use the underlying asset for the lease term, and a lease liability, representing the liability to make lease payments. The accounting update also requires that for finance leases, a lessee recognize interest expense on the lease liability, separately from the amortization of the right-of-use asset in the statements of earnings, while for operating leases, such amounts should be recognized as a combined expense. In addition, this accounting update requires expanded disclosures about the nature and terms of lease agreements.

This change was applied prospectively from January 1, 2019 and there is no impact on our previously presented results. Upon adoption, in accordance with the new lease standard, we elected to not reassess the lease classification or initial direct costs of existing leases, and to not reassess whether existing contracts contain a lease. In addition, we have elected to account for each contract’s lease and non-lease components as a single lease component. The adoption of the new lease standard resulted in a reduction of beginning retained earnings of $2.4 million after-tax as a cumulative effect of adoption of an accounting change. Upon adoption, the company recorded a gross up of approximately $670 million on its consolidated statements of financial condition to recognize the right-of-use assets, included in fixed assets, net and lease liabilities, included in accounts payable and accrued expenses.

Recently Issued Accounting Guidance

Goodwill Impairment Testing

In January 2017, the FASB issued ASU 2017-04, “Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment,” which simplifies the subsequent measurement of goodwill and eliminates Step 2 from the goodwill impairment test. Under the accounting update, the annual, or interim, goodwill impairment test is performed by comparing the fair value of a reporting unit with its carrying amount, and an impairment charge should be recognized for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. The accounting update is effective for annual or any interim impairment tests in fiscal years beginning after December 15, 2019 (January 1, 2020 for our company) and early adoption is permitted. We are currently evaluating the impact of the accounting update, but the adoption is not expected to have a material impact on our consolidated financial statements.

Financial Instruments – Credit Losses

In June 2016, the FASB issued ASU 2016-13, “Financial Instruments − Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments.” This accounting update impacts the impairment model for certain financial assets measured at amortized cost by requiring a current expected credit loss (“CECL”) methodology to estimate expected credit losses over the entire life of the financial asset, recorded at inception or purchase. CECL will replace the loss model currently applicable to bank loans, held-to-maturity securities, and other receivables carried at amortized cost.

The accounting update also eliminates the concept of other-than-temporary impairment for available-for-sale securities. Impairments on available-for-sale securities will be required to be recognized in earnings through an allowance, when the fair value is less than amortized cost and a credit loss exists or the securities are expected to be sold before recovery of amortized cost. Under the accounting update, there may be an ability to determine there are no expected credit losses in certain circumstances, e.g., based on collateral arrangements for lending and financing transactions or based on the credit quality of the borrower or issuer.

Overall, the amendments in this accounting update are expected to accelerate the recognition of credit losses for portfolios where CECL models will be applied. The accounting update is effective for fiscal years beginning after December 15, 2019 (January 1, 2020 for our company) with early adoption permitted as of January 1, 2019. We are currently evaluating the impact of the accounting update, but the adoption is not expected to have a material impact on our consolidated financial statements.

Revenue Recognition

Commissions. We earn commission revenue by executing, settling, and clearing transactions for clients primarily in OTC and listed equity securities, insurance products, and options. Trade execution and clearing and custody services, when provided together, represent a single performance obligation as the services are not separately identifiable in the context of the contract. Commission revenues associated with combined trade execution and clearing and custody services, as well as trade execution services on a standalone basis, are recognized at a point in time on trade-date. Commission revenues are generally paid on settlement date and we record a receivable between trade-date and payment on settlement date.

Investment Banking. We provide our clients with a full range of capital markets and financial advisory services. Capital markets services include underwriting and placement agent services in both the equity and debt capital markets, including private equity placements, initial public offerings, follow-on offerings, underwriting and distributing public and private debt.

Capital raising revenues are recognized at a point in time on trade-date, as the client obtains the control and benefit of the capital markets offering at that point. Costs associated with capital raising transactions are deferred until the related revenue is recognized or the engagement is otherwise concluded, and are recorded on a gross basis within other operating expenses in the consolidated statements of operations as we are acting as a principal in the arrangement. Any expenses reimbursed by our clients are recognized as investment banking revenues.

Revenues from financial advisory services primarily consist of fees generated in connection with merger, acquisition and restructuring transactions. Advisory fees from mergers and acquisitions engagements are recognized at a point in time when the related transaction is completed, as the performance obligation is to successfully broker a specific transaction. Fees received prior to the completion of the transaction are deferred within accounts payable and accrued expenses on the consolidated statements of financial condition. Advisory fees from restructuring engagements are recognized over time using a time elapsed measure of progress as our clients simultaneously receive and consume the benefits of those services as they are provided. A significant portion of the fees we receive for our advisory services are considered variable as they are contingent upon a future event (e.g., completion of a transaction or third party emergence from bankruptcy) and are excluded from the transaction price until the uncertainty associated with the variable consideration is subsequently resolved, which is expected to occur upon achievement of the specified milestone. Payment for advisory services are generally due promptly upon completion of a specified milestone or, for retainer fees, periodically over the course of the engagement. We recognize a receivable between the date of completion of the milestone and payment by the customer. Expenses associated with investment banking advisory engagements are deferred only to the extent they are explicitly reimbursable by the client and the related revenue is recognized at the same time as the associated revenues. All other investment banking advisory related expenses, including expenses incurred related to restructuring assignments, are expensed as incurred. All investment banking advisory expenses are recognized within other operating expenses on the consolidated statements of operations and any expenses reimbursed by our clients are recognized as investment banking revenues.

Asset Management Fees. We earn management and performance fees in connection with investment advisory services provided to institutional and individual clients. Investment advisory fees are charged based on the value of assets in fee-based accounts and are affected by changes in the balances of client assets due to market fluctuations and levels of net new client assets. Fees are charged either in advance based on fixed rates applied to the value of the customers’ account at the beginning of the period or periodically based on contracted rates and account performance. Contracts can be terminated at any time with no incremental payments due to our company upon termination. If the contract is terminated by the customer fees are prorated for the period and fees charged for the post termination period are refundable to the customer.