Recent Accounting Pronouncements	6 Months Ended
Jun. 30, 2018
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements ASU 2014-09 – In May 2014, the Financial Accounting Standards Board ("FASB") issued ASU 2014-09. ASU 2014-09 provides amendments to ASC 605, "Revenue Recognition" and creates ASC 606, "Revenue from Contracts with Customers," which changes the requirements for revenue recognition and amends the disclosure requirements. In August 2015, the FASB issued ASU No. 2015-14, "Deferral of the Effective Date," which provides amendments that defer the effective date of ASU 2014-09 by one year. In April 2016, the FASB issued ASU No. 2016-10, "Identifying Performance Obligations and Licensing," which provides clarification to identifying performance obligations and the licensing implementation guidance in ASU 2014-09. In May 2016, the FASB issued ASU No. 2016-12, "Narrow-Scope Improvements and Practical Expedients," which provides clarification on certain issues identified in the guidance on assessing collectability, presentation of sales taxes, noncash consideration, and completed contracts and contract modifications at transition in ASU 2014-09. The amendments in these updates are effective either retrospectively to each prior reporting period presented, or as a cumulative-effect adjustment as of the date of adoption, during interim and annual periods beginning after December 15, 2017, with early adoption permitted beginning after December 15, 2016. The Company adopted ASU 2014-09 on January 1, 2018 using the modified retrospective method of transition, which requires a cumulative-effect adjustment as of the date of adoption. The Company did not have a cumulative-effect adjustment as of the date of adoption. Following the adoption of ASU 2014-09, success related advisory fees, for which payment is generally dependent on the closing of a strategic transaction, a financing arrangement or some other defined outcome, are considered variable consideration as defined by the standard. ASU 2014-09 requires that revenue be recognized when it is probable that variable consideration will not be reversed in a future period. Accordingly, revenue recognition for such fees could be accelerated under ASU 2014-09 in rare circumstances, which will require careful analysis and judgment. Under legacy U.S. GAAP, the Company recognized such fees upon closing regardless of the probability of the outcome. The effect of the timing of revenue recognition could be material to any given reporting period. Furthermore, legacy U.S. GAAP allowed expenses related to underwriting transactions to be reflected net in related revenues. Under ASU 2014-09, those expenses are presented gross in the results of operations. See Notes 2 and 4 for further information. ASU 2016-01 - In January 2016, the FASB issued ASU No. 2016-01, "Recognition and Measurement of Financial Assets and Financial Liabilities" ("ASU 2016-01"). ASU 2016-01 provides amendments to ASC 825, "Financial Instruments," which change the requirements for certain aspects of recognition, measurement and presentation of financial assets and liabilities and amend the disclosure requirements. The amendments in this update are effective during interim and annual periods beginning after December 15, 2017. The amendments in this update should be applied by means of a cumulative-effect adjustment to the balance sheet as of the beginning of the fiscal year of adoption and the amendments related to equity securities without readily determinable fair values should be applied prospectively. The Company adopted ASU 2016-01 on January 1, 2018, which resulted in a cumulative effect adjustment of cumulative unrealized losses, net of tax, on available-for-sale equity securities included in Accumulated Other Comprehensive Income (Loss) to Retained Earnings of ($2,229). Following the adoption of ASU 2016-01, unrealized gains and losses on these securities are recorded in Other Revenue, Including Interest and Investments, on the Unaudited Condensed Consolidated Statements of Operations. The Company also holds equity securities without readily determinable fair values, which were accounted for under the cost method of accounting under legacy U.S. GAAP. Following the adoption of ASU 2016-01, the Company elected to measure each of its former cost method investments at its cost minus impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer. See Notes 7 and 9 for further information. ASU 2016-02 - In February 2016, the FASB issued ASU No. 2016-02, "Leases (Topic 842)" ("ASU 2016-02"). ASU 2016-02 supersedes ASC 840, "Leases," and includes requirements for the recognition of a right-of-use asset and lease liability on the balance sheet by lessees for those leases classified as operating leases under previous guidance. The amendments in this update are effective using a modified retrospective approach at the beginning of the earliest period presented, during interim and annual periods beginning after December 15, 2018, with early adoption permitted. The Company anticipates adopting ASU 2016-02 on January 1, 2019 using the modified retrospective approach. The Company is in the process of evaluating its lease agreements under ASU 2016-02, including its lease agreement to expand its New York headquarters signed on July 1, 2018. See Note 16 for further information. The adoption will result in the present value of the Company's lease commitments which have a term in excess of one year being reflected on the Company's Statements of Financial Condition as a long-term asset with a corresponding long-term liability. The Company's lease commitments primarily relate to office space, as discussed in Note 16 and in Note 18 to the Company's consolidated financial statements in the Company's Annual Report on Form 10-K for the year ended December 31, 2017. The impact on the Company's earnings is not expected to be materially different from the current expense related to leases as required under legacy U.S. GAAP, which is primarily reflected in Occupancy and Equipment Rental expense on the Unaudited Condensed Consolidated Statements of Operations. ASU 2016-13 - In June 2016, the FASB issued ASU No. 2016-13, "Measurement of Credit Losses on Financial Instruments" ("ASU 2016-13"). ASU 2016-13 provides amendments to ASC 326, "Financial Instruments - Credit Losses," which amend the guidance on the impairment of financial instruments and adds an impairment model (the current expected credit loss (CECL) model) that is based on expected losses rather than incurred losses. Entities will recognize an allowance for its estimate of expected credit losses as of the end of each reporting period. The amendments in this update are effective during interim and annual periods beginning after December 15, 2019, with early adoption permitted after December 15, 2018. The Company currently uses the specific identification method for establishing credit provisions and write-offs of its trade accounts receivable. The Company anticipates adopting ASU 2016-13 on January 1, 2020 and does not anticipate a material difference between the current method and the CECL model. ASU 2016-15 - In August 2016, the FASB issued ASU No. 2016-15, "Classification of Certain Cash Receipts and Cash Payments" ("ASU 2016-15"). ASU 2016-15 provides amendments to ASC 230, "Statement of Cash Flows," ("ASC 230") which provide guidance on the classification of certain cash receipts and payments in the statement of cash flows. The amendments in this update are effective retrospectively, or prospectively, if retrospective application is impracticable, during interim and annual periods beginning after December 15, 2017, with early adoption permitted. The adoption of ASU 2016-15 did not have a material impact on the Company's financial condition, results of operations and cash flows, or disclosures thereto. ASU 2016-18 - In November 2016, the FASB issued ASU No. 2016-18, "Restricted Cash" ("ASU 2016-18"). ASU 2016-18 provides amendments to ASC 230, which require that a statement of cash flows explain the change during the period in the total of cash, cash equivalents and amounts generally described as restricted cash and restricted cash equivalents. The amendments in this update are effective retrospectively during interim and annual periods beginning after December 15, 2017, with early adoption permitted. The adoption of ASU 2016-18 resulted in restricted cash balances being included in the Unaudited Condensed Consolidated Statements of Cash Flows and expanded disclosure on these restricted cash balances. See Note 16 for further information. ASU 2017-01 - In January 2017, the FASB issued ASU No. 2017-01, "Clarifying the Definition of a Business" ("ASU 2017-01"). ASU 2017-01 provides amendments to ASC 805, "Business Combinations," which clarify the definition of a business with the objective of adding guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The amendments in this update are effective prospectively during interim and annual periods beginning after December 15, 2017, with early adoption permitted. The adoption of ASU 2017-01 did not have a material impact on the Company's financial condition, results of operations and cash flows, or disclosures thereto. ASU 2017-09 - In May 2017, the FASB issued ASU No. 2017-09, "Scope of Modification Accounting" ("ASU 2017-09"). ASU 2017-09 provides amendments to ASC 718, "Compensation - Stock Compensation," ("ASC 718") which provide guidance and clarity around which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting. The amendments in this update are effective prospectively during interim and annual periods beginning after December 15, 2017, with early adoption permitted. The adoption of ASU 2017-09 did not have a material impact on the Company's financial condition, results of operations and cash flows, or disclosures thereto. ASU 2018-02 - In February 2018, the FASB issued ASU No. 2018-02, "Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income" ("ASU 2018-02"). ASU 2018-02 provides amendments to ASC 220, “Income Statement - Reporting Other Comprehensive Income,” which allow a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. The amendments in this update are effective either in the period of adoption or retrospectively, to each period (or periods) in which the effect of the change in the U.S. federal corporate income tax rate in the Tax Cuts and Jobs Act is recognized, during interim and annual periods beginning after December 15, 2018, with early adoption permitted. The Company is currently assessing the impact of this update on the Company's financial condition, results of operations and cash flows, or disclosures thereto. ASU 2018-05 - In March 2018, the FASB issued ASU No. 2018-05, "Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118" ("ASU 2018-05"). ASU 2018-05 adds various SEC paragraphs to ASC 740, “Income Taxes,” ("ASC 740") pursuant to the issuance of SEC Staff Accounting Bulletin No. 118 ("SAB 118"). The amendments in this update were effective upon issuance. See Note 18 for further information. ASU 2018-07 - In June 2018, the FASB issued ASU No. 2018-07, "Improvements to Nonemployee Share-Based Payment Accounting" ("ASU 2018-07"). ASU 2018-07 provides amendments to ASC 718 to align the accounting for share-based payment awards issued to employees and nonemployees, particularly surrounding the measurement date and impact of performance conditions. The amendments in this update are effective during interim and annual periods beginning after December 15, 2018, with early adoption permitted. The amendments in this update should be applied by means of a cumulative-effect adjustment to retained earnings as of the beginning of the fiscal year of adoption for liability-classified awards that have not been settled and equity-classified awards for which a measurement date has not been established by the date of adoption, and prospectively for all new awards granted after the date of adoption. The Company is currently assessing the impact of this update on the Company's financial condition, results of operations and cash flows, or disclosures thereto.

Recent Accounting Pronouncements

ASU 2014-09 – In May 2014, the Financial Accounting Standards Board ("FASB") issued ASU 2014-09. ASU 2014-09 provides amendments to ASC 605, "Revenue Recognition" and creates ASC 606, "Revenue from Contracts with Customers," which changes the requirements for revenue recognition and amends the disclosure requirements. In August 2015, the FASB issued ASU No. 2015-14, "Deferral of the Effective Date," which provides amendments that defer the effective date of ASU 2014-09 by one year. In April 2016, the FASB issued ASU No. 2016-10, "Identifying Performance Obligations and Licensing," which provides clarification to identifying performance obligations and the licensing implementation guidance in ASU 2014-09. In May 2016, the FASB issued ASU No. 2016-12, "Narrow-Scope Improvements and Practical Expedients," which provides clarification on certain issues identified in the guidance on assessing collectability, presentation of sales taxes, noncash consideration, and completed contracts and contract modifications at transition in ASU 2014-09. The amendments in these updates are effective either retrospectively to each prior reporting period presented, or as a cumulative-effect adjustment as of the date of adoption, during interim and annual periods beginning after December 15, 2017, with early adoption permitted beginning after December 15, 2016.

The Company adopted ASU 2014-09 on January 1, 2018 using the modified retrospective method of transition, which requires a cumulative-effect adjustment as of the date of adoption. The Company did not have a cumulative-effect adjustment as of the date of adoption. Following the adoption of ASU 2014-09, success related advisory fees, for which payment is generally dependent on the closing of a strategic transaction, a financing arrangement or some other defined outcome, are considered variable consideration as defined by the standard. ASU 2014-09 requires that revenue be recognized when it is probable that variable consideration will not be reversed in a future period. Accordingly, revenue recognition for such fees could be accelerated under ASU 2014-09 in rare circumstances, which will require careful analysis and judgment. Under legacy U.S. GAAP, the Company recognized such fees upon closing regardless of the probability of the outcome. The effect of the timing of revenue recognition could be material to any given reporting period. Furthermore, legacy U.S. GAAP allowed expenses related to underwriting transactions to be reflected net in related revenues. Under ASU 2014-09, those expenses are presented gross in the results of operations. See Notes 2 and 4 for further information.

ASU 2016-01 - In January 2016, the FASB issued ASU No. 2016-01, "Recognition and Measurement of Financial Assets and Financial Liabilities" ("ASU 2016-01"). ASU 2016-01 provides amendments to ASC 825, "Financial Instruments," which change the requirements for certain aspects of recognition, measurement and presentation of financial assets and liabilities and amend the disclosure requirements. The amendments in this update are effective during interim and annual periods beginning after December 15, 2017. The amendments in this update should be applied by means of a cumulative-effect adjustment to the balance sheet as of the beginning of the fiscal year of adoption and the amendments related to equity securities without readily determinable fair values should be applied prospectively.

The Company adopted ASU 2016-01 on January 1, 2018, which resulted in a cumulative effect adjustment of cumulative unrealized losses, net of tax, on available-for-sale equity securities included in Accumulated Other Comprehensive Income (Loss) to Retained Earnings of ($2,229). Following the adoption of ASU 2016-01, unrealized gains and losses on these securities are recorded in Other Revenue, Including Interest and Investments, on the Unaudited Condensed Consolidated Statements of Operations. The Company also holds equity securities without readily determinable fair values, which were accounted for under the cost method of accounting under legacy U.S. GAAP. Following the adoption of ASU 2016-01, the Company elected to measure each of its former cost method investments at its cost minus impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer. See Notes 7 and 9 for further information.

ASU 2016-02 - In February 2016, the FASB issued ASU No. 2016-02, "Leases (Topic 842)" ("ASU 2016-02"). ASU 2016-02 supersedes ASC 840, "Leases," and includes requirements for the recognition of a right-of-use asset and lease liability on the balance sheet by lessees for those leases classified as operating leases under previous guidance. The amendments in this update are effective using a modified retrospective approach at the beginning of the earliest period presented, during interim and annual periods beginning after December 15, 2018, with early adoption permitted. The Company anticipates adopting ASU 2016-02 on January 1, 2019 using the modified retrospective approach. The Company is in the process of evaluating its lease agreements under ASU 2016-02, including its lease agreement to expand its New York headquarters signed on July 1, 2018. See Note 16 for further information. The adoption will result in the present value of the Company's lease commitments which have a term in excess of one year being reflected on the Company's Statements of Financial Condition as a long-term asset with a corresponding long-term liability. The Company's lease commitments primarily relate to office space, as discussed in Note 16 and in Note 18 to the Company's consolidated financial statements in the Company's Annual Report on Form 10-K for the year ended December 31, 2017. The impact on the Company's earnings is not expected to be materially different from the current expense related to leases as required under legacy U.S. GAAP, which is primarily reflected in Occupancy and Equipment Rental expense on the Unaudited Condensed Consolidated Statements of Operations.

ASU 2016-13 - In June 2016, the FASB issued ASU No. 2016-13, "Measurement of Credit Losses on Financial Instruments" ("ASU 2016-13"). ASU 2016-13 provides amendments to ASC 326, "Financial Instruments - Credit Losses," which amend the guidance on the impairment of financial instruments and adds an impairment model (the current expected credit loss (CECL) model) that is based on expected losses rather than incurred losses. Entities will recognize an allowance for its estimate of expected credit losses as of the end of each reporting period. The amendments in this update are effective during interim and annual periods beginning after December 15, 2019, with early adoption permitted after December 15, 2018. The Company currently uses the specific identification method for establishing credit provisions and write-offs of its trade accounts receivable. The Company anticipates adopting ASU 2016-13 on January 1, 2020 and does not anticipate a material difference between the current method and the CECL model.

ASU 2016-15 - In August 2016, the FASB issued ASU No. 2016-15, "Classification of Certain Cash Receipts and Cash Payments" ("ASU 2016-15"). ASU 2016-15 provides amendments to ASC 230, "Statement of Cash Flows," ("ASC 230") which provide guidance on the classification of certain cash receipts and payments in the statement of cash flows. The amendments in this update are effective retrospectively, or prospectively, if retrospective application is impracticable, during interim and annual periods beginning after December 15, 2017, with early adoption permitted. The adoption of ASU 2016-15 did not have a material impact on the Company's financial condition, results of operations and cash flows, or disclosures thereto.

ASU 2016-18 - In November 2016, the FASB issued ASU No. 2016-18, "Restricted Cash" ("ASU 2016-18"). ASU 2016-18 provides amendments to ASC 230, which require that a statement of cash flows explain the change during the period in the total of cash, cash equivalents and amounts generally described as restricted cash and restricted cash equivalents. The amendments in this update are effective retrospectively during interim and annual periods beginning after December 15, 2017, with early adoption permitted. The adoption of ASU 2016-18 resulted in restricted cash balances being included in the Unaudited Condensed Consolidated Statements of Cash Flows and expanded disclosure on these restricted cash balances. See Note 16 for further information.

ASU 2017-01 - In January 2017, the FASB issued ASU No. 2017-01, "Clarifying the Definition of a Business" ("ASU 2017-01"). ASU 2017-01 provides amendments to ASC 805, "Business Combinations," which clarify the definition of a business with the objective of adding guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The amendments in this update are effective prospectively during interim and annual periods beginning after December 15, 2017, with early adoption permitted. The adoption of ASU 2017-01 did not have a material impact on the Company's financial condition, results of operations and cash flows, or disclosures thereto.

ASU 2017-09 - In May 2017, the FASB issued ASU No. 2017-09, "Scope of Modification Accounting" ("ASU 2017-09"). ASU 2017-09 provides amendments to ASC 718, "Compensation - Stock Compensation," ("ASC 718") which provide guidance and clarity around which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting. The amendments in this update are effective prospectively during interim and annual periods beginning after December 15, 2017, with early adoption permitted. The adoption of ASU 2017-09 did not have a material impact on the Company's financial condition, results of operations and cash flows, or disclosures thereto.

ASU 2018-02 - In February 2018, the FASB issued ASU No. 2018-02, "Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income" ("ASU 2018-02"). ASU 2018-02 provides amendments to ASC 220, “Income Statement - Reporting Other Comprehensive Income,” which allow a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. The amendments in this update are effective either in the period of adoption or retrospectively, to each period (or periods) in which the effect of the change in the U.S. federal corporate income tax rate in the Tax Cuts and Jobs Act is recognized, during interim and annual periods beginning after December 15, 2018, with early adoption permitted. The Company is currently assessing the impact of this update on the Company's financial condition, results of operations and cash flows, or disclosures thereto.

ASU 2018-05 - In March 2018, the FASB issued ASU No. 2018-05, "Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118" ("ASU 2018-05"). ASU 2018-05 adds various SEC paragraphs to ASC 740, “Income Taxes,” ("ASC 740") pursuant to the issuance of SEC Staff Accounting Bulletin No. 118 ("SAB 118"). The amendments in this update were effective upon issuance. See Note 18 for further information.

ASU 2018-07 - In June 2018, the FASB issued ASU No. 2018-07, "Improvements to Nonemployee Share-Based Payment Accounting" ("ASU 2018-07"). ASU 2018-07 provides amendments to ASC 718 to align the accounting for share-based payment awards issued to employees and nonemployees, particularly surrounding the measurement date and impact of performance conditions. The amendments in this update are effective during interim and annual periods beginning after December 15, 2018, with early adoption permitted. The amendments in this update should be applied by means of a cumulative-effect adjustment to retained earnings as of the beginning of the fiscal year of adoption for liability-classified awards that have not been settled and equity-classified awards for which a measurement date has not been established by the date of adoption, and prospectively for all new awards granted after the date of adoption. The Company is currently assessing the impact of this update on the Company's financial condition, results of operations and cash flows, or disclosures thereto.