Basis of Presentation	6 Months Ended
Basis of Presentation	Jun. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements of Argo Group International Holdings, Ltd. (“Argo Group,” “we” or the “Company”) and its subsidiaries have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and with the instructions for Form 10-Q and Article 10 of Regulation S-X. Argo Group is an underwriter of specialty insurance and reinsurance products in the property and casualty market. The preparation of interim financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenues and expenses during the reporting period. The major estimates reflected in our consolidated financial statements include, but are not limited to, reserves for losses and loss adjustment expenses; reinsurance recoverables, including the reinsurance recoverables allowance for expected credit losses; estimates of written and earned premiums; reinsurance premium receivable; fair value of investments and assessment of potential impairment, including the allowance for credit losses on fixed maturity securities; valuation of goodwill and intangibles and our deferred tax asset valuation allowance. Actual results could differ from those estimates. Certain financial information that normally is included in annual financial statements, including certain financial statement footnotes, prepared in accordance with GAAP, is not required for interim reporting purposes and has been condensed or omitted. These statements should be read in conjunction with the consolidated financial statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2019, filed with the Securities and Exchange Commission ("SEC") on February 28, 2020. The interim financial information as of, and for the three and six months ended, June 30, 2020 and 2019 is unaudited. However, in the opinion of management, the interim information includes all adjustments, consisting of normal recurring accruals, necessary for a fair presentation of the results presented for the interim periods. The operating results for the interim periods are not necessarily indicative of the results to be expected for the full year. All significant intercompany amounts have been eliminated in consolidation. Certain reclassifications have been made to financial information presented for prior years to conform to the current year’s presentation. During the first half of both 2020 and 2019, we incurred non-recurring costs associated with a number of activities that began with proxy solicitation efforts and shareholder engagement. For the three and six months ended June 30, 2019, these costs were $7.5 million and $8.0 million, respectively, and were previously included in the line item "Underwriting, Acquisition and Insurance Expenses" in the Consolidated Statements of Income in our Quarterly Report on Form 10-Q for the three and six months ended June 30, 2019. To conform to the current year's presentation, these amounts have been reclassified out of "Underwriting, acquisition and insurance expenses" and into "Other corporate expenses" in the Consolidated Statements of (Loss) Income herein. Please see Note 12, "Underwriting, Acquisition and Insurance Expenses & Other Corporate Expenses" for further discussion. Sale of Trident Brand and Platform On April 30, 2020, we sold our Trident Public Risk Solutions (“Trident”) brand and underwriting platform to Paragon Insurance Holdings, LLC (“Paragon”) and received $38 million in cash, with additional consideration in future periods depending on performance post-closing. We recognized a pre-tax gain of $32.3 million related to the sale, which is included in "Net realized investment gains (losses)" in our Consolidated Statements of (Loss) Income for the three and six months ended June 30, 2020. Trident was one of the business units within our U.S. Operations reporting segment. Paragon will continue to write business on Argo paper through a managing general agency agreement, and we will retain Trident’s claims operations and provide claims services to Paragon for the public entity business. Acquisition of Ariel Indemnity Limited Effective June 12, 2020, Argo Group and our subsidiary Argo Re, Ltd. (“Argo Re”) acquired 100% of the capital stock of Ariel Indemnity Limited (“AIL”) for consideration of $55.6 million. The acquisition of AIL was made pursuant to the former owners (the “Sellers”) of Maybrooke Holdings, S.A. (“Maybrooke”) exercising a put option within the Administrative Services Agreement (“ASA”) between the Company and the Sellers. The ASA was part of the stock purchase agreement between the Company and the Sellers related to our February 6, 2017 acquisition of Maybrooke, the since-liquidated holding company of our Ariel Re platform. The $55.6 million sales price is equal to the 2019 year-end tangible net worth of the AIL, less certain administrative costs. Upon acquiring AIL, we dissolved AIL and merged it into Argo Re. The net assets of AIL are primarily comprised of certain invested assets and receivables, as well as run-off reserves associated with a loss portfolio transfer agreement between AIL and the former Ariel Reinsurance Company, Ltd. ("ARL") legal entity. ARL was merged into Argo Re in December 2017. The acquisition is being accounted for in accordance with ASC 805, “Business Combinations.” Purchase accounting, as defined by ASC 805, requires that the assets acquired, and liabilities assumed be recognized at their fair values as of the acquisition date. We are in the process of finalizing our determination of fair values and, as such, provisional fair value amounts for AIL have been recorded for the three and six months ended June 30, 2020. Based on our initial purchase price allocation, we do not believe that any intangible assets, including goodwill, will be material. We anticipate closing the fair value measurement period by the end of 2020. AIL’s financial position, results of operations and cash flows were not material to our consolidated financial results as of and for the three and six months ended June 30, 2020. Risks and Uncertainties Certain risks and uncertainties are inherent to our day-to-day operations. Adverse changes in the economy could lower demand for our insurance products or negatively impact our investment results, both of which could have an adverse effect on the revenue and profitability of our operations. The global COVID-19 pandemic has resulted in and is expected to continue to result in significant disruptions in economic activity and financial markets. The cumulative effects of COVID-19 on the Company, and the effect of any other public health outbreak, cannot be predicted at this time, but could reduce demand for our insurance policies, result in increased level of losses, settlement expenses or other operating costs, reduce the market value of invested assets held by the Company or negatively impact the fair value of our goodwill.