Argo Group International (ARGO-PA) 10-K 15 Mar 21 2020 FY Annual report Financial data

Cover

Cover - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Mar. 09, 2021	Jun. 30, 2020
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	1-15259
Entity Registrant Name	ARGO GROUP INTERNATIONAL HOLDINGS, LTD.
Entity Incorporation, State or Country Code	D0
Entity Tax Identification Number	98-0214719
Entity Address, Address Line One	90 Pitts Bay Road
Entity Address, City or Town	Pembroke
Entity Address, Postal Zip Code	HM08
Entity Address, Country	BM
City Area Code	441
Local Phone Number	296-5858
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 1,151.6
Entity Common Stock, Shares Outstanding		34,706,786
Documents Incorporated by Reference	Part III of this report incorporates by reference specific portions of the Registrant's Proxy Statement relating to the 2021 Annual General Meeting of Shareholders.
Entity Central Index Key	0001091748
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Common Shares
Document Information [Line Items]
Title of 12(b) Security	Common Stock, par value of $1.00 per share
Trading Symbol	ARGO
Security Exchange Name	NYSE
Guarantee of Argo Group U.S., Inc. 6.500% Senior Notes due 2042
Document Information [Line Items]
Title of 12(b) Security	Argo Group U.S., Inc. 6.500% Senior Notes due 2042 and the Guarantee with respects thereto
Trading Symbol	ARGD
Security Exchange Name	NYSE
Depositary Shares
Document Information [Line Items]
Title of 12(b) Security	Depositary Shares, each representing a 1/1000th Interest in a shareof Series A 7.00% Non-Cumulative Preference Shares, par value $1.00 per share
Trading Symbol	ARGOPrA
Security Exchange Name	NYSE

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Investments:
Fixed maturities available-for-sale, at fair value (cost: 2020 - $3,981.1, 2019 - $3,601.5; allowance for expected credit losses: 2020 - $6.6)	$ 4,107.1	$ 3,629.9
Equity securities, at fair value (cost: 2020 - $162.5; 2019 - $122.8)	176.7	136
Other investments (cost: 2020 - $429.4; 2019 - $484.2)	429.4	486.6
Short-term investments, at fair value (cost: 2020 - $541.4; 2019 - $844.8)	542.6	845
Total investments	5,255.8	5,097.5
Cash	148.8	137.8
Accrued investment income	21.8	25.7
Premiums receivable	679.8	676.5
Reinsurance recoverables	3,009	3,107.2
Goodwill	147.3	161.4
Intangible assets, net of accumulated amortization	60.5	91.8
Current income taxes receivable, net	3	0
Deferred tax assets, net	16.7	10.6
Deferred acquisition costs, net	163.6	160.2
Ceded unearned premiums	575.1	545
Operating leases right-of-use assets	82	91.8
Other assets	294.7	387.9
Assets held for sale	7.7	15.4
Total assets	10,465.8	10,508.8
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	5,406	5,157.6
Unearned premiums	1,464.8	1,410.9
Accrued underwriting expenses and other liabilities	167.6	221.9
Ceded reinsurance payable, net	950.4	1,201.2
Funds held	64.7	55.2
Senior unsecured fixed rate notes	140.2	140
Other indebtedness	60.7	181.3
Junior subordinated debentures	257.8	257.4
Current income taxes payable, net	0	13.9
Operating lease liabilities	95.8	105.7
Total liabilities	8,608	8,745.1
Commitments and contingencies (Note 19)
Shareholders' equity:
Preferred shares and additional paid-in capital - $1.00 par, 30,000,000 shares authorized; 6,000 and 0 shares issued at December 31, 2020 and December 31, 2019, respectively; liquidation preference $25,000	144	0
Common shares - $1.00 par, 500,000,000 shares authorized; 46,009,966 and 45,698,470 shares issued at December 31, 2020 and December 31, 2019, respectively	46	45.7
Additional paid-in capital	1,380.2	1,376.6
Treasury shares (11,315,889 shares at December 31, 2020 and December 31, 2019, respectively)	(455.1)	(455.1)
Retained earnings	684.1	793.7
Accumulated other comprehensive income, net of taxes	58.6	2.8
Total shareholders' equity	1,857.8	1,763.7
Total liabilities and shareholders' equity	$ 10,465.8	$ 10,508.8

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Fixed maturities available-for-sale, cost	$ 3,981.1	$ 3,601.5
Allowance for expected credit losses	6.6	0
Equity securities, cost	162.5	122.8
Other investments, cost	429.4	484.2
Short-term investments, cost	$ 541.4	$ 844.8
Preferred shares, par value (in dollars per share)	$ 1	$ 1
Preferred shares, authorized (in shares)	30,000,000	30,000,000
Preferred shares, issued (in shares)	6,000	0
Preferred stock, liquidation preference (in dollars per share)	$ 25,000
Common shares, par value (in dollars per share)	$ 1	$ 1
Common shares, shares authorized (in shares)	500,000,000	500,000,000
Common shares, shares issued (in shares)	46,009,966	45,698,470
Treasury shares (in shares)	11,315,889	11,315,889

Consolidated Statements of Inco

Consolidated Statements of Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Premiums and other revenue:
Earned premiums	$ 1,780.5	$ 1,729.7	$ 1,731.5
Net investment income	112.7	151.1	132.3
Fee and other income	7.9	9.1	9
Net realized investment gains (losses):
Net realized investment gains (losses)	22.4	120.9	33.1
Change in fair value of equity securities	10.3	(40.8)	(105.1)
Credit losses on fixed maturities	(39.9)	0	0
Net realized investment (losses) gains	(7.2)	80.1	(72)
Total revenue	1,893.9	1,970	1,800.8
Expenses:
Losses and loss adjustment expenses	1,208.8	1,220.7	1,040.8
Underwriting, acquisition and insurance expenses	679.4	666	656.1
Other corporate expenses	5.8	37.6	0
Interest expense	26.9	34.1	31.9
Fee and other expense	4	5.8	7.1
Foreign currency exchange losses (gains)	15.4	(9.8)	3.9
Impairment of goodwill	0	15.6	0
Total expenses	1,940.3	1,970	1,739.8
(Loss) income before income taxes	(46.4)	0	61
Income tax provision	7.7	14.1	4
Net (loss) income	(54.1)	(14.1)	57
Dividends on preferred shares	4.6	0	0
Net (loss) income attributable to common shareholders	$ (58.7)	$ (14.1)	$ 57
Net (loss) income attributable to common shareholders per common share:
Basic (in dollars per share)	$ (1.70)	$ (0.41)	$ 1.68
Diluted (in dollars per share)	(1.70)	(0.41)	1.65
Dividend declared per common share (in dollars per share)	$ 1.24	$ 1.24	$ 1.08
Weighted average common shares:
Basic (in shares)	34,614,813	34,205,954	33,922,009
Diluted (in shares)	34,614,813	34,205,954	34,678,781
Net realized investment gains (losses) before other-than-temporary impairment losses	$ (7.2)	$ 100.4	$ (64.4)
Other-than-temporary impairment losses recognized in earnings:
Other-than-temporary impairment losses on fixed maturities	0	(20.3)	(6.6)
Other-than-temporary impairment losses on other invested assets	0	0	(1)
Impairment losses recognized in earnings	$ 0	$ (20.3)	$ (7.6)

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (54.1)	$ (14.1)	$ 57
Other comprehensive income (loss):
Foreign currency translation adjustments	(15.3)	(0.2)	(3.4)
Defined benefit pension plans:
Net (loss) gain arising during the year	(0.6)	(1.8)	1.2
Unrealized gains (losses) on fixed maturity securities:
Gains (losses) arising during the year	95.2	88	(93.9)
Reclassification adjustment for (gains) losses included in net income	(12.8)	9.9	5.4
Other comprehensive income before tax	66.5	95.9	(90.7)
Defined benefit pension plans:
Net (loss) gain arising during the year	(0.1)	(0.4)	0.2
Unrealized gains (losses) on fixed maturity securities:
Gains (losses) arising during the year	16.5	14.2	(13.5)
Reclassification adjustment for losses included in net income	0	1.2	0.5
Income tax provision (benefit) related to other comprehensive income	16.4	15	(12.8)
Other comprehensive income (loss), net of tax	50.1	80.9	(77.9)
Comprehensive (loss) income	$ (4)	$ 66.8	$ (20.9)

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment	Preferred Shares and Additional Paid-in Capital	Common Shares	Additional Paid-In Capital	Treasury Shares	Retained Earnings	Retained EarningsCumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss)Cumulative Effect, Period of Adoption, Adjustment
Beginning Balance at Dec. 31, 2017	$ 1,812.9			$ 40.4	$ 1,129.1	$ (423.4)	$ 970.2		$ 96.6
Beginning Balance (Accounting Standards Update 2016-01) at Dec. 31, 2017		$ 1.7						$ 119.2		$ (117.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	57						57
Other comprehensive income - change in fair value of fixed maturities, net of taxes	(75.5)								(75.5)
Other comprehensive loss, net - other	(2.4)								(2.4)
Activity under stock incentive plans	15.9			0.6	15.3
Retirement of common shares (tax payments on equity compensation)	(7.4)			(0.1)	(7.3)
Employee stock purchase plan	2				2
Cash dividend declared - common shares	(37.5)						(37.5)
Repurchase of common shares	(31.7)					(31.7)
15% Stock Dividend	0			4.4	232.9		(237.3)
Cumulative effect of adoption of ASU 2018-02, net of taxes	0						(20.7)		20.7
Ending Balance at Dec. 31, 2018	1,735			45.3	1,372	(455.1)	850.9		(78.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	87.6
Ending Balance at Mar. 31, 2019	1,865.3
Beginning Balance at Dec. 31, 2018	1,735			45.3	1,372	(455.1)	850.9		(78.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	114.6
Ending Balance at Jun. 30, 2019	1,911.9
Beginning Balance at Dec. 31, 2018	1,735			45.3	1,372	(455.1)	850.9		(78.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	88.6
Ending Balance at Sep. 30, 2019	1,875.4
Beginning Balance at Dec. 31, 2018	1,735			45.3	1,372	(455.1)	850.9		(78.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(14.1)						(14.1)
Other comprehensive income - change in fair value of fixed maturities, net of taxes	82.5								82.5
Other comprehensive loss, net - other	(1.6)								(1.6)
Activity under stock incentive plans	16.3			0.6	15.7
Retirement of common shares (tax payments on equity compensation)	(13.8)			(0.2)	(13.6)
Employee stock purchase plan	2.5				2.5
Cash dividend declared - common shares	(43.1)						(43.1)
Ending Balance at Dec. 31, 2019	1,763.7	(2.2)	$ 0	45.7	1,376.6	(455.1)	793.7	(7.9)	2.8	5.7
Beginning Balance at Mar. 31, 2019	1,865.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	27
Ending Balance at Jun. 30, 2019	1,911.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(26)
Ending Balance at Sep. 30, 2019	1,875.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(102.7)
Ending Balance at Dec. 31, 2019	1,763.7	(2.2)	0	45.7	1,376.6	(455.1)	793.7	(7.9)	2.8	5.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(24.7)
Ending Balance at Mar. 31, 2020	1,613.5
Beginning Balance at Dec. 31, 2019	1,763.7	(2.2)	0	45.7	1,376.6	(455.1)	793.7	(7.9)	2.8	5.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(30.1)
Ending Balance at Jun. 30, 2020	1,707.7
Beginning Balance at Dec. 31, 2019	1,763.7	(2.2)	0	45.7	1,376.6	(455.1)	793.7	(7.9)	2.8	5.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(53.2)
Ending Balance at Sep. 30, 2020	1,848.7
Beginning Balance at Dec. 31, 2019	1,763.7	$ (2.2)	0	45.7	1,376.6	(455.1)	793.7	$ (7.9)	2.8	$ 5.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(54.1)						(54.1)
Preferred shares issued	144		144
Other comprehensive income - change in fair value of fixed maturities, net of taxes	65.9								65.9
Other comprehensive loss, net - other	(15.8)								(15.8)
Activity under stock incentive plans	8.1			0.4	7.7
Retirement of common shares (tax payments on equity compensation)	(6.7)			(0.1)	(6.6)
Employee stock purchase plan	2.5				2.5
Dividends on preferred shares	(4.6)						(4.6)
Cash dividend declared - common shares	$ (43)						(43)
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Ending Balance at Dec. 31, 2020	$ 1,857.8		$ 144	$ 46	$ 1,380.2	$ (455.1)	$ 684.1		$ 58.6
Beginning Balance at Mar. 31, 2020	1,613.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(5.4)
Ending Balance at Jun. 30, 2020	1,707.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(23.1)
Ending Balance at Sep. 30, 2020	$ 1,848.7

Consolidated Statements of Sh_2

Consolidated Statements of Shareholders' Equity (Parenthetical)	12 Months Ended
	Dec. 31, 2018$ / sharesshares
Statement of Stockholders' Equity [Abstract]
Common shares repurchased (in shares) | shares	530,882
Repurchase of common shares, weighted average price (in dollars per share)	$ 59.83
Stock dividend declared (in percentage)	15.00%
Cash dividend declared - common shares, per share (in dollars per share)	$ 1.08

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net (loss) income	$ (54.1)	$ (14.1)	$ 57
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Amortization and depreciation	33.2	27.3	31.9
Share-based payments expense	8.7	16.9	18.3
Deferred income tax benefit, net	(21.6)	(23.5)	(21.4)
Net realized investment (losses) gains	(7.2)	80.1	(72)
Undistributed loss (earnings) from alternative investment portfolio	(8.6)	(19.9)	(19)
Loss on disposals of long-lived assets, net	1.9	7.2	0.3
Impairment of goodwill	0	15.6	0
Change in:
Accrued investment income	3.9	1.5	(3.5)
Receivables	84.8	(455.1)	(558.3)
Deferred acquisition costs	(4.6)	7	(7.3)
Ceded unearned premiums	(33.2)	(87.8)	(47.6)
Reserves for losses and loss adjustment expenses	280.2	509	338.3
Unearned premiums	63.7	111.7	76.4
Ceded reinsurance payable and funds held	(238.2)	243.3	232
Income taxes	(17.5)	11.4	3.3
Accrued underwriting expenses and other liabilities	(43.7)	(10.6)	111.6
Other, net	9.8	(77)	17.8
Cash provided by operating activities	71.9	182.8	301.8
Cash flows from investing activities:
Sales of fixed maturity investments	1,080	1,394.3	1,259.1
Maturities and mandatory calls of fixed maturity investments	569.8	522.2	418.6
Sales of equity securities	25.4	374.7	238.9
Sales of other investments	103.9	83.1	101.8
Purchases of fixed maturity investments	(2,038.1)	(1,859.1)	(1,936)
Purchases of equity securities	(78.9)	(61.2)	(170.5)
Purchases of other investments	(35.5)	(63.7)	(42.6)
Change in foreign regulatory deposits and voluntary pools	(5.4)	0	13
Change in short-term investments	285.4	(490.4)	(132.2)
Settlements of foreign currency exchange forward contracts	9.4	0.3	(1.5)
Proceeds from sale of Ariel Re, net of cash transferred	28.3	0	0
Proceeds from sale of Trident assets	38	0	0
Cash acquired with acquisition of ArgoGlobal Assicurazioni	0	0	15.6
Purchases of fixed assets	(20.2)	(29.9)	(32.2)
Other, net	13.6	(13.1)	(0.3)
Cash used in investing activities	(24.3)	(142.8)	(268.3)
Cash flows from financing activities:
Payment of long-term debt	(125)	(0.6)	0
Issuance of preferred shares, net of issuance costs	144	0	0
Activity under stock incentive plans	1.8	1.9	1.6
Repurchase of Company's common shares	0	0	(31.7)
Payment of cash dividends to preferred shareholders	(4.6)	0	0
Payment of cash dividends to common shareholders	(43)	(43.1)	(37.5)
Cash used in financing activities	(26.8)	(41.8)	(67.6)
Effect of exchange rate changes on cash	(9.8)	(0.1)	(2.8)
Change in cash	11	(1.9)	(36.9)
Cash, beginning of year	137.8	139.7	176.6
Cash, end of period	$ 148.8	$ 137.8	$ 139.7

Business and Significant Accoun

Business and Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Business and Significant Accounting Policies	Business and Significant Accounting Policies Business Argo Group International Holdings, Ltd. (“Argo Group,” “we” or the “Company”) is an underwriter of specialty insurance products in the property and casualty market. Argo Group U.S., Inc. is a subsidiary of Argo Financial Holding (Ireland) UC (“Argo Ireland”). Argo Underwriting Agency Limited (“Syndicate 1200”) is a subsidiary of Argo International Holdings, Ltd., Argo Re Ltd. (“Argo Re”), a Bermuda based company, is the parent of both Argo Ireland and Argo International Holdings, Ltd. Argo Re is directly owned by Argo Group. Effective November 25, 2020, we closed on the sale of our reinsurance business, Ariel Re, to Pelican Ventures and J.C. Flowers & Co. Ariel Re is the reinsurance platform through which Lloyd’s Syndicate 1910 reinsurance business is underwritten. Under the terms of the agreement, the buying group’s corporate member will provide Syndicate 1910’s capital for the 2021 Lloyd’s year of account, and Argo Group has agreed to retain historical reserves and the remaining exposure for the 2020 and prior Lloyd’s years of account. On December 23, 2020, we announced an agreement to sell our Italian operations, ArgoGlobal Assicurazioni (“ArgoGlobal Assicurazioni”) to Perfuturo Capital AG, a Swiss Holding Company. Closing of the transaction is subject to regulatory approval and is expected to occur in early 2021. Under the terms of the agreement, Argo Re will reinsure substantially all of ArgoGlobal Assicurazioni's legacy business as of the effective date of the agreement for all underwriting years. We conduct our ongoing business through two primary segments - U.S. Operations and International Operations. In addition to these main business segments, we have a Run-off Lines segment for certain products we no longer underwrite. U.S. Operations is comprised of the Excess and Surplus Lines businesses focusing on the U.S.-based risks that the standard, admitted insurance market is unwilling or unable to write, and through other specialized admitted and non-admitted business distributed through retail, wholesale, and managing general brokers/agents in the specialty insurance market. Excess and Surplus Lines products are underwritten by Colony Insurance Company (“Colony”). The other U.S. specialized admitted and non-admitted businesses consist of the following operations: Argo Pro, U.S. Specialty Programs, Argo Surety, Rockwood Casualty Insurance Company (“Rockwood”), Argo Insurance, Inland Marine and Argo Cyber. International Operations is comprised of the Lloyd’s Syndicate platform (Syndicate 1200 and Syndicate 1910), Argo Insurance Bermuda, Continental Europe and Latin America. Syndicate 1200 and Syndicate 1910 insurance products are underwritten by Argo Underwriting Agency Limited based in London, under the Lloyd’s of London (“Lloyd’s”) global franchise. As discussed above, we sold our reinsurance business during the fourth quarter of 2020, through which Syndicate 1910 business is underwritten. The additional International Operations business include Argo Insurance Bermuda, ArgoGlobal SE in Malta, ArgoGlobal Assicurazioni in Italy, and Argo Seguros in Brazil. These businesses provide a broad range of commercial property, casualty, professional liability and specialty coverages in a number of countries and jurisdictions outside the United States (“U.S.”). Our Run-off Lines segment includes liabilities associated with other liability policies that were issued in the 1960s, 1970s and into the 1980s, as well as the former risk-management business and other business no longer underwritten. Basis of Presentation and Use of Estimates The consolidated financial statements of Argo Group and its subsidiaries have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The preparation of consolidated 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. Specifically, estimates for reserves for losses and loss adjustment expenses are based upon past claim experience modified for current trends as well as prevailing economic, legal and social conditions. Although management believes that amounts included in the accompanying consolidated financial statements are reasonable, such estimates may be more or less than the amounts ultimately paid when the claims are settled. The estimates are continually reviewed and any changes are reflected in current operating results. Further, the nature of loss exposures involves significant variability due to the nature of the long-tailed payments on certain claims. As such, losses and loss adjustment expenses could vary significantly from the recorded amounts. The consolidated financial statements include the accounts and operations of Argo Group and its subsidiaries. All material intercompany accounts and transactions have been eliminated. Certain amounts in prior years’ financial statements have been reclassified to conform to the current presentation. Amounts related to trade capital providers, who are third-party capital participants that provide underwriting capital to both Syndicate 1200 and Syndicate 1910, are included in the balance sheet. Trade capital providers participate on a quota share basis, assuming 100% of their contractual participation in the underwriting syndicate results and with such results settled on a year of account basis. We have evaluated our investment in our eleven statutory trusts (collectively, the “Trusts”) and one charitable foundation (the “Foundation”) under the Financial Accounting Standards Board’s (“FASB’s”) provisions for consolidation of variable interest entities under Accounting Standards Codification (“ASC”) Topic 810-10, “Consolidation,” as amended. We determined that the Trusts and the Foundation are variable interest entities due to the fact that the Trusts and the Foundation do not have sufficient equity to finance their activities without additional subordinate financial support from other parties. We do not have any power to direct the activities that impact the Trusts’ or the Foundation’s economic performance. We are not entitled to receive a majority of the residual returns of the Trusts. Additionally, we are not responsible for absorbing the majority of the expected losses of the Trusts; therefore, we are not the primary beneficiary and, accordingly, the Trusts are not included in our consolidated financial statements. The expenses and donations of the charitable foundation in Bermuda are paid by Argo Group and have been included in the consolidated results. Risks and Uncertainties Related to COVID-19 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 may 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. Our liquidity and capital resources were not materially impacted by COVID-19 and related economic conditions during the year ended December 31, 2020. Stock Dividends On February 20, 2018, our Board of Directors (the “Board”) declared a 15% stock dividend, payable on March 21, 2018, to shareholders of record at the close of business on March 7, 2018. As a result of the stock dividend, 4,397,520 additional shares were issued. Cash was paid in lieu of fractional shares of our common shares. Excluding repurchased shares, all references to common shares and related per share amounts in this document and related disclosures have been adjusted to reflect the stock dividend for all periods presented. Cash Cash consists of cash deposited in banks, generally in concentration and operating accounts. Interest-bearing cash accounts are classified as short-term investments. Investments Investments in fixed maturities at December 31, 2020 and 2019 include bonds and structured securities. Equity securities include common stocks, preferred stocks and mutual funds. Other investments consist of foreign regulatory deposits, hedge funds, private equity funds, private equity direct investments, and voluntary pools. Short-term investments consist of money market funds, certificates of deposit, bonds, sovereign debt and interest-bearing cash accounts. Investments maturing in less than one year are classified as short-term investments in our consolidated financial statements. The amortized cost of fixed maturity securities is adjusted for amortization of premiums and accretion of discounts. This amortization or accretion is included in “Net investment income” in our Consolidated Statements of Income (Loss). For the structured securities portion of the fixed maturity securities portfolio, we recognize income using a constant effective yield based on anticipated prepayments and the estimated economic life of the securities. Premium or discount on high investment grade securities (rated AA or higher) is amortized into income using the retrospective method. Premium or discount on lower grade securities (rated less than AA) is amortized into income using the prospective method. Our investments in fixed maturities are considered available-for-sale and are carried at fair value. As available-for-sale investments, changes in the fair value of fixed maturities are not recognized in income during the period, but rather are recognized as a separate component of shareholders’ equity until realized. Fair value of these investments is estimated using prices obtained from third-party pricing services, where available. For securities where we were unable to obtain fair values from a pricing service or broker, fair values were estimated using information obtained from investment advisors. We performed several processes to ascertain the reasonableness of these investment values by (1) obtaining and reviewing internal control reports for our service providers that obtain fair values from third-party pricing services, (2) discussing with our investment managers their process for reviewing and validating pricing obtained from outside services and obtaining values for all securities from our investment managers and (3) comparing the security pricing received from the investment managers with the prices used in the consolidated financial statements and obtaining additional information for variances that exceeded a certain threshold. As of December 31, 2020, investments reported at fair value for which we did not receive a fair value from a pricing service or broker accounted for less than 1% of our investment portfolio. The actual value at which such securities could be sold or settled with willing buyer or seller may differ from such estimated fair values depending on a number of factors including, but not limited to, current and future economic conditions, the quantity sold or settled, the presence of an active market and the availability of a willing buyer or seller. The cost of securities sold is based on the specific identification method. Our investments in equity securities are reported at fair value. Beginning with the adoption of Accounting Standards Update (“ASU”) 2016-01, effective January 1, 2018, changes in the fair value of equity securities are now included in “Net realized investment (gains) losses” in our consolidated statements of income. Changes in the value of other investments consisting of hedge funds, private equity funds, private equity direct investments and voluntary pools are principally recognized to income during the period using the equity method of accounting. Our foreign regulatory deposits are assets held in trust in jurisdictions where there is a legal and regulatory requirement to maintain funds locally in order to protect policyholders. Lloyd’s is the appointed investment manager for the funds. The underlying assets are invested in government securities, agency securities and corporate bonds whose values are obtained from Lloyd’s. Foreign currency future contracts held by us are valued by our counterparties using market driven foreign currency exchanges rates. We regularly review our investments to identify and evaluate those that may have credit impairments. For fixed maturity securities, the evaluation for credit losses is generally based on the present value of expected cash flows of the security as compared to the amortized book value, the financial condition, near-term and long-term prospects for the issuer, including industry conditions, implications of rating agency actions, the likelihood of principal and interest recoverability and whether it is more likely than not we will be required to sell the investment prior to the anticipated recovery in value. Effective January 1, 2020 with the adoption of ASU 2016-13 Financial Instruments-Credit Losses, we recognize credit losses on fixed maturities through an allowance account. For fixed maturities that we do not intend to sell or for which it is more likely than not we will not be required to sell prior to the anticipated recovery in value, we separate the credit component of the impairment from the component related to all other market factors and report the credit loss component to net realized investment gains (losses) in the Consolidated Statement of Income (Loss). The impairment related to all other market factors is reported as a separate component of shareholder’s equity in other comprehensive income (loss). The credit loss allowance account is adjusted for any additional credit losses or subsequent recoveries and the cost basis of the fixed maturity security is not adjusted. For fixed maturity securities that we intend to sell or for which it is more likely than not that we will be required to sell before an anticipated recovery in value, the full amount of the impairment is recognized in net realized investment gains (losses) in the Consolidated Statement of Income and the cost basis of the fixed maturity security is adjusted to reflect the recognized realized loss. The new cost basis is not adjusted for any recoveries in fair value. We report accrued investment income separately from fixed maturity securities and have elected to not measure an allowance for credit losses for accrued investment income. The write-off of investment income accrued for fixed maturities that have defaulted on interest payments is recognized as a loss in net realized investment gains (losses), in the period of the default, in the Consolidated Statement of Income (Loss). All investment balances include amounts relating to trade capital providers. The results of operations and other comprehensive income exclude amounts relating to trade capital providers. Trade capital providers’ participation in the syndicate results are included in reinsurance recoverable for ceded losses and reinsurance payable for ceded premiums. Receivables Premiums receivable, representing amounts due from insureds, are presented net of an allowance for uncollectible premiums, including expected credit losses, both dispute and credit related. Premiums receivable include amounts relating to the trade capital providers’ quota share. The allowance is based upon our ongoing review of amounts outstanding, historical loss data, including delinquencies and write-offs, current and forecasted economic conditions and other relevant factors. Credit risk is partially mitigated by our ability to cancel the policy if the policyholder does not pay the premium. Reinsurance recoverables represent amounts of paid losses and loss adjustment expenses, case reserves and incurred but not reported (“IBNR”) amounts ceded to reinsurers under reinsurance treaties. Reinsurance recoverables also reflect amounts that are due from trade capital providers. Amounts recoverable from reinsurers are estimated in a manner consistent with the associated claim liability. We report our reinsurance recoverables net of an allowance for estimated uncollectible reinsurance, including expected credit losses. The allowance is based upon our ongoing review of amounts outstanding, length of collection periods, changes in reinsurer credit standing, disputes, applicable coverage defenses and other relevant factors. We use the rating-based method to estimate the uncollectible reinsurance reserves due to credit losses. Under this method, reinsurance credit risk is estimated by considering the reinsurers probability of default. Reinsurance recoverables are forecasted out of the assumed billing periods and a liquidation factor is applied based on the rating of the reinsurer and adjusted as needed based on our historical experience with the reinsurers. Additionally, reinsurance receivable balances are evaluated to identify any dispute risk and when required, an additional reserve is recorded. Amounts deemed to be uncollectible, including amounts due from known insolvent reinsurers, are written off against the allowance. Changes in the allowance, as well as any subsequent collections of amounts previously written off, are reported as part of underwriting expense. We evaluate and monitor the financial condition of our reinsurers under voluntary reinsurance arrangements to minimize our exposure to significant losses from reinsurer insolvencies. Recoveries occur when subsequent collection or litigation results in the receipt of amounts previously written off. Amounts recovered are applied against the allowance for expected credit losses. For further disclosures about the allowance for expected credit losses, see Note 5, “Allowance for Credit Losses.” Earned Premiums Premium revenue is generally recognized ratably over the policy period. Premiums that have yet to be earned are reported as “unearned premiums” in our consolidated balance sheets. Unearned premium balances include cessions to reinsurers including trade capital providers, while the earned premium recognized in our consolidated statements of income (loss) excludes amounts relating to trade capital providers. The trade capital providers’ quota share amount is included in “ceded reinsurance payable, net”. Assumed reinstatement premiums that reinstate coverage are written and earned at the time the associated loss event occurs. The original premium is earned over the remaining exposure period of the contract. Reinstatement premiums are estimated based upon contract terms for reported losses and estimated for incurred but not reported losses. Retrospectively Rated Policies We have written a number of workers compensation, property and other liability policies that are retrospectively rated. Under this type of policy, the policyholder or coverholder may be entitled, subsequent to coverage expiration, to a refund or may owe additional premiums based on the amount of losses incurred under the policy. The retrospective premium adjustments on certain policies are limited to a minimum or maximum premium adjustment, which is calculated as a percentage of the standard amount of premium charged during the life of the policy. Accrued retrospectively rated premiums have been determined based on estimated ultimate loss experience of the individual policyholder accounts. The estimated liability for return of premiums under retrospectively rated policies is included in “Unearned premiums” in our consolidated balance sheets and was $6.5 million and $5.4 million at December 31, 2020 and 2019, respectively. The estimated amount included in premiums receivables for additional premiums due under retrospectively rated policies was $0.2 million and $0.3 million at December 31, 2020 and 2019, respectively. Deferred Acquisition Costs Policy acquisition costs, which include commissions, premium taxes, fees and certain other costs of underwriting policies, are deferred, when such class of policies are profitable, and amortized over the same period in which the related premiums are earned. To qualify for capitalization, the policy acquisition cost must be directly related to the successful acquisition of an insurance contract. Anticipated investment income is considered in determining whether the deferred acquisition costs are recoverable and whether a premium deficiency exists. We continually review the methods of making such estimates and establishing the deferred costs with any adjustments made in the accounting period in which the adjustment arose. The 2020 and 2019 net amortization of policy acquisition costs will not equal the change in our consolidated balance sheets as the trade capital providers’ share is not reflected in our consolidated statements of income (loss) and differences arise from foreign currency exchange rates applied to deferred acquisition costs which are treated as a nonmonetary asset. Leases We determine if a contract contains a lease at inception and recognize operating lease right-of-use assets and operating lease liabilities based on the present value of the future minimum lease payments at the commencement date. As our leases do not provide an implicit interest rate, we use our incremental borrowing rate based on the information available at the commencement date to determine the present value of future payments. Lease agreements have lease and non-lease components. We account for these components separately, therefore our operating lease right-of-use asset and operating lease liabilities represent base rent only. Lease expense is recognized on a straight-line basis over the lease term. Renewal options are evaluated prior to the expiration date and recorded upon exercise. We adopted ASU 2016-02, “Leases” (Topic 842) on the effective date of January 1, 2019 and applied the following practical expedients: • We have elected to adopt this standard using the option transition method, which allows companies to continue applying the guidance under the lease standard in effect at that time in the comparative periods presented in the consolidated financial statements. The adoption of the standard had no effect on our consolidated shareholders’ equity. Prior periods were not restated. • We have elected the “package of practical expedients,” which permits us not to reassess under the new standard our prior conclusion about lease identification, lease classification and initial direct costs. • Where we are the lessor, we have elected the practical expedient which permits us to not separate non-lease components from the associated lease components if the non-lease components otherwise would be accounted for in accordance with the new revenue standard. Reserves for Losses and Loss Adjustment Expenses Liabilities for unpaid losses and loss adjustment expenses include the accumulation of individual case estimates for claims reported as well as estimates of IBNR claims and estimates of claim settlement expenses. Reinsurance recoverables on unpaid claims and claim expenses represent estimates of the portion of such liabilities that will be recoverable from reinsurers. Amounts recoverable from reinsurers are recognized as assets at the same time and in a manner consistent with the unpaid claims liabilities associated with the reinsurance policy. Reinsurance In the normal course of business, our insurance and reinsurance subsidiaries cede risks above certain retention levels to other insurance companies. Reinsurance recoverables include claims we paid and estimates of unpaid losses and loss adjustment expenses that are subject to reimbursement under reinsurance and retrocessional contracts. The method for determining reinsurance recoverables for unpaid losses and loss adjustment expenses involves reviewing actuarial estimates of gross unpaid losses and loss adjustment expenses to determine our ability to cede unpaid losses and loss adjustment expenses under our existing reinsurance contracts. This method is continually reviewed and updated and any resulting adjustments are reflected in earnings in the period identified. Reinsurance premiums, commissions and expense reimbursements are accounted for on a basis consistent with those used in accounting for the original policies issued and the term of the reinsurance contracts. Amounts recoverable from reinsurers for losses and loss adjustment expenses for which our insurance and reinsurance subsidiaries have not been relieved of their legal obligations to the policyholder are reported as assets. Goodwill and Intangible Assets Goodwill and intangible assets are allocated to the segment in which the results of operations for the acquired company are reported (see Note 20, “Segment Information” for further discussion). Intangible assets with a finite life are amortized over the estimated useful life of the asset. Goodwill and intangible assets with an indefinite useful life are not amortized. Goodwill and intangible assets are tested for impairment on an annual basis or more frequently if events or changes in circumstances indicate that the carrying amount may not be recoverable. We perform our annual goodwill impairment test on the first day of the fourth quarter of each year, October 1, of each year. As a result of the reviews performed on each of our reporting units for each of the years ended December 31, 2020 and 2018, we determined that the estimated fair value exceeded the respective carrying value of our reporting units for those years and goodwill was not impaired. In conjunction with our annual test, the fair value of each reporting unit exceeded its carrying value for the year ended December 31, 2019, except for our European reporting unit. As a result of this testing, we determined that the goodwill of the European reporting unit, which is included in our International Operations segment, was fully impaired and recorded a pre-tax charge of $15.6 million. Our European reporting unit was adversely impacted by a continuing soft market. Additionally, we incurred higher than expected losses and loss adjustment expenses due to adverse prior accident year loss reserve development resulting from the receipt of new information in the second half of 2019 relating to claims trends across various lines of business, coupled with increased current accident year losses and loss adjustment expenses as a result of these claim trends. Using these facts and trends, we calculated the discounted cash flows for the European reporting unit, which resulted in the indication that the carrying value of the reporting unit exceeded its fair value, resulting in the impairment. Other indefinite-lived intangible assets and intangible assets with finite lives were also reviewed for impairment as of October 1 of each year. As a result of the reviews performed on each of the entity’s reporting units for the three years ended December 31, 2020, 2019 and 2018, the Company determined that the other indefinite-lived intangible assets and finite-lived intangible assets were not impaired. On April 30, 2020, we sold our Trident Public Risk Solutions (“Trident”) brand and wrote off $4.9 million of goodwill as a result of the Trident transaction. On November 25, 2020, we sold Ariel Re’s premium renewal rights and wrote off $9.2 million of goodwill and $30.2 million of intangible assets, net of accumulated amortization, as a result of the Ariel Re transaction. For more information about these transactions, see Note 3, “Recent Acquisitions, Disposals & Other Transactions.” The following table presents our intangible assets and accumulated amortization at December 31: December 31, 2020 2019 (in millions) Gross Carrying Accumulated Gross Carrying Accumulated Lloyd's capacity $ 60.5 n/a $ 89.0 n/a Distribution network 45.5 45.5 50.2 48.2 Other 6.2 6.2 8.1 7.3 $ 112.2 $ 51.7 $ 147.3 $ 55.5 During the years ended December 31, 2020, 2019 and 2018, amortization expense was $1.1 million, $1.7 million and $3.3 million, respectively, and is included in “underwriting, acquisition and insurance expenses” in our consolidated statements of income (loss). The entirety of the amortization expense recorded in the year 2020 relates to Ariel Re and was calculated pro-rata before the sale. As of December 31, 2020, all of our intangible assets have been fully amortized and we have no estimated amortization expense. Property and Equipment Property and equipment used in operations, including certain costs incurred to develop or obtain computer software for internal use, are capitalized and carried at cost less accumulated depreciation and are reported in “other assets” in our consolidated balance sheets. Depreciation is calculated using a straight-line method over the estimated useful lives of the assets, generally three The depreciation expense for the years ended December 31, 2020, 2019 and 2018 was $24.1 million, $24.4 million and $24.5 million, respectively. Assets Held for Sale In December 2019, we entered into a series of agreements with a real estate firm to market and sell four company owned condominiums. During 2020, we sold two of the condominiums. One of the remaining two condominiums was sold in January 2021, and the remaining property is anticipated to be sold in 2021. We have classified these properties and other corporate assets as “Assets held for sale” of $7.7 million and $15.4 million in our Consolidated Balance Sheets as of December 31, 2020 and 2019, respectively. We have recorded the assets at their fair market values as of December 31, 2020 and 2019 based on independent appraisals and active listing prices. As a result of the reclassification to “Assets held for sale,” we recorded pre-tax losses of $0.8 million and $3.7 million, which are included in “Other corporate expenses” in our Consolidated Statements of Income (Loss) for the years ended December 31, 2020 and 2019, respectively. These assets and the related pre-tax losses are reported as part of our Corporate and Other reporting segment in Note 20, “Segment Information.” Derivative Instruments We enter into short-term, currency spot and forward contracts to manage operational currency exposure on our Canadian dollar (“CAD”) investment portfolio and certain catastrophic events, minimize negative impacts to investment portfolio returns, and gain exposure to a total return strategy which invests in multiple currencies. The forward contracts are typically thirty to ninety days and are renewed as management deems necessary to accomplish the objectives of the contracts. These foreign currency forward contracts are carried at fair value in our Consolidated Balance Sheets in “Other assets” at December 31, 2020 and 2019, respectively. The realized and unrealized gains and losses are included in “Net realized investment and other gains (losses) in our Consolidated Statements of Income. The forwards contracts are not designated as hedges for accounting purposes. Share-Based Payments Compensation expense for share-based payments is recognized based on the measurement-date fair value for awards that will settle in shares. Compensation expense for awards that are settled in equity are recognized on a straight line pro rata basis over the vesting period, adjusted for expected forfeitures. See Note 15, “Share-based Compensation” for related disclosures. Foreign Currency Exchange Gain (Loss) The U.S. dollar is the functional currency of all but three of our foreign operations. Monetary assets and liabilities in foreign operations that are denominated in foreign currencies are revalued at the exchange rates in effect at the balance sheet date. The re

Accounting Changes and Error Co

Accounting Changes and Error Corrections	12 Months Ended
	Dec. 31, 2020
Accounting Changes and Error Corrections [Abstract]
Revisions of Previously Issued Financial Statements	Revisions of Previously Issued Financial Statements In connection with the preparation, review and audit of the Company's consolidated financial statements required to be included in this Annual Report on Form 10-K for the year ended December 31, 2020, management identified certain immaterial errors in our historical financial statements primarily related to the accounting for (1) foreign currency exchange gains and losses associated with a specific reinsurance contract and (2) errors in the Company’s tax provision primarily related to the Company’s allocation of certain corporate-level expenses to our subsidiary companies, as well as other previously identified immaterial errors. In accordance with the guidance set forth in SEC Staff Bulletin 99, Materiality , and SEC Staff Accounting Bulletin 108, Considering the Effects of Prior Year Misstatements when Quantifying Misstatements in Current Year Financials , the Company concluded these errors were not material to the previously issued Consolidated Financial Statements, however, correcting the cumulative effect of the errors in 2020 would materially misstate the 2020 consolidated financial statements. Accordingly, we are revising our historical financial statements to correct the immaterial errors. We will revise previously reported financial information for these immaterial errors in our future filings, as applicable. As a result of the aforementioned revisions, the financial results herein vary from those furnished as an exhibit to the Form 8-K the Company filed with the Securities and Exchange Commission on February 17, 2021. The adjustments to the Company’s annual and quarterly previously issued financial statements are shown on the following pages, grouped by (1) the audited financial statements and (2) interim period unaudited financial statements, as well as (3) the related adjustments to the Company’s parent company financial information. The Company’s parent company financial information is disclosed on Schedule II of this Annual Report on Form 10-K. All adjustments to the Statements of Cash Flows for the periods affected by the errors noted below were reclassifications within cash provided by operating activities. Adjusted Consolidated Balance Sheet as of December 31, 2019: December 31, 2019 (in millions) As reported Adjustments As adjusted Fixed maturities available-for-sale, at fair value $ 3,633.5 $ (3.6) $ 3,629.9 Equity securities available-for-sale, at fair value 124.4 11.6 136.0 Other investments 496.5 (9.9) 486.6 Total investments 5,099.4 (1.9) 5,097.5 Premiums receivable 688.2 (11.7) 676.5 Reinsurance recoverables 3,104.6 2.6 3,107.2 Deferred tax asset, net 6.1 4.5 10.6 Other assets 387.1 0.8 387.9 Total assets 10,514.5 (5.7) 10,508.8 Accrued underwriting expenses and other liabilities 226.0 (4.1) 221.9 Ceded reinsurance payable, net 1,203.1 (1.9) 1,201.2 Funds held 50.6 4.6 55.2 Current income taxes payable, net 0.8 13.1 13.9 Total liabilities 8,733.4 11.7 8,745.1 Retained earnings 811.1 (17.4) 793.7 Total shareholders’ equity 1,781.1 (17.4) 1,763.7 Total liabilities and shareholders' equity 10,514.5 (5.7) 10,508.8 Adjusted Consolidated Statement of Income (Loss) for the three months and year ended December 31, 2019: Three Months Ended December 31, 2019 Year Ended December 31, 2019 As reported Adjustments As adjusted As reported Adjustments As adjusted (in millions, except per share amounts) (Unaudited) Earned premiums $ 425.8 $ — $ 425.8 $ 1,729.5 $ 0.2 $ 1,729.7 Net realized investment gains 21.7 0.1 21.8 80.0 0.1 80.1 Total revenue 484.5 0.1 484.6 1,969.7 0.3 1,970.0 Underwriting, acquisition and insurance expenses 180.2 — 180.2 665.8 0.2 666.0 Interest expense 8.3 0.1 8.4 33.6 0.5 34.1 Foreign currency exchange gains (3.4) (1.1) (4.5) (9.6) (0.2) (9.8) Total expenses 587.8 (1.0) 586.8 1,969.5 0.5 1,970.0 (Loss) income before income taxes (103.3) 1.1 (102.2) 0.2 (0.2) — Income tax provision — 0.5 0.5 8.6 5.5 14.1 Net loss (103.3) 0.6 (102.7) (8.4) (5.7) (14.1) Net loss per common share: Basic $ (3.01) $ 0.02 $ (2.99) $ (0.25) $ (0.16) $ (0.41) Diluted $ (3.01) $ 0.02 $ (2.99) $ (0.25) $ (0.16) $ (0.41) Consolidated Balance Sheet impact on opening balances as of January 1, 2019 and 2018: Impact on opening balances as of January 1, 2019 (in millions) As reported Adjustments As adjusted Equity securities available-for-sale, at fair value $ 354.5 $ 11.6 $ 366.1 Other investments 489.8 (9.9) 479.9 Cash 139.2 0.5 139.7 Premiums receivable 649.9 (4.7) 645.2 Reinsurance recoverables 2,688.3 0.9 2,689.2 Current income taxes receivable, net 8.2 (8.2) — Deferred tax asset, net — 1.3 1.3 Accrued underwriting expenses and other liabilities 261.9 1.1 263.0 Ceded reinsurance payable, net 970.5 (1.3) 969.2 Funds held 37.2 7.2 44.4 Current income taxes payable, net — 2.4 2.4 Deferred tax liabilities, net 6.2 (6.2) — Retained earnings 862.6 (11.7) 850.9 Impact on opening balances as of January 1, 2018 (in millions) As reported Adjustments As adjusted Other investments $ 543.6 $ 0.8 $ 544.4 Premiums receivable 598.6 (4.6) 594.0 Current income taxes receivable, net 1.4 (1.2) 0.2 Other assets 309.6 0.2 309.8 Accrued underwriting expenses and other liabilities 146.9 (0.3) 146.6 Ceded reinsurance payable, net 734.0 0.4 734.4 Deferred tax liabilities, net 31.3 1.9 33.2 Retained earnings 977.0 (6.8) 970.2 Adjusted Consolidated Statement of Income (Loss) for the year ended December 31, 2018: Year Ended December 31, 2018 (in millions, except per share amounts) As reported Adjustments As adjusted Earned premiums $ 1,731.7 $ (0.2) $ 1,731.5 Net investment income 133.1 (0.8) 132.3 Total revenue 1,801.8 (1.0) 1,800.8 Underwriting, acquisition and insurance expenses 654.7 1.4 656.1 Interest expense 31.6 0.3 31.9 Foreign currency exchange losses (gains) (0.1) 4.0 3.9 Total expenses 1,734.1 5.7 1,739.8 (Loss) income before income taxes 67.7 (6.7) 61.0 Income tax (benefit) provision 4.1 (0.1) 4.0 Net (loss) income 63.6 (6.6) 57.0 Net income (loss) per common share: Basic $ 1.87 $ (0.19) $ 1.68 Diluted $ 1.83 $ (0.18) $ 1.65 Adjusted Consolidated Balance Sheet as of September 30, 2020: September 30, 2020 As reported Adjustments As adjusted (in millions) (Unaudited) Premiums receivable $ 797.0 $ (6.8) $ 790.2 Current income taxes receivable, net 11.2 (3.7) 7.5 Deferred tax asset, net 17.0 (2.2) 14.8 Other assets 358.5 0.1 358.6 Total assets 10,734.3 (12.6) 10,721.7 Accrued underwriting expenses and other liabilities 202.8 2.5 205.3 Ceded reinsurance payable, net 1,085.0 0.7 1,085.7 Total liabilities 8,869.8 3.2 8,873.0 Retained earnings 714.2 (15.8) 698.4 Total shareholders' equity 1,864.5 (15.8) 1,848.7 Total liabilities and shareholders' equity 10,734.3 (12.6) 10,721.7 Adjusted Consolidated Statement of Income (Loss) for the three and nine months ended September 30, 2020: Three Months Ended September 30, 2020 Nine Months Ended September 30, 2020 As reported Adjustments As adjusted As reported Adjustments As adjusted (in millions, except per share amounts) (Unaudited) (Unaudited) Net realized investment (losses) gains $ (5.7) $ — $ (5.7) $ 33.3 $ (0.1) $ 33.2 Change in fair value of equity securities 10.5 — 10.5 (12.0) (1.7) (13.7) Net realized investment losses (5.7) — (5.7) (21.7) (1.8) (23.5) Total revenue 483.5 — 483.5 1,377.0 (1.8) 1,375.2 Underwriting, acquisition and insurance expenses 164.3 0.2 164.5 493.7 0.2 493.9 Interest expense 6.8 0.1 6.9 21.3 0.4 21.7 Foreign currency exchange losses 11.6 (3.2) 8.4 15.0 (1.4) 13.6 Total expenses 512.9 (2.9) 510.0 1,422.3 (0.8) 1,421.5 Loss before income taxes (29.4) 2.9 (26.5) (45.3) (1.0) (46.3) Income tax provision 0.2 (3.6) (3.4) 9.5 (2.6) 6.9 Net loss (29.6) 6.5 (23.1) (54.8) 1.6 (53.2) Net loss attributable to common shareholders (31.6) 6.5 (25.1) (56.8) 1.6 (55.2) Net loss attributable to common shareholders per common share: Basic $ (0.91) $ 0.19 $ (0.72) $ (1.64) $ 0.04 $ (1.60) Diluted $ (0.91) $ 0.19 $ (0.72) $ (1.64) $ 0.04 $ (1.60) Adjusted Consolidated Balance Sheet as of June 30, 2020: June 30, 2020 As reported Adjustments As adjusted (in millions) (Unaudited) Premiums receivable $ 800.2 $ (15.2) $ 785.0 Deferred tax asset, net 18.9 (3.0) 15.9 Other assets 414.7 (0.2) 414.5 Total assets 10,396.7 (18.4) 10,378.3 Accrued underwriting expenses and other liabilities 154.8 2.2 157.0 Ceded reinsurance payable, net 1,042.7 (4.7) 1,038.0 Current income taxes payable, net 27.1 6.4 33.5 Total liabilities 8,666.7 3.9 8,670.6 Retained earnings 756.7 (22.3) 734.4 Total shareholders' equity 1,730.0 (22.3) 1,707.7 Total liabilities and shareholders' equity 10,396.7 (18.4) 10,378.3 Adjusted Consolidated Statement of Income (Loss) for the three and six months ended June 30, 2020: Three Months Ended June 30, 2020 Six Months Ended June 30, 2020 As reported Adjustments As adjusted As reported Adjustments As adjusted (in millions, except per share amounts) (Unaudited) (Unaudited) Net investment income 1.5 (0.1) 1.4 37.0 — 37.0 Net realized investment gains $ 11.1 $ — $ 11.1 $ 39.0 $ (0.1) $ 38.9 Change in fair value of equity securities 16.8 (1.7) 15.1 (22.5) (1.7) (24.2) Net realized investment gains (losses) 20.1 (1.7) 18.4 (16.0) (1.8) (17.8) Total revenue 457.0 (1.8) 455.2 893.5 (1.8) 891.7 Underwriting, acquisition and insurance expenses 161.4 (0.1) 161.3 329.4 — 329.4 Interest expense 6.8 0.2 7.0 14.5 0.3 14.8 Foreign currency exchange losses 6.4 (2.1) 4.3 3.4 1.8 5.2 Total expenses 451.3 (2.0) 449.3 909.4 2.1 911.5 Income (loss) before income taxes 5.7 0.2 5.9 (15.9) (3.9) (19.8) Income tax provision 12.1 (0.8) 11.3 9.3 1.0 10.3 Net loss (6.4) 1.0 (5.4) (25.2) (4.9) (30.1) Net loss per common share: Basic $ (0.18) $ 0.02 $ (0.16) $ (0.73) $ (0.14) $ (0.87) Diluted $ (0.18) $ 0.02 $ (0.16) $ (0.73) $ (0.14) $ (0.87) Adjusted Consolidated Balance Sheet as of March 31, 2020: March 31, 2020 As reported Adjustments As adjusted (in millions) (Unaudited) Equity securities available-for-sale, at fair value $ 132.9 $ 11.6 $ 144.5 Other investments 422.4 (9.9) 412.5 Total investments 4,811.4 1.7 4,813.1 Premiums receivable 739.1 (20.9) 718.2 Deferred tax asset, net 44.5 (3.6) 40.9 Other assets 435.4 (0.6) 434.8 Total assets 10,201.3 (23.4) 10,177.9 Accrued underwriting expenses and other liabilities 185.3 2.1 187.4 Ceded reinsurance payable, net 1,094.8 (8.8) 1,086.0 Current income taxes payable, net 17.7 6.6 24.3 Total liabilities 8,564.5 (0.1) 8,564.4 Retained earnings 773.7 (23.3) 750.4 Total shareholders' equity 1,636.8 (23.3) 1,613.5 Total liabilities and shareholders' equity 10,201.3 (23.4) 10,177.9 Adjusted Consolidated Statement of Income (Loss) for the three months ended March 31, 2020: Three Months Ended March 31, 2020 As reported Adjustments As adjusted (in millions, except per share amounts) (Unaudited) Net investment income 35.5 0.1 35.6 Net realized investment gains $ 27.9 $ (0.1) $ 27.8 Net realized investment losses (36.1) (0.1) (36.2) Total revenue 436.5 — 436.5 Underwriting, acquisition and insurance expenses 168.0 0.1 168.1 Interest expense 7.7 0.1 7.8 Foreign currency exchange gains (losses) (3.0) 3.9 0.9 Total expenses 458.1 4.1 462.2 Loss before income taxes (21.6) (4.1) (25.7) Income tax benefit (2.8) 1.8 (1.0) Net loss (18.8) (5.9) (24.7) Net loss per common share: Basic $ (0.55) $ (0.17) $ (0.72) Diluted $ (0.55) $ (0.17) $ (0.72) Adjusted Consolidated Balance Sheet as of September 30, 2019: September 30, 2019 As reported Adjustments As adjusted (in millions) (Unaudited) Equity securities, at fair value $ 400.6 $ 11.6 $ 412.2 Other investments 500.0 (9.9) 490.1 Total investments 5,127.0 1.7 5,128.7 Premiums receivable 740.3 (12.8) 727.5 Current income taxes receivable, net 0.2 (0.2) — Other assets 390.6 (0.1) 390.5 Total assets 10,445.8 (11.4) 10,434.4 Accrued underwriting expenses and other liabilities 283.9 1.8 285.7 Ceded reinsurance payable, net 1,175.7 (2.9) 1,172.8 Current income taxes payable, net — 9.8 9.8 Deferred tax liabilities, net 19.9 (2.1) 17.8 Total liabilities 8,552.4 6.6 8,559.0 Retained earnings 925.0 (18.0) 907.0 Total shareholders' equity 1,893.4 (18.0) 1,875.4 Total liabilities and shareholders' equity 10,445.8 (11.4) 10,434.4 Adjusted Consolidated Statement of Income (Loss) for the three and nine months ended September 30, 2019: Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 As reported Adjustments As adjusted As reported Adjustments As adjusted (in millions, except per share amounts) (Unaudited) (Unaudited) Earned premiums $ 451.5 $ — $ 451.5 $ 1,303.7 $ 0.2 $ 1,303.9 Total revenue 487.4 — 487.4 1,485.2 0.2 1,485.4 Underwriting, acquisition and insurance expenses 164.0 — 164.0 485.6 0.2 485.8 Interest expense 7.5 0.2 7.7 25.3 0.4 25.7 Foreign currency exchange gains (1.6) 0.7 (0.9) (6.2) 0.9 (5.3) Total expenses 513.6 0.9 514.5 1,381.7 1.5 1,383.2 (Loss) income before income taxes (26.2) (0.9) (27.1) 103.5 (1.3) 102.2 Income tax (benefit) provision (1.1) — (1.1) 8.6 5.0 13.6 Net (loss) income (25.1) (0.9) (26.0) 94.9 (6.3) 88.6 Net (loss) income attributable to common shareholders (25.1) (0.9) (26.0) 94.9 (6.3) 88.6 Net (loss) income per common share: Basic $ (0.73) $ (0.03) $ (0.76) $ 2.78 $ (0.19) $ 2.59 Diluted $ (0.73) $ (0.03) $ (0.76) $ 2.73 $ (0.18) $ 2.55 Adjusted Consolidated Balance Sheet as of June 30, 2019: June 30, 2019 As reported Adjustments As adjusted (in millions) (Unaudited) Equity securities, at fair value $ 421.0 $ 11.6 $ 432.6 Other investments 509.4 (9.9) 499.5 Total investments 4,877.6 1.7 4,879.3 Premiums receivable 728.0 (11.2) 716.8 Current income taxes receivable, net 3.8 (3.8) — Total assets 10,166.7 (13.3) 10,153.4 Accrued underwriting expenses and other liabilities 279.4 1.6 281.0 Ceded reinsurance payable, net 1,052.8 (2.0) 1,050.8 Current income taxes payable, net — 6.2 6.2 Deferred tax liabilities, net 25.4 (2.0) 23.4 Total liabilities 8,237.7 3.8 8,241.5 Retained earnings 959.9 (17.1) 942.8 Total shareholders' equity 1,929.0 (17.1) 1,911.9 Total liabilities and shareholders' equity 10,166.7 (13.3) 10,153.4 Adjusted Consolidated Statement of Income (Loss) for the three and six months ended June 30, 2019: Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 As reported Adjustments As adjusted As reported Adjustments As adjusted (in millions, except per share amounts) (Unaudited) (Unaudited) Earned premiums $ 431.7 $ — $ 431.7 $ 852.2 $ 0.2 $ 852.4 Total revenue 488.6 — 488.6 997.8 0.2 998.0 Underwriting, acquisition and insurance expenses 161.4 0.2 161.6 321.6 0.2 321.8 Interest expense 9.3 0.1 9.4 17.8 0.2 18.0 Foreign currency exchange gains (5.3) 1.5 (3.8) (4.6) 0.2 (4.4) Total expenses 459.0 1.8 460.8 868.1 0.6 868.7 Income before income taxes 29.6 (1.8) 27.8 129.7 (0.4) 129.3 Income tax provision 0.8 — 0.8 9.7 5.0 14.7 Net income 28.8 (1.8) 27.0 120.0 (5.4) 114.6 Net income per common share: Basic $ 0.84 $ (0.05) $ 0.79 $ 3.52 $ (0.16) $ 3.36 Diluted $ 0.83 $ (0.05) $ 0.78 $ 3.45 $ (0.15) $ 3.30 Adjusted Consolidated Balance Sheet as of March 31, 2019: March 31, 2019 As reported Adjustments As adjusted (in millions) (Unaudited) Equity securities, at fair value $ 403.2 $ 11.6 $ 414.8 Other investments 483.3 (9.9) 473.4 Total investments 4,903.5 1.7 4,905.2 Premiums receivable 673.2 (8.3) 664.9 Current income taxes receivable, net 5.0 (5.0) — Total assets 9,954.5 (11.6) 9,942.9 Accrued underwriting expenses and other liabilities 248.2 1.3 249.5 Ceded reinsurance payable, net 1,047.1 (0.7) 1,046.4 Current income taxes payable, net — 5.1 5.1 Deferred tax liabilities, net 20.7 (2.0) 18.7 Total liabilities 8,073.9 3.7 8,077.6 Retained earnings 943.0 (15.3) 927.7 Total shareholders' equity 1,880.6 (15.3) 1,865.3 Total liabilities and shareholders' equity 9,954.5 (11.6) 9,942.9 Adjusted Consolidated Statement of Income (Loss) for the three months ended March 31, 2019: Three Months Ended March 31, 2019 As reported Adjustments As adjusted (in millions, except per share amounts) (Unaudited) Earned premiums $ 420.5 $ 0.2 $ 420.7 Total revenue 509.2 0.2 509.4 Interest expense 8.5 0.1 8.6 Foreign currency exchange losses (gains) 0.7 (1.3) (0.6) Total expenses 409.1 (1.2) 407.9 Income before income taxes 100.1 1.4 101.5 Income tax provision 8.9 5.0 13.9 Net income 91.2 (3.6) 87.6 Net income per common share: Basic $ 2.68 $ (0.10) $ 2.58 Diluted $ 2.63 $ (0.11) $ 2.52 Adjusted Condensed Financial Information of the Registrant as of December 31, 2019: December 31, 2019 (in millions) As reported Adjustments As adjusted Investments in subsidiaries $ 1,916.7 $ (17.4) $ 1,899.3 Total assets 1,974.7 (17.4) 1,957.3 Total shareholders’ equity 1,781.1 (17.4) 1,763.7 Total liabilities and shareholders' equity 1,974.7 (17.4) 1,957.3 Adjusted Condensed Financial Information of the Registrant for the years ended December 31, 2019 and 2018: Year Ended December 31, 2019 Year Ended December 31, 2018 (in millions) As reported Adjustments As adjusted As reported Adjustments As adjusted Equity in undistributed earnings of subsidiaries $ (22.8) $ 46.4 $ 23.6 $ 44.8 $ 29.9 $ 74.7 Net (loss) income (8.4) (5.7) (14.1) 63.6 (6.6) 57.0

Recent Acquisitions, Disposals

Recent Acquisitions, Disposals & Other Transactions	12 Months Ended
	Dec. 31, 2020
Business Combinations [Abstract]
Recent Acquisitions, Disposals & Other Transactions	Recent Acquisitions, Disposals & Other Transactions Sale of Trident Brand and Platform On April 30, 2020, we sold our 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 Income (Loss) for the year ended December 31, 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 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. The fair values disclosed herein were determined based on management’s best estimates and the finalization of certain valuation analyses during the fourth quarter of 2020. Provisional fair values were recorded in the Company’s interim consolidated financial statements and notes for the period ending September 30, 2020. AIL’s financial position, results of operations, and cash flows were not material to our consolidated financial results as of and for the year ended December 31, 2020. No goodwill or intangible assets were recognized from this transaction. Reinsurance-to-close ("RITC") of ArgoGlobal Syndicate 1200 On October 12, 2020, ArgoGlobal, the Lloyd’s insurer and member of Argo, announced a reinsurance-to-close (“RITC”) transaction with legacy specialist RiverStone. RiverStone provided an RITC of ArgoGlobal’s Syndicate 1200 for 2017 and prior years with net technical provision of approximately $217 million. The transaction received regulatory approval on January 29, 2021, with the RITC becoming effective on January 1, 2021. Sale of Ariel Re On November 25, 2020, we closed on the sale of our reinsurance business, Ariel Re, to Pelican Ventures and J.C. Flowers & Co. Under the terms of the agreement, we received $30 million at closing. Ariel Re is the reinsurance platform through which Lloyd’s Syndicate 1910 reinsurance business is underwritten. We recognized a loss of $9.4 million related to the sale, which is included in "Net realized investment (losses) gains" in our Consolidated Statements of Income (Loss) for the year ended December 31, 2020. Ariel Re is one of the business units within our International Operations reporting segment. Pelican Ventures and affiliates will capitalize the 2021 year of account, and Argo will maintain responsibility for all years of account 2020 and prior. Additionally, in accordance with the transaction agreement, Ariel Re’s equity interests in ArgoGlobal Services (Hong Kong) Limited (“AGSL”) and Ariel Re Bda Limited (“ARBL”) were transferred to Pelican Ventures and J.C. Flowers & Co. AGSL is authorized in Hong Kong by the Insurance Agency of Hong Kong as an insurance agent and is a Lloyd's approved coverholder. ARBL is an exempted company limited by shares, incorporated in Bermuda and registered as an insurance agent under the Bermuda Insurance Act. Sale of ArgoGlobal Assicurazioni S.p.A On December 23, 2020, we announced an agreement to sell our Italian operations, ArgoGlobal Assicurazioni, to Perfuturo Capital AG (“Perfuturo”), a Swiss Holding Company. Closing of the transaction is subject to regulatory approval and is expected to occur in early 2021. Pursuant to the Argo Reinsurance Agreement, Argo Re will reinsure substantially all of ArgoGlobal Assicurazioni's legacy business as of the effective date of the agreement for all underwriting years.

Investments

Investments	12 Months Ended
	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Investments	Investments Included in “total investments” in our consolidated balance sheets at December 31, 2020 and 2019 is $140.3 million and $156.8 million, respectively, of assets managed on behalf of the trade capital providers, who are third-party participants that provide underwriting capital to the operations of Syndicates 1200 and 1910. Fixed Maturities The amortized cost, gross unrealized gains, gross unrealized losses and fair value in fixed maturity investments were as follows: December 31, 2020 (in millions) Amortized Gross Gross Allowance for Credit Losses (1) Fair Fixed maturities U.S. Governments $ 385.4 $ 14.7 $ 0.3 $ — $ 399.8 Foreign Governments 284.1 11.6 0.7 0.2 294.8 Obligations of states and political subdivisions 163.1 7.7 0.3 0.1 170.4 Corporate bonds 1,925.9 75.3 13.3 6.1 1,981.8 Commercial mortgage-backed securities 324.8 15.2 0.3 — 339.7 Residential mortgage-backed securities 491.4 17.4 0.6 — 508.2 Asset-backed securities 120.5 2.9 0.4 0.2 122.8 Collateralized loan obligations 285.9 4.9 1.2 — 289.6 Total fixed maturities $ 3,981.1 $ 149.7 $ 17.1 $ 6.6 $ 4,107.1 December 31, 2019 (in millions) Amortized Gross Gross Allowance for Credit Losses Fair Fixed maturities U.S. Governments $ 352.2 $ 2.3 $ 1.2 $ — $ 353.3 Foreign Governments 244.8 4.6 0.7 — 248.7 Obligations of states and political subdivisions 145.8 6.9 0.1 — 152.6 Corporate bonds 1,775.4 37.7 34.7 — 1,778.4 Commercial mortgage-backed securities 213.5 4.6 1.1 — 217.0 Residential mortgage-backed securities 479.0 10.4 0.6 — 488.8 Asset-backed securities 164.1 1.4 0.2 — 165.3 Collateralized loan obligations 226.7 0.5 1.4 — 225.8 Total fixed maturities $ 3,601.5 $ 68.4 $ 40.0 $ — $ 3,629.9 Contractual Maturity The amortized cost and fair values of fixed maturity investments as of December 31, 2020, by contractual maturity, were as follows: (in millions) Amortized Fair Due in one year or less $ 324.9 $ 329.7 Due after one year through five years 1,743.6 1,791.9 Due after five years through ten years 607.8 639.3 Thereafter 82.2 85.9 Structured securities 1,222.6 1,260.3 Total $ 3,981.1 $ 4,107.1 The expected maturities may differ from the contractual maturities because debtors may have the right to call or prepay obligations. Other Invested Assets Details regarding the carrying value and unfunded investment commitments of the other invested assets portfolio as of December 31, 2020 and 2019 were as follows: December 31, 2020 (in millions) Carrying Unfunded Investment Type Hedge funds $ 111.2 $ — Private equity 211.4 80.0 Overseas deposits 102.1 — Other 4.7 — Total other investments $ 429.4 $ 80.0 December 31, 2019 (in millions) Carrying Unfunded Investment Type Hedge funds $ 109.5 $ — Private equity 258.2 110.0 Overseas deposits 114.6 — Other 4.3 — Total other invested assets $ 486.6 $ 110.0 The following describes each investment type: • Hedge funds : Hedge funds include funds that primarily buy and sell stocks including short sales, multi-strategy credit, relative value credit and distressed credit. • Private equity : Private equity includes buyout funds, real asset/infrastructure funds, credit special situations funds, mezzanine lending funds and direct investments and strategic non-controlling minority investments in private companies that are principally accounted for using the equity method of accounting. • Overseas deposits : Overseas deposits are principally invested in short-term sovereign fixed income and investment grade corporate securities and international stocks. • Other : Other includes participation in investment pools. Unrealized Losses and Other-than-temporary Impairments An aging of unrealized losses on our investments in fixed maturities is presented below: December 31, 2020 Less Than One Year One Year or Greater Total (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed maturities U.S. Governments $ 40.6 $ 0.3 $ — $ — $ 40.6 $ 0.3 Foreign Governments 18.0 0.5 0.1 0.2 18.1 0.7 Obligations of states and political subdivisions 5.2 0.3 — — 5.2 0.3 Corporate bonds 202.5 6.7 17.5 6.6 220.0 13.3 Commercial mortgage-backed securities 21.8 0.3 — — 21.8 0.3 Residential mortgage-backed securities 74.4 0.4 3.0 0.2 77.4 0.6 Asset-backed securities 4.6 0.4 — — 4.6 0.4 Collateralized loan obligations 121.1 0.9 49.1 0.3 170.2 1.2 Total fixed maturities $ 488.2 $ 9.8 $ 69.7 $ 7.3 $ 557.9 $ 17.1 December 31, 2019 Less Than One Year One Year or Greater Total (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed maturities U.S. Governments $ 114.6 $ 1.1 $ 17.0 $ 0.1 $ 131.6 $ 1.2 Foreign Governments (1) 119.2 0.7 5.1 — 124.3 0.7 Obligations of states and political subdivisions (1) 0.7 — 2.1 0.1 2.8 0.1 Corporate bonds 249.7 18.9 63.6 15.8 313.3 34.7 Commercial mortgage-backed securities (1) 74.8 1.1 4.9 — 79.7 1.1 Residential mortgage-backed securities 66.9 0.3 25.2 0.3 92.1 0.6 Asset-backed securities 22.5 0.1 18.9 0.1 41.4 0.2 Collateralized loan obligations 54.9 0.8 116.7 0.6 171.6 1.4 Total fixed maturities $ 703.3 $ 23.0 $ 253.5 $ 17.0 $ 956.8 $ 40.0 (1) Unrealized losses are less than $0.1 million. We hold a total of 5,301 fixed maturity securities, of which 928 were in an unrealized loss position for less than one year and 149 were in an unrealized loss position for a period one year or greater as of December 31, 2020. For fixed maturities for which a decline in the fair value between the amortized cost is due to credit-related factors, an allowance is established for the difference between the estimated recoverable value and amortized cost with a corresponding charge to realized investment losses in the Statement of Income (Loss). The allowance is limited to the difference between amortized cost and fair value. The estimated recoverable value is the present value of cash flows expected to be collected, as determined by management. The difference between fair value and amortized cost that is not associated with credit-related factors is recognized in the Statement of Comprehensive Income (Loss). Accrued interest is excluded from the measurement of the allowance for credit losses. When determining if a credit loss has been incurred, we may consider the historical performance of the security, available market information and security specific considerations such as the priority payment of the security. In addition, inputs used in our analysis include, but are not limited to, credit ratings and downgrades, delinquency rates, missed scheduled interest or principal payments, purchase yields, underlying asset performance, collateral types, modeled default rates, modeled severity rates, call/prepayment rates, expected cash flows, industry concentrations, and potential or filed bankruptcies or restructurings. We evaluate for credit losses each period. If we determine that all or a portion of a fixed maturity is uncollectible, the uncollectible amortized cost is written off with a corresponding reduction to the allowance for credit losses. If we collect cash flows that were previously written off, the recovery is recognized in realized investment gains. We also consider whether we intend to sell an available-for-sale security or if it is more likely than not that we will be required to sell the security before recovery of its amortized cost. In these instances, a decline in fair value is recognized in net realized gains (losses) in the Statement of Income based on the fair value of the security at the time of assessment, resulting in a new cost basis for the security. Prior to the adoption of ASU 2016-13, the evaluation for a credit loss was generally based on the present value of expected cash flows of the security as compared to the amortized cost. For structured securities, frequency and severity of loss inputs were used in projecting future cash flows of the securities. Loss frequency was measured on the credit default rate, which included factors such as loan-to-value ratios and credit scores of borrowers. If a determination was made that the unrealized loss was other-than-temporary, a realized loss was recognized in the realized investment losses in the Statement of Income (Loss) and the amortized cost basis of the security was reduced to reflect the loss. Foreign Governments Obligations of states and political subdivisions Corporate bonds Asset backed securities Total Beginning balance, January 1, 2020 $ — $ — $ — $ — $ — Additions-initial adoption of accounting standard — — 6.8 0.1 6.9 Securities for which allowance was not previously recorded 0.3 0.3 15.3 — 15.9 Securities sold during the period (0.2) — (39.0) (0.1) (39.3) Additional net increases (decreases) in existing allowance 0.1 (0.2) 23.0 0.2 23.1 Ending balance, December 31, 2020 $ 0.2 $ 0.1 $ 6.1 $ 0.2 $ 6.6 Total credit impairment losses included in net realized investment (losses) gains in the Consolidated Statement of Income was $39.9 million for the year ended December 31, 2020. Total other-than-temporary impairment losses included in net realized investments losses (gains) was $20.3 million for the year ended December 31, 2019. Net Investment Income Investment income and expenses were as follows: For the Years Ended December 31, (in millions) 2020 2019 2018 Investment income: Interest on fixed maturities $ 108.6 $ 129.5 $ 115.0 Dividends on equity securities 2.8 11.1 12.5 Income on alternative investments 10.4 22.4 19.0 Income on short-term and other investments 3.9 8.9 9.5 Investment income 125.7 171.9 156.0 Investment expenses (13.0) (20.8) (23.7) Net investment income $ 112.7 $ 151.1 $ 132.3 Net Realized Investment Gains and Losses The following table presents our gross realized investment gains (losses): For the Years Ended December 31, (in millions) 2020 2019 2018 Realized gains on fixed maturities and other Fixed maturities $ 37.1 $ 22.2 $ 17.7 Other investments, including short-terms 93.8 0.1 0.2 Other assets 32.3 33.0 41.4 163.2 55.3 59.3 Realized losses on fixed maturities and other Fixed maturities (35.2) (11.7) (16.0) Other investments, including short-terms (78.6) (31.3) (40.0) Other assets (9.9) — — Credit losses on fixed maturities (39.9) — — Other-than-temporary impairment losses — (20.3) (7.6) (163.6) (63.3) (63.6) Equity securities Net realized (losses) gains on equity securities (17.1) 128.9 37.4 Change in unrealized gains (losses) on equity securities held at the end of the period 10.3 (40.8) (105.1) Net realized (losses) gains on equity securities (6.8) 88.1 (67.7) Net realized investment and other (losses) gains before income taxes (7.2) 80.1 (72.0) Income tax (benefit) provision 1.3 16.2 11.2 Net realized investment (losses) gains, net of income taxes $ (8.5) $ 63.9 $ (83.2) The cost of securities sold is based on the specific identification method. Changes in unrealized appreciation (depreciation) related to investments are summarized as follows: For the Years Ended December 31, (in millions) 2020 2019 2018 Change in unrealized gains Fixed maturities $ 96.0 $ 93.3 $ (88.1) Other investments (14.3) 4.4 0.1 Other and short-term investments 0.7 0.2 (0.5) Net unrealized investment gains (losses) before income taxes 82.4 97.9 (88.5) Income tax provision (benefit) 16.5 15.4 (13.0) Net unrealized investment gains (losses), net of income taxes $ 65.9 $ 82.5 $ (75.5) Foreign Currency Exchange Forward Contracts We entered into foreign currency exchange forward contracts to manage operational currency exposure on our CAD investment portfolio and loss reserves due to certain catastrophic events and other claims, minimize negative impacts to investment portfolio returns, and gain exposure to a total return strategy which invests in multiple currencies. The currency forward contracts are carried at fair value in our consolidated balance sheets in “other assets” at December 31, 2020 and 2019. The gains and losses are included in “net realized investment and other gains” in our consolidated statements of income. The fair value of our foreign currency exchange forward contracts as of December 31 was as follows: (in millions) December 31, 2020 December 31, 2019 Operational currency exposure $ 0.4 $ (0.8) Asset manager investment exposure (0.2) (0.3) Total return strategy 0.7 2.2 Total $ 0.9 $ 1.1 The following table presents our gross investment realized gains and losses on our foreign currency exchange forward contracts: For the Years Ended December 31, (in millions) 2020 2019 2018 Realized gains Operational currency exposure 13.2 5.7 9.7 Asset manager investment exposure 2.2 2.7 5.8 Total return strategy 61.6 22.5 26.7 Gross realized investment gains 77.0 30.9 42.2 Realized losses Operational currency exposure (8.6) (10.6) (7.9) Asset manager investment exposure (4.0) (0.8) (3.0) Total return strategy (62.3) (17.6) (28.6) Gross realized investment losses (74.9) (29.0) (39.5) Net realized investment gains (losses) on foreign $ 2.1 $ 1.9 $ 2.7 Regulatory Deposits, Pledged Securities and Letters of Credit We are required to maintain assets on deposit with various regulatory authorities to support our insurance and reinsurance operations. We maintain assets pledged as collateral in support of irrevocable letters of credit issued under the terms of certain reinsurance agreements for reported loss and loss expense reserves. The following table presents our components of restricted assets at December 31: (in millions) December 31, 2020 December 31, 2019 Securities on deposit for regulatory and other purposes $ 227.5 $ 192.5 Securities pledged as collateral for letters of credit and other 189.4 169.9 Securities and cash on deposit supporting Lloyd’s business 409.2 412.8 Total restricted investments $ 826.1 $ 775.2 Fair Value Measurements Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value measurement assumes that the transaction to sell the asset or transfer the liability occurs in the principal market for the asset or liability, or in the absence of a principal market, the most advantageous market. Market participants are buyers and sellers in the principal (or most advantageous) market that are independent, knowledgeable, able to transact for the asset or liability and willing to transfer the asset or liability. Valuation techniques consistent with the market and income approach are used to measure fair value. The inputs of these valuation techniques are categorized into three levels. • Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that can be accessed at the reporting date. We define actively traded as a security that has traded in the past seven days. We receive one quote per instrument for Level 1 inputs. • Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. We receive one quote per instrument for Level 2 inputs. • Level 3 inputs are unobservable inputs. Unobservable inputs reflect our own assumptions about the assumptions market participants would use in pricing the asset or liability based on the best information available in the circumstances. We receive fair value prices from third-party pricing services and our outside investment managers. These prices are determined using observable market information such as dealer quotes, market spreads, cash flows, yield curves, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the security’s terms and conditions, among other things. We have reviewed the processes used by the third-party providers for pricing the securities, and have determined that these processes result in fair values consistent with GAAP requirements. In addition, we review these prices for reasonableness, and have not adjusted any prices received from the third-party providers as of December 31, 2020 and 2019. A description of the valuation techniques we use to measure assets at fair value is as follows: Fixed Maturities (Available-for-Sale) Levels 1 and 2: • U.S. Treasury securities are typically valued using Level 1 inputs. For these securities, we obtain fair value measurements from third-party pricing services using quoted prices (unadjusted) in active markets at the reporting date. • U.S. Government agencies, non-U.S. Government securities, obligations of states and political subdivisions, credit securities and foreign denominated government and credit securities are reported at fair value using Level 2 inputs. For these securities, we obtain fair value measurements from third-party pricing services. Observable data may include dealer quotes, market spreads, yield curves, live trading levels, trade execution data, credit information and the security’s terms and conditions, among other things. • Asset and mortgage-backed securities and collateralized loan obligations are reported at fair value using Level 2 inputs. For these securities, we obtain fair value measurements from third-party pricing services. Observable data may include dealer quotes, market spreads, cash flows, yield curves, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the security’s terms and conditions, among other things. Fixed Maturities Level 3: We own term loans that are valued using unobservable inputs. Equity Securities Level 1: Equity securities are principally reported at fair value using Level 1 inputs. For these securities, we obtain fair value measurements from a third-party pricing service using quoted prices (unadjusted) in active markets at the reporting date. Equity Securities Level 3: We own certain equity securities that are reported at fair value using Level 3 inputs. The valuation techniques for these securities include the following: • Fair value measurements for an investment in an equity fund obtained by applying final prices provided by the administrator of the fund, which is based upon certain estimates and assumptions. • Fair value measurements from a broker and an independent valuation service, both based upon estimates and assumptions. Other Investments Level 2: Foreign regulatory deposits are assets held in trust in jurisdictions where there is a legal and regulatory requirement to maintain funds locally in order to protect policyholders. Lloyd’s is the appointed investment manager for the funds. These assets are invested in short-term government securities, agency securities and corporate bonds and are valued using Level 2 inputs based upon values obtained from Lloyd’s. Short-term Investments: Short-term investments are principally reported at fair value using Level 1 inputs, with the exception of short-term corporate and governmental bonds reported at fair value using Level 2 inputs as described in the fixed maturities section above. Values for the investments categorized as Level 1 are obtained from various financial institutions as of the reporting date. Based on an analysis of the inputs, our financial assets measured at fair value on a recurring basis have been categorized as follows: Fair Value Measurements at Reporting Date Using (in millions) December 31, 2020 Level 1 (a) Level 2 (b) Level 3 (c) Fixed maturities U.S. Governments $ 399.8 $ 383.5 $ 16.3 $ — Foreign Governments 294.8 — 294.8 — Obligations of states and political subdivisions 170.4 — 170.4 — Corporate bonds 1,981.8 — 1,974.8 7.0 Commercial mortgage-backed securities 339.7 — 339.7 — Residential mortgage-backed securities 508.2 — 508.2 — Asset-backed securities 122.8 — 122.8 — Collateralized loan obligations 289.6 — 289.6 — Total fixed maturities 4,107.1 383.5 3,716.6 7.0 Equity securities 176.7 159.2 — 17.5 Other investments 102.5 0.4 102.1 — Short-term investments 542.6 526.5 16.1 — $ 4,928.9 $ 1,069.6 $ 3,834.8 $ 24.5 (a) Quoted prices in active markets for identical asset (b) Significant other observable inputs (c) Significant unobservable inputs Fair Value Measurements at Reporting Date Using (in millions) December 31, 2019 Level 1 (a) Level 2 (b) Level 3 (c) Fixed maturities U.S. Governments $ 353.3 $ 347.8 $ 5.5 $ — Foreign Governments 248.7 — 248.7 — Obligations of states and political subdivisions 152.6 — 152.6 — Corporate bonds 1,778.4 — 1,771.0 7.4 Commercial mortgage-backed securities 217.0 — 217.0 — Residential mortgage-backed securities 488.8 — 488.8 — Asset-backed securities 165.3 — 165.3 — Collateralized loan obligations 225.8 — 225.8 — Total fixed maturities 3,629.9 347.8 3,274.7 7.4 Equity securities 136.0 117.8 — 18.2 Other investments 96.3 — 96.3 — Short-term investments 845.0 823.5 21.5 — $ 4,707.2 $ 1,289.1 $ 3,392.5 $ 25.6 (a) Quoted prices in active markets for identical asset (b) Significant other observable inputs (c) Significant unobservable inputs The fair value measurements in the tables above do not equal “total investments” on our consolidated balance sheets as they exclude certain other investments that are accounted for under the equity-method of accounting. A reconciliation of the beginning and ending balances for the investments categorized as Level 3 are as follows: Fair Value Measurements Using Observable Inputs (Level 3) (in millions) Credit Financial Equity Total Beginning balance, January 1, 2020 $ 7.4 $ 18.2 $ 25.6 Transfers into Level 3 — — — Transfers out of Level 3 — — — Total gains or losses (realized/unrealized): Included in net income — (5.9) (5.9) Included in other comprehensive income (0.5) — (0.5) Purchases, issuances, sales, and settlements: Purchases 0.1 5.2 5.3 Issuances — — — Sales — — — Settlements — — — Ending balance, December 31, 2020 $ 7.0 $ 17.5 $ 24.5 Amount of total gains or losses for the year included in net income attributable to the change in unrealized gains or losses relating to assets still held at December 31, 2020 $ — $ — $ — (in millions) Credit Financial Equity Total Beginning balance, January 1, 2019 $ 2.2 $ 19.8 $ 22.0 Transfers into Level 3 3.5 — 3.5 Transfers out of Level 3 — — — Total gains or losses (realized/unrealized): Included in net income (0.4) (1.6) (2.0) Included in other comprehensive loss 0.6 — 0.6 Purchases, issuances, sales, and settlements: Purchases 1.9 — 1.9 Issuances — — — Sales (0.4) — (0.4) Settlements — — — Ending balance, December 31, 2019 $ 7.4 $ 18.2 $ 25.6 Amount of total gains or losses for the year included in net income attributable to the change in unrealized gains or losses relating to assets still held at December 31, 2019 $ — $ — $ — At December 31, 2020 and 2019, we did not have any financial assets or financial liabilities measured at fair value on a nonrecurring basis or any financial liabilities on a recurring basis.

Allowance for Credit Losses

Allowance for Credit Losses	12 Months Ended
	Dec. 31, 2020
Credit Loss [Abstract]
Allowance for Credit Losses	Allowance for Credit Losses Premiums receivable The following table represents the balances of premiums receivable, net of allowance for uncollectible premiums, including expected credit losses, at December 31, 2020 and January 1, 2020, and the changes in the allowance for the year ended December 31, 2020. (in millions) Premiums Receivable, Net of Allowance for Estimated Uncollectible Premiums Allowance for Estimated Uncollectible Premiums Balance, January 1, 2020 $ 676.5 $ 7.9 Cumulative effect of adoption of ASU 2016-13 — Current period change for estimated uncollectible premiums 3.6 Write-offs of uncollectible premiums receivable (2.4) Foreign exchange adjustments 0.3 Balance, December 31, 2020 $ 679.8 $ 9.4 Reinsurance Recoverables The following table presents the balances of reinsurance recoverables, net of the allowance for estimated uncollectible reinsurance, including expected credit losses, at December 31, 2020 and January 1, 2020, and changes in the allowance for estimated uncollectible reinsurance for the year ended December 31, 2020. (in millions) Reinsurance Recoverables, Net of Allowance for Estimated Uncollectible Reinsurance Allowance for Estimated Uncollectible Reinsurance Balance, January 1, 2020 $ 3,107.2 $ 1.1 Cumulative effect of adoption of ASU 2016-13 2.5 Current period change for estimated uncollectible reinsurance 0.9 Write-offs of uncollectible reinsurance recoverables (0.4) Balance, December 31, 2020 $ 3,009.0 $ 4.1 Of the total reinsurance recoverable balance outstanding at December 31, 2020, reinsurers representing 90.3% were rated A- or better. We primarily utilize A.M. Best credit ratings when determining the allowance, adjusted as needed based on our historical experience with the reinsurers. Certain of our reinsurance recoverables are collateralized by letters of credit, funds held or trust agreements.

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases	Leases Our operating lease obligations are for office facilities, corporate housing and equipment. Our leases have remaining lease terms ranging between less than 1 year to 13 years, some of which include options to extend the leases. Expenses associated with leases totaled $20.3 million for the year ended December 31, 2020, as compared to $23.4 million for the year ended December 31, 2019. The components of lease expense and other lease information as of and during the year ended December 31, 2020 and 2019 are as follows: December 31, (in millions) 2020 2019 Operating leases right-of-use assets $ 82.0 $ 91.8 Operating lease liabilities 95.8 105.7 Operating lease weighted-average remaining lease term 10.50 9.91 Operating lease weighted-average discount rate 3.77 % 3.86 % For the Year Ended December 31, (in millions) 2020 2019 Operating lease costs $ 15.3 $ 19.3 Variable lease costs 5.4 4.5 Sublease income (0.4) (0.4) Total lease costs $ 20.3 $ 23.4 Operating cash flows from operating leases (fixed payments) $ 15.7 $ 17.5 Operating cash flows from operating leases (liability reduction) $ 12.8 $ 18.3 Our finance leases and short-term leases as of December 31, 2020 and 2019 were not material. Future minimum lease payments under operating leases as of December 31, 2020 were as follows: December 31, (in millions) 2020 2021 14.7 2022 13.2 2023 11.1 2024 9.8 2025 9.6 Thereafter 58.4 Total future minimum lease payments $ 116.8 Future lease obligations — Less imputed interest (21.0) Total operating lease liability $ 95.8 We have certain investment properties that we lease to independent, third parties. These properties consist of an office building that is currently leased through August 2026 and one condominium that is leased on a short-term basis. The carrying value of the office building is included in “Other assets” on our consolidated balance sheet. The condominium was placed for sale in December 2019, and sold in January 2021. The carrying value of this condominium is included in the “Assets held for Sale” on our consolidated balance sheet. Income for these leased properties was $2.6 million for the year ended December 31, 2020 and $2.8 million for the year ended December 31, 2019. Income for these leased properties is included in “fee and other income” on our consolidated statements of income (loss).

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2020
Insurance [Abstract]
Reinsurance	Reinsurance We reinsure certain risks with other insurance companies. Such arrangements serve to limit our maximum loss on certain individual risks as well as on catastrophes and large or unusually hazardous risks. We are liable to our insureds for reinsurance ceded in the event our reinsurers do not meet their obligations. Thus, a credit exposure exists with respect to reinsurance ceded to the extent that any reinsurer is unable or unwilling to meet the obligations assumed under the reinsurance contracts. Our allowance for uncollectible reinsurance balances receivable on paid losses and incurred claims was $4.1 million and $1.1 million as of December 31, 2020 and 2019, respectively (see Note 5, “Allowance for Credit Losses” for additional information). Under certain reinsurance agreements, collateral, including letters of credit, is held to secure performance of reinsurers in meeting their obligations. The amount of such collateral was $1,131.4 million and $1,184.7 million at December 31, 2020 and 2019, respectively. The collateral we hold does not apply to our entire outstanding reinsurance recoverable. Rather, collateral is provided on an individual contract basis as appropriate. For each individual reinsurer, the collateral held may exceed or fall below the total outstanding recoverable from that individual reinsurer. The long-term nature of the reinsurance contracts creates a credit risk to us over time arising from potentially uncollectible reinsurance. To mitigate that counterparty risk, we evaluate our reinsurers to assess their financial condition. The factors that underlie these reviews include a financial risk assessment as well as an internal assessment of the capitalization and the operational risk of the reinsurer. As a result of these reviews, we may make changes to the approved markets that are used in both our treaty and facultative reinsurance programs. Estimated losses recoverable from reinsurers and the ceded portion of unearned premiums are reported as assets in our consolidated balance sheets. Included in “reinsurance recoverables” are paid loss recoverables of $509.1 million and $672.3 million as of December 31, 2020 and 2019, respectively. “Earned premiums” and “losses and loss adjustment expenses” are reported net of reinsurance in our consolidated statements of income (loss). Losses and loss adjustment expenses of $1,208.8 million, $1,220.7 million and $1,040.8 million for the years ended December 31, 2020, 2019 and 2018, respectively, are net of amounts ceded to reinsurers of $941.3 million, $1,031.1 million and $888.9 million, respectively. We are required to accept certain assigned risks and other legally mandated reinsurance obligations. Prior to the mid-1980s, we assumed various forms of casualty reinsurance for which we continue to maintain reserves for losses and loss adjustment expenses (see Note 9, “Run-off Lines”). For such assumed reinsurance transactions, we engage in various monitoring steps that are common with assumed reinsurance such as ongoing claims reviews. We assumed property related reinsurance primarily through our subsidiaries, Argo Re and Ariel Re, and casualty related reinsurance primarily through Syndicate 1200. Premiums were as follows: For the Years Ended December 31, (in millions) 2020 2019 2018 Direct written premiums $ 2,676.1 $ 2,510.4 $ 2,292.9 Reinsurance ceded to other companies (1,423.2) (1,375.5) (1,189.0) Reinsurance assumed from other companies 557.2 619.7 661.4 Net written premiums $ 1,810.1 $ 1,754.6 $ 1,765.3 Direct earned premiums $ 2,660.6 $ 2,412.4 $ 2,201.0 Reinsurance ceded to other companies (1,388.6) (1,286.7) (1,137.2) Reinsurance assumed from other companies 508.5 604.0 667.7 Net earned premiums $ 1,780.5 $ 1,729.7 $ 1,731.5 Percentage of reinsurance assumed to net earned premiums 28.6 % 34.9 % 38.6 %

Reserves for Losses and Loss Ad

Reserves for Losses and Loss Adjustment Expenses	12 Months Ended
	Dec. 31, 2020
Insurance [Abstract]
Reserves for Losses and Loss Adjustment Expenses	Reserves for Losses and Loss Adjustment Expenses The following table provides a reconciliation of reserves for losses and loss adjustment expenses (“LAE”): For the Years Ended December 31, (in millions) 2020 2019 2018 Net reserves beginning of the year $ 2,722.7 $ 2,562.9 $ 2,488.0 Net AIL reserves acquired 27.9 — — Net ArgoGlobal Assicurazioni reserves acquired — — 43.4 Add: Losses and LAE incurred during current calendar year, net of reinsurance: Current accident year 1,201.1 1,082.6 1,058.8 Prior accident years 7.7 138.1 (18.0) Losses and LAE incurred during calendar year, net of reinsurance 1,208.8 1,220.7 1,040.8 Deduct: Losses and LAE payments made during current calendar year, net of reinsurance: Current accident year 253.4 224.3 273.3 Prior accident years 866.4 806.0 665.6 Losses and LAE payments made during current calendar year, net of reinsurance: 1,119.8 1,030.3 938.9 Change in participation interest (1) 32.8 (14.4) (25.5) Foreign exchange adjustments 33.7 (16.2) (44.9) Net reserves - end of year 2,906.1 2,722.7 2,562.9 Add: Reinsurance recoverables on unpaid losses and LAE, end of year 2,499.9 2,434.9 2,091.7 Gross reserves - end of year $ 5,406.0 $ 5,157.6 $ 4,654.6 (1) Amount represents (decrease) increase in reserves due to change in our Syndicate 1200 and Syndicate 1910 participation. Reserves for losses and LAE represent the estimated indemnity cost and related adjustment expenses necessary to investigate and settle claims. Such estimates are based upon individual case estimates for reported claims, estimates from ceding companies for reinsurance assumed and actuarial estimates for losses that have been incurred but not yet reported to the insurer. Any change in probable ultimate liabilities is reflected in current operating results. Underwriting results for the year ended December 31, 2020 included net losses and loss adjustment expenses attributed to the COVID-19 pandemic of $73.2 million, primarily resulting from contingency and property exposures in the Company’s International Operations ($66.7 million) and property exposures in its U.S. Operations ($6.5 million). Property losses relate to sub-limited affirmative business interruption coverage, primarily in certain International markets, as well as expected costs associated with claims handling. The impact from the unfavorable (favorable) development of prior accident years’ losses and LAE reserves on each reporting segment is presented below: For the Years Ended December 31, (in millions) 2020 2019 2018 U.S. Operations $ 2.4 $ 15.7 $ (20.8) International Operations (6.2) 110.4 (9.5) Run-off Lines 11.5 12.0 12.3 Total unfavorable prior-year development $ 7.7 $ 138.1 $ (18.0) The following describes the primary factors behind each segment’s prior accident year reserve development for the years ended December 31, 2020, 2019 and 2018 : Year ended December 31, 2020: • U.S. Operations: Net unfavorable development in liability and professional lines, partially offset by favorable development in specialty and property. • International Operations: Net favorable development primarily related to favorable development in Reinsurance, partially offset by unfavorable development in Bermuda Insurance. The favorable development in Reinsurance was due to experience on catastrophe losses from recent years and decreases on claims from older accident years. The unfavorable movement in Bermuda Insurance was driven by professional and liability losses. • Run-off Lines: Net unfavorable loss reserve development in asbestos and environmental lines and other run-off lines, partially offset by favorable loss reserve development on prior accident years in risk management workers compensation. Year ended December 31, 2019: • U.S. Operations: Net unfavorable development in professional, property and liability lines partially offset by favorable development in specialty lines. The unfavorable professional lines development was driven by movements on individual large management liability claims primarily impacting accident years 2015 through 2017. The unfavorable property development was primarily driven by large excess claims resulting from the 2017 and 2018 catastrophe events. The unfavorable liability lines development was driven by actual loss activity greater than expected. The three most recent accident years showed unfavorable development partially offset by favorable development on older years. The favorable specialty lines development was driven by favorable experience in the surety business across multiple accident years. • International Operations: Net unfavorable development was primarily concentrated in liability and professional lines. The charges impacted our Bermuda casualty and professional divisions, and our Syndicate 1200 and European operations. The charges in our Bermuda business stemmed from public utility business in our casualty division, which we previously exited, as well as updated estimates on a number of other casualty and professional claims based on new information received in the last three quarters of 2019. As it relates to Syndicate 1200, the adverse development generally related to businesses that we have previously exited or where aggressive remedial underwriting actions have been taken. As it relates to Europe, the adverse development primarily related to certain coverholders whose contracts were previously terminated or where aggressive remedial underwriting actions have been taken as well as unexpected movements in large professional liability losses. This unfavorable development was primarily due to obtaining additional information on several individual claims, including investigations regarding causes of the incidents leading to the losses, reports provided by outside counsel, audits of the underlying losses and recent court decisions, settlements and jury awards. The result was an increase in the number of claims with the potential for underlying losses to reach our attachment point, particularly within our Bermuda Operations. Adverse development in Syndicate 1200 related to large claims involving the marine and energy and liability divisions. Losses on small and medium enterprise package business were also higher than expected. The unfavorable development during the year was also attributable to the results of ongoing audits, underwriting reviews, and updates from third-party coverholders, which included the identification of differences from original expectations with regard to the classes written, the distribution of writings by geography, and the rates charged by the coverholders. • Run-off Lines: Net unfavorable development in asbestos and environmental and other run-off segments partially offset by favorable development in risk management workers compensation. The change in asbestos was driven by assumed business where accounts are staying open longer than expected. The change in environmental was driven by individual claims on direct business. Year ended December 31, 2018: • U.S. Operations: Net favorable development in general liability and surety lines, partially offset by unfavorable development in commercial multi-peril lines. • International Operations: Net favorable development in property partially offset by unfavorable development within specialty and liability lines. • Run-off Lines: Net unfavorable development in liability lines as well as asbestos and environmental. In the opinion of management, our reserves represent the best estimate of our ultimate liabilities, based on currently known facts, current law, current technology and reasonable assumptions where facts are not known. Due to the significant uncertainties and related management judgments, there can be no assurance that future favorable or unfavorable loss development, which may be material, will not occur. The spread of COVID-19 and related economic shutdown has increased the uncertainty that is always present in our estimate of the ultimate cost of loss and settlement expense. Actuarial models base future emergence on historic experience, with adjustments for current trends, and the appropriateness of these assumptions involved more uncertainty as of December 31, 2020. We expect there will be impacts to the timing of loss emergence and ultimate loss ratios for certain coverages we underwrite. The industry is experiencing new issues, including the temporary suspension of civil court cases in most states, the extension of certain statutes of limitations and the impact on our insureds from a significant reduction in economic activity. Our booked reserves include consideration of these factors, but legislative, regulatory or judicial actions could result in loss reserve deficiencies and reduce earnings in future periods. Short-Duration Contract Disclosures Our basis for disaggregating short-duration contracts is by each of our two ongoing reporting segments, U.S. Operations and International Operations, further disaggregated within each segment by our operating divisions and the primary insurance and reinsurance lines of business we write. We have chosen to disaggregate the data in this way so as to not obscure useful information by otherwise aggregating items with significantly different characteristics. See Note 20, “Segment Information,” for additional information regarding our two ongoing reporting segments. Operating Divisions Our U.S. Operations reporting segment is comprised of two primary operating divisions, Excess and Surplus Lines and Specialty Admitted, while International Operations’ primary operating divisions are Argo Insurance Bermuda, Reinsurance and Syndicate 1200. Each of these operating divisions are further described below. Excess and Surplus Lines The Excess and Surplus Lines division focuses on U.S.-based risks that the standard (admitted) market is unwilling or unable to underwrite. The standard market’s limited appetite for such coverage is often driven by the insured’s unique risk characteristics, the perils involved, the nature of the business, and/or the insured’s loss experience. We are often able to underwrite these risks with more flexible policy terms through our Excess and Surplus Lines division. We underwrite this business on both an admitted and non-admitted basis. Specialty Admitted This Specialty Admitted division provides coverages designed to meet the specialized insurance needs of U.S.-based businesses within certain well-defined markets. It targets business classes and industries with distinct risk profiles that can benefit from specially designed insurance programs, tailored loss control and expert claims handling. This division serves its targeted niche markets with a narrowly focused underwriting profile and specialized knowledge of the businesses it serves. Argo Insurance Bermuda Argo Insurance Bermuda offers casualty, property and professional lines, which serves the needs of global clients by providing the following coverages: property, general and products liability, directors and officers liability, errors and omissions liability and employment practices liability. Reinsurance The Reinsurance division operates in two areas - treaty property and specialty. This business is focused on mainly North American commercial properties and writes on both a primary and excess basis. Business is written on an open market basis through retail and wholesale brokers. Treaty property reinsurance is predominantly catastrophe-focused. Specialty reinsurance encompasses marine, energy, aviation, terrorism and property. This reinsurance portfolio is focused on treaties where high-quality exposure and experience data allow our underwriters to quantify the risk. Syndicate 1200 The Syndicate 1200 division is focused on underwriting property, specialty and non-U.S. liability insurance through Argo Underwriting Agency, Ltd. on behalf of Lloyd’s Syndicate 1200 within the Lloyd’s of London global franchise. Lines of Business We use an underwriting committee structure to monitor and evaluate the operating performance of our lines of business. The underwriting committees are organized to allow products or coverages with similar characteristics to be managed and evaluated in distinct groups. Using this approach, our insurance business is categorized into underwriting groups, which are Liability, Professional, Property and Specialty. Noted below are descriptions of the types of characteristics considered to disaggregate our business into these groups, as well as other qualitative factors to consider when using the information contained in the following incurred and paid claims development tables. Liability Our Liability business generally covers exposures where most claims are reported without a significant time lag between the event that gives rise to a claim and the date the claim is reported to us. However, since facts and information are frequently not complete at the time claims are reported to us, and because protracted litigation is sometimes involved, it can be several years before the ultimate value of these claims is determined. In our Argo Bermuda Insurance division, much of the business covers higher layers, potentially increasing the time it takes to fully determine our exposure. Professional Much of our Professional business is written on a claims-made basis resulting in coverage only for claims that are reported to us during the year in which the policy is effective, thus reducing the number of claims that will become known to us after the end of the policy expiration date. However, facts and information are frequently not complete at the time claims are reported to us, and protracted litigation is sometimes involved. It can be several years before the ultimate value of these claims is determined. In our Argo Bermuda Insurance division, much of the business covers higher layers, potentially increasing the time it takes to fully determine our exposure. Property Property losses are generally reported within a short period of time from the date of loss, and in most instances, property claims are settled and paid within a relatively short timeframe. However, Property can be impacted by catastrophe losses which can be more complex than non-catastrophe Property claims due to factors such as difficulty accessing impacted areas and other physical, legal and regulatory impediments potentially extending the period of time it takes to settle and pay claims. The impacts of catastrophe losses can be more significant in our Reinsurance and Syndicate 1200 divisions. Specialty Specialty lines losses are generally reported within a short period of time from the date of loss, and in most instances, Specialty lines claims are settled and paid within a relatively short timeframe. However, Specialty lines can be impacted by larger losses where facts and information are frequently not complete at the time claims are reported to us. These large losses can be more complex than smaller Specialty claims due to factors such as difficulty determining actual damages and other physical, legal and regulatory impediments potentially extending the period of time it takes to settle and pay claims. Descriptions of the primary types of coverages, as disclosed in the following tables, included in the significant lines of business for each operating division are noted below: Excess and Surplus Lines • Liability: primary and excess specialty casualty, contract liability, commercial multi-peril, product liability, environmental liability, and auto liability Specialty Admitted • Liability: workers compensation, general liability, auto liability, and various public entity liability risks • Professional: management liability and errors and omissions liability • Specialty: surety and inland marine Argo Insurance Bermuda • Liability: long-tail excess casualty and general liability Reinsurance • Property: property catastrophe reinsurance and excess property direct and facultative insurance Syndicate 1200 • Liability : general liability, international casualty and motor treaties • Professional : professional indemnity, directors and officer’s liability, and medical malpractice • Property : direct and facultative excess insurance, North American and international binders, and residential collateral protection for lending institutions • Specialty : personal accident, aviation, cargo, yachts, and onshore and offshore marine Run-off Lines Segment We have a Run-off Lines segment for certain products that we no longer underwrite, including asbestos and environmental claims. We have excluded the Run-off Lines segment from the following disaggregated short-duration contract disclosures due to its insignificance to our consolidated financial position and results of operations, both quantitatively and qualitatively. Gross reserves for losses and LAE in Run-off Lines account for less than 5% of our consolidated gross reserves for losses and LAE, and are primarily related to accident years prior to the mid-1990s. As such, claims development tables for the most recent ten Accident Years Presented Prior to the acquisition of Ariel Re in February 2017, Ariel Re’s ultimate claims and claim adjustment expense data was not historically available by accident years and line of business. As a result, it is not practical, nor would it be consistent to provide information for calendar years 2016 and prior by accident year at our line of business level. Beginning with the 2017 calendar year, we began accumulating such claims information by accident year and line of business, and have included such in the tabular disclosures below for the Reinsurance operating division, Property line of business disaggregation category. Accordingly, calendar years prior to 2017 for the aforementioned tabular disclosures relate only to our Reinsurance business prior to the acquisition of Ariel Re. Foreign Currency Portions of the business we write in the Syndicate 1200, Argo Bermuda Insurance and Reinsurance divisions are denominated in foreign currencies. We have used the December 31, 2020 balance sheet foreign exchange rates to recast the incurred and paid claims information for all periods presented in the following claims development tables in order to eliminate the effects of changes in foreign currency translation rates. Lloyd’s Reinsurance to Close Process Syndicate 1200 and Syndicate 1910 are subject to the reinsurance to close process at Lloyd’s where a year of account stays open for three years and is then reinsured into the next year of account. As a result, our economic participation on the years reinsured into the next year of account can change, perhaps significantly. We recast the incurred and paid claims information for all periods presented in the following claims development tables in order to eliminate the effects of the changes in economic participation. . Reserves for IBNR Claims Reserves for IBNR claims are based on the estimated ultimate cost of settling claims, including the effects of inflation and other social and economic factors, using past experience adjusted for current trends and any other factors that would modify past experience. We use a variety of statistical and actuarial techniques to analyze current claims costs, including frequency and severity data and prevailing economic, social and legal factors. Each such method has its own set of assumptions and outputs, and each has strengths and weaknesses in different areas. Since no single estimation method is superior to another method in all situations, the methods and assumptions used to project loss reserves will vary by coverage and product. We use what we believe to be the most appropriate set of actuarial methods and assumptions for each product line grouping and coverage. While the loss projection methods may vary by product line and coverage, the general approach for calculating IBNR remains the same: ultimate losses are forecasted first, and that amount is reduced by the amount of cumulative paid claims and case reserves. Reserves established in prior years are adjusted as loss experience develops and new information becomes available. Adjustments to previously estimated reserves are reflected in the results of operations in the year in which they are made. As described above, various actuarial methods are used to determine the reserves for losses and LAE recorded in our consolidated balance sheets. Weightings of methods at a detailed level may change from evaluation to evaluation based on a number of observations, measures, and time elements. There were no significant changes to the methods and assumptions underlying our consolidated reserve estimations and selections as of December 31, 2020. Incurred & Paid Claims Development Disclosures The following tables provide information about incurred and cumulative paid losses and allocated loss adjustment expenses (“ALAE”), net of reinsurance. The following tables also include IBNR reserves plus expected development on reported claims and the cumulative number of reported claims as of December 31, 2020. Reporting Segment: U.S. Operations Operating Division: Excess and Surplus Lines Line of Business: Liability (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 202.9 $ 206.0 $ 205.8 $ 200.0 $ 193.5 $ 192.8 $ 189.0 $ 187.8 $ 185.8 $ 187.4 2012 189.6 196.0 189.7 183.6 184.4 182.1 182.3 181.0 182.0 2013 217.9 222.6 224.3 227.2 220.4 216.0 214.2 216.0 2014 213.0 215.2 213.2 211.9 212.3 210.0 218.1 2015 232.5 237.1 228.6 226.4 224.8 233.9 2016 246.4 250.6 243.1 248.3 250.0 2017 253.3 244.3 249.0 257.7 2018 278.8 269.5 254.0 2019 269.8 268.8 2020 266.2 Total $ 2,334.1 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 17.6 $ 53.8 $ 91.0 $ 122.9 $ 146.6 $ 162.4 $ 170.0 $ 174.4 $ 177.5 $ 179.2 2012 17.2 52.8 89.1 120.8 142.4 157.5 163.4 170.3 174.9 2013 17.6 60.2 100.4 135.2 163.7 179.6 192.2 200.3 2014 15.0 52.2 95.9 131.6 154.5 172.8 186.7 2015 16.5 51.9 91.4 131.5 162.8 182.4 2016 17.4 52.8 95.5 149.5 177.4 2017 11.5 38.7 88.0 149.6 2018 15.0 47.0 98.2 2019 14.9 61.2 2020 12.5 Total $ 1,422.4 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 24.1 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 935.8 As of December 31, 2020 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2011 $ 187.4 $ 3.0 8,526 2012 182.0 3.4 7,494 2013 216.0 5.3 7,484 2014 218.1 9.9 6,812 2015 233.9 17.4 6,509 2016 250.0 29.8 6,283 2017 257.7 36.7 7,172 2018 254.0 83.0 6,810 2019 268.8 147.6 5,985 2020 266.2 223.7 3,407 (1) Information presented for calendar years prior to 2020 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. Reporting Segment: U.S. Operations Operating Division: Specialty Admitted Line of Business: Liability (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 140.3 $ 155.1 $ 159.0 $ 157.5 $ 158.2 $ 154.0 $ 153.7 $ 154.0 $ 151.6 $ 150.4 2012 140.3 146.3 149.7 153.3 151.5 147.7 146.6 146.2 146.3 2013 126.6 133.2 136.7 133.2 131.1 130.6 128.9 128.8 2014 115.6 121.9 116.9 114.5 111.5 111.9 109.3 2015 107.3 106.7 101.7 102.3 103.1 101.6 2016 96.1 99.9 99.3 104.7 105.2 2017 121.5 129.5 135.3 140.0 2018 147.3 160.9 160.5 2019 151.3 154.9 2020 138.1 Total $ 1,335.1 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 23.2 $ 57.5 $ 85.9 $ 111.3 $ 126.1 $ 135.1 $ 139.8 $ 143.1 $ 144.0 $ 145.1 2012 20.1 51.0 80.7 105.8 120.8 127.9 131.9 135.0 138.2 2013 18.9 49.4 74.0 93.6 102.8 109.7 114.7 118.0 2014 17.4 38.8 58.7 75.3 86.1 93.5 96.5 2015 17.2 35.0 48.8 64.2 73.6 81.5 2016 11.1 31.7 48.6 67.6 78.2 2017 16.3 44.4 70.9 88.9 2018 19.4 52.0 77.6 2019 17.5 52.4 2020 13.0 Total $ 889.4 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 35.5 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 481.2 As of December 31, 2020 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2011 $ 150.4 $ 3.4 28,201 2012 146.3 3.8 23,681 2013 128.8 5.5 19,003 2014 109.3 6.2 16,404 2015 101.6 9.1 14,768 2016 105.2 10.4 11,946 2017 140.0 19.8 13,988 2018 160.5 40.1 15,891 2019 154.9 62.4 14,946 2020 138.1 89.9 8,986 (1) Information presented for calendar years prior to 2020 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. Reporting Segment: U.S. Operations Operating Division: Specialty Admitted Line of Business: Professional (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 35.0 $ 35.0 $ 35.0 $ 32.5 $ 28.2 $ 26.9 $ 26.6 $ 26.0 $ 25.8 $ 25.7 2012 27.8 28.3 28.6 25.8 24.0 24.5 24.9 24.7 24.4 2013 20.9 21.5 21.1 19.0 19.8 19.5 18.3 18.1 2014 22.4 22.4 26.0 33.7 36.2 35.4 35.1 2015 29.9 29.5 33.2 34.0 37.1 37.9 2016 44.2 44.8 45.1 42.9 35.5 2017 60.1 61.8 78.3 87.9 2018 70.8 73.2 79.2 2019 94.4 96.8 2020 152.6 Total $ 593.2 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 3.2 $ 11.8 $ 17.8 $ 22.0 $ 24.0 $ 25.4 $ 25.7 $ 25.7 $ 25.7 $ 25.7 2012 2.3 8.6 16.9 19.9 21.4 22.6 23.5 24.2 24.0 2013 1.9 6.3 10.9 14.2 17.6 17.5 17.9 17.9 2014 2.3 5.4 15.1 24.1 25.5 32.3 33.3 2015 1.8 8.3 15.6 20.8 26.2 31.3 2016 2.4 11.9 24.6 28.9 30.8 2017 3.5 24.9 38.0 59.7 2018 4.5 16.7 43.8 2019 4.9 32.9 2020 13.3 Total $ 312.7 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 6.8 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 287.3 As of December 31, 2020 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2011 $ 25.7 $ — 821 2012 24.4 0.1 642 2013 18.1 0.2 622 2014 35.1 0.4 1,045 2015 37.9 1.5 1,843 2016 35.5 2.5 3,251 2017 87.9 1.4 3,747 2018 79.2 7.4 4,287 2019 96.8 39.7 5,049 2020 152.6 124.9 4,739 (1) Information presented for calendar years prior to 2020 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. Reporting Segment: U.S. Operations Operating Division: Specialty Admitted Line of Business: Specialty (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 0.2 $ 3.9 $ 3.4 $ 3.4 $ 3.6 $ 2.6 $ 2.0 $ 1.7 $ 1.7 $ 1.7 2012 7.5 6.7 4.9 4.3 4.0 3.9 3.5 3.6 3.3 2013 10.0 8.6 4.6 2.5 1.7 0.9 0.9 0.9 2014 13.1 13.1 8.9 6.0 4.8 4.6 4.6 2015 14.8 14.3 9.5 5.5 1.2 0.5 2016 15.0 15.0 11.2 6.2 4.7 2017 16.2 16.2 7.6 0.9 2018 20.9 17.4 3.3 2019 22.7 8.6 2020 25.4 Total $ 53.9 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ — $ 1.6 $ 1.4 $ 1.3 $ 1.2 $ 1.7 $ 1.7 $ 1.7 $ 1.7 $ 1.7 2012 3.6 3.3 3.3 3.3 3.3 3.4 3.3 3.4 3.4 2013 0.4 0.9 0.9 0.9 0.9 0.9 0.9 0.9 2014 1.1 3.3 4.0 4.0 4.1 4.1 4.0 2015 0.2 0.1 0.2 0.3 0.3 0.3 2016 1.3 1.6 2.2 2.2 2.2 2017 0.3 0.1 — 0.1 2018 — 0.7 1.7 2019 0.7 0.7 2020 0.3 Total $ 15.3 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 0.7 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 39.3 As of December 31, 2020 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2011 $ 1.7 $ — 80 2012 3.3 — 130 2013 0.9 — 50 2014 4.6 0.6 50 2015 0.5 0.2 24 2016 4.7 0.5 61 2017 0.9 0.6 104 2018 3.3 0.7 123 2019 8.6 7.1 253 2020 25.4 19.8 309 (1) Information presented for calendar years prior to 2020 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. Reporting Segment: International Operations Operating Division: Reinsurance Line of Business: Property (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 120.3 $ 110.4 $ 112.6 $ 110.6 $ 109.9 $ 113.7 $ 129.0 $ 135.6 $ 136.1 $ 135.4 2012 47.2 51.4 50.4 51.7 46.5 55.3 59.8 61.0 60.1 2013 32.5 34.5 34.0 32.3 32.9 32.4 31.9 32.3 2014 26.7 26.8 25.0 30.6 31.9 32.5 31.7 2015 27.2 23.8 62.6 60.5 57.9 52.7 2016 44.7 44.9 39.2 47.3 44.8 2017 109.0 107.7 111.2 103.9 2018 69.3 82.9 79.5 2019 63.2 70.1 2020 56.6 Total $ 667.1 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 43.1 $ 70.3 $ 92.3 $ 100.5 $ 102.8 $ 107.8 $ 123.6 $ 130.6 $ 132.7 $ 132.3 2012 12.4 31.2 40.6 49.7 44.1 52.2 58.0 60.1 59.3 2013 4.3 17.2 27.3 29.8 31.2 31.2 31.3 32.1 2014 2.8 12.9 19.0 30.1 30.6 32.1 31.6 2015 4.2 11.3 50.0 53.1 54.8 51.1 2016 14.0 25.4 29.7 42.8 43.0 2017 49.7 92.9 112.6 102.6 2018 24.9 71.5 78.0 2019 9.3 57.6 2020 11.60 Total $ 599.2 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 2.5 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 70.4 As of December 31, 2020 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2011 $ 135.4 $ 0.1 463 2012 60.1 — 278 2013 32.3 — 219 2014 31.7 — 223 2015 52.7 — 222 2016 44.8 1.1 395 2017 103.9 (9.8) 847 2018 79.5 (13.7) 714 2019 70.1 0.2 385 2020 56.6 33.7 398 (1) Information presented for calendar years prior to 2020 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. Reporting Segment: International Operations Operating Division: Argo Insurance Bermuda Line of Business: Liability (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 6.6 $ 6.6 $ 6.6 $ 4.4 $ 2.2 $ 1.6 $ 1.0 $ — $ — $ — 2012 7.4 7.4 7.4 5.6 4.4 1.7 — 0.6 0.6 2013 8.5 8.5 8.5 8.5 4.9 2.2 5.3 5.3 2014 9.8 9.8 9.8 6.2 1.5 2.3 2.3 2015 11.3 14.3 24.8 35.4 45.4 45.1 2016 13.9 14.0 14.0 6.6 6.1 2017 17.1 17.3 26.9 30.3 2018 8.9 32.1 26.6 2019 13.3 13.6 2020 23.3 Total $ 153.2 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ — $ — $ — $ — $ — $ — $ — $ — $ — $ — 2012 — — — — — — — — — 2013 — — — — 2.3 2.3 2.3 2.4 2014 — — 0.1 0.1 1.2 1.2 1.4 2015 — — 16.1 20.3 26.6 34.8 2016 — — — 0.1 0.1 2017 — 3.3 3.4 17.9 2018 — 13.8 18.3 2019 — 0.1 2020 0.8 Total $ 75.8 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance — Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 77.4 As of December 31, 2020 Accident Year

Run-off Lines

Run-off Lines	12 Months Ended
	Dec. 31, 2020
Discontinued Operations and Disposal Groups [Abstract]
Run-off Lines	Run-off Lines We have discontinued active underwriting of certain lines of business, including those lines that were previously recorded in Argo Group’s risk-management segment. All current activity within these lines is related to the management of claims and other administrative functions. Also included in Run-off Lines are other liability reserves, which include exposure to claims for asbestos and environmental liabilities written in past years. The other liability reserves are often characterized by long elapsed periods between the occurrence of a claim and ultimate payment to resolve the claim. We use a specialized staff dedicated to administer and settle these claims. The following table presents our gross reserves for Run-off Lines as of December 31: December 31, (in millions) 2020 2019 Asbestos and Environmental: Reinsurance assumed $ 29.4 $ 26.7 Other 29.9 25.9 Total Asbestos and Environmental 59.3 52.6 Risk-management 162.4 188.1 Run-off reinsurance lines 0.5 0.5 Other run-off lines 14.3 12.3 Gross reserves - Run-off Lines $ 236.5 $ 253.5 We have received asbestos and environmental liability claims arising from other liability coverage primarily written in the 1960s, 1970s and into the early 1980s. Asbestos and environmental claims originate from policies directly underwritten by us and from reinsurance assumed during this period, including a portion assumed from the London market. The following table represents the total gross reserves for our asbestos exposure: December 31, (in millions) 2020 2019 2018 Direct written Case reserves $ 3.1 $ 2.7 $ 2.7 Unallocated loss adjustment expense ("ULAE") 0.5 0.5 0.5 Incurred but not reported ("IBNR") 20.2 16.1 19.1 Total direct written reserves 23.8 19.3 22.3 Assumed domestic Case reserves 8.4 9.1 8.7 ULAE 0.8 0.8 0.8 IBNR 12.8 11.2 12.0 Total assumed domestic reserves 22.0 21.1 21.5 Assumed London Case reserves 1.4 1.3 1.5 ULAE — — — IBNR 1.6 1.1 1.5 Total assumed London reserves 3.0 2.4 3.0 Total asbestos reserves $ 48.8 $ 42.8 $ 46.8 The following table presents our underwriting losses for Run-off Lines: For the Years Ended December 31, (in millions) 2020 2019 2018 Asbestos and Environmental: Reinsurance assumed $ (5.7) $ (4.4) $ (3.9) Other (11.7) (3.9) (4.1) Total Asbestos and Environmental (17.4) (8.3) (8.0) Risk-management 4.3 (4.9) (2.6) Run-off reinsurance lines 0.4 0.7 — Other run-off lines (3.4) (1.7) (5.3) Total underwriting loss - Run-off Lines $ (16.1) $ (14.2) $ (15.9) Reserves for asbestos and environmental claims cannot be estimated with traditional loss reserving techniques that rely on historical accident year loss development factors. The uncertainty in the asbestos and environmental reserves estimates arises from several factors including lack of actuarially credible historical data, inapplicability of standard actuarial projection techniques, uncertainty with regards to claim costs, coverage interpretations and judicial, statutory and regulatory provisions under which the claims may be ultimately resolved. It is impossible to predict how the courts will interpret coverage issues and these resolutions may have a material impact on the ultimate resolution of the asbestos and environmental liabilities. We use a variety of estimation methods to calculate reserves as a whole; however, reserves for asbestos and environmental claims were determined using a variety of methods which rely on historical claim reporting and average claim cost information. We apply greatest weight to the method that projects future calendar period claims and average claim costs because it best captures the unique claim characteristics of our underlying exposures. Although management has recorded its best estimate of loss reserves, due to the uncertainties of estimation of liability that may arise as discussed herein, further deterioration of claims could occur in the future.

Long-term Debt

Long-term Debt	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Long-term Debt	Long-term Debt Junior Subordinated Debentures Through a series of trusts, that are wholly-owned subsidiaries (non-consolidated), we issued debt. The debentures are variable with the rate being reset quarterly and subject to certain interest rate ceilings. Interest payments are payable quarterly. The debentures are all unsecured and are subordinated to other indebtedness. At December 31, 2020 and 2019, all debentures were eligible for redemption subject to certain terms and conditions at a price equal to 100% of the principal plus accrued and unpaid interest. A summary of our outstanding junior subordinated debentures is presented below: December 31, 2020 (in millions) Issue Date Trust Preferred Pools Maturity Rate Structure Interest Rate at December 31, 2020 Amount Argo Group 5/15/2003 PXRE Capital Statutory Trust II 5/15/2033 3M LIBOR + 4.10% 4.32% $ 18.0 11/6/2003 PXRE Capital Trust VI 9/30/2033 3M LIBOR + 3.90% 4.15% 10.3 Argo Group US 5/15/2003 Argonaut Group Statutory Trust I 5/15/2033 3M LIBOR + 4.10% 4.32% 15.5 12/16/2003 Argonaut Group Statutory Trust III 1/8/2034 3M LIBOR + 4.10% 4.34% 12.3 4/29/2004 Argonaut Group Statutory Trust IV 4/29/2034 3M LIBOR + 3.85% 4.07% 13.4 5/26/2004 Argonaut Group Statutory Trust V 5/24/2034 3M LIBOR + 3.85% 4.05% 12.4 5/12/2004 Argonaut Group Statutory Trust VI 6/17/2034 3M LIBOR + 3.80% 4.03% 13.4 9/17/2004 Argonaut Group Statutory Trust VII 12/15/2034 3M LIBOR + 3.60% 3.82% 15.5 9/22/2004 Argonaut Group Statutory Trust VIII 9/22/2034 3M LIBOR + 3.55% 3.79% 15.5 10/22/2004 Argonaut Group Statutory Trust IX 12/15/2034 3M LIBOR + 3.60% 3.82% 15.5 9/14/2005 Argonaut Group Statutory Trust X 9/15/2035 3M LIBOR + 3.40% 3.62% 30.9 Total Outstanding $ 172.7 December 31, 2019 (in millions) Issue Date Trust Preferred Pools Maturity Rate Structure Interest Rate at December 31, 2019 Amount Argo Group 5/15/2003 PXRE Capital Statutory Trust II 5/15/2033 3M LIBOR + 4.10% 6.01% $ 18.1 11/6/2003 PXRE Capital Trust VI 9/30/2033 3M LIBOR + 3.90% 5.84% 10.3 Argo Group US 5/15/2003 Argonaut Group Statutory Trust I 5/15/2033 3M LIBOR + 4.10% 6.01% 15.5 12/16/2003 Argonaut Group Statutory Trust III 1/8/2034 3M LIBOR + 4.10% 6.09% 12.3 4/29/2004 Argonaut Group Statutory Trust IV 4/29/2034 3M LIBOR + 3.85% 5.76% 13.4 5/26/2004 Argonaut Group Statutory Trust V 5/24/2034 3M LIBOR + 3.85% 5.76% 12.3 5/12/2004 Argonaut Group Statutory Trust VI 6/17/2034 3M LIBOR + 3.80% 5.70% 13.4 9/17/2004 Argonaut Group Statutory Trust VII 12/15/2034 3M LIBOR + 3.60% 5.49% 15.5 9/22/2004 Argonaut Group Statutory Trust VIII 9/22/2034 3M LIBOR + 3.55% 5.48% 15.5 10/22/2004 Argonaut Group Statutory Trust IX 12/15/2034 3M LIBOR + 3.60% 5.49% 15.5 9/14/2005 Argonaut Group Statutory Trust X 9/15/2035 3M LIBOR + 3.40% 5.29% 30.9 Total Outstanding $ 172.7 Junior Subordinated Debentures from Maybrooke Acquisition Unsecured junior subordinated debentures with a principal balance of $91.8 million were assumed through the acquisition of Maybrooke (“the acquired debt”). As part of the ongoing liquidation of the Maybrooke holding company, which began subsequent to our acquisition in 2018, the acquired debt was ultimately assigned to Argo Re and is carried on our consolidated balance sheet at $85.1 million, which represents the debt’s fair value at the date of acquisition plus accumulated accretion of discount to par value, as required by accounting for business combinations under ASC 805. At December 31, 2020, the acquired debt was eligible for redemption at par. Interest accrues on the acquired debt based on a variable rate, which is reset quarterly. Interest payments are payable quarterly. A summary of the terms of the acquired debt outstanding is presented below: December 31, 2020 (in millions) Issue Date Maturity Rate Structure Interest Rate at December 31, 2020 Principal at December 31, 2020 Carrying Value at December 31, 2020 9/13/2007 9/15/2037 3 month LIBOR + 3.15% 3.37 % $ 91.8 $ 85.1 December 31, 2019 (in millions) Issue Date Maturity Rate Structure Interest Rate at December 31, 2019 Principal at December 31, 2019 Carrying Value at December 31, 2019 9/13/2007 9/15/2037 3 month LIBOR + 3.15% 5.04 % $ 91.8 $ 84.7 Other Indebtedness Our consolidated balance sheets include various long-term debt instruments under the caption “other indebtedness,” as detailed in the table below. Information regarding the terms and principal amounts of each of these debt instruments is also provided. (in millions) December 31, Debt Type 2020 2019 Floating rate loan stock $ 60.7 $ 56.3 Term loan — 125.0 Total other indebtedness $ 60.7 $ 181.3 Floating Rate Loan Stock This unsecured debt was assumed through the acquisition of Argo Underwriting Agency, Ltd. At December 31, 2020 and 2019, all notes were eligible for redemption subject to certain terms and conditions at a price equal to 100% of the principal plus accrued and unpaid interest. Interest on the U.S. dollar and euro notes is due semiannually and quarterly, respectively. A summary of the notes outstanding at December 31, 2020 and 2019 is presented below: December 31, 2020 (in millions) Currency Issue Date Maturity Rate Structure Interest Rate at December 31, 2020 Amount U.S. Dollar 12/8/2004 11/15/2034 6 month LIBOR + 4.2% 4.54% $ 6.5 U.S. Dollar 10/31/2006 1/15/2036 6 month LIBOR + 4.0% 4.34% 10.0 Total U.S. Dollar notes 16.5 Euro 9/6/2005 8/22/2035 3 month LIBOR + 4.0% 3.47% 14.7 Euro 10/31/2006 11/22/2036 3 month LIBOR + 4.0% 3.47% 12.9 Euro 6/8/2007 9/15/2037 3 month LIBOR + 3.9% 3.36% 16.6 Total Euro notes 44.2 Total notes outstanding $ 60.7 December 31, 2019 (in millions) Currency Issue Date Maturity Rate Structure Interest Rate at December 31, 2019 Amount U.S. Dollar 12/8/2004 11/15/2034 6 month LIBOR + 4.2% 6.41% $ 6.5 U.S. Dollar 10/31/2006 1/15/2036 6 month LIBOR + 4.0% 6.21% 10.0 Total U.S. Dollar notes 16.5 Euro 9/6/2005 8/22/2035 3 month LIBOR + 4.0% 3.58% 13.3 Euro 10/31/2006 11/22/2036 3 month LIBOR + 4.0% 3.58% 11.6 Euro 6/8/2007 9/15/2037 3 month LIBOR + 3.9% 3.47% 14.9 Total Euro notes 39.8 Total notes outstanding $ 56.3 No principal payments have been made since the acquisition of Argo Underwriting Agency, Ltd. The floating rate loan stock denominated in euros fluctuates due to foreign currency translation. The outstanding balance on these loans was $44.2 million and $39.8 million as of December 31, 2020 and 2019, respectively. The foreign currency translation adjustment is recorded in our consolidated statements of income (loss). Borrowing Under Revolving Credit Facility On November 2, 2018, each of Argo Group, Argo Group U.S., Inc., Argo International Holdings Limited, and Argo Underwriting Agency Limited (the “Borrowers”) entered into a new $325 million credit agreement (the “Credit Agreement”) with JPMorgan Chase Bank, N.A., as administrative agent. The Credit Agreement matures on November 2, 2023, and replaced the prior $325 million Credit Agreement (the “Prior Agreement”), dated as of March 3, 2017. In connection with the consummation of the Credit Agreement, Argo Group borrowed $125 million as a term loan due on November 2, 2021, which amount was used on the issue date, November 2, 2018, to pay off in its entirety the $125 million of borrowings previously outstanding under the Prior Agreement. At December 31, 2019, the term loan had a three month LIBOR+ 1.25% rate structure and an interest rate of 3.18%. In addition, the Credit Agreement provided for a $200 million revolving credit facility, and the commitments thereunder shall expire on November 2, 2023 unless extended in accordance with the terms of the Credit Agreement. On September 17, 2020, the Company used most of the net proceeds from the Preferred Stock Offering (as defined in Note 12, “Shareholders’ Equity”) to pay off the term loan. Borrowings under the Credit Agreement may be used for general corporate purposes, including working capital, permitted acquisitions and letters of credit, and each of the Borrowers has agreed to be jointly and severally liable for the obligations of the other Borrowers under the Credit Agreement. The Credit Agreement contains customary events of default. If an event of default occurs and is continuing, the Borrowers could be required immediately to repay all amounts outstanding under the Credit Agreement. Lenders holding at least a majority of the loans and commitments under the Credit Agreement could elect to accelerate the maturity of the loans and/or terminate the commitments under the Credit Agreement upon the occurrence and during the continuation of an event of default. Included in the Credit Agreement is a provision that allows up to $200.0 million of the revolving credit facility to be used for letters of credit (“LOCs”), subject to availability. At December 31, 2020 and 2019, there were no borrowings outstanding and $70.5 million of LOCs, respectively, issued against the Credit Facility. Letter of Credit Facilities Argo Re may be required to secure its obligations under various reinsurance contracts in certain circumstances. In order satisfy these requirements, Argo Re has entered into one committed and two uncommitted secured bilateral LOC facilities with commercial banks and generally uses these facilities to issue LOCs in support of non-admitted reinsurance obligations in the U.S. and other jurisdictions. The committed LOC facility has a term of one year and includes customary conditions and event of default provisions. The uncommitted LOC facilities do not have a term and issuance of LOCs is at the discretion of the lenders. The availability of letters of credit under these secured facilities are subject to a borrowing base requirement, determined on the basis of specified percentages of the market value of eligible categories of securities pledged to the lender. On December 31, 2020, committed and uncommitted letter of credit facilities totaled $205 million. In addition to the bilateral, secured letters of credit facilities described above, Argo Re can use other forms of collateral to secure these reinsurance obligations including trust accounts, cash deposits, LOCs issued by commercial banks on an uncommitted basis and the Credit Agreement. On December 31, 2020, LOCs totaling $167.0 million were outstanding, of which $58.1 million were issued against the committed, secured bilateral LOC facility and $108.9 million were issued by commercial banks against the uncommitted, secured bilateral LOC facilities. Collateral with a market value of $189.4 million was pledged to these banks as security against these LOCs. In 2018, Argo Group executed a LOC facility with a commercial bank to issue LOCs in favor of Lloyd’s to support its Funds at Lloyd’s requirements. This facility had an initial term of one year, and was unsecured, renewable and included customary conditions and event of default provisions. This facility was terminated in 2020. At December 31, 2019, a LOC in the amount of £23.3 million was issued in favor of Lloyd’s, which allowed the Company to reduce its other collateral pledged to Lloyd’s by a comparable amount. Other Debt Argo Group also has entered into agreements with commercial banks to issue unsecured LOCs that support its insurance and general operations. LOCs in the amount of $3.9 million and $3.1 million were outstanding as of December 31, 2020 and December 31, 2019, respectively. The following table presents maturities of long-term debt as of December 31, 2020: For the Years Ended (in millions) Total 2021 2022 2023 2024 2025 Thereafter Long-term debt: Junior subordinated debentures (1) 411.0 10.1 10.1 10.1 10.1 10.1 360.5 Senior unsecured fixed rate notes (2) 347.0 9.3 9.4 9.3 9.4 9.3 300.3 Floating rate loan stock (3) 94.4 2.3 2.3 2.3 2.3 2.3 82.9 (1) Interest only on Junior Subordinated Debentures through 2037. Interest calculated based on the rate in effect at December 31, 2020. Principal due beginning May 2033. (2) Interest only on Senior Unsecured Fixed Rate Notes through 2042. Interest calculated based on the rate in effect at December 31, 2020. Principal due September 2042. (3) Interest only on Floating Rate Loan Stock through 2034. Interest calculated based on the rate in effect at December 31, 2020. Principal due beginning November 2034. Senior Unsecured Fixed Rate Notes See Note 24, “Senior Unsecured Fixed Rate Notes,” for disclosures about our Senior Notes.

Disclosures about Fair Value of

Disclosures about Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Disclosures about Fair Value of Financial Instruments	Disclosures about Fair Value of Financial Instruments Cash. The carrying amount approximates fair value. Investment securities and short-term investments . See Note 4, “Investments,” for additional information. Premiums receivable and reinsurance recoverables on paid losses. The carrying value of current receivables and reinsurance recoverables on paid losses approximates fair value. Debt. At December 31, 2020 and 2019, the fair value of our debt instruments is determined using both Level 1 and Level 2 inputs, as previously defined in Note 4, “Investments”. We receive fair value prices from third-party pricing services for our financial instruments as well as for similar financial instruments. These prices are determined using observable market information such as publicly traded quoted prices, and trading prices for similar financial instruments actively being traded in the current market. We have reviewed the processes used by the third-party providers for pricing the securities and have determined that these processes result in fair values consistent with GAAP requirements. In addition, we review these prices for reasonableness, and have not adjusted any prices received from the third-party providers as of December 31, 2020 and December 31, 2019. A description of the valuation techniques we use to measure these liabilities at fair value is as follows: Senior Unsecured Fixed Rate Notes Level 1: • Our senior unsecured fixed rate notes are valued using Level 1 inputs. For these securities, we obtain fair value measurements from a third-party pricing service using quoted prices (unadjusted) in active markets at the reporting date. Junior Subordinated Debentures and Floating Rate Loan Stock Level 2: • Our trust preferred debentures, subordinated debentures and floating rate loan stock are typically valued using Level 2 inputs. For these securities, we obtain fair value measurements from a third-party pricing service using quoted prices for similar securities being traded in active markets at the reporting date, as our specific debt instruments are more infrequently traded. A summary of our financial instruments whose carrying value did not equal fair value is shown below: December 31, 2020 2019 (in millions) Carrying Fair Carrying Fair Junior subordinated debentures: Trust preferred debentures $ 172.7 $ 173.6 $ 172.7 $ 174.0 Subordinated debentures 85.1 92.3 84.7 92.5 Total junior subordinated debentures 257.8 265.9 257.4 266.5 Senior unsecured fixed rate notes 140.2 146.7 140.0 144.2 Floating rate loan stock 60.7 61.0 56.3 56.8 Based on an analysis of the inputs, our financial instruments measured at fair value on a recurring basis have been categorized as follows: Fair Value Measurements at Reporting Date Using (in millions) December 31, 2020 Level 1 (a) Level 2 (b) Level 3 (c) Junior subordinated debentures: Trust preferred debentures $ 173.6 $ — $ 173.6 $ — Subordinated debentures 92.3 — 92.3 — Total junior subordinated debentures 265.9 — 265.9 — Senior unsecured fixed rate notes 146.7 146.7 — — Floating rate loan stock 61.0 — 61.0 — 473.6 146.7 326.9 — (a) Quoted prices in active markets for identical assets (b) Significant other observable inputs (c) Significant unobservable inputs Fair Value Measurements at Reporting Date Using (in millions) December 31, 2019 Level 1 (a) Level 2 (b) Level 3 (c) Junior subordinated debentures: Trust preferred debentures $ 174.0 $ — $ 174.0 $ — Subordinated debentures 92.5 — 92.5 — Total junior subordinated debentures 266.5 — 266.5 — Senior unsecured fixed rate notes 144.2 144.2 — — Floating rate loan stock 56.8 — 56.8 — 467.5 144.2 323.3 — (a) Quoted prices in active markets for identical assets (b) Significant other observable inputs (c) Significant unobservable inputs

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Shareholders' Equity	Shareholders’ Equity Preferred Stock On July 9, 2020, the Company issued 6,000 shares of its Series A Preference Shares (equivalent to 6,000,000 depositary shares, each representing a 1/1,000th interest in a Series A Preference Share) with a $25,000 liquidation preference per share (equivalent to $25 per depositary share) (the “Preferred Stock Offering”). Net proceeds from the sale of the depositary shares were approximately $144 million after deducting underwriting discounts and estimated offering expenses payable by the Company. On September 17, 2020, the Company used most of the net proceeds to repay the $125 million principal outstanding on its term loan, previously reported in the line item “Other indebtedness” on our Consolidated Balance Sheets, and intends to use the remainder of the proceeds for working capital to support continued growth in insurance operations. Dividends to the holders of the Series A Preference Shares will be payable on a non-cumulative basis only when, as and if declared by our Board of Directors or a duly authorized committee thereof, quarterly in arrears on the 15th of March, June, September, and December of each year, commencing on September 15, 2020, at a rate equal to 7.00% of the liquidation preference per annum (equivalent to $1,750 per Series A Preference Share and $1.75 per depositary share per annum) up to but excluding September 15, 2025. Beginning on September 15, 2025, any such dividends will be payable on a non-cumulative basis, only when, as and if declared by our Board of Directors or a duly authorized committee thereof, during each reset period, at a rate per annum equal to the Five-Year U.S. Treasury Rate as of the most recent reset dividend determination date (as described in the Company’s prospectus supplement dated July 7, 2020) plus 6.712% of the liquidation preference per annum. So long as any Series A Preference Shares remain outstanding, unless dividends on all outstanding Series A Preference Shares payable on a dividend payment date have been declared and paid or provided for in full, (1) no dividend shall be paid or declared on our common shares or any other junior shares or any parity shares, other than a dividend payable solely in our common shares, other junior shares or (solely in the case of parity shares) other parity shares, as applicable, and (2) no common shares, other junior shares or parity shares shall be purchased, redeemed or otherwise acquired for consideration by us, directly or indirectly (other than (i) as a result of a reclassification of junior shares for or into other junior shares, or a reclassification of parity shares for or into other parity shares, or the exchange or conversion of one junior share for or into another junior share or the exchange or conversion of one parity share for or into another parity share, (ii) through the use of the proceeds of a substantially contemporaneous sale of junior shares or (solely in the case of parity shares) other parity shares, as applicable, or (iii) as required by or necessary to fulfill the terms of any employment contract, benefit plan or similar arrangement with or for the benefit of one or more employees, directors or consultants), in each case, during the following dividend period. Upon any voluntary or involuntary liquidation, dissolution or winding-up of Argo Group holders of the Series A Preference Shares are entitled to receive out of our assets available for distribution to shareholders, before any distribution is made to holders of our common shares or other junior shares, a liquidating distribution in the amount of $25,000 per Series A Preference Share (equivalent to $25 per depositary share) plus the amount of declared and unpaid dividends, if any, to the date fixed for distribution, without interest on such unpaid dividends. Distributions will be made pro rata in accordance with the respective aggregate liquidation preferences of the Series A Preference Shares and any parity shares, and only to the extent of our assets, if any, that are available after satisfaction of all liabilities to creditors. Neither the depositary shares nor the underlying Series A Preference Shares will be convertible into, or exchangeable for, shares of any other class or series of stock or other securities of Argo Group or our subsidiaries. Neither the depositary shares nor the underlying Series A Preference Shares have a stated maturity or will be subject to any sinking fund, retirement fund, or purchase fund or other obligation of ours to redeem, repurchase or retire the depositary shares or the Series A Preference Shares. We may redeem the Series A Preference Shares at our option, in whole or in part, from time to time, on or after September 15, 2025, at a redemption price equal to $25,000 per share (equivalent to $25 per depositary share), plus the amount of declared and unpaid dividends, if any, without interest on such unpaid dividends. In addition, we may redeem the Series A Preference Shares in specified circumstances relating to certain corporate, regulatory, rating agency or tax events; provided that no such redemption may occur prior to September 15, 2025 unless one of the redemption requirements is satisfied. The depositary shares will be redeemed only if and to the extent the related Series A Preference Shares are redeemed by us. The Series A Preference Shares will not have voting rights, except under limited circumstances. During 2020, our Board declared quarterly cash dividends totaling $768.056 on each share of our Series A Preference Shares, or $0.768056 per depositary share, outstanding to our shareholders of record. For the year ended December 31, 2020, we paid cash dividends totaling $4.6 million to our preferred shareholders. We are authorized to issue 30 million shares of $1.00 par value preferred shares. As of December 31, 2020 and 2019, 6,000 and 0 preferred shares were issued and outstanding, respectively. Common Stock On February 20, 2018, our Board declared a 15% stock dividend, payable on March 21, 2018, to shareholders of record at the close of business on March 7, 2018. As a result of the stock dividend, 4,397,520 additional shares were issued. Cash was paid in lieu of fractional shares of our common shares. Excluding repurchased shares, all references to common shares and related per share amounts in this document and related disclosures have been adjusted to reflect the stock dividend for all periods presented. During 2020, our Board declared quarterly cash dividends totaling $1.24 on each share of common stock outstanding to our shareholders of record. For the year ended December 31, 2020, we paid cash dividends totaling $43.0 million to our common shareholders. During 2019, our Board declared quarterly cash dividends totaling $1.24 on each share of common stock outstanding. For the year ended December 31, 2019, we paid cash dividends totaling $43.1 million to our shareholders. During 2018, our Board declared quarterly cash dividends totaling $1.08 on each share of common stock outstanding. For the year ended December 31, 2018, we paid cash dividends totaling $37.5 million to our shareholders. On May 3, 2016, our Board authorized the repurchase of up to $150.0 million of our common shares (“2016 Repurchase Authorization”). The 2016 Repurchase Authorization supersedes all the previous Repurchase Authorizations. As of December 31, 2020, availability under the 2016 Repurchase Authorization for future repurchases of our common shares was $53.3 million. For the years ended December 31, 2020 and 2019, we did not repurchase any common shares. The repurchase of common stock is also subject to the terms of our Series A Preference Shares, pursuant to which we may not (other than in limited circumstances) purchase, redeem or otherwise acquire our common stock unless the full dividends for the latest completed dividend period on all outstanding shares of our Series A Preferred Stock have been declared and paid or provided for.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) A summary of changes in accumulated other comprehensive income (loss), net of taxes (where applicable) by component for the year ended December 31, 2020 and 2019 is presented below: (in millions) Foreign Currency Translation Adjustments Unrealized Defined Benefit Pension Plans Total Balance, January 1, 2019 $ (22.4) $ (49.0) $ (6.7) $ (78.1) Other comprehensive (loss) income before reclassifications (0.2) 73.8 (1.4) 72.2 Amounts reclassified from accumulated other comprehensive income — 8.7 — 8.7 Net current-period other comprehensive (loss) income (0.2) 82.5 (1.4) 80.9 Balance, December 31, 2019 (22.6) 33.5 (8.1) 2.8 Other comprehensive (loss) income before reclassifications (15.3) 78.7 (0.5) 62.9 Amounts reclassified from accumulated other comprehensive income — (12.8) — (12.8) Net current-period other comprehensive (loss) income (15.3) 65.9 (0.5) 50.1 Cumulative effect of adoption of ASU 2016-13 — 5.7 — 5.7 Balance, December 31, 2020 $ (37.9) $ 105.1 $ (8.6) $ 58.6 The amounts reclassified from accumulated other comprehensive (loss) income shown in the above table have been included in the following captions in our Consolidated Statements of Income (Loss): For the Years Ended December 31, (in millions) 2020 2019 2018 Unrealized gains and losses on securities: Net realized investment (gains) loss $ (12.8) $ 9.9 $ 5.4 Benefit for income taxes — (1.2) (0.5) Net of taxes $ (12.8) $ 8.7 $ 4.9

Net (Loss) Income Per Common Sh

Net (Loss) Income Per Common Share	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Net (Loss) Income Per Common Share	Net (Loss) Income Per Common Share The following table presents the calculation of net (loss) income per common share on a basic and diluted basis: For the Years Ended December 31, (in millions, except number of shares and per share amounts) 2020 2019 2018 Net (loss) income $ (54.1) $ (14.1) $ 57.0 Less: Preferred share dividends 4.6 — — Net (loss) income attributable to common shareholders (58.7) (14.1) 57.0 Weighted average common shares outstanding - basic 34,614,813 34,205,954 33,922,009 Effect of dilutive securities: Equity compensation awards — — 756,772 Weighted average common shares outstanding - diluted 34,614,813 34,205,954 34,678,781 Net (loss) income per common share: Basic $ (1.70) $ (0.41) $ 1.68 Diluted $ (1.70) $ (0.41) $ 1.65 Excluded from the weighted average common shares outstanding calculation are 11,315,889 shares, which are held as treasury shares, at December 31, 2020, 2019 and 2018, respectively. The shares are excluded as of their repurchase date. Due to the net losses incurred during the years ended December 31, 2020 and 2019, the potentially dilutive securities that were anti-dilutive, and therefore, omitted from the calculation were 197,035 and 587,462 shares, respectively. In 2018, there were no anti-dilutive shares of common stock to be excluded from the computation of diluted net income per common share.

Share-based Compensation

Share-based Compensation	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Share-based Compensation	Share-based Compensation The fair value method of accounting is used for share-based compensation plans. Under the fair value method, compensation cost is measured based on the fair value of the award at the measurement date and recognized over the requisite service period, less estimated forfeiture. We estimate forfeitures based on historical forfeitures patterns, thereby recognizing expense only for those awards that are expected to vest. The estimate of forfeitures is adjusted as actual forfeitures differ from our estimate, resulting in recognition of compensation expense only for those awards that actually vest. The compensation expense recognized under all our share-based payment plans was $8.7 million ($7.8 million, net of tax), $16.9 million ($15.5 million, net of tax) and $18.3 million ($16.5 million, net of tax) for the years ended December 31, 2020, 2019 and 2018, respectively. The compensation expense is included in “Underwriting, acquisition and insurance expenses” in our Consolidated Statements of Income (Loss). We present all tax benefits resulting from the exercise of stock options and vesting of non-vested shares as cash flows from operating activities. Excess tax benefits are realized tax benefits from tax deductions for exercised options and vested shares in excess of the deferred tax asset attributable to stock compensation costs for such options. Such tax benefits and cash flows were immaterial for all reporting periods. Argo Group’s 2019 Omnibus Incentive Plan In May 2019, our shareholders approved the 2019 Omnibus Incentive Plan (the “2019 Plan”), which provides equity-based and cash-based performance-related incentives to key employees, non-employee directors and other service providers. The intent of the 2019 Plan is to encourage and provide for the acquisition of an ownership interest in Argo Group, enabling us to attract and retain qualified and competent persons to serve as members of our management team and the Board of Directors. The 2019 Plan authorizes 1,885,000 shares of common stock to be granted as equity-based awards. No further grants will be made under any prior plan; however, any awards under a prior plan that are outstanding as of the effective date shall remain subject to the terms and conditions of, and be governed by, such prior plan. Awards granted under the 2019 Plan may be in the form of stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance awards, other stock-based awards or other cash-based awards. Awards may be granted either alone or in addition to or in tandem with other awards authorized under the 2019 Plan. Awards that are settled in stock will count as one share for the purposes of reducing the share reserve under the 2019 Plan. Shares issued under this plan may be shares that are authorized and unissued or shares that we reacquired, including shares purchased on the open market. Stock options and stock appreciation rights are required to have an exercise price that is not less than the fair market value on the date of grant. The term of these awards is not to exceed ten years. Restricted Shares A summary of restricted share activity as of December 31, 2020 and changes during the year then ended is as follows: Shares Weighted-Average Outstanding at January 1, 2020 471,271 $ 60.09 Granted 399,578 $ 32.53 Vested and issued (177,918) $ 51.25 Expired or forfeited (165,057) $ 50.89 Outstanding at December 31, 2020 527,874 $ 43.37 As of December 31, 2020, there was $14.6 million of total unrecognized compensation cost related to restricted share compensation arrangements granted by Argo Group. The weighted-average period over which this unrecognized expense is expected to be recognized is 2.2 years. The total fair value of shares vested during the year ended December 31, 2020 was $10.0 million. A summary of stock-settled SARs activity as of December 31, 2020 and changes during the year then ended is as follows: Shares Weighted-Average Outstanding at January 1, 2020 625,368 $ 33.60 Exercised (470,182) $ 32.75 Expired or forfeited (15,031) $ 37.85 Outstanding at December 31, 2020 140,155 $ 35.98 As of December 31, 2020, all stock-settled SARS are fully vested. Upon exercise of the stock-settled SARs, the employee is entitled to receive shares of our common stock equal to the appreciation of the stock as compared to the exercise price. There was no expense recognized for the year ended December 31, 2020 for stock-settled SARs. For the year ended December 31, 2020, 470,182 stock-settled SARs were exercised resulting in 124,220 shares being issued. Aggregate intrinsic value of the stock-settled SARs at December 31, 2020 was $1.1 million. The remaining weighted average contractual term at December 31, 2020 was 0.85 years. Included in the total shares outstanding at December 31, 2020 are 124,892 restricted shares whose vesting is contingent on the employee meeting defined performance conditions. Employees have a specified time period in which to meet the performance condition (typically three years) and forfeit the grant (on a pro rata basis) if the performance conditions are not met in the specified time frame. We evaluate the likelihood of the employee completing the performance condition and include this estimate in the determination of the forfeiture factor for the grants. Employees Share Purchase Plans We have established an employee stock purchase plan for eligible employees (Argo Group’s 2007 Employee Share Purchase Plan). Under this plan, newly issued shares of our common stock may be purchased over an offering period of three months at 85% of the lower of the market value on the first day of the offering period or on the designated purchase date at the end of the offering period. We have also established a “Save As You Earn Plan” for our United Kingdom (“U.K.”) employees. Under this plan, newly issued shares of our common stock may be purchased over an offering period of three

Underwriting, Acquisition and I

Underwriting, Acquisition and Insurance Expenses & Other Corporate Expenses	12 Months Ended
	Dec. 31, 2020
Underwriting Acquisition And Insurance Expenses [Abstract]
Underwriting, Acquisition and Insurance Expenses & Other Corporate Expenses	Underwriting, Acquisition and Insurance Expenses & Other Corporate Expenses Underwriting, Acquisition and Insurance Expenses Underwriting, acquisition and insurance expenses were as follows: For the Years Ended December 31, (in millions) 2020 2019 2018 Commissions $ 268.0 $ 241.3 $ 281.3 General expenses 391.0 379.3 352.2 Premium taxes, boards and bureaus 29.7 33.0 32.5 688.7 653.6 666.0 Net deferral of policy acquisition costs (9.3) 12.4 (9.9) Total underwriting, acquisition and insurance expenses $ 679.4 $ 666.0 $ 656.1 Other Corporate Expenses During the years ended December 31, 2020 and December 31, 2019, we incurred costs of $5.8 million and $37.6 million, respectively, primarily in connection with the previously disclosed corporate governance and compensation matters, including responding to the 2019 subpoena from the SEC related to the Company's disclosure of certain compensation-related perquisites received by the Company's former chief executive officer. During the second quarter of 2020, the Company reached a settlement with the SEC related to its investigation, which required that the Company pay a $900,000 civil penalty, which is included in other corporate expenses for the year ended December 31, 2020. Other corporate expenses includes costs associated with the review of group reserves and the write-down of certain long-lived assets.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes We are incorporated under the laws of Bermuda and, under current Bermuda law, are not obligated to pay any taxes in Bermuda based upon income or capital gains. We have received an undertaking from the Supervisor of Insurance in Bermuda pursuant to the provisions of the Exempted Undertakings Tax Protection Act, 2011, which exempts us from any Bermuda taxes computed on profits, income or any capital asset, gain or appreciation or any tax in the nature of estate duty or inheritance tax, at least until the year 2035. We do not consider ourselves to be engaged in a trade or business in the U.S. or the U.K. and, accordingly, do not expect to be subject to direct U.S. or U.K. income taxation. We have subsidiaries based in the U.K. that are subject to the tax laws of that country. Under current law, these subsidiaries are taxed at the applicable corporate tax rates. Certain U.K. subsidiaries are deemed to be engaged in business in the U.S., and therefore, are subject to U.S. corporate tax in respect of a proportion of their U.S. underwriting business only. Relief is available against the U.K. tax liabilities in respect of overseas taxes paid that arise from the underwriting business. Our U.K. subsidiaries file separate U.K. income tax returns. We have subsidiaries based in the U.S. that are subject to U.S. tax laws. Under current law, these subsidiaries are taxed at the applicable corporate tax rates. Our U.S. subsidiaries generally file a consolidated U.S. federal income tax return. We also have operations in Belgium, Brazil, France, Ireland, Italy, Malta, Spain, and Switzerland, which also are subject to income taxes imposed by the jurisdiction in which they operate. We have operations in Barbados and the United Arab Emirates, which are not subject to income tax under the laws of those countries. The following table presents the components of income tax provision (benefit) included in the amounts reported in our consolidated financial statements: For the Years Ended December 31, (in millions) 2020 2019 2018 Current income tax provision (benefit) related to: United States (Federal) $ 28.0 $ 37.3 $ 20.8 United States (State) $ 1.4 $ 1.7 $ 1.4 United Kingdom (0.1) (1.5) 3.1 Other jurisdictions — (1) 0.1 0.1 Total current income tax provision 29.3 37.6 25.4 Deferred income tax provision (benefit) related to: United States (5.1) (17.7) (21.6) United Kingdom (16.6) (5.8) 0.1 Other jurisdictions 0.1 — 0.1 Total deferred income tax (benefit) (21.6) (23.5) (21.4) Income tax provision (benefit) $ 7.7 $ 14.1 $ 4.0 (1) Tax expense for the respective year was less than $0.1 million. Our expected income tax provision (benefit) computed on pre-tax income (loss) at the weighted average tax rate has been calculated as the sum of the pre-tax income (loss) in each jurisdiction multiplied by that jurisdiction’s applicable statutory tax rate. For the years ended December 31, 2020, 2019 and 2018, pre-tax income (loss) attributable to our operations and the operations’ effective tax rates were as follows: (in millions) 2020 2019 2018 Pre-Tax Effective Pre-Tax Effective Pre-Tax Effective Bermuda $ (56.2) — % $ (34.7) — % $ 22.0 — % United States 103.3 22.7 % 84.7 24.6 % 12.1 (1.0) % United Kingdom (100.6) 15.7 % (45.9) 14.9 % 24.1 14.7 % Belgium 0.2 30.7 % — (1) 15.8 % — (1) — % (2) Brazil 3.9 — % 5.2 — % (0.5) — % United Arab Emirates 2.1 — % 0.4 — % 0.8 — % Ireland 1.8 — % (0.1) — % (0.2) — % Italy 0.6 — % (7.4) — % 0.9 — % Malta (1.4) — % (2.0) — % 1.7 — % Luxembourg — — % — — % — (1) — % Switzerland (0.1) — % (0.2) (0.2) % 0.1 18.4 % Pre-tax income (loss) $ (46.4) (16.6) % $ — — % (2) $ 61.0 6.6 % (1) Pre-tax income for the respective year was less than $0.1 million. (2) Not meaningful. Our effective tax rate may vary significantly from period to period depending on the jurisdiction generating the pre-tax income (loss) and its corresponding statutory tax rate. The geographic distribution of pre-tax income (loss) can fluctuate significantly between periods given the inherent nature of our business. A reconciliation of the difference between the provision for income taxes and the expected tax provision (benefit) at the weighted average tax rate is as follows: For the Years Ended December 31, (in millions) 2020 2019 2018 Income tax provision (benefit) at expected rate $ 4.0 $ 8.9 $ 7.7 Tax effect of: Nontaxable investment income (0.7) (1.2) (1.9) Foreign exchange adjustments 1.6 (0.1) (0.6) Impairment of goodwill 1.0 2.9 — Withholding taxes 0.1 0.2 0.4 Change in uncertain tax position liability 0.7 1.4 1.8 Change in valuation allowance 0.5 (1.8) (1.5) Impact of change in tax rate related to TCJA — — (0.8) Other 0.5 3.8 (1.1) Income tax provision (benefit) $ 7.7 $ 14.1 $ 4.0 The net deferred tax asset (liability) comprises the tax effects of temporary differences related to the following assets and liabilities: December 31, (in millions) 2020 2019 Deferred tax assets: Losses and loss adjustment expense reserve discounting $ 29.2 $ 24.6 Unearned premiums 25.9 25.3 Net operating loss carryforwards 27.9 28.3 Investment in limited partnership interests 7.8 10.3 Investments 2.0 2.2 Right of use assets 12.7 14.5 Accrued compensation 6.3 3.8 Stock option expense 0.7 1.1 United Kingdom underwriting results 21.9 4.2 Other 9.6 6.3 Deferred tax assets, gross 144.0 120.6 Deferred tax liabilities: Unrealized gains on equity securities (5.7) (2.6) Unrealized gains on fixed maturities and other investment securities (22.3) (6.1) Unrealized gains on limited partnership interests (14.7) (15.6) Depreciable fixed assets (20.5) (21.6) Deferred acquisition costs (20.4) (18.6) Lease liability (11.7) (14.0) TCJA reserve transitional liability (2.7) (3.2) Other (0.7) (0.2) Deferred tax liabilities, gross (98.7) (81.9) Deferred tax assets, net before valuation allowance $ 45.3 $ 38.7 Valuation allowance (28.6) (28.1) Deferred tax asset (liabilities), net $ 16.7 $ 10.6 Net deferred tax assets (liabilities) - Other jurisdictions $ 21.4 $ 4.4 Net deferred tax liabilities - United States (4.7) 6.2 (1) Deferred tax asset (liabilities), net $ 16.7 $ 10.6 (1) Net deferred tax liability for the respective year was less than $0.1 million. Our gross deferred tax assets are supported by taxes paid in previous periods, reversal of taxable temporary differences and recognition of future taxable income. Management regularly evaluates the recoverability of the deferred tax assets and makes any necessary adjustments to them based upon any changes in management’s expectations of future taxable income. Realization of deferred tax assets is dependent upon our generation of future taxable income sufficient to recover tax benefits that cannot be recovered from taxes paid in the carryback period, generally for our U.S. property and casualty insurers two years for net operating losses and for all our U.S. subsidiaries three years for capital losses. If a company determines that any of its deferred tax assets will not result in future tax benefits, a valuation allowance must be established for the portion of these assets that are not expected to be realized. The net change in valuation allowance for deferred tax assets was an increase of $0.5 million in 2020, relating to the following: Internal Revenue Code Section 382 limited net operating loss carryforwards within the U.S., cumulative losses incurred since inception, and valuation allowances acquired through or related to acquisitions. Based upon a review of our available evidence, both positive and negative discussed above, our management concluded that it is more-likely-than-not that the other deferred tax assets will be realized. For tax return purposes, as of December 31, 2020, we had NOL carryforwards in Brazil, Italy, Malta, and the United States. The amount and timing of realizing the benefits of NOL carryforwards depend on future taxable income and limitations imposed by tax laws. Only a portion of the United States NOL carryforwards has been recognized as mentioned above in the consolidated financial statements and is included in net deferred tax liabilities. The NOL amounts by jurisdiction and year of expiration are as follows: (in millions) December 31, 2020 Expiration Net operating loss carryforwards by jurisdiction: Brazil $ 0.7 Indefinite Italy 49.6 Indefinite Malta 14.3 Indefinite United States 43.3 2025 - 2037 For any uncertain tax positions not meeting the “more-likely-than-not” recognition threshold, accounting standards require recognition, measurement and disclosure in a company’s financial statements. Included in the balances at December 31, 2020 and 2019 were $8.2 million and $7.5 million, respectively, of unrecognized tax benefits that, if recognized, would affect the annual effective tax rate. The Company believes it is reasonably possible that $4.3 million of the total amount of uncertain tax benefits will decrease within the next 12 months as a result of a lapse of the statute of limitations or settlement with taxing authorities. Related interest in the amount of $0.5 million, $0.5 million, and $0.3 million has been recorded in the line item “Interest Expense” in our Consolidated Statements of Income (Loss) for the year ended December 31, 2020, 2019, and 2018, respectively. Related penalty in the amount of $0.1 million, $0.2 million, and $0.5 million has been recorded in the line item “Underwriting, acquisition and insurance expenses” in our Consolidated Statements of Income (Loss) for the year ended December 31, 2020, 2019, and 2018, respectively. The following is a reconciliation of the beginning and ending amount of unrecognized tax benefits for the years ended December 31, 2020 and 2019: (in millions) 2020 2019 Balance at January 1 $ 7.5 $ 6.1 Additions for tax positions of prior years — — Reductions for tax positions of prior years — — Additions based on tax positions related to current year 0.7 1.4 Reductions based on tax positions related to current year — — Reductions based on settlements with taxing authorities — — Expiration of statute of limitations — — Balance at December 31 $ 8.2 $ 7.5 Our U.S. subsidiaries are no longer subject to U.S. federal and state income tax examinations by tax authorities for years before 2015. Our U.K. subsidiaries are no longer subject to U.K. income tax examinations by Her Majesty’s Revenue and Customs for years before 2018. Numerous foreign jurisdictions in which we operate have provided or proposed income-tax relief in response to the COVID-19 pandemic. Within the U.S., the Coronavirus Aid, Relief, and Economic Securities Act (the “CARES Act”) was enacted on March 27, 2020. The Company does not anticipate the CARES Act to have a material impact on its financial statements and will continue to analyze it and other income-tax relief measures in response to the COVID-19 pandemic.

Pension Benefits and Savings Pl

Pension Benefits and Savings Plans	12 Months Ended
	Dec. 31, 2020
Retirement Benefits [Abstract]
Pension Benefits and Savings Plans	Pension Benefits and Savings Plans Argo Group U.S., Inc. sponsors a qualified defined benefit plan and non-qualified unfunded supplemental defined benefit plans, all of which were curtailed effective February 2004. As of December 31, 2020 and 2019, the qualified pension plan was underfunded by $4.2 million and $3.7 million, respectively. The non-qualified pension plans were unfunded by $2.0 million at December 31, 2020 and 2019, respectively. Underfunded and unfunded amounts are included in “accrued underwriting expenses and other liabilities” in our consolidated balance sheets. Based on the current funding status of the pension plan, effects of the curtailment and expected changes in pension plan asset values and pension obligations, we do not believe any significant funding of the pension plan will be required during the year ending December 31, 2021. Net periodic benefit costs were $0.1 million and $0.3 million for the years ended December 31, 2020 and 2019, respectively. Net periodic benefit cost were minimal for the year ended December 31, 2018. Substantially all of our employees are either eligible or mandated by applicable laws to participate in employee savings plans. Under these plans, a percentage of an employee’s pay may be or is mandated based on applicable laws to be contributed to various savings alternatives. The plans also call for our contributions under several formulae. Charges to income related to our contributions were $9.2 million, $8.9 million and $7.9 million in 2020, 2019 and 2018, respectively.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Argo Group’s subsidiaries are parties to legal actions incidental to their business. Based on the opinion of legal counsel, management believes that the resolution of these matters will not materially affect our financial condition or results of operations. We have contractual commitments to invest up to $80.0 million related to our limited partnership investments at December 31, 2020. These commitments will be funded as required by the partnership agreements which can be called to be fulfilled at any time, not to exceed twelve years.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
Segment Information	Segment Information We are primarily engaged in underwriting property and casualty insurance and reinsurance. We have two ongoing reporting segments: U.S. Operations and International Operations. Additionally, we have a Run-off Lines segment for certain products that we no longer underwrite. We consider many factors, including the nature of each segment’s insurance and reinsurance products, production sources, distribution strategies and the regulatory environment, in determining how to aggregate reporting segments. Transactions between segments are reported in the segment that initiated the transaction. In evaluating the operating performance of our segments, we focus on core underwriting and investing results before the consideration of realized gains or losses from the sales of investments. Realized investment gains are reported as a component of the Corporate and Other segment, as decisions regarding the acquisition and disposal of securities reside with the corporate investment function and are not under the control of the individual business segments. Identifiable assets by segment are those assets used in the operation of each segment. Revenue and income before income taxes for each segment were as follows: For the Years Ended December 31, (in millions) 2020 2019 2018 Revenue: Earned premiums U.S. Operations $ 1,207.6 $ 1,119.9 $ 1,078.7 International Operations 572.5 609.6 652.5 Run-off Lines 0.4 0.2 0.3 Total earned premiums 1,780.5 1,729.7 1,731.5 Net investment income U.S. Operations 80.3 100.0 82.9 International Operations 26.7 44.2 32.9 Run-off Lines 4.0 5.7 8.1 Corporate and Other 1.7 1.2 8.4 Total net investment income 112.7 151.1 132.3 Fee and other income 7.9 9.1 9.0 Net realized investment (losses) gains (7.2) 80.1 (72.0) Total revenue $ 1,893.9 $ 1,970.0 $ 1,800.8 For the Years Ended December 31, (in millions) 2020 2019 2018 Income (loss) before income taxes U.S. Operations $ 111.7 $ 139.3 $ 161.2 International Operations (82.1) (137.0) 32.0 Run-off Lines (12.9) (9.8) (9.3) Total segment income (loss) before taxes 16.7 (7.5) 183.9 Corporate and Other (34.7) (44.8) (47.0) Net realized investment and other (losses) gains (7.2) 80.1 (72.0) Foreign currency exchange (losses) gains (15.4) 9.8 (3.9) Other corporate expenses (5.8) (37.6) — Total (loss) income before income taxes $ (46.4) $ — $ 61.0 The table below presents earned premiums by geographic location for the years ended December 31, 2020, 2019 and 2018. For this disclosure, we determine geographic location by the country of domicile of our subsidiaries that underwrite the business and not by the location of insureds or reinsureds from whom the business was generated. For the Years Ended December 31, (in millions) 2020 2019 2018 United States $ 1,205.0 $ 1,115.8 $ 1,072.9 United Kingdom 361.1 391.5 455.8 Bermuda 96.5 80.7 85.4 Malta 59.5 85.0 61.0 All other jurisdictions 58.4 56.7 56.4 Total earned premiums $ 1,780.5 $ 1,729.7 $ 1,731.5 The following table represents identifiable assets: December 31, (in millions) 2020 2019 U.S. Operations $ 6,032.2 $ 5,013.7 International Operations 3,899.4 4,996.0 Run-off Lines 335.9 356.9 Corporate and Other 198.3 142.2 Total $ 10,465.8 $ 10,508.8 Included in total assets at December 31, 2020 and 2019 are $825.9 million and $916.3 million, respectively, in assets associated with trade capital providers. The following table represents goodwill and intangible assets, net of accumulated amortization, as of December 31, 2020 and 2019: Goodwill Intangible Assets, Net of (in millions) 2020 2019 2020 2019 U.S. Operations $ 118.6 $ 123.5 $ — $ — International Operations 28.7 37.9 60.5 91.8 Total $ 147.3 $ 161.4 $ 60.5 $ 91.8

Statutory Accounting Principles

Statutory Accounting Principles	12 Months Ended
	Dec. 31, 2020
Statutory Accounting Principles [Abstract]
Statutory Accounting Principles	Statutory Accounting Principles Financial Information The statutory capital and surplus for our principal operating subsidiaries was as follows: Statutory capital and surplus (1) December 31, (in millions) 2020 2019 Bermuda $ 1,482.8 $ 1,460.8 United Kingdom (2) 534.7 443.1 United States 1,072.1 1,051.4 (1) Such amounts include ownership interests in affiliate insurance and reinsurance subsidiaries. (2) Capital on deposit with Lloyd’s in U.S. dollars The statutory net income (loss) for our principal operating subsidiaries was as follows: Statutory net income (loss) (1) For the Years Ended December 31, (in millions) 2020 2019 2018 Bermuda $ (35.9) $ 7.1 $ 47.4 United Kingdom (2) (53.0) (15.1) (9.5) United States 76.4 196.1 110.8 (1) Such amounts include ownership interests in affiliate insurance and reinsurance subsidiaries. (2) In U.S. dollars Dividends As an insurance and reinsurance holding company, we are largely dependent on dividends and other permitted payments from our insurance and reinsurance subsidiaries to pay cash dividends to our shareholders, for debt service and for our operating expenses. The ability of our insurance and reinsurance subsidiaries to pay dividends to us is subject to certain restrictions imposed by the jurisdictions of domicile that regulate our insurance and reinsurance subsidiaries and each jurisdiction has calculations for the amount of dividends that an insurance and reinsurance company can pay without the approval of the insurance regulator. The payment of dividends to our shareholders is governed by the Bermuda Companies Act of 1981, as amended, which permits the payment of dividends so long as (i) we are not, or would not be after the payment, unable to pay our liabilities as they become due and (ii) the realizable value of our assets is in excess of our liabilities after taking such payment into account. In light of these restrictions, we have no material restrictions on dividend payments that may be made to our shareholders at December 31, 2020. Argo Re is the direct subsidiary of Argo Group, and therefore, has direct dividend paying capabilities to the parent. As of December 31, 2020, Argo Re’s solvency and liquidity margins and statutory capital and surplus were in excess of the minimum levels required by the Insurance Act. As of December 31, 2020 and 2019, the minimum statutory capital and surplus required to be maintained by Argo Re was $201.3 million and $242.9 million, respectively. Argo Re is generally prohibited from declaring or paying, in any financial year, dividends of more than 25% of its total statutory capital and surplus (as shown on its previous financial year’s statutory balance sheet) unless it files (at least seven days before payment of such dividends) with the Bermuda Monetary Authority (“BMA”) an affidavit signed by at least two directors (one of whom must be a Bermuda resident director if any of the insurer’s directors are resident in Bermuda) and the principal representative stating that it will continue to meet its solvency margin and minimum liquidity ratio. Argo Re may not reduce its total statutory capital by 15% or more, as set out in its previous year’s financial statements, unless it has received the prior approval of the BMA. Based on these regulatory restrictions, the maximum amount available for payment of dividends to Argo Group by Argo Re during 2020 without prior regulatory approval is $370.7 million. In 2020, 2019, and 2018 Argo Re paid a cash dividend of $58.8 million, $52.1 million, and $36.5 million respectively, to Argo Group. The proceeds of the dividends were used to repay intercompany balances related primarily to the funding of dividend and interest payments and other corporate expenses. Our U.S. insurance subsidiaries file financial statements prepared in accordance with statutory accounting principles prescribed or permitted by insurance regulatory authorities of the state in which they are underwriting business. The differences between statutory-based financial statements and financial statements prepared in accordance with GAAP vary between jurisdictions. The principal differences are that for statutory-based financial statements, deferred policy acquisition costs are not recognized, a portion of the deferred federal income tax asset is non-admitted, bonds are generally carried at amortized cost, certain assets are non-admitted and charged directly to surplus, a collectability allowance related to reinsurance recoverables is charged directly to surplus and outstanding losses and unearned premium are presented net of reinsurance. As an intermediate insurance holding company, Argo Group U.S., Inc. is largely dependent on dividends and other permitted payments from its insurance subsidiaries to service its debt, fund operating expenses and pay dividends to Argo Ireland. Various state insurance laws restrict the amount that may be transferred to Argo Group U.S., Inc. from its subsidiaries in the form of dividends without prior approval of regulatory authorities. In addition, that portion of the insurance subsidiaries’ net equity that results from the difference between statutory insurance principles and GAAP would not be available for dividends. In December 2020, Argo Group U.S., Inc. received an ordinary dividend in the amount of $10.0 million in cash from Rockwood. In December 2020, Argo Group U.S., Inc. received an ordinary dividend in the amount of $50.0 million in cash from Argonaut Insurance Company. In December 2019, Argo Group U.S., Inc. received an ordinary dividend in the amount of $30.0 million in cash from Rockwood. In December 2019, Argo Group U.S., Inc. received an ordinary dividend in the amount of $50.0 million in cash from Argonaut Insurance Company. In December 2018, Argo Group U.S., Inc. received an ordinary dividend in the amount of $20.0 million in cash from Rockwood. Argonaut Insurance Company is a direct subsidiary of Argo Group U.S., Inc. and is regulated by the Illinois Division of Insurance. During 2021, Argonaut Insurance Company may be permitted to pay dividends of up to $97.5 million without approval from the Illinois Division of Insurance. Rockwood, a direct subsidiary of Argo Group U.S., Inc., is regulated by the Pennsylvania Department of Insurance. Rockwood may not be permitted to pay dividends without approval from the Pennsylvania Department of Insurance during 2021. Each department of insurance may require prior approval for the payment of all dividends, based on business and regulatory conditions of the insurance companies. Argo Underwriting Agency Ltd. (“AUA”) is our wholly-owned subsidiary through which we conduct the operations of Syndicates 1200 and 1910. Dividend payments from AUA to the immediate parent are not restricted by regulatory authority. Dividend payments will be subject to the earnings, operations, financial condition, capital and general business requirements of AUA.

Insurance Assessments

Insurance Assessments	12 Months Ended
	Dec. 31, 2020
Insurance [Abstract]
Insurance Assessments	Insurance AssessmentsWe are required to participate in statutorily created insolvency guarantee, weather-related loss protection associations, and second-injury funds in all states in the U.S. where we are authorized to transact business. These associations were formed for the purpose of paying the claims of insolvent companies. We are assessed a pro-rata share of such claims based upon our premium writings, subject to a maximum annual assessment per line of insurance. Certain of these assessments can be recovered through premium tax offsets or policy surcharges. We do not believe that assessments on current insolvencies will have a material impact on our financial condition or results of operations. We have accrued assessments of $6.7 million and $6.9 million at December 31, 2020 and 2019, respectively.

Transactions with Related Parti

Transactions with Related Parties	12 Months Ended
	Dec. 31, 2020
Related Party Transactions [Abstract]
Transactions with Related Parties	Transactions with Related PartiesIn 2013, our Surety unit received a submission through its established broker network to issue approximately $13 million of surety bonds on behalf of Kinetica Partners, LLC (“Kinetica”) in connection with a Gulf of Mexico pipeline project. Mr. Gary Woods, the former Chairman of our Board who served in such role until the 2020 Annual General Meeting, is also the Chairman of the board of directors of Kinetica, and beneficially owns 10% of Kinetica through a family trust. The submission was underwritten, priced and bound in the ordinary course of business by the Surety unit. The terms and conditions of the surety bonds that were issued and the premium charged to Kinetica for issuance of the bonds, were consistent with those routinely applied and charged for similarly situated risks bound for unrelated third-parties. As of December 31, 2020, approximately $12 million of the surety bonds were still outstanding. Per the Surety unit’s standard requirements in connection with the issuance of surety bonds, Kinetica and Mr. Woods, in his personal capacity, among others, executed our Surety unit’s standard form of indemnity agreement holding our Surety unit harmless against any and all losses and expenses incurred resulting from the issuance of the surety bonds.

Senior Unsecured Fixed Rate Not

Senior Unsecured Fixed Rate Notes	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Senior Unsecured Fixed Rate Notes	Senior Unsecured Fixed Rate Notes In September 2012, Argo Group (the “Parent Guarantor”), through its subsidiary Argo Group U.S., Inc. (the “Subsidiary Issuer”), issued $143,750,000 aggregate principal amount of the Subsidiary Issuer’s 6.5% Senior Notes due September 15, 2042 (the “Notes”). The Notes are unsecured and unsubordinated obligations of the Subsidiary Issuer and rank equally in right of payment with all of the Subsidiary Issuer’s other unsecured and unsubordinated debt. The Notes are guaranteed on a full and unconditional senior unsecured basis by the Parent Guarantor. The Notes may be redeemed, for cash, in whole or in part, on or after September 15, 2017, at the Subsidiary Issuer’s option, at any time and from time to time, prior to maturity at a redemption price equal to 100% of the principal amount of the Notes to be redeemed, plus accrued but unpaid interest on the principal amount being redeemed to, but not including, the redemption date. In accordance with ASU 2015-3, “Simplifying the Presentation of Debt Issuance Costs” (Topic 835), we present the unamortized debt issuance costs in the balance sheet as a direct deduction from the carrying value of the debt liability. At December 31, 2020 and 2019, the Notes consisted of the following: (in millions) December 31, 2020 December 31, 2019 Senior unsecured fixed rate notes Principal $ 143.8 $ 143.8 Less: unamortized debt issuance costs (3.6) (3.8) Senior unsecured fixed rate notes, less unamortized debt issuance costs $ 140.2 $ 140.0 In accordance with Article 10 of SEC Regulation S-X, we have elected to present condensed consolidating financial information in lieu of separate financial statements for the Subsidiary Issuer. The following tables present condensed consolidating financial information at December 31, 2020 and 2019 and for the three years ended December 31, 2020, 2019 and 2018 of the Parent Guarantor and the Subsidiary Issuer. The Subsidiary Issuer is an indirect wholly-owned subsidiary of the Parent Guarantor. Investments in subsidiaries are accounted for by the Parent Guarantor under the equity method for purposes of the supplemental consolidating presentation. Earnings of subsidiaries are reflected in the Parent Guarantor’s investment accounts and earnings. The Parent Guarantor fully and unconditionally guarantees certain of the debt of the Subsidiary Issuer. Condensed consolidating financial information of the Subsidiary Issuer is presented on a consolidated basis and consists principally of the net assets, results of operations and cash flows of operating insurance company subsidiaries. CONDENSED CONSOLIDATING BALANCE SHEET DECEMBER 31, 2020 (in millions) Argo Group Argo Group Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Assets Investments $ 0.6 $ 3,628.8 $ 1,626.4 $ — $ 5,255.8 Cash 3.0 17.4 128.4 — 148.8 Accrued investment income — 16.7 5.1 — 21.8 Premiums receivable — 267.5 412.3 — 679.8 Reinsurance recoverables — 1,761.2 1,247.8 — 3,009.0 Goodwill and other intangible assets, net — 118.5 89.3 — 207.8 Current income taxes receivable, net — (5.6) 8.6 — 3.0 Deferred tax assets, net — (4.6) 21.3 — 16.7 Deferred acquisition costs, net — 97.1 66.5 — 163.6 Ceded unearned premiums — 340.6 234.5 — 575.1 Operating lease right-of-use assets 6.2 51.7 24.1 — 82.0 Other assets 14.5 153.5 126.7 — 294.7 Assets held for sale — 7.4 0.3 — 7.7 Intercompany note receivable — 59.0 (59.0) — — Investments in subsidiaries 1,881.9 — — (1,881.9) — Total assets $ 1,906.2 $ 6,509.2 $ 3,932.3 $ (1,881.9) $ 10,465.8 Liabilities and Shareholders' Equity Reserves for losses and loss adjustment expenses $ — $ 3,348.7 $ 2,057.3 $ — $ 5,406.0 Unearned premiums — 951.2 513.6 — 1,464.8 Funds held and ceded reinsurance payable, net — 489.0 526.1 — 1,015.1 Debt 28.4 284.5 145.8 — 458.7 Accrued underwriting expenses and other liabilities 6.3 67.8 93.5 — 167.6 Operating lease liabilities 6.2 60.4 29.2 — 95.8 Due to (from) affiliates 7.5 0.9 (0.9) (7.5) — Total liabilities 48.4 5,202.5 3,364.6 (7.5) 8,608.0 Total shareholders' equity 1,857.8 1,306.7 567.7 (1,874.4) 1,857.8 Total liabilities and shareholders' equity $ 1,906.2 $ 6,509.2 $ 3,932.3 $ (1,881.9) $ 10,465.8 (1) Includes all other subsidiaries of Argo Group and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING BALANCE SHEET DECEMBER 31, 2019 (in millions) Argo Group Argo Group Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Assets Investments $ 0.6 $ 3,405.6 $ 1,691.3 $ — $ 5,097.5 Cash 1.9 31.6 104.3 — 137.8 Accrued investment income — 18.2 7.5 — 25.7 Premiums receivable — 236.0 440.5 — 676.5 Reinsurance recoverables — 1,689.4 1,417.8 — 3,107.2 Goodwill and other intangible assets, net 40.6 123.4 89.2 — 253.2 Deferred tax assets, net — 6.8 3.8 — 10.6 Deferred acquisition costs, net — 88.4 71.8 — 160.2 Ceded unearned premiums — 306.4 238.6 — 545.0 Operating lease right-of-use assets 7.1 59.6 25.1 — 91.8 Other assets 7.8 165.8 214.3 — 387.9 Assets held for sale — 15.4 — — 15.4 Intercompany note receivable — 56.7 (56.7) — — Investments in subsidiaries 1,899.3 — — (1,899.3) — Total assets $ 1,957.3 $ 6,203.3 $ 4,247.5 $ (1,899.3) $ 10,508.8 Liabilities and Shareholders' Equity Reserves for losses and loss adjustment expenses $ — $ 3,037.5 $ 2,120.1 $ — $ 5,157.6 Unearned premiums — 899.8 511.1 — 1,410.9 Funds held and ceded reinsurance payable, net — 650.6 605.8 — 1,256.4 Debt 153.4 284.3 141.0 — 578.7 Current income taxes payable, net — 21.3 (7.4) — 13.9 Accrued underwriting expenses and other liabilities 13.6 89.5 118.8 — 221.9 Operating lease liabilities 7.3 68.9 29.5 — 105.7 Due to (from) affiliates 19.3 (13.4) 13.4 (19.3) — Total liabilities 193.6 5,038.5 3,532.3 (19.3) 8,745.1 Total shareholders' equity 1,763.7 1,164.8 715.2 (1,880.0) 1,763.7 Total liabilities and shareholders' equity $ 1,957.3 $ 6,203.3 $ 4,247.5 $ (1,899.3) $ 10,508.8 (1) Includes all other subsidiaries of Argo Group and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF INCOME (LOSS) FOR THE YEAR ENDED DECEMBER 31, 2020 (in millions) Argo Group Argo Group Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Premiums and other revenue: Earned premiums $ — $ 1,204.3 $ 576.2 $ — $ 1,780.5 Net investment income — 87.3 25.4 — 112.7 Fee and other income — 2.6 5.3 — 7.9 Net realized investment (losses) gains (8.3) 4.5 (3.4) — (7.2) Total revenue (8.3) 1,298.7 603.5 — 1,893.9 Expenses: Losses and loss adjustment expenses — 764.5 444.3 — 1,208.8 Underwriting, acquisition and insurance expenses 20.4 411.0 248.0 — 679.4 Other corporate expenses 4.4 1.4 — — 5.8 Interest expense 3.6 16.7 6.6 — 26.9 Fee and other expense — 2.1 1.9 — 4.0 Foreign currency exchange (gains) losses — (0.4) 15.8 — 15.4 Total expenses 28.4 1,195.3 716.6 — 1,940.3 (Loss) income before income taxes (36.7) 103.4 (113.1) — (46.4) Provision (benefit) for income taxes — 23.6 (15.9) — 7.7 Net (loss) income before equity in earnings of subsidiaries (36.7) 79.8 (97.2) — (54.1) Equity in undistributed earnings of subsidiaries (17.4) — — 17.4 — Net (loss) income $ (54.1) $ 79.8 $ (97.2) $ 17.4 $ (54.1) Dividends on preferred shares 4.6 $ — $ — $ — 4.6 Net (loss) income attributable to common shareholders $ (58.7) $ 79.8 $ (97.2) $ 17.4 $ (58.7) (1) Includes all other subsidiaries of Argo Group and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF INCOME (LOSS) FOR THE YEAR ENDED DECEMBER 31, 2019 (in millions) Argo Group Argo Group Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Premiums and other revenue: Earned premiums $ — $ 1,044.1 $ 685.6 $ — $ 1,729.7 Net investment (expenses) income (2.9) 103.3 50.7 — 151.1 Fee and other income — 3.2 5.9 — 9.1 Net realized investment (losses) gains (0.1) 80.9 (0.7) — 80.1 Total revenue (3.0) 1,231.5 741.5 — 1,970.0 Expenses: Losses and loss adjustment expenses — 696.8 523.9 — 1,220.7 Underwriting, acquisition and insurance expenses 1.3 415.4 249.3 — 666.0 Other corporate expenses 26.8 10.8 — — 37.6 Interest expense 6.6 18.9 8.6 — 34.1 Fee and other expense — 4.2 1.6 — 5.8 Foreign currency exchange losses (gains) — 0.7 (10.5) — (9.8) Impairment of goodwill — — 15.6 — 15.6 Total expenses 34.7 1,146.8 788.5 — 1,970.0 (Loss) income before income taxes (37.7) 84.7 (47.0) — — Provision (benefit) for income taxes — 20.9 (6.8) — 14.1 Net (loss) income before equity in earnings of subsidiaries (37.7) 63.8 (40.2) — (14.1) Equity in undistributed earnings of subsidiaries 23.6 — — (23.6) — Net (loss) income attributable to common shareholders $ (14.1) $ 63.8 $ (40.2) $ (23.6) $ (14.1) (1) Includes all other subsidiaries of Argo Group and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF INCOME FOR THE YEAR ENDED DECEMBER 31, 2018 (in millions) Argo Group Argo Group Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Premiums and other revenue: Earned premiums $ — $ 861.7 $ 869.8 $ — $ 1,731.5 Net investment (expense) income (2.7) 78.6 56.4 — 132.3 Fee and other income — 4.4 4.6 — 9.0 Net realized investment gains (losses) 2.5 (51.3) (20.5) (2.7) (72.0) Total revenue (0.2) 893.4 910.3 (2.7) 1,800.8 Expenses: Losses and loss adjustment expenses — 523.7 517.1 — 1,040.8 Underwriting, acquisition and insurance expenses 11.3 334.1 310.7 — 656.1 Interest expense 6.2 18.5 7.2 — 31.9 Fee and other expense — 5.3 1.8 — 7.1 Foreign currency exchange losses — 0.2 3.7 — 3.9 Total expenses 17.5 881.8 840.5 — 1,739.8 (Loss) income before income taxes (17.7) 11.6 69.8 (2.7) 61.0 Benefit for income taxes — 0.1 3.9 — 4.0 Net (loss) income before equity in earnings of subsidiaries (17.7) 11.5 65.9 (2.7) 57.0 Equity in undistributed earnings of subsidiaries 74.7 — — (74.7) — Net (loss) income attributable to common shareholders $ 57.0 $ 11.5 $ 65.9 $ (77.4) $ 57.0 (1) Includes all other subsidiaries of Argo Group and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS FOR YEAR ENDED DECEMBER 31, 2020 (in millions) Argo Group Argo Group Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Net cash flows from operating activities $ 5.0 $ 98.9 $ (32.0) $ — $ 71.9 Cash flows from investing activities: Proceeds from sales of investments — 711.4 497.9 — 1,209.3 Maturities and mandatory calls of fixed maturity investments — 427.7 142.1 — 569.8 Purchases of investments — (1,624.0) (528.5) — (2,152.5) Change in short-term investments and foreign regulatory deposits — 310.7 (30.7) — 280.0 Settlements of foreign currency exchange forward contracts 0.1 (1.8) 11.1 — 9.4 Capital contribution to subsidiaries (145.3) — — 145.3 — Dividend received from subsidiaries 13.1 — — (13.1) — Proceeds from sale of Ariel Re, net of cash transferred 30.0 — (1.7) 28.3 Proceeds from sale of Trident assets — 38.0 — 38.0 Purchases of fixed assets and other, net — 24.9 (31.5) — (6.6) Cash (used in) provided by investing activities (102.1) (113.1) 58.7 132.2 (24.3) Cash flows from financing activities: Payment on long-term debt — — (125.0) — (125.0) Issuance of preferred shares, net of issuance costs 144.0 — — 144.0 Capital contribution from parent — — 145.3 (145.3) — Payment of cash dividend to parent — — (13.1) 13.1 — Activity under stock incentive plans 1.8 — — — 1.8 Payment of cash dividends to preferred shareholders (4.6) — — — (4.6) Payment of cash dividend to common shareholders (43.0) — — — (43.0) Cash provided by (used in) financing activities 98.2 — 7.2 (132.2) (26.8) Effect of exchange rate changes on cash — — (9.8) — (9.8) Change in cash 1.1 (14.2) 24.1 — 11.0 Cash, beginning of year 1.9 31.6 104.3 — 137.8 Cash, end of period $ 3.0 $ 17.4 $ 128.4 $ — $ 148.8 (1) Includes all other subsidiaries of Argo Group and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS FOR YEAR ENDED DECEMBER 31, 2019 (in millions) Argo Group Argo Group Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Net cash flows from operating activities $ 38.4 $ 124.3 $ 20.1 $ — $ 182.8 Cash flows from investing activities: Proceeds from sales of investments — 1,297.3 554.8 — 1,852.1 Maturities and mandatory calls of fixed maturity investments — 292.8 229.4 — 522.2 Purchases of investments — (1,303.8) (680.2) — (1,984.0) Change in short-term investments and foreign regulatory deposits 3.2 (351.4) (142.2) — (490.4) Settlements of foreign currency exchange forward contracts (0.2) 1.8 (1.3) — 0.3 Purchases of fixed assets and other, net — (41.4) (1.6) — (43.0) Cash provided by (used in) investing activities 3.0 (104.7) (41.1) — (142.8) Cash flows from financing activities: Payment on the intercompany note — (19.1) 19.1 — — Payment on note payable — (0.6) — — (0.6) Activity under stock incentive plans 1.9 — — — 1.9 Payment of cash dividend to common shareholders (43.1) — — — (43.1) Cash (used in) provided by financing activities (41.2) (19.7) 19.1 — (41.8) Effect of exchange rate changes on cash — — (0.1) — (0.1) Change in cash 0.2 (0.1) (2.0) — (1.9) Cash, beginning of year 1.7 31.7 106.3 — 139.7 Cash, end of period $ 1.9 31.6 104.3 — 137.8 (1) Includes all other subsidiaries of Argo Group and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS FOR YEAR ENDED DECEMBER 31, 2018 (in millions) Argo Group Argo Group Other Subsidiaries and Eliminations (1) Consolidating Adjustments ( 2) Total Net cash flows from operating activities $ 72.4 $ 182.4 $ 47.0 $ — $ 301.8 Cash flows from investing activities: Proceeds from sales of investments — 1,067.7 532.1 — 1,599.8 Maturities and mandatory calls of fixed maturity investments — 344.9 73.7 — 418.6 Purchases of investments — (1,508.3) (640.8) — (2,149.1) Change in short-term investments and foreign regulatory deposits (3.4) (105.0) (10.8) — (119.2) Settlements of foreign currency exchange forward contracts (0.5) 2.2 (3.2) — (1.5) Cash acquired with acquisition of ArgoGlobal Assicurazioni — — 15.6 — 15.6 Purchases of fixed assets and other, net (0.1) (19.0) (13.4) — (32.5) Cash used in investing activities (4.0) (217.5) (46.8) — (268.3) Cash flows from financing activities: Borrowing under the intercompany note — 19.0 (19.0) — — Activity under stock incentive plans 1.6 — — — 1.6 Repurchase of Company's common shares (31.7) — — — (31.7) Payment of cash dividend to common shareholders (37.5) — — — (37.5) Cash (used in) provided by financing activities (67.6) 19.0 (19.0) — (67.6) Effect of exchange rate changes on cash — — (2.8) — (2.8) Change in cash 0.8 (16.1) (21.6) — (36.9) Cash, beginning of year 0.9 47.8 127.9 — 176.6 Cash, end of year $ 1.7 $ 31.7 $ 106.3 $ — $ 139.7 (1) Includes all other subsidiaries of Argo Group and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations.

Schedule II Condensed Financial

Schedule II Condensed Financial Information of Registrant	12 Months Ended
	Dec. 31, 2020
Condensed Financial Information Disclosure [Abstract]
Schedule II Condensed Financial Information of Registrant	SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT (in millions) BALANCE SHEETS December 31, 2020 2019 Assets Short-term investments $ 0.6 $ 0.6 Investment in subsidiaries 1,881.9 1,899.3 Cash 3.0 1.9 Goodwill and other intangible assets, net — 40.6 Operating lease right-of-use assets 6.2 7.1 Other assets 14.5 7.8 Total assets $ 1,906.2 $ 1,957.3 Liabilities and Shareholders' Equity Junior subordinated debentures $ 28.4 $ 28.4 Other indebtedness — 125.0 Accrued underwriting expenses and other liabilities 6.3 13.6 Operating lease liabilities 6.2 7.3 Due to subsidiaries 7.5 19.3 Total liabilities 48.4 193.6 Shareholders' equity 1,857.8 1,763.7 Total liabilities and shareholders' equity $ 1,906.2 $ 1,957.3 STATEMENTS OF INCOME (LOSS) For the Years Ended December 31, 2020 2019 2018 Revenue: Net investment expense $ — $ (2.9) $ (2.7) Net realized investment (loss) gains (8.3) (0.1) 2.5 Total revenue (8.3) (3.0) (0.2) Expenses: Interest expense 3.6 6.6 6.2 Operating expenses 20.4 1.3 11.3 Other corporate expenses 4.4 26.8 — Total expenses 28.4 34.7 17.5 Net income before equity in earnings of subsidiaries (1) (36.7) (37.7) (17.7) Equity in undistributed earnings of subsidiaries (17.4) 23.6 74.7 Net (loss) income $ (54.1) $ (14.1) $ 57.0 Dividends on preferred shares 4.6 — — Net (loss) income attributable to common shareholders $ (58.7) $ (14.1) $ 57.0 (1) Argo Group is not subject to taxation. ARGO GROUP INTERNATIONAL HOLDINGS, LTD. SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT (in millions) STATEMENTS OF CASH FLOWS For the Years Ended December 31, 2020 2019 2018 Cash flows from operating activities: Net (loss) income $ (54.1) $ (14.1) $ 57.0 Adjustments to reconcile net income to net cash provided by (used in) operating activities: Amortization and depreciation 1.1 1.3 1.4 Share-based payments expense 3.6 8.1 7.0 Net realized investment and other losses (gains) 8.3 0.1 (2.5) Loss on disposal of fixed assets 0.1 — — Undistributed earnings of subsidiaries 17.4 (23.6) (74.7) Change in: Prepaid assets (2.2) 2.5 (2.3) Accrued underwriting expenses (9.1) 7.3 (4.4) Due to subsidiaries 47.7 68.9 94.1 Other, net (7.8) (12.1) (3.2) Cash provided by operating activities 5.0 38.4 72.4 Cash flows from investing activities: Change in short-term investments — 3.2 (3.4) Settlements of foreign currency exchange forward contracts 0.1 (0.2) (0.5) Capital contribution to subsidiaries (145.3) — — Proceed from sale of Ariel Re 30.0 — — Dividend received from subsidiaries 13.1 — — Purchases of fixed assets and other, net — — (0.1) Cash (used in) provided by investing activities (102.1) 3.0 (4.0) Cash flows from financing activities: Issuance for preferred shares, net of issuance costs 144.0 — — Activity under stock incentive plans 1.8 1.9 1.6 Repurchase of Company's common shares — — (31.7) Payment of cash dividend to preferred shareholders (4.6) — — Payment of cash dividend to common shareholders (43.0) (43.1) (37.5) Cash provided by (used in) financing activities 98.2 (41.2) (67.6) Change in cash 1.1 0.2 0.8 Cash, beginning of year 1.9 1.7 0.9 Cash, end of year $ 3.0 $ 1.9 $ 1.7

Schedule III Supplemental Insur

Schedule III Supplemental Insurance Information	12 Months Ended
	Dec. 31, 2020
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Abstract]
Schedule III Supplemental Insurance Information	SCHEDULE III SUPPLEMENTAL INSURANCE INFORMATION FOR THE YEARS ENDED DECEMBER 31, 2020, 2019 AND 2018 (in millions) Segment DAC (a) Reserves for Losses and Loss Adjustment Expenses (b) UPR (c) Premium Revenue (d) Net Investment Income (l) Loss & LAE (e) Amortization (Deferral) DAC (f) (2) Other Operating Expenses (3) Net Premiums Written (g) Year Ended December 31, 2020 U.S. Operations 98.2 3,091.9 939.2 1,207.6 80.3 768.7 (8.6) 399.7 1,223.0 International Operations 65.4 2,077.6 525.4 572.5 26.7 428.6 (0.7) 249.1 586.6 Run-off Lines — 236.5 0.2 0.4 4.0 11.5 — 5.0 0.5 Corporate and Other — — — — 1.7 — — 34.9 — Total $ 163.6 $ 5,406.0 $ 1,464.8 $ 1,780.5 $ 112.7 $ 1,208.8 $ (9.3) $ 688.7 $ 1,810.1 Year Ended December 31, 2019 U.S. Operations 89.7 2,775.1 896.1 1,119.9 100.0 690.4 (2.5) 371.2 1,166.3 International Operations 70.5 2,129.0 514.7 609.6 44.2 518.3 14.9 235.3 588.1 Run-off Lines — 253.5 0.1 0.2 5.7 12.0 — 2.4 0.2 Corporate and Other — — — — 1.2 — — 44.7 — Total $ 160.2 $ 5,157.6 $ 1,410.9 $ 1,729.7 $ 151.1 $ 1,220.7 $ 12.4 $ 653.6 $ 1,754.6 Year Ended December 31, 2018 U.S. Operations 87.2 2,498.9 793.3 1,078.7 82.9 628.2 (6.4) 361.2 1,125.5 International Operations 80.1 1,890.1 507.6 652.5 32.9 400.3 (3.5) 250.2 639.5 Run-off Lines — 265.6 — 0.3 8.1 12.3 — 3.9 0.3 Corporate and Other — — — — 8.4 — — 50.7 — Total $ 167.3 $ 4,654.6 $ 1,300.9 $ 1,731.5 $ 132.3 $ 1,040.8 $ (9.9) $ 666.0 $ 1,765.3 (a) Deferred policy acquisition costs. (b) Future policy benefits, losses, claims and loss expenses. (c) Unearned premiums. (d) Premium revenue, net (premiums earned). (e) Benefits, claims, losses and settlement expenses. (f) Amortization (deferral) of deferred policy acquisition costs. (g) Premiums written, net. (1) Net investment income allocated based upon each segment’s share of investable funds. (2) The amortization (deferral) of DAC will not equal the change in the balance sheet. See Note 1, “Business and Significant Accounting Policies” for further discussion. (3) Other insurance expenses allocated based on specific identification, where possible, and related activities.

Schedule V Valuation and Qualif

Schedule V Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2020
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule V Valuation and Qualifying Accounts	SCHEDULE V VALUATION AND QUALIFYING ACCOUNTS (in millions) Balance at Charged to Capital Loss Net Operating Charged to Deductions Balance at Year Ended December 31, 2020 Deducted from assets: Valuation allowance for deferred tax asset $ 28.1 $ 0.5 $ — $ — $ — $ — $ 28.6 Year Ended December 31, 2019 Deducted from assets: Valuation allowance for deferred tax asset $ 29.9 $ (1.8) $ — $ — $ — $ — $ 28.1 Year Ended December 31, 2018 Deducted from assets: Valuation allowance for deferred tax asset $ 20.1 $ (1.5) $ — $ 11.3 $ — $ — $ 29.9

Schedule VI Supplemental Inform

Schedule VI Supplemental Information for Property-Casualty Insurance Companies	12 Months Ended
	Dec. 31, 2020
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Abstract]
Schedule VI Supplemental Information for Property-Casualty Insurance Companies	SCHEDULE VI SUPPLEMENTAL INFORMATION FOR PROPERTY-CASUALTY INSURANCE COMPANIES (in millions) For the Years Ended December 31, 2020 2019 2018 Deferred acquisition costs $ 163.6 $ 160.2 $ 167.3 Reserves for losses and loss adjustment expenses $ 5,406.0 $ 5,157.6 $ 4,654.6 Unamortized discount in reserves for losses $ 17.8 $ 17.9 $ 16.9 Unearned premiums $ 1,464.8 $ 1,410.9 $ 1,300.9 Premiums earned $ 1,780.5 $ 1,729.7 $ 1,731.5 Net investment income $ 112.7 $ 151.1 $ 132.3 Losses and loss adjustment expenses incurred: Current year $ 1,201.1 $ 1,082.6 $ 1,058.8 Prior years 7.7 138.1 (18.0) Losses and loss adjustment expenses incurred $ 1,208.8 $ 1,220.7 $ 1,040.8 (Deferral) amortization of policy acquisition costs (1) $ (9.3) $ 12.4 $ (9.9) Paid losses and loss adjustment expenses, net of reinsurance $ 1,119.8 $ 1,030.3 $ 938.9 Gross premiums written $ 3,233.3 $ 3,130.2 $ 2,954.2 (1) The amortization (deferral) of policy acquisition costs will not equal the change in the balance sheet. For further discussion, see Note 1, “Business and Significant Accounting Policies.”

Business and Significant Acco_2

Business and Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Business	Business Argo Group International Holdings, Ltd. (“Argo Group,” “we” or the “Company”) is an underwriter of specialty insurance products in the property and casualty market. Argo Group U.S., Inc. is a subsidiary of Argo Financial Holding (Ireland) UC (“Argo Ireland”). Argo Underwriting Agency Limited (“Syndicate 1200”) is a subsidiary of Argo International Holdings, Ltd., Argo Re Ltd. (“Argo Re”), a Bermuda based company, is the parent of both Argo Ireland and Argo International Holdings, Ltd. Argo Re is directly owned by Argo Group. Effective November 25, 2020, we closed on the sale of our reinsurance business, Ariel Re, to Pelican Ventures and J.C. Flowers & Co. Ariel Re is the reinsurance platform through which Lloyd’s Syndicate 1910 reinsurance business is underwritten. Under the terms of the agreement, the buying group’s corporate member will provide Syndicate 1910’s capital for the 2021 Lloyd’s year of account, and Argo Group has agreed to retain historical reserves and the remaining exposure for the 2020 and prior Lloyd’s years of account. On December 23, 2020, we announced an agreement to sell our Italian operations, ArgoGlobal Assicurazioni (“ArgoGlobal Assicurazioni”) to Perfuturo Capital AG, a Swiss Holding Company. Closing of the transaction is subject to regulatory approval and is expected to occur in early 2021. Under the terms of the agreement, Argo Re will reinsure substantially all of ArgoGlobal Assicurazioni's legacy business as of the effective date of the agreement for all underwriting years. We conduct our ongoing business through two primary segments - U.S. Operations and International Operations. In addition to these main business segments, we have a Run-off Lines segment for certain products we no longer underwrite. U.S. Operations is comprised of the Excess and Surplus Lines businesses focusing on the U.S.-based risks that the standard, admitted insurance market is unwilling or unable to write, and through other specialized admitted and non-admitted business distributed through retail, wholesale, and managing general brokers/agents in the specialty insurance market. Excess and Surplus Lines products are underwritten by Colony Insurance Company (“Colony”). The other U.S. specialized admitted and non-admitted businesses consist of the following operations: Argo Pro, U.S. Specialty Programs, Argo Surety, Rockwood Casualty Insurance Company (“Rockwood”), Argo Insurance, Inland Marine and Argo Cyber. International Operations is comprised of the Lloyd’s Syndicate platform (Syndicate 1200 and Syndicate 1910), Argo Insurance Bermuda, Continental Europe and Latin America. Syndicate 1200 and Syndicate 1910 insurance products are underwritten by Argo Underwriting Agency Limited based in London, under the Lloyd’s of London (“Lloyd’s”) global franchise. As discussed above, we sold our reinsurance business during the fourth quarter of 2020, through which Syndicate 1910 business is underwritten. The additional International Operations business include Argo Insurance Bermuda, ArgoGlobal SE in Malta, ArgoGlobal Assicurazioni in Italy, and Argo Seguros in Brazil. These businesses provide a broad range of commercial property, casualty, professional liability and specialty coverages in a number of countries and jurisdictions outside the United States (“U.S.”). Our Run-off Lines segment includes liabilities associated with other liability policies that were issued in the 1960s, 1970s and into the 1980s, as well as the former risk-management business and other business no longer underwritten.
Basis of Presentation and Use of Estimates	Basis of Presentation and Use of Estimates The consolidated financial statements of Argo Group and its subsidiaries have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The preparation of consolidated 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. Specifically, estimates for reserves for losses and loss adjustment expenses are based upon past claim experience modified for current trends as well as prevailing economic, legal and social conditions. Although management believes that amounts included in the accompanying consolidated financial statements are reasonable, such estimates may be more or less than the amounts ultimately paid when the claims are settled. The estimates are continually reviewed and any changes are reflected in current operating results. Further, the nature of loss exposures involves significant variability due to the nature of the long-tailed payments on certain claims. As such, losses and loss adjustment expenses could vary significantly from the recorded amounts. The consolidated financial statements include the accounts and operations of Argo Group and its subsidiaries. All material intercompany accounts and transactions have been eliminated. Certain amounts in prior years’ financial statements have been reclassified to conform to the current presentation. Amounts related to trade capital providers, who are third-party capital participants that provide underwriting capital to both Syndicate 1200 and Syndicate 1910, are included in the balance sheet. Trade capital providers participate on a quota share basis, assuming 100% of their contractual participation in the underwriting syndicate results and with such results settled on a year of account basis. We have evaluated our investment in our eleven statutory trusts (collectively, the “Trusts”) and one charitable foundation (the “Foundation”) under the Financial Accounting Standards Board’s (“FASB’s”) provisions for consolidation of variable interest entities under Accounting Standards Codification (“ASC”) Topic 810-10, “Consolidation,” as amended. We determined that the Trusts and the Foundation are variable interest entities due to the fact that the Trusts and the Foundation do not have sufficient equity to finance their activities without additional subordinate financial support from other parties. We do not have any power to direct the activities that impact the Trusts’ or the Foundation’s economic performance. We are not entitled to receive a majority of the residual returns of the Trusts. Additionally, we are not responsible for absorbing the majority of the expected losses of the Trusts; therefore, we are not the primary beneficiary and, accordingly, the Trusts are not included in our consolidated financial statements. The expenses and donations of the charitable foundation in Bermuda are paid by Argo Group and have been included in the consolidated results.
Stock Dividends	Stock DividendsOn February 20, 2018, our Board of Directors (the “Board”) declared a 15% stock dividend, payable on March 21, 2018, to shareholders of record at the close of business on March 7, 2018. As a result of the stock dividend, 4,397,520 additional shares were issued. Cash was paid in lieu of fractional shares of our common shares. Excluding repurchased shares, all references to common shares and related per share amounts in this document and related disclosures have been adjusted to reflect the stock dividend for all periods presented
Cash	Cash Cash consists of cash deposited in banks, generally in concentration and operating accounts. Interest-bearing cash accounts are classified as short-term investments.
Investments	Investments Investments in fixed maturities at December 31, 2020 and 2019 include bonds and structured securities. Equity securities include common stocks, preferred stocks and mutual funds. Other investments consist of foreign regulatory deposits, hedge funds, private equity funds, private equity direct investments, and voluntary pools. Short-term investments consist of money market funds, certificates of deposit, bonds, sovereign debt and interest-bearing cash accounts. Investments maturing in less than one year are classified as short-term investments in our consolidated financial statements. The amortized cost of fixed maturity securities is adjusted for amortization of premiums and accretion of discounts. This amortization or accretion is included in “Net investment income” in our Consolidated Statements of Income (Loss). For the structured securities portion of the fixed maturity securities portfolio, we recognize income using a constant effective yield based on anticipated prepayments and the estimated economic life of the securities. Premium or discount on high investment grade securities (rated AA or higher) is amortized into income using the retrospective method. Premium or discount on lower grade securities (rated less than AA) is amortized into income using the prospective method. Our investments in fixed maturities are considered available-for-sale and are carried at fair value. As available-for-sale investments, changes in the fair value of fixed maturities are not recognized in income during the period, but rather are recognized as a separate component of shareholders’ equity until realized. Fair value of these investments is estimated using prices obtained from third-party pricing services, where available. For securities where we were unable to obtain fair values from a pricing service or broker, fair values were estimated using information obtained from investment advisors. We performed several processes to ascertain the reasonableness of these investment values by (1) obtaining and reviewing internal control reports for our service providers that obtain fair values from third-party pricing services, (2) discussing with our investment managers their process for reviewing and validating pricing obtained from outside services and obtaining values for all securities from our investment managers and (3) comparing the security pricing received from the investment managers with the prices used in the consolidated financial statements and obtaining additional information for variances that exceeded a certain threshold. As of December 31, 2020, investments reported at fair value for which we did not receive a fair value from a pricing service or broker accounted for less than 1% of our investment portfolio. The actual value at which such securities could be sold or settled with willing buyer or seller may differ from such estimated fair values depending on a number of factors including, but not limited to, current and future economic conditions, the quantity sold or settled, the presence of an active market and the availability of a willing buyer or seller. The cost of securities sold is based on the specific identification method. Our investments in equity securities are reported at fair value. Beginning with the adoption of Accounting Standards Update (“ASU”) 2016-01, effective January 1, 2018, changes in the fair value of equity securities are now included in “Net realized investment (gains) losses” in our consolidated statements of income. Changes in the value of other investments consisting of hedge funds, private equity funds, private equity direct investments and voluntary pools are principally recognized to income during the period using the equity method of accounting. Our foreign regulatory deposits are assets held in trust in jurisdictions where there is a legal and regulatory requirement to maintain funds locally in order to protect policyholders. Lloyd’s is the appointed investment manager for the funds. The underlying assets are invested in government securities, agency securities and corporate bonds whose values are obtained from Lloyd’s. Foreign currency future contracts held by us are valued by our counterparties using market driven foreign currency exchanges rates. We regularly review our investments to identify and evaluate those that may have credit impairments. For fixed maturity securities, the evaluation for credit losses is generally based on the present value of expected cash flows of the security as compared to the amortized book value, the financial condition, near-term and long-term prospects for the issuer, including industry conditions, implications of rating agency actions, the likelihood of principal and interest recoverability and whether it is more likely than not we will be required to sell the investment prior to the anticipated recovery in value. Effective January 1, 2020 with the adoption of ASU 2016-13 Financial Instruments-Credit Losses, we recognize credit losses on fixed maturities through an allowance account. For fixed maturities that we do not intend to sell or for which it is more likely than not we will not be required to sell prior to the anticipated recovery in value, we separate the credit component of the impairment from the component related to all other market factors and report the credit loss component to net realized investment gains (losses) in the Consolidated Statement of Income (Loss). The impairment related to all other market factors is reported as a separate component of shareholder’s equity in other comprehensive income (loss). The credit loss allowance account is adjusted for any additional credit losses or subsequent recoveries and the cost basis of the fixed maturity security is not adjusted. For fixed maturity securities that we intend to sell or for which it is more likely than not that we will be required to sell before an anticipated recovery in value, the full amount of the impairment is recognized in net realized investment gains (losses) in the Consolidated Statement of Income and the cost basis of the fixed maturity security is adjusted to reflect the recognized realized loss. The new cost basis is not adjusted for any recoveries in fair value. We report accrued investment income separately from fixed maturity securities and have elected to not measure an allowance for credit losses for accrued investment income. The write-off of investment income accrued for fixed maturities that have defaulted on interest payments is recognized as a loss in net realized investment gains (losses), in the period of the default, in the Consolidated Statement of Income (Loss).
Receivables	Receivables Premiums receivable, representing amounts due from insureds, are presented net of an allowance for uncollectible premiums, including expected credit losses, both dispute and credit related. Premiums receivable include amounts relating to the trade capital providers’ quota share. The allowance is based upon our ongoing review of amounts outstanding, historical loss data, including delinquencies and write-offs, current and forecasted economic conditions and other relevant factors. Credit risk is partially mitigated by our ability to cancel the policy if the policyholder does not pay the premium. Reinsurance recoverables represent amounts of paid losses and loss adjustment expenses, case reserves and incurred but not reported (“IBNR”) amounts ceded to reinsurers under reinsurance treaties. Reinsurance recoverables also reflect amounts that are due from trade capital providers. Amounts recoverable from reinsurers are estimated in a manner consistent with the associated claim liability. We report our reinsurance recoverables net of an allowance for estimated uncollectible reinsurance, including expected credit losses. The allowance is based upon our ongoing review of amounts outstanding, length of collection periods, changes in reinsurer credit standing, disputes, applicable coverage defenses and other relevant factors. We use the rating-based method to estimate the uncollectible reinsurance reserves due to credit losses. Under this method, reinsurance credit risk is estimated by considering the reinsurers probability of default. Reinsurance recoverables are forecasted out of the assumed billing periods and a liquidation factor is applied based on the rating of the reinsurer and adjusted as needed based on our historical experience with the reinsurers. Additionally, reinsurance receivable balances are evaluated to identify any dispute risk and when required, an additional reserve is recorded. Amounts deemed to be uncollectible, including amounts due from known insolvent reinsurers, are written off against the allowance. Changes in the allowance, as well as any subsequent collections of amounts previously written off, are reported as part of underwriting expense. We evaluate and monitor the financial condition of our reinsurers under voluntary reinsurance arrangements to minimize our exposure to significant losses from reinsurer insolvencies. Recoveries occur when subsequent collection or litigation results in the receipt of amounts previously written off. Amounts recovered
Earned Premiums	Earned Premiums Premium revenue is generally recognized ratably over the policy period. Premiums that have yet to be earned are reported as “unearned premiums” in our consolidated balance sheets. Unearned premium balances include cessions to reinsurers including trade capital providers, while the earned premium recognized in our consolidated statements of income (loss) excludes amounts relating to trade capital providers. The trade capital providers’ quota share amount is included in “ceded reinsurance payable, net”. Assumed reinstatement premiums that reinstate coverage are written and earned at the time the associated loss event occurs. The original premium is earned over the remaining exposure period of the contract. Reinstatement premiums are estimated based upon contract terms for reported losses and estimated for incurred but not reported losses.
Retrospectively Rated Policies	Retrospectively Rated PoliciesWe have written a number of workers compensation, property and other liability policies that are retrospectively rated. Under this type of policy, the policyholder or coverholder may be entitled, subsequent to coverage expiration, to a refund or may owe additional premiums based on the amount of losses incurred under the policy. The retrospective premium adjustments on certain policies are limited to a minimum or maximum premium adjustment, which is calculated as a percentage of the standard amount of premium charged during the life of the policy. Accrued retrospectively rated premiums have been determined based on estimated ultimate loss experience of the individual policyholder accounts.
Deferred Acquisition Costs	Deferred Acquisition Costs Policy acquisition costs, which include commissions, premium taxes, fees and certain other costs of underwriting policies, are deferred, when such class of policies are profitable, and amortized over the same period in which the related premiums are earned. To qualify for capitalization, the policy acquisition cost must be directly related to the successful acquisition of an insurance contract. Anticipated investment income is considered in determining whether the deferred acquisition costs are recoverable and whether a premium deficiency exists. We continually review the methods of making such estimates and establishing the deferred costs with any adjustments made in the accounting period in which the adjustment arose. The 2020 and 2019 net amortization of policy acquisition costs will not equal the change in our consolidated balance sheets as the trade capital providers’ share is not reflected in our consolidated statements of income (loss) and differences arise from foreign currency exchange rates applied to deferred acquisition costs which are treated as a nonmonetary asset.
Leases	Leases We determine if a contract contains a lease at inception and recognize operating lease right-of-use assets and operating lease liabilities based on the present value of the future minimum lease payments at the commencement date. As our leases do not provide an implicit interest rate, we use our incremental borrowing rate based on the information available at the commencement date to determine the present value of future payments. Lease agreements have lease and non-lease components. We account for these components separately, therefore our operating lease right-of-use asset and operating lease liabilities represent base rent only. Lease expense is recognized on a straight-line basis over the lease term. Renewal options are evaluated prior to the expiration date and recorded upon exercise. We adopted ASU 2016-02, “Leases” (Topic 842) on the effective date of January 1, 2019 and applied the following practical expedients: • We have elected to adopt this standard using the option transition method, which allows companies to continue applying the guidance under the lease standard in effect at that time in the comparative periods presented in the consolidated financial statements. The adoption of the standard had no effect on our consolidated shareholders’ equity. Prior periods were not restated. • We have elected the “package of practical expedients,” which permits us not to reassess under the new standard our prior conclusion about lease identification, lease classification and initial direct costs.
Leases	Where we are the lessor, we have elected the practical expedient which permits us to not separate non-lease components from the associated lease components if the non-lease components otherwise would be accounted for in accordance with the new revenue standard.
Reserves for Losses and Loss Adjustment Expenses	Reserves for Losses and Loss Adjustment Expenses Liabilities for unpaid losses and loss adjustment expenses include the accumulation of individual case estimates for claims reported as well as estimates of IBNR claims and estimates of claim settlement expenses. Reinsurance recoverables on unpaid claims and claim expenses represent estimates of the portion of such liabilities that will be recoverable from reinsurers. Amounts recoverable from reinsurers are recognized as assets at the same time and in a manner consistent with the unpaid claims liabilities associated with the reinsurance policy.
Reinsurance	Reinsurance In the normal course of business, our insurance and reinsurance subsidiaries cede risks above certain retention levels to other insurance companies. Reinsurance recoverables include claims we paid and estimates of unpaid losses and loss adjustment expenses that are subject to reimbursement under reinsurance and retrocessional contracts. The method for determining reinsurance recoverables for unpaid losses and loss adjustment expenses involves reviewing actuarial estimates of gross unpaid losses and loss adjustment expenses to determine our ability to cede unpaid losses and loss adjustment expenses under our existing reinsurance contracts. This method is continually reviewed and updated and any resulting adjustments are reflected in earnings in the period identified. Reinsurance premiums, commissions and expense reimbursements are accounted for on a basis consistent with those used in accounting for the original policies issued and the term of the reinsurance contracts. Amounts recoverable from reinsurers for losses and loss adjustment expenses for which our insurance and reinsurance subsidiaries have not been relieved of their legal obligations to the policyholder are reported as assets.
Goodwill and Intangible Assets	Goodwill and Intangible Assets Goodwill and intangible assets are allocated to the segment in which the results of operations for the acquired company are reported (see Note 20, “Segment Information” for further discussion). Intangible assets with a finite life are amortized over the estimated useful life of the asset. Goodwill and intangible assets with an indefinite useful life are not amortized. Goodwill and intangible assets are tested for impairment on an annual basis or more frequently if events or changes in circumstances indicate that the carrying amount may not be recoverable. We perform our annual goodwill impairment test on the first day of the fourth quarter of each year, October 1, of each year. As a result of the reviews performed on each of our reporting units for each of the years ended December 31, 2020 and 2018, we determined that the estimated fair value exceeded the respective carrying value of our reporting units for those years and goodwill was not impaired. In conjunction with our annual test, the fair value of each reporting unit exceeded its carrying value for the year ended December 31, 2019, except for our European reporting unit. As a result of this testing, we determined that the goodwill of the European reporting unit, which is included in our International Operations segment, was fully impaired and recorded a pre-tax charge of $15.6 million. Our European reporting unit was adversely impacted by a continuing soft market. Additionally, we incurred higher than expected losses and loss adjustment expenses due to adverse prior accident year loss reserve development resulting from the receipt of new information in the second half of 2019 relating to claims trends across various lines of business, coupled with increased current accident year losses and loss adjustment expenses as a result of these claim trends. Using these facts and trends, we calculated the discounted cash flows for the European reporting unit, which resulted in the indication that the carrying value of the reporting unit exceeded its fair value, resulting in the impairment.
Property and Equipment	Property and EquipmentProperty and equipment used in operations, including certain costs incurred to develop or obtain computer software for internal use, are capitalized and carried at cost less accumulated depreciation and are reported in “other assets” in our consolidated balance sheets. Depreciation is calculated using a straight-line method over the estimated useful lives of the assets, generally three
Derivative Instruments	Derivative Instruments We enter into short-term, currency spot and forward contracts to manage operational currency exposure on our Canadian dollar (“CAD”) investment portfolio and certain catastrophic events, minimize negative impacts to investment portfolio returns, and gain exposure to a total return strategy which invests in multiple currencies. The forward contracts are typically thirty to ninety days and are renewed as management deems necessary to accomplish the objectives of the contracts. These foreign currency forward contracts are carried at fair value in our Consolidated Balance Sheets in “Other assets” at December 31, 2020 and 2019, respectively. The realized and unrealized gains and losses are included in “Net realized investment and other gains (losses) in our Consolidated Statements of Income. The forwards contracts are not designated as hedges for accounting purposes.
Share-Based Payments	Share-Based Payments Compensation expense for share-based payments is recognized based on the measurement-date fair value for awards that will settle in shares. Compensation expense for awards that are settled in equity are recognized on a straight line pro rata basis over the vesting period, adjusted for expected forfeitures. See Note 15, “Share-based Compensation” for related disclosures.
Foreign Currency Exchange Gain (Loss)	Foreign Currency Exchange Gain (Loss) The U.S. dollar is the functional currency of all but three of our foreign operations. Monetary assets and liabilities in foreign operations that are denominated in foreign currencies are revalued at the exchange rates in effect at the balance sheet date. The resulting gains and losses from changes in the foreign exchange rates are reflected in net income. Revenues and expenses denominated in foreign currencies are translated at the prevailing exchange rate during the period with the resulting foreign exchange gains and losses included in net income for the period. In the case of our foreign currency denominated available-for-sale investments, the change in exchange rates between the local currency and our functional currency at each balance sheet date represents an unrealized appreciation or depreciation in value of these securities and is included as a component of accumulated other comprehensive income (loss).
Income Taxes	Income Taxes Deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates in effect for the year in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in net income in the period in which the change is enacted. We recognize potential accrued interest and penalties within our global operations in “interest expense” and “underwriting, acquisition and insurance expenses,” respectively, in our consolidated statements of income (loss) related to unrecognized tax benefits.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In June 2016, the Financial Accounting Standards Board ("FASB") issued ASU 2016-13, “Measurement of Credit Losses on Financial Instruments” (Topic 326), commonly referred to as current expected credit losses or CECL. ASU 2016-13 requires organizations to estimate credit losses on certain types of financial instruments, including receivables and available-for-sale debt securities, by introducing an approach based on expected losses. The expected loss approach will require entities to incorporate considerations of historical information, current information and reasonable and supportable forecasts. The updated guidance also amends the previous other-than-temporary impairment model for available-for-sale debt securities by requiring the recognition of impairments relating to credit losses through an allowance account and limits the amount of credit loss to the difference between a security’s amortized cost basis and its fair value. In addition, the length of time a security has been in an unrealized loss position will no longer impact the determination of whether a credit loss exists. The guidance is effective for fiscal years beginning after December 15, 2019, including interim periods within the year of adoption. The guidance requires a modified retrospective transition method. We adopted the updated guidance effective January 1, 2020 using the modified retrospective approach, which resulted in a $7.9 million net of tax reduction to retained earnings. Partially offsetting this reduction of retained earnings was a $5.7 million net of tax increase in other comprehensive income representing the reclassification of unrealized investment losses to credit losses under this accounting update. The cumulative effect adjustment decreased shareholders’ equity $2.2 million. Please see Note 4, “Investments” and Note 5, “Allowance for Credit Losses” for further discussion of the impact of ASU 2016-13 on our financial position and results of operations at and for the year ended December 31, 2020. In January 2017, the FASB issued ASU 2017-04, “Intangibles – Goodwill and Other” (Topic 350). ASU 2017-4 eliminates the requirement to calculate the implied fair value of goodwill that is done in Step 2 of the goodwill impairment test to measure a goodwill impairment loss. Instead, entities will record an impairment loss based on the excess of a reporting unit’s carrying amount over its fair value. The guidance was applied prospectively and is effective for annual and interim impairment tests performed in periods beginning after December 15, 2019. This ASU did not have a material impact on our financial results or disclosures. In August 2018, the FASB issued ASU 2018-13, “Fair Value Measurement (Topic 820).” ASU 2018-13 eliminates, adds and modifies certain disclosure requirements on fair value measurements. The guidance is effective for fiscal years beginning after December 15, 2019, including interim periods within the year of adoption. The amendments on changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements, and the narrative description of measurement uncertainty are applied prospectively for only the most recent interim or annual period presented in the initial fiscal year of adoption. All other amendments are applied retrospectively to all periods presented upon their effective date. Early adoption is permitted. This ASU did not have a material impact on our financial results or disclosures.

Business and Significant Acco_3

Business and Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Intangible Assets And Accumulated Amortization	The following table presents our intangible assets and accumulated amortization at December 31: December 31, 2020 2019 (in millions) Gross Carrying Accumulated Gross Carrying Accumulated Lloyd's capacity $ 60.5 n/a $ 89.0 n/a Distribution network 45.5 45.5 50.2 48.2 Other 6.2 6.2 8.1 7.3 $ 112.2 $ 51.7 $ 147.3 $ 55.5
Supplemental Cash Flow Information	Interest paid and income taxes paid (recovered) were as follows: For the Years Ended December 31, (in millions) 2020 2019 2018 Senior unsecured fixed rate notes $ 9.3 $ 9.3 $ 9.3 Junior subordinated debentures 11.9 16.2 15.5 Other indebtedness 5.2 7.6 6.5 Total interest paid $ 26.4 $ 33.1 $ 31.3 Income taxes paid 47.7 24.0 — Income taxes recovered (1.8) (0.1) 24.8 Income taxes paid, net $ 45.9 $ 23.9 $ 24.8

Revisions of Previously Issued

Revisions of Previously Issued Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Changes and Error Corrections [Abstract]
Schedule of Revisions of Previously Issued Financial Statements	The adjustments to the Company’s annual and quarterly previously issued financial statements are shown on the following pages, grouped by (1) the audited financial statements and (2) interim period unaudited financial statements, as well as (3) the related adjustments to the Company’s parent company financial information. The Company’s parent company financial information is disclosed on Schedule II of this Annual Report on Form 10-K. All adjustments to the Statements of Cash Flows for the periods affected by the errors noted below were reclassifications within cash provided by operating activities. Adjusted Consolidated Balance Sheet as of December 31, 2019: December 31, 2019 (in millions) As reported Adjustments As adjusted Fixed maturities available-for-sale, at fair value $ 3,633.5 $ (3.6) $ 3,629.9 Equity securities available-for-sale, at fair value 124.4 11.6 136.0 Other investments 496.5 (9.9) 486.6 Total investments 5,099.4 (1.9) 5,097.5 Premiums receivable 688.2 (11.7) 676.5 Reinsurance recoverables 3,104.6 2.6 3,107.2 Deferred tax asset, net 6.1 4.5 10.6 Other assets 387.1 0.8 387.9 Total assets 10,514.5 (5.7) 10,508.8 Accrued underwriting expenses and other liabilities 226.0 (4.1) 221.9 Ceded reinsurance payable, net 1,203.1 (1.9) 1,201.2 Funds held 50.6 4.6 55.2 Current income taxes payable, net 0.8 13.1 13.9 Total liabilities 8,733.4 11.7 8,745.1 Retained earnings 811.1 (17.4) 793.7 Total shareholders’ equity 1,781.1 (17.4) 1,763.7 Total liabilities and shareholders' equity 10,514.5 (5.7) 10,508.8 Adjusted Consolidated Statement of Income (Loss) for the three months and year ended December 31, 2019: Three Months Ended December 31, 2019 Year Ended December 31, 2019 As reported Adjustments As adjusted As reported Adjustments As adjusted (in millions, except per share amounts) (Unaudited) Earned premiums $ 425.8 $ — $ 425.8 $ 1,729.5 $ 0.2 $ 1,729.7 Net realized investment gains 21.7 0.1 21.8 80.0 0.1 80.1 Total revenue 484.5 0.1 484.6 1,969.7 0.3 1,970.0 Underwriting, acquisition and insurance expenses 180.2 — 180.2 665.8 0.2 666.0 Interest expense 8.3 0.1 8.4 33.6 0.5 34.1 Foreign currency exchange gains (3.4) (1.1) (4.5) (9.6) (0.2) (9.8) Total expenses 587.8 (1.0) 586.8 1,969.5 0.5 1,970.0 (Loss) income before income taxes (103.3) 1.1 (102.2) 0.2 (0.2) — Income tax provision — 0.5 0.5 8.6 5.5 14.1 Net loss (103.3) 0.6 (102.7) (8.4) (5.7) (14.1) Net loss per common share: Basic $ (3.01) $ 0.02 $ (2.99) $ (0.25) $ (0.16) $ (0.41) Diluted $ (3.01) $ 0.02 $ (2.99) $ (0.25) $ (0.16) $ (0.41) Consolidated Balance Sheet impact on opening balances as of January 1, 2019 and 2018: Impact on opening balances as of January 1, 2019 (in millions) As reported Adjustments As adjusted Equity securities available-for-sale, at fair value $ 354.5 $ 11.6 $ 366.1 Other investments 489.8 (9.9) 479.9 Cash 139.2 0.5 139.7 Premiums receivable 649.9 (4.7) 645.2 Reinsurance recoverables 2,688.3 0.9 2,689.2 Current income taxes receivable, net 8.2 (8.2) — Deferred tax asset, net — 1.3 1.3 Accrued underwriting expenses and other liabilities 261.9 1.1 263.0 Ceded reinsurance payable, net 970.5 (1.3) 969.2 Funds held 37.2 7.2 44.4 Current income taxes payable, net — 2.4 2.4 Deferred tax liabilities, net 6.2 (6.2) — Retained earnings 862.6 (11.7) 850.9 Impact on opening balances as of January 1, 2018 (in millions) As reported Adjustments As adjusted Other investments $ 543.6 $ 0.8 $ 544.4 Premiums receivable 598.6 (4.6) 594.0 Current income taxes receivable, net 1.4 (1.2) 0.2 Other assets 309.6 0.2 309.8 Accrued underwriting expenses and other liabilities 146.9 (0.3) 146.6 Ceded reinsurance payable, net 734.0 0.4 734.4 Deferred tax liabilities, net 31.3 1.9 33.2 Retained earnings 977.0 (6.8) 970.2 Adjusted Consolidated Statement of Income (Loss) for the year ended December 31, 2018: Year Ended December 31, 2018 (in millions, except per share amounts) As reported Adjustments As adjusted Earned premiums $ 1,731.7 $ (0.2) $ 1,731.5 Net investment income 133.1 (0.8) 132.3 Total revenue 1,801.8 (1.0) 1,800.8 Underwriting, acquisition and insurance expenses 654.7 1.4 656.1 Interest expense 31.6 0.3 31.9 Foreign currency exchange losses (gains) (0.1) 4.0 3.9 Total expenses 1,734.1 5.7 1,739.8 (Loss) income before income taxes 67.7 (6.7) 61.0 Income tax (benefit) provision 4.1 (0.1) 4.0 Net (loss) income 63.6 (6.6) 57.0 Net income (loss) per common share: Basic $ 1.87 $ (0.19) $ 1.68 Diluted $ 1.83 $ (0.18) $ 1.65 Adjusted Consolidated Balance Sheet as of September 30, 2020: September 30, 2020 As reported Adjustments As adjusted (in millions) (Unaudited) Premiums receivable $ 797.0 $ (6.8) $ 790.2 Current income taxes receivable, net 11.2 (3.7) 7.5 Deferred tax asset, net 17.0 (2.2) 14.8 Other assets 358.5 0.1 358.6 Total assets 10,734.3 (12.6) 10,721.7 Accrued underwriting expenses and other liabilities 202.8 2.5 205.3 Ceded reinsurance payable, net 1,085.0 0.7 1,085.7 Total liabilities 8,869.8 3.2 8,873.0 Retained earnings 714.2 (15.8) 698.4 Total shareholders' equity 1,864.5 (15.8) 1,848.7 Total liabilities and shareholders' equity 10,734.3 (12.6) 10,721.7 Adjusted Consolidated Statement of Income (Loss) for the three and nine months ended September 30, 2020: Three Months Ended September 30, 2020 Nine Months Ended September 30, 2020 As reported Adjustments As adjusted As reported Adjustments As adjusted (in millions, except per share amounts) (Unaudited) (Unaudited) Net realized investment (losses) gains $ (5.7) $ — $ (5.7) $ 33.3 $ (0.1) $ 33.2 Change in fair value of equity securities 10.5 — 10.5 (12.0) (1.7) (13.7) Net realized investment losses (5.7) — (5.7) (21.7) (1.8) (23.5) Total revenue 483.5 — 483.5 1,377.0 (1.8) 1,375.2 Underwriting, acquisition and insurance expenses 164.3 0.2 164.5 493.7 0.2 493.9 Interest expense 6.8 0.1 6.9 21.3 0.4 21.7 Foreign currency exchange losses 11.6 (3.2) 8.4 15.0 (1.4) 13.6 Total expenses 512.9 (2.9) 510.0 1,422.3 (0.8) 1,421.5 Loss before income taxes (29.4) 2.9 (26.5) (45.3) (1.0) (46.3) Income tax provision 0.2 (3.6) (3.4) 9.5 (2.6) 6.9 Net loss (29.6) 6.5 (23.1) (54.8) 1.6 (53.2) Net loss attributable to common shareholders (31.6) 6.5 (25.1) (56.8) 1.6 (55.2) Net loss attributable to common shareholders per common share: Basic $ (0.91) $ 0.19 $ (0.72) $ (1.64) $ 0.04 $ (1.60) Diluted $ (0.91) $ 0.19 $ (0.72) $ (1.64) $ 0.04 $ (1.60) Adjusted Consolidated Balance Sheet as of June 30, 2020: June 30, 2020 As reported Adjustments As adjusted (in millions) (Unaudited) Premiums receivable $ 800.2 $ (15.2) $ 785.0 Deferred tax asset, net 18.9 (3.0) 15.9 Other assets 414.7 (0.2) 414.5 Total assets 10,396.7 (18.4) 10,378.3 Accrued underwriting expenses and other liabilities 154.8 2.2 157.0 Ceded reinsurance payable, net 1,042.7 (4.7) 1,038.0 Current income taxes payable, net 27.1 6.4 33.5 Total liabilities 8,666.7 3.9 8,670.6 Retained earnings 756.7 (22.3) 734.4 Total shareholders' equity 1,730.0 (22.3) 1,707.7 Total liabilities and shareholders' equity 10,396.7 (18.4) 10,378.3 Adjusted Consolidated Statement of Income (Loss) for the three and six months ended June 30, 2020: Three Months Ended June 30, 2020 Six Months Ended June 30, 2020 As reported Adjustments As adjusted As reported Adjustments As adjusted (in millions, except per share amounts) (Unaudited) (Unaudited) Net investment income 1.5 (0.1) 1.4 37.0 — 37.0 Net realized investment gains $ 11.1 $ — $ 11.1 $ 39.0 $ (0.1) $ 38.9 Change in fair value of equity securities 16.8 (1.7) 15.1 (22.5) (1.7) (24.2) Net realized investment gains (losses) 20.1 (1.7) 18.4 (16.0) (1.8) (17.8) Total revenue 457.0 (1.8) 455.2 893.5 (1.8) 891.7 Underwriting, acquisition and insurance expenses 161.4 (0.1) 161.3 329.4 — 329.4 Interest expense 6.8 0.2 7.0 14.5 0.3 14.8 Foreign currency exchange losses 6.4 (2.1) 4.3 3.4 1.8 5.2 Total expenses 451.3 (2.0) 449.3 909.4 2.1 911.5 Income (loss) before income taxes 5.7 0.2 5.9 (15.9) (3.9) (19.8) Income tax provision 12.1 (0.8) 11.3 9.3 1.0 10.3 Net loss (6.4) 1.0 (5.4) (25.2) (4.9) (30.1) Net loss per common share: Basic $ (0.18) $ 0.02 $ (0.16) $ (0.73) $ (0.14) $ (0.87) Diluted $ (0.18) $ 0.02 $ (0.16) $ (0.73) $ (0.14) $ (0.87) Adjusted Consolidated Balance Sheet as of March 31, 2020: March 31, 2020 As reported Adjustments As adjusted (in millions) (Unaudited) Equity securities available-for-sale, at fair value $ 132.9 $ 11.6 $ 144.5 Other investments 422.4 (9.9) 412.5 Total investments 4,811.4 1.7 4,813.1 Premiums receivable 739.1 (20.9) 718.2 Deferred tax asset, net 44.5 (3.6) 40.9 Other assets 435.4 (0.6) 434.8 Total assets 10,201.3 (23.4) 10,177.9 Accrued underwriting expenses and other liabilities 185.3 2.1 187.4 Ceded reinsurance payable, net 1,094.8 (8.8) 1,086.0 Current income taxes payable, net 17.7 6.6 24.3 Total liabilities 8,564.5 (0.1) 8,564.4 Retained earnings 773.7 (23.3) 750.4 Total shareholders' equity 1,636.8 (23.3) 1,613.5 Total liabilities and shareholders' equity 10,201.3 (23.4) 10,177.9 Adjusted Consolidated Statement of Income (Loss) for the three months ended March 31, 2020: Three Months Ended March 31, 2020 As reported Adjustments As adjusted (in millions, except per share amounts) (Unaudited) Net investment income 35.5 0.1 35.6 Net realized investment gains $ 27.9 $ (0.1) $ 27.8 Net realized investment losses (36.1) (0.1) (36.2) Total revenue 436.5 — 436.5 Underwriting, acquisition and insurance expenses 168.0 0.1 168.1 Interest expense 7.7 0.1 7.8 Foreign currency exchange gains (losses) (3.0) 3.9 0.9 Total expenses 458.1 4.1 462.2 Loss before income taxes (21.6) (4.1) (25.7) Income tax benefit (2.8) 1.8 (1.0) Net loss (18.8) (5.9) (24.7) Net loss per common share: Basic $ (0.55) $ (0.17) $ (0.72) Diluted $ (0.55) $ (0.17) $ (0.72) Adjusted Consolidated Balance Sheet as of September 30, 2019: September 30, 2019 As reported Adjustments As adjusted (in millions) (Unaudited) Equity securities, at fair value $ 400.6 $ 11.6 $ 412.2 Other investments 500.0 (9.9) 490.1 Total investments 5,127.0 1.7 5,128.7 Premiums receivable 740.3 (12.8) 727.5 Current income taxes receivable, net 0.2 (0.2) — Other assets 390.6 (0.1) 390.5 Total assets 10,445.8 (11.4) 10,434.4 Accrued underwriting expenses and other liabilities 283.9 1.8 285.7 Ceded reinsurance payable, net 1,175.7 (2.9) 1,172.8 Current income taxes payable, net — 9.8 9.8 Deferred tax liabilities, net 19.9 (2.1) 17.8 Total liabilities 8,552.4 6.6 8,559.0 Retained earnings 925.0 (18.0) 907.0 Total shareholders' equity 1,893.4 (18.0) 1,875.4 Total liabilities and shareholders' equity 10,445.8 (11.4) 10,434.4 Adjusted Consolidated Statement of Income (Loss) for the three and nine months ended September 30, 2019: Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 As reported Adjustments As adjusted As reported Adjustments As adjusted (in millions, except per share amounts) (Unaudited) (Unaudited) Earned premiums $ 451.5 $ — $ 451.5 $ 1,303.7 $ 0.2 $ 1,303.9 Total revenue 487.4 — 487.4 1,485.2 0.2 1,485.4 Underwriting, acquisition and insurance expenses 164.0 — 164.0 485.6 0.2 485.8 Interest expense 7.5 0.2 7.7 25.3 0.4 25.7 Foreign currency exchange gains (1.6) 0.7 (0.9) (6.2) 0.9 (5.3) Total expenses 513.6 0.9 514.5 1,381.7 1.5 1,383.2 (Loss) income before income taxes (26.2) (0.9) (27.1) 103.5 (1.3) 102.2 Income tax (benefit) provision (1.1) — (1.1) 8.6 5.0 13.6 Net (loss) income (25.1) (0.9) (26.0) 94.9 (6.3) 88.6 Net (loss) income attributable to common shareholders (25.1) (0.9) (26.0) 94.9 (6.3) 88.6 Net (loss) income per common share: Basic $ (0.73) $ (0.03) $ (0.76) $ 2.78 $ (0.19) $ 2.59 Diluted $ (0.73) $ (0.03) $ (0.76) $ 2.73 $ (0.18) $ 2.55 Adjusted Consolidated Balance Sheet as of June 30, 2019: June 30, 2019 As reported Adjustments As adjusted (in millions) (Unaudited) Equity securities, at fair value $ 421.0 $ 11.6 $ 432.6 Other investments 509.4 (9.9) 499.5 Total investments 4,877.6 1.7 4,879.3 Premiums receivable 728.0 (11.2) 716.8 Current income taxes receivable, net 3.8 (3.8) — Total assets 10,166.7 (13.3) 10,153.4 Accrued underwriting expenses and other liabilities 279.4 1.6 281.0 Ceded reinsurance payable, net 1,052.8 (2.0) 1,050.8 Current income taxes payable, net — 6.2 6.2 Deferred tax liabilities, net 25.4 (2.0) 23.4 Total liabilities 8,237.7 3.8 8,241.5 Retained earnings 959.9 (17.1) 942.8 Total shareholders' equity 1,929.0 (17.1) 1,911.9 Total liabilities and shareholders' equity 10,166.7 (13.3) 10,153.4 Adjusted Consolidated Statement of Income (Loss) for the three and six months ended June 30, 2019: Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 As reported Adjustments As adjusted As reported Adjustments As adjusted (in millions, except per share amounts) (Unaudited) (Unaudited) Earned premiums $ 431.7 $ — $ 431.7 $ 852.2 $ 0.2 $ 852.4 Total revenue 488.6 — 488.6 997.8 0.2 998.0 Underwriting, acquisition and insurance expenses 161.4 0.2 161.6 321.6 0.2 321.8 Interest expense 9.3 0.1 9.4 17.8 0.2 18.0 Foreign currency exchange gains (5.3) 1.5 (3.8) (4.6) 0.2 (4.4) Total expenses 459.0 1.8 460.8 868.1 0.6 868.7 Income before income taxes 29.6 (1.8) 27.8 129.7 (0.4) 129.3 Income tax provision 0.8 — 0.8 9.7 5.0 14.7 Net income 28.8 (1.8) 27.0 120.0 (5.4) 114.6 Net income per common share: Basic $ 0.84 $ (0.05) $ 0.79 $ 3.52 $ (0.16) $ 3.36 Diluted $ 0.83 $ (0.05) $ 0.78 $ 3.45 $ (0.15) $ 3.30 Adjusted Consolidated Balance Sheet as of March 31, 2019: March 31, 2019 As reported Adjustments As adjusted (in millions) (Unaudited) Equity securities, at fair value $ 403.2 $ 11.6 $ 414.8 Other investments 483.3 (9.9) 473.4 Total investments 4,903.5 1.7 4,905.2 Premiums receivable 673.2 (8.3) 664.9 Current income taxes receivable, net 5.0 (5.0) — Total assets 9,954.5 (11.6) 9,942.9 Accrued underwriting expenses and other liabilities 248.2 1.3 249.5 Ceded reinsurance payable, net 1,047.1 (0.7) 1,046.4 Current income taxes payable, net — 5.1 5.1 Deferred tax liabilities, net 20.7 (2.0) 18.7 Total liabilities 8,073.9 3.7 8,077.6 Retained earnings 943.0 (15.3) 927.7 Total shareholders' equity 1,880.6 (15.3) 1,865.3 Total liabilities and shareholders' equity 9,954.5 (11.6) 9,942.9 Adjusted Consolidated Statement of Income (Loss) for the three months ended March 31, 2019: Three Months Ended March 31, 2019 As reported Adjustments As adjusted (in millions, except per share amounts) (Unaudited) Earned premiums $ 420.5 $ 0.2 $ 420.7 Total revenue 509.2 0.2 509.4 Interest expense 8.5 0.1 8.6 Foreign currency exchange losses (gains) 0.7 (1.3) (0.6) Total expenses 409.1 (1.2) 407.9 Income before income taxes 100.1 1.4 101.5 Income tax provision 8.9 5.0 13.9 Net income 91.2 (3.6) 87.6 Net income per common share: Basic $ 2.68 $ (0.10) $ 2.58 Diluted $ 2.63 $ (0.11) $ 2.52 Adjusted Condensed Financial Information of the Registrant as of December 31, 2019: December 31, 2019 (in millions) As reported Adjustments As adjusted Investments in subsidiaries $ 1,916.7 $ (17.4) $ 1,899.3 Total assets 1,974.7 (17.4) 1,957.3 Total shareholders’ equity 1,781.1 (17.4) 1,763.7 Total liabilities and shareholders' equity 1,974.7 (17.4) 1,957.3 Adjusted Condensed Financial Information of the Registrant for the years ended December 31, 2019 and 2018: Year Ended December 31, 2019 Year Ended December 31, 2018 (in millions) As reported Adjustments As adjusted As reported Adjustments As adjusted Equity in undistributed earnings of subsidiaries $ (22.8) $ 46.4 $ 23.6 $ 44.8 $ 29.9 $ 74.7 Net (loss) income (8.4) (5.7) (14.1) 63.6 (6.6) 57.0

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Schedule of Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Fair Value of Investments	The amortized cost, gross unrealized gains, gross unrealized losses and fair value in fixed maturity investments were as follows: December 31, 2020 (in millions) Amortized Gross Gross Allowance for Credit Losses (1) Fair Fixed maturities U.S. Governments $ 385.4 $ 14.7 $ 0.3 $ — $ 399.8 Foreign Governments 284.1 11.6 0.7 0.2 294.8 Obligations of states and political subdivisions 163.1 7.7 0.3 0.1 170.4 Corporate bonds 1,925.9 75.3 13.3 6.1 1,981.8 Commercial mortgage-backed securities 324.8 15.2 0.3 — 339.7 Residential mortgage-backed securities 491.4 17.4 0.6 — 508.2 Asset-backed securities 120.5 2.9 0.4 0.2 122.8 Collateralized loan obligations 285.9 4.9 1.2 — 289.6 Total fixed maturities $ 3,981.1 $ 149.7 $ 17.1 $ 6.6 $ 4,107.1 December 31, 2019 (in millions) Amortized Gross Gross Allowance for Credit Losses Fair Fixed maturities U.S. Governments $ 352.2 $ 2.3 $ 1.2 $ — $ 353.3 Foreign Governments 244.8 4.6 0.7 — 248.7 Obligations of states and political subdivisions 145.8 6.9 0.1 — 152.6 Corporate bonds 1,775.4 37.7 34.7 — 1,778.4 Commercial mortgage-backed securities 213.5 4.6 1.1 — 217.0 Residential mortgage-backed securities 479.0 10.4 0.6 — 488.8 Asset-backed securities 164.1 1.4 0.2 — 165.3 Collateralized loan obligations 226.7 0.5 1.4 — 225.8 Total fixed maturities $ 3,601.5 $ 68.4 $ 40.0 $ — $ 3,629.9
Schedule of Amortized Cost and Fair Values of Fixed Maturity Investments, by Contractual Maturity	The amortized cost and fair values of fixed maturity investments as of December 31, 2020, by contractual maturity, were as follows: (in millions) Amortized Fair Due in one year or less $ 324.9 $ 329.7 Due after one year through five years 1,743.6 1,791.9 Due after five years through ten years 607.8 639.3 Thereafter 82.2 85.9 Structured securities 1,222.6 1,260.3 Total $ 3,981.1 $ 4,107.1
Schedule of Carrying Value Redemption Characteristics and Unfunded Investment Commitments of Other Invested Assets Portfolio	Details regarding the carrying value and unfunded investment commitments of the other invested assets portfolio as of December 31, 2020 and 2019 were as follows: December 31, 2020 (in millions) Carrying Unfunded Investment Type Hedge funds $ 111.2 $ — Private equity 211.4 80.0 Overseas deposits 102.1 — Other 4.7 — Total other investments $ 429.4 $ 80.0 December 31, 2019 (in millions) Carrying Unfunded Investment Type Hedge funds $ 109.5 $ — Private equity 258.2 110.0 Overseas deposits 114.6 — Other 4.3 — Total other invested assets $ 486.6 $ 110.0
Schedule of Aging of Unrealized Losses on Company's Investments in Fixed Maturities, Equity Securities and Other Investments	An aging of unrealized losses on our investments in fixed maturities is presented below: December 31, 2020 Less Than One Year One Year or Greater Total (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed maturities U.S. Governments $ 40.6 $ 0.3 $ — $ — $ 40.6 $ 0.3 Foreign Governments 18.0 0.5 0.1 0.2 18.1 0.7 Obligations of states and political subdivisions 5.2 0.3 — — 5.2 0.3 Corporate bonds 202.5 6.7 17.5 6.6 220.0 13.3 Commercial mortgage-backed securities 21.8 0.3 — — 21.8 0.3 Residential mortgage-backed securities 74.4 0.4 3.0 0.2 77.4 0.6 Asset-backed securities 4.6 0.4 — — 4.6 0.4 Collateralized loan obligations 121.1 0.9 49.1 0.3 170.2 1.2 Total fixed maturities $ 488.2 $ 9.8 $ 69.7 $ 7.3 $ 557.9 $ 17.1 December 31, 2019 Less Than One Year One Year or Greater Total (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed maturities U.S. Governments $ 114.6 $ 1.1 $ 17.0 $ 0.1 $ 131.6 $ 1.2 Foreign Governments (1) 119.2 0.7 5.1 — 124.3 0.7 Obligations of states and political subdivisions (1) 0.7 — 2.1 0.1 2.8 0.1 Corporate bonds 249.7 18.9 63.6 15.8 313.3 34.7 Commercial mortgage-backed securities (1) 74.8 1.1 4.9 — 79.7 1.1 Residential mortgage-backed securities 66.9 0.3 25.2 0.3 92.1 0.6 Asset-backed securities 22.5 0.1 18.9 0.1 41.4 0.2 Collateralized loan obligations 54.9 0.8 116.7 0.6 171.6 1.4 Total fixed maturities $ 703.3 $ 23.0 $ 253.5 $ 17.0 $ 956.8 $ 40.0 (1) Unrealized losses are less than $0.1 million.
Schedule of Debt Securities, Available-for-sale, Allowance for Credit Loss	Foreign Governments Obligations of states and political subdivisions Corporate bonds Asset backed securities Total Beginning balance, January 1, 2020 $ — $ — $ — $ — $ — Additions-initial adoption of accounting standard — — 6.8 0.1 6.9 Securities for which allowance was not previously recorded 0.3 0.3 15.3 — 15.9 Securities sold during the period (0.2) — (39.0) (0.1) (39.3) Additional net increases (decreases) in existing allowance 0.1 (0.2) 23.0 0.2 23.1 Ending balance, December 31, 2020 $ 0.2 $ 0.1 $ 6.1 $ 0.2 $ 6.6
Schedule of Investment Income and Expenses	Investment income and expenses were as follows: For the Years Ended December 31, (in millions) 2020 2019 2018 Investment income: Interest on fixed maturities $ 108.6 $ 129.5 $ 115.0 Dividends on equity securities 2.8 11.1 12.5 Income on alternative investments 10.4 22.4 19.0 Income on short-term and other investments 3.9 8.9 9.5 Investment income 125.7 171.9 156.0 Investment expenses (13.0) (20.8) (23.7) Net investment income $ 112.7 $ 151.1 $ 132.3
Schedule of Company's Gross Realized Investment Gains (Losses)	The following table presents our gross realized investment gains (losses): For the Years Ended December 31, (in millions) 2020 2019 2018 Realized gains on fixed maturities and other Fixed maturities $ 37.1 $ 22.2 $ 17.7 Other investments, including short-terms 93.8 0.1 0.2 Other assets 32.3 33.0 41.4 163.2 55.3 59.3 Realized losses on fixed maturities and other Fixed maturities (35.2) (11.7) (16.0) Other investments, including short-terms (78.6) (31.3) (40.0) Other assets (9.9) — — Credit losses on fixed maturities (39.9) — — Other-than-temporary impairment losses — (20.3) (7.6) (163.6) (63.3) (63.6) Equity securities Net realized (losses) gains on equity securities (17.1) 128.9 37.4 Change in unrealized gains (losses) on equity securities held at the end of the period 10.3 (40.8) (105.1) Net realized (losses) gains on equity securities (6.8) 88.1 (67.7) Net realized investment and other (losses) gains before income taxes (7.2) 80.1 (72.0) Income tax (benefit) provision 1.3 16.2 11.2 Net realized investment (losses) gains, net of income taxes $ (8.5) $ 63.9 $ (83.2)
Schedule of Changes in Unrealized Appreciation (Depreciation)	Changes in unrealized appreciation (depreciation) related to investments are summarized as follows: For the Years Ended December 31, (in millions) 2020 2019 2018 Change in unrealized gains Fixed maturities $ 96.0 $ 93.3 $ (88.1) Other investments (14.3) 4.4 0.1 Other and short-term investments 0.7 0.2 (0.5) Net unrealized investment gains (losses) before income taxes 82.4 97.9 (88.5) Income tax provision (benefit) 16.5 15.4 (13.0) Net unrealized investment gains (losses), net of income taxes $ 65.9 $ 82.5 $ (75.5)
Schedule of Fair Value of Foreign Currency Exchange Forward Contracts	The fair value of our foreign currency exchange forward contracts as of December 31 was as follows: (in millions) December 31, 2020 December 31, 2019 Operational currency exposure $ 0.4 $ (0.8) Asset manager investment exposure (0.2) (0.3) Total return strategy 0.7 2.2 Total $ 0.9 $ 1.1
Schedule of Realized Gains and Losses of Investment on Foreign Currency Exchange Forward Contracts	The following table presents our gross investment realized gains and losses on our foreign currency exchange forward contracts: For the Years Ended December 31, (in millions) 2020 2019 2018 Realized gains Operational currency exposure 13.2 5.7 9.7 Asset manager investment exposure 2.2 2.7 5.8 Total return strategy 61.6 22.5 26.7 Gross realized investment gains 77.0 30.9 42.2 Realized losses Operational currency exposure (8.6) (10.6) (7.9) Asset manager investment exposure (4.0) (0.8) (3.0) Total return strategy (62.3) (17.6) (28.6) Gross realized investment losses (74.9) (29.0) (39.5) Net realized investment gains (losses) on foreign $ 2.1 $ 1.9 $ 2.7
Schedule of Restricted Assets	The following table presents our components of restricted assets at December 31: (in millions) December 31, 2020 December 31, 2019 Securities on deposit for regulatory and other purposes $ 227.5 $ 192.5 Securities pledged as collateral for letters of credit and other 189.4 169.9 Securities and cash on deposit supporting Lloyd’s business 409.2 412.8 Total restricted investments $ 826.1 $ 775.2
Financial Assets Measured at Fair Value on Recurring Basis	Based on an analysis of the inputs, our financial assets measured at fair value on a recurring basis have been categorized as follows: Fair Value Measurements at Reporting Date Using (in millions) December 31, 2020 Level 1 (a) Level 2 (b) Level 3 (c) Fixed maturities U.S. Governments $ 399.8 $ 383.5 $ 16.3 $ — Foreign Governments 294.8 — 294.8 — Obligations of states and political subdivisions 170.4 — 170.4 — Corporate bonds 1,981.8 — 1,974.8 7.0 Commercial mortgage-backed securities 339.7 — 339.7 — Residential mortgage-backed securities 508.2 — 508.2 — Asset-backed securities 122.8 — 122.8 — Collateralized loan obligations 289.6 — 289.6 — Total fixed maturities 4,107.1 383.5 3,716.6 7.0 Equity securities 176.7 159.2 — 17.5 Other investments 102.5 0.4 102.1 — Short-term investments 542.6 526.5 16.1 — $ 4,928.9 $ 1,069.6 $ 3,834.8 $ 24.5 (a) Quoted prices in active markets for identical asset (b) Significant other observable inputs (c) Significant unobservable inputs Fair Value Measurements at Reporting Date Using (in millions) December 31, 2019 Level 1 (a) Level 2 (b) Level 3 (c) Fixed maturities U.S. Governments $ 353.3 $ 347.8 $ 5.5 $ — Foreign Governments 248.7 — 248.7 — Obligations of states and political subdivisions 152.6 — 152.6 — Corporate bonds 1,778.4 — 1,771.0 7.4 Commercial mortgage-backed securities 217.0 — 217.0 — Residential mortgage-backed securities 488.8 — 488.8 — Asset-backed securities 165.3 — 165.3 — Collateralized loan obligations 225.8 — 225.8 — Total fixed maturities 3,629.9 347.8 3,274.7 7.4 Equity securities 136.0 117.8 — 18.2 Other investments 96.3 — 96.3 — Short-term investments 845.0 823.5 21.5 — $ 4,707.2 $ 1,289.1 $ 3,392.5 $ 25.6 (a) Quoted prices in active markets for identical asset (b) Significant other observable inputs (c) Significant unobservable inputs
Schedule of Reconciliation of Beginning and Ending Balances for Investments Categorized as Level 3	A reconciliation of the beginning and ending balances for the investments categorized as Level 3 are as follows: Fair Value Measurements Using Observable Inputs (Level 3) (in millions) Credit Financial Equity Total Beginning balance, January 1, 2020 $ 7.4 $ 18.2 $ 25.6 Transfers into Level 3 — — — Transfers out of Level 3 — — — Total gains or losses (realized/unrealized): Included in net income — (5.9) (5.9) Included in other comprehensive income (0.5) — (0.5) Purchases, issuances, sales, and settlements: Purchases 0.1 5.2 5.3 Issuances — — — Sales — — — Settlements — — — Ending balance, December 31, 2020 $ 7.0 $ 17.5 $ 24.5 Amount of total gains or losses for the year included in net income attributable to the change in unrealized gains or losses relating to assets still held at December 31, 2020 $ — $ — $ — (in millions) Credit Financial Equity Total Beginning balance, January 1, 2019 $ 2.2 $ 19.8 $ 22.0 Transfers into Level 3 3.5 — 3.5 Transfers out of Level 3 — — — Total gains or losses (realized/unrealized): Included in net income (0.4) (1.6) (2.0) Included in other comprehensive loss 0.6 — 0.6 Purchases, issuances, sales, and settlements: Purchases 1.9 — 1.9 Issuances — — — Sales (0.4) — (0.4) Settlements — — — Ending balance, December 31, 2019 $ 7.4 $ 18.2 $ 25.6 Amount of total gains or losses for the year included in net income attributable to the change in unrealized gains or losses relating to assets still held at December 31, 2019 $ — $ — $ —

Allowance for Credit Losses (Ta

Allowance for Credit Losses (Tables)	12 Months Ended
	Dec. 31, 2020
Credit Loss [Abstract]
Premium Receivable, Allowance for Credit Loss	The following table represents the balances of premiums receivable, net of allowance for uncollectible premiums, including expected credit losses, at December 31, 2020 and January 1, 2020, and the changes in the allowance for the year ended December 31, 2020. (in millions) Premiums Receivable, Net of Allowance for Estimated Uncollectible Premiums Allowance for Estimated Uncollectible Premiums Balance, January 1, 2020 $ 676.5 $ 7.9 Cumulative effect of adoption of ASU 2016-13 — Current period change for estimated uncollectible premiums 3.6 Write-offs of uncollectible premiums receivable (2.4) Foreign exchange adjustments 0.3 Balance, December 31, 2020 $ 679.8 $ 9.4
Reinsurance Recoverable, Allowance for Credit Loss	Reinsurance Recoverables The following table presents the balances of reinsurance recoverables, net of the allowance for estimated uncollectible reinsurance, including expected credit losses, at December 31, 2020 and January 1, 2020, and changes in the allowance for estimated uncollectible reinsurance for the year ended December 31, 2020. (in millions) Reinsurance Recoverables, Net of Allowance for Estimated Uncollectible Reinsurance Allowance for Estimated Uncollectible Reinsurance Balance, January 1, 2020 $ 3,107.2 $ 1.1 Cumulative effect of adoption of ASU 2016-13 2.5 Current period change for estimated uncollectible reinsurance 0.9 Write-offs of uncollectible reinsurance recoverables (0.4) Balance, December 31, 2020 $ 3,009.0 $ 4.1

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Lessee, Assets and Liabilities	The components of lease expense and other lease information as of and during the year ended December 31, 2020 and 2019 are as follows: December 31, (in millions) 2020 2019 Operating leases right-of-use assets $ 82.0 $ 91.8 Operating lease liabilities 95.8 105.7 Operating lease weighted-average remaining lease term 10.50 9.91 Operating lease weighted-average discount rate 3.77 % 3.86 %
Lease, Cost	For the Year Ended December 31, (in millions) 2020 2019 Operating lease costs $ 15.3 $ 19.3 Variable lease costs 5.4 4.5 Sublease income (0.4) (0.4) Total lease costs $ 20.3 $ 23.4 Operating cash flows from operating leases (fixed payments) $ 15.7 $ 17.5 Operating cash flows from operating leases (liability reduction) $ 12.8 $ 18.3
Lessee, Operating Lease, Liability, Maturity	Future minimum lease payments under operating leases as of December 31, 2020 were as follows: December 31, (in millions) 2020 2021 14.7 2022 13.2 2023 11.1 2024 9.8 2025 9.6 Thereafter 58.4 Total future minimum lease payments $ 116.8 Future lease obligations — Less imputed interest (21.0) Total operating lease liability $ 95.8

Reinsurance (Tables)

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2020
Insurance [Abstract]
Schedule of Reinsurance Premiums	Premiums were as follows: For the Years Ended December 31, (in millions) 2020 2019 2018 Direct written premiums $ 2,676.1 $ 2,510.4 $ 2,292.9 Reinsurance ceded to other companies (1,423.2) (1,375.5) (1,189.0) Reinsurance assumed from other companies 557.2 619.7 661.4 Net written premiums $ 1,810.1 $ 1,754.6 $ 1,765.3 Direct earned premiums $ 2,660.6 $ 2,412.4 $ 2,201.0 Reinsurance ceded to other companies (1,388.6) (1,286.7) (1,137.2) Reinsurance assumed from other companies 508.5 604.0 667.7 Net earned premiums $ 1,780.5 $ 1,729.7 $ 1,731.5 Percentage of reinsurance assumed to net earned premiums 28.6 % 34.9 % 38.6 %

Reserves for Losses and Loss _2

Reserves for Losses and Loss Adjustment Expenses (Tables)	12 Months Ended
	Dec. 31, 2020
Insurance [Abstract]
Reserves for Losses and Loss Adjustment Expenses	The following table provides a reconciliation of reserves for losses and loss adjustment expenses (“LAE”): For the Years Ended December 31, (in millions) 2020 2019 2018 Net reserves beginning of the year $ 2,722.7 $ 2,562.9 $ 2,488.0 Net AIL reserves acquired 27.9 — — Net ArgoGlobal Assicurazioni reserves acquired — — 43.4 Add: Losses and LAE incurred during current calendar year, net of reinsurance: Current accident year 1,201.1 1,082.6 1,058.8 Prior accident years 7.7 138.1 (18.0) Losses and LAE incurred during calendar year, net of reinsurance 1,208.8 1,220.7 1,040.8 Deduct: Losses and LAE payments made during current calendar year, net of reinsurance: Current accident year 253.4 224.3 273.3 Prior accident years 866.4 806.0 665.6 Losses and LAE payments made during current calendar year, net of reinsurance: 1,119.8 1,030.3 938.9 Change in participation interest (1) 32.8 (14.4) (25.5) Foreign exchange adjustments 33.7 (16.2) (44.9) Net reserves - end of year 2,906.1 2,722.7 2,562.9 Add: Reinsurance recoverables on unpaid losses and LAE, end of year 2,499.9 2,434.9 2,091.7 Gross reserves - end of year $ 5,406.0 $ 5,157.6 $ 4,654.6 (1) Amount represents (decrease) increase in reserves due to change in our Syndicate 1200 and Syndicate 1910 participation.
Impact from (Favorable) Unfavorable Development of Prior Accident Years’ Loss and LAE Reserves on Each Reporting Segment	The impact from the unfavorable (favorable) development of prior accident years’ losses and LAE reserves on each reporting segment is presented below: For the Years Ended December 31, (in millions) 2020 2019 2018 U.S. Operations $ 2.4 $ 15.7 $ (20.8) International Operations (6.2) 110.4 (9.5) Run-off Lines 11.5 12.0 12.3 Total unfavorable prior-year development $ 7.7 $ 138.1 $ (18.0)
Summary of Information About Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	The following tables provide information about incurred and cumulative paid losses and allocated loss adjustment expenses (“ALAE”), net of reinsurance. The following tables also include IBNR reserves plus expected development on reported claims and the cumulative number of reported claims as of December 31, 2020. Reporting Segment: U.S. Operations Operating Division: Excess and Surplus Lines Line of Business: Liability (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 202.9 $ 206.0 $ 205.8 $ 200.0 $ 193.5 $ 192.8 $ 189.0 $ 187.8 $ 185.8 $ 187.4 2012 189.6 196.0 189.7 183.6 184.4 182.1 182.3 181.0 182.0 2013 217.9 222.6 224.3 227.2 220.4 216.0 214.2 216.0 2014 213.0 215.2 213.2 211.9 212.3 210.0 218.1 2015 232.5 237.1 228.6 226.4 224.8 233.9 2016 246.4 250.6 243.1 248.3 250.0 2017 253.3 244.3 249.0 257.7 2018 278.8 269.5 254.0 2019 269.8 268.8 2020 266.2 Total $ 2,334.1 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 17.6 $ 53.8 $ 91.0 $ 122.9 $ 146.6 $ 162.4 $ 170.0 $ 174.4 $ 177.5 $ 179.2 2012 17.2 52.8 89.1 120.8 142.4 157.5 163.4 170.3 174.9 2013 17.6 60.2 100.4 135.2 163.7 179.6 192.2 200.3 2014 15.0 52.2 95.9 131.6 154.5 172.8 186.7 2015 16.5 51.9 91.4 131.5 162.8 182.4 2016 17.4 52.8 95.5 149.5 177.4 2017 11.5 38.7 88.0 149.6 2018 15.0 47.0 98.2 2019 14.9 61.2 2020 12.5 Total $ 1,422.4 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 24.1 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 935.8 As of December 31, 2020 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2011 $ 187.4 $ 3.0 8,526 2012 182.0 3.4 7,494 2013 216.0 5.3 7,484 2014 218.1 9.9 6,812 2015 233.9 17.4 6,509 2016 250.0 29.8 6,283 2017 257.7 36.7 7,172 2018 254.0 83.0 6,810 2019 268.8 147.6 5,985 2020 266.2 223.7 3,407 (1) Information presented for calendar years prior to 2020 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. Reporting Segment: U.S. Operations Operating Division: Specialty Admitted Line of Business: Liability (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 140.3 $ 155.1 $ 159.0 $ 157.5 $ 158.2 $ 154.0 $ 153.7 $ 154.0 $ 151.6 $ 150.4 2012 140.3 146.3 149.7 153.3 151.5 147.7 146.6 146.2 146.3 2013 126.6 133.2 136.7 133.2 131.1 130.6 128.9 128.8 2014 115.6 121.9 116.9 114.5 111.5 111.9 109.3 2015 107.3 106.7 101.7 102.3 103.1 101.6 2016 96.1 99.9 99.3 104.7 105.2 2017 121.5 129.5 135.3 140.0 2018 147.3 160.9 160.5 2019 151.3 154.9 2020 138.1 Total $ 1,335.1 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 23.2 $ 57.5 $ 85.9 $ 111.3 $ 126.1 $ 135.1 $ 139.8 $ 143.1 $ 144.0 $ 145.1 2012 20.1 51.0 80.7 105.8 120.8 127.9 131.9 135.0 138.2 2013 18.9 49.4 74.0 93.6 102.8 109.7 114.7 118.0 2014 17.4 38.8 58.7 75.3 86.1 93.5 96.5 2015 17.2 35.0 48.8 64.2 73.6 81.5 2016 11.1 31.7 48.6 67.6 78.2 2017 16.3 44.4 70.9 88.9 2018 19.4 52.0 77.6 2019 17.5 52.4 2020 13.0 Total $ 889.4 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 35.5 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 481.2 As of December 31, 2020 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2011 $ 150.4 $ 3.4 28,201 2012 146.3 3.8 23,681 2013 128.8 5.5 19,003 2014 109.3 6.2 16,404 2015 101.6 9.1 14,768 2016 105.2 10.4 11,946 2017 140.0 19.8 13,988 2018 160.5 40.1 15,891 2019 154.9 62.4 14,946 2020 138.1 89.9 8,986 (1) Information presented for calendar years prior to 2020 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. Reporting Segment: U.S. Operations Operating Division: Specialty Admitted Line of Business: Professional (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 35.0 $ 35.0 $ 35.0 $ 32.5 $ 28.2 $ 26.9 $ 26.6 $ 26.0 $ 25.8 $ 25.7 2012 27.8 28.3 28.6 25.8 24.0 24.5 24.9 24.7 24.4 2013 20.9 21.5 21.1 19.0 19.8 19.5 18.3 18.1 2014 22.4 22.4 26.0 33.7 36.2 35.4 35.1 2015 29.9 29.5 33.2 34.0 37.1 37.9 2016 44.2 44.8 45.1 42.9 35.5 2017 60.1 61.8 78.3 87.9 2018 70.8 73.2 79.2 2019 94.4 96.8 2020 152.6 Total $ 593.2 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 3.2 $ 11.8 $ 17.8 $ 22.0 $ 24.0 $ 25.4 $ 25.7 $ 25.7 $ 25.7 $ 25.7 2012 2.3 8.6 16.9 19.9 21.4 22.6 23.5 24.2 24.0 2013 1.9 6.3 10.9 14.2 17.6 17.5 17.9 17.9 2014 2.3 5.4 15.1 24.1 25.5 32.3 33.3 2015 1.8 8.3 15.6 20.8 26.2 31.3 2016 2.4 11.9 24.6 28.9 30.8 2017 3.5 24.9 38.0 59.7 2018 4.5 16.7 43.8 2019 4.9 32.9 2020 13.3 Total $ 312.7 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 6.8 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 287.3 As of December 31, 2020 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2011 $ 25.7 $ — 821 2012 24.4 0.1 642 2013 18.1 0.2 622 2014 35.1 0.4 1,045 2015 37.9 1.5 1,843 2016 35.5 2.5 3,251 2017 87.9 1.4 3,747 2018 79.2 7.4 4,287 2019 96.8 39.7 5,049 2020 152.6 124.9 4,739 (1) Information presented for calendar years prior to 2020 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. Reporting Segment: U.S. Operations Operating Division: Specialty Admitted Line of Business: Specialty (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 0.2 $ 3.9 $ 3.4 $ 3.4 $ 3.6 $ 2.6 $ 2.0 $ 1.7 $ 1.7 $ 1.7 2012 7.5 6.7 4.9 4.3 4.0 3.9 3.5 3.6 3.3 2013 10.0 8.6 4.6 2.5 1.7 0.9 0.9 0.9 2014 13.1 13.1 8.9 6.0 4.8 4.6 4.6 2015 14.8 14.3 9.5 5.5 1.2 0.5 2016 15.0 15.0 11.2 6.2 4.7 2017 16.2 16.2 7.6 0.9 2018 20.9 17.4 3.3 2019 22.7 8.6 2020 25.4 Total $ 53.9 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ — $ 1.6 $ 1.4 $ 1.3 $ 1.2 $ 1.7 $ 1.7 $ 1.7 $ 1.7 $ 1.7 2012 3.6 3.3 3.3 3.3 3.3 3.4 3.3 3.4 3.4 2013 0.4 0.9 0.9 0.9 0.9 0.9 0.9 0.9 2014 1.1 3.3 4.0 4.0 4.1 4.1 4.0 2015 0.2 0.1 0.2 0.3 0.3 0.3 2016 1.3 1.6 2.2 2.2 2.2 2017 0.3 0.1 — 0.1 2018 — 0.7 1.7 2019 0.7 0.7 2020 0.3 Total $ 15.3 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 0.7 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 39.3 As of December 31, 2020 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2011 $ 1.7 $ — 80 2012 3.3 — 130 2013 0.9 — 50 2014 4.6 0.6 50 2015 0.5 0.2 24 2016 4.7 0.5 61 2017 0.9 0.6 104 2018 3.3 0.7 123 2019 8.6 7.1 253 2020 25.4 19.8 309 (1) Information presented for calendar years prior to 2020 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. Reporting Segment: International Operations Operating Division: Reinsurance Line of Business: Property (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 120.3 $ 110.4 $ 112.6 $ 110.6 $ 109.9 $ 113.7 $ 129.0 $ 135.6 $ 136.1 $ 135.4 2012 47.2 51.4 50.4 51.7 46.5 55.3 59.8 61.0 60.1 2013 32.5 34.5 34.0 32.3 32.9 32.4 31.9 32.3 2014 26.7 26.8 25.0 30.6 31.9 32.5 31.7 2015 27.2 23.8 62.6 60.5 57.9 52.7 2016 44.7 44.9 39.2 47.3 44.8 2017 109.0 107.7 111.2 103.9 2018 69.3 82.9 79.5 2019 63.2 70.1 2020 56.6 Total $ 667.1 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 43.1 $ 70.3 $ 92.3 $ 100.5 $ 102.8 $ 107.8 $ 123.6 $ 130.6 $ 132.7 $ 132.3 2012 12.4 31.2 40.6 49.7 44.1 52.2 58.0 60.1 59.3 2013 4.3 17.2 27.3 29.8 31.2 31.2 31.3 32.1 2014 2.8 12.9 19.0 30.1 30.6 32.1 31.6 2015 4.2 11.3 50.0 53.1 54.8 51.1 2016 14.0 25.4 29.7 42.8 43.0 2017 49.7 92.9 112.6 102.6 2018 24.9 71.5 78.0 2019 9.3 57.6 2020 11.60 Total $ 599.2 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 2.5 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 70.4 As of December 31, 2020 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2011 $ 135.4 $ 0.1 463 2012 60.1 — 278 2013 32.3 — 219 2014 31.7 — 223 2015 52.7 — 222 2016 44.8 1.1 395 2017 103.9 (9.8) 847 2018 79.5 (13.7) 714 2019 70.1 0.2 385 2020 56.6 33.7 398 (1) Information presented for calendar years prior to 2020 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. Reporting Segment: International Operations Operating Division: Argo Insurance Bermuda Line of Business: Liability (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 6.6 $ 6.6 $ 6.6 $ 4.4 $ 2.2 $ 1.6 $ 1.0 $ — $ — $ — 2012 7.4 7.4 7.4 5.6 4.4 1.7 — 0.6 0.6 2013 8.5 8.5 8.5 8.5 4.9 2.2 5.3 5.3 2014 9.8 9.8 9.8 6.2 1.5 2.3 2.3 2015 11.3 14.3 24.8 35.4 45.4 45.1 2016 13.9 14.0 14.0 6.6 6.1 2017 17.1 17.3 26.9 30.3 2018 8.9 32.1 26.6 2019 13.3 13.6 2020 23.3 Total $ 153.2 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ — $ — $ — $ — $ — $ — $ — $ — $ — $ — 2012 — — — — — — — — — 2013 — — — — 2.3 2.3 2.3 2.4 2014 — — 0.1 0.1 1.2 1.2 1.4 2015 — — 16.1 20.3 26.6 34.8 2016 — — — 0.1 0.1 2017 — 3.3 3.4 17.9 2018 — 13.8 18.3 2019 — 0.1 2020 0.8 Total $ 75.8 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance — Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 77.4 As of December 31, 2020 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2011 $ — $ — 1,426 2012 0.6 0.6 1,390 2013 5.3 1.9 1,197 2014 2.3 0.3 1,345 2015 45.1 6.2 1,607 2016 6.1 5.9 1,924 2017 30.3 6.3 2,092 2018 26.6 8.2 1,049 2019 13.6 12.6 1,088 2020 23.3 16.1 1,083 (1) Information presented for calendar years prior to 2020 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. Reporting Segment: International Operations Operating Division: Syndicate 1200 Line of Business: Liability (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 8.6 $ 9.1 $ 11.5 $ 11.6 $ 10.9 $ 10.7 $ 11.4 $ 11.5 $ 12.1 $ 12.2 2012 9.0 11.2 15.5 14.8 14.4 15.3 15.6 16.1 16.5 2013 23.7 28.0 27.5 25.6 25.9 26.4 27.6 28.2 2014 39.1 38.1 35.3 34.9 35.6 37.3 38.3 2015 35.9 30.8 31.2 30.8 34.3 34.2 2016 26.7 28.2 27.3 29.5 29.5 2017 25.6 24.2 27.6 28.1 2018 23.2 21.4 20.8 2019 16.8 15.7 2020 14.5 Total $ 238.0 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 0.3 $ 0.8 $ 1.7 $ 3.6 $ 5.7 $ 7.4 $ 8.3 $ 9.2 $ 10.3 $ 10.3 2012 0.4 1.2 2.6 5.9 8.5 10.4 12.3 13.2 13.5 2013 1.6 3.4 7.3 11.9 16.3 20.7 23.5 24.0 2014 2.0 4.8 10.3 14.2 21.1 25.8 26.2 2015 0.9 5.3 7.5 12.9 18.3 18.8 2016 2.0 5.8 11.0 15.7 16.5 2017 1.8 7.1 11.7 12.9 2018 2.7 7.4 10.7 2019 1.3 4.0 2020 1.3 Total $ 138.2 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 1.2 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 101.0 As of December 31, 2020 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims 2011 $ 12.2 $ — 2012 16.5 — 2013 28.2 0.3 2014 38.3 0.9 2015 34.2 1.2 2016 29.5 1.8 2017 28.1 5.1 2018 20.8 7.4 2019 15.7 8.8 2020 14.5 11.7 (1) Information presented for calendar years prior to 2020 is required supplementary information and is unaudited. Reporting Segment: International Operations Operating Division: Syndicate 1200 Line of Business: Professional (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 20.2 $ 22.2 $ 19.6 $ 16.4 $ 15.5 $ 15.6 $ 16.1 $ 16.6 $ 17.1 $ 18.0 2012 14.3 14.2 14.5 14.4 14.5 15.6 16.0 16.4 16.0 2013 23.2 23.2 23.3 22.9 23.3 23.9 24.6 25.1 2014 36.0 37.3 37.6 41.3 43.0 43.9 45.2 2015 39.0 38.4 40.3 39.9 42.1 43.2 2016 33.6 28.0 26.9 31.4 34.4 2017 24.8 21.9 24.3 27.7 2018 21.8 17.1 19.9 2019 22.2 23.2 2020 26.9 Total $ 279.6 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 1.1 $ 2.6 $ 4.4 $ 7.0 $ 8.7 $ 11.2 $ 11.9 $ 13.5 $ 14.2 $ 14.3 2012 0.6 1.9 4.6 6.1 8.7 10.0 11.9 13.1 13.3 2013 1.8 3.7 7.6 12.4 16.3 18.7 21.3 21.6 2014 1.7 6.8 15.6 25.0 29.6 34.2 34.8 2015 2.3 8.8 15.4 20.9 26.4 27.1 2016 2.2 5.9 11.0 17.7 19.0 2017 1.1 5.4 10.1 11.1 2018 1.2 5.4 10.1 2019 2.7 7.3 2020 2.0 Total $ 160.6 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 2.5 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 121.5 As of December 31, 2020 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims 2011 $ 18.0 $ 0.2 2012 16.0 0.8 2013 25.1 1.8 2014 45.2 4.0 2015 43.2 5.5 2016 34.4 5.6 2017 27.7 9.0 2018 19.9 7.2 2019 23.2 11.8 2020 26.9 21.7 (1) Information presented for calendar years prior to 2020 is required supplementary information and is unaudited. Reporting Segment: International Operations Operating Division: Syndicate 1200 Line of Business: Property (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 110.9 $ 116.1 $ 110.2 $ 97.0 $ 95.2 $ 94.6 $ 94.4 $ 94.0 $ 93.7 $ 93.4 2012 90.0 89.7 93.9 93.0 92.0 91.6 90.9 90.4 91.7 2013 84.3 80.1 79.0 77.5 77.0 76.3 75.1 76.6 2014 70.4 64.6 66.0 66.0 65.7 63.6 63.5 2015 56.0 66.5 73.2 74.3 73.0 74.7 2016 70.8 86.2 92.1 91.1 91.0 2017 83.3 90.4 94.9 93.8 2018 64.0 63.8 60.1 2019 43.2 41.6 2020 57.3 Total $ 743.7 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 24.0 $ 48.2 $ 63.2 $ 75.0 $ 80.8 $ 82.5 $ 83.8 $ 83.7 $ 83.1 $ 83.5 2012 30.1 48.5 63.9 75.0 77.4 78.2 78.6 78.4 79.0 2013 45.0 57.5 70.0 74.1 74.3 73.7 72.7 73.6 2014 29.9 52.0 57.9 59.3 59.5 57.3 58.1 2015 23.0 43.0 51.4 58.8 58.2 59.7 2016 39.3 61.3 78.0 79.2 83.0 2017 26.1 63.6 72.5 79.6 2018 34.0 56.2 57.9 2019 20.6 33.8 2020 17.6 Total $ 625.8 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 7.8 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 125.7 As of December 31, 2020 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims 2011 $ 93.4 $ — 2012 91.7 — 2013 76.6 — 2014 63.5 — 2015 74.7 — 2016 91.0 — 2017 93.8 0.9 2018 60.1 1.8 2019 41.6 4.2 2020 57.3 34.4 (1) Information presented for calendar years prior to 2020 is required supplementary information and is unaudited. Reporting Segment: International Operations Operating Division: Syndicate 1200 Line of Business: Specialty (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 39.3 $ 41.2 $ 39.8 $ 35.0 $ 34.2 $ 34.2 $ 34.0 $ 33.7 $ 33.6 $ 33.5 2012 53.6 57.5 62.0 60.5 60.2 59.9 59.4 59.0 58.9 2013 77.2 82.8 84.1 83.7 83.1 83.0 82.0 81.6 2014 93.8 100.4 101.8 102.6 102.6 100.7 101.3 2015 91.4 89.7 95.2 97.4 96.9 95.7 2016 87.4 85.8 89.7 91.9 90.7 2017 80.4 77.0 86.9 86.1 2018 68.0 73.3 75.7 2019 79.3 77.7 2020 100.4 Total $ 801.6 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2011 $ 11.9 $ 20.1 $ 24.3 $ 27.8 $ 29.2 $ 29.8 $ 30.1 $ 30.0 $ 29.8 $ 30.0 2012 18.4 28.2 39.9 46.8 49.8 50.7 51.1 51.1 51.4 2013 31.8 53.6 70.2 77.7 79.0 79.5 79.0 80.0 2014 38.5 73.0 84.2 89.0 91.0 89.8 91.1 2015 31.8 55.4 65.7 75.0 76.4 78.3 2016 38.4 57.5 69.4 76.3 79.9 2017 18.1 44.2 59.3 65.2 2018 21.6 53.3 66.2 2019 30.3 55.1 2020 25.8 Total $ 623.0 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 1.8 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 180.4 As of December 31, 2020 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims 2011 $ 33.5 $ — 2012 58.9 — 2013 81.6 — 2014 101.3 — 2015 95.7 — 2016 90.7 1.6 2017 86.1 3.6 2018 75.7 5.2 2019 77.7 12.9 2020 100.4 51.5 (1) Information presented for calendar years prior to 2020 is required supplementary information and is unaudited.
Summary of Reconciliation of Net Incurred and Paid Development to Liability for Unpaid Losses and LAE in Consolidated Balance Sheets	The reconciliation of the net incurred and paid development tables to the liability for unpaid losses and LAE in our consolidated balance sheets is as follows: (in millions) As of December 31, 2020 Liabilities for unpaid losses and ALAE: US Operations: Excess and Surplus Lines - Liability $ 935.8 Commercial Specialty - Liability 481.2 Commercial Specialty - Professional 287.3 Commercial Specialty - Specialty 39.3 International Operations: Reinsurance - Property 70.4 Argo Insurance Bermuda- Liability 77.4 Syndicate 1200 - Liability 101.0 Syndicate 1200 - Professional 121.5 Syndicate 1200 - Property 125.7 Syndicate 1200 - Specialty 180.4 Run-off Lines 165.5 Other lines 270.8 Total liabilities for unpaid losses and ALAE, net of reinsurance 2,856.3 Reinsurance recoverables on unpaid losses and LAE: US Operations: Excess and Surplus Lines - Liability 419.9 Commercial Specialty - Liability 376.1 Commercial Specialty - Professional 199.7 Commercial Specialty - Specialty 29.0 International Operations: Reinsurance - Property 288.6 Argo Insurance Bermuda- Liability 172.3 Syndicate 1200 - Liability 53.4 Syndicate 1200 - Professional 84.3 Syndicate 1200 - Property 102.6 Syndicate 1200 - Specialty 122.8 Run-off Lines 75.9 Other lines 575.3 Total reinsurance recoverables on unpaid losses and LAE 2,499.9 Unallocated loss adjustment expenses 67.6 Unamortized reserve discount (17.8) Gross liability for unpaid losses and LAE $ 5,406.0
Schedule of Supplementary Unaudited Information About Annual Percentage Payout of Incurred Losses and ALAE, Net of Reinsurance	The following table provides supplementary unaudited information about the annual percentage payout of incurred losses and ALAE, net of reinsurance, as of December 31, 2020: Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance (1) Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 U.S. Operations: Excess and Surplus Lines - Liability 6.7% 15.7% 20.9% 20.8% 12.7% 8.5% 5.1% 3.3% 2.1% 1.3% Specialty Admitted - Liability 14.1% 22.0% 18.6% 16.3% 9.6% 6.1% 4.0% 2.7% 1.8% 1.3% Specialty Admitted- Professional 6.1% 22.8% 27.3% 20.4% 9.2% 6.2% 3.4% 1.9% 1.1% 0.6% Specialty Admitted - Specialty 53.7% 11.6% 28.7% 3.6% 1.4% 0.6% 0.2% 0.1% N/A N/A International Operations: Reinsurance - Property 24.9% 34.0% 20.7% 14.5% 2.5% 1.2% 0.7% 0.4% 0.3% 0.2% Argo Insurance Bermuda - Liability N/A 20.8% 15.6% 14.8% 12.2% 9.3% 6.9% 5.1% 3.7% 2.8% Syndicate 1200 - Liability 5.8% 12.1% 13.4% 15.0% 16.0% 11.7% 6.9% 5.2% 3.7% 2.7% Syndicate 1200 - Professional 6.1% 13.7% 18.5% 17.6% 12.4% 8.7% 5.9% 4.5% 3.2% 2.3% Syndicate 1200 - Property 42.8% 30.2% 14.3% 8.4% 2.7% 0.8% 0.4% 0.2% 0.1% N/A Syndicate 1200 - Specialty 37.4% 31.0% 16.7% 9.2% 3.0% 1.5% 0.6% 0.3% 0.1% N/A (1) The average annual percentage payout is calculated from a paid losses and ALAE development pattern based on an actuarial analysis of the paid losses and ALAE movements by accident year for each disaggregation category. The paid losses and ALAE development pattern provides the expected percentage of ultimate losses and ALAE to be paid in each year. The pattern considers all accident years included in the claims development tables .
Schedule of Information About Discounted Liabilities for Unpaid Losses and LAE	The following tables provide information about these discounted liabilities for unpaid losses and LAE: Carrying Amount of Reserves for Losses & LAE Aggregate Amount of Discount As of December 31, As of December 31, (in millions, except discount percentages) 2020 2019 2018 2020 2019 2018 U.S. Operations: Specialty Admitted - Liability $ 150.4 $ 153.1 $ 140.8 $ 12.9 $ 13.0 $ 11.9 Run-off Lines 128.4 148.9 163.1 4.9 4.9 5.0 Total $ 278.8 $ 302.0 $ 303.9 $ 17.8 $ 17.9 $ 16.9 Interest Accretion (1) Discount Rate For the Years Ended December 31, As of December 31, 2020 2019 2018 2020 2019 2018 U.S. Operations: Specialty Admitted - Liability $ 1.9 $ 1.3 $ 1.3 2.25% 2.25% 2.25% Run-off Lines — 0.2 2.1 3.50% 3.50% 3.50% Total $ 1.9 $ 1.5 $ 3.4 (1) Interest accretion is recorded in the line item “Losses and loss adjustment expenses” in our Consolidated Statements of Income (Loss).

Run-off Lines (Tables)

Run-off Lines (Tables)	12 Months Ended
	Dec. 31, 2020
Discontinued Operations and Disposal Groups [Abstract]
Gross Reserves for Run-Off Lines	The following table presents our gross reserves for Run-off Lines as of December 31: December 31, (in millions) 2020 2019 Asbestos and Environmental: Reinsurance assumed $ 29.4 $ 26.7 Other 29.9 25.9 Total Asbestos and Environmental 59.3 52.6 Risk-management 162.4 188.1 Run-off reinsurance lines 0.5 0.5 Other run-off lines 14.3 12.3 Gross reserves - Run-off Lines $ 236.5 $ 253.5
Total Gross Reserves for Asbestos Exposure	The following table represents the total gross reserves for our asbestos exposure: December 31, (in millions) 2020 2019 2018 Direct written Case reserves $ 3.1 $ 2.7 $ 2.7 Unallocated loss adjustment expense ("ULAE") 0.5 0.5 0.5 Incurred but not reported ("IBNR") 20.2 16.1 19.1 Total direct written reserves 23.8 19.3 22.3 Assumed domestic Case reserves 8.4 9.1 8.7 ULAE 0.8 0.8 0.8 IBNR 12.8 11.2 12.0 Total assumed domestic reserves 22.0 21.1 21.5 Assumed London Case reserves 1.4 1.3 1.5 ULAE — — — IBNR 1.6 1.1 1.5 Total assumed London reserves 3.0 2.4 3.0 Total asbestos reserves $ 48.8 $ 42.8 $ 46.8
Underwriting Losses for Run-Off Lines	The following table presents our underwriting losses for Run-off Lines: For the Years Ended December 31, (in millions) 2020 2019 2018 Asbestos and Environmental: Reinsurance assumed $ (5.7) $ (4.4) $ (3.9) Other (11.7) (3.9) (4.1) Total Asbestos and Environmental (17.4) (8.3) (8.0) Risk-management 4.3 (4.9) (2.6) Run-off reinsurance lines 0.4 0.7 — Other run-off lines (3.4) (1.7) (5.3) Total underwriting loss - Run-off Lines $ (16.1) $ (14.2) $ (15.9)

Long-term Debt (Tables)

Long-term Debt (Tables)	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Schedule of Long-term Debt	A summary of our outstanding junior subordinated debentures is presented below: December 31, 2020 (in millions) Issue Date Trust Preferred Pools Maturity Rate Structure Interest Rate at December 31, 2020 Amount Argo Group 5/15/2003 PXRE Capital Statutory Trust II 5/15/2033 3M LIBOR + 4.10% 4.32% $ 18.0 11/6/2003 PXRE Capital Trust VI 9/30/2033 3M LIBOR + 3.90% 4.15% 10.3 Argo Group US 5/15/2003 Argonaut Group Statutory Trust I 5/15/2033 3M LIBOR + 4.10% 4.32% 15.5 12/16/2003 Argonaut Group Statutory Trust III 1/8/2034 3M LIBOR + 4.10% 4.34% 12.3 4/29/2004 Argonaut Group Statutory Trust IV 4/29/2034 3M LIBOR + 3.85% 4.07% 13.4 5/26/2004 Argonaut Group Statutory Trust V 5/24/2034 3M LIBOR + 3.85% 4.05% 12.4 5/12/2004 Argonaut Group Statutory Trust VI 6/17/2034 3M LIBOR + 3.80% 4.03% 13.4 9/17/2004 Argonaut Group Statutory Trust VII 12/15/2034 3M LIBOR + 3.60% 3.82% 15.5 9/22/2004 Argonaut Group Statutory Trust VIII 9/22/2034 3M LIBOR + 3.55% 3.79% 15.5 10/22/2004 Argonaut Group Statutory Trust IX 12/15/2034 3M LIBOR + 3.60% 3.82% 15.5 9/14/2005 Argonaut Group Statutory Trust X 9/15/2035 3M LIBOR + 3.40% 3.62% 30.9 Total Outstanding $ 172.7 December 31, 2019 (in millions) Issue Date Trust Preferred Pools Maturity Rate Structure Interest Rate at December 31, 2019 Amount Argo Group 5/15/2003 PXRE Capital Statutory Trust II 5/15/2033 3M LIBOR + 4.10% 6.01% $ 18.1 11/6/2003 PXRE Capital Trust VI 9/30/2033 3M LIBOR + 3.90% 5.84% 10.3 Argo Group US 5/15/2003 Argonaut Group Statutory Trust I 5/15/2033 3M LIBOR + 4.10% 6.01% 15.5 12/16/2003 Argonaut Group Statutory Trust III 1/8/2034 3M LIBOR + 4.10% 6.09% 12.3 4/29/2004 Argonaut Group Statutory Trust IV 4/29/2034 3M LIBOR + 3.85% 5.76% 13.4 5/26/2004 Argonaut Group Statutory Trust V 5/24/2034 3M LIBOR + 3.85% 5.76% 12.3 5/12/2004 Argonaut Group Statutory Trust VI 6/17/2034 3M LIBOR + 3.80% 5.70% 13.4 9/17/2004 Argonaut Group Statutory Trust VII 12/15/2034 3M LIBOR + 3.60% 5.49% 15.5 9/22/2004 Argonaut Group Statutory Trust VIII 9/22/2034 3M LIBOR + 3.55% 5.48% 15.5 10/22/2004 Argonaut Group Statutory Trust IX 12/15/2034 3M LIBOR + 3.60% 5.49% 15.5 9/14/2005 Argonaut Group Statutory Trust X 9/15/2035 3M LIBOR + 3.40% 5.29% 30.9 Total Outstanding $ 172.7 A summary of the terms of the acquired debt outstanding is presented below: December 31, 2020 (in millions) Issue Date Maturity Rate Structure Interest Rate at December 31, 2020 Principal at December 31, 2020 Carrying Value at December 31, 2020 9/13/2007 9/15/2037 3 month LIBOR + 3.15% 3.37 % $ 91.8 $ 85.1 December 31, 2019 (in millions) Issue Date Maturity Rate Structure Interest Rate at December 31, 2019 Principal at December 31, 2019 Carrying Value at December 31, 2019 9/13/2007 9/15/2037 3 month LIBOR + 3.15% 5.04 % $ 91.8 $ 84.7 (in millions) December 31, Debt Type 2020 2019 Floating rate loan stock $ 60.7 $ 56.3 Term loan — 125.0 Total other indebtedness $ 60.7 $ 181.3 December 31, 2020 (in millions) Currency Issue Date Maturity Rate Structure Interest Rate at December 31, 2020 Amount U.S. Dollar 12/8/2004 11/15/2034 6 month LIBOR + 4.2% 4.54% $ 6.5 U.S. Dollar 10/31/2006 1/15/2036 6 month LIBOR + 4.0% 4.34% 10.0 Total U.S. Dollar notes 16.5 Euro 9/6/2005 8/22/2035 3 month LIBOR + 4.0% 3.47% 14.7 Euro 10/31/2006 11/22/2036 3 month LIBOR + 4.0% 3.47% 12.9 Euro 6/8/2007 9/15/2037 3 month LIBOR + 3.9% 3.36% 16.6 Total Euro notes 44.2 Total notes outstanding $ 60.7 December 31, 2019 (in millions) Currency Issue Date Maturity Rate Structure Interest Rate at December 31, 2019 Amount U.S. Dollar 12/8/2004 11/15/2034 6 month LIBOR + 4.2% 6.41% $ 6.5 U.S. Dollar 10/31/2006 1/15/2036 6 month LIBOR + 4.0% 6.21% 10.0 Total U.S. Dollar notes 16.5 Euro 9/6/2005 8/22/2035 3 month LIBOR + 4.0% 3.58% 13.3 Euro 10/31/2006 11/22/2036 3 month LIBOR + 4.0% 3.58% 11.6 Euro 6/8/2007 9/15/2037 3 month LIBOR + 3.9% 3.47% 14.9 Total Euro notes 39.8 Total notes outstanding $ 56.3
Schedule of Outstanding Balance	The following table presents maturities of long-term debt as of December 31, 2020: For the Years Ended (in millions) Total 2021 2022 2023 2024 2025 Thereafter Long-term debt: Junior subordinated debentures (1) 411.0 10.1 10.1 10.1 10.1 10.1 360.5 Senior unsecured fixed rate notes (2) 347.0 9.3 9.4 9.3 9.4 9.3 300.3 Floating rate loan stock (3) 94.4 2.3 2.3 2.3 2.3 2.3 82.9 (1) Interest only on Junior Subordinated Debentures through 2037. Interest calculated based on the rate in effect at December 31, 2020. Principal due beginning May 2033. (2) Interest only on Senior Unsecured Fixed Rate Notes through 2042. Interest calculated based on the rate in effect at December 31, 2020. Principal due September 2042. (3) Interest only on Floating Rate Loan Stock through 2034. Interest calculated based on the rate in effect at December 31, 2020. Principal due beginning November 2034.

Disclosures about Fair Value _2

Disclosures about Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Summary of Company's Financial Instruments Whose Carrying Amount Did Not Equal Fair Value	A summary of our financial instruments whose carrying value did not equal fair value is shown below: December 31, 2020 2019 (in millions) Carrying Fair Carrying Fair Junior subordinated debentures: Trust preferred debentures $ 172.7 $ 173.6 $ 172.7 $ 174.0 Subordinated debentures 85.1 92.3 84.7 92.5 Total junior subordinated debentures 257.8 265.9 257.4 266.5 Senior unsecured fixed rate notes 140.2 146.7 140.0 144.2 Floating rate loan stock 60.7 61.0 56.3 56.8 Based on an analysis of the inputs, our financial instruments measured at fair value on a recurring basis have been categorized as follows: Fair Value Measurements at Reporting Date Using (in millions) December 31, 2020 Level 1 (a) Level 2 (b) Level 3 (c) Junior subordinated debentures: Trust preferred debentures $ 173.6 $ — $ 173.6 $ — Subordinated debentures 92.3 — 92.3 — Total junior subordinated debentures 265.9 — 265.9 — Senior unsecured fixed rate notes 146.7 146.7 — — Floating rate loan stock 61.0 — 61.0 — 473.6 146.7 326.9 — (a) Quoted prices in active markets for identical assets (b) Significant other observable inputs (c) Significant unobservable inputs Fair Value Measurements at Reporting Date Using (in millions) December 31, 2019 Level 1 (a) Level 2 (b) Level 3 (c) Junior subordinated debentures: Trust preferred debentures $ 174.0 $ — $ 174.0 $ — Subordinated debentures 92.5 — 92.5 — Total junior subordinated debentures 266.5 — 266.5 — Senior unsecured fixed rate notes 144.2 144.2 — — Floating rate loan stock 56.8 — 56.8 — 467.5 144.2 323.3 — (a) Quoted prices in active markets for identical assets (b) Significant other observable inputs (c) Significant unobservable inputs

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Changes in Accumulated Other Comprehensive Income (Loss)	A summary of changes in accumulated other comprehensive income (loss), net of taxes (where applicable) by component for the year ended December 31, 2020 and 2019 is presented below: (in millions) Foreign Currency Translation Adjustments Unrealized Defined Benefit Pension Plans Total Balance, January 1, 2019 $ (22.4) $ (49.0) $ (6.7) $ (78.1) Other comprehensive (loss) income before reclassifications (0.2) 73.8 (1.4) 72.2 Amounts reclassified from accumulated other comprehensive income — 8.7 — 8.7 Net current-period other comprehensive (loss) income (0.2) 82.5 (1.4) 80.9 Balance, December 31, 2019 (22.6) 33.5 (8.1) 2.8 Other comprehensive (loss) income before reclassifications (15.3) 78.7 (0.5) 62.9 Amounts reclassified from accumulated other comprehensive income — (12.8) — (12.8) Net current-period other comprehensive (loss) income (15.3) 65.9 (0.5) 50.1 Cumulative effect of adoption of ASU 2016-13 — 5.7 — 5.7 Balance, December 31, 2020 $ (37.9) $ 105.1 $ (8.6) $ 58.6
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	The amounts reclassified from accumulated other comprehensive (loss) income shown in the above table have been included in the following captions in our Consolidated Statements of Income (Loss): For the Years Ended December 31, (in millions) 2020 2019 2018 Unrealized gains and losses on securities: Net realized investment (gains) loss $ (12.8) $ 9.9 $ 5.4 Benefit for income taxes — (1.2) (0.5) Net of taxes $ (12.8) $ 8.7 $ 4.9

Net (Loss) Income Per Common _2

Net (Loss) Income Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Net Income Per Common Share on Basic and Diluted Basis	The following table presents the calculation of net (loss) income per common share on a basic and diluted basis: For the Years Ended December 31, (in millions, except number of shares and per share amounts) 2020 2019 2018 Net (loss) income $ (54.1) $ (14.1) $ 57.0 Less: Preferred share dividends 4.6 — — Net (loss) income attributable to common shareholders (58.7) (14.1) 57.0 Weighted average common shares outstanding - basic 34,614,813 34,205,954 33,922,009 Effect of dilutive securities: Equity compensation awards — — 756,772 Weighted average common shares outstanding - diluted 34,614,813 34,205,954 34,678,781 Net (loss) income per common share: Basic $ (1.70) $ (0.41) $ 1.68 Diluted $ (1.70) $ (0.41) $ 1.65

Share-based Compensation (Table

Share-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Summary of Restricted Share Activity	A summary of restricted share activity as of December 31, 2020 and changes during the year then ended is as follows: Shares Weighted-Average Outstanding at January 1, 2020 471,271 $ 60.09 Granted 399,578 $ 32.53 Vested and issued (177,918) $ 51.25 Expired or forfeited (165,057) $ 50.89 Outstanding at December 31, 2020 527,874 $ 43.37
Summary of Stock-Settled SARs Activity	A summary of stock-settled SARs activity as of December 31, 2020 and changes during the year then ended is as follows: Shares Weighted-Average Outstanding at January 1, 2020 625,368 $ 33.60 Exercised (470,182) $ 32.75 Expired or forfeited (15,031) $ 37.85 Outstanding at December 31, 2020 140,155 $ 35.98

Underwriting, Acquisition and_2

Underwriting, Acquisition and Insurance Expenses & Other Corporate Expenses (Tables)	12 Months Ended
	Dec. 31, 2020
Underwriting Acquisition And Insurance Expenses [Abstract]
Underwriting, Acquisition and Insurance Expenses	Underwriting, acquisition and insurance expenses were as follows: For the Years Ended December 31, (in millions) 2020 2019 2018 Commissions $ 268.0 $ 241.3 $ 281.3 General expenses 391.0 379.3 352.2 Premium taxes, boards and bureaus 29.7 33.0 32.5 688.7 653.6 666.0 Net deferral of policy acquisition costs (9.3) 12.4 (9.9) Total underwriting, acquisition and insurance expenses $ 679.4 $ 666.0 $ 656.1

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Tax Provision (Benefit) Expense	The following table presents the components of income tax provision (benefit) included in the amounts reported in our consolidated financial statements: For the Years Ended December 31, (in millions) 2020 2019 2018 Current income tax provision (benefit) related to: United States (Federal) $ 28.0 $ 37.3 $ 20.8 United States (State) $ 1.4 $ 1.7 $ 1.4 United Kingdom (0.1) (1.5) 3.1 Other jurisdictions — (1) 0.1 0.1 Total current income tax provision 29.3 37.6 25.4 Deferred income tax provision (benefit) related to: United States (5.1) (17.7) (21.6) United Kingdom (16.6) (5.8) 0.1 Other jurisdictions 0.1 — 0.1 Total deferred income tax (benefit) (21.6) (23.5) (21.4) Income tax provision (benefit) $ 7.7 $ 14.1 $ 4.0 (1) Tax expense for the respective year was less than $0.1 million.
Schedule of Earned Premiums by Geographic Location	For the years ended December 31, 2020, 2019 and 2018, pre-tax income (loss) attributable to our operations and the operations’ effective tax rates were as follows: (in millions) 2020 2019 2018 Pre-Tax Effective Pre-Tax Effective Pre-Tax Effective Bermuda $ (56.2) — % $ (34.7) — % $ 22.0 — % United States 103.3 22.7 % 84.7 24.6 % 12.1 (1.0) % United Kingdom (100.6) 15.7 % (45.9) 14.9 % 24.1 14.7 % Belgium 0.2 30.7 % — (1) 15.8 % — (1) — % (2) Brazil 3.9 — % 5.2 — % (0.5) — % United Arab Emirates 2.1 — % 0.4 — % 0.8 — % Ireland 1.8 — % (0.1) — % (0.2) — % Italy 0.6 — % (7.4) — % 0.9 — % Malta (1.4) — % (2.0) — % 1.7 — % Luxembourg — — % — — % — (1) — % Switzerland (0.1) — % (0.2) (0.2) % 0.1 18.4 % Pre-tax income (loss) $ (46.4) (16.6) % $ — — % (2) $ 61.0 6.6 % (1) Pre-tax income for the respective year was less than $0.1 million. (2) Not meaningful.
Reconciliation of Difference Between Provision for Income Taxes and Expected Tax Provision at Weighted Average Tax Rate	A reconciliation of the difference between the provision for income taxes and the expected tax provision (benefit) at the weighted average tax rate is as follows: For the Years Ended December 31, (in millions) 2020 2019 2018 Income tax provision (benefit) at expected rate $ 4.0 $ 8.9 $ 7.7 Tax effect of: Nontaxable investment income (0.7) (1.2) (1.9) Foreign exchange adjustments 1.6 (0.1) (0.6) Impairment of goodwill 1.0 2.9 — Withholding taxes 0.1 0.2 0.4 Change in uncertain tax position liability 0.7 1.4 1.8 Change in valuation allowance 0.5 (1.8) (1.5) Impact of change in tax rate related to TCJA — — (0.8) Other 0.5 3.8 (1.1) Income tax provision (benefit) $ 7.7 $ 14.1 $ 4.0
Schedule of Net Deferred Tax Liability Comprises Tax Effect Related to Assets and Liabilities	The net deferred tax asset (liability) comprises the tax effects of temporary differences related to the following assets and liabilities: December 31, (in millions) 2020 2019 Deferred tax assets: Losses and loss adjustment expense reserve discounting $ 29.2 $ 24.6 Unearned premiums 25.9 25.3 Net operating loss carryforwards 27.9 28.3 Investment in limited partnership interests 7.8 10.3 Investments 2.0 2.2 Right of use assets 12.7 14.5 Accrued compensation 6.3 3.8 Stock option expense 0.7 1.1 United Kingdom underwriting results 21.9 4.2 Other 9.6 6.3 Deferred tax assets, gross 144.0 120.6 Deferred tax liabilities: Unrealized gains on equity securities (5.7) (2.6) Unrealized gains on fixed maturities and other investment securities (22.3) (6.1) Unrealized gains on limited partnership interests (14.7) (15.6) Depreciable fixed assets (20.5) (21.6) Deferred acquisition costs (20.4) (18.6) Lease liability (11.7) (14.0) TCJA reserve transitional liability (2.7) (3.2) Other (0.7) (0.2) Deferred tax liabilities, gross (98.7) (81.9) Deferred tax assets, net before valuation allowance $ 45.3 $ 38.7 Valuation allowance (28.6) (28.1) Deferred tax asset (liabilities), net $ 16.7 $ 10.6 Net deferred tax assets (liabilities) - Other jurisdictions $ 21.4 $ 4.4 Net deferred tax liabilities - United States (4.7) 6.2 (1) Deferred tax asset (liabilities), net $ 16.7 $ 10.6 (1) Net deferred tax liability for the respective year was less than $0.1 million.
Schedule of Net Operating Loss Carryforwards Amounts by Jurisdiction and Year of Expiration	The NOL amounts by jurisdiction and year of expiration are as follows: (in millions) December 31, 2020 Expiration Net operating loss carryforwards by jurisdiction: Brazil $ 0.7 Indefinite Italy 49.6 Indefinite Malta 14.3 Indefinite United States 43.3 2025 - 2037
Schedule of Unrecognized Tax Benefits	The following is a reconciliation of the beginning and ending amount of unrecognized tax benefits for the years ended December 31, 2020 and 2019: (in millions) 2020 2019 Balance at January 1 $ 7.5 $ 6.1 Additions for tax positions of prior years — — Reductions for tax positions of prior years — — Additions based on tax positions related to current year 0.7 1.4 Reductions based on tax positions related to current year — — Reductions based on settlements with taxing authorities — — Expiration of statute of limitations — — Balance at December 31 $ 8.2 $ 7.5

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
Revenue and Income (Loss) Before Income Taxes for Each Segment	Revenue and income before income taxes for each segment were as follows: For the Years Ended December 31, (in millions) 2020 2019 2018 Revenue: Earned premiums U.S. Operations $ 1,207.6 $ 1,119.9 $ 1,078.7 International Operations 572.5 609.6 652.5 Run-off Lines 0.4 0.2 0.3 Total earned premiums 1,780.5 1,729.7 1,731.5 Net investment income U.S. Operations 80.3 100.0 82.9 International Operations 26.7 44.2 32.9 Run-off Lines 4.0 5.7 8.1 Corporate and Other 1.7 1.2 8.4 Total net investment income 112.7 151.1 132.3 Fee and other income 7.9 9.1 9.0 Net realized investment (losses) gains (7.2) 80.1 (72.0) Total revenue $ 1,893.9 $ 1,970.0 $ 1,800.8 For the Years Ended December 31, (in millions) 2020 2019 2018 Income (loss) before income taxes U.S. Operations $ 111.7 $ 139.3 $ 161.2 International Operations (82.1) (137.0) 32.0 Run-off Lines (12.9) (9.8) (9.3) Total segment income (loss) before taxes 16.7 (7.5) 183.9 Corporate and Other (34.7) (44.8) (47.0) Net realized investment and other (losses) gains (7.2) 80.1 (72.0) Foreign currency exchange (losses) gains (15.4) 9.8 (3.9) Other corporate expenses (5.8) (37.6) — Total (loss) income before income taxes $ (46.4) $ — $ 61.0
Schedule of Earned Premiums by Geographic Location	The table below presents earned premiums by geographic location for the years ended December 31, 2020, 2019 and 2018. For this disclosure, we determine geographic location by the country of domicile of our subsidiaries that underwrite the business and not by the location of insureds or reinsureds from whom the business was generated. For the Years Ended December 31, (in millions) 2020 2019 2018 United States $ 1,205.0 $ 1,115.8 $ 1,072.9 United Kingdom 361.1 391.5 455.8 Bermuda 96.5 80.7 85.4 Malta 59.5 85.0 61.0 All other jurisdictions 58.4 56.7 56.4 Total earned premiums $ 1,780.5 $ 1,729.7 $ 1,731.5
Identifiable Assets	The following table represents identifiable assets: December 31, (in millions) 2020 2019 U.S. Operations $ 6,032.2 $ 5,013.7 International Operations 3,899.4 4,996.0 Run-off Lines 335.9 356.9 Corporate and Other 198.3 142.2 Total $ 10,465.8 $ 10,508.8
Schedule of Goodwill and Intangible Assets Net of Accumulated Amortization	The following table represents goodwill and intangible assets, net of accumulated amortization, as of December 31, 2020 and 2019: Goodwill Intangible Assets, Net of (in millions) 2020 2019 2020 2019 U.S. Operations $ 118.6 $ 123.5 $ — $ — International Operations 28.7 37.9 60.5 91.8 Total $ 147.3 $ 161.4 $ 60.5 $ 91.8

Statutory Accounting Principl_2

Statutory Accounting Principles (Tables)	12 Months Ended
	Dec. 31, 2020
Statutory Accounting Principles [Abstract]
Statutory Capital and Surplus for Principal Operating Subsidiaries	The statutory capital and surplus for our principal operating subsidiaries was as follows: Statutory capital and surplus (1) December 31, (in millions) 2020 2019 Bermuda $ 1,482.8 $ 1,460.8 United Kingdom (2) 534.7 443.1 United States 1,072.1 1,051.4 (1) Such amounts include ownership interests in affiliate insurance and reinsurance subsidiaries. (2) Capital on deposit with Lloyd’s in U.S. dollars
Statutory Net Income (Loss) for Principal Operating Subsidiaries	The statutory net income (loss) for our principal operating subsidiaries was as follows: Statutory net income (loss) (1) For the Years Ended December 31, (in millions) 2020 2019 2018 Bermuda $ (35.9) $ 7.1 $ 47.4 United Kingdom (2) (53.0) (15.1) (9.5) United States 76.4 196.1 110.8 (1) Such amounts include ownership interests in affiliate insurance and reinsurance subsidiaries. (2) In U.S. dollars

Senior Unsecured Fixed Rate N_2

Senior Unsecured Fixed Rate Notes (Tables)	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Schedule Of Unamortized Debt Issuance Costs Deducted From Carrying Value Of Debt Liability	At December 31, 2020 and 2019, the Notes consisted of the following: (in millions) December 31, 2020 December 31, 2019 Senior unsecured fixed rate notes Principal $ 143.8 $ 143.8 Less: unamortized debt issuance costs (3.6) (3.8) Senior unsecured fixed rate notes, less unamortized debt issuance costs $ 140.2 $ 140.0
Condensed Consolidating Balance Sheet	CONDENSED CONSOLIDATING BALANCE SHEET DECEMBER 31, 2020 (in millions) Argo Group Argo Group Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Assets Investments $ 0.6 $ 3,628.8 $ 1,626.4 $ — $ 5,255.8 Cash 3.0 17.4 128.4 — 148.8 Accrued investment income — 16.7 5.1 — 21.8 Premiums receivable — 267.5 412.3 — 679.8 Reinsurance recoverables — 1,761.2 1,247.8 — 3,009.0 Goodwill and other intangible assets, net — 118.5 89.3 — 207.8 Current income taxes receivable, net — (5.6) 8.6 — 3.0 Deferred tax assets, net — (4.6) 21.3 — 16.7 Deferred acquisition costs, net — 97.1 66.5 — 163.6 Ceded unearned premiums — 340.6 234.5 — 575.1 Operating lease right-of-use assets 6.2 51.7 24.1 — 82.0 Other assets 14.5 153.5 126.7 — 294.7 Assets held for sale — 7.4 0.3 — 7.7 Intercompany note receivable — 59.0 (59.0) — — Investments in subsidiaries 1,881.9 — — (1,881.9) — Total assets $ 1,906.2 $ 6,509.2 $ 3,932.3 $ (1,881.9) $ 10,465.8 Liabilities and Shareholders' Equity Reserves for losses and loss adjustment expenses $ — $ 3,348.7 $ 2,057.3 $ — $ 5,406.0 Unearned premiums — 951.2 513.6 — 1,464.8 Funds held and ceded reinsurance payable, net — 489.0 526.1 — 1,015.1 Debt 28.4 284.5 145.8 — 458.7 Accrued underwriting expenses and other liabilities 6.3 67.8 93.5 — 167.6 Operating lease liabilities 6.2 60.4 29.2 — 95.8 Due to (from) affiliates 7.5 0.9 (0.9) (7.5) — Total liabilities 48.4 5,202.5 3,364.6 (7.5) 8,608.0 Total shareholders' equity 1,857.8 1,306.7 567.7 (1,874.4) 1,857.8 Total liabilities and shareholders' equity $ 1,906.2 $ 6,509.2 $ 3,932.3 $ (1,881.9) $ 10,465.8 (1) Includes all other subsidiaries of Argo Group and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING BALANCE SHEET DECEMBER 31, 2019 (in millions) Argo Group Argo Group Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Assets Investments $ 0.6 $ 3,405.6 $ 1,691.3 $ — $ 5,097.5 Cash 1.9 31.6 104.3 — 137.8 Accrued investment income — 18.2 7.5 — 25.7 Premiums receivable — 236.0 440.5 — 676.5 Reinsurance recoverables — 1,689.4 1,417.8 — 3,107.2 Goodwill and other intangible assets, net 40.6 123.4 89.2 — 253.2 Deferred tax assets, net — 6.8 3.8 — 10.6 Deferred acquisition costs, net — 88.4 71.8 — 160.2 Ceded unearned premiums — 306.4 238.6 — 545.0 Operating lease right-of-use assets 7.1 59.6 25.1 — 91.8 Other assets 7.8 165.8 214.3 — 387.9 Assets held for sale — 15.4 — — 15.4 Intercompany note receivable — 56.7 (56.7) — — Investments in subsidiaries 1,899.3 — — (1,899.3) — Total assets $ 1,957.3 $ 6,203.3 $ 4,247.5 $ (1,899.3) $ 10,508.8 Liabilities and Shareholders' Equity Reserves for losses and loss adjustment expenses $ — $ 3,037.5 $ 2,120.1 $ — $ 5,157.6 Unearned premiums — 899.8 511.1 — 1,410.9 Funds held and ceded reinsurance payable, net — 650.6 605.8 — 1,256.4 Debt 153.4 284.3 141.0 — 578.7 Current income taxes payable, net — 21.3 (7.4) — 13.9 Accrued underwriting expenses and other liabilities 13.6 89.5 118.8 — 221.9 Operating lease liabilities 7.3 68.9 29.5 — 105.7 Due to (from) affiliates 19.3 (13.4) 13.4 (19.3) — Total liabilities 193.6 5,038.5 3,532.3 (19.3) 8,745.1 Total shareholders' equity 1,763.7 1,164.8 715.2 (1,880.0) 1,763.7 Total liabilities and shareholders' equity $ 1,957.3 $ 6,203.3 $ 4,247.5 $ (1,899.3) $ 10,508.8 (1) Includes all other subsidiaries of Argo Group and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations.
Condensed Consolidating Statement of Income	CONDENSED CONSOLIDATING STATEMENT OF INCOME (LOSS) FOR THE YEAR ENDED DECEMBER 31, 2020 (in millions) Argo Group Argo Group Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Premiums and other revenue: Earned premiums $ — $ 1,204.3 $ 576.2 $ — $ 1,780.5 Net investment income — 87.3 25.4 — 112.7 Fee and other income — 2.6 5.3 — 7.9 Net realized investment (losses) gains (8.3) 4.5 (3.4) — (7.2) Total revenue (8.3) 1,298.7 603.5 — 1,893.9 Expenses: Losses and loss adjustment expenses — 764.5 444.3 — 1,208.8 Underwriting, acquisition and insurance expenses 20.4 411.0 248.0 — 679.4 Other corporate expenses 4.4 1.4 — — 5.8 Interest expense 3.6 16.7 6.6 — 26.9 Fee and other expense — 2.1 1.9 — 4.0 Foreign currency exchange (gains) losses — (0.4) 15.8 — 15.4 Total expenses 28.4 1,195.3 716.6 — 1,940.3 (Loss) income before income taxes (36.7) 103.4 (113.1) — (46.4) Provision (benefit) for income taxes — 23.6 (15.9) — 7.7 Net (loss) income before equity in earnings of subsidiaries (36.7) 79.8 (97.2) — (54.1) Equity in undistributed earnings of subsidiaries (17.4) — — 17.4 — Net (loss) income $ (54.1) $ 79.8 $ (97.2) $ 17.4 $ (54.1) Dividends on preferred shares 4.6 $ — $ — $ — 4.6 Net (loss) income attributable to common shareholders $ (58.7) $ 79.8 $ (97.2) $ 17.4 $ (58.7) (1) Includes all other subsidiaries of Argo Group and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF INCOME (LOSS) FOR THE YEAR ENDED DECEMBER 31, 2019 (in millions) Argo Group Argo Group Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Premiums and other revenue: Earned premiums $ — $ 1,044.1 $ 685.6 $ — $ 1,729.7 Net investment (expenses) income (2.9) 103.3 50.7 — 151.1 Fee and other income — 3.2 5.9 — 9.1 Net realized investment (losses) gains (0.1) 80.9 (0.7) — 80.1 Total revenue (3.0) 1,231.5 741.5 — 1,970.0 Expenses: Losses and loss adjustment expenses — 696.8 523.9 — 1,220.7 Underwriting, acquisition and insurance expenses 1.3 415.4 249.3 — 666.0 Other corporate expenses 26.8 10.8 — — 37.6 Interest expense 6.6 18.9 8.6 — 34.1 Fee and other expense — 4.2 1.6 — 5.8 Foreign currency exchange losses (gains) — 0.7 (10.5) — (9.8) Impairment of goodwill — — 15.6 — 15.6 Total expenses 34.7 1,146.8 788.5 — 1,970.0 (Loss) income before income taxes (37.7) 84.7 (47.0) — — Provision (benefit) for income taxes — 20.9 (6.8) — 14.1 Net (loss) income before equity in earnings of subsidiaries (37.7) 63.8 (40.2) — (14.1) Equity in undistributed earnings of subsidiaries 23.6 — — (23.6) — Net (loss) income attributable to common shareholders $ (14.1) $ 63.8 $ (40.2) $ (23.6) $ (14.1) (1) Includes all other subsidiaries of Argo Group and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF INCOME FOR THE YEAR ENDED DECEMBER 31, 2018 (in millions) Argo Group Argo Group Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Premiums and other revenue: Earned premiums $ — $ 861.7 $ 869.8 $ — $ 1,731.5 Net investment (expense) income (2.7) 78.6 56.4 — 132.3 Fee and other income — 4.4 4.6 — 9.0 Net realized investment gains (losses) 2.5 (51.3) (20.5) (2.7) (72.0) Total revenue (0.2) 893.4 910.3 (2.7) 1,800.8 Expenses: Losses and loss adjustment expenses — 523.7 517.1 — 1,040.8 Underwriting, acquisition and insurance expenses 11.3 334.1 310.7 — 656.1 Interest expense 6.2 18.5 7.2 — 31.9 Fee and other expense — 5.3 1.8 — 7.1 Foreign currency exchange losses — 0.2 3.7 — 3.9 Total expenses 17.5 881.8 840.5 — 1,739.8 (Loss) income before income taxes (17.7) 11.6 69.8 (2.7) 61.0 Benefit for income taxes — 0.1 3.9 — 4.0 Net (loss) income before equity in earnings of subsidiaries (17.7) 11.5 65.9 (2.7) 57.0 Equity in undistributed earnings of subsidiaries 74.7 — — (74.7) — Net (loss) income attributable to common shareholders $ 57.0 $ 11.5 $ 65.9 $ (77.4) $ 57.0 (1) Includes all other subsidiaries of Argo Group and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations.
Condensed Consolidating Statement of Cash Flows	CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS FOR YEAR ENDED DECEMBER 31, 2020 (in millions) Argo Group Argo Group Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Net cash flows from operating activities $ 5.0 $ 98.9 $ (32.0) $ — $ 71.9 Cash flows from investing activities: Proceeds from sales of investments — 711.4 497.9 — 1,209.3 Maturities and mandatory calls of fixed maturity investments — 427.7 142.1 — 569.8 Purchases of investments — (1,624.0) (528.5) — (2,152.5) Change in short-term investments and foreign regulatory deposits — 310.7 (30.7) — 280.0 Settlements of foreign currency exchange forward contracts 0.1 (1.8) 11.1 — 9.4 Capital contribution to subsidiaries (145.3) — — 145.3 — Dividend received from subsidiaries 13.1 — — (13.1) — Proceeds from sale of Ariel Re, net of cash transferred 30.0 — (1.7) 28.3 Proceeds from sale of Trident assets — 38.0 — 38.0 Purchases of fixed assets and other, net — 24.9 (31.5) — (6.6) Cash (used in) provided by investing activities (102.1) (113.1) 58.7 132.2 (24.3) Cash flows from financing activities: Payment on long-term debt — — (125.0) — (125.0) Issuance of preferred shares, net of issuance costs 144.0 — — 144.0 Capital contribution from parent — — 145.3 (145.3) — Payment of cash dividend to parent — — (13.1) 13.1 — Activity under stock incentive plans 1.8 — — — 1.8 Payment of cash dividends to preferred shareholders (4.6) — — — (4.6) Payment of cash dividend to common shareholders (43.0) — — — (43.0) Cash provided by (used in) financing activities 98.2 — 7.2 (132.2) (26.8) Effect of exchange rate changes on cash — — (9.8) — (9.8) Change in cash 1.1 (14.2) 24.1 — 11.0 Cash, beginning of year 1.9 31.6 104.3 — 137.8 Cash, end of period $ 3.0 $ 17.4 $ 128.4 $ — $ 148.8 (1) Includes all other subsidiaries of Argo Group and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS FOR YEAR ENDED DECEMBER 31, 2019 (in millions) Argo Group Argo Group Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Net cash flows from operating activities $ 38.4 $ 124.3 $ 20.1 $ — $ 182.8 Cash flows from investing activities: Proceeds from sales of investments — 1,297.3 554.8 — 1,852.1 Maturities and mandatory calls of fixed maturity investments — 292.8 229.4 — 522.2 Purchases of investments — (1,303.8) (680.2) — (1,984.0) Change in short-term investments and foreign regulatory deposits 3.2 (351.4) (142.2) — (490.4) Settlements of foreign currency exchange forward contracts (0.2) 1.8 (1.3) — 0.3 Purchases of fixed assets and other, net — (41.4) (1.6) — (43.0) Cash provided by (used in) investing activities 3.0 (104.7) (41.1) — (142.8) Cash flows from financing activities: Payment on the intercompany note — (19.1) 19.1 — — Payment on note payable — (0.6) — — (0.6) Activity under stock incentive plans 1.9 — — — 1.9 Payment of cash dividend to common shareholders (43.1) — — — (43.1) Cash (used in) provided by financing activities (41.2) (19.7) 19.1 — (41.8) Effect of exchange rate changes on cash — — (0.1) — (0.1) Change in cash 0.2 (0.1) (2.0) — (1.9) Cash, beginning of year 1.7 31.7 106.3 — 139.7 Cash, end of period $ 1.9 31.6 104.3 — 137.8 (1) Includes all other subsidiaries of Argo Group and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS FOR YEAR ENDED DECEMBER 31, 2018 (in millions) Argo Group Argo Group Other Subsidiaries and Eliminations (1) Consolidating Adjustments ( 2) Total Net cash flows from operating activities $ 72.4 $ 182.4 $ 47.0 $ — $ 301.8 Cash flows from investing activities: Proceeds from sales of investments — 1,067.7 532.1 — 1,599.8 Maturities and mandatory calls of fixed maturity investments — 344.9 73.7 — 418.6 Purchases of investments — (1,508.3) (640.8) — (2,149.1) Change in short-term investments and foreign regulatory deposits (3.4) (105.0) (10.8) — (119.2) Settlements of foreign currency exchange forward contracts (0.5) 2.2 (3.2) — (1.5) Cash acquired with acquisition of ArgoGlobal Assicurazioni — — 15.6 — 15.6 Purchases of fixed assets and other, net (0.1) (19.0) (13.4) — (32.5) Cash used in investing activities (4.0) (217.5) (46.8) — (268.3) Cash flows from financing activities: Borrowing under the intercompany note — 19.0 (19.0) — — Activity under stock incentive plans 1.6 — — — 1.6 Repurchase of Company's common shares (31.7) — — — (31.7) Payment of cash dividend to common shareholders (37.5) — — — (37.5) Cash (used in) provided by financing activities (67.6) 19.0 (19.0) — (67.6) Effect of exchange rate changes on cash — — (2.8) — (2.8) Change in cash 0.8 (16.1) (21.6) — (36.9) Cash, beginning of year 0.9 47.8 127.9 — 176.6 Cash, end of year $ 1.7 $ 31.7 $ 106.3 $ — $ 139.7 (1) Includes all other subsidiaries of Argo Group and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations.

Business and Significant Acco_4

Business and Significant Accounting Policies - Additional Information (Detail) $ in Millions	Nov. 25, 2020USD ($)	Apr. 30, 2020USD ($)	Mar. 21, 2018shares	Feb. 20, 2018shares	Jan. 31, 2021property	Dec. 31, 2020USD ($)	Dec. 31, 2020USD ($)segmenttrustpropertyfoundation	Dec. 31, 2019USD ($)property	Dec. 31, 2018USD ($)	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Jan. 01, 2020USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2017USD ($)
Business And Significant Accounting Policies [Line Items]
Number of reportable segments | segment							2
Percentage of contractual participation							100.00%
Number of statutory trusts | trust							11
Number of charitable foundations | foundation							1
Stock dividend declared (in percentage)									15.00%
Estimated liability for return of premiums							$ 6.5	$ 5.4
Estimated amount of premiums receivables due							0.2	0.3
Impairment of goodwill						$ 15.6	0	15.6	$ 0
Amortization expense							1.1	1.7	3.3
Accumulated depreciation for property and equipment						163.3	163.3	153.2
Net book value of property and equipment						130.4	130.4	140.4
Depreciation expense							$ 24.1	$ 24.4	24.5
Number of properties held for sale | property								4
Number of properties sold | property							2
Assets held for sale						7.7	$ 7.7	$ 15.4
Foreign currency translation adjustment						(37.9)	(37.9)	22.6
Decrease in stockholder's equity						(1,857.8)	(1,857.8)	(1,763.7)	(1,735)	$ (1,848.7)	$ (1,707.7)	$ (1,613.5)		$ (1,875.4)	$ (1,911.9)	$ (1,865.3)	$ (1,812.9)
Subsequent Event
Business And Significant Accounting Policies [Line Items]
Number of properties sold | property					1
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Trident
Business And Significant Accounting Policies [Line Items]
Goodwill derecognized		$ 4.9
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Ariel Re
Business And Significant Accounting Policies [Line Items]
Goodwill derecognized	$ 9.2
Intangible assets derecognized	$ 30.2
Disposal Group, Held-for-sale, Not Discontinued Operations
Business And Significant Accounting Policies [Line Items]
Assets held for sale						7.7	7.7	15.4
Disposal Group, Held-for-sale, Not Discontinued Operations | Other Corporate Expense
Business And Significant Accounting Policies [Line Items]
Asset held for sale reclassification losses, pre-tax							0.8	3.7
Retained Earnings
Business And Significant Accounting Policies [Line Items]
Decrease in stockholder's equity						(684.1)	(684.1)	(793.7)	(850.9)								(970.2)
AOCI Attributable to Parent
Business And Significant Accounting Policies [Line Items]
Decrease in stockholder's equity						$ (58.6)	$ (58.6)	(2.8)	$ 78.1								$ (96.6)
Cumulative Effect, Period of Adoption, Adjustment
Business And Significant Accounting Policies [Line Items]
Decrease in stockholder's equity								2.2					$ 2.2
Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings
Business And Significant Accounting Policies [Line Items]
Decrease in stockholder's equity								7.9					7.9
Cumulative Effect, Period of Adoption, Adjustment | AOCI Attributable to Parent
Business And Significant Accounting Policies [Line Items]
Decrease in stockholder's equity								$ (5.7)					$ 5.7
Minimum
Business And Significant Accounting Policies [Line Items]
Useful life							3 years
Maximum
Business And Significant Accounting Policies [Line Items]
Useful life							39 years
Stock Dividend
Business And Significant Accounting Policies [Line Items]
Stock dividend declared (in percentage)				15.00%
Additional stock issued as dividend (in shares) | shares			4,397,520	4,397,520

Business and Significant Acco_5

Business and Significant Accounting Policies - Intangible Assets and Accumulated Amortization (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 112.2	$ 147.3
Accumulated Amortization	51.7	55.5
Lloyd's capacity
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	60.5	89
Distribution network
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	45.5	50.2
Accumulated Amortization	45.5	48.2
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	6.2	8.1
Accumulated Amortization	$ 6.2	$ 7.3

Business and Significant Acco_6

Business and Significant Accounting Policies - Schedule of Interest Paid (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure - Business and Significant Accounting Policies - Supplemental Cash Flow Information - Schedule of Interest Paid (Detail) [Line Items]
Total interest paid	$ 26.4	$ 33.1	$ 31.3
Income taxes paid	47.7	24	0
Income taxes recovered	(1.8)	(0.1)	24.8
Income taxes paid, net	45.9	23.9	24.8
Senior unsecured fixed rate notes
Disclosure - Business and Significant Accounting Policies - Supplemental Cash Flow Information - Schedule of Interest Paid (Detail) [Line Items]
Total interest paid	9.3	9.3	9.3
Junior subordinated debentures
Disclosure - Business and Significant Accounting Policies - Supplemental Cash Flow Information - Schedule of Interest Paid (Detail) [Line Items]
Total interest paid	11.9	16.2	15.5
Other indebtedness
Disclosure - Business and Significant Accounting Policies - Supplemental Cash Flow Information - Schedule of Interest Paid (Detail) [Line Items]
Total interest paid	$ 5.2	$ 7.6	$ 6.5

Revisions of Previously Issue_2

Revisions of Previously Issued Financial Statements - Adjusted Consolidated Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Fixed maturities available-for-sale, at fair value	$ 4,107.1				$ 3,629.9
Equity securities available-for-sale, at fair value	176.7			$ 144.5	136	$ 412.2	$ 432.6	$ 414.8	$ 366.1
Other investments	429.4			412.5	486.6	490.1	499.5	473.4	479.9		$ 544.4
Total investments	5,255.8			4,813.1	5,097.5	5,128.7	4,879.3	4,905.2
Cash	148.8				137.8				139.7
Premiums receivable	679.8	$ 790.2	$ 785	718.2	676.5	727.5	716.8	664.9	645.2		594
Reinsurance recoverables	3,009				3,107.2				2,689.2
Current income taxes receivable, net		7.5				0	0	0	0		0.2
Deferred tax assets, net	16.7	14.8	15.9	40.9	10.6				1.3
Other assets	294.7	358.6	414.5	434.8	387.9	390.5					309.8
Investment in subsidiaries	0				0
Total assets	10,465.8	10,721.7	10,378.3	10,177.9	10,508.8	10,434.4	10,153.4	9,942.9
Accrued underwriting expenses and other liabilities	167.6	205.3	157	187.4	221.9	285.7	281	249.5	263		146.6
Ceded reinsurance payable, net	950.4	1,085.7	1,038	1,086	1,201.2	1,172.8	1,050.8	1,046.4	969.2		734.4
Funds held	64.7				55.2				44.4
Current income taxes payable, net	0		33.5	24.3	13.9	9.8	6.2	5.1	2.4
Deferred tax liabilities, net						17.8	23.4	18.7	0		33.2
Total liabilities	8,608	8,873	8,670.6	8,564.4	8,745.1	8,559	8,241.5	8,077.6
Retained earnings	684.1	698.4	734.4	750.4	793.7	907	942.8	927.7	850.9		970.2
Shareholders' equity	1,857.8	1,848.7	1,707.7	1,613.5	1,763.7	1,875.4	1,911.9	1,865.3		$ 1,735		$ 1,812.9
Total liabilities and shareholders' equity	10,465.8	10,721.7	10,378.3	10,177.9	10,508.8	10,434.4	10,153.4	9,942.9
Argo Group
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total investments	0.6				0.6
Cash	3				1.9					$ 1.7		$ 0.9
Premiums receivable	0				0
Reinsurance recoverables	0				0
Deferred tax assets, net	0				0
Other assets	14.5				7.8
Investment in subsidiaries	1,881.9				1,899.3
Total assets	1,906.2				1,957.3
Accrued underwriting expenses and other liabilities	6.3				13.6
Current income taxes payable, net					0
Total liabilities	48.4				193.6
Shareholders' equity	1,857.8				1,763.7
Total liabilities and shareholders' equity	$ 1,906.2				1,957.3
Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Fixed maturities available-for-sale, at fair value					3,633.5
Equity securities available-for-sale, at fair value				132.9	124.4	400.6	421	403.2	354.5
Other investments				422.4	496.5	500	509.4	483.3	489.8		543.6
Total investments				4,811.4	5,099.4	5,127	4,877.6	4,903.5
Cash									139.2
Premiums receivable		797	800.2	739.1	688.2	740.3	728	673.2	649.9		598.6
Reinsurance recoverables					3,104.6				2,688.3
Current income taxes receivable, net		11.2				0.2	3.8	5	8.2		1.4
Deferred tax assets, net		17	18.9	44.5	6.1				0
Other assets		358.5	414.7	435.4	387.1	390.6					309.6
Total assets		10,734.3	10,396.7	10,201.3	10,514.5	10,445.8	10,166.7	9,954.5
Accrued underwriting expenses and other liabilities		202.8	154.8	185.3	226	283.9	279.4	248.2	261.9		146.9
Ceded reinsurance payable, net		1,085	1,042.7	1,094.8	1,203.1	1,175.7	1,052.8	1,047.1	970.5		734
Funds held					50.6				37.2
Current income taxes payable, net			27.1	17.7	0.8	0	0	0	0
Deferred tax liabilities, net						19.9	25.4	20.7	6.2		31.3
Total liabilities		8,869.8	8,666.7	8,564.5	8,733.4	8,552.4	8,237.7	8,073.9
Retained earnings		714.2	756.7	773.7	811.1	925	959.9	943	862.6		977
Shareholders' equity		1,864.5	1,730	1,636.8	1,781.1	1,893.4	1,929	1,880.6
Total liabilities and shareholders' equity		10,734.3	10,396.7	10,201.3	10,514.5	10,445.8	10,166.7	9,954.5
Previously Reported | Argo Group
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Investment in subsidiaries					1,916.7
Total assets					1,974.7
Shareholders' equity					1,781.1
Total liabilities and shareholders' equity					1,974.7
Revision of Prior Period, Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Fixed maturities available-for-sale, at fair value					(3.6)
Equity securities available-for-sale, at fair value				11.6	11.6	11.6	11.6	11.6	11.6
Other investments				(9.9)	(9.9)	(9.9)	(9.9)	(9.9)	(9.9)		0.8
Total investments				1.7	(1.9)	1.7	1.7	1.7
Cash									0.5
Premiums receivable		(6.8)	(15.2)	(20.9)	(11.7)	(12.8)	(11.2)	(8.3)	(4.7)		(4.6)
Reinsurance recoverables					2.6				0.9
Current income taxes receivable, net		(3.7)				(0.2)	(3.8)	(5)	(8.2)		(1.2)
Deferred tax assets, net		(2.2)	(3)	(3.6)	4.5				1.3
Other assets		0.1	(0.2)	(0.6)	0.8	(0.1)					0.2
Total assets		(12.6)	(18.4)	(23.4)	(5.7)	(11.4)	(13.3)	(11.6)
Accrued underwriting expenses and other liabilities		2.5	2.2	2.1	(4.1)	1.8	1.6	1.3	1.1		(0.3)
Ceded reinsurance payable, net		0.7	(4.7)	(8.8)	(1.9)	(2.9)	(2)	(0.7)	(1.3)		0.4
Funds held					4.6				7.2
Current income taxes payable, net			6.4	6.6	13.1	9.8	6.2	5.1	2.4
Deferred tax liabilities, net						(2.1)	(2)	(2)	(6.2)		1.9
Total liabilities		3.2	3.9	(0.1)	11.7	6.6	3.8	3.7
Retained earnings		(15.8)	(22.3)	(23.3)	(17.4)	(18)	(17.1)	(15.3)	$ (11.7)		$ (6.8)
Shareholders' equity		(15.8)	(22.3)	(23.3)	(17.4)	(18)	(17.1)	(15.3)
Total liabilities and shareholders' equity		$ (12.6)	$ (18.4)	$ (23.4)	(5.7)	$ (11.4)	$ (13.3)	$ (11.6)
Revision of Prior Period, Adjustment | Argo Group
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Investment in subsidiaries					(17.4)
Total assets					(17.4)
Shareholders' equity					(17.4)
Total liabilities and shareholders' equity					$ (17.4)

Revisions of Previously Issue_3

Revisions of Previously Issued Financial Statements - Adjusted Condensed Consolidating Statement of Income (Loss) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended							6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Earned premiums				$ 425.8	$ 451.5	$ 431.7	$ 420.7		$ 852.4		$ 1,303.9	$ 1,780.5	$ 1,729.7	$ 1,731.5
Net investment income		$ 1.4	$ 35.6					$ 37				112.7	151.1	132.3
Net realized investment gains (losses)	$ (5.7)	11.1	27.8					38.9		$ 33.2		22.4	120.9	33.1
Change in fair value of equity securities	10.5	15.1						(24.2)		(13.7)		10.3	(40.8)	(105.1)
Net realized investment (losses) gains	(5.7)	18.4	(36.2)	21.8				(17.8)		(23.5)		(7.2)	80.1	(72)
Total revenue	483.5	455.2	436.5	484.6	487.4	488.6	509.4	891.7	998	1,375.2	1,485.4	1,893.9	1,970	1,800.8
Underwriting, acquisition and insurance expenses	164.5	161.3	168.1	180.2	164	161.6		329.4	321.8	493.9	485.8	679.4	666	656.1
Interest expense	6.9	7	7.8	8.4	7.7	9.4	8.6	14.8	18	21.7	25.7	26.9	34.1	31.9
Foreign currency exchange loss	8.4	4.3	0.9	(4.5)	(0.9)	(3.8)	(0.6)	5.2	(4.4)	13.6	(5.3)	15.4	(9.8)	3.9
Total expenses	510	449.3	462.2	586.8	514.5	460.8	407.9	911.5	868.7	1,421.5	1,383.2	1,940.3	1,970	1,739.8
(Loss) income before income taxes	(26.5)	5.9	(25.7)	(102.2)	(27.1)	27.8	101.5	(19.8)	129.3	(46.3)	102.2	(46.4)	0	61
Income tax provision	(3.4)	11.3	(1)	0.5	(1.1)	0.8	13.9	10.3	14.7	6.9	13.6	7.7	14.1	4
Equity in undistributed earnings of subsidiaries												0	0	0
Net (loss) income	(23.1)	$ (5.4)	$ (24.7)	$ (102.7)	(26)	$ 27	$ 87.6	$ (30.1)	$ 114.6	(53.2)	88.6	(54.1)	(14.1)	57
Net (loss) income attributable to common shareholders	$ (25.1)				$ (26)					$ (55.2)	$ 88.6	$ (58.7)	$ (14.1)	$ 57
Net (loss) income attributable to common shareholders per common share:
Basic (in dollars per share)	$ (0.72)	$ (0.16)	$ (0.72)	$ (2.99)	$ (0.76)	$ 0.79	$ 2,580,000	$ (0.87)	$ 3.36	$ (1.60)	$ 2.59	$ (1.70)	$ (0.41)	$ 1.68
Diluted (in dollars per share)	$ (0.72)	$ (0.16)	$ (0.72)	$ (2.99)	$ (0.76)	$ 0.78	$ 2,520,000	$ (0.87)	$ 3.30	$ (1.60)	$ 2.55	$ (1.70)	$ (0.41)	$ 1.65
Argo Group
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Earned premiums												$ 0	$ 0	$ 0
Net investment income												0	(2.9)	(2.7)
Net realized investment (losses) gains												(8.3)	(0.1)	2.5
Total revenue												(8.3)	(3)	(0.2)
Underwriting, acquisition and insurance expenses												20.4	1.3	11.3
Interest expense												3.6	6.6	6.2
Foreign currency exchange loss												0	0	0
Total expenses												28.4	34.7	17.5
(Loss) income before income taxes												(36.7)	(37.7)	(17.7)
Income tax provision												0	0	0
Equity in undistributed earnings of subsidiaries												(17.4)	23.6	74.7
Net (loss) income												(54.1)	(14.1)	57
Net (loss) income attributable to common shareholders												$ (58.7)	(14.1)	57
Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Earned premiums				$ 425.8	$ 451.5	$ 431.7	$ 420.5		$ 852.2		$ 1,303.7		1,729.5	1,731.7
Net investment income		$ 1.5	$ 35.5					$ 37						133.1
Net realized investment gains (losses)	$ (5.7)	11.1	27.9					39		$ 33.3
Change in fair value of equity securities	10.5	16.8						(22.5)		(12)
Net realized investment (losses) gains	(5.7)	20.1	(36.1)	21.7				(16)		(21.7)			80
Total revenue	483.5	457	436.5	484.5	487.4	488.6	509.2	893.5	997.8	1,377	1,485.2		1,969.7	1,801.8
Underwriting, acquisition and insurance expenses	164.3	161.4	168	180.2	164	161.4		329.4	321.6	493.7	485.6		665.8	654.7
Interest expense	6.8	6.8	7.7	8.3	7.5	9.3	8.5	14.5	17.8	21.3	25.3		33.6	31.6
Foreign currency exchange loss	11.6	6.4	(3)	(3.4)	(1.6)	(5.3)	0.7	3.4	(4.6)	15	(6.2)		(9.6)	(0.1)
Total expenses	512.9	451.3	458.1	587.8	513.6	459	409.1	909.4	868.1	1,422.3	1,381.7		1,969.5	1,734.1
(Loss) income before income taxes	(29.4)	5.7	(21.6)	(103.3)	(26.2)	29.6	100.1	(15.9)	129.7	(45.3)	103.5		0.2	67.7
Income tax provision	0.2	12.1	(2.8)	0	(1.1)	0.8	8.9	9.3	9.7	9.5	8.6		8.6	4.1
Net (loss) income	(29.6)	$ (6.4)	$ (18.8)	$ (103.3)	(25.1)	$ 28.8	$ 91.2	$ (25.2)	$ 120	(54.8)	94.9		$ (8.4)	$ 63.6
Net (loss) income attributable to common shareholders	$ (31.6)				$ (25.1)					$ (56.8)	$ 94.9
Net (loss) income attributable to common shareholders per common share:
Basic (in dollars per share)	$ (0.91)	$ (0.18)	$ (0.55)	$ (3.01)	$ (0.73)	$ 0.84	$ 2,680,000	$ (0.73)	$ 3.52	$ (1.64)	$ 2.78		$ (0.25)	$ 1.87
Diluted (in dollars per share)	$ (0.91)	$ (0.18)	$ (0.55)	$ (3.01)	$ (0.73)	$ 0.83	$ 2,630,000	$ (0.73)	$ 3.45	$ (1.64)	$ 2.73		$ (0.25)	$ 1.83
Previously Reported | Argo Group
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Equity in undistributed earnings of subsidiaries													$ (22.8)	$ 44.8
Net (loss) income													(8.4)	63.6
Revision of Prior Period, Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Earned premiums				$ 0	$ 0	$ 0	$ 0.2		$ 0.2		$ 0.2		0.2	(0.2)
Net investment income		$ (0.1)	$ 0.1					$ 0						(0.8)
Net realized investment gains (losses)	$ 0	0	(0.1)					(0.1)		$ (0.1)
Change in fair value of equity securities	0	(1.7)						(1.7)		(1.7)
Net realized investment (losses) gains	0	(1.7)	(0.1)	0.1				(1.8)		(1.8)			0.1
Total revenue	0	(1.8)	0	0.1	0	0	0.2	(1.8)	0.2	(1.8)	0.2		0.3	(1)
Underwriting, acquisition and insurance expenses	0.2	(0.1)	0.1	0	0	0.2		0	0.2	0.2	0.2		0.2	1.4
Interest expense	0.1	0.2	0.1	0.1	0.2	0.1	0.1	0.3	0.2	0.4	0.4		0.5	0.3
Foreign currency exchange loss	(3.2)	(2.1)	3.9	(1.1)	0.7	1.5	(1.3)	1.8	0.2	(1.4)	0.9		(0.2)	4
Total expenses	(2.9)	(2)	4.1	(1)	0.9	1.8	(1.2)	2.1	0.6	(0.8)	1.5		0.5	5.7
(Loss) income before income taxes	2.9	0.2	(4.1)	1.1	(0.9)	(1.8)	1.4	(3.9)	(0.4)	(1)	(1.3)		(0.2)	(6.7)
Income tax provision	(3.6)	(0.8)	1.8	0.5	0	0	5	1	5	(2.6)	5		5.5	(0.1)
Net (loss) income	6.5	$ 1	$ (5.9)	$ 0.6	(0.9)	$ (1.8)	$ (3.6)	$ (4.9)	$ (5.4)	1.6	(6.3)		$ (5.7)	$ (6.6)
Net (loss) income attributable to common shareholders	$ 6.5				$ (0.9)					$ 1.6	$ (6.3)
Net (loss) income attributable to common shareholders per common share:
Basic (in dollars per share)	$ 0.19	$ 0.02	$ (0.17)	$ 0.02	$ (0.03)	$ (0.05)	$ (100,000)	$ (0.14)	$ (0.16)	$ 0.04	$ (0.19)		$ (0.16)	$ (0.19)
Diluted (in dollars per share)	$ 0.19	$ 0.02	$ (0.17)	$ 0.02	$ (0.03)	$ (0.05)	$ (110,000)	$ (0.14)	$ (0.15)	$ 0.04	$ (0.18)		$ (0.16)	$ (0.18)
Revision of Prior Period, Adjustment | Argo Group
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Equity in undistributed earnings of subsidiaries													$ 46.4	$ 29.9
Net (loss) income													$ (5.7)	$ (6.6)

Recent Acquisitions, Disposal_2

Recent Acquisitions, Disposals & Other Transactions - Acquisitions (Details) - USD ($) $ in Millions	Jun. 12, 2020	Oct. 12, 2020
ArgoGlobal | RiverStone | ArgoGlobal Syndicate 1200
Business Acquisition [Line Items]
Reinsurance-to-close transaction, net technical provision		$ 217
Ariel Indemnity Limited
Business Acquisition [Line Items]
Percentage of capital stock acquired	100.00%
Consideration transferred	$ 55.6

Recent Acquisitions, Disposal_3

Recent Acquisitions, Disposals & Other Transactions - Sale of Business Unit (Details) - Disposal Group, Disposed of by Sale, Not Discontinued Operations - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Nov. 25, 2020	Apr. 30, 2020
Trident
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash consideration received from sale			$ 38
Gain (loss) on disposal, pre-tax	$ 32.3
Ariel Re
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash consideration received from sale		$ 30
Gain (loss) on disposal, pre-tax	$ (9.4)

Investments - Additional Inform

Investments - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)securityproperty	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Amortized Cost And Fair Value Debt Securities [Abstract]
Fair value of investments, assets managed on behalf of the trade capital providers	$ 140.3	$ 156.8
Number of securities in an unrealized loss position, total | security	5,301
Number of securities in an unrealized loss position for less than one year | property	928
Number of securities in an unrealized loss position for a period of one year or greater | property	149
Impairment losses	$ 0	20.3	$ 7.6
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Credit impairment losses	39.9	$ 0	$ 0
Gain (Loss) on Investments
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Credit impairment losses	$ 39.9

Investments - Schedule of Amort

Investments - Schedule of Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Fair Value of Investments (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Schedule of Invested Assets [Line Items]
Amortized Cost	$ 3,981.1	$ 3,601.5
Allowance for Credit Losses	6.6	0
Fair Value	4,107.1	3,629.9
Fixed maturities
Schedule of Invested Assets [Line Items]
Amortized Cost	3,981.1	3,601.5
Gross Unrealized Gains	149.7	68.4
Gross Unrealized Losses	17.1	40
Allowance for Credit Losses	6.6	0
Fair Value	4,107.1	3,629.9
Fixed maturities | U.S. Governments
Schedule of Invested Assets [Line Items]
Amortized Cost	385.4	352.2
Gross Unrealized Gains	14.7	2.3
Gross Unrealized Losses	0.3	1.2
Allowance for Credit Losses	0	0
Fair Value	399.8	353.3
Fixed maturities | Foreign Governments
Schedule of Invested Assets [Line Items]
Amortized Cost	284.1	244.8
Gross Unrealized Gains	11.6	4.6
Gross Unrealized Losses	0.7	0.7
Allowance for Credit Losses	0.2	0
Fair Value	294.8	248.7
Fixed maturities | Obligations of states and political subdivisions
Schedule of Invested Assets [Line Items]
Amortized Cost	163.1	145.8
Gross Unrealized Gains	7.7	6.9
Gross Unrealized Losses	0.3	0.1
Allowance for Credit Losses	0.1	0
Fair Value	170.4	152.6
Fixed maturities | Corporate bonds
Schedule of Invested Assets [Line Items]
Amortized Cost	1,925.9	1,775.4
Gross Unrealized Gains	75.3	37.7
Gross Unrealized Losses	13.3	34.7
Allowance for Credit Losses	6.1	0
Fair Value	1,981.8	1,778.4
Fixed maturities | Commercial mortgage-backed securities
Schedule of Invested Assets [Line Items]
Amortized Cost	324.8	213.5
Gross Unrealized Gains	15.2	4.6
Gross Unrealized Losses	0.3	1.1
Allowance for Credit Losses	0	0
Fair Value	339.7	217
Fixed maturities | Residential mortgage-backed securities
Schedule of Invested Assets [Line Items]
Amortized Cost	491.4	479
Gross Unrealized Gains	17.4	10.4
Gross Unrealized Losses	0.6	0.6
Allowance for Credit Losses	0	0
Fair Value	508.2	488.8
Fixed maturities | Asset backed securities
Schedule of Invested Assets [Line Items]
Amortized Cost	120.5	164.1
Gross Unrealized Gains	2.9	1.4
Gross Unrealized Losses	0.4	0.2
Allowance for Credit Losses	0.2	0
Fair Value	122.8	165.3
Fixed maturities | Collateralized loan obligations
Schedule of Invested Assets [Line Items]
Amortized Cost	285.9	226.7
Gross Unrealized Gains	4.9	0.5
Gross Unrealized Losses	1.2	1.4
Allowance for Credit Losses	0	0
Fair Value	$ 289.6	$ 225.8

Investments - Schedule of Amo_2

Investments - Schedule of Amortized Cost and Fair Values of Fixed Maturity Investments, by Contractual Maturity (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Amortized Cost
Due in one year or less	$ 324.9
Due after one year through five years	1,743.6
Due after five years through ten years	607.8
Thereafter	82.2
Structured securities	1,222.6
Total	3,981.1
Fair Value
Due in one year or less	329.7
Due after one year through five years	1,791.9
Due after five years through ten years	639.3
Thereafter	85.9
Structured securities	$ 1,260.3
Total		$ 4,107.1

Investments - Schedule of Carry

Investments - Schedule of Carrying Value and Unfunded Investment Commitments of Other Invested Assets Portfolio (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019
Schedule of Investments [Line Items]
Carrying Value	$ 5,255.8	$ 4,813.1	$ 5,097.5	$ 5,128.7	$ 4,879.3	$ 4,905.2
Hedge funds
Schedule of Investments [Line Items]
Carrying Value	111.2		109.5
Unfunded Commitments	0		0
Private equity
Schedule of Investments [Line Items]
Carrying Value	211.4		258.2
Unfunded Commitments	80		110
Overseas deposits
Schedule of Investments [Line Items]
Carrying Value	102.1		114.6
Unfunded Commitments	0		0
Other
Schedule of Investments [Line Items]
Carrying Value	4.7		4.3
Unfunded Commitments	0		0
Total other investments
Schedule of Investments [Line Items]
Carrying Value	429.4		486.6
Unfunded Commitments	$ 80		$ 110

Investments - Schedule of Aging

Investments - Schedule of Aging of Unrealized Losses on Company's Investments in Fixed Maturities, Equity Securities and Other Investments (Detail) - Fixed maturities - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	$ 488.2	$ 703.3
Unrealized Losses, Less Than One Year	9.8	23
Fair Value, One Year or Greater	69.7	253.5
Unrealized Losses, One Year or Greater	7.3	17
Fair Value, Total	557.9	956.8
Unrealized Losses, Total	17.1	40
U.S. Governments
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	40.6	114.6
Unrealized Losses, Less Than One Year	0.3	1.1
Fair Value, One Year or Greater	0	17
Unrealized Losses, One Year or Greater	0	0.1
Fair Value, Total	40.6	131.6
Unrealized Losses, Total	0.3	1.2
Foreign Governments
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	18	119.2
Unrealized Losses, Less Than One Year	0.5	0.7
Fair Value, One Year or Greater	0.1	5.1
Unrealized Losses, One Year or Greater	0.2	0
Fair Value, Total	18.1	124.3
Unrealized Losses, Total	0.7	0.7
Obligations of states and political subdivisions
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	5.2	0.7
Unrealized Losses, Less Than One Year	0.3	0
Fair Value, One Year or Greater	0	2.1
Unrealized Losses, One Year or Greater	0	0.1
Fair Value, Total	5.2	2.8
Unrealized Losses, Total	0.3	0.1
Corporate bonds
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	202.5	249.7
Unrealized Losses, Less Than One Year	6.7	18.9
Fair Value, One Year or Greater	17.5	63.6
Unrealized Losses, One Year or Greater	6.6	15.8
Fair Value, Total	220	313.3
Unrealized Losses, Total	13.3	34.7
Commercial mortgage-backed securities
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	21.8	74.8
Unrealized Losses, Less Than One Year	0.3	1.1
Fair Value, One Year or Greater	0	4.9
Unrealized Losses, One Year or Greater	0	0
Fair Value, Total	21.8	79.7
Unrealized Losses, Total	0.3	1.1
Residential mortgage-backed securities
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	74.4	66.9
Unrealized Losses, Less Than One Year	0.4	0.3
Fair Value, One Year or Greater	3	25.2
Unrealized Losses, One Year or Greater	0.2	0.3
Fair Value, Total	77.4	92.1
Unrealized Losses, Total	0.6	0.6
Asset backed securities
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	4.6	22.5
Unrealized Losses, Less Than One Year	0.4	0.1
Fair Value, One Year or Greater	0	18.9
Unrealized Losses, One Year or Greater	0	0.1
Fair Value, Total	4.6	41.4
Unrealized Losses, Total	0.4	0.2
Collateralized loan obligations
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	121.1	54.9
Unrealized Losses, Less Than One Year	0.9	0.8
Fair Value, One Year or Greater	49.1	116.7
Unrealized Losses, One Year or Greater	0.3	0.6
Fair Value, Total	170.2	171.6
Unrealized Losses, Total	$ 1.2	$ 1.4

Investments - Allowance for Cre

Investments - Allowance for Credit Losses (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance, January 1, 2020	$ 0
Securities for which allowance was not previously recorded	15.9
Securities sold during the period	(39.3)
Additional net increases (decreases) in existing allowance	23.1
Ending balance, December 31, 2020	6.6
Foreign Governments
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance, January 1, 2020	0
Securities for which allowance was not previously recorded	0.3
Securities sold during the period	(0.2)
Additional net increases (decreases) in existing allowance	0.1
Ending balance, December 31, 2020	0.2
Obligations of states and political subdivisions
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance, January 1, 2020	0
Securities for which allowance was not previously recorded	0.3
Securities sold during the period	0
Additional net increases (decreases) in existing allowance	(0.2)
Ending balance, December 31, 2020	0.1
Corporate bonds
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance, January 1, 2020	0
Securities for which allowance was not previously recorded	15.3
Securities sold during the period	(39)
Additional net increases (decreases) in existing allowance	23
Ending balance, December 31, 2020	6.1
Asset backed securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance, January 1, 2020	0
Securities for which allowance was not previously recorded	0
Securities sold during the period	(0.1)
Additional net increases (decreases) in existing allowance	0.2
Ending balance, December 31, 2020	0.2
Cumulative Effect, Period of Adoption, Adjustment
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance, January 1, 2020	6.9
Cumulative Effect, Period of Adoption, Adjustment | Foreign Governments
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance, January 1, 2020	0
Cumulative Effect, Period of Adoption, Adjustment | Obligations of states and political subdivisions
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance, January 1, 2020	0
Cumulative Effect, Period of Adoption, Adjustment | Corporate bonds
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance, January 1, 2020	6.8
Cumulative Effect, Period of Adoption, Adjustment | Asset backed securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance, January 1, 2020	$ 0.1

Investments - Schedule of Inves

Investments - Schedule of Investment Income and Expenses (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investment income:
Interest on fixed maturities				$ 108.6	$ 129.5	$ 115
Dividends on equity securities				2.8	11.1	12.5
Income on alternative investments				10.4	22.4	19
Income on short-term and other investments				3.9	8.9	9.5
Investment income				125.7	171.9	156
Investment expenses				(13)	(20.8)	(23.7)
Net investment income	$ 1.4	$ 35.6	$ 37	$ 112.7	$ 151.1	$ 132.3

Investments - Schedule of Compa

Investments - Schedule of Company's Gross Realized Investment Gains (Losses) (Detail) - USD ($) $ in Millions	3 Months Ended				6 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2020	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other							$ 163.2	$ 55.3	$ 59.3
Realized losses on fixed maturities and other							(163.6)	(63.3)	(63.6)
Credit losses on fixed maturities							(39.9)	0	0
Net realized (losses) gains on equity securities							(17.1)	128.9	37.4
Change in unrealized gains (losses) on equity securities held at the end of the period	$ 10.5	$ 15.1			$ (24.2)	$ (13.7)	10.3	(40.8)	(105.1)
Net realized (losses) gains on equity securities							(6.8)	88.1	(67.7)
Net realized investment (losses) gains	$ (5.7)	$ 18.4	$ (36.2)	$ 21.8	$ (17.8)	$ (23.5)	(7.2)	80.1	(72)
Income tax (benefit) provision							1.3	16.2	11.2
Net realized investment (losses) gains, net of income taxes							(8.5)	63.9	(83.2)
Fixed maturities
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other							37.1	22.2	17.7
Realized losses on fixed maturities and other							(35.2)	(11.7)	(16)
Other investments, including short-terms
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other							93.8	0.1	0.2
Realized losses on fixed maturities and other							(78.6)	(31.3)	(40)
Other assets
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other							32.3	33	41.4
Realized losses on fixed maturities and other							(9.9)	0	0
Credit losses on fixed maturities
Schedule of Investments [Line Items]
Credit losses on fixed maturities							(39.9)	0	0
Other-than-temporary impairment losses
Schedule of Investments [Line Items]
Realized losses on fixed maturities and other							$ 0	$ (20.3)	$ (7.6)

Investments - Schedule of Chang

Investments - Schedule of Changes in Unrealized Appreciation (Depreciation) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Net unrealized investment gains (losses) before income taxes	$ 82.4	$ 97.9	$ (88.5)
Income tax provision (benefit)	16.5	15.4	(13)
Net unrealized investment gains (losses), net of income taxes	65.9	82.5	(75.5)
Fixed maturities
Schedule of Investments [Line Items]
Net unrealized investment gains (losses) before income taxes	96	93.3	(88.1)
Other assets
Schedule of Investments [Line Items]
Net unrealized investment gains (losses) before income taxes	(14.3)	4.4	0.1
Other and short-term investments
Schedule of Investments [Line Items]
Net unrealized investment gains (losses) before income taxes	$ 0.7	$ 0.2	$ (0.5)

Investments - Schedule of Fair

Investments - Schedule of Fair Value of Foreign Currency Exchange Forward Contracts (Detail) - Foreign Currency Exchange Forward Contracts - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Derivative assets (liabilities), at fair value, net	$ 0.9	$ 1.1
Operational currency exposure
Schedule of Investments [Line Items]
Derivative assets (liabilities), at fair value, net	0.4	(0.8)
Asset manager investment exposure
Schedule of Investments [Line Items]
Derivative assets (liabilities), at fair value, net	(0.2)	(0.3)
Total return strategy
Schedule of Investments [Line Items]
Derivative assets (liabilities), at fair value, net	$ 0.7	$ 2.2

Investments - Schedule of Reali

Investments - Schedule of Realized Gains and Losses of Investment on Foreign Currency Exchange Forward Contracts (Detail) - Foreign Currency Exchange Forward Contracts - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Gross realized investment gains	$ 77	$ 30.9	$ 42.2
Gross realized investment losses	(74.9)	(29)	(39.5)
Net realized investment gains (losses) on foreign    currency exchange forward contracts	2.1	1.9	2.7
Operational currency exposure
Schedule of Investments [Line Items]
Gross realized investment gains	13.2	5.7	9.7
Gross realized investment losses	(8.6)	(10.6)	(7.9)
Asset manager investment exposure
Schedule of Investments [Line Items]
Gross realized investment gains	2.2	2.7	5.8
Gross realized investment losses	(4)	(0.8)	(3)
Total return strategy
Schedule of Investments [Line Items]
Gross realized investment gains	61.6	22.5	26.7
Gross realized investment losses	$ (62.3)	$ (17.6)	$ (28.6)

Investments - Components of Res

Investments - Components of Restricted Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Securities pledged as collateral for letters of credit and other	$ 189.4	$ 169.9
Securities and cash on deposit supporting Lloyd’s business	409.2	412.8
Total restricted investments	826.1	775.2
Securities on deposit for regulatory and other purposes
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Securities on deposit for regulatory and other purposes	$ 227.5	$ 192.5

Investments - Financial Assets

Investments - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	$ 5,255.8	$ 4,813.1	$ 5,097.5	$ 5,128.7	$ 4,879.3	$ 4,905.2
Other assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	429.4		486.6
Fair Value, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	4,928.9		4,707.2
Fair Value, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	1,069.6		1,289.1
Fair Value, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	3,834.8		3,392.5
Fair Value, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	24.5		25.6
Fair Value, Recurring | Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	4,107.1		3,629.9
Fair Value, Recurring | Fixed maturities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	383.5		347.8
Fair Value, Recurring | Fixed maturities | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	3,716.6		3,274.7
Fair Value, Recurring | Fixed maturities | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	7		7.4
Fair Value, Recurring | Fixed maturities | Collateralized loan obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	289.6		225.8
Fair Value, Recurring | Fixed maturities | Collateralized loan obligations | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0		0
Fair Value, Recurring | Fixed maturities | Collateralized loan obligations | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	289.6		225.8
Fair Value, Recurring | Fixed maturities | Collateralized loan obligations | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0		0
Fair Value, Recurring | Fixed maturities | U.S. Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	399.8		353.3
Fair Value, Recurring | Fixed maturities | U.S. Governments | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	383.5		347.8
Fair Value, Recurring | Fixed maturities | U.S. Governments | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	16.3		5.5
Fair Value, Recurring | Fixed maturities | U.S. Governments | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0		0
Fair Value, Recurring | Fixed maturities | Foreign Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	294.8		248.7
Fair Value, Recurring | Fixed maturities | Foreign Governments | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0		0
Fair Value, Recurring | Fixed maturities | Foreign Governments | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	294.8		248.7
Fair Value, Recurring | Fixed maturities | Foreign Governments | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0		0
Fair Value, Recurring | Fixed maturities | Obligations of states and political subdivisions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	170.4		152.6
Fair Value, Recurring | Fixed maturities | Obligations of states and political subdivisions | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0		0
Fair Value, Recurring | Fixed maturities | Obligations of states and political subdivisions | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	170.4		152.6
Fair Value, Recurring | Fixed maturities | Obligations of states and political subdivisions | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0		0
Fair Value, Recurring | Fixed maturities | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	1,981.8		1,778.4
Fair Value, Recurring | Fixed maturities | Corporate bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0		0
Fair Value, Recurring | Fixed maturities | Corporate bonds | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	1,974.8		1,771
Fair Value, Recurring | Fixed maturities | Corporate bonds | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	7		7.4
Fair Value, Recurring | Fixed maturities | Commercial mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	339.7		217
Fair Value, Recurring | Fixed maturities | Commercial mortgage-backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0		0
Fair Value, Recurring | Fixed maturities | Commercial mortgage-backed securities | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	339.7		217
Fair Value, Recurring | Fixed maturities | Commercial mortgage-backed securities | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0		0
Fair Value, Recurring | Fixed maturities | Residential mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	508.2		488.8
Fair Value, Recurring | Fixed maturities | Residential mortgage-backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0		0
Fair Value, Recurring | Fixed maturities | Residential mortgage-backed securities | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	508.2		488.8
Fair Value, Recurring | Fixed maturities | Residential mortgage-backed securities | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0		0
Fair Value, Recurring | Fixed maturities | Asset backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	122.8		165.3
Fair Value, Recurring | Fixed maturities | Asset backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0		0
Fair Value, Recurring | Fixed maturities | Asset backed securities | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	122.8		165.3
Fair Value, Recurring | Fixed maturities | Asset backed securities | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0		0
Fair Value, Recurring | Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	176.7		136
Fair Value, Recurring | Equity securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	159.2		117.8
Fair Value, Recurring | Equity securities | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0		0
Fair Value, Recurring | Equity securities | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	17.5		18.2
Fair Value, Recurring | Other assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	102.5		96.3
Fair Value, Recurring | Other assets | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0.4		0
Fair Value, Recurring | Other assets | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	102.1		96.3
Fair Value, Recurring | Other assets | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0		0
Fair Value, Recurring | Other investments, including short-terms
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	542.6		845
Fair Value, Recurring | Other investments, including short-terms | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	526.5		823.5
Fair Value, Recurring | Other investments, including short-terms | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	16.1		21.5
Fair Value, Recurring | Other investments, including short-terms | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	$ 0		$ 0

Investments - Schedule of Recon

Investments - Schedule of Reconciliation of Beginning and Ending Balances for Investments Categorized as Level 3 (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 25.6	$ 22
Transfers into Level 3	0	3.5
Transfers out of Level 3	0	0
Total gains or losses (realized/unrealized):
Included in net income	(5.9)	(2)
Included in other comprehensive income	(0.5)	0.6
Purchases, issuances, sales, and settlements:
Purchases	5.3	1.9
Issuances	0	0
Sales	0	(0.4)
Settlements	0	0
Ending balance	24.5	25.6
Amount of total gains or losses for the year included in net income (loss) attributable to the change in unrealized gains or losses relating to assets still held at end of period	0	0
Credit Financial
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	7.4	2.2
Transfers into Level 3	0	3.5
Transfers out of Level 3	0	0
Total gains or losses (realized/unrealized):
Included in net income	0	(0.4)
Included in other comprehensive income	(0.5)	0.6
Purchases, issuances, sales, and settlements:
Purchases	0.1	1.9
Issuances	0	0
Sales	0	(0.4)
Settlements	0	0
Ending balance	7	7.4
Amount of total gains or losses for the year included in net income (loss) attributable to the change in unrealized gains or losses relating to assets still held at end of period	0	0
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	18.2	19.8
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Total gains or losses (realized/unrealized):
Included in net income	(5.9)	(1.6)
Included in other comprehensive income	0	0
Purchases, issuances, sales, and settlements:
Purchases	5.2	0
Issuances	0	0
Sales	0	0
Settlements	0	0
Ending balance	17.5	18.2
Amount of total gains or losses for the year included in net income (loss) attributable to the change in unrealized gains or losses relating to assets still held at end of period	$ 0	$ 0

Allowance for Credit Losses - P

Allowance for Credit Losses - Premium Receivables (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jan. 01, 2019	Jan. 01, 2018
Financing Receivable, Allowance for Credit Loss [Line Items]
Premiums receivable	$ 679.8	$ 790.2	$ 785	$ 718.2	$ 676.5	$ 727.5	$ 716.8	$ 664.9	$ 645.2	$ 594
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Balance, January 1, 2020	$ 7.9
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Current period change for estimated uncollectible premiums	$ 3.6
Write-offs of uncollectible premiums receivable	(2.4)
Foreign exchange adjustments	0.3
Balance, December 31, 2020	9.4
Cumulative Effect, Period of Adoption, Adjustment
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Balance, January 1, 2020	$ 0

Allowance for Credit Losses - R

Allowance for Credit Losses - Reinsurance Recoverables (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Reinsurance recoverables, net	$ 3,009	$ 3,107.2
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Balance, January 1, 2020	$ 1.1
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Current period change for estimated uncollectible reinsurance	$ 0.9
Write-offs of uncollectible reinsurance recoverables	(0.4)
Balance, December 31, 2020	$ 4.1
Percent rated A- or better	90.30%
Cumulative Effect, Period of Adoption, Adjustment
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Balance, January 1, 2020	$ 2.5

Leases - Additional Information

Leases - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)property	Dec. 31, 2019USD ($)
Lessee, Lease, Description [Line Items]
Lease cost	$ 20.3	$ 23.4
Number of leased properties | property	1
Lease income	$ 2.6	$ 2.8
Minimum
Lessee, Lease, Description [Line Items]
Lease term	1 year
Maximum
Lessee, Lease, Description [Line Items]
Lease term	13 years

Leases - Components of Leases (

Leases - Components of Leases (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating leases right-of-use assets	$ 82	$ 91.8
Operating lease liabilities	$ 95.8	$ 105.7
Operating lease weighted-average remaining lease term	10 years 6 months	9 years 10 months 28 days
Operating lease weighted-average discount rate	3.77%	3.86%

Leases - Lease Cost (Details)

Leases - Lease Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating lease costs	$ 15.3	$ 19.3
Variable lease costs	5.4	4.5
Sublease income	(0.4)	(0.4)
Total lease costs	20.3	23.4
Operating cash flows from operating leases (fixed payments)	15.7	17.5
Operating cash flows from operating leases (liability reduction)	$ 12.8	$ 18.3

Leases - Lease Maturity (Detail

Leases - Lease Maturity (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2021	$ 14.7
2022	13.2
2023	11.1
2023	9.8
2025	9.6
Thereafter	58.4
Total future minimum lease payments	116.8
Future lease obligations	0
Less imputed interest	(21)
Total operating lease liability	$ 95.8	$ 105.7

Reinsurance - Additional Inform

Reinsurance - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Insurance [Abstract]
Reinsurance recoverables, allowance for doubtful accounts	$ 4.1	$ 1.1
Amount of collateral under reinsurance agreement	1,131.4	1,184.7
Paid loss recoverables in insurance recoverables	509.1	672.3
Losses and loss adjustment expenses	1,208.8	1,220.7	$ 1,040.8
Net of amounts ceded to reinsurers	$ 941.3	$ 1,031.1	$ 888.9

Reinsurance - Schedule of Reins

Reinsurance - Schedule of Reinsurance Premium (Detail) - USD ($) $ in Millions	3 Months Ended				6 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2019	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Insurance [Abstract]
Direct written premiums							$ 2,676.1	$ 2,510.4	$ 2,292.9
Reinsurance ceded to other companies							(1,423.2)	(1,375.5)	(1,189)
Reinsurance assumed from other companies							557.2	619.7	661.4
Net written premiums							1,810.1	1,754.6	1,765.3
Direct earned premiums							2,660.6	2,412.4	2,201
Reinsurance ceded to other companies							(1,388.6)	(1,286.7)	(1,137.2)
Reinsurance assumed from other companies							508.5	604	667.7
Net earned premiums	$ 425.8	$ 451.5	$ 431.7	$ 420.7	$ 852.4	$ 1,303.9	$ 1,780.5	$ 1,729.7	$ 1,731.5
Percentage of reinsurance assumed to net earned premiums							28.60%	34.90%	38.60%

Reserves for Losses and Loss _3

Reserves for Losses and Loss Adjustment Expenses - Reserves for Losses and Loss Adjustment Expenses (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Net reserves beginning of the year	$ 2,722.7	$ 2,562.9	$ 2,488
Net AIL reserves acquired	27.9	0	0
Net ArgoGlobal Assicurazioni reserves acquired	0	0	43.4
Losses and LAE incurred during current calendar year, net of reinsurance:
Current accident year	1,201.1	1,082.6	1,058.8
Prior accident years	7.7	138.1	(18)
Losses and LAE incurred during calendar year, net of reinsurance	1,208.8	1,220.7	1,040.8
Losses and LAE payments made during current calendar year, net of reinsurance:
Current accident year	253.4	224.3	273.3
Prior accident years	866.4	806	665.6
Losses and LAE payments made during current calendar year, net of reinsurance:	1,119.8	1,030.3	938.9
Change in participation interest	32.8	(14.4)	(25.5)
Foreign exchange adjustments	33.7	(16.2)	(44.9)
Net reserves - end of year	2,906.1	2,722.7	2,562.9
Reinsurance recoverables on unpaid losses and LAE, end of year	2,499.9	2,434.9	2,091.7
Reserves for losses and loss adjustment expenses	$ 5,406	$ 5,157.6	$ 4,654.6

Reserves for Losses and Loss _4

Reserves for Losses and Loss Adjustment Expenses - Impact from (Favorable) Unfavorable Development of Prior Accident Years' Loss and LAE Reserves on Each Reporting Segment (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total unfavorable (favorable) prior-year development	$ 7.7	$ 138.1	$ (18)
U.S. Operations
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total unfavorable (favorable) prior-year development	2.4	15.7	(20.8)
International Operations
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total unfavorable (favorable) prior-year development	(6.2)	110.4	(9.5)
Run-off Lines
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total unfavorable (favorable) prior-year development	$ 11.5	$ 12	$ 12.3

Reserves for Losses and Loss _5

Reserves for Losses and Loss Adjustment Expenses - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)segment
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Loss adjustment expenses related to pandemic	$ 73.2
Number of reportable segments | segment	2
Claims remain outstanding period	10 years
Number of reporting segments | segment	2
U.S. Operations
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Loss adjustment expenses related to pandemic	$ 6.5
International Operations
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Loss adjustment expenses related to pandemic	$ 66.7
Run-off Lines
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Percentage of gross reserves for losses	5.00%

Reserves for Losses and Loss _6

Reserves for Losses and Loss Adjustment Expenses - Summary of Information about Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance (Detail) $ in Millions	Dec. 31, 2020USD ($)claim	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)
Claims Development [Line Items]
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	$ 2,856.3
U.S. Operations | Excess and Surplus Lines | Liability
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	2,334.1
Cumulative paid losses & ALAE, net of reinsurance	1,422.4
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance	24.1
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	935.8
U.S. Operations | Excess and Surplus Lines | Liability | Accident Year 2011
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	187.4	$ 185.8	$ 187.8	$ 189	$ 192.8	$ 193.5	$ 200	$ 205.8	$ 206	$ 202.9
Cumulative paid losses & ALAE, net of reinsurance	179.2	177.5	174.4	170	162.4	146.6	122.9	91	53.8	17.6
IBNR & Expected Development on Reported Claims	$ 3
Cumulative Number of Reported Claims | claim	8,526
U.S. Operations | Excess and Surplus Lines | Liability | Accident Year 2012
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 182	181	182.3	182.1	184.4	183.6	189.7	196	189.6
Cumulative paid losses & ALAE, net of reinsurance	174.9	170.3	163.4	157.5	142.4	120.8	89.1	52.8	17.2
IBNR & Expected Development on Reported Claims	$ 3.4
Cumulative Number of Reported Claims | claim	7,494
U.S. Operations | Excess and Surplus Lines | Liability | Accident Year 2013
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 216	214.2	216	220.4	227.2	224.3	222.6	217.9
Cumulative paid losses & ALAE, net of reinsurance	200.3	192.2	179.6	163.7	135.2	100.4	60.2	17.6
IBNR & Expected Development on Reported Claims	$ 5.3
Cumulative Number of Reported Claims | claim	7,484
U.S. Operations | Excess and Surplus Lines | Liability | Accident Year 2014
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 218.1	210	212.3	211.9	213.2	215.2	213
Cumulative paid losses & ALAE, net of reinsurance	186.7	172.8	154.5	131.6	95.9	52.2	15
IBNR & Expected Development on Reported Claims	$ 9.9
Cumulative Number of Reported Claims | claim	6,812
U.S. Operations | Excess and Surplus Lines | Liability | Accident Year 2015
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 233.9	224.8	226.4	228.6	237.1	232.5
Cumulative paid losses & ALAE, net of reinsurance	182.4	162.8	131.5	91.4	51.9	16.5
IBNR & Expected Development on Reported Claims	$ 17.4
Cumulative Number of Reported Claims | claim	6,509
U.S. Operations | Excess and Surplus Lines | Liability | Accident Year 2016
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 250	248.3	243.1	250.6	246.4
Cumulative paid losses & ALAE, net of reinsurance	177.4	149.5	95.5	52.8	17.4
IBNR & Expected Development on Reported Claims	$ 29.8
Cumulative Number of Reported Claims | claim	6,283
U.S. Operations | Excess and Surplus Lines | Liability | Accident Year 2017
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 257.7	249	244.3	253.3
Cumulative paid losses & ALAE, net of reinsurance	149.6	88	38.7	11.5
IBNR & Expected Development on Reported Claims	$ 36.7
Cumulative Number of Reported Claims | claim	7,172
U.S. Operations | Excess and Surplus Lines | Liability | Accident Year 2018
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 254	269.5	278.8
Cumulative paid losses & ALAE, net of reinsurance	98.2	47	15
IBNR & Expected Development on Reported Claims	$ 83
Cumulative Number of Reported Claims | claim	6,810
U.S. Operations | Excess and Surplus Lines | Liability | Accident Year 2019
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 268.8	269.8
Cumulative paid losses & ALAE, net of reinsurance	61.2	14.9
IBNR & Expected Development on Reported Claims	$ 147.6
Cumulative Number of Reported Claims | claim	5,985
U.S. Operations | Excess and Surplus Lines | Liability | Accident Year 2020
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 266.2
Cumulative paid losses & ALAE, net of reinsurance	12.5
IBNR & Expected Development on Reported Claims	$ 223.7
Cumulative Number of Reported Claims | claim	3,407
U.S. Operations | Specialty Admitted | Liability
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 1,335.1
Cumulative paid losses & ALAE, net of reinsurance	889.4
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance	35.5
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	481.2
U.S. Operations | Specialty Admitted | Liability | Accident Year 2011
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	150.4	151.6	154	153.7	154	158.2	157.5	159	155.1	140.3
Cumulative paid losses & ALAE, net of reinsurance	145.1	144	143.1	139.8	135.1	126.1	111.3	85.9	57.5	23.2
IBNR & Expected Development on Reported Claims	$ 3.4
Cumulative Number of Reported Claims | claim	28,201
U.S. Operations | Specialty Admitted | Liability | Accident Year 2012
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 146.3	146.2	146.6	147.7	151.5	153.3	149.7	146.3	140.3
Cumulative paid losses & ALAE, net of reinsurance	138.2	135	131.9	127.9	120.8	105.8	80.7	51	20.1
IBNR & Expected Development on Reported Claims	$ 3.8
Cumulative Number of Reported Claims | claim	23,681
U.S. Operations | Specialty Admitted | Liability | Accident Year 2013
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 128.8	128.9	130.6	131.1	133.2	136.7	133.2	126.6
Cumulative paid losses & ALAE, net of reinsurance	118	114.7	109.7	102.8	93.6	74	49.4	18.9
IBNR & Expected Development on Reported Claims	$ 5.5
Cumulative Number of Reported Claims | claim	19,003
U.S. Operations | Specialty Admitted | Liability | Accident Year 2014
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 109.3	111.9	111.5	114.5	116.9	121.9	115.6
Cumulative paid losses & ALAE, net of reinsurance	96.5	93.5	86.1	75.3	58.7	38.8	17.4
IBNR & Expected Development on Reported Claims	$ 6.2
Cumulative Number of Reported Claims | claim	16,404
U.S. Operations | Specialty Admitted | Liability | Accident Year 2015
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 101.6	103.1	102.3	101.7	106.7	107.3
Cumulative paid losses & ALAE, net of reinsurance	81.5	73.6	64.2	48.8	35	17.2
IBNR & Expected Development on Reported Claims	$ 9.1
Cumulative Number of Reported Claims | claim	14,768
U.S. Operations | Specialty Admitted | Liability | Accident Year 2016
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 105.2	104.7	99.3	99.9	96.1
Cumulative paid losses & ALAE, net of reinsurance	78.2	67.6	48.6	31.7	11.1
IBNR & Expected Development on Reported Claims	$ 10.4
Cumulative Number of Reported Claims | claim	11,946
U.S. Operations | Specialty Admitted | Liability | Accident Year 2017
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 140	135.3	129.5	121.5
Cumulative paid losses & ALAE, net of reinsurance	88.9	70.9	44.4	16.3
IBNR & Expected Development on Reported Claims	$ 19.8
Cumulative Number of Reported Claims | claim	13,988
U.S. Operations | Specialty Admitted | Liability | Accident Year 2018
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 160.5	160.9	147.3
Cumulative paid losses & ALAE, net of reinsurance	77.6	52	19.4
IBNR & Expected Development on Reported Claims	$ 40.1
Cumulative Number of Reported Claims | claim	15,891
U.S. Operations | Specialty Admitted | Liability | Accident Year 2019
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 154.9	151.3
Cumulative paid losses & ALAE, net of reinsurance	52.4	17.5
IBNR & Expected Development on Reported Claims	$ 62.4
Cumulative Number of Reported Claims | claim	14,946
U.S. Operations | Specialty Admitted | Liability | Accident Year 2020
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 138.1
Cumulative paid losses & ALAE, net of reinsurance	13
IBNR & Expected Development on Reported Claims	$ 89.9
Cumulative Number of Reported Claims | claim	8,986
U.S. Operations | Specialty Admitted | Professional
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 593.2
Cumulative paid losses & ALAE, net of reinsurance	312.7
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance	6.8
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	287.3
U.S. Operations | Specialty Admitted | Professional | Accident Year 2011
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	25.7	25.8	26	26.6	26.9	28.2	32.5	35	35	35
Cumulative paid losses & ALAE, net of reinsurance	25.7	25.7	25.7	25.7	25.4	24	22	17.8	11.8	3.2
IBNR & Expected Development on Reported Claims	$ 0
Cumulative Number of Reported Claims | claim	821
U.S. Operations | Specialty Admitted | Professional | Accident Year 2012
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 24.4	24.7	24.9	24.5	24	25.8	28.6	28.3	27.8
Cumulative paid losses & ALAE, net of reinsurance	24	24.2	23.5	22.6	21.4	19.9	16.9	8.6	2.3
IBNR & Expected Development on Reported Claims	$ 0.1
Cumulative Number of Reported Claims | claim	642
U.S. Operations | Specialty Admitted | Professional | Accident Year 2013
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 18.1	18.3	19.5	19.8	19	21.1	21.5	20.9
Cumulative paid losses & ALAE, net of reinsurance	17.9	17.9	17.5	17.6	14.2	10.9	6.3	1.9
IBNR & Expected Development on Reported Claims	$ 0.2
Cumulative Number of Reported Claims | claim	622
U.S. Operations | Specialty Admitted | Professional | Accident Year 2014
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 35.1	35.4	36.2	33.7	26	22.4	22.4
Cumulative paid losses & ALAE, net of reinsurance	33.3	32.3	25.5	24.1	15.1	5.4	2.3
IBNR & Expected Development on Reported Claims	$ 0.4
Cumulative Number of Reported Claims | claim	1,045
U.S. Operations | Specialty Admitted | Professional | Accident Year 2015
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 37.9	37.1	34	33.2	29.5	29.9
Cumulative paid losses & ALAE, net of reinsurance	31.3	26.2	20.8	15.6	8.3	1.8
IBNR & Expected Development on Reported Claims	$ 1.5
Cumulative Number of Reported Claims | claim	1,843
U.S. Operations | Specialty Admitted | Professional | Accident Year 2016
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 35.5	42.9	45.1	44.8	44.2
Cumulative paid losses & ALAE, net of reinsurance	30.8	28.9	24.6	11.9	2.4
IBNR & Expected Development on Reported Claims	$ 2.5
Cumulative Number of Reported Claims | claim	3,251
U.S. Operations | Specialty Admitted | Professional | Accident Year 2017
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 87.9	78.3	61.8	60.1
Cumulative paid losses & ALAE, net of reinsurance	59.7	38	24.9	3.5
IBNR & Expected Development on Reported Claims	$ 1.4
Cumulative Number of Reported Claims | claim	3,747
U.S. Operations | Specialty Admitted | Professional | Accident Year 2018
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 79.2	73.2	70.8
Cumulative paid losses & ALAE, net of reinsurance	43.8	16.7	4.5
IBNR & Expected Development on Reported Claims	$ 7.4
Cumulative Number of Reported Claims | claim	4,287
U.S. Operations | Specialty Admitted | Professional | Accident Year 2019
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 96.8	94.4
Cumulative paid losses & ALAE, net of reinsurance	32.9	4.9
IBNR & Expected Development on Reported Claims	$ 39.7
Cumulative Number of Reported Claims | claim	5,049
U.S. Operations | Specialty Admitted | Professional | Accident Year 2020
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 152.6
Cumulative paid losses & ALAE, net of reinsurance	13.3
IBNR & Expected Development on Reported Claims	$ 124.9
Cumulative Number of Reported Claims | claim	4,739
U.S. Operations | Specialty Admitted | Specialty
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 53.9
Cumulative paid losses & ALAE, net of reinsurance	15.3
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance	0.7
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	39.3
U.S. Operations | Specialty Admitted | Specialty | Accident Year 2011
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	1.7	1.7	1.7	2	2.6	3.6	3.4	3.4	3.9	0.2
Cumulative paid losses & ALAE, net of reinsurance	1.7	1.7	1.7	1.7	1.7	1.2	1.3	1.4	1.6	0
IBNR & Expected Development on Reported Claims	$ 0
Cumulative Number of Reported Claims | claim	80
U.S. Operations | Specialty Admitted | Specialty | Accident Year 2012
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 3.3	3.6	3.5	3.9	4	4.3	4.9	6.7	7.5
Cumulative paid losses & ALAE, net of reinsurance	3.4	3.4	3.3	3.4	3.3	3.3	3.3	3.3	3.6
IBNR & Expected Development on Reported Claims	$ 0
Cumulative Number of Reported Claims | claim	130
U.S. Operations | Specialty Admitted | Specialty | Accident Year 2013
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 0.9	0.9	0.9	1.7	2.5	4.6	8.6	10
Cumulative paid losses & ALAE, net of reinsurance	0.9	0.9	0.9	0.9	0.9	0.9	0.9	0.4
IBNR & Expected Development on Reported Claims	$ 0
Cumulative Number of Reported Claims | claim	50
U.S. Operations | Specialty Admitted | Specialty | Accident Year 2014
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 4.6	4.6	4.8	6	8.9	13.1	13.1
Cumulative paid losses & ALAE, net of reinsurance	4	4.1	4.1	4	4	3.3	1.1
IBNR & Expected Development on Reported Claims	$ 0.6
Cumulative Number of Reported Claims | claim	50
U.S. Operations | Specialty Admitted | Specialty | Accident Year 2015
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 0.5	1.2	5.5	9.5	14.3	14.8
Cumulative paid losses & ALAE, net of reinsurance	0.3	0.3	0.3	0.2	0.1	0.2
IBNR & Expected Development on Reported Claims	$ 0.2
Cumulative Number of Reported Claims | claim	24
U.S. Operations | Specialty Admitted | Specialty | Accident Year 2016
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 4.7	6.2	11.2	15	15
Cumulative paid losses & ALAE, net of reinsurance	2.2	2.2	2.2	1.6	1.3
IBNR & Expected Development on Reported Claims	$ 0.5
Cumulative Number of Reported Claims | claim	61
U.S. Operations | Specialty Admitted | Specialty | Accident Year 2017
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 0.9	7.6	16.2	16.2
Cumulative paid losses & ALAE, net of reinsurance	0.1	0	0.1	0.3
IBNR & Expected Development on Reported Claims	$ 0.6
Cumulative Number of Reported Claims | claim	104
U.S. Operations | Specialty Admitted | Specialty | Accident Year 2018
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 3.3	17.4	20.9
Cumulative paid losses & ALAE, net of reinsurance	1.7	0.7	0
IBNR & Expected Development on Reported Claims	$ 0.7
Cumulative Number of Reported Claims | claim	123
U.S. Operations | Specialty Admitted | Specialty | Accident Year 2019
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 8.6	22.7
Cumulative paid losses & ALAE, net of reinsurance	0.7	0.7
IBNR & Expected Development on Reported Claims	$ 7.1
Cumulative Number of Reported Claims | claim	253
U.S. Operations | Specialty Admitted | Specialty | Accident Year 2020
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 25.4
Cumulative paid losses & ALAE, net of reinsurance	0.3
IBNR & Expected Development on Reported Claims	$ 19.8
Cumulative Number of Reported Claims | claim	309
International Operations | Reinsurance Division | Property
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 667.1
Cumulative paid losses & ALAE, net of reinsurance	599.2
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance	2.5
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	70.4
International Operations | Reinsurance Division | Property | Accident Year 2011
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	135.4	136.1	135.6	129	113.7	109.9	110.6	112.6	110.4	120.3
Cumulative paid losses & ALAE, net of reinsurance	132.3	132.7	130.6	123.6	107.8	102.8	100.5	92.3	70.3	43.1
IBNR & Expected Development on Reported Claims	$ 0.1
Cumulative Number of Reported Claims | claim	463
International Operations | Reinsurance Division | Property | Accident Year 2012
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 60.1	61	59.8	55.3	46.5	51.7	50.4	51.4	47.2
Cumulative paid losses & ALAE, net of reinsurance	59.3	60.1	58	52.2	44.1	49.7	40.6	31.2	12.4
IBNR & Expected Development on Reported Claims	$ 0
Cumulative Number of Reported Claims | claim	278
International Operations | Reinsurance Division | Property | Accident Year 2013
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 32.3	31.9	32.4	32.9	32.3	34	34.5	32.5
Cumulative paid losses & ALAE, net of reinsurance	32.1	31.3	31.2	31.2	29.8	27.3	17.2	4.3
IBNR & Expected Development on Reported Claims	$ 0
Cumulative Number of Reported Claims | claim	219
International Operations | Reinsurance Division | Property | Accident Year 2014
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 31.7	32.5	31.9	30.6	25	26.8	26.7
Cumulative paid losses & ALAE, net of reinsurance	31.6	32.1	30.6	30.1	19	12.9	2.8
IBNR & Expected Development on Reported Claims	$ 0
Cumulative Number of Reported Claims | claim	223
International Operations | Reinsurance Division | Property | Accident Year 2015
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 52.7	57.9	60.5	62.6	23.8	27.2
Cumulative paid losses & ALAE, net of reinsurance	51.1	54.8	53.1	50	11.3	4.2
IBNR & Expected Development on Reported Claims	$ 0
Cumulative Number of Reported Claims | claim	222
International Operations | Reinsurance Division | Property | Accident Year 2016
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 44.8	47.3	39.2	44.9	44.7
Cumulative paid losses & ALAE, net of reinsurance	43	42.8	29.7	25.4	14
IBNR & Expected Development on Reported Claims	$ 1.1
Cumulative Number of Reported Claims | claim	395
International Operations | Reinsurance Division | Property | Accident Year 2017
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 103.9	111.2	107.7	109
Cumulative paid losses & ALAE, net of reinsurance	102.6	112.6	92.9	49.7
IBNR & Expected Development on Reported Claims	$ (9.8)
Cumulative Number of Reported Claims | claim	847
International Operations | Reinsurance Division | Property | Accident Year 2018
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 79.5	82.9	69.3
Cumulative paid losses & ALAE, net of reinsurance	78	71.5	24.9
IBNR & Expected Development on Reported Claims	$ (13.7)
Cumulative Number of Reported Claims | claim	714
International Operations | Reinsurance Division | Property | Accident Year 2019
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 70.1	63.2
Cumulative paid losses & ALAE, net of reinsurance	57.6	9.3
IBNR & Expected Development on Reported Claims	$ 0.2
Cumulative Number of Reported Claims | claim	385
International Operations | Reinsurance Division | Property | Accident Year 2020
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 56.6
Cumulative paid losses & ALAE, net of reinsurance	11.6
IBNR & Expected Development on Reported Claims	$ 33.7
Cumulative Number of Reported Claims | claim	398
International Operations | Bermuda Insurance | Liability
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 153.2
Cumulative paid losses & ALAE, net of reinsurance	75.8
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance	0
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	77.4
International Operations | Bermuda Insurance | Liability | Accident Year 2011
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	0	0	0	1	1.6	2.2	4.4	6.6	6.6	6.6
Cumulative paid losses & ALAE, net of reinsurance	0	0	0	0	0	0	0	0	0	0
IBNR & Expected Development on Reported Claims	$ 0
Cumulative Number of Reported Claims | claim	1,426
International Operations | Bermuda Insurance | Liability | Accident Year 2012
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 0.6	0.6	0	1.7	4.4	5.6	7.4	7.4	7.4
Cumulative paid losses & ALAE, net of reinsurance	0	0	0	0	0	0	0	0	0
IBNR & Expected Development on Reported Claims	$ 0.6
Cumulative Number of Reported Claims | claim	1,390
International Operations | Bermuda Insurance | Liability | Accident Year 2013
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 5.3	5.3	2.2	4.9	8.5	8.5	8.5	8.5
Cumulative paid losses & ALAE, net of reinsurance	2.4	2.3	2.3	2.3	0	0	0	0
IBNR & Expected Development on Reported Claims	$ 1.9
Cumulative Number of Reported Claims | claim	1,197
International Operations | Bermuda Insurance | Liability | Accident Year 2014
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 2.3	2.3	1.5	6.2	9.8	9.8	9.8
Cumulative paid losses & ALAE, net of reinsurance	1.4	1.2	1.2	0.1	0.1	0	0
IBNR & Expected Development on Reported Claims	$ 0.3
Cumulative Number of Reported Claims | claim	1,345
International Operations | Bermuda Insurance | Liability | Accident Year 2015
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 45.1	45.4	35.4	24.8	14.3	11.3
Cumulative paid losses & ALAE, net of reinsurance	34.8	26.6	20.3	16.1	0	0
IBNR & Expected Development on Reported Claims	$ 6.2
Cumulative Number of Reported Claims | claim	1,607
International Operations | Bermuda Insurance | Liability | Accident Year 2016
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 6.1	6.6	14	14	13.9
Cumulative paid losses & ALAE, net of reinsurance	0.1	0.1	0	0	0
IBNR & Expected Development on Reported Claims	$ 5.9
Cumulative Number of Reported Claims | claim	1,924
International Operations | Bermuda Insurance | Liability | Accident Year 2017
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 30.3	26.9	17.3	17.1
Cumulative paid losses & ALAE, net of reinsurance	17.9	3.4	3.3	0
IBNR & Expected Development on Reported Claims	$ 6.3
Cumulative Number of Reported Claims | claim	2,092
International Operations | Bermuda Insurance | Liability | Accident Year 2018
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 26.6	32.1	8.9
Cumulative paid losses & ALAE, net of reinsurance	18.3	13.8	0
IBNR & Expected Development on Reported Claims	$ 8.2
Cumulative Number of Reported Claims | claim	1,049
International Operations | Bermuda Insurance | Liability | Accident Year 2019
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 13.6	13.3
Cumulative paid losses & ALAE, net of reinsurance	0.1	0
IBNR & Expected Development on Reported Claims	$ 12.6
Cumulative Number of Reported Claims | claim	1,088
International Operations | Bermuda Insurance | Liability | Accident Year 2020
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 23.3
Cumulative paid losses & ALAE, net of reinsurance	0.8
IBNR & Expected Development on Reported Claims	$ 16.1
Cumulative Number of Reported Claims | claim	1,083
International Operations | Syndicate 1200 | Liability
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	$ 238
Cumulative paid losses & ALAE, net of reinsurance	138.2
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance	1.2
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	101
International Operations | Syndicate 1200 | Liability | Accident Year 2011
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	12.2	12.1	11.5	11.4	10.7	10.9	11.6	11.5	9.1	8.6
Cumulative paid losses & ALAE, net of reinsurance	10.3	10.3	9.2	8.3	7.4	5.7	3.6	1.7	0.8	0.3
IBNR & Expected Development on Reported Claims	0
International Operations | Syndicate 1200 | Liability | Accident Year 2012
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	16.5	16.1	15.6	15.3	14.4	14.8	15.5	11.2	9
Cumulative paid losses & ALAE, net of reinsurance	13.5	13.2	12.3	10.4	8.5	5.9	2.6	1.2	0.4
IBNR & Expected Development on Reported Claims	0
International Operations | Syndicate 1200 | Liability | Accident Year 2013
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	28.2	27.6	26.4	25.9	25.6	27.5	28	23.7
Cumulative paid losses & ALAE, net of reinsurance	24	23.5	20.7	16.3	11.9	7.3	3.4	1.6
IBNR & Expected Development on Reported Claims	0.3
International Operations | Syndicate 1200 | Liability | Accident Year 2014
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	38.3	37.3	35.6	34.9	35.3	38.1	39.1
Cumulative paid losses & ALAE, net of reinsurance	26.2	25.8	21.1	14.2	10.3	4.8	2
IBNR & Expected Development on Reported Claims	0.9
International Operations | Syndicate 1200 | Liability | Accident Year 2015
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	34.2	34.3	30.8	31.2	30.8	35.9
Cumulative paid losses & ALAE, net of reinsurance	18.8	18.3	12.9	7.5	5.3	0.9
IBNR & Expected Development on Reported Claims	1.2
International Operations | Syndicate 1200 | Liability | Accident Year 2016
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	29.5	29.5	27.3	28.2	26.7
Cumulative paid losses & ALAE, net of reinsurance	16.5	15.7	11	5.8	2
IBNR & Expected Development on Reported Claims	1.8
International Operations | Syndicate 1200 | Liability | Accident Year 2017
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	28.1	27.6	24.2	25.6
Cumulative paid losses & ALAE, net of reinsurance	12.9	11.7	7.1	1.8
IBNR & Expected Development on Reported Claims	5.1
International Operations | Syndicate 1200 | Liability | Accident Year 2018
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	20.8	21.4	23.2
Cumulative paid losses & ALAE, net of reinsurance	10.7	7.4	2.7
IBNR & Expected Development on Reported Claims	7.4
International Operations | Syndicate 1200 | Liability | Accident Year 2019
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	15.7	16.8
Cumulative paid losses & ALAE, net of reinsurance	4	1.3
IBNR & Expected Development on Reported Claims	8.8
International Operations | Syndicate 1200 | Liability | Accident Year 2020
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	14.5
Cumulative paid losses & ALAE, net of reinsurance	1.3
IBNR & Expected Development on Reported Claims	11.7
International Operations | Syndicate 1200 | Professional
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	279.6
Cumulative paid losses & ALAE, net of reinsurance	160.6
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance	2.5
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	121.5
International Operations | Syndicate 1200 | Professional | Accident Year 2011
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	18	17.1	16.6	16.1	15.6	15.5	16.4	19.6	22.2	20.2
Cumulative paid losses & ALAE, net of reinsurance	14.3	14.2	13.5	11.9	11.2	8.7	7	4.4	2.6	1.1
IBNR & Expected Development on Reported Claims	0.2
International Operations | Syndicate 1200 | Professional | Accident Year 2012
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	16	16.4	16	15.6	14.5	14.4	14.5	14.2	14.3
Cumulative paid losses & ALAE, net of reinsurance	13.3	13.1	11.9	10	8.7	6.1	4.6	1.9	0.6
IBNR & Expected Development on Reported Claims	0.8
International Operations | Syndicate 1200 | Professional | Accident Year 2013
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	25.1	24.6	23.9	23.3	22.9	23.3	23.2	23.2
Cumulative paid losses & ALAE, net of reinsurance	21.6	21.3	18.7	16.3	12.4	7.6	3.7	1.8
IBNR & Expected Development on Reported Claims	1.8
International Operations | Syndicate 1200 | Professional | Accident Year 2014
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	45.2	43.9	43	41.3	37.6	37.3	36
Cumulative paid losses & ALAE, net of reinsurance	34.8	34.2	29.6	25	15.6	6.8	1.7
IBNR & Expected Development on Reported Claims	4
International Operations | Syndicate 1200 | Professional | Accident Year 2015
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	43.2	42.1	39.9	40.3	38.4	39
Cumulative paid losses & ALAE, net of reinsurance	27.1	26.4	20.9	15.4	8.8	2.3
IBNR & Expected Development on Reported Claims	5.5
International Operations | Syndicate 1200 | Professional | Accident Year 2016
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	34.4	31.4	26.9	28	33.6
Cumulative paid losses & ALAE, net of reinsurance	19	17.7	11	5.9	2.2
IBNR & Expected Development on Reported Claims	5.6
International Operations | Syndicate 1200 | Professional | Accident Year 2017
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	27.7	24.3	21.9	24.8
Cumulative paid losses & ALAE, net of reinsurance	11.1	10.1	5.4	1.1
IBNR & Expected Development on Reported Claims	9
International Operations | Syndicate 1200 | Professional | Accident Year 2018
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	19.9	17.1	21.8
Cumulative paid losses & ALAE, net of reinsurance	10.1	5.4	1.2
IBNR & Expected Development on Reported Claims	7.2
International Operations | Syndicate 1200 | Professional | Accident Year 2019
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	23.2	22.2
Cumulative paid losses & ALAE, net of reinsurance	7.3	2.7
IBNR & Expected Development on Reported Claims	11.8
International Operations | Syndicate 1200 | Professional | Accident Year 2020
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	26.9
Cumulative paid losses & ALAE, net of reinsurance	2
IBNR & Expected Development on Reported Claims	21.7
International Operations | Syndicate 1200 | Specialty
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	801.6
Cumulative paid losses & ALAE, net of reinsurance	623
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance	1.8
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	180.4
International Operations | Syndicate 1200 | Specialty | Accident Year 2011
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	33.5	33.6	33.7	34	34.2	34.2	35	39.8	41.2	39.3
Cumulative paid losses & ALAE, net of reinsurance	30	29.8	30	30.1	29.8	29.2	27.8	24.3	20.1	11.9
IBNR & Expected Development on Reported Claims	0
International Operations | Syndicate 1200 | Specialty | Accident Year 2012
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	58.9	59	59.4	59.9	60.2	60.5	62	57.5	53.6
Cumulative paid losses & ALAE, net of reinsurance	51.4	51.1	51.1	50.7	49.8	46.8	39.9	28.2	18.4
IBNR & Expected Development on Reported Claims	0
International Operations | Syndicate 1200 | Specialty | Accident Year 2013
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	81.6	82	83	83.1	83.7	84.1	82.8	77.2
Cumulative paid losses & ALAE, net of reinsurance	80	79	79.5	79	77.7	70.2	53.6	31.8
IBNR & Expected Development on Reported Claims	0
International Operations | Syndicate 1200 | Specialty | Accident Year 2014
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	101.3	100.7	102.6	102.6	101.8	100.4	93.8
Cumulative paid losses & ALAE, net of reinsurance	91.1	89.8	91	89	84.2	73	38.5
IBNR & Expected Development on Reported Claims	0
International Operations | Syndicate 1200 | Specialty | Accident Year 2015
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	95.7	96.9	97.4	95.2	89.7	91.4
Cumulative paid losses & ALAE, net of reinsurance	78.3	76.4	75	65.7	55.4	31.8
IBNR & Expected Development on Reported Claims	0
International Operations | Syndicate 1200 | Specialty | Accident Year 2016
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	90.7	91.9	89.7	85.8	87.4
Cumulative paid losses & ALAE, net of reinsurance	79.9	76.3	69.4	57.5	38.4
IBNR & Expected Development on Reported Claims	1.6
International Operations | Syndicate 1200 | Specialty | Accident Year 2017
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	86.1	86.9	77	80.4
Cumulative paid losses & ALAE, net of reinsurance	65.2	59.3	44.2	18.1
IBNR & Expected Development on Reported Claims	3.6
International Operations | Syndicate 1200 | Specialty | Accident Year 2018
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	75.7	73.3	68
Cumulative paid losses & ALAE, net of reinsurance	66.2	53.3	21.6
IBNR & Expected Development on Reported Claims	5.2
International Operations | Syndicate 1200 | Specialty | Accident Year 2019
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	77.7	79.3
Cumulative paid losses & ALAE, net of reinsurance	55.1	30.3
IBNR & Expected Development on Reported Claims	12.9
International Operations | Syndicate 1200 | Specialty | Accident Year 2020
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	100.4
Cumulative paid losses & ALAE, net of reinsurance	25.8
IBNR & Expected Development on Reported Claims	51.5
International Operations | Syndicate 1200 | Property
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	743.7
Cumulative paid losses & ALAE, net of reinsurance	625.8
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance	7.8
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	125.7
International Operations | Syndicate 1200 | Property | Accident Year 2011
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	93.4	93.7	94	94.4	94.6	95.2	97	110.2	116.1	110.9
Cumulative paid losses & ALAE, net of reinsurance	83.5	83.1	83.7	83.8	82.5	80.8	75	63.2	48.2	$ 24
IBNR & Expected Development on Reported Claims	0
International Operations | Syndicate 1200 | Property | Accident Year 2012
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	91.7	90.4	90.9	91.6	92	93	93.9	89.7	90
Cumulative paid losses & ALAE, net of reinsurance	79	78.4	78.6	78.2	77.4	75	63.9	48.5	$ 30.1
IBNR & Expected Development on Reported Claims	0
International Operations | Syndicate 1200 | Property | Accident Year 2013
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	76.6	75.1	76.3	77	77.5	79	80.1	84.3
Cumulative paid losses & ALAE, net of reinsurance	73.6	72.7	73.7	74.3	74.1	70	57.5	$ 45
IBNR & Expected Development on Reported Claims	0
International Operations | Syndicate 1200 | Property | Accident Year 2014
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	63.5	63.6	65.7	66	66	64.6	70.4
Cumulative paid losses & ALAE, net of reinsurance	58.1	57.3	59.5	59.3	57.9	52	$ 29.9
IBNR & Expected Development on Reported Claims	0
International Operations | Syndicate 1200 | Property | Accident Year 2015
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	74.7	73	74.3	73.2	66.5	56
Cumulative paid losses & ALAE, net of reinsurance	59.7	58.2	58.8	51.4	43	$ 23
IBNR & Expected Development on Reported Claims	0
International Operations | Syndicate 1200 | Property | Accident Year 2016
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	91	91.1	92.1	86.2	70.8
Cumulative paid losses & ALAE, net of reinsurance	83	79.2	78	61.3	$ 39.3
IBNR & Expected Development on Reported Claims	0
International Operations | Syndicate 1200 | Property | Accident Year 2017
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	93.8	94.9	90.4	83.3
Cumulative paid losses & ALAE, net of reinsurance	79.6	72.5	63.6	$ 26.1
IBNR & Expected Development on Reported Claims	0.9
International Operations | Syndicate 1200 | Property | Accident Year 2018
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	60.1	63.8	64
Cumulative paid losses & ALAE, net of reinsurance	57.9	56.2	$ 34
IBNR & Expected Development on Reported Claims	1.8
International Operations | Syndicate 1200 | Property | Accident Year 2019
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	41.6	43.2
Cumulative paid losses & ALAE, net of reinsurance	33.8	$ 20.6
IBNR & Expected Development on Reported Claims	4.2
International Operations | Syndicate 1200 | Property | Accident Year 2020
Claims Development [Line Items]
Incurred losses & ALAE, net of reinsurance	57.3
Cumulative paid losses & ALAE, net of reinsurance	17.6
IBNR & Expected Development on Reported Claims	$ 34.4

Reserves for Losses and Loss _7

Reserves for Losses and Loss Adjustment Expenses - Summary of Reconciliation of Net Incurred and Paid Development to Liability for Unpaid Losses and LAE in Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	$ 2,856.3
Total reinsurance recoverables on unpaid losses and LAE	2,499.9
Unallocated loss adjustment expenses	67.6
Unamortized reserve discount	(17.8)	$ (17.9)	$ (16.9)
Reserves for losses and loss adjustment expenses	5,406	5,157.6	4,654.6
U.S. Operations | Excess and Surplus Lines | Liability
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	935.8
Total reinsurance recoverables on unpaid losses and LAE	419.9
U.S. Operations | Specialty Admitted | Liability
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	481.2
Total reinsurance recoverables on unpaid losses and LAE	376.1
Unamortized reserve discount	(12.9)	(13)	(11.9)
U.S. Operations | Specialty Admitted | Professional
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	287.3
Total reinsurance recoverables on unpaid losses and LAE	199.7
U.S. Operations | Specialty Admitted | Specialty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	39.3
Total reinsurance recoverables on unpaid losses and LAE	29
International Operations | Reinsurance Division | Property
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	70.4
Total reinsurance recoverables on unpaid losses and LAE	288.6
International Operations | Bermuda Insurance | Liability
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	77.4
Total reinsurance recoverables on unpaid losses and LAE	172.3
International Operations | Syndicate 1200 | Liability
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	101
Total reinsurance recoverables on unpaid losses and LAE	53.4
International Operations | Syndicate 1200 | Professional
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	121.5
Total reinsurance recoverables on unpaid losses and LAE	84.3
International Operations | Syndicate 1200 | Property
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	125.7
Total reinsurance recoverables on unpaid losses and LAE	102.6
International Operations | Syndicate 1200 | Specialty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	180.4
Total reinsurance recoverables on unpaid losses and LAE	122.8
Run-off Lines
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	165.5
Total reinsurance recoverables on unpaid losses and LAE	75.9
Unamortized reserve discount	(4.9)	$ (4.9)	$ (5)
Other Lines
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	270.8
Total reinsurance recoverables on unpaid losses and LAE	$ 575.3

Reserves for Losses and Loss _8

Reserves for Losses and Loss Adjustment Expenses - Schedule of Supplementary Unaudited Information About Annual Percentage Payout of Incurred Losses and ALAE, Net of Reinsurance (Detail)	Dec. 31, 2020
U.S. Operations | Excess and Surplus Lines | Liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	6.70%
Year 2	15.70%
Year 3	20.90%
Year 4	20.80%
Year 5	12.70%
Year 6	8.50%
Year 7	5.10%
Year 8	3.30%
Year 9	2.10%
Year 10	1.30%
U.S. Operations | Specialty Admitted | Liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	14.10%
Year 2	22.00%
Year 3	18.60%
Year 4	16.30%
Year 5	9.60%
Year 6	6.10%
Year 7	4.00%
Year 8	2.70%
Year 9	1.80%
Year 10	1.30%
U.S. Operations | Specialty Admitted | Professional
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	6.10%
Year 2	22.80%
Year 3	27.30%
Year 4	20.40%
Year 5	9.20%
Year 6	6.20%
Year 7	3.40%
Year 8	1.90%
Year 9	1.10%
Year 10	0.60%
U.S. Operations | Specialty Admitted | Specialty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	53.70%
Year 2	11.60%
Year 3	28.70%
Year 4	3.60%
Year 5	1.40%
Year 6	0.60%
Year 7	0.20%
Year 8	0.10%
International Operations | Reinsurance Division | Property
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	24.90%
Year 2	34.00%
Year 3	20.70%
Year 4	14.50%
Year 5	2.50%
Year 6	1.20%
Year 7	0.70%
Year 8	0.40%
Year 9	0.30%
Year 10	0.20%
International Operations | Bermuda Insurance | Liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 2	20.80%
Year 3	15.60%
Year 4	14.80%
Year 5	12.20%
Year 6	9.30%
Year 7	6.90%
Year 8	5.10%
Year 9	3.70%
Year 10	2.80%
International Operations | Syndicate 1200 | Liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	5.80%
Year 2	12.10%
Year 3	13.40%
Year 4	15.00%
Year 5	16.00%
Year 6	11.70%
Year 7	6.90%
Year 8	5.20%
Year 9	3.70%
Year 10	2.70%
International Operations | Syndicate 1200 | Professional
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	6.10%
Year 2	13.70%
Year 3	18.50%
Year 4	17.60%
Year 5	12.40%
Year 6	8.70%
Year 7	5.90%
Year 8	4.50%
Year 9	3.20%
Year 10	2.30%
International Operations | Syndicate 1200 | Property
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	42.80%
Year 2	30.20%
Year 3	14.30%
Year 4	8.40%
Year 5	2.70%
Year 6	0.80%
Year 7	0.40%
Year 8	0.20%
Year 9	0.10%
International Operations | Syndicate 1200 | Specialty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	37.40%
Year 2	31.00%
Year 3	16.70%
Year 4	9.20%
Year 5	3.00%
Year 6	1.50%
Year 7	0.60%
Year 8	0.30%
Year 9	0.10%

Reserves for Losses and Loss _9

Reserves for Losses and Loss Adjustment Expenses - Schedule of Information About Discounted Liabilities For Unpaid Losses and LAE (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Short-duration Insurance Contracts, Discounted Liabilities [Line Items]
Carrying Amount of Reserves for Losses & LAE	$ 278.8	$ 302	$ 303.9
Aggregate Amount of Discount	17.8	17.9	16.9
Interest Accretion	1.9	1.5	3.4
U.S. Operations | Specialty Admitted | Liability
Short-duration Insurance Contracts, Discounted Liabilities [Line Items]
Carrying Amount of Reserves for Losses & LAE	150.4	153.1	140.8
Aggregate Amount of Discount	12.9	13	11.9
Interest Accretion	$ 1.9	$ 1.3	$ 1.3
Discount Rate	2.25%	2.25%	2.25%
Run-off Lines
Short-duration Insurance Contracts, Discounted Liabilities [Line Items]
Carrying Amount of Reserves for Losses & LAE	$ 128.4	$ 148.9	$ 163.1
Aggregate Amount of Discount	4.9	4.9	5
Interest Accretion	$ 0	$ 0.2	$ 2.1
Discount Rate	3.50%	3.50%	3.50%

Run-off Lines - Gross Reserves

Run-off Lines - Gross Reserves for Run-Off Lines (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	$ 59.3	$ 52.6
Gross reserves - Run-off Lines	236.5	253.5
Reinsurance assumed
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	29.4	26.7
Other
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	29.9	25.9
Risk-management
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross reserves - Run-off Lines	162.4	188.1
Run-off reinsurance lines
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross reserves - Run-off Lines	0.5	0.5
Other run-off lines
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross reserves - Run-off Lines	$ 14.3	$ 12.3

Run-off Lines - Total Gross Res

Run-off Lines - Total Gross Reserves for Asbestos Exposure (Detail) - Asbestos and Environmental Claims - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total direct written reserves	$ 23.8	$ 19.3	$ 22.3
Total asbestos reserves	48.8	42.8	46.8
Case reserves
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total direct written reserves	3.1	2.7	2.7
Unallocated loss adjustment expense ("ULAE")
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total direct written reserves	0.5	0.5	0.5
Incurred but not reported ("IBNR")
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total direct written reserves	20.2	16.1	19.1
Assumed domestic
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total assumed reserves	22	21.1	21.5
Assumed domestic | Case reserves
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total assumed reserves	8.4	9.1	8.7
Assumed domestic | Unallocated loss adjustment expense ("ULAE")
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total assumed reserves	0.8	0.8	0.8
Assumed domestic | Incurred but not reported ("IBNR")
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total assumed reserves	12.8	11.2	12
Assumed London
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total assumed reserves	3	2.4	3
Assumed London | Case reserves
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total assumed reserves	1.4	1.3	1.5
Assumed London | Unallocated loss adjustment expense ("ULAE")
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total assumed reserves	0	0	0
Assumed London | Incurred but not reported ("IBNR")
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total assumed reserves	$ 1.6	$ 1.1	$ 1.5

Run-off Lines - Underwriting Lo

Run-off Lines - Underwriting Losses for Run-Off Lines (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	$ (17.4)	$ (8.3)	$ (8)
Total underwriting loss - Run-off Lines	(16.1)	(14.2)	(15.9)
Reinsurance assumed
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	(5.7)	(4.4)	(3.9)
Other
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	(11.7)	(3.9)	(4.1)
Risk-management
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total underwriting loss - Run-off Lines	4.3	(4.9)	(2.6)
Run-off reinsurance lines
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total underwriting loss - Run-off Lines	0.4	0.7	0
Other run-off lines
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total underwriting loss - Run-off Lines	$ (3.4)	$ (1.7)	$ (5.3)

Long-term Debt - Additional Inf

Long-term Debt - Additional Information (Detail) £ in Millions	Nov. 02, 2018USD ($)	Dec. 31, 2020USD ($)debtInstrument	Dec. 31, 2019USD ($)	Dec. 31, 2019GBP (£)	Mar. 02, 2017USD ($)
Debt Instrument [Line Items]
Redemption price, percentage		100.00%
Junior subordinated debentures		$ 257,800,000	$ 257,400,000
Floating rate loan stock denominated in Euros		44,200,000	39,800,000
Principal		143,800,000	143,800,000
Amount of collateral under reinsurance agreement		1,131,400,000	$ 1,184,700,000
Letter of Credit
Debt Instrument [Line Items]
Letter of credit facility amount outstanding		167,000,000
New Credit Agreement
Debt Instrument [Line Items]
Line of credit, maximum borrowing amount	$ 325,000,000
New Credit Agreement | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Interest rate basis spread			1.25%
Debt instrument interest rate stated percentage			3.18%	3.18%
New Credit Agreement | Term loan
Debt Instrument [Line Items]
Principal	125,000,000
New Credit Agreement | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit, maximum borrowing amount	200,000,000
Principal	200,000,000
Letter of credit facility amount outstanding	0
New Credit Agreement | Letter of Credit
Debt Instrument [Line Items]
Letter of credit facility amount outstanding	70,500,000
Prior Agreement
Debt Instrument [Line Items]
Line of credit, maximum borrowing amount					$ 325,000,000
Repayments of borrowings	$ 125,000,000
Reinsurance Credit Facilities, Secured Bilateral Line of Credit Facilities | Letter of Credit
Debt Instrument [Line Items]
Letter of credit facility amount outstanding		205,000,000
Amount of collateral under reinsurance agreement		189,400,000
Committed Secured Bilateral Facility | Letter of Credit
Debt Instrument [Line Items]
Letter of credit facility amount outstanding		$ 58,100,000
Number of letters of credit | debtInstrument		1
Debt instrument, term		1 year
Uncommitted Secured Bilateral Facility | Letter of Credit
Debt Instrument [Line Items]
Letter of credit facility amount outstanding		$ 108,900,000
Number of letters of credit | debtInstrument		2
Funds at Lloyd's Instrument | Letter of Credit
Debt Instrument [Line Items]
Letter of credit facility amount outstanding | £				£ 23.3
Unsecured Line of Credit Facility | Letter of Credit
Debt Instrument [Line Items]
Amount of collateral under reinsurance agreement		$ 3,900,000	$ 3,100,000
Junior subordinated debentures
Debt Instrument [Line Items]
Redemption price, percentage		100.00%	100.00%
Junior Subordinated Debentures, Maybrooke
Debt Instrument [Line Items]
Junior subordinated debentures		$ 91,800,000
Unsecured debentures		85,100,000	$ 84,700,000
Principal		$ 91,800,000	$ 91,800,000
Debt instrument interest rate stated percentage		3.37%	5.04%	5.04%
Junior Subordinated Debentures, Maybrooke | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Interest rate basis spread		3.15%	3.15%
Unsecured debt
Debt Instrument [Line Items]
Redemption price, percentage			100.00%

Long-term Debt - Schedule of Ju

Long-term Debt - Schedule of Junior Subordinated Debentures (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Junior subordinated debentures, Amount	$ 257.8	$ 257.4
Argo Group
Debt Instrument [Line Items]
Junior subordinated debentures, Amount	$ 28.4	$ 28.4
Trust Preferred Debentures | Argo Group | PXRE Capital Statutory Trust II
Debt Instrument [Line Items]
Interest rate	4.32%	6.01%
Junior subordinated debentures, Amount	$ 18	$ 18.1
Trust Preferred Debentures | Argo Group | PXRE Capital Trust VI
Debt Instrument [Line Items]
Interest rate	4.15%	5.84%
Junior subordinated debentures, Amount	$ 10.3	$ 10.3
Trust Preferred Debentures | Argo Group US
Debt Instrument [Line Items]
Junior subordinated debentures, Amount	$ 172.7	$ 172.7
Trust Preferred Debentures | Argo Group US | Argonaut Group Statutory Trust I
Debt Instrument [Line Items]
Interest rate	4.32%	6.01%
Junior subordinated debentures, Amount	$ 15.5	$ 15.5
Trust Preferred Debentures | Argo Group US | Argonaut Group Statutory Trust III
Debt Instrument [Line Items]
Interest rate	4.34%	6.09%
Junior subordinated debentures, Amount	$ 12.3	$ 12.3
Trust Preferred Debentures | Argo Group US | Argonaut Group Statutory Trust IV
Debt Instrument [Line Items]
Interest rate	4.07%	5.76%
Junior subordinated debentures, Amount	$ 13.4	$ 13.4
Trust Preferred Debentures | Argo Group US | Argonaut Group Statutory Trust V
Debt Instrument [Line Items]
Interest rate	4.05%	5.76%
Junior subordinated debentures, Amount	$ 12.4	$ 12.3
Trust Preferred Debentures | Argo Group US | Argonaut Group Statutory Trust VI
Debt Instrument [Line Items]
Interest rate	4.03%	5.70%
Junior subordinated debentures, Amount	$ 13.4	$ 13.4
Trust Preferred Debentures | Argo Group US | Argonaut Group Statutory Trust VII
Debt Instrument [Line Items]
Interest rate	3.82%	5.49%
Junior subordinated debentures, Amount	$ 15.5	$ 15.5
Trust Preferred Debentures | Argo Group US | Argonaut Group Statutory Trust VIII
Debt Instrument [Line Items]
Interest rate	3.79%	5.48%
Junior subordinated debentures, Amount	$ 15.5	$ 15.5
Trust Preferred Debentures | Argo Group US | Argonaut Group Statutory Trust IX
Debt Instrument [Line Items]
Interest rate	3.82%	5.49%
Junior subordinated debentures, Amount	$ 15.5	$ 15.5
Trust Preferred Debentures | Argo Group US | Argonaut Group Statutory Trust X
Debt Instrument [Line Items]
Interest rate	3.62%	5.29%
Junior subordinated debentures, Amount	$ 30.9	$ 30.9
London Interbank Offered Rate (LIBOR) | Trust Preferred Debentures | Argo Group | PXRE Capital Statutory Trust II
Debt Instrument [Line Items]
Interest rate basis spread	4.10%	4.10%
London Interbank Offered Rate (LIBOR) | Trust Preferred Debentures | Argo Group | PXRE Capital Trust VI
Debt Instrument [Line Items]
Interest rate basis spread	3.90%	3.90%
London Interbank Offered Rate (LIBOR) | Trust Preferred Debentures | Argo Group US | Argonaut Group Statutory Trust I
Debt Instrument [Line Items]
Interest rate basis spread	4.10%	4.10%
London Interbank Offered Rate (LIBOR) | Trust Preferred Debentures | Argo Group US | Argonaut Group Statutory Trust III
Debt Instrument [Line Items]
Interest rate basis spread	4.10%	4.10%
London Interbank Offered Rate (LIBOR) | Trust Preferred Debentures | Argo Group US | Argonaut Group Statutory Trust IV
Debt Instrument [Line Items]
Interest rate basis spread	3.85%	3.85%
London Interbank Offered Rate (LIBOR) | Trust Preferred Debentures | Argo Group US | Argonaut Group Statutory Trust V
Debt Instrument [Line Items]
Interest rate basis spread	3.85%	3.85%
London Interbank Offered Rate (LIBOR) | Trust Preferred Debentures | Argo Group US | Argonaut Group Statutory Trust VI
Debt Instrument [Line Items]
Interest rate basis spread	3.80%	3.80%
London Interbank Offered Rate (LIBOR) | Trust Preferred Debentures | Argo Group US | Argonaut Group Statutory Trust VII
Debt Instrument [Line Items]
Interest rate basis spread	3.60%	3.60%
London Interbank Offered Rate (LIBOR) | Trust Preferred Debentures | Argo Group US | Argonaut Group Statutory Trust VIII
Debt Instrument [Line Items]
Interest rate basis spread	3.55%	3.55%
London Interbank Offered Rate (LIBOR) | Trust Preferred Debentures | Argo Group US | Argonaut Group Statutory Trust IX
Debt Instrument [Line Items]
Interest rate basis spread	3.60%	3.60%
London Interbank Offered Rate (LIBOR) | Trust Preferred Debentures | Argo Group US | Argonaut Group Statutory Trust X
Debt Instrument [Line Items]
Interest rate basis spread	3.40%	3.40%

Long-term Debt - Schedule of Ma

Long-term Debt - Schedule of Maybrooke Junior Subordinated Debentures (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Principal	$ 143,800,000	$ 143,800,000
Junior Subordinated Debentures, Maybrooke
Debt Instrument [Line Items]
Interest rate	3.37%	5.04%
Principal	$ 91,800,000	$ 91,800,000
Carrying Value	$ 85,100,000	$ 84,700,000
London Interbank Offered Rate (LIBOR) | Junior Subordinated Debentures, Maybrooke
Debt Instrument [Line Items]
Interest rate basis spread	3.15%	3.15%

Long-term Debt- Schedule of Ter

Long-term Debt- Schedule of Terms and Principal Amounts of Other Indebtedness (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Other indebtedness	$ 60.7	$ 181.3
Term loan
Debt Instrument [Line Items]
Other indebtedness	0	125
Floating rate loan stock
Debt Instrument [Line Items]
Other indebtedness	$ 60.7	$ 56.3

Long-term Debt - Schedule of Fl

Long-term Debt - Schedule of Floating Rate Loan Stock, Notes Outstanding (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Amount	$ 60.7	$ 56.3
Floating Rate Loan Stock, U.S. Dollar, Start Year 2004
Debt Instrument [Line Items]
Interest rate	4.54%	6.41%
Amount	$ 6.5	$ 6.5
Floating Rate Loan Stock, U.S. Dollar, Start Year 2006
Debt Instrument [Line Items]
Interest rate	4.34%	6.21%
Amount	$ 10	$ 10
Floating Rate Loan Stock, U.S. Dollar
Debt Instrument [Line Items]
Amount	$ 16.5	$ 16.5
Floating Rate Loan Stock, Euro, Start Year 2005
Debt Instrument [Line Items]
Interest rate	3.47%	3.58%
Amount	$ 14.7	$ 13.3
Floating Rate Loan Stock, Euro, Start Year 2006
Debt Instrument [Line Items]
Interest rate	3.47%	3.58%
Amount	$ 12.9	$ 11.6
Floating Rate Loan Stock, Euro, Start Year 2007
Debt Instrument [Line Items]
Interest rate	3.36%	3.47%
Amount	$ 16.6	$ 14.9
Floating Rate Loan Stock, Euro
Debt Instrument [Line Items]
Amount	$ 44.2	$ 39.8
London Interbank Offered Rate (LIBOR) | Floating Rate Loan Stock, U.S. Dollar, Start Year 2004
Debt Instrument [Line Items]
Interest rate basis spread	4.20%	4.20%
London Interbank Offered Rate (LIBOR) | Floating Rate Loan Stock, U.S. Dollar, Start Year 2006
Debt Instrument [Line Items]
Interest rate basis spread	4.00%	4.00%
London Interbank Offered Rate (LIBOR) | Floating Rate Loan Stock, Euro, Start Year 2005
Debt Instrument [Line Items]
Interest rate basis spread	4.00%	4.00%
London Interbank Offered Rate (LIBOR) | Floating Rate Loan Stock, Euro, Start Year 2006
Debt Instrument [Line Items]
Interest rate basis spread	4.00%	4.00%
London Interbank Offered Rate (LIBOR) | Floating Rate Loan Stock, Euro, Start Year 2007
Debt Instrument [Line Items]
Interest rate basis spread	3.90%	3.90%

Long-term Debt - Schedule of Lo

Long-term Debt - Schedule of Long-term Debt Maturity (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Total	$ 458.7	$ 578.7
Junior subordinated debentures
Debt Instrument [Line Items]
Total	411
2021	10.1
2022	10.1
2023	10.1
2024	10.1
2025	10.1
Thereafter	360.5
Senior unsecured fixed rate notes
Debt Instrument [Line Items]
Total	347
2021	9.3
2022	9.4
2023	9.3
2024	9.4
2025	9.3
Thereafter	300.3
Floating rate loan stock
Debt Instrument [Line Items]
Total	94.4
2021	2.3
2022	2.3
2023	2.3
2024	2.3
2025	2.3
Thereafter	$ 82.9

Disclosures about Fair Value _3

Disclosures about Fair Value of Financial Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Junior subordinated debentures | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	$ 257.8	$ 257.4
Junior subordinated debentures | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	265.9	266.5
Junior subordinated debentures | Trust Preferred Debentures | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	172.7	172.7
Junior subordinated debentures | Trust Preferred Debentures | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	173.6	174
Junior subordinated debentures | Junior Subordinated Debentures, Maybrooke | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	85.1	84.7
Junior subordinated debentures | Junior Subordinated Debentures, Maybrooke | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	92.3	92.5
Senior unsecured fixed rate notes | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	140.2	140
Senior unsecured fixed rate notes | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	146.7	144.2
Floating rate loan stock | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	60.7	56.3
Floating rate loan stock | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	$ 61	$ 56.8

Disclosures about Fair Value _4

Disclosures about Fair Value of Financial Instruments - Summary of Fair Values Measured on Recurring Basis (Details) - Fair Value, Recurring - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	$ 473.6	$ 467.5
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	146.7	144.2
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	326.9	323.3
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Junior subordinated debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	265.9	266.5
Junior subordinated debentures | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Junior subordinated debentures | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	265.9	266.5
Junior subordinated debentures | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Senior unsecured fixed rate notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	146.7	144.2
Senior unsecured fixed rate notes | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	146.7	144.2
Senior unsecured fixed rate notes | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Senior unsecured fixed rate notes | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Floating rate loan stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	61	56.8
Floating rate loan stock | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Floating rate loan stock | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	61	56.8
Floating rate loan stock | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Trust Preferred Debentures | Junior subordinated debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	173.6	174
Trust Preferred Debentures | Junior subordinated debentures | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Trust Preferred Debentures | Junior subordinated debentures | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	173.6	174
Trust Preferred Debentures | Junior subordinated debentures | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Junior Subordinated Debentures, Maybrooke | Junior subordinated debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	92.3	92.5
Junior Subordinated Debentures, Maybrooke | Junior subordinated debentures | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Junior Subordinated Debentures, Maybrooke | Junior subordinated debentures | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	92.3	92.5
Junior Subordinated Debentures, Maybrooke | Junior subordinated debentures | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	$ 0	$ 0

Shareholders' Equity - Addition

Shareholders' Equity - Additional Information (Detail) - USD ($)	Sep. 17, 2020	Jul. 09, 2020	Mar. 21, 2018	Feb. 20, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	May 03, 2016
Class of Stock [Line Items]
Preferred shares, issued (in shares)					6,000	0
Depositary shares issued (in shares)		6,000,000
Preferred stock, liquidation preference (in dollars per share)					$ 25,000
Depositary share, liquidation preference (in dollars per share)		$ 25
Proceeds from sale of depositary shares		$ 144,000,000
Extinguishment of debt, amount	$ 125,000,000
Preferred stock, per depositary share amounts of preferred dividends (in dollars per share)		$ 1.75
Depositary shares, dividends declared (in dollars per share)					$ 0.768056
Preferred shares, authorized (in shares)					30,000,000	30,000,000
Preferred shares, par value (in dollars per share)					$ 1	$ 1
Preferred shares, outstanding (in shares)					6,000	0
Stock dividend declared (in percentage)							15.00%
Dividend declared per common share (in dollars per share)					$ 1.24	$ 1.24	$ 1.08
Cash dividends paid to common stockholders					$ 43,000,000	$ 43,100,000	$ 37,500,000
Common shares repurchased on open market (in shares)					0	0	530,882
Series A Preferred Stock
Class of Stock [Line Items]
Preferred shares, issued (in shares)		6,000
Preferred stock, liquidation preference (in dollars per share)		$ 25,000
Preferred stock, dividend rate (in percentage)		7.00%
Preferred stock dividends (in dollars per share)		$ 1,750
Dividends declared per preferred share (in dollars per share)					$ 768.056
Payments of dividends					$ 4,600,000
Series A Preferred Stock | US Treasury (UST) Interest Rate
Class of Stock [Line Items]
Preferred stock, dividend payment rate, Basis spread on variable rate (in percentage)		6.712%
2016 Repurchase Authorization
Class of Stock [Line Items]
Remaining number of shares available under repurchase authorization, value					$ 53,300,000
Maximum | 2016 Repurchase Authorization
Class of Stock [Line Items]
Total number of shares authorized for purchase, value								$ 150,000,000
Stock Dividend
Class of Stock [Line Items]
Stock dividend declared (in percentage)				15.00%
Additional stock issued as dividend (in shares)			4,397,520	4,397,520

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 1,763.7	$ 1,735	$ 1,812.9
Other comprehensive (loss) income before reclassifications	62.9	72.2
Amounts reclassified from accumulated other comprehensive income	(12.8)	8.7
Net current-period other comprehensive (loss) income	50.1	80.9
Ending Balance	1,857.8	1,763.7	1,735
Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(2.2)
Ending Balance		(2.2)
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(22.6)	(22.4)
Other comprehensive (loss) income before reclassifications	(15.3)	(0.2)
Amounts reclassified from accumulated other comprehensive income	0	0
Net current-period other comprehensive (loss) income	(15.3)	(0.2)
Ending Balance	(37.9)	(22.6)	(22.4)
Foreign Currency Translation Adjustments | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	0
Ending Balance		0
Unrealized Gains and Losses on Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	33.5	(49)
Other comprehensive (loss) income before reclassifications	78.7	73.8
Amounts reclassified from accumulated other comprehensive income	(12.8)	8.7	4.9
Net current-period other comprehensive (loss) income	65.9	82.5
Ending Balance	105.1	33.5	(49)
Unrealized Gains and Losses on Securities | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	5.7
Ending Balance		5.7
Defined Benefit Pension Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(8.1)	(6.7)
Other comprehensive (loss) income before reclassifications	(0.5)	(1.4)
Amounts reclassified from accumulated other comprehensive income	0	0
Net current-period other comprehensive (loss) income	(0.5)	(1.4)
Ending Balance	(8.6)	(8.1)	(6.7)
Defined Benefit Pension Plans | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	0
Ending Balance		0
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	2.8	(78.1)	96.6
Ending Balance	58.6	2.8	$ (78.1)
AOCI Attributable to Parent | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 5.7
Ending Balance		$ 5.7

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Loss) - Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Unrealized gains and losses on securities:
Net of taxes	$ (12.8)	$ 8.7
Unrealized Gains and Losses on Securities
Unrealized gains and losses on securities:
Net realized investment (gains) loss	(12.8)	9.9	$ 5.4
Benefit for income taxes	0	(1.2)	(0.5)
Net of taxes	$ (12.8)	$ 8.7	$ 4.9

Net (Loss) Income Per Common _3

Net (Loss) Income Per Common Share - Net (Loss) Income Per Common Share on Basic and Diluted Basis (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended							6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Net (loss) income	$ (23.1)	$ (5.4)	$ (24.7)	$ (102.7)	$ (26)	$ 27	$ 87.6	$ (30.1)	$ 114.6	$ (53.2)	$ 88.6	$ (54.1)	$ (14.1)	$ 57
Dividends on preferred shares												4.6	0	0
Net (loss) income attributable to common shareholders	$ (25.1)				$ (26)					$ (55.2)	$ 88.6	$ (58.7)	$ (14.1)	$ 57
Weighted average common shares outstanding - basic (in shares)												34,614,813	34,205,954	33,922,009
Effect of dilutive securities:
Equity compensation awards (in shares)												0	0	756,772
Weighted average common shares outstanding - diluted (in shares)												34,614,813	34,205,954	34,678,781
Net (loss) income per common share:
Basic (in dollars per share)	$ (0.72)	$ (0.16)	$ (0.72)	$ (2.99)	$ (0.76)	$ 0.79	$ 2,580,000	$ (0.87)	$ 3.36	$ (1.60)	$ 2.59	$ (1.70)	$ (0.41)	$ 1.68
Diluted (in dollars per share)	$ (0.72)	$ (0.16)	$ (0.72)	$ (2.99)	$ (0.76)	$ 0.78	$ 2,520,000	$ (0.87)	$ 3.30	$ (1.60)	$ 2.55	$ (1.70)	$ (0.41)	$ 1.65

Net (Loss) Income Per Common _4

Net (Loss) Income Per Common Share - Additional Information (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Treasury shares (in shares)	11,315,889	11,315,889	11,315,889
Anti-dilutive securities excluded from computation of diluted net income per common share (in shares)	197,035	587,462	0

Share-based Compensation - Addi

Share-based Compensation - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	May 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment expense		$ 8,700,000	$ 16,900,000	$ 18,300,000
Share-based payments expense, net of tax		7,800,000	$ 15,500,000	16,500,000
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee service share-based compensation, unrecognized compensation costs on non-vested awards		$ 14,600,000
Employee service share-based compensation, unrecognized compensation costs recognition period		2 years 2 months 12 days
Share-based compensation, restricted shares , vested in period, fair value		$ 10,000,000
Options outstanding (in shares)		527,874	471,271
Restricted Stock Units (RSUs) | Performance Condition
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding (in shares)		124,892
Stock-Settled SARs Activity
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment expense		$ 0
Exercised (in shares)		470,182
Share based compensation arrangement by share based payment award, shares issued (in shares)		124,220
Share based compensation arrangement by share based payment award options exercises, intrinsic value		$ 1,100,000
Remaining contractual term		10 months 6 days
Share-based Payment Arrangement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment expense		$ 700,000	$ 500,000	$ 400,000
2019 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of additional shares authorized (in shares)	1,885,000
Expiration period	10 years
2007 Employee Share Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period, years		3 months
Discount from market price		85.00%
Earn Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount from market price		85.00%
Earn Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period, years		3 years
Earn Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period, years		5 years

Share-based Compensation - Summ

Share-based Compensation - Summary of Restricted Share Activity (Detail) - Restricted Stock Units (RSUs)	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Shares
Outstanding, beginning balance (in shares) | shares	471,271
Granted (in shares) | shares	399,578
Vested and issued (in shares) | shares	(177,918)
Expired or forfeited (in shares) | shares	(165,057)
Outstanding, ending balance (in shares) | shares	527,874
Weighted-Average Grant Date Fair Value
Outstanding, weighted-average grant date fair value, beginning balance (in dollars per share) | $ / shares	$ 60.09
Granted (in dollars per share) | $ / shares	32.53
Vested and issued (in dollars per share) | $ / shares	51.25
Expired or forfeited (in dollars per share) | $ / shares	50.89
Outstanding, weighted-average grant date fair value, ending balance (in dollars per share) | $ / shares	$ 43.37

Share-based Compensation - Su_2

Share-based Compensation - Summary of Stock-Settled SARs Activity (Detail) - Stock-Settled SARs Activity	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Shares
Outstanding, beginning balance (in shares) | shares	625,368
Exercised (in shares) | shares	(470,182)
Expired or forfeited (in shares) | shares	(15,031)
Outstanding, ending balance (in shares) | shares	140,155
Weighted-Average Exercise Price
Outstanding, weighted-average exercise price, beginning balance (in dollars per share) | $ / shares	$ 33.60
Exercised (in dollars per share) | $ / shares	32.75
Expired or forfeited (in dollars per share) | $ / shares	37.85
Outstanding, weighted-average exercise price, ending balance (in dollars per share) | $ / shares	$ 35.98

Underwriting, Acquisition and_3

Underwriting, Acquisition and Insurance Expenses & Other Corporate Expenses (Detail) - USD ($) $ in Millions	3 Months Ended						6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Underwriting Acquisition And Insurance Expenses [Abstract]
Commissions											$ 268	$ 241.3	$ 281.3
General expenses											391	379.3	352.2
Premium taxes, boards and bureaus											29.7	33	32.5
Underwriting, acquisition and insurance expenses, total											688.7	653.6	666
Net deferral of policy acquisition costs											(9.3)	12.4	(9.9)
Total underwriting, acquisition and insurance expenses	$ 164.5	$ 161.3	$ 168.1	$ 180.2	$ 164	$ 161.6	$ 329.4	$ 321.8	$ 493.9	$ 485.8	679.4	666	656.1
Other corporate expenses											$ 5.8	$ 37.6	$ 0
Civil penalties		$ 0.9

Income Taxes - Income Tax (Bene

Income Taxes - Income Tax (Benefit) Provision Expense (Detail) - USD ($) $ in Millions	3 Months Ended							6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current income tax provision (benefit) related to:
United States (Federal)												$ 28	$ 37.3	$ 20.8
United States (State)												1.4	1.7	1.4
United Kingdom												(0.1)	(1.5)	3.1
Other jurisdictions												0	0.1	0.1
Total current income tax provision												29.3	37.6	25.4
Deferred income tax provision (benefit) related to:
United States												(5.1)	(17.7)	(21.6)
United Kingdom												(16.6)	(5.8)	0.1
Other jurisdictions												0.1	0	0.1
Total deferred income tax (benefit)												(21.6)	(23.5)	(21.4)
Income tax provision (benefit)	$ (3.4)	$ 11.3	$ (1)	$ 0.5	$ (1.1)	$ 0.8	$ 13.9	$ 10.3	$ 14.7	$ 6.9	$ 13.6	$ 7.7	$ 14.1	$ 4

Income Taxes - Schedule of Pre-

Income Taxes - Schedule of Pre-Tax Income (Loss) and Effective Income Tax Rates (Detail) - USD ($) $ in Millions	3 Months Ended							6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (26.5)	$ 5.9	$ (25.7)	$ (102.2)	$ (27.1)	$ 27.8	$ 101.5	$ (19.8)	$ 129.3	$ (46.3)	$ 102.2	$ (46.4)	$ 0	$ 61
Effective Tax Rate												(16.60%)	0.00%	6.60%
Bermuda
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)												$ (56.2)	$ (34.7)	$ 22
Effective Tax Rate												0.00%	0.00%	0.00%
United States (Federal)
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)												$ 103.3	$ 84.7	$ 12.1
Effective Tax Rate												22.70%	24.60%	(1.00%)
United Kingdom
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)												$ (100.6)	$ (45.9)	$ 24.1
Effective Tax Rate												15.70%	14.90%	14.70%
Belgium
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)												$ 0.2	$ 0	$ 0
Effective Tax Rate												30.70%	15.80%	0.00%
Brazil
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)												$ 3.9	$ 5.2	$ (0.5)
Effective Tax Rate												0.00%	0.00%	0.00%
United Arab Emirates
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)												$ 2.1	$ 0.4	$ 0.8
Effective Tax Rate												0.00%	0.00%	0.00%
Ireland
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)												$ 1.8	$ (0.1)	$ (0.2)
Effective Tax Rate												0.00%	0.00%	0.00%
Italy
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)												$ 0.6	$ (7.4)	$ 0.9
Effective Tax Rate												0.00%	0.00%	0.00%
Malta
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)												$ (1.4)	$ (2)	$ 1.7
Effective Tax Rate												0.00%	0.00%	0.00%
Luxembourg
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)												$ 0	$ 0	$ 0
Effective Tax Rate												0.00%	0.00%	0.00%
Switzerland
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)												$ (0.1)	$ (0.2)	$ 0.1
Effective Tax Rate												0.00%	(0.20%)	18.40%

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Difference Between Provision for Income Taxes and Expected Tax Provision at Weighted Average Tax Rate (Detail) - USD ($) $ in Millions	3 Months Ended							6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income tax provision (benefit) at expected rate												$ 4	$ 8.9	$ 7.7
Tax effect of:
Nontaxable investment income												(0.7)	(1.2)	(1.9)
Foreign exchange adjustments												1.6	(0.1)	(0.6)
Impairment of goodwill												1	2.9	0
Withholding taxes												0.1	0.2	0.4
Change in uncertain tax position liability												0.7	1.4	1.8
Change in valuation allowance												0.5	(1.8)	(1.5)
Impact of change in tax rate related to TCJA												0	0	(0.8)
Other												0.5	3.8	(1.1)
Income tax provision (benefit)	$ (3.4)	$ 11.3	$ (1)	$ 0.5	$ (1.1)	$ 0.8	$ 13.9	$ 10.3	$ 14.7	$ 6.9	$ 13.6	$ 7.7	$ 14.1	$ 4

Income Taxes - Schedule of Net

Income Taxes - Schedule of Net Deferred Tax Liability Comprises Tax Effect Related to Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Losses and loss adjustment expense reserve discounting	$ 29.2	$ 24.6
Unearned premiums	25.9	25.3
Net operating loss carryforwards	27.9	28.3
Investment in limited partnership interests	7.8	10.3
Investments	2	2.2
Right of use assets	12.7	14.5
Accrued compensation	6.3	3.8
Stock option expense	0.7	1.1
United Kingdom underwriting results	21.9	4.2
Other	9.6	6.3
Deferred tax assets, gross	144	120.6
Deferred tax liabilities:
Unrealized gains on equity securities	(5.7)	(2.6)
Unrealized gains on fixed maturities and other investment securities	(22.3)	(6.1)
Unrealized gains on limited partnership interests	(14.7)	(15.6)
Depreciable fixed assets	(20.5)	(21.6)
Deferred acquisition costs	(20.4)	(18.6)
Lease liability	(11.7)	(14)
TCJA reserve transitional liability	(2.7)	(3.2)
Other	(0.7)	(0.2)
Deferred tax liabilities, gross	(98.7)	(81.9)
Deferred tax assets, net before valuation allowance	45.3	38.7
Valuation allowance	(28.6)	(28.1)
Net deferred assets	16.7	10.6
Net deferred assets	16.7	10.6
Foreign Tax Authority
Deferred tax liabilities:
Net deferred assets	21.4	4.4
Net deferred assets	21.4	4.4
Domestic Tax Authority
Deferred tax liabilities:
Net deferred liabilities	$ (4.7)
Net deferred assets		6.2
Net deferred assets		$ 6.2

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Net operating losses carryback period	2 years
Capital losses carryback period	3 years
Net change in valuation allowance, for deferred tax asset	$ 0.5
Unrecognized tax benefits	8.2	$ 7.5	$ 6.1
Decrease in unrecognized tax benefits is reasonably possible	4.3
Unrecognized tax benefits, interest expense on income taxes	0.5	0.5	0.3
Tax penalty expense	$ 0.1	$ 0.2	$ 0.5

Income Taxes - Schedule of Ne_2

Income Taxes - Schedule of Net Operating Loss Carryforwards Amounts by Jurisdiction and Year of Expiration (Detail) $ in Millions	Dec. 31, 2020USD ($)
Brazil | Indefinite Expiration
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards by jurisdiction:	$ 0.7
Italy | Indefinite Expiration
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards by jurisdiction:	49.6
Malta | Indefinite Expiration
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards by jurisdiction:	14.3
United States (Federal) | Expiration Year From 2025 - 2037
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards by jurisdiction:	$ 43.3

Income Taxes - Schedule of Unre

Income Taxes - Schedule of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Balance at January 1	$ 7.5	$ 6.1
Additions for tax positions of prior years	0	0
Reductions for tax positions of prior years	0	0
Additions based on tax positions related to current year	0.7	1.4
Reductions based on tax positions related to current year	0	0
Reductions based on settlements with taxing authorities	0	0
Expiration of statute of limitations	0	0
Balance at December 31	$ 8.2	$ 7.5

Pension Benefits and Savings _2

Pension Benefits and Savings Plans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 0.1	$ 0.3
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer towards savings plan	9.2	8.9	$ 7.9
Qualified Plan | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Underfunded amount	4.2	3.7
Nonqualified Plan | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Underfunded amount	$ 2	$ 2

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - Maximum $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Commitments And Contingencies [Line Items]
Contractual commitments related to its limited partnership investments, up to	$ 80
Contractual commitments period	12 years

Segment Information - Additiona

Segment Information - Additional Information (Detail) $ in Millions	Nov. 25, 2020USD ($)	Apr. 30, 2020USD ($)	Dec. 31, 2020USD ($)segment	Dec. 31, 2019USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment			2
Assets associated with trade capital providers			$ 825.9	$ 916.3
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale			$ 7.7	$ 15.4
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Trident
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Goodwill derecognized		$ 4.9
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Ariel Re
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Goodwill derecognized	$ 9.2
Intangible assets derecognized	$ 30.2

Segment Information - Revenue a

Segment Information - Revenue and Income (Loss) Before Income Taxes for Each Segment (Detail) - USD ($) $ in Millions	3 Months Ended							6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Earned premiums				$ 425.8	$ 451.5	$ 431.7	$ 420.7		$ 852.4		$ 1,303.9	$ 1,780.5	$ 1,729.7	$ 1,731.5
Net investment income		$ 1.4	$ 35.6					$ 37				112.7	151.1	132.3
Fee and other income												7.9	9.1	9
Net realized investment and other (losses) gains	$ (5.7)	18.4	(36.2)	21.8				(17.8)		$ (23.5)		(7.2)	80.1	(72)
Total revenue	483.5	455.2	436.5	484.6	487.4	488.6	509.4	891.7	998	1,375.2	1,485.4	1,893.9	1,970	1,800.8
Foreign currency exchange (losses) gains	(8.4)	(4.3)	(0.9)	4.5	0.9	3.8	0.6	(5.2)	4.4	(13.6)	5.3	(15.4)	9.8	(3.9)
Other corporate expenses												(5.8)	(37.6)	0
Net (loss) income before income taxes	$ (26.5)	$ 5.9	$ (25.7)	$ (102.2)	$ (27.1)	$ 27.8	$ 101.5	$ (19.8)	$ 129.3	$ (46.3)	$ 102.2	(46.4)	0	61
U.S. Operations
Segment Reporting Information [Line Items]
Earned premiums												1,207.6	1,119.9	1,078.7
Net investment income												80.3	100	82.9
International Operations
Segment Reporting Information [Line Items]
Earned premiums												572.5	609.6	652.5
Net investment income												26.7	44.2	32.9
Run-off Lines
Segment Reporting Information [Line Items]
Earned premiums												0.4	0.2	0.3
Net investment income												4	5.7	8.1
Operating Segments
Segment Reporting Information [Line Items]
Net (loss) income before income taxes												16.7	(7.5)	183.9
Operating Segments | U.S. Operations
Segment Reporting Information [Line Items]
Earned premiums												1,207.6	1,119.9	1,078.7
Net investment income												80.3	100	82.9
Net (loss) income before income taxes												111.7	139.3	161.2
Operating Segments | International Operations
Segment Reporting Information [Line Items]
Earned premiums												572.5	609.6	652.5
Net investment income												26.7	44.2	32.9
Net (loss) income before income taxes												(82.1)	(137)	32
Operating Segments | Run-off Lines
Segment Reporting Information [Line Items]
Earned premiums												0.4	0.2	0.3
Net investment income												4	5.7	8.1
Net (loss) income before income taxes												(12.9)	(9.8)	(9.3)
Corporate and Other
Segment Reporting Information [Line Items]
Net investment income												1.7	1.2	8.4
Net (loss) income before income taxes												$ (34.7)	$ (44.8)	$ (47)

Segment Information - Schedule

Segment Information - Schedule of Earned Premiums by Geographic Location (Detail) - USD ($) $ in Millions	3 Months Ended				6 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2019	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	$ 425.8	$ 451.5	$ 431.7	$ 420.7	$ 852.4	$ 1,303.9	$ 1,780.5	$ 1,729.7	$ 1,731.5
United States (Federal)
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums							1,205	1,115.8	1,072.9
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums							361.1	391.5	455.8
Bermuda
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums							96.5	80.7	85.4
Malta
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums							59.5	85	61
All other jurisdictions
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums							$ 58.4	$ 56.7	$ 56.4

Segment Information - Identifia

Segment Information - Identifiable Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	$ 10,465.8	$ 10,721.7	$ 10,378.3	$ 10,177.9	$ 10,508.8	$ 10,434.4	$ 10,153.4	$ 9,942.9
Operating Segments | U.S. Operations
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	6,032.2				5,013.7
Operating Segments | International Operations
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	3,899.4				4,996
Operating Segments | Run-off Lines
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	335.9				356.9
Corporate and Other
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	$ 198.3				$ 142.2

Segment Information - Schedul_2

Segment Information - Schedule of Goodwill and Intangible Assets Net of Accumulated Amortization (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Goodwill	$ 147.3	$ 161.4
Intangible Assets, Net of Accumulated Amortization	60.5	91.8
U.S. Operations
Segment Reporting Information [Line Items]
Goodwill	118.6	123.5
Intangible Assets, Net of Accumulated Amortization	0	0
International Operations
Segment Reporting Information [Line Items]
Goodwill	28.7	37.9
Intangible Assets, Net of Accumulated Amortization	$ 60.5	$ 91.8

Statutory Accounting Principl_3

Statutory Accounting Principles - Statutory Capital and Surplus for Principal Operating Subsidiaries (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Bermuda
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	$ 1,482.8	$ 1,460.8
United Kingdom
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	534.7	443.1
United States (Federal)
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	$ 1,072.1	$ 1,051.4

Statutory Accounting Principl_4

Statutory Accounting Principles - Statutory Net Income (Loss) for Principal Operating Subsidiaries (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Bermuda
Statutory Accounting Practices [Line Items]
Statutory net income (loss)	$ (35.9)	$ 7.1	$ 47.4
United Kingdom
Statutory Accounting Practices [Line Items]
Statutory net income (loss)	(53)	(15.1)	(9.5)
United States (Federal)
Statutory Accounting Practices [Line Items]
Statutory net income (loss)	$ 76.4	$ 196.1	$ 110.8

Statutory Accounting Principl_5

Statutory Accounting Principles - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Argo Re
Statutory Accounting Practices [Line Items]
Maximum permissible limit for dividend	25.00%		25.00%
Reduction in total statutory capital			15.00%
Maximum permitted amount of dividends			$ 370.7
Cash dividends			58.8	$ 52.1	$ 36.5
Rockwood Casualty Insurance Company
Statutory Accounting Practices [Line Items]
Cash dividends	$ 10	$ 30
Argonaut Insurance Company
Statutory Accounting Practices [Line Items]
Maximum permitted amount of dividends			97.5
Cash dividends		50	50
Minimum
Statutory Accounting Practices [Line Items]
Minimum statutory capital and surplus balance	$ 201.3	$ 242.9	$ 201.3	$ 242.9

Insurance Assessments (Detail)

Insurance Assessments (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Insurance [Abstract]
Insurance assessments on current insolvencies	$ 6.7	$ 6.9

Transactions with Related Par_2

Transactions with Related Parties Transactions with Related Parties (Detail) - Kinetica - Affiliated Entity - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2013
Schedule Of Other Related Party Transactions [Line Items]
Surety bonds issued		$ 13
Percentage of investment ownership		10.00%
Surety bonds outstanding	$ 12

Senior Unsecured Fixed Rate N_3

Senior Unsecured Fixed Rate Notes - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Junior subordinated debentures principal balance		$ 143,800,000	$ 143,800,000
Redemption price, percentage		100.00%
Senior unsecured fixed rate notes
Schedule of Equity Method Investments [Line Items]
Junior subordinated debentures principal balance	$ 143,750,000
Debt instrument interest rate stated percentage	6.50%
Redemption price, percentage	100.00%

Senior Unsecured Fixed Rate N_4

Senior Unsecured Fixed Rate Notes - Schedule Of Unamortized Debt Issuance Costs Deducted From Carrying Value Of Debt Liability (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Senior unsecured fixed rate notes
Principal	$ 143.8	$ 143.8
Less: unamortized debt issuance costs	(3.6)	(3.8)
Senior unsecured fixed rate notes, less unamortized debt issuance costs	$ 140.2	$ 140

Senior Unsecured Fixed Rate N_5

Senior Unsecured Fixed Rate Notes - Condensed Consolidating Balance Sheet (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Investments	$ 5,255.8			$ 4,813.1	$ 5,097.5	$ 5,128.7	$ 4,879.3	$ 4,905.2
Cash	148.8				137.8				$ 139.7
Accrued investment income	21.8				25.7
Premiums receivable	679.8	$ 790.2	$ 785	718.2	676.5	727.5	716.8	664.9	645.2		$ 594
Reinsurance recoverables	3,009				3,107.2				2,689.2
Goodwill and other intangible assets, net	207.8				253.2
Current income taxes receivable, net	3				0
Deferred tax assets, net	16.7	14.8	15.9	40.9	10.6				1.3
Deferred acquisition costs, net	163.6				160.2
Ceded unearned premiums	575.1				545
Operating leases right-of-use assets	82				91.8
Other assets	294.7	358.6	414.5	434.8	387.9	390.5					309.8
Assets held for sale	7.7				15.4
Intercompany note receivable	0				0
Investment in subsidiaries	0				0
Total assets	10,465.8	10,721.7	10,378.3	10,177.9	10,508.8	10,434.4	10,153.4	9,942.9
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	5,406				5,157.6					$ 4,654.6
Unearned premiums	1,464.8				1,410.9
Funds held and ceded reinsurance payable, net	1,015.1				1,256.4
Debt	458.7				578.7
Current income taxes payable, net	0		33.5	24.3	13.9	9.8	6.2	5.1	2.4
Accrued underwriting expenses and other liabilities	167.6	205.3	157	187.4	221.9	285.7	281	249.5	$ 263		$ 146.6
Operating lease liabilities	95.8				105.7
Due to (from) affiliates	0				0
Total liabilities	8,608	8,873	8,670.6	8,564.4	8,745.1	8,559	8,241.5	8,077.6
Total shareholders' equity	1,857.8	1,848.7	1,707.7	1,613.5	1,763.7	1,875.4	1,911.9	1,865.3		1,735		$ 1,812.9
Total liabilities and shareholders' equity	10,465.8	$ 10,721.7	$ 10,378.3	$ 10,177.9	10,508.8	$ 10,434.4	$ 10,153.4	$ 9,942.9
Consolidating Adjustments
Assets
Investments	0				0
Cash	0				0
Accrued investment income	0				0
Premiums receivable	0				0
Reinsurance recoverables	0				0
Goodwill and other intangible assets, net	0				0
Current income taxes receivable, net	0
Deferred tax assets, net	0				0
Deferred acquisition costs, net	0				0
Ceded unearned premiums	0				0
Operating leases right-of-use assets	0				0
Other assets	0				0
Assets held for sale	0				0
Intercompany note receivable	0				0
Investment in subsidiaries	(1,881.9)				(1,899.3)
Total assets	(1,881.9)				(1,899.3)
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	0				0
Unearned premiums	0				0
Funds held and ceded reinsurance payable, net	0				0
Debt	0				0
Current income taxes payable, net					0
Accrued underwriting expenses and other liabilities	0				0
Operating lease liabilities	0				0
Due to (from) affiliates	(7.5)				(19.3)
Total liabilities	(7.5)				(19.3)
Total shareholders' equity	(1,874.4)				(1,880)
Total liabilities and shareholders' equity	(1,881.9)				(1,899.3)
Other Subsidiaries and Eliminations
Assets
Investments	1,626.4				1,691.3
Cash	128.4				104.3
Accrued investment income	5.1				7.5
Premiums receivable	412.3				440.5
Reinsurance recoverables	1,247.8				1,417.8
Goodwill and other intangible assets, net	89.3				89.2
Current income taxes receivable, net	8.6
Deferred tax assets, net	21.3				3.8
Deferred acquisition costs, net	66.5				71.8
Ceded unearned premiums	234.5				238.6
Operating leases right-of-use assets	24.1				25.1
Other assets	126.7				214.3
Assets held for sale	0.3				0
Intercompany note receivable	(59)				(56.7)
Investment in subsidiaries	0				0
Total assets	3,932.3				4,247.5
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	2,057.3				2,120.1
Unearned premiums	513.6				511.1
Funds held and ceded reinsurance payable, net	526.1				605.8
Debt	145.8				141
Current income taxes payable, net					(7.4)
Accrued underwriting expenses and other liabilities	93.5				118.8
Operating lease liabilities	29.2				29.5
Due to (from) affiliates	(0.9)				13.4
Total liabilities	3,364.6				3,532.3
Total shareholders' equity	567.7				715.2
Total liabilities and shareholders' equity	3,932.3				4,247.5
Argo Group International Holdings, Ltd (Parent  Guarantor)
Assets
Investments	0.6				0.6
Cash	3				1.9					$ 1.7		$ 0.9
Accrued investment income	0				0
Premiums receivable	0				0
Reinsurance recoverables	0				0
Goodwill and other intangible assets, net	0				40.6
Current income taxes receivable, net	0
Deferred tax assets, net	0				0
Deferred acquisition costs, net	0				0
Ceded unearned premiums	0				0
Operating leases right-of-use assets	6.2				7.1
Other assets	14.5				7.8
Assets held for sale	0				0
Intercompany note receivable	0				0
Investment in subsidiaries	1,881.9				1,899.3
Total assets	1,906.2				1,957.3
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	0				0
Unearned premiums	0				0
Funds held and ceded reinsurance payable, net	0				0
Debt	28.4				153.4
Current income taxes payable, net					0
Accrued underwriting expenses and other liabilities	6.3				13.6
Operating lease liabilities	6.2				7.3
Due to (from) affiliates	7.5				19.3
Total liabilities	48.4				193.6
Total shareholders' equity	1,857.8				1,763.7
Total liabilities and shareholders' equity	1,906.2				1,957.3
Argo Group  U.S., Inc. and Subsidiaries (Subsidiary Issuer)
Assets
Investments	3,628.8				3,405.6
Cash	17.4				31.6
Accrued investment income	16.7				18.2
Premiums receivable	267.5				236
Reinsurance recoverables	1,761.2				1,689.4
Goodwill and other intangible assets, net	118.5				123.4
Current income taxes receivable, net	(5.6)
Deferred tax assets, net	(4.6)				6.8
Deferred acquisition costs, net	97.1				88.4
Ceded unearned premiums	340.6				306.4
Operating leases right-of-use assets	51.7				59.6
Other assets	153.5				165.8
Assets held for sale	7.4				15.4
Intercompany note receivable	59				56.7
Investment in subsidiaries	0				0
Total assets	6,509.2				6,203.3
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	3,348.7				3,037.5
Unearned premiums	951.2				899.8
Funds held and ceded reinsurance payable, net	489				650.6
Debt	284.5				284.3
Current income taxes payable, net					21.3
Accrued underwriting expenses and other liabilities	67.8				89.5
Operating lease liabilities	60.4				68.9
Due to (from) affiliates	0.9				(13.4)
Total liabilities	5,202.5				5,038.5
Total shareholders' equity	1,306.7				1,164.8
Total liabilities and shareholders' equity	$ 6,509.2				$ 6,203.3

Senior Unsecured Fixed Rate N_6

Senior Unsecured Fixed Rate Notes - Condensed Consolidating Statement of Income (Loss) (Detail) - USD ($) $ in Millions	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Premiums and other revenue:
Earned premiums					$ 425.8	$ 451.5	$ 431.7	$ 420.7		$ 852.4		$ 1,303.9	$ 1,780.5	$ 1,729.7	$ 1,731.5
Net investment income			$ 1.4	$ 35.6					$ 37				112.7	151.1	132.3
Fee and other income													7.9	9.1	9
Net realized investment (losses) gains		$ (5.7)	18.4	(36.2)	21.8				(17.8)		$ (23.5)		(7.2)	80.1	(72)
Total revenue		483.5	455.2	436.5	484.6	487.4	488.6	509.4	891.7	998	1,375.2	1,485.4	1,893.9	1,970	1,800.8
Expenses:
Losses and loss adjustment expenses													1,208.8	1,220.7	1,040.8
Underwriting, acquisition and insurance expenses		164.5	161.3	168.1	180.2	164	161.6		329.4	321.8	493.9	485.8	679.4	666	656.1
Other corporate expenses													5.8	37.6	0
Interest expense		6.9	7	7.8	8.4	7.7	9.4	8.6	14.8	18	21.7	25.7	26.9	34.1	31.9
Fee and other expense													4	5.8	7.1
Foreign currency exchange losses (gains)		8.4	4.3	0.9	(4.5)	(0.9)	(3.8)	(0.6)	5.2	(4.4)	13.6	(5.3)	15.4	(9.8)	3.9
Impairment of goodwill	$ 15.6												0	15.6	0
Total expenses		510	449.3	462.2	586.8	514.5	460.8	407.9	911.5	868.7	1,421.5	1,383.2	1,940.3	1,970	1,739.8
Net (loss) income before income taxes		(26.5)	5.9	(25.7)	(102.2)	(27.1)	27.8	101.5	(19.8)	129.3	(46.3)	102.2	(46.4)	0	61
Provision (benefit) for income taxes		(3.4)	11.3	(1)	0.5	(1.1)	0.8	13.9	10.3	14.7	6.9	13.6	7.7	14.1	4
Net (loss) income before equity in earnings of subsidiaries													(54.1)	(14.1)	57
Equity in undistributed earnings of subsidiaries													0	0	0
Net (loss) income		(23.1)	$ (5.4)	$ (24.7)	$ (102.7)	(26)	$ 27	$ 87.6	$ (30.1)	$ 114.6	(53.2)	88.6	(54.1)	(14.1)	57
Dividends on preferred shares													4.6	0	0
Net (loss) income attributable to common shareholders		$ (25.1)				$ (26)					$ (55.2)	$ 88.6	(58.7)	(14.1)	57
Consolidating Adjustments
Premiums and other revenue:
Earned premiums													0	0	0
Net investment income													0	0	0
Fee and other income													0	0	0
Net realized investment (losses) gains													0	0	(2.7)
Total revenue													0	0	(2.7)
Expenses:
Losses and loss adjustment expenses													0	0	0
Underwriting, acquisition and insurance expenses													0	0	0
Other corporate expenses													0	0
Interest expense													0	0	0
Fee and other expense													0	0	0
Foreign currency exchange losses (gains)													0	0	0
Impairment of goodwill														0
Total expenses													0	0	0
Net (loss) income before income taxes													0	0	(2.7)
Provision (benefit) for income taxes													0	0	0
Net (loss) income before equity in earnings of subsidiaries													0	0	(2.7)
Equity in undistributed earnings of subsidiaries													17.4	(23.6)	(74.7)
Net (loss) income													17.4	(23.6)	(77.4)
Dividends on preferred shares													0
Net (loss) income attributable to common shareholders													17.4
Other Subsidiaries and Eliminations
Premiums and other revenue:
Earned premiums													576.2	685.6	869.8
Net investment income													25.4	50.7	56.4
Fee and other income													5.3	5.9	4.6
Net realized investment (losses) gains													(3.4)	(0.7)	(20.5)
Total revenue													603.5	741.5	910.3
Expenses:
Losses and loss adjustment expenses													444.3	523.9	517.1
Underwriting, acquisition and insurance expenses													248	249.3	310.7
Other corporate expenses													0	0
Interest expense													6.6	8.6	7.2
Fee and other expense													1.9	1.6	1.8
Foreign currency exchange losses (gains)													15.8	(10.5)	3.7
Impairment of goodwill														15.6
Total expenses													716.6	788.5	840.5
Net (loss) income before income taxes													(113.1)	(47)	69.8
Provision (benefit) for income taxes													(15.9)	(6.8)	3.9
Net (loss) income before equity in earnings of subsidiaries													(97.2)	(40.2)	65.9
Equity in undistributed earnings of subsidiaries													0	0	0
Net (loss) income													(97.2)	(40.2)	65.9
Dividends on preferred shares													0
Net (loss) income attributable to common shareholders													(97.2)
Argo Group International Holdings, Ltd (Parent  Guarantor)
Premiums and other revenue:
Earned premiums													0	0	0
Net investment income													0	(2.9)	(2.7)
Fee and other income													0	0	0
Net realized investment (losses) gains													(8.3)	(0.1)	2.5
Total revenue													(8.3)	(3)	(0.2)
Expenses:
Losses and loss adjustment expenses													0	0	0
Underwriting, acquisition and insurance expenses													20.4	1.3	11.3
Other corporate expenses													4.4	26.8	0
Interest expense													3.6	6.6	6.2
Fee and other expense													0	0	0
Foreign currency exchange losses (gains)													0	0	0
Impairment of goodwill														0
Total expenses													28.4	34.7	17.5
Net (loss) income before income taxes													(36.7)	(37.7)	(17.7)
Provision (benefit) for income taxes													0	0	0
Net (loss) income before equity in earnings of subsidiaries													(36.7)	(37.7)	(17.7)
Equity in undistributed earnings of subsidiaries													(17.4)	23.6	74.7
Net (loss) income													(54.1)	(14.1)	57
Dividends on preferred shares													4.6	0	0
Net (loss) income attributable to common shareholders													(58.7)	(14.1)	57
Argo Group  U.S., Inc. and Subsidiaries (Subsidiary Issuer)
Premiums and other revenue:
Earned premiums													1,204.3	1,044.1	861.7
Net investment income													87.3	103.3	78.6
Fee and other income													2.6	3.2	4.4
Net realized investment (losses) gains													4.5	80.9	(51.3)
Total revenue													1,298.7	1,231.5	893.4
Expenses:
Losses and loss adjustment expenses													764.5	696.8	523.7
Underwriting, acquisition and insurance expenses													411	415.4	334.1
Other corporate expenses													1.4	10.8
Interest expense													16.7	18.9	18.5
Fee and other expense													2.1	4.2	5.3
Foreign currency exchange losses (gains)													(0.4)	0.7	0.2
Impairment of goodwill														0
Total expenses													1,195.3	1,146.8	881.8
Net (loss) income before income taxes													103.4	84.7	11.6
Provision (benefit) for income taxes													23.6	20.9	0.1
Net (loss) income before equity in earnings of subsidiaries													79.8	63.8	11.5
Equity in undistributed earnings of subsidiaries													0	0	0
Net (loss) income													79.8	$ 63.8	$ 11.5
Dividends on preferred shares													0
Net (loss) income attributable to common shareholders													$ 79.8

Senior Unsecured Fixed Rate N_7

Senior Unsecured Fixed Rate Notes - Condensed Consolidating Statement of Cash Flows (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities	$ 71.9	$ 182.8	$ 301.8
Cash flows from investing activities:
Proceeds from sales of investments	1,209.3	1,852.1	1,599.8
Maturities and mandatory calls of fixed maturity investments	569.8	522.2	418.6
Purchases of investments	(2,152.5)	(1,984)	(2,149.1)
Change in short-term investments and foreign regulatory deposits	280	(490.4)	(119.2)
Settlements of foreign currency exchange forward contracts	9.4	0.3	(1.5)
Capital contribution to subsidiaries	0
Dividend received from subsidiaries	0
Proceeds from sale of Ariel Re, net of cash transferred	28.3	0	0
Proceeds from sale of Trident assets	38	0	0
Cash acquired with acquisition of ArgoGlobal Assicurazioni	0	0	15.6
Purchases of fixed assets and other, net	(6.6)	(43)	(32.5)
Cash used in investing activities	(24.3)	(142.8)	(268.3)
Cash flows from financing activities:
Payment on the intercompany note		0
Payment of long-term debt	(125)	(0.6)	0
Borrowing under the intercompany note			0
Issuance of preferred shares, net of issuance costs	144	0	0
Capital contribution from parent	0
Payment of cash dividend to parent	0
Activity under stock incentive plans	1.8	1.9	1.6
Repurchase of Company's common shares	0	0	(31.7)
Payment of cash dividends to preferred shareholders	(4.6)	0	0
Payment of cash dividends to common shareholders	(43)	(43.1)	(37.5)
Cash used in financing activities	(26.8)	(41.8)	(67.6)
Effect of exchange rate changes on cash	(9.8)	(0.1)	(2.8)
Change in cash	11	(1.9)	(36.9)
Cash, beginning of year	137.8	139.7	176.6
Cash, end of period	148.8	137.8	139.7
Consolidating Adjustments
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities	0	0	0
Cash flows from investing activities:
Proceeds from sales of investments	0	0	0
Maturities and mandatory calls of fixed maturity investments	0	0	0
Purchases of investments	0	0	0
Change in short-term investments and foreign regulatory deposits	0	0	0
Settlements of foreign currency exchange forward contracts	0	0	0
Capital contribution to subsidiaries	145.3
Dividend received from subsidiaries	(13.1)
Proceeds from sale of Ariel Re, net of cash transferred
Proceeds from sale of Trident assets
Cash acquired with acquisition of ArgoGlobal Assicurazioni			0
Purchases of fixed assets and other, net	0	0	0
Cash used in investing activities	132.2	0	0
Cash flows from financing activities:
Payment on the intercompany note		0
Payment of long-term debt	0	0
Borrowing under the intercompany note			0
Issuance of preferred shares, net of issuance costs	0
Capital contribution from parent	(145.3)
Payment of cash dividend to parent	13.1
Activity under stock incentive plans	0	0	0
Repurchase of Company's common shares			0
Payment of cash dividends to preferred shareholders	0
Payment of cash dividends to common shareholders	0	0	0
Cash used in financing activities	(132.2)	0	0
Effect of exchange rate changes on cash	0	0	0
Change in cash	0	0	0
Cash, beginning of year	0	0	0
Cash, end of period	0	0	0
Other Subsidiaries and Eliminations
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities	(32)	20.1	47
Cash flows from investing activities:
Proceeds from sales of investments	497.9	554.8	532.1
Maturities and mandatory calls of fixed maturity investments	142.1	229.4	73.7
Purchases of investments	(528.5)	(680.2)	(640.8)
Change in short-term investments and foreign regulatory deposits	(30.7)	(142.2)	(10.8)
Settlements of foreign currency exchange forward contracts	11.1	(1.3)	(3.2)
Capital contribution to subsidiaries	0
Dividend received from subsidiaries	0
Proceeds from sale of Ariel Re, net of cash transferred	(1.7)
Proceeds from sale of Trident assets	0
Cash acquired with acquisition of ArgoGlobal Assicurazioni			15.6
Purchases of fixed assets and other, net	(31.5)	(1.6)	(13.4)
Cash used in investing activities	58.7	(41.1)	(46.8)
Cash flows from financing activities:
Payment on the intercompany note		19.1
Payment of long-term debt	(125)	0
Borrowing under the intercompany note			(19)
Issuance of preferred shares, net of issuance costs
Capital contribution from parent	145.3
Payment of cash dividend to parent	(13.1)
Activity under stock incentive plans	0	0	0
Repurchase of Company's common shares			0
Payment of cash dividends to preferred shareholders	0
Payment of cash dividends to common shareholders	0	0	0
Cash used in financing activities	7.2	19.1	(19)
Effect of exchange rate changes on cash	(9.8)	(0.1)	(2.8)
Change in cash	24.1	(2)	(21.6)
Cash, beginning of year	104.3	106.3	127.9
Cash, end of period	128.4	104.3	106.3
Argo Group International Holdings, Ltd (Parent  Guarantor)
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities	5	38.4	72.4
Cash flows from investing activities:
Proceeds from sales of investments	0	0	0
Maturities and mandatory calls of fixed maturity investments	0	0	0
Purchases of investments	0	0	0
Change in short-term investments and foreign regulatory deposits	0	3.2	(3.4)
Settlements of foreign currency exchange forward contracts	0.1	(0.2)	(0.5)
Capital contribution to subsidiaries	(145.3)	0	0
Dividend received from subsidiaries	13.1	0	0
Proceeds from sale of Ariel Re, net of cash transferred	30	0	0
Proceeds from sale of Trident assets	0
Cash acquired with acquisition of ArgoGlobal Assicurazioni			0
Purchases of fixed assets and other, net	0	0	(0.1)
Cash used in investing activities	(102.1)	3	(4)
Cash flows from financing activities:
Payment on the intercompany note		0
Payment of long-term debt	0	0
Borrowing under the intercompany note			0
Issuance of preferred shares, net of issuance costs	144	0	0
Capital contribution from parent	0
Payment of cash dividend to parent	0
Activity under stock incentive plans	1.8	1.9	1.6
Repurchase of Company's common shares	0	0	(31.7)
Payment of cash dividends to preferred shareholders	(4.6)	0	0
Payment of cash dividends to common shareholders	(43)	(43.1)	(37.5)
Cash used in financing activities	98.2	(41.2)	(67.6)
Effect of exchange rate changes on cash	0	0	0
Change in cash	1.1	0.2	0.8
Cash, beginning of year	1.9	1.7	0.9
Cash, end of period	3	1.9	1.7
Argo Group  U.S., Inc. and Subsidiaries (Subsidiary Issuer)
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities	98.9	124.3	182.4
Cash flows from investing activities:
Proceeds from sales of investments	711.4	1,297.3	1,067.7
Maturities and mandatory calls of fixed maturity investments	427.7	292.8	344.9
Purchases of investments	(1,624)	(1,303.8)	(1,508.3)
Change in short-term investments and foreign regulatory deposits	310.7	(351.4)	(105)
Settlements of foreign currency exchange forward contracts	(1.8)	1.8	2.2
Capital contribution to subsidiaries	0
Dividend received from subsidiaries	0
Proceeds from sale of Ariel Re, net of cash transferred	0
Proceeds from sale of Trident assets	38
Cash acquired with acquisition of ArgoGlobal Assicurazioni			0
Purchases of fixed assets and other, net	24.9	(41.4)	(19)
Cash used in investing activities	(113.1)	(104.7)	(217.5)
Cash flows from financing activities:
Payment on the intercompany note		(19.1)
Payment of long-term debt	0	(0.6)
Borrowing under the intercompany note			19
Issuance of preferred shares, net of issuance costs	0
Capital contribution from parent	0
Payment of cash dividend to parent	0
Activity under stock incentive plans	0	0	0
Repurchase of Company's common shares			0
Payment of cash dividends to preferred shareholders	0
Payment of cash dividends to common shareholders	0	0	0
Cash used in financing activities	0	(19.7)	19
Effect of exchange rate changes on cash	0	0	0
Change in cash	(14.2)	(0.1)	(16.1)
Cash, beginning of year	31.6	31.7	47.8
Cash, end of period	$ 17.4	$ 31.6	$ 31.7

Schedule II Condensed Financi_2

Schedule II Condensed Financial Information of Registrant - Schedule of Balance Sheets (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Investment in subsidiaries	$ 0				$ 0
Cash	148.8				137.8				$ 139.7
Goodwill and other intangible assets, net	207.8				253.2
Operating leases right-of-use assets	82				91.8
Other assets	294.7	$ 358.6	$ 414.5	$ 434.8	387.9	$ 390.5					$ 309.8
Total assets	10,465.8	10,721.7	10,378.3	10,177.9	10,508.8	10,434.4	$ 10,153.4	$ 9,942.9
Liabilities and Shareholders' Equity
Junior subordinated debentures	257.8				257.4
Other indebtedness	60.7				181.3
Accrued underwriting expenses and other liabilities	167.6	205.3	157	187.4	221.9	285.7	281	249.5	$ 263		$ 146.6
Operating lease liabilities	95.8				105.7
Total liabilities	8,608	8,873	8,670.6	8,564.4	8,745.1	8,559	8,241.5	8,077.6
Shareholders' equity	1,857.8	1,848.7	1,707.7	1,613.5	1,763.7	1,875.4	1,911.9	1,865.3		$ 1,735		$ 1,812.9
Total liabilities and shareholders' equity	10,465.8	$ 10,721.7	$ 10,378.3	$ 10,177.9	10,508.8	$ 10,434.4	$ 10,153.4	$ 9,942.9
Argo Group International Holdings, Ltd (Parent  Guarantor)
Assets
Short-term investments	0.6				0.6
Investment in subsidiaries	1,881.9				1,899.3
Cash	3				1.9					$ 1.7		$ 0.9
Goodwill and other intangible assets, net	0				40.6
Operating leases right-of-use assets	6.2				7.1
Other assets	14.5				7.8
Total assets	1,906.2				1,957.3
Liabilities and Shareholders' Equity
Junior subordinated debentures	28.4				28.4
Other indebtedness	0				125
Accrued underwriting expenses and other liabilities	6.3				13.6
Operating lease liabilities	6.2				7.3
Due to subsidiaries	7.5				19.3
Total liabilities	48.4				193.6
Shareholders' equity	1,857.8				1,763.7
Total liabilities and shareholders' equity	$ 1,906.2				$ 1,957.3

Schedule II Condensed Financi_3

Schedule II Condensed Financial Information of Registrant - Schedule of Statements of Income (Detail) - USD ($) $ in Millions	3 Months Ended							6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue:
Net investment expense		$ 1.4	$ 35.6					$ 37				$ 112.7	$ 151.1	$ 132.3
Net realized investment (losses) gains	$ (5.7)	18.4	(36.2)	$ 21.8				(17.8)		$ (23.5)		(7.2)	80.1	(72)
Total revenue	483.5	455.2	436.5	484.6	$ 487.4	$ 488.6	$ 509.4	891.7	$ 998	1,375.2	$ 1,485.4	1,893.9	1,970	1,800.8
Expenses:
Interest expense	6.9	7	7.8	8.4	7.7	9.4	8.6	14.8	18	21.7	25.7	26.9	34.1	31.9
Other corporate expenses												5.8	37.6	0
Total expenses	510	449.3	462.2	586.8	514.5	460.8	407.9	911.5	868.7	1,421.5	1,383.2	1,940.3	1,970	1,739.8
Net (loss) income before equity in earnings of subsidiaries												(54.1)	(14.1)	57
Equity in undistributed earnings of subsidiaries												0	0	0
Net (loss) income	(23.1)	$ (5.4)	$ (24.7)	$ (102.7)	(26)	$ 27	$ 87.6	$ (30.1)	$ 114.6	(53.2)	88.6	(54.1)	(14.1)	57
Dividends on preferred shares												4.6	0	0
Net (loss) income attributable to common shareholders	$ (25.1)				$ (26)					$ (55.2)	$ 88.6	(58.7)	(14.1)	57
Argo Group International Holdings, Ltd (Parent  Guarantor)
Revenue:
Net investment expense												0	(2.9)	(2.7)
Net realized investment (losses) gains												(8.3)	(0.1)	2.5
Total revenue												(8.3)	(3)	(0.2)
Expenses:
Interest expense												3.6	6.6	6.2
Operating expenses												20.4	1.3	11.3
Other corporate expenses												4.4	26.8	0
Total expenses												28.4	34.7	17.5
Net (loss) income before equity in earnings of subsidiaries												(36.7)	(37.7)	(17.7)
Equity in undistributed earnings of subsidiaries												(17.4)	23.6	74.7
Net (loss) income												(54.1)	(14.1)	57
Dividends on preferred shares												4.6	0	0
Net (loss) income attributable to common shareholders												$ (58.7)	$ (14.1)	$ 57

Schedule II Condensed Financi_4

Schedule II Condensed Financial Information of Registrant - Schedule of Statements of Cash Flows (Detail) - USD ($) $ in Millions	3 Months Ended							6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net (loss) income	$ (23.1)	$ (5.4)	$ (24.7)	$ (102.7)	$ (26)	$ 27	$ 87.6	$ (30.1)	$ 114.6	$ (53.2)	$ 88.6	$ (54.1)	$ (14.1)	$ 57
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Amortization and depreciation												33.2	27.3	31.9
Share-based payments expense												8.7	16.9	18.3
Loss on disposals of long-lived assets, net												1.9	7.2	0.3
Undistributed earnings of subsidiaries												0	0	0
Change in:
Accrued underwriting expenses and other liabilities												(43.7)	(10.6)	111.6
Other, net												9.8	(77)	17.8
Cash provided by operating activities												71.9	182.8	301.8
Cash flows from investing activities:
Change in short-term investments												285.4	(490.4)	(132.2)
Settlements of foreign currency exchange forward contracts												9.4	0.3	(1.5)
Capital contribution to subsidiaries												0
Proceeds from sale of Ariel Re, net of cash transferred												28.3	0	0
Dividend received from subsidiaries												0
Purchases of fixed assets and other, net												(6.6)	(43)	(32.5)
Cash used in investing activities												(24.3)	(142.8)	(268.3)
Cash flows from financing activities:
Issuance of preferred shares, net of issuance costs												144	0	0
Activity under stock incentive plans												1.8	1.9	1.6
Repurchase of Company's common shares												0	0	(31.7)
Payment of cash dividends to preferred shareholders												(4.6)	0	0
Payment of cash dividends to common shareholders												(43)	(43.1)	(37.5)
Cash used in financing activities												(26.8)	(41.8)	(67.6)
Cash, beginning of year			137.8					137.8		137.8		137.8
Cash, end of period				137.8								148.8	137.8
Argo Group International Holdings, Ltd (Parent  Guarantor)
Cash flows from operating activities:
Net (loss) income												(54.1)	(14.1)	57
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Amortization and depreciation												1.1	1.3	1.4
Share-based payments expense												3.6	8.1	7
Net realized investment and other losses (gains)												8.3	0.1	(2.5)
Loss on disposals of long-lived assets, net												0.1	0	0
Undistributed earnings of subsidiaries												17.4	(23.6)	(74.7)
Change in:
Prepaid assets												(2.2)	2.5	(2.3)
Accrued underwriting expenses and other liabilities												(9.1)	7.3	(4.4)
Due to subsidiaries												47.7	68.9	94.1
Other, net												(7.8)	(12.1)	(3.2)
Cash provided by operating activities												5	38.4	72.4
Cash flows from investing activities:
Change in short-term investments												0	3.2	(3.4)
Settlements of foreign currency exchange forward contracts												0.1	(0.2)	(0.5)
Capital contribution to subsidiaries												(145.3)	0	0
Proceeds from sale of Ariel Re, net of cash transferred												30	0	0
Dividend received from subsidiaries												13.1	0	0
Purchases of fixed assets and other, net												0	0	(0.1)
Cash used in investing activities												(102.1)	3	(4)
Cash flows from financing activities:
Issuance of preferred shares, net of issuance costs												144	0	0
Activity under stock incentive plans												1.8	1.9	1.6
Repurchase of Company's common shares												0	0	(31.7)
Payment of cash dividends to preferred shareholders												(4.6)	0	0
Payment of cash dividends to common shareholders												(43)	(43.1)	(37.5)
Cash used in financing activities												98.2	(41.2)	(67.6)
Change in cash												1.1	0.2	0.8
Cash, beginning of year			$ 1.9				$ 1.7	$ 1.9	$ 1.7	$ 1.9	$ 1.7	1.9	1.7	0.9
Cash, end of period				$ 1.9								$ 3	$ 1.9	$ 1.7

Schedule III Supplemental Ins_2

Schedule III Supplemental Insurance Information (Detail) - USD ($) $ in Millions	3 Months Ended						6 Months Ended		9 Months Ended	12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
DAC			$ 160.2							$ 163.6	$ 160.2	$ 167.3
Reserves for Losses and Loss Adjustment Expenses			5,157.6							5,406	5,157.6	4,654.6
UPR			1,410.9							1,464.8	1,410.9	1,300.9
Premium Revenue			425.8	$ 451.5	$ 431.7	$ 420.7		$ 852.4	$ 1,303.9	1,780.5	1,729.7	1,731.5
Net investment income	$ 1.4	$ 35.6					$ 37			112.7	151.1	132.3
Loss & LAE										1,208.8	1,220.7	1,040.8
Amortization (Deferral) DAC										(9.3)	12.4	(9.9)
Other Operating Expenses			653.6							688.7	653.6	666
Net Premiums Written										1,810.1	1,754.6	1,765.3
U.S. Operations
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
DAC			89.7							98.2	89.7	87.2
Reserves for Losses and Loss Adjustment Expenses			2,775.1							3,091.9	2,775.1	2,498.9
UPR			896.1							939.2	896.1	793.3
Premium Revenue										1,207.6	1,119.9	1,078.7
Net investment income										80.3	100	82.9
Loss & LAE										768.7	690.4	628.2
Amortization (Deferral) DAC										(8.6)	(2.5)	(6.4)
Other Operating Expenses			371.2							399.7	371.2	361.2
Net Premiums Written										1,223	1,166.3	1,125.5
International Operations
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
DAC			70.5							65.4	70.5	80.1
Reserves for Losses and Loss Adjustment Expenses			2,129							2,077.6	2,129	1,890.1
UPR			514.7							525.4	514.7	507.6
Premium Revenue										572.5	609.6	652.5
Net investment income										26.7	44.2	32.9
Loss & LAE										428.6	518.3	400.3
Amortization (Deferral) DAC										(0.7)	14.9	(3.5)
Other Operating Expenses			235.3							249.1	235.3	250.2
Net Premiums Written										586.6	588.1	639.5
Run-off Lines
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
DAC			0							0	0	0
Reserves for Losses and Loss Adjustment Expenses			253.5							236.5	253.5	265.6
UPR			0.1							0.2	0.1	0
Premium Revenue										0.4	0.2	0.3
Net investment income										4	5.7	8.1
Loss & LAE										11.5	12	12.3
Amortization (Deferral) DAC										0	0	0
Other Operating Expenses			2.4							5	2.4	3.9
Net Premiums Written										0.5	0.2	0.3
Corporate and Other
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
DAC			0							0	0	0
Reserves for Losses and Loss Adjustment Expenses			0							0	0	0
UPR			0							0	0	0
Premium Revenue										0	0	0
Net investment income										1.7	1.2	8.4
Loss & LAE										0	0	0
Amortization (Deferral) DAC										0	0	0
Other Operating Expenses			$ 44.7							34.9	44.7	50.7
Net Premiums Written										$ 0	$ 0	$ 0

Schedule V Valuation and Qual_2

Schedule V Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 28.1	$ 29.9	$ 20.1
Charged to Cost and Expense	0.5	(1.8)	(1.5)
Capital Loss Carryforward	0	0	0
Net Operating Loss Carryforward	0	0	11.3
Charged to Other Accounts	0	0	0
Deductions	0	0	0
Balance at End of Year	$ 28.6	$ 28.1	$ 29.9

Schedule VI Supplemental Info_2

Schedule VI Supplemental Information for Property-Casualty Insurance Companies (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Abstract]
Deferred acquisition costs				$ 163.6	$ 160.2	$ 167.3
Reserves for losses and loss adjustment expenses				5,406	5,157.6	4,654.6
Unamortized discount in reserves for losses				17.8	17.9	16.9
Unearned premiums				1,464.8	1,410.9	1,300.9
Premiums earned				1,780.5	1,729.7	1,731.5
Net investment income	$ 1.4	$ 35.6	$ 37	112.7	151.1	132.3
Current year				1,201.1	1,082.6	1,058.8
Prior years				7.7	138.1	(18)
Losses and loss adjustment expenses incurred				1,208.8	1,220.7	1,040.8
Amortization (Deferral) DAC				(9.3)	12.4	(9.9)
Paid losses and loss adjustment expenses, net of reinsurance				1,119.8	1,030.3	938.9
Gross premiums written				$ 3,233.3	$ 3,130.2	$ 2,954.2