Argo Group International (ARGO-PA) 10-Q 6 Aug 20 2020 Q2 Quarterly report Financial data

Cover

Cover - shares	6 Months Ended
	Jun. 30, 2020	Aug. 03, 2020
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 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	110 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 Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		34,665,252
Entity Central Index Key	0001091748
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Amendment Flag	false
Common Stock
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	Guarantee of Argo Group U.S., Inc.  6.500% Senior Notes due 2042
Trading Symbol	ARGD
Security Exchange Name	NYSE
Depositary Shares
Document Information [Line Items]
Title of 12(b) Security	Depositary Shares, Each Representing a 1/1,000th Interest in a 7.00% Resettable Fixed Rate Preference Share, Series A, par value $1.00 per share
Trading Symbol	ARGOPrA
Security Exchange Name	NYSE

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019	[1]
Investments:
Fixed maturities available-for-sale, at fair value (cost: 2020 - $3,688.6, 2019 - $3,605.0; allowance for expected credit losses: 2020 - $40.2)	$ 3,707.4	$ 3,633.5
Equity securities, at fair value (cost: 2020 - $167.9; 2019 - $122.8)	147.5	124.4
Other investments (cost: 2020 - $384.6; 2019 - $482.5)	384.5	496.5
Short-term investments, at fair value (cost: 2020 - $611.8; 2019 - $844.8)	612.1	845
Total investments	4,851.5	5,099.4
Cash	187.7	137.8
Accrued investment income	23.4	25.7
Premiums receivable	800.2	688.2
Reinsurance recoverables	2,942.8	3,104.6
Goodwill	156.5	161.4
Intangible assets, net of accumulated amortization	91.1	91.8
Deferred tax asset, net	18.9	6.1
Deferred acquisition costs, net	153.5	160.2
Ceded unearned premiums	656.5	545
Operating lease right-of-use assets	87.2	91.8
Other assets	414.7	387.1
Assets held for sale	12.7	15.4
Total assets	10,396.7	10,514.5
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	5,216.3	5,157.6
Unearned premiums	1,481.2	1,410.9
Accrued underwriting expenses and other liabilities	154.8	226
Ceded reinsurance payable, net	1,042.7	1,203.1
Funds held	66.7	50.6
Senior unsecured fixed rate notes	140.1	140
Other indebtedness	181	181.3
Junior subordinated debentures	257.6	257.4
Current income taxes payable, net	27.1	0.8
Operating lease liabilities	99.2	105.7
Total liabilities	8,666.7	8,733.4
Commitments and contingencies (Note 14)
Shareholders' equity:
Common shares - $1.00 par, 500,000,000 shares authorized; 45,960,777 and 45,698,470 shares issued at June 30, 2020 and December 31, 2019, respectively	46	45.7
Additional paid-in capital	1,376.5	1,376.6
Treasury shares (11,315,889 shares at June 30, 2020 and December 31, 2019, respectively)	(455.1)	(455.1)
Retained earnings	756.7	811.1
Accumulated other comprehensive income, net of taxes	5.9	2.8
Total shareholders' equity	1,730	1,781.1
Total liabilities and shareholders' equity	$ 10,396.7	$ 10,514.5
[1]	Derived from audited consolidated financial statements.

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Fixed maturities available-for-sale, cost	$ 3,688.6	$ 3,605
Allowance for Credit Losses	40.2	0
Equity securities, cost	167.9	122.8
Other investments, cost	384.6	482.5
Short-term investments, cost	$ 611.8	$ 844.8
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)	45,960,777	45,698,470
Treasury shares (in shares)	11,315,889	11,315,889

Condensed Consolidated Statemen

Condensed Consolidated Statements of (Loss) Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Premiums and other revenue:
Earned premiums	$ 433.4	$ 431.7	$ 868.4	$ 852.2
Net investment income	1.5	42.8	37	76.7
Fee and other income	2	2.1	4.1	4.4
Net realized investment gains (losses):
Net realized investment gains (losses)	11.1	(0.6)	39	(2.3)
Change in fair value of equity securities	16.8	12.6	(22.5)	66.8
Credit losses on fixed maturity securities	(7.8)	0	(32.5)	0
Net realized investment gains (losses)	20.1	12	(16)	64.5
Total revenue	457	488.6	893.5	997.8
Expenses:
Losses and loss adjustment expenses	273.2	284.8	554.1	522.7
Underwriting, acquisition and insurance expenses	161.4	161.4	329.4	321.6
Other corporate expenses	2.5	7.5	5.8	8
Interest expense	6.8	9.3	14.5	17.8
Fee and other expense	1	1.3	2.2	2.6
Foreign currency exchange losses (gains)	6.4	(5.3)	3.4	(4.6)
Total expenses	451.3	459	909.4	868.1
Income (loss) before income taxes	5.7	29.6	(15.9)	129.7
Income tax provision	12.1	0.8	9.3	9.7
Net (loss) income	$ (6.4)	$ 28.8	$ (25.2)	$ 120
Net (loss) income per common share:
Basic (in dollars per share)	$ (0.18)	$ 0.84	$ (0.73)	$ 3.52
Diluted (in dollars per share)	(0.18)	0.83	(0.73)	3.45
Dividends declared per common share (in dollars per share)	$ 0.31	$ 0.31	$ 0.62	$ 0.62
Weighted average common shares:
Basic (in shares)	34,634,353	34,195,250	34,551,935	34,090,372
Diluted (in shares)	34,634,353	34,779,991	34,551,935	34,759,548
Net realized investment gains (losses) before other-than-temporary impairment losses	$ 20.1	$ 14.5	$ (16)	$ 71.3
Other-than-temporary impairment losses recognized in earnings:
Other-than-temporary impairment losses on fixed maturities	0	(2.5)	0	(6.8)
Impairment losses recognized in earnings	0	(2.5)	0	(6.8)
Net realized investment gains (losses)	$ 11.1	$ (0.6)	$ 39	$ (2.3)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive (Loss) Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (6.4)	$ 28.8	$ (25.2)	$ 120
Other comprehensive income (loss):
Foreign currency translation adjustments	(4.2)	(0.3)	(7.6)	(0.1)
Unrealized gains (losses) on fixed maturity securities:
Gains arising during the year	152.9	41.9	30.1	98.7
Reclassification adjustment for (gains) losses included in net income	(16.5)	1.8	(19.9)	4.9
Other comprehensive income before tax	132.2	43.4	2.6	103.5
Income tax provision related to other comprehensive income:
Gains arising during the year	27	6.7	5.9	15.8
Reclassification adjustment for (gains) losses included in net income	(2.6)	0.2	(0.7)	0.7
Income tax provision related to other comprehensive income	24.4	6.9	5.2	16.5
Other comprehensive income (loss), net of tax	107.8	36.5	(2.6)	87
Comprehensive income (loss)	$ 101.4	$ 65.3	$ (27.8)	$ 207

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total		Cumulative Effect, Period of Adoption, Adjustment	Common Stock	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, 2018	$ 1,746.7			$ 45.3	$ 1,372	$ (455.1)	$ 862.6		$ (78.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	120						120
Other comprehensive income (loss) - change in fair value of fixed maturities, net of taxes	87.1								87.1
Other comprehensive income (loss) - other	(0.1)								(0.1)
Activity under stock incentive plans	7.8			0.4	7.4
Retirement of common shares (tax payments on equity compensation)	(10.9)			(0.1)	(10.8)
Employee stock purchase plan	1.1				1.1
Cash dividends declared - common shares	(22.7)						(22.7)
Ending Balance at Jun. 30, 2019	1,929			45.6	1,369.7	(455.1)	959.9		8.9
Beginning Balance at Dec. 31, 2018	$ 1,746.7			45.3	1,372	(455.1)	862.6		(78.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Ending Balance at Dec. 31, 2019	$ 1,781.1	[1]	$ (2.2)	45.7	1,376.6	(455.1)	811.1	$ (7.9)	2.8	$ 5.7
Beginning Balance at Mar. 31, 2019	1,880.6			45.4	1,374.9	(455.1)	943		(27.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	28.8						28.8
Other comprehensive income (loss) - change in fair value of fixed maturities, net of taxes	36.8								36.8
Other comprehensive income (loss) - other	(0.3)								(0.3)
Activity under stock incentive plans	3.6			0.3	3.3
Retirement of common shares (tax payments on equity compensation)	(9.3)			(0.1)	(9.2)
Employee stock purchase plan	0.7				0.7
Cash dividends declared - common shares	(11.9)						(11.9)
Ending Balance at Jun. 30, 2019	1,929			45.6	1,369.7	(455.1)	959.9		8.9
Beginning Balance at Dec. 31, 2019	1,781.1	[1]	$ (2.2)	45.7	1,376.6	(455.1)	811.1	$ (7.9)	2.8	$ 5.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	(25.2)						(25.2)
Other comprehensive income (loss) - change in fair value of fixed maturities, net of taxes	5								5
Other comprehensive income (loss) - other	(7.6)								(7.6)
Activity under stock incentive plans	5.3			0.4	4.9
Retirement of common shares (tax payments on equity compensation)	(6.5)			(0.1)	(6.4)
Employee stock purchase plan	1.4				1.4
Cash dividends declared - common shares	$ (21.3)						(21.3)
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Ending Balance at Jun. 30, 2020	$ 1,730			46	1,376.5	(455.1)	756.7		5.9
Beginning Balance at Mar. 31, 2020	1,636.8			45.9	1,374.2	(455.1)	773.7		(101.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	(6.4)						(6.4)
Other comprehensive income (loss) - change in fair value of fixed maturities, net of taxes	112								112
Other comprehensive income (loss) - other	(4.2)								(4.2)
Activity under stock incentive plans	2.2			0.1	2.1
Retirement of common shares (tax payments on equity compensation)	(0.7)			0	(0.7)
Employee stock purchase plan	0.9			0	0.9
Cash dividends declared - common shares	(10.6)						(10.6)
Ending Balance at Jun. 30, 2020	$ 1,730			$ 46	$ 1,376.5	$ (455.1)	$ 756.7		$ 5.9
[1]	Derived from audited consolidated financial statements.

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Shareholders' Equity (Parenthetical) - $ / shares	May 07, 2020	May 24, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Stockholders' Equity [Abstract]
Dividends declared per common share (in dollars per share)	$ 0.31	$ 0.31	$ 0.31	$ 0.31	$ 0.62	$ 0.62

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net income	$ (25.2)	$ 120
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Amortization and depreciation	14.1	13.8
Share-based payments expense	5.4	8.8
Deferred income tax (benefit) provision, net	(18.4)	3.2
Net realized investment losses (gains)	16	(64.5)
Undistributed earnings (loss) from alternative investment portfolio	20.9	(11.4)
Loss on disposals of long-lived assets, net	0.2	0.1
Change in:
Accrued investment income	2.3	0.5
Receivables	31.2	(161.9)
Deferred acquisition costs	5.1	3.5
Ceded unearned premiums	(115.6)	(136.2)
Reserves for losses and loss adjustment expenses	98.5	83.2
Unearned premiums	82.2	103
Ceded reinsurance payable and funds held	(140.7)	80.3
Income taxes	25.5	4.4
Accrued underwriting expenses and other liabilities	(70.1)	12.8
Other, net	(34.5)	(64.5)
Cash used in operating activities	(103.1)	(4.9)
Cash flows from investing activities:
Sales of fixed maturity investments	746	751.6
Maturities and mandatory calls of fixed maturity investments	255	168.8
Sales of equity securities	8.1	32.2
Sales of other investments	94.2	31.1
Purchases of fixed maturity investments	(1,103.6)	(888.5)
Purchases of equity securities	(59.5)	(32.4)
Purchases of other investments	(14.3)	(38.2)
Change in foreign regulatory deposits and voluntary pools	5	6.3
Change in short-term investments	212.5	67.7
Settlements of foreign currency exchange forward contracts	7	9.9
Proceeds from sale of Trident assets	38	0
Purchases of fixed assets	(7.6)	(15.7)
Other, net	(5)	(22.5)
Cash provided by investing activities	175.8	70.3
Cash flows from financing activities:
Activity under stock incentive plans	1	0.9
Payment of cash dividends to common shareholders	(21.3)	(22.7)
Cash used in financing activities	(20.3)	(21.8)
Effect of exchange rate changes on cash	(2.5)	(0.5)
Change in cash	49.9	43.1
Cash, beginning of year	137.8	139.2
Cash, end of period	$ 187.7	$ 182.3

Basis of Presentation

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

Recently Adopted Accounting Pro

Recently Adopted Accounting Pronouncements	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Recently Adopted Accounting Pronouncements	Recently Issued Accounting Pronouncements & Updates to Accounting Policies Recently Issued Accounting Pronouncements In June 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("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 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. Updates to Accounting Policies The following accounting policies have been updated to reflect the adoption of ASU 2016-13, as described above. Investment Impairments of Available for Sale Fixed Maturities 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. 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. Reinsurance Recoverables 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. 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. Premiums and Unearned Premium Reserves Premiums are recognized as revenues pro rata over the policy period. Unearned premium reserves represent the unexpired portion of policy premiums. Accrued retrospective premiums are included in premium balances receivable. Premiums receivable balances are reported net of an allowance for expected losses, both dispute and credit related. 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.

Investments

Investments	6 Months Ended
	Jun. 30, 2020
Investments, Debt and Equity Securities [Abstract]
Investments	InvestmentsIncluded in “Total investments” in our Consolidated Balance Sheets at June 30, 2020 and December 31, 2019 is $119.1 million and $158.6 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, allowance for credit losses, and fair value of fixed maturity investments were as follows: June 30, 2020 (in millions) Amortized Gross Gross Allowance for Credit Losses (1) Fair Fixed maturities U.S. Governments $ 324.0 $ 18.6 $ — $ — $ 342.6 Foreign Governments 256.1 6.1 3.7 0.3 258.2 Obligations of states and political subdivisions 165.3 6.9 0.8 0.1 171.3 Corporate bonds 1,762.6 58.4 49.2 39.7 1,732.1 Commercial mortgage-backed securities 242.5 10.9 0.2 — 253.2 Residential mortgage-backed securities 512.3 20.2 2.3 — 530.2 Asset-backed securities 152.6 2.7 2.3 0.1 152.9 Collateralized loan obligations 273.2 1.5 7.8 — 266.9 Total fixed maturities $ 3,688.6 $ 125.3 $ 66.3 $ 40.2 $ 3,707.4 (1) Effective January 1, 2020 we adopted ASC-326 and as a result any credit impairment losses on our available-for-sale fixed maturities are recorded as an allowance, subject to reversal. Prior periods have not been restated to conform with the current year presentation. See Note 1. December 31, 2019 (in millions) Amortized Gross Gross Fair Fixed maturities U.S. Governments $ 353.5 $ 2.3 $ 1.2 $ 354.6 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 1,777.4 37.7 34.7 1,780.4 Commercial mortgage-backed securities 213.5 4.6 1.1 217.0 Residential mortgage-backed securities 479.1 10.4 0.6 488.9 Asset-backed securities 164.2 1.5 0.2 165.5 Collateralized loan obligations 226.7 0.5 1.4 225.8 Total fixed maturities $ 3,605.0 $ 68.5 $ 40.0 $ 3,633.5 Contractual Maturity The amortized cost and fair values of fixed maturity investments as of June 30, 2020, by contractual maturity, were as follows: (in millions) Amortized Fair Due in one year or less $ 316.3 $ 316.8 Due after one year through five years 1,540.7 1,523.5 Due after five years through ten years 579.8 592.4 Thereafter 71.2 71.5 Structured securities 1,180.6 1,203.2 Total $ 3,688.6 $ 3,707.4 The expected maturities may differ from the contractual maturities because debtors may have the right to call or prepay obligations. Other Investments Details regarding the carrying value and unfunded investment commitments of other investments as of June 30, 2020 and December 31, 2019 were as follows: June 30, 2020 (in millions) Carrying Unfunded Investment Type Hedge funds $ 98.0 $ — Private equity 190.5 96.1 Overseas deposits 91.7 — Other 4.3 — Total other investments $ 384.5 $ 96.1 December 31, 2019 (in millions) Carrying Unfunded Investment Type Hedge funds $ 109.5 $ — Private equity 268.1 110.0 Overseas deposits 114.6 — Other 4.3 — Total other investments $ 496.5 $ 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: June 30, 2020 Less Than One Year One Year or Greater Total (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed maturities U.S. Governments (1) $ 1.3 $ — $ — $ — $ 1.3 $ — Foreign Governments 124.4 3.7 — — 124.4 3.7 Obligations of states and political subdivisions 18.1 0.8 — — 18.1 0.8 Corporate bonds 356.2 26.2 30.8 23.0 387.0 49.2 Commercial mortgage-backed securities 21.8 0.2 — — 21.8 0.2 Residential mortgage-backed securities 71.1 1.5 8.3 0.8 79.4 2.3 Asset-backed securities 30.9 2.2 3.9 0.1 34.8 2.3 Collateralized loan obligations 189.8 6.1 56.9 1.7 246.7 7.8 Total fixed maturities $ 813.6 $ 40.7 $ 99.9 $ 25.6 $ 913.5 $ 66.3 (1) Unrealized losses are less than $0.1 million. 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) 117.6 0.7 5.1 — 122.7 0.7 Obligations of states and political subdivisions (1) 0.7 — 2.1 0.1 2.8 0.1 Corporate bonds 249.4 18.9 63.6 15.8 313.0 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 54.7 0.8 116.7 0.6 171.4 1.4 Total fixed maturities $ 701.2 $ 23.0 $ 253.5 $ 17.0 $ 954.7 $ 40.0 (1) Unrealized losses are less than $0.1 million. We hold a total of 4,833 fixed income securities, of which 1,509 were in an unrealized loss position for less than one year and 223 were in an unrealized loss position for a period one year or greater as of June 30, 2020. Following the adoption of ASC 326, as described in Note 1, beginning January 1, 2020 we complete a detailed analysis each quarter to assess whether the decline in the fair value of a fixed maturity security below its amortized cost basis is the result of a credit loss. All available-for-sale securities with unrealized losses are reviewed. We consider many factors in completing this detailed analysis to determine where a credit loss exists. Inputs used in determining if a credit loss has occurred include, but are not limited to, credit ratings and downgrades, 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. We also take into consideration information about the financial condition of the issuer and other industry factors that could negatively impact the capital markets. Credit losses recognized for the three and six months ended June 30, 2020 primarily related to corporate bonds in the energy, retail and hospitality sectors. If the decline in fair value of an available-for-sale fixed maturity security below its amortized cost is considered to be the result of a credit loss, we compare the estimated present value of the cash flows expected to be collected to the amortized cost of the security. The extent to which the estimated present value of the cash flows expected to be collected is less than the amortized cost of the security represents the credit loss, which is recorded as an allowance and recognized in net realized gains (losses) in the Statement of (Loss) Income. The allowance is limited to the difference between the fair value and the amortized cost of the security. Any remaining decline in fair value represents the non-credit portion of the impairment, which is recognized in other comprehensive income. 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. The following table presents a reconciliation of the beginning and ending balances for the allowance for credit losses on available-for-sale fixed maturity securities: For the Six Months Ended (in millions) 2020 Beginning balance, January 1, 2020 $ — Additions related to initial adoption of accounting standard 6.9 Provision for expected credit losses 32.5 Increases due to sales/defaults of credit-impaired securities 0.8 Ending balance, June 30, 2020 $ 40.2 Total credit impairment losses included in net realized investment gains (losses) in the Consolidated Statement of Income was $7.8 million and $32.5 million for the three and six months ended June 30, 2020, respectively. Total other-than-temporary impairment losses included in net realized investments gains (losses) was $2.5 million and $6.8 million for the three and six months ending June 30, 2019, respectively. Investment Gains and Losses The following table presents our gross realized investment gains (losses): For the Three Months Ended For the Six Months Ended (in millions) 2020 2019 2020 2019 Realized gains on fixed maturities and other Fixed maturities $ 2.5 $ 5.7 $ 23.3 $ 9.4 Other investments 11.5 5.5 59.7 14.3 Other assets 32.5 — 32.5 — 46.5 11.2 115.5 23.7 Realized losses on fixed maturities and other Fixed maturities (10.5) (4.7) (18.2) (7.2) Other investments (13.9) (5.2) (45.7) (13.3) Credit losses on fixed maturities (7.8) (2.5) (32.5) (6.8) (32.2) (12.4) (96.4) (27.3) Equity securities Net realized (losses) gains on equity securities (11.0) 0.6 (12.6) 1.3 Change in unrealized (losses) gains on equity securities held at the end of the period 16.8 12.6 (22.5) 66.8 Net realized gains (losses) on equity securities 5.8 13.2 (35.1) 68.1 Net realized investment and other gains (losses) before income taxes 20.1 12.0 (16.0) 64.5 Income tax provision (benefit) 6.7 2.6 (1.3) 12.2 Net realized investment gains (losses) net of income taxes $ 13.4 $ 9.4 $ (14.7) $ 52.3 The cost of securities sold is based on the specific identification method. Changes in unrealized gains related to investments are summarized as follows: For the Three Months Ended For the Six Months Ended (in millions) 2020 2019 2020 2019 Change in unrealized gains Fixed maturities $ 136.2 $ 39.2 $ 24.4 $ 99.1 Other investments — — (14.2) — Other and short-term investments 0.2 4.5 — 4.5 Net unrealized investment gains before income taxes 136.4 43.7 10.2 103.6 Income tax provision 24.4 6.9 5.2 16.5 Net unrealized investment gains, net of income taxes $ 112.0 $ 36.8 $ 5.0 $ 87.1 Foreign Currency Exchange Forward Contracts We entered into foreign currency exchange forward contracts to manage operational currency exposure on our Canadian dollar 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 currency forward contracts are carried at fair value in our Consolidated Balance Sheets in “Other liabilities" and "Other assets” at June 30, 2020 and December 31, 2019, respectively. The net realized gains and (losses) are included in “Net realized investment (losses) gains” in our Consolidated Statements of (Loss) Income. The fair value of our foreign currency exchange forward contracts as of June 30, 2020 and December 31, 2019 was as follows: (in millions) June 30, 2020 December 31, 2019 Operational currency exposure $ (0.7) $ (0.8) Asset manager investment exposure (0.1) (0.3) Total return strategy (3.6) 2.2 Total $ (4.4) $ 1.1 The following table represents our gross investment realized gains and losses on our foreign currency exchange forward contracts: For the Three Months Ended For the Six Months Ended (in millions) 2020 2019 2020 2019 Realized gains Operational currency exposure $ 0.5 $ 0.6 $ 5.9 $ 0.8 Asset manager investment exposure 0.2 0.3 1.0 1.4 Total return strategy 8.2 5.9 33.2 12.3 Gross realized investment gains 8.9 6.8 40.1 14.5 Realized losses Operational currency exposure (3.0) (2.5) (4.7) (4.6) Asset manager investment exposure (0.6) (0.3) (1.0) (0.5) Total return strategy (8.6) (3.9) (36.6) (8.6) Gross realized investment losses (12.2) (6.7) (42.3) (13.7) Net realized investment (losses) gains on foreign currency exchange forward contracts $ (3.3) $ 0.1 $ (2.2) $ 0.8 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: (in millions) June 30, 2020 December 31, 2019 Securities on deposit for regulatory and other purposes $ 230.1 $ 192.5 Securities pledged as collateral for letters of credit and other 140.9 169.9 Securities and cash on deposit supporting Lloyd’s business 344.3 412.8 Total restricted investments $ 715.3 $ 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 approach, income approach and/or cost 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 judgments 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 June 30, 2020 and December 31, 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: • United States 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. • United States 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 (Available-for-Sale) Levels 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) June 30, Level 1 (a) Level 2 (b) Level 3 (c) Fixed maturities U.S. Governments $ 342.6 $ 338.9 $ 3.7 $ — Foreign Governments 258.2 — 258.2 — Obligations of states and political subdivisions 171.3 — 171.3 — Corporate bonds 1,732.1 — 1,724.7 7.4 Commercial mortgage-backed securities 253.2 — 253.2 — Residential mortgage-backed securities 530.2 — 530.2 — Asset-backed securities 152.9 — 152.9 — Collateralized loan obligations 266.9 — 266.9 — Total fixed maturities 3,707.4 338.9 3,361.1 7.4 Equity securities 147.5 133.1 — 14.4 Other investments 91.7 — 91.7 — Short-term investments 612.1 574.6 37.5 — $ 4,558.7 $ 1,046.6 $ 3,490.3 $ 21.8 (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, Level 1 (a) Level 2 (b) Level 3 (c) Fixed maturities U.S. Governments $ 354.6 $ 349.1 $ 5.5 $ — Foreign Governments 248.7 — 248.7 — Obligations of states and political subdivisions 152.6 — 152.6 — Corporate bonds 1,780.4 — 1,773.0 7.4 Commercial mortgage-backed securities 217.0 — 217.0 — Residential mortgage-backed securities 488.9 — 488.9 — Asset-backed securities 165.5 — 165.5 — Collateralized loan obligations 225.8 — 225.8 — Total fixed maturities 3,633.5 349.1 3,277.0 7.4 Equity securities 124.4 117.8 — 6.6 Other investments 96.3 — 96.3 — Short-term investments 845.0 823.5 21.5 — $ 4,699.2 $ 1,290.4 $ 3,394.8 $ 14.0 (a) Quoted prices in active markets for identical assets (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 $ 6.6 $ 14.0 Transfers into Level 3 — — — Transfers out of Level 3 — — — Total gains or losses (realized/unrealized): Included in net income — 0.1 0.1 Included in other comprehensive income — — — Purchases, issuances, sales, and settlements: Purchases — 7.7 7.7 Issuances — — — Sales — — — Settlements — — — Ending balance, June 30, 2020 $ 7.4 $ 14.4 $ 21.8 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 June 30, 2020 $ — $ — $ — (in millions) Credit Financial Equity Total Beginning balance, January 1, 2019 $ 2.2 $ 8.2 $ 10.4 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 $ 6.6 $ 14.0 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 June 30, 2020 and December 31, 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	6 Months Ended
	Jun. 30, 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 expected credit losses, at June 30, 2020 and January 1, 2020, and the changes in the allowance for expected credit losses for the six months ended June 30, 2020. (in millions) Premiums Receivable, Net of Allowance for Estimated Uncollectible Premiums Allowance for Estimated Uncollectible Premiums Balance, January 1, 2020 $ 688.2 $ 7.9 Cumulative effect of adoption of ASU 2016-13 — Current period change for estimated uncollectible premiums 0.6 Write-offs of uncollectible premiums receivable — Balance, June 30, 2020 $ 800.2 $ 8.5 Reinsurance Recoverables The following table presents the balances of reinsurance recoverables, net of the allowance for estimated uncollectible reinsurance, at June 30, 2020 and January 1, 2020, and changes in the allowance for estimated uncollectible reinsurance for the six months ended June 30, 2020. (in millions) Reinsurance Recoverables, Net of Allowance for Estimated Uncollectible Reinsurance Allowance for Estimated Uncollectible Reinsurance Balance, January 1, 2020 $ 3,104.6 $ 1.1 Cumulative effect of adoption of ASU 2016-13 2.5 Current period change for estimated uncollectible reinsurance — Write-offs of uncollectible reinsurance recoverables — Balance, June 30, 2020 $ 2,942.8 $ 3.6 Of the total reinsurance recoverable balance outstanding at June 30, 2020, reinsurers representing 91.1% 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.

Reserves for Losses and Loss Ad

Reserves for Losses and Loss Adjustment Expenses	6 Months Ended
	Jun. 30, 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 Six Months Ended (in millions) 2020 2019 Net reserves beginning of the year $ 2,722.7 $ 2,562.9 Net AIL reserves acquired 27.9 — Add: Losses and LAE incurred during current calendar year, net of reinsurance: Current accident year 549.6 502.9 Prior accident years 4.5 19.8 Losses and LAE incurred during calendar year, net of reinsurance 554.1 522.7 Deduct: Losses and LAE payments made during current calendar year, net of reinsurance: Current accident year 125.3 89.8 Prior accident years 451.5 432.4 Losses and LAE payments made during current calendar year, net of reinsurance: 576.8 522.2 Change in participation interest (1) 33.0 (14.4) Foreign exchange adjustments (8.5) (13.0) Net reserves - end of period 2,752.4 2,536.0 Add: Reinsurance recoverables on unpaid losses and LAE, end of period 2,463.9 2,199.7 Gross reserves - end of period $ 5,216.3 $ 4,735.7 (1) Amount represents the change in reserves due to changing our participation in Syndicates 1200 and 1910. 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 three and six months ended June 30, 2020 included net losses and loss adjustment expenses attributed to the COVID-19 pandemic of $17.4 million and $43.6 million, respectively, primarily resulting from contingency and property exposures in the Company’s International Operations and property exposures in its U.S. Operations. 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 development of prior accident years’ loss and LAE reserves on each reporting segment is presented below: For the Six Months Ended (in millions) 2020 2019 U.S. Operations $ 2.7 $ (9.1) International Operations 1.1 27.2 Run-off Lines 0.7 1.7 Total unfavorable prior-year development $ 4.5 $ 19.8 The following describes the primary factors behind each segment’s prior accident year reserve development for the six months ended June 30, 2020 and 2019: Six months ended June 30, 2020: • U.S. Operations: Unfavorable development in general liability, commercial auto liability and special property partially offset by favorable development in specialty related to our surety business unit. • International Operations: Unfavorable development in general liability and surety lines offset by favorable development in special property and specialty. • Run-off Lines: Unfavorable development in other run-off lines partially offset by favorable development in risk management workers compensation. Six months ended June 30, 2019: • U.S. Operations: Favorable development in general liability and surety lines, partially offset by unfavorable development in property and commercial multi-peril lines. • International Operations: Unfavorable development was primarily related to certain liability, property and specialty lines. The liability charges included public utility business in our Bermuda casualty division, which we previously exited, and to a lesser extent our European and Syndicate 1200 operations. As it relates to Europe, the adverse development primarily related to certain cover-holders whose contracts were previously terminated. As it relates to Syndicate 1200, the adverse development related to businesses that we have previously exited or where aggressive remedial underwriting actions have been taken. The International Operations unfavorable development includes $26.4 million recognized during the second quarter of 2019. The timing of recognizing this unfavorable development was primarily due to obtaining additional information on several individual claims, including reports provided by outside counsel, audits of the underlying losses and recent jury awards. The result was an increase in the number of claims with the potential for underlying losses to reach our attachment point, particularly on aggregate treaty contracts within our Bermuda Operations. The second quarter 2019 unfavorable development was also attributable to the results of recent audits, underwriting reviews, and updated data from third party cover-holders, 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 cover-holders. • Run-off Lines: Unfavorable development in other run-off lines, partially offset by favorable development in risk management workers compensation . 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 June 30, 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.

Disclosures about Fair Value of

Disclosures about Fair Value of Financial Instruments	6 Months Ended
	Jun. 30, 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 3, “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 June 30, 2020 and December 31, 2019, the fair value of our debt instruments is determined using both Level 1 and Level 2 inputs, as previously defined in Note 3, "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 June 30, 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: June 30, 2020 December 31, 2019 (in millions) Carrying Fair Carrying Fair Junior subordinated debentures: Trust preferred debentures $ 172.7 $ 173.8 $ 172.7 $ 174.0 Subordinated debentures 84.9 92.4 84.7 92.5 Total junior subordinated debentures 257.6 266.2 257.4 266.5 Senior unsecured fixed rate notes 140.1 146.7 140.0 144.2 Floating rate loan stock 56.0 56.3 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) June 30, 2020 Level 1 (a) Level 2 (b) Level 3 (c) Junior subordinated debentures: Trust preferred debentures $ 173.8 $ — $ 173.8 $ — Subordinated debentures 92.4 — 92.4 — Total junior subordinated debentures 266.2 — 266.2 — Senior unsecured fixed rate notes 146.7 146.7 — — Floating rate loan stock 56.3 — 56.3 — 469.2 146.7 322.5 — (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	6 Months Ended
	Jun. 30, 2020
Equity [Abstract]
Shareholders' Equity	Shareholders’ Equity On May 7, 2020, our Board of Directors declared a quarterly cash dividend in the amount of $0.31 on each share of common stock outstanding. On June 12, 2020, we paid $10.6 million to our shareholders of record on May 29, 2020. On May 24, 2019, our Board of Directors declared a quarterly cash dividend in the amount of $0.31 on each share of common stock outstanding. On June 21, 2019, we paid $11.9 million to our shareholders of record on June 7, 2019. On May 3, 2016, our Board of Directors authorized the repurchase of up to $150.0 million of our common shares (“2016 Repurchase Authorization”). The 2016 Repurchase Authorization supersedes all previous repurchase authorizations. As of June 30, 2020, availability under the 2016 Repurchase Authorization for future repurchases of our common shares was $53.3 million. We did not repurchase any common shares for the six months ended June 30, 2020.

Accumulated Other Comprehensive

Accumulated Other Comprehensive (Loss) Income	6 Months Ended
	Jun. 30, 2020
Equity [Abstract]
Accumulated Other Comprehensive (Loss) Income	Accumulated Other Comprehensive (Loss) Income A summary of changes in accumulated other comprehensive (loss) income, net of taxes (where applicable) by component for the six months ended June 30, 2020, and 2019 is presented below: (in millions) Foreign Currency Translation Adjustments Unrealized Defined Benefit Pension Plans Total Balance, January 1, 2020 $ (22.6) $ 33.5 $ (8.1) $ 2.8 Other comprehensive loss before reclassifications (7.6) 24.2 — 16.6 Amounts reclassified from accumulated other comprehensive loss — (19.2) — (19.2) Net current-period other comprehensive loss (7.6) 5.0 — (2.6) Cumulative effect of adoption of ASU 2016-13 — 5.7 — 5.7 Balance, June 30, 2020 $ (30.2) $ 44.2 $ (8.1) $ 5.9 (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 income before reclassifications (0.1) 82.9 — 82.8 Amounts reclassified from accumulated other comprehensive income — 4.2 — 4.2 Net current-period other comprehensive income (0.1) 87.1 — 87.0 Balance, June 30, 2019 $ (22.5) $ 38.1 $ (6.7) $ 8.9 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 (Loss) Income: For the Three Months Ended For the Six Months Ended (in millions) 2020 2019 2020 2019 Unrealized gains and losses on securities: Net realized investment (gains) loss $ (16.5) $ 1.8 $ (19.9) $ 4.9 Provision (benefit) for income taxes 2.6 (0.2) 0.7 (0.7) Net of taxes $ (13.9) $ 1.6 $ (19.2) $ 4.2

Net (Loss) Income Per Common Sh

Net (Loss) Income Per Common Share	6 Months Ended
	Jun. 30, 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 Three Months Ended For the Six Months Ended (in millions, except number of shares and per share amounts) 2020 2019 2020 2019 Net (loss) income $ (6.4) $ 28.8 $ (25.2) $ 120.0 Weighted average common shares outstanding - basic 34,634,353 34,195,250 34,551,935 34,090,372 Effect of dilutive securities: Equity compensation awards — 584,741 — 669,176 Weighted average common shares outstanding - diluted 34,634,353 34,779,991 34,551,935 34,759,548 Net (loss) income per common share: Basic $ (0.18) $ 0.84 $ (0.73) $ 3.52 Diluted $ (0.18) $ 0.83 $ (0.73) $ 3.45 Excluded from the weighted average common shares outstanding calculation at June 30, 2020 and 2019 are 11,315,889 shares, which are held as treasury shares. The shares are excluded as of their repurchase date.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	6 Months Ended
	Jun. 30, 2020
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	Supplemental Cash Flow Information Interest paid and income taxes paid (recovered) were as follows: For the Six Months Ended (in millions) 2020 2019 Senior unsecured fixed rate notes $ 4.7 $ 4.7 Junior subordinated debentures 6.7 8.3 Other indebtedness 3.4 3.8 Total interest paid $ 14.8 $ 16.8 Income taxes paid 1.6 1.3 Income taxes recovered (0.7) — Income taxes paid, net $ 0.9 $ 1.3

Share-based Compensation

Share-based Compensation	6 Months Ended
	Jun. 30, 2020
Share-based Payment Arrangement [Abstract]
Share-based Compensation	Share-based Compensation 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 June 30, 2020 and changes during the six months then ended is as follows: Shares Weighted-Average Outstanding at January 1, 2020 471,271 $ 60.09 Granted 399,578 $ 32.72 Vested and issued (161,081) $ 51.45 Expired or forfeited (69,499) $ 58.42 Outstanding at June 30, 2020 640,269 $ 44.00 The restricted shares vest over one Stock-Settled SARs A summary of stock-settled SARs activity as of June 30, 2020 and changes during the six months then ended is as follows: Shares Weighted-Average Outstanding at January 1, 2020 625,368 $ 33.60 Exercised (415,274) $ 32.25 Expired or forfeited — $ — Outstanding at June 30, 2020 210,094 $ 36.26 As of June 30, 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 three and six months ended June 30, 2020 for stock-settled SARs. There was no expense recognized for the three months ended June 30, 2019. For the six months ended June 30, 2019, expense recognized for the stock-settled SARs was $0.4 million. As of June 30, 2020, there was no unrecognized compensation cost related to stock-settled SARs outstanding.

Underwriting, Acquisition and I

Underwriting, Acquisition and Insurance Expenses & Other Corporate Expenses	6 Months Ended
	Jun. 30, 2020
Underwriting, Acquisition and Insurance Expenses & Other Corporate 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 Three Months Ended For the Six Months Ended (in millions) 2020 2019 2020 2019 Commissions $ 57.2 $ 56.7 $ 122.5 $ 120.0 General expenses 93.3 91.5 192.2 180.1 Premium taxes, boards and bureaus 6.5 7.9 14.5 16.2 157.0 156.1 329.2 316.3 Net deferral of policy acquisition costs 4.4 5.3 0.2 5.3 Total underwriting, acquisition and insurance expenses $ 161.4 $ 161.4 $ 329.4 $ 321.6 Other Corporate Expenses During the three and six months ended June 30, 2020 and 2019, we incurred costs of $2.5 million and $5.8 million, and $7.5 million and $8.0 million, respectively, 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 $0.9 million civil penalty, and is included in the other corporate expenses for the three and six months ended June 30, 2020. These non-recurring costs are included in the line item “Other corporate expenses” in the Company’s Consolidated Statements of (Loss) Income, and have been excluded from the calculation of our expense ratio.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 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 United States or the United Kingdom and, accordingly, do not expect to be subject to direct United States or United Kingdom income taxation. We have subsidiaries based in the United Kingdom that are subject to the tax laws of that country. Under current law, these subsidiaries are taxed at the applicable corporate tax rates. Certain of the United Kingdom subsidiaries are deemed to be engaged in business in the United States, and therefore, are subject to United States corporate tax in respect of a proportion of their United States underwriting business only. Relief is available against the United Kingdom tax liabilities in respect of overseas taxes paid that arise from the underwriting business. Our United Kingdom subsidiaries file separate United Kingdom income tax returns. We have subsidiaries based in the United States that are subject to United States tax laws. Under current law, these subsidiaries are taxed at the applicable corporate tax rates. Our United States subsidiaries generally file a consolidated United States 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. Our expected income tax provision 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 three and six months ended June 30, 2020 and 2019, pre-tax income (loss) attributable to our operations and the corresponding operations’ effective tax rates were as follows: For the Three Months Ended June 30, 2020 2019 (in millions) Pre-Tax Effective Pre-Tax Effective Bermuda $ (31.1) — % $ 15.0 — % United States 67.9 23.2 % 22.3 14.8 % United Kingdom (29.2) 12.8 % (8.9) 26.7 % Belgium 0.1 20.0 % (0.3) 29.5 % Brazil 0.6 — % 2.0 — % United Arab Emirates 0.5 — % — (1) — % Ireland — (1) — % — (1) — % Italy (1.8) — % 0.2 — % Malta (1.3) — % (0.7) (0.1) % Switzerland — (1) — % — (1) — % Pre-tax Income $ 5.7 209.4 % $ 29.6 2.9 % (1) Pre-tax income (loss) for the respective year was less than $0.1 million. For the Six Months Ended June 30, 2020 2019 Pre-Tax Effective Pre-Tax Effective Bermuda $ (52.9) — % $ 47.0 — % United States 57.3 17.3 % 91.8 14.5 % United Kingdom (27.5) 2.4 % (12.4) 28.1 % Belgium 0.1 31.0 % (0.3) 29.7 % Brazil 2.8 — % 3.8 — % United Arab Emirates 1.3 — % 0.2 — % Ireland — (1) — % (0.1) — % Italy 1.7 — % (0.5) — % Malta 1.3 — % 0.2 0.5 % Switzerland — (1) — % — (1) — % Pre-tax Income $ (15.9) (58.7) % $ 129.7 7.5 % (1) Pre-tax income (loss) for the respective year was less than $0.1 million. 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 inherit nature of our business. A reconciliation of the difference between the provision for income taxes and the expected tax provision at the weighted average tax rate is as follows: For the Three Months Ended For the Six Months Ended (in millions) 2020 2019 2020 2019 Income tax provision (benefit) at expected rate $ 8.6 $ 3.6 $ 9.4 $ 18.5 Tax effect of: Nontaxable investment income (0.2) (0.3) (0.3) (0.7) Foreign exchange adjustments 1.5 0.1 (0.6) 0.6 Goodwill 1.0 — 1.0 — Withholding taxes — (1) 0.1 0.1 0.2 Change in valuation allowance — (1) — (1) — (1) (0.6) Other 1.2 (2.7) (0.3) (8.3) Income tax provision $ 12.1 $ 0.8 $ 9.3 $ 9.7 (1) Tax effect of the adjustment 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 during 2020, which was negligible, related to the following: Internal Revenue Code Section 382 limited net operating loss carryforwards within the United States, 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 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. We had no material unrecognized tax benefits as of June 30, 2020 and 2019. Our United States subsidiaries are no longer subject to U.S. federal and state income tax examinations by tax authorities for years before 2015. Our United Kingdom subsidiaries are no longer subject to United Kingdom income tax examinations by Her Majesty’s Revenue and Customs for years before 2016. 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.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and ContingenciesArgo 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 $96.1 million related to our limited partnership investments at June 30, 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 thirteen years

Segment Information

Segment Information	6 Months Ended
	Jun. 30, 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 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 (loss) income before income taxes for each segment were as follows: For the Three Months Ended For the Six Months Ended (in millions) 2020 2019 2020 2019 Revenue: Earned premiums U.S. Operations $ 301.6 $ 284.0 $ 604.1 $ 557.8 International Operations 131.8 147.6 264.1 294.3 Run-off Lines — 0.1 0.2 0.1 Total earned premiums 433.4 431.7 868.4 852.2 Net investment income U.S. Operations 0.8 29.6 26.0 52.7 International Operations 0.5 11.5 9.1 20.6 Run-off Lines 0.1 1.3 1.3 2.7 Corporate and Other 0.1 0.4 0.6 0.7 Total net investment income 1.5 42.8 37.0 76.7 Fee and other income 2.0 2.1 4.1 4.4 Net realized investment gains (losses) 20.1 12.0 (16.0) 64.5 Total revenue $ 457.0 $ 488.6 $ 893.5 $ 997.8 For the Three Months Ended For the Six Months Ended (in millions) 2020 2019 2020 2019 Income (loss) before income taxes U.S. Operations $ 31.2 $ 53.2 $ 68.1 $ 96.1 International Operations (27.5) (21.0) (39.8) (4.8) Run-off Lines (1.3) (1.1) (0.8) (0.5) Total segment income before taxes 2.4 31.1 27.5 90.8 Corporate and Other (7.9) (11.3) (18.2) (22.2) Net realized investment and other gains (losses) 20.1 12.0 (16.0) 64.5 Foreign currency exchange (losses) gains (6.4) 5.3 (3.4) 4.6 Other corporate expenses (2.5) (7.5) (5.8) (8.0) Total income (loss) before income taxes $ 5.7 $ 29.6 $ (15.9) $ 129.7 The table below presents earned premiums by geographic location for the three and six months ended June 30, 2020 and 2019. 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 Three Months Ended For the Six Months Ended (in millions) 2020 2019 2020 2019 United States $ 301.4 $ 283.2 $ 601.1 $ 555.8 United Kingdom 75.5 96.6 162.2 193.7 Bermuda 25.3 19.2 46.5 35.8 Malta 18.5 20.2 30.3 41.0 All other jurisdictions 12.7 12.5 28.3 25.9 Total earned premiums $ 433.4 $ 431.7 $ 868.4 $ 852.2 The following table represents identifiable assets: (in millions) June 30, 2020 December 31, 2019 U.S. Operations $ 5,744.9 $ 5,009.0 International Operations 4,132.2 5,002.4 Run-off Lines 331.1 356.9 Corporate and Other 188.5 146.2 Total $ 10,396.7 $ 10,514.5 Included in total assets at June 30, 2020 and December 31, 2019 are $780.7 million and $916.3 million, respectively, in assets associated with trade capital providers.

Senior Unsecured Fixed Rate Not

Senior Unsecured Fixed Rate Notes	6 Months Ended
	Jun. 30, 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 US (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 June 30, 2020 and December 31, 2019, the Notes consisted of the following: (in millions) June 30, 2020 December 31, 2019 Senior unsecured fixed rate notes Principal $ 143.8 $ 143.8 Less: unamortized debt issuance costs (3.7) (3.8) Senior unsecured fixed rate notes, less unamortized debt issuance costs $ 140.1 $ 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 June 30, 2020 and December 31, 2019 and for the three and six months ended June 30, 2020 and 2019, 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. CONDENSED CONSOLIDATING BALANCE SHEET JUNE 30, 2020 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Assets Investments $ 0.6 $ 3,402.0 $ 1,448.9 $ — $ 4,851.5 Cash 1.9 41.6 144.2 — 187.7 Accrued investment income — 17.4 6.0 — 23.4 Premiums receivable — 298.4 501.8 — 800.2 Reinsurance recoverables — 1,740.3 1,202.5 — 2,942.8 Goodwill and other intangible assets, net 39.9 118.5 89.2 — 247.6 Deferred tax assets, net — 11.7 7.2 — 18.9 Deferred acquisition costs, net — 86.0 67.5 — 153.5 Ceded unearned premiums — 337.4 319.1 — 656.5 Operating lease right-of-use assets 6.8 55.3 25.1 — 87.2 Other assets 9.6 146.2 258.9 — 414.7 Assets held for sale — 12.4 0.3 — 12.7 Intercompany note receivable — 72.9 (72.9) — — Investments in subsidiaries 1,904.2 — — (1,904.2) — Total assets $ 1,963.0 $ 6,340.1 $ 3,997.8 $ (1,904.2) $ 10,396.7 Liabilities and Shareholders' Equity Reserves for losses and loss adjustment expenses $ — $ 3,181.7 $ 2,034.6 $ — $ 5,216.3 Unearned premiums — 900.7 580.5 — 1,481.2 Funds held and ceded reinsurance payable, net — 566.7 542.7 — 1,109.4 Debt 153.4 284.4 140.9 — 578.7 Current income taxes payable, net — 33.2 (6.1) — 27.1 Accrued underwriting expenses and other liabilities 5.4 83.4 66.0 — 154.8 Operating lease liabilities 6.9 64.1 28.2 — 99.2 Due to (from) affiliates 67.3 (11.7) 11.7 (67.3) — Total liabilities 233.0 5,102.5 3,398.5 (67.3) 8,666.7 Total shareholders' equity 1,730.0 1,237.6 599.3 (1,836.9) 1,730.0 Total liabilities and shareholders' equity $ 1,963.0 $ 6,340.1 $ 3,997.8 $ (1,904.2) $ 10,396.7 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. 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 US, Inc. Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Assets Investments $ 0.6 $ 3,405.6 $ 1,693.2 $ — $ 5,099.4 Cash 1.9 31.6 104.3 — 137.8 Accrued investment income — 18.2 7.5 — 25.7 Premiums receivable — 231.3 456.9 — 688.2 Reinsurance recoverables — 1,689.4 1,415.2 — 3,104.6 Goodwill and other intangible assets, net 40.6 123.4 89.2 — 253.2 Deferred tax assets, net — 0.4 5.7 — 6.1 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 7.8 165.8 213.5 — 387.1 Assets held for sale — 15.4 — — 15.4 Intercompany note receivable — 56.7 (56.7) — — Investments in subsidiaries 1,916.7 — — (1,916.7) — Total assets $ 1,974.7 $ 6,192.2 $ 4,264.3 $ (1,916.7) $ 10,514.5 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 — 645.9 607.8 — 1,253.7 Debt 153.4 284.3 141.0 — 578.7 Current income taxes payable, net — 8.2 (7.4) — 0.8 Accrued underwriting expenses and other liabilities 13.6 87.6 124.8 — 226.0 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 5,018.8 3,540.3 (19.3) 8,733.4 Total shareholders' equity 1,781.1 1,173.4 724.0 (1,897.4) 1,781.1 Total liabilities and shareholders' equity $ 1,974.7 $ 6,192.2 $ 4,264.3 $ (1,916.7) $ 10,514.5 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF (LOSS) INCOME FOR THE THREE MONTHS ENDED JUNE 30, 2020 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Premiums and other revenue: Earned premiums $ — $ 300.7 $ 132.7 $ — $ 433.4 Net investment income (expenses) — 5.8 (4.3) — 1.5 Fee and other income — 0.6 1.4 — 2.0 Net realized investment gains (losses) 1.4 33.1 (14.4) — 20.1 Total revenue 1.4 340.2 115.4 — 457.0 Expenses: Losses and loss adjustment expenses — 167.7 105.5 — 273.2 Underwriting, acquisition and insurance expenses 3.2 101.7 56.5 — 161.4 Other corporate expenses 2.6 (0.1) — — 2.5 Interest expense 1.1 4.0 1.7 — 6.8 Fee and other expense — 0.6 0.4 — 1.0 Foreign currency exchange losses — — 6.4 — 6.4 Total expenses 6.9 273.9 170.5 — 451.3 (Loss) income before income taxes (5.5) 66.3 (55.1) — 5.7 Provision (benefit) for income taxes — 15.8 (3.7) — 12.1 Net (loss) income before equity in earnings of subsidiaries (5.5) 50.5 (51.4) — (6.4) Equity in undistributed earnings of subsidiaries (0.9) — — 0.9 — Net (loss) income $ (6.4) $ 50.5 $ (51.4) $ 0.9 $ (6.4) (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF INCOME FOR THE THREE MONTHS ENDED JUNE 30, 2019 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Premiums and other revenue: Earned premiums $ — $ 260.1 $ 171.6 $ — $ 431.7 Net investment (expense) income (0.6) 28.1 15.3 — 42.8 Fee and other income — 0.7 1.4 — 2.1 Net realized investment (losses) gains (0.1) 15.0 (2.9) — 12.0 Total revenue (0.7) 303.9 185.4 — 488.6 Expenses: Losses and loss adjustment expenses — 171.3 113.5 — 284.8 Underwriting, acquisition and insurance expenses 0.7 104.2 56.5 — 161.4 Other corporate expenses 7.5 — — — 7.5 Interest expense 1.7 5.2 2.4 — 9.3 Fee and other expense — 0.9 0.4 — 1.3 Foreign currency exchange gains — (0.1) (5.2) — (5.3) Total expenses 9.9 281.5 167.6 — 459.0 (Loss) income before income taxes (10.6) 22.4 17.8 — 29.6 Provision (benefit) for income taxes — 3.3 (2.5) — 0.8 Net (loss) income before equity in earnings of subsidiaries (10.6) 19.1 20.3 — 28.8 Equity in undistributed earnings of subsidiaries 39.4 — — (39.4) — Net income $ 28.8 $ 19.1 $ 20.3 $ (39.4) $ 28.8 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF INCOME FOR THE SIX MONTHS ENDED JUNE 30, 2020 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries Consolidating Total Premiums and other revenue: Earned premiums $ — $ 602.2 $ 266.2 $ — $ 868.4 Net investment income — 30.4 6.6 — 37.0 Fee and other income — 1.4 2.7 — 4.1 Net realized investment gains (losses) 1.3 (7.5) (9.8) — (16.0) Total revenue 1.3 626.5 265.7 — 893.5 Expenses: Losses and loss adjustment expenses — 358.2 195.9 — 554.1 Underwriting, acquisition and insurance expenses 9.0 203.5 116.9 — 329.4 Other corporate expenses 5.2 0.6 — — 5.8 Interest expense 2.5 8.3 3.7 — 14.5 Fee and other expense — 1.3 0.9 — 2.2 Foreign currency exchange (gains) losses — (1.0) 4.4 — 3.4 Total expenses 16.7 570.9 321.8 — 909.4 (Loss) income before income taxes (15.4) 55.6 (56.1) — (15.9) Provision (benefit) for income taxes — 9.9 (0.6) — 9.3 Net (loss) income before equity in earnings of subsidiaries (15.4) 45.7 (55.5) — (25.2) Equity in undistributed earnings of subsidiaries (9.8) — — 9.8 — Net (loss) income $ (25.2) $ 45.7 $ (55.5) $ 9.8 $ (25.2) (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF INCOME FOR THE SIX MONTHS ENDED JUNE 30, 2019 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries Consolidating Total Premiums and other revenue: Earned premiums $ — $ 526.6 $ 325.6 $ — $ 852.2 Net investment (expenses) income (1.3) 51.9 26.1 — 76.7 Fee and other income — 1.8 2.6 — 4.4 Net realized investment (losses) gains (0.2) 60.9 3.8 — 64.5 Total revenue (1.5) 641.2 358.1 — 997.8 Expenses: Losses and loss adjustment expenses — 329.3 193.4 — 522.7 Underwriting, acquisition and insurance expenses 0.9 208.3 112.4 — 321.6 Other corporate expenses 8.0 — — — 8.0 Interest expense 3.4 9.9 4.5 — 17.8 Fee and other expense — 1.7 0.9 — 2.6 Foreign currency exchange losses (gains) — 0.2 (4.8) — (4.6) Total expenses 12.3 549.4 306.4 — 868.1 (Loss) income before income taxes (13.8) 91.8 51.7 — 129.7 Provision (benefit) for income taxes — 13.3 (3.6) — 9.7 Net (loss) income before equity in earnings of subsidiaries (13.8) 78.5 55.3 — 120.0 Equity in undistributed earnings of subsidiaries 133.8 — — (133.8) — Net income $ 120.0 $ 78.5 $ 55.3 $ (133.8) $ 120.0 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS FOR THE SIX MONTHS ENDED JUNE 30, 2020 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Net cash flows from operating activities $ 20.3 $ (21.0) $ (102.4) $ — $ (103.1) Cash flows from investing activities: Proceeds from sales of investments — 454.1 394.2 — 848.3 Maturities and mandatory calls of fixed maturity investments — 184.4 70.6 — 255.0 Purchases of investments — (935.0) (242.4) — (1,177.4) Change in short-term investments and foreign regulatory deposits (0.1) 270.9 (53.3) — 217.5 Settlements of foreign currency exchange forward contracts 0.1 — 6.9 — 7.0 Sale of Trident's assets — 38.0 — — 38.0 Issuance of intercompany note, net — (15.0) 15.0 — — Purchases of fixed assets and other, net — 33.6 (46.2) — (12.6) Cash provided by investing activities — 31.0 144.8 — 175.8 Cash flows from financing activities: Activity under stock incentive plans 1.0 — — — 1.0 Payment of cash dividend to common shareholders (21.3) — — — (21.3) Cash used in financing activities (20.3) — — — (20.3) Effect of exchange rate changes on cash — — (2.5) — (2.5) Change in cash — 10.0 39.9 — 49.9 Cash, beginning of year 1.9 31.6 104.3 — 137.8 Cash, end of period $ 1.9 $ 41.6 $ 144.2 $ — $ 187.7 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS FOR THE SIX MONTHS ENDED JUNE 30, 2019 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Net cash flows from operating activities $ 19.3 $ (5.5) $ (18.7) $ — $ (4.9) Cash flows from investing activities: Proceeds from sales of investments — 507.1 307.8 — 814.9 Maturities and mandatory calls of fixed maturity investments — 131.8 37.0 — 168.8 Purchases of investments — (686.4) (272.7) — (959.1) Change in short-term investments and foreign regulatory deposits 2.8 74.7 (3.5) — 74.0 Settlements of foreign currency exchange forward contracts (0.1) 0.9 9.1 — 9.9 Purchases of fixed assets and other, net — (6.9) (31.3) — (38.2) Cash provided by investing activities 2.7 21.2 46.4 — 70.3 Cash flows from financing activities: Payment on the intercompany note — (19.1) 19.1 — — Activity under stock incentive plans 0.9 — — — 0.9 Payment of cash dividend to common shareholders (22.7) — — — (22.7) Cash (used in) provided by financing activities (21.8) (19.1) 19.1 — (21.8) Effect of exchange rate changes on cash — — (0.5) — (0.5) Change in cash 0.2 (3.4) 46.3 — 43.1 Cash, beginning of year 1.7 31.7 105.8 — 139.2 Cash, end of period $ 1.9 $ 28.3 $ 152.1 $ — $ 182.3 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations.

Subsequent Event

Subsequent Event	6 Months Ended
	Jun. 30, 2020
Subsequent Events [Abstract]
Subsequent Event	Subsequent Event On July 9, 2020, the Company consummated its public offering of 6,000,000 depositary shares (the “Depositary Shares”), each of which represents a 1/1,000th interest in a share of its 7.00% Resettable Fixed Rate Preference Shares, Series A, par value of $1.00 per share with a liquidation preference of $25,000 per share (equivalent to $25 per Depositary Share) (the “Preference Shares”). 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. The Company intends to use the net proceeds from the offering to repay its term loan, which has $125 million principal remaining outstanding, and for working capital to support continued growth in insurance operations. Dividends on the 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 day 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.

Basis of Presentation (Policies

Basis of Presentation (Policies)	6 Months Ended
	Jun. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements of Argo Group International Holdings, Ltd. (“Argo Group,” “we” or the “Company”) and its subsidiaries have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and with the instructions for Form 10-Q and Article 10 of Regulation S-X. Argo Group is an underwriter of specialty insurance and reinsurance products in the property and casualty market. The preparation of interim financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenues and expenses during the reporting period. The major estimates reflected in our consolidated financial statements include, but are not limited to, reserves for losses and loss adjustment expenses; reinsurance recoverables, including the reinsurance recoverables allowance for expected credit losses; estimates of written and earned premiums; reinsurance premium receivable; fair value of investments and assessment of potential impairment, including the allowance for credit losses on fixed maturity securities; valuation of goodwill and intangibles and our deferred tax asset valuation allowance. Actual results could differ from those estimates. Certain financial information that normally is included in annual financial statements, including certain financial statement footnotes, prepared in accordance with GAAP, is not required for interim reporting purposes and has been condensed or omitted. These statements should be read in conjunction with the consolidated financial statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2019, filed with the Securities and Exchange Commission ("SEC") on February 28, 2020. The interim financial information as of, and for the three and six months ended, June 30, 2020 and 2019 is unaudited. However, in the opinion of management, the interim information includes all adjustments, consisting of normal recurring accruals, necessary for a fair presentation of the results presented for the interim periods. The operating results for the interim periods are not necessarily indicative of the results to be expected for the full year. All significant intercompany amounts have been eliminated in consolidation. Certain reclassifications have been made to financial information presented for prior years to conform to the current year’s presentation.
Reclassification	Certain reclassifications have been made to financial information presented for prior years to conform to the current year’s presentation.
Acquisition	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.
Recently Adopted Accounting Pronouncements	Recently Issued Accounting Pronouncements In June 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("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 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. Updates to Accounting Policies The following accounting policies have been updated to reflect the adoption of ASU 2016-13, as described above. Investment Impairments of Available for Sale Fixed Maturities 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. 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. Reinsurance Recoverables 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. 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. Premiums and Unearned Premium Reserves Premiums are recognized as revenues pro rata over the policy period. Unearned premium reserves represent the unexpired portion of policy premiums. Accrued retrospective premiums are included in premium balances receivable. Premiums receivable balances are reported net of an allowance for expected losses, both dispute and credit related. 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.

Investments (Tables)

Investments (Tables)	6 Months Ended
	Jun. 30, 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, allowance for credit losses, and fair value of fixed maturity investments were as follows: June 30, 2020 (in millions) Amortized Gross Gross Allowance for Credit Losses (1) Fair Fixed maturities U.S. Governments $ 324.0 $ 18.6 $ — $ — $ 342.6 Foreign Governments 256.1 6.1 3.7 0.3 258.2 Obligations of states and political subdivisions 165.3 6.9 0.8 0.1 171.3 Corporate bonds 1,762.6 58.4 49.2 39.7 1,732.1 Commercial mortgage-backed securities 242.5 10.9 0.2 — 253.2 Residential mortgage-backed securities 512.3 20.2 2.3 — 530.2 Asset-backed securities 152.6 2.7 2.3 0.1 152.9 Collateralized loan obligations 273.2 1.5 7.8 — 266.9 Total fixed maturities $ 3,688.6 $ 125.3 $ 66.3 $ 40.2 $ 3,707.4 (1) Effective January 1, 2020 we adopted ASC-326 and as a result any credit impairment losses on our available-for-sale fixed maturities are recorded as an allowance, subject to reversal. Prior periods have not been restated to conform with the current year presentation. See Note 1. December 31, 2019 (in millions) Amortized Gross Gross Fair Fixed maturities U.S. Governments $ 353.5 $ 2.3 $ 1.2 $ 354.6 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 1,777.4 37.7 34.7 1,780.4 Commercial mortgage-backed securities 213.5 4.6 1.1 217.0 Residential mortgage-backed securities 479.1 10.4 0.6 488.9 Asset-backed securities 164.2 1.5 0.2 165.5 Collateralized loan obligations 226.7 0.5 1.4 225.8 Total fixed maturities $ 3,605.0 $ 68.5 $ 40.0 $ 3,633.5
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 June 30, 2020, by contractual maturity, were as follows: (in millions) Amortized Fair Due in one year or less $ 316.3 $ 316.8 Due after one year through five years 1,540.7 1,523.5 Due after five years through ten years 579.8 592.4 Thereafter 71.2 71.5 Structured securities 1,180.6 1,203.2 Total $ 3,688.6 $ 3,707.4
Schedule of Carrying Value and Unfunded Investment Commitments of Other Invested Assets Portfolio	Details regarding the carrying value and unfunded investment commitments of other investments as of June 30, 2020 and December 31, 2019 were as follows: June 30, 2020 (in millions) Carrying Unfunded Investment Type Hedge funds $ 98.0 $ — Private equity 190.5 96.1 Overseas deposits 91.7 — Other 4.3 — Total other investments $ 384.5 $ 96.1 December 31, 2019 (in millions) Carrying Unfunded Investment Type Hedge funds $ 109.5 $ — Private equity 268.1 110.0 Overseas deposits 114.6 — Other 4.3 — Total other investments $ 496.5 $ 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: June 30, 2020 Less Than One Year One Year or Greater Total (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed maturities U.S. Governments (1) $ 1.3 $ — $ — $ — $ 1.3 $ — Foreign Governments 124.4 3.7 — — 124.4 3.7 Obligations of states and political subdivisions 18.1 0.8 — — 18.1 0.8 Corporate bonds 356.2 26.2 30.8 23.0 387.0 49.2 Commercial mortgage-backed securities 21.8 0.2 — — 21.8 0.2 Residential mortgage-backed securities 71.1 1.5 8.3 0.8 79.4 2.3 Asset-backed securities 30.9 2.2 3.9 0.1 34.8 2.3 Collateralized loan obligations 189.8 6.1 56.9 1.7 246.7 7.8 Total fixed maturities $ 813.6 $ 40.7 $ 99.9 $ 25.6 $ 913.5 $ 66.3 (1) Unrealized losses are less than $0.1 million. 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) 117.6 0.7 5.1 — 122.7 0.7 Obligations of states and political subdivisions (1) 0.7 — 2.1 0.1 2.8 0.1 Corporate bonds 249.4 18.9 63.6 15.8 313.0 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 54.7 0.8 116.7 0.6 171.4 1.4 Total fixed maturities $ 701.2 $ 23.0 $ 253.5 $ 17.0 $ 954.7 $ 40.0 (1) Unrealized losses are less than $0.1 million.
Debt Securities, Available-for-sale, Allowance for Credit Loss	The following table presents a reconciliation of the beginning and ending balances for the allowance for credit losses on available-for-sale fixed maturity securities: For the Six Months Ended (in millions) 2020 Beginning balance, January 1, 2020 $ — Additions related to initial adoption of accounting standard 6.9 Provision for expected credit losses 32.5 Increases due to sales/defaults of credit-impaired securities 0.8 Ending balance, June 30, 2020 $ 40.2
Schedule of Company's Gross Realized Investment Gains (Losses)	The following table presents our gross realized investment gains (losses): For the Three Months Ended For the Six Months Ended (in millions) 2020 2019 2020 2019 Realized gains on fixed maturities and other Fixed maturities $ 2.5 $ 5.7 $ 23.3 $ 9.4 Other investments 11.5 5.5 59.7 14.3 Other assets 32.5 — 32.5 — 46.5 11.2 115.5 23.7 Realized losses on fixed maturities and other Fixed maturities (10.5) (4.7) (18.2) (7.2) Other investments (13.9) (5.2) (45.7) (13.3) Credit losses on fixed maturities (7.8) (2.5) (32.5) (6.8) (32.2) (12.4) (96.4) (27.3) Equity securities Net realized (losses) gains on equity securities (11.0) 0.6 (12.6) 1.3 Change in unrealized (losses) gains on equity securities held at the end of the period 16.8 12.6 (22.5) 66.8 Net realized gains (losses) on equity securities 5.8 13.2 (35.1) 68.1 Net realized investment and other gains (losses) before income taxes 20.1 12.0 (16.0) 64.5 Income tax provision (benefit) 6.7 2.6 (1.3) 12.2 Net realized investment gains (losses) net of income taxes $ 13.4 $ 9.4 $ (14.7) $ 52.3
Schedule of Changes in Unrealized Appreciation (Depreciation)	Changes in unrealized gains related to investments are summarized as follows: For the Three Months Ended For the Six Months Ended (in millions) 2020 2019 2020 2019 Change in unrealized gains Fixed maturities $ 136.2 $ 39.2 $ 24.4 $ 99.1 Other investments — — (14.2) — Other and short-term investments 0.2 4.5 — 4.5 Net unrealized investment gains before income taxes 136.4 43.7 10.2 103.6 Income tax provision 24.4 6.9 5.2 16.5 Net unrealized investment gains, net of income taxes $ 112.0 $ 36.8 $ 5.0 $ 87.1
Schedule of Fair Value of Foreign Currency Exchange Forward Contracts	The fair value of our foreign currency exchange forward contracts as of June 30, 2020 and December 31, 2019 was as follows: (in millions) June 30, 2020 December 31, 2019 Operational currency exposure $ (0.7) $ (0.8) Asset manager investment exposure (0.1) (0.3) Total return strategy (3.6) 2.2 Total $ (4.4) $ 1.1
Schedule of Realized Gains and Losses of Investment on Foreign Currency Exchange Forward Contracts	The following table represents our gross investment realized gains and losses on our foreign currency exchange forward contracts: For the Three Months Ended For the Six Months Ended (in millions) 2020 2019 2020 2019 Realized gains Operational currency exposure $ 0.5 $ 0.6 $ 5.9 $ 0.8 Asset manager investment exposure 0.2 0.3 1.0 1.4 Total return strategy 8.2 5.9 33.2 12.3 Gross realized investment gains 8.9 6.8 40.1 14.5 Realized losses Operational currency exposure (3.0) (2.5) (4.7) (4.6) Asset manager investment exposure (0.6) (0.3) (1.0) (0.5) Total return strategy (8.6) (3.9) (36.6) (8.6) Gross realized investment losses (12.2) (6.7) (42.3) (13.7) Net realized investment (losses) gains on foreign currency exchange forward contracts $ (3.3) $ 0.1 $ (2.2) $ 0.8
Schedule of Restricted Assets	The following table presents our components of restricted assets: (in millions) June 30, 2020 December 31, 2019 Securities on deposit for regulatory and other purposes $ 230.1 $ 192.5 Securities pledged as collateral for letters of credit and other 140.9 169.9 Securities and cash on deposit supporting Lloyd’s business 344.3 412.8 Total restricted investments $ 715.3 $ 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) June 30, Level 1 (a) Level 2 (b) Level 3 (c) Fixed maturities U.S. Governments $ 342.6 $ 338.9 $ 3.7 $ — Foreign Governments 258.2 — 258.2 — Obligations of states and political subdivisions 171.3 — 171.3 — Corporate bonds 1,732.1 — 1,724.7 7.4 Commercial mortgage-backed securities 253.2 — 253.2 — Residential mortgage-backed securities 530.2 — 530.2 — Asset-backed securities 152.9 — 152.9 — Collateralized loan obligations 266.9 — 266.9 — Total fixed maturities 3,707.4 338.9 3,361.1 7.4 Equity securities 147.5 133.1 — 14.4 Other investments 91.7 — 91.7 — Short-term investments 612.1 574.6 37.5 — $ 4,558.7 $ 1,046.6 $ 3,490.3 $ 21.8 (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, Level 1 (a) Level 2 (b) Level 3 (c) Fixed maturities U.S. Governments $ 354.6 $ 349.1 $ 5.5 $ — Foreign Governments 248.7 — 248.7 — Obligations of states and political subdivisions 152.6 — 152.6 — Corporate bonds 1,780.4 — 1,773.0 7.4 Commercial mortgage-backed securities 217.0 — 217.0 — Residential mortgage-backed securities 488.9 — 488.9 — Asset-backed securities 165.5 — 165.5 — Collateralized loan obligations 225.8 — 225.8 — Total fixed maturities 3,633.5 349.1 3,277.0 7.4 Equity securities 124.4 117.8 — 6.6 Other investments 96.3 — 96.3 — Short-term investments 845.0 823.5 21.5 — $ 4,699.2 $ 1,290.4 $ 3,394.8 $ 14.0 (a) Quoted prices in active markets for identical assets (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 $ 6.6 $ 14.0 Transfers into Level 3 — — — Transfers out of Level 3 — — — Total gains or losses (realized/unrealized): Included in net income — 0.1 0.1 Included in other comprehensive income — — — Purchases, issuances, sales, and settlements: Purchases — 7.7 7.7 Issuances — — — Sales — — — Settlements — — — Ending balance, June 30, 2020 $ 7.4 $ 14.4 $ 21.8 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 June 30, 2020 $ — $ — $ — (in millions) Credit Financial Equity Total Beginning balance, January 1, 2019 $ 2.2 $ 8.2 $ 10.4 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 $ 6.6 $ 14.0 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)	6 Months Ended
	Jun. 30, 2020
Credit Loss [Abstract]
Premium Receivable, Allowance for Credit Loss	The following table represents the balances of premiums receivable, net of allowance for expected credit losses, at June 30, 2020 and January 1, 2020, and the changes in the allowance for expected credit losses for the six months ended June 30, 2020. (in millions) Premiums Receivable, Net of Allowance for Estimated Uncollectible Premiums Allowance for Estimated Uncollectible Premiums Balance, January 1, 2020 $ 688.2 $ 7.9 Cumulative effect of adoption of ASU 2016-13 — Current period change for estimated uncollectible premiums 0.6 Write-offs of uncollectible premiums receivable — Balance, June 30, 2020 $ 800.2 $ 8.5
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, at June 30, 2020 and January 1, 2020, and changes in the allowance for estimated uncollectible reinsurance for the six months ended June 30, 2020. (in millions) Reinsurance Recoverables, Net of Allowance for Estimated Uncollectible Reinsurance Allowance for Estimated Uncollectible Reinsurance Balance, January 1, 2020 $ 3,104.6 $ 1.1 Cumulative effect of adoption of ASU 2016-13 2.5 Current period change for estimated uncollectible reinsurance — Write-offs of uncollectible reinsurance recoverables — Balance, June 30, 2020 $ 2,942.8 $ 3.6

Reserves for Losses and Loss _2

Reserves for Losses and Loss Adjustment Expenses (Tables)	6 Months Ended
	Jun. 30, 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 Six Months Ended (in millions) 2020 2019 Net reserves beginning of the year $ 2,722.7 $ 2,562.9 Net AIL reserves acquired 27.9 — Add: Losses and LAE incurred during current calendar year, net of reinsurance: Current accident year 549.6 502.9 Prior accident years 4.5 19.8 Losses and LAE incurred during calendar year, net of reinsurance 554.1 522.7 Deduct: Losses and LAE payments made during current calendar year, net of reinsurance: Current accident year 125.3 89.8 Prior accident years 451.5 432.4 Losses and LAE payments made during current calendar year, net of reinsurance: 576.8 522.2 Change in participation interest (1) 33.0 (14.4) Foreign exchange adjustments (8.5) (13.0) Net reserves - end of period 2,752.4 2,536.0 Add: Reinsurance recoverables on unpaid losses and LAE, end of period 2,463.9 2,199.7 Gross reserves - end of period $ 5,216.3 $ 4,735.7 (1) Amount represents the change in reserves due to changing our participation in Syndicates 1200 and 1910.
Impact from (Favorable) Unfavorable Development of Prior Accident Years’ Loss and LAE Reserves on Each Reporting Segment	The impact from the unfavorable development of prior accident years’ loss and LAE reserves on each reporting segment is presented below: For the Six Months Ended (in millions) 2020 2019 U.S. Operations $ 2.7 $ (9.1) International Operations 1.1 27.2 Run-off Lines 0.7 1.7 Total unfavorable prior-year development $ 4.5 $ 19.8

Disclosures about Fair Value _2

Disclosures about Fair Value of Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 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: June 30, 2020 December 31, 2019 (in millions) Carrying Fair Carrying Fair Junior subordinated debentures: Trust preferred debentures $ 172.7 $ 173.8 $ 172.7 $ 174.0 Subordinated debentures 84.9 92.4 84.7 92.5 Total junior subordinated debentures 257.6 266.2 257.4 266.5 Senior unsecured fixed rate notes 140.1 146.7 140.0 144.2 Floating rate loan stock 56.0 56.3 56.3 56.8
Fair Value, Assets Measured on Recurring and Nonrecurring Basis	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) June 30, 2020 Level 1 (a) Level 2 (b) Level 3 (c) Junior subordinated debentures: Trust preferred debentures $ 173.8 $ — $ 173.8 $ — Subordinated debentures 92.4 — 92.4 — Total junior subordinated debentures 266.2 — 266.2 — Senior unsecured fixed rate notes 146.7 146.7 — — Floating rate loan stock 56.3 — 56.3 — 469.2 146.7 322.5 — (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 (Loss) Income (Tables)	6 Months Ended
	Jun. 30, 2020
Equity [Abstract]
Changes in Accumulated Other Comprehensive (Loss) Income	A summary of changes in accumulated other comprehensive (loss) income, net of taxes (where applicable) by component for the six months ended June 30, 2020, and 2019 is presented below: (in millions) Foreign Currency Translation Adjustments Unrealized Defined Benefit Pension Plans Total Balance, January 1, 2020 $ (22.6) $ 33.5 $ (8.1) $ 2.8 Other comprehensive loss before reclassifications (7.6) 24.2 — 16.6 Amounts reclassified from accumulated other comprehensive loss — (19.2) — (19.2) Net current-period other comprehensive loss (7.6) 5.0 — (2.6) Cumulative effect of adoption of ASU 2016-13 — 5.7 — 5.7 Balance, June 30, 2020 $ (30.2) $ 44.2 $ (8.1) $ 5.9 (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 income before reclassifications (0.1) 82.9 — 82.8 Amounts reclassified from accumulated other comprehensive income — 4.2 — 4.2 Net current-period other comprehensive income (0.1) 87.1 — 87.0 Balance, June 30, 2019 $ (22.5) $ 38.1 $ (6.7) $ 8.9
Amounts Reclassified from Accumulated Other Comprehensive (Loss) Income	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 (Loss) Income: For the Three Months Ended For the Six Months Ended (in millions) 2020 2019 2020 2019 Unrealized gains and losses on securities: Net realized investment (gains) loss $ (16.5) $ 1.8 $ (19.9) $ 4.9 Provision (benefit) for income taxes 2.6 (0.2) 0.7 (0.7) Net of taxes $ (13.9) $ 1.6 $ (19.2) $ 4.2

Net (Loss) Income Per Common _2

Net (Loss) Income Per Common Share (Tables)	6 Months Ended
	Jun. 30, 2020
Earnings Per Share [Abstract]
Net Income (Loss) 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 Three Months Ended For the Six Months Ended (in millions, except number of shares and per share amounts) 2020 2019 2020 2019 Net (loss) income $ (6.4) $ 28.8 $ (25.2) $ 120.0 Weighted average common shares outstanding - basic 34,634,353 34,195,250 34,551,935 34,090,372 Effect of dilutive securities: Equity compensation awards — 584,741 — 669,176 Weighted average common shares outstanding - diluted 34,634,353 34,779,991 34,551,935 34,759,548 Net (loss) income per common share: Basic $ (0.18) $ 0.84 $ (0.73) $ 3.52 Diluted $ (0.18) $ 0.83 $ (0.73) $ 3.45

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	6 Months Ended
	Jun. 30, 2020
Supplemental Cash Flow Elements [Abstract]
Schedule of Interest Paid and Income Taxes Paid (Recovered)	Interest paid and income taxes paid (recovered) were as follows: For the Six Months Ended (in millions) 2020 2019 Senior unsecured fixed rate notes $ 4.7 $ 4.7 Junior subordinated debentures 6.7 8.3 Other indebtedness 3.4 3.8 Total interest paid $ 14.8 $ 16.8 Income taxes paid 1.6 1.3 Income taxes recovered (0.7) — Income taxes paid, net $ 0.9 $ 1.3

Share-based Compensation (Table

Share-based Compensation (Tables)	6 Months Ended
	Jun. 30, 2020
Share-based Payment Arrangement [Abstract]
Summary of Restricted Share Activity	A summary of restricted share activity as of June 30, 2020 and changes during the six months then ended is as follows: Shares Weighted-Average Outstanding at January 1, 2020 471,271 $ 60.09 Granted 399,578 $ 32.72 Vested and issued (161,081) $ 51.45 Expired or forfeited (69,499) $ 58.42 Outstanding at June 30, 2020 640,269 $ 44.00
Stock Settled Share Appreciation Rights	A summary of stock-settled SARs activity as of June 30, 2020 and changes during the six months then ended is as follows: Shares Weighted-Average Outstanding at January 1, 2020 625,368 $ 33.60 Exercised (415,274) $ 32.25 Expired or forfeited — $ — Outstanding at June 30, 2020 210,094 $ 36.26

Underwriting, Acquisition and_2

Underwriting, Acquisition and Insurance Expenses & Other Corporate Expenses (Tables)	6 Months Ended
	Jun. 30, 2020
Underwriting, Acquisition and Insurance Expenses & Other Corporate Expenses [Abstract]
Underwriting, Acquisition and Insurance Expenses	Underwriting, acquisition and insurance expenses were as follows: For the Three Months Ended For the Six Months Ended (in millions) 2020 2019 2020 2019 Commissions $ 57.2 $ 56.7 $ 122.5 $ 120.0 General expenses 93.3 91.5 192.2 180.1 Premium taxes, boards and bureaus 6.5 7.9 14.5 16.2 157.0 156.1 329.2 316.3 Net deferral of policy acquisition costs 4.4 5.3 0.2 5.3 Total underwriting, acquisition and insurance expenses $ 161.4 $ 161.4 $ 329.4 $ 321.6

Income Taxes (Tables)

Income Taxes (Tables)	6 Months Ended
	Jun. 30, 2020
Income Tax Disclosure [Abstract]
Schedule of Pre-Tax Income (Loss) and Effective Income Tax Rates	For the three and six months ended June 30, 2020 and 2019, pre-tax income (loss) attributable to our operations and the corresponding operations’ effective tax rates were as follows: For the Three Months Ended June 30, 2020 2019 (in millions) Pre-Tax Effective Pre-Tax Effective Bermuda $ (31.1) — % $ 15.0 — % United States 67.9 23.2 % 22.3 14.8 % United Kingdom (29.2) 12.8 % (8.9) 26.7 % Belgium 0.1 20.0 % (0.3) 29.5 % Brazil 0.6 — % 2.0 — % United Arab Emirates 0.5 — % — (1) — % Ireland — (1) — % — (1) — % Italy (1.8) — % 0.2 — % Malta (1.3) — % (0.7) (0.1) % Switzerland — (1) — % — (1) — % Pre-tax Income $ 5.7 209.4 % $ 29.6 2.9 % (1) Pre-tax income (loss) for the respective year was less than $0.1 million. For the Six Months Ended June 30, 2020 2019 Pre-Tax Effective Pre-Tax Effective Bermuda $ (52.9) — % $ 47.0 — % United States 57.3 17.3 % 91.8 14.5 % United Kingdom (27.5) 2.4 % (12.4) 28.1 % Belgium 0.1 31.0 % (0.3) 29.7 % Brazil 2.8 — % 3.8 — % United Arab Emirates 1.3 — % 0.2 — % Ireland — (1) — % (0.1) — % Italy 1.7 — % (0.5) — % Malta 1.3 — % 0.2 0.5 % Switzerland — (1) — % — (1) — % Pre-tax Income $ (15.9) (58.7) % $ 129.7 7.5 % (1) Pre-tax income (loss) for the respective year was less than $0.1 million.
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 at the weighted average tax rate is as follows: For the Three Months Ended For the Six Months Ended (in millions) 2020 2019 2020 2019 Income tax provision (benefit) at expected rate $ 8.6 $ 3.6 $ 9.4 $ 18.5 Tax effect of: Nontaxable investment income (0.2) (0.3) (0.3) (0.7) Foreign exchange adjustments 1.5 0.1 (0.6) 0.6 Goodwill 1.0 — 1.0 — Withholding taxes — (1) 0.1 0.1 0.2 Change in valuation allowance — (1) — (1) — (1) (0.6) Other 1.2 (2.7) (0.3) (8.3) Income tax provision $ 12.1 $ 0.8 $ 9.3 $ 9.7 (1) Tax effect of the adjustment for the respective year was less than $0.1 million.

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Jun. 30, 2020
Segment Reporting [Abstract]
Revenue and Income (Loss) Before Income Taxes for Each Segment	Revenue and (loss) income before income taxes for each segment were as follows: For the Three Months Ended For the Six Months Ended (in millions) 2020 2019 2020 2019 Revenue: Earned premiums U.S. Operations $ 301.6 $ 284.0 $ 604.1 $ 557.8 International Operations 131.8 147.6 264.1 294.3 Run-off Lines — 0.1 0.2 0.1 Total earned premiums 433.4 431.7 868.4 852.2 Net investment income U.S. Operations 0.8 29.6 26.0 52.7 International Operations 0.5 11.5 9.1 20.6 Run-off Lines 0.1 1.3 1.3 2.7 Corporate and Other 0.1 0.4 0.6 0.7 Total net investment income 1.5 42.8 37.0 76.7 Fee and other income 2.0 2.1 4.1 4.4 Net realized investment gains (losses) 20.1 12.0 (16.0) 64.5 Total revenue $ 457.0 $ 488.6 $ 893.5 $ 997.8 For the Three Months Ended For the Six Months Ended (in millions) 2020 2019 2020 2019 Income (loss) before income taxes U.S. Operations $ 31.2 $ 53.2 $ 68.1 $ 96.1 International Operations (27.5) (21.0) (39.8) (4.8) Run-off Lines (1.3) (1.1) (0.8) (0.5) Total segment income before taxes 2.4 31.1 27.5 90.8 Corporate and Other (7.9) (11.3) (18.2) (22.2) Net realized investment and other gains (losses) 20.1 12.0 (16.0) 64.5 Foreign currency exchange (losses) gains (6.4) 5.3 (3.4) 4.6 Other corporate expenses (2.5) (7.5) (5.8) (8.0) Total income (loss) before income taxes $ 5.7 $ 29.6 $ (15.9) $ 129.7
Schedule of Earned Premiums by Geographic Location	The table below presents earned premiums by geographic location for the three and six months ended June 30, 2020 and 2019. 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 Three Months Ended For the Six Months Ended (in millions) 2020 2019 2020 2019 United States $ 301.4 $ 283.2 $ 601.1 $ 555.8 United Kingdom 75.5 96.6 162.2 193.7 Bermuda 25.3 19.2 46.5 35.8 Malta 18.5 20.2 30.3 41.0 All other jurisdictions 12.7 12.5 28.3 25.9 Total earned premiums $ 433.4 $ 431.7 $ 868.4 $ 852.2
Identifiable Assets	The following table represents identifiable assets: (in millions) June 30, 2020 December 31, 2019 U.S. Operations $ 5,744.9 $ 5,009.0 International Operations 4,132.2 5,002.4 Run-off Lines 331.1 356.9 Corporate and Other 188.5 146.2 Total $ 10,396.7 $ 10,514.5

Senior Unsecured Fixed Rate N_2

Senior Unsecured Fixed Rate Notes (Tables)	6 Months Ended
	Jun. 30, 2020
Debt Disclosure [Abstract]
Schedule of Unamortized Debt Issuance Costs Deducted From Carrying Value of Debt Liability	At June 30, 2020 and December 31, 2019, the Notes consisted of the following: (in millions) June 30, 2020 December 31, 2019 Senior unsecured fixed rate notes Principal $ 143.8 $ 143.8 Less: unamortized debt issuance costs (3.7) (3.8) Senior unsecured fixed rate notes, less unamortized debt issuance costs $ 140.1 $ 140.0
Condensed Consolidating Balance Sheet	CONDENSED CONSOLIDATING BALANCE SHEET JUNE 30, 2020 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Assets Investments $ 0.6 $ 3,402.0 $ 1,448.9 $ — $ 4,851.5 Cash 1.9 41.6 144.2 — 187.7 Accrued investment income — 17.4 6.0 — 23.4 Premiums receivable — 298.4 501.8 — 800.2 Reinsurance recoverables — 1,740.3 1,202.5 — 2,942.8 Goodwill and other intangible assets, net 39.9 118.5 89.2 — 247.6 Deferred tax assets, net — 11.7 7.2 — 18.9 Deferred acquisition costs, net — 86.0 67.5 — 153.5 Ceded unearned premiums — 337.4 319.1 — 656.5 Operating lease right-of-use assets 6.8 55.3 25.1 — 87.2 Other assets 9.6 146.2 258.9 — 414.7 Assets held for sale — 12.4 0.3 — 12.7 Intercompany note receivable — 72.9 (72.9) — — Investments in subsidiaries 1,904.2 — — (1,904.2) — Total assets $ 1,963.0 $ 6,340.1 $ 3,997.8 $ (1,904.2) $ 10,396.7 Liabilities and Shareholders' Equity Reserves for losses and loss adjustment expenses $ — $ 3,181.7 $ 2,034.6 $ — $ 5,216.3 Unearned premiums — 900.7 580.5 — 1,481.2 Funds held and ceded reinsurance payable, net — 566.7 542.7 — 1,109.4 Debt 153.4 284.4 140.9 — 578.7 Current income taxes payable, net — 33.2 (6.1) — 27.1 Accrued underwriting expenses and other liabilities 5.4 83.4 66.0 — 154.8 Operating lease liabilities 6.9 64.1 28.2 — 99.2 Due to (from) affiliates 67.3 (11.7) 11.7 (67.3) — Total liabilities 233.0 5,102.5 3,398.5 (67.3) 8,666.7 Total shareholders' equity 1,730.0 1,237.6 599.3 (1,836.9) 1,730.0 Total liabilities and shareholders' equity $ 1,963.0 $ 6,340.1 $ 3,997.8 $ (1,904.2) $ 10,396.7 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. 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 US, Inc. Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Assets Investments $ 0.6 $ 3,405.6 $ 1,693.2 $ — $ 5,099.4 Cash 1.9 31.6 104.3 — 137.8 Accrued investment income — 18.2 7.5 — 25.7 Premiums receivable — 231.3 456.9 — 688.2 Reinsurance recoverables — 1,689.4 1,415.2 — 3,104.6 Goodwill and other intangible assets, net 40.6 123.4 89.2 — 253.2 Deferred tax assets, net — 0.4 5.7 — 6.1 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 7.8 165.8 213.5 — 387.1 Assets held for sale — 15.4 — — 15.4 Intercompany note receivable — 56.7 (56.7) — — Investments in subsidiaries 1,916.7 — — (1,916.7) — Total assets $ 1,974.7 $ 6,192.2 $ 4,264.3 $ (1,916.7) $ 10,514.5 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 — 645.9 607.8 — 1,253.7 Debt 153.4 284.3 141.0 — 578.7 Current income taxes payable, net — 8.2 (7.4) — 0.8 Accrued underwriting expenses and other liabilities 13.6 87.6 124.8 — 226.0 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 5,018.8 3,540.3 (19.3) 8,733.4 Total shareholders' equity 1,781.1 1,173.4 724.0 (1,897.4) 1,781.1 Total liabilities and shareholders' equity $ 1,974.7 $ 6,192.2 $ 4,264.3 $ (1,916.7) $ 10,514.5 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations.
Condensed Consolidating Statement of Income	CONDENSED CONSOLIDATING STATEMENT OF (LOSS) INCOME FOR THE THREE MONTHS ENDED JUNE 30, 2020 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Premiums and other revenue: Earned premiums $ — $ 300.7 $ 132.7 $ — $ 433.4 Net investment income (expenses) — 5.8 (4.3) — 1.5 Fee and other income — 0.6 1.4 — 2.0 Net realized investment gains (losses) 1.4 33.1 (14.4) — 20.1 Total revenue 1.4 340.2 115.4 — 457.0 Expenses: Losses and loss adjustment expenses — 167.7 105.5 — 273.2 Underwriting, acquisition and insurance expenses 3.2 101.7 56.5 — 161.4 Other corporate expenses 2.6 (0.1) — — 2.5 Interest expense 1.1 4.0 1.7 — 6.8 Fee and other expense — 0.6 0.4 — 1.0 Foreign currency exchange losses — — 6.4 — 6.4 Total expenses 6.9 273.9 170.5 — 451.3 (Loss) income before income taxes (5.5) 66.3 (55.1) — 5.7 Provision (benefit) for income taxes — 15.8 (3.7) — 12.1 Net (loss) income before equity in earnings of subsidiaries (5.5) 50.5 (51.4) — (6.4) Equity in undistributed earnings of subsidiaries (0.9) — — 0.9 — Net (loss) income $ (6.4) $ 50.5 $ (51.4) $ 0.9 $ (6.4) (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF INCOME FOR THE THREE MONTHS ENDED JUNE 30, 2019 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Premiums and other revenue: Earned premiums $ — $ 260.1 $ 171.6 $ — $ 431.7 Net investment (expense) income (0.6) 28.1 15.3 — 42.8 Fee and other income — 0.7 1.4 — 2.1 Net realized investment (losses) gains (0.1) 15.0 (2.9) — 12.0 Total revenue (0.7) 303.9 185.4 — 488.6 Expenses: Losses and loss adjustment expenses — 171.3 113.5 — 284.8 Underwriting, acquisition and insurance expenses 0.7 104.2 56.5 — 161.4 Other corporate expenses 7.5 — — — 7.5 Interest expense 1.7 5.2 2.4 — 9.3 Fee and other expense — 0.9 0.4 — 1.3 Foreign currency exchange gains — (0.1) (5.2) — (5.3) Total expenses 9.9 281.5 167.6 — 459.0 (Loss) income before income taxes (10.6) 22.4 17.8 — 29.6 Provision (benefit) for income taxes — 3.3 (2.5) — 0.8 Net (loss) income before equity in earnings of subsidiaries (10.6) 19.1 20.3 — 28.8 Equity in undistributed earnings of subsidiaries 39.4 — — (39.4) — Net income $ 28.8 $ 19.1 $ 20.3 $ (39.4) $ 28.8 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. 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 THE SIX MONTHS ENDED JUNE 30, 2020 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Net cash flows from operating activities $ 20.3 $ (21.0) $ (102.4) $ — $ (103.1) Cash flows from investing activities: Proceeds from sales of investments — 454.1 394.2 — 848.3 Maturities and mandatory calls of fixed maturity investments — 184.4 70.6 — 255.0 Purchases of investments — (935.0) (242.4) — (1,177.4) Change in short-term investments and foreign regulatory deposits (0.1) 270.9 (53.3) — 217.5 Settlements of foreign currency exchange forward contracts 0.1 — 6.9 — 7.0 Sale of Trident's assets — 38.0 — — 38.0 Issuance of intercompany note, net — (15.0) 15.0 — — Purchases of fixed assets and other, net — 33.6 (46.2) — (12.6) Cash provided by investing activities — 31.0 144.8 — 175.8 Cash flows from financing activities: Activity under stock incentive plans 1.0 — — — 1.0 Payment of cash dividend to common shareholders (21.3) — — — (21.3) Cash used in financing activities (20.3) — — — (20.3) Effect of exchange rate changes on cash — — (2.5) — (2.5) Change in cash — 10.0 39.9 — 49.9 Cash, beginning of year 1.9 31.6 104.3 — 137.8 Cash, end of period $ 1.9 $ 41.6 $ 144.2 $ — $ 187.7 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS FOR THE SIX MONTHS ENDED JUNE 30, 2019 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Net cash flows from operating activities $ 19.3 $ (5.5) $ (18.7) $ — $ (4.9) Cash flows from investing activities: Proceeds from sales of investments — 507.1 307.8 — 814.9 Maturities and mandatory calls of fixed maturity investments — 131.8 37.0 — 168.8 Purchases of investments — (686.4) (272.7) — (959.1) Change in short-term investments and foreign regulatory deposits 2.8 74.7 (3.5) — 74.0 Settlements of foreign currency exchange forward contracts (0.1) 0.9 9.1 — 9.9 Purchases of fixed assets and other, net — (6.9) (31.3) — (38.2) Cash provided by investing activities 2.7 21.2 46.4 — 70.3 Cash flows from financing activities: Payment on the intercompany note — (19.1) 19.1 — — Activity under stock incentive plans 0.9 — — — 0.9 Payment of cash dividend to common shareholders (22.7) — — — (22.7) Cash (used in) provided by financing activities (21.8) (19.1) 19.1 — (21.8) Effect of exchange rate changes on cash — — (0.5) — (0.5) Change in cash 0.2 (3.4) 46.3 — 43.1 Cash, beginning of year 1.7 31.7 105.8 — 139.2 Cash, end of period $ 1.9 $ 28.3 $ 152.1 $ — $ 182.3 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations.

Basis of Presentation - Additio

Basis of Presentation - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Other corporate expenses	$ 2.5	$ 7.5	$ 5.8	$ 8

Basis of Presentation - Acquisi

Basis of Presentation - Acquisition (Detail) - AIL $ in Millions	Jun. 12, 2020USD ($)
Business Acquisition [Line Items]
Percentage of capital stock acquired	100.00%
Consideration transferred	$ 55.6

Basis of Presentation - Sale of

Basis of Presentation - Sale of Business Unit (Details) - Disposal Group, Disposed of by Sale, Not Discontinued Operations - Trident - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Apr. 30, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash consideration received from sale			$ 38
Gain on disposal, pre-tax	$ 32.3	$ 32.3

Recently Adopted Accounting P_2

Recently Adopted Accounting Pronouncements (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019		Mar. 31, 2020	Jan. 01, 2020	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201613Member
Decrease in stockholder's equity	$ (1,730)	$ (1,781.1)	[1]	$ (1,636.8)		$ (1,929)	$ (1,880.6)	$ (1,746.7)
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in stockholder's equity		2.2			$ 2.2
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in stockholder's equity	(756.7)	(811.1)		(773.7)		(959.9)	(943)	(862.6)
Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in stockholder's equity		7.9			7.9
Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in stockholder's equity	$ (5.9)	(2.8)		$ 101.9		$ (8.9)	$ 27.6	$ 78.1
Accumulated Other Comprehensive Income (Loss) | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in stockholder's equity		$ (5.7)			$ 5.7
[1]	Derived from audited consolidated financial statements.

Investments - Additional Inform

Investments - Additional Information (Detail) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020USD ($)security	Jun. 30, 2019USD ($)	Jun. 30, 2020USD ($)security	Jun. 30, 2019USD ($)	Dec. 31, 2019USD ($)
Investments, Debt and Equity Securities [Abstract]
Fair value of investments, assets managed on behalf of the trade capital providers | $	$ 119.1		$ 119.1		$ 158.6
Number of securities in an unrealized loss position, total | security	4,833		4,833
Number of securities in an unrealized loss position for less than one year | security	1,509		1,509
Number of securities in an unrealized loss position for a period of one year or greater | security	223		223
Provision for expected credit losses | $	$ 7.8		$ 32.5
Impairment losses | $	$ 0	$ 2.5	$ 0	$ 6.8

Investments - Schedule of Amort

Investments - Schedule of Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Fair Value of Investments (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Fixed maturities
Amortized cost	$ 3,688.6	$ 3,605
Allowance for Credit Losses	40.2	0
Fair Value	3,707.4	3,633.5	[1]
Fixed maturities
Fixed maturities
Amortized cost	3,688.6	3,605
Gross Unrealized Gains	125.3	68.5
Gross Unrealized Losses	66.3	40
Allowance for Credit Losses	40.2
Fair Value	3,707.4	3,633.5
Fixed maturities | U.S. Governments
Fixed maturities
Amortized cost	324	353.5
Gross Unrealized Gains	18.6	2.3
Gross Unrealized Losses	0	1.2
Allowance for Credit Losses	0
Fair Value	342.6	354.6
Fixed maturities | Foreign Governments
Fixed maturities
Amortized cost	256.1	244.8
Gross Unrealized Gains	6.1	4.6
Gross Unrealized Losses	3.7	0.7
Allowance for Credit Losses	0.3
Fair Value	258.2	248.7
Fixed maturities | Obligations of States and Political Subdivisions
Fixed maturities
Amortized cost	165.3	145.8
Gross Unrealized Gains	6.9	6.9
Gross Unrealized Losses	0.8	0.1
Allowance for Credit Losses	0.1
Fair Value	171.3	152.6
Fixed maturities | Corporate Bonds
Fixed maturities
Amortized cost	1,762.6	1,777.4
Gross Unrealized Gains	58.4	37.7
Gross Unrealized Losses	49.2	34.7
Allowance for Credit Losses	39.7
Fair Value	1,732.1	1,780.4
Fixed maturities | Commercial Mortgage-backed Securities
Fixed maturities
Amortized cost	242.5	213.5
Gross Unrealized Gains	10.9	4.6
Gross Unrealized Losses	0.2	1.1
Allowance for Credit Losses	0
Fair Value	253.2	217
Fixed maturities | Residential Mortgage-backed Securities
Fixed maturities
Amortized cost	512.3	479.1
Gross Unrealized Gains	20.2	10.4
Gross Unrealized Losses	2.3	0.6
Allowance for Credit Losses	0
Fair Value	530.2	488.9
Fixed maturities | Asset-backed Securities
Fixed maturities
Amortized cost	152.6	164.2
Gross Unrealized Gains	2.7	1.5
Gross Unrealized Losses	2.3	0.2
Allowance for Credit Losses	0.1
Fair Value	152.9	165.5
Fixed maturities | Collateralized Debt Obligations
Fixed maturities
Amortized cost	273.2	226.7
Gross Unrealized Gains	1.5	0.5
Gross Unrealized Losses	7.8	1.4
Allowance for Credit Losses	0
Fair Value	$ 266.9	$ 225.8
[1]	Derived from audited consolidated financial statements.

Investments - Schedule of Amo_2

Investments - Schedule of Amortized Cost and Fair Values of Fixed Maturity Investments, by Contractual Maturity (Detail) $ in Millions	Jun. 30, 2020USD ($)
Amortized Cost
Due in one year or less	$ 316.3
Due after one year through five years	1,540.7
Due after five years through ten years	579.8
Thereafter	71.2
Structured securities	1,180.6
Total	3,688.6
Fair Value
Due in one year or less	316.8
Due after one year through five years	1,523.5
Due after five years through ten years	592.4
Thereafter	71.5
Structured securities	1,203.2
Total	$ 3,707.4

Investments - Schedule of Carry

Investments - Schedule of Carrying Value and Unfunded Investment Commitments of Other Invested Assets Portfolio (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Carrying Value	$ 4,851.5	$ 5,099.4	[1]
Hedge funds
Schedule of Investments [Line Items]
Carrying Value	98	109.5
Unfunded Commitments	0	0
Private equity
Schedule of Investments [Line Items]
Carrying Value	190.5	268.1
Unfunded Commitments	96.1	110
Overseas Deposits
Schedule of Investments [Line Items]
Carrying Value	91.7	114.6
Unfunded Commitments	0	0
Other
Schedule of Investments [Line Items]
Carrying Value	4.3	4.3
Unfunded Commitments	0	0
Other Investments
Schedule of Investments [Line Items]
Carrying Value	384.5	496.5
Unfunded Commitments	$ 96.1	$ 110
[1]	Derived from audited consolidated financial statements.

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	Jun. 30, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	$ 813.6	$ 701.2
Unrealized Losses, Less Than One Year	40.7	23
Fair Value, One Year or Greater	99.9	253.5
Unrealized Losses, One Year or Greater	25.6	17
Fair Value, Total	913.5	954.7
Unrealized Losses, Total	66.3	40
U.S. Governments
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	1.3	114.6
Unrealized Losses, Less Than One Year	0	1.1
Fair Value, One Year or Greater	0	17
Unrealized Losses, One Year or Greater	0	0.1
Fair Value, Total	1.3	131.6
Unrealized Losses, Total	0	1.2
Foreign Governments
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	124.4	117.6
Unrealized Losses, Less Than One Year	3.7	0.7
Fair Value, One Year or Greater	0	5.1
Unrealized Losses, One Year or Greater	0	0
Fair Value, Total	124.4	122.7
Unrealized Losses, Total	3.7	0.7
Obligations of States and Political Subdivisions
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	18.1	0.7
Unrealized Losses, Less Than One Year	0.8	0
Fair Value, One Year or Greater	0	2.1
Unrealized Losses, One Year or Greater	0	0.1
Fair Value, Total	18.1	2.8
Unrealized Losses, Total	0.8	0.1
Corporate Bonds
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	356.2	249.4
Unrealized Losses, Less Than One Year	26.2	18.9
Fair Value, One Year or Greater	30.8	63.6
Unrealized Losses, One Year or Greater	23	15.8
Fair Value, Total	387	313
Unrealized Losses, Total	49.2	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	0.2	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	0.2	1.1
Residential Mortgage-backed Securities
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	71.1	66.9
Unrealized Losses, Less Than One Year	1.5	0.3
Fair Value, One Year or Greater	8.3	25.2
Unrealized Losses, One Year or Greater	0.8	0.3
Fair Value, Total	79.4	92.1
Unrealized Losses, Total	2.3	0.6
Asset-backed Securities
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	30.9	22.5
Unrealized Losses, Less Than One Year	2.2	0.1
Fair Value, One Year or Greater	3.9	18.9
Unrealized Losses, One Year or Greater	0.1	0.1
Fair Value, Total	34.8	41.4
Unrealized Losses, Total	2.3	0.2
Collateralized Debt Obligations
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	189.8	54.7
Unrealized Losses, Less Than One Year	6.1	0.8
Fair Value, One Year or Greater	56.9	116.7
Unrealized Losses, One Year or Greater	1.7	0.6
Fair Value, Total	246.7	171.4
Unrealized Losses, Total	$ 7.8	$ 1.4

Investments - Allowance for Cre

Investments - Allowance for Credit Losses (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance, January 1, 2020		$ 0
Provision for expected credit losses	$ 7.8	32.5
Increases due to sales/defaults of credit-impaired securities		0.8
Ending balance, June 30, 2020	$ 40.2	40.2
Cumulative Effect, Period of Adoption, Adjustment
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance, January 1, 2020		$ 6.9

Investments - Schedule of Compa

Investments - Schedule of Company's Gross Realized Investment Gains (Losses) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other	$ 46.5	$ 11.2	$ 115.5	$ 23.7
Realized losses on fixed maturities and other	(32.2)	(12.4)	(96.4)	(27.3)
Credit losses on fixed maturity securities	(7.8)	0	(32.5)	0
Net realized (losses) gains on equity securities	(11)	0.6	(12.6)	1.3
Change in unrealized (losses) gains on equity securities held at the end of the period	16.8	12.6	(22.5)	66.8
Net realized gains (losses) on equity securities	5.8	13.2	(35.1)	68.1
Net realized investment and other gains (losses) before income taxes	20.1	12	(16)	64.5
Income tax provision (benefit)	6.7	2.6	(1.3)	12.2
Net realized investment gains (losses) net of income taxes	13.4	9.4	(14.7)	52.3
Income tax provision	24.4	6.9	5.2	16.5
Fixed maturities
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other	2.5	5.7	23.3	9.4
Realized losses on fixed maturities and other	(10.5)	(4.7)	(18.2)	(7.2)
Other investments
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other	11.5	5.5	59.7	14.3
Realized losses on fixed maturities and other	(13.9)	(5.2)	(45.7)	(13.3)
Other assets
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other	32.5	0	32.5	0
Credit losses on fixed maturities
Schedule of Investments [Line Items]
Credit losses on fixed maturity securities	$ (7.8)	$ (2.5)	$ (32.5)	$ (6.8)

Investments - Schedule of Chang

Investments - Schedule of Changes in Unrealized Appreciation (Depreciation) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Schedule of Investments [Line Items]
Net unrealized investment gains before income taxes	$ 136.4	$ 43.7	$ 10.2	$ 103.6
Income tax provision	24.4	6.9	5.2	16.5
Net unrealized investment gains, net of income taxes	112	36.8	5	87.1
Fixed maturities
Schedule of Investments [Line Items]
Net unrealized investment gains before income taxes	136.2	39.2	24.4	99.1
Other investments
Schedule of Investments [Line Items]
Net unrealized investment gains before income taxes	0	0	(14.2)	0
Other and short-term investments
Schedule of Investments [Line Items]
Net unrealized investment gains before income taxes	$ 0.2	$ 4.5	$ 0	$ 4.5

Investments - Schedule of Fair

Investments - Schedule of Fair Value of Foreign Currency Exchange Forward Contracts (Detail) - Foreign Currency Exchange Forward Contracts - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Foreign currency exchange, fair value	$ (4.4)	$ 1.1
Operational currency exposure
Schedule of Investments [Line Items]
Foreign currency exchange, fair value	(0.7)	(0.8)
Asset manager investment exposure
Schedule of Investments [Line Items]
Foreign currency exchange, fair value	(0.1)	(0.3)
Total return strategy
Schedule of Investments [Line Items]
Foreign currency exchange, fair value	$ (3.6)	$ 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	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Schedule of Investments [Line Items]
Gross realized investment gains	$ 8.9	$ 6.8	$ 40.1	$ 14.5
Gross realized investment losses	(12.2)	(6.7)	(42.3)	(13.7)
Net realized investment (losses) gains on foreign currency exchange forward contracts	(3.3)	0.1	(2.2)	0.8
Operational currency exposure
Schedule of Investments [Line Items]
Gross realized investment gains	0.5	0.6	5.9	0.8
Gross realized investment losses	(3)	(2.5)	(4.7)	(4.6)
Asset manager investment exposure
Schedule of Investments [Line Items]
Gross realized investment gains	0.2	0.3	1	1.4
Gross realized investment losses	(0.6)	(0.3)	(1)	(0.5)
Total return strategy
Schedule of Investments [Line Items]
Gross realized investment gains	8.2	5.9	33.2	12.3
Gross realized investment losses	$ (8.6)	$ (3.9)	$ (36.6)	$ (8.6)

Investments - Components of Res

Investments - Components of Restricted Assets (Detail) - USD ($) $ in Millions	Jun. 30, 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	$ 140.9	$ 169.9
Securities and cash on deposit supporting Lloyd’s business	344.3	412.8
Total restricted investments	715.3	775.2
Securities Deposits for Regulatory and Other Purposes
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Securities on deposit for regulatory and other purposes	$ 230.1	$ 192.5

Investments - Financial Assets

Investments - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	$ 4,851.5	$ 5,099.4	[1]
Fair Value, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	4,558.7	4,699.2
Fair Value, Recurring | Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	3,707.4	3,633.5
Fair Value, Recurring | Fixed maturities | Collateralized Loan Obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	266.9	225.8
Fair Value, Recurring | Fixed maturities | U.S. Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	342.6	354.6
Fair Value, Recurring | Fixed maturities | Foreign Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	258.2	248.7
Fair Value, Recurring | Fixed maturities | Obligations of States and Political Subdivisions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	171.3	152.6
Fair Value, Recurring | Fixed maturities | Corporate Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	1,732.1	1,780.4
Fair Value, Recurring | Fixed maturities | Commercial Mortgage-backed Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	253.2	217
Fair Value, Recurring | Fixed maturities | Residential Mortgage-backed Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	530.2	488.9
Fair Value, Recurring | Fixed maturities | Asset-backed Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	152.9	165.5
Fair Value, Recurring | Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	147.5	124.4
Fair Value, Recurring | Other investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	91.7	96.3
Fair Value, Recurring | Short-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	612.1	845
Fair Value, Recurring | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	1,046.6	1,290.4
Fair Value, Recurring | Level 1 | Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	338.9	349.1
Fair Value, Recurring | Level 1 | Fixed maturities | Collateralized Loan Obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring | Level 1 | Fixed maturities | U.S. Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	338.9	349.1
Fair Value, Recurring | Level 1 | Fixed maturities | Foreign Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring | Level 1 | Fixed maturities | Obligations of States and Political Subdivisions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring | Level 1 | Fixed maturities | Corporate Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring | Level 1 | Fixed maturities | Commercial Mortgage-backed Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring | Level 1 | Fixed maturities | Residential Mortgage-backed Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring | Level 1 | Fixed maturities | Asset-backed Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring | Level 1 | Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	133.1	117.8
Fair Value, Recurring | Level 1 | Other investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring | Level 1 | Short-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	574.6	823.5
Fair Value, Recurring | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	3,490.3	3,394.8
Fair Value, Recurring | Level 2 | Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	3,361.1	3,277
Fair Value, Recurring | Level 2 | Fixed maturities | Collateralized Loan Obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	266.9	225.8
Fair Value, Recurring | Level 2 | Fixed maturities | U.S. Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	3.7	5.5
Fair Value, Recurring | Level 2 | Fixed maturities | Foreign Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	258.2	248.7
Fair Value, Recurring | Level 2 | Fixed maturities | Obligations of States and Political Subdivisions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	171.3	152.6
Fair Value, Recurring | Level 2 | Fixed maturities | Corporate Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	1,724.7	1,773
Fair Value, Recurring | Level 2 | Fixed maturities | Commercial Mortgage-backed Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	253.2	217
Fair Value, Recurring | Level 2 | Fixed maturities | Residential Mortgage-backed Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	530.2	488.9
Fair Value, Recurring | Level 2 | Fixed maturities | Asset-backed Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	152.9	165.5
Fair Value, Recurring | Level 2 | Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring | Level 2 | Other investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	91.7	96.3
Fair Value, Recurring | Level 2 | Short-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	37.5	21.5
Fair Value, Recurring | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	21.8	14
Fair Value, Recurring | Level 3 | Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	7.4	7.4
Fair Value, Recurring | Level 3 | Fixed maturities | Collateralized Loan Obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring | Level 3 | Fixed maturities | U.S. Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring | Level 3 | Fixed maturities | Foreign Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring | Level 3 | Fixed maturities | Obligations of States and Political Subdivisions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring | Level 3 | Fixed maturities | Corporate Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	7.4	7.4
Fair Value, Recurring | Level 3 | Fixed maturities | Commercial Mortgage-backed Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring | Level 3 | Fixed maturities | Residential Mortgage-backed Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring | Level 3 | Fixed maturities | Asset-backed Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring | Level 3 | Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	14.4	6.6
Fair Value, Recurring | Level 3 | Other investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring | Level 3 | Short-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	$ 0	$ 0
[1]	Derived from audited consolidated financial statements.

Investments - Schedule of Recon

Investments - Schedule of Reconciliation of Beginning and Ending Balances for Investments Categorized as Level 3 (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 14	$ 10.4
Transfers into Level 3	0	3.5
Transfers out of Level 3	0	0
Included in net income	0.1	(2)
Included in other comprehensive income	0	0.6
Purchases	7.7	1.9
Issuances	0	0
Sales	0	(0.4)
Settlements	0	0
Ending balance	21.8	14
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 June 30, 2020	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
Included in net income	0	(0.4)
Included in other comprehensive income	0	0.6
Purchases	0	1.9
Issuances	0	0
Sales	0	(0.4)
Settlements	0	0
Ending balance	7.4	7.4
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 June 30, 2020	0	0
Equity Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	6.6	8.2
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Included in net income	0.1	(1.6)
Included in other comprehensive income	0	0
Purchases	7.7	0
Issuances	0	0
Sales	0	0
Settlements	0	0
Ending balance	14.4	6.6
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 June 30, 2020	$ 0	$ 0

- Premiums Receivable (Details)

- Premiums Receivable (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Premiums receivable	$ 800.2	$ 688.2	[1]
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Balance, January 1, 2020	$ 7.9
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201613Member
Current period change for estimated uncollectible premiums	$ 0.6
Write-offs of uncollectible premiums receivable	0
Balance, June 30, 2020	8.5	$ 7.9
Cumulative Effect, Period of Adoption, Adjustment
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Balance, January 1, 2020	$ 0
Balance, June 30, 2020		$ 0
[1]	Derived from audited consolidated financial statements.

- Reinsurance Recoverables (Det

- Reinsurance Recoverables (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Reinsurance recoverables, net	$ 2,942.8	$ 3,104.6
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Balance, January 1, 2020	$ 1.1
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201613Member
Current period change for estimated uncollectible reinsurance	$ 0
Write-offs of uncollectible reinsurance recoverables	0
Balance, June 30, 2020	$ 3.6	$ 1.1
Percent rated A- or better	91.10%
Cumulative Effect, Period of Adoption, Adjustment
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Balance, January 1, 2020	$ 2.5
Balance, June 30, 2020		$ 2.5

Reserves for Losses and Loss _3

Reserves for Losses and Loss Adjustment Expenses - Reserves for Losses and Loss Adjustment Expenses (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	[1]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Net reserves beginning of the year			$ 2,722.7	$ 2,562.9
Net AIL reserves acquired			27.9	0
Losses and LAE incurred during current calendar year, net of reinsurance:
Current accident year			549.6	502.9
Prior accident years			4.5	19.8
Losses and LAE incurred during calendar year, net of reinsurance	$ 273.2	$ 284.8	554.1	522.7
Losses and LAE payments made during current calendar year, net of reinsurance:
Current accident year			125.3	89.8
Prior accident years			451.5	432.4
Losses and LAE payments made during current calendar year, net of reinsurance:			576.8	522.2
Change in participation interest			33	(14.4)
Foreign exchange adjustments			(8.5)	(13)
Net reserves - end of period	2,752.4	2,536	2,752.4	2,536
Reinsurance recoverables on unpaid losses and LAE, end of period	2,463.9	2,199.7	2,463.9	2,199.7
Gross reserves - end of period	$ 5,216.3	$ 4,735.7	$ 5,216.3	$ 4,735.7	$ 5,157.6
[1]	Derived from audited consolidated financial statements.

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	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Net losses and adjustment expenses related to pandemic	$ 17.4		$ 43.6
Total unfavorable prior-year development			4.5	$ 19.8
U.S. Operations
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total unfavorable prior-year development			2.7	(9.1)
International Operations
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total unfavorable prior-year development		$ 26.4	1.1	27.2
Run-off Lines
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total unfavorable prior-year development			$ 0.7	$ 1.7

Disclosures about Fair Value _3

Disclosures about Fair Value of Financial Instruments - Summary of Company's Financial Instruments Whose Carrying Amount Did Not Equal Fair Value (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Junior subordinated debentures | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	$ 257.6	$ 257.4
Junior subordinated debentures | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	266.2	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	173.8	174
Junior subordinated debentures | Trust preferred debentures | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	84.9	84.7
Junior subordinated debentures | Trust preferred debentures | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	92.4	92.5
Senior unsecured fixed rate notes | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	140.1	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	56	56.3
Floating rate loan stock | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	$ 56.3	$ 56.8

Disclosures about Fair Value _4

Disclosures about Fair Value of Financial Instruments Disclosures about Fair Value of Financial Instruments - Summary of Fair Values Measured on Recurring Basis (Details) - Fair Value, Recurring - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	$ 469.2	$ 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	322.5	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	266.2	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	266.2	266.5
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 | Trust preferred debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	173.8	174
Junior subordinated debentures | Trust preferred debentures | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	0	0
Junior subordinated debentures | Trust preferred debentures | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	173.8	174
Junior subordinated debentures | Trust preferred debentures | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	0	0
Junior subordinated debentures | Subordinated debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	92.4	92.5
Junior subordinated debentures | Subordinated debentures | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	0	0
Junior subordinated debentures | Subordinated debentures | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	92.4	92.5
Junior subordinated debentures | 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	56.3	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	56.3	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

Shareholders Equity - Additiona

Shareholders Equity - Additional Information (Detail) - USD ($)	Jun. 12, 2020	May 07, 2020	Jun. 21, 2019	May 24, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	May 03, 2016
Class of Stock [Line Items]
Dividends declared per common share (in dollars per share)		$ 0.31		$ 0.31	$ 0.31	$ 0.31	$ 0.62	$ 0.62
Cash dividends paid - common shares, total	$ 10,600,000		$ 11,900,000		$ 10,600,000	$ 11,900,000	$ 21,300,000	$ 22,700,000
2016 Repurchase Authorization
Class of Stock [Line Items]
Total number of shares authorized for purchase									$ 150,000,000
Remaining number of shares available under repurchase authorization					$ 53,300,000		$ 53,300,000

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive (Loss) Income - Changes in Accumulated Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended			12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020		Jun. 30, 2019	Dec. 31, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 1,636.8	$ 1,880.6	$ 1,781.1	[1]	$ 1,746.7	$ 1,746.7
Other comprehensive loss before reclassifications			16.6		82.8
Amounts reclassified from accumulated other comprehensive loss			(19.2)		4.2
Net current-period other comprehensive loss			$ (2.6)		87
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member			us-gaap:AccountingStandardsUpdate201613Member
Ending Balance	1,730	1,929	$ 1,730		1,929	$ 1,781.1	[1]
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)	(22.4)
Other comprehensive loss before reclassifications			(7.6)		(0.1)
Amounts reclassified from accumulated other comprehensive loss			0		0
Net current-period other comprehensive loss			(7.6)		(0.1)
Ending Balance	(30.2)	(22.5)	(30.2)		(22.5)	(22.6)
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 Holding Gains on Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			33.5		(49)	(49)
Other comprehensive loss before reclassifications			24.2		82.9
Amounts reclassified from accumulated other comprehensive loss	(13.9)	1.6	(19.2)		4.2
Net current-period other comprehensive loss			5		87.1
Ending Balance	44.2	38.1	44.2		38.1	33.5
Unrealized Holding Gains 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)	(6.7)
Other comprehensive loss before reclassifications			0		0
Amounts reclassified from accumulated other comprehensive loss			0		0
Net current-period other comprehensive loss			0		0
Ending Balance	(8.1)	(6.7)	(8.1)		(6.7)	(8.1)
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
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(101.9)	(27.6)	2.8		(78.1)	(78.1)
Ending Balance	$ 5.9	$ 8.9	5.9		$ 8.9	2.8
Accumulated Other Comprehensive Income (Loss) | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			$ 5.7
Ending Balance						$ 5.7
[1]	Derived from audited consolidated financial statements.

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive (Loss) Income - Amounts Reclassified from Accumulated Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Unrealized gains and losses on securities:
Net of taxes			$ (19.2)	$ 4.2
Unrealized Gains and Losses on Securities
Unrealized gains and losses on securities:
Net realized investment (gains) loss	$ (16.5)	$ 1.8	(19.9)	4.9
Provision (benefit) for income taxes	2.6	(0.2)	0.7	(0.7)
Net of taxes	$ (13.9)	$ 1.6	$ (19.2)	$ 4.2

Net (Loss) Income Per Common _3

Net (Loss) Income Per Common Share - Net Income (Loss) Per Common Share on Basic and Diluted Basis (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net (loss) income	$ (6.4)	$ 28.8	$ (25.2)	$ 120
Weighted average common shares outstanding - basic (in shares)	34,634,353	34,195,250	34,551,935	34,090,372
Effect of dilutive securities:
Equity compensation awards (in shares)	0	584,741	0	669,176
Weighted average common shares outstanding - diluted (in shares)	34,634,353	34,779,991	34,551,935	34,759,548
Net (loss) income per common share:
Basic (in dollars per share)	$ (0.18)	$ 0.84	$ (0.73)	$ 3.52
Diluted (in dollars per share)	$ (0.18)	$ 0.83	$ (0.73)	$ 3.45

Net (Loss) Income Per Common _4

Net (Loss) Income Per Common Share - Additional Information (Detail) - shares	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Jun. 30, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Treasury shares (in shares)	11,315,889	11,315,889	11,315,889	11,315,889
Equity compensation awards with anti-dilutive effect (in shares)	5,084	5,084

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information - Schedule of Interest Paid and Income Taxes Paid (Recovered) (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Supplemental Cash Flow [Line Items]
Total interest paid	$ 14.8	$ 16.8
Income taxes paid	1.6	1.3
Income taxes recovered	(0.7)	0
Income taxes paid, net	0.9	1.3
Senior Unsecured Fixed Rate Notes
Supplemental Cash Flow [Line Items]
Total interest paid	4.7	4.7
Junior subordinated debentures
Supplemental Cash Flow [Line Items]
Total interest paid	6.7	8.3
Other Indebtedness
Supplemental Cash Flow [Line Items]
Total interest paid	$ 3.4	$ 3.8

Share-based Compensation - Addi

Share-based Compensation - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	May 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment arrangement, expense		$ 2,100,000	$ 3,500,000	$ 5,200,000	$ 7,200,000
Employee service share-based compensation, unrecognized compensation costs on non-vested awards		23,200,000		$ 23,200,000
Restricted Stock Units (RSUs) | 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				1 year
Restricted Stock Units (RSUs) | 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				4 years
Stock-Settled SARs Activity
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment arrangement, expense		0	$ 0	$ 0	$ 400,000
Employee service share-based compensation, unrecognized compensation costs on non-vested awards		$ 0		$ 0
2019 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, number of shares authorized (in shares)	1,885,000
Expiration period	10 years

Share-based Compensation - Summ

Share-based Compensation - Summary of Restricted Share Activity (Detail) - Restricted Stock Units (RSUs)	6 Months Ended
	Jun. 30, 2020$ / sharesshares
Shares
Outstanding, beginning balance (in shares) | shares	471,271
Granted (in shares) | shares	399,578
Vested and issued (in shares) | shares	(161,081)
Expired or forfeited (in shares) | shares	(69,499)
Outstanding, ending balance (in shares) | shares	640,269
Weighted-Average Grant Date Fair Value
Outstanding, beginning balance (in dollars per share) | $ / shares	$ 60.09
Granted (in dollars per share) | $ / shares	32.72
Vested and issued (in dollars per share) | $ / shares	51.45
Expired or forfeited (in dollars per share) | $ / shares	58.42
Outstanding, ending balance (in dollars per share) | $ / shares	$ 44

Share-based Compensation - Su_2

Share-based Compensation - Summary of SARs Activity (Detail) - Stock-Settled SARs Activity	6 Months Ended
	Jun. 30, 2020$ / sharesshares
Shares
Outstanding, beginning balance (in shares) | shares	625,368
Exercised (in shares) | shares	(415,274)
Expired or forfeited (in shares) | shares	0
Outstanding, ending balance (in shares) | shares	210,094
Weighted-Average Exercise Price
Outstanding, beginning balance (in dollars per share) | $ / shares	$ 33.60
Exercised (in dollars per share) | $ / shares	32.25
Expired or forfeited (in dollars per share) | $ / shares	0
Outstanding, ending balance (in dollars per share) | $ / shares	$ 36.26

Underwriting, Acquisition and_3

Underwriting, Acquisition and Insurance Expenses & Other Corporate Expenses (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Underwriting, Acquisition and Insurance Expenses & Other Corporate Expenses [Abstract]
Commissions	$ 57.2	$ 56.7	$ 122.5	$ 120
General expenses	93.3	91.5	192.2	180.1
Premium taxes, boards and bureaus	6.5	7.9	14.5	16.2
Underwriting, acquisition and insurance expenses, total	157	156.1	329.2	316.3
Net deferral of policy acquisition costs	4.4	5.3	0.2	5.3
Total underwriting, acquisition and insurance expenses	161.4	161.4	329.4	321.6
Other corporate expenses	2.5	$ 7.5	5.8	$ 8
Civil penalties	$ 0.9		$ 0.9

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Net operating losses carryback period	2 years
Capital losses carryback period	3 years
Unrecognized tax benefits	$ 0	$ 0

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
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 5.7	$ 29.6	$ (15.9)	$ 129.7
Effective Tax Rate	209.40%	2.90%	(58.70%)	7.50%
Bermuda
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (31.1)	$ 15	$ (52.9)	$ 47
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
United States
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 67.9	$ 22.3	$ 57.3	$ 91.8
Effective Tax Rate	23.20%	14.80%	17.30%	14.50%
United Kingdom
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (29.2)	$ (8.9)	$ (27.5)	$ (12.4)
Effective Tax Rate	12.80%	26.70%	2.40%	28.10%
Belgium
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0.1	$ (0.3)	$ 0.1	$ (0.3)
Effective Tax Rate	20.00%	29.50%	31.00%	29.70%
Brazil
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0.6	$ 2	$ 2.8	$ 3.8
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
United Arab Emirates
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0.5	$ 0	$ 1.3	$ 0.2
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
Ireland
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0	$ 0	$ 0	$ (0.1)
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
Italy
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (1.8)	$ 0.2	$ 1.7	$ (0.5)
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
Malta
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (1.3)	$ (0.7)	$ 1.3	$ 0.2
Effective Tax Rate	0.00%	(0.10%)	0.00%	0.50%
Switzerland
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0	$ 0	$ 0	$ 0
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%

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
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Income tax provision (benefit) at expected rate	$ 8.6	$ 3.6	$ 9.4	$ 18.5
Tax effect of:
Nontaxable investment income	(0.2)	(0.3)	(0.3)	(0.7)
Foreign exchange adjustments	1.5	0.1	(0.6)	0.6
Goodwill	1	0	1	0
Withholding taxes	0	0.1	0.1	0.2
Change in valuation allowance	0	0	0	(0.6)
Other	1.2	(2.7)	(0.3)	(8.3)
Income tax provision	$ 12.1	$ 0.8	$ 9.3	$ 9.7

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2020USD ($)
Commitments and Contingencies Disclosure [Abstract]
Contractual commitments related to its limited partnership investments (up to)	$ 96.1
Contractual commitments period (not to exceed)	13 years

Segment Information - Additiona

Segment Information - Additional Information (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2020USD ($)segment	Dec. 31, 2019USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment	2
Assets associated with trade capital providers | $	$ 780.7	$ 916.3

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
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Earned premiums	$ 433.4	$ 431.7	$ 868.4	$ 852.2
Net investment income	1.5	42.8	37	76.7
Fee and other income	2	2.1	4.1	4.4
Net realized investment gains (losses)	20.1	12	(16)	64.5
Foreign currency exchange (losses) gains	(6.4)	5.3	(3.4)	4.6
Other corporate expenses	(2.5)	(7.5)	(5.8)	(8)
Total revenue	457	488.6	893.5	997.8
Income (loss) before income taxes	5.7	29.6	(15.9)	129.7
Operating Segments
Segment Reporting Information [Line Items]
Income (loss) before income taxes	2.4	31.1	27.5	90.8
Corporate and Other
Segment Reporting Information [Line Items]
Net investment income	0.1	0.4	0.6	0.7
Income (loss) before income taxes	(7.9)	(11.3)	(18.2)	(22.2)
U.S. Operations | Operating Segments
Segment Reporting Information [Line Items]
Earned premiums	301.6	284	604.1	557.8
Net investment income	0.8	29.6	26	52.7
Income (loss) before income taxes	31.2	53.2	68.1	96.1
International Operations | Operating Segments
Segment Reporting Information [Line Items]
Earned premiums	131.8	147.6	264.1	294.3
Net investment income	0.5	11.5	9.1	20.6
Income (loss) before income taxes	(27.5)	(21)	(39.8)	(4.8)
Run-off Lines | Operating Segments
Segment Reporting Information [Line Items]
Earned premiums	0	0.1	0.2	0.1
Net investment income	0.1	1.3	1.3	2.7
Income (loss) before income taxes	$ (1.3)	$ (1.1)	$ (0.8)	$ (0.5)

Segment Information - Schedule

Segment Information - Schedule of Earned Premiums by Geographic Location (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	$ 433.4	$ 431.7	$ 868.4	$ 852.2
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	301.4	283.2	601.1	555.8
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	75.5	96.6	162.2	193.7
Bermuda
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	25.3	19.2	46.5	35.8
Malta
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	18.5	20.2	30.3	41
All other jurisdictions
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	$ 12.7	$ 12.5	$ 28.3	$ 25.9

Segment Information - Identifia

Segment Information - Identifiable Assets (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	$ 10,396.7	$ 10,514.5	[1]
Operating Segments | U.S. Operations
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	5,744.9	5,009
Operating Segments | International Operations
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	4,132.2	5,002.4
Operating Segments | Run-off Lines
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	331.1	356.9
Corporate and Other
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	$ 188.5	$ 146.2
[1]	Derived from audited consolidated financial statements.

Senior Unsecured Fixed Rate N_3

Senior Unsecured Fixed Rate Notes - Additional Information (Detail) - USD ($)	1 Months Ended
	Sep. 30, 2012	Jun. 30, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Principal amount of senior notes		$ 143,800,000	$ 143,800,000
Senior Unsecured Fixed Rate Notes
Schedule of Equity Method Investments [Line Items]
Principal amount of senior notes	$ 143,750,000
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	Jun. 30, 2020	Dec. 31, 2019
Debt Disclosure [Abstract]
Principal	$ 143.8	$ 143.8
Less: unamortized debt issuance costs	(3.7)	(3.8)
Senior unsecured fixed rate notes, less unamortized debt issuance costs	$ 140.1	$ 140	[1]
[1]	Derived from audited consolidated financial statements.

Senior Unsecured Fixed Rate N_5

Senior Unsecured Fixed Rate Notes - Condensed Consolidating Balance Sheet (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019		Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Assets
Investments	$ 4,851.5		$ 5,099.4	[1]
Cash	187.7		137.8	[1]
Accrued investment income	23.4		25.7	[1]
Premiums receivable	800.2		688.2	[1]
Reinsurance recoverables	2,942.8		3,104.6	[1]
Goodwill and other intangible assets, net	247.6		253.2
Deferred tax asset, net	18.9		6.1	[1]
Deferred acquisition costs, net	153.5		160.2	[1]
Ceded unearned premiums	656.5		545	[1]
Operating lease right-of-use assets	87.2		91.8	[1]
Other assets	414.7		387.1	[1]
Assets held for sale	12.7		15.4	[1]
Intercompany note receivable	0		0
Investments in subsidiaries	0		0
Total assets	10,396.7		10,514.5	[1]
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	5,216.3		5,157.6	[1]	$ 4,735.7
Unearned premiums	1,481.2		1,410.9	[1]
Funds held and ceded reinsurance payable, net	1,109.4		1,253.7
Debt	578.7		578.7
Current income taxes payable, net	27.1		0.8	[1]
Accrued underwriting expenses and other liabilities	154.8		226	[1]
Operating lease liabilities	99.2		105.7	[1]
Due to (from) affiliates	0		0
Total liabilities	8,666.7		8,733.4	[1]
Total shareholders' equity	1,730	$ 1,636.8	1,781.1	[1]	$ 1,929	$ 1,880.6	$ 1,746.7
Total liabilities and shareholders' equity	10,396.7		10,514.5	[1]
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
Deferred tax asset, net	0		0
Deferred acquisition costs, net	0		0
Ceded unearned premiums	0		0
Operating lease right-of-use assets	0		0
Other assets	0		0
Assets held for sale	0		0
Intercompany note receivable	0		0
Investments in subsidiaries	(1,904.2)		(1,916.7)
Total assets	(1,904.2)		(1,916.7)
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		0
Accrued underwriting expenses and other liabilities	0		0
Operating lease liabilities	0		0
Due to (from) affiliates	(67.3)		(19.3)
Total liabilities	(67.3)		(19.3)
Total shareholders' equity	(1,836.9)		(1,897.4)
Total liabilities and shareholders' equity	(1,904.2)		(1,916.7)
Other Subsidiaries and Eliminations
Assets
Investments	1,448.9		1,693.2
Cash	144.2		104.3
Accrued investment income	6		7.5
Premiums receivable	501.8		456.9
Reinsurance recoverables	1,202.5		1,415.2
Goodwill and other intangible assets, net	89.2		89.2
Deferred tax asset, net	7.2		5.7
Deferred acquisition costs, net	67.5		71.8
Ceded unearned premiums	319.1		238.6
Operating lease right-of-use assets	25.1		25.1
Other assets	258.9		213.5
Assets held for sale	0.3		0
Intercompany note receivable	(72.9)		(56.7)
Investments in subsidiaries	0		0
Total assets	3,997.8		4,264.3
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	2,034.6		2,120.1
Unearned premiums	580.5		511.1
Funds held and ceded reinsurance payable, net	542.7		607.8
Debt	140.9		141
Current income taxes payable, net	(6.1)		(7.4)
Accrued underwriting expenses and other liabilities	66		124.8
Operating lease liabilities	28.2		29.5
Due to (from) affiliates	11.7		13.4
Total liabilities	3,398.5		3,540.3
Total shareholders' equity	599.3		724
Total liabilities and shareholders' equity	3,997.8		4,264.3
Argo Group International Holdings, Ltd (Parent Guarantor)
Assets
Investments	0.6		0.6
Cash	1.9		1.9
Accrued investment income	0		0
Premiums receivable	0		0
Reinsurance recoverables	0		0
Goodwill and other intangible assets, net	39.9		40.6
Deferred tax asset, net	0		0
Deferred acquisition costs, net	0		0
Ceded unearned premiums	0		0
Operating lease right-of-use assets	6.8		7.1
Other assets	9.6		7.8
Assets held for sale	0		0
Intercompany note receivable	0		0
Investments in subsidiaries	1,904.2		1,916.7
Total assets	1,963		1,974.7
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	153.4		153.4
Current income taxes payable, net	0		0
Accrued underwriting expenses and other liabilities	5.4		13.6
Operating lease liabilities	6.9		7.3
Due to (from) affiliates	67.3		19.3
Total liabilities	233		193.6
Total shareholders' equity	1,730		1,781.1
Total liabilities and shareholders' equity	1,963		1,974.7
Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer)
Assets
Investments	3,402		3,405.6
Cash	41.6		31.6
Accrued investment income	17.4		18.2
Premiums receivable	298.4		231.3
Reinsurance recoverables	1,740.3		1,689.4
Goodwill and other intangible assets, net	118.5		123.4
Deferred tax asset, net	11.7		0.4
Deferred acquisition costs, net	86		88.4
Ceded unearned premiums	337.4		306.4
Operating lease right-of-use assets	55.3		59.6
Other assets	146.2		165.8
Assets held for sale	12.4		15.4
Intercompany note receivable	72.9		56.7
Investments in subsidiaries	0		0
Total assets	6,340.1		6,192.2
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	3,181.7		3,037.5
Unearned premiums	900.7		899.8
Funds held and ceded reinsurance payable, net	566.7		645.9
Debt	284.4		284.3
Current income taxes payable, net	33.2		8.2
Accrued underwriting expenses and other liabilities	83.4		87.6
Operating lease liabilities	64.1		68.9
Due to (from) affiliates	(11.7)		(13.4)
Total liabilities	5,102.5		5,018.8
Total shareholders' equity	1,237.6		1,173.4
Total liabilities and shareholders' equity	$ 6,340.1		$ 6,192.2
[1]	Derived from audited consolidated financial statements.

Senior Unsecured Fixed Rate N_6

Senior Unsecured Fixed Rate Notes - Condensed Consolidating Statement of (Loss) Income (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Premiums and other revenue:
Earned premiums	$ 433.4	$ 431.7	$ 868.4	$ 852.2
Net investment (expense) income	1.5	42.8	37	76.7
Fee and other income	2	2.1	4.1	4.4
Net realized investment and other gains (losses) before income taxes	20.1	12	(16)	64.5
Total revenue	457	488.6	893.5	997.8
Expenses:
Losses and loss adjustment expenses	273.2	284.8	554.1	522.7
Underwriting, acquisition and insurance expenses	161.4	161.4	329.4	321.6
Other corporate expenses	2.5	7.5	5.8	8
Interest expense	6.8	9.3	14.5	17.8
Fee and other expense	1	1.3	2.2	2.6
Foreign currency exchange losses (gains)	6.4	(5.3)	3.4	(4.6)
Total expenses	451.3	459	909.4	868.1
Income (loss) before income taxes	5.7	29.6	(15.9)	129.7
Income tax provision	12.1	0.8	9.3	9.7
Net (loss) income before equity in earnings of subsidiaries	(6.4)	28.8	(25.2)	120
Equity in undistributed earnings of subsidiaries	0	0	0	0
Net (loss) income	(6.4)	28.8	(25.2)	120
Consolidating Adjustments
Premiums and other revenue:
Earned premiums	0	0	0	0
Net investment (expense) income	0	0	0	0
Fee and other income	0	0	0	0
Net realized investment and other gains (losses) before income taxes	0	0	0	0
Total revenue	0	0	0	0
Expenses:
Losses and loss adjustment expenses	0	0	0	0
Underwriting, acquisition and insurance expenses	0	0	0	0
Other corporate expenses	0	0	0	0
Interest expense	0	0	0	0
Fee and other expense	0	0	0	0
Foreign currency exchange losses (gains)	0	0	0	0
Total expenses	0	0	0	0
Income (loss) before income taxes	0	0	0	0
Income tax provision	0	0	0	0
Net (loss) income before equity in earnings of subsidiaries	0	0	0	0
Equity in undistributed earnings of subsidiaries	0.9	(39.4)	9.8	(133.8)
Net (loss) income	0.9	(39.4)	9.8	(133.8)
Other Subsidiaries and Eliminations
Premiums and other revenue:
Earned premiums	132.7	171.6	266.2	325.6
Net investment (expense) income	(4.3)	15.3	6.6	26.1
Fee and other income	1.4	1.4	2.7	2.6
Net realized investment and other gains (losses) before income taxes	(14.4)	(2.9)	(9.8)	3.8
Total revenue	115.4	185.4	265.7	358.1
Expenses:
Losses and loss adjustment expenses	105.5	113.5	195.9	193.4
Underwriting, acquisition and insurance expenses	56.5	56.5	116.9	112.4
Other corporate expenses	0	0	0	0
Interest expense	1.7	2.4	3.7	4.5
Fee and other expense	0.4	0.4	0.9	0.9
Foreign currency exchange losses (gains)	6.4	(5.2)	4.4	(4.8)
Total expenses	170.5	167.6	321.8	306.4
Income (loss) before income taxes	(55.1)	17.8	(56.1)	51.7
Income tax provision	(3.7)	(2.5)	(0.6)	(3.6)
Net (loss) income before equity in earnings of subsidiaries	(51.4)	20.3	(55.5)	55.3
Equity in undistributed earnings of subsidiaries	0	0	0	0
Net (loss) income	(51.4)	20.3	(55.5)	55.3
Argo Group International Holdings, Ltd (Parent Guarantor)
Premiums and other revenue:
Earned premiums	0	0	0	0
Net investment (expense) income	0	(0.6)	0	(1.3)
Fee and other income	0	0	0	0
Net realized investment and other gains (losses) before income taxes	1.4	(0.1)	1.3	(0.2)
Total revenue	1.4	(0.7)	1.3	(1.5)
Expenses:
Losses and loss adjustment expenses	0	0	0	0
Underwriting, acquisition and insurance expenses	3.2	0.7	9	0.9
Other corporate expenses	2.6	7.5	5.2	8
Interest expense	1.1	1.7	2.5	3.4
Fee and other expense	0	0	0	0
Foreign currency exchange losses (gains)	0	0	0	0
Total expenses	6.9	9.9	16.7	12.3
Income (loss) before income taxes	(5.5)	(10.6)	(15.4)	(13.8)
Income tax provision	0	0	0	0
Net (loss) income before equity in earnings of subsidiaries	(5.5)	(10.6)	(15.4)	(13.8)
Equity in undistributed earnings of subsidiaries	(0.9)	39.4	(9.8)	133.8
Net (loss) income	(6.4)	28.8	(25.2)	120
Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer)
Premiums and other revenue:
Earned premiums	300.7	260.1	602.2	526.6
Net investment (expense) income	5.8	28.1	30.4	51.9
Fee and other income	0.6	0.7	1.4	1.8
Net realized investment and other gains (losses) before income taxes	33.1	15	(7.5)	60.9
Total revenue	340.2	303.9	626.5	641.2
Expenses:
Losses and loss adjustment expenses	167.7	171.3	358.2	329.3
Underwriting, acquisition and insurance expenses	101.7	104.2	203.5	208.3
Other corporate expenses	(0.1)	0	0.6	0
Interest expense	4	5.2	8.3	9.9
Fee and other expense	0.6	0.9	1.3	1.7
Foreign currency exchange losses (gains)	0	(0.1)	(1)	0.2
Total expenses	273.9	281.5	570.9	549.4
Income (loss) before income taxes	66.3	22.4	55.6	91.8
Income tax provision	15.8	3.3	9.9	13.3
Net (loss) income before equity in earnings of subsidiaries	50.5	19.1	45.7	78.5
Equity in undistributed earnings of subsidiaries	0	0	0	0
Net (loss) income	$ 50.5	$ 19.1	$ 45.7	$ 78.5

Senior Unsecured Fixed Rate N_7

Senior Unsecured Fixed Rate Notes - Condensed Consolidating Statement of Cash Flows (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities	$ (103.1)	$ (4.9)
Cash flows from investing activities:
Proceeds from sales of investments	848.3	814.9
Maturities and mandatory calls of fixed maturity investments	255	168.8
Purchases of investments	(1,177.4)	(959.1)
Change in short-term investments and foreign regulatory deposits	217.5	74
Settlements of foreign currency exchange forward contracts	7	9.9
Proceeds from sale of Trident assets	38	0
Issuance of intercompany note, net	0
Purchases of fixed assets and other, net	(12.6)	(38.2)
Cash provided by investing activities	175.8	70.3
Cash flows from financing activities:
Payment on the intercompany note		0
Activity under stock incentive plans	1	0.9
Payment of cash dividends to common shareholders	(21.3)	(22.7)
Cash used in financing activities	(20.3)	(21.8)
Effect of exchange rate changes on cash	(2.5)	(0.5)
Change in cash	49.9	43.1
Cash, beginning of year	137.8	139.2
Cash, end of period	187.7	182.3
Argo Group International Holdings, Ltd (Parent Guarantor)
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities	20.3	19.3
Cash flows from investing activities:
Proceeds from sales of investments	0	0
Maturities and mandatory calls of fixed maturity investments	0	0
Purchases of investments	0	0
Change in short-term investments and foreign regulatory deposits	(0.1)	2.8
Settlements of foreign currency exchange forward contracts	0.1	(0.1)
Proceeds from sale of Trident assets	0
Issuance of intercompany note, net	0
Purchases of fixed assets and other, net	0	0
Cash provided by investing activities	0	2.7
Cash flows from financing activities:
Payment on the intercompany note		0
Activity under stock incentive plans	1	0.9
Payment of cash dividends to common shareholders	(21.3)	(22.7)
Cash used in financing activities	(20.3)	(21.8)
Effect of exchange rate changes on cash	0	0
Change in cash	0	0.2
Cash, beginning of year	1.9	1.7
Cash, end of period	1.9	1.9
Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer)
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities	(21)	(5.5)
Cash flows from investing activities:
Proceeds from sales of investments	454.1	507.1
Maturities and mandatory calls of fixed maturity investments	184.4	131.8
Purchases of investments	(935)	(686.4)
Change in short-term investments and foreign regulatory deposits	270.9	74.7
Settlements of foreign currency exchange forward contracts	0	0.9
Proceeds from sale of Trident assets	38
Issuance of intercompany note, net	(15)
Purchases of fixed assets and other, net	33.6	(6.9)
Cash provided by investing activities	31	21.2
Cash flows from financing activities:
Payment on the intercompany note		19.1
Activity under stock incentive plans	0	0
Payment of cash dividends to common shareholders	0	0
Cash used in financing activities	0	(19.1)
Effect of exchange rate changes on cash	0	0
Change in cash	10	(3.4)
Cash, beginning of year	31.6	31.7
Cash, end of period	41.6	28.3
Other Subsidiaries and Eliminations
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities	(102.4)	(18.7)
Cash flows from investing activities:
Proceeds from sales of investments	394.2	307.8
Maturities and mandatory calls of fixed maturity investments	70.6	37
Purchases of investments	(242.4)	(272.7)
Change in short-term investments and foreign regulatory deposits	(53.3)	(3.5)
Settlements of foreign currency exchange forward contracts	6.9	9.1
Proceeds from sale of Trident assets	0
Issuance of intercompany note, net	15
Purchases of fixed assets and other, net	(46.2)	(31.3)
Cash provided by investing activities	144.8	46.4
Cash flows from financing activities:
Payment on the intercompany note		(19.1)
Activity under stock incentive plans	0	0
Payment of cash dividends to common shareholders	0	0
Cash used in financing activities	0	19.1
Effect of exchange rate changes on cash	(2.5)	(0.5)
Change in cash	39.9	46.3
Cash, beginning of year	104.3	105.8
Cash, end of period	144.2	152.1
Consolidating Adjustments
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities	0	0
Cash flows from investing activities:
Proceeds from sales of investments	0	0
Maturities and mandatory calls of fixed maturity investments	0	0
Purchases of investments	0	0
Change in short-term investments and foreign regulatory deposits	0	0
Settlements of foreign currency exchange forward contracts	0	0
Proceeds from sale of Trident assets	0
Issuance of intercompany note, net	0
Purchases of fixed assets and other, net	0	0
Cash provided by investing activities	0	0
Cash flows from financing activities:
Payment on the intercompany note		0
Activity under stock incentive plans	0	0
Payment of cash dividends to common shareholders	0	0
Cash used in financing activities	0	0
Effect of exchange rate changes on cash	0	0
Change in cash	0	0
Cash, beginning of year	0	0
Cash, end of period	$ 0	$ 0

Subsequent Event (Details)

Subsequent Event (Details) - Subsequent Event $ / shares in Units, $ in Millions	Jul. 09, 2020USD ($)$ / sharesRateshares
Subsequent Event [Line Items]
Fractional interest per one preference share	0.001
Term loan principal outstanding | $	$ 125
Depositary Shares
Subsequent Event [Line Items]
Depositary shares issued (in shares) | shares	6,000,000
Liquidation preference per depository share (in dollars per share)	$ 25
Preferred dividends, per depositary share amounts (in dollars per share)	$ 1.75
Proceeds From Sale of Depositary Shares | $	$ 144
Series A Preferred Stock
Subsequent Event [Line Items]
Preferred stock, dividend rate (in percentage)	7.00%
Preferred stock par value (in dollars per share)	$ 1
Liquidation preference (in dollars per share)	25,000
Preferred dividends (in dollars per share)	$ 1,750
Series A Preferred Stock | U.S. Treasury Rate
Subsequent Event [Line Items]
Basis spread on U.S. Treasury Rate | Rate	6.712%