Argo Group International (ARGO-PA) 10-Q 8 Nov 19 2019 Q3 Quarterly report Financial data

Cover

Cover - shares	9 Months Ended
	Sep. 30, 2019	Nov. 05, 2019
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2019
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		34,323,365
Entity Central Index Key	0001091748
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Amendment Flag	false
Common Stock [Member]
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 [Member]
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

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	[1]
Investments:
Fixed maturities available-for-sale, at fair value (cost: 2019 - $3,716.6; 2018 - $3,529.1)	$ 3,745.6	$ 3,460.4
Equity securities, at fair value (cost: 2019 - $298.6; 2018 - $310.6)	400.6	354.5
Other investments (cost: 2019 - $486.0; 2018 - $482.0)	500	489.8
Short-term investments, at fair value (cost: 2019 - $481.5; 2018 - $482.3)	480.8	482.3
Total investments	5,127	4,787
Cash	145.1	139.2
Accrued investment income	27.7	27.2
Premiums receivable	740.3	649.9
Reinsurance recoverables	2,873.8	2,688.3
Goodwill	177	177
Intangible assets, net of accumulated amortization	92.2	93.5
Current income taxes receivable, net	0.2	8.2
Deferred acquisition costs, net	159.5	167.3
Ceded unearned premiums	603.8	457.7
Operating lease right-of-use assets	108.6
Other assets	390.6	362.9
Total assets	10,445.8	9,558.2
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	4,842.5	4,654.6
Unearned premiums	1,495.5	1,300.9
Accrued underwriting expenses and other liabilities	283.9	261.9
Ceded reinsurance payable, net	1,175.7	970.5
Funds held	36.1	37.2
Senior unsecured fixed rate notes	139.9	139.8
Other indebtedness	181.4	183.4
Junior subordinated debentures	257.3	257
Deferred tax liabilities, net	19.9	6.2
Operating lease liabilities	120.2	0
Total liabilities	8,552.4	7,811.5
Commitments and contingencies (Note 14)
Shareholders' equity:
Common shares - $1.00 par, 500,000,000 shares authorized; 45,629,710 and 45,276,999 shares issued at September 30, 2019 and December 31, 2018, respectively	45.6	45.3
Additional paid-in capital	1,373.2	1,372
Treasury shares (11,315,889 shares at September 30, 2019 and December 31, 2018, respectively)	(455.1)	(455.1)
Retained earnings	925	862.6
Accumulated other comprehensive income (loss), net of taxes	4.7	(78.1)
Total shareholders' equity	1,893.4	1,746.7
Total liabilities and shareholders' equity	$ 10,445.8	$ 9,558.2
[1]	Derived from audited consolidated financial statements.

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Fixed maturities available-for-sale, cost	$ 3,716.6	$ 3,529.1
Equity securities, cost	298.6	310.6
Other investments, cost	486	482
Short-term investments, cost	$ 481.5	$ 482.3
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)	45,629,710	45,276,999
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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Premiums and other revenue:
Earned premiums	$ 451.5	$ 446.9	$ 1,303.7	$ 1,279.3
Net investment income	40.2	34.5	116.9	103.7
Fee and other income	1.9	3.3	6.3	7.2
Net realized investment (losses) gains:
Net realized investment gains	2.6	9.7	0.3	31.1
Change in fair value of equity securities	(8.8)	4.5	58	(22.1)
Net realized investment (losses) gains	(6.2)	14.2	58.3	9
Total revenue	487.4	498.9	1,485.2	1,399.2
Expenses:
Losses and loss adjustment expenses	338.8	277.5	861.5	760.2
Underwriting, acquisition and insurance expenses	167.7	168	497.3	485
Interest expense	7.5	7.9	25.3	23.4
Fee and other expense	1.2	1.9	3.8	5.5
Foreign currency exchange gains	(1.6)	(1.7)	(6.2)	(2.3)
Total expenses	513.6	453.6	1,381.7	1,271.8
(Loss) income before income taxes	(26.2)	45.3	103.5	127.4
Income tax (benefit) provision	(1.1)	4.7	8.6	20.2
Net (loss) income	$ (25.1)	$ 40.6	$ 94.9	$ 107.2
Net (loss) income per common share:
Basic (in dollars per share)	$ (0.73)	$ 1.20	$ 2.78	$ 3.16
Diluted (in dollars per share)	(0.73)	1.17	2.73	3.09
Dividend declared per common share (in dollars per share)	$ 0.31	$ 0.27	$ 0.93	$ 0.81
Weighted average common shares:
Basic (in shares)	34,299,999	33,956,695	34,161,016	33,921,632
Diluted (in shares)	34,299,999	34,656,328	34,769,622	34,688,843
Net realized investment (losses) gains before other-than-temporary impairment losses	$ (1.2)	$ 14.2	$ 70.1	$ 10.9
Other-than-temporary impairment losses recognized in earnings:
Other-than-temporary impairment losses on fixed maturities	(5)	0	(11.8)	(1.9)
Impairment losses recognized in earnings	$ (5)	$ 0	$ (11.8)	$ (1.9)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive (Loss) Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (25.1)	$ 40.6	$ 94.9	$ 107.2
Other comprehensive (loss) income:
Foreign currency translation adjustments	0	(0.8)	(0.1)	(4.8)
Unrealized gains (losses) on securities:
Gains (losses) arising during the year	(7.4)	(2.4)	91.3	(63.8)
Reclassification adjustment for losses included in net income	2.8	(2.4)	7.7	0.2
Other comprehensive (loss) income before tax	(4.6)	(5.6)	98.9	(68.4)
Income tax provision related to other comprehensive income (loss):
(Losses) gains arising during the year	(0.7)	(1.1)	15.1	(10.4)
Reclassification adjustment for losses included in net income	0.3	(0.3)	1	(0.1)
Income tax (benefit) provision related to other comprehensive (loss) income	(0.4)	(1.4)	16.1	(10.5)
Other comprehensive (loss) income, net of tax	(4.2)	(4.2)	82.8	(57.9)
Comprehensive (loss) income	$ (29.3)	$ 36.4	$ 177.7	$ 49.3

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total		Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Shares [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) Member]
Beginning Balance at Dec. 31, 2017	$ 1,819.7		$ 40.4	$ 1,129.1	$ (423.4)	$ 977	$ 96.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	107.2					107.2
Other comprehensive income (loss) - change in fair value of fixed maturities, net of taxes	(58.2)						(58.2)
Other comprehensive income (loss), net - Other	0.3						0.3
Repurchase of common share	(30)				(30)
Activity under stock incentive plans	12.7		0.5	12.2
Retirement of common shares (tax payments on equity compensation)	(7)		(0.1)	(6.9)
Employee stock purchase plan	1.4			1.4
15% Stock Dividend			4.4	232.9		(237.3)
Cash dividends declared - common shares	(28)					(28)
Ending Balance at Sep. 30, 2018	1,818.1		45.2	1,368.7	(453.4)	915.7	(58.1)
Beginning Balance at Dec. 31, 2018	1,746.7	[1]	45.3	1,372	(455.1)	862.6	(78.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	94.9					94.9
Other comprehensive income (loss) - change in fair value of fixed maturities, net of taxes	82.9						82.9
Other comprehensive income (loss), net - Other	(0.1)						(0.1)
Activity under stock incentive plans	11		0.4	10.6
Retirement of common shares (tax payments on equity compensation)	(11.2)		(0.1)	(11.1)
Employee stock purchase plan	1.7			1.7
Cash dividends declared - common shares	(32.5)					(32.5)
Ending Balance at Sep. 30, 2019	$ 1,893.4		$ 45.6	$ 1,373.2	$ (455.1)	$ 925	$ 4.7
[1]	Derived from audited consolidated financial statements.

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Shareholders' Equity (Parenthetical) - $ / shares	Aug. 06, 2019	May 24, 2019	May 08, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Stockholders' Equity [Abstract]
Common shares repurchased (in shares)							500,989
Repurchase of common shares, weighted average price (in dollars per share)							$ 59.83
Stock dividend percent					15.00%		15.00%
Dividend declared per common share (in dollars per share)	$ 0.31	$ 0.31	$ 0.27	$ 0.31	$ 0.27	$ 0.93	$ 0.81

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net income	$ 94.9	$ 107.2
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization and depreciation	20.4	23.1
Share-based payments expense	11.7	14.4
Deferred income tax benefit, net	(2.2)	(7.4)
Net realized investment gains	(58.3)	(9)
Undistributed earnings from alternative investment portfolio	(19.4)	(20.7)
Change in:
Accrued investment income	(0.5)	(2.7)
Receivables	(282.6)	(148.5)
Deferred acquisition costs	7.5	(15.2)
Ceded unearned premiums	(147.1)	(114.6)
Reserves for losses and loss adjustment expenses	194.9	(19.2)
Unearned premiums	197.7	179.4
Ceded reinsurance payable and funds held	204.8	151.3
Income taxes	7.9	8.8
Accrued underwriting expenses and other liabilities	8.5	85.8
Other, net	(42.5)	(1.7)
Cash provided by operating activities	195.7	231
Cash flows from investing activities:
Sales of fixed maturity investments	1,046.3	1,158.6
Maturities and mandatory calls of fixed maturity investments	292.2	375.1
Sales of equity securities	66.3	165
Sales of other investments	67.7	93.6
Purchases of fixed maturity investments	(1,535)	(1,787)
Purchases of equity securities	(49.9)	(156)
Purchases of other investments	(54.6)	(34.2)
Change in foreign regulatory deposits and voluntary pools	2.3	13.4
Change in short-term investments	0	(47.2)
Settlements of foreign currency exchange forward contracts	(1.2)	2
Cash acquired with acquisition of Ariscom	0	15.6
Purchases of fixed assets	(22.9)	(35.8)
Other, net	29.6	3.6
Cash used in investing activities	(159.2)	(233.3)
Cash flows from financing activities:
Payment on note payable	(0.6)	0
Activity under stock incentive plans	1.4	1
Repurchase of Company's common shares	0	(30)
Payment of cash dividends to common shareholders	(32.5)	(28)
Cash used in financing activities	(31.7)	(57)
Effect of exchange rate changes on cash	1.1	1.2
Change in cash	5.9	(58.1)
Cash, beginning of year	139.2	176.6
Cash, end of period	$ 145.1	$ 118.5

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2019
Accounting Policies [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. 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 doubtful accounts; estimates of written and earned premiums; reinsurance premium receivable; fair value of investments and assessment of potential impairment; 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, 2018 , filed with the Securities and Exchange Commission on February 25, 2019. The interim financial information as of, and for the three and nine months ended, September 30, 2019 and 2018 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.

Recently Issued Accounting Pron

Recently Issued Accounting Pronouncements	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In August 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update ("ASU") 2018-13, "Fair Value Measurement" (Topic 820). ASU 2018-13 eliminates, adds and modifies certain disclosure requirements on fair value measurements. The guidance is effective for fiscal years beginning after December 15, 2019, including interim periods within the year of adoption. The amendments on changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements, and the narrative description of measurement uncertainty are applied prospectively for only the most recent interim or annual period presented in the initial fiscal year adoption. All other amendments are applied retrospectively to all periods presented upon their effective date. Early adoption is permitted. We are currently in the process of evaluating the impact that the adoption of the ASU will have on our financial disclosures. In June 2016, the FASB issued ASU 2016-13, “Measurement of Credit Losses on Financial Instruments” (Topic 326). ASU 2016-13 requires organizations to estimate credit losses on certain types of financial instruments, including receivables and available-for-sale debt securities, by introducing an approach based on expected losses. The expected loss approach will require entities to incorporate considerations of historical information, current information and reasonable and supportable forecasts. The guidance is effective for fiscal years beginning after December 15, 2019, including interim periods within the year of adoption. The guidance requires a modified retrospective transition method and early adoption is permitted. We are currently in the process of evaluating the impact that the adoption of the ASU will have on our financial results and disclosures. In February 2016, the FASB issued ASU 2016-02, “Leases” (Topic 842). ASU 2016-02 requires organizations that lease assets to recognize on the balance sheet the assets and liabilities for the rights and obligations created by those leases. Additionally, the ASU modifies current guidance for lessors' accounting. In July 2018, the FASB issued ASU 2018-11, "Leases: Targeted Improvements" (Topic 842), which provides for an alternative transition method by allowing entities to initially apply the new leases standard at the adoption date (such as January 1, 2019) and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption (comparative periods presented in the financial statements will continue to be in accordance with current GAAP (Topic 840, Leases). The standard was effective for annual and interim periods beginning after December 15, 2018, with earlier application permitted. We have entered into operating leases for office space and certain other assets. We adopted the new standard on the effective date of January 1, 2019. We applied the following practical expedients: • We have elected to adopt this standard using the option transition method, which allows companies to continue applying the guidance under the lease standard in effect at that time in the comparative periods presented in the consolidated financial statements. The adoption of the standard had no effect on our consolidated shareholders’ equity. Prior periods were not restated. • We have elected the "package of practical expedients", which permits us not to reassess under the new standard our prior conclusion about lease identification, lease classification and initial direct costs. • Where we are the lessor, we have elected the practical expedient which permits us to not separate non-lease components from the associated lease components if the non-lease components otherwise would be accounted for in accordance with the new revenue standard. For the majority of our asset classes, we elected not to separate lease and non-lease components. As a result, our right-of-use assets and lease liabilities represent base rent components of our leases. We have elected to not apply the practical expedient which allows the use of hindsight in determining the lease term and in assessing impairment of the entity’s right-of-use assets. The remaining practical expedients did not specifically apply to our lease population as of the adoption date. Please see Note 4 - “Leases” for further discussion on the impact of the adoption of this standard.

Investments

Investments	9 Months Ended
	Sep. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Investments	Investments Included in “Total investments” in our Consolidated Balance Sheets at September 30, 2019 and December 31, 2018 is $159.6 million and $133.4 million , respectively, of assets managed on behalf of the trade capital providers, who are third-party participants that provide underwriting capital to the operations of Syndicates 1200 and 1910. Fixed Maturities The amortized cost, gross unrealized gains, gross unrealized losses and fair value of fixed maturity investments were as follows: September 30, 2019 (in millions) Amortized Gross Gross Fair Fixed maturities U.S. Governments $ 324.9 $ 3.9 $ 0.5 $ 328.3 Foreign Governments 262.6 4.2 2.3 264.5 Obligations of states and political subdivisions 152.6 7.6 0.1 160.1 Corporate bonds 1,862.0 39.0 39.2 1,861.8 Commercial mortgage-backed securities 213.3 6.0 0.3 219.0 Residential mortgage-backed securities 510.3 11.9 0.9 521.3 Asset-backed securities 165.6 1.7 0.3 167.0 Collateralized loan obligations 225.3 0.3 2.0 223.6 Total fixed maturities $ 3,716.6 $ 74.6 $ 45.6 $ 3,745.6 December 31, 2018 (in millions) Amortized Gross Gross Fair Fixed maturities U.S. Governments $ 240.9 $ 0.2 $ 4.9 $ 236.2 Foreign Governments 224.1 0.5 7.8 216.8 Obligations of states and political subdivisions 236.7 4.3 1.2 239.8 Corporate bonds 1,808.7 7.5 58.7 1,757.5 Commercial mortgage-backed securities 205.3 0.7 3.2 202.8 Residential mortgage-backed securities 413.1 3.4 5.7 410.8 Asset-backed securities 173.6 0.4 1.2 172.8 Collateralized loan obligations 226.7 0.5 3.5 223.7 Total fixed maturities $ 3,529.1 $ 17.5 $ 86.2 $ 3,460.4 Contractual Maturity The amortized cost and fair values of fixed maturity investments as of September 30, 2019 , by contractual maturity, were as follows: (in millions) Amortized Fair Due in one year or less $ 242.5 $ 242.2 Due after one year through five years 1,584.3 1,577.1 Due after five years through ten years 669.5 683.5 Thereafter 105.8 111.9 Structured securities 1,114.5 1,130.9 Total $ 3,716.6 $ 3,745.6 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 September 30, 2019 and December 31, 2018 were as follows: September 30, 2019 (in millions) Carrying Unfunded Investment Type Hedge funds $ 119.3 $ — Private equity 263.9 94.2 Long only funds 112.5 — Other 4.3 — Total other investments $ 500.0 $ 94.2 December 31, 2018 (in millions) Carrying Unfunded Investment Type Hedge funds $ 120.6 $ — Private equity 211.8 120.5 Long only funds 153.0 — Other 4.4 — Total other investments $ 489.8 $ 120.5 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. • Long only funds: Our long only funds include a fund that primarily owns international stocks and funds that primarily own investment-grade corporate and sovereign fixed income securities. • 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: September 30, 2019 Less Than One Year One Year or Greater Total (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed maturities U.S. Governments $ 75.0 $ 0.4 $ 18.8 $ 0.1 $ 93.8 $ 0.5 Foreign Governments 108.2 2.1 9.6 0.2 117.8 2.3 Obligations of states and political subdivisions 1.1 — 2.4 0.1 3.5 0.1 Corporate bonds 355.6 32.3 100.0 6.9 455.6 39.2 Commercial mortgage-backed securities 53.8 0.2 5.3 0.1 59.1 0.3 Residential mortgage-backed securities 57.1 0.4 43.9 0.5 101.0 0.9 Asset-backed securities 17.9 0.2 19.4 0.1 37.3 0.3 Collateralized loan obligations 138.8 1.8 54.1 0.2 192.9 2.0 Total fixed maturities $ 807.5 $ 37.4 $ 253.5 $ 8.2 $ 1,061.0 $ 45.6 December 31, 2018 Less Than One Year One Year or Greater Total (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed maturities U.S. Governments $ 28.2 $ 0.2 $ 173.0 $ 4.7 $ 201.2 $ 4.9 Foreign Governments 73.4 3.6 125.0 4.2 198.4 7.8 Obligations of states and political subdivisions 53.3 0.6 25.3 0.6 78.6 1.2 Corporate bonds 964.3 45.7 440.8 13.0 1,405.1 58.7 Commercial mortgage-backed securities 48.5 0.6 90.6 2.6 139.1 3.2 Residential mortgage-backed securities 63.5 0.7 176.1 5.0 239.6 5.7 Asset-backed securities 73.6 0.6 64.2 0.6 137.8 1.2 Collateralized loan obligations 209.5 3.3 10.3 0.2 219.8 3.5 Total fixed maturities $ 1,514.3 $ 55.3 $ 1,105.3 $ 30.9 $ 2,619.6 $ 86.2 We regularly evaluate our investments for other-than-temporary impairment. For fixed maturity securities, the evaluation for a credit loss is generally based on the present value of expected cash flows of the security as compared to the amortized book value. For structured securities, frequency and severity of loss inputs are used in projecting future cash flows of the securities. Loss frequency is measured as the credit default rate, which includes such factors as loan-to-value ratios and credit scores of borrowers. We also recognize other-than-temporary losses on fixed maturity securities that we intend to sell. Effective January 1, 2018, the Company adopted ASU 2016-01. As a result, changes in the fair value of equity securities are recognized in net realized investment gains in the Consolidated Statements of (Loss) Income. We hold a total of 9,615 securities, of which 1,219 were in an unrealized loss position for less than one year and 424 were in an unrealized loss position for a period one year or greater as of September 30, 2019 . Unrealized losses greater than twelve months on fixed maturities were the result of a number of factors, including increased credit spreads, foreign currency fluctuations and higher market yields relative to the date the securities were purchased, and for structured securities, by the performance of the underlying collateral, as well. In considering whether or not an investment is other-than-temporarily impaired, we also considered that we do not intend to sell the investments and it is unlikely that we will be required to sell the investments before recovery of their amortized cost bases, which may be maturity. We do not consider these investments to be other-than-temporarily impaired at September 30, 2019 . We recognized other-than-temporary losses on our fixed maturities portfolio as follows: For the Three Months Ended For the Nine Months Ended (in millions) 2019 2018 2019 2018 Other-than-temporary impairment: Corporate bonds $ (5.0 ) $ — $ (11.8 ) $ (1.9 ) Other-than-temporary impairment losses $ (5.0 ) $ — $ (11.8 ) $ (1.9 ) Net Realized Investment Gains and Losses The following table presents our gross realized investment gains (losses): For the Three Months Ended For the Nine Months Ended (in millions) 2019 2018 2019 2018 Realized gains on fixed maturities and other Fixed maturities $ 3.7 $ 4.6 $ 13.0 $ 15.8 Other investments 7.5 7.4 21.9 34.7 Other Assets and Short Term Investments — 0.2 $ — 0.2 11.2 12.2 34.9 50.7 Realized losses on fixed maturities and other Fixed maturities (1.6 ) (2.8 ) (8.7 ) (14.2 ) Other investments (8.4 ) (8.8 ) (21.8 ) (34.4 ) Other-than-temporary impairment losses on fixed maturities (5.0 ) — (11.8 ) (1.9 ) (15.0 ) (11.6 ) (42.3 ) (50.5 ) Equity securities Net realized gains on equity securities 6.4 9.1 7.7 30.9 Change in unrealized (losses) gains on equity securities held at the end of the period (8.8 ) 4.5 58.0 (22.1 ) Net realized (losses) gains on equity securities (2.4 ) 13.6 65.7 8.8 Net realized investment (losses) gains before income taxes (6.2 ) 14.2 58.3 9.0 Income tax benefit (provision) 0.3 (3.3 ) (11.9 ) (2.8 ) Net realized investment (losses) gains net of income taxes $ (5.9 ) $ 10.9 $ 46.4 $ 6.2 The cost of securities sold is based on the specific identification method. Changes in unrealized gains (losses) related to investments are summarized as follows: For the Three Months Ended For the Nine Months Ended (in millions) 2019 2018 2019 2018 Change in unrealized gains (losses) Fixed maturities $ (3.8 ) $ (4.3 ) $ 95.3 $ (63.2 ) Other investments — — 4.4 0.1 Other and short-term investments (0.8 ) (0.5 ) (0.7 ) (0.5 ) Net unrealized investment gains (losses) before income taxes (4.6 ) (4.8 ) 99.0 (63.6 ) Income tax (provision) benefit 0.4 1.4 (16.1 ) 10.5 Net unrealized investment gains (losses), net of income taxes $ (4.2 ) $ (3.4 ) $ 82.9 $ (53.1 ) Foreign Currency Exchange Forward Contracts We entered into foreign currency exchange forward contracts to manage operational currency exposure on our Canadian dollar investment portfolio, 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.” The 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 September 30, 2019 and December 31, 2018 was as follows: (in millions) September 30, 2019 December 31, 2018 Operational currency exposure $ (1.4 ) $ 4.4 Asset manager investment exposure 0.9 (0.3 ) Total return strategy — (1.5 ) Total $ (0.5 ) $ 2.6 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 Nine Months Ended (in millions) 2019 2018 2019 2018 Realized gains Operational currency exposure $ 1.3 $ 0.4 $ 2.2 $ 6.4 Asset manager investment exposure 1.8 1.4 3.1 14.4 Total return strategy 6.5 5.6 18.8 12.5 Gross realized investment gains 9.6 7.4 24.1 33.3 Realized losses Operational currency exposure (3.2 ) (2.7 ) (7.8 ) (7.0 ) Asset manager investment exposure (0.1 ) (0.9 ) (0.6 ) (12.5 ) Total return strategy (7.1 ) (5.2 ) (15.7 ) (13.3 ) Gross realized investment losses (10.4 ) (8.8 ) (24.1 ) (32.8 ) Net realized investment (losses) gains on foreign currency exchange forward contracts $ (0.8 ) $ (1.4 ) $ — $ 0.5 Regulatory Deposits, Pledged Securities and Letters of Credit We are required to maintain assets on deposit with various regulatory authorities to support our insurance and reinsurance operations. We maintain assets pledged as collateral in support of irrevocable letters of credit issued under the terms of certain reinsurance agreements for reported loss and loss expense reserves. The following table presents our components of restricted assets at September 30: (in millions) September 30, 2019 September 30, 2018 Securities on deposit for regulatory and other purposes $ 198.8 $ 180.6 Securities pledged as collateral for letters of credit 129.5 76.5 Securities and cash on deposit supporting Lloyd’s business 403.6 418.4 Total restricted investments $ 731.9 $ 675.5 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 September 30, 2019 and December 31,2018. 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. Transfers Between Level 1 and Level 2 Securities: There were no transfers between Level 1 and Level 2 securities and one transfer from Level 2 to Level 3 securities during the nine months ended September 30, 2019 . 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) September 30, 2019 Level 1 (a) Level 2 (b) Level 3 (c) Fixed maturities U.S. Governments $ 328.3 $ 323.0 $ 5.3 $ — Foreign Governments 264.5 — 264.5 — Obligations of states and political subdivisions 160.1 — 160.1 — Corporate bonds 1,861.8 1.2 1,853.8 6.8 Commercial mortgage-backed securities 219.0 — 219.0 — Residential mortgage-backed securities 521.3 — 521.3 — Asset-backed securities 167.0 — 167.0 — Collateralized loan obligations 223.6 — 223.6 — Total fixed maturities 3,745.6 324.2 3,414.6 6.8 Equity securities 400.6 392.1 8.5 Other investments 405.9 — 405.9 — Short-term investments 480.8 449.3 31.5 — $ 5,032.9 $ 1,165.6 $ 3,852.0 $ 15.3 (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, 2018 Level 1 (a) Level 2 (b) Level 3 (c) Fixed maturities U.S. Governments $ 236.2 $ 226.7 $ 9.5 $ — Foreign Governments 216.8 — 216.8 — Obligations of states and political subdivisions 239.8 — 239.8 — Corporate bonds 1,757.5 — 1,755.3 2.2 Commercial mortgage-backed securities 202.8 — 202.8 — Residential mortgage-backed securities 410.8 — 410.8 — Asset-backed securities 172.8 — 172.8 — Collateralized loan obligations 223.7 — 223.7 — Total fixed maturities 3,460.4 226.7 3,231.5 2.2 Equity securities 354.5 346.3 — 8.2 Other investments 114.4 — 114.4 — Short-term investments 482.3 453.9 28.4 — $ 4,411.6 $ 1,026.9 $ 3,374.3 $ 10.4 (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, 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 — 0.3 0.3 Included in other comprehensive income (0.5 ) — (0.5 ) Purchases, issuances, sales, and settlements: Purchases 1.9 — 1.9 Issuances — — — Sales (0.3 ) — (0.3 ) Settlements — — — Ending balance, September 30, 2019 $ 6.8 $ 8.5 $ 15.3 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 September 30, 2019 $ — $ — $ — (in millions) Credit Financial Equity Total Beginning balance, January 1, 2018 $ 1.9 $ 2.3 $ 4.2 Transfers into Level 3 — — — Transfers out of Level 3 — — — Total gains or losses (realized/unrealized): Included in net income — 0.2 0.2 Included in other comprehensive loss 0.3 — 0.3 Purchases, issuances, sales, and settlements: Purchases — 7.3 7.3 Issuances — — — Sales — (1.6 ) (1.6 ) Settlements — — — Ending balance, December 31, 2018 $ 2.2 $ 8.2 $ 10.4 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 December 31, 2018 $ — $ — $ — At September 30, 2019 and December 31, 2018 , 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.

Leases

Leases	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Leases	Leases We adopted ASU 2016-02, "Leases" on January 1, 2019, which resulted in the recognition of operating leases on the balance sheet beginning in 2019 and forward. See Note 2, “Recently Issued Accounting Pronouncements,” for additional information on the adoption of the ASU. We determine if a contract contains a lease at inception and recognize operating lease right-of-use assets and operating lease liabilities based on the present value of the future minimum lease payments at the commencement date. As our leases do not provide an implicit interest rate, we use our incremental borrowing rate based on the information available at the commencement date to determine the present value of future payments. Lease agreements have lease and non-lease components. We account for these components separately, therefore our operating lease right-of-use asset and operating lease liabilities represent base rent only. Lease expense is recognized on a straight-line basis over the lease term. Our operating lease obligations are for office facilities, corporate housing, and equipment, including corporate aviation. Our leases have remaining lease terms of less than 1 year to 14 years , some of which include options to extend the leases. Expenses associated with leases totaled $5.0 million and $17.1 million for the three and nine months ended September 30, 2019 , respectively, as compared to $5.2 million and $18.2 million for the three and nine months ended September 30, 2018 . The components of lease expense and other lease information as of and during the nine months ended September 30, 2019 are as follows: (in millions) September 30, 2019 Operating leases right-of-use assets $ 108.6 Operating lease liabilities 120.2 Operating lease weighted-average remaining lease term 10.31 Operating lease weighted-average discount rate 3.93 % (in millions) For the Three Months Ended For the Nine Months Ended September 30, 2019 Operating lease costs $ 5.1 $ 15.3 Variable lease costs — 2.1 Sublease income (0.1 ) (0.3 ) Total lease costs $ 5.0 $ 17.1 Operating cash flows from operating leases (fixed payments) $ 14.1 Operating cash flows from operating leases (liability reduction) 11.5 Our finance leases and short-term leases as of September 30, 2019 were not material. Future minimum lease payments under operating leases as of September 30, 2019 and December 31, 2018 were as follows: (in millions) September 30, 2019 December 31, 2018 2019 $ 4.7 $ 18.7 2020 18.6 18.6 2021 17.5 17.5 2022 14.8 14.7 2023 12.3 12.3 Thereafter 79.4 80.1 Total future minimum lease payments $ 147.3 $ 161.9 Future lease obligations (0.5 ) Less imputed interest (26.6 ) N/A Total operating lease liability $ 120.2 N/A We have certain investment properties that we lease to independent, third parties. These properties consist of an office building that is currently leased through August 2026 and three condominiums that are leased on a short-term basis. The carrying value of these assets are included in "Other assets" on our Consolidated Balance Sheet. Income for these leased properties was $0.7 million for each of the three months ended September 30, 2019 and 2018, and $2.2 million for each of the nine months ended September 30, 2019 and 2018. Income for these leased properties are included in "Fee and other income" on our Consolidated Statements of (Loss) Income.

Reserves for Losses and Loss Ad

Reserves for Losses and Loss Adjustment Expenses	9 Months Ended
	Sep. 30, 2019
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 Nine Months Ended (in millions) 2019 2018 Net reserves beginning of the year $ 2,562.9 $ 2,488.0 Net reserves acquired — 49.4 Add: Losses and LAE incurred during current calendar year, net of reinsurance: Current accident year 799.9 764.3 Prior accident years 61.6 (4.1 ) Losses and LAE incurred during calendar year, net of reinsurance 861.5 760.2 Deduct: Losses and LAE payments made during current calendar year, net of reinsurance: Current accident year 163.6 223.2 Prior accident years 615.8 469.0 Losses and LAE payments made during current calendar year, net of reinsurance: 779.4 692.2 Change in participation interest (1) (14.4 ) (29.4 ) Foreign exchange adjustments (26.3 ) (20.8 ) Net reserves - end of period 2,604.3 2,555.2 Add: Reinsurance recoverables on unpaid losses and LAE, end of period 2,238.2 1,736.5 Gross reserves - end of period $ 4,842.5 $ 4,291.7 (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. The impact from the unfavorable (favorable) development of prior accident years’ loss and LAE reserves on each reporting segment is presented below: For the Nine Months Ended (in millions) 2019 2018 U.S. Operations $ (9.8 ) $ (14.8 ) International Operations 69.5 (0.8 ) Run-off Lines 1.9 11.5 Total unfavorable (favorable) prior-year development $ 61.6 $ (4.1 ) The following describes the primary factors behind each segment’s prior accident year reserve development for the nine months ended September 30, 2019 and 2018 : Nine months ended September 30, 2019 : • U.S. Operations: Favorable development in general liability and specialty lines, partially offset by unfavorable development in professional and property lines. • International Operations: Unfavorable development was primarily concentrated in liability and professional lines. The charges impacted our Bermuda casualty and professional divisions, and to a lesser extent our European and Syndicate 1200 operations. The charges stemmed from public utility business in our Bermuda casualty division, which we previously exited, as well as updated estimates on a number of other claims based on new information received in the second and third quarters of 2019. As it relates to Europe, the adverse development primarily related to certain cover-holders whose contracts were previously terminated or where aggressive remedial underwriting actions have been taken. As it relates to Syndicate 1200, the adverse development largely related to businesses that we have previously exited or where aggressive remedial underwriting actions have been taken. The International Operations unfavorable development includes $68.7 million recognized during the second and third quarters of 2019. This unfavorable development was primarily due to obtaining additional information on several individual claims, including investigations regarding causes of the incidents leading to the losses, reports provided by outside counsel, audits of the underlying losses and recent court decisions, settlements and jury awards. The result was an increase in the number of claims with the potential for underlying losses to reach our attachment point, particularly within our Bermuda Operations. The unfavorable development in the second and third quarters of 2019 was also attributable to the results of ongoing 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. Adverse development in Syndicate 1200 related to large claims involving the marine and energy and liability divisions. Losses on small and medium enterprise package business were also higher than expected. • Run-off Lines: Unfavorable development in other run-off lines, partially offset by favorable development in risk management workers compensation. Nine months ended September 30, 2018 : • U.S. Operations: Favorable development in certain liability and specialty lines, partially offset by adverse charges in older accident years relating to professional lines. • International Operations: Favorable development in property reinsurance and professional lines, partially offset by unfavorable movements in property insurance in our Europe and Syndicate 1200 divisions. • Run-off Lines: Unfavorable development in liability lines as well as asbestos and environmental. In the opinion of management, our reserves represent the best estimate of our ultimate liabilities, based on currently known facts, current law, current technology and assumptions considered reasonable 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.

Disclosures about Fair Value of

Disclosures about Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2019
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 September 30, 2019 and December 31, 2018 , 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 September 30, 2019 and December 31, 2018. 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: September 30, 2019 December 31, 2018 (in millions) Carrying Fair Carrying Fair Junior subordinated debentures: Trust preferred debentures $ 172.7 $ 160.7 $ 172.7 $ 163.2 Subordinated debentures 84.6 85.4 84.3 85.0 Total junior subordinated debentures 257.3 246.1 257.0 248.2 Senior unsecured fixed rate notes 139.9 143.4 139.8 139.5 Floating rate loan stock 56.4 52.5 57.8 54.5 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) September 30, 2019 Level 1 (a) Level 2 (b) Level 3 (c) Junior subordinated debentures: Trust preferred debentures $ 160.7 $ — $ 160.7 $ — Subordinated debentures 85.4 — 85.4 — Total junior subordinated debentures 246.1 — 246.1 — Senior unsecured fixed rate notes 143.4 143.4 — — Floating rate loan stock 52.5 — 52.5 — 688.1 143.4 544.7 — (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, 2018 Level 1 (a) Level 2 (b) Level 3 (c) Junior subordinated debentures: Trust preferred debentures $ 163.2 $ — $ 163.2 $ — Subordinated debentures 85.0 — 85.0 — Total junior subordinated debentures 248.2 — 248.2 — Senior unsecured fixed rate notes 139.8 139.8 — — Floating rate loan stock 57.8 — 57.8 — 445.8 139.8 306.0 — (a) Quoted prices in active markets for identical assets (b) Significant other observable inputs (c) Significant unobservable inputs

Shareholders' Equity

Shareholders' Equity	9 Months Ended
	Sep. 30, 2019
Equity [Abstract]
Shareholders' Equity	Shareholders’ Equity On August 6, 2019, our Board of Directors declared a quarterly cash dividend in the amount of $0.31 on each share of common stock outstanding. On September 13, 2019, we paid $10.9 million to our shareholders of record on August 30, 2019. 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 $10.8 million to our shareholders of record on June 7, 2019 . On May 8, 2018, our Board of Directors declared a quarterly cash dividend in the amount of $0.27 on each share of common stock outstanding. On June 15, 2018, we paid $9.4 million to our shareholders of record on June 1, 2018. On February 20, 2018, the Board of Directors declared a 15% stock dividend, payable March 21, 2018 to all shareholders of record at the close of business on March 7, 2018. As a result of the stock dividend, 4,397,520 additional shares were issued. Cash was paid in lieu of fractional shares of our common shares. Excluding repurchased shares, all references to common shares and related per share amounts in this document and related disclosures have been adjusted to reflect the stock dividend for all periods presented. 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 September 30, 2019 , 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 nine months ended September 30, 2019 .

Accumulated Other Comprehensive

Accumulated Other Comprehensive (Loss) Income	9 Months Ended
	Sep. 30, 2019
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 nine months ended September 30, 2019 , and 2018 is presented below: (in millions) Foreign Currency Translation Adjustments Unrealized Defined Benefit Pension Plans Total Balance, January 1, 2019 $ (22.4 ) $ (49.0 ) $ (6.7 ) $ (78.1 ) Other comprehensive (loss) income before reclassifications (0.1 ) 76.2 — 76.1 Amounts reclassified from accumulated other comprehensive income — 6.7 — 6.7 Net current-period other comprehensive (loss) income (0.1 ) 82.9 — 82.8 Balance at September 30, 2019 $ (22.5 ) $ 33.9 $ (6.7 ) $ 4.7 (in millions) Foreign Currency Translation Adjustments Unrealized Defined Benefit Pension Plans Total Balance, January 1, 2018 $ (19.0 ) $ 121.9 $ (6.3 ) $ 96.6 Other comprehensive loss before reclassifications (4.8 ) (53.4 ) — (58.2 ) Amounts reclassified from accumulated other comprehensive loss — 0.3 — 0.3 Net current-period other comprehensive loss (4.8 ) (53.1 ) — (57.9 ) Cumulative effect of adoption of ASU 2016-01 — (117.5 ) — (117.5 ) Cumulative effect of adoption of ASU 2018-02 — 22.1 (1.4 ) 20.7 Balance at September 30, 2018 $ (23.8 ) $ (26.6 ) $ (7.7 ) $ (58.1 ) 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 September 30, For the Nine Months Ended September 30, (in millions) 2019 2018 2019 2018 Unrealized gains and losses on securities: Net realized investment loss (gains) $ 2.8 $ (2.4 ) $ 7.7 $ 0.2 (Benefit) provision for income taxes (0.3 ) 0.3 (1.0 ) 0.1 Net of taxes $ 2.5 $ (2.1 ) $ 6.7 $ 0.3

Net (Loss) Income Per Common Sh

Net (Loss) Income Per Common Share	9 Months Ended
	Sep. 30, 2019
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 Nine Months Ended (in millions, except number of shares and per share amounts) 2019 2018 2019 2018 Net (loss) income $ (25.1 ) $ 40.6 $ 94.9 $ 107.2 Weighted average common shares outstanding - basic 34,299,999 33,956,695 34,161,016 33,921,632 Effect of dilutive securities: Equity compensation awards — 699,633 608,606 767,211 Weighted average common shares outstanding - diluted 34,299,999 34,656,328 34,769,622 34,688,843 Net (loss) income per common share: Basic $ (0.73 ) $ 1.20 $ 2.78 $ 3.16 Diluted $ (0.73 ) $ 1.17 $ 2.73 $ 3.09 Excluded from the weighted average common shares outstanding calculation at September 30, 2019 and 2018 are 11,315,889 shares and 11,285,996 shares, respectively, which are held as treasury shares. The shares are excluded as of their repurchase date. For the three months ended September 30, 2019 , 489,376 shares were not included in the calculation of diluted net loss per common share as these instruments were anti-dilutive . For the nine months ended September 30, 2019 , 2,331 shares were not included in the calculation of diluted net income per common share as these instruments were anti-dilutive . For the three and nine months ended September 30, 2018 , there were no equity compensation awards with an anti-dilutive effect.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	9 Months Ended
	Sep. 30, 2019
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 Nine Months Ended September 30, (in millions) 2019 2018 Senior unsecured fixed rate notes $ 7.0 $ 7.0 Junior subordinated debentures 12.3 11.2 Other indebtedness 7.2 4.9 Total interest paid $ 26.5 $ 23.1 Income taxes paid 4.8 18.1 Income taxes recovered (0.1 ) — Income taxes paid, net $ 4.7 $ 18.1

Share-based Compensation

Share-based Compensation	9 Months Ended
	Sep. 30, 2019
Share-based Payment Arrangement [Abstract]
Share-based Compensation	Share-based Compensation The fair value method of accounting is used for share-based compensation plans. Under the fair value method, compensation cost is measured based on the fair value of the award at the measurement date and recognized over the requisite service period. We use the Black-Scholes model to estimate the fair values on the measurement date for share options and share appreciation rights (“SARs”). The Black-Scholes model uses several assumptions to value a share award. The risk-free rate of return assumption is based on the five -year U.S. Treasury constant maturity rate on the measurement date. The expected dividend yield is based on our history and expected dividend payouts. The expected award life is based upon the average holding period over the history of the incentive plan. The expected volatility assumption is based on the historical change in our stock price over the previous five years preceding the measurement date. The following table summarizes the assumptions we used for the nine months ended September 30, 2019 and 2018 : For the Nine Months Ended September 30, 2019 2018 Risk-free rate of return 1.66% 2.96% Expected dividend yields 1.76% 1.84% Expected award life (years) 4.50 4.49 Expected volatility 18.73% 17.82% 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 September 30, 2019 and changes during the nine months then ended is as follows: Shares Weighted-Average Outstanding at January 1, 2019 897,005 $ 46.92 Granted 209,557 $ 68.65 Vested and issued (403,316 ) $ 35.74 Expired or forfeited (59,635 ) $ 55.41 Outstanding at September 30, 2019 643,611 $ 59.93 The restricted shares vest over one to four years . Expense recognized under this plan for the restricted shares was $3.2 million and $10.5 million for the three and nine months ended September 30, 2019 respectively, as compared to $2.6 million and $10.9 million for the three and nine months ended September 30, 2018 , respectively. Compensation expense for all share-based compensation awards is included in “Underwriting, acquisition and insurance expenses” in the accompanying Consolidated Statements of (Loss) Income. As of September 30, 2019 , there was $28.0 million of total unrecognized compensation cost related to restricted share compensation arrangements granted by Argo Group. Stock-Settled SARs A summary of stock-settled SARs activity as of September 30, 2019 and changes during the nine months then ended is as follows: Shares Weighted-Average Outstanding at January 1, 2019 810,759 $ 33.88 Exercised (148,729 ) $ 34.71 Expired or forfeited (7,167 ) $ 37.85 Outstanding at September 30, 2019 654,863 $ 33.68 As of September 30, 2019 , 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 months ending September 30, 2019 for stock-settled SARs. Expense recognized for the nine months ended September 30, 2019 for the stock-settled SARs was $0.4 million . Expense recognized for the stock-settled SARs was $0.4 million and $1.8 million for the three and nine months ended September 30, 2018 , respectively. As of September 30, 2019 , there was no unrecognized compensation cost related to stock-settled SARs outstanding. Cash-Settled SARs A summary of cash-settled SARs activity as of September 30, 2019 and changes during the nine months then ended is as follows: Shares Weighted-Average Outstanding at January 1, 2019 58,428 $ 30.71 Exercised (48,722 ) $ 30.34 Expired or forfeited (1,193 ) $ 19.37 Outstanding at September 30, 2019 8,513 $ 34.39 As of September 30, 2019 , all the cash-settled SARs are fully vested. Upon exercise of the cash-settled SARs, the employee is entitled to receive cash payment for the appreciation in the value of our common stock over the exercise price. We account for the cash-settled SARs as liability awards, which require the awards to be revalued at each reporting period. Expense recognized for the cash-settled SARs was $(0.1) million and $0.5 million for the three and nine months ended September 30, 2019 respectively, as compared to $0.5 million and $1.2 million for the three and nine months ended September 30, 2018 . As of September 30, 2019 , respectively, there was no unrecognized compensation cost related to cash-settled SARs outstanding.

Underwriting, Acquisition and I

Underwriting, Acquisition and Insurance Expenses	9 Months Ended
	Sep. 30, 2019
Underwriting Acquisition And Insurance Expenses [Abstract]
Underwriting, Acquisition and Insurance Expenses	Underwriting, Acquisition and Insurance Expenses The components of our underwriting, acquisition and insurance expenses are detailed in the table below. General expenses include certain costs associated with our holding company. For the Three Months Ended For the Nine Months Ended (in millions) 2019 2018 2019 2018 Commissions $ 58.0 $ 88.0 $ 178.0 $ 212.7 General expenses 92.9 83.2 281.0 261.6 Premium taxes, boards and bureaus 10.8 9.8 27.0 27.2 161.7 181.0 486.0 501.5 Net deferral of policy acquisition costs 6.0 (13.0 ) 11.3 (16.5 ) Total underwriting, acquisition and insurance expenses $ 167.7 $ 168.0 $ 497.3 $ 485.0 General expenses in the table above include $3.7 million and $11.7 million of expenses associated with proxy solicitation and related activities for the three and nine months ended September 30, 2019 , respectively. Given the unique and non-recurring nature of the events that gave rise to these expenses, these costs are not included in the calculation of our expense and combined ratios. There were no comparable costs incurred for the three and nine months ended September 30, 2018 .

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2019
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. Eight 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 nine months ended September 30, 2019 and 2018 , pre-tax income (loss) attributable to our operations and the corresponding operations’ effective tax rates were as follows: For the Three Months Ended September 30, 2019 2018 (in millions) Pre-Tax Effective Pre-Tax Effective Bermuda $ (7.8 ) — % $ 6.4 — % United States 7.7 16.4 % 34.8 13.4 % United Kingdom (17.9 ) 13.1 % 3.5 (5.0 )% Belgium (0.1 ) 28.6 % — (1) 30.8 % Brazil 1.2 — % 0.4 — % United Arab Emirates — (1) — % 0.2 — % Ireland — (1) — % (0.1 ) — % Italy (3.6 ) — % (1.8 ) — % Malta (5.6 ) — % 1.8 — % Luxembourg — — % — (1) — % Switzerland (0.1 ) 1.0 % 0.1 21.2 % Pre-tax income (loss) $ (26.2 ) 4.1 % $ 45.3 10.2 % (1) Pre-tax income (loss) for the respective year was less than $0.1 million . For the Nine Months Ended September 30, 2019 2018 (in millions) Pre-Tax Effective Pre-Tax Effective Bermuda $ 39.1 — % $ (1.8 ) — % United States 99.5 14.6 % 114.2 15.6 % United Kingdom (30.3 ) 19.2 % 16.3 12.3 % Belgium (0.4 ) 29.4 % — (1) 33.3 % Brazil 5.0 — % (1.0 ) — % United Arab Emirates 0.3 — % 0.5 — % Ireland (0.1 ) — % (0.2 ) — % Italy (4.1 ) — % (2.9 ) — % Malta (5.4 ) — % 2.2 — % Luxembourg — — % — (1) — % Switzerland (0.1 ) 0.9 % 0.1 21.2 % Pre-tax income $ 103.5 8.4 % $ 127.4 15.8 % (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 Nine Months Ended (in millions) 2019 2018 2019 2018 Income tax provision at expected rate $ (4.1 ) $ 8.4 $ 14.4 $ 26.8 Tax effect of: Nontaxable investment income (0.4 ) (0.4 ) (1.1 ) (1.4 ) Foreign exchange adjustments 0.7 (1.0 ) 1.3 (1.2 ) Withholding taxes — 0.2 0.2 0.5 Prior period adjustments — (1) (2.2 ) (1.8 ) (2.1 ) Change in valuation allowance 2.2 (0.2 ) 1.6 (3.6 ) Other 0.5 (0.1 ) (6.0 ) 1.2 Income tax provision $ (1.1 ) $ 4.7 $ 8.6 $ 20.2 (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 US property and casualty insurers two years for net operating losses and for all our US subsidiaries three years for capital losses. If a company determines that any of its deferred tax assets will not result in future tax benefits, a valuation allowance must be established for the portion of these assets that are not expected to be realized. The net change in valuation allowance for deferred tax assets was an increase of $1.6 million in 2019 relating 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 September 30, 2019 and 2018 . 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 2017.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Argo Group’s subsidiaries are parties to legal actions incidental to their business. Based on the opinion of legal counsel, management believes that the resolution of these matters will not materially affect our financial condition or results of operations. We have contractual commitments to invest up to $94.2 million related to our limited partnership investments at September 30, 2019 . 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	9 Months Ended
	Sep. 30, 2019
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 Nine Months Ended (in millions) 2019 2018 2019 2018 Revenue: Earned premiums U.S. Operations $ 290.8 $ 278.3 $ 848.6 $ 807.6 International Operations 160.7 168.5 455.0 471.4 Run-off Lines — 0.1 0.1 0.3 Total earned premiums 451.5 446.9 1,303.7 1,279.3 Net investment income U.S. Operations 27.4 21.4 80.1 64.7 International Operations 10.7 8.4 31.3 25.6 Run-off Lines 1.7 2.1 4.4 6.3 Corporate and Other 0.4 2.6 1.1 7.1 Total net investment income 40.2 34.5 116.9 103.7 Fee and other income 1.9 3.3 6.3 7.2 Net realized investment (losses) gains (6.2 ) 14.2 58.3 9.0 Total revenue $ 487.4 $ 498.9 $ 1,485.2 $ 1,399.2 For the Three Months Ended For the Nine Months Ended (in millions) 2019 2018 2019 2018 Income (loss) before income taxes U.S. Operations $ 42.2 $ 50.3 $ 138.3 $ 126.8 International Operations (52.9 ) (1.2 ) (57.7 ) 34.9 Run-off Lines 0.7 (7.6 ) 0.2 (8.6 ) Total segment (loss) income before taxes (10.0 ) 41.5 80.8 153.1 Corporate and Other (7.9 ) (12.1 ) (30.1 ) (37.0 ) Net realized investment and other (losses) gains (6.2 ) 14.2 58.3 9.0 Foreign currency exchange gains 1.6 1.7 6.2 2.3 Other corporate expenses (3.7 ) — (11.7 ) — Total (loss) income before income taxes $ (26.2 ) $ 45.3 $ 103.5 $ 127.4 The table below presents earned premiums by geographic location for the three and nine months ended September 30, 2019 and 2018 . For this disclosure, we determine geographic location by the country of domicile of our subsidiaries that underwrite the business and not by the location of insureds or reinsureds from whom the business was generated. For the Three Months Ended For the Nine Months Ended (in millions) 2019 2018 2019 2018 United States $ 289.6 $ 276.5 $ 845.4 $ 803.7 United Kingdom 101.9 117.2 295.6 333.3 Bermuda 24.3 23.3 60.1 64.7 Malta 21.3 18.2 62.3 39.6 All other jurisdictions 14.4 11.7 40.3 38.0 Total earned premiums $ 451.5 $ 446.9 $ 1,303.7 $ 1,279.3 The following table represents identifiable assets: (in millions) September 30, 2019 December 31, 2018 U.S. Operations $ 5,477.4 $ 4,707.8 International Operations 4,403.8 3,984.7 Run-off Lines 375.9 444.8 Corporate and Other 188.7 420.9 Total $ 10,445.8 $ 9,558.2 Included in total assets at September 30, 2019 and December 31, 2018 are $884.6 million and $880.4 million , respectively, in assets associated with trade capital providers.

Senior Unsecured Fixed Rate Not

Senior Unsecured Fixed Rate Notes	9 Months Ended
	Sep. 30, 2019
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 ASC 835-30, “Interest-Imputation of Interest” we present the unamortized debt issuance costs in the balance sheet as a direct deduction from the carrying value of the debt liability. At September 30, 2019 and December 31, 2018 , the Notes consisted of the following: (in millions) September 30, 2019 December 31, 2018 Senior unsecured fixed rate notes Principal $ 143.8 $ 143.8 Less: unamortized debt issuance costs (3.9 ) (4.0 ) Senior unsecured fixed rate notes, less unamortized debt issuance costs $ 139.9 $ 139.8 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 September 30, 2019 and December 31, 2018 and for the three and nine months ended September 30, 2019 and 2018, of the Parent Guarantor and the Subsidiary Issuer. The Subsidiary Issuer is an indirect wholly-owned subsidiary of the Parent Guarantor. Investments in subsidiaries are accounted for by the Parent Guarantor under the equity method for purposes of the supplemental consolidating presentation. Earnings of subsidiaries are reflected in the Parent Guarantor’s investment accounts and earnings. The Parent Guarantor fully and unconditionally guarantees certain of the debt of the Subsidiary Issuer. Condensed consolidating financial information of the Subsidiary Issuer is presented on a consolidated basis and consists principally of the net assets, results of operations and cash flows of operating insurance company subsidiaries. CONDENSED CONSOLIDATING BALANCE SHEET SEPTEMBER 30, 2019 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries Consolidating Total Assets Investments $ 0.3 $ 3,416.4 $ 1,710.3 $ — $ 5,127.0 Cash 3.2 43.1 98.8 — 145.1 Accrued investment income — 19.8 7.9 — 27.7 Premiums receivable — 261.6 478.7 — 740.3 Reinsurance recoverables — 1,661.9 1,211.9 — 2,873.8 Goodwill and other intangible assets, net 40.9 123.5 104.8 — 269.2 Current income taxes receivable, net — — 0.2 — 0.2 Deferred acquisition costs, net — 92.6 66.9 — 159.5 Ceded unearned premiums — 294.9 308.9 — 603.8 Operating lease right-of-use assets 7.8 71.9 28.9 — 108.6 Other assets 10.5 170.2 209.9 — 390.6 Intercompany note receivable — 55.9 (55.9 ) — — Investments in subsidiaries 2,053.6 — — (2,053.6 ) — Total assets $ 2,116.3 $ 6,211.8 $ 4,171.3 $ (2,053.6 ) $ 10,445.8 Liabilities and Shareholders' Equity Reserves for losses and loss adjustment expenses $ — $ 2,944.7 $ 1,897.8 $ — $ 4,842.5 Unearned premiums — 896.8 598.7 — 1,495.5 Funds held and ceded reinsurance payable, net — 665.4 546.4 — 1,211.8 Debt 153.4 284.2 141.0 — 578.6 Deferred tax liabilities, net — 25.3 (5.4 ) — 19.9 Accrued underwriting expenses and other liabilities 11.0 125.6 147.3 — 283.9 Operating lease liabilities 8.0 81.5 30.7 — 120.2 Due to (from) affiliates 50.5 (4.2 ) 4.2 (50.5 ) — Total liabilities 222.9 5,019.3 3,360.7 (50.5 ) 8,552.4 Total shareholders' equity 1,893.4 1,192.5 810.6 (2,003.1 ) 1,893.4 Total liabilities and shareholders' equity $ 2,116.3 $ 6,211.8 $ 4,171.3 $ (2,053.6 ) $ 10,445.8 (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 BALANCE SHEET DECEMBER 31, 2018 (in millions) Argo Group Argo Group US, Inc. Other Subsidiaries Consolidating Total Assets Investments $ 3.8 $ 3,175.9 $ 1,607.3 $ — $ 4,787.0 Cash 1.7 31.7 105.8 — 139.2 Accrued investment income — 20.3 6.9 — 27.2 Premiums receivable — 229.5 420.4 — 649.9 Reinsurance recoverables — 1,635.2 1,053.1 — 2,688.3 Goodwill and other intangible assets, net 41.9 123.8 104.8 — 270.5 Current income taxes receivable, net — 9.1 (0.9 ) — 8.2 Deferred acquisition costs, net — 86.2 81.1 — 167.3 Ceded unearned premiums — 250.4 207.3 — 457.7 Other assets 15.7 165.3 181.9 — 362.9 Intercompany note receivable — 53.7 (53.7 ) — — Investments in subsidiaries 1,852.7 — — (1,852.7 ) — Total assets $ 1,915.8 $ 5,781.1 $ 3,714.0 $ (1,852.7 ) $ 9,558.2 Liabilities and Shareholders' Equity Reserves for losses and loss adjustment expenses $ — $ 2,771.4 $ 1,883.2 $ — $ 4,654.6 Unearned premiums — 797.4 503.5 — 1,300.9 Funds held and ceded reinsurance payable, net — 739.3 268.4 — 1,007.7 Debt 153.4 284.7 142.1 — 580.2 Deferred tax liabilities, net — 5.6 0.6 — 6.2 Accrued underwriting expenses and other liabilities 7.2 112.4 142.3 — 261.9 Due to (from) affiliates 8.5 2.0 (2.0 ) (8.5 ) — Intercompany note payable — 19.1 (19.1 ) — — Total liabilities 169.1 4,731.9 2,919.0 (8.5 ) 7,811.5 Total shareholders' equity 1,746.7 1,049.2 795.0 (1,844.2 ) 1,746.7 Total liabilities and shareholders' equity $ 1,915.8 $ 5,781.1 $ 3,714.0 $ (1,852.7 ) $ 9,558.2 (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 (LOSS) INCOME FOR THE THREE MONTHS ENDED SEPTEMBER 30, 2019 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries Consolidating Total Premiums and other revenue: Earned premiums $ — $ 265.5 $ 186.0 $ — $ 451.5 Net investment (expense) income (0.9 ) 27.7 13.4 — 40.2 Fee and other income — 0.7 1.2 — 1.9 Net realized investment (losses) gains (0.3 ) (0.3 ) (5.6 ) — (6.2 ) Total revenue (1.2 ) 293.6 195.0 — 487.4 Expenses: Losses and loss adjustment expenses — 177.7 161.1 — 338.8 Underwriting, acquisition and insurance expenses 2.0 103.5 62.2 — 167.7 Interest expense 1.7 4.0 1.8 — 7.5 Fee and other expense — 0.7 0.5 — 1.2 Foreign currency exchange losses (gains) — 0.1 (1.7 ) — (1.6 ) Total expenses 3.7 286.0 223.9 — 513.6 (Loss) income before income taxes (4.9 ) 7.6 (28.9 ) — (26.2 ) Provision (benefit) for income taxes — 1.2 (2.3 ) — (1.1 ) Net (loss) income before equity in earnings of subsidiaries (4.9 ) 6.4 (26.6 ) — (25.1 ) Equity in undistributed earnings of subsidiaries (20.2 ) — — 20.2 — Net (loss) income $ (25.1 ) $ 6.4 $ (26.6 ) $ 20.2 $ (25.1 ) (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 SEPTEMBER 30, 2018 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries Consolidating Total Premiums and other revenue: Earned premiums $ — $ 222.9 $ 224.0 $ — $ 446.9 Net investment (expense) income (0.6 ) 21.1 14.0 — 34.5 Fee and other income — 2.2 1.1 — 3.3 Net realized investment (losses) gains (0.3 ) 16.2 (1.7 ) — 14.2 Total revenue (0.9 ) 262.4 237.4 — 498.9 Expenses: Losses and loss adjustment expenses — 136.9 140.6 — 277.5 Underwriting, acquisition and insurance expenses 3.3 85.0 79.7 — 168.0 Interest expense 1.6 4.6 1.7 — 7.9 Fee and other expense — 1.2 0.7 — 1.9 Foreign currency exchange gains — — (1.7 ) — (1.7 ) Total expenses 4.9 227.7 221.0 — 453.6 (Loss) income before income taxes (5.8 ) 34.7 16.4 — 45.3 Provision for income taxes — 4.7 — — 4.7 Net (loss) income before equity in earnings of subsidiaries (5.8 ) 30.0 16.4 — 40.6 Equity in undistributed earnings of subsidiaries 46.4 — — (46.4 ) — Net income $ 40.6 $ 30.0 $ 16.4 $ (46.4 ) $ 40.6 (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 NINE MONTHS ENDED SEPTEMBER 30, 2019 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries Consolidating Total Premiums and other revenue: Earned premiums $ — $ 792.1 $ 511.6 $ — $ 1,303.7 Net investment (expense) income (2.2 ) 79.6 39.5 — 116.9 Fee and other income — 2.5 3.8 — 6.3 Net realized investment (losses) gains (0.5 ) 60.6 (1.8 ) — 58.3 Total revenue (2.7 ) 934.8 553.1 — 1,485.2 Expenses: Losses and loss adjustment expenses — 507.0 354.5 — 861.5 Underwriting, acquisition and insurance expenses 10.9 311.8 174.6 — 497.3 Interest expense 5.1 13.9 6.3 — 25.3 Fee and other expense — 2.4 1.4 — 3.8 Foreign currency exchange losses (gains) — 0.3 (6.5 ) — (6.2 ) Total expenses 16.0 835.4 530.3 — 1,381.7 (Loss) income before income taxes (18.7 ) 99.4 22.8 — 103.5 Provision (benefit) for income taxes — 14.5 (5.9 ) — 8.6 Net (loss) income before equity in earnings of subsidiaries (18.7 ) 84.9 28.7 — 94.9 Equity in undistributed earnings of subsidiaries 113.6 — — (113.6 ) — Net income $ 94.9 $ 84.9 $ 28.7 $ (113.6 ) $ 94.9 (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 NINE MONTHS ENDED SEPTEMBER 30, 2018 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries Consolidating Total Premiums and other revenue: Earned premiums $ — $ 646.8 $ 632.5 $ — $ 1,279.3 Net investment (expense) income (2.0 ) 62.2 43.5 — 103.7 Fee and other income — 3.7 3.5 — 7.2 Net realized investment (losses) gains (0.2 ) 15.3 (6.1 ) — 9.0 Total revenue (2.2 ) 728.0 673.4 — 1,399.2 Expenses: Losses and loss adjustment expenses — 346.7 413.5 — 760.2 Underwriting, acquisition and insurance expenses 11.5 250.2 223.3 — 485.0 Interest expense 4.5 13.4 5.5 — 23.4 Fee and other expense — 3.7 1.8 — 5.5 Foreign currency exchange losses (gains) — 0.2 (2.5 ) — (2.3 ) Total expenses 16.0 614.2 641.6 — 1,271.8 (Loss) income before income taxes (18.2 ) 113.8 31.8 — 127.4 Provision for income taxes — 17.9 2.3 — 20.2 Net (loss) income before equity in earnings of subsidiaries (18.2 ) 95.9 29.5 — 107.2 Equity in undistributed earnings of subsidiaries 125.4 — — (125.4 ) — Net income $ 107.2 $ 95.9 $ 29.5 $ (125.4 ) $ 107.2 (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 CASH FLOWS FOR THE NINE MONTHS ENDED SEPTEMBER 30, 2019 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries Consolidating Total Net cash flows from operating activities $ 29.2 $ 124.6 $ 41.9 $ — $ 195.7 Cash flows from investing activities: Proceeds from sales of investments — 744.2 436.1 — 1,180.3 Maturities and mandatory calls of fixed maturity investments — 219.2 73.0 — 292.2 Purchases of investments — (1,091.2 ) (548.3 ) — (1,639.5 ) Change in short-term investments and foreign regulatory deposits 3.5 34.7 (35.9 ) — 2.3 Settlements of foreign currency exchange forward contracts (0.1 ) 1.4 (2.5 ) — (1.2 ) Purchases of fixed assets and other, net — (1.8 ) 8.5 — 6.7 Cash provided by (used in) investing activities 3.4 (93.5 ) (69.1 ) — (159.2 ) Cash flows from financing activities: Payment on the intercompany note — (19.1 ) 19.1 — — Payment on note payable — (0.6 ) — — (0.6 ) Activity under stock incentive plans 1.4 — — — 1.4 Payment of cash dividend to common shareholders (32.5 ) — — — (32.5 ) Cash (used in) provided by financing activities (31.1 ) (19.7 ) 19.1 — (31.7 ) Effect of exchange rate changes on cash — — 1.1 — 1.1 Change in cash 1.5 11.4 (7.0 ) — 5.9 Cash, beginning of year 1.7 31.7 105.8 — 139.2 Cash, end of period $ 3.2 $ 43.1 $ 98.8 $ — $ 145.1 (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 NINE MONTHS ENDED SEPTEMBER 30, 2018 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries Consolidating Total Net cash flows from operating activities $ 57.7 $ 151.3 $ 22.0 $ — $ 231.0 Cash flows from investing activities: Proceeds from sales of investments — 963.2 454.0 — 1,417.2 Maturities and mandatory calls of fixed maturity investments — 302.5 72.6 — 375.1 Purchases of investments — (1,346.8 ) (630.4 ) — (1,977.2 ) Change in short-term investments and foreign regulatory deposits — (65.0 ) 31.2 — (33.8 ) Settlements of foreign currency exchange forward contracts 0.2 0.5 1.3 — 2.0 Cash acquired with acquisition of Ariscom — — 15.6 — 15.6 Purchases of fixed assets and other, net (0.1 ) (38.5 ) 6.4 — (32.2 ) Cash provided by (used in) investing activities 0.1 (184.1 ) (49.3 ) — (233.3 ) Cash flows from financing activities: Borrowing under intercompany note, net — 19.0 (19.0 ) — — Activity under stock incentive plans 1.0 — — — 1.0 Repurchase of Company's common shares (30.0 ) — — — (30.0 ) Payment of cash dividend to common shareholders (28.0 ) — — — (28.0 ) Cash (used in) provided by financing activities (57.0 ) 19.0 (19.0 ) — (57.0 ) Effect of exchange rate changes on cash — — 1.2 — 1.2 Change in cash 0.8 (13.8 ) (45.1 ) — (58.1 ) Cash, beginning of year 0.9 47.8 127.9 — 176.6 Cash, end of period $ 1.7 $ 34.0 $ 82.8 $ — $ 118.5 (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	9 Months Ended
	Sep. 30, 2019
Subsequent Events [Abstract]
Subsequent Event	Subsequent Event On November 5, 2019, Mark E. Watson III retired from his position as President and Chief Executive Officer of Argo Group International Holdings, Ltd. (the “Company”), effective immediately. Mr. Watson will resign from the Board of Directors, effective December 30, 2019. Additionally, the Company’s Board of Directors appointed Kevin J. Rehnberg, 56, to serve as the Company’s Interim President and Chief Executive Officer, effective immediately and subject to Bermuda regulatory approval. On November 5, 2019, the Company and Mr. Watson entered into a binding term sheet (the “Term Sheet”) that will form the basis of a separation agreement between the parties that will be negotiated and is expected to be finalized during the fourth quarter of 2019 (the “Separation Agreement”). Upon executing the Separation Agreement, the Company expects to recognize certain expenses related to cash and stock compensation payable to Mr. Watson in accordance with the provisions of the Term Sheet, which are summarized as follows: • Effective as of the date on which the Separation Agreement becomes fully enforceable and binding, Mr. Watson will fully vest in 77,396 shares from his restricted stock grants awarded between 2016 through 2019. At that time, the Company will recognize stock compensation expense associated with the vesting of these shares based on the closing price of the Company's common stock on that date (approximately $4 million based on the November 6, 2019 closing price). Additionally, Mr. Watson forfeits his unvested market-based stock awards upon his retirement, resulting in the reversal of previously recognized stock compensation expense of approximately $1 million , to be recorded during the fourth quarter of 2019. • Mr. Watson will place 35,296 of the aforementioned vested shares into an escrow account, all or a portion of which will be used to satisfy his reimbursing the Company for certain of his personal expenses that were paid for by the Company, in an amount to be determined after the Company concludes its investigation into such expenses. Any shares not needed to satisfy Mr. Watson's reimbursement obligation to the Company will be released to Mr. Watson. • The Company will pay Mr. Watson $1,750,000 within ten days after he executes the Separation Agreement, and an additional $750,000 upon re-execution of the Separation Agreement on or following December 31, 2019. Due to the above, there will be tax impacts that the Company is currently evaluating.

Basis of Presentation (Policies

Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
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. 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 doubtful accounts; estimates of written and earned premiums; reinsurance premium receivable; fair value of investments and assessment of potential impairment; 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, 2018 , filed with the Securities and Exchange Commission on February 25, 2019. The interim financial information as of, and for the three and nine months ended, September 30, 2019 and 2018
Reclassification	Certain reclassifications have been made to financial information presented for prior years to conform to the current year’s presentation.
Recently Issued Accounting Pronouncements	In August 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update ("ASU") 2018-13, "Fair Value Measurement" (Topic 820). ASU 2018-13 eliminates, adds and modifies certain disclosure requirements on fair value measurements. The guidance is effective for fiscal years beginning after December 15, 2019, including interim periods within the year of adoption. The amendments on changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements, and the narrative description of measurement uncertainty are applied prospectively for only the most recent interim or annual period presented in the initial fiscal year adoption. All other amendments are applied retrospectively to all periods presented upon their effective date. Early adoption is permitted. We are currently in the process of evaluating the impact that the adoption of the ASU will have on our financial disclosures. In June 2016, the FASB issued ASU 2016-13, “Measurement of Credit Losses on Financial Instruments” (Topic 326). ASU 2016-13 requires organizations to estimate credit losses on certain types of financial instruments, including receivables and available-for-sale debt securities, by introducing an approach based on expected losses. The expected loss approach will require entities to incorporate considerations of historical information, current information and reasonable and supportable forecasts. The guidance is effective for fiscal years beginning after December 15, 2019, including interim periods within the year of adoption. The guidance requires a modified retrospective transition method and early adoption is permitted. We are currently in the process of evaluating the impact that the adoption of the ASU will have on our financial results and disclosures. In February 2016, the FASB issued ASU 2016-02, “Leases” (Topic 842). ASU 2016-02 requires organizations that lease assets to recognize on the balance sheet the assets and liabilities for the rights and obligations created by those leases. Additionally, the ASU modifies current guidance for lessors' accounting. In July 2018, the FASB issued ASU 2018-11, "Leases: Targeted Improvements" (Topic 842), which provides for an alternative transition method by allowing entities to initially apply the new leases standard at the adoption date (such as January 1, 2019) and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption (comparative periods presented in the financial statements will continue to be in accordance with current GAAP (Topic 840, Leases). The standard was effective for annual and interim periods beginning after December 15, 2018, with earlier application permitted. We have entered into operating leases for office space and certain other assets. We adopted the new standard on the effective date of January 1, 2019. We applied the following practical expedients: • We have elected to adopt this standard using the option transition method, which allows companies to continue applying the guidance under the lease standard in effect at that time in the comparative periods presented in the consolidated financial statements. The adoption of the standard had no effect on our consolidated shareholders’ equity. Prior periods were not restated. • We have elected the "package of practical expedients", which permits us not to reassess under the new standard our prior conclusion about lease identification, lease classification and initial direct costs. • Where we are the lessor, we have elected the practical expedient which permits us to not separate non-lease components from the associated lease components if the non-lease components otherwise would be accounted for in accordance with the new revenue standard. For the majority of our asset classes, we elected not to separate lease and non-lease components. As a result, our right-of-use assets and lease liabilities represent base rent components of our leases. We have elected to not apply the practical expedient which allows the use of hindsight in determining the lease term and in assessing impairment of the entity’s right-of-use assets. The remaining practical expedients did not specifically apply to our lease population as of the adoption date. Please see Note 4 - “Leases” for further discussion on the impact of the adoption of this standard.

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Schedule of Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Fair Value of Investments	The amortized cost, gross unrealized gains, gross unrealized losses and fair value of fixed maturity investments were as follows: September 30, 2019 (in millions) Amortized Gross Gross Fair Fixed maturities U.S. Governments $ 324.9 $ 3.9 $ 0.5 $ 328.3 Foreign Governments 262.6 4.2 2.3 264.5 Obligations of states and political subdivisions 152.6 7.6 0.1 160.1 Corporate bonds 1,862.0 39.0 39.2 1,861.8 Commercial mortgage-backed securities 213.3 6.0 0.3 219.0 Residential mortgage-backed securities 510.3 11.9 0.9 521.3 Asset-backed securities 165.6 1.7 0.3 167.0 Collateralized loan obligations 225.3 0.3 2.0 223.6 Total fixed maturities $ 3,716.6 $ 74.6 $ 45.6 $ 3,745.6 December 31, 2018 (in millions) Amortized Gross Gross Fair Fixed maturities U.S. Governments $ 240.9 $ 0.2 $ 4.9 $ 236.2 Foreign Governments 224.1 0.5 7.8 216.8 Obligations of states and political subdivisions 236.7 4.3 1.2 239.8 Corporate bonds 1,808.7 7.5 58.7 1,757.5 Commercial mortgage-backed securities 205.3 0.7 3.2 202.8 Residential mortgage-backed securities 413.1 3.4 5.7 410.8 Asset-backed securities 173.6 0.4 1.2 172.8 Collateralized loan obligations 226.7 0.5 3.5 223.7 Total fixed maturities $ 3,529.1 $ 17.5 $ 86.2 $ 3,460.4
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 September 30, 2019 , by contractual maturity, were as follows: (in millions) Amortized Fair Due in one year or less $ 242.5 $ 242.2 Due after one year through five years 1,584.3 1,577.1 Due after five years through ten years 669.5 683.5 Thereafter 105.8 111.9 Structured securities 1,114.5 1,130.9 Total $ 3,716.6 $ 3,745.6
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 September 30, 2019 and December 31, 2018 were as follows: September 30, 2019 (in millions) Carrying Unfunded Investment Type Hedge funds $ 119.3 $ — Private equity 263.9 94.2 Long only funds 112.5 — Other 4.3 — Total other investments $ 500.0 $ 94.2 December 31, 2018 (in millions) Carrying Unfunded Investment Type Hedge funds $ 120.6 $ — Private equity 211.8 120.5 Long only funds 153.0 — Other 4.4 — Total other investments $ 489.8 $ 120.5
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: September 30, 2019 Less Than One Year One Year or Greater Total (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed maturities U.S. Governments $ 75.0 $ 0.4 $ 18.8 $ 0.1 $ 93.8 $ 0.5 Foreign Governments 108.2 2.1 9.6 0.2 117.8 2.3 Obligations of states and political subdivisions 1.1 — 2.4 0.1 3.5 0.1 Corporate bonds 355.6 32.3 100.0 6.9 455.6 39.2 Commercial mortgage-backed securities 53.8 0.2 5.3 0.1 59.1 0.3 Residential mortgage-backed securities 57.1 0.4 43.9 0.5 101.0 0.9 Asset-backed securities 17.9 0.2 19.4 0.1 37.3 0.3 Collateralized loan obligations 138.8 1.8 54.1 0.2 192.9 2.0 Total fixed maturities $ 807.5 $ 37.4 $ 253.5 $ 8.2 $ 1,061.0 $ 45.6 December 31, 2018 Less Than One Year One Year or Greater Total (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed maturities U.S. Governments $ 28.2 $ 0.2 $ 173.0 $ 4.7 $ 201.2 $ 4.9 Foreign Governments 73.4 3.6 125.0 4.2 198.4 7.8 Obligations of states and political subdivisions 53.3 0.6 25.3 0.6 78.6 1.2 Corporate bonds 964.3 45.7 440.8 13.0 1,405.1 58.7 Commercial mortgage-backed securities 48.5 0.6 90.6 2.6 139.1 3.2 Residential mortgage-backed securities 63.5 0.7 176.1 5.0 239.6 5.7 Asset-backed securities 73.6 0.6 64.2 0.6 137.8 1.2 Collateralized loan obligations 209.5 3.3 10.3 0.2 219.8 3.5 Total fixed maturities $ 1,514.3 $ 55.3 $ 1,105.3 $ 30.9 $ 2,619.6 $ 86.2
Schedule of Recognized Other-than-temporary Losses on Fixed Maturities and Equity Portfolios	We recognized other-than-temporary losses on our fixed maturities portfolio as follows: For the Three Months Ended For the Nine Months Ended (in millions) 2019 2018 2019 2018 Other-than-temporary impairment: Corporate bonds $ (5.0 ) $ — $ (11.8 ) $ (1.9 ) Other-than-temporary impairment losses $ (5.0 ) $ — $ (11.8 ) $ (1.9 )
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 Nine Months Ended (in millions) 2019 2018 2019 2018 Realized gains on fixed maturities and other Fixed maturities $ 3.7 $ 4.6 $ 13.0 $ 15.8 Other investments 7.5 7.4 21.9 34.7 Other Assets and Short Term Investments — 0.2 $ — 0.2 11.2 12.2 34.9 50.7 Realized losses on fixed maturities and other Fixed maturities (1.6 ) (2.8 ) (8.7 ) (14.2 ) Other investments (8.4 ) (8.8 ) (21.8 ) (34.4 ) Other-than-temporary impairment losses on fixed maturities (5.0 ) — (11.8 ) (1.9 ) (15.0 ) (11.6 ) (42.3 ) (50.5 ) Equity securities Net realized gains on equity securities 6.4 9.1 7.7 30.9 Change in unrealized (losses) gains on equity securities held at the end of the period (8.8 ) 4.5 58.0 (22.1 ) Net realized (losses) gains on equity securities (2.4 ) 13.6 65.7 8.8 Net realized investment (losses) gains before income taxes (6.2 ) 14.2 58.3 9.0 Income tax benefit (provision) 0.3 (3.3 ) (11.9 ) (2.8 ) Net realized investment (losses) gains net of income taxes $ (5.9 ) $ 10.9 $ 46.4 $ 6.2
Schedule Of Changes In Unrealized Appreciation (Depreciation)	Changes in unrealized gains (losses) related to investments are summarized as follows: For the Three Months Ended For the Nine Months Ended (in millions) 2019 2018 2019 2018 Change in unrealized gains (losses) Fixed maturities $ (3.8 ) $ (4.3 ) $ 95.3 $ (63.2 ) Other investments — — 4.4 0.1 Other and short-term investments (0.8 ) (0.5 ) (0.7 ) (0.5 ) Net unrealized investment gains (losses) before income taxes (4.6 ) (4.8 ) 99.0 (63.6 ) Income tax (provision) benefit 0.4 1.4 (16.1 ) 10.5 Net unrealized investment gains (losses), net of income taxes $ (4.2 ) $ (3.4 ) $ 82.9 $ (53.1 )
Schedule of Fair Value of Foreign Currency Exchange Forward Contracts	The fair value of our foreign currency exchange forward contracts as of September 30, 2019 and December 31, 2018 was as follows: (in millions) September 30, 2019 December 31, 2018 Operational currency exposure $ (1.4 ) $ 4.4 Asset manager investment exposure 0.9 (0.3 ) Total return strategy — (1.5 ) Total $ (0.5 ) $ 2.6
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 Nine Months Ended (in millions) 2019 2018 2019 2018 Realized gains Operational currency exposure $ 1.3 $ 0.4 $ 2.2 $ 6.4 Asset manager investment exposure 1.8 1.4 3.1 14.4 Total return strategy 6.5 5.6 18.8 12.5 Gross realized investment gains 9.6 7.4 24.1 33.3 Realized losses Operational currency exposure (3.2 ) (2.7 ) (7.8 ) (7.0 ) Asset manager investment exposure (0.1 ) (0.9 ) (0.6 ) (12.5 ) Total return strategy (7.1 ) (5.2 ) (15.7 ) (13.3 ) Gross realized investment losses (10.4 ) (8.8 ) (24.1 ) (32.8 ) Net realized investment (losses) gains on foreign currency exchange forward contracts $ (0.8 ) $ (1.4 ) $ — $ 0.5
Schedule of Restricted Assets	The following table presents our components of restricted assets at September 30: (in millions) September 30, 2019 September 30, 2018 Securities on deposit for regulatory and other purposes $ 198.8 $ 180.6 Securities pledged as collateral for letters of credit 129.5 76.5 Securities and cash on deposit supporting Lloyd’s business 403.6 418.4 Total restricted investments $ 731.9 $ 675.5
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) September 30, 2019 Level 1 (a) Level 2 (b) Level 3 (c) Fixed maturities U.S. Governments $ 328.3 $ 323.0 $ 5.3 $ — Foreign Governments 264.5 — 264.5 — Obligations of states and political subdivisions 160.1 — 160.1 — Corporate bonds 1,861.8 1.2 1,853.8 6.8 Commercial mortgage-backed securities 219.0 — 219.0 — Residential mortgage-backed securities 521.3 — 521.3 — Asset-backed securities 167.0 — 167.0 — Collateralized loan obligations 223.6 — 223.6 — Total fixed maturities 3,745.6 324.2 3,414.6 6.8 Equity securities 400.6 392.1 8.5 Other investments 405.9 — 405.9 — Short-term investments 480.8 449.3 31.5 — $ 5,032.9 $ 1,165.6 $ 3,852.0 $ 15.3 (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, 2018 Level 1 (a) Level 2 (b) Level 3 (c) Fixed maturities U.S. Governments $ 236.2 $ 226.7 $ 9.5 $ — Foreign Governments 216.8 — 216.8 — Obligations of states and political subdivisions 239.8 — 239.8 — Corporate bonds 1,757.5 — 1,755.3 2.2 Commercial mortgage-backed securities 202.8 — 202.8 — Residential mortgage-backed securities 410.8 — 410.8 — Asset-backed securities 172.8 — 172.8 — Collateralized loan obligations 223.7 — 223.7 — Total fixed maturities 3,460.4 226.7 3,231.5 2.2 Equity securities 354.5 346.3 — 8.2 Other investments 114.4 — 114.4 — Short-term investments 482.3 453.9 28.4 — $ 4,411.6 $ 1,026.9 $ 3,374.3 $ 10.4 (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, 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 — 0.3 0.3 Included in other comprehensive income (0.5 ) — (0.5 ) Purchases, issuances, sales, and settlements: Purchases 1.9 — 1.9 Issuances — — — Sales (0.3 ) — (0.3 ) Settlements — — — Ending balance, September 30, 2019 $ 6.8 $ 8.5 $ 15.3 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 September 30, 2019 $ — $ — $ — (in millions) Credit Financial Equity Total Beginning balance, January 1, 2018 $ 1.9 $ 2.3 $ 4.2 Transfers into Level 3 — — — Transfers out of Level 3 — — — Total gains or losses (realized/unrealized): Included in net income — 0.2 0.2 Included in other comprehensive loss 0.3 — 0.3 Purchases, issuances, sales, and settlements: Purchases — 7.3 7.3 Issuances — — — Sales — (1.6 ) (1.6 ) Settlements — — — Ending balance, December 31, 2018 $ 2.2 $ 8.2 $ 10.4 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 December 31, 2018 $ — $ — $ —

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Lessee, Assets and Liabilities	The components of lease expense and other lease information as of and during the nine months ended September 30, 2019 are as follows: (in millions) September 30, 2019 Operating leases right-of-use assets $ 108.6 Operating lease liabilities 120.2 Operating lease weighted-average remaining lease term 10.31 Operating lease weighted-average discount rate 3.93 %
Lease, Cost	(in millions) For the Three Months Ended For the Nine Months Ended September 30, 2019 Operating lease costs $ 5.1 $ 15.3 Variable lease costs — 2.1 Sublease income (0.1 ) (0.3 ) Total lease costs $ 5.0 $ 17.1 Operating cash flows from operating leases (fixed payments) $ 14.1 Operating cash flows from operating leases (liability reduction) 11.5
Lessee, Operating Lease, Liability, Maturity	Future minimum lease payments under operating leases as of September 30, 2019 and December 31, 2018 were as follows: (in millions) September 30, 2019 December 31, 2018 2019 $ 4.7 $ 18.7 2020 18.6 18.6 2021 17.5 17.5 2022 14.8 14.7 2023 12.3 12.3 Thereafter 79.4 80.1 Total future minimum lease payments $ 147.3 $ 161.9 Future lease obligations (0.5 ) Less imputed interest (26.6 ) N/A Total operating lease liability $ 120.2 N/A

Reserves for Losses and Loss _2

Reserves for Losses and Loss Adjustment Expenses (Tables)	9 Months Ended
	Sep. 30, 2019
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 Nine Months Ended (in millions) 2019 2018 Net reserves beginning of the year $ 2,562.9 $ 2,488.0 Net reserves acquired — 49.4 Add: Losses and LAE incurred during current calendar year, net of reinsurance: Current accident year 799.9 764.3 Prior accident years 61.6 (4.1 ) Losses and LAE incurred during calendar year, net of reinsurance 861.5 760.2 Deduct: Losses and LAE payments made during current calendar year, net of reinsurance: Current accident year 163.6 223.2 Prior accident years 615.8 469.0 Losses and LAE payments made during current calendar year, net of reinsurance: 779.4 692.2 Change in participation interest (1) (14.4 ) (29.4 ) Foreign exchange adjustments (26.3 ) (20.8 ) Net reserves - end of period 2,604.3 2,555.2 Add: Reinsurance recoverables on unpaid losses and LAE, end of period 2,238.2 1,736.5 Gross reserves - end of period $ 4,842.5 $ 4,291.7 (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 (favorable) development of prior accident years’ loss and LAE reserves on each reporting segment is presented below: For the Nine Months Ended (in millions) 2019 2018 U.S. Operations $ (9.8 ) $ (14.8 ) International Operations 69.5 (0.8 ) Run-off Lines 1.9 11.5 Total unfavorable (favorable) prior-year development $ 61.6 $ (4.1 )

Disclosures about Fair Value _2

Disclosures about Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2019
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: September 30, 2019 December 31, 2018 (in millions) Carrying Fair Carrying Fair Junior subordinated debentures: Trust preferred debentures $ 172.7 $ 160.7 $ 172.7 $ 163.2 Subordinated debentures 84.6 85.4 84.3 85.0 Total junior subordinated debentures 257.3 246.1 257.0 248.2 Senior unsecured fixed rate notes 139.9 143.4 139.8 139.5 Floating rate loan stock 56.4 52.5 57.8 54.5
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) September 30, 2019 Level 1 (a) Level 2 (b) Level 3 (c) Junior subordinated debentures: Trust preferred debentures $ 160.7 $ — $ 160.7 $ — Subordinated debentures 85.4 — 85.4 — Total junior subordinated debentures 246.1 — 246.1 — Senior unsecured fixed rate notes 143.4 143.4 — — Floating rate loan stock 52.5 — 52.5 — 688.1 143.4 544.7 — (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, 2018 Level 1 (a) Level 2 (b) Level 3 (c) Junior subordinated debentures: Trust preferred debentures $ 163.2 $ — $ 163.2 $ — Subordinated debentures 85.0 — 85.0 — Total junior subordinated debentures 248.2 — 248.2 — Senior unsecured fixed rate notes 139.8 139.8 — — Floating rate loan stock 57.8 — 57.8 — 445.8 139.8 306.0 — (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)	9 Months Ended
	Sep. 30, 2019
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 nine months ended September 30, 2019 , and 2018 is presented below: (in millions) Foreign Currency Translation Adjustments Unrealized Defined Benefit Pension Plans Total Balance, January 1, 2019 $ (22.4 ) $ (49.0 ) $ (6.7 ) $ (78.1 ) Other comprehensive (loss) income before reclassifications (0.1 ) 76.2 — 76.1 Amounts reclassified from accumulated other comprehensive income — 6.7 — 6.7 Net current-period other comprehensive (loss) income (0.1 ) 82.9 — 82.8 Balance at September 30, 2019 $ (22.5 ) $ 33.9 $ (6.7 ) $ 4.7 (in millions) Foreign Currency Translation Adjustments Unrealized Defined Benefit Pension Plans Total Balance, January 1, 2018 $ (19.0 ) $ 121.9 $ (6.3 ) $ 96.6 Other comprehensive loss before reclassifications (4.8 ) (53.4 ) — (58.2 ) Amounts reclassified from accumulated other comprehensive loss — 0.3 — 0.3 Net current-period other comprehensive loss (4.8 ) (53.1 ) — (57.9 ) Cumulative effect of adoption of ASU 2016-01 — (117.5 ) — (117.5 ) Cumulative effect of adoption of ASU 2018-02 — 22.1 (1.4 ) 20.7 Balance at September 30, 2018 $ (23.8 ) $ (26.6 ) $ (7.7 ) $ (58.1 )
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 September 30, For the Nine Months Ended September 30, (in millions) 2019 2018 2019 2018 Unrealized gains and losses on securities: Net realized investment loss (gains) $ 2.8 $ (2.4 ) $ 7.7 $ 0.2 (Benefit) provision for income taxes (0.3 ) 0.3 (1.0 ) 0.1 Net of taxes $ 2.5 $ (2.1 ) $ 6.7 $ 0.3

Net (Loss) Income Per Common _2

Net (Loss) Income Per Common Share (Tables)	9 Months Ended
	Sep. 30, 2019
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 Nine Months Ended (in millions, except number of shares and per share amounts) 2019 2018 2019 2018 Net (loss) income $ (25.1 ) $ 40.6 $ 94.9 $ 107.2 Weighted average common shares outstanding - basic 34,299,999 33,956,695 34,161,016 33,921,632 Effect of dilutive securities: Equity compensation awards — 699,633 608,606 767,211 Weighted average common shares outstanding - diluted 34,299,999 34,656,328 34,769,622 34,688,843 Net (loss) income per common share: Basic $ (0.73 ) $ 1.20 $ 2.78 $ 3.16 Diluted $ (0.73 ) $ 1.17 $ 2.73 $ 3.09

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	9 Months Ended
	Sep. 30, 2019
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 Nine Months Ended September 30, (in millions) 2019 2018 Senior unsecured fixed rate notes $ 7.0 $ 7.0 Junior subordinated debentures 12.3 11.2 Other indebtedness 7.2 4.9 Total interest paid $ 26.5 $ 23.1 Income taxes paid 4.8 18.1 Income taxes recovered (0.1 ) — Income taxes paid, net $ 4.7 $ 18.1

Share-based Compensation (Table

Share-based Compensation (Tables)	9 Months Ended
	Sep. 30, 2019
Share-based Payment Arrangement [Abstract]
Fair Value Assumptions	The following table summarizes the assumptions we used for the nine months ended September 30, 2019 and 2018 : For the Nine Months Ended September 30, 2019 2018 Risk-free rate of return 1.66% 2.96% Expected dividend yields 1.76% 1.84% Expected award life (years) 4.50 4.49 Expected volatility 18.73% 17.82%
Summary of Restricted Share Activity	A summary of restricted share activity as of September 30, 2019 and changes during the nine months then ended is as follows: Shares Weighted-Average Outstanding at January 1, 2019 897,005 $ 46.92 Granted 209,557 $ 68.65 Vested and issued (403,316 ) $ 35.74 Expired or forfeited (59,635 ) $ 55.41 Outstanding at September 30, 2019 643,611 $ 59.93
Stock Settled Share Appreciation Rights	A summary of stock-settled SARs activity as of September 30, 2019 and changes during the nine months then ended is as follows: Shares Weighted-Average Outstanding at January 1, 2019 810,759 $ 33.88 Exercised (148,729 ) $ 34.71 Expired or forfeited (7,167 ) $ 37.85 Outstanding at September 30, 2019 654,863 $ 33.68
Summary of Cash-Settled SARs Activity	A summary of cash-settled SARs activity as of September 30, 2019 and changes during the nine months then ended is as follows: Shares Weighted-Average Outstanding at January 1, 2019 58,428 $ 30.71 Exercised (48,722 ) $ 30.34 Expired or forfeited (1,193 ) $ 19.37 Outstanding at September 30, 2019 8,513 $ 34.39

Underwriting, Acquisition and_2

Underwriting, Acquisition and Insurance Expenses (Tables)	9 Months Ended
	Sep. 30, 2019
Underwriting Acquisition And Insurance Expenses [Abstract]
Underwriting, Acquisition and Insurance Expenses	The components of our underwriting, acquisition and insurance expenses are detailed in the table below. General expenses include certain costs associated with our holding company. For the Three Months Ended For the Nine Months Ended (in millions) 2019 2018 2019 2018 Commissions $ 58.0 $ 88.0 $ 178.0 $ 212.7 General expenses 92.9 83.2 281.0 261.6 Premium taxes, boards and bureaus 10.8 9.8 27.0 27.2 161.7 181.0 486.0 501.5 Net deferral of policy acquisition costs 6.0 (13.0 ) 11.3 (16.5 ) Total underwriting, acquisition and insurance expenses $ 167.7 $ 168.0 $ 497.3 $ 485.0

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Schedule of Pre-Tax Income (Loss) and Effective Income Tax Rates	For the three and nine months ended September 30, 2019 and 2018 , pre-tax income (loss) attributable to our operations and the corresponding operations’ effective tax rates were as follows: For the Three Months Ended September 30, 2019 2018 (in millions) Pre-Tax Effective Pre-Tax Effective Bermuda $ (7.8 ) — % $ 6.4 — % United States 7.7 16.4 % 34.8 13.4 % United Kingdom (17.9 ) 13.1 % 3.5 (5.0 )% Belgium (0.1 ) 28.6 % — (1) 30.8 % Brazil 1.2 — % 0.4 — % United Arab Emirates — (1) — % 0.2 — % Ireland — (1) — % (0.1 ) — % Italy (3.6 ) — % (1.8 ) — % Malta (5.6 ) — % 1.8 — % Luxembourg — — % — (1) — % Switzerland (0.1 ) 1.0 % 0.1 21.2 % Pre-tax income (loss) $ (26.2 ) 4.1 % $ 45.3 10.2 % (1) Pre-tax income (loss) for the respective year was less than $0.1 million . For the Nine Months Ended September 30, 2019 2018 (in millions) Pre-Tax Effective Pre-Tax Effective Bermuda $ 39.1 — % $ (1.8 ) — % United States 99.5 14.6 % 114.2 15.6 % United Kingdom (30.3 ) 19.2 % 16.3 12.3 % Belgium (0.4 ) 29.4 % — (1) 33.3 % Brazil 5.0 — % (1.0 ) — % United Arab Emirates 0.3 — % 0.5 — % Ireland (0.1 ) — % (0.2 ) — % Italy (4.1 ) — % (2.9 ) — % Malta (5.4 ) — % 2.2 — % Luxembourg — — % — (1) — % Switzerland (0.1 ) 0.9 % 0.1 21.2 % Pre-tax income $ 103.5 8.4 % $ 127.4 15.8 % (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 Nine Months Ended (in millions) 2019 2018 2019 2018 Income tax provision at expected rate $ (4.1 ) $ 8.4 $ 14.4 $ 26.8 Tax effect of: Nontaxable investment income (0.4 ) (0.4 ) (1.1 ) (1.4 ) Foreign exchange adjustments 0.7 (1.0 ) 1.3 (1.2 ) Withholding taxes — 0.2 0.2 0.5 Prior period adjustments — (1) (2.2 ) (1.8 ) (2.1 ) Change in valuation allowance 2.2 (0.2 ) 1.6 (3.6 ) Other 0.5 (0.1 ) (6.0 ) 1.2 Income tax provision $ (1.1 ) $ 4.7 $ 8.6 $ 20.2 (1) Tax effect of the adjustment for the respective year was less than $0.1 million .

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2019
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 Nine Months Ended (in millions) 2019 2018 2019 2018 Revenue: Earned premiums U.S. Operations $ 290.8 $ 278.3 $ 848.6 $ 807.6 International Operations 160.7 168.5 455.0 471.4 Run-off Lines — 0.1 0.1 0.3 Total earned premiums 451.5 446.9 1,303.7 1,279.3 Net investment income U.S. Operations 27.4 21.4 80.1 64.7 International Operations 10.7 8.4 31.3 25.6 Run-off Lines 1.7 2.1 4.4 6.3 Corporate and Other 0.4 2.6 1.1 7.1 Total net investment income 40.2 34.5 116.9 103.7 Fee and other income 1.9 3.3 6.3 7.2 Net realized investment (losses) gains (6.2 ) 14.2 58.3 9.0 Total revenue $ 487.4 $ 498.9 $ 1,485.2 $ 1,399.2 For the Three Months Ended For the Nine Months Ended (in millions) 2019 2018 2019 2018 Income (loss) before income taxes U.S. Operations $ 42.2 $ 50.3 $ 138.3 $ 126.8 International Operations (52.9 ) (1.2 ) (57.7 ) 34.9 Run-off Lines 0.7 (7.6 ) 0.2 (8.6 ) Total segment (loss) income before taxes (10.0 ) 41.5 80.8 153.1 Corporate and Other (7.9 ) (12.1 ) (30.1 ) (37.0 ) Net realized investment and other (losses) gains (6.2 ) 14.2 58.3 9.0 Foreign currency exchange gains 1.6 1.7 6.2 2.3 Other corporate expenses (3.7 ) — (11.7 ) — Total (loss) income before income taxes $ (26.2 ) $ 45.3 $ 103.5 $ 127.4
Schedule of Earned Premiums by Geographic Location	The table below presents earned premiums by geographic location for the three and nine months ended September 30, 2019 and 2018 . For this disclosure, we determine geographic location by the country of domicile of our subsidiaries that underwrite the business and not by the location of insureds or reinsureds from whom the business was generated. For the Three Months Ended For the Nine Months Ended (in millions) 2019 2018 2019 2018 United States $ 289.6 $ 276.5 $ 845.4 $ 803.7 United Kingdom 101.9 117.2 295.6 333.3 Bermuda 24.3 23.3 60.1 64.7 Malta 21.3 18.2 62.3 39.6 All other jurisdictions 14.4 11.7 40.3 38.0 Total earned premiums $ 451.5 $ 446.9 $ 1,303.7 $ 1,279.3
Identifiable Assets	The following table represents identifiable assets: (in millions) September 30, 2019 December 31, 2018 U.S. Operations $ 5,477.4 $ 4,707.8 International Operations 4,403.8 3,984.7 Run-off Lines 375.9 444.8 Corporate and Other 188.7 420.9 Total $ 10,445.8 $ 9,558.2

Senior Unsecured Fixed Rate N_2

Senior Unsecured Fixed Rate Notes (Tables)	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Schedule Of Unamortized Debt Issuance Costs Deducted From Carrying Value Of Debt Liability	At September 30, 2019 and December 31, 2018 , the Notes consisted of the following: (in millions) September 30, 2019 December 31, 2018 Senior unsecured fixed rate notes Principal $ 143.8 $ 143.8 Less: unamortized debt issuance costs (3.9 ) (4.0 ) Senior unsecured fixed rate notes, less unamortized debt issuance costs $ 139.9 $ 139.8
Condensed Consolidating Balance Sheet	CONDENSED CONSOLIDATING BALANCE SHEET SEPTEMBER 30, 2019 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries Consolidating Total Assets Investments $ 0.3 $ 3,416.4 $ 1,710.3 $ — $ 5,127.0 Cash 3.2 43.1 98.8 — 145.1 Accrued investment income — 19.8 7.9 — 27.7 Premiums receivable — 261.6 478.7 — 740.3 Reinsurance recoverables — 1,661.9 1,211.9 — 2,873.8 Goodwill and other intangible assets, net 40.9 123.5 104.8 — 269.2 Current income taxes receivable, net — — 0.2 — 0.2 Deferred acquisition costs, net — 92.6 66.9 — 159.5 Ceded unearned premiums — 294.9 308.9 — 603.8 Operating lease right-of-use assets 7.8 71.9 28.9 — 108.6 Other assets 10.5 170.2 209.9 — 390.6 Intercompany note receivable — 55.9 (55.9 ) — — Investments in subsidiaries 2,053.6 — — (2,053.6 ) — Total assets $ 2,116.3 $ 6,211.8 $ 4,171.3 $ (2,053.6 ) $ 10,445.8 Liabilities and Shareholders' Equity Reserves for losses and loss adjustment expenses $ — $ 2,944.7 $ 1,897.8 $ — $ 4,842.5 Unearned premiums — 896.8 598.7 — 1,495.5 Funds held and ceded reinsurance payable, net — 665.4 546.4 — 1,211.8 Debt 153.4 284.2 141.0 — 578.6 Deferred tax liabilities, net — 25.3 (5.4 ) — 19.9 Accrued underwriting expenses and other liabilities 11.0 125.6 147.3 — 283.9 Operating lease liabilities 8.0 81.5 30.7 — 120.2 Due to (from) affiliates 50.5 (4.2 ) 4.2 (50.5 ) — Total liabilities 222.9 5,019.3 3,360.7 (50.5 ) 8,552.4 Total shareholders' equity 1,893.4 1,192.5 810.6 (2,003.1 ) 1,893.4 Total liabilities and shareholders' equity $ 2,116.3 $ 6,211.8 $ 4,171.3 $ (2,053.6 ) $ 10,445.8 (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 BALANCE SHEET DECEMBER 31, 2018 (in millions) Argo Group Argo Group US, Inc. Other Subsidiaries Consolidating Total Assets Investments $ 3.8 $ 3,175.9 $ 1,607.3 $ — $ 4,787.0 Cash 1.7 31.7 105.8 — 139.2 Accrued investment income — 20.3 6.9 — 27.2 Premiums receivable — 229.5 420.4 — 649.9 Reinsurance recoverables — 1,635.2 1,053.1 — 2,688.3 Goodwill and other intangible assets, net 41.9 123.8 104.8 — 270.5 Current income taxes receivable, net — 9.1 (0.9 ) — 8.2 Deferred acquisition costs, net — 86.2 81.1 — 167.3 Ceded unearned premiums — 250.4 207.3 — 457.7 Other assets 15.7 165.3 181.9 — 362.9 Intercompany note receivable — 53.7 (53.7 ) — — Investments in subsidiaries 1,852.7 — — (1,852.7 ) — Total assets $ 1,915.8 $ 5,781.1 $ 3,714.0 $ (1,852.7 ) $ 9,558.2 Liabilities and Shareholders' Equity Reserves for losses and loss adjustment expenses $ — $ 2,771.4 $ 1,883.2 $ — $ 4,654.6 Unearned premiums — 797.4 503.5 — 1,300.9 Funds held and ceded reinsurance payable, net — 739.3 268.4 — 1,007.7 Debt 153.4 284.7 142.1 — 580.2 Deferred tax liabilities, net — 5.6 0.6 — 6.2 Accrued underwriting expenses and other liabilities 7.2 112.4 142.3 — 261.9 Due to (from) affiliates 8.5 2.0 (2.0 ) (8.5 ) — Intercompany note payable — 19.1 (19.1 ) — — Total liabilities 169.1 4,731.9 2,919.0 (8.5 ) 7,811.5 Total shareholders' equity 1,746.7 1,049.2 795.0 (1,844.2 ) 1,746.7 Total liabilities and shareholders' equity $ 1,915.8 $ 5,781.1 $ 3,714.0 $ (1,852.7 ) $ 9,558.2 (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	CONDENSED CONSOLIDATING STATEMENT OF (LOSS) INCOME FOR THE THREE MONTHS ENDED SEPTEMBER 30, 2019 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries Consolidating Total Premiums and other revenue: Earned premiums $ — $ 265.5 $ 186.0 $ — $ 451.5 Net investment (expense) income (0.9 ) 27.7 13.4 — 40.2 Fee and other income — 0.7 1.2 — 1.9 Net realized investment (losses) gains (0.3 ) (0.3 ) (5.6 ) — (6.2 ) Total revenue (1.2 ) 293.6 195.0 — 487.4 Expenses: Losses and loss adjustment expenses — 177.7 161.1 — 338.8 Underwriting, acquisition and insurance expenses 2.0 103.5 62.2 — 167.7 Interest expense 1.7 4.0 1.8 — 7.5 Fee and other expense — 0.7 0.5 — 1.2 Foreign currency exchange losses (gains) — 0.1 (1.7 ) — (1.6 ) Total expenses 3.7 286.0 223.9 — 513.6 (Loss) income before income taxes (4.9 ) 7.6 (28.9 ) — (26.2 ) Provision (benefit) for income taxes — 1.2 (2.3 ) — (1.1 ) Net (loss) income before equity in earnings of subsidiaries (4.9 ) 6.4 (26.6 ) — (25.1 ) Equity in undistributed earnings of subsidiaries (20.2 ) — — 20.2 — Net (loss) income $ (25.1 ) $ 6.4 $ (26.6 ) $ 20.2 $ (25.1 ) (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 SEPTEMBER 30, 2018 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries Consolidating Total Premiums and other revenue: Earned premiums $ — $ 222.9 $ 224.0 $ — $ 446.9 Net investment (expense) income (0.6 ) 21.1 14.0 — 34.5 Fee and other income — 2.2 1.1 — 3.3 Net realized investment (losses) gains (0.3 ) 16.2 (1.7 ) — 14.2 Total revenue (0.9 ) 262.4 237.4 — 498.9 Expenses: Losses and loss adjustment expenses — 136.9 140.6 — 277.5 Underwriting, acquisition and insurance expenses 3.3 85.0 79.7 — 168.0 Interest expense 1.6 4.6 1.7 — 7.9 Fee and other expense — 1.2 0.7 — 1.9 Foreign currency exchange gains — — (1.7 ) — (1.7 ) Total expenses 4.9 227.7 221.0 — 453.6 (Loss) income before income taxes (5.8 ) 34.7 16.4 — 45.3 Provision for income taxes — 4.7 — — 4.7 Net (loss) income before equity in earnings of subsidiaries (5.8 ) 30.0 16.4 — 40.6 Equity in undistributed earnings of subsidiaries 46.4 — — (46.4 ) — Net income $ 40.6 $ 30.0 $ 16.4 $ (46.4 ) $ 40.6 (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 NINE MONTHS ENDED SEPTEMBER 30, 2019 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries Consolidating Total Premiums and other revenue: Earned premiums $ — $ 792.1 $ 511.6 $ — $ 1,303.7 Net investment (expense) income (2.2 ) 79.6 39.5 — 116.9 Fee and other income — 2.5 3.8 — 6.3 Net realized investment (losses) gains (0.5 ) 60.6 (1.8 ) — 58.3 Total revenue (2.7 ) 934.8 553.1 — 1,485.2 Expenses: Losses and loss adjustment expenses — 507.0 354.5 — 861.5 Underwriting, acquisition and insurance expenses 10.9 311.8 174.6 — 497.3 Interest expense 5.1 13.9 6.3 — 25.3 Fee and other expense — 2.4 1.4 — 3.8 Foreign currency exchange losses (gains) — 0.3 (6.5 ) — (6.2 ) Total expenses 16.0 835.4 530.3 — 1,381.7 (Loss) income before income taxes (18.7 ) 99.4 22.8 — 103.5 Provision (benefit) for income taxes — 14.5 (5.9 ) — 8.6 Net (loss) income before equity in earnings of subsidiaries (18.7 ) 84.9 28.7 — 94.9 Equity in undistributed earnings of subsidiaries 113.6 — — (113.6 ) — Net income $ 94.9 $ 84.9 $ 28.7 $ (113.6 ) $ 94.9 (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 NINE MONTHS ENDED SEPTEMBER 30, 2018 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries Consolidating Total Premiums and other revenue: Earned premiums $ — $ 646.8 $ 632.5 $ — $ 1,279.3 Net investment (expense) income (2.0 ) 62.2 43.5 — 103.7 Fee and other income — 3.7 3.5 — 7.2 Net realized investment (losses) gains (0.2 ) 15.3 (6.1 ) — 9.0 Total revenue (2.2 ) 728.0 673.4 — 1,399.2 Expenses: Losses and loss adjustment expenses — 346.7 413.5 — 760.2 Underwriting, acquisition and insurance expenses 11.5 250.2 223.3 — 485.0 Interest expense 4.5 13.4 5.5 — 23.4 Fee and other expense — 3.7 1.8 — 5.5 Foreign currency exchange losses (gains) — 0.2 (2.5 ) — (2.3 ) Total expenses 16.0 614.2 641.6 — 1,271.8 (Loss) income before income taxes (18.2 ) 113.8 31.8 — 127.4 Provision for income taxes — 17.9 2.3 — 20.2 Net (loss) income before equity in earnings of subsidiaries (18.2 ) 95.9 29.5 — 107.2 Equity in undistributed earnings of subsidiaries 125.4 — — (125.4 ) — Net income $ 107.2 $ 95.9 $ 29.5 $ (125.4 ) $ 107.2 (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 Cash Flows	CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS FOR THE NINE MONTHS ENDED SEPTEMBER 30, 2019 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries Consolidating Total Net cash flows from operating activities $ 29.2 $ 124.6 $ 41.9 $ — $ 195.7 Cash flows from investing activities: Proceeds from sales of investments — 744.2 436.1 — 1,180.3 Maturities and mandatory calls of fixed maturity investments — 219.2 73.0 — 292.2 Purchases of investments — (1,091.2 ) (548.3 ) — (1,639.5 ) Change in short-term investments and foreign regulatory deposits 3.5 34.7 (35.9 ) — 2.3 Settlements of foreign currency exchange forward contracts (0.1 ) 1.4 (2.5 ) — (1.2 ) Purchases of fixed assets and other, net — (1.8 ) 8.5 — 6.7 Cash provided by (used in) investing activities 3.4 (93.5 ) (69.1 ) — (159.2 ) Cash flows from financing activities: Payment on the intercompany note — (19.1 ) 19.1 — — Payment on note payable — (0.6 ) — — (0.6 ) Activity under stock incentive plans 1.4 — — — 1.4 Payment of cash dividend to common shareholders (32.5 ) — — — (32.5 ) Cash (used in) provided by financing activities (31.1 ) (19.7 ) 19.1 — (31.7 ) Effect of exchange rate changes on cash — — 1.1 — 1.1 Change in cash 1.5 11.4 (7.0 ) — 5.9 Cash, beginning of year 1.7 31.7 105.8 — 139.2 Cash, end of period $ 3.2 $ 43.1 $ 98.8 $ — $ 145.1 (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 NINE MONTHS ENDED SEPTEMBER 30, 2018 (in millions) (Unaudited) Argo Group Argo Group US, Inc. Other Subsidiaries Consolidating Total Net cash flows from operating activities $ 57.7 $ 151.3 $ 22.0 $ — $ 231.0 Cash flows from investing activities: Proceeds from sales of investments — 963.2 454.0 — 1,417.2 Maturities and mandatory calls of fixed maturity investments — 302.5 72.6 — 375.1 Purchases of investments — (1,346.8 ) (630.4 ) — (1,977.2 ) Change in short-term investments and foreign regulatory deposits — (65.0 ) 31.2 — (33.8 ) Settlements of foreign currency exchange forward contracts 0.2 0.5 1.3 — 2.0 Cash acquired with acquisition of Ariscom — — 15.6 — 15.6 Purchases of fixed assets and other, net (0.1 ) (38.5 ) 6.4 — (32.2 ) Cash provided by (used in) investing activities 0.1 (184.1 ) (49.3 ) — (233.3 ) Cash flows from financing activities: Borrowing under intercompany note, net — 19.0 (19.0 ) — — Activity under stock incentive plans 1.0 — — — 1.0 Repurchase of Company's common shares (30.0 ) — — — (30.0 ) Payment of cash dividend to common shareholders (28.0 ) — — — (28.0 ) Cash (used in) provided by financing activities (57.0 ) 19.0 (19.0 ) — (57.0 ) Effect of exchange rate changes on cash — — 1.2 — 1.2 Change in cash 0.8 (13.8 ) (45.1 ) — (58.1 ) Cash, beginning of year 0.9 47.8 127.9 — 176.6 Cash, end of period $ 1.7 $ 34.0 $ 82.8 $ — $ 118.5 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations.

Investments - Additional Inform

Investments - Additional Information (Detail) $ in Millions	Sep. 30, 2019USD ($)security	Dec. 31, 2018USD ($)
Investments, Debt and Equity Securities [Abstract]
Fair value of investments, assets managed on behalf of the trade capital providers | $	$ 159.6	$ 133.4
Number of securities in an unrealized loss position, total	9,615
Number of securities in an unrealized loss position for less than one year	1,219
Number of securities in an unrealized loss position for a period of one year or greater	424

Investments - Schedule of Amort

Investments - Schedule of Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Fair Value of Investments (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fixed maturities
Amortized Cost	$ 3,716.6	$ 3,529.1
Fair Value	3,745.6	3,460.4	[1]
Fixed Maturities [Member]
Fixed maturities
Amortized Cost	3,716.6	3,529.1
Gross Unrealized Gains	74.6	17.5
Gross Unrealized Losses	45.6	86.2
Fair Value	3,745.6	3,460.4
Fixed Maturities [Member] | U.S. Governments [Member]
Fixed maturities
Amortized Cost	324.9	240.9
Gross Unrealized Gains	3.9	0.2
Gross Unrealized Losses	0.5	4.9
Fair Value	328.3	236.2
Fixed Maturities [Member] | Foreign Governments [Member]
Fixed maturities
Amortized Cost	262.6	224.1
Gross Unrealized Gains	4.2	0.5
Gross Unrealized Losses	2.3	7.8
Fair Value	264.5	216.8
Fixed Maturities [Member] | Obligations of States and Political Subdivisions [Member]
Fixed maturities
Amortized Cost	152.6	236.7
Gross Unrealized Gains	7.6	4.3
Gross Unrealized Losses	0.1	1.2
Fair Value	160.1	239.8
Fixed Maturities [Member] | Corporate Bonds [Member]
Fixed maturities
Amortized Cost	1,862	1,808.7
Gross Unrealized Gains	39	7.5
Gross Unrealized Losses	39.2	58.7
Fair Value	1,861.8	1,757.5
Fixed Maturities [Member] | Commercial Mortgage-backed Securities [Member]
Fixed maturities
Amortized Cost	213.3	205.3
Gross Unrealized Gains	6	0.7
Gross Unrealized Losses	0.3	3.2
Fair Value	219	202.8
Fixed Maturities [Member] | Residential Mortgage-backed Securities [Member]
Fixed maturities
Amortized Cost	510.3	413.1
Gross Unrealized Gains	11.9	3.4
Gross Unrealized Losses	0.9	5.7
Fair Value	521.3	410.8
Fixed Maturities [Member] | Asset-backed Securities [Member]
Fixed maturities
Amortized Cost	165.6	173.6
Gross Unrealized Gains	1.7	0.4
Gross Unrealized Losses	0.3	1.2
Fair Value	167	172.8
Fixed Maturities [Member] | Collateralized Debt Obligations [Member]
Fixed maturities
Amortized Cost	225.3	226.7
Gross Unrealized Gains	0.3	0.5
Gross Unrealized Losses	2	3.5
Fair Value	$ 223.6	$ 223.7
[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	Sep. 30, 2019USD ($)
Amortized Cost
Due in one year or less	$ 242.5
Due after one year through five years	1,584.3
Due after five years through ten years	669.5
Thereafter	105.8
Structured securities	1,114.5
Total	3,716.6
Fair Value
Due in one year or less	242.2
Due after one year through five years	1,577.1
Due after five years through ten years	683.5
Thereafter	111.9
Structured securities	1,130.9
Total	$ 3,745.6

Investments - Schedule of Carry

Investments - Schedule of Carrying Value and Unfunded Investment Commitments of Other Invested Assets Portfolio (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Carrying Value	$ 5,127	$ 4,787	[1]
Hedge funds [Member]
Schedule of Investments [Line Items]
Carrying Value	119.3	120.6
Unfunded Commitments	0	0
Private equity [Member]
Schedule of Investments [Line Items]
Carrying Value	263.9	211.8
Unfunded Commitments	94.2	120.5
Long only funds [Member]
Schedule of Investments [Line Items]
Carrying Value	112.5	153
Unfunded Commitments	0	0
Other [Member]
Schedule of Investments [Line Items]
Carrying Value	4.3	4.4
Unfunded Commitments	0	0
Other Investments [Member]
Schedule of Investments [Line Items]
Carrying Value	500	489.8
Unfunded Commitments	$ 94.2	$ 120.5
[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 [Member] - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	$ 807.5	$ 1,514.3
Unrealized Losses, Less Than One Year	37.4	55.3
Fair Value, One Year or Greater	253.5	1,105.3
Unrealized Losses, One Year or Greater	8.2	30.9
Fair Value, Total	1,061	2,619.6
Unrealized Losses, Total	45.6	86.2
U.S. Governments [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	75	28.2
Unrealized Losses, Less Than One Year	0.4	0.2
Fair Value, One Year or Greater	18.8	173
Unrealized Losses, One Year or Greater	0.1	4.7
Fair Value, Total	93.8	201.2
Unrealized Losses, Total	0.5	4.9
Foreign Governments [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	108.2	73.4
Unrealized Losses, Less Than One Year	2.1	3.6
Fair Value, One Year or Greater	9.6	125
Unrealized Losses, One Year or Greater	0.2	4.2
Fair Value, Total	117.8	198.4
Unrealized Losses, Total	2.3	7.8
Obligations of States and Political Subdivisions [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	1.1	53.3
Unrealized Losses, Less Than One Year	0	0.6
Fair Value, One Year or Greater	2.4	25.3
Unrealized Losses, One Year or Greater	0.1	0.6
Fair Value, Total	3.5	78.6
Unrealized Losses, Total	0.1	1.2
Corporate Bonds [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	355.6	964.3
Unrealized Losses, Less Than One Year	32.3	45.7
Fair Value, One Year or Greater	100	440.8
Unrealized Losses, One Year or Greater	6.9	13
Fair Value, Total	455.6	1,405.1
Unrealized Losses, Total	39.2	58.7
Commercial Mortgage-backed Securities [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	53.8	48.5
Unrealized Losses, Less Than One Year	0.2	0.6
Fair Value, One Year or Greater	5.3	90.6
Unrealized Losses, One Year or Greater	0.1	2.6
Fair Value, Total	59.1	139.1
Unrealized Losses, Total	0.3	3.2
Residential Mortgage-backed Securities [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	57.1	63.5
Unrealized Losses, Less Than One Year	0.4	0.7
Fair Value, One Year or Greater	43.9	176.1
Unrealized Losses, One Year or Greater	0.5	5
Fair Value, Total	101	239.6
Unrealized Losses, Total	0.9	5.7
Asset-backed Securities [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	17.9	73.6
Unrealized Losses, Less Than One Year	0.2	0.6
Fair Value, One Year or Greater	19.4	64.2
Unrealized Losses, One Year or Greater	0.1	0.6
Fair Value, Total	37.3	137.8
Unrealized Losses, Total	0.3	1.2
Collateralized Debt Obligations [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	138.8	209.5
Unrealized Losses, Less Than One Year	1.8	3.3
Fair Value, One Year or Greater	54.1	10.3
Unrealized Losses, One Year or Greater	0.2	0.2
Fair Value, Total	192.9	219.8
Unrealized Losses, Total	$ 2	$ 3.5

Investments - Schedule of Recog

Investments - Schedule of Recognized Other-than-temporary Losses on Fixed Maturities and Equity Portfolios (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Other-than-temporary impairment:
Other-than-temporary impairment losses	$ (5)	$ 0	$ (11.8)	$ (1.9)
Corporate Bonds [Member]
Other-than-temporary impairment:
Other-than-temporary impairment losses	$ (5)	$ 0	$ (11.8)	$ (1.9)

Investments - Schedule of Compa

Investments - Schedule of Company's Gross Realized Investment Gains (Losses) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other	$ 11.2	$ 12.2	$ 34.9	$ 50.7
Realized losses on fixed maturities and other	(15)	(11.6)	(42.3)	(50.5)
Net realized gains on equity securities	6.4	9.1	7.7	30.9
Change in unrealized (losses) gains on equity securities held at the end of the period	(8.8)	4.5	58	(22.1)
Net realized (losses) gains on equity securities	(2.4)	13.6	65.7	8.8
Net realized investment (losses) gains before income taxes	(6.2)	14.2	58.3	9
Income tax benefit (provision)	0.3	(3.3)	(11.9)	(2.8)
Net realized investment (losses) gains net of income taxes	(5.9)	10.9	46.4	6.2
Fixed Maturities [Member]
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other	3.7	4.6	13	15.8
Realized losses on fixed maturities and other	(1.6)	(2.8)	(8.7)	(14.2)
Other Investments [Member]
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other	7.5	7.4	21.9	34.7
Realized losses on fixed maturities and other	(8.4)	(8.8)	(21.8)	(34.4)
Other Assets and Short-term Investments [Member]
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other	0	0.2	0	0.2
Other-Than-Temporary Impairment Losses on Fixed Maturities [Member]
Schedule of Investments [Line Items]
Realized losses on fixed maturities and other	$ (5)	$ 0	$ (11.8)	$ (1.9)

Investments - Schedule of Chang

Investments - Schedule of Changes in Unrealized Appreciation (Depreciation) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Schedule of Investments [Line Items]
Net unrealized investment gains (losses) before income taxes	$ (4.6)	$ (4.8)	$ 99	$ (63.6)
Income tax (provision) benefit	0.4	1.4	(16.1)	10.5
Net unrealized investment gains (losses), net of income taxes	(4.2)	(3.4)	82.9	(53.1)
Fixed Maturities [Member]
Schedule of Investments [Line Items]
Net unrealized investment gains (losses) before income taxes	(3.8)	(4.3)	95.3	(63.2)
Other Investment [Member]
Schedule of Investments [Line Items]
Net unrealized investment gains (losses) before income taxes	0	0	4.4		$ 0.1
Short-term Investments [Member]
Schedule of Investments [Line Items]
Net unrealized investment gains (losses) before income taxes	$ (0.8)	$ (0.5)	$ (0.7)	$ (0.5)

Investments - Schedule of Fair

Investments - Schedule of Fair Value of Foreign Currency Exchange Forward Contracts (Detail) - Foreign Currency Exchange Forward Contracts [Member] - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Foreign currency exchange, fair value	$ (0.5)	$ 2.6
Operational Currency Exposure [Member]
Schedule of Investments [Line Items]
Foreign currency exchange, fair value	(1.4)	4.4
Asset Manager Investment Exposure [Member]
Schedule of Investments [Line Items]
Foreign currency exchange, fair value	0.9	(0.3)
Total return strategy [Member]
Schedule of Investments [Line Items]
Foreign currency exchange, fair value	$ 0	$ (1.5)

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 [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Schedule of Investments [Line Items]
Gross realized investment gains	$ 9.6	$ 7.4	$ 24.1	$ 33.3
Gross realized investment losses	(10.4)	(8.8)	(24.1)	(32.8)
Net realized investment (losses) gains on foreign currency exchange forward contracts	(0.8)	(1.4)	0	0.5
Operational Currency Exposure [Member]
Schedule of Investments [Line Items]
Gross realized investment gains	1.3	0.4	2.2	6.4
Gross realized investment losses	(3.2)	(2.7)	(7.8)	(7)
Asset Manager Investment Exposure [Member]
Schedule of Investments [Line Items]
Gross realized investment gains	1.8	1.4	3.1	14.4
Gross realized investment losses	(0.1)	(0.9)	(0.6)	(12.5)
Total return strategy [Member]
Schedule of Investments [Line Items]
Gross realized investment gains	6.5	5.6	18.8	12.5
Gross realized investment losses	$ (7.1)	$ (5.2)	$ (15.7)	$ (13.3)

Investments - Components of Res

Investments - Components of Restricted Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Securities pledged as collateral for letters of credit	$ 129.5	$ 76.5
Securities and cash on deposit supporting Lloyd’s business	403.6	418.4
Total restricted investments	731.9	675.5
Securities Deposits For Regulatory and Other Purposes [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Securities on deposit for regulatory and other purposes	$ 198.8	$ 180.6

Investments - Financial Assets

Investments - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	$ 5,127	$ 4,787	[1]
Other Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	500	489.8
Fair Value, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	5,032.9	4,411.6
Fair Value, Recurring [Member] | Fixed Maturities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	3,745.6	3,460.4
Fair Value, Recurring [Member] | Fixed Maturities [Member] | Collateralized Loan Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	223.6	223.7
Fair Value, Recurring [Member] | Fixed Maturities [Member] | U.S. Governments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	328.3	236.2
Fair Value, Recurring [Member] | Fixed Maturities [Member] | Foreign Governments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	264.5	216.8
Fair Value, Recurring [Member] | Fixed Maturities [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	160.1	239.8
Fair Value, Recurring [Member] | Fixed Maturities [Member] | Corporate Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	1,861.8	1,757.5
Fair Value, Recurring [Member] | Fixed Maturities [Member] | Commercial Mortgage-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	219	202.8
Fair Value, Recurring [Member] | Fixed Maturities [Member] | Residential Mortgage-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	521.3	410.8
Fair Value, Recurring [Member] | Fixed Maturities [Member] | Asset-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	167	172.8
Fair Value, Recurring [Member] | Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	400.6	354.5
Fair Value, Recurring [Member] | Other Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	405.9	114.4
Fair Value, Recurring [Member] | Short-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	480.8	482.3
Fair Value, Recurring [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	1,165.6	1,026.9
Fair Value, Recurring [Member] | Level 1 [Member] | Fixed Maturities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	324.2	226.7
Fair Value, Recurring [Member] | Level 1 [Member] | Fixed Maturities [Member] | Collateralized Loan Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Fixed Maturities [Member] | U.S. Governments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	323	226.7
Fair Value, Recurring [Member] | Level 1 [Member] | Fixed Maturities [Member] | Foreign Governments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Fixed Maturities [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Fixed Maturities [Member] | Corporate Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	1.2	0
Fair Value, Recurring [Member] | Level 1 [Member] | Fixed Maturities [Member] | Commercial Mortgage-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Fixed Maturities [Member] | Residential Mortgage-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Fixed Maturities [Member] | Asset-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	392.1	346.3
Fair Value, Recurring [Member] | Level 1 [Member] | Other Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Short-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	449.3	453.9
Fair Value, Recurring [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	3,852	3,374.3
Fair Value, Recurring [Member] | Level 2 [Member] | Fixed Maturities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	3,414.6	3,231.5
Fair Value, Recurring [Member] | Level 2 [Member] | Fixed Maturities [Member] | Collateralized Loan Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	223.6	223.7
Fair Value, Recurring [Member] | Level 2 [Member] | Fixed Maturities [Member] | U.S. Governments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	5.3	9.5
Fair Value, Recurring [Member] | Level 2 [Member] | Fixed Maturities [Member] | Foreign Governments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	264.5	216.8
Fair Value, Recurring [Member] | Level 2 [Member] | Fixed Maturities [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	160.1	239.8
Fair Value, Recurring [Member] | Level 2 [Member] | Fixed Maturities [Member] | Corporate Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	1,853.8	1,755.3
Fair Value, Recurring [Member] | Level 2 [Member] | Fixed Maturities [Member] | Commercial Mortgage-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	219	202.8
Fair Value, Recurring [Member] | Level 2 [Member] | Fixed Maturities [Member] | Residential Mortgage-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	521.3	410.8
Fair Value, Recurring [Member] | Level 2 [Member] | Fixed Maturities [Member] | Asset-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	167	172.8
Fair Value, Recurring [Member] | Level 2 [Member] | Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value		0
Fair Value, Recurring [Member] | Level 2 [Member] | Other Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	405.9	114.4
Fair Value, Recurring [Member] | Level 2 [Member] | Short-term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	31.5	28.4
Fair Value, Recurring [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	15.3	10.4
Fair Value, Recurring [Member] | Level 3 [Member] | Fixed Maturities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	6.8	2.2
Fair Value, Recurring [Member] | Level 3 [Member] | Fixed Maturities [Member] | Collateralized Loan Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Fixed Maturities [Member] | U.S. Governments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Fixed Maturities [Member] | Foreign Governments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Fixed Maturities [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Fixed Maturities [Member] | Corporate Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	6.8	2.2
Fair Value, Recurring [Member] | Level 3 [Member] | Fixed Maturities [Member] | Commercial Mortgage-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Fixed Maturities [Member] | Residential Mortgage-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Fixed Maturities [Member] | Asset-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	8.5	8.2
Fair Value, Recurring [Member] | Level 3 [Member] | Other Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Short-term Investments [Member]
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	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 10.4	$ 4.2
Transfers into Level 3	3.5	0
Transfers out of Level 3	0	0
Included in net income	0.3	0.2
Included in other comprehensive income	(0.5)	0.3
Purchases	1.9	7.3
Issuances	0	0
Sales	(0.3)	(1.6)
Settlements	0	0
Ending balance	15.3	10.4
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 September 30, 2019	0	0
Credit-Financial [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	2.2	1.9
Transfers into Level 3	3.5	0
Transfers out of Level 3	0	0
Included in net income	0	0
Included in other comprehensive income	(0.5)	0.3
Purchases	1.9	0
Issuances	0	0
Sales	(0.3)	0
Settlements	0	0
Ending balance	6.8	2.2
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 September 30, 2019	0	0
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	8.2	2.3
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Included in net income	0.3	0.2
Included in other comprehensive income	0	0
Purchases	0	7.3
Issuances	0	0
Sales	0	(1.6)
Settlements	0	0
Ending balance	8.5	8.2
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 September 30, 2019	$ 0	$ 0

Leases - Additional Information

Leases - Additional Information (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)property	Sep. 30, 2018USD ($)
Lessee, Lease, Description [Line Items]
Lease cost	$ 5	$ 5.2	$ 17.1	$ 18.2
Number of leased properties | property			3
Lease income	$ 0.7	$ 0.7	$ 2.2	$ 2.2
Minimum [Member]
Lessee, Lease, Description [Line Items]
Lease term	1 year		1 year
Maximum [Member]
Lessee, Lease, Description [Line Items]
Lease term	14 years		14 years

Leases - Components of Leases (

Leases - Components of Leases (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	[1]
Leases [Abstract]
Operating lease right-of-use assets	$ 108.6
Operating lease liabilities	$ 120.2	$ 0
Operating lease weighted-average remaining lease term	10 years 3 months 21 days
Operating lease weighted-average discount rate	3.93%
[1]	Derived from audited consolidated financial statements.

Leases - Lease Cost (Details)

Leases - Lease Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Leases [Abstract]
Operating lease costs	$ 5.1		$ 15.3
Variable lease costs	0		2.1
Sublease income	(0.1)		(0.3)
Total lease costs	$ 5	$ 5.2	17.1	$ 18.2
Operating cash flows from operating leases (fixed payments)			14.1
Operating cash flows from operating leases (liability reduction)			$ 11.5

Leases - Lease Maturity (Detail

Leases - Lease Maturity (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2019	$ 4.7
2020	18.6
2021	17.5
2022	14.8
2023	12.3
Thereafter	79.4
Total future minimum lease payments	147.3
Future lease obligations	(0.5)
Less imputed interest	(26.6)
Total operating lease liability	$ 120.2	$ 0	[1]
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2019		18.7
2020		18.6
2021		17.5
2022		14.7
2023		12.3
Thereafter		80.1
Total future minimum lease payments		$ 161.9
[1]	Derived from audited consolidated financial statements.

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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	[1]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Net reserves beginning of the year			$ 2,562.9	$ 2,488
Net reserves acquired			0	49.4
Losses and LAE incurred during current calendar year, net of reinsurance:
Current accident year			799.9	764.3
Prior accident years			61.6	(4.1)
Losses and LAE incurred during calendar year, net of reinsurance	$ 338.8	$ 277.5	861.5	760.2
Losses and LAE payments made during current calendar year, net of reinsurance:
Current accident year			163.6	223.2
Prior accident years			615.8	469
Losses and LAE payments made during current calendar year, net of reinsurance:			779.4	692.2
Change in participation interest			(14.4)	(29.4)
Foreign exchange adjustments			(26.3)	(20.8)
Net reserves - end of period	2,604.3	2,555.2	2,604.3	2,555.2
Reinsurance recoverables on unpaid losses and LAE, end of period	2,238.2	1,736.5	2,238.2	1,736.5
Gross reserves - end of period	$ 4,842.5	$ 4,291.7	$ 4,842.5	$ 4,291.7	$ 4,654.6
[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	6 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total unfavorable (favorable) prior-year development		$ 61.6	$ (4.1)
U.S. Operations [Member]
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total unfavorable (favorable) prior-year development		(9.8)	(14.8)
International Operations [Member]
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total unfavorable (favorable) prior-year development	$ 68.7	69.5	(0.8)
Run Off Lines [Member]
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total unfavorable (favorable) prior-year development		$ 1.9	$ 11.5

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	Sep. 30, 2019	Dec. 31, 2018
Junior Subordinated Debentures [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	$ 257.3	$ 257
Junior Subordinated Debentures [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	246.1	248.2
Junior Subordinated Debentures [Member] | Trust Preferred Debentures [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	172.7	172.7
Junior Subordinated Debentures [Member] | Trust Preferred Debentures [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	160.7	163.2
Junior Subordinated Debentures [Member] | Junior Subordinated Debentures [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	84.6	84.3
Junior Subordinated Debentures [Member] | Junior Subordinated Debentures [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	85.4	85
Senior Unsecured Fixed Rate Notes [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	139.9	139.8
Senior Unsecured Fixed Rate Notes [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	143.4	139.5
Floating Rate Loan Stock [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	56.4	57.8
Floating Rate Loan Stock [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	$ 52.5	$ 54.5

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 [Member] - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	$ 688.1	$ 445.8
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	143.4	139.8
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	544.7	306
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	0	0
Junior Subordinated Debentures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	246.1	248.2
Junior Subordinated Debentures [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	0	0
Junior Subordinated Debentures [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	246.1	248.2
Junior Subordinated Debentures [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	0	0
Junior Subordinated Debentures [Member] | Trust Preferred Debentures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	160.7	163.2
Junior Subordinated Debentures [Member] | Trust Preferred Debentures [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	0	0
Junior Subordinated Debentures [Member] | Trust Preferred Debentures [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	160.7	163.2
Junior Subordinated Debentures [Member] | Trust Preferred Debentures [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	0	0
Junior Subordinated Debentures [Member] | Maybrooke Junior Subordinated Debentures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	85.4	85
Junior Subordinated Debentures [Member] | Maybrooke Junior Subordinated Debentures [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	0	0
Junior Subordinated Debentures [Member] | Maybrooke Junior Subordinated Debentures [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	85.4	85
Junior Subordinated Debentures [Member] | Maybrooke Junior Subordinated Debentures [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	0	0
Senior Unsecured Fixed Rate Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	143.4	139.8
Senior Unsecured Fixed Rate Notes [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	143.4	139.8
Senior Unsecured Fixed Rate Notes [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	0	0
Senior Unsecured Fixed Rate Notes [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	0	0
Floating Rate Loan Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	52.5	57.8
Floating Rate Loan Stock [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	0	0
Floating Rate Loan Stock [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments	52.5	57.8
Floating Rate Loan Stock [Member] | Level 3 [Member]
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 ($)	Sep. 13, 2019	Aug. 06, 2019	Jun. 21, 2019	May 24, 2019	Jun. 15, 2018	May 08, 2018	Mar. 07, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Feb. 20, 2018	May 03, 2016
Class of Stock [Line Items]
Dividend declared per common share (in dollars per share)		$ 0.31		$ 0.31		$ 0.27		$ 0.31	$ 0.27	$ 0.93	$ 0.81
Cash dividends paid - common shares, total	$ 10,900,000		$ 10,800,000		$ 9,400,000					$ 32,500,000	$ 28,000,000
Stock dividend percent									15.00%		15.00%
2016 Repurchase Authorization [Member]
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
Stock Dividend [Member]
Class of Stock [Line Items]
Stock dividend percent												15.00%
Additional stock issued as dividend (in shares)							4,397,520

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive (Loss) Income - Changes in Accumulated Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended			12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019		Sep. 30, 2018	Dec. 31, 2018		Jan. 01, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			$ 1,746.7	[1]	$ 1,819.7	$ 1,819.7
Other comprehensive (loss) income before reclassifications			76.1		(58.2)
Amounts reclassified from accumulated other comprehensive income			6.7		0.3
Net current-period other comprehensive (loss) income			82.8		(57.9)
Ending Balance	$ 1,893.4	$ 1,818.1	1,893.4		1,818.1	1,746.7	[1]
Foreign Currency Translation Adjustments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			(22.4)		(19)	(19)
Other comprehensive (loss) income before reclassifications			(0.1)		(4.8)
Amounts reclassified from accumulated other comprehensive income			0		0
Net current-period other comprehensive (loss) income			(0.1)		(4.8)
Ending Balance	(22.5)	(23.8)	(22.5)		(23.8)	(22.4)
Foreign Currency Translation Adjustments [Member] | ASU 2016-01 [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of adoption of ASU								$ 0
Foreign Currency Translation Adjustments [Member] | ASU 2018-02 [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of adoption of ASU								0
Unrealized Holding Gains on Securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			(49)		121.9	121.9
Other comprehensive (loss) income before reclassifications			76.2		(53.4)
Amounts reclassified from accumulated other comprehensive income	2.5	(2.1)	6.7		0.3	0.3
Net current-period other comprehensive (loss) income			82.9		(53.1)
Ending Balance	33.9	(26.6)	33.9		(26.6)	(49)
Unrealized Holding Gains on Securities [Member] | ASU 2016-01 [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of adoption of ASU								(117.5)
Unrealized Holding Gains on Securities [Member] | ASU 2018-02 [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of adoption of ASU								22.1
Defined Benefit Pension Plans [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			(6.7)		(6.3)	(6.3)
Other comprehensive (loss) income before reclassifications			0		0
Amounts reclassified from accumulated other comprehensive income			0		0
Net current-period other comprehensive (loss) income			0		0
Ending Balance	(6.7)	(7.7)	(6.7)		(7.7)	(6.7)
Defined Benefit Pension Plans [Member] | ASU 2016-01 [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of adoption of ASU								0
Defined Benefit Pension Plans [Member] | ASU 2018-02 [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of adoption of ASU								(1.4)
Accumulated Other Comprehensive Income (Loss) Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			(78.1)		96.6	96.6
Ending Balance	$ 4.7	$ (58.1)	$ 4.7		$ (58.1)	$ (78.1)
Accumulated Other Comprehensive Income (Loss) Member] | ASU 2016-01 [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of adoption of ASU								(117.5)
Accumulated Other Comprehensive Income (Loss) Member] | ASU 2018-02 [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of adoption of ASU								$ 20.7
[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		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Unrealized gains and losses on securities:
Net of taxes			$ 6.7	$ 0.3
Unrealized Gains and Losses on Securities [Member]
Unrealized gains and losses on securities:
Net realized investment loss (gains)	$ 2.8	$ (2.4)	7.7		$ 0.2
(Benefit) provision for income taxes	(0.3)	0.3	(1)		0.1
Net of taxes	$ 2.5	$ (2.1)	$ 6.7	$ 0.3	$ 0.3

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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net (loss) income	$ (25.1)	$ 40.6	$ 94.9	$ 107.2
Weighted average common shares outstanding - basic (in shares)	34,299,999	33,956,695	34,161,016	33,921,632
Effect of dilutive securities:
Equity compensation awards (in shares)	0	699,633	608,606	767,211
Weighted average common shares outstanding - diluted (in shares)	34,299,999	34,656,328	34,769,622	34,688,843
Net (loss) income per common share:
Basic (in dollars per share)	$ (0.73)	$ 1.20	$ 2.78	$ 3.16
Diluted (in dollars per share)	$ (0.73)	$ 1.17	$ 2.73	$ 3.09

Net (Loss) Income Per Common _4

Net (Loss) Income Per Common Share - Additional Information (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Earnings Per Share [Abstract]
Treasury shares (in shares)	11,315,889	11,285,996	11,315,889	11,285,996	11,315,889
Equity compensation awards with anti-dilutive effect (in shares)	489,376	0	2,331	0

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information - Schedule of Interest Paid and Income Taxes Paid (Recovered) (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Supplemental Cash Flow [Line Items]
Total interest paid	$ 26.5	$ 23.1
Income taxes paid	4.8	18.1
Income taxes recovered	(0.1)	0
Income taxes paid, net	4.7	18.1
Senior Unsecured Fixed Rate Notes [Member]
Supplemental Cash Flow [Line Items]
Total interest paid	7	7
Junior Subordinated Debentures [Member]
Supplemental Cash Flow [Line Items]
Total interest paid	12.3	11.2
Other Indebtedness [Member]
Supplemental Cash Flow [Line Items]
Total interest paid	$ 7.2	$ 4.9

Share-based Compensation - Addi

Share-based Compensation - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	May 31, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period, years				5 years
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, compensation expense		$ 3,200,000	$ 2,600,000	$ 10,500,000	$ 10,900,000
Employee service share-based compensation, unrecognized compensation costs on non-vested awards		28,000,000		$ 28,000,000
Restricted Stock Units (RSUs) [Member] | Minimum [Member]
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) [Member] | Maximum [Member]
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 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, compensation expense		0	400,000	$ 400,000	1,800,000
Employee service share-based compensation, unrecognized compensation costs on non-vested awards		0		0
Cash Settled S A Rs Activity [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, compensation expense		(100,000)	$ 500,000	500,000	$ 1,200,000
Employee service share-based compensation, unrecognized compensation costs on non-vested awards		$ 0		$ 0
2019 Plan [Member]
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 - Fair

Share-based Compensation - Fair Value Assumptions (Detail)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Share-based Payment Arrangement [Abstract]
Risk-free rate of return	1.66%	2.96%
Expected dividend yields	1.76%	1.84%
Expected award life (years)	4 years 6 months	4 years 5 months 26 days
Expected volatility	18.73%	17.82%

Share-based Compensation - Summ

Share-based Compensation - Summary of Restricted Share Activity (Detail) - Restricted Stock Units (RSUs) [Member]	9 Months Ended
	Sep. 30, 2019$ / sharesshares
Shares
Outstanding, beginning balance (in shares) | shares	897,005
Granted (in shares) | shares	209,557
Vested and issued (in shares) | shares	(403,316)
Expired or forfeited (in shares) | shares	(59,635)
Outstanding, ending balance (in shares) | shares	643,611
Weighted-Average Grant Date Fair Value
Outstanding, beginning balance (in dollars per share) | $ / shares	$ 46.92
Granted (in dollars per share) | $ / shares	68.65
Vested and issued (in dollars per share) | $ / shares	35.74
Expired or forfeited (in dollars per share) | $ / shares	55.41
Outstanding, ending balance (in dollars per share) | $ / shares	$ 59.93

Share-based Compensation - Su_2

Share-based Compensation - Summary of SARs Activity (Detail)	9 Months Ended
	Sep. 30, 2019$ / sharesshares
Stock-Settled SARs Activity [Member]
Shares
Outstanding, beginning balance (in shares) | shares	810,759
Exercised (in shares) | shares	(148,729)
Expired or forfeited (in shares) | shares	(7,167)
Outstanding, ending balance (in shares) | shares	654,863
Weighted-Average Exercise Price
Outstanding, beginning balance (in dollars per share) | $ / shares	$ 33.88
Exercised (in dollars per share) | $ / shares	34.71
Expired or forfeited (in dollars per share) | $ / shares	37.85
Outstanding, ending balance (in dollars per share) | $ / shares	$ 33.68
Cash Settled S A Rs Activity [Member]
Shares
Outstanding, beginning balance (in shares) | shares	58,428
Exercised (in shares) | shares	(48,722)
Expired or forfeited (in shares) | shares	(1,193)
Outstanding, ending balance (in shares) | shares	8,513
Weighted-Average Exercise Price
Outstanding, beginning balance (in dollars per share) | $ / shares	$ 30.71
Exercised (in dollars per share) | $ / shares	30.34
Expired or forfeited (in dollars per share) | $ / shares	19.37
Outstanding, ending balance (in dollars per share) | $ / shares	$ 34.39

Underwriting, Acquisition and_3

Underwriting, Acquisition and Insurance Expenses (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Underwriting Acquisition And Insurance Expenses [Abstract]
Commissions	$ 58	$ 88	$ 178	$ 212.7
General expenses	92.9	83.2	281	261.6
Premium taxes, boards and bureaus	10.8	9.8	27	27.2
Underwriting, acquisition and insurance expenses, total	161.7	181	486	501.5
Net deferral of policy acquisition costs	6	(13)	11.3	(16.5)
Total underwriting, acquisition and insurance expenses	167.7	$ 168	497.3	$ 485
Proxy solicitation and related expense	$ 3.7		$ 11.7

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)subsidiary	Sep. 30, 2018USD ($)
Income Tax Disclosure [Abstract]
Number of subsidiaries subject to corporate tax | subsidiary			8
Net operating losses carryback period			2 years
Capital losses carryback period			3 years
Change in valuation allowance	$ 2,200,000	$ (200,000)	$ 1,600,000	$ (3,600,000)
Unrecognized tax benefits	$ 0	$ 0	$ 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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (26.2)	$ 45.3	$ 103.5	$ 127.4
Effective Tax Rate	4.10%	10.20%	8.40%	15.80%
Bermuda [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (7.8)	$ 6.4	$ 39.1	$ (1.8)
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
United States [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 7.7	$ 34.8	$ 99.5	$ 114.2
Effective Tax Rate	16.40%	13.40%	14.60%	15.60%
United Kingdom [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (17.9)	$ 3.5	$ (30.3)	$ 16.3
Effective Tax Rate	13.10%	(5.00%)	19.20%	12.30%
Belgium [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (0.1)	$ 0	$ (0.4)	$ 0
Effective Tax Rate	28.60%	30.80%	29.40%	33.30%
Brazil [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 1.2	$ 0.4	$ 5	$ (1)
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
United Arab Emirates [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0	$ 0.2	$ 0.3	$ 0.5
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
Ireland [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0	$ (0.1)	$ (0.1)	$ (0.2)
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
Italy [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (3.6)	$ (1.8)	$ (4.1)	$ (2.9)
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
Malta [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (5.6)	$ 1.8	$ (5.4)	$ 2.2
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
Luxembourg [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0	$ 0	$ 0	$ 0
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
Switzerland [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (0.1)	$ 0.1	$ (0.1)	$ 0.1
Effective Tax Rate	1.00%	21.20%	0.90%	21.20%

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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income tax provision at expected rate	$ (4.1)	$ 8.4	$ 14.4	$ 26.8
Tax effect of:
Nontaxable investment income	(0.4)	(0.4)	(1.1)	(1.4)
Foreign exchange adjustments	0.7	(1)	1.3	(1.2)
Withholding taxes	0	0.2	0.2	0.5
Prior period adjustments	0	(2.2)	(1.8)	(2.1)
Change in valuation allowance	2.2	(0.2)	1.6	(3.6)
Other	0.5	(0.1)	(6)	1.2
Income tax provision	$ (1.1)	$ 4.7	$ 8.6	$ 20.2

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2019USD ($)
Commitments and Contingencies Disclosure [Abstract]
Contractual commitments related to its limited partnership investments (up to)	$ 94.2
Contractual commitments period (not to exceed)	13 years

Segment Information - Additiona

Segment Information - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2019USD ($)segment	Dec. 31, 2018USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment	2
Assets associated with trade capital providers | $	$ 884.6	$ 880.4

Segment Information - Revenue a

Segment Information - Revenue and Income (Loss) Before Income Taxes for Each Segment (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Earned premiums	$ 451.5	$ 446.9	$ 1,303.7	$ 1,279.3
Net investment income	40.2	34.5	116.9	103.7
Fee and other income	1.9	3.3	6.3	7.2
Net realized investment (losses) gains before income taxes	(6.2)	14.2	58.3	9
Foreign currency exchange gains	1.6	1.7	6.2	2.3
Other corporate expenses	(3.7)	0	(11.7)	0
Total revenue	487.4	498.9	1,485.2	1,399.2
Income (loss) before income taxes	(26.2)	45.3	103.5	127.4
Operating Segments [Member]
Segment Reporting Information [Line Items]
Income (loss) before income taxes	(10)	41.5	80.8	153.1
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net investment income	0.4	2.6	1.1	7.1
Income (loss) before income taxes	(7.9)	(12.1)	(30.1)	(37)
U.S. Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned premiums	290.8	278.3	848.6	807.6
Net investment income	27.4	21.4	80.1	64.7
Income (loss) before income taxes	42.2	50.3	138.3	126.8
International Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned premiums	160.7	168.5	455	471.4
Net investment income	10.7	8.4	31.3	25.6
Income (loss) before income taxes	(52.9)	(1.2)	(57.7)	34.9
Run Off Lines [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned premiums	0	0.1	0.1	0.3
Net investment income	1.7	2.1	4.4	6.3
Income (loss) before income taxes	$ 0.7	$ (7.6)	$ 0.2	$ (8.6)

Segment Information - Schedule

Segment Information - Schedule of Earned Premiums by Geographic Location (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	$ 451.5	$ 446.9	$ 1,303.7	$ 1,279.3
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	289.6	276.5	845.4	803.7
United Kingdom [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	101.9	117.2	295.6	333.3
Bermuda [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	24.3	23.3	60.1	64.7
Malta [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	21.3	18.2	62.3	39.6
Other Jurisdiction [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	$ 14.4	$ 11.7	$ 40.3	$ 38

Segment Information - Identifia

Segment Information - Identifiable Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	$ 10,445.8	$ 9,558.2	[1]
Operating Segments [Member] | U.S. Operations [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	5,477.4	4,707.8
Operating Segments [Member] | International Operations [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	4,403.8	3,984.7
Operating Segments [Member] | Run Off Lines [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	375.9	444.8
Corporate and Other [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	$ 188.7	$ 420.9
[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	Sep. 30, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Principal amount of senior note		$ 143,800,000	$ 143,800,000
Senior Unsecured Fixed Rate Notes [Member]
Schedule of Equity Method Investments [Line Items]
Principal amount of senior note	$ 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	Sep. 30, 2019	Dec. 31, 2018
Debt Disclosure [Abstract]
Principal	$ 143.8	$ 143.8
Less: unamortized debt issuance costs	(3.9)	(4)
Senior unsecured fixed rate notes, less unamortized debt issuance costs	$ 139.9	$ 139.8	[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	Sep. 30, 2019	Dec. 31, 2018		Sep. 30, 2018	Dec. 31, 2017
Assets
Investments	$ 5,127	$ 4,787	[1]
Cash	145.1	139.2	[1]
Accrued investment income	27.7	27.2	[1]
Premiums receivable	740.3	649.9	[1]
Reinsurance recoverables	2,873.8	2,688.3	[1]
Goodwill and other intangible assets, net	269.2	270.5
Current income taxes receivable, net	0.2	8.2	[1]
Deferred acquisition costs, net	159.5	167.3	[1]
Ceded unearned premiums	603.8	457.7	[1]
Operating lease right-of-use assets	108.6
Other assets	390.6	362.9	[1]
Intercompany note receivable	0	0
Investments in subsidiaries	0	0
Total assets	10,445.8	9,558.2	[1]
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	4,842.5	4,654.6	[1]	$ 4,291.7
Unearned premiums	1,495.5	1,300.9	[1]
Funds held and ceded reinsurance payable, net	1,211.8	1,007.7
Debt	578.6	580.2
Deferred tax liabilities, net	19.9	6.2	[1]
Accrued underwriting expenses and other liabilities	283.9	261.9	[1]
Operating lease liabilities	120.2	0	[1]
Due to (from) affiliates	0	0
Intercompany note payable		0
Total liabilities	8,552.4	7,811.5	[1]
Total shareholders' equity	1,893.4	1,746.7	[1]	$ 1,818.1	$ 1,819.7
Total liabilities and shareholders' equity	10,445.8	9,558.2	[1]
Consolidating Adjustments [Member]
Assets
Investments	0	0
Cash	0	0
Accrued investment income	0	0
Premiums receivable	0	0
Reinsurance recoverables	0	0
Goodwill and other intangible assets, net	0	0
Current income taxes receivable, net	0	0
Deferred acquisition costs, net	0	0
Ceded unearned premiums	0	0
Operating lease right-of-use assets	0
Other assets	0	0
Intercompany note receivable	0	0
Investments in subsidiaries	(2,053.6)	(1,852.7)
Total assets	(2,053.6)	(1,852.7)
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
Deferred tax liabilities, net	0	0
Accrued underwriting expenses and other liabilities	0	0
Operating lease liabilities	0
Due to (from) affiliates	(50.5)	(8.5)
Intercompany note payable		0
Total liabilities	(50.5)	(8.5)
Total shareholders' equity	(2,003.1)	(1,844.2)
Total liabilities and shareholders' equity	(2,053.6)	(1,852.7)
Other Subsidiaries and Eliminations [Member]
Assets
Investments	1,710.3	1,607.3
Cash	98.8	105.8
Accrued investment income	7.9	6.9
Premiums receivable	478.7	420.4
Reinsurance recoverables	1,211.9	1,053.1
Goodwill and other intangible assets, net	104.8	104.8
Current income taxes receivable, net	0.2	(0.9)
Deferred acquisition costs, net	66.9	81.1
Ceded unearned premiums	308.9	207.3
Operating lease right-of-use assets	28.9
Other assets	209.9	181.9
Intercompany note receivable	(55.9)	(53.7)
Investments in subsidiaries	0	0
Total assets	4,171.3	3,714
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	1,897.8	1,883.2
Unearned premiums	598.7	503.5
Funds held and ceded reinsurance payable, net	546.4	268.4
Debt	141	142.1
Deferred tax liabilities, net	(5.4)	0.6
Accrued underwriting expenses and other liabilities	147.3	142.3
Operating lease liabilities	30.7
Due to (from) affiliates	4.2	(2)
Intercompany note payable		(19.1)
Total liabilities	3,360.7	2,919
Total shareholders' equity	810.6	795
Total liabilities and shareholders' equity	4,171.3	3,714
Argo Group International Holdings, Ltd (Parent Guarantor) [Member]
Assets
Investments	0.3	3.8
Cash	3.2	1.7
Accrued investment income	0	0
Premiums receivable	0	0
Reinsurance recoverables	0	0
Goodwill and other intangible assets, net	40.9	41.9
Current income taxes receivable, net	0	0
Deferred acquisition costs, net	0	0
Ceded unearned premiums	0	0
Operating lease right-of-use assets	7.8
Other assets	10.5	15.7
Intercompany note receivable	0	0
Investments in subsidiaries	2,053.6	1,852.7
Total assets	2,116.3	1,915.8
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
Deferred tax liabilities, net	0	0
Accrued underwriting expenses and other liabilities	11	7.2
Operating lease liabilities	8
Due to (from) affiliates	50.5	8.5
Intercompany note payable		0
Total liabilities	222.9	169.1
Total shareholders' equity	1,893.4	1,746.7
Total liabilities and shareholders' equity	2,116.3	1,915.8
Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) [Member]
Assets
Investments	3,416.4	3,175.9
Cash	43.1	31.7
Accrued investment income	19.8	20.3
Premiums receivable	261.6	229.5
Reinsurance recoverables	1,661.9	1,635.2
Goodwill and other intangible assets, net	123.5	123.8
Current income taxes receivable, net	0	9.1
Deferred acquisition costs, net	92.6	86.2
Ceded unearned premiums	294.9	250.4
Operating lease right-of-use assets	71.9
Other assets	170.2	165.3
Intercompany note receivable	55.9	53.7
Investments in subsidiaries	0	0
Total assets	6,211.8	5,781.1
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	2,944.7	2,771.4
Unearned premiums	896.8	797.4
Funds held and ceded reinsurance payable, net	665.4	739.3
Debt	284.2	284.7
Deferred tax liabilities, net	25.3	5.6
Accrued underwriting expenses and other liabilities	125.6	112.4
Operating lease liabilities	81.5
Due to (from) affiliates	(4.2)	2
Intercompany note payable		19.1
Total liabilities	5,019.3	4,731.9
Total shareholders' equity	1,192.5	1,049.2
Total liabilities and shareholders' equity	$ 6,211.8	$ 5,781.1
[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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Premiums and other revenue:
Earned premiums	$ 451.5	$ 446.9	$ 1,303.7	$ 1,279.3
Net investment (expense) income	40.2	34.5	116.9	103.7
Fee and other income	1.9	3.3	6.3	7.2
Net realized investment (losses) gains	(6.2)	14.2	58.3	9
Total revenue	487.4	498.9	1,485.2	1,399.2
Expenses:
Losses and loss adjustment expenses	338.8	277.5	861.5	760.2
Underwriting, acquisition and insurance expenses	167.7	168	497.3	485
Interest expense	7.5	7.9	25.3	23.4
Fee and other expense	1.2	1.9	3.8	5.5
Foreign currency exchange gains	(1.6)	(1.7)	(6.2)	(2.3)
Total expenses	513.6	453.6	1,381.7	1,271.8
(Loss) income before income taxes	(26.2)	45.3	103.5	127.4
Income tax (benefit) provision	(1.1)	4.7	8.6	20.2
Net (loss) income before equity in earnings of subsidiaries	(25.1)	40.6	94.9	107.2
Equity in undistributed earnings of subsidiaries	0	0	0	0
Net (loss) income	(25.1)	40.6	94.9	107.2
Consolidating Adjustments [Member]
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 (losses) gains	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
Interest expense	0	0	0	0
Fee and other expense	0	0	0	0
Foreign currency exchange gains	0	0	0	0
Total expenses	0	0	0	0
(Loss) income before income taxes	0	0	0	0
Income tax (benefit) provision	0	0	0	0
Net (loss) income before equity in earnings of subsidiaries	0	0	0	0
Equity in undistributed earnings of subsidiaries	20.2	(46.4)	(113.6)	(125.4)
Net (loss) income	20.2	(46.4)	(113.6)	(125.4)
Other Subsidiaries and Eliminations [Member]
Premiums and other revenue:
Earned premiums	186	224	511.6	632.5
Net investment (expense) income	13.4	14	39.5	43.5
Fee and other income	1.2	1.1	3.8	3.5
Net realized investment (losses) gains	(5.6)	(1.7)	(1.8)	(6.1)
Total revenue	195	237.4	553.1	673.4
Expenses:
Losses and loss adjustment expenses	161.1	140.6	354.5	413.5
Underwriting, acquisition and insurance expenses	62.2	79.7	174.6	223.3
Interest expense	1.8	1.7	6.3	5.5
Fee and other expense	0.5	0.7	1.4	1.8
Foreign currency exchange gains	(1.7)	(1.7)	(6.5)	(2.5)
Total expenses	223.9	221	530.3	641.6
(Loss) income before income taxes	(28.9)	16.4	22.8	31.8
Income tax (benefit) provision	(2.3)	0	(5.9)	2.3
Net (loss) income before equity in earnings of subsidiaries	(26.6)	16.4	28.7	29.5
Equity in undistributed earnings of subsidiaries	0	0	0	0
Net (loss) income	(26.6)	16.4	28.7	29.5
Argo Group International Holdings, Ltd (Parent Guarantor) [Member]
Premiums and other revenue:
Earned premiums	0	0	0	0
Net investment (expense) income	(0.9)	(0.6)	(2.2)	(2)
Fee and other income	0	0	0	0
Net realized investment (losses) gains	(0.3)	(0.3)	(0.5)	(0.2)
Total revenue	(1.2)	(0.9)	(2.7)	(2.2)
Expenses:
Losses and loss adjustment expenses	0	0	0	0
Underwriting, acquisition and insurance expenses	2	3.3	10.9	11.5
Interest expense	1.7	1.6	5.1	4.5
Fee and other expense	0	0	0	0
Foreign currency exchange gains	0	0	0	0
Total expenses	3.7	4.9	16	16
(Loss) income before income taxes	(4.9)	(5.8)	(18.7)	(18.2)
Income tax (benefit) provision	0	0	0	0
Net (loss) income before equity in earnings of subsidiaries	(4.9)	(5.8)	(18.7)	(18.2)
Equity in undistributed earnings of subsidiaries	(20.2)	46.4	113.6	125.4
Net (loss) income	(25.1)	40.6	94.9	107.2
Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) [Member]
Premiums and other revenue:
Earned premiums	265.5	222.9	792.1	646.8
Net investment (expense) income	27.7	21.1	79.6	62.2
Fee and other income	0.7	2.2	2.5	3.7
Net realized investment (losses) gains	(0.3)	16.2	60.6	15.3
Total revenue	293.6	262.4	934.8	728
Expenses:
Losses and loss adjustment expenses	177.7	136.9	507	346.7
Underwriting, acquisition and insurance expenses	103.5	85	311.8	250.2
Interest expense	4	4.6	13.9	13.4
Fee and other expense	0.7	1.2	2.4	3.7
Foreign currency exchange gains	0.1	0	0.3	0.2
Total expenses	286	227.7	835.4	614.2
(Loss) income before income taxes	7.6	34.7	99.4	113.8
Income tax (benefit) provision	1.2	4.7	14.5	17.9
Net (loss) income before equity in earnings of subsidiaries	6.4	30	84.9	95.9
Equity in undistributed earnings of subsidiaries	0	0	0	0
Net (loss) income	$ 6.4	$ 30	$ 84.9	$ 95.9

Senior Unsecured Fixed Rate N_7

Senior Unsecured Fixed Rate Notes - Condensed Consolidating Statement of Cash Flows (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Condensed Financial Statements, Captions [Line Items]
Borrowing under intercompany note, net		$ 0
Net cash flows from operating activities	$ 195.7	231
Cash flows from investing activities:
Proceeds from sales of investments	1,180.3	1,417.2
Maturities and mandatory calls of fixed maturity investments	292.2	375.1
Purchases of investments	(1,639.5)	(1,977.2)
Change in short-term investments and foreign regulatory deposits	2.3	(33.8)
Settlements of foreign currency exchange forward contracts	(1.2)	2
Cash acquired with acquisition of Ariscom	0	15.6
Purchases of fixed assets and other, net	6.7	(32.2)
Cash used in investing activities	(159.2)	(233.3)
Cash flows from financing activities:
Payment on the intercompany note	0
Payment on note payable	(0.6)	0
Activity under stock incentive plans	1.4	1
Repurchase of Company's common shares	0	(30)
Payment of cash dividends to common shareholders	(32.5)	(28)
Cash used in financing activities	(31.7)	(57)
Effect of exchange rate changes on cash	1.1	1.2
Change in cash	5.9	(58.1)
Cash, beginning of year	139.2	176.6
Cash, end of period	145.1	118.5
Argo Group International Holdings, Ltd (Parent Guarantor) [Member]
Condensed Financial Statements, Captions [Line Items]
Borrowing under intercompany note, net		0
Net cash flows from operating activities	29.2	57.7
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	3.5	0
Settlements of foreign currency exchange forward contracts	(0.1)	0.2
Cash acquired with acquisition of Ariscom		0
Purchases of fixed assets and other, net	0	(0.1)
Cash used in investing activities	3.4	0.1
Cash flows from financing activities:
Payment on the intercompany note	0
Payment on note payable	0
Activity under stock incentive plans	1.4	1
Repurchase of Company's common shares		(30)
Payment of cash dividends to common shareholders	(32.5)	(28)
Cash used in financing activities	(31.1)	(57)
Effect of exchange rate changes on cash	0	0
Change in cash	1.5	0.8
Cash, beginning of year	1.7	0.9
Cash, end of period	3.2	1.7
Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) [Member]
Condensed Financial Statements, Captions [Line Items]
Borrowing under intercompany note, net		19
Net cash flows from operating activities	124.6	151.3
Cash flows from investing activities:
Proceeds from sales of investments	744.2	963.2
Maturities and mandatory calls of fixed maturity investments	219.2	302.5
Purchases of investments	(1,091.2)	(1,346.8)
Change in short-term investments and foreign regulatory deposits	34.7	(65)
Settlements of foreign currency exchange forward contracts	1.4	0.5
Cash acquired with acquisition of Ariscom		0
Purchases of fixed assets and other, net	(1.8)	(38.5)
Cash used in investing activities	(93.5)	(184.1)
Cash flows from financing activities:
Payment on the intercompany note	(19.1)
Payment on note payable	(0.6)
Activity under stock incentive plans	0	0
Repurchase of Company's common shares		0
Payment of cash dividends to common shareholders	0	0
Cash used in financing activities	(19.7)	19
Effect of exchange rate changes on cash	0	0
Change in cash	11.4	(13.8)
Cash, beginning of year	31.7	47.8
Cash, end of period	43.1	34
Other Subsidiaries and Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Borrowing under intercompany note, net		(19)
Net cash flows from operating activities	41.9	22
Cash flows from investing activities:
Proceeds from sales of investments	436.1	454
Maturities and mandatory calls of fixed maturity investments	73	72.6
Purchases of investments	(548.3)	(630.4)
Change in short-term investments and foreign regulatory deposits	(35.9)	31.2
Settlements of foreign currency exchange forward contracts	(2.5)	1.3
Cash acquired with acquisition of Ariscom		15.6
Purchases of fixed assets and other, net	8.5	6.4
Cash used in investing activities	(69.1)	(49.3)
Cash flows from financing activities:
Payment on the intercompany note	19.1
Payment on note payable	0
Activity under stock incentive plans	0	0
Repurchase of Company's common shares		0
Payment of cash dividends to common shareholders	0	0
Cash used in financing activities	19.1	(19)
Effect of exchange rate changes on cash	1.1	1.2
Change in cash	(7)	(45.1)
Cash, beginning of year	105.8	127.9
Cash, end of period	98.8	82.8
Consolidating Adjustments [Member]
Condensed Financial Statements, Captions [Line Items]
Borrowing under intercompany note, net		0
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
Cash acquired with acquisition of Ariscom		0
Purchases of fixed assets and other, net	0	0
Cash used in investing activities	0	0
Cash flows from financing activities:
Payment on the intercompany note	0
Payment on note payable	0
Activity under stock incentive plans	0	0
Repurchase of Company's common shares		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) - Forecast [Member] - Separation Agreement [Member] - Chief Executive Officer [Member] $ in Thousands	3 Months Ended
	Dec. 31, 2019USD ($)shares
Subsequent Event [Line Items]
Shares vested (in shares) | shares	77,396
Fair value of shares issued	$ 4,000
Compensation expense	1,000
Amount to be paid after separation agreement	$ 1,750
Period for payment	10 days
Amount to be paid after re-execution of separation agreement	$ 750
Number of shares placed in escrow | shares	35,296

Uncategorized Items - argo10-q0

Label	Element	Value
Accounting Standards Update 2016-01 [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 117,500,000
Accounting Standards Update 2018-02 [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ (20,700,000)