Argo Group International (ARGO-PA) 10-K27 Feb 152014 FY Annual reportFinancial data

Company Profile

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Feb. 23, 2015	Jun. 30, 2014
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Trading Symbol	AGII
Entity Registrant Name	Argo Group International Holdings, Ltd.
Entity Central Index Key	1091748
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		25,721,708
Entity Public Float			$1,307.10

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Assets
Available-for-sale (cost: 2014 - $2,817.2; 2013 - $2,760.1)	$2,840.70	$2,814.40
Equity securities, at fair value (cost: 2014 - $307.3; 2013 - $346.9)	486.3	534.3
Other investments (cost: 2014 - $488.9; 2013 - $377.4)	495.1	378.9
Short-term investments, at fair value (cost: 2014 - $275.8; 2013 - $351.6)	275.8	351.6
Total investments	4,097.90	4,079.20
Cash	81	157.4
Accrued investment income	22.1	25.7
Premiums receivable	353.6	348.4
Reinsurance recoverables	997.2	1,263.50
Goodwill	152.2	153.8
Intangible assets, net of accumulated amortization	78.6	86
Current income taxes receivable, net	14.9
Deferred acquisition costs, net	124.6	113.9
Ceded unearned premiums	207.6	196.3
Other assets	226.6	166.8
Total assets	6,356.30	6,591
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	3,042.40	3,230.30
Unearned premiums	817.2	779.1
Accrued underwriting expenses	143.1	122.3
Ceded reinsurance payable, net	178.8	354.7
Funds held	55	43.7
Senior unsecured fixed rate notes	143.8	143.8
Other indebtedness	62	66.3
Junior subordinated debentures	172.7	193.3
Current income taxes payable, net		5.2
Deferred tax liabilities, net	53	28.7
Other liabilities	41.6	60.6
Total liabilities	4,709.60	5,028
Commitments and contingencies (Note 18)
Shareholders' equity:
Common shares - $1.00 par, 500,000,000 shares authorized; 34,318,224 and 34,066,889 shares issued and outstanding at December 31, 2014 and 2013, respectively	34.3	34.1
Additional paid-in capital	836.3	827.3
Treasury shares (8,606,489 and 7,558,345 shares at December 31, 2014 and 2013, respectively)	-301.4	-250.6
Retained earnings	969.4	804.4
Accumulated other comprehensive income, net of taxes	108.1	147.8
Total shareholders' equity	1,646.70	1,563
Total liabilities and shareholders' equity	$6,356.30	$6,591

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Statement Of Financial Position [Abstract]
Available-for-sale cost	$2,817.20	$2,760.10
Equity securities cost	307.3	346.9
Other investments cost	488.9	377.4
Short-term investments, Cost	$275.80	$351.60
Common shares, par value	$1	$1
Common shares, shares authorized	500,000,000	500,000,000
Common shares, shares issued	34,318,224	34,066,889
Common shares, shares outstanding	34,318,224	34,066,889
Treasury shares, shares	8,606,489	7,558,345

Consolidated_Statements_of_Inc

Consolidated Statements of Income (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Premiums and other revenue:
Earned premiums	$1,338.10		$1,303.80		$1,186.50
Net investment income	86.6		100		118.8
Net realized investment and other gains	94		71.3		25.7
Total revenue	1,518.70		1,475.10		1,331
Expenses:
Losses and loss adjustment expenses	747.4		742		747.6
Other reinsurance-related expenses			19.2		27.3
Underwriting, acquisition and insurance expenses	539.2		510.8		464.5
Interest expense	19.9		20.2		23.7
Fee expense (income), net	0.6		4.9		-5.3
Debt extinguishment costs					2.2
Foreign currency exchange (gain) loss	-7.8		-1.7		4.3
Impairment of intangible assets	3.4
Total expenses	1,302.70		1,295.40		1,264.30
Income before income taxes	216		179.7		66.7
Provision for income taxes	32.8		36.5		14.4
Net income	183.2		143.2		52.3
Net income per common share:
Basic	$7.02	[1]	$5.33	[1]	$1.86
Diluted	$6.90	[1]	$5.14	[1]	$1.83
Dividend declared per common share	$0.69		$0.59		$0.44
Weighted average common shares:
Basic	26,082,114		26,851,341		28,095,210
Diluted	26,557,151		27,869,533		28,650,448
Net realized investment and other gains before other-than-temporary impairment losses	96.3		79.1		29.4
Other-than-temporary impairment losses recognized in earnings:
Other-than-temporary impairment losses on fixed maturities	-1.2		-6		-1.5
Other-than-temporary impairment losses on equity securities	-1.1		-1.8		-2.2
Impairment losses recognized in earnings	-2.3		-7.8		-3.7
Net realized investment and other gains	$94		$71.30		$25.70

[1]	Basic and diluted net income per common share are computed independently for each quarter and full year based on the respective average number of common shares outstanding; therefore, the sum of the quarterly net income per common share data may not equal the net income per common share for the year.

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement Of Income And Comprehensive Income [Abstract]
Net income	$183.20	$143.20	$52.30
Other comprehensive income (loss):
Foreign currency translation adjustments	-4.1	-2.8	-2.3
Defined benefit pension plans:
Net (loss) gain arising during the year	-3.7	2	-0.9
Unrealized gains on securities:
(Losses) gains arising during the year	-5.7	1.2	87.4
Reclassification adjustment for gains included in net income	-30.6	-59.8	-14.4
Other comprehensive (loss) income before tax	-44.1	-59.4	69.8
Defined benefit pension plans:
Net (loss) gain arising during the year	-1.3	0.7	-0.3
Unrealized gains (losses) on securities:
Gains arising during the year	6.8	1	24.4
Reclassification adjustment for gains included in net income	-9.9	-19.4	-4
Income tax (benefit) provision related to other comprehensive income (loss)	-4.4	-17.7	20.1
Other comprehensive (loss) income, net of tax	-39.7	-41.7	49.7
Comprehensive income	$143.50	$101.50	$102

Consolidated_Statements_of_Sha

Consolidated Statements of Shareholders' Equity (USD $)	Total	Common Shares [Member]	Additional Paid-In Capital [Member]	Treasury Shares [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
In Millions	Total	Common Shares [Member]	Additional Paid-In Capital [Member]	Treasury Shares [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning Balance at Dec. 31, 2011	$1,463	$31.30	$716.80	($160.90)	$736	$139.80
Net income	52.3				52.3
Other comprehensive income (loss)	49.7					49.7
Repurchase of common shares (1,488,308, 1,098,732, and 1,048,144 at a weighted average price of $29.92, $41.04, and $48.48 for 2012, 2013, and 2014 respectively)	-44.6			-44.6
Activity under stock incentive plans	5.2	0.1	5.1
Retirement of common shares (tax payments on equity compensation)	-0.4		-0.4
Employee stock purchase plan	1.2		1.2
Cash dividend declared - common shares	-12.3				-12.3
Ending Balance at Dec. 31, 2012	1,514.10	31.4	722.7	-205.5	776	189.5
Net income	143.2				143.2
Other comprehensive income (loss)	-41.7					-41.7
Repurchase of common shares (1,488,308, 1,098,732, and 1,048,144 at a weighted average price of $29.92, $41.04, and $48.48 for 2012, 2013, and 2014 respectively)	-45.1			-45.1
Activity under stock incentive plans	8.7	0.2	8.5
Retirement of common shares (tax payments on equity compensation)	-1.9		-1.9
Deferred tax - share-based payments	0.1		0.1
Employee stock purchase plan	1.4	0.1	1.3
10% stock dividend		2.4	96.6		-99
Cash dividend declared - common shares	-15.8				-15.8
Ending Balance at Dec. 31, 2013	1,563	34.1	827.3	-250.6	804.4	147.8
Net income	183.2				183.2
Other comprehensive income (loss)	-39.7					-39.7
Repurchase of common shares (1,488,308, 1,098,732, and 1,048,144 at a weighted average price of $29.92, $41.04, and $48.48 for 2012, 2013, and 2014 respectively)	-50.8			-50.8
Activity under stock incentive plans	8.7	0.2	8.5
Retirement of common shares (tax payments on equity compensation)	-1.1		-1.1
Deferred tax - share-based payments	0.1		0.1
Employee stock purchase plan	1.5		1.5
Cash dividend declared - common shares	-18.2				-18.2
Ending Balance at Dec. 31, 2014	$1,646.70	$34.30	$836.30	($301.40)	$969.40	$108.10

Consolidated_Statements_of_Sha1

Consolidated Statements of Shareholders' Equity (Parenthetical) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement Of Stockholders Equity [Abstract]
Common shares repurchased	1,048,144	1,098,732	1,488,308
Repurchase of common shares, weighted average price	$48.48	$41.04	$29.92
Stock dividend declared		10.00%
Cash dividend declared - common shares, per share	$0.69	$0.59	$0.44

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income	$183.20	$143.20	$52.30
Adjustments to reconcile net income to net cash provided (used) by operating activities:
Amortization and depreciation	37.2	39.6	36.6
Share-based payments expense	19.6	23.3	10.5
Excess tax (benefit) expense from share-based payment arrangements	-0.1	-0.2
Deferred income tax provision, net	27.6	3.8	5
Net realized investment and other gains	-94	-71.3	-25.7
Loss on disposals of fixed assets, net		0.2	0.3
Debt extinguishment costs			2.2
Impairment of intangible assets	3.4
Change in:
Accrued investment income	3.4	5.3	2
Receivables	256.7	86.7	24.9
Deferred acquisition costs	-7.3	-14.1	2.1
Ceded unearned premiums	-12.4	-4	-14.5
Reserves for losses and loss adjustment expenses	-182	-8.9	-78.9
Unearned premiums	39.1	51.4	72.6
Ceded reinsurance payable and funds held	-163.9	-246.4	-67.5
Income taxes	-19.7	17	-1.7
Accrued underwriting expenses	11.7	-4	21
Other, net	28	-21.8	-10.7
Cash provided (used) by operating activities	130.5	-0.2	30.5
Cash flows from investing activities:
Sales of fixed maturity investments	1,104.90	1,795.40	1,117.80
Maturities and mandatory calls of fixed maturity investments	323	281.8	483
Sales of equity securities	123.9	163.4	10.4
Sales of other investments	33.2	7.5	2.5
Purchases of fixed maturity investments	-1,531.50	-1,822.90	-1,501.50
Purchases of equity securities	-55.8	-80	-104.4
Purchases of other investments	-149.5	-72.9	-15.6
Change in foreign regulatory deposits and voluntary pools	21.2	-7.7	-21
Change in short-term investments	75.3	-145.3	58.7
Settlements of foreign currency exchange forward contracts	-1.1	-3.9	0.4
Purchases of fixed assets	-39	-26.1	-34.1
Other, net	-25.9	31.5	0.1
Cash (used) provided by investing activities	-121.3	120.8	-3.7
Cash flows from financing activities:
Proceeds from issuance of senior unsecured fixed rate notes, net			138.7
Payment on note payable	-0.1
Redemption of trust preferred securities, net	-18		-117.2
Activity under stock incentive plans	4.6	2.6	1.2
Repurchase of Company's common shares	-50.8	-46.5	-44.2
Excess tax expense from share-based payment arrangements	0.1	0.2
Payment of cash dividends to common shareholders	-18.2	-15.8	-12.3
Cash used by financing activities	-82.4	-59.5	-33.8
Effect of exchange rate changes on cash	-3.2	0.5	0.1
Change in cash	-76.4	61.6	-6.9
Cash, beginning of year	157.4	95.8	102.7
Cash, end of year	$81	$157.40	$95.80

Business_and_Significant_Accou

Business and Significant Accounting Policies

12 Months Ended

Dec. 31, 2014

Accounting Policies [Abstract]

Business and Significant Accounting Policies

Business

Argo Group International Holdings, Ltd. (“Argo Group,” “we” or the “Company”) is an international underwriter of specialty insurance and reinsurance products in the property and casualty market. Argo Group US, Inc. (“Argo Group US”) is a subsidiary of Argo Financial Holding (Ireland), Ltd. (“Argo Ireland”). Argo Underwriting Agency Limited (“ArgoGlobal Syndicate 1200”) is a subsidiary of Argo International Holdings, Ltd. Argo Re, Ltd. (“Argo Re”), a Bermuda based company, is the parent of both Argo Ireland and Argo International Holdings, Ltd. Argo Re is directly owned by Argo Group.

We conduct our ongoing business through four segments.

Excess and Surplus Lines products are underwritten under two operating platforms: Colony Specialty and Argo Pro.

Commercial Specialty consists of the following operations: Argo Insurance, Rockwood Casualty Insurance Company (“Rockwood”), Argo Surety, Trident Insurance Services, Alteris and ARIS Title Insurance Corporation (“ARIS”).

International Specialty products are provided by our Bermuda operations, which include Argo Re and Argo Insurance – Casualty and Professional Lines and Argo Seguros Brasil S.A. based in Brazil.

Syndicate 1200 products are underwritten by ArgoGlobal Syndicate 1200 based in London, on behalf of one underwriting syndicate under the Lloyd’s of London (“Lloyd’s”) global franchise.

Our Run-off Lines segment includes liabilities associated with other liability policies that were issued in the 1960s, 1970s and into the 1980s, as well as the former risk management business and other business no longer underwritten.

Basis of Presentation and Use of Estimates

The consolidated financial statements of Argo Group and its subsidiaries have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenues and expenses during the reporting period. The major estimates reflected in our consolidated financial statements include, but are not limited to, reserves for losses and loss adjustment expenses; reinsurance recoverables, including the reinsurance recoverables allowance for 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.

Specifically, estimates for reserves for losses and loss adjustment expenses are based upon past claim experience modified for current trends as well as prevailing economic, legal and social conditions. Although management believes that amounts included in the accompanying consolidated financial statements are reasonable, such estimates may be more or less than the amounts ultimately paid when the claims are settled. The estimates are continually reviewed and any changes are reflected in current operating results. Further, the nature of loss exposures involves significant variability due to the nature of the long-tailed payments on certain claims. As such, losses and loss adjustment expenses could vary significantly from the recorded amounts.

The consolidated financial statements include the accounts and operations of Argo Group and its subsidiaries. All material intercompany accounts and transactions have been eliminated. Certain amounts in prior years’ financial statements have been reclassified to conform to the current presentation. Amounts related to trade capital providers, who are third-party capital participants that provide underwriting capital to the Syndicate 1200 segment, are included in the balance sheet. Trade capital providers participate on a quota share basis, assuming 100% of their contractual participation in the underwriting syndicate results and with such results settled on a year of account basis.

In 2009, the Financial Accounting Standards Board (“FASB”) issued revised accounting standards regarding consolidation of variable interest entities. We reevaluated our investment in our twelve statutory trusts (collectively, the “Trusts”) and two charitable foundations (collectively, the “Foundations”). We determined that the Trusts and Foundations continue to be variable interest entities due to the fact that the Trusts and Foundations do not have sufficient equity to finance their activities without additional subordinate financial support from other parties. We do not have any power to direct the activities that impact the Trusts or Foundations’ economic performance. We are not entitled to receive a majority of the residual returns of the Trusts and U.S. charitable foundations. Additionally, we are not responsible for absorbing the majority of the expected losses of the Trusts or U.S. charitable foundations; therefore, we are not the primary beneficiary and, accordingly, the Trusts and U.S. charitable foundations are not included in our consolidated financial statements. The expenses and donations of the charitable foundations in Bermuda are paid by Argo Group and have been included in the consolidated results.

We have used a series of special purpose reinsurance companies to provide reinsurance coverage through a series of transactions, including insurance linked securities. Under the provisions of Accounting Standards Codification (“ASC”) Topic 810-10, “Consolidation,” these reinsurance companies are variable interest entities. However, we do not have a variable interest in these entities, and therefore are not required to consolidate them in our consolidated financial statements.

Stock Dividends

On May 7, 2013, our Board of Directors declared a 10% stock dividend, payable on June 17, 2013, to shareholders of record at the close of business on June 3, 2013. As a result of the stock dividend, 2,447,839 additional shares were issued. Cash was paid in lieu of fractional shares of our common shares. All references to share and per share amounts in this document and related disclosures have been adjusted to reflect the stock dividend for all periods presented.

On February 17, 2015, our Board of Directors declared a 10% stock dividend payable on March 16, 2015, to shareholders of record at the close of business on March 2, 2015. The share numbers and per share amounts disclosed in the Consolidated Financial Statements and Notes to the Consolidated Financial Statements have not been retroactively adjusted to give effect to the stock dividend. For additional details regarding the stock dividend, see Note 27, “Subsequent Event.”

Cash

Cash consists of cash deposited in banks, generally in concentration and operating accounts. Interest-bearing cash accounts are classified as short-term investments.

Investments

Investments in fixed maturities at December 31, 2014 and 2013 include bonds and structured securities. Equity securities include common and preferred stocks. Other investments consist of foreign regulatory deposits, hedge funds, private equity funds, private equity direct investments, voluntary pools and foreign exchange currency forward contracts. Short-term investments consist of money market funds, certificates of deposit, bonds, sovereign debt and interest-bearing cash accounts. Investments maturing in less than one year are classified as short-term investments in our consolidated financial statements.

The amortized cost of fixed maturity securities is adjusted for amortization of premiums and accretion of discounts. This amortization or accretion is included in “Net investment income” in our Consolidated Statements of Income.

For the structured securities portion of the fixed maturity securities portfolio, we recognize income using a constant effective yield based on anticipated prepayments and the estimated economic life of the securities. Premium or discount on high investment grade securities (rated AA or higher) is amortized into income using the retrospective method. Premium or discount on lower grade securities (rated less than AA) is amortized into income using the prospective method.

Our investments in fixed maturities and equity securities with readily determinable fair value are considered available-for-sale and are carried at fair value. Changes in the fair value of investments classified as available-for-sale are not recognized to income during the period, but rather are recognized as a separate component of shareholders’ equity until realized. Fair value of these investments is estimated using prices obtained from third-party pricing services, where available. For securities where we were unable to obtain fair values from a pricing service or broker, fair values were estimated using information obtained from investment advisors. We performed several processes to ascertain the reasonableness of these investment values by i) obtaining and reviewing internal control reports for our service providers that obtain fair values from third-party pricing services, ii) discussing with our investment managers their process for reviewing and validating pricing obtained from outside services and obtaining values for all securities from our investment managers and iii) comparing the security pricing received from the investment managers with the prices used in the consolidated financial statements and obtaining additional information for variances that exceeded a certain threshold. As of December 31, 2014, investments we hold for which we did not receive a fair value from a pricing service or broker accounted for less than 1% of our investment portfolio. The actual value at which these securities could actually be sold or settled with a willing buyer or seller may differ from our estimated fair values depending on a number of factors including, but not limited to, current and future economic conditions, quantity sold or settled, presence of an active market and availability of a willing buyer or seller. The cost of securities sold is based on the specific identification method.

Changes in the value of other investments consisting of hedge funds, private equity funds, private equity direct investments and voluntary pools are principally recognized to income during the period using the equity method of accounting. Our foreign regulatory deposits are assets held in trust in jurisdictions where there is a legal and regulatory requirement to maintain funds locally in order to protect policyholders. Lloyd’s is the appointed investment manager for the funds. The underlying assets are invested in government securities, agency securities and corporate bonds whose values are obtained from Lloyd’s. Foreign currency future contracts held by us are valued by our counterparty using market driven foreign currency exchange rates.

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. Loss severity includes such factors as trends in real estate values and proceeds at foreclosure. We also recognize other-than-temporary losses on our fixed maturity securities that we intend to sell.

All investment balances include amounts relating to trade capital providers. The results of operations and other comprehensive income exclude amounts relating to trade capital providers. Trade capital providers’ participation in the syndicate results are included in reinsurance recoverable for ceded losses and reinsurance payable for ceded premiums.

Receivables

Premiums receivable, representing amounts due from insureds, are presented net of an allowance for doubtful accounts. The allowances for doubtful accounts were $5.2 million and $4.5 million at December 31, 2014 and 2013, respectively. Premiums receivable include amounts relating to the trade capital providers’ quota share.

Reinsurance recoverables represent amounts of paid losses and loss adjustment expenses, case reserves and incurred but not reported (“IBNR”) amounts ceded to reinsurers under reinsurance treaties. Reinsurance recoverables also reflect amounts that are due from trade capital providers. Reinsurance recoverables are presented in our Consolidated Balance Sheets net of an allowance for doubtful accounts of $3.4 million and $3.7 million at December 31, 2014 and 2013, respectively (see Note 4, “Reinsurance” for related disclosures).

An estimate of amounts that are likely to be charged off is established as an allowance for doubtful accounts as of the balance sheet date. Our estimate includes specific insured and reinsurance balances that are considered probable to be charged off after all collection efforts have ceased and in accordance with historical write-off trends based on aging categories. Premiums receivable and reinsurance recoverables on paid losses written off, net of recoveries against the allowance for doubtful accounts or directly to the income statement are as follows:

For the Years Ended December 31,

(in millions)

2014

2013

2012

Premiums receivable

1.1

0.2

0.3

Reinsurance recoverables

0.5

(0.0

)

(0.4

)

Net written off (recovered)

1.6

0.2

(0.1

)

Recoveries occur when subsequent collection or litigation results in the receipt of amounts previously written off. Amounts recovered are applied against the bad debt expense account.

Earned Premiums

Premium revenue is recognized ratably over the policy period, with an adjustment, where appropriate, to reflect the risk profile of certain classes of business, particularly those exposed to seasonal weather related events. Premiums that have yet to be earned are reported as “Unearned premiums” in our Consolidated Balance Sheets.

Unearned premium balances include cessions to reinsurers including trade capital providers, while the earned premium recognized in our Consolidated Statements of Income excludes amounts relating to trade capital providers. The trade capital providers’ quota share amount is included in “Ceded reinsurance payable, net”.

Assumed reinstatement premiums that reinstate coverage are written and earned at the time the associated loss event occurs. The original premium is earned over the remaining exposure period of the contract. Reinstatement premiums are estimated based upon contract terms for reported losses and estimated for incurred but not reported losses.

Retrospectively Rated Policies

We have written a number of workers compensation, property and other liability policies that are retrospectively rated. Under this type of policy, the policyholder or coverholder may be entitled, subsequent to coverage expiration, to a refund or may owe additional premiums based on the amount of losses incurred under the policy. The retrospective premium adjustments on certain policies are limited to a minimum or maximum premium adjustment, which is calculated as a percentage of the standard amount of premium charged during the life of the policy. Accrued retrospectively rated premiums have been determined based on estimated ultimate loss experience of the individual policyholder accounts. The estimated liability for return of premiums under retrospectively rated policies is included in “Unearned premiums” in our Consolidated Balance Sheets and was $5.8 million and $6.8 million at December 31, 2014 and 2013, respectively.

Deferred Acquisition Costs

Policy acquisition costs, which include commissions, premium taxes, fees and certain other costs of underwriting policies, are deferred, when such policies are profitable, and amortized over the same period in which the related premiums are earned. To qualify for capitalization, the policy acquisition cost must be directly related to the successful acquisition of an insurance contract. Anticipated investment income is considered in determining whether the deferred acquisition costs are recoverable and whether a premium deficiency exists. We continually review the methods of making such estimates and establishing the deferred costs with any adjustments made in the accounting period in which the adjustment arose.

The 2014 and 2013 net amortization of policy acquisition costs will not equal the change in our Consolidated Balance Sheets as the trade capital providers’ share is not reflected in our Consolidated Statements of Income and differences arise from foreign currency exchange rates applied to deferred acquisition costs which are treated as a nonmonetary asset.

Reserves for Losses and Loss Adjustment Expenses

Liabilities for unpaid losses and loss adjustment expenses include the accumulation of individual case estimates for claims reported as well as estimates of IBNR claims and estimates of claim settlement expenses. Reinsurance recoverables on unpaid claims and claim expenses represent estimates of the portion of such liabilities that will be recoverable from reinsurers. Amounts recoverable from reinsurers are recognized as assets at the same time and in a manner consistent with the unpaid claims liabilities associated with the reinsurance policy.

Reinsurance

In the normal course of business, our insurance and reinsurance subsidiaries reinsure various risks above certain retention levels with other insurance enterprises. Reinsurance recoverables include claims we paid and estimates of unpaid losses and loss adjustment expenses that are subject to reimbursement under reinsurance and retrocessional contracts. The method for determining reinsurance recoverables for unpaid losses and loss adjustment expenses involves reviewing actuarial estimates of gross unpaid losses and loss adjustment expenses to determine our ability to cede unpaid losses and loss adjustment expenses under our existing reinsurance contracts. This method is continually reviewed and updated and any resulting adjustments are reflected in earnings in the period identified. Reinsurance premiums, commissions and expense reimbursements are accounted for on a basis consistent with those used in accounting for the original policies issued and the term of the reinsurance contracts. Amounts recoverable from reinsurers for losses and loss adjustment expenses for which our insurance and reinsurance subsidiaries have not been relieved of their legal obligations to the policyholder are reported as assets.

Goodwill and Intangible Assets

Goodwill and intangible assets are allocated to the segment in which the results of operations for the acquired company are reported (see Note 20, “Segment Information” for further discussion). Intangible assets with a finite life are amortized over the estimated useful life of the asset. Goodwill and intangible assets with an indefinite useful life are not amortized. Goodwill and intangible assets are tested for impairment on an annual basis or more frequently if events or changes in circumstances indicate that the carrying amount may not be recoverable. For goodwill, we may perform a qualitative test to determine whether it is more-likely-than-not that the fair value of a reporting unit is less than its carrying amount as a basis for determining whether it is necessary to perform the quantitative two-step goodwill impairment test. Based on prior goodwill impairment testing, we determined the performance of the quantitative two-step impairment test was required for 2014. The first step is to identify if a potential impairment exists by comparing the fair value of a reporting unit with its carrying amount, including goodwill (“Step 1”). If the fair value of a reporting unit exceeds its carrying value amount, goodwill of the reporting unit is not considered to have a potential impairment and the second step is not necessary. However, if the carrying amount of the reporting unit exceeds its fair value, the second step (“Step 2”) is performed to determine if goodwill is impaired and to measure the amount of impairment loss to recognize, if any. Step 2 compares the implied fair value of goodwill with the carrying amount of goodwill. If the implied value of goodwill is less than the carrying amount of goodwill, it is written down to its fair value with a corresponding expense reflected in the Consolidated Statements of Income. The implied goodwill is calculated based on a hypothetical purchase price allocation, similar to the requirements in the accounting guidance for business combinations, whereby the implied fair value of the reporting unit is allocated to the fair value of the assets and liabilities of the reporting unit.

We perform our goodwill impairment test on the first day of the fourth quarter of each year, or October 1 of each year. In performing Step 1 of the impairment test, we estimated the fair value of reporting units using an average of three valuation methods: a comparable company analysis, a precedent transaction analysis and a discounted cash flow analysis. All three methods require management to make various judgments and assumptions. The discounted cash flow analysis included projections of earned premiums, loss ratios, expense growth and discount rates for each reporting unit. Assumptions about such future cash flows are based on our budgets, business plans, economic projections, anticipated future cash flows and market data. Finally, the comparable company analysis and precedent transaction analysis required judgment in selecting comparable companies and comparable transactions for use in the calculations. In all instances, future changes in these judgments and assumptions could cause impairment of goodwill.

For the years ended December 31, 2014, 2013 and 2012, all of our reporting units passed Step 1 of the goodwill impairment analysis. However, based on carrying values of the reporting units as of December 31, 2014, a 39% decline in the fair value of the Excess and Surplus Lines reporting unit, 21% decline in the fair value of the Commercial Specialty reporting unit or 16% decline in the fair value of the Syndicate 1200 segment would have resulted in the carrying values of these reporting units being in excess of their respective fair values, resulting in the need to perform Step 2, which could have resulted in a material impairment to our goodwill. Any decline in the fair value of these reporting units could result in the carrying value of the reporting unit being in excess of fair value, triggering Step 2 of the impairment testing model, which could result in an impairment of goodwill.

For the year ended December 31, 2014, we determined as a result of the slower than anticipated development of revenues for our art title insurance company, the likelihood of near term recovery of the intangible assets, including goodwill, was not probable. Therefore, we wrote-off $1.6 million of goodwill and $1.8 million of indefinite lived intangible assets related to this operating unit.

As noted above, we have elected to make the first day of the fourth quarter the annual impairment assessment date for goodwill and indefinite-lived intangible assets. An impairment analysis subsequent to this date has not been performed as management believes that no additional indicators of impairment have arisen, such as significant additional pricing competition, unexpected significant declines in operating results, divestiture of a significant component of the business or a significant decline in our market capitalization.

The following table presents our intangible assets and accumulated amortization at December 31:

31-Dec-14

31-Dec-13

(in millions)

Gross Carrying

Accumulated

Gross Carrying

Accumulated

Amount

Amortization

Amount

Amortization

Lloyd's capacity

60.5

n/a

60.5

n/a

Title plant

—

n/a

1.8

n/a

Distribution network

44.8

27.9

44.8

23.1

Additional Lloyd's capacity

4.8

3.9

4.8

3.2

Other

1.5

1.2

1.5

1.1

111.6

113.4

27.4

The weighted average useful life by category at December 31, 2014 was 9.8 years for the distribution network, 5.0 years for the additional Lloyd’s capacity and 9.1 years for other. The weighted average useful life for all categories was 9.3 years at December 31, 2014.

During the twelve months ended December 31, 2014, 2013 and 2012, amortization expense was $5.6 million, $6.1 million and $5.2 million, respectively, and is included in “Underwriting, acquisition and insurance expenses” in our Consolidated Statements of Income.

The estimated amortization expense for the years ended December 31, 2015, 2016, 2017, 2018 and 2019 is $5.4 million, $5.1 million, $4.5 million, $2.4 million and $0.4 million, respectively.

Property and Equipment

Property and equipment used in operations, including certain costs incurred to develop or obtain computer software for internal use, are capitalized and carried at cost less accumulated depreciation and are reported in “Other assets” in our Consolidated Balance Sheets. Depreciation is calculated using a straight-line method over the estimated useful lives of the assets, generally three to thirty two years. The accumulated depreciation for property and equipment was $81.7 million and $65.5 million at December 31, 2014 and 2013, respectively. The net book value of our property and equipment at December 31, 2014 and 2013 was $102.7 million and $79.0 million, respectively. The depreciation expense at December 31, 2014, 2013 and 2012 was $15.1 million, $15.5 million and $12.6 million, respectively.

Derivative Instruments

We enter into short-term, currency spot and forward contracts to mitigate foreign exchange rate exposure in our non-U.S. Dollar denominated fixed maturity investments. The forward contracts used are typically less than sixty days and are renewed as long as the non-U.S. Dollar denominated fixed maturity investments are held in our portfolio. Forward contracts are designated as hedges for accounting purposes. We also enter into foreign currency exchange forward contracts to manage currency exposure on losses related to global catastrophe events. These foreign currency forward contracts are carried at fair value in our Consolidated Balance Sheets in “Other investments.” The realized and unrealized gains and losses are included in “Net realized investment and other gains” in our Consolidated Statements of Income.

Through our subsidiary Argo Re, in 2011, we entered into two reinsurance contracts with a special purpose reinsurance company that provided us with protection against certain severe catastrophe events and the occurrence of multiple significant catastrophe events during the same year. The special purpose reinsurance company provided the reinsurance through two catastrophe bond transactions that were supported by two collateralized facilities. The reinsurance contracts were deemed to be derivatives. We recorded these contracts at fair value, and such fair value was included in “Other assets” in our Consolidated Balance Sheets with any changes in the value reflected in “Other reinsurance-related expenses” in our Consolidated Statements of Income. See Note 5, “Derivative Instruments” for related disclosures.

Share-Based Payments

Compensation expense for share-based payments is recognized based on the measurement-date fair value for awards that will settle in shares. Awards that are expected to be settled in cash are accounted for as liability awards, resulting in the fair value of the award being measured at each reporting date until the award is exercised, forfeited or expires unexercised. Compensation expense for awards that are settled in equity are recognized on a straight line pro rata basis over the vesting period. Compensation expense for awards that are settled in cash are recognized on the accelerated recognition method over the award’s vesting period. See Note 14, “Share-based Compensation” for related disclosures.

Foreign Currency Exchange Gain (Loss)

The U.S. Dollar is the functional currency of all but two of our foreign operations. Monetary assets and liabilities in foreign operations that are denominated in foreign currencies are revalued at the exchange rates in effect at the balance sheet date. The resulting gains and losses from changes in the foreign exchange rates are reflected in net income. Revenues and expenses denominated in foreign currencies are translated at the prevailing exchange rate during the period with the resulting foreign exchange gains and losses included in net income for the period. In the case of our foreign currency denominated available-for-sale investments, the change in exchange rates between the local currency and our functional currency at each balance sheet date represents an unrealized appreciation or depreciation in value of these securities and is included as a component of accumulated other comprehensive gain.

Translation gains and losses related to our operations in Brazil and Malta are recorded as a component of shareholders’ equity in our Consolidated Balance Sheets. At December 31, 2014 and 2013, the foreign currency translation adjustments were a loss of $15.6 million and $11.5 million, respectively.

Income Taxes

Deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates in effect for the year in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in net income in the period in which the change is enacted.

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 December 31, 2014, 2013 and 2012. Our United States subsidiaries are no longer subject to U.S. federal and state income tax examinations by tax authorities for years before 2011. Our United Kingdom subsidiaries are no longer subject to United Kingdom income tax examinations by Her Majesty’s Revenue and Customs for years before 2012.

Supplemental Cash Flow Information

Income taxes paid. We paid income taxes of $23.7 million, $14.2 million and $21.0 million in 2014, 2013 and 2012, respectively.

Income taxes recovered. We recovered income taxes of $0.1 million and $10.0 million in 2014 and 2012, respectively. We did not recover any income taxes in 2013.

Interest paid. Interest paid was as follows:

For the Years Ended December 31,

(in millions)

2014

2013

2012

Senior unsecured fixed rate notes

9.3

2.1

Junior subordinated debentures

7.6

7.9

21.3

Other indebtedness

2.8

2.6

3.1

Total interest paid

19.7

19.8

26.5

Non-cash operating activities transactions. In our Consolidated Balance Sheet at December 31, 2012, “Reinsurance recoverables” and “Ceded reinsurance payable, net” each included $252.3 million from the whole account quota share reinsurance transaction (see Note 6, “Reserves for Losses and Loss Adjustment Expenses” for further discussion). As cash had not been settled in 2012 related to this transaction, $252.3 million has been excluded from both the change in “Receivables” and the change in “Ceded reinsurance payable and funds held” for the year ended December 31, 2012. During 2013, $52.7 million was received related to the “Reinsurance recoverables” and is reflected in “Receivables” and $155.0 million was paid related to the “Ceded reinsurance payable, net” and is reflected in “Ceded reinsurance payable and funds held” in our Consolidated Statements of Cash Flows. Additionally, the “Reinsurance recoverable” was increased by $9.2 million for a change in the estimated loss which has not been settled in cash as of December 31, 2013 and is therefore excluded from “Receivables” in our Consolidated Statements of Cash Flows. Subject to a Split Reinsurance to Close arrangement previously approved by the Prudential Regulatory Authority, the liabilities assumed by the whole account quota share provider were legally transferred to that quota share provider on January 18, 2014 with an inception date of January 1, 2014.

Our Consolidated Statements of Cash Flows contains a reconciliation of net income to “Net cash (used) provided by operating activities,” which includes, among other things, certain adjustments for non-cash items. For the year ended December 31, 2014, the adjustment for “Net realized and other gains” includes a $43.3 million non-cash item related to the pre-tax realized gain recognized on the sale of a real estate holding, as the proceeds from this sale are currently held in escrow and recorded as a receivable within “Other assets” in our Consolidated Balance Sheet at December 31, 2014. See Note 3, “Sale of Real Estate Holding” for further discussion.

Recently Issued Accounting Pronouncements

In May 2014, the FASB issued ASU 2014-09, “Revenue from Contracts with Customers” (Topic 606). The ASU is a comprehensive new revenue recognition model that requires a company to recognize revenue to depict the transfer of goods or services to a customer at an amount that reflects the consideration it expects to receive in exchange for those goods or services. The ASU provides a five-step analysis of transactions to determine when and how revenue is recognized and requires additional disclosures sufficient to describe the nature, amount, timing and uncertainty of revenue and cash flows for these transactions. This ASU is effective for annual reporting periods beginning after December 15, 2016 and early adoption is not permitted. Accordingly, we will adopt this ASU on January 1, 2017. Companies may use either a “full retrospective” adoption, meaning the update is applied to all periods presented, or a “modified retrospective” adoption, meaning the update is applied only to the most current period presented in the financial statements. While insurance contracts are excluded from this ASU, fee income related to our brokerage operations and management of the third-party capital for our underwriting Syndicate at Lloyd’s will be subject to this updated guidance. We are currently evaluating what impact this ASU will have on our financial results and disclosures and which adoption method to apply.

Investments

Investments	12 Months Ended
Investments	Dec. 31, 2014
Investments Debt And Equity Securities [Abstract]
Investments	2	Investments
	Composition of Invested Assets
	The amortized cost, gross unrealized gains, gross unrealized losses and fair value of investments as of December 31 were as follows:

	31-Dec-14
	(in millions)		Amortized			Gross			Gross			Fair
			Cost			Unrealized			Unrealized			Value
						Gains			Losses
	Fixed maturities
	USD denominated:
	U.S. Governments		$	184		$	1.3		$	0.3		$	185
	Non-U.S. Governments			79.9			0.6			0.6			79.9
	Obligations of states and political subdivisions			468.1			22.9			0.3			490.7
	Credit-Financial			508.1			12.3			2.3			518.1
	Credit-Industrial			493.7			9.4			3.5			499.6
	Credit-Utility			142.7			3.2			3.9			142
	Structured securities:
	CMO/MBS-agency (1)			168			8			0.7			175.3
	CMO/MBS-non agency			13.2			0.8			—			14
	CMBS (2)			178.6			1.6			0.2			180
	ABS (3)			221.4			0.6			1			221
	Foreign denominated:
	Governments			148.4			1.2			9.4			140.2
	Credit			211.1			2.7			18.9			194.9
	Total fixed maturities			2,817.20			64.6			41.1			2,840.70
	Equity securities			307.3			184.1			5.1			486.3
	Other investments			488.9			7.5			1.3			495.1
	Short-term investments			275.8			—			—			275.8
	Total investments		$	3,889.20		$	256.2		$	47.5		$	4,097.90

	(1)	Collateralized mortgage obligations/mortgage-backed securities (“CMO/MBS”).
	(2)	Commercial mortgage-backed securities (“CMBS”).
	(3)	Asset-backed securities (“ABS”).

	31-Dec-13
	(in millions)		Amortized			Gross			Gross			Fair
			Cost			Unrealized			Unrealized			Value
						Gains			Losses
	Fixed maturities
	USD denominated:
	U.S. Governments		$	273.4		$	2.4		$	0.5		$	275.3
	Non-U.S. Governments			60.9			0.3			1			60.2
	Obligations of states and political subdivisions			563.7			22.9			8.8			577.8
	Credit-Financial			426.3			15.4			1.8			439.9
	Credit-Industrial			385.5			13.8			2.2			397.1
	Credit-Utility			162			5.4			0.8			166.6
	Structured securities:
	CMO/MBS-agency (1)			219.4			9.2			1.7			226.9
	CMO/MBS-non agency			19.4			0.8			—			20.2
	CMBS (2)			162.7			3.1			1			164.8
	ABS (3)			123.6			0.8			0.6			123.8
	Foreign denominated:
	Governments			207.7			4.9			5.9			206.7
	Credit			155.5			4.4			4.8			155.1
	Total fixed maturities			2,760.10			83.4			29.1			2,814.40
	Equity securities			346.9			188.6			1.2			534.3
	Other investments			377.4			2.8			1.3			378.9
	Short-term investments			351.6			—			—			351.6
	Total investments		$	3,836.00		$	274.8		$	31.6		$	4,079.20

	(1)	Collateralized mortgage obligations/mortgage-backed securities (“CMO/MBS”).
	(2)	Commercial mortgage-backed securities (“CMBS”).
	(3)	Asset-backed securities (“ABS”).

Included in “Total investments” in our Consolidated Balance Sheets at December 31, 2014 and 2013 is $75.2 million and $87.3 million, respectively, of assets managed on behalf of the trade capital providers, who are third-party participants that provide underwriting capital to our Syndicate 1200 segment.
Contractual Maturity
The amortized cost and fair values of fixed maturity investments as of December 31, 2014, by contractual maturity, were as follows:

(in millions)		Amortized			Fair
(in millions)		Cost			Value
Due in one year or less		$	238.7		$	235.3
Due after one year through five years			1,326.20			1,328.50
Due after five years through ten years			507.7			519.1
Thereafter			163.4			167.5
Structured securities			581.2			590.3
Total		$	2,817.20		$	2,840.70

The expected maturities may differ from the contractual maturities because debtors may have the right to call or prepay obligations.

Other Invested Assets

Details regarding the carrying value, redemption characteristics and unfunded investment commitments of the other invested assets portfolio as of December 31, 2014 and 2013 were as follows:

31-Dec-14
(in millions)		Carrying Value				Unfunded Commitments
Investment Type
Hedge funds		$	153.2			$	—
Private equity			123.6				72.9
Long only funds			104.4				—
Other investments			113.9				—
Total other invested assets		$	495.1			$	72.9

31-Dec-13
(in millions)		Carrying Value				Unfunded Commitments
Investment Type
Hedge funds		$	87.9			$	—
Private equity			93.8				35.7
Long only funds			62				—
Other investments			135.2				—
Total other invested assets		$	378.9			$	35.7

The following describes each investment type:

·	Hedge funds: Hedge funds include equity long/short, multi-strategy credit, relative value credit and distressed event credit funds.
·	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: These funds include a long-only fund that invests in high yield fixed income securities and funds that primarily invests in distressed debt.
·	Other investments: Other investments include assets on deposit with various regulatory authorities to support Syndicate 1200 segment’s insurance and reinsurance operations and foreign exchange currency forward contracts to manage exposure on losses related to global catastrophic events, our Canadian dollar investment portfolio and certain Euro denominated investments.
Unrealized Losses and Other-than-temporary Impairments
An aging of unrealized losses on our investments in fixed maturities, equity securities, other investments and short-term investments is presented below:

31-Dec-14		Less Than One Year						One Year or Greater						Total
(in millions)		Fair			Unrealized			Fair			Unrealized			Fair			Unrealized
(in millions)		Value			Losses			Value			Losses			Value			Losses
Fixed maturities
USD denominated:
U.S. Governments		$	55		$	0.2		$	15.7		$	0.1		$	70.7		$	0.3
Non-U.S. Governments			36.5			0.4			5.2			0.2			41.7			0.6
Obligations of states and political			10.4			0.1			16.6			0.2			27			0.3
subdivisions			10.4			0.1			16.6			0.2			27			0.3
Credit-Financial			195.7			2.2			11.1			0.1			206.8			2.3
Credit-Industrial			240.8			3.3			12.2			0.2			253			3.5
Credit-Utility			63.1			3.8			1.9			0.1			65			3.9
Structured securities:
CMO/MBS-agency			10.1			0.1			19.2			0.6			29.3			0.7
CMBS			49.3			0.1			6			0.1			55.3			0.2
ABS			129.2			0.7			8.1			0.3			137.3			1
Foreign denominated:
Governments			123.7			9.3			11.2			0.1			134.9			9.4
Credit			190.8			18.7			0.9			0.2			191.7			18.9
Total fixed maturities			1,104.60			38.9			108.1			2.2			1,212.70			41.1
Equity securities			53.6			5.1			—			—			53.6			5.1
Other investments			(0.9	)		1.3			—			—			(0.9	)		1.3
Short-term investments			—			—			—			—			—			—
Total		$	1,157.30		$	45.3		$	108.1		$	2.2		$	1,265.40		$	47.5

31-Dec-13		Less Than One Year						One Year or Greater						Total
(in millions)		Fair			Unrealized			Fair			Unrealized			Fair			Unrealized
(in millions)		Value			Losses			Value			Losses			Value			Losses
Fixed maturities
USD denominated:
U.S. Governments		$	55.3		$	0.5		$	—		$	—		$	55.3		$	0.5
Non-U.S. Governments			36.3			1			—			—			36.3			1
Obligations of states and political			154.6			8.8			3.1			—			157.7			8.8
subdivisions (2)			154.6			8.8			3.1			—			157.7			8.8
Credit-Financial			88.7			1.7			2.4			0.1			91.1			1.8
Credit-Industrial			85.7			2			2.9			0.2			88.6			2.2
Credit-Utility			21.2			0.7			1.9			0.1			23.1			0.8
Structured securities:
CMO/MBS-agency			58.4			1.2			5.6			0.5			64			1.7
CMBS (2)			24.2			1			1.1			—			25.3			1
ABS			59.1			0.1			5.6			0.5			64.7			0.6
Foreign denominated:
Governments			170.5			5.9			—			—			170.5			5.9
Credit			125.3			4.8			—			—			125.3			4.8
Total fixed maturities			879.3			27.7			22.6			1.4			901.9			29.1
Equity securities			25.5			1.2			—			—			25.5			1.2
Other investments			(1.3	)		1.3			—			—			(1.3	)		1.3
Short-term investments (1)			4.5			—			—			—			4.5			—
Total		$	908		$	30.2		$	22.6		$	1.4		$	930.6		$	31.6

(1)	Unrealized losses less than one year are less than $0.1 million.
(2)	Unrealized losses one year or greater are less than $0.1 million.
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. For equity securities and other investments, the length of time and the amount of decline in fair value are the principal factors in determining other-than-temporary impairment. We also recognize other-than-temporary losses on fixed maturity securities that we intend to sell.
We hold a total of 6,165 securities, of which 2,031 were in an unrealized loss position for less than one year and 139 were in an unrealized loss position for a period one year or greater as of December 31, 2014. 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 an investment is other-then-temporarily impaired or not, 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. In situations where we did not recognize other-than-temporary losses on investments in our equity portfolio, we have evaluated the near-term prospects of the investment in relation to the severity and duration of the impairment and based on that evaluation, have the ability and intent to hold these investments until a recovery of the cost basis. We do not consider these investments to be other-than-temporarily impaired at December 31, 2014.

We recognized other-than-temporary losses on our fixed maturities portfolio of $1.2 million, $6.0 million and $1.5 million for 2014, 2013 and 2012, respectively. We recognized other-than-temporary losses on our equity portfolio of $1.1 million, $1.8 million and $2.2 million for 2014, 2013 and 2012, respectively.
Net Investment Income and Realized Gains and Losses
Investment income and expenses were as follows:

		For the Years Ended December 31,
(in millions)		2014			2013			2012
Investment income:
Interest and dividends on fixed maturities		$	76.3		$	87.7		$	105.9
Dividends on equity securities			15.8			17.7			15.2
Interest on short-term and other investments			5.3			5			7.3
Other			(1.0	)		(1.0	)		(0.4	)
Investment income			96.4			109.4			128
Investment expenses			(9.8	)		(9.4	)		(9.2	)
Net investment income		$	86.6		$	100		$	118.8

The following table presents our gross realized investment gains (losses) and other:

		For the Years Ended December 31,
(in millions)		2014			2013			2012
Realized gains
Fixed maturities		$	17		$	33.5		$	27.2
Equity securities			29.2			59.1			0.4
Other investments			44.8			38.9			21.5
Short-term investments			0.1			0.1			0.5
Other assets			2			—			4.8
Gain on sale of real estate holdings			43.3			—			—
Gross realized investment gains and other			136.4			131.6			54.4
Realized losses
Fixed maturities			(12.2	)		(19.6	)		(9.1	)
Equity securities			(0.6	)		(1.4	)		(0.5	)
Other investments			(21.8	)		(30.8	)		(15.1	)
Short-term investments			(0.9	)		(0.7	)		(0.3	)
Other assets			(4.6	)		—			—
Other-than-temporary impairment losses on fixed			(1.2	)		(6.0	)		(1.5	)
maturities			(1.2	)		(6.0	)		(1.5	)
Other-than-temporary impairment losses on equity			(1.1	)		(1.8	)		(2.2	)
securities			(1.1	)		(1.8	)		(2.2	)
Gross realized investment and other losses			(42.4	)		(60.3	)		(28.7	)
Net realized investment gains and other		$	94		$	71.3		$	25.7

Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments are summarized as follows:

(in millions)		Fixed			Equity			Other			Other			Real Estate Holdings			Tax			Total
(in millions)		Maturities			Maturities			Investments			Other			Real Estate Holdings			Effects			Total
Year Ended December 31, 2014
Realized before impairments		$	4.8		$	28.6		$	23		$	(3.4	)	$	43.3		$	(34.0	)	$	62.3
Realized - impairments			(1.2	)		(1.1	)		—			—			—			0.8			(1.5	)
Change in unrealized			(30.5	)		(8.4	)		2.5			—			—			3.1			(33.3	)
Year Ended December 31, 2013
Realized before impairments		$	13.9		$	57.7		$	8.1		$	(0.6	)	$	—		$	(26.2	)	$	52.9
Realized - impairments			(6.0	)		(1.8	)		—			—			—			2.7			(5.1	)
Change in unrealized			(102.6	)		39.5			4.5			—			—			18.4			(40.2	)
Year Ended December 31, 2012
Realized before impairments		$	18.1		$	(0.1	)	$	6.4		$	5		$	—		$	(7.2	)	$	22.2
Realized - impairments			(1.5	)		(2.2	)		—			—			—			1.3			(2.4	)
Change in unrealized			39.5			35.9			(2.4	)		—			—			(20.4	)		52.6

We enter into short-term, currency spot and forward contracts to mitigate foreign exchange rate exposure for certain non-U.S. Dollar denominated fixed maturity investments. The forward contracts used are typically less than sixty days and are renewed as long as the non-U.S. Dollar denominated fixed maturity investments are held in our portfolio. These forward contracts are designated as fair value hedges for accounting purposes.
As of December 31, 2013 and 2012, we hedged $0.1 million and $2.3 million, respectively, of non-U.S. Dollar denominated fixed maturity investments in emerging market debt with $0.1 million and $2.2 million, respectively, of foreign exchange contracts. The net realized effect on income was not significant for the reporting periods. These emerging market debt fixed income investments were sold and the related hedging program discontinued in 2014. The net realized effect on income was not significant during 2014.

We also enter into foreign currency exchange forward contracts to manage currency exposure on losses related to global catastrophe events. These currency forward contracts are carried at fair value in our Consolidated Balance Sheets in “Other investments.” The realized and unrealized gains and losses are included in “Net realized investment and other gains” in our Consolidated Statements of Income. The notional amount of the currency forward contracts was $20.6 million, $57.2 million and $102.8 million as of December 31, 2014, 2013 and 2012, respectively. The fair value of the currency forward contracts was a loss of $0.6 million, $1.3 million and $1.9 million as of December 31, 2014, 2013 and 2012, respectively. For the years ended December 31, 2014, 2013 and 2012, we recognized $4.6 million, $7.8 million and $8.0 million in realized gains and $4.9 million, $10.4 million and $7.5 million in realized losses, respectively, from the currency forward contracts.

In 2014, we entered into foreign currency exchange forward contracts to manage currency exposure on our Canadian dollar (“CAD”) investment portfolio. The currency forward contracts are carried at fair value in our Consolidated Balance Sheets in “Other investments.” The realized and unrealized gains and losses are included in “Net realized investment and other gains” in our Consolidated Statements of Income. The notional amount of the currency forward contracts was CAD $141.8 million ($118.1 million) as of December 31, 2014. The fair value of the currency forward contracts was a loss of $0.6 million as of December 31, 2014. For the year ended December 31, 2014, we recognized $4.6 million in realized gains and $2.2 million in realized losses, respectively, from the CAD currency forward contracts.

Also in 2014, we entered into foreign currency exchange forward contracts to manage currency exposure on certain Euro denominated investments. The currency forward contracts are carried at fair value in our Consolidated Balance Sheets in “Other investments”. The realized and unrealized gains and losses are included in “Net realized investment and other gains” in our Consolidated Statements of Income. The fair value of the currency forward contracts was $2.3 million as of December 31, 2014. For the year ended December 31, 2014, we recognized $6.0 million in realized gains and $2.4 million in realized losses, respectively, from these currency forward contracts.
Regulatory Deposits, Pledged Securities and Letters of Credit
At December 31, 2014, the amortized cost and fair value of investments on deposit with U.S., Canadian and various agencies for regulatory purposes were $186.6 million and $194.2 million, respectively. At December 31, 2013, the amortized cost and fair value of investments on deposit with U.S. and various agencies for regulatory purposes were $196.7 million and $203.4 million, respectively.

At December 31, 2014, investments with an amortized cost of $55.0 million and fair value of $55.3 million were pledged as collateral in support of irrevocable letters of credit (“LOC’s”) in the amount of $43.6 million issued under the terms of certain reinsurance agreements in respect of reported loss and loss expense reserves. At December 31, 2013, investments with an amortized cost of $97.7 million and fair value of $98.6 million were pledged as collateral in support of irrevocable LOC’s in the amount of $60.2 million issued under the terms of certain reinsurance agreements in respect of reported loss and loss expense reserves.

Our Corporate member’s capital supporting our Lloyd’s business was $217.9 million and $250.8 million at December 31, 2014 and 2013, respectively.
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 assumptions about the assumptions market participants would use in pricing the asset or liability based on the best information available in the circumstances.
We receive fair value prices from third-party pricing services and our outside investment managers. These prices are determined using observable market information such as dealer quotes, market spreads, cash flows, yield curves, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the security’s terms and conditions, among other things. We have reviewed the processes used by the third-party providers for pricing the securities, and have determined that these processes result in fair values consistent with GAAP requirements. In addition, we review these prices for reasonableness, and have not adjusted any prices received from the third-party providers as of December 31, 2014. 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 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.
—	CMO/MBS agency, CMO/MBS non-agency, CMBS, ABS residential and ABS non-residential 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, 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.
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 2: We own interests in equity and mutual funds that are reported at fair value using Level 2 inputs. The valuations are based on the funds’ net asset value per share, determined weekly or at the end of each month. The underlying assets in the funds are valued primarily on the basis of closing market quotations or official closing prices on each valuation day.
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 are obtained from the National Association of Insurance Commissioners’ Security Valuation Office at the reporting date.
—	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.
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. Foreign currency future contracts are valued by our counterparty using market driven foreign currency exchange rates and are considered Level 2 investments.
Short-term Investments: Short-term investments are principally reported at fair value using Level 1 inputs, with the exception of short-term corporate 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.
Other Assets Level 3: We had one reinsurance contract deemed a derivative in 2013. The fair values were estimated by management taking into account changes in the market for insurance linked securities with similar economic characteristics and potential recoveries from events preceding the valuation date. See Note 5, “Derivative Instruments” for related disclosures.
Transfers Between Level 1 and Level 2 Securities: There were no transfers between Level 1 and Level 2 securities during 2014 or 2013.
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)		31-Dec-14			Level 1 (a)			Level 2 (b)			Level 3 (c)
Fixed maturities
USD denominated:
U.S. Governments		$	185		$	99.2		$	85.8		$	—
Non-U.S. Governments			79.9			—			79.9			—
Obligations of states and political subdivisions			490.7			—			490.7			—
Credit-Financial			518.1			—			518.1			—
Credit-Industrial			499.6			—			499.6			—
Credit-Utility			142			—			142			—
Structured securities:
CMO/MBS-agency			175.3			—			175.3			—
CMO/MBS-non agency			14			—			14			—
CMBS			180			—			180			—
ABS			221			—			221			—
Foreign denominated:
Governments			140.2			—			140.2			—
Credit			194.9			—			194.9			—
Total fixed maturities			2,840.70			99.2			2,741.50			—
Equity securities			486.3			485.4			—			0.9
Other investments			97.3			—			97.3			—
Short-term investments			275.8			273.9			1.9			—
Other assets			—			—			—			—
		$	3,700.10		$	858.5		$	2,840.70		$	0.9

(a)	Quoted prices in active markets for identical assets
(b)	Significant other observable inputs
(c)	Significant unobservable inputs

					Fair Value Measurements at Reporting Date Using
(in millions)		31-Dec-13			Level 1 (a)			Level 2 (b)			Level 3 (c)
Fixed maturities
USD denominated:
U.S. Governments		$	275.3		$	143.8		$	131.5		$	—
Non-U.S. Governments			60.2			—			60.2			—
Obligations of states and political subdivisions			577.8			—			577.8			—
Credit-Financial			439.9			—			439.9			—
Credit-Industrial			397.1			—			397.1			—
Credit-Utility			166.6			—			166.6			—
Structured securities:
CMO/MBS-agency			226.9			—			226.9			—
CMO/MBS-non agency			20.2			—			20.2			—
CMBS			164.8			—			164.8			—
ABS			123.8			—			123.8			—
Foreign denominated:
Governments			206.7			—			206.7			—
Credit			155.1			—			155.1			—
Total fixed maturities			2,814.40			143.8			2,670.60			—
Equity securities			534.3			476.7			56.3			1.3
Other investments			117.8			—			117.8			—
Short-term investments			351.6			347			4.6			—
Other assets			2.6			—			—			2.6
		$	3,820.70		$	967.5		$	2,849.30		$	3.9

(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 and include reinsurance contracts that are classified as “Other assets”.
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)		Equity			Other			Total
(in millions)		Securities			Assets			Total
Beginning balance, January 1, 2014		$	1.3		$	2.6		$	3.9
Transfers into Level 3			—			—			—
Transfers out of Level 3			—			—			—
Total gains or losses (realized/unrealized):
Included in net income (loss)			—			—			—
Included in other comprehensive income (loss)			0.1			—			0.1
Purchases, issuances, sales, and settlements
Purchases			—			—			—
Issuances			—			—			—
Sales			(0.5	)		—			(0.5	)
Settlements			—			(2.6	)		(2.6	)
Ending balance, December 31, 2014		$	0.9		$	—		$	0.9
Amount of total gains or losses for the year included in		$	—		$	—		$	—
net income (loss) attributable to the change in
unrealized gains or losses relating to assets still held
at December 31, 2014

(in millions)		Equity			Other			Total
(in millions)		Securities			Assets			Total
Beginning balance, January 1, 2013		$	1.8		$	6.9		$	8.7
Transfers into Level 3			—			—			—
Transfers out of Level 3			—			—			—
Total gains or losses (realized/unrealized):
Included in net income (loss)			0.1			—			0.1
Included in other comprehensive income (loss)			—			—			—
Purchases, issuances, sales, and settlements
Purchases			—			—			—
Issuances			—			—			—
Sales			(0.6	)		—			(0.6	)
Settlements			—			(4.3	)		(4.3	)
Ending balance, December 31, 2013		$	1.3		$	2.6		$	3.9
Amount of total gains or losses for the year included in		$	—		$	—		$	—
net income (loss) attributable to the change in
unrealized gains or losses relating to assets still held
at December 31, 2013

At December 31, 2014 and 2013, 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.

Sale_of_Real_Estate_Holding

Sale of Real Estate Holding	12 Months Ended
	Dec. 31, 2014
Other Real Estate [Abstract]
Sale of Real Estate Holding	3	Sale of Real Estate Holding
	On December 30, 2014, AGI Properties, Inc. (“AGIP”), a subsidiary of Argonaut Insurance Company, sold a parcel of real estate in Torrance, California for a sales price of $45.0 million, with net proceeds of approximately $43.6 million. The funds are being held in escrow, with AGIP named as beneficiary. The sale of this property met full gain recognition under ASC 360-20, “Property, Plant, and Equipment – Real Estate Sales,” and resulted in a pre-tax realized gain of $43.3 million. This amount is included in the Company’s “Net realized investment and other gains” line on its Consolidated Statements of Income.

Reinsurance

Reinsurance	12 Months Ended
Reinsurance	Dec. 31, 2014
Insurance [Abstract]
Reinsurance	4	Reinsurance
	We reinsure certain risks with other insurance companies. Such arrangements serve to limit our maximum loss on certain individual risks as well as on catastrophes and large or unusually hazardous risks. We are liable for reinsurance ceded in the event our reinsurers do not meet their obligations. Thus, a credit exposure exists with respect to reinsurance ceded to the extent that any reinsurer is unable or unwilling to meet the obligations assumed under the reinsurance contracts. Our allowance for uncollectible reinsurance balances receivable on paid losses and incurred claims was $3.4 million and $3.7 million as of December 31, 2014 and 2013, respectively. Under certain reinsurance agreements, collateral, including letters of credit, is held to secure performance of reinsurers in meeting their obligations. The amount of such collateral was $359.4 million and $335.5 million at December 31, 2014 and 2013, respectively. The collateral we hold does not apply to our entire outstanding reinsurance recoverable. Rather, collateral is provided on an individual contract basis as appropriate. For each individual reinsurer, the collateral held may exceed or fall below the total outstanding recoverable from that individual reinsurer.
	The long-term nature of the reinsurance contracts creates a credit risk to us over time arising from potentially uncollectible reinsurance. To mitigate that counterparty risk, we evaluate our reinsurers to assess their financial condition. The factors that underlie these reviews include a financial risk assessment as well as an internal assessment of the capitalization and the operational risk of the reinsurer. As a result of these reviews, we may make changes to the approved markets that are used in both our treaty and facultative reinsurance programs.
	Estimated losses recoverable from reinsurers and the ceded portion of unearned premiums are reported as assets in our Consolidated Balance Sheets. Included in “Reinsurance recoverables” are paid loss recoverables of $91.9 million and $140.8 million as of December 31, 2014 and 2013, respectively. “Earned Premiums” and “Losses and loss adjustment expenses” are reported net of reinsurance in our Consolidated Statements of Income.
	Losses and loss adjustment expenses of $747.4 million, $742.0 million and $747.6 million for the years ended December 31, 2014, 2013 and 2012, respectively, are net of amounts ceded to reinsurers of $246.6 million, $292.8 million and $223.6 million, respectively.
	We are required to accept certain assigned risks and other legally mandated reinsurance obligations. Prior to the mid-1980s, we assumed various forms of casualty reinsurance for which we continue to maintain reserves for losses and loss adjustment expenses (see Note 21, “Run-off Lines”). For such assumed reinsurance transactions, we engage in various monitoring steps that are common with assumed reinsurance such as ongoing claims reviews. We currently assume property related reinsurance primarily through our subsidiary, Argo Re and casualty related reinsurance primarily through ArgoGlobal Syndicate 1200 (see Note 20, “Segment Information”).
	Premiums were as follows:

			For the Years Ended December 31,
	(in millions)		2014			2013			2012
	Direct written premiums		$	1,585.50		$	1,576.10		$	1,428.60
	Reinsurance ceded to other companies			(537.5	)		(537.1	)		(501.2	)
	Reinsurance assumed from other companies			319.9			312.3			317.1
	Net written premiums		$	1,367.90		$	1,351.30		$	1,244.50
	Direct earned premiums		$	1,551.80		$	1,541.00		$	1,372.20
	Reinsurance ceded to other companies			(524.8	)		(533.7	)		(487.0	)
	Reinsurance assumed from other companies			311.1			296.5			301.3
	Net earned premiums		$	1,338.10		$	1,303.80		$	1,186.50
	Percentage of reinsurance assumed to net earned			23.2	%		22.7	%		25.4	%
	premiums			23.2	%		22.7	%		25.4	%

Derivative_Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 2014
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Derivative Instruments	5	Derivative Instruments
	Through our subsidiary Argo Re, in 2011 we entered into two reinsurance contracts with a special purpose reinsurance company that provided us with protection against certain severe catastrophe events and the occurrence of multiple significant catastrophe events during the same year. The first contract was effective June 18, 2011 and provided coverage of $100 million for hurricanes and earthquakes in the U.S., windstorms in Europe and earthquakes in Japan based on the occurrence of second and subsequent events on a per-occurrence basis over an 18-month coverage period. The first contract expired in December 2012. The second contract entered into on December 28, 2011 and effective January 1, 2012, provided coverage of $100 million for hurricanes and earthquakes (including fire) in the U.S. and covered losses for the first and subsequent events on a per-occurrence basis over a 24-month coverage period. The second contract expired in December 2013. Both of these transactions ignored the effects of inuring reinsurance, creating the remote possibility of a double recovery on covered events, and were therefore deemed to be derivatives.
	We recorded these contracts at fair value, and such fair value is included in “Other assets” in our Consolidated Balance Sheets with any changes in the value reflected in “Other reinsurance-related expenses” in our Consolidated Statements of Income. As there is no quoted fair value available for these derivatives, the fair value was estimated by management taking into account changes in the market for insurance linked services with similar economic characteristics and potential recoveries from events preceding the valuation date. Included in “Other reinsurance-related expenses” for the years ended December 31, 2013 and 2012 were $19.2 million and $27.3 million, respectively, which was incurred due to the change in the fair value of the derivative, principally due to the passage of the transaction’s risk coverage term. Included in “Other assets” in our Consolidated Balance Sheets at December 31, 2013 was $2.6 million, which represented the fair value of the contract at that date. As these contracts expired in December 2012 and December 2013, no expense was recorded during 2014, nor was it reflected on our Consolidated Balance Sheet at December 31, 2014.
	The special purpose reinsurance company that was the counterparty to this transaction was a variable interest entity under the provisions of ASC Topic 810-10, “Consolidation.” Argo Group was not the primary beneficiary of this entity and was therefore not required to consolidate it in our consolidated financial statements.

Reserves_for_Losses_and_Loss_A

Reserves for Losses and Loss Adjustment Expenses	12 Months Ended
	Dec. 31, 2014
Insurance [Abstract]
Reserves for Losses and Loss Adjustment Expenses	6	Reserves for Losses and Loss Adjustment Expenses
	The following table provides a reconciliation of reserves for losses and loss adjustment expenses (“LAE”):

			For the Years Ended December 31,
	(in millions)		2014			2013			2012
	Net reserves beginning of the year		$	2,107.60		$	2,110.90		$	2,336.70
	Add:
	Net reserves from assumed retroactive insurance			—			—			13
	contract (1)
	Losses and LAE incurred during current calendar
	year, net of reinsurance:
	Current accident year			785.1			775.6			780.5
	Prior accident years			(37.7	)		(33.6	)		(32.9	)
	Losses and LAE incurred during calendar year, net			747.4			742			747.6
	of reinsurance
	Deduct:
	Net reserves ceded - whole account quota share			—			—			192.2
	reinsurance transaction (2)
	Losses and LAE payments made during current
	calendar year, net of reinsurance:
	Current accident year			185.9			199.3			217.7
	Prior accident years			550.8			554.2			578.8
	Losses and LAE payments made during current			736.7			753.5			796.5
	calendar year, net of reinsurance:
	Change in participation interest (3)			37.8			10.4			(3.1	)
	Foreign exchange adjustments			(19.0	)		(2.2	)		5.4
	Net reserves - end of year			2,137.10			2,107.60			2,110.90
	Add:
	Reinsurance recoverables on unpaid losses and LAE,			905.3			1,122.70			1,112.60
	end of year
	Gross reserves - end of year		$	3,042.40		$	3,230.30		$	3,223.50

	(1)	Amount represents reserves assumed resulting from participation in Brazilian Motor Third-Party Liability Insurance Pool effective January 1, 2012.
	(2)	Amount represents reserves ceded resulting from a whole account quota share reinsurance transaction of 2009 and prior year of account reserves of the syndicate effective December 2012.
	(3)	Amount represents (decrease) increase in reserves due to change in syndicate participation.
	On December 31, 2012, our Syndicate 1200 segment entered into a retroactive whole account quota share contract covering the 2009 and prior years of account. The counterparty was another syndicate within the Lloyd’s market. As a result of this transaction, reserves for losses and LAE at December 31, 2012 were net of $192.2 million ceded under this quota share agreement. Subject to a Split Reinsurance to Close arrangement previously approved by the Prudential Regulatory Authority, the liabilities assumed by the whole account quota share provider were legally transferred to that quota share provider on January 18, 2014 with an inception date of January 1, 2014.
	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.
	Impacting losses and LAE for the year ended December 31, 2014 was $37.7 million in favorable prior years’ loss reserve development comprised of the following: $47.4 million of net favorable development in the Excess and Surplus Lines segment primarily caused by favorable development in the general and products liability lines, partially offset by unfavorable development in commercial automobile; $6.8 million of net unfavorable development in the Commercial Specialty segment, primarily driven by unfavorable development in general liability due to increases in claim severity, as well as unfavorable development in auto liability lines, partially offset by favorable development in short-tail and workers compensation lines; $0.4 million of net favorable development in the International Specialty segment; $21.1 million of favorable development in the Syndicate 1200 segment primarily driven by favorable development in various property classes, as well as favorable development in professional indemnity, partially offset by unfavorable development in general liability; $24.4 million of unfavorable development in the Run-off Lines segment primarily caused by $10.3 million of unfavorable development in workers compensation lines driven by increasing medical costs on older claims, as well as $13.5 million in asbestos liability driven by increasing defense costs on primary business and activity on assumed business including the impact of arbitrations and commutations.
	Net favorable loss development recognized in 2013 for prior accident years was a $33.6 million reduction to losses and LAE. The Excess and Surplus Lines segment had net favorable loss development of $43.9 million primarily due to favorable development in the general and products liability lines of business, partially offset by unfavorable development in commercial automobile losses. The Commercial Specialty segment had net unfavorable loss development of $1.1 million primarily attributable to unfavorable development in general liability due to increases in claim severity and unfavorable development in automobile liability, partially offset by favorable development in workers compensation and short-tail lines. The International Specialty segment had net negligible prior year loss development. The Syndicate 1200 segment had net favorable loss development of $6.2 million primarily attributable to favorable development in various property classes, partially offset by unfavorable development in liability lines associated with municipality business. The Run-off Lines segment had net unfavorable development of $15.5 million primarily due to $10.5 million of unfavorable development in the asbestos liability driven by higher defense costs for claims from general liability policies written on a direct basis, as well as commutation and settlement activity, and $2.0 million of unfavorable development in the medical malpractice liability line due to the loss of the New York Liquidation Bureau funding for structured settlement annuity payments.
	Net favorable loss development recognized in 2012 for prior accident years was a $32.9 million reduction to losses and LAE. The Excess and Surplus Lines segment had net favorable loss development of $48.0 million primarily driven by favorable development in the general and products liability lines of business. The Commercial Specialty segment had net unfavorable loss development of $22.2 million primarily driven by unfavorable development in general liability due to increases in claim severity, unfavorable development in the automobile liability lines of business, partially offset by favorable development in workers compensation. The International Specialty segment had net favorable loss development of $7.2 million primarily attributable to short-tail non-catastrophe losses. The Syndicate 1200 segment had net favorable loss development of $9.7 million primarily driven by favorable development in the property facultative, North American binder and Directors and Officers classes of business, partially offset by unfavorable development in the general liability property class of business. The Run-off Lines segment had net unfavorable development of $9.8 million primarily due to $9.1 million of unfavorable development in asbestos claims driven by increasing defense costs in the primary book and increasing settlement costs in the assumed book, partially offset by favorable development in workers compensation and run-off reinsurance claims.
	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 loss development, favorable or unfavorable, will not occur.
	Pension-type reserves (tabular reserves) are indemnity reserves that are calculated using discounts determined with reference to actuarial tables, which incorporate interest and contingencies such as mortality, remarriage, inflation or recovery from disability applied to a reasonably determinable payment stream. We discounted certain workers compensation pension-type reserves using a maximum interest rate of 3.5% in 2014, 2013 and 2012. The amount of unamortized discount was $17.6 million, $19.5 million and $20.8 million at December 31, 2014, 2013 and 2012, respectively.

Junior_Subordinated_Debentures

Junior Subordinated Debentures

12 Months Ended

Dec. 31, 2014

Junior Subordinated Debentures

Senior Unsecured Fixed Rate Notes

In September 2012, through our wholly owned subsidiary Argo Group US, we issued $143,750,000 aggregate principal amount of Argo Group US’s 6.5% Senior Notes due September 15, 2042 (the “Notes”). The Notes bear interest at 6.5%, payable quarterly in cash in arrears on the 15th day of March, June, September and December of each year, beginning on December 15, 2012. The Notes are unsecured and unsubordinated obligations of Argo Group US and rank equally in right of payment with all of Argo Group US’s other unsecured and unsubordinated debt. The Notes are guaranteed on a full and unconditional senior unsecured basis by Argo Group. The Notes may be redeemed, for cash, in whole or in part, on or after September 15, 2017, at Argo Group US’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. The outstanding principal balance on the Notes was $143.8 million at December 31, 2014 and 2013.

The proceeds, net of issuance costs, from the sale of the Notes were $138.7 million and were used to repay $118.6 million of principal related to two of our trust preferred securities, with the remainder used for general corporate purposes.

Junior Subordinated Debentures [Member]

Junior Subordinated Debentures

Through a series of trusts, that are wholly-owned subsidiaries (non-consolidated), we issued debt. The debentures are variable with the rate being reset quarterly and subject to certain interest rate ceilings. Interest payments are payable quarterly. The debentures are all unsecured and are subordinated to other indebtedness. All are redeemable subject to certain terms and conditions at a price equal to 100% of the principal plus accrued and unpaid interest.

On July 16, 2014, Argo Group US, Inc. purchased the outstanding PXRE Capital Trust V $20,000,000 Junior Subordinated Debt Securities (“Capital Trust V”) at a discount equal to 90.0% of the principal amount plus accrued and unpaid interest through the date of purchase for a total price of $18.2 million, resulting in the recognition of a $2.0 million pre-tax realized gain. As of December 31, 2014, the Capital Trust V has not yet been redeemed and interest will continue to accrue and be paid until the redemption date. In accordance with ASC Topic 405, “Liabilities,” we have eliminated the outstanding debt, associated interest and intercompany balances related to the purchase of the Capital Trust V since the purchase by Argo Group US, Inc.

On October 1, 2012, we gave notice of redemption to the trustee of our 8.85% PXRE Capital Trust I $103,093,000 Junior Subordinated Debt Securities (“Capital Trust I”). Capital Trust I was redeemed on November 13, 2012 at a redemption price equal to 102.090% of its principal amount, plus accrued and unpaid interest through the date of redemption. Additionally, on October 8, 2012, we gave notice of redemption to the trustee of our 9.75% PXRE Capital Trust III $15,464,000 Junior Subordinated Debt Securities (“Capital Trust III”). Capital Trust III was redeemed on November 23, 2012 at a redemption price equal to 100.975% of its principal amount, plus accrued and unpaid interest through the date of redemption. Interest on Capital Trust I and Capital Trust III ceased to accrue on and after the redemption dates. Subsequent to redemption, we received $3.1 million and $0.5 million for our ownership in Capital Trust I and Capital Trust III, respectively. Redemption of Capital Trust I and Capital Trust III resulted in a call premium of $2.1 million and $0.1 million, respectively, shown in “Debt extinguishment costs” in our Consolidated Statement of Income for the year ended December 31, 2012. Capital Trust I had an unamortized discount of $0.4 million that was written off to “Interest expense” in our Consolidated Statement of Income for the year ended December 31, 2012.

A summary of our outstanding junior subordinated debentures is presented below:

(in millions)

Issue Date

Trust Preferred Pools

Maturity

Redeemable

Rate Structure

Interest Rate at December 31, 2014

Amount

Argo Group

5/15/03

PXRE Capital Statutory Trust II

5/15/33

5/15/08

3M LIBOR + 4.10%

4.33%

18.1

11/6/03

PXRE Capital Trust VI

9/30/33

9/30/08

3M LIBOR + 3.90%

4.16%

10.3

Argo Group US

5/15/03

Argonaut Group Statutory Trust I

5/15/33

5/15/08

3M LIBOR + 4.10%

4.33%

15.5

12/16/03

Argonaut Group Statutory Trust III

1/8/34

1/8/09

3M LIBOR + 4.10%

4.33%

12.3

4/29/04

Argonaut Group Statutory Trust IV

4/29/34

4/29/09

3M LIBOR + 3.85%

4.08%

13.4

5/26/04

Argonaut Group Statutory Trust V

5/24/34

5/24/09

3M LIBOR + 3.85%

4.08%

12.3

5/12/04

Argonaut Group Statutory Trust VI

5/12/34

6/1/09

3M LIBOR + 3.80%

4.04%

13.4

9/17/04

Argonaut Group Statutory Trust VII

12/15/34

9/17/09

3M LIBOR + 3.60%

3.84%

15.5

9/22/04

Argonaut Group Statutory Trust VIII

9/22/34

9/22/09

3M LIBOR + 3.55%

3.80%

15.5

10/22/04

Argonaut Group Statutory Trust IX

12/15/34

12/15/09

3M LIBOR + 3.60%

3.84%

15.5

9/15/05

Argonaut Group Statutory Trust X

9/15/35

9/15/10

3M LIBOR + 3.40%

3.64%

30.9

Total Outstanding

172.7

(in millions)

Issue Date

Trust Preferred Pools

Maturity

Redeemable

Rate Structure

Interest Rate at December 31, 2013

Amount

Argo Group

5/15/03

PXRE Capital Statutory Trust II

5/15/33

5/15/08

3M LIBOR + 4.10%

4.34%

18.1

10/29/03

PXRE Capital Trust V

10/29/33

10/29/08

3M LIBOR + 3.85%

4.09%

20.6

11/6/03

PXRE Capital Trust VI

9/30/33

9/30/08

3M LIBOR + 3.90%

4.15%

10.3

Argo Group US

5/15/03

Argonaut Group Statutory Trust I

5/15/33

5/15/08

3M LIBOR + 4.10%

4.34%

15.5

12/16/03

Argonaut Group Statutory Trust III

1/8/34

1/8/09

3M LIBOR + 4.10%

4.34%

12.3

4/29/04

Argonaut Group Statutory Trust IV

4/29/34

4/29/09

3M LIBOR + 3.85%

4.09%

13.4

5/26/04

Argonaut Group Statutory Trust V

5/24/34

5/24/09

3M LIBOR + 3.85%

4.09%

12.3

5/12/04

Argonaut Group Statutory Trust VI

5/12/34

6/1/09

3M LIBOR + 3.80%

4.04%

13.4

9/17/04

Argonaut Group Statutory Trust VII

12/15/34

9/17/09

3M LIBOR + 3.60%

3.84%

15.5

9/22/04

Argonaut Group Statutory Trust VIII

9/22/34

9/22/09

3M LIBOR + 3.55%

3.80%

15.5

10/22/04

Argonaut Group Statutory Trust IX

12/15/34

12/15/09

3M LIBOR + 3.60%

3.84%

15.5

9/15/05

Argonaut Group Statutory Trust X

9/15/35

9/15/10

3M LIBOR + 3.40%

3.64%

30.9

Total Outstanding

193.3

Other_Indebtedness

Other Indebtedness

12 Months Ended

Dec. 31, 2014

Debt Disclosure [Abstract]

Other Indebtedness

Floating Rate Loan Stock

This debt was assumed through the acquisition of ArgoGlobal Syndicate 1200. These notes are unsecured. All are redeemable subject to certain terms and conditions at a price equal to 100% of the principal plus accrued and unpaid interest. Interest on the U.S. Dollar and Euro notes is due semiannually and quarterly, respectively. A summary of the notes outstanding at December 31, 2014 and 2013 is presented below:

(in millions)

Issue Date

Currency

Maturity

Redeemable

Rate Structure

Interest Rate at December 31, 2014

Amount

12/8/04

U.S. Dollar

11/15/34

12/8/09

6 month LIBOR + 4.2%

4.53%

6.5

9/6/05

Euro

8/22/35

9/6/10

3 month LIBOR + 4.0%

4.08%

14.9

10/31/06

U.S. Dollar

1/15/36

1/15/11

6 month LIBOR + 4.0%

4.33%

10/31/06

Euro

11/22/36

10/31/11

3 month LIBOR + 4.0%

4.08%

13.1

6/8/07

Euro

9/15/37

6/8/12

3 month LIBOR + 3.9%

3.98%

16.8

61.3

(in millions)

Issue Date

Currency

Maturity

Redeemable

Rate Structure

Interest Rate at December 31, 2013

Amount

12/8/04

U.S. Dollar

11/15/34

12/8/09

6 month LIBOR + 4.2%

4.60%

6.5

9/6/05

Euro

8/22/35

9/6/10

3 month LIBOR + 4.0%

4.22%

16.3

10/31/06

U.S. Dollar

1/15/36

1/15/11

6 month LIBOR + 4.0%

4.40%

10/31/06

Euro

11/22/36

10/31/11

3 month LIBOR + 4.0%

4.22%

14.3

6/8/07

Euro

9/15/37

6/8/12

3 month LIBOR + 3.9%

4.12%

18.4

65.5

No principal payments have been made since the acquisition of ArgoGlobal Syndicate 1200. The floating rate loan stock denominated in Euros fluctuates due to foreign currency translation. The outstanding balance on these loans was $44.8 million and $49.0 million as of December 31, 2014 and 2013, respectively. The foreign currency translation adjustment is recorded in our Consolidated Statements of Income.

Borrowing Under Revolving Credit Facility

On March 7, 2014, each of Argo Group, Argo Group US, Inc., Argo International Holdings Limited and Argo Underwriting Agency Limited (the “Borrowers”) entered into a $175.0 million Credit Agreement (“New Credit Agreement”) with JPMorgan Chase Bank, N.A., as administrative agent. The New Credit Agreement replaced and terminated the previous $150.0 million Credit Agreement. The New Credit Agreement provides for a $175.0 million revolving credit facility with a maturity date of March 7, 2018 unless extended in accordance with the terms of the New Credit Agreement. Borrowings under the New Credit Agreement may be used for general corporate purposes, including working capital and permitted acquisitions, and each of the Borrowers has agreed to be jointly and severally liable for the obligations of the other Borrowers under the New Credit Agreement.

The New Credit Agreement contains customary events of default. If an event of default occurs and is continuing, the Borrowers might be required immediately to repay all amounts outstanding under the New Credit Agreement. Lenders holding at least a majority of the loans and commitments under the New Credit Agreement may elect to accelerate the maturity of the loans and/or terminate the commitments under the New Credit Agreement upon the occurrence and during the continuation of an event of default.

Included in the New Credit Agreement is a provision that allows up to $17.5 million of the revolving credit facility to be used for LOCs, subject to availability. On March 7, 2014, the $0.2 million LOC outstanding under the previous $150.0 million Credit Agreement was transferred to the New Credit Agreement. At December 31, 2014 and 2013, there were no borrowings outstanding and $0.2 million in LOCs against the New Credit Facility.

Other Debt

As part of the ARIS Title Insurance Corporation (“ARIS”) acquisition, at December 31, 2014 and 2013, we had a note payable for $0.7 million and $0.8 million, respectively. The note had a variable interest rate of 2.00% above 30-day LIBOR, with the variable interest rate being reset quarterly and subject to certain interest rate ceilings. Interest payments are payable quarterly. The note payable matures on April 1, 2019.

Disclosures_about_Fair_Value_o

Disclosures about Fair Value of Financial Instruments	12 Months Ended
Disclosures about Fair Value of Financial Instruments	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Disclosures about Fair Value of Financial Instruments	10	Disclosures about Fair Value of Financial Instruments
	Cash. The carrying amount approximates fair value.
	Investment securities and short-term investments. See Note 2, “Investments,” for additional information.
	Premiums receivable and reinsurance recoverables on paid losses. The carrying value of current receivables approximates fair value. At December 31, 2014 and 2013, the carrying values of premiums receivable over 90 days were $12.4 million and $9.8 million, respectively. Included in “Reinsurance recoverables” in our Consolidated Balance Sheets at December 31, 2014 and 2013, are amounts that are due from trade capital providers associated with the operations of ArgoGlobal Syndicate 1200. Upon settlement, the receivable is offset against the liability also reflected in our accompanying Consolidated Balance Sheets. At December 31, 2014 and 2013, the payable was in excess of the receivable. Of our reinsurance recoverables on paid losses, excluding amounts attributable to ArgoGlobal Syndicate 1200’s trade capital providers, at December 31, 2014 and 2013, the carrying values over 90 days were $9.9 million and $22.2 million, respectively. Our methodology for establishing our allowances for doubtful accounts includes specifically identifying all potential uncollectible balances regardless of aging. At December 31, 2014 and 2013, the allowance for doubtful accounts for premiums receivable was $5.2 million and $4.5 million, respectively, and the allowance for doubtful accounts for reinsurance recoverables on paid losses was $1.8 million and $1.6 million, respectively. Premiums receivable over 90 days were secured by collateral in the amount of $0.3 million and $0.4 million at December 31, 2014 and 2013, respectively. Reinsurance recoverables on paid losses over 90 days were secured by collateral in the amount of $0.4 million and $0.3 at December 31, 2014 and 2013, respectively.
	At December 31, 2014 and 2013, the fair value of our Junior subordinated debentures, Senior unsecured fixed rate notes and Other indebtedness was estimated using appropriate market indices or quoted prices from external sources based on current market conditions.
	A summary of our financial instruments whose carrying value did not equal fair value is shown below:

			31-Dec-14				31-Dec-13
	(in millions)		Carrying		Fair		Carrying		Fair
	(in millions)		Amount		Value		Amount		Value
	Junior subordinated debentures		$	172.7	$	155.5	$	193.3	$	155.5
	Senior unsecured fixed rate notes			143.8		132.3		143.8		116.2
	Other indebtedness:
	Floating rate loan stock			61.3		55.2		65.5		52.7
	Note payable			0.7		0.6		0.8		0.6
			$	378.5	$	343.6	$	403.4	$	325

Shareholders_Equity

Shareholders' Equity	12 Months Ended
Shareholders' Equity	Dec. 31, 2014
Equity [Abstract]
Shareholders' Equity	11	Shareholders’ Equity
	On February 17, 2015, our Board of Directors declared a 10% stock dividend, payable on March 16, 2015, to shareholders of record at the close of business on March 2, 2015. For additional details regarding the aforementioned stock dividend, see Note 27, “Subsequent Event.” In addition, our Board of Directors declared a quarterly cash dividend in the amount of $0.20 on each share of common stock outstanding, on a post-stock dividend basis. The cash dividend will be paid on March 19, 2015 to shareholders of record at the close of business on March 2, 2015.
	On February 18, 2014, our Board of Directors declared a quarterly cash dividend in the amount of $0.15 on each share of common stock outstanding. On May 5, 2014, August 5, 2014 and November 4, 2014, our Board of Directors declared a quarterly cash dividend in the amount of $0.18 on each share of common stock outstanding. On March 17, 2014, June 16, 2014, September 15, 2014 and December 15, 2014, we paid $4.0 million, $4.7 million, $4.7 million and $4.8 million to our shareholders of record on March 3, 2014, June 2, 2014, September 1, 2014 and December 1, 2014, respectively. For the year ended December 31, 2014, we paid cash dividends totaling $18.2 million to our shareholders.
	On February 15, 2013, our Board of Directors declared a quarterly cash dividend in the amount of $0.15 on each shares of common stock outstanding or $0.14 on each share outstanding adjusted for the 10% stock dividend discussed below. On March 15, 2013, we paid $3.7 million to our shareholders of record on March 1, 2013.
	On May 7, 2013, our Board of Directors declared a 10% stock dividend, payable on June 17, 2013, to shareholders of record at the close of business on June 3, 2013. As a result of the stock dividend, 2,447,839 additional shares were issued. Cash was paid in lieu of fractional shares of our common shares. All references to share and per share amounts in this document and related disclosures have been adjusted to reflect the stock dividend for all periods presented.
	On May 7, 2013, August 6, 2013 and November 4, 2013, our Board of Directors declared a quarterly cash dividend in the amount of $0.15 on each share of common stock outstanding, on a post stock dividend basis. On March 15, 2013, June 20, 2013, September 16, 2013 and December 16, 2013, we paid $3.7 million, $4.1 million, $4.0 million and $4.0 million to our shareholders of record on March 1, 2013, June 3, 2013, September 2, 2013 and December 2, 2013, respectively. For the year ended December 31, 2013, we paid cash dividends totaling $15.8 million to our shareholders.
	On February 15, 2012, May 8, 2012, August 7, 2012 and November 6, 2012, our Board of Directors declared a quarterly cash dividend in the amount of $0.11 on each share of common stock outstanding. On March 15, 2012, June 15, 2012, September 18, 2012 and December 17, 2012, we paid $3.2 million, $3.1 million, $3.0 million and $3.0 million to our shareholders of record on March 1, 2012, June 1, 2012, September 4, 2012 and December 3, 2012, respectively. For the year ended December 31, 2012, we paid cash dividends totaling $12.3 million to our shareholders.
	We are authorized to issue 30 million shares of $1.00 par value preferred shares. As of December 31, 2014 and 2013, no preferred shares were issued and outstanding.
	On November 5, 2013, our Board of Directors authorized the repurchase of up to $150.0 million of our common shares (“2013 Repurchase Authorization”). The 2013 Repurchase Authorization supersedes all the previous Repurchase Authorizations. As of December 31, 2014, availability under the 2013 Repurchase Authorization for future repurchases of our common shares was $92.8 million.
	For the year ended December 31, 2014, we repurchased 301,758 common shares on the open market for $14.9 million. These shares are being held as treasury shares in accordance with the provisions of the Bermuda Companies Act 1981.
	In 2014, we repurchased shares under Securities Exchange Act of 1934 Rule 10b5-1 trading plans as follows:

	Date		2014		Number of		Average Price		Total Cost		Repurchase
	Trading Plan		Purchase		Shares		of Shares		(in millions)		Authorization
	Initiated		Period		Repurchased		Repurchased				Year
	12/17/13		02/04/14-02/12/14			15,789	$	43.28	$	0.7	2013
	3/18/14		03/18/14-04/28/14			436,867	$	45.81	$	20	2013
	6/13/14		06/17/14-07/04/14			41,362	$	49.94	$	2.1	2013
	9/12/14		09/16/14-10/28/14			229,633	$	51.98	$	11.9	2013
	12/15/14		12/16/14-12/23/14			22,735	$	53.44	$	1.2	2013

	At December 31, 2014, we had the following authorized, unissued common shares reserved for future issuance:

	Reserve Name		Shares Reserved
	2014 Long-Term Incentive Plan			4,130,532
	2007 Employee Share Purchase Plan			1,600,886
	Historical stock compensation plans			3,968
	Total			5,735,386

	Shares reserved under the historical plans represent all grants issued and outstanding under terminated plans as of December 31, 2014. (See Note 14, “Share-based Compensation” for further discussion.)

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Accumulated Other Comprehensive Income (Loss)	12	Accumulated Other Comprehensive Income (Loss)
	In February 2013, the FASB issued ASU 2013-02 that amends ASC 220, “Comprehensive Income.” See Note 1, “Business and Significant Accounting Policies” for additional information regarding the provisions of this update. Effective January 1, 2013, we adopted the update prospectively.
	A summary of changes in accumulated other comprehensive income (loss), net of taxes (where applicable) by component is presented below:

	(in millions)		Foreign Currency Translation Adjustments			Unrealized			Defined Benefit Pension Plans			Total
						Holding Gains
						on Securities
	Balance, January 1, 2013		$	(8.7	)	$	204.1		$	(5.9	)	$	189.5
	Other comprehensive (loss) income before			(2.8	)		0.2			1.3			(1.3	)
	reclassifications
	Amounts reclassified from accumulated other			—			(40.4	)		—			(40.4	)
	comprehensive income (loss)
	Net current-period other comprehensive (loss)			(2.8	)		(40.2	)		1.3			(41.7	)
	income
	Balance, December 31, 2013			(11.5	)		163.9			(4.6	)		147.8
	Other comprehensive loss before			(4.1	)		(12.5	)		(2.4	)		(19.0	)
	reclassifications
	Amounts reclassified from accumulated other			—			(20.7	)		—			(20.7	)
	comprehensive loss
	Net current-period other comprehensive loss			(4.1	)		(33.2	)		(2.4	)		(39.7	)
	Balance, December 31, 2014		$	(15.6	)	$	130.7		$	(7.0	)	$	108.1

	The amounts reclassified from accumulated other comprehensive income (loss) shown in the above table have been included in the following captions in our Consolidated Statements of Income:

			For the Years Ended December 31,
	(in millions)		2014			2013			2012
	Unrealized gains and losses on securities:
	Net realized investment gains		$	(30.6	)	$	(59.8	)	$	(14.4	)
	Provision for income taxes			9.9			19.4			4
	Net of taxes		$	(20.7	)	$	(40.4	)	$	(10.4	)

Net_Income_Per_Common_Share

Net Income Per Common Share	12 Months Ended
Net Income Per Common Share	Dec. 31, 2014
Earnings Per Share [Abstract]
Net Income Per Common Share	13	Net Income Per Common Share
	The following table presents the calculation of net income per common share on a basic and diluted basis:

			For the Years Ended December 31,
	(in millions, except number of shares and per share amounts)		2014		2013		2012
	Net income		$	183.2	$	143.2	$	52.3
	Weighted average common shares outstanding - basic			26,082,114		26,851,341		28,095,210
	Effect of dilutive securities:
	Equity compensation awards			475,037		1,018,192		555,238
	Weighted average common shares outstanding - diluted			26,557,151		27,869,533		28,650,448
	Net income per common share:
	Basic		$	7.02	$	5.33	$	1.86
	Diluted		$	6.9	$	5.14	$	1.83

	Excluded from the weighted average common shares outstanding calculation at December 31, 2014, 2013 and 2012 are 8,606,489 shares, 7,558,345 shares and 6,459,613 shares, respectively, which are held as treasury shares. The shares are excluded as of their repurchase date. In 2014, equity compensation awards to purchase 1,700 shares of common stock were excluded from the computation of diluted net income per common share as these instruments were anti-dilutive. These instruments expire at varying times from 2015 through 2021. In 2013, equity compensation awards to purchase 3,300 shares of common stock were excluded from the computation of diluted net income per common share as these instruments were anti-dilutive. These instruments expired or will expire at varying times from 2014 through 2020. In 2012, equity compensation awards to purchase 550,632 shares of common stock were excluded from the computation of diluted net income per common share as these instruments were anti-dilutive. These instruments expired or will expire at varying times from 2013 through 2019.
	On February 17, 2015, our Board of Directors declared a 10% stock dividend payable on March 16, 2015, to shareholders of record at the close of business on March 2, 2015. The share numbers and per share amounts shown in the table above have not been retroactively adjusted to give effect to the stock dividend. For additional details regarding the stock dividend, see Note 27, “Subsequent Event.”

Sharebased_Compensation

Share-based Compensation	12 Months Ended
Share-based Compensation	Dec. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-based Compensation	14	Share-based Compensation
	The fair value method of accounting is used for equity-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 volatility assumption is based on the historical change in our stock price over the previous five years preceding the measurement date. 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 award life is based upon the average holding period over the history of the incentive plan. The expected dividend yield is based on our history and expected dividend payouts.
	The following table summarizes the assumptions we used:

			For the Years Ended December 31,
			2014		2013		2012
	Risk-free rate of return		1.53% to 1.77%		0.80% to 1.71%		0.68% to 1.11%
	Expected dividend yields		1.49% to 1.55%		1.49% to 1.67%		1.58% to 1.67%
	Expected award life (years)		4.67 to 4.85		4.91 to 5.07		5.03 to 5.06
	Expected volatility		22.84% to 25.46%		26.30% to 32.07%		32.12% to 32.84%

	We estimate forfeitures based on historical forfeitures patterns, thereby recognizing expense only for those awards that are expected to vest. The estimate of forfeitures is adjusted as actual forfeitures differ from our estimate, resulting in recognition of compensation expense only for those awards that actually vest.
	The compensation expense recognized under all our share-based payment plans was $19.6 million ($16.2 million, net of tax), $23.0 million ($18.3 million, net of tax) and $10.3 million ($8.4 million, net of tax) for the years ended December 31, 2014, 2013 and 2012, respectively. The compensation expense is included in “Underwriting, acquisition and insurance expenses” in our Consolidated Statements of Income.
	We present all tax benefits resulting from the exercise of stock options and vesting of non-vested shares as cash flows from financing activities. Excess tax benefits are realized tax benefits from tax deductions for exercised options and vested shares in excess of the deferred tax asset attributable to stock compensation costs for such options. Such tax benefits and cash flows were immaterial for all reporting periods.
	Argo Group’s Long-Term Incentive Plans
	In November 2007, our shareholders approved the 2007 Long-Term Incentive Plan (the “2007 Plan”), which provides for an aggregate of 4.5 million shares of our common stock that may be issued to executives, non-employee directors, and other key employees. As of May 2014, 1,457,800 shares remained available for grant under the 2007 Plan. In May 2014, our shareholders approved the 2014 Long-Term Incentive Plan (the “2014 Plan”), which provides for an additional 2.8 million shares of our common stock to be available for issuance to executives, non-employee directors and other key employees. The share awards may be in the form of share options, SARs, restricted shares, restricted share awards, restricted share units awards, performance awards, other share-based awards and other cash-based awards. 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. Share options and SARs will count as one share for the purposes of the limits under the incentive plans; restricted shares, restricted share units, performance units, performance shares or other share-based incentive awards which settle in common shares will count as 2.75 shares for purpose of the limits under the 2014 Plan.
	Share options may be in the form of incentive share options, non-qualified share options and restorative options. Share options are required to have an exercise price that is not less than the market value on the date of grant. We are prohibited from repricing the options. The term of the share options cannot exceed seven years from the grant date.
	A summary of option activity as of December 31, 2014 and changes during the year then ended is as follows:

			Shares				Weighted-Average		Weighted-Average	Aggregate
							Exercise Price		Remaining	Intrinsic
									Contractual Term	Value
	Outstanding at January 1, 2014			158,092			$	34.27
	Granted			—			$	—
	Exercised			(108,184	)		$	34.38
	Expired or forfeited			(1,773	)		$	32.03
	Outstanding at December 31, 2014			48,135			$	34.11	0.3	$	1,028,247
	Vested and exercisable at end of year			48,135			$	34.11	0.3	$	1,028,247

	Options outstanding under this plan vested over a one to five year period, subject to continued employment. As of December 31, 2014, all options under this plan were fully vested. Cash received for the exercise of options under this plan was $3.7 million for the year ended December 31, 2014.
	The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying awards and the quoted price of our common stock for those options where the exercise price was below the quoted price at December 31, 2014.
	There were no options granted under this plan during the years ended December 31, 2014, 2013, and 2012.
	A summary of restricted share activity as of December 31, 2014 and changes during the year then ended is as follows:

			Shares				Weighted-Average
							Grant Date
							Fair Value
	Outstanding at January 1, 2014			257,975			$	32.97
	Granted			123,229			$	45.61
	Vested and issued			(60,198	)		$	31.65
	Expired or forfeited			(35,511	)		$	33.08
	Outstanding at December 31, 2014			285,495			$	38.69

	As of December 31, 2014, there was $6.8 million of total unrecognized compensation cost related to restricted share compensation arrangements granted by Argo Group. The weighted-average period over which this unrecognized expense is expected to be recognized is 1.7 years. The total fair value of shares vested during the year ended December 31, 2014 was $1.9 million.
	A summary of stock-settled SARs activity as of December 31, 2014 and changes during the year then ended is as follows:

			Shares				Weighted-Average
			Shares				Exercise Price
	Outstanding at January 1, 2014			1,288,698			$	29.46
	Granted			188,273			$	43.23
	Exercised			(124,541	)		$	28.93
	Expired or forfeited			(155,909	)		$	32.72
	Outstanding at December 31, 2014			1,196,521			$	31.26
	Vested or expected to vest as of end of year			1,102,211			$	30.81
	Exercisable at end of year			763,302			$	28.27

	The stock-settled SARs vest over a one to four year period. 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. For the year ended December 31, 2014, 124,541 stock-settled SARs were exercised resulting in 49,742 shares being issued. As of December 31, 2014, there was $2.6 million of total unrecognized compensation cost related to stock-settled SARs outstanding. The weighted-average period over which this unrecognized expense is expected to be recognized is 2.0 years. Aggregate intrinsic value of the stock-settled SARs at December 31, 2014 was $26.5 million.
	A summary of cash-settled SARs activity as of December 31, 2014 and changes during the year then ended is as follows:

			Shares				Weighted-Average
			Shares				Exercise Price
	Outstanding at January 1, 2014			1,743,758			$	33
	Granted			756,853			$	44.28
	Exercised			(446,209	)		$	30.96
Expired or forfeited			(230,633	)		$	36.15
Outstanding at December 31, 2014			1,823,769			$	37.78
Vested or expected to vest as of end of year			1,518,831			$	37.42
Exercisable at end of year			421,995			$	31.79

The cash-settled SARs vest over a one to four year period. 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. For the year ended December 31, 2014, 446,209 cash-settled SARs were exercised resulting in $9.3 million in cash payments. As of December 31, 2014, there was $10.1 million of total unrecognized compensation cost related to cash-settled SARs outstanding. The weighted-average period over which this unrecognized expense is expected to be recognized is 2.4 years. Aggregate intrinsic value of the cash-settled SARs at December 31, 2014 was $32.3 million. The liability for cash-settled SARs was $24.4 million and $19.4 million at December 31, 2014 and 2013, respectively.
Included in the total shares outstanding at December 31, 2014 are 30,050 restricted shares, 2,563,467 cash-settled SARs and 160,204 stock-settled SARs whose vesting is contingent on the employee meeting defined performance conditions. Employees have a specified time period in which to meet the performance condition (typically one year) and forfeit the grant (on a pro rata basis) if the performance conditions are not met in the specified time frame. We evaluate the likelihood of the employee completing the performance condition and include this estimate in the determination of the forfeiture factor for the grants.
We have granted to certain key employees restricted share units, which provide the employee with the economic equivalent of stock ownership. Each restricted share unit is valued at the closing price of our common stock on the national exchange on which it is listed as of the date credited, and fluctuates daily thereafter. The restricted share units outstanding under this plan vest over a 24 to 48 month period, subject to continued employment. Upon vesting, the employee receives a cash payment equivalent to the number of restricted share units vested valued at the closing market price of our common shares. Total expense recognized for the restricted share units totaled $0.5 million, $0.9 million, and $0.6 million for the years ended December 31, 2014, 2013, and 2012, respectively. Cash payments paid for vested awards under this plan totaled $0.4 million and $1.2 million for the years ended December 31, 2014 and 2013, respectively.
Employees Share Purchase Plans
We have established an employee stock purchase plan for eligible employees (Argo Group’s 2007 Employee Share Purchase Plan). Under this plan, our common stock may be purchased over an offering period of three months at 85% of the lower of the market value on the first day of the offering period or on the designated purchase date at the end of the offering period. We have also established a Save As You Earn Plan for our United Kingdom employees (Argo Group’s Save As You Earn Plan). Under this plan, our common stock may be purchased over an offering period of three or five years at 85% of the market value of the common shares on the first day of the offering period. Expense recognized under these plans for the years ended December 31, 2014, 2013, and 2012 was $0.3 million, $0.3 million and $0.2 million, respectively.
Argo Group International Holdings, Ltd. Deferred Compensation Plan for Non-Employee Directors
Until December 16, 2013, the non-employee members of our Board of Directors were entitled to participate in the Argo Group International Holdings, Ltd. Deferred Compensation Plan for Non-Employee Directors (“Directors Plan”), a non-funded and non-qualified deferred compensation plan. Under the Directors Plan, non-employee directors could elect each year to defer payment of 0%, 50% or 100% of their cash compensation payable during the next calendar year. While no further deferrals were permitted under the Directors Plan from and after December 16, 2013, and certain amounts thereunder were paid out prior to the end of 2013, additional deferred amounts remain subject to the terms of the Directors Plan and will be paid out in accordance with the terms of the Directors Plan. Deferred amounts are credited with interest earned at a rate two percent above the prime commercial lending rate, to be reset each May 1. In addition, the Directors Plan calls for us to grant a match equal to 75% of the cash compensation amounts deferred in the form of “Stock Units,” which provide directors with the economic equivalent of stock ownership and were credited as a bookkeeping entry to each director’s “Stock Unit Account.” Each Stock Unit is valued at the closing price of our common stock on the national exchange on which it is listed as of the date credited for all purposes under the Directors Plan and fluctuates daily thereafter on that same basis. The Directors Plan provided for a Stock Unit Account to be established for each non-employee director upon their election to the Board and credits their account with an initial bookkeeping entry for 1,650 Stock Units. In conjunction with the termination of the Directors Plan, all cash balances and related interest for the years 2010 through 2013 were settled resulting in $1.9 million in cash payments for the year ended December 31, 2013. Remaining distributions from the Directors Plan will occur six months after the non-employee director ceases to be a member of the Board, the date on which a change in control (as defined in the Directors Plan) occurs or December 1, 2017, whichever comes first, and will be made in cash. The non-employee directors are responsible for all tax requirements on the deferred compensation and any related earnings. Under the Directors Plan, we recorded compensation expense of $0.7 million, $2.0 million and $1.2 million for the years ended December 31, 2014, 2013, and 2012, respectively. The liability for remaining distributions under the Directors Plan was $4.2 million and $3.5 million at December 31, 2014 and 2013, respectively.

Underwriting_Acquisition_and_I

Underwriting, Acquisition and Insurance Expenses	12 Months Ended
Underwriting, Acquisition and Insurance Expenses	Dec. 31, 2014
Text Block [Abstract]
Underwriting, Acquisition and Insurance Expenses	15	Underwriting, Acquisition and Insurance Expenses
	Underwriting, acquisition and insurance expenses were as follows:

			For the Years Ended December 31,
	(in millions)		2014			2013			2012
	Commissions		$	231.1		$	229.6		$	198.2
	General expenses			288			272.8			248
	Premium taxes, boards and bureaus			25.5			24.2			22.8
				544.6			526.6			469
	Net deferral of policy acquisition costs			(5.4	)		(15.8	)		(4.5	)
	Total underwriting, acquisition and insurance expenses		$	539.2		$	510.8		$	464.5

	Included in general expenses for the years ended December 31, 2014, 2013 and 2012 is $19.6 million, $23.0 million and $10.3 million, respectively, of expense for our total equity compensation.

Income_Taxes

Income Taxes	12 Months Ended
Income Taxes	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	16	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. Six 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. Corporate income tax losses incurred in the United Kingdom can be carried forward, for application against future income, indefinitely. 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 file a consolidated United States federal income tax return.
	We also have operations in Belgium, Switzerland, Brazil, France, Malta, Spain and Ireland, which also are subject to income taxes imposed by the jurisdiction in which they operate. We have operations in the United Arab Emirates, which are not subject to income tax under the laws of that country.
	Our income tax provision includes the following components:

			For the Years Ended December 31,
	(in millions)		2014				2013			2012
	Current tax provision		$	5.2			$	32.7		$	9.4
	Deferred tax provision related to:
	Future tax deductions			58.4				0.1			2.9
	Valuation allowance change			(30.8	)			3.7			2.1
	Income tax provision		$	32.8			$	36.5		$	14.4

	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 years ended December 31, 2014, 2013 and 2012, pre-tax income (loss) attributable to our operations and the operations’ effective tax rates were as follows:

	(in millions)		2014							2013							2012
			Pre-Tax				Effective			Pre-Tax				Effective			Pre-Tax				Effective
			Income (Loss)				Tax			Income (Loss)				Tax			Income (Loss)				Tax
							Rate							Rate							Rate
	Bermuda		$	102.8				0	%	$	50.5				0	%	$	10				0	%
	United States			98				28.1	%		120.9				28.2	%		52				21.3	%
	United Kingdom			21.5				24.8	%		18.5				12	%		14				24.4	%
	Belgium			—		-1		63.8	%		0.2				103	%		(0.1	)			98.4	%
	Brazil			(2.2	)			0	%		(9.7	)			0	%		(6.5	)			0	%
	United Arab Emirates			(0.9	)			0	%		1.1				0	%		—		-1		0	%
	Ireland			(1.1	)			0	%		(0.1	)			0	%		(0.2	)			0	%
	Malta			(2.2	)			0	%		(1.7	)			0	%		(2.6	)			0	%
	France			—				0	%		—				0	%		—				0	%
	Switzerland			0.1				17.6	%		—		-1		5.6	%		0.1				22.8	%
	Pre-tax income		$	216						$	179.7						$	66.7

	(1)	Pre-tax income for the respective year was less than $0.1 million.
	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 Years Ended December 31,
	(in millions)		2014				2013			2012
	Income tax provision at expected rate		$	37.2			$	43.1		$	18.5
	Tax effect of:
	Tax-exempt interest			(4.5	)			(5.6	)		(5.6	)
	Dividends received deduction			(2.3	)			(2.3	)		(2.2	)
	Valuation allowance change			(30.8	)			3.7			2.1
	Other permanent adjustments, net			(0.7	)			0.3			1.8
	Adjustment for prior year tax return			(0.9	)			(1.6	)		0.2
	Prior period adjustment for deferred			1.5				—			—
	United States state tax expense (benefit)			2.5				0.3			(0.3	)
	PXRE Reinsurance capital loss carryforward			29.8				—			—
	Other foreign adjustments			0.7				(0.1	)		—
	Prior year foreign taxes			0.1				1.1			—
	Deferred tax rate reduction			(0.4	)			(1.2	)		(0.6	)
	Foreign exchange adjustments			0.2				(1.7	)		0.5
	Foreign withholding taxes			0.4				0.5			—
	Income tax provision		$	32.8			$	36.5		$	14.4
	Income tax provision - Foreign		$	5.2			$	2.4		$	3.3
	Income tax provision - United States, Federal			23.3				33.2			11.5
	Income tax provision (benefit) - United States, state			3.9				0.4			(0.4	)
	Foreign withholding tax - United States			0.4				0.5			—
	Income tax provision		$	32.8			$	36.5		$	14.4

	The consolidated provision for income taxes for the year ended December 31, 2014 was affected by a $1.3 million decrease for additional taxes reported on the prior year tax return, a $0.4 million reduction for change in the United Kingdom deferred tax rate and a $1.0 million increase for the foreign exchange adjustment on the translation from Sterling to the U.S. Dollar within the Syndicate 1200 segment. Additionally, a $29.8 million increase is recognized due to the expiration of the PXRE Reinsurance Company capital loss carryforward benefit, which was offset by the related Valuation Allowance.
	The consolidated provision for income taxes for the year ended December 31, 2013 was affected by a $1.6 million decrease for additional taxes reported on the prior year tax return, a $1.2 million reduction for change in the United Kingdom deferred tax rate and a $1.7 million decrease for the foreign exchange adjustment on the translation from Sterling to the U.S. Dollar within the Syndicate 1200 segment.
	The consolidated provision for income taxes for the year ended December 31, 2012 was affected by a $0.2 million increase for additional taxes reported on the prior year tax return, $0.6 million reduction for the change in the United Kingdom deferred tax rate and $0.5 million increase for the foreign exchange adjustment on the translation from Sterling to the U.S. Dollar within the Syndicate 1200 segment.
We recognize potential accrued interest and penalties within our global operations in “Interest expense” and “Underwriting, acquisition and insurance expenses,” respectively, in our Consolidated Statements of Income.
Deferred taxes arise from temporary differences in the recognition of revenues and expenses for tax and financial reporting purposes. The net deferred tax liability as of December 31, 2014 and 2013 resulted from the tax-effected temporary differences shown in the following table. Due primarily to changes in unrealized gains on available-for-sale investment securities, the net deferred tax liability increased by $24.3 million and decreased $15.1 million for the years ended December 31, 2014 and 2013, respectively.

		December 31,
(in millions)		2014				2013
Deferred tax assets:
Unrealized losses on fixed maturities and other investment securities		$	—			$	—
Losses and loss adjustment expense reserve discounting			25.1				28.4
Unearned premiums			24.8				23
Capital loss carryforward			—				29.8
Allowance for bad debt			2				1.9
Accrual for contingent commissions			0.3				0.4
Net operating loss carryforward			18.8				19.8
Impairment of investment values			8.2				10.6
United States amortization of intangible assets			4.3				3.1
Accrued bonus			6.7				5.7
Accrued vacation			1.7				1.6
Stock option expense			8				6.4
United Kingdom interest			—				0.8
Brazil operating losses			7.4				8
Malta operating losses			2.1				1.7
Depreciable fixed asset			5.2				—
Other			7				9.1
Deferred tax assets, gross			121.6				150.3
Deferred tax liabilities:
Unrealized gains on equity securities			(62.3	)			(65.1	)
Unrealized gains on fixed maturities and other investment securities			(15.3	)			(16.1	)
Deferred acquisition costs			(20.3	)			(19.5	)
United States amortization of intangible assets			(3.5	)			(3.3	)
United Kingdom underwriting losses			(9.0	)			(4.8	)
United Kingdom amortization of intangible assets			(2.3	)			(2.8	)
Brussels pension			(0.1	)			(0.2	)
Internally developed software			(21.5	)			—
Unrealized FV gain on LP			(10.5	)			(9.2	)
Other			(4.4	)			(1.8	)
Deferred tax liabilities, gross			(149.2	)			(122.8	)
Deferred tax assets, net before valuation allowance			(27.6	)			27.5
Valuation allowance			(25.4	)			(56.2	)
Deferred tax liabilities, net		$	(53.0	)		$	(28.7	)
Net deferred tax liabilities - Foreign		$	(11.8	)		$	(7.0	)
Net deferred tax liabilities - United States			(41.2	)			(21.7	)
Deferred tax liabilities, net		$	(53.0	)		$	(28.7	)

Our net deferred tax assets (liabilities) are supported by taxes paid in previous periods, reversal of taxable temporary differences and recognition of future 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 sufficient taxable income in the future to recover tax benefits that cannot be recovered from taxes paid in the carryback period, which is generally two years for net operating losses and three years for capital losses for our United States operations. At December 31, 2014, we had a total net deferred tax liability of $27.6 million prior to any valuation allowance. Management has concluded that a valuation allowance is required for a portion of the tax effected net capital loss carryforward of $18.0 million generated from PXRE Corporation and for the tax effected net operating loss carryforward of $1.0 million from ARIS. The capital loss carryforward generated from the sale of PXRE Reinsurance Company expired on December 31, 2013. Of the PXRE Corporation loss carryforwards, $16.5 million will expire if not used by December 31, 2025 and $1.5 million will expire if not used by December 31, 2027. Of the ARIS loss carryforward, $0.2 million will expire if not used by December 31, 2027, $0.4 million will expire if not used by December 31, 2028 and $0.4 million will expire if not used by December 31, 2029. The valuation allowances have been established as Internal Revenue Code Section 382 limits the application of net operating loss and net capital loss carryforwards following an ownership change. The loss carryforwards available per year are $2.8 million as required by Internal Revenue Code Section 382. Further, due to cumulative losses since inception, management has concluded that a valuation allowance is required for the full amount of the tax effected net operating losses generated by our Brazil and Malta entities. Accordingly, a valuation allowance of $25.4 million is required as of December 31, 2014 of which $15.9 million relates to the PXRE Corporation and ARIS loss carryforwards, $7.4 million relates to Brazil operations, and $2.1 million relates to Malta operations. During the year ended December 31, 2014, the valuation allowance was reduced by $29.8 million pertaining to the expiration of the PXRE Reinsurance Company capital loss carryforward, reduced by $0.8 million pertaining to PXRE Corporation and ARIS loss carryforwards, decreased by $0.6 million pertaining to our Brazil operations and increased by $0.4 million pertaining to our Malta operations.
We had no material unrecognized tax benefits as of December 31, 2014, 2013 and 2012. Our United States subsidiaries are no longer subject to U.S. federal and state income tax examinations by tax authorities for years before 2011. Our United Kingdom subsidiaries are no longer subject to United Kingdom income tax examinations by Her Majesty’s Revenue and Customs for years before 2012.

Pension_Benefits

Pension Benefits	12 Months Ended
Pension Benefits	Dec. 31, 2014
Compensation And Retirement Disclosure [Abstract]
Pension Benefits	17	Pension Benefits
	Argo Group US sponsors a qualified defined benefit plan and non-qualified unfunded supplemental defined benefit plans, all of which were curtailed effective February 2004. The following tables set forth the change in plan assets and the change in projected benefit obligation, as of December 31 with respect to these plans. The assets and liabilities of the plans were measured as of December 31 of the respective years presented.

	(in millions)		2014				2013
	Change in plan assets
	Fair value of plan assets at beginning of year		$	20.2			$	20.1
	Actual return on plan assets			1				1.9
	Employer contributions			0.2				0.2
	Settlements and benefits paid			(2.2	)			(2.0	)
	Fair value of plan assets at end of year		$	19.2			$	20.2

	(in millions)		2014				2013
	Change in projected benefit obligation
	Projected benefit obligation at beginning of year		$	22.6			$	24.6
	Interest cost			1				0.8
	Actuarial loss (gain)			4.3				(0.8	)
	Settlements and benefits paid			(2.1	)			(2.0	)
	Projected benefit obligation at end of year		$	25.8			$	22.6

	As of December 31, 2014 and 2013, the qualified pension plan was underfunded by $4.4 million and $0.3 million, respectively. The non-qualified pension plans were unfunded by $2.2 million at both December 31, 2014 and 2013. Underfunded and unfunded amounts are included in “Other liabilities” in our Consolidated Balance Sheets.
	Assumptions used to determine benefit obligations at December 31 were as follows:

			2014				2013
	Weighted average discount rate			3.37%				4.42%
	Expected rate of increase in future compensation levels		n/a				n/a

	Assumptions used to determine net periodic benefit cost follows:

			For the Years Ended December 31,
			2014				2013				2012
	Weighted average discount rate			4.39%				3.63%				4.50%
	Expected return on plan assets			6.00%				6.00%				6.00%
	Expected rate of increase in future compensation levels		n/a				n/a				n/a

	In 2014, 2013, and 2012, the expected return on plan assets was ascertained using multiple factors that include market conditions, duration of the fixed maturity portion of the portfolio and long-term return forecasts provided by several asset management companies.
	Components of net periodic benefit cost follows:

			For the Years Ended December 31,
	(in millions)		2014				2013				2012
	Interest cost		$	1			$	0.8			$	1
	Expected return on plan assets			(1.2	)			(1.0	)			(1.1	)
	Settlement charge			0.4				—				—
	Amortization of actuarial loss			0.3				0.3				0.3
	Net periodic benefit cost		$	0.5			$	0.1			$	0.2

	We estimate that $0.4 million of unrecognized actuarial loss will be amortized from accumulated other comprehensive gain into net periodic benefit cost during 2015.
	The projected benefit obligation for the non-qualified unfunded supplemental defined benefit plans, with accumulated benefit obligations in excess of plan assets, was $2.2 million at both December 31, 2014 and 2013. The fair value of plan assets for these plans was zero for these same periods. The accumulated benefit obligation for all defined benefit plans is equal to the projected benefit obligation for each of the years presented.
	Our investment policy for the qualified plan requires the investments be prudently selected and properly diversified so as to minimize the risk of large losses in accordance with applicable laws including the Employee Retirement Income Security Act of 1974. The overall investment strategy is to achieve a balance of long-term growth of capital and current income, taking into account the need for liquidity to pay benefits as they come due. Periodic shifts in the asset allocation may be made based on the assessment of current and prospective market conditions.
	The investment policy for the qualified plan contains asset allocation guidelines with target allocations that remain effective until such time as the investment policy is revised. At December 31, 2014, the target allocations were 65% fixed maturity investments, highly liquid fixed maturity investments, and cash; and 35% equity investments. The target asset allocation percentages were selected based on risk diversification needs, expected distribution patterns and asset manager recommendations. The actual asset allocation as of December 31, 2014 was 67.4% fixed maturity investments, highly liquid fixed maturity investments and cash; and 32.6% equity investments, of which 25.1% and 7.5% were allocated between U.S. and international equities, respectively. These allocations were in compliance with the investment policy that allows the investment manager based on its judgment and market conditions to deviate from the target allocations.
	Following is a description of the valuation techniques used to measure the plan’s assets at fair value.
	Mutual funds: Fair value is determined using observable, market-based inputs on the valuation date.
	Short-term investment fund: Fair value is determined based on the net asset values provided by the plan trustee.
	The methods described above may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. Furthermore, while it is believed the valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different fair value measurement at the reporting date.
	The fair values of the plan assets by asset category are as follows:

	(in millions)						Fair Value Measurements
	(in millions)						at Reporting Date Using
			31-Dec-14				Level 1 (a)				Level 2 (b)				Level 3 (c)
	Equity Securities:
	Mutual Funds:
	Large cap U.S. equity		$	2.9			$	2.9			$	—			$	—
	Small-mid cap U.S. equity			1.2				1.2				—				—
	International equity			1.5				1.5				—				—
	Real estate			0.6				0.6				—				—
U.S. and global government and corporate fixed maturity			12.6				12.6				—				—
Cash and short-term investments:
Short-term investment fund (1)			0.4				—				0.4				—
Total		$	19.2			$	18.8			$	0.4			$	—

(a)	Quoted prices in active markets for identical assets
(b)	Significant other observable inputs
(c)	Significant unobservable inputs
(1)	Assets invested in one common collective trust composed of high-grade money market money instruments with short maturities.

(in millions)						Fair Value Measurements
(in millions)						at Reporting Date Using
		December 31, 2013				Level 1 (a)				Level 2 (b)				Level 3 (c)
Equity Securities:
Mutual Funds:
Large cap U.S. equity		$	3.2			$	3.2			$	—			$	—
Small-mid cap U.S. equity			1.4				1.4				—				—
International equity			1.5				1.5				—				—
Real estate			0.5				0.5				—				—
Convertible bonds and equities			0.2				0.2				—				—
U.S. and global government and corporate fixed maturity			12.9				12.9				—				—
Cash and short-term investments:
Short-term investment fund (1)			0.5				—				0.5				—
Total		$	20.2			$	19.7			$	0.5			$	—

(a)	Quoted prices in active markets for identical assets
(b)	Significant other observable inputs
(c)	Significant unobservable inputs
(1)	Assets invested in one common collective trust composed of high-grade money market money instruments with short maturities.
Based on the current funding status of the pension plan, effects of the curtailment and expected changes in pension plan asset values and pension obligations, we do not believe any significant funding of the pension plan will be required during the year ending December 31, 2015.
We expect to make the following benefit payments:

(in millions)		Pension
(in millions)		Benefits
2015		$	1.7
2016			1.6
2017			1.9
2018			1.7
2019			1.8
Years 2020 to 2024			7.9
Total		$	16.6

Substantially all of our employees are either eligible or mandated by applicable laws to participate in employee savings plans. Under these plans, a percentage of the employee’s pay may be or is mandated based on applicable laws to be contributed to various savings alternatives. The plans also call for our contributions under several formulae. Charges to income related to our contributions were $7.1 million, $6.8 million and $6.3 million in 2014, 2013 and 2012, respectively.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	18	Commitments and Contingencies
	Argo Group’s subsidiaries are parties to legal actions incidental to their business. Based on the opinion of 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 $72.9 million related to our limited partnership investments at December 31, 2014. These commitments will be funded as required by the partnership agreements.

Leases

Leases	12 Months Ended
Leases	Dec. 31, 2014
Leases [Abstract]
Leases	19	Leases
	We lease office space and equipment under lease agreements that expire at various intervals and are subject to renewal options at market rates prevailing at the time of renewal. At December 31, 2014, the future minimum payments under non-cancelable operating leases are as follows:

	(in millions)		Amount Due
	2015		$	11.2
	2016			9.1
	2017			8.1
	2018			7.8
	2019			6.1
	Thereafter			9.4
	Total		$	51.7

	We incurred lease expense of $51.7 million, $57.6 million and $55.3 million for the years ended December 31, 2014, 2013 and 2012, respectively.

Segment_Information

Segment Information	12 Months Ended
Segment Information	Dec. 31, 2014
Segment Reporting [Abstract]
Segment Information	20	Segment Information
	We are primarily engaged in underwriting property and casualty insurance and reinsurance. We have four ongoing reporting segments: Excess and Surplus Lines, Commercial Specialty, International Specialty and Syndicate 1200. 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.
	In evaluating the operating performance of our segments, we focus on core underwriting and investing results before the consideration of realized gains or losses from the sales of investments. Realized investment gains are reported as a component of the Corporate and Other segment, as decisions regarding the acquisition and disposal of securities reside with the investment function and are not under the control of the individual business segments. Identifiable assets by segment are those assets used in the operation of each segment.
	Revenue and income (loss) before income taxes for each segment were as follows:

			For the Years Ended December 31,
	(in millions)		2014				2013				2012
	Revenue:
	Earned premiums
	Excess and Surplus Lines		$	485.2			$	460.2			$	399.3
	Commercial Specialty			291.9				299				317.5
	International Specialty			148.3				142.4				130.1
	Syndicate 1200			411.1				401.7				337.9
	Run-off Lines			1.6				0.5				1.7
	Total earned premiums			1,338.10				1,303.80				1,186.50
	Net investment income
	Excess and Surplus Lines			36.7				42.2				51.1
	Commercial Specialty			18.7				22.8				27.6
	International Specialty			8.2				8.4				12.3
	Syndicate 1200			10.2				11				15.3
	Run-off Lines			9.7				10.8				12.5
	Corporate and Other			3.1				4.8				-
	Total net investment income			86.6				100				118.8
	Net realized investment and other gains			94				71.3				25.7
	Total revenue		$	1,518.70			$	1,475.10			$	1,331.00

			For the Years Ended December 31,
	(in millions)		2014				2013				2012
	Income (loss) before income taxes
	Excess and Surplus Lines		$	106			$	89.4			$	74.1
	Commercial Specialty			8.9				21.4				(24.8	)
	International Specialty			21.1				11.3				11.3
	Syndicate 1200			44.1				37.3				28.1
	Run-off Lines			(23.0	)			(10.6	)			(0.9	)
	Total segment income before taxes			157.1				148.8				87.8
	Corporate and Other			(35.1	)			(40.4	)			(46.8	)
	Net realized investment and other gains			94				71.3				25.7
	Total income before income taxes		$	216			$	179.7			$	66.7

	The table below presents earned premiums by geographic location. For this disclosure, we determine geographic location by the country of domicile of our subsidiaries that underwrite the business and not by the location of insureds or reinsureds from whom the business was generated.

			For the Years Ended December 31,
	(in millions)		2014				2013				2012
	Bermuda		$	101.5			$	101.7			$	120.4
	Brazil			44.3				38.7				26.6
	Malta			2.1				1.8				0.3
	United Kingdom			411.7				401.7				320.8
	United States			778.5				759.9				718.4
	Total earned premiums		$	1,338.10			$	1,303.80			$	1,186.50

	The following table represents identifiable assets:

			December 31,
	(in millions)		2014				2013
	Excess and Surplus Lines		$	2,350.70			$	2,252.20
	Commercial Specialty			1,358.50				1,333.40
	International Specialty			776.8				743.6
	Syndicate 1200			1,258.50				1,638.80
	Run-off Lines			552.8				555.9
	Corporate and Other			59				67.1
	Total		$	6,356.30			$	6,591.00

	Included in total assets at December 31, 2014 and 2013 are $315.4 million and $386.8 million, respectively, in assets associated with trade capital providers.
The following table represents goodwill and intangible assets, net of accumulated amortization as of December 31:

		Goodwill								Intangible Assets, Net of
		Goodwill								Accumulated Amortization
(in millions)		2014				2013				2014				2013
Excess and Surplus Lines		$	76.4			$	76.4			$	2.8			$	3.4
Commercial Specialty			47.1				48.7				5.5				9
Syndicate 1200			28.7				28.7				70.3				73.6
Total		$	152.2			$	153.8			$	78.6			$	86

Runoff_Lines

Run-off Lines	12 Months Ended
Run-off Lines	Dec. 31, 2014
Discontinued Operations And Disposal Groups [Abstract]
Run-off Lines	21	Run-off Lines
	We have discontinued active underwriting of certain lines of business, including those lines that were previously recorded in Argonaut Group’s Risk Management segment. All current activity within these lines is related to the management of claims and other administrative functions. Also included in Run-off Lines are other liability reserves, which include exposure to claims for asbestos and environmental liabilities written in past years. The other liability reserves are often characterized by long elapsed periods between the occurrence of a claim and ultimate payment to resolve the claim. We use a specialized staff dedicated to administer and settle these claims.
	The following table presents our gross reserves for Run-off Lines as of December 31:

			December 31,
	(in millions)		2014			2013
	Asbestos and Environmental:
	Reinsurance assumed		$	40.1		$	45.2
	Other			13.8			12.3
	Total Asbestos and Environmental			53.9			57.5
	Risk management			257.1			264.3
	Run-off reinsurance lines			4.1			5.8
	Other run-off lines			3.4			4.9
	Total Run-off Lines		$	318.5		$	332.5

	We have received asbestos and environmental liability claims arising from other liability coverage primarily written in the 1960s, 1970s and into the mid-1980s. Asbestos and environmental claims originate from policies directly underwritten by us and from reinsurance assumed during this period, including a portion assumed from the London market. The following table represents the total gross reserves for our asbestos exposure:

			December 31,
	(in millions)		2014			2013			2012
	Direct written
	Case reserves		$	2.5		$	1.7		$	2
	Unallocated loss adjustment expense ("ULAE")			1			1.3			1.7
	Incurred but not reported ("IBNR")			7.6			6.4			4.3
	Total direct written reserves			11.1			9.4			8
	Assumed domestic
	Case reserves			13.2			15.7			18.4
	ULAE			1.6			2.2			2.7
	IBNR			15.8			15.8			17.4
	Total assumed domestic reserves			30.6			33.7			38.5
	Assumed London
	Case reserves			4.7			5.8			5.9
	ULAE			0.2			0.4			0.6
	IBNR			1.2			1.4			2.5
	Total assumed London reserves			6.1			7.6			9
	Total asbestos reserves		$	47.8		$	50.7		$	55.5

	The following table presents our net underwriting results for Run-off Lines:

			For the Years Ended December 31,
	(in millions)		2014			2013			2012
	Asbestos and Environmental:
	Reinsurance assumed		$	(8.3	)	$	(3.8	)	$	(3.6	)
	Other			(5.0	)		(7.2	)		(5.5	)
	Total Asbestos and Environmental			(13.3	)		(11.0	)		(9.1	)
	Risk management			(15.5	)		(5.9	)		0.9
	Run-off reinsurance lines			(1.5	)		(1.9	)		(1.1	)
	Other run-off lines			(0.7	)		(0.8	)		(1.6	)
	Total Run-off Lines		$	(31.0	)	$	(19.6	)	$	(10.9	)

	Reserves for asbestos and environmental claims cannot be estimated with traditional loss reserving techniques that rely on historical accident year loss development factors. The uncertainty in the asbestos and environmental reserves estimates arises from several factors including lack of historical data, inapplicability of standard actuarial projection techniques, uncertainty with regards to claim costs, coverage interpretations and judicial, statutory and regulatory provisions under which the claims may be ultimately resolved. It is impossible to predict how the courts will interpret coverage issues and these resolutions may have a material impact on the ultimate resolution of the asbestos and environmental liabilities. We use a variety of estimation methods to calculate reserves as a whole; however, reserves for asbestos and environmental claims were determined primarily based on the report year method with some weight applied to other methods. The report year method relies most heavily on our historical claims and severity information. Other methods rely more heavily on industry information. Although management has recorded its best estimate of loss reserves, due to the uncertainties of estimation of liabilities that may arise as discussed herein, further deterioration of claims could occur in the future.
	Please see Note 6, “Reserves for Losses and Loss Adjustment Expenses” for further discussion.

Statutory_Accounting_Principle

Statutory Accounting Principles	12 Months Ended
Statutory Accounting Principles	Dec. 31, 2014
Statutory Accounting Principles [Abstract]
Statutory Accounting Principles	22	Statutory Accounting Principles
	Financial Information
	The statutory capital and surplus for our principal operating subsidiaries was as follows:

	Statutory capital and surplus (1)		December 31,
	(in millions)		2014		2013
	Bermuda		$	1,278.30	$	1,218.20
	United Kingdom (2)			224.5		225.8
	United States			790.4		822.3

	(1)	Such amounts include ownership interests in affiliate insurance and reinsurance subsidiaries.
	(2)	Capital on deposit with Lloyd’s in U.S. Dollars
	The statutory net income (loss) for our principal operating subsidiaries was as follows:

	Statutory net income (loss) (1)		For the Years Ended December 31,
	(in millions)		2014		2013		2012
	Bermuda		$	145.7	$	124.2	$	(4.2	)
	United Kingdom (2)			28.7		42.3		40.7
	United States			117.7		117.4		42.9

	(1)	Such amounts include ownership interests in affiliate insurance and reinsurance subsidiaries.
	(2)	In U.S. Dollars
	Dividends
	As an insurance and reinsurance holding company, we are largely dependent on dividends and other permitted payments from our insurance and reinsurance subsidiaries to pay cash dividends to our shareholders, for debt service and for our operating expenses. The ability of our insurance and reinsurance subsidiaries to pay dividends to us is subject to certain restrictions imposed by the jurisdictions of domicile that regulate our insurance and reinsurance subsidiaries and each jurisdiction has calculations for the amount of dividends that an insurance and reinsurance company can pay without the approval of the insurance regulator.
	The payment of dividends to our shareholders is governed by the Bermuda Companies Act of 1981, as amended, which permits the payment of dividends so long as (i) we are not, or would not be after the payment, unable to pay our liabilities as they become due or (ii) the realizable value of our assets is in excess of our liabilities after taking such payment into account. In light of these restrictions, we have no additional material restrictions on dividend payments that may be made to our shareholders at December 31, 2014.
	Argo Re is the direct subsidiary of Argo Group, and therefore, has direct dividend paying capabilities to the parent. As of December 31, 2014, Argo Re’s solvency and liquidity margins and statutory capital and surplus were in excess of the minimum levels required by the Insurance Act. As of December 31, 2014 and 2013, the minimum statutory capital and surplus required to be maintained by Argo Re was $340.9 million and $348.8 million, respectively.
	Argo Re is generally prohibited from declaring or paying, in any financial year, dividends of more than 25% of its total statutory capital and surplus (as shown on its previous financial year’s statutory balance sheet) unless it files (at least seven days before payment of such dividends) with the Bermuda Monetary Authority (“BMA”) an affidavit signed by at least two directors (one of whom must be a Bermuda resident director if any of the insurer’s directors are resident in Bermuda) and the principal representative stating that it will continue to meet its solvency margin and minimum liquidity ratio. Argo Re may not reduce its total statutory capital by 15% or more, as set out in its previous year’s financial statements, unless it has received the prior approval of the BMA. Based on these regulatory restrictions, the maximum amount available for payment of dividends to Argo Group by Argo Re during 2015 without prior regulatory approval is $319.6 million.
	In 2014 and 2013, Argo Re paid cash dividends of $40.9 million and $84.5 million, respectively, to Argo Group which were used to repay intercompany notes in 2014 and intercompany notes and receivables in 2013. Argo Re did not pay dividends to Argo Group in 2012.
	Our U.S. insurance subsidiaries file financial statements prepared in accordance with statutory accounting principles prescribed or permitted by insurance regulatory authorities of the state in which they are domiciled. The differences between statutory-based financial statements and financial statements prepared in accordance with GAAP vary between jurisdictions. The principal differences are that for statutory-based financial statements, deferred policy acquisition costs are not recognized, a portion of the deferred federal income tax asset is non-admitted, bonds are generally carried at amortized cost, certain assets are non-admitted and charged directly to surplus, a collectability allowance related to reinsurance recoverables are charged directly to surplus and outstanding losses and unearned premium are presented net of reinsurance.
	As an intermediate insurance holding company, Argo Group US is largely dependent on dividends and other permitted payments from its insurance subsidiaries to service its debt, fund operating expenses and pay dividends to Argo Ireland. Various state insurance laws restrict the amount that may be transferred to Argo Group US from its subsidiaries in the form of dividends without prior approval of regulatory authorities. In addition, that portion of the insurance subsidiaries’ net equity that results from the difference between statutory insurance principles and GAAP would not be available for dividends.
	In December 2014, Argo Group US received an extraordinary dividend in the amount of $20.0 million in cash from Rockwood. In December 2014, Argo Group US received an ordinary dividend of $48.8 million, in the form of $0.1 million in cash and $48.7 million in securities, from Argonaut Insurance Company. In December 2014, Argo Group US received an extraordinary dividend of $55.2 million, in the form of $0.2 million in cash and $55.0 million in securities, from Colony Insurance Company (“Colony”).
	In December 2013, Argo Group US received an ordinary dividend in the amount of $9.5 million in cash from Rockwood, an ordinary dividend in the amount of $24.8 million, in the form of $0.1 million in cash and $24.7 million in the form of securities, from Argonaut Insurance Company, and an extraordinary dividend of $76.2 million, in the form of $0.3 million in cash and $75.9 million in the form of securities, from Colony.
	In September 2012, Argo Group US received an ordinary dividend in the amount of $10.0 million in cash from Rockwood and an ordinary dividend of $59.0 million, in the form of securities, from Colony.
	Argonaut Insurance Company is a direct subsidiary of Argo Group US and is regulated by the Illinois Division of Insurance. During 2015, based on the state of domicile’s ordinary dividend calculation, Argonaut Insurance Company may be permitted to pay dividends of up to $39.1 million without approval from the Illinois Division of Insurance. Colony, a direct subsidiary of Argo Group US, is regulated by the Virginia Bureau of Insurance. Colony may be permitted to pay dividends of up to $71.7 million without approval from the Virginia Department of Insurance during 2015. Rockwood, a direct subsidiary of Argo Group US, is regulated by the Pennsylvania Department of Insurance. Rockwood may be permitted to pay dividends of up to $13.3 million without approval from the Pennsylvania Department of Insurance during 2015. Each department of insurance may require prior approval for the payment of all dividends, based on business and regulatory conditions of the insurance companies.
	Dividend payments from ArgoGlobal Syndicate 1200 to its immediate parent are not restricted by regulatory authority. Dividend payments will be at the discretion of ArgoGlobal Syndicate 1200’s Board of Directors and will be subject to the earnings, operations, financial condition, capital and general business requirements of ArgoGlobal Syndicate 1200.
	Certain assets of our subsidiaries are pledged to regulatory agencies, serve as collateral for letters of credit or are assigned as the assets of the trade capital providers of our Lloyd’s syndicate, and therefore, are not available funds that may be paid up as dividends to Argo Group. See Note 2, “Investments” and Note 20, “Segment Information” for further discussion.

Insurance_Assessments

Insurance Assessments	12 Months Ended
	Dec. 31, 2014
Insurance [Abstract]
Insurance Assessments	23	Insurance Assessments
	We are required to participate in statutorily created insolvency guarantee and weather-related loss protection associations in all states in the U.S. where we are authorized to transact business. These associations were formed for the purpose of paying the claims of insolvent companies. We are assessed a pro-rata share of such claims based upon our premium writings, subject to a maximum annual assessment per line of insurance. Certain of these assessments can be recovered through premium tax offsets or policy surcharges. We do not believe that assessments on current insolvencies will have a material impact on our financial condition or results of operations. We have accrued assessments of $17.0 million and $16.6 million at December 31, 2014 and 2013, respectively.

Transactions_with_Related_Part

Transactions with Related Parties	12 Months Ended
	Dec. 31, 2014
Related Party Transactions [Abstract]
Transactions with Related Parties	24	Transactions with Related Parties
	In 2013, our Surety unit received a submission through its established broker network to issue approximately $13 million of surety bonds on behalf of Kinetica Partners, LLC (“Kinetica”) in connection with a Gulf of Mexico pipeline project. Mr. Gary Woods, Chairman of our Board of Directors, is the President of Kinetica, and beneficially owns 10% of Kinetica through a family trust. The submission was underwritten, priced and bound in the ordinary course of business by the Surety unit. The terms and conditions of the surety bonds that were issued and the premium charged to Kinetica for issuance of the bonds, were consistent with those routinely applied and charged for similarly situated risks bound for unrelated third-parties. Per the Surety unit’s standard requirements in connection with the issuance of surety bonds, Kinetica and Mr. Woods, in his personal capacity, among others, executed our Surety unit’s standard form of indemnity agreement holding our Surety unit harmless against any and all losses and expenses incurred resulting from the issuance of the surety bonds.

Unaudited_Quarterly_Financial_

Unaudited Quarterly Financial Data	12 Months Ended
Unaudited Quarterly Financial Data	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Unaudited Quarterly Financial Data	25	Unaudited Quarterly Financial Data
	The following tables represent unaudited quarterly financial data for the years ended December 31, 2014 and 2013. In the opinion of management, all adjustments necessary to present fairly the results of operations for such periods have been made. Total revenue, net income before income taxes and net income include realized gains or losses from the sale of investments and other. We cannot anticipate when or if similar gains or losses may occur in the future. Since financial results rely heavily on estimates, caution should be used in drawing specific conclusions from quarterly consolidated results.

	(in millions, except per share amounts)		1st Quarter		2nd Quarter			3rd Quarter		4th Quarter		Year
	2014
	Total revenue		$	360.1	$	375.2		$	371.3	$	412.1	$	1,518.70
	Net income before income taxes			42.7		44.7			48.3		80.3		216
	Net income			40.2		38.6			44.7		59.7		183.2
	Net income per common share :
	Basic*		$	1.52	$	1.48		$	1.72	$	2.32	$	7.02
	Diluted*		$	1.49	$	1.45		$	1.69	$	2.28	$	6.9
	Comprehensive income		$	41.3	$	64.1		$	6.8	$	31.3	$	143.5

	(in millions, except per share amounts)		1st Quarter		2nd Quarter			3rd Quarter		4th Quarter		Year
	2013
	Total revenue		$	341.6	$	363.8		$	363.7	$	406	$	1,475.10
	Net income before income taxes			37.5		42.8			32.9		66.5		179.7
	Net income			32.7		31.7			31		47.8		143.2
	Net income per common share :
	Basic*		$	1.2	$	1.18		$	1.17	$	1.8	$	5.33
	Diluted*		$	1.16	$	1.13		$	1.12	$	1.74	$	5.14
	Comprehensive income (loss)		$	45.7	$	(35.2	)	$	47.2	$	43.8	$	101.5

	*	Basic and diluted net income per common share are computed independently for each quarter and full year based on the respective average number of common shares outstanding; therefore, the sum of the quarterly net income per common share data may not equal the net income per common share for the year.

Information_Provided_in_Connec

Information Provided in Connection with Outstanding Debt of Subsidiaries	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Information Provided in Connection with Outstanding Debt of Subsidiaries	26	Information Provided in Connection with Outstanding Debt of Subsidiaries
	The following tables present condensed consolidating financial information at December 31, 2014 and 2013 and for the three years ended December 31, 2014, 2013 and 2012, for Argo Group (the “Parent Guarantor”) and Argo Group US (the “Subsidiary Issuer”). The Subsidiary Issuer is an indirect 100 percent-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
	31-Dec-14
	(in millions)

			Argo Group			Argo Group US, Inc.				Other Subsidiaries				Consolidating				Total
			International			and Subsidiaries				and Eliminations (1)				Adjustments (2)
			Holdings, Ltd			(Subsidiary Issuer)
			(Parent Guarantor)
	Assets
	Investments		$	0.7		$	2,841.50			$	1,255.70			$	—			$	4,097.90
	Cash			—			49.3				31.7				—				81
	Accrued investment income			—			17.8				4.3				—				22.1
	Premiums receivable			—			154.6				199				—				353.6
	Reinsurance recoverables			—			1,173.60				(176.4	)			—				997.2
	Goodwill and other intangible assets, net			—			131.7				99.1				—				230.8
	Current income taxes receivable, net			—			10.1				4.8				—				14.9
	Deferred acquisition costs, net			—			58				66.6				—				124.6
	Ceded unearned premiums			—			98.5				109.1				—				207.6
	Other assets			9.6			174.1				67.9				(25.0	)			226.6
	Due from (to) affiliates			2.9			(19.8	)			19.8				(2.9	)			—
	Intercompany note receivable			—			72				(72.0	)			—				—
	Investments in subsidiaries			1,698.00			—				—				(1,698.0	)			—
	Total assets		$	1,711.20		$	4,761.40			$	1,609.60			$	(1,725.9	)		$	6,356.30
	Liabilities and Shareholders' Equity
	Reserves for losses and loss adjustment		$	—		$	2,136.40			$	906			$	—			$	3,042.40
	expenses		$	—		$	2,136.40			$	906			$	—			$	3,042.40
	Unearned premiums			—			448.9				368.3				—				817.2
	Funds held and ceded reinsurance payable,			—			675.1				(441.3	)			—				233.8
	net			—			675.1				(441.3	)			—				233.8
	Long-term debt			49			288.7				61.4				(20.6	)			378.5
	Deferred tax liabilities, net			—			41.2				11.8				—				53
	Accrued underwriting expenses and other liabilities			15.5			104.2				65				—				184.7
	Total liabilities			64.5			3,694.50				971.2				(20.6	)			4,709.60
	Total shareholders' equity			1,646.70			1,066.90				638.4				(1,705.3	)			1,646.70
	Total liabilities and shareholders' equity		$	1,711.20		$	4,761.40			$	1,609.60			$	(1,725.9	)		$	6,356.30

	(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
	31-Dec-13
	(in millions)

			Argo Group			Argo Group US, Inc.				Other Subsidiaries				Consolidating				Total
			International			and Subsidiaries				and Eliminations (1)				Adjustments (2)
			Holdings, Ltd			(Subsidiary Issuer)
			(Parent Guarantor)
	Assets
	Investments		$	1.1		$	2,785.10			$	1,293.00			$	—			$	4,079.20
	Cash			—			132.1				25.3				—				157.4
	Accrued investment income			—			19.7				6				—				25.7
	Premiums receivable			—			150.8				197.6				—				348.4
	Reinsurance recoverables			—			1,145.90				117.6				—				1,263.50
	Goodwill and other intangible assets, net			—			137.4				102.4				—				239.8
	Current income taxes receivable, net			—			0.5				(0.5	)			—				—
	Deferred acquisition costs, net			—			55.6				58.3				—				113.9
Ceded unearned premiums			—			88.2				108.1				—				196.3
Other assets			4.6			97.8				64.4				—				166.8
Due from affiliates			3.1			1.5				(1.5	)			(3.1	)			—
Intercompany note receivable			—			87.4				(87.4	)			—				—
Investments in subsidiaries			1,625.20			—				—				(1,625.2	)			—
Total assets		$	1,634.00		$	4,702.00			$	1,883.30			$	(1,628.3	)		$	6,591.00
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment		$	—		$	2,157.00			$	1,073.30			$	—			$	3,230.30
expenses		$	—		$	2,157.00			$	1,073.30			$	—			$	3,230.30
Unearned premiums			—			425.5				353.6				—				779.1
Funds held and ceded reinsurance payable, net			—			642.4				(244.0	)			—				398.4
Long-term debt			49			288.9				65.5				—				403.4
Current income taxes payable, net			—			8.9				(3.7	)			—				5.2
Deferred tax liabilities, net			—			22.8				5.9				—				28.7
Accrued underwriting expenses and other			15.4			98.2				69.3				—				182.9
liabilities			15.4			98.2				69.3				—				182.9
Intercompany note payable			6.6			—				—				(6.6	)			—
Total liabilities			71			3,643.70				1,319.90				(6.6	)			5,028.00
Total shareholders' equity			1,563.00			1,058.30				563.4				(1,621.7	)			1,563.00
Total liabilities and shareholders' equity		$	1,634.00		$	4,702.00			$	1,883.30			$	(1,628.3	)		$	6,591.00

(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 YEAR ENDED DECEMBER 31, 2014
(in millions)

		Argo Group			Argo Group US, Inc.				Other Subsidiaries				Consolidating				Total
		International			and Subsidiaries				and Eliminations (1)				Adjustments (2)
		Holdings, Ltd			(Subsidiary Issuer)
		(Parent Guarantor)
Premiums and other revenue:
Earned premiums		$	—		$	461			$	877.1			$	—			$	1,338.10
Net investment income (expense)			40.5			56.7				(10.6	)			—				86.6
Net realized investment gains and			2			86.9				7.1				(2.0	)			94
other			2			86.9				7.1				(2.0	)			94
Total revenue			42.5			604.6				873.6				(2.0	)			1,518.70
Expenses:
Losses and loss adjustment expenses			—			285.6				461.8				—				747.4
Underwriting, acquisition and insurance			17.3			199.9				322				—				539.2
expenses			17.3			199.9				322				—				539.2
Interest expense			2.3			15.2				2.7				(0.3	)			19.9
Fee expense (income), net			—			2.4				(1.8	)			—				0.6
Foreign currency exchange loss (gain)			—			0.4				(8.2	)			—				(7.8	)
Impairment of intangible assets			—			3.4				—				—				3.4
Total expenses			19.6			506.9				776.5				(0.3	)			1,302.70
Income before income taxes			22.9			97.7				97.1				(1.7	)			216
Provision for income taxes			—			27.5				5.3				—				32.8
Net income before equity in earnings of			22.9			70.2				91.8				(1.7	)			183.2
subsidiaries			22.9			70.2				91.8				(1.7	)			183.2
Equity in undistributed earnings of			160.3			—				—				(160.3	)			—
subsidiaries			160.3			—				—				(160.3	)			—
Net income		$	183.2		$	70.2			$	91.8			$	(162.0	)		$	183.2

(1)	Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations.
(2)	Includes all Argo Group parent company eliminations.



CONDENSED CONSOLIDATING STATEMENT OF INCOME
FOR THE YEAR ENDED DECEMBER 31, 2013
(in millions)

		Argo Group			Argo Group US, Inc.				Other Subsidiaries				Consolidating				Total
		International			and Subsidiaries				and Eliminations (1)				Adjustments (2)
		Holdings, Ltd			(Subsidiary Issuer)
		(Parent Guarantor)
Premiums and other revenue:
Earned premiums		$	—		$	439.9			$	863.9			$	—			$	1,303.80
Net investment income (expense)			84.5			73.4				(57.9	)			—				100
Net realized investment gains (losses) and			—			72.2				(0.9	)			—				71.3
other			—			72.2				(0.9	)			—				71.3
Total revenue			84.5			585.5				805.1				—				1,475.10
Expenses:
Losses and loss adjustment expenses			—			268.6				473.4				—				742
Other reinsurance-related expenses			—			—				19.2				—				19.2
Underwriting, acquisition and insurance			27.4			176.9				306.5				—				510.8
expenses			27.4			176.9				306.5				—				510.8
Interest expense			3.3			15.2				2.9				(1.2	)			20.2
Fee expense, net			-			4.1				0.8				-				4.9
Foreign currency exchange gain			—			(0.3	)			(1.4	)			—				(1.7	)
Total expenses			30.7			464.5				801.4				(1.2	)			1,295.40
Income before income taxes			53.8			121				3.7				1.2				179.7
Provision for income taxes			—			34.1				2.4				—				36.5
Net income before equity in earnings of			53.8			86.9				1.3				1.2				143.2
subsidiaries			53.8			86.9				1.3				1.2				143.2
Equity in undistributed earnings of			89.4			—				—				(89.4	)			—
subsidiaries			89.4			—				—				(89.4	)			—
Net income		$	143.2		$	86.9			$	1.3			$	(88.2	)		$	143.2

(1)	Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations.
(2)	Includes all Argo Group parent company eliminations.



CONDENSED CONSOLIDATING STATEMENT OF INCOME
FOR THE YEAR ENDED DECEMBER 31, 2012
(in millions)

		Argo Group			Argo Group US, Inc.				Other Subsidiaries				Consolidating				Total
		International			and Subsidiaries				and Eliminations (1)				Adjustments (2)
		Holdings, Ltd			(Subsidiary Issuer)
		(Parent Guarantor)
Premiums and other revenue:
Earned premiums		$	—		$	434.2			$	752.3			$	—			$	1,186.50
Net investment income			0.1			86.6				32.1				—				118.8
Net realized investment (losses) gains and			(0.8	)		19.5				7				—				25.7
other			(0.8	)		19.5				7				—				25.7
Total revenue			(0.7	)		540.3				791.4				—				1,331.00
Expenses:
Losses and loss adjustment expenses			—			300.6				447				—				747.6
Other reinsurance-related expenses			—			—				27.3				—				27.3
Underwriting, acquisition and insurance expenses			27.1			169.8				267.6				—				464.5
Interest expense			3.9			17.1				3				(0.3	)			23.7
Fee expense (income), net			-			(1.3	)			(4.0	)			-				(5.3	)
Debt extinguishment costs			0.1			2.1				—				—				2.2
Foreign currency exchange loss			—			—				4.3				—				4.3
Total expenses			31.1			488.3				745.2				(0.3	)			1,264.30
(Loss) income before income taxes			(31.8	)		52				46.2				0.3				66.7
Provision for income taxes			—			11.1				3.3				—				14.4
Net (loss) income before equity in earnings of			(31.8	)		40.9				42.9				0.3				52.3
subsidiaries			(31.8	)		40.9				42.9				0.3				52.3
Equity in undistributed earnings of			84.1			—				—				(84.1	)			—
subsidiaries			84.1			—				—				(84.1	)			—
Net income (loss)		$	52.3		$	40.9			$	42.9			$	(83.8	)		$	52.3

(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 YEAR ENDED DECEMBER 31, 2014
(in millions)

		Argo Group			Argo Group US, Inc.				Other Subsidiaries				Consolidating				Total
		International			and Subsidiaries				and Eliminations (1)				Adjustments (2)
		Holdings, Ltd			(Subsidiary Issuer)
		(Parent Guarantor)
Net cash flows from operating activities		$	25.7		$	43.2			$	37.2			$	24.4			$	130.5
Cash flows from investing activities:
Proceeds from sales of investments			—			803.8				458.2				—				1,262.00
Maturities and mandatory calls of fixed			—			192.1				130.9				—				323
maturity investments			—			192.1				130.9				—				323
Purchases of investments			—			(1,126.1	)			(610.7	)			—				(1,736.8	)
Change in short-term investments and			0.5			76				20				—				96.5
foreign regulatory deposits			0.5			76				20				—				96.5
Settlements of foreign currency exchange			1.3			—				(2.4	)			—				(1.1	)
forward contracts			1.3			—				(2.4	)			—				(1.1	)
Issuance of intercompany note, net			—			14.5				(7.6	)			(6.9	)			—
Purchases of fixed assets and other, net			(7.0	)		(35.5	)			(16.0	)			(6.4	)			(64.9	)
Cash (used) provided by investing activities			(5.2	)		(75.2	)			(27.6	)			(13.3	)			(121.3	)
Cash flows from financing activities:
Borrowings under intercompany note, net			(6.9	)		—				—				6.9				—
Activity under stock incentive plans			4.6			—				—				—				4.6
Redemption of trust preferred securities, net			—			—				—				(18.0	)			(18.0	)
Payment on note payable			—			(0.1	)			—				—				(0.1	)
Repurchase of Company's common shares			—			(50.8	)			—				—				(50.8	)
Excess tax expense from share-based			—			0.1				—				—				0.1
payment arrangements			—			0.1				—				—				0.1
Payment of cash dividend to common			(18.2	)		—				—				—				(18.2	)
shareholders			(18.2	)		—				—				—				(18.2	)
Cash (used) provided by financing activities			(20.5	)		(50.8	)			—				(11.1	)			(82.4	)
Effect of exchange rate changes on cash			—			—				(3.2	)			—				(3.2	)
Change in cash			—			(82.8	)			6.4				(—	)			(76.4	)
Cash, beginning of year			—			132.1				25.3				—				157.4
Cash, end of year		$	—		$	49.3			$	31.7			$	(—	)		$	81

(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 YEAR ENDED DECEMBER 31, 2013
(in millions)

		Argo Group			Argo Group US, Inc.				Other Subsidiaries				Consolidating				Total
		International			and Subsidiaries				and Eliminations (1)				Adjustments (2)
		Holdings, Ltd			(Subsidiary Issuer)
		(Parent Guarantor)
Net cash flows from operating activities		$	63.2		$	62.5			$	(125.9	)		$	—			$	(0.2	)
Cash flows from investing activities:
Proceeds from sales of investments			—			1,130.20				836.1				—				1,966.30
Maturities and mandatory calls of fixed			—			168.9				112.9				—				281.8
maturity investments			—			168.9				112.9				—				281.8
Purchases of investments			—			(1,156.7	)			(819.1	)			—				(1,975.8	)
Change in short-term investments and			(1.4	)		(119.1	)			(32.5	)			—				(153.0	)
foreign regulatory deposits			(1.4	)		(119.1	)			(32.5	)			—				(153.0	)
Settlements of foreign currency exchange			0.7			—				(4.6	)			—				(3.9	)
forward contracts			0.7			—				(4.6	)			—				(3.9	)
Issuance of intercompany note, net			—			35				14.3				(49.3	)			—
Purchases of fixed assets and other, net			—			(16.3	)			21.7				—				5.4
Cash (used) provided by investing activities			(0.7	)		42				128.8				(49.3	)			120.8
Cash flows from financing activities:
Borrowings under intercompany note, net			(49.3	)		—				—				49.3				—
Activity under stock incentive plans			2.6			—				—				—				2.6
Repurchase of Company's common shares			—			(46.5	)			—				—				(46.5	)
Excess tax expense from share-based			—			0.2				—				—				0.2
payment arrangements			—			0.2				—				—				0.2
Payment of cash dividend to common			(15.8	)		—				—				—				(15.8	)
shareholders			(15.8	)		—				—				—				(15.8	)
Cash (used) provided by financing activities			(62.5	)		(46.3	)			—				49.3				(59.5	)
Effect of exchange rate changes on cash			—			—				0.5				—				0.5
Change in cash			—			58.2				3.4				—				61.6
Cash, beginning of year			—			73.9				21.9				—				95.8
Cash, end of year		$	—		$	132.1			$	25.3			$	—			$	157.4

(1)	Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations.
(2)	Includes all Argo Group parent company eliminations.



CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS
FOR YEAR ENDED DECEMBER 31, 2012
(in millions)

		Argo Group			Argo Group US, Inc.				Other Subsidiaries				Consolidating				Total
		International			and Subsidiaries				and Eliminations (1)				Adjustments (2)
		Holdings, Ltd			(Subsidiary Issuer)
		(Parent Guarantor)
Net cash flows from operating activities		$	(30.2	)	$	5.5			$	55.2			$	—			$	30.5
Cash flows from investing activities:
Proceeds from sales of investments			—			573.8				556.9				—				1,130.70
Maturities and mandatory calls of fixed			—			326.2				156.8				—				483
maturity investments			—			326.2				156.8				—				483
Purchases of investments			—			(889.1	)			(732.4	)			—				(1,621.5	)
Change in short-term investments and			(0.9	)		35.1				3.5				—				37.7
foreign regulatory deposits			(0.9	)		35.1				3.5				—				37.7
Settlements of foreign currency exchange			2.3			—				(1.9	)			—				0.4
forward contracts			2.3			—				(1.9	)			—				0.4
Issuance of intercompany note, net			—			(26.0	)			(29.0	)			55				—
Purchases of fixed assets and other, net			—			(29.1	)			(4.9	)			—				(34.0	)
Cash provided (used) by investing activities			1.4			(9.1	)			(51.0	)			55				(3.7	)
Cash flows from financing activities:
Borrowings under intercompany note, net			55			—				—				(55.0	)			—
Proceeds from issuance of senior			—			138.7				—				—				138.7
unsecured fixed rate notes			—			138.7				—				—				138.7
Redemption of trust preferred securities,			(15.1	)		(102.1	)			—				—				(117.2	)
net			(15.1	)		(102.1	)			—				—				(117.2	)
Activity under stock incentive plans			1.2			—				—				—				1.2
Repurchase of Company's common shares			—			(44.2	)			—				—				(44.2	)
Payment of cash dividend to common			(12.3	)		—				—				—				(12.3	)
shareholders			(12.3	)		—				—				—				(12.3	)
Cash provided (used) by financing activities			28.8			(7.6	)			—				(55.0	)			(33.8	)
Effect of exchange rate changes on cash			—			—				0.1				—				0.1
Change in cash			—			(11.2	)			4.3				—				(6.9	)
Cash, beginning of year			—			85.1				17.6				—				102.7
Cash, end of year		$	—		$	73.9			$	21.9			$	—			$	95.8

(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	12 Months Ended
Subsequent Event	Dec. 31, 2014
Subsequent Events [Abstract]
Subsequent Event	27	Subsequent Event
	On February 17, 2015, our Board of Directors declared a 10% stock dividend payable on March 16, 2015, to shareholders of record at the close of business on March 2, 2015. Based upon information available to us as of the dividend declaration date, we estimate approximately 2.6 million shares will be issued upon payment of the stock dividend. The share numbers and per share amounts disclosed in the Consolidated Financial Statements and Notes to the Consolidated Financial Statements have not been retroactively adjusted to give effect to the stock dividend. Presented below are pro forma basic and diluted net income per common share after giving effect for the stock dividend:

			For the Years Ended December 31,
			2014		2013		2012
	Pro forma net income per common share:
	Basic		$	6.39	$	4.85	$	1.69
	Diluted		$	6.27	$	4.67	$	1.66

	The pro forma impact of the stock dividend on the Consolidated Balance Sheet at December 31, 2014 is an increase in common stock of $2.6 million, an increase in additional paid-in capital of $132.5 million and a decrease to retained earnings of $135.1 million.

Schedule_II_Condensed_Financia

Schedule II Condensed Financial Information of Registrant	12 Months Ended
Schedule II Condensed Financial Information of Registrant	Dec. 31, 2014
Condensed Financial Information Of Parent Company Only Disclosure [Abstract]
Schedule II Condensed Financial Information of Registrant	ARGO GROUP INTERNATIONAL HOLDINGS, LTD.
	SCHEDULE II
	CONDENSED FINANCIAL INFORMATION OF REGISTRANT
	(in millions)

	BALANCE SHEETS				December 31,
					2014				2013
	Assets
	Other investments, unrealized loss on foreign currency				$	(1.2	)		$	(1.4	)
	exchange forward contracts				$	(1.2	)		$	(1.4	)
	Short-term investments					1.9				2.5
	Investment in subsidiaries					1,698.00				1,625.20
	Due from subsidiaries					2.9				3.1
	Other assets					9.6				4.6
	Total assets				$	1,711.20			$	1,634.00
	Liabilities and Shareholders' Equity
	Junior subordinated debentures				$	49			$	49
	Intercompany note payable					—				6.6
	Accrued underwriting expenses					15.5				15.4
	Total liabilities					64.5				71
	Shareholders' equity					1,646.70				1,563.00
	Total liabilities and shareholders' equity				$	1,711.20			$	1,634.00

	STATEMENTS OF INCOME		For the Years Ended December 31,
			2014				2013				2012
	Revenue:
	Net investment income (1)		$	40.5			$	84.5			$	0.1
	Net realized investment losses			2				—				(0.8	)
	Total revenue			42.5				84.5				(0.7	)
	Expenses:
	Interest expense			2.3				3.3				3.9
	Debt extinguishment costs			—				—				0.1
	Other expenses			17.3				27.4				27.1
	Total expenses			19.6				30.7				31.1
	Net income (loss) before equity in earnings (losses) of			22.9				53.8				(31.8	)
	subsidiaries (2)			22.9				53.8				(31.8	)
	Equity in undistributed earnings of subsidiaries			160.3				89.4				84.1
	Net income		$	183.2			$	143.2			$	52.3

	(1)	For the years ended December 31, 2014 and 2013, net investment income includes intercompany dividends of $40.9 million and $84.5 million, respectively.
	(2)	Argo Group International Holdings, Ltd. is not subject to taxation.



	ARGO GROUP INTERNATIONAL HOLDINGS, LTD.
	SCHEDULE II
	CONDENSED FINANCIAL INFORMATION OF REGISTRANT
	(in millions)

	STATEMENTS OF CASH FLOWS		For the Years Ended December 31,
			2014				2013				2012
	Cash flows from operating activities:
	Net income		$	183.2			$	143.2			$	52.3
	Adjustments to reconcile net income
	to net cash provided (used) by operating
	activities:
	Amortization and depreciation			—				0.7				0.9
	Share-based payments expense			5.7				8.7				4.8
	Net realized investment and other gains			(2.0	)			—				—
	Debt extinguishment costs			—				—				0.1
	Undistributed earnings of subsidiaries			(160.3	)			(89.4	)			(84.1	)
	Change in:
	Prepaid assets			2				(0.1	)			0.9
	Accrued underwriting expenses			(2.2	)			(0.9	)			0.9
Due to subsidiaries			(0.6	)			0.2				(7.0	)
Interest on intercompany note payable			0.3				0.8				0.3
Other assets and liabilities, net			(0.4	)			—				0.7
Cash provided (used) by operating activities			25.7				63.2				(30.2	)
Cash flows from investing activities:
Change in short-term investments			0.5				(1.4	)			(0.9	)
Settlements of foreign currency exchange forward			1.3				0.7				2.3
contracts			1.3				0.7				2.3
Purchases of fixed assets			(7.0	)			—				—
Cash (used) provided by investing activities			(5.2	)			(0.7	)			1.4
Cash flows from financing activities:
Borrowings under intercompany note payable, net			(6.9	)			(49.3	)			55
Activity under stock incentive plans			4.6				2.6				1.2
Redemption of trust preferred securities, net			—				—				(15.1	)
Payment of cash dividend to common shareholders			(18.2	)			(15.8	)			(12.3	)
Cash (used) provided by financing activities			(20.5	)			(62.5	)			28.8
Change in cash			—				—				—
Cash, beginning of year			—				—				—
Cash, end of year		$	—			$	—			$	—

Schedule_III_Supplemental_Insu

Schedule III Supplemental Insurance Information	12 Months Ended
Schedule III Supplemental Insurance Information	Dec. 31, 2014
Supplementary Insurance Information [Abstract]
Schedule III Supplemental Insurance Information	ARGO GROUP INTERNATIONAL HOLDINGS, LTD.
	SCHEDULE III
	SUPPLEMENTAL INSURANCE INFORMATION
	FOR THE YEARS ENDED DECEMBER 31, 2014, 2013 AND 2012
	(in millions)

	Segment		DAC		Reserves for		UPR		Premium		Net		Loss		Amortization			Other		Premiums
			(a)		Losses and Loss		(c)		Revenue		Investment		& LAE		(Deferral)			Operating		Written
					Adjustment				(d)		Income		(e)		DAC			Expenses		(g)
					Expenses						(l)				(f) (2)			-3
					(b)
	Year Ended December 31, 2014
	Excess and Surplus Lines		$	36.9	$	1,165.40	$	274.9	$	485.2	$	36.7	$	248	$	1.9		$	159.7	$	487.8
	Commercial Specialty			22.5		652.2		172.9		291.9		18.7		189.1		(4.3	)		107.8		301.1
	International Specialty			0.8		306.3		123.9		148.3		8.2		77.8		1.7			52.8		156.6
	Syndicate 1200			64.4		600		245.5		411.1		10.2		208.1		(4.7	)		172.5		420.8
	Run-off Lines			—		318.5		—		1.6		9.7		24.4		—			8.2		1.6
	Corporate and Other			—		—		—		—		3.1		—		—			43.6		—
	Total		$	124.6	$	3,042.40	$	817.2	$	1,338.10	$	86.6	$	747.4	$	(5.4	)	$	544.6	$	1,367.90
	Year Ended December 31, 2013
	Excess and Surplus Lines		$	38.8	$	1,171.80	$	264.8	$	460.2	$	42.2	$	244	$	(1.4	)	$	158.6	$	478.7
	Commercial Specialty			18.1		653.4		159.4		299		22.8		194		0.4			97		288.2
	International Specialty			2.2		295.6		117.1		142.4		8.4		79.9		(1.0	)		51.1		155.4
	Syndicate 1200			54.8		777		237.8		401.7		11		208.6		(13.8	)		170		428.5
	Run-off Lines			—		332.5		—		0.5		10.8		15.5		—			4.6		0.5
	Corporate and Other			—		—		—		—		4.8		—		—			45.3		—
	Total		$	113.9	$	3,230.30	$	779.1	$	1,303.80	$	100	$	742	$	(15.8	)	$	526.6	$	1,351.30
	Year Ended December 31, 2012
	Excess and Surplus Lines		$	37.3	$	1,209.00	$	239	$	399.3	$	51.1	$	223.3	$	(2.5	)	$	146.4	$	420.8
	Commercial Specialty			18.6		660		173		317.5		27.6		257		3.4			104.9		306.4
	International Specialty			1.4		257.3		102.5		130.1		12.3		73.5		0.1			43.7		145.5
	Syndicate 1200			42.1		738.9		215.7		337.9		15.3		184		(5.5	)		139.4		370.2
	Run-off Lines			—		358.3		—		1.7		12.5		9.8		—			2.8		1.6
	Corporate and Other			—		—		—		—		—		—		—			31.8		—
	Total		$	99.4	$	3,223.50	$	730.2	$	1,186.50	$	118.8	$	747.6	$	(4.5	)	$	469	$	1,244.50

	(a)	Deferred Policy Acquisition Cost
	(b)	Future Policy Benefits, Losses, Claims and Loss Expenses
	(c)	Unearned Premiums
	(d)	Premium Revenue, net (premiums earned)
	(e)	Benefits, Claims, Losses and Settlement Expenses
	(f)	Amortization (Deferral) of Deferred Policy Acquisition Costs
	(g)	Premiums Written, net
	(1)	Net Investment Income allocated based upon each segment’s share of investable funds.
	(2)	The amortization (deferral) of DAC will not equal the change in the balance sheet. See Note 1, “Business and Significant Accounting Policies” for further discussion.
	(3)	Other Insurance Expenses allocated based on specific identification, where possible, and related activities.

Schedule_V_Valuation_and_Quali

Schedule V Valuation and Qualifying Accounts	12 Months Ended
Schedule V Valuation and Qualifying Accounts	Dec. 31, 2014
Valuation And Qualifying Accounts [Abstract]
Schedule V Valuation and Qualifying Accounts	ARGO GROUP INTERNATIONAL HOLDINGS, LTD.
	SCHEDULE V
	VALUATION AND QUALIFYING ACCOUNTS
	(in millions)

		Balance at		Charged to			Capital Loss		Net Operating		Charged to			Deductions		Balance at
		Beginning		Cost and			Carryforward		Loss		Other					End of Year
		of Year		Expense					Carryforward		Accounts
	Year Ended December 31, 2014
	Deducted from assets:
	Valuation allowance for deferred tax asset	$	56.2	$	(30.7	)	$	—	$	—	$	(0.1	)	$	—	$	25.4
	Year Ended December 31, 2013
	Deducted from assets:
	Valuation allowance for deferred tax asset	$	52.5	$	(1.0	)	$	—	$	—	$	4.7		$	—	$	56.2
	Year Ended December 31, 2012
	Deducted from assets:
	Valuation allowance for deferred tax asset	$	50.4	$	(1.0	)	$	—	$	—	$	3.1		$	—	$	52.5

Schedule_VI_Supplemental_Infor

Schedule VI Supplemental Information for Property-Casualty Insurance Companies	12 Months Ended
	Dec. 31, 2014
Supplemental Information For Property Casualty Insurance Underwriters [Abstract]
Schedule VI Supplemental Information for Property-Casualty Insurance Companies	ARGO GROUP INTERNATIONAL HOLDINGS, LTD.
	SCHEDULE VI
	SUPPLEMENTAL INFORMATION FOR PROPERTY-CASUALTY INSURANCE COMPANIES
	(in millions)

			For the Years Ended December 31,
			2014			2013			2012
	Deferred acquisition costs		$	124.6		$	113.9		$	99.4
	Reserves for losses and loss adjustment expenses		$	3,042.40		$	3,230.30		$	3,223.50
	Unamortized discount in reserves for losses		$	17.6		$	19.5		$	20.8
	Unearned premiums		$	817.2		$	779.1		$	730.2
	Premiums earned		$	1,338.10		$	1,303.80		$	1,186.50
	Net investment income		$	86.6		$	100		$	118.8
	Losses and loss adjustment expenses incurred:
	Current year		$	785.1		$	775.6		$	780.5
	Prior years			(37.7	)		(33.6	)		(32.9	)
	Losses and loss adjustment expenses incurred		$	747.4		$	742		$	747.6
	(Deferral) amortization of policy acquisition costs (1)		$	(5.4	)	$	(15.8	)	$	(4.5	)
	Paid losses and loss adjustment expenses, net of		$	736.7		$	753.5		$	796.5
	reinsurance		$	736.7		$	753.5		$	796.5
	Gross premiums written		$	1,905.40		$	1,888.40		$	1,745.70

	(1)	The amortization (deferral) of policy acquisition costs will not equal the change in the balance sheet. For further discussion, see Note 1, “Business and Significant Accounting Policies.”

Business_and_Significant_Accou1

Business and Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2014

Accounting Policies [Abstract]

Business

We conduct our ongoing business through four segments.

Excess and Surplus Lines products are underwritten under two operating platforms: Colony Specialty and Argo Pro.

International Specialty products are provided by our Bermuda operations, which include Argo Re and Argo Insurance – Casualty and Professional Lines and Argo Seguros Brasil S.A. based in Brazil.

Syndicate 1200 products are underwritten by ArgoGlobal Syndicate 1200 based in London, on behalf of one underwriting syndicate under the Lloyd’s of London (“Lloyd’s”) global franchise.

Basis of Presentation and Use of Estimates

10% Stock Dividend

Stock Dividends

Cash

Cash consists of cash deposited in banks, generally in concentration and operating accounts. Interest-bearing cash accounts are classified as short-term investments.

Investments

Receivables

For the Years Ended December 31,

(in millions)

2014

2013

2012

Premiums receivable

1.1

0.2

0.3

Reinsurance recoverables

0.5

(0.0

)

(0.4

)

Net written off (recovered)

1.6

0.2

(0.1

)

Recoveries occur when subsequent collection or litigation results in the receipt of amounts previously written off. Amounts recovered are applied against the bad debt expense account.

Earned Premiums

Retrospectively Rated Policies

Deferred Acquisition Costs

Reserves for Losses and Loss Adjustment Expenses

Reinsurance

Goodwill and Intangible Assets

The following table presents our intangible assets and accumulated amortization at December 31:

31-Dec-14

31-Dec-13

(in millions)

Gross Carrying

Accumulated

Gross Carrying

Accumulated

Amount

Amortization

Amount

Amortization

Lloyd's capacity

60.5

n/a

60.5

n/a

Title plant

—

n/a

1.8

n/a

Distribution network

44.8

27.9

44.8

23.1

Additional Lloyd's capacity

4.8

3.9

4.8

3.2

Other

1.5

1.2

1.5

1.1

111.6

113.4

27.4

The estimated amortization expense for the years ended December 31, 2015, 2016, 2017, 2018 and 2019 is $5.4 million, $5.1 million, $4.5 million, $2.4 million and $0.4 million, respectively.

Property and Equipment

Derivative Instruments

Share-Based Payments

Foreign Currency Exchange Gain (Loss)

Income Taxes

Supplemental Cash Flow Information

Income taxes paid. We paid income taxes of $23.7 million, $14.2 million and $21.0 million in 2014, 2013 and 2012, respectively.

Income taxes recovered. We recovered income taxes of $0.1 million and $10.0 million in 2014 and 2012, respectively. We did not recover any income taxes in 2013.

Interest paid. Interest paid was as follows:

For the Years Ended December 31,

(in millions)

2014

2013

2012

Senior unsecured fixed rate notes

9.3

2.1

Junior subordinated debentures

7.6

7.9

21.3

Other indebtedness

2.8

2.6

3.1

Total interest paid

19.7

19.8

26.5

Recently Issued Accounting Pronouncements

Business_and_Significant_Accou2

Business and Significant Accounting Policies (Tables)	12 Months Ended
Business and Significant Accounting Policies (Tables)	Dec. 31, 2014
Accounting Policies [Abstract]
Summary of Receivables	Premiums receivable and reinsurance recoverables on paid losses written off, net of recoveries against the allowance for doubtful accounts or directly to the income statement are as follows:

		For the Years Ended December 31,
	(in millions)	2014		2013			2012
	Premiums receivable	$	1.1	$	0.2		$	0.3
	Reinsurance recoverables		0.5		(0.0	)		(0.4	)
	Net written off (recovered)	$	1.6	$	0.2		$	(0.1	)

Intangible Assets And Accumulated Amortization	The following table presents our intangible assets and accumulated amortization at December 31:

		31-Dec-14					31-Dec-13
	(in millions)	Gross Carrying		Accumulated			Gross Carrying			Accumulated
	(in millions)	Amount		Amortization			Amount			Amortization
	Lloyd's capacity	$	60.5	n/a			$	60.5		n/a
	Title plant		—	n/a				1.8		n/a
	Distribution network		44.8		27.9			44.8			23.1
	Additional Lloyd's capacity		4.8		3.9			4.8			3.2
	Other		1.5		1.2			1.5			1.1
		$	111.6	$	33		$	113.4		$	27.4

Supplemental Cash Flow Information	Interest paid. Interest paid was as follows:

		For the Years Ended December 31,
	(in millions)	2014		2013			2012
	Senior unsecured fixed rate notes	$	9.3	$	9.3		$	2.1
	Junior subordinated debentures		7.6		7.9			21.3
	Other indebtedness		2.8		2.6			3.1
	Total interest paid	$	19.7	$	19.8		$	26.5

Investments_Tables

Investments (Tables)	12 Months Ended
Investments (Tables)	Dec. 31, 2014
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 investments as of December 31 were as follows:

	31-Dec-14
	(in millions)		Amortized			Gross			Gross			Fair
			Cost			Unrealized			Unrealized			Value
						Gains			Losses
	Fixed maturities
	USD denominated:
	U.S. Governments		$	184		$	1.3		$	0.3		$	185
	Non-U.S. Governments			79.9			0.6			0.6			79.9
	Obligations of states and political subdivisions			468.1			22.9			0.3			490.7
	Credit-Financial			508.1			12.3			2.3			518.1
	Credit-Industrial			493.7			9.4			3.5			499.6
	Credit-Utility			142.7			3.2			3.9			142
	Structured securities:
	CMO/MBS-agency (1)			168			8			0.7			175.3
	CMO/MBS-non agency			13.2			0.8			—			14
	CMBS (2)			178.6			1.6			0.2			180
	ABS (3)			221.4			0.6			1			221
	Foreign denominated:
	Governments			148.4			1.2			9.4			140.2
	Credit			211.1			2.7			18.9			194.9
	Total fixed maturities			2,817.20			64.6			41.1			2,840.70
	Equity securities			307.3			184.1			5.1			486.3
	Other investments			488.9			7.5			1.3			495.1
	Short-term investments			275.8			—			—			275.8
	Total investments		$	3,889.20		$	256.2		$	47.5		$	4,097.90

	(1)	Collateralized mortgage obligations/mortgage-backed securities (“CMO/MBS”).
	(2)	Commercial mortgage-backed securities (“CMBS”).
	(3)	Asset-backed securities (“ABS”).

	31-Dec-13
	(in millions)		Amortized			Gross			Gross			Fair
			Cost			Unrealized			Unrealized			Value
						Gains			Losses
	Fixed maturities
	USD denominated:
	U.S. Governments		$	273.4		$	2.4		$	0.5		$	275.3
	Non-U.S. Governments			60.9			0.3			1			60.2
	Obligations of states and political subdivisions			563.7			22.9			8.8			577.8
	Credit-Financial			426.3			15.4			1.8			439.9
	Credit-Industrial			385.5			13.8			2.2			397.1
	Credit-Utility			162			5.4			0.8			166.6
	Structured securities:
	CMO/MBS-agency (1)			219.4			9.2			1.7			226.9
	CMO/MBS-non agency			19.4			0.8			—			20.2
	CMBS (2)			162.7			3.1			1			164.8
	ABS (3)			123.6			0.8			0.6			123.8
	Foreign denominated:
	Governments			207.7			4.9			5.9			206.7
	Credit			155.5			4.4			4.8			155.1
	Total fixed maturities			2,760.10			83.4			29.1			2,814.40
	Equity securities			346.9			188.6			1.2			534.3
	Other investments			377.4			2.8			1.3			378.9
	Short-term investments			351.6			—			—			351.6
	Total investments		$	3,836.00		$	274.8		$	31.6		$	4,079.20

	(1)	Collateralized mortgage obligations/mortgage-backed securities (“CMO/MBS”).
	(2)	Commercial mortgage-backed securities (“CMBS”).
	(3)	Asset-backed securities (“ABS”).
Schedule of Amortized Cost and Fair Values of Fixed Maturity Investments, by Contractual Maturity	The amortized cost and fair values of fixed maturity investments as of December 31, 2014, by contractual maturity, were as follows:

	(in millions)		Amortized			Fair
	(in millions)		Cost			Value
	Due in one year or less		$	238.7		$	235.3
	Due after one year through five years			1,326.20			1,328.50
	Due after five years through ten years			507.7			519.1
	Thereafter			163.4			167.5
	Structured securities			581.2			590.3
	Total		$	2,817.20		$	2,840.70

Schedule Of Carrying Value Redemption Characteristics And Unfunded Investment Commitments Of Other Invested Assets Portfolio
	Details regarding the carrying value, redemption characteristics and unfunded investment commitments of the other invested assets portfolio as of December 31, 2014 and 2013 were as follows:

	31-Dec-14
	(in millions)		Carrying Value				Unfunded Commitments
	Investment Type
	Hedge funds		$	153.2			$	—
	Private equity			123.6				72.9
	Long only funds			104.4				—
	Other investments			113.9				—
	Total other invested assets		$	495.1			$	72.9

	31-Dec-13
	(in millions)		Carrying Value				Unfunded Commitments
	Investment Type
	Hedge funds		$	87.9			$	—
	Private equity			93.8				35.7
	Long only funds			62				—
	Other investments			135.2				—
	Total other invested assets		$	378.9			$	35.7

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, equity securities, other investments and short-term investments is presented below:

	31-Dec-14		Less Than One Year						One Year or Greater						Total
	(in millions)		Fair			Unrealized			Fair			Unrealized			Fair			Unrealized
	(in millions)		Value			Losses			Value			Losses			Value			Losses
	Fixed maturities
	USD denominated:
	U.S. Governments		$	55		$	0.2		$	15.7		$	0.1		$	70.7		$	0.3
	Non-U.S. Governments			36.5			0.4			5.2			0.2			41.7			0.6
	Obligations of states and political			10.4			0.1			16.6			0.2			27			0.3
	subdivisions			10.4			0.1			16.6			0.2			27			0.3
	Credit-Financial			195.7			2.2			11.1			0.1			206.8			2.3
	Credit-Industrial			240.8			3.3			12.2			0.2			253			3.5
	Credit-Utility			63.1			3.8			1.9			0.1			65			3.9
	Structured securities:
	CMO/MBS-agency			10.1			0.1			19.2			0.6			29.3			0.7
	CMBS			49.3			0.1			6			0.1			55.3			0.2
	ABS			129.2			0.7			8.1			0.3			137.3			1
	Foreign denominated:
	Governments			123.7			9.3			11.2			0.1			134.9			9.4
	Credit			190.8			18.7			0.9			0.2			191.7			18.9
	Total fixed maturities			1,104.60			38.9			108.1			2.2			1,212.70			41.1
	Equity securities			53.6			5.1			—			—			53.6			5.1
	Other investments			(0.9	)		1.3			—			—			(0.9	)		1.3
	Short-term investments			—			—			—			—			—			—
	Total		$	1,157.30		$	45.3		$	108.1		$	2.2		$	1,265.40		$	47.5

	31-Dec-13		Less Than One Year						One Year or Greater						Total
	(in millions)		Fair			Unrealized			Fair			Unrealized			Fair			Unrealized
	(in millions)		Value			Losses			Value			Losses			Value			Losses
	Fixed maturities
	USD denominated:
	U.S. Governments		$	55.3		$	0.5		$	—		$	—		$	55.3		$	0.5
	Non-U.S. Governments			36.3			1			—			—			36.3			1
	Obligations of states and political			154.6			8.8			3.1			—			157.7			8.8
	subdivisions (2)			154.6			8.8			3.1			—			157.7			8.8
	Credit-Financial			88.7			1.7			2.4			0.1			91.1			1.8
	Credit-Industrial			85.7			2			2.9			0.2			88.6			2.2
	Credit-Utility			21.2			0.7			1.9			0.1			23.1			0.8
	Structured securities:
	CMO/MBS-agency			58.4			1.2			5.6			0.5			64			1.7
	CMBS (2)			24.2			1			1.1			—			25.3			1
	ABS			59.1			0.1			5.6			0.5			64.7			0.6
	Foreign denominated:
	Governments			170.5			5.9			—			—			170.5			5.9
	Credit			125.3			4.8			—			—			125.3			4.8
	Total fixed maturities			879.3			27.7			22.6			1.4			901.9			29.1
	Equity securities			25.5			1.2			—			—			25.5			1.2
	Other investments			(1.3	)		1.3			—			—			(1.3	)		1.3
	Short-term investments (1)			4.5			—			—			—			4.5			—
	Total		$	908		$	30.2		$	22.6		$	1.4		$	930.6		$	31.6

	(1)	Unrealized losses less than one year are less than $0.1 million.
	(2)	Unrealized losses one year or greater are less than $0.1 million.
Schedule of Investment Income and Expenses	Investment income and expenses were as follows:

			For the Years Ended December 31,
	(in millions)		2014			2013			2012
	Investment income:
	Interest and dividends on fixed maturities		$	76.3		$	87.7		$	105.9
	Dividends on equity securities			15.8			17.7			15.2
	Interest on short-term and other investments			5.3			5			7.3
	Other			(1.0	)		(1.0	)		(0.4	)
	Investment income			96.4			109.4			128
	Investment expenses			(9.8	)		(9.4	)		(9.2	)
	Net investment income		$	86.6		$	100		$	118.8

Schedule of Company's Gross Realized Investment Gains (Losses)	The following table presents our gross realized investment gains (losses) and other:

			For the Years Ended December 31,
	(in millions)		2014			2013			2012
	Realized gains
	Fixed maturities		$	17		$	33.5		$	27.2
	Equity securities			29.2			59.1			0.4
	Other investments			44.8			38.9			21.5
	Short-term investments			0.1			0.1			0.5
	Other assets			2			—			4.8
	Gain on sale of real estate holdings			43.3			—			—
	Gross realized investment gains and other			136.4			131.6			54.4
	Realized losses
	Fixed maturities			(12.2	)		(19.6	)		(9.1	)
	Equity securities			(0.6	)		(1.4	)		(0.5	)
	Other investments			(21.8	)		(30.8	)		(15.1	)
	Short-term investments			(0.9	)		(0.7	)		(0.3	)
	Other assets			(4.6	)		—			—
	Other-than-temporary impairment losses on fixed			(1.2	)		(6.0	)		(1.5	)
	maturities			(1.2	)		(6.0	)		(1.5	)
	Other-than-temporary impairment losses on equity			(1.1	)		(1.8	)		(2.2	)
	securities			(1.1	)		(1.8	)		(2.2	)
	Gross realized investment and other losses			(42.4	)		(60.3	)		(28.7	)
	Net realized investment gains and other		$	94		$	71.3		$	25.7

Schedule of Realized Gains (Losses) and Changes in Unrealized Appreciation (Depreciation)	Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments are summarized as follows:

	(in millions)		Fixed			Equity			Other			Other			Real Estate Holdings			Tax			Total
	(in millions)		Maturities			Maturities			Investments			Other			Real Estate Holdings			Effects			Total
	Year Ended December 31, 2014
	Realized before impairments		$	4.8		$	28.6		$	23		$	(3.4	)	$	43.3		$	(34.0	)	$	62.3
	Realized - impairments			(1.2	)		(1.1	)		—			—			—			0.8			(1.5	)
	Change in unrealized			(30.5	)		(8.4	)		2.5			—			—			3.1			(33.3	)
	Year Ended December 31, 2013
	Realized before impairments		$	13.9		$	57.7		$	8.1		$	(0.6	)	$	—		$	(26.2	)	$	52.9
	Realized - impairments			(6.0	)		(1.8	)		—			—			—			2.7			(5.1	)
	Change in unrealized			(102.6	)		39.5			4.5			—			—			18.4			(40.2	)
	Year Ended December 31, 2012
	Realized before impairments		$	18.1		$	(0.1	)	$	6.4		$	5		$	—		$	(7.2	)	$	22.2
	Realized - impairments			(1.5	)		(2.2	)		—			—			—			1.3			(2.4	)
	Change in unrealized			39.5			35.9			(2.4	)		—			—			(20.4	)		52.6

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)		31-Dec-14			Level 1 (a)			Level 2 (b)			Level 3 (c)
	Fixed maturities
	USD denominated:
	U.S. Governments		$	185		$	99.2		$	85.8		$	—
	Non-U.S. Governments			79.9			—			79.9			—
	Obligations of states and political subdivisions			490.7			—			490.7			—
	Credit-Financial			518.1			—			518.1			—
	Credit-Industrial			499.6			—			499.6			—
	Credit-Utility			142			—			142			—
	Structured securities:
	CMO/MBS-agency			175.3			—			175.3			—
	CMO/MBS-non agency			14			—			14			—
	CMBS			180			—			180			—
	ABS			221			—			221			—
	Foreign denominated:
	Governments			140.2			—			140.2			—
	Credit			194.9			—			194.9			—
	Total fixed maturities			2,840.70			99.2			2,741.50			—
	Equity securities			486.3			485.4			—			0.9
	Other investments			97.3			—			97.3			—
	Short-term investments			275.8			273.9			1.9			—
	Other assets			—			—			—			—
			$	3,700.10		$	858.5		$	2,840.70		$	0.9

	(a)	Quoted prices in active markets for identical assets
	(b)	Significant other observable inputs
	(c)	Significant unobservable inputs

						Fair Value Measurements at Reporting Date Using
	(in millions)		31-Dec-13			Level 1 (a)			Level 2 (b)			Level 3 (c)
	Fixed maturities
	USD denominated:
	U.S. Governments		$	275.3		$	143.8		$	131.5		$	—
	Non-U.S. Governments			60.2			—			60.2			—
	Obligations of states and political subdivisions			577.8			—			577.8			—
	Credit-Financial			439.9			—			439.9			—
	Credit-Industrial			397.1			—			397.1			—
	Credit-Utility			166.6			—			166.6			—
	Structured securities:
	CMO/MBS-agency			226.9			—			226.9			—
	CMO/MBS-non agency			20.2			—			20.2			—
	CMBS			164.8			—			164.8			—
	ABS			123.8			—			123.8			—
	Foreign denominated:
	Governments			206.7			—			206.7			—
	Credit			155.1			—			155.1			—
	Total fixed maturities			2,814.40			143.8			2,670.60			—
	Equity securities			534.3			476.7			56.3			1.3
	Other investments			117.8			—			117.8			—
	Short-term investments			351.6			347			4.6			—
	Other assets			2.6			—			—			2.6
			$	3,820.70		$	967.5		$	2,849.30		$	3.9

	(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)		Equity			Other			Total
	(in millions)		Securities			Assets			Total
	Beginning balance, January 1, 2014		$	1.3		$	2.6		$	3.9
	Transfers into Level 3			—			—			—
	Transfers out of Level 3			—			—			—
	Total gains or losses (realized/unrealized):
	Included in net income (loss)			—			—			—
	Included in other comprehensive income (loss)			0.1			—			0.1
	Purchases, issuances, sales, and settlements
	Purchases			—			—			—
	Issuances			—			—			—
	Sales			(0.5	)		—			(0.5	)
	Settlements			—			(2.6	)		(2.6	)
	Ending balance, December 31, 2014		$	0.9		$	—		$	0.9
	Amount of total gains or losses for the year included in		$	—		$	—		$	—
	net income (loss) attributable to the change in
	unrealized gains or losses relating to assets still held
	at December 31, 2014

	(in millions)		Equity			Other			Total
	(in millions)		Securities			Assets			Total
	Beginning balance, January 1, 2013		$	1.8		$	6.9		$	8.7
	Transfers into Level 3			—			—			—
	Transfers out of Level 3			—			—			—
	Total gains or losses (realized/unrealized):
	Included in net income (loss)			0.1			—			0.1
	Included in other comprehensive income (loss)			—			—			—
	Purchases, issuances, sales, and settlements
	Purchases			—			—			—
	Issuances			—			—			—
	Sales			(0.6	)		—			(0.6	)
	Settlements			—			(4.3	)		(4.3	)
	Ending balance, December 31, 2013		$	1.3		$	2.6		$	3.9
	Amount of total gains or losses for the year included in		$	—		$	—		$	—
	net income (loss) attributable to the change in
	unrealized gains or losses relating to assets still held
	at December 31, 2013

Reinsurance_Tables

Reinsurance (Tables)	12 Months Ended
Reinsurance (Tables)	Dec. 31, 2014
Insurance [Abstract]
Schedule of Reinsurance Premiums	Premiums were as follows:

		For the Years Ended December 31,
	(in millions)	2014			2013			2012
	Direct written premiums	$	1,585.50		$	1,576.10		$	1,428.60
	Reinsurance ceded to other companies		(537.5	)		(537.1	)		(501.2	)
	Reinsurance assumed from other companies		319.9			312.3			317.1
	Net written premiums	$	1,367.90		$	1,351.30		$	1,244.50
	Direct earned premiums	$	1,551.80		$	1,541.00		$	1,372.20
	Reinsurance ceded to other companies		(524.8	)		(533.7	)		(487.0	)
	Reinsurance assumed from other companies		311.1			296.5			301.3
	Net earned premiums	$	1,338.10		$	1,303.80		$	1,186.50
	Percentage of reinsurance assumed to net earned		23.2	%		22.7	%		25.4	%
	premiums		23.2	%		22.7	%		25.4	%

Reserves_for_Losses_and_Loss_A1

Reserves for Losses and Loss Adjustment Expenses (Tables)	12 Months Ended
	Dec. 31, 2014
Insurance [Abstract]
Reserves for Losses and Loss Adjustment Expenses	The following table provides a reconciliation of reserves for losses and loss adjustment expenses (“LAE”):

			For the Years Ended December 31,
	(in millions)		2014			2013			2012
	Net reserves beginning of the year		$	2,107.60		$	2,110.90		$	2,336.70
	Add:
	Net reserves from assumed retroactive insurance			—			—			13
	contract (1)
	Losses and LAE incurred during current calendar
	year, net of reinsurance:
	Current accident year			785.1			775.6			780.5
	Prior accident years			(37.7	)		(33.6	)		(32.9	)
	Losses and LAE incurred during calendar year, net			747.4			742			747.6
	of reinsurance
	Deduct:
	Net reserves ceded - whole account quota share			—			—			192.2
	reinsurance transaction (2)
	Losses and LAE payments made during current
	calendar year, net of reinsurance:
	Current accident year			185.9			199.3			217.7
	Prior accident years			550.8			554.2			578.8
	Losses and LAE payments made during current			736.7			753.5			796.5
	calendar year, net of reinsurance:
	Change in participation interest (3)			37.8			10.4			(3.1	)
	Foreign exchange adjustments			(19.0	)		(2.2	)		5.4
	Net reserves - end of year			2,137.10			2,107.60			2,110.90
	Add:
	Reinsurance recoverables on unpaid losses and LAE,			905.3			1,122.70			1,112.60
	end of year
	Gross reserves - end of year		$	3,042.40		$	3,230.30		$	3,223.50

	(1)	Amount represents reserves assumed resulting from participation in Brazilian Motor Third-Party Liability Insurance Pool effective January 1, 2012.
	(2)	Amount represents reserves ceded resulting from a whole account quota share reinsurance transaction of 2009 and prior year of account reserves of the syndicate effective December 2012.
	(3)	Amount represents (decrease) increase in reserves due to change in syndicate participation.

Junior_Subordinated_Debentures1

Junior Subordinated Debentures (Tables)

12 Months Ended

Dec. 31, 2014

Debt Disclosure [Abstract]

Schedule of Junior Subordinated Debentures

A summary of our outstanding junior subordinated debentures is presented below:

(in millions)

Issue Date

Trust Preferred Pools

Maturity

Redeemable

Rate Structure

Interest Rate at December 31, 2014

Amount

Argo Group

5/15/03

PXRE Capital Statutory Trust II

5/15/33

5/15/08

3M LIBOR + 4.10%

4.33%

18.1

11/6/03

PXRE Capital Trust VI

9/30/33

9/30/08

3M LIBOR + 3.90%

4.16%

10.3

Argo Group US

5/15/03

Argonaut Group Statutory Trust I

5/15/33

5/15/08

3M LIBOR + 4.10%

4.33%

15.5

12/16/03

Argonaut Group Statutory Trust III

1/8/34

1/8/09

3M LIBOR + 4.10%

4.33%

12.3

4/29/04

Argonaut Group Statutory Trust IV

4/29/34

4/29/09

3M LIBOR + 3.85%

4.08%

13.4

5/26/04

Argonaut Group Statutory Trust V

5/24/34

5/24/09

3M LIBOR + 3.85%

4.08%

12.3

5/12/04

Argonaut Group Statutory Trust VI

5/12/34

6/1/09

3M LIBOR + 3.80%

4.04%

13.4

9/17/04

Argonaut Group Statutory Trust VII

12/15/34

9/17/09

3M LIBOR + 3.60%

3.84%

15.5

9/22/04

Argonaut Group Statutory Trust VIII

9/22/34

9/22/09

3M LIBOR + 3.55%

3.80%

15.5

10/22/04

Argonaut Group Statutory Trust IX

12/15/34

12/15/09

3M LIBOR + 3.60%

3.84%

15.5

9/15/05

Argonaut Group Statutory Trust X

9/15/35

9/15/10

3M LIBOR + 3.40%

3.64%

30.9

Total Outstanding

172.7

(in millions)

Issue Date

Trust Preferred Pools

Maturity

Redeemable

Rate Structure

Interest Rate at December 31, 2013

Amount

Argo Group

5/15/03

PXRE Capital Statutory Trust II

5/15/33

5/15/08

3M LIBOR + 4.10%

4.34%

18.1

10/29/03

PXRE Capital Trust V

10/29/33

10/29/08

3M LIBOR + 3.85%

4.09%

20.6

11/6/03

PXRE Capital Trust VI

9/30/33

9/30/08

3M LIBOR + 3.90%

4.15%

10.3

Argo Group US

5/15/03

Argonaut Group Statutory Trust I

5/15/33

5/15/08

3M LIBOR + 4.10%

4.34%

15.5

12/16/03

Argonaut Group Statutory Trust III

1/8/34

1/8/09

3M LIBOR + 4.10%

4.34%

12.3

4/29/04

Argonaut Group Statutory Trust IV

4/29/34

4/29/09

3M LIBOR + 3.85%

4.09%

13.4

5/26/04

Argonaut Group Statutory Trust V

5/24/34

5/24/09

3M LIBOR + 3.85%

4.09%

12.3

5/12/04

Argonaut Group Statutory Trust VI

5/12/34

6/1/09

3M LIBOR + 3.80%

4.04%

13.4

9/17/04

Argonaut Group Statutory Trust VII

12/15/34

9/17/09

3M LIBOR + 3.60%

3.84%

15.5

9/22/04

Argonaut Group Statutory Trust VIII

9/22/34

9/22/09

3M LIBOR + 3.55%

3.80%

15.5

10/22/04

Argonaut Group Statutory Trust IX

12/15/34

12/15/09

3M LIBOR + 3.60%

3.84%

15.5

9/15/05

Argonaut Group Statutory Trust X

9/15/35

9/15/10

3M LIBOR + 3.40%

3.64%

30.9

Total Outstanding

193.3

Other_Indebtedness_Tables

Other Indebtedness (Tables)

12 Months Ended

Dec. 31, 2014

Debt Disclosure [Abstract]

Schedule of Floating Rate Loan Stock, Notes Outstanding

A summary of the notes outstanding at December 31, 2014 and 2013 is presented below:

(in millions)

Issue Date

Currency

Maturity

Redeemable

Rate Structure

Interest Rate at December 31, 2014

Amount

12/8/04

U.S. Dollar

11/15/34

12/8/09

6 month LIBOR + 4.2%

4.53%

6.5

9/6/05

Euro

8/22/35

9/6/10

3 month LIBOR + 4.0%

4.08%

14.9

10/31/06

U.S. Dollar

1/15/36

1/15/11

6 month LIBOR + 4.0%

4.33%

10/31/06

Euro

11/22/36

10/31/11

3 month LIBOR + 4.0%

4.08%

13.1

6/8/07

Euro

9/15/37

6/8/12

3 month LIBOR + 3.9%

3.98%

16.8

61.3

(in millions)

Issue Date

Currency

Maturity

Redeemable

Rate Structure

Interest Rate at December 31, 2013

Amount

12/8/04

U.S. Dollar

11/15/34

12/8/09

6 month LIBOR + 4.2%

4.60%

6.5

9/6/05

Euro

8/22/35

9/6/10

3 month LIBOR + 4.0%

4.22%

16.3

10/31/06

U.S. Dollar

1/15/36

1/15/11

6 month LIBOR + 4.0%

4.40%

10/31/06

Euro

11/22/36

10/31/11

3 month LIBOR + 4.0%

4.22%

14.3

6/8/07

Euro

9/15/37

6/8/12

3 month LIBOR + 3.9%

4.12%

18.4

65.5

Disclosures_about_Fair_Value_o1

Disclosures about Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2014
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:

		31-Dec-14				31-Dec-13
	(in millions)	Carrying		Fair		Carrying		Fair
	(in millions)	Amount		Value		Amount		Value
	Junior subordinated debentures	$	172.7	$	155.5	$	193.3	$	155.5
	Senior unsecured fixed rate notes		143.8		132.3		143.8		116.2
	Other indebtedness:
	Floating rate loan stock		61.3		55.2		65.5		52.7
	Note payable		0.7		0.6		0.8		0.6
		$	378.5	$	343.6	$	403.4	$	325

Shareholders_Equity_Tables

Shareholders' Equity (Tables)	12 Months Ended
Shareholders' Equity (Tables)	Dec. 31, 2014
Equity [Abstract]
Schedule of Repurchase of Shares	In 2014, we repurchased shares under Securities Exchange Act of 1934 Rule 10b5-1 trading plans as follows:

	Date	2014		Number of		Average Price		Total Cost		Repurchase
	Trading Plan	Purchase		Shares		of Shares		(in millions)		Authorization
	Initiated	Period		Repurchased		Repurchased				Year
	12/17/13	02/04/14-02/12/14			15,789	$	43.28	$	0.7	2013
	3/18/14	03/18/14-04/28/14			436,867	$	45.81	$	20	2013
	6/13/14	06/17/14-07/04/14			41,362	$	49.94	$	2.1	2013
	9/12/14	09/16/14-10/28/14			229,633	$	51.98	$	11.9	2013
	12/15/14	12/16/14-12/23/14			22,735	$	53.44	$	1.2	2013

Schedule of Authorized and Unissued Common Shares Reserved	At December 31, 2014, we had the following authorized, unissued common shares reserved for future issuance:

	Reserve Name	Shares Reserved
	2014 Long-Term Incentive Plan		4,130,532
	2007 Employee Share Purchase Plan		1,600,886
	Historical stock compensation plans		3,968
	Total		5,735,386

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Changes in Accumulated Other Comprehensive Income (Loss)	A summary of changes in accumulated other comprehensive income (loss), net of taxes (where applicable) by component is presented below:

	(in millions)	Foreign Currency Translation Adjustments			Unrealized			Defined Benefit Pension Plans			Total
					Holding Gains
					on Securities
	Balance, January 1, 2013	$	(8.7	)	$	204.1		$	(5.9	)	$	189.5
	Other comprehensive (loss) income before		(2.8	)		0.2			1.3			(1.3	)
	reclassifications
	Amounts reclassified from accumulated other		—			(40.4	)		—			(40.4	)
	comprehensive income (loss)
	Net current-period other comprehensive (loss)		(2.8	)		(40.2	)		1.3			(41.7	)
	income
	Balance, December 31, 2013		(11.5	)		163.9			(4.6	)		147.8
	Other comprehensive loss before		(4.1	)		(12.5	)		(2.4	)		(19.0	)
	reclassifications
	Amounts reclassified from accumulated other		—			(20.7	)		—			(20.7	)
	comprehensive loss
	Net current-period other comprehensive loss		(4.1	)		(33.2	)		(2.4	)		(39.7	)
	Balance, December 31, 2014	$	(15.6	)	$	130.7		$	(7.0	)	$	108.1

Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	The amounts reclassified from accumulated other comprehensive income (loss) shown in the above table have been included in the following captions in our Consolidated Statements of Income:

		For the Years Ended December 31,
	(in millions)	2014			2013			2012
	Unrealized gains and losses on securities:
	Net realized investment gains	$	(30.6	)	$	(59.8	)	$	(14.4	)
	Provision for income taxes		9.9			19.4			4
	Net of taxes	$	(20.7	)	$	(40.4	)	$	(10.4	)

Net_Income_Per_Common_Share_Ta

Net Income Per Common Share (Tables)	12 Months Ended
Net Income Per Common Share (Tables)	Dec. 31, 2014
Earnings Per Share [Abstract]
Net Income Per Common Share on Basic and Diluted Basis	The following table presents the calculation of net income per common share on a basic and diluted basis:

		For the Years Ended December 31,
	(in millions, except number of shares and per share amounts)	2014		2013		2012
	Net income	$	183.2	$	143.2	$	52.3
	Weighted average common shares outstanding - basic		26,082,114		26,851,341		28,095,210
	Effect of dilutive securities:
	Equity compensation awards		475,037		1,018,192		555,238
	Weighted average common shares outstanding - diluted		26,557,151		27,869,533		28,650,448
	Net income per common share:
	Basic	$	7.02	$	5.33	$	1.86
	Diluted	$	6.9	$	5.14	$	1.83

Sharebased_Compensation_Tables

Share-based Compensation (Tables)	12 Months Ended
Share-based Compensation (Tables)	Dec. 31, 2014
Fair Value Assumptions	The following table summarizes the assumptions we used:

		For the Years Ended December 31,
		2014		2013	2012
	Risk-free rate of return	1.53% to 1.77%		0.80% to 1.71%	0.68% to 1.11%
	Expected dividend yields	1.49% to 1.55%		1.49% to 1.67%	1.58% to 1.67%
	Expected award life (years)	4.67 to 4.85		4.91 to 5.07	5.03 to 5.06
	Expected volatility	22.84% to 25.46%		26.30% to 32.07%	32.12% to 32.84%

2014 Plan [Member]
Summary of Option Activity	A summary of option activity as of December 31, 2014 and changes during the year then ended is as follows:

		Shares			Weighted-Average		Weighted-Average	Aggregate
					Exercise Price		Remaining	Intrinsic
							Contractual Term	Value
	Outstanding at January 1, 2014		158,092		$	34.27
	Granted		—		$	—
	Exercised		(108,184	)	$	34.38
	Expired or forfeited		(1,773	)	$	32.03
	Outstanding at December 31, 2014		48,135		$	34.11	0.3	$	1,028,247
	Vested and exercisable at end of year		48,135		$	34.11	0.3	$	1,028,247

Summary of Restricted Share Activity	A summary of restricted share activity as of December 31, 2014 and changes during the year then ended is as follows:

		Shares			Weighted-Average
					Grant Date
					Fair Value
	Outstanding at January 1, 2014		257,975		$	32.97
	Granted		123,229		$	45.61
	Vested and issued		(60,198	)	$	31.65
	Expired or forfeited		(35,511	)	$	33.08
	Outstanding at December 31, 2014		285,495		$	38.69

2014 Plan [Member] \| Stock-Settled SARs Activity [Member]
Summary of Stock-Settled SARs Activity	A summary of stock-settled SARs activity as of December 31, 2014 and changes during the year then ended is as follows:

		Shares			Weighted-Average
		Shares			Exercise Price
	Outstanding at January 1, 2014		1,288,698		$	29.46
	Granted		188,273		$	43.23
	Exercised		(124,541	)	$	28.93
	Expired or forfeited		(155,909	)	$	32.72
	Outstanding at December 31, 2014		1,196,521		$	31.26
	Vested or expected to vest as of end of year		1,102,211		$	30.81
	Exercisable at end of year		763,302		$	28.27

2014 Plan [Member] \| Cash-Settled SARs Activity [Member]
Summary of Stock-Settled SARs Activity	A summary of cash-settled SARs activity as of December 31, 2014 and changes during the year then ended is as follows:

		Shares			Weighted-Average
		Shares			Exercise Price
	Outstanding at January 1, 2014		1,743,758		$	33
	Granted		756,853		$	44.28
	Exercised		(446,209	)	$	30.96
	Expired or forfeited		(230,633	)	$	36.15
	Outstanding at December 31, 2014		1,823,769		$	37.78
	Vested or expected to vest as of end of year		1,518,831		$	37.42
	Exercisable at end of year		421,995		$	31.79

Underwriting_Acquisition_and_I1

Underwriting, Acquisition and Insurance Expenses (Tables)	12 Months Ended
Underwriting, Acquisition and Insurance Expenses (Tables)	Dec. 31, 2014
Text Block [Abstract]
Underwriting, Acquisition and Insurance Expenses	Underwriting, acquisition and insurance expenses were as follows:

		For the Years Ended December 31,
	(in millions)	2014			2013			2012
	Commissions	$	231.1		$	229.6		$	198.2
	General expenses		288			272.8			248
	Premium taxes, boards and bureaus		25.5			24.2			22.8
			544.6			526.6			469
	Net deferral of policy acquisition costs		(5.4	)		(15.8	)		(4.5	)
	Total underwriting, acquisition and insurance expenses	$	539.2		$	510.8		$	464.5

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
Income Taxes (Tables)	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Tax Provision (Benefit)	Our income tax provision includes the following components:

			For the Years Ended December 31,
	(in millions)		2014				2013			2012
	Current tax provision		$	5.2			$	32.7		$	9.4
	Deferred tax provision related to:
	Future tax deductions			58.4				0.1			2.9
	Valuation allowance change			(30.8	)			3.7			2.1
	Income tax provision		$	32.8			$	36.5		$	14.4

Schedule of Pre-Tax Income (Loss) and Effective Income Tax Rates	For the years ended December 31, 2014, 2013 and 2012, pre-tax income (loss) attributable to our operations and the operations’ effective tax rates were as follows:

	(in millions)		2014							2013							2012
			Pre-Tax				Effective			Pre-Tax				Effective			Pre-Tax				Effective
			Income (Loss)				Tax			Income (Loss)				Tax			Income (Loss)				Tax
							Rate							Rate							Rate
	Bermuda		$	102.8				0	%	$	50.5				0	%	$	10				0	%
	United States			98				28.1	%		120.9				28.2	%		52				21.3	%
	United Kingdom			21.5				24.8	%		18.5				12	%		14				24.4	%
	Belgium			—		-1		63.8	%		0.2				103	%		(0.1	)			98.4	%
	Brazil			(2.2	)			0	%		(9.7	)			0	%		(6.5	)			0	%
	United Arab Emirates			(0.9	)			0	%		1.1				0	%		—		-1		0	%
	Ireland			(1.1	)			0	%		(0.1	)			0	%		(0.2	)			0	%
	Malta			(2.2	)			0	%		(1.7	)			0	%		(2.6	)			0	%
	France			—				0	%		—				0	%		—				0	%
	Switzerland			0.1				17.6	%		—		-1		5.6	%		0.1				22.8	%
	Pre-tax income		$	216						$	179.7						$	66.7

	(1)	Pre-tax income 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 Years Ended December 31,
	(in millions)		2014				2013			2012
	Income tax provision at expected rate		$	37.2			$	43.1		$	18.5
	Tax effect of:
	Tax-exempt interest			(4.5	)			(5.6	)		(5.6	)
	Dividends received deduction			(2.3	)			(2.3	)		(2.2	)
	Valuation allowance change			(30.8	)			3.7			2.1
	Other permanent adjustments, net			(0.7	)			0.3			1.8
	Adjustment for prior year tax return			(0.9	)			(1.6	)		0.2
	Prior period adjustment for deferred			1.5				—			—
	United States state tax expense (benefit)			2.5				0.3			(0.3	)
	PXRE Reinsurance capital loss carryforward			29.8				—			—
	Other foreign adjustments			0.7				(0.1	)		—
	Prior year foreign taxes			0.1				1.1			—
	Deferred tax rate reduction			(0.4	)			(1.2	)		(0.6	)
	Foreign exchange adjustments			0.2				(1.7	)		0.5
	Foreign withholding taxes			0.4				0.5			—
	Income tax provision		$	32.8			$	36.5		$	14.4
	Income tax provision - Foreign		$	5.2			$	2.4		$	3.3
	Income tax provision - United States, Federal			23.3				33.2			11.5
	Income tax provision (benefit) - United States, state			3.9				0.4			(0.4	)
	Foreign withholding tax - United States			0.4				0.5			—
	Income tax provision		$	32.8			$	36.5		$	14.4

Schedule of Deferred Tax Assets and Liabilities
			December 31,
	(in millions)		2014				2013
	Deferred tax assets:
	Unrealized losses on fixed maturities and other investment securities		$	—			$	—
	Losses and loss adjustment expense reserve discounting			25.1				28.4
	Unearned premiums			24.8				23
	Capital loss carryforward			—				29.8
	Allowance for bad debt			2				1.9
	Accrual for contingent commissions			0.3				0.4
	Net operating loss carryforward			18.8				19.8
	Impairment of investment values			8.2				10.6
	United States amortization of intangible assets			4.3				3.1
	Accrued bonus			6.7				5.7
	Accrued vacation			1.7				1.6
	Stock option expense			8				6.4
	United Kingdom interest			—				0.8
	Brazil operating losses			7.4				8
	Malta operating losses			2.1				1.7
	Depreciable fixed asset			5.2				—
	Other			7				9.1
	Deferred tax assets, gross			121.6				150.3
	Deferred tax liabilities:
	Unrealized gains on equity securities			(62.3	)			(65.1	)
	Unrealized gains on fixed maturities and other investment securities			(15.3	)			(16.1	)
	Deferred acquisition costs			(20.3	)			(19.5	)
	United States amortization of intangible assets			(3.5	)			(3.3	)
	United Kingdom underwriting losses			(9.0	)			(4.8	)
	United Kingdom amortization of intangible assets			(2.3	)			(2.8	)
	Brussels pension			(0.1	)			(0.2	)
	Internally developed software			(21.5	)			—
	Unrealized FV gain on LP			(10.5	)			(9.2	)
	Other			(4.4	)			(1.8	)
	Deferred tax liabilities, gross			(149.2	)			(122.8	)
	Deferred tax assets, net before valuation allowance			(27.6	)			27.5
	Valuation allowance			(25.4	)			(56.2	)
	Deferred tax liabilities, net		$	(53.0	)		$	(28.7	)
	Net deferred tax liabilities - Foreign		$	(11.8	)		$	(7.0	)
	Net deferred tax liabilities - United States			(41.2	)			(21.7	)
	Deferred tax liabilities, net		$	(53.0	)		$	(28.7	)

Pension_Benefits_Tables

Pension Benefits (Tables)	12 Months Ended
Pension Benefits (Tables)	Dec. 31, 2014
Compensation And Retirement Disclosure [Abstract]
Schedule of Change in Plan Assets	The assets and liabilities of the plans were measured as of December 31 of the respective years presented.

	(in millions)		2014			2013
	Change in plan assets
	Fair value of plan assets at beginning of year		$	20.2		$	20.1
	Actual return on plan assets			1			1.9
	Employer contributions			0.2			0.2
	Settlements and benefits paid			(2.2	)		(2.0	)
	Fair value of plan assets at end of year		$	19.2		$	20.2

Schedule of Change in Projected Benefit Obligation
	(in millions)		2014			2013
	Change in projected benefit obligation
	Projected benefit obligation at beginning of year		$	22.6		$	24.6
	Interest cost			1			0.8
	Actuarial loss (gain)			4.3			(0.8	)
	Settlements and benefits paid			(2.1	)		(2.0	)
	Projected benefit obligation at end of year		$	25.8		$	22.6

Schedule of Assumptions to Determine Benefit Obligations	Assumptions used to determine benefit obligations at December 31 were as follows:

			2014			2013
	Weighted average discount rate			3.37%			4.42%
	Expected rate of increase in future compensation levels		n/a			n/a

Schedule of Assumptions to Determine Net Periodic Benefit Cost	Assumptions used to determine net periodic benefit cost follows:

			For the Years Ended December 31,
			2014			2013			2012
	Weighted average discount rate			4.39%			3.63%			4.50%
	Expected return on plan assets			6.00%			6.00%			6.00%
	Expected rate of increase in future compensation levels		n/a			n/a			n/a

Components of Net Periodic Benefit Cost	Components of net periodic benefit cost follows:

			For the Years Ended December 31,
	(in millions)		2014			2013			2012
	Interest cost		$	1		$	0.8		$	1
	Expected return on plan assets			(1.2	)		(1.0	)		(1.1	)
	Settlement charge			0.4			—			—
	Amortization of actuarial loss			0.3			0.3			0.3
	Net periodic benefit cost		$	0.5		$	0.1		$	0.2

Schedule of Fair Value Measurement	The fair values of the plan assets by asset category are as follows:

	(in millions)					Fair Value Measurements
	(in millions)					at Reporting Date Using
			31-Dec-14			Level 1 (a)			Level 2 (b)			Level 3 (c)
	Equity Securities:
	Mutual Funds:
	Large cap U.S. equity		$	2.9		$	2.9		$	—		$	—
	Small-mid cap U.S. equity			1.2			1.2			—			—
	International equity			1.5			1.5			—			—
	Real estate			0.6			0.6			—			—
	U.S. and global government and corporate fixed maturity			12.6			12.6			—			—
	Cash and short-term investments:
	Short-term investment fund (1)			0.4			—			0.4			—
	Total		$	19.2		$	18.8		$	0.4		$	—

	(a)	Quoted prices in active markets for identical assets
	(b)	Significant other observable inputs
	(c)	Significant unobservable inputs
	(1)	Assets invested in one common collective trust composed of high-grade money market money instruments with short maturities.

	(in millions)					Fair Value Measurements
	(in millions)					at Reporting Date Using
			December 31, 2013			Level 1 (a)			Level 2 (b)			Level 3 (c)
	Equity Securities:
	Mutual Funds:
	Large cap U.S. equity		$	3.2		$	3.2		$	—		$	—
	Small-mid cap U.S. equity			1.4			1.4			—			—
	International equity			1.5			1.5			—			—
	Real estate			0.5			0.5			—			—
	Convertible bonds and equities			0.2			0.2			—			—
	U.S. and global government and corporate fixed maturity			12.9			12.9			—			—
	Cash and short-term investments:
	Short-term investment fund (1)			0.5			—			0.5			—
	Total		$	20.2		$	19.7		$	0.5		$	—

	(a)	Quoted prices in active markets for identical assets
	(b)	Significant other observable inputs
	(c)	Significant unobservable inputs
	(1)	Assets invested in one common collective trust composed of high-grade money market money instruments with short maturities.
Schedule of Expected Benefit Payments	We expect to make the following benefit payments:

	(in millions)		Pension
	(in millions)		Benefits
	2015		$	1.7
	2016			1.6
	2017			1.9
	2018			1.7
	2019			1.8
	Years 2020 to 2024			7.9
	Total		$	16.6

Leases_Tables

Leases (Tables)	12 Months Ended
Leases (Tables)	Dec. 31, 2014
Leases [Abstract]
Schedule of Future Minimum Payments Under Non-Cancelable Operating Leases	At December 31, 2014, the future minimum payments under non-cancelable operating leases are as follows:

	(in millions)	Amount Due
	2015	$	11.2
	2016		9.1
	2017		8.1
	2018		7.8
	2019		6.1
	Thereafter		9.4
	Total	$	51.7

Segment_Information_Tables

Segment Information (Tables)	12 Months Ended
Segment Information (Tables)	Dec. 31, 2014
Segment Reporting [Abstract]
Revenue and Income (Loss) Before Income Taxes for Each Segment	Revenue and income (loss) before income taxes for each segment were as follows:

		For the Years Ended December 31,
	(in millions)	2014			2013			2012
	Revenue:
	Earned premiums
	Excess and Surplus Lines	$	485.2		$	460.2		$	399.3
	Commercial Specialty		291.9			299			317.5
	International Specialty		148.3			142.4			130.1
	Syndicate 1200		411.1			401.7			337.9
	Run-off Lines		1.6			0.5			1.7
	Total earned premiums		1,338.10			1,303.80			1,186.50
	Net investment income
	Excess and Surplus Lines		36.7			42.2			51.1
	Commercial Specialty		18.7			22.8			27.6
	International Specialty		8.2			8.4			12.3
	Syndicate 1200		10.2			11			15.3
	Run-off Lines		9.7			10.8			12.5
	Corporate and Other		3.1			4.8			-
	Total net investment income		86.6			100			118.8
	Net realized investment and other gains		94			71.3			25.7
	Total revenue	$	1,518.70		$	1,475.10		$	1,331.00

		For the Years Ended December 31,
	(in millions)	2014			2013			2012
	Income (loss) before income taxes
	Excess and Surplus Lines	$	106		$	89.4		$	74.1
	Commercial Specialty		8.9			21.4			(24.8	)
	International Specialty		21.1			11.3			11.3
	Syndicate 1200		44.1			37.3			28.1
	Run-off Lines		(23.0	)		(10.6	)		(0.9	)
	Total segment income before taxes		157.1			148.8			87.8
	Corporate and Other		(35.1	)		(40.4	)		(46.8	)
	Net realized investment and other gains		94			71.3			25.7
	Total income before income taxes	$	216		$	179.7		$	66.7

Schedule of Earned Premiums by Geographic Location	The table below presents earned premiums by geographic location. For this disclosure, we determine geographic location by the country of domicile of our subsidiaries that underwrite the business and not by the location of insureds or reinsureds from whom the business was generated.

		For the Years Ended December 31,
	(in millions)	2014			2013			2012
	Bermuda	$	101.5		$	101.7		$	120.4
	Brazil		44.3			38.7			26.6
	Malta		2.1			1.8			0.3
	United Kingdom		411.7			401.7			320.8
	United States		778.5			759.9			718.4
	Total earned premiums	$	1,338.10		$	1,303.80		$	1,186.50

Identifiable Assets	The following table represents identifiable assets:

		December 31,
	(in millions)	2014			2013
	Excess and Surplus Lines	$	2,350.70		$	2,252.20
	Commercial Specialty		1,358.50			1,333.40
	International Specialty		776.8			743.6
	Syndicate 1200		1,258.50			1,638.80
	Run-off Lines		552.8			555.9
	Corporate and Other		59			67.1
	Total	$	6,356.30		$	6,591.00

Schedule of Goodwill and Intangible Assets Net of Accumulated Amortization	The following table represents goodwill and intangible assets, net of accumulated amortization as of December 31:

		Goodwill						Intangible Assets, Net of
		Goodwill						Accumulated Amortization
	(in millions)	2014			2013			2014			2013
	Excess and Surplus Lines	$	76.4		$	76.4		$	2.8		$	3.4
	Commercial Specialty		47.1			48.7			5.5			9
	Syndicate 1200		28.7			28.7			70.3			73.6
	Total	$	152.2		$	153.8		$	78.6		$	86

Runoff_Lines_Tables

Run-off Lines (Tables)	12 Months Ended
Run-off Lines (Tables)	Dec. 31, 2014
Gross Reserves for Run-Off Lines	The following table presents our gross reserves for Run-off Lines as of December 31:

		December 31,
	(in millions)	2014			2013
	Asbestos and Environmental:
	Reinsurance assumed	$	40.1		$	45.2
	Other		13.8			12.3
	Total Asbestos and Environmental		53.9			57.5
	Risk management		257.1			264.3
	Run-off reinsurance lines		4.1			5.8
	Other run-off lines		3.4			4.9
	Total Run-off Lines	$	318.5		$	332.5

Total Gross Reserves for Asbestos Exposure	The following table represents the total gross reserves for our asbestos exposure:

		December 31,
	(in millions)	2014			2013			2012
	Direct written
	Case reserves	$	2.5		$	1.7		$	2
	Unallocated loss adjustment expense ("ULAE")		1			1.3			1.7
	Incurred but not reported ("IBNR")		7.6			6.4			4.3
	Total direct written reserves		11.1			9.4			8
	Assumed domestic
	Case reserves		13.2			15.7			18.4
	ULAE		1.6			2.2			2.7
	IBNR		15.8			15.8			17.4
	Total assumed domestic reserves		30.6			33.7			38.5
	Assumed London
	Case reserves		4.7			5.8			5.9
	ULAE		0.2			0.4			0.6
	IBNR		1.2			1.4			2.5
	Total assumed London reserves		6.1			7.6			9
	Total asbestos reserves	$	47.8		$	50.7		$	55.5

Run Off Lines
Net Under writing Results for Run-Off Lines	The following table presents our net underwriting results for Run-off Lines:

		For the Years Ended December 31,
	(in millions)	2014			2013			2012
	Asbestos and Environmental:
	Reinsurance assumed	$	(8.3	)	$	(3.8	)	$	(3.6	)
	Other		(5.0	)		(7.2	)		(5.5	)
	Total Asbestos and Environmental		(13.3	)		(11.0	)		(9.1	)
	Risk management		(15.5	)		(5.9	)		0.9
	Run-off reinsurance lines		(1.5	)		(1.9	)		(1.1	)
	Other run-off lines		(0.7	)		(0.8	)		(1.6	)
	Total Run-off Lines	$	(31.0	)	$	(19.6	)	$	(10.9	)

Statutory_Accounting_Principle1

Statutory Accounting Principles (Tables)	12 Months Ended
Statutory Accounting Principles (Tables)	Dec. 31, 2014
Statutory Accounting Principles [Abstract]
Statutory Capital and Surplus for Principal Operating Subsidiaries	The statutory capital and surplus for our principal operating subsidiaries was as follows:

	Statutory capital and surplus (1)		December 31,
	(in millions)		2014		2013
	Bermuda		$	1,278.30	$	1,218.20
	United Kingdom (2)			224.5		225.8
	United States			790.4		822.3

	(1)	Such amounts include ownership interests in affiliate insurance and reinsurance subsidiaries.
	(2)	Capital on deposit with Lloyd’s in U.S. Dollars
Statutory Net Income (Loss) for Principal Operating Subsidiaries	The statutory net income (loss) for our principal operating subsidiaries was as follows:

	Statutory net income (loss) (1)		For the Years Ended December 31,
	(in millions)		2014		2013		2012
	Bermuda		$	145.7	$	124.2	$	(4.2	)
	United Kingdom (2)			28.7		42.3		40.7
	United States			117.7		117.4		42.9

	(1)	Such amounts include ownership interests in affiliate insurance and reinsurance subsidiaries.
	(2)	In U.S. Dollars

Unaudited_Quarterly_Financial_1

Unaudited Quarterly Financial Data (Tables)	12 Months Ended
Unaudited Quarterly Financial Data (Tables)	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data	(in millions, except per share amounts)		1st Quarter		2nd Quarter			3rd Quarter		4th Quarter		Year
	2014
	Total revenue		$	360.1	$	375.2		$	371.3	$	412.1	$	1,518.70
	Net income before income taxes			42.7		44.7			48.3		80.3		216
	Net income			40.2		38.6			44.7		59.7		183.2
	Net income per common share :
	Basic*		$	1.52	$	1.48		$	1.72	$	2.32	$	7.02
	Diluted*		$	1.49	$	1.45		$	1.69	$	2.28	$	6.9
	Comprehensive income		$	41.3	$	64.1		$	6.8	$	31.3	$	143.5

	(in millions, except per share amounts)		1st Quarter		2nd Quarter			3rd Quarter		4th Quarter		Year
	2013
	Total revenue		$	341.6	$	363.8		$	363.7	$	406	$	1,475.10
	Net income before income taxes			37.5		42.8			32.9		66.5		179.7
	Net income			32.7		31.7			31		47.8		143.2
	Net income per common share :
	Basic*		$	1.2	$	1.18		$	1.17	$	1.8	$	5.33
	Diluted*		$	1.16	$	1.13		$	1.12	$	1.74	$	5.14
	Comprehensive income (loss)		$	45.7	$	(35.2	)	$	47.2	$	43.8	$	101.5

	*	Basic and diluted net income per common share are computed independently for each quarter and full year based on the respective average number of common shares outstanding; therefore, the sum of the quarterly net income per common share data may not equal the net income per common share for the year.

Information_Provided_in_Connec1

Information Provided in Connection with Outstanding Debt of Subsidiaries (Tables)	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Condensed Consolidating Balance Sheet	CONDENSED CONSOLIDATING BALANCE SHEET
	31-Dec-14
	(in millions)

			Argo Group				Argo Group US, Inc.				Other Subsidiaries				Consolidating				Total
			International				and Subsidiaries				and Eliminations (1)				Adjustments (2)
			Holdings, Ltd				(Subsidiary Issuer)
			(Parent Guarantor)
	Assets
	Investments		$	0.7			$	2,841.50			$	1,255.70			$	—			$	4,097.90
	Cash			—				49.3				31.7				—				81
	Accrued investment income			—				17.8				4.3				—				22.1
	Premiums receivable			—				154.6				199				—				353.6
	Reinsurance recoverables			—				1,173.60				(176.4	)			—				997.2
	Goodwill and other intangible assets, net			—				131.7				99.1				—				230.8
	Current income taxes receivable, net			—				10.1				4.8				—				14.9
	Deferred acquisition costs, net			—				58				66.6				—				124.6
	Ceded unearned premiums			—				98.5				109.1				—				207.6
	Other assets			9.6				174.1				67.9				(25.0	)			226.6
	Due from (to) affiliates			2.9				(19.8	)			19.8				(2.9	)			—
	Intercompany note receivable			—				72				(72.0	)			—				—
	Investments in subsidiaries			1,698.00				—				—				(1,698.0	)			—
	Total assets		$	1,711.20			$	4,761.40			$	1,609.60			$	(1,725.9	)		$	6,356.30
	Liabilities and Shareholders' Equity
	Reserves for losses and loss adjustment		$	—			$	2,136.40			$	906			$	—			$	3,042.40
	expenses		$	—			$	2,136.40			$	906			$	—			$	3,042.40
	Unearned premiums			—				448.9				368.3				—				817.2
	Funds held and ceded reinsurance payable,			—				675.1				(441.3	)			—				233.8
	net			—				675.1				(441.3	)			—				233.8
	Long-term debt			49				288.7				61.4				(20.6	)			378.5
	Deferred tax liabilities, net			—				41.2				11.8				—				53
	Accrued underwriting expenses and other liabilities			15.5				104.2				65				—				184.7
	Total liabilities			64.5				3,694.50				971.2				(20.6	)			4,709.60
	Total shareholders' equity			1,646.70				1,066.90				638.4				(1,705.3	)			1,646.70
	Total liabilities and shareholders' equity		$	1,711.20			$	4,761.40			$	1,609.60			$	(1,725.9	)		$	6,356.30

	(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
	31-Dec-13
	(in millions)

			Argo Group				Argo Group US, Inc.				Other Subsidiaries				Consolidating				Total
			International				and Subsidiaries				and Eliminations (1)				Adjustments (2)
			Holdings, Ltd				(Subsidiary Issuer)
			(Parent Guarantor)
	Assets
	Investments		$	1.1			$	2,785.10			$	1,293.00			$	—			$	4,079.20
	Cash			—				132.1				25.3				—				157.4
	Accrued investment income			—				19.7				6				—				25.7
	Premiums receivable			—				150.8				197.6				—				348.4
	Reinsurance recoverables			—				1,145.90				117.6				—				1,263.50
	Goodwill and other intangible assets, net			—				137.4				102.4				—				239.8
	Current income taxes receivable, net			—				0.5				(0.5	)			—				—
	Deferred acquisition costs, net			—				55.6				58.3				—				113.9
	Ceded unearned premiums			—				88.2				108.1				—				196.3
	Other assets			4.6				97.8				64.4				—				166.8
	Due from affiliates			3.1				1.5				(1.5	)			(3.1	)			—
	Intercompany note receivable			—				87.4				(87.4	)			—				—
	Investments in subsidiaries			1,625.20				—				—				(1,625.2	)			—
	Total assets		$	1,634.00			$	4,702.00			$	1,883.30			$	(1,628.3	)		$	6,591.00
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment		$	—			$	2,157.00			$	1,073.30			$	—			$	3,230.30
expenses		$	—			$	2,157.00			$	1,073.30			$	—			$	3,230.30
Unearned premiums			—				425.5				353.6				—				779.1
Funds held and ceded reinsurance payable, net			—				642.4				(244.0	)			—				398.4
Long-term debt			49				288.9				65.5				—				403.4
Current income taxes payable, net			—				8.9				(3.7	)			—				5.2
Deferred tax liabilities, net			—				22.8				5.9				—				28.7
Accrued underwriting expenses and other			15.4				98.2				69.3				—				182.9
liabilities			15.4				98.2				69.3				—				182.9
Intercompany note payable			6.6				—				—				(6.6	)			—
Total liabilities			71				3,643.70				1,319.90				(6.6	)			5,028.00
Total shareholders' equity			1,563.00				1,058.30				563.4				(1,621.7	)			1,563.00
Total liabilities and shareholders' equity		$	1,634.00			$	4,702.00			$	1,883.30			$	(1,628.3	)		$	6,591.00

(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 INCOME
	FOR THE YEAR ENDED DECEMBER 31, 2014
	(in millions)

			Argo Group				Argo Group US, Inc.				Other Subsidiaries				Consolidating				Total
			International				and Subsidiaries				and Eliminations (1)				Adjustments (2)
			Holdings, Ltd				(Subsidiary Issuer)
			(Parent Guarantor)
	Premiums and other revenue:
	Earned premiums		$	—			$	461			$	877.1			$	—			$	1,338.10
	Net investment income (expense)			40.5				56.7				(10.6	)			—				86.6
	Net realized investment gains and			2				86.9				7.1				(2.0	)			94
	other			2				86.9				7.1				(2.0	)			94
	Total revenue			42.5				604.6				873.6				(2.0	)			1,518.70
	Expenses:
	Losses and loss adjustment expenses			—				285.6				461.8				—				747.4
	Underwriting, acquisition and insurance			17.3				199.9				322				—				539.2
	expenses			17.3				199.9				322				—				539.2
	Interest expense			2.3				15.2				2.7				(0.3	)			19.9
	Fee expense (income), net			—				2.4				(1.8	)			—				0.6
	Foreign currency exchange loss (gain)			—				0.4				(8.2	)			—				(7.8	)
	Impairment of intangible assets			—				3.4				—				—				3.4
	Total expenses			19.6				506.9				776.5				(0.3	)			1,302.70
	Income before income taxes			22.9				97.7				97.1				(1.7	)			216
	Provision for income taxes			—				27.5				5.3				—				32.8
	Net income before equity in earnings of			22.9				70.2				91.8				(1.7	)			183.2
	subsidiaries			22.9				70.2				91.8				(1.7	)			183.2
	Equity in undistributed earnings of			160.3				—				—				(160.3	)			—
	subsidiaries			160.3				—				—				(160.3	)			—
	Net income		$	183.2			$	70.2			$	91.8			$	(162.0	)		$	183.2

	(1)	Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations.
	(2)	Includes all Argo Group parent company eliminations.



	CONDENSED CONSOLIDATING STATEMENT OF INCOME
	FOR THE YEAR ENDED DECEMBER 31, 2013
	(in millions)

			Argo Group				Argo Group US, Inc.				Other Subsidiaries				Consolidating				Total
			International				and Subsidiaries				and Eliminations (1)				Adjustments (2)
			Holdings, Ltd				(Subsidiary Issuer)
			(Parent Guarantor)
	Premiums and other revenue:
	Earned premiums		$	—			$	439.9			$	863.9			$	—			$	1,303.80
	Net investment income (expense)			84.5				73.4				(57.9	)			—				100
	Net realized investment gains (losses) and			—				72.2				(0.9	)			—				71.3
	other			—				72.2				(0.9	)			—				71.3
	Total revenue			84.5				585.5				805.1				—				1,475.10
	Expenses:
	Losses and loss adjustment expenses			—				268.6				473.4				—				742
	Other reinsurance-related expenses			—				—				19.2				—				19.2
	Underwriting, acquisition and insurance			27.4				176.9				306.5				—				510.8
	expenses			27.4				176.9				306.5				—				510.8
	Interest expense			3.3				15.2				2.9				(1.2	)			20.2
	Fee expense, net			-				4.1				0.8				-				4.9
	Foreign currency exchange gain			—				(0.3	)			(1.4	)			—				(1.7	)
	Total expenses			30.7				464.5				801.4				(1.2	)			1,295.40
	Income before income taxes			53.8				121				3.7				1.2				179.7
	Provision for income taxes			—				34.1				2.4				—				36.5
	Net income before equity in earnings of			53.8				86.9				1.3				1.2				143.2
	subsidiaries			53.8				86.9				1.3				1.2				143.2
	Equity in undistributed earnings of			89.4				—				—				(89.4	)			—
subsidiaries				89.4				—				—				(89.4	)			—
Net income		$	143.2			$	86.9			$	1.3			$	(88.2	)		$	143.2

(1)	Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations.
(2)	Includes all Argo Group parent company eliminations.



CONDENSED CONSOLIDATING STATEMENT OF INCOME
FOR THE YEAR ENDED DECEMBER 31, 2012
(in millions)

		Argo Group				Argo Group US, Inc.				Other Subsidiaries				Consolidating				Total
		International				and Subsidiaries				and Eliminations (1)				Adjustments (2)
		Holdings, Ltd				(Subsidiary Issuer)
		(Parent Guarantor)
Premiums and other revenue:
Earned premiums		$	—			$	434.2			$	752.3			$	—			$	1,186.50
Net investment income			0.1				86.6				32.1				—				118.8
Net realized investment (losses) gains and			(0.8	)			19.5				7				—				25.7
other			(0.8	)			19.5				7				—				25.7
Total revenue			(0.7	)			540.3				791.4				—				1,331.00
Expenses:
Losses and loss adjustment expenses			—				300.6				447				—				747.6
Other reinsurance-related expenses			—				—				27.3				—				27.3
Underwriting, acquisition and insurance expenses			27.1				169.8				267.6				—				464.5
Interest expense			3.9				17.1				3				(0.3	)			23.7
Fee expense (income), net			-				(1.3	)			(4.0	)			-				(5.3	)
Debt extinguishment costs			0.1				2.1				—				—				2.2
Foreign currency exchange loss			—				—				4.3				—				4.3
Total expenses			31.1				488.3				745.2				(0.3	)			1,264.30
(Loss) income before income taxes			(31.8	)			52				46.2				0.3				66.7
Provision for income taxes			—				11.1				3.3				—				14.4
Net (loss) income before equity in earnings of			(31.8	)			40.9				42.9				0.3				52.3
subsidiaries			(31.8	)			40.9				42.9				0.3				52.3
Equity in undistributed earnings of			84.1				—				—				(84.1	)			—
subsidiaries			84.1				—				—				(84.1	)			—
Net income (loss)		$	52.3			$	40.9			$	42.9			$	(83.8	)		$	52.3

(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 YEAR ENDED DECEMBER 31, 2014
	(in millions)

			Argo Group				Argo Group US, Inc.				Other Subsidiaries				Consolidating				Total
			International				and Subsidiaries				and Eliminations (1)				Adjustments (2)
			Holdings, Ltd				(Subsidiary Issuer)
			(Parent Guarantor)
	Net cash flows from operating activities		$	25.7			$	43.2			$	37.2			$	24.4			$	130.5
	Cash flows from investing activities:
	Proceeds from sales of investments			—				803.8				458.2				—				1,262.00
	Maturities and mandatory calls of fixed			—				192.1				130.9				—				323
	maturity investments			—				192.1				130.9				—				323
	Purchases of investments			—				(1,126.1	)			(610.7	)			—				(1,736.8	)
	Change in short-term investments and			0.5				76				20				—				96.5
	foreign regulatory deposits			0.5				76				20				—				96.5
	Settlements of foreign currency exchange			1.3				—				(2.4	)			—				(1.1	)
	forward contracts			1.3				—				(2.4	)			—				(1.1	)
	Issuance of intercompany note, net			—				14.5				(7.6	)			(6.9	)			—
	Purchases of fixed assets and other, net			(7.0	)			(35.5	)			(16.0	)			(6.4	)			(64.9	)
	Cash (used) provided by investing activities			(5.2	)			(75.2	)			(27.6	)			(13.3	)			(121.3	)
	Cash flows from financing activities:
	Borrowings under intercompany note, net			(6.9	)			—				—				6.9				—
	Activity under stock incentive plans			4.6				—				—				—				4.6
	Redemption of trust preferred securities, net			—				—				—				(18.0	)			(18.0	)
	Payment on note payable			—				(0.1	)			—				—				(0.1	)
	Repurchase of Company's common shares			—				(50.8	)			—				—				(50.8	)
	Excess tax expense from share-based			—				0.1				—				—				0.1
	payment arrangements			—				0.1				—				—				0.1
	Payment of cash dividend to common			(18.2	)			—				—				—				(18.2	)
	shareholders			(18.2	)			—				—				—				(18.2	)
	Cash (used) provided by financing activities			(20.5	)			(50.8	)			—				(11.1	)			(82.4	)
	Effect of exchange rate changes on cash			—				—				(3.2	)			—				(3.2	)
	Change in cash			—				(82.8	)			6.4				(—	)			(76.4	)
	Cash, beginning of year			—				132.1				25.3				—				157.4
	Cash, end of year		$	—			$	49.3			$	31.7			$	(—	)		$	81

	(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 YEAR ENDED DECEMBER 31, 2013
	(in millions)

			Argo Group				Argo Group US, Inc.				Other Subsidiaries				Consolidating				Total
			International				and Subsidiaries				and Eliminations (1)				Adjustments (2)
			Holdings, Ltd				(Subsidiary Issuer)
			(Parent Guarantor)
	Net cash flows from operating activities		$	63.2			$	62.5			$	(125.9	)		$	—			$	(0.2	)
	Cash flows from investing activities:
	Proceeds from sales of investments			—				1,130.20				836.1				—				1,966.30
	Maturities and mandatory calls of fixed			—				168.9				112.9				—				281.8
	maturity investments			—				168.9				112.9				—				281.8
	Purchases of investments			—				(1,156.7	)			(819.1	)			—				(1,975.8	)
	Change in short-term investments and			(1.4	)			(119.1	)			(32.5	)			—				(153.0	)
	foreign regulatory deposits			(1.4	)			(119.1	)			(32.5	)			—				(153.0	)
	Settlements of foreign currency exchange			0.7				—				(4.6	)			—				(3.9	)
	forward contracts			0.7				—				(4.6	)			—				(3.9	)
	Issuance of intercompany note, net			—				35				14.3				(49.3	)			—
	Purchases of fixed assets and other, net			—				(16.3	)			21.7				—				5.4
	Cash (used) provided by investing activities			(0.7	)			42				128.8				(49.3	)			120.8
	Cash flows from financing activities:
Borrowings under intercompany note, net			(49.3	)			—				—				49.3				—
Activity under stock incentive plans			2.6				—				—				—				2.6
Repurchase of Company's common shares			—				(46.5	)			—				—				(46.5	)
Excess tax expense from share-based			—				0.2				—				—				0.2
payment arrangements			—				0.2				—				—				0.2
Payment of cash dividend to common			(15.8	)			—				—				—				(15.8	)
shareholders			(15.8	)			—				—				—				(15.8	)
Cash (used) provided by financing activities			(62.5	)			(46.3	)			—				49.3				(59.5	)
Effect of exchange rate changes on cash			—				—				0.5				—				0.5
Change in cash			—				58.2				3.4				—				61.6
Cash, beginning of year			—				73.9				21.9				—				95.8
Cash, end of year		$	—			$	132.1			$	25.3			$	—			$	157.4

(1)	Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations.
(2)	Includes all Argo Group parent company eliminations.



CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS
FOR YEAR ENDED DECEMBER 31, 2012
(in millions)

		Argo Group				Argo Group US, Inc.				Other Subsidiaries				Consolidating				Total
		International				and Subsidiaries				and Eliminations (1)				Adjustments (2)
		Holdings, Ltd				(Subsidiary Issuer)
		(Parent Guarantor)
Net cash flows from operating activities		$	(30.2	)		$	5.5			$	55.2			$	—			$	30.5
Cash flows from investing activities:
Proceeds from sales of investments			—				573.8				556.9				—				1,130.70
Maturities and mandatory calls of fixed			—				326.2				156.8				—				483
maturity investments			—				326.2				156.8				—				483
Purchases of investments			—				(889.1	)			(732.4	)			—				(1,621.5	)
Change in short-term investments and			(0.9	)			35.1				3.5				—				37.7
foreign regulatory deposits			(0.9	)			35.1				3.5				—				37.7
Settlements of foreign currency exchange			2.3				—				(1.9	)			—				0.4
forward contracts			2.3				—				(1.9	)			—				0.4
Issuance of intercompany note, net			—				(26.0	)			(29.0	)			55				—
Purchases of fixed assets and other, net			—				(29.1	)			(4.9	)			—				(34.0	)
Cash provided (used) by investing activities			1.4				(9.1	)			(51.0	)			55				(3.7	)
Cash flows from financing activities:
Borrowings under intercompany note, net			55				—				—				(55.0	)			—
Proceeds from issuance of senior			—				138.7				—				—				138.7
unsecured fixed rate notes			—				138.7				—				—				138.7
Redemption of trust preferred securities,			(15.1	)			(102.1	)			—				—				(117.2	)
net			(15.1	)			(102.1	)			—				—				(117.2	)
Activity under stock incentive plans			1.2				—				—				—				1.2
Repurchase of Company's common shares			—				(44.2	)			—				—				(44.2	)
Payment of cash dividend to common			(12.3	)			—				—				—				(12.3	)
shareholders			(12.3	)			—				—				—				(12.3	)
Cash provided (used) by financing activities			28.8				(7.6	)			—				(55.0	)			(33.8	)
Effect of exchange rate changes on cash			—				—				0.1				—				0.1
Change in cash			—				(11.2	)			4.3				—				(6.9	)
Cash, beginning of year			—				85.1				17.6				—				102.7
Cash, end of year		$	—			$	73.9			$	21.9			$	—			$	95.8

(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_Tables

Subsequent Event (Tables)	12 Months Ended
Subsequent Event (Tables)	Dec. 31, 2014
Subsequent Events [Abstract]
Pro Forma Basic and Diluted Net Income per Common Share after Stock Dividend	Presented below are pro forma basic and diluted net income per common share after giving effect for the stock dividend:

		For the Years Ended December 31,
		2014		2013		2012
	Pro forma net income per common share:
	Basic	$	6.39	$	4.85	$	1.69
	Diluted	$	6.27	$	4.67	$	1.66

Business_and_Significant_Accou3

Business and Significant Accounting Policies - Additional Information (Detail) (USD $)

0 Months Ended

3 Months Ended

12 Months Ended

0 Months Ended

In Millions, except Share data, unless otherwise specified

Dec. 30, 2014

Dec. 31, 2014

Sep. 30, 2014

Jun. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2009

Feb. 17, 2015

7-May-13

Institution

Trust

Business And Significant Accounting Policies [Line Items]

Percentage of contractual participation

100.00%

Number of Statutory Trusts

Number of Charitable Foundations

Stock dividend declared

10.00%

Additional stock issued as dividend

2,447,839

Dividends declaration date

30-Nov-14

5-Aug-14

5-May-14

4-Nov-13

6-Aug-13

7-May-13

15-Feb-13

6-Nov-12

7-Aug-12

8-May-12

15-Feb-12

18-Feb-14

7-May-13

Dividends payable date

31-Dec-14

15-Sep-14

16-Jun-14

16-Dec-13

16-Sep-13

20-Jun-13

15-Mar-13

17-Dec-12

18-Sep-12

15-Jun-12

15-Mar-12

17-Mar-14

17-Jun-13

Dividend payable, date of record

31-Dec-14

1-Sep-14

2-Jun-14

2-Dec-13

2-Sep-13

3-Jun-13

1-Mar-13

3-Dec-12

4-Sep-12

1-Jun-12

1-Mar-12

3-Mar-14

3-Jun-13

Short-term investments, maturity term

1 year

Percentage of investment portfolio in fair value from pricing service or broker

1.00%

Allowance for doubtful accounts

$5.20

$4.50

$5.20

$4.50

Reinsurance recoverables, allowance for doubtful accounts

3.4

3.7

3.4

3.7

Estimated liability for return of premiums

5.8

6.8

Goodwill, Written off related to sale of operating unit

1.6

Indefinite-lived Intangible Assets Acquired

1.8

Weighted average useful life

0 years

Amortization expense

5.6

6.1

5.2

Estimated amortization expense for 2015

5.4

Estimated amortization expense for 2016

5.1

Estimated amortization expense for 2017

2.4

Estimated amortization expense for 2018

4.5

Estimated amortization expense for 2019

0.4

Accumulated depreciation for property and equipment

81.7

65.5

81.7

65.5

Net book value of property and equipment

102.7

Depreciation expense

15.1

15.5

12.6

Foreign currency translation adjustment

-15.6

-11.5

-15.6

-11.5

Income taxes paid

23.7

14.2

Income taxes recovered

0.1

Reinsurance recoverables

52.7

252.3

Ceded reinsurance payable

155

252.3

155

252.3

Increase in Reinsurance recoverable

9.2

Proceeds from sale of real estate

$43.60

$43.30

Minimum [Member]

Business And Significant Accounting Policies [Line Items]

Property, Plant and Equipment, Useful Life

3 years

Maximum [Member]

Business And Significant Accounting Policies [Line Items]

Property, Plant and Equipment, Useful Life

31 years 6 months

Distribution Network [Member]

Business And Significant Accounting Policies [Line Items]

Weighted average useful life

0 years

Additional Lloyd's Capacity [Member]

Business And Significant Accounting Policies [Line Items]

Weighted average useful life

0 years

Other [Member]

Business And Significant Accounting Policies [Line Items]

Weighted average useful life

0 years

Excess and Surplus Lines [Member]

Business And Significant Accounting Policies [Line Items]

Percentage of decline in the fair value of reporting units

39.00%

Commercial Specialty [Member]

Business And Significant Accounting Policies [Line Items]

Percentage of decline in the fair value of reporting units

21.00%

Syndicate 1200 [Member]

Business And Significant Accounting Policies [Line Items]

Percentage of decline in the fair value of reporting units

16.00%

Subsequent Event

Business And Significant Accounting Policies [Line Items]

Stock dividend declared

10.00%

Additional stock issued as dividend

2,600,000

Dividends declaration date

17-Feb-15

Dividends payable date

16-Mar-15

Dividend payable, date of record

2-Mar-15

Business_and_Significant_Accou4

Business and Significant Accounting Policies - Summary of Receivables (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Premiums receivable	$1.10	$0.20	$0.30
Reinsurance recoverables	0.5	0	-0.4
Net written off (recovered)	$1.60	$0.20	($0.10)

Business_and_Significant_Accou5

Business and Significant Accounting Policies - Intangible Assets and Accumulated Amortization (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$111.60	$113.40
Accumulated Amortization	33	27.4
Lloyd's Capacity [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	60.5	60.5
Title Plant [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount		1.8
Distribution Network [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	44.8	44.8
Accumulated Amortization	27.9	23.1
Additional Lloyd's Capacity [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	4.8	4.8
Accumulated Amortization	3.9	3.2
Other [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	1.5	1.5
Accumulated Amortization	$1.20	$1.10

Business_and_Significant_Accou6

Business and Significant Accounting Policies - Supplemental Cash Flow Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure - Business and Significant Accounting Policies - Supplemental Cash Flow Information (Detail) [Line Items]
Total interest paid	$19.70	$19.80	$26.50
Senior Unsecured Fixed Rate Notes [Member]
Disclosure - Business and Significant Accounting Policies - Supplemental Cash Flow Information (Detail) [Line Items]
Total interest paid	9.3	9.3	2.1
Junior Subordinated Debentures [Member]
Disclosure - Business and Significant Accounting Policies - Supplemental Cash Flow Information (Detail) [Line Items]
Total interest paid	7.6	7.9	21.3
Other Indebtedness [Member]
Disclosure - Business and Significant Accounting Policies - Supplemental Cash Flow Information (Detail) [Line Items]
Total interest paid	$2.80	$2.60	$3.10

Investments_Schedule_of_Amorti

Investments - Schedule of Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Fair Value of Investments (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$3,889.20		$3,836
Gross Unrealized Gains	256.2		274.8
Gross Unrealized Losses	47.5		31.6
Fair Value	4,097.90		4,079.20
Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	488.9		377.4
Gross Unrealized Gains	7.5		2.8
Gross Unrealized Losses	1.3		1.3
Fair Value	495.1		378.9
Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,817.20		2,760.10
Gross Unrealized Gains	64.6		83.4
Gross Unrealized Losses	41.1		29.1
Fair Value	2,840.70		2,814.40
Fixed Maturities [Member] \| U.S. Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	184		273.4
Gross Unrealized Gains	1.3		2.4
Gross Unrealized Losses	0.3		0.5
Fair Value	185		275.3
Fixed Maturities [Member] \| Non-U.S. Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	79.9		60.9
Gross Unrealized Gains	0.6		0.3
Gross Unrealized Losses	0.6		1
Fair Value	79.9		60.2
Fixed Maturities [Member] \| Obligations of States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	468.1		563.7
Gross Unrealized Gains	22.9		22.9
Gross Unrealized Losses	0.3		8.8
Fair Value	490.7		577.8
Fixed Maturities [Member] \| Credit-Financial [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	508.1		426.3
Gross Unrealized Gains	12.3		15.4
Gross Unrealized Losses	2.3		1.8
Fair Value	518.1		439.9
Fixed Maturities [Member] \| Credit-Industrial [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	493.7		385.5
Gross Unrealized Gains	9.4		13.8
Gross Unrealized Losses	3.5		2.2
Fair Value	499.6		397.1
Fixed Maturities [Member] \| Credit-Utility [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	142.7		162
Gross Unrealized Gains	3.2		5.4
Gross Unrealized Losses	3.9		0.8
Fair Value	142		166.6
Fixed Maturities [Member] \| CMO/MBS-Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	168	[1]	219.4	[1]
Gross Unrealized Gains	8	[1]	9.2	[1]
Gross Unrealized Losses	0.7	[1]	1.7	[1]
Fair Value	175.3	[1]	226.9	[1]
Fixed Maturities [Member] \| CMO/MBS-Non Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13.2		19.4
Gross Unrealized Gains	0.8		0.8
Gross Unrealized Losses	0		0
Fair Value	14		20.2
Fixed Maturities [Member] \| CMBS [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	178.6	[2]	162.7	[2]
Gross Unrealized Gains	1.6	[2]	3.1	[2]
Gross Unrealized Losses	0.2	[2]	1	[2]
Fair Value	180	[2]	164.8	[2]
Fixed Maturities [Member] \| ABS [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	221.4	[3]	123.6	[3]
Gross Unrealized Gains	0.6	[3]	0.8	[3]
Gross Unrealized Losses	1	[3]	0.6	[3]
Fair Value	221	[3]	123.8	[3]
Fixed Maturities [Member] \| Foreign Denominated: Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	148.4		207.7
Gross Unrealized Gains	1.2		4.9
Gross Unrealized Losses	9.4		5.9
Fair Value	140.2		206.7
Fixed Maturities [Member] \| Foreign Denominated: Credit [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	211.1		155.5
Gross Unrealized Gains	2.7		4.4
Gross Unrealized Losses	18.9		4.8
Fair Value	194.9		155.1
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	307.3		346.9
Gross Unrealized Gains	184.1		188.6
Gross Unrealized Losses	5.1		1.2
Fair Value	486.3		534.3
Short-Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	275.8		351.6
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		0
Fair Value	$275.80		$351.60

[1]	Collateralized mortgage obligations/mortgage-backed securities (bCMO/MBSb).
[2]	Commercial mortgage-backed securities (bCMBSb).
[3]	Asset-backed securities (bABSb).

Investments_Additional_Informa

Investments - Additional Information (Detail)	12 Months Ended								12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 28, 2011	Jun. 18, 2011	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2013
	USD ($)	USD ($)	USD ($)	Contract	USD ($)	USD ($)	Securities Pledged as Collateral [Member]	Securities Pledged as Collateral [Member]	Canadian Dollar [Member]	Euro [Member]	Currency Forward Contracts [Member]	Currency Forward Contracts [Member]	Currency Forward Contracts [Member]	Currency Forward Contracts [Member]	Currency Forward Contracts [Member]	Non-U.S. Denominated Fixed Maturity Investments [Member]	Non-U.S. Denominated Fixed Maturity Investments [Member]	Deposit with Various U.S. Canadian Insurance and Other Agencies [Member]	Deposit with Various U.S. Insurance and Other Agencies [Member]
	Security	Contract					USD ($)	USD ($)	USD ($)	USD ($)	USD ($)	USD ($)	USD ($)	Canadian Dollar [Member]	Canadian Dollar [Member]	USD ($)	USD ($)	United States [Member]	United States [Member]
														USD ($)	CAD			USD ($)	USD ($)
Schedule of Investments [Line Items]
Fair value of investments, assets managed on behalf of the trade capital providers	$75,200,000	$87,300,000
Number of securities in an unrealized loss position, total	6,165
Number of securities in an unrealized loss position for less than one year	2,031
Number of securities in an unrealized loss position for a period of one year or greater	139
Other-than-temporary losses on fixed maturities portfolio	1,200,000	6,000,000	1,500,000
Other-than-temporary losses equity portfolio	1,100,000	1,800,000	2,200,000
Total notional amount of the Company's holdings in non-U.S. Dollar denominated higher yielding fixed maturity investments		100,000	2,300,000													100,000	2,200,000
Notional amount of the currency forward contracts					100,000,000	100,000,000					20,600,000	57,200,000	102,800,000	118,100,000	141,800,000
Fair value of the currency forward contracts	600,000	1,300,000	1,900,000						600,000	2,300,000
Realized gains from currency forward contracts	4,600,000	7,800,000	8,000,000						4,600,000	6,000,000
Realized losses from currency forward contracts	4,900,000	10,400,000	7,500,000						2,200,000	2,400,000
Amortized Cost	3,889,200,000	3,836,000,000																186,600,000	196,700,000
Fair Value	4,097,900,000	4,079,200,000																194,200,000	203,400,000
Pledged assets separately reported, securities pledged under letters of credit facilities, at amortized cost							55,000,000	97,700,000
Pledged assets separately reported, securities pledged under letters of credit facilities, at fair value							55,300,000	98,600,000
Reported loss incurred	43,600,000	60,200,000
Reported loss expense reserve	43,600,000	60,200,000
Securities pledged to Lloyd's	217,900,000	250,800,000
Number of reinsurance contracts		1		2
Transfers between Level 1 and Level 2 securities	$0	$0

Investments_Schedule_of_Amorti1

Investments - Schedule of Amortized Cost and Fair Values of Fixed Maturity Investments, by Contractual Maturity (Detail) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified	Dec. 31, 2014
Investments Debt And Equity Securities [Abstract]
Amortized Cost, Due in one year or less	$238.70
Amortized Cost, Due after one year through five years	1,326.20
Amortized Cost, Due after five years through ten years	507.7
Amortized Cost, Thereafter	163.4
Amortized Cost, Structured securities	581.2
Amortized Cost, Total	2,817.20
Fair Value, Due in one year or less	235.3
Fair Value, Due after one year through five years	1,328.50
Fair Value, Due after five years through ten years	519.1
Fair Value, Thereafter	167.5
Fair Value, Structured securities	590.3
Fair Value, Total	$2,840.70

Investments_Schedule_of_Carryi

Investments - Schedule of Carrying Value Redemption Characteristics and Unfunded Investment Commitments of Other Invested Assets Portfolio (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Investments [Line Items]
Carrying Value	$4,097.90	$4,079.20
Hedge funds [Member]
Schedule of Investments [Line Items]
Carrying Value	153.2	87.9
Private equity [Member]
Schedule of Investments [Line Items]
Carrying Value	123.6	93.8
Unfunded Commitments	72.9	35.7
Long only funds [Member]
Schedule of Investments [Line Items]
Carrying Value	104.4	62
Other Investments [Member]
Schedule of Investments [Line Items]
Carrying Value	113.9	135.2
Other invested assets [Member]
Schedule of Investments [Line Items]
Carrying Value	495.1	378.9
Unfunded Commitments	$72.90	$35.70

Investments_Schedule_of_Aging_

Investments - Schedule of Aging of Unrealized Losses on Company's Investments in Fixed Maturities, Equity Securities and Other Investments (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	$1,157.30		$908
Unrealized Losses, Less Than One Year	45.3		30.2
Fair Value, One Year or Greater	108.1		22.6
Unrealized Losses, One Year or Greater	2.2		1.4
Fair Value, Total	1,265.40		930.6
Unrealized Losses, Total	47.5		31.6
Other Investments [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	-0.9		-1.3
Unrealized Losses, Less Than One Year	1.3		1.3
Fair Value, One Year or Greater	0		0
Unrealized Losses, One Year or Greater	0		0
Fair Value, Total	-0.9		-1.3
Unrealized Losses, Total	1.3		1.3
Fixed Maturities [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	1,104.60		879.3
Unrealized Losses, Less Than One Year	38.9		27.7
Fair Value, One Year or Greater	108.1		22.6
Unrealized Losses, One Year or Greater	2.2		1.4
Fair Value, Total	1,212.70		901.9
Unrealized Losses, Total	41.1		29.1
Fixed Maturities [Member] \| U.S. Governments [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	55		55.3
Unrealized Losses, Less Than One Year	0.2		0.5
Fair Value, One Year or Greater	15.7		0
Unrealized Losses, One Year or Greater	0.1		0
Fair Value, Total	70.7		55.3
Unrealized Losses, Total	0.3		0.5
Fixed Maturities [Member] \| Non-U.S. Governments [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	36.5		36.3
Unrealized Losses, Less Than One Year	0.4		1
Fair Value, One Year or Greater	5.2		0
Unrealized Losses, One Year or Greater	0.2		0
Fair Value, Total	41.7		36.3
Unrealized Losses, Total	0.6		1
Fixed Maturities [Member] \| Obligations of States and Political Subdivisions [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	10.4		154.6
Unrealized Losses, Less Than One Year	0.1		8.8
Fair Value, One Year or Greater	16.6		3.1
Unrealized Losses, One Year or Greater	0.2		0
Fair Value, Total	27		157.7
Unrealized Losses, Total	0.3		8.8
Fixed Maturities [Member] \| Credit-Financial [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	195.7		88.7
Unrealized Losses, Less Than One Year	2.2		1.7
Fair Value, One Year or Greater	11.1		2.4
Unrealized Losses, One Year or Greater	0.1		0.1
Fair Value, Total	206.8		91.1
Unrealized Losses, Total	2.3		1.8
Fixed Maturities [Member] \| Credit-Industrial [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	240.8		85.7
Unrealized Losses, Less Than One Year	3.3		2
Fair Value, One Year or Greater	12.2		2.9
Unrealized Losses, One Year or Greater	0.2		0.2
Fair Value, Total	253		88.6
Unrealized Losses, Total	3.5		2.2
Fixed Maturities [Member] \| Credit-Utility [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	63.1		21.2
Unrealized Losses, Less Than One Year	3.8		0.7
Fair Value, One Year or Greater	1.9		1.9
Unrealized Losses, One Year or Greater	0.1		0.1
Fair Value, Total	65		23.1
Unrealized Losses, Total	3.9		0.8
Fixed Maturities [Member] \| CMO/MBS-Agency [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	10.1		58.4
Unrealized Losses, Less Than One Year	0.1		1.2
Fair Value, One Year or Greater	19.2		5.6
Unrealized Losses, One Year or Greater	0.6		0.5
Fair Value, Total	29.3		64
Unrealized Losses, Total	0.7	[1]	1.7	[1]
Fixed Maturities [Member] \| CMBS [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	49.3		24.2
Unrealized Losses, Less Than One Year	0.1		1
Fair Value, One Year or Greater	6		1.1
Unrealized Losses, One Year or Greater	0.1		0
Fair Value, Total	55.3		25.3
Unrealized Losses, Total	0.2	[2]	1	[2]
Fixed Maturities [Member] \| ABS [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	129.2		59.1
Unrealized Losses, Less Than One Year	0.7		0.1
Fair Value, One Year or Greater	8.1		5.6
Unrealized Losses, One Year or Greater	0.3		0.5
Fair Value, Total	137.3		64.7
Unrealized Losses, Total	1	[3]	0.6	[3]
Fixed Maturities [Member] \| Foreign Denominated: Governments [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	123.7		170.5
Unrealized Losses, Less Than One Year	9.3		5.9
Fair Value, One Year or Greater	11.2		0
Unrealized Losses, One Year or Greater	0.1		0
Fair Value, Total	134.9		170.5
Unrealized Losses, Total	9.4		5.9
Fixed Maturities [Member] \| Foreign Denominated: Credit [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	190.8		125.3
Unrealized Losses, Less Than One Year	18.7		4.8
Fair Value, One Year or Greater	0.9		0
Unrealized Losses, One Year or Greater	0.2		0
Fair Value, Total	191.7		125.3
Unrealized Losses, Total	18.9		4.8
Equity Securities [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	53.6		25.5
Unrealized Losses, Less Than One Year	5.1		1.2
Fair Value, One Year or Greater	0		0
Unrealized Losses, One Year or Greater	0		0
Fair Value, Total	53.6		25.5
Unrealized Losses, Total	5.1		1.2
Short-Term Investments [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	0		4.5
Unrealized Losses, Less Than One Year	0		0
Fair Value, One Year or Greater	0		0
Unrealized Losses, One Year or Greater	0		0
Fair Value, Total	0		4.5
Unrealized Losses, Total	$0		$0

[1]	Collateralized mortgage obligations/mortgage-backed securities (bCMO/MBSb).
[2]	Commercial mortgage-backed securities (bCMBSb).
[3]	Asset-backed securities (bABSb).

Investments_Schedule_of_Aging_1

Investments - Schedule of Aging of Unrealized Losses on Company's Investments in Fixed Maturities, Equity Securities and Other Investments (Parenthetical) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Investments Debt And Equity Securities [Abstract]
Unrealized losses less than one year	$0.10	$0.10
Unrealized losses one year or greater	$0.10	$0.10

Investments_Schedule_of_Invest

Investments - Schedule of Investment Income and Expenses (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Amortized Cost And Fair Value Debt Securities [Abstract]
Interest and dividends on fixed maturities	$76.30	$87.70	$105.90
Dividends on equity securities	15.8	17.7	15.2
Interest on short-term and other investments	5.3	5	7.3
Other	-1	-1	-0.4
Investment income	96.4	109.4	128
Investment expenses	-9.8	-9.4	-9.2
Net investment income	$86.60	$100	$118.80

Investments_Schedule_of_Compan

Investments - Schedule of Company's Gross Realized Investment Gains (Losses) (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Investments [Line Items]
Gross realized investment gains and other	$136.40	$131.60	$54.40
Gross realized investment and other losses	-42.4	-60.3	-28.7
Net realized investment and other gains	94	71.3	25.7
Other Investments [Member]
Schedule of Investments [Line Items]
Gross realized investment gains and other	44.8	38.9	21.5
Gross realized investment and other losses	-21.8	-30.8	-15.1
Other Assets [Member]
Schedule of Investments [Line Items]
Gross realized investment gains and other	2		4.8
Gross realized investment and other losses	-4.6
Fixed Maturities [Member]
Schedule of Investments [Line Items]
Gross realized investment gains and other	17	33.5	27.2
Gross realized investment and other losses	-12.2	-19.6	-9.1
Equity Securities [Member]
Schedule of Investments [Line Items]
Gross realized investment gains and other	29.2	59.1	0.4
Gross realized investment and other losses	-0.6	-1.4	-0.5
Short-Term Investments [Member]
Schedule of Investments [Line Items]
Gross realized investment gains and other	0.1	0.1	0.5
Gross realized investment and other losses	-0.9	-0.7	-0.3
Gain On Sale Of Real Estate Holdings [Member]
Schedule of Investments [Line Items]
Gross realized investment gains and other	43.3
Other-Than-Temporary Impairment Losses on Fixed Maturities [Member]
Schedule of Investments [Line Items]
Gross realized investment and other losses	-1.2	-6	-1.5
Other-Than-Temporary Impairment Losses on Equity Securities [Member]
Schedule of Investments [Line Items]
Gross realized investment and other losses	($1.10)	($1.80)	($2.20)

Investments_Schedule_of_Realiz

Investments - Schedule of Realized Gains (Losses) and Changes in Unrealized of Appreciation(Depreciation) (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Investments [Line Items]
Realized before impairments	$62.30	$52.90	$22.20
Realized - impairments	-1.5	-5.1	-2.4
Change in unrealized	-33.3	-40.2	52.6
Other Investments [Member]
Schedule of Investments [Line Items]
Realized before impairments	23	8.1	6.4
Change in unrealized	2.5	4.5	-2.4
Other Assets [Member]
Schedule of Investments [Line Items]
Realized before impairments	-3.4	-0.6	5
Fixed Maturities [Member]
Schedule of Investments [Line Items]
Realized before impairments	4.8	13.9	18.1
Realized - impairments	-1.2	-6	-1.5
Change in unrealized	-30.5	-102.6	39.5
Equity Securities [Member]
Schedule of Investments [Line Items]
Realized before impairments	28.6	57.7	-0.1
Realized - impairments	-1.1	-1.8	-2.2
Change in unrealized	-8.4	39.5	35.9
Real Estate Holdings [Member]
Schedule of Investments [Line Items]
Realized before impairments	43.3
Tax Effects [Member]
Schedule of Investments [Line Items]
Realized before impairments	-34	-26.2	-7.2
Realized - impairments	0.8	2.7	1.3
Change in unrealized	$3.10	$18.40	($20.40)

Investments_Financial_Assets_M

Investments - Financial Assets Measured at Fair Value on Recurring Basis (Detail) (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	$4,097.90		$4,079.20
Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	3,700.10		3,820.70
Other Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	495.1		378.9
Other Investments [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	97.3		117.8
Other Assets [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		2.6
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	858.5		967.5
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Other Investments [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Other Assets [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	2,840.70		2,849.30
Significant Other Observable Inputs (Level 2) [Member] \| Other Investments [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	97.3		117.8
Significant Other Observable Inputs (Level 2) [Member] \| Other Assets [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Significant Unobservable Inputs (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0.9		3.9
Significant Unobservable Inputs (Level 3) [Member] \| Other Investments [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Significant Unobservable Inputs (Level 3) [Member] \| Other Assets [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		2.6
Fixed Maturities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	2,840.70		2,814.40
Fixed Maturities [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	2,840.70		2,814.40
Fixed Maturities [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	99.2		143.8
Fixed Maturities [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	2,741.50		2,670.60
Fixed Maturities [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| U.S. Governments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	185		275.3
Fixed Maturities [Member] \| U.S. Governments [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	185		275.3
Fixed Maturities [Member] \| U.S. Governments [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	99.2		143.8
Fixed Maturities [Member] \| U.S. Governments [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	85.8		131.5
Fixed Maturities [Member] \| U.S. Governments [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| Non-U.S. Governments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	79.9		60.2
Fixed Maturities [Member] \| Non-U.S. Governments [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	79.9		60.2
Fixed Maturities [Member] \| Non-U.S. Governments [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| Non-U.S. Governments [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	79.9		60.2
Fixed Maturities [Member] \| Non-U.S. Governments [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| Obligations of States and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	490.7		577.8
Fixed Maturities [Member] \| Obligations of States and Political Subdivisions [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	490.7		577.8
Fixed Maturities [Member] \| Obligations of States and Political Subdivisions [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| Obligations of States and Political Subdivisions [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	490.7		577.8
Fixed Maturities [Member] \| Obligations of States and Political Subdivisions [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| Credit-Financial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	518.1		439.9
Fixed Maturities [Member] \| Credit-Financial [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	518.1		439.9
Fixed Maturities [Member] \| Credit-Financial [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| Credit-Financial [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	518.1		439.9
Fixed Maturities [Member] \| Credit-Financial [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| Credit-Industrial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	499.6		397.1
Fixed Maturities [Member] \| Credit-Industrial [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	499.6		397.1
Fixed Maturities [Member] \| Credit-Industrial [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| Credit-Industrial [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	499.6		397.1
Fixed Maturities [Member] \| Credit-Industrial [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| Credit-Utility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	142		166.6
Fixed Maturities [Member] \| Credit-Utility [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	142		166.6
Fixed Maturities [Member] \| Credit-Utility [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| Credit-Utility [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	142		166.6
Fixed Maturities [Member] \| Credit-Utility [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| CMO/MBS-Agency [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	175.3	[1]	226.9	[1]
Fixed Maturities [Member] \| CMO/MBS-Agency [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	175.3		226.9
Fixed Maturities [Member] \| CMO/MBS-Agency [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| CMO/MBS-Agency [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	175.3		226.9
Fixed Maturities [Member] \| CMO/MBS-Agency [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| CMO/MBS-Non Agency [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	14		20.2
Fixed Maturities [Member] \| CMO/MBS-Non Agency [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	14		20.2
Fixed Maturities [Member] \| CMO/MBS-Non Agency [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| CMO/MBS-Non Agency [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	14		20.2
Fixed Maturities [Member] \| CMO/MBS-Non Agency [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| CMBS [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	180	[2]	164.8	[2]
Fixed Maturities [Member] \| CMBS [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	180		164.8
Fixed Maturities [Member] \| CMBS [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| CMBS [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	180		164.8
Fixed Maturities [Member] \| CMBS [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| ABS [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	221	[3]	123.8	[3]
Fixed Maturities [Member] \| ABS [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	221		123.8
Fixed Maturities [Member] \| ABS [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| ABS [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	221		123.8
Fixed Maturities [Member] \| ABS [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| Foreign Denominated: Governments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	140.2		206.7
Fixed Maturities [Member] \| Foreign Denominated: Governments [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	140.2		206.7
Fixed Maturities [Member] \| Foreign Denominated: Governments [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| Foreign Denominated: Governments [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	140.2		206.7
Fixed Maturities [Member] \| Foreign Denominated: Governments [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| Foreign Denominated: Credit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	194.9		155.1
Fixed Maturities [Member] \| Foreign Denominated: Credit [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	194.9		155.1
Fixed Maturities [Member] \| Foreign Denominated: Credit [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Fixed Maturities [Member] \| Foreign Denominated: Credit [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	194.9		155.1
Fixed Maturities [Member] \| Foreign Denominated: Credit [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		0
Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	486.3		534.3
Equity Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	486.3		534.3
Equity Securities [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	485.4		476.7
Equity Securities [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0		56.3
Equity Securities [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0.9		1.3
Short-Term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	275.8		351.6
Short-Term Investments [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	275.8		351.6
Short-Term Investments [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	273.9		347
Short-Term Investments [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	1.9		4.6
Short-Term Investments [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	$0		$0

[1]	Collateralized mortgage obligations/mortgage-backed securities (bCMO/MBSb).
[2]	Commercial mortgage-backed securities (bCMBSb).
[3]	Asset-backed securities (bABSb).

Investments_Schedule_of_Reconc

Investments - Schedule of Reconciliation of Beginning and Ending Balances for Investments Categorized as Level 3 (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$3.90	$8.70
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Included in net income (loss)	0	0.1
Included in other comprehensive income (loss)	0.1	0
Purchases	0	0
Issuances	0	0
Sales	-0.5	-0.6
Settlements	-2.6	-4.3
Ending balance	0.9	3.9
Amount of total gains or losses for the year included in net income (loss) attributable to the change in unrealized gains or losses relating to assets still held at end of period	0	0
Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	2.6	6.9
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Included in net income (loss)	0	0
Included in other comprehensive income (loss)	0	0
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements	-2.6	-4.3
Ending balance	0	2.6
Amount of total gains or losses for the year included in net income (loss) attributable to the change in unrealized gains or losses relating to assets still held at end of period	0	0
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	1.3	1.8
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Included in net income (loss)	0	0.1
Included in other comprehensive income (loss)	0.1	0
Purchases	0	0
Issuances	0	0
Sales	-0.5	-0.6
Settlements	0	0
Ending balance	0.9	1.3
Amount of total gains or losses for the year included in net income (loss) attributable to the change in unrealized gains or losses relating to assets still held at end of period	$0	$0

Sale_of_Real_Estate_Holding_Ad

Sale of Real Estate Holding - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Dec. 30, 2014	Dec. 31, 2014
Other Real Estate [Abstract]
Sale Price of Real Estate	$45
Proceeds from sale of real estate	43.6	43.3
Gain on disposition of property plant equipment	$43.30

Reinsurance_Additional_Informa

Reinsurance - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reinsurance Disclosures [Abstract]
Reinsurance recoverables, allowance for doubtful accounts	$3.40	$3.70
Amount of collateral under reinsurance agreement	359.4	335.5
Paid loss recoverables in insurance recoverables	91.9	140.8
Losses and loss adjustment expenses	747.4	742	747.6
Net of amounts ceded to reinsurers	$246.60	$292.80	$223.60

Reinsurance_Schedule_of_Reinsu

Reinsurance - Schedule of Reinsurance Premium (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Premiums Written And Earned [Abstract]
Direct written premiums	$1,585.50	$1,576.10	$1,428.60
Reinsurance ceded to other companies	-537.5	-537.1	-501.2
Reinsurance assumed from other companies	319.9	312.3	317.1
Net written premiums	1,367.90	1,351.30	1,244.50
Direct earned premiums	1,551.80	1,541	1,372.20
Reinsurance ceded to other companies	-524.8	-533.7	-487
Reinsurance assumed from other companies	311.1	296.5	301.3
Net earned premiums	$1,338.10	$1,303.80	$1,186.50
Percentage of reinsurance assumed to net earned premiums	23.20%	22.70%	25.40%

Derivative_Instruments_Additio

Derivative Instruments - Additional Information (Detail) (USD $)	0 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Dec. 28, 2011	Jun. 18, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2014
	Dec. 28, 2011	Jun. 18, 2011	Contract	Dec. 31, 2012	Contract	Dec. 31, 2014
Offsetting [Abstract]
Number of reinsurance contracts			1		2
Coverage amount	$100	$100
Coverage period, months	24 months	18 months
Other reinsurance-related expenses			19.2	27.3
Other assets			$2.60			$0

Reserves_for_Losses_and_Loss_A2

Reserves for Losses and Loss Adjustment Expenses - Reinsurance Recoverables (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Liability for Claims and Claims Adjustment Expense [Abstract]
Net reserves beginning of the year	$2,107.60	$2,110.90	$2,336.70
Net reserves from assumed retroactive insurance contract			13
Losses and LAE incurred during current calendar year, net of reinsurance:
Current accident year	785.1	775.6	780.5
Prior accident years	-37.7	-33.6	-32.9
Losses and LAE incurred during calendar year, net of reinsurance	747.4	742	747.6
Net reserves ceded - whole account quota share reinsurance transaction			192.2
Losses and LAE payments made during current calendar year, net of reinsurance:
Current accident year	185.9	199.3	217.7
Prior accident years	550.8	554.2	578.8
Losses and LAE payments made during current calendar year, net of reinsurance	736.7	753.5	796.5
Change in participation interest	37.8	10.4	-3.1
Foreign exchange adjustments	-19	-2.2	5.4
Net reserves - end of year	2,137.10	2,107.60	2,110.90
Reinsurance recoverables on unpaid losses and LAE, end of year	905.3	1,122.70	1,112.60
Gross reserves - end of year	$3,042.40	$3,230.30	$3,223.50

Reserves_for_Losses_and_Loss_A3

Reserves for Losses and Loss Adjustment Expenses - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Reserves For Losses And Loss Adjustment Expenses [Line Items]
Net reserves ceded - whole account quota share reinsurance transaction			$192.20
Liability for unpaid claims and claims adjustment expense, incurred claims, prior years	37.7	33.6	32.9
Workers compensation pension, maximum interest rate	3.50%	3.50%	3.50%
Workers compensation pension, unamortized discount	17.6	19.5	20.8
Excess and Surplus Lines [Member]
Schedule Of Reserves For Losses And Loss Adjustment Expenses [Line Items]
Liability for unpaid claims and claims adjustment expense, incurred claims, prior years	47.4	43.9	48
Commercial Specialty [Member]
Schedule Of Reserves For Losses And Loss Adjustment Expenses [Line Items]
Liability for unpaid claims and claims adjustment expense, incurred claims, prior years	6.8	1.1	22.2
International Specialty [Member]
Schedule Of Reserves For Losses And Loss Adjustment Expenses [Line Items]
Liability for unpaid claims and claims adjustment expense, incurred claims, prior years	0.4		7.2
Syndicate 1200 Segment [Member]
Schedule Of Reserves For Losses And Loss Adjustment Expenses [Line Items]
Liability for unpaid claims and claims adjustment expense, incurred claims, prior years	21.1	6.2	9.7
Run Off Lines
Schedule Of Reserves For Losses And Loss Adjustment Expenses [Line Items]
Liability for unpaid claims and claims adjustment expense, incurred claims, prior years	24.4	15.5	9.8
Medical Malpractice Liability [Member]
Schedule Of Reserves For Losses And Loss Adjustment Expenses [Line Items]
Liability for unpaid claims and claims adjustment expense, incurred claims, prior years	13.5	2
Unfavorable Development [Member]
Schedule Of Reserves For Losses And Loss Adjustment Expenses [Line Items]
Liability for unpaid claims and claims adjustment expense, incurred claims, prior years	$10.30	$10.50	$9.10

Senior_Unsecured_Fixed_Rate_No

Senior Unsecured Fixed Rate Notes - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Debt instrument maturity date		1-Apr-19
Debt Instrument, Redemption Price, Percentage	100.00%
Senior unsecured fixed rate notes	$143,800,000	$143,800,000
Proceeds, net of issuance costs, from sale of notes			138,700,000
Redemption of trust preferred securities			118,600,000
Senior Unsecured Fixed Rate Notes [Member]
Debt Instrument [Line Items]
Principal amount of senior note			$143,750,000
Debt instrument interest rate stated percentage			6.50%
Debt instrument maturity date	15-Sep-42
Initial maturity date	9/15/17
Debt Instrument, Redemption Price, Percentage			100.00%

Junior_Subordinated_Debentures2

Junior Subordinated Debentures - Additional Information (Detail) (USD $)	12 Months Ended	0 Months Ended	12 Months Ended
	Dec. 31, 2014	Jul. 16, 2014	Dec. 31, 2012	Dec. 31, 2013	Nov. 13, 2012
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%
Junior subordinated debentures	$172,700,000			$193,300,000
Junior Subordinated Debentures [Member]
Debt Instrument [Line Items]
Junior subordinated debentures		20,000,000
Percentage of debt securities redeemed as compare to principal amount		90.00%
Redemption received on debt securities		18,200,000
Recognition of pre-tax gain		2,000,000
Eight Point Eight Five Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage			100.00%
Eight Point Eight Five Junior Subordinated Debt [Member] \| P X R E Capital Trust One
Debt Instrument [Line Items]
Percentage of debt securities redeemed as compare to principal amount			102.09%
Redemption received on debt securities			3,100,000
Debt instrument interest rate stated percentage			8.85%
Value of securities redeemed to trustee			103,093,000
Debt extinguishment costs			2,100,000
Unamortized discount			400,000
Nine Point Seven Five Junior Subordinated Debt [Member] \| P X R E Capital Trust One
Debt Instrument [Line Items]
Percentage of debt securities redeemed as compare to principal amount			100.98%
Redemption received on debt securities			500,000
Debt instrument interest rate stated percentage					9.75%
Value of securities redeemed to trustee					15,464,000
Debt extinguishment costs			100,000

Junior_Subordinated_Debentures3

Junior Subordinated Debentures - Schedule of Junior Subordinated Debentures (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Junior subordinated debentures, Maturity date		1-Apr-19
Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Amount	$172.70	$193.30
PXRE Capital Statutory Trust II [Member] \| Argo Group [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	15-May-03	15-May-03
Junior subordinated debentures, Maturity date	15-May-33	15-May-33
Junior subordinated debentures, Redeemable date	5/15/08	5/15/08
Junior subordinated debentures, Rate Structure	3M LIBOR + 4.10%	3M LIBOR + 4.10%
Junior subordinated debentures, interest rate stated percentage	4.33%	4.34%
Junior subordinated debentures, Amount	18.1	18.1
PXRE Capital Trust V [Member] \| Argo Group [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date		29-Oct-03
Junior subordinated debentures, Maturity date		29-Oct-33
Junior subordinated debentures, Redeemable date		10/29/08
Junior subordinated debentures, Rate Structure		3M LIBOR + 3.85%
Junior subordinated debentures, interest rate stated percentage		4.09%
Junior subordinated debentures, Amount		20.6
PXRE Capital Trust VI [Member] \| Argo Group [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	6-Nov-03	6-Nov-03
Junior subordinated debentures, Maturity date	30-Sep-33	30-Sep-33
Junior subordinated debentures, Redeemable date	9/30/08	9/30/08
Junior subordinated debentures, Rate Structure	3M LIBOR + 3.90%	3M LIBOR + 3.90%
Junior subordinated debentures, interest rate stated percentage	4.16%	4.15%
Junior subordinated debentures, Amount	10.3	10.3
Argonaut Group Statutory Trust I [Member] \| Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	15-May-03	15-May-03
Junior subordinated debentures, Maturity date	15-May-33	15-May-33
Junior subordinated debentures, Redeemable date	5/15/08	5/15/08
Junior subordinated debentures, Rate Structure	3M LIBOR + 4.10%	3M LIBOR + 4.10%
Junior subordinated debentures, interest rate stated percentage	4.33%	4.34%
Junior subordinated debentures, Amount	15.5	15.5
Argonaut Group Statutory Trust III [Member] \| Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	16-Dec-03	16-Dec-03
Junior subordinated debentures, Maturity date	8-Jan-34	8-Jan-34
Junior subordinated debentures, Redeemable date	1/8/09	1/8/09
Junior subordinated debentures, Rate Structure	3M LIBOR + 4.10%	3M LIBOR + 4.10%
Junior subordinated debentures, interest rate stated percentage	4.33%	4.34%
Junior subordinated debentures, Amount	12.3	12.3
Argonaut Group Statutory Trust IV [Member] \| Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	29-Apr-04	29-Apr-04
Junior subordinated debentures, Maturity date	29-Apr-34	29-Apr-34
Junior subordinated debentures, Redeemable date	4/29/09	4/29/09
Junior subordinated debentures, Rate Structure	3M LIBOR + 3.85%	3M LIBOR + 3.85%
Junior subordinated debentures, interest rate stated percentage	4.08%	4.09%
Junior subordinated debentures, Amount	13.4	13.4
Junior Subordinated Debentures [Member] \| Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	26-May-04	26-May-04
Junior subordinated debentures, Maturity date	24-May-34	24-May-34
Junior subordinated debentures, Redeemable date	5/24/09	5/24/09
Junior subordinated debentures, Rate Structure	3M LIBOR + 3.85%	3M LIBOR + 3.85%
Junior subordinated debentures, interest rate stated percentage	4.08%	4.09%
Junior subordinated debentures, Amount	12.3	12.3
Argonaut Group Statutory Trust VI [Member] \| Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	12-May-04	12-May-04
Junior subordinated debentures, Maturity date	12-May-34	12-May-34
Junior subordinated debentures, Redeemable date	6/1/09	6/1/09
Junior subordinated debentures, Rate Structure	3M LIBOR + 3.80%	3M LIBOR + 3.80%
Junior subordinated debentures, interest rate stated percentage	4.04%	4.04%
Junior subordinated debentures, Amount	13.4	13.4
Argonaut Group Statutory Trust VII [Member] \| Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	17-Sep-04	17-Sep-04
Junior subordinated debentures, Maturity date	15-Dec-34	15-Dec-34
Junior subordinated debentures, Redeemable date	9/17/09	9/17/09
Junior subordinated debentures, Rate Structure	3M LIBOR + 3.60%	3M LIBOR + 3.60%
Junior subordinated debentures, interest rate stated percentage	3.84%	3.84%
Junior subordinated debentures, Amount	15.5	15.5
Argonaut Group Statutory Trust VIII [Member] \| Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	22-Sep-04	22-Sep-04
Junior subordinated debentures, Maturity date	22-Sep-34	22-Sep-34
Junior subordinated debentures, Redeemable date	9/22/09	9/22/09
Junior subordinated debentures, Rate Structure	3M LIBOR + 3.55%	3M LIBOR + 3.55%
Junior subordinated debentures, interest rate stated percentage	3.80%	3.80%
Junior subordinated debentures, Amount	15.5	15.5
Argonaut Group Statutory Trust IX [Member] \| Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	22-Oct-04	22-Oct-04
Junior subordinated debentures, Maturity date	15-Dec-34	15-Dec-34
Junior subordinated debentures, Redeemable date	12/15/09	12/15/09
Junior subordinated debentures, Rate Structure	3M LIBOR + 3.60%	3M LIBOR + 3.60%
Junior subordinated debentures, interest rate stated percentage	3.84%	3.84%
Junior subordinated debentures, Amount	15.5	15.5
Argonaut Group Statutory Trust X [Member] \| Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	15-Sep-05	15-Sep-05
Junior subordinated debentures, Maturity date	15-Sep-35	15-Sep-35
Junior subordinated debentures, Redeemable date	9/15/10	9/15/10
Junior subordinated debentures, Rate Structure	3M LIBOR + 3.40%	3M LIBOR + 3.40%
Junior subordinated debentures, interest rate stated percentage	3.64%	3.64%
Junior subordinated debentures, Amount	$30.90	$30.90

Other_Indebtedness_Additional_

Other Indebtedness - Additional Information (Detail) (USD $)	12 Months Ended		0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Mar. 07, 2014
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%
Floating rate loan stock denominated in Euros	$44,800,000	$49,000,000
Credit agreement with major money center banks, amount			150,000,000
Maximum borrowing capacity under revolving credit facility before amendment			150,000,000
Note payable as part of ARIS acquisition	700,000	800,000
Variable interest rate of note payable, above 30-day LIBOR		2.00%
Junior subordinated debentures, Maturity date		1-Apr-19
New Credit Agreement [Member]
Debt Instrument [Line Items]
Credit agreement with major money center banks, amount			175,000,000
Revolving credit facility maturity date	7-Mar-18
Letter of credit facility amount	0	0
Amount drawn under revolving letter of credit			200,000
New Credit Agreement [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Letter of credit facility amount	$17,500,000

Other_Indebtedness_Schedule_of

Other Indebtedness - Schedule of Floating Rate Loan Stock, Notes Outstanding (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Other indebtedness, Amount	$61.30	$65.50
Floating Rate Loan Stock, U.S. Dollar, Start Year 2004 [Member]
Debt Instrument [Line Items]
Other indebtedness, Issue Date	8-Dec-04	8-Dec-04
Other indebtedness, Maturity	11/15/34	11/15/34
Other indebtedness, Redeemable Date	12/8/09	12/8/09
Other indebtedness, Rate Structure	6 month LIBOR + 4.2%	6 month LIBOR + 4.2%
Junior subordinated debentures, interest rate stated percentage	4.53%	4.60%
Other indebtedness, Amount	6.5	6.5
Floating Rate Loan Stock, Euro, Start Year 2005 [Member]
Debt Instrument [Line Items]
Other indebtedness, Issue Date	6-Sep-05	6-Sep-05
Other indebtedness, Maturity	8/22/35	8/22/35
Other indebtedness, Redeemable Date	9/6/10	9/6/10
Other indebtedness, Rate Structure	3 month LIBOR + 4.0%	3 month LIBOR + 4.0%
Junior subordinated debentures, interest rate stated percentage	4.08%	4.22%
Other indebtedness, Amount	14.9	16.3
Floating Rate Loan Stock, U.S.Dollar, Start Year 2006 [Member]
Debt Instrument [Line Items]
Other indebtedness, Issue Date	31-Oct-06	31-Oct-06
Other indebtedness, Maturity	1/15/36	1/15/36
Other indebtedness, Redeemable Date	1/15/11	1/15/11
Other indebtedness, Rate Structure	6 month LIBOR + 4.0%	6 month LIBOR + 4.0%
Junior subordinated debentures, interest rate stated percentage	4.33%	4.40%
Other indebtedness, Amount	10	10
Floating Rate Loan Stock, Euro, Start Year 2006 [Member]
Debt Instrument [Line Items]
Other indebtedness, Issue Date	31-Oct-06	31-Oct-06
Other indebtedness, Maturity	11/22/36	11/22/36
Other indebtedness, Redeemable Date	10/31/11	10/31/11
Other indebtedness, Rate Structure	3 month LIBOR + 4.0%	3 month LIBOR + 4.0%
Junior subordinated debentures, interest rate stated percentage	4.08%	4.22%
Other indebtedness, Amount	13.1	14.3
Floating Rate Loan Stock, Euro, Start Year 2007 [Member]
Debt Instrument [Line Items]
Other indebtedness, Issue Date	8-Jun-07	8-Jun-07
Other indebtedness, Maturity	9/15/37	9/15/37
Other indebtedness, Redeemable Date	6/8/12	6/8/12
Other indebtedness, Rate Structure	3 month LIBOR + 3.9%	3 month LIBOR + 3.9%
Junior subordinated debentures, interest rate stated percentage	3.98%	4.12%
Other indebtedness, Amount	$16.80	$18.40

Disclosures_about_Fair_Value_o2

Disclosures about Fair Value of Financial Instruments - Additional Information (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Financial Instruments Owned and Pledged as Collateral [Line Items]
Premiums receivable	$353.60	$348.40
Reinsurance recoverable	997.2	1,263.50
Premiums receivable, allowance for doubtful accounts	5.2	4.5
Reinsurance recoverables, allowance for doubtful accounts	3.4	3.7
Over 90 Days [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Premiums receivable	12.4	9.8
Reinsurance recoverable	9.9	22.2
Reinsurance recoverables, allowance for doubtful accounts	1.8	1.6
Premiums receivables, secured by collateral	0.3	0.4
Reinsurance recoverables, secured by collateral	$0.40	$0.30

Disclosures_about_Fair_Value_o3

Disclosures about Fair Value of Financial Instruments - Summary of Company's Financial Instruments Whose Carrying Amount Did Not Equal Fair Value (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	$378.50	$403.40
Fair Value	343.6	325
Junior Subordinated Debentures [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	172.7	193.3
Fair Value	155.5	155.5
Senior Unsecured Fixed Rate Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	143.8	143.8
Fair Value	132.3	116.2
Other Indebtedness [Member] \| Floating Rate Loan Stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	61.3	65.5
Fair Value	55.2	52.7
Other Indebtedness [Member] \| Notes Payable [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	0.7	0.8
Fair Value	$0.60	$0.60

Shareholders_Equity_Additional

Shareholders Equity - Additional Information (Detail) (USD $)

0 Months Ended

1 Months Ended

3 Months Ended

12 Months Ended

0 Months Ended

In Millions, except Share data, unless otherwise specified

Nov. 30, 2014

Sep. 15, 2014

Aug. 05, 2014

Jun. 16, 2014

5-May-14

Mar. 17, 2014

Feb. 18, 2014

Dec. 16, 2013

Nov. 04, 2013

Sep. 16, 2013

Aug. 06, 2013

Jun. 20, 2013

7-May-13

Mar. 15, 2013

Feb. 15, 2013

Dec. 17, 2012

Nov. 06, 2012

Sep. 18, 2012

Aug. 07, 2012

Jun. 15, 2012

8-May-12

Mar. 15, 2012

Feb. 15, 2012

Dec. 31, 2014

Sep. 30, 2014

Jun. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Nov. 05, 2013

Feb. 17, 2015

Class Of Stock [Line Items]

Dividends declaration date

30-Nov-14

5-Aug-14

5-May-14

4-Nov-13

6-Aug-13

7-May-13

15-Feb-13

6-Nov-12

7-Aug-12

8-May-12

15-Feb-12

18-Feb-14

7-May-13

Stock dividend declared

10.00%

Dividends payable date

31-Dec-14

15-Sep-14

16-Jun-14

16-Dec-13

16-Sep-13

20-Jun-13

15-Mar-13

17-Dec-12

18-Sep-12

15-Jun-12

15-Mar-12

17-Mar-14

17-Jun-13

Dividend declared per common share

$0.18

$0.15

$0.11

$0.69

$0.59

$0.44

Dividend payable, date of record

31-Dec-14

1-Sep-14

2-Jun-14

2-Dec-13

2-Sep-13

3-Jun-13

1-Mar-13

3-Dec-12

4-Sep-12

1-Jun-12

1-Mar-12

3-Mar-14

3-Jun-13

Cash dividends paid - common shares, total

$4.70

$4.10

$3.70

$3.10

$3.20

$4.80

$18.20

$15.80

$12.30

Additional stock issued as dividend

2,447,839

Preferred shares, authorized

30,000,000

Preferred shares, par value

Preferred shares, issued

Preferred shares, outstanding

Total number of shares authorized for purchase, Value

50.8

45.1

44.6

Common shares repurchased

301,758

Common shares repurchased, total cost

14.9

2013 Repurchase Authorization [Member]

Class Of Stock [Line Items]

Total number of shares authorized for purchase, Value

$92.80

$150

10% Stock Dividend [Member]

Class Of Stock [Line Items]

Dividend declared per common share

$0.14

Subsequent Event

Class Of Stock [Line Items]

Dividends declaration date

17-Feb-15

Stock dividend declared

10.00%

Dividends payable date

16-Mar-15

Dividend declared per common share

$0.20

Dividend payable, date of record

2-Mar-15

Additional stock issued as dividend

2,600,000

Shareholders_Equity_Schedule_o

Shareholders Equity - Schedule of Repurchase of Shares (Detail) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity Class Of Treasury Stock [Line Items]
Number of Shares Repurchased	1,048,144	1,098,732	1,488,308
Total Cost	$14.90
12/17/2013 [Member]
Equity Class Of Treasury Stock [Line Items]
Date Trading Plan Initiated	17-Dec-13
2014 Purchase Period	02/04/14-02/12/14
Number of Shares Repurchased	15,789
Average Price of Shares Repurchased	$43.28
Total Cost	0.7
12/17/2013 [Member] \| Treasury Shares Period Start Date [Member]
Equity Class Of Treasury Stock [Line Items]
Trading Plans Purchase Period Date Range Start	2/4/14
12/17/2013 [Member] \| Treasury Shares Period End Date [Member]
Equity Class Of Treasury Stock [Line Items]
Trading Plans Purchase Period Date Range Start	2/12/14
3/18/2014 [Member]
Equity Class Of Treasury Stock [Line Items]
Date Trading Plan Initiated	18-Mar-14
2014 Purchase Period	03/18/14-04/28/14
Number of Shares Repurchased	436,867
Average Price of Shares Repurchased	$45.81
Total Cost	20
3/18/2014 [Member] \| Treasury Shares Period Start Date [Member]
Equity Class Of Treasury Stock [Line Items]
Trading Plans Purchase Period Date Range Start	3/18/14
3/18/2014 [Member] \| Treasury Shares Period End Date [Member]
Equity Class Of Treasury Stock [Line Items]
Trading Plans Purchase Period Date Range Start	4/28/14
6/13/2014 [Member]
Equity Class Of Treasury Stock [Line Items]
Date Trading Plan Initiated	13-Jun-14
2014 Purchase Period	06/17/14-07/04/14
Number of Shares Repurchased	41,362
Average Price of Shares Repurchased	$49.94
Total Cost	2.1
6/13/2014 [Member] \| Treasury Shares Period Start Date [Member]
Equity Class Of Treasury Stock [Line Items]
Trading Plans Purchase Period Date Range Start	6/17/14
6/13/2014 [Member] \| Treasury Shares Period End Date [Member]
Equity Class Of Treasury Stock [Line Items]
Trading Plans Purchase Period Date Range Start	7/4/14
9/12/2014 [Member]
Equity Class Of Treasury Stock [Line Items]
Date Trading Plan Initiated	12-Sep-14
2014 Purchase Period	09/16/14-10/28/14
Number of Shares Repurchased	229,633
Average Price of Shares Repurchased	$51.98
Total Cost	11.9
9/12/2014 [Member] \| Treasury Shares Period Start Date [Member]
Equity Class Of Treasury Stock [Line Items]
Trading Plans Purchase Period Date Range Start	9/16/14
9/12/2014 [Member] \| Treasury Shares Period End Date [Member]
Equity Class Of Treasury Stock [Line Items]
Trading Plans Purchase Period Date Range Start	9/30/14
12/15/2014 [Member]
Equity Class Of Treasury Stock [Line Items]
Date Trading Plan Initiated	15-Dec-14
2014 Purchase Period	12/16/14-12/23/14
Number of Shares Repurchased	22,735
Average Price of Shares Repurchased	$53.44
Total Cost	$1.20
12/15/2014 [Member] \| Treasury Shares Period Start Date [Member]
Equity Class Of Treasury Stock [Line Items]
Trading Plans Purchase Period Date Range Start	12/16/14
12/15/2014 [Member] \| Treasury Shares Period End Date [Member]
Equity Class Of Treasury Stock [Line Items]
Trading Plans Purchase Period Date Range Start	12/23/14
12/17/2013 Repurchase Authorization [Member]
Equity Class Of Treasury Stock [Line Items]
Repurchase Authorization Year	2013
3/18/2014 Repurchase Authorization [Member]
Equity Class Of Treasury Stock [Line Items]
Repurchase Authorization Year	2013
6/13/2014 Repurchase Authorization [Member]
Equity Class Of Treasury Stock [Line Items]
Repurchase Authorization Year	2013
9/12/2014 Repurchase Authorization [Member]
Equity Class Of Treasury Stock [Line Items]
Repurchase Authorization Year	2013
12/15/2014 Repurchase Authorization [Member]
Equity Class Of Treasury Stock [Line Items]
Repurchase Authorization Year	2013

Shareholders_Equity_Schedule_o1

Shareholders' Equity - Schedule of Authorized and Unissued Common Shares Reserved (Detail)	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Shares Reserved	5,735,386
2011 Long-Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Shares Reserved	4,130,532
2007 Employee Share Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Shares Reserved	1,600,886
Historical Stock Compensation Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Shares Reserved	3,968

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Beginning Balance	$147.80	$189.50
Other comprehensive (loss) income before reclassifications	-19	-1.3
Amounts reclassified from accumulated other comprehensive income (loss)	-20.7	-40.4
Other comprehensive (loss) income, net of tax	-39.7	-41.7	49.7
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Ending Balance	108.1	147.8	189.5
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Beginning Balance	-11.5	-8.7
Other comprehensive (loss) income before reclassifications	-4.1	-2.8
Other comprehensive (loss) income, net of tax	-4.1	-2.8
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Ending Balance	-15.6	-11.5
Unrealized Holding Gains on Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Beginning Balance	163.9	204.1
Other comprehensive (loss) income before reclassifications	-12.5	0.2
Amounts reclassified from accumulated other comprehensive income (loss)	-20.7	-40.4
Other comprehensive (loss) income, net of tax	-33.2	-40.2
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Ending Balance	130.7	163.9
Defined Benefit Pension Plans
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Beginning Balance	-4.6	-5.9
Other comprehensive (loss) income before reclassifications	-2.4	1.3
Other comprehensive (loss) income, net of tax	-2.4	1.3
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Ending Balance	($7)	($4.60)

Accumulated_Other_Comprehensiv3

Accumulated Other Comprehensive Income (Loss) - Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Unrealized gains and losses on securities:
Net realized investment gains	($30.60)	($59.80)	($14.40)
Provision for income taxes	9.9	19.4	4
Net of taxes	-20.7	-40.4
Unrealized Holding Gains on Securities
Unrealized gains and losses on securities:
Net of taxes	-20.7	-40.4
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Unrealized Holding Gains on Securities
Unrealized gains and losses on securities:
Net realized investment gains	-30.6	-59.8	-14.4
Provision for income taxes	9.9	19.4	4
Net of taxes	($20.70)	($40.40)	($10.40)

Net_Income_Per_Common_Share_Ne

Net Income Per Common Share - Net Income Per Common Share on Basic and Diluted Basis (Detail) (USD $)	3 Months Ended																12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Earnings Per Share [Abstract]
Net income	$59.70		$44.70		$38.60		$40.20		$47.80		$31		$31.70		$32.70		$183.20		$143.20		$52.30
Weighted average common shares outstanding - basic																	26,082,114		26,851,341		28,095,210
Effect of dilutive securities:
Equity compensation awards																	475,037		1,018,192		555,238
Weighted average common shares outstanding - diluted																	26,557,151		27,869,533		28,650,448
Net income per common share - basic	$2.32	[1]	$1.72	[1]	$1.48	[1]	$1.52	[1]	$1.80	[1]	$1.17	[1]	$1.18	[1]	$1.20	[1]	$7.02	[1]	$5.33	[1]	$1.86
Net income per common share - diluted	$2.28	[1]	$1.69	[1]	$1.45	[1]	$1.49	[1]	$1.74	[1]	$1.12	[1]	$1.13	[1]	$1.16	[1]	$6.90	[1]	$5.14	[1]	$1.83

[1]	Basic and diluted net income per common share are computed independently for each quarter and full year based on the respective average number of common shares outstanding; therefore, the sum of the quarterly net income per common share data may not equal the net income per common share for the year.

Net_Income_Per_Common_Share_Ad

Net Income Per Common Share - Additional Information (Detail)

3 Months Ended

12 Months Ended

0 Months Ended

Dec. 31, 2014

Sep. 30, 2014

Jun. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Feb. 17, 2015

7-May-13

Net Income Loss Per Common Share [Line Items]

Treasury shares, shares

8,606,489

7,558,345

6,459,613

8,606,489

7,558,345

6,459,613

Antidilutive securities excluded from computation of diluted net income per share, shares

1,700

3,300

550,632

Stock dividend declared

10.00%

Dividends declaration date

30-Nov-14

5-Aug-14

5-May-14

4-Nov-13

6-Aug-13

7-May-13

15-Feb-13

6-Nov-12

7-Aug-12

8-May-12

15-Feb-12

18-Feb-14

7-May-13

Dividends payable date

31-Dec-14

15-Sep-14

16-Jun-14

16-Dec-13

16-Sep-13

20-Jun-13

15-Mar-13

17-Dec-12

18-Sep-12

15-Jun-12

15-Mar-12

17-Mar-14

17-Jun-13

Dividend payable, date of record

31-Dec-14

1-Sep-14

2-Jun-14

2-Dec-13

2-Sep-13

3-Jun-13

1-Mar-13

3-Dec-12

4-Sep-12

1-Jun-12

1-Mar-12

3-Mar-14

3-Jun-13

Subsequent Event

Net Income Loss Per Common Share [Line Items]

Stock dividend declared

10.00%

Dividends declaration date

17-Feb-15

Dividends payable date

16-Mar-15

Dividend payable, date of record

2-Mar-15

Sharebased_Compensation_Additi

Share-based Compensation - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-based compensation arrangement by share-based payment award, award vesting period, years	5 years	5 years
Schedule Of Share Repurchase Programs [Line Items]
Share-based payments expense	$19.60	$23.30	$10.50
2007 Employee Share Purchase Plan [Member]
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-based compensation arrangement by share-based payment award, award vesting period, years	3 months
Schedule Of Share Repurchase Programs [Line Items]
Share-based payments expense	19.6	23	10.3
Employee service share-based compensation, tax benefit from compensation expense	$16.20	$18.30	$8.40

Sharebased_Compensation_Fair_V

Share-based Compensation - Fair Value Assumptions (Detail)	12 Months Ended
Share-based Compensation - Fair Value Assumptions (Detail)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free rate of return, minimum	1.53%	0.80%	0.68%
Expected volatility, minimum	22.84%	26.30%	32.12%
Risk-free rate of return, maximum	1.77%	1.71%	1.11%
Expected volatility, maximum	25.46%	32.07%	32.84%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yields	1.49%	1.49%	1.58%
Expected award life (years)	4 years 8 months 1 day	4 years 10 months 28 days	5 years 11 days
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yields	1.55%	1.67%	1.67%
Expected award life (years)	4 years 10 months 6 days	5 years 26 days	5 years 22 days

ShareBased_Compensation_2014_L

Share-Based Compensation - 2014 Long-Term Incentive Plan - Additional Information (Detail) (USD $)	12 Months Ended			1 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	31-May-14	Nov. 30, 2007
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, number of shares authorized	5,735,386
Share-based compensation arrangement by share-based payment award, award vesting period, years	5 years	5 years
Cash received for exercise of stock options	$3.70
Options granted during the period	0	0	0
Exercised, shares	446,209
Share-based payments expense	19.6	23.3	10.5
Employee Stock Option \| 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
Employee Stock Option \| 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	5 years
2007 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					4,500,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant				1,457,800
Exercised, shares	108,184
Share based compensation arrangement by share based payment award options, outstanding	48,135	158,092
2014 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, additional number of shares authorized				2,800,000
Count of restricted shares, settle in common shares	2.75
Restricted Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee service share-based compensation, unrecognized compensation costs on non-vested awards	6.8
Employee service share-based compensation, unrecognized compensation costs weighted-average period, years	1 year 8 months 12 days
Share-based compensation arrangement by share-based payment award, total fair value of shares vested	1.9
Employee service share-based compensation, cash paid to exercise of stock options	0.4	1.2
Restricted Share Units [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	24 months
Restricted Share Units [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	48 months
Restricted Share Units [Member] \| Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement by share based payment award options, outstanding	30,050
Stock-Settled SARs Activity [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee service share-based compensation, unrecognized compensation costs on non-vested awards	2.6
Employee service share-based compensation, unrecognized compensation costs weighted-average period, years	2 years
Exercised, shares	124,541
Share based compensation arrangement by share based payment award, shares issued	49,742
Share based compensation arrangement by share based payment award options exercises, intrinsic value	26.5
Stock-Settled SARs Activity [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
Stock-Settled SARs Activity [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] \| Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement by share based payment award options, outstanding	160,204
Cash-Settled SARs Activity [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee service share-based compensation, unrecognized compensation costs on non-vested awards	10.1
Employee service share-based compensation, unrecognized compensation costs weighted-average period, years	2 years 4 months 24 days
Share based compensation arrangement by share based payment award options exercises, intrinsic value	32.3
Employee service share-based compensation, cash paid to exercise of stock options	9.3
Liability for stock awards	24.4	19.4
Share-based payments expense	$0.50	$0.90	$0.60
Cash-Settled SARs Activity [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
Cash-Settled SARs Activity [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
Cash-Settled SARs Activity [Member] \| Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement by share based payment award options, outstanding	2,563,467

Sharebased_Compensation_Summar

Share-based Compensation - Summary of Option Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Shares	0	0	0
Exercised, shares	-446,209
2007 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Outstanding at January 1, 2014	158,092
Exercised, shares	-108,184
Expired or forfeited, Shares	-1,773
Shares, Outstanding at December 31, 2014	48,135
Vested and exercisable at end of year, Shares	48,135
Weighted-Average Exercise Price, Outstanding at January 1, 2014	34.27
Exercised, Weighted-Average Exercise Price	34.38
Expired or forfeited, Weighted-Average Exercise Price	32.03
Weighted-Average Exercise Price, Outstanding at December 31, 2014	34.11
Vested and exercisable at end of year, Weighted-Average Exercise Price	34.11
Weighted-Average Remaining Contractual Term, Outstanding at end of the year	3 months 18 days
Vested and exercisable at end of year, Weighted-Average Remaining Contractual Term	3 months 18 days
Aggregate Intrinsic Value, Outstanding at end of the year	1,028,247
Vested and exercisable at end of year, Aggregate Intrinsic Value	1,028,247

Sharebased_Compensation_Summar1

Share-based Compensation - Summary of Restricted Share Activity (Detail) (Restricted Share Units [Member], USD $)	12 Months Ended
	Dec. 31, 2014
Restricted Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Outstanding at January 1, 2014	257,975
Granted, Shares	123,229
Vested and issued, Shares	-60,198
Expired or forfeited, Shares	-35,511
Shares, Outstanding at December 31, 2014	285,495
Weighted-Average Grant Date Fair Value, Outstanding at January 1, 2014	$32.97
Granted, Weighted-Average Grant Date Fair Value	$45.61
Vested and issued, Weighted-Average Grant Date Fair Value	$31.65
Expired or forfeited, Weighted-Average Grant Date Fair Value	$33.08
Weighted-Average Grant Date Fair Value, Outstanding at December 31, 2014	$38.69

Sharebased_Compensation_Summar2

Share-based Compensation - Summary of Stock-Settled SARs Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Shares	0	0	0
Exercised, shares	-446,209
Stock-Settled SARs Activity [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Outstanding at January 1, 2014	1,288,698
Granted, Shares	188,273
Exercised, shares	-124,541
Expired or forfeited, Shares	-155,909
Shares, Outstanding at December 31, 2014	1,196,521
Vested or expected to vest as of year end, Shares	1,102,211
Exercisable at end of year, Shares	763,302
Weighted-Average Exercise Price, Outstanding at January 1, 2014	29.46
Granted, Weighted-Average Exercise Price	43.23
Exercised, Weighted-Average Exercise Price	28.93
Expired or forfeited, Weighted-Average Exercise Price	32.72
Weighted-Average Exercise Price, Outstanding at December 31, 2014	31.26
Vested or expected to vest as of year end, Weighted-Average Exercise Price	30.81
Exercisable at end of year, Weighted-Average Exercise Price	28.27

Sharebased_Compensation_Summar3

Share-based Compensation - Summary of Cash-Settled SARs Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Shares	0	0	0
Exercised, shares	-446,209
Cash-Settled SARs Activity [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Outstanding at January 1, 2014	1,743,758
Granted, Shares	756,853
Exercised, shares	-446,209
Expired or forfeited, Shares	-230,633
Shares, Outstanding at December 31, 2014	1,823,769
Vested or expected to vest as of year end, Shares	1,518,831
Exercisable at end of year, Shares	421,995
Weighted-Average Exercise Price, Outstanding at January 1, 2014	33
Granted, Weighted-Average Exercise Price	44.28
Exercised, Weighted-Average Exercise Price	30.96
Expired or forfeited, Weighted-Average Exercise Price	36.15
Weighted-Average Exercise Price, Outstanding at December 31, 2014	37.78
Vested or expected to vest as of year end, Weighted-Average Exercise Price	37.42
Exercisable at end of year, Weighted-Average Exercise Price	31.79

ShareBased_Compensation_Employ

Share-Based Compensation - Employees Share Purchase Plans - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Share Repurchase Programs [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period, years	5 years	5 years
Share-based payments expense	$19.60	$23.30	$10.50
2007 Employee Share Purchase Plan [Member]
Schedule Of Share Repurchase Programs [Line Items]
Share-based compensation arrangement by share-based payment award, discount from market price	85.00%
Share-based compensation arrangement by share-based payment award, award vesting period, years	3 months
Share-based payments expense	19.6	23	10.3
Earn Plan [Member] \| Maximum [Member]
Schedule Of Share Repurchase Programs [Line Items]
Share-based compensation arrangement by share-based payment award, discount from market price	85.00%
Share-based compensation arrangement by share-based payment award, award vesting period, years	3 years
Earn Plan [Member] \| Minimum [Member]
Schedule Of Share Repurchase Programs [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period, years	5 years
Stock Compensation Plan [Member]
Schedule Of Share Repurchase Programs [Line Items]
Share-based payments expense	$0.30	$0.30	$0.20

ShareBased_Compensation_Deferr

Share-Based Compensation - Deferred Compensation Plan for Non-Employee Directors - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Share Repurchase Programs [Line Items]
Deferred compensation arrangement with individual, description	Under the Directors Plan, non-employee directors could elect each year to defer payment of 0%, 50% or 100% of their cash compensation payable during the next calendar year.
Deferred compensation arrangement with individual, employer contribution percentage		75.00%
Deferred compensation arrangement with individual, shares authorized for issuance		1,650
Share-based payments expense	$19.60	$23.30	$10.50
2007 Plan [Member]
Schedule Of Share Repurchase Programs [Line Items]
Deferred compensation arrangement with individual, interest rate	Two percent above the prime rate
Share-based compensation arrangement by share-based payment award, discount from market price		50.00%
2007 Plan [Member] \| Minimum [Member]
Schedule Of Share Repurchase Programs [Line Items]
Share-based compensation arrangement by share-based payment award, discount from market price		0.00%
2007 Plan [Member] \| Maximum [Member]
Schedule Of Share Repurchase Programs [Line Items]
Share-based compensation arrangement by share-based payment award, discount from market price		100.00%
Deferred Compensation Plan [Member]
Schedule Of Share Repurchase Programs [Line Items]
Employee service share-based compensation, cash paid to exercise of stock options		1.9
Share-based payments expense	0.7	2	1.2
Liability for stock awards	$4.20	$3.50
Distribution Network [Member]
Schedule Of Share Repurchase Programs [Line Items]
Deferred compensation arrangement with individual, distributions period, months		6 months

Underwriting_Acquisition_and_I2

Underwriting, Acquisition and Insurance Expenses - Underwriting, Acquisition and Insurance Expenses (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other Income And Expenses [Abstract]
Commissions	$231.10	$229.60	$198.20
General expenses	288	272.8	248
Premium taxes, boards and bureaus	25.5	24.2	22.8
Underwriting Acquisition and Insurance Expenses, Total	544.6	526.6	469
Net deferral of policy acquisition costs	-5.4	-15.8	-4.5
Total underwriting, acquisition and insurance expenses	$539.20	$510.80	$464.50

Underwriting_Acquisition_and_I3

Underwriting, Acquisition and Insurance Expenses - Additional Information (Detail) (Stock Compensation Plan [Member], USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock Compensation Plan [Member]
Underwriting Acquisition And Insurance Expense [Line Items]
Expense associated with cash settled stock appreciation rights	$19.60	$23	$10.30

Income_Taxes_Income_Tax_Provis

Income Taxes - Income Tax Provision (Benefit) (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Current tax provision	$5.20	$32.70	$9.40
Future tax deductions	58.4	0.1	2.9
Valuation allowance change	-30.8	3.7	2.1
Income tax provision	$32.80	$36.50	$14.40

Income_Taxes_Schedule_of_PreTa

Income Taxes - Schedule of Pre-Tax Income (Loss) and Effective Income Tax Rates (Detail) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Examination [Line Items]
Pre-tax income (loss)	$80.30	$48.30	$44.70	$42.70	$66.50	$32.90	$42.80	$37.50	$216	$179.70	$66.70
Bermuda [Member]
Income Tax Examination [Line Items]
Pre-tax income (loss)									102.8	50.5	10
Effective Tax Rate									0.00%	0.00%	0.00%
United States [Member]
Income Tax Examination [Line Items]
Pre-tax income (loss)									98	120.9	52
Effective Tax Rate									28.10%	28.20%	21.30%
United Kingdom [Member]
Income Tax Examination [Line Items]
Pre-tax income (loss)									21.5	18.5	14
Effective Tax Rate									24.80%	12.00%	24.40%
Belgium [Member]
Income Tax Examination [Line Items]
Pre-tax income (loss)										0.2	-0.1
Effective Tax Rate									63.80%	103.00%	98.40%
Brazil [Member]
Income Tax Examination [Line Items]
Pre-tax income (loss)									-2.2	-9.7	-6.5
Effective Tax Rate									0.00%	0.00%	0.00%
United Arab Emirates [Member]
Income Tax Examination [Line Items]
Pre-tax income (loss)									-0.9	1.1
Effective Tax Rate									0.00%	0.00%	0.00%
Ireland [Member]
Income Tax Examination [Line Items]
Pre-tax income (loss)									-1.1	-0.1	-0.2
Effective Tax Rate									0.00%	0.00%	0.00%
Malta [Member]
Income Tax Examination [Line Items]
Pre-tax income (loss)									-2.2	-1.7	-2.6
Effective Tax Rate									0.00%	0.00%	0.00%
France [Member]
Income Tax Examination [Line Items]
Effective Tax Rate									0.00%	0.00%	0.00%
Switzerland [Member]
Income Tax Examination [Line Items]
Pre-tax income (loss)									$0.10		$0.10
Effective Tax Rate									17.60%	5.60%	22.80%

Income_Taxes_Schedule_of_PreTa1

Income Taxes - Schedule of Pre-Tax Income (Loss) and Effective Income Tax Rates (Parenthetical) (Detail) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Examination [Line Items]
Pre-tax income (loss)	$80.30	$48.30	$44.70	$42.70	$66.50	$32.90	$42.80	$37.50	$216	$179.70	$66.70
United Arab Emirates [Member]
Income Tax Examination [Line Items]
Pre-tax income (loss)									-0.9	1.1
Switzerland [Member]
Income Tax Examination [Line Items]
Pre-tax income (loss)									0.1		0.1
Maximum [Member] \| United Arab Emirates [Member]
Income Tax Examination [Line Items]
Pre-tax income (loss)											0.1
Maximum [Member] \| Switzerland [Member]
Income Tax Examination [Line Items]
Pre-tax income (loss)										$0.10

Income_Taxes_Reconciliation_of

Income Taxes - Reconciliation of Difference Between Provision for Income Taxes and Expected Tax Provision at Weighted Average Tax Rate (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Examination [Line Items]
Income tax provision at expected rate	$37.20	$43.10	$18.50
Tax-exempt interest	-4.5	-5.6	-5.6
Dividends received deduction	-2.3	-2.3	-2.2
Valuation allowance change	-30.8	3.7	2.1
Other permanent adjustments, net	-0.7	0.3	1.8
Adjustment for prior year tax return	-0.9	-1.6	0.2
United States state tax expense (benefit)	2.5	0.3	-0.3
PXRE Reinsurance capital loss carryforward	29.8
Other foreign adjustments	0.7	-0.1
Deferred tax rate reduction	-0.4	-1.2	-0.6
Foreign exchange adjustments	0.2	-1.7	0.5
Foreign withholding taxes	0.4	0.5
Income tax provision	32.8	36.5	14.4
Income tax provision - Foreign	5.2	2.4	3.3
Income tax provision - United States, Federal	23.3	33.2	11.5
Income tax provision (benefit) - United States, state	3.9	0.4	-0.4
Foreign withholding tax - United States	0.4	0.5
Income tax provision	32.8	36.5	14.4
Scenario, Previously Reported [Member]
Income Tax Examination [Line Items]
Prior period adjustment for deferred	1.5
Prior year foreign taxes	$0.10	$1.10

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
Income Taxes - Additional Information (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	$1,300,000	$1,600,000
Deferred tax rate reduction	400,000	1,200,000	600,000
Foreign exchange adjustments	1,000,000	1,700,000	500,000
Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions			200,000
Deferred tax decreased and Increase balance	24,300,000	-15,100,000
Total net deferred tax liabilities	27,600,000
Net operating loss carryforward	18,000,000
Valuation allowance	25,400,000	56,200,000
Loss carryforwards per year	2,800,000
Reduced valuation allowance	29,800,000
Unrecognized tax benefits	0	0	0
ARIS [Member]
Income Tax Contingency [Line Items]
Net operating loss carryforward	1,000,000
United Kingdom [Member]
Income Tax Contingency [Line Items]
Deferred tax rate reduction	400,000
Malta [Member]
Income Tax Contingency [Line Items]
Valuation allowance	15,900,000
Decreased valuation allowance	600,000
Brazil [Member]
Income Tax Contingency [Line Items]
Valuation allowance	7,400,000
Increased valuation allowance	400,000
PXRE Reinsurance Company [Member]
Income Tax Contingency [Line Items]
Increase of recognized benefit	29,800,000
Valuation allowance	2,100,000
Reduced valuation allowance	800,000
December 31, 2025 [Member]
Income Tax Contingency [Line Items]
Loss carryforwards, amounts expiring if not utilized	16,500,000
December 31, 2027 [Member]
Income Tax Contingency [Line Items]
Loss carryforwards, amounts expiring if not utilized	1,500,000
December 31, 2027 [Member] \| ARIS [Member]
Income Tax Contingency [Line Items]
Loss carryforwards, amounts expiring if not utilized	200,000
December 31, 2028 [Member] \| ARIS [Member]
Income Tax Contingency [Line Items]
Loss carryforwards, amounts expiring if not utilized	400,000
December 31, 2029 [Member] \| ARIS [Member]
Income Tax Contingency [Line Items]
Loss carryforwards, amounts expiring if not utilized	$400,000

Income_Taxes_Schedule_of_Defer

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Income Tax Examination [Line Items]
Unrealized losses on fixed maturities and other investment securities	$0	$0
Losses and loss adjustment expense reserve discounting	25.1	28.4
Unearned premiums	24.8	23
Capital loss carryforward	0	29.8
Allowance for bad debt	2	1.9
Accrual for contingent commissions	0.3	0.4
Net operating loss carryforward	18.8	19.8
Impairment of investment values	8.2	10.6
United States amortization of intangible assets	4.3	3.1
Accrued bonus	6.7	5.7
Accrued vacation	1.7	1.6
Stock option expense	8	6.4
United Kingdom interest	0	0.8
Depreciable fixed asset	5.2	0
Other	7	9.1
Deferred tax assets, gross	121.6	150.3
Unrealized gains on equity securities	-62.3	-65.1
Unrealized gains on fixed maturities and other investment securities	-15.3	-16.1
Deferred acquisition costs	-20.3	-19.5
United States amortization of intangible assets	-3.5	-3.3
United Kingdom underwriting losses	-9	-4.8
United Kingdom amortization of intangible assets	-2.3	-2.8
Brussels pension	-0.1	-0.2
Internally developed software	-21.5	0
Unrealized FV gain on LP	-10.5	-9.2
Other	-4.4	-1.8
Deferred tax liabilities, gross	-149.2	-122.8
Deferred tax assets, net before valuation allowance	-27.6	27.5
Valuation allowance	-25.4	-56.2
Deferred tax liabilities, net	-53	-28.7
Net deferred tax liabilities - Foreign	-11.8	-7
Net deferred tax liabilities - United States	-41.2	-21.7
Brazil [Member]
Income Tax Examination [Line Items]
Operating losses	7.4	8
Malta [Member]
Income Tax Examination [Line Items]
Operating losses	$2.10	$1.70

Pension_Benefits_Schedule_of_C

Pension Benefits - Schedule of Change in Plan Assets (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Compensation And Retirement Disclosure [Abstract]
Fair value of plan assets at beginning of year	$20.20	$20.10
Actual return on plan assets	1	1.9
Employer contributions	0.2	0.2
Settlements and benefits paid	-2.2	-2
Fair value of plan assets at end of year	$19.20	$20.20

Pension_Benefits_Schedule_of_C1

Pension Benefits - Schedule of Change in Projected Benefit Obligation (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Compensation And Retirement Disclosure [Abstract]
Projected benefit obligation at beginning of year	$22.60	$24.60
Interest cost	1	0.8	1
Actuarial loss (gain)	4.3	-0.8
Settlements and benefits paid	-2.1	-2
Projected benefit obligation at end of year	$25.80	$22.60	$24.60

Pension_Benefits_Additional_In

Pension Benefits - Additional Information (Detail) (USD $)	12 Months Ended
Pension Benefits - Additional Information (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Unrecognized actuarial loss	$400,000
Defined benefit plans with accumulated benefit obligations in excess of plan assets	2,200,000	2,200,000
Fair value of plan assets	0	0
Contributions by employer towards savings plan	7,100,000	6,800,000	6,300,000
Qualified Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Amount of pension related to plan	4,400,000	300,000
Non- Qualified Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Amount of pension related to plan	$2,200,000	$2,200,000
Target Thresholds [Member] \| Fixed Income Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Defined Benefit Plan, Target Allocation Percentage	65.00%
Target Thresholds [Member] \| Equity Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Defined Benefit Plan, Target Allocation Percentage	35.00%
Actual Asset Allocation [Member] \| Fixed Income Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Defined Benefit Plan, Target Allocation Percentage	67.40%
Actual Asset Allocation [Member] \| United States [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Defined Benefit Plan, Target Allocation Percentage	25.10%
Actual Asset Allocation [Member] \| Foreign Equities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Defined Benefit Plan, Target Allocation Percentage	7.50%
Actual Asset Allocation [Member] \| Equity Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Defined Benefit Plan, Target Allocation Percentage	32.60%

Pension_Benefits_Schedule_of_A

Pension Benefits - Schedule of Assumptions to Determine Benefit Obligations (Detail)	Dec. 31, 2014	Dec. 31, 2013
Compensation And Retirement Disclosure [Abstract]
Weighted average discount rate	3.37%	4.42%

Pension_Benefits_Schedule_of_A1

Pension Benefits - Schedule of Assumptions to Determine Net Periodic Benefit Cost (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Compensation And Retirement Disclosure [Abstract]
Weighted average discount rate	4.39%	3.63%	4.50%
Expected return on plan assets	6.00%	6.00%	6.00%

Pension_Benefits_Components_of

Pension Benefits - Components of Net Periodic Benefit Cost (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Compensation And Retirement Disclosure [Abstract]
Interest cost	$1	$0.80	$1
Expected return on plan assets	-1.2	-1	-1.1
Settlement charge	0.4
Amortization of actuarial loss	0.3	0.3	0.3
Net periodic benefit cost	$0.50	$0.10	$0.20

Pension_Benefits_Schedule_of_F

Pension Benefits - Schedule of Fair Value Measurement (Detail) (USD $)	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	$19.20		$20.20		$20.10
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	18.8		19.7
Significant Other Observable Inputs (Level 2) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	0.4		0.5
Mutual Funds \| Real Estate [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	0.6		0.5
Mutual Funds \| Large Cap U.S. Equity [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	2.9		3.2
Mutual Funds \| Small-Mid Cap U.S. Equity [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	1.2		1.4
Mutual Funds \| International Equity [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	1.5		1.5
Mutual Funds \| U.S. and Global Government and Corporate Fixed Maturity [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	12.6		12.9
Mutual Funds \| Convertible Bonds And Equities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total			0.2
Mutual Funds \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Real Estate [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	0.6		0.5
Mutual Funds \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Large Cap U.S. Equity [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	2.9		3.2
Mutual Funds \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Small-Mid Cap U.S. Equity [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	1.2		1.4
Mutual Funds \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| International Equity [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	1.5		1.5
Mutual Funds \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| U.S. and Global Government and Corporate Fixed Maturity [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	12.6		12.9
Mutual Funds \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Convertible Bonds And Equities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total			0.2
Cash And Short-Term Investments [Member] \| Short-Term Investments [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	0.4	[1]	0.5	[2]
Cash And Short-Term Investments [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Short-Term Investments [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	$0.40	[1]	$0.50	[2]

[1]	Assets invested in one common collective trust composed of high-grade money market money instruments with short maturities.
[2]	Assets invested in one common collective trust composed of high-grade money market money instruments with short maturities

Pension_Benefits_Schedule_of_E

Pension Benefits - Schedule of Expected Benefit Payments (Detail) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified	Dec. 31, 2014
Compensation And Retirement Disclosure [Abstract]
2015	$1.70
2016	1.6
2017	1.9
2018	1.7
2019	1.8
Years 2020 to 2024	7.9
Total	$16.60

Commitments_and_Contingencies_

Commitments and Contingencies - Additional Information (Detail) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified	Dec. 31, 2014
Commitments And Contingencies Disclosure [Abstract]
Contractual commitments related to its limited partnership investments	$72.90

Leases_Schedule_of_Future_Mini

Leases - Schedule of Future Minimum Payments Under Non-Cancelable Operating Leases (Detail) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified	Dec. 31, 2014
Leases [Abstract]
2015	$11.20
2016	9.1
2017	8.1
2018	7.8
2019	6.1
Thereafter	9.4
Total	$51.70

Lease_Additional_Information_D

Lease - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Leases [Abstract]
Operating leases expense	$51.70	$57.60	$55.30

Segment_Information_Additional

Segment Information - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
	Segment	Dec. 31, 2013
Segment Reporting [Abstract]
Number of reportable segments	4
Assets associated with trade capital providers	$315.40	$386.80

Segment_Information_Revenue_an

Segment Information - Revenue and Income (Loss) Before Income Taxes for Each Segment (Detail) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Earned premiums									$1,338.10	$1,303.80	$1,186.50
Net investment income									86.6	100	118.8
Net realized investment and other gains									94	71.3	25.7
Total revenue	412.1	371.3	375.2	360.1	406	363.7	363.8	341.6	1,518.70	1,475.10	1,331
Income (loss) before income taxes	80.3	48.3	44.7	42.7	66.5	32.9	42.8	37.5	216	179.7	66.7
Excess and Surplus Lines [Member]
Segment Reporting Information [Line Items]
Earned premiums									485.2	460.2	399.3
Net investment income									36.7	42.2	51.1
Commercial Specialty [Member]
Segment Reporting Information [Line Items]
Earned premiums									291.9	299	317.5
Net investment income									18.7	22.8	27.6
International Specialty [Member]
Segment Reporting Information [Line Items]
Earned premiums									148.3	142.4	130.1
Net investment income									8.2	8.4	12.3
Syndicate 1200 [Member]
Segment Reporting Information [Line Items]
Earned premiums									411.1	401.7	337.9
Net investment income									10.2	11	15.3
Run Off Lines
Segment Reporting Information [Line Items]
Earned premiums									1.6	0.5	1.7
Net investment income									9.7	10.8	12.5
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net investment income									3.1	4.8
Net realized investment and other gains									-35.1	-40.4	-46.8
Operating Segments
Segment Reporting Information [Line Items]
Income (loss) before income taxes									157.1	148.8	87.8
Operating Segments \| Excess and Surplus Lines [Member]
Segment Reporting Information [Line Items]
Net investment income									36.7	42.2	51.1
Income (loss) before income taxes									106	89.4	74.1
Operating Segments \| Commercial Specialty [Member]
Segment Reporting Information [Line Items]
Net investment income									18.7	22.8	27.6
Income (loss) before income taxes									8.9	21.4	-24.8
Operating Segments \| International Specialty [Member]
Segment Reporting Information [Line Items]
Net investment income									8.2	8.4	12.3
Income (loss) before income taxes									21.1	11.3	11.3
Operating Segments \| Syndicate 1200 [Member]
Segment Reporting Information [Line Items]
Net investment income									10.2	11	15.3
Income (loss) before income taxes									44.1	37.3	28.1
Operating Segments \| Run Off Lines
Segment Reporting Information [Line Items]
Net investment income									9.7	10.8	12.5
Income (loss) before income taxes									($23)	($10.60)	($0.90)

Segment_Information_Schedule_o

Segment Information - Schedule of Earned Premiums by Geographic Location (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	$1,338.10	$1,303.80	$1,186.50
Bermuda [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	101.5	101.7	120.4
Brazil [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	44.3	38.7	26.6
Malta [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	2.1	1.8	0.3
United Kingdom [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	411.7	401.7	320.8
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	$778.50	$759.90	$718.40

Segment_Information_Identifiab

Segment Information - Identifiable Assets (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	$6,356.30	$6,591
Excess and Surplus Lines [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	2,350.70	2,252.20
Commercial Specialty [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	1,358.50	1,333.40
International Specialty [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	776.8	743.6
Syndicate 1200 [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	1,258.50	1,638.80
Run Off Lines
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	552.8	555.9
Corporate and Other [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	$59	$67.10

Segment_Information_Schedule_o1

Segment Information - Schedule of Goodwill and Intangible Assets Net of Accumulated Amortization (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Goodwill	$152.20	$153.80
Intangible assets, net of accumulated amortization	78.6	86
Excess and Surplus Lines [Member]
Segment Reporting Information [Line Items]
Goodwill	76.4	76.4
Intangible assets, net of accumulated amortization	2.8	3.4
Commercial Specialty [Member]
Segment Reporting Information [Line Items]
Goodwill	47.1	48.7
Intangible assets, net of accumulated amortization	5.5	9
Syndicate 1200 [Member]
Segment Reporting Information [Line Items]
Goodwill	28.7	28.7
Intangible assets, net of accumulated amortization	$70.30	$73.60

RunOff_Lines_Gross_Reserves_fo

Run-Off Lines - Gross Reserves for Run-Off Lines (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	$53.90	$57.50
Total Run-off Lines	318.5	332.5
Reinsurance Assumed [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	40.1	45.2
Other [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	13.8	12.3
Risk Management [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Run-off Lines	257.1	264.3
Run-Off Reinsurance Lines [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Run-off Lines	4.1	5.8
Other Run-Off Lines [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Run-off Lines	$3.40	$4.90

RunOff_Lines_Total_Gross_Reser

Run-Off Lines - Total Gross Reserves for Asbestos Exposure (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total direct written reserves	$11.10	$9.40	$8
Total assumed domestic reserves	30.6	33.7	38.5
Total assumed London reserves	6.1	7.6	9
Total asbestos reserves	47.8	50.7	55.5
Case Reserves [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total direct written reserves	2.5	1.7	2
Total assumed domestic reserves	13.2	15.7	18.4
Total assumed London reserves	4.7	5.8	5.9
ULAE [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total direct written reserves	1	1.3	1.7
Total assumed domestic reserves	1.6	2.2	2.7
Total assumed London reserves	0.2	0.4	0.6
IBNR [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total direct written reserves	7.6	6.4	4.3
Total assumed domestic reserves	15.8	15.8	17.4
Total assumed London reserves	$1.20	$1.40	$2.50

RunOff_Lines_Net_Underwriting_

Run-Off Lines - Net Underwriting Results for Run-Off Lines (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	($13.30)	($11)	($9.10)
Total Run-off Lines	-31	-19.6	-10.9
Reinsurance Assumed [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	-8.3	-3.8	-3.6
Other [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	-5	-7.2	-5.5
Risk Management [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Run-off Lines	-15.5	-5.9	0.9
Run-Off Reinsurance Lines [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Run-off Lines	-1.5	-1.9	-1.1
Other Run-Off Lines [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Run-off Lines	($0.70)	($0.80)	($1.60)

Statutory_Accounting_Principle2

Statutory Accounting Principle - Statutory Capital and Surplus for Principal Operating Subsidiaries (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Bermuda [Member]
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	$1,278.30	$1,218.20
United Kingdom [Member]
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	224.5	225.8
United States [Member]
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	$790.40	$822.30

Statutory_Accounting_Principle3

Statutory Accounting Principles - Statutory Net Income (Loss) for Principal Operating Subsidiaries (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Bermuda [Member]
Statutory Accounting Practices [Line Items]
Statutory net income (loss)	$145.70	$124.20	($4.20)
United Kingdom [Member]
Statutory Accounting Practices [Line Items]
Statutory net income (loss)	28.7	42.3	40.7
United States [Member]
Statutory Accounting Practices [Line Items]
Statutory net income (loss)	$117.70	$117.40	$42.90

Statutory_Accounting_Principle4

Statutory Accounting Principles - Additional Information (Detail) (USD $)	12 Months Ended		1 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Sep. 30, 2012	Dec. 31, 2015
Agro Re [Member]
Statutory Accounting Practices [Line Items]
Maximum permissible limit for dividend	25.00%
Reduction in total statutory capital	15.00%
Maximum permitted amount of dividends	$319.60
Cash dividends	40.9	84.5
Rockwood Casualty Insurance Company [Member]
Statutory Accounting Practices [Line Items]
Cash dividends	20
Dividend received from subsidiary		9.5	10
Rockwood Casualty Insurance Company [Member] \| Scenario Forecast [Member]
Statutory Accounting Practices [Line Items]
Maximum permitted amount of dividends				13.3
Argonaut Insurance Company [Member]
Statutory Accounting Practices [Line Items]
Cash dividends	0.1
Dividends, Securities	48.7	24.7
Value of ordinary dividends	48.8	24.8
Dividend received from subsidiary		0.1
Argonaut Insurance Company [Member] \| Scenario Forecast [Member]
Statutory Accounting Practices [Line Items]
Maximum permitted amount of dividends				39.1
Colony Insurance Company [Member]
Statutory Accounting Practices [Line Items]
Cash dividends	0.2
Dividends, Securities	55	75.9	59
Value of extraordinary dividends	55.2	76.2
Dividend received from subsidiary		0.3
Colony Insurance Company [Member] \| Scenario Forecast [Member]
Statutory Accounting Practices [Line Items]
Maximum permitted amount of dividends				71.7
Minimum [Member]
Statutory Accounting Practices [Line Items]
Minimum statutory capital and surplus balance	$340.90	$348.80

Insurance_Assessments_Addition

Insurance Assessments - Additional Information (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Insurance [Abstract]
Insurance assessments on current insolvencies	$17	$16.60

Transactions_with_Related_Part1

Transactions with Related Parties - Additional Information (Detail) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified	Dec. 31, 2014
Schedule Of Other Related Party Transactions [Line Items]
Percentage of investment ownership	100.00%
Kinetica [Member]
Schedule Of Other Related Party Transactions [Line Items]
Surety bonds issued	13
Percentage of investment ownership	10.00%

Unaudited_Quarterly_Financial_2

Unaudited Quarterly Financial Data - Quarterly Financial Data (Detail) (USD $)	3 Months Ended																12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$412.10		$371.30		$375.20		$360.10		$406		$363.70		$363.80		$341.60		$1,518.70		$1,475.10		$1,331
Income (loss) before income taxes	80.3		48.3		44.7		42.7		66.5		32.9		42.8		37.5		216		179.7		66.7
Net income	59.7		44.7		38.6		40.2		47.8		31		31.7		32.7		183.2		143.2		52.3
Net income per common share:
Basic	$2.32	[1]	$1.72	[1]	$1.48	[1]	$1.52	[1]	$1.80	[1]	$1.17	[1]	$1.18	[1]	$1.20	[1]	$7.02	[1]	$5.33	[1]	$1.86
Diluted	$2.28	[1]	$1.69	[1]	$1.45	[1]	$1.49	[1]	$1.74	[1]	$1.12	[1]	$1.13	[1]	$1.16	[1]	$6.90	[1]	$5.14	[1]	$1.83
Comprehensive income (loss)	$31.30		$6.80		$64.10		$41.30		$43.80		$47.20		($35.20)		$45.70		$143.50		$101.50		$102

[1]	Basic and diluted net income per common share are computed independently for each quarter and full year based on the respective average number of common shares outstanding; therefore, the sum of the quarterly net income per common share data may not equal the net income per common share for the year.

Information_Provided_in_Connec2

Information Provided in Connection With Outstanding Debt of Subsidiaries - Additional Information (Detail)	Dec. 31, 2014
Debt Disclosure [Abstract]
Ownership Percentage	100.00%

Information_Provided_in_Connec3

Information Provided in Connection with Outstanding Debt of Subsidiaries - Condensed Consolidating Balance Sheet (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assets
Carrying Value	$4,097.90	$4,079.20
Cash	81	157.4	95.8	102.7
Accrued investment income	22.1	25.7
Premiums receivable	353.6	348.4
Reinsurance recoverables	997.2	1,263.50
Goodwill and other intangible assets, net	230.8	239.8
Current income taxes receivable, net	14.9
Deferred acquisition costs, net	124.6	113.9
Ceded unearned premiums	207.6	196.3
Other assets	226.6	166.8
Total assets	6,356.30	6,591
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	3,042.40	3,230.30	3,223.50
Unearned premiums	817.2	779.1
Funds held and ceded reinsurance payable, net	233.8	398.4
Long-term debt	378.5	403.4
Current income taxes payable, net		5.2
Deferred tax liabilities, net	53	28.7
Accrued underwriting expenses and other liabilities	184.7	182.9
Total liabilities	4,709.60	5,028
Total shareholders' equity	1,646.70	1,563	1,514.10	1,463
Total liabilities and shareholders' equity	6,356.30	6,591
Consolidating Adjustments [Member]
Assets
Other assets	-25
Due from (to) affiliates	-2.9	-3.1
Investments in subsidiaries	-1,698	-1,625.20
Total assets	-1,725.90	-1,628.30
Liabilities and Shareholders' Equity
Long-term debt	-20.6
Total liabilities	-20.6	-6.6
Total shareholders' equity	-1,705.30	-1,621.70
Total liabilities and shareholders' equity	-1,725.90	-1,628.30
Intercompany note payable		-6.6
Argo Group International Holdings, Ltd (Parent Guarantor) [Member]
Assets
Carrying Value	0.7	1.1
Other assets	9.6	4.6
Due from (to) affiliates	2.9	3.1
Investments in subsidiaries	1,698	1,625.20
Total assets	1,711.20	1,634
Liabilities and Shareholders' Equity
Long-term debt	49	49
Accrued underwriting expenses and other liabilities	15.5	15.4
Total liabilities	64.5	71
Total shareholders' equity	1,646.70	1,563
Total liabilities and shareholders' equity	1,711.20	1,634
Intercompany note payable		6.6
Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) [Member]
Assets
Carrying Value	2,841.50	2,785.10
Cash	49.3	132.1	73.9	85.1
Accrued investment income	17.8	19.7
Premiums receivable	154.6	150.8
Reinsurance recoverables	1,173.60	1,145.90
Goodwill and other intangible assets, net	131.7	137.4
Current income taxes receivable, net	10.1	0.5
Deferred acquisition costs, net	58	55.6
Ceded unearned premiums	98.5	88.2
Other assets	174.1	97.8
Due from (to) affiliates	-19.8	1.5
Intercompany note receivable	72	87.4
Total assets	4,761.40	4,702
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	2,136.40	2,157
Unearned premiums	448.9	425.5
Funds held and ceded reinsurance payable, net	675.1	642.4
Long-term debt	288.7	288.9
Current income taxes payable, net		8.9
Deferred tax liabilities, net	41.2	22.8
Accrued underwriting expenses and other liabilities	104.2	98.2
Total liabilities	3,694.50	3,643.70
Total shareholders' equity	1,066.90	1,058.30
Total liabilities and shareholders' equity	4,761.40	4,702
Other Subsidiaries and Eliminations [Member]
Assets
Carrying Value	1,255.70	1,293
Cash	31.7	25.3	21.9	17.6
Accrued investment income	4.3	6
Premiums receivable	199	197.6
Reinsurance recoverables	-176.4	117.6
Goodwill and other intangible assets, net	99.1	102.4
Current income taxes receivable, net	4.8	-0.5
Deferred acquisition costs, net	66.6	58.3
Ceded unearned premiums	109.1	108.1
Other assets	67.9	64.4
Due from (to) affiliates	19.8	-1.5
Intercompany note receivable	-72	-87.4
Total assets	1,609.60	1,883.30
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	906	1,073.30
Unearned premiums	368.3	353.6
Funds held and ceded reinsurance payable, net	-441.3	-244
Long-term debt	61.4	65.5
Current income taxes payable, net		-3.7
Deferred tax liabilities, net	11.8	5.9
Accrued underwriting expenses and other liabilities	65	69.3
Total liabilities	971.2	1,319.90
Total shareholders' equity	638.4	563.4
Total liabilities and shareholders' equity	$1,609.60	$1,883.30

Information_Provided_in_Connec4

Information Provided in Connection with Outstanding Debt of Subsidiaries - Condensed Consolidating Statement of Income (Detail) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Premiums and other revenue:
Earned premiums									$1,338.10	$1,303.80	$1,186.50
Net investment income									86.6	100	118.8
Net realized investment and other gains									94	71.3	25.7
Total revenue	412.1	371.3	375.2	360.1	406	363.7	363.8	341.6	1,518.70	1,475.10	1,331
Expenses:
Losses and loss adjustment expenses									747.4	742	747.6
Other reinsurance-related expenses										19.2	27.3
Underwriting, acquisition and insurance expenses									539.2	510.8	464.5
Interest expense									19.9	20.2	23.7
Debt extinguishment costs											2.2
Fee expense (income), net									0.6	4.9	-5.3
Foreign currency exchange (gain) loss									-7.8	-1.7	4.3
Impairment of intangible assets									3.4
Total expenses									1,302.70	1,295.40	1,264.30
Income (loss) before income taxes	80.3	48.3	44.7	42.7	66.5	32.9	42.8	37.5	216	179.7	66.7
Provision for income taxes									32.8	36.5	14.4
Net income (loss) before equity in earnings (losses) of subsidiaries									183.2	143.2	52.3
Net income	59.7	44.7	38.6	40.2	47.8	31	31.7	32.7	183.2	143.2	52.3
Consolidating Adjustments [Member]
Premiums and other revenue:
Net realized investment and other gains									-2
Total revenue									-2
Expenses:
Interest expense									-0.3	-1.2	-0.3
Total expenses									-0.3	-1.2	-0.3
Income (loss) before income taxes									-1.7	1.2	0.3
Net income (loss) before equity in earnings (losses) of subsidiaries									-1.7	1.2	0.3
Equity in undistributed earnings of subsidiaries									-160.3	-89.4	-84.1
Net income									-162	-88.2	-83.8
Argo Group International Holdings, Ltd (Parent Guarantor) [Member]
Premiums and other revenue:
Net investment income									40.5	84.5	0.1
Net realized investment and other gains									2		-0.8
Total revenue									42.5	84.5	-0.7
Expenses:
Underwriting, acquisition and insurance expenses									17.3	27.4	27.1
Interest expense									2.3	3.3	3.9
Debt extinguishment costs											0.1
Total expenses									19.6	30.7	31.1
Income (loss) before income taxes									22.9	53.8	-31.8
Net income (loss) before equity in earnings (losses) of subsidiaries									22.9	53.8	-31.8
Equity in undistributed earnings of subsidiaries									160.3	89.4	84.1
Net income									183.2	143.2	52.3
Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) [Member]
Premiums and other revenue:
Earned premiums									461	439.9	434.2
Net investment income									56.7	73.4	86.6
Net realized investment and other gains									86.9	72.2	19.5
Total revenue									604.6	585.5	540.3
Expenses:
Losses and loss adjustment expenses									285.6	268.6	300.6
Underwriting, acquisition and insurance expenses									199.9	176.9	169.8
Interest expense									15.2	15.2	17.1
Debt extinguishment costs											2.1
Fee expense (income), net									2.4	4.1	-1.3
Foreign currency exchange (gain) loss									0.4	-0.3
Impairment of intangible assets									3.4
Total expenses									506.9	464.5	488.3
Income (loss) before income taxes									97.7	121	52
Provision for income taxes									27.5	34.1	11.1
Net income (loss) before equity in earnings (losses) of subsidiaries									70.2	86.9	40.9
Net income									70.2	86.9	40.9
Other Subsidiaries and Eliminations [Member]
Premiums and other revenue:
Earned premiums									877.1	863.9	752.3
Net investment income									-10.6	-57.9	32.1
Net realized investment and other gains									7.1	-0.9	7
Total revenue									873.6	805.1	791.4
Expenses:
Losses and loss adjustment expenses									461.8	473.4	447
Other reinsurance-related expenses										19.2	27.3
Underwriting, acquisition and insurance expenses									322	306.5	267.6
Interest expense									2.7	2.9	3
Fee expense (income), net									-1.8	0.8	-4
Foreign currency exchange (gain) loss									-8.2	-1.4	4.3
Total expenses									776.5	801.4	745.2
Income (loss) before income taxes									97.1	3.7	46.2
Provision for income taxes									5.3	2.4	3.3
Net income (loss) before equity in earnings (losses) of subsidiaries									91.8	1.3	42.9
Net income									$91.80	$1.30	$42.90

Information_Provided_in_Connec5

Information Provided in Connection with Outstanding Debt of Subsidiaries - Condensed Consolidating Statement of Cash Flows (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities	$130.50	($0.20)	$30.50
Cash flows from investing activities:
Proceeds from sales of investments	1,262	1,966.30	1,130.70
Maturities and mandatory calls of fixed maturity investments	323	281.8	483
Purchases of investments	-1,736.80	-1,975.80	-1,621.50
Change in short-term investments and foreign regulatory deposits	96.5	-153	37.7
Settlements of foreign currency exchange forward contracts	-1.1	-3.9	0.4
Purchases of fixed assets and other, net	-64.9	5.4	-34
Cash (used) provided by investing activities	-121.3	120.8	-3.7
Cash flows from financing activities:
Proceeds, net of issuance costs, from sale of notes			138.7
Activity under stock incentive plans	4.6	2.6	1.2
Redemption of trust preferred securities, net	-18		-117.2
Payment on note payable	-0.1
Repurchase of Company's common shares	-50.8	-46.5	-44.2
Excess tax expense from share-based payment arrangements	0.1	0.2
Payment of cash dividends to common shareholders	-18.2	-15.8	-12.3
Cash used by financing activities	-82.4	-59.5	-33.8
Effect of exchange rate changes on cash	-3.2	0.5	0.1
Change in cash	-76.4	61.6	-6.9
Cash, beginning of year	157.4	95.8	102.7
Cash, end of year	81	157.4	95.8
Consolidating Adjustments [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities	24.4
Cash flows from investing activities:
Issuance of intercompany note, net	-6.9	-49.3	55
Purchases of fixed assets and other, net	-6.4
Cash (used) provided by investing activities	-13.3	-49.3	55
Cash flows from financing activities:
Borrowings under intercompany note, net	6.9	49.3	-55
Redemption of trust preferred securities, net	-18
Cash used by financing activities	-11.1	49.3	-55
Argo Group International Holdings, Ltd (Parent Guarantor) [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities	25.7	63.2	-30.2
Cash flows from investing activities:
Change in short-term investments and foreign regulatory deposits	0.5	-1.4	-0.9
Settlements of foreign currency exchange forward contracts	1.3	0.7	2.3
Purchases of fixed assets and other, net	-7
Cash (used) provided by investing activities	-5.2	-0.7	1.4
Cash flows from financing activities:
Borrowings under intercompany note, net	-6.9	-49.3	55
Activity under stock incentive plans	4.6	2.6	1.2
Redemption of trust preferred securities, net			-15.1
Payment of cash dividends to common shareholders	-18.2	-15.8	-12.3
Cash used by financing activities	-20.5	-62.5	28.8
Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities	43.2	62.5	5.5
Cash flows from investing activities:
Proceeds from sales of investments	803.8	1,130.20	573.8
Maturities and mandatory calls of fixed maturity investments	192.1	168.9	326.2
Purchases of investments	-1,126.10	-1,156.70	-889.1
Change in short-term investments and foreign regulatory deposits	76	-119.1	35.1
Issuance of intercompany note, net	14.5	35	-26
Purchases of fixed assets and other, net	-35.5	-16.3	-29.1
Cash (used) provided by investing activities	-75.2	42	-9.1
Cash flows from financing activities:
Proceeds, net of issuance costs, from sale of notes			138.7
Redemption of trust preferred securities, net			-102.1
Payment on note payable	-0.1
Repurchase of Company's common shares	-50.8	-46.5	-44.2
Excess tax expense from share-based payment arrangements	0.1	0.2
Cash used by financing activities	-50.8	-46.3	-7.6
Change in cash	-82.8	58.2	-11.2
Cash, beginning of year	132.1	73.9	85.1
Cash, end of year	49.3	132.1	73.9
Other Subsidiaries and Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities	37.2	-125.9	55.2
Cash flows from investing activities:
Proceeds from sales of investments	458.2	836.1	556.9
Maturities and mandatory calls of fixed maturity investments	130.9	112.9	156.8
Purchases of investments	-610.7	-819.1	-732.4
Change in short-term investments and foreign regulatory deposits	20	-32.5	3.5
Settlements of foreign currency exchange forward contracts	-2.4	-4.6	-1.9
Issuance of intercompany note, net	-7.6	14.3	-29
Purchases of fixed assets and other, net	-16	21.7	-4.9
Cash (used) provided by investing activities	-27.6	128.8	-51
Cash flows from financing activities:
Effect of exchange rate changes on cash	-3.2	0.5	0.1
Change in cash	6.4	3.4	4.3
Cash, beginning of year	25.3	21.9	17.6
Cash, end of year	$31.70	$25.30	$21.90

Subsequent_Event_Additional_In

Subsequent Event - Additional Information (Details) (USD $)

3 Months Ended

12 Months Ended

0 Months Ended

In Millions, except Share data, unless otherwise specified

Dec. 31, 2014

Sep. 30, 2014

Jun. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2014

Dec. 31, 2013

Feb. 17, 2015

7-May-13

Subsequent Event [Line Items]

Dividends declaration date

30-Nov-14

5-Aug-14

5-May-14

4-Nov-13

6-Aug-13

7-May-13

15-Feb-13

6-Nov-12

7-Aug-12

8-May-12

15-Feb-12

18-Feb-14

7-May-13

Stock dividend declared

10.00%

Dividends payable date

31-Dec-14

15-Sep-14

16-Jun-14

16-Dec-13

16-Sep-13

20-Jun-13

15-Mar-13

17-Dec-12

18-Sep-12

15-Jun-12

15-Mar-12

17-Mar-14

17-Jun-13

Dividend payable, date of record

31-Dec-14

1-Sep-14

2-Jun-14

2-Dec-13

2-Sep-13

3-Jun-13

1-Mar-13

3-Dec-12

4-Sep-12

1-Jun-12

1-Mar-12

3-Mar-14

3-Jun-13

Additional stock issued as dividend

2,447,839

Pro Forma | Common Shares [Member]

Subsequent Event [Line Items]

Impact of stock dividend

2.6

Pro Forma | Additional Paid-In Capital [Member]

Subsequent Event [Line Items]

Impact of stock dividend

132.5

Pro Forma | Retained Earnings [Member]

Subsequent Event [Line Items]

Impact of stock dividend

-135.1

Subsequent Event

Subsequent Event [Line Items]

Dividends declaration date

17-Feb-15

Stock dividend declared

10.00%

Dividends payable date

16-Mar-15

Dividend payable, date of record

2-Mar-15

Additional stock issued as dividend

2,600,000

Subsequent_Event_Pro_Forma_Bas

Subsequent Event - Pro Forma Basic and Diluted Net Income per Common Share after Stock Dividend (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pro forma net income per common share:
Basic	$6.39	$4.85	$1.69
Diluted	$6.27	$4.67	$1.66

Schedule_II_Schedule_of_Balanc

Schedule II - Schedule of Balance Sheets (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]
Other assets	$226.60	$166.80
Total assets	6,356.30	6,591
Accrued underwriting expenses	143.1	122.3
Total liabilities	4,709.60	5,028
Shareholders' equity	1,646.70	1,563	1,514.10	1,463
Total liabilities and shareholders' equity	6,356.30	6,591
Argo Group International Holdings, Ltd (Parent Guarantor) [Member]
Condensed Financial Statements, Captions [Line Items]
Other investments, unrealized loss on foreign currency exchange forward contracts	-1.2	-1.4
Short-term investments	1.9	2.5
Investment in subsidiaries	1,698	1,625.20
Due from subsidiaries	2.9	3.1
Other assets	9.6	4.6
Total assets	1,711.20	1,634
Junior subordinated debentures, Amount	49	49
Intercompany note payable		7
Accrued underwriting expenses	15.5	15.4
Total liabilities	64.5	71
Shareholders' equity	1,646.70	1,563
Total liabilities and shareholders' equity	$1,711.20	$1,634

Schedule_II_Schedule_of_Statem

Schedule II - Schedule of Statements of Income (Detail) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Net investment income									$86.60	$100	$118.80
Net realized investment losses									94	71.3	25.7
Total revenue	412.1	371.3	375.2	360.1	406	363.7	363.8	341.6	1,518.70	1,475.10	1,331
Interest expense									19.9	20.2	23.7
Debt extinguishment costs											2.2
Other expenses									539.2	510.8	464.5
Net income (loss) before equity in earnings (losses) of subsidiaries									183.2	143.2	52.3
Net income	59.7	44.7	38.6	40.2	47.8	31	31.7	32.7	183.2	143.2	52.3
Argo Group International Holdings, Ltd (Parent Guarantor) [Member]
Condensed Financial Statements, Captions [Line Items]
Net investment income									40.5	84.5	0.1
Net realized investment losses									2		-0.8
Total revenue									42.5	84.5	-0.7
Interest expense									2.3	3.3	3.9
Debt extinguishment costs											0.1
Other expenses									17.3	27.4	27.1
Total expenses									19.6	30.7	31.1
Net income (loss) before equity in earnings (losses) of subsidiaries									22.9	53.8	-31.8
Equity in undistributed earnings of subsidiaries									160.3	89.4	84.1
Net income									$183.20	$143.20	$52.30

Schedule_II_Schedule_of_Statem1

Schedule II - Schedule of Statements of Income (Parenthetical) (Detail) (Argo Group International Holdings, Ltd (Parent Guarantor) [Member], USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Argo Group International Holdings, Ltd (Parent Guarantor) [Member]
Condensed Financial Statements, Captions [Line Items]
Intercompany dividend	$40.90	$84.50

Schedule_II_Schedule_of_Statem2

Schedule II - Schedule of Statements of Cash Flows (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Net income	$183.20	$143.20	$52.30
Amortization and depreciation	37.2	39.6	36.6
Share-based payments expense	19.6	23.3	10.5
Net realized investment and other gains	-94	-71.3	-25.7
Debt extinguishment costs			2.2
Accrued underwriting expenses	11.7	-4	21
Other assets and liabilities, net	28	-21.8	-10.7
Cash provided (used) by operating activities	130.5	-0.2	30.5
Change in short-term investments	75.3	-145.3	58.7
Settlements of foreign currency exchange forward contracts	-1.1	-3.9	0.4
Purchases of fixed assets	-39	-26.1	-34.1
Cash (used) provided by investing activities	-121.3	120.8	-3.7
Activity under stock incentive plans	4.6	2.6	1.2
Redemption of trust preferred securities, net	-18		-117.2
Payment of cash dividends to common shareholders	-18.2	-15.8	-12.3
Cash used by financing activities	-82.4	-59.5	-33.8
Change in cash	-76.4	61.6	-6.9
Cash, beginning of year	157.4	95.8	102.7
Cash, end of year	81	157.4	95.8
Argo Group International Holdings, Ltd (Parent Guarantor) [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	183.2	143.2	52.3
Amortization and depreciation		0.7	0.9
Share-based payments expense	5.7	8.7	4.8
Net realized investment and other gains	-2		0.8
Debt extinguishment costs			0.1
Undistributed earnings of subsidiaries	-160.3	-89.4	-84.1
Prepaid assets	2	-0.1	0.9
Accrued underwriting expenses	-2.2	-0.9	0.9
Due to subsidiaries	-0.6	0.2	-7
Interest on intercompany note payable	0.3	0.8	0.3
Other assets and liabilities, net	-0.4		0.7
Cash provided (used) by operating activities	25.7	63.2	-30.2
Change in short-term investments	0.5	-1.4	-0.9
Settlements of foreign currency exchange forward contracts	1.3	0.7	2.3
Purchases of fixed assets	-7
Cash (used) provided by investing activities	-5.2	-0.7	1.4
Borrowings under intercompany note payable, net	-6.9	-49.3	55
Activity under stock incentive plans	4.6	2.6	1.2
Redemption of trust preferred securities, net			-15.1
Payment of cash dividends to common shareholders	-18.2	-15.8	-12.3
Cash used by financing activities	($20.50)	($62.50)	$28.80

Schedule_III_Supplemental_Insu1

Schedule III - Supplemental Insurance Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplementary Insurance Information [Line Items]
Deferred Acquisition Costs	$124.60	$113.90	$99.40
Reserves for Losses and Loss Adjustment Expenses	3,042.40	3,230.30	3,223.50
Unearned Premiums	817.2	779.1	730.2
Earned premiums	1,338.10	1,303.80	1,186.50
Net investment income	86.6	100	118.8
Benefits, Claims and Claim Adjustment Expenses	747.4	742	747.6
Amortization (Deferral) of Deferred Acquisition Costs	-5.4	-15.8	-4.5
Other Insurance Expenses	544.6	526.6	469
Premiums Written, net	1,367.90	1,351.30	1,244.50
Excess and Surplus Lines [Member]
Supplementary Insurance Information [Line Items]
Deferred Acquisition Costs	36.9	38.8	37.3
Reserves for Losses and Loss Adjustment Expenses	1,165.40	1,171.80	1,209
Unearned Premiums	274.9	264.8	239
Earned premiums	485.2	460.2	399.3
Net investment income	36.7	42.2	51.1
Benefits, Claims and Claim Adjustment Expenses	248	244	223.3
Amortization (Deferral) of Deferred Acquisition Costs	1.9	-1.4	-2.5
Other Insurance Expenses	159.7	158.6	146.4
Premiums Written, net	487.8	478.7	420.8
Commercial Specialty [Member]
Supplementary Insurance Information [Line Items]
Deferred Acquisition Costs	22.5	18.1	18.6
Reserves for Losses and Loss Adjustment Expenses	652.2	653.4	660
Unearned Premiums	172.9	159.4	173
Earned premiums	291.9	299	317.5
Net investment income	18.7	22.8	27.6
Benefits, Claims and Claim Adjustment Expenses	189.1	194	257
Amortization (Deferral) of Deferred Acquisition Costs	-4.3	0.4	3.4
Other Insurance Expenses	107.8	97	104.9
Premiums Written, net	301.1	288.2	306.4
International Specialty [Member]
Supplementary Insurance Information [Line Items]
Deferred Acquisition Costs	0.8	2.2	1.4
Reserves for Losses and Loss Adjustment Expenses	306.3	295.6	257.3
Unearned Premiums	123.9	117.1	102.5
Earned premiums	148.3	142.4	130.1
Net investment income	8.2	8.4	12.3
Benefits, Claims and Claim Adjustment Expenses	77.8	79.9	73.5
Amortization (Deferral) of Deferred Acquisition Costs	1.7	-1	0.1
Other Insurance Expenses	52.8	51.1	43.7
Premiums Written, net	156.6	155.4	145.5
Syndicate 1200 [Member]
Supplementary Insurance Information [Line Items]
Deferred Acquisition Costs	64.4	54.8	42.1
Reserves for Losses and Loss Adjustment Expenses	600	777	738.9
Unearned Premiums	245.5	237.8	215.7
Earned premiums	411.1	401.7	337.9
Net investment income	10.2	11	15.3
Benefits, Claims and Claim Adjustment Expenses	208.1	208.6	184
Amortization (Deferral) of Deferred Acquisition Costs	-4.7	-13.8	-5.5
Other Insurance Expenses	172.5	170	139.4
Premiums Written, net	420.8	428.5	370.2
Run Off Lines
Supplementary Insurance Information [Line Items]
Reserves for Losses and Loss Adjustment Expenses	318.5	332.5	358.3
Earned premiums	1.6	0.5	1.7
Net investment income	9.7	10.8	12.5
Benefits, Claims and Claim Adjustment Expenses	24.4	15.5	9.8
Other Insurance Expenses	8.2	4.6	2.8
Premiums Written, net	1.6	0.5	1.6
Corporate and Other [Member]
Supplementary Insurance Information [Line Items]
Net investment income	3.1	4.8
Other Insurance Expenses	$43.60	$45.30	$31.80

Schedule_V_Valuation_and_Quali1

Schedule V - Valuation and Qualifying Accounts (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Valuation And Qualifying Accounts [Abstract]
Valuation allowance for deferred tax asset, Balance at Beginning of Year	$56.20	$52.50	$50.40
Valuation allowance for deferred tax asset, Charged to Cost and Expense	-30.7	-1	-1
Valuation allowance for deferred tax asset, Charged to Other Accounts	-0.1	4.7	3.1
Valuation allowance for deferred tax asset, Balance at End of Year	$25.40	$56.20	$52.50

Schedule_VI_Supplemental_Infor1

Schedule VI - Supplemental Information for Property-Casualty Insurance Companies (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplemental Information For Property Casualty Insurance Underwriters [Abstract]
Deferred acquisition costs	$124.60	$113.90	$99.40
Reserves for losses and loss adjustment expenses	3,042.40	3,230.30	3,223.50
Unamortized discount in reserves for losses	17.6	19.5	20.8
Unearned premiums	817.2	779.1	730.2
Premiums earned	1,338.10	1,303.80	1,186.50
Net investment income	86.6	100	118.8
Losses and loss adjustment expenses incurred: Current Year	785.1	775.6	780.5
Prior accident years	-37.7	-33.6	-32.9
Losses and loss adjustment expenses incurred	747.4	742	747.6
Amortization (Deferral) of Deferred Acquisition Costs	-5.4	-15.8	-4.5
Paid losses and loss adjustment expenses, net of reinsurance	736.7	753.5	796.5
Gross premiums written	$1,905.40	$1,888.40	$1,745.70