Argo Group International (ARGO-PA) 10-K 24 Feb 17 2016 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Feb. 21, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Trading Symbol	AGII
Entity Registrant Name	Argo Group International Holdings, Ltd.
Entity Central Index Key	1,091,748
Current Fiscal Year End Date	--12-31
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		30,019,038
Entity Public Float			$ 1,536.6

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Assets
Available-for-sale (cost: 2016 - $2,938.8; 2015 - $2,971.0)	$ 2,932,400,000	$ 2,927,300,000
Equity securities, at fair value (cost: 2016 - $335.2; 2015 - $349.7)	447,400,000	463,900,000
Other investments (cost: 2016 - $531.6; 2015 - $506.9)	539,000,000	513,700,000
Short-term investments, at fair value (cost: 2016 - $405.5; 2015 - $211.2)	405,500,000	210,800,000
Total investments	4,324,300,000	4,115,700,000
Cash	86,000,000	121,700,000
Accrued investment income	20,700,000	21,600,000
Premiums receivable	463,800,000	404,500,000
Reinsurance recoverables	1,385,600,000	1,121,100,000
Goodwill	152,200,000	152,200,000
Other intangible assets, net of accumulated amortization	67,700,000	73,300,000
Current income taxes receivable, net	0	11,600,000
Deferred acquisition costs, net	139,100,000	132,400,000
Ceded unearned premiums	302,800,000	250,800,000
Other assets	262,800,000	220,700,000
Total assets	7,205,000,000	6,625,600,000
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	3,350,800,000	3,123,600,000
Unearned premiums	970,000,000	886,700,000
Accrued underwriting expenses	115,000,000	133,900,000
Ceded reinsurance payable, net	466,600,000	312,400,000
Funds held	77,100,000	77,600,000
Senior unsecured fixed rate notes	139,500,000	139,300,000
Other indebtedness	55,400,000	55,200,000
Junior subordinated debentures	172,700,000	172,700,000
Current income taxes payable, net	8,100,000	0
Deferred tax liabilities, net	24,100,000	23,600,000
Other liabilities	33,000,000	32,500,000
Total liabilities	5,412,300,000	4,957,500,000
Commitments and contingencies (Note 17)	0	0
Shareholders' equity:
Common shares - $1.00 par, 500,000,000 shares authorized; 40,042,330 and 37,104,294 shares issued at December 31, 2016 and December 31, 2015, respectively	40,000,000	37,100,000
Additional paid-in capital	1,123,300,000	964,900,000
Treasury shares (10,028,755 and 9,181,644 shares at December 31, 2016 and December 31, 2015, respectively)	(378,200,000)	(331,100,000)
Retained earnings	959,900,000	985,700,000
Accumulated other comprehensive income, net of taxes	47,700,000	11,500,000
Total shareholders' equity	1,792,700,000	1,668,100,000
Total liabilities and shareholders' equity	$ 7,205,000,000	$ 6,625,600,000

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Available-for-sale cost	$ 2,938.8	$ 2,971
Equity securities cost	335.2	349.7
Other investments cost	531.6	506.9
Short-term investments, Cost	$ 405.5	$ 211.2
Common shares, par value	$ 1	$ 1
Common shares, shares authorized	500,000,000	500,000,000
Common shares, shares issued	40,042,330	37,104,294
Treasury shares, shares	10,028,755	9,181,644

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Premiums and other revenue:
Earned premiums	$ 1,410.8		$ 1,371.9		$ 1,338.1
Net investment income	115.1		88.6		106.1
Fee and other income	24.5		22.2		20.7
Net realized investment and other gains	26.1		24.1		74.5
Total revenue	1,576.5		1,506.8		1,539.4
Expenses:
Losses and loss adjustment expenses	810.1		766.1		747.4
Underwriting, acquisition and insurance expenses	547		536.7		537
Interest expense	19.6		19		19.9
Fee and other expense	22.4		25.8		23.5
Foreign currency exchange gain	(4.5)		(18.3)		(7.8)
Impairment of intangible assets	0		0		3.4
Total expenses	1,394.6		1,329.3		1,323.4
Income before income taxes	181.9		177.5		216
Provision for income taxes	35.2		14.3		32.8
Net income	$ 146.7		$ 163.2		$ 183.2
Net income per common share:
Basic	$ 4.86	[1]	$ 5.31	[1]	$ 5.80
Diluted	4.75	[1]	5.20	[1]	5.70
Dividends declared per common share	$ 0.86		$ 0.73		$ 0.57
Weighted average common shares:
Basic	30,166,440		30,769,089		31,559,422
Diluted	30,845,710		31,385,460		32,134,218
Net realized investment and other gains before other-than-temporary impairment losses	$ 36.3		$ 36		$ 76.8
Other-than-temporary impairment losses recognized in earnings:
Other-than-temporary impairment losses on fixed maturities	(1.7)		(2.2)		(1.2)
Other-than-temporary impairment losses on equity securities	(8.5)		(9.7)		(1.1)
Impairment losses recognized in earnings	(10.2)		(11.9)		(2.3)
Net realized investment and other gains	$ 26.1		$ 24.1		$ 74.5
[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 Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 146.7	$ 163.2	$ 183.2
Other comprehensive income (loss):
Foreign currency translation adjustments	4	(6)	(4.1)
Defined benefit pension plans:
Net gain (loss) arising during the year	(0.3)	0.4	(3.7)
Unrealized (losses) gains on securities:
(Losses) gains arising during the year	58.1	(121.1)	(5.7)
Reclassification adjustment for gains included in net income	(23.2)	(7.2)	(30.6)
Other comprehensive income (loss) before tax	38.6	(133.9)	(44.1)
Defined benefit pension plans:
Net gain (loss) arising during the year	(0.1)	0.3	(1.3)
Unrealized (loss) gains on securities:
(Loss) gains arising during the year	15.7	(31.3)	6.8
Reclassification adjustment for gains included in net income	(13.2)	(6.3)	(9.9)
Income tax provision (benefit) related to other comprehensive loss	2.4	(37.3)	(4.4)
Other comprehensive income (loss), net of tax	36.2	(96.6)	(39.7)
Comprehensive income	$ 182.9	$ 66.6	$ 143.5

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity - USD ($) $ 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, 2013	$ 1,563	$ 34.1	$ 827.3	$ (250.6)	$ 804.4	$ 147.8
Net income	183.2	0	0	0	183.2	0
Other comprehensive income (loss), net of tax	(39.7)	0	0	0	0	(39.7)
Repurchase of common shares (1,048,144, 575,155 and 847,111 at a weighted average price of $48.48, $51.58, and $55.64 for 2014, 2015, and 2016 respectively)	(50.8)	0	0	(50.8)	0	0
Activity under stock incentive plans	8.7	0.2	8.5	0	0	0
Retirement of common shares (tax payments on equity compensation)	(1.1)	0	(1.1)	0	0	0
Deferred tax - share-based payments	0.1	0	0.1	0	0	0
Employee stock purchase plan	1.5	0	1.5	0	0	0
Cash dividends declared - common shares	(18.2)	0	0	0	(18.2)	0
Ending Balance at Dec. 31, 2014	1,646.7	34.3	836.3	(301.4)	969.4	108.1
Net income	163.2	0	0	0	163.2	0
Other comprehensive income (loss), net of tax	(96.6)	0	0	0	0	(96.6)
Repurchase of common shares (1,048,144, 575,155 and 847,111 at a weighted average price of $48.48, $51.58, and $55.64 for 2014, 2015, and 2016 respectively)	(29.7)	0	0	(29.7)	0	0
Activity under stock incentive plans	9.2	0.3	8.9	0	0	0
Retirement of common shares (tax payments on equity compensation)	(4.1)	(0.1)	(4)	0	0	0
Deferred tax - share-based payments	0.6	0	0.6	0	0	0
Employee stock purchase plan	1.5	0	1.5	0	0	0
10% stock dividend	0	2.6	121.6	0	(124.2)	0
Cash dividends declared - common shares	(22.7)	0	0	0	(22.7)	0
Ending Balance at Dec. 31, 2015	1,668.1	37.1	964.9	(331.1)	985.7	11.5
Net income	146.7	0	0	0	146.7	0
Other comprehensive income (loss), net of tax	36.2	0	0	0	0	36.2
Repurchase of common shares (1,048,144, 575,155 and 847,111 at a weighted average price of $48.48, $51.58, and $55.64 for 2014, 2015, and 2016 respectively)	(47.1)	0	0	(47.1)	0	0
Activity under stock incentive plans	15.4	0.2	15.2	0	0	0
Retirement of common shares (tax payments on equity compensation)	(2.1)	0	(2.1)	0	0	0
Deferred tax - share-based payments	0.7	0	0.7	0	0	0
Employee stock purchase plan	1.4	0	1.4	0	0	0
10% stock dividend	0	2.7	143.2	0	(145.9)	0
Cash dividends declared - common shares	(26.6)	0	0	0	(26.6)	0
Ending Balance at Dec. 31, 2016	$ 1,792.7	$ 40	$ 1,123.3	$ (378.2)	$ 959.9	$ 47.7

Consolidated Statements of Sha7

Consolidated Statements of Shareholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	May 03, 2016	Feb. 17, 2015
Statement Of Stockholders Equity [Abstract]
Common shares repurchased	847,111	575,155	1,048,144
Repurchase of common shares, weighted average price	$ 55.64	$ 51.58	$ 48.48
Stock dividend declared	10.00%	10.00%		10.00%	10.00%
Cash dividend declared - common shares, per share	$ 0.86	$ 0.73	$ 0.57

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income	$ 146.7	$ 163.2	$ 183.2
Adjustments to reconcile net income to net cash provided (used) by operating activities:
Amortization and depreciation	35.4	38.7	37.2
Share-based payments expense	19.8	29.1	19.6
Excess tax benefit from share-based payment arrangements	(0.6)	(0.6)	(0.1)
Deferred income tax (benefit) provision, net	(1.1)	8.3	27.6
Net realized investment and other gains	(26.1)	(24.1)	(74.5)
Undistributed earnings from alternative investment portfolio	(23.9)	(3)	(19.5)
(Gain) loss on disposals of fixed assets, net	(0.1)	0.2	0
Amortization of debt issuance costs	0.2	0.2	0.2
Impairment of intangible assets	0	0	3.4
Change in:
Accrued investment income	0.9	0.5	3.4
Receivables	(318)	(182.6)	256.7
Deferred acquisition costs	(6.4)	(8.5)	(7.3)
Ceded unearned premiums	(51.2)	(45.9)	(12.4)
Reserves for losses and loss adjustment expenses	220.2	94.3	(182)
Unearned premiums	80.1	76.5	39.1
Ceded reinsurance payable and funds held	153.6	157.2	(163.9)
Income taxes	19.9	3.3	(19.7)
Accrued underwriting expenses	(18.9)	(24.6)	11.7
Other, net	(49.1)	0.4	27.8
Cash provided by operating activities	181.4	282.6	130.5
Cash flows from investing activities:
Sales of fixed maturity investments	1,138.4	787.5	1,104.9
Maturities and mandatory calls of fixed maturity investments	1,002.7	843.9	323
Sales of equity securities	208.3	122	123.9
Sales of other investments	96.8	58.4	33.2
Purchases of fixed maturity investments	(2,137.3)	(1,842.8)	(1,531.5)
Purchases of equity securities	(146.9)	(114.1)	(55.8)
Purchases of other investments	(96.3)	(77.2)	(149.5)
Change in foreign regulatory deposits and voluntary pools	(1.3)	3.5	21.2
Change in short-term investments	(193.9)	46.1	75.3
Settlements of foreign currency exchange forward contracts	(5.4)	(10.1)	(1.1)
Purchases of fixed assets	(32.1)	(18.9)	(39)
Other, net	21.9	8.1	(25.9)
Cash used in investing activities	(145.1)	(193.6)	(121.3)
Cash flows from financing activities:
Payment on note payable	0	0	(0.1)
Redemption of trust preferred securities, net	0	0	(18)
Activity under stock incentive plans	1	1.8	4.6
Repurchase of Company's common shares	(47.1)	(29.7)	(50.8)
Excess tax benefit from share-based payment arrangements	0.6	0.6	0.1
Payment of cash dividends to common shareholders	(26.6)	(22.7)	(18.2)
Cash used in financing activities	(72.1)	(50)	(82.4)
Effect of exchange rate changes on cash	0.1	1.7	(3.2)
Change in cash	(35.7)	40.7	(76.4)
Cash, beginning of year	121.7	81	157.4
Cash, end of year	$ 86	$ 121.7	$ 81

Business and Significant Accoun

Business and Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Business and Significant Accounting Policies	1. 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) UC (“Argo Ireland”). Argo Underwriting Agency Limited (“Syndicate 1200”) is a subsidiary of Argo International Holdings, Ltd. Argo Re, Ltd. (“Argo Re”), a Bermuda based company, is the parent of both Argo Ireland and Argo International Holdings, Ltd. Argo Re is directly owned by Argo Group. We conduct our ongoing business through four segments. Excess and Surplus Lines products are underwritten by Colony Insurance Company (“Colony”). Commercial Specialty consists of the following operations: Argo Insurance, Rockwood Casualty Insurance Company (“Rockwood”), Argo Pro, 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 Argo Underwriting Agency Limited based in London, on behalf of one underwriting syndicate under the Lloyd’s of London (“Lloyd’s”) global franchise. Our Run-off Lines 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 other 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. We have evaluated our investment in our twelve statutory trusts (collectively, the “Trusts”) and two charitable foundations (collectively, the “Foundations”) under the Financial Accounting Standards Board’s (“FASB’s”) provisions for consolidation of variable interest entities under Accounting Standards Codification (“ASC”) Topic 810-10, “Consolidation,” as amended. We determined that the Trusts and Foundations are 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 ASC Topic 810-10, 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. During the first quarter of 2016, we evaluated our accounting for income from our alternative investment portfolio and determined that as we manage these investments to appreciate in value on a quarter-to-quarter basis, it is more appropriate to classify the change in value as net investment income as opposed to realized investment gains (losses). As a result, net investment income for the year ended December 31, 2016 includes $23.9 million related to the appreciation of our alternative investment portfolio. Net investment income and net realized investment and other gains for the years ended December 31, 2015 and 2014 have been reclassified to reflect the current presentation. Specifically, net investment income for the years ended December 31, 2015 and 2014 include increases of $3.0 million and $19.5 million, respectively, related to the alternative investment portfolio, and net realized investment and other gains were decreased by the same amounts for the respective years. Additionally, beginning in 2016, we began presenting “Fee and other income” and “Fee and other expense” as separate financial statement line items. The presentation for prior years’ financial statements has been reclassified to conform to the current presentation. Stock Dividends On May 3, 2016, our Board of Directors declared a 10% stock dividend, payable on June 15, 2016, to shareholders of record at the close of business on June 1, 2016. As a result of the stock dividend, 2,735,542 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. As a result of the stock dividend, 2,554,506 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. 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, 2016 and 2015 include bonds and structured securities. Equity securities include common stocks, preferred stocks and mutual funds. Other investments consist of foreign regulatory deposits, hedge funds, private equity funds, private equity direct investments, 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 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 in income during the period, but rather are recognized as a separate component of shareholders’ equity until realized. Fair value of these investments is estimated using prices obtained from third-party pricing services, where available. For securities where we were unable to obtain fair values from a pricing service or broker, fair values were estimated using information obtained from investment advisors. We performed several processes to ascertain the reasonableness of these investment values by 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, 2016 than 1% of Changes in the value of other investments consisting of hedge funds, private equity funds, private equity direct investments and voluntary pools are principally recognized to income during the period using the equity method of accounting. Our foreign regulatory deposits are assets held in trust in jurisdictions where there is a legal and regulatory requirement to maintain funds locally in order to protect policyholders. Lloyd’s is the appointed investment manager for the funds. The underlying assets are invested in government securities, agency securities and corporate bonds whose values are obtained from Lloyd’s. Foreign currency future contracts held by us are valued by our counterparties using market driven foreign currency 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 $2.7 million and $3.5 million at December 31, 2016 and 2015, 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 $2.1 million and $3.2 million at December 31, 2016 and 2015, 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) 2016 2015 2014 Premiums receivable $ 1.1 $ 1.0 $ 1.1 Reinsurance recoverables — 0.2 0.5 Net written off $ 1.1 $ 1.2 $ 1.6 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. 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 $5.7 million and $6.5 million at December 31, 2016 and 2015, respectively. The estimated amount included in premiums receivables for additional premiums due under retrospectively rated policies was $0.1 million and $0.1 at December 31, 2016 and 2015, respectively. Deferred Acquisition Costs Policy acquisition costs, which include commissions, premium taxes, fees and certain other costs of underwriting policies, are deferred, when such class of policies are profitable, and amortized over the same period in which the related premiums are earned. To qualify for capitalization, the policy acquisition cost must be directly related to the successful acquisition of an insurance contract. Anticipated investment income is considered in determining whether the deferred acquisition costs are recoverable and whether a premium deficiency exists. We continually review the methods of making such estimates and establishing the deferred costs with any adjustments made in the accounting period in which the adjustment arose. The 2016 and 2015 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 19, “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 goodwill impairment test. Based on prior goodwill impairment testing, we determined the performance of the quantitative impairment test was required for 2016. The first step of the quantitative test 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, 2016, 2015 and 2014, all of our reporting units passed Step 1 of the goodwill impairment analysis as the fair value of each reporting unit were in excess of their carrying values. Therefore, Step 2 of the goodwill impairment analysis was not required. Any future 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: December 31, 2016 December 31, 2015 (in millions) Gross Carrying Amount Accumulated Amortization Gross Carrying Amount Accumulated Amortization Lloyd's capacity $ 60.5 n/a $ 60.5 n/a Distribution network 45.5 38.5 45.5 33.2 Additional Lloyd's capacity 4.8 4.8 4.8 4.6 Other 1.4 1.2 1.6 1.3 $ 112.2 $ 44.5 $ 112.4 $ 39.1 The weighted average useful life by category at December 31, 2016 was 9.3 years for the distribution network, 5.0 years for the additional Lloyd’s capacity and 8.7 years for other. The weighted average useful life for all categories was 8.9 years at December 31, 2016. During the years ended December 31, 2016, 2015 and 2014, amortization expense was $5.5 million, $7.5 million and $5.6 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, 2017, 2018 and 2019 is $4.7 million, $2.1 million and $0.4 million, respectively. There is no estimated amortization expense for either of the years ended December 31, 2020 and 2021. 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 nine years. The accumulated depreciation for property and equipment was $101.6 million and $85.1 million at December 31, 2016 and 2015, respectively. The net book value of our property and equipment at December 31, 2016 and 2015 was $142.2 million and $133.1 million, respectively. The depreciation expense at December 31, 2016, 2015 and 2014 was $20.9 million, $17.5 million and $15.1 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. 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 13, “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, 2016 and 2015, the foreign currency translation adjustments were a loss of $17.6 million and $21.6 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. 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. Supplemental Cash Flow Information Income taxes paid. We paid income taxes of $16.6 million, $10.9 million and $23.7 million in 2016, 2015 and 2014, respectively. Income taxes recovered. We recovered income taxes of $0.5 million, $11.7 million and $0.1 million in 2016, 2015 and 2014, respectively. Interest paid as follows: For the Years Ended December 31, (in millions) 2016 2015 2014 Senior unsecured fixed rate notes $ 9.3 $ 9.3 $ 9.3 Junior subordinated debentures 7.7 7.0 7.6 Other indebtedness 2.3 2.4 2.8 Total interest paid $ 19.3 $ 18.7 $ 19.7 Non-cash operating activities transactions. 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 were held in escrow and recorded as a receivable within “Other assets” in our Consolidated Balance Sheet at December 31, 2014. Recently Issued Accounting Pronouncements In December 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-19, “Technical Corrections and Improvements.” ASU 2016-19 clarifies guidance, corrects errors and makes minor improvements affecting a variety of topics in the FASB Accounting Standards Codification. We have adopted this ASU, effective immediately, and it does not have an impact on our financial results or disclosures. In October 2016, the FASB issued ASU 2016-16, “Intra-Entity Transfers of Assets Other Than Inventory” (Topic 740). ASU 2016-16 requires entities to recognize current and deferred income tax resulting from an intra-entity asset transfer when the transfer occurs. Prior to issuance of this ASU, U.S. GAAP did not allow recognition of income tax consequences until the asset had been sold to a third party. ASU 2016-16 requires adoption through a cumulative-effect adjustment to the balance sheet as of the beginning of the fiscal year of adoption with early adoption permitted. The ASU is effective in annual periods beginning after December 15, 2017, including interim periods therein. We are currently evaluating the impact that this ASU will have on our financial results and disclosures, but do not anticipate that any such potential impact would be material. In August 2016, the FASB issued ASU 2016-15, “Classification of Certain Cash Receipts and Cash Payments” (Topic 230). ASU 2016-15 will reduce diversity in practice on how eight specific cash receipts and payments are classified on the statement of cash flows. The ASU is effective for fiscal years beginning after December 15, 2017, including interim periods within those years. We anticipate that this ASU will have no net effect on our consolidated statements of cash flows, but will likely have an immaterial impact on the classification of specific cash receipts and payments within the statement. In

Subsequent Event

Subsequent Event	12 Months Ended
	Dec. 31, 2016
Subsequent Events [Abstract]
Subsequent Event	2. Subsequent Event Acquisition of Maybrooke Effective February 6, 2017, we completed the acquisition of Maybrooke Holdings, S.A. (“Maybrooke”) whereby we acquired all of the issued and outstanding capital stock of Maybrooke. The purchase price of $235.3 million was paid in cash from funds on hand and available under our credit facility (see Note 8, “Other Indebtedness”). Through the acquisition of Maybrooke, we acquired Ariel Re (“Ariel”), a global underwriter of specialty insurance and reinsurance business written primarily through its Lloyd’s Syndicate 1910. Ariel provides Argo Group with enhanced scale in its London- and Bermuda-based platforms, which was a primary strategic objective associated with the acquisition. We have taken certain actions and incurred certain costs associated with the transaction prior to the acquisition date, totaling $0.4 million, which are reflected in “Underwriting, acquisition and insurance expenses” in our Consolidated Statements of Income for the year ended December 31, 2016. However, the assets acquired and liabilities assumed and the results of Maybrooke’s operations are not reflected in our Consolidated Financial Statements as of and for the year ended December 31, 2016 as the closing date of the acquisition and effective control of Maybrooke was consummated on February 6, 2017. The acquisition will be accounted for under the acquisition method of accounting in accordance with ASC 805, “Business Combinations.” Such accounting will include the effects of any post-closing purchase price adjustments and the disclosure of any additional costs associated with the transaction incurred after December 31, 2016. The acquisition method of accounting requires, among other things, that all assets acquired and liabilities assumed be recognized at their fair values as of the acquisition date. Due to the close proximity of the acquisition date and the filing of this annual report on Form 10-K for the year ended December 31, 2016, the initial accounting for the business combination is incomplete. Therefore, it is impracticable that we provide the amounts to be recognized as of the acquisition date for major classes of assets acquired and liabilities assumed, as well as the pro forma revenues and earnings of the combined entity for the year ended December 31, 2016. This information will be included in our quarterly report on Form 10-Q for the period ended March 31, 2017.

Investments

Investments	12 Months Ended
	Dec. 31, 2016
Investments Debt And Equity Securities [Abstract]
Investments	3. 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: December 31, 2016 (in millions) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Fixed maturities U.S. Governments $ 275.1 $ 0.6 $ 4.5 $ 271.2 Foreign Governments 244.2 1.1 8.0 237.3 Obligations of states and political subdivisions 375.7 8.9 1.8 382.8 Corporate bonds 1,316.9 23.3 19.5 1,320.7 Commercial mortgage-backed securities 154.9 0.4 1.6 153.7 Residential mortgage-backed securities 174.8 3.7 1.7 176.8 Asset-backed securities 127.6 0.1 2.1 125.6 Collateralized loan obligations 269.6 3.8 9.1 264.3 Total fixed maturities 2,938.8 41.9 48.3 2,932.4 Equity securities 335.2 117.9 5.7 447.4 Other investments 531.6 7.5 0.1 539.0 Short-term investments 405.5 — — 405.5 Total investments $ 4,211.1 $ 167.3 $ 54.1 $ 4,324.3 December 31, 2015 (in millions) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Fixed maturities U.S. Governments $ 207.9 $ 0.7 $ 0.7 $ 207.9 Foreign Governments 263.1 0.8 20.8 243.1 Obligations of states and political subdivisions 467.6 20.7 0.3 488.0 Corporate bonds 1,355.1 13.6 48.8 1,319.9 Commercial mortgage-backed securities 151.5 0.3 1.6 150.2 Residential mortgage-backed securities 167.8 5.8 0.5 173.1 Asset-backed securities 131.1 0.3 2.9 128.5 Collateralized loan obligations 226.9 0.9 11.2 216.6 Total fixed maturities 2,971.0 43.1 86.8 2,927.3 Equity securities 349.7 131.5 17.3 463.9 Other investments 506.9 6.9 0.1 513.7 Short-term investments 211.2 — 0.4 210.8 Total investments $ 4,038.8 $ 181.5 $ 104.6 $ 4,115.7 Included in “Total investments” in our Consolidated Balance Sheets at December 31, 2016 and 2015 is $131.9 million and $95.3 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, 2016, by contractual maturity, were as follows: (in millions) Amortized Cost Fair Value Due in one year or less $ 266.9 $ 262.1 Due after one year through five years 1,237.9 1,239.9 Due after five years through ten years 545.9 547.0 Thereafter 161.2 163.0 Structured securities 726.9 720.4 Total $ 2,938.8 $ 2,932.4 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, 2016 and 2015 were as follows: December 31, 2016 (in millions) Carrying Value Unfunded Commitments Investment Type Hedge funds $ 180.9 $ — Private equity 179.0 93.4 Long only funds 170.7 — Other investments 8.4 — Total other invested assets $ 539.0 $ 93.4 December 31, 2015 (in millions) Carrying Value Unfunded Commitments Investment Type Hedge funds $ 146.9 $ — Private equity 144.1 90.2 Long only funds 211.0 — Other investments 11.7 — Total other invested assets $ 513.7 $ 90.2 The following describes each investment type: • Hedge funds: Hedge funds include funds that primarily buy and sell stocks including short sales, multi-strategy credit, relative value credit and distressed credit. • Private equity: Private equity includes buyout funds, real asset/infrastructure funds, credit special situations funds, mezzanine lending funds and direct investments and strategic non-controlling minority investments in private companies that are principally accounted for using the equity method of accounting. • Long only funds: Our long only funds include a fund that primarily owns international stocks and funds that primarily own investment-grade corporate and sovereign fixed income securities. For 2015, long-only funds also included a fund that owned high-yield fixed income securities. • Other investments: Other investments include participation in investment pools, foreign exchange currency forward contracts to manage our foreign currency exposure and a portfolio of foreign exchange currency forward contracts that are actively traded by an external currency manager for a total return strategy. 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: December 31, 2016 Less Than One Year One Year or Greater Total (in millions) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Fixed maturities U.S. Governments $ 183.4 $ 4.5 $ — $ — $ 183.4 $ 4.5 Foreign Governments 201.2 8.0 — — 201.2 8.0 Obligations of states and political subdivisions 72.6 1.7 1.8 0.1 74.4 1.8 Corporate bonds 490.5 17.7 50.6 1.8 541.1 19.5 Commercial mortgage-backed securities 70.6 1.5 7.1 0.1 77.7 1.6 Residential mortgage-backed securities (2) 87.5 1.7 4.4 — 91.9 1.7 Asset-backed securities 69.7 1.4 8.2 0.7 77.9 2.1 Collateralized loan obligations 122.5 8.6 16.9 0.5 139.4 9.1 Total fixed maturities 1,298.0 45.1 89.0 3.2 1,387.0 48.3 Equity securities 62.1 5.7 — — 62.1 5.7 Other investments 0.3 0.1 — — 0.3 0.1 Short-term investments (1) 4.8 — — — 4.8 — Total $ 1,365.2 $ 50.9 $ 89.0 $ 3.2 $ 1,454.2 $ 54.1 December 31, 2015 Less Than One Year One Year or Greater Total (in millions) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Fixed maturities U.S. Governments (2) $ 138.3 $ 0.7 $ 0.4 $ — $ 138.7 $ 0.7 Foreign Governments 217.6 20.7 2.5 0.1 220.1 20.8 Obligations of states and political subdivisions (1) 9.3 — 8.8 0.3 18.1 0.3 Corporate bonds 844.7 41.1 77.8 7.7 922.5 48.8 Commercial mortgage-backed securities 108.1 1.3 9.8 0.3 117.9 1.6 Residential mortgage-backed securities (2) 52.1 0.5 1.5 — 53.6 0.5 Asset-backed securities 108.2 2.6 6.9 0.3 115.1 2.9 Collateralized loan obligations 183.4 10.7 13.1 0.5 196.5 11.2 Total fixed maturities 1,661.7 77.6 120.8 9.2 1,782.5 86.8 Equity securities 112.4 17.3 — — 112.4 17.3 Other investments 0.3 0.1 — — 0.3 0.1 Short-term investments 5.8 0.4 — — 5.8 0.4 Total $ 1,780.2 $ 95.4 $ 120.8 $ 9.2 $ 1,901.0 $ 104.6 (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 7,401 securities, of which 2,194 were in an unrealized loss position for less than one year and 182 were in an unrealized loss position for a period one year or greater as of December 31, 2016. 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 investment and it is unlikely that we will be required to sell the investment before recovery of its 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, 2016. We recognized other-than-temporary losses on our fixed maturities and equity portfolios as follows: For the Years Ended December 31, (in millions) 2016 2015 2014 Other-than-temporary impairment: Obligations of states and political subdivisions $ — $ — $ (0.6 ) Corporate bonds (1.7 ) (2.2 ) (0.6 ) Equity securities (8.5 ) (9.7 ) (1.1 ) Other-than-temporary impairment losses $ (10.2 ) $ (11.9 ) $ (2.3 ) Net Investment Income and Realized Gains and Losses Investment income and expenses were as follows: For the Years Ended December 31, (in millions) 2016 2015 2014 Investment income: Interest on fixed maturities $ 88.9 $ 78.2 $ 76.3 Dividends on equity securities 15.6 16.3 15.8 Income on alternative investments 29.9 10.0 24.5 Income on short-term and other investments 0.4 0.2 0.3 Other — — 4.2 Investment income 134.8 104.7 121.1 Investment expenses (19.7 ) (16.1 ) (15.0 ) Net investment income $ 115.1 $ 88.6 $ 106.1 The following table presents our gross realized investment gains (losses) and other: For the Years Ended December 31, (in millions) 2016 2015 2014 Realized gains Fixed maturities $ 21.5 $ 12.3 $ 17.0 Equity securities 57.5 40.5 29.2 Other investments 47.5 37.6 16.9 Short-term investments 0.5 1.2 0.1 Other assets 1.2 — 2.0 Gain on sale of real estate holdings — 0.3 43.3 Gross realized investment and other gains 128.2 91.9 108.5 Realized losses Fixed maturities (35.9 ) (23.5 ) (12.2 ) Equity securities (9.7 ) (6.6 ) (0.6 ) Other investments (46.0 ) (24.0 ) (13.4 ) Short-term investments (0.3 ) (1.8 ) (0.9 ) Other assets — — (4.6 ) Other-than-temporary impairment losses on fixed maturities (1.7 ) (2.2 ) (1.2 ) Other-than-temporary impairment losses on equity securities (8.5 ) (9.7 ) (1.1 ) Gross realized investment and other losses (102.1 ) (67.8 ) (34.0 ) Net realized investment and other gains before income taxes 26.1 24.1 74.5 Income tax expense (11.6 ) (10.0 ) (27.8 ) Net realized investment and other gains, net of income taxes $ 14.5 $ 14.1 $ 46.7 Changes in unrealized appreciation (depreciation) related to investments are summarized as follows: For the Years Ended December 31, (in millions) 2016 2015 2014 Change in unrealized gains (losses) Fixed maturities $ 36.5 $ (65.3 ) $ (30.5 ) Equity securities (2.6 ) (64.1 ) (8.4 ) Other investments 0.6 1.5 2.5 Short-term investments 0.4 (0.4 ) — Net unrealized investment and other gains (losses) before income taxes 34.9 (128.3 ) (36.4 ) Income tax benefit (2.4 ) 37.6 3.1 Net unrealized investment and other gains (losses), net of income taxes $ 32.5 $ (90.7 ) $ (33.3 ) Foreign Currency Exchange Forward Contracts We entered into foreign currency exchange forward contracts to manage operational currency exposure on our Canadian dollar (“CAD”) investment portfolio, minimize negative impacts to investment portfolio returns, and gain exposure to a total return strategy which invests in multiple currencies. The currency forward contracts are carried at fair value in our Consolidated Balance Sheets in “Other investments”. The gains and losses are included in “Net realized investment and other gains” in our Consolidated Statements of Income. The fair value of our foreign currency exchange forward contracts as of December 31 was as follows: (in millions) December 31, 2016 December 31, 2015 Operational currency exposure (1) $ — $ 5.2 Asset manager investment exposure 0.7 2.9 Total return strategy 3.3 (0.8 ) $ 4.0 $ 7.3 (1) CAD currency exposure less than $0.1 million. The following table presents our gross investment realized gains and losses on our foreign currency exchange forward contracts: For the Years Ended December 31, (in millions) 2016 2015 2014 Realized gains Global catastrophe (1) $ — $ 0.5 $ 4.6 Operational currency exposure 10.9 26.1 4.6 Asset manager investment exposure 9.0 8.5 6.0 Total return strategy 25.6 1.4 — Gross realized investment gains 45.5 36.5 15.2 Realized losses Global catastrophe — (2.3 ) (4.9 ) Operational currency exposure (18.0 ) (12.9 ) (2.2 ) Asset manager investment exposure (4.5 ) (2.3 ) (2.4 ) Total return strategy (21.0 ) (3.8 ) — Gross realized investment losses (43.5 ) (21.3 ) (9.5 ) Net realized investment gains on foreign currency exchange forward contracts $ 2.0 $ 15.2 $ 5.7 (1) Regulatory Deposits, Pledged Securities and Letters of Credit We are required to maintain assets on deposit with various regulatory authorities to support our insurance and reinsurance operations. We maintain assets pledged as collateral in support of irrevocable letters of credit issued under the terms of certain reinsurance agreements for reported loss and loss expense reserves. The following table presents our components of restricted assets at December 31, 2016 (in millions) December 31, 2016 December 31, 2015 Securities on deposit for regulatory and other purposes $ 168.7 $ 192.8 Securities pledged as collateral for letters of credit 35.9 35.0 Securities on deposit supporting Lloyd’s business 161.8 202.5 Total restricted investments $ 366.4 $ 430.3 Fair Value Measurements Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value measurement assumes that the transaction to sell the asset or transfer the liability occurs in the principal market for the asset or liability, or in the absence of a principal market, the most advantageous market. Market participants are buyers and sellers in the principal (or most advantageous) market that are independent, knowledgeable, able to transact for the asset or liability and willing to transfer the asset or liability. Valuation techniques consistent with the market and income approach are used to measure fair value. The inputs of these valuation techniques are categorized into three levels. • Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that can be accessed at the reporting date. We define actively traded as a security that has traded in the past seven days. We receive one quote per instrument for Level 1 inputs. • Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. We receive one quote per instrument for Level 2 inputs. • Level 3 inputs are unobservable inputs. Unobservable inputs reflect our own assumptions about the assumptions market participants would use in pricing the asset or liability based on the best information available in the circumstances. We receive fair value prices from third-party pricing services and our outside investment managers. These prices are determined using observable market information such as dealer quotes, market spreads, cash flows, yield curves, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the security’s terms and conditions, among other things. We have reviewed the processes used by the third-party providers for pricing the securities, and have determined that these processes result in fair values consistent with GAAP requirements. In addition, we review these prices for reasonableness, and have not adjusted any prices received from the third-party providers as of December 31, 2016 and 2015. A description of the valuation techniques we use to measure assets at fair value is as follows: Fixed Maturities (Available-for-Sale) Levels 1 and 2: • United States Treasury securities are typically valued using Level 1 inputs. For these securities, we obtain fair value measurements from third-party pricing services using quoted prices (unadjusted) in active markets at the reporting date. • United States Government agencies, non-U.S. Government securities, obligations of states and political subdivisions, credit securities and foreign denominated government and credit securities are reported at fair value using Level 2 inputs. For these securities, we obtain fair value measurements from third-party pricing services. Observable data may include dealer quotes, market spreads, yield curves, live trading levels, trade execution data, credit information and the security’s terms and conditions, among other things. • Asset and mortgage-backed securities and collateralized loan obligations are reported at fair value using Level 2 inputs. For these securities, we obtain fair value measurements from third-party pricing services. Observable data may include dealer quotes, market spreads, cash flows, yield curves, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the security’s terms and conditions, among other things. Fixed Maturities Level 3: • We own a $2.0 million term loan that is valued using unobservable inputs. Equity Securities Level 1: Equity securities are principally reported at fair value using Level 1 inputs. For these securities, we obtain fair value measurements from a third-party pricing service using quoted prices (unadjusted) in active markets at the reporting date. Equity Securities Level 2: We own interests in a mutual fund that is reported at fair value using Level 2 inputs. The valuation is based on the funds’ net asset value per share, 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 and governmental bonds reported at fair value using Level 2 inputs as described in the fixed maturities section above. Values for the investments categorized as Level 1 are obtained from various financial institutions as of the reporting date. Transfers Between Level 1 and Level 2 Securities: There were no transfers between Level 1 and Level 2 securities during 2016 or 2015. Based on an analysis of the inputs, our financial assets measured at fair value on a recurring basis have been categorized as follows: Fair (in millions) December 31, 2016 Level 1 (a) Level 2 (b) Level 3 (c) Fixed maturities U.S. Governments $ 271.2 $ 228.0 $ 43.2 $ — Foreign Governments 237.3 — 237.3 — Obligations of states and political subdivisions 382.8 — 382.8 — Corporate bonds 1,320.7 — 1,318.7 2.0 Commercial mortgage-backed securities 153.7 — 153.7 — Residential mortgage-backed securities 176.8 — 176.8 — Asset-backed securities 125.6 — 125.6 — Collateralized loan obligations 264.3 — 264.3 — Total fixed maturities 2,932.4 228.0 2,702.4 2.0 Equity securities 447.4 444.9 2.1 0.4 Other investments 95.5 — 95.5 — Short-term investments 405.5 375.1 30.4 — $ 3,880.8 $ 1,048.0 $ 2,830.4 $ 2.4 (a) Quoted prices in active markets for identical assets (b) Significant other observable inputs (c) Significant unobservable inputs Fair Value Measurements at Reporting Date Using (in millions) December 31, 2015 Level 1 (a) Level 2 (b) Level 3 (c) Fixed maturities U.S. Governments $ 207.9 $ 150.4 $ 57.5 $ — Foreign Governments 243.1 — 243.1 — Obligations of states and political subdivisions 488.0 — 488.0 — Corporate bonds 1,319.9 — 1,319.9 — Commercial mortgage-backed securities 150.2 — 150.2 — Residential mortgage-backed securities 173.1 — 173.1 — Asset-backed securities 128.5 — 128.5 — Collateralized loan obligations 216.6 — 216.6 — Total fixed maturities 2,927.3 150.4 2,776.9 — Equity securities 463.9 457.6 5.6 0.7 Other investments 97.2 — 97.2 — Short-term investments 210.8 203.6 7.2 — $ 3,699.2 $ 811.6 $ 2,886.9 $ 0.7 (a) Quoted prices in active markets for identical assets (b) Significant other observable inputs (c) Significant unobservable inputs The fair value measurements in the tables above do not equal “Total investments” on our Consolidated Balance Sheets as they exclude certain other investments that are accounted for under the equity-method of accounting. A reconciliation of the beginning and ending balances for the investments categorized as Level 3 are as follows: Fair Value Measurements Using Observable Inputs (Level 3) (in millions) Credit Financial Equity Securities Total Beginning balance, January 1, 2016 $ — $ 0.7 $ 0.7 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) — — — Purchases, issuances, sales, and settlements: Purchases 2.0 — 2.0 Issuances — — — Sales — (0.3 ) (0.3 ) Settlements — — — Ending balance, December 31, 2016 $ 2.0 $ 0.4 $ 2.4 Amount of total gains or losses for the year included in net income (loss) attributable to the change in unrealized gains or losses relating to assets still held at December 31, 2016 $ — $ — $ — (in millions) Credit Financial Equity Securities Total Beginning balance, January 1, 2015 $ — $ 0.9 $ 0.9 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) — — — Purchases, issuances, sales, and settlements: Purchases — — — Issuances — — — Sales — (0.2 ) (0.2 ) Settlements — — — Ending balance, December 31, 2015 $ — $ 0.7 $ 0.7 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, 2015 $ — $ — $ — At December 31, 2016 and 2015, 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.

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2016
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 $2.1 million and $3.2 million as of December 31, 2016 and 2015, 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 $492.6 million and $421.6 million at December 31, 2016 and 2015, 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 $215.0 million and $130.8 million as of December 31, 2016 and 2015, 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 $810.1 million, $766.1 million and $747.4 million for the years ended December 31, 2016, 2015 and 2014, respectively, are net of amounts ceded to reinsurers of $419.3 million, $284.6 million and $246.6 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 6, “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 Syndicate 1200 (see Note 19, “Segment Information”). Premiums were as follows: For the Years Ended December 31, (in millions) 2016 2015 2014 Direct written premiums $ 1,792.5 $ 1,651.4 $ 1,585.5 Reinsurance ceded to other companies (724.6 ) (610.0 ) (537.5 ) Reinsurance assumed from other companies 372.3 360.7 319.9 Net written premiums $ 1,440.2 $ 1,402.1 $ 1,367.9 Direct earned premiums $ 1,722.8 $ 1,602.2 $ 1,551.8 Reinsurance ceded to other companies (675.8 ) (563.7 ) (524.8 ) Reinsurance assumed from other companies 363.8 333.4 311.1 Net earned premiums $ 1,410.8 $ 1,371.9 $ 1,338.1 Percentage of reinsurance assumed to net earned premiums 25.8 % 24.3 % 23.2 %

Reserves for Losses and Loss Ad

Reserves for Losses and Loss Adjustment Expenses	12 Months Ended
	Dec. 31, 2016
Insurance [Abstract]
Reserves for Losses and Loss Adjustment Expenses	5. 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) 2016 2015 2014 Net reserves beginning of the year $ 2,133.3 $ 2,137.1 $ 2,107.6 Add: Losses and LAE incurred during current calendar year, net of reinsurance: Current accident year 843.4 798.5 785.1 Prior accident years (33.3 ) (32.4 ) (37.7 ) Losses and LAE incurred during calendar year, net of reinsurance 810.1 766.1 747.4 Deduct: Losses and LAE payments made during current calendar year, net of reinsurance: Current accident year 178.9 169.0 185.9 Prior accident years 537.6 564.5 550.8 Losses and LAE payments made during current calendar year, net of reinsurance: 716.5 733.5 736.7 Change in participation interest (1) (36.3 ) (1.2 ) 37.8 Foreign exchange adjustments (10.4 ) (35.2 ) (19.0 ) Net reserves - end of year 2,180.2 2,133.3 2,137.1 Add: Reinsurance recoverables on unpaid losses and LAE, end of year 1,170.6 990.3 905.3 Gross reserves - end of year $ 3,350.8 $ 3,123.6 $ 3,042.4 (1) Amount represents (decrease) increase in reserves due to change in our Syndicate 1200 participation. Reserves for losses and LAE represent the estimated indemnity cost and related adjustment expenses necessary to investigate and settle claims. Such estimates are based upon individual case estimates for reported claims, estimates from ceding companies for reinsurance assumed and actuarial estimates for losses that have been incurred but not yet reported to the insurer. Any change in probable ultimate liabilities is reflected in current operating results. The impact from the (favorable) unfavorable development of prior accident years’ losses and LAE reserves on each reporting segment is presented below: For the Years Ended December 31, (in millions) 2016 2015 2014 Excess and Surplus Lines $ (13.2 ) $ (25.5 ) $ (38.9 ) Commercial Specialty (22.7 ) 2.5 (1.7 ) International Specialty (11.0 ) (7.7 ) (0.4 ) Syndicate 1200 (5.0 ) (10.3 ) (21.1 ) Run-off Lines 18.6 8.6 24.4 Total favorable prior-year development $ (33.3 ) $ (32.4 ) $ (37.7 ) The following describes the primary factors behind each segment’s prior accident year reserve development for the years ended December 31, 2016, 2015 and 2014: Year ended December 31, 2016: • Excess and Surplus Lines: Favorable development in the general and products liability lines, commercial automobile, and property lines • Commercial Specialty: Favorable development in workers compensation, surety, auto liability, and property, partially offset by unfavorable development in other liabilities • International Specialty: Favorable development in the property reinsurance line, professional liability, and the Brazil unit, partially offset by unfavorable development in the casualty unit • Syndicate 1200: Favorable development in various property classes, general liability, and marine and energy, partially offset by unfavorable development in specialty lines • Run-off Lines: Unfavorable development in risk management, asbestos and environmental liability, and other run-off segments Year ended December 31, 2015: • Excess and Surplus Lines: Favorable development in the general and products liability lines and commercial automobile, partially offset by unfavorable development in property lines • Commercial Specialty: Unfavorable development in general liability and workers compensation due to an increase in claim severity, partially offset by favorable development in short-tail, directors and officers, auto liability lines, and errors and omissions. • International Specialty: Favorable development in the property reinsurance line, professional liability and the casualty unit, partially offset by unfavorable development in the Brazil unit • Syndicate 1200: Favorable development in various property classes and general liability, partially offset by unfavorable development in accident & health lines • Run-off Lines: Unfavorable development primarily in workers compensation lines and asbestos and environmental liability, partially offset by favorable development in run-off reinsurance claims Year ended December 31, 2014: • Excess and Surplus Lines: Favorable development in the general and products liability lines, partially offset by unfavorable development in commercial automobile • Commercial Specialty: Favorable development in short-tail, workers compensation, and errors and omissions, partially offset by unfavorable development in general liability and auto liability lines • International Specialty: Favorable development in professional liability and the casualty unit, partially offset by unfavorable development in the property reinsurance line and the Brazil unit • Syndicate 1200: Favorable development in various property classes and professional indemnity, partially offset by unfavorable development in general liability • Run-off Lines: Unfavorable development in workers compensation lines and asbestos liability In the opinion of management, our reserves represent the best estimate of our ultimate liabilities, based on currently known facts, current law, current technology and assumptions considered reasonable where facts are not known. Due to the significant uncertainties and related management judgments, there can be no assurance that future favorable or unfavorable loss development, which may be material, will not occur. Short-Duration Contract Disclosures ASU 2015-09, “Disclosures about Short-Duration Contracts” (Topic 944), requires insurers to make disclosures about their liability for unpaid claims and claim adjustment expenses for short-duration insurance contracts. These disclosures include tables showing incurred and paid claims development information (net of reinsurance and excluding unallocated loss adjustment expenses) which are disaggregated based on the characteristics of the insurance contracts that the insurer writes and other factors specific to the reporting entity. The information should be disclosed by accident year for the number of years claims typically remain outstanding, but need not be more than 10 years, including a reconciliation of the disaggregated information to the consolidated statement of financial position. The basis for our disaggregation of this information is by each of our four ongoing operating segments, further disaggregated within each segment by the significant insurance products we write. See Note 19, “Segment Information,” for additional information regarding our four ongoing operating segments. Significant Insurance Products We use an underwriting committee structure to monitor and evaluate the financial performance of our insurance products to effectively manage our business. The underwriting committees are organized to allow products or coverages with similar characteristics to be managed and evaluated in distinct groups. Using this approach, the majority of our insurance business is categorized under one of our three underwriting groups, which are Casualty, Professional and Property. Noted below are descriptions of the types of characteristics considered to disaggregate our business into these three groups, as well as other qualitative factors to consider when using the information contained in the following incurred and paid claims development tables. Casualty Our Casualty business generally covers exposures where most claims are reported without a significant time lag between the event that gives rise to a claim and the date the claim is reported to us. However, since facts and information are frequently not complete at the time claims are reported to us, and because protracted litigation is sometimes involved, it can be several years before the ultimate value of these claims is determined. In our International Specialty segment, much of the business covers higher layers, potentially increasing the time it takes to fully determine our exposure. Professional Much of our Professional business is written on a claims-made basis resulting in coverage only for claims that are reported to us during the year, thus reducing the number of claims that will become known to us after the end of the year. However, facts and information are frequently not complete at the time claims are reported to us, and protracted litigation is sometimes involved. It can be several years before the ultimate value of these claims is determined. In International Specialty, much of the business covers higher layers, potentially increasing the time it takes to fully determine our exposure. Property Property losses are generally reported within a short period of time from the date of loss, and in most instances, property claims are settled and paid within a relatively short timeframe. However, Property can be impacted by catastrophe losses which can be more complex than non-catastrophe Property claims due to factors such as difficulty accessing impacted areas and other physical, legal and regulatory impediments potentially extending the period of time it takes to settle and pay claims. The impacts of catastrophe losses can be more significant in our International Specialty and Syndicate 1200 segments. Descriptions of the primary types of coverages included in each of the insurance product groups for each operating segment are noted below: Excess and Surplus Lines • Casualty: primary and excess specialty casualty, contract liability, commercial multi-peril, product liability, environmental liability, allied medical, and auto liability Commercial Specialty • Casualty: workers compensation, general liability, auto liability, and various public entity liability risks • Professional: management liability and errors and omissions liability International Specialty • Casualty: long-tail casualty and general liability • Professional: product liability, directors and officer’s liability, errors and omissions liability, employment practices liability, and professional and engineering liability for commercial markets in Brazil and Continental Europe • Property: catastrophe reinsurance and direct and facultative excess reinsurance Syndicate 1200 • Casualty: general liability, international casualty and motor treaties • Professional: professional indemnity, directors and officer’s liability, and medical malpractice • Property: direct and facultative excess reinsurance, North American and international binders, and residential collateral protection for lending institutions Run-off Lines Segment We have a Run-off Lines segment for certain products that we no longer underwrite, including asbestos and environmental claims. We have excluded the Run-off Lines segment from the following disaggregated short-duration contract disclosures due to its insignificance to our consolidated financial position and results of operations, both quantitatively and qualitatively. Gross reserves for losses and LAE in Run-off Lines account for less than 9% of our consolidated gross reserves for losses and LAE, and are primarily related to accident years prior to the mid-1990s. As such, claims development tables for the most recent 10 accident years would not provide meaningful information to users of our financial statements, as the majority of the remaining reserves for losses and LAE would be for accident years not separately presented. See Note 6, “Run-off Lines,” for further information on this segment, including discussion of prior accidents years’ development. Accident Years Presented We reevaluated and changed our reportable segments in 2011 to more appropriately align our operating structure with the management of the business. As such, prior to calendar year 2011 we did not track ultimate claims and claim adjustment expenses by accident year at a level of detail consistent with the current segmentation of our business, with the exception of the business in Syndicate 1200. As a result, it is impracticable to obtain the information necessary to provide historical ultimate claims and claim adjustment expense estimates prior to December 31, 2011 in the following incurred and paid claims development tables for all disaggregation categories except those associated with Syndicate 1200. Syndicate 1200 ultimate claims and claim adjustment expenses are provided beginning with accident year 2010 due to the retroactive whole account quota share contract we entered into on December 31, 2012. As a result of this transaction, reserves for losses and LAE prior to accident year 2010 were legally transferred to another syndicate within the Lloyd’s market. Under this quota share contract, we did not retain any direct indemnity or credit risk for the reserves prior to accident year 2010. Foreign Currency Portions of the business we write in the Syndicate 1200 and International Specialty segments are denominated in foreign currencies. We have used the December 31, 2016 balance sheet foreign exchange rates to recast the incurred and paid claims information for all periods presented in the following claims development tables in order to eliminate the effects of changes in foreign currency translation rates. Reserves for Incurred But Not Reported (“IBNR”) Claims Reserves for IBNR claims are based on the estimated ultimate cost of settling claims, including the effects of inflation and other social and economic factors, using past experience adjusted for current trends and any other factors that would modify past experience. We use a variety of statistical and actuarial techniques to analyze current claims costs, including frequency and severity data and prevailing economic, social and legal factors. Each such method has its own set of assumptions and outputs, and each has strengths and weaknesses in different areas. Since no single estimation method is superior to another method in all situations, the methods and assumptions used to project loss reserves will vary by coverage and product. We use what we believe to be the most appropriate set of actuarial methods and assumptions for each product line grouping and coverage. While the loss projection methods may vary by product line and coverage, the general approach for calculating IBNR remains the same: ultimate losses are forecasted first, and that amount is reduced by the amount of cumulative paid claims and case reserves. Reserves established in prior years are adjusted as loss experience develops and new information becomes available. Adjustments to previously estimated reserves are reflected in the results of operations in the year in which they are made. As described above, various actuarial methods are utilized to determine the reserves for losses and LAE recorded in our Consolidated Balance Sheets. Weightings of methods at a detailed level may change from evaluation to evaluation based on a number of observations, measures, and time elements. There were no significant changes to the methods and assumptions underlying our consolidated reserve estimations and selections as of December 31, 2016. Incurred & Paid Claims Development Disclosures The following tables provide information about incurred and cumulative paid losses and allocated loss adjustment expenses (“ALAE”), net of reinsurance. The following tables also include IBNR reserves plus expected development on reported claims and the cumulative number of reported claims as of December 31, 2016. Excess and Surplus Lines Casualty Products (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 202.9 $ 206.0 $ 205.8 $ 200.0 $ 193.5 $ 192.8 2012 189.6 196.0 189.7 183.6 184.4 2013 217.9 222.6 224.3 227.2 2014 213.0 215.1 213.1 2015 232.3 237.0 2016 246.5 Total $ 1,301.0 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 17.6 $ 53.8 $ 91.0 $ 122.9 $ 146.6 $ 162.4 2012 17.2 52.8 89.1 120.8 142.4 2013 17.6 60.2 100.4 135.2 2014 15.0 52.2 95.9 2015 16.5 51.9 2016 17.4 Total $ 605.2 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 96.8 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 792.6 As of December 31, 2016 Incurred IBNR & Expected Cumulative Accident Losses & ALAE, Development on Number of Year Net of Reinsurance Reported Claims Reported Claims (2) 2011 $ 192.8 $ 21.1 8,324 2012 184.4 26.5 7,222 2013 227.2 51.5 7,016 2014 213.1 69.9 5,978 2015 237.0 131.2 5,035 2016 246.5 190.8 3,605 (1) Information presented for calendar years prior to 2016 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured at a coverage level by occurrence. Reported occurrences that do not result in a liability are included as reported claims. Commercial Specialty Casualty Products (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 140.6 $ 155.1 $ 159.0 $ 157.5 $ 158.2 $ 154.0 2012 140.3 146.3 149.7 152.2 151.5 2013 126.6 133.2 135.1 133.2 2014 115.5 118.6 116.9 2015 102.6 106.7 2016 95.9 Total $ 758.2 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 23.1 $ 57.5 $ 85.9 $ 111.3 $ 126.1 $ 135.1 2012 20.1 51.0 80.7 105.3 120.8 2013 18.9 49.4 73.6 93.6 2014 17.4 38.4 58.7 2015 16.4 35.0 2016 11.1 Total $ 454.3 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 70.3 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 374.2 As of December 31, 2016 Incurred IBNR & Expected Cumulative Accident Losses & ALAE, Development on Number of Year Net of Reinsurance Reported Claims Reported Claims (2) 2011 $ 154.0 $ 9.1 28,462 2012 151.5 15.3 24,078 2013 133.2 16.9 19,117 2014 116.9 29.1 16,577 2015 106.7 40.5 13,758 2016 95.9 55.6 9,720 (1) Information presented for calendar years prior to 2016 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. Commercial Specialty Professional Products (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 35.0 $ 35.0 $ 35.0 $ 32.5 $ 28.2 $ 26.9 2012 27.8 28.3 28.6 25.8 24.0 2013 20.9 21.5 21.1 19.0 2014 22.4 22.4 26.0 2015 29.9 29.5 2016 44.2 Total $ 169.6 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 3.2 $ 11.8 $ 17.8 $ 22.0 $ 24.0 $ 25.4 2012 2.3 8.6 16.9 19.9 21.4 2013 1.9 6.3 10.9 14.2 2014 2.3 5.4 15.1 2015 1.8 8.3 2016 2.4 Total $ 86.8 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 0.8 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 83.6 As of December 31, 2016 Incurred IBNR & Expected Cumulative Accident Losses & ALAE, Development on Number of Year Net of Reinsurance Reported Claims Reported Claims (2) 2011 $ 26.9 $ 0.7 815 2012 24.0 1.7 634 2013 19.0 1.6 611 2014 26.0 3.3 978 2015 29.5 11.7 1,647 2016 44.2 38.8 2,392 (1) Information presented for calendar years prior to 2016 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. International Specialty Casualty Products (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 6.6 $ 6.6 $ 6.6 $ 4.4 $ 2.2 $ 1.6 2012 7.4 7.4 7.4 5.7 4.5 2013 9.1 9.5 9.6 9.6 2014 10.7 11.0 10.7 2015 12.6 15.3 2016 15.3 Total $ 57.0 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ — $ — $ — $ — $ — $ — 2012 — — — 0.1 0.1 2013 0.4 0.8 0.9 0.9 2014 0.3 0.7 0.8 2015 0.3 0.6 2016 0.5 Total $ 2.9 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 0.4 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 54.5 As of December 31, 2016 Incurred IBNR & Expected Cumulative Accident Losses & ALAE, Development on Number of Year Net of Reinsurance Reported Claims Reported Claims (2) 2011 $ 1.6 $ 1.6 1,416 2012 4.5 4.4 1,395 2013 9.6 8.5 1,416 2014 10.7 6.7 1,989 2015 15.3 6.3 2,487 2016 15.3 14.5 2,531 (1) Information presented for calendar years prior to 2016 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. International Specialty Professional Products (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 3.2 $ 3.2 $ 3.2 $ 2.3 $ 1.3 $ 0.8 2012 3.5 3.5 3.4 2.7 2.7 2013 5.8 6.4 6.2 4.9 2014 8.2 8.1 7.6 2015 10.8 10.8 2016 11.0 Total $ 37.8 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ — $ — $ — $ — $ — $ — 2012 — — — — 1.5 2013 0.5 0.9 1.4 1.4 2014 0.7 1.3 1.7 2015 1.3 2.1 2016 0.9 Total $ 7.6 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 30.2 As of December 31, 2016 Incurred IBNR & Expected Cumulative Accident Losses & ALAE, Development on Number of Year Net of Reinsurance Reported Claims Reported Claims (2) 2011 $ 0.8 $ 0.8 789 2012 2.7 1.2 986 2013 4.9 3.2 1,124 2014 7.6 4.7 1,275 2015 10.8 7.5 1,305 2016 11.0 8.7 1,315 (1) Information presented for calendar years prior to 2016 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. International Specialty Property Products (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 114.9 $ 102.9 $ 105.0 $ 102.9 $ 102.2 $ 102.1 2012 47.3 51.5 50.5 51.7 46.5 2013 33.9 35.7 35.1 33.3 2014 28.0 28.2 26.2 2015 28.2 24.5 2016 45.5 Total $ 278.1 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 39.9 $ 65.1 $ 86.2 $ 93.7 $ 96.0 $ 97.2 2012 12.4 31.2 40.7 49.7 44.1 2013 4.9 18.7 28.5 30.8 2014 3.3 13.7 20.3 2015 4.6 11.8 2016 14.8 Total $ 219.0 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 4.4 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 63.5 As of December 31, 2016 Incurred IBNR & Expected Cumulative Accident Losses & ALAE, Development on Number of Year Net of Reinsurance Reported Claims Reported Claims (2) 2011 $ 102.1 $ — 400 2012 46.5 0.9 299 2013 33.3 0.8 351 2014 26.2 2.6 339 2015 24.5 5.5 443 2016 45.5 19.5 742 (1) Information presented for calendar years prior to 2016 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. Syndicate 1200 Casualty Products (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2010 $ 5.7 $ 4.8 $ 4.5 $ 6.1 $ 5.9 $ 5.8 $ 5.8 2011 8.0 8.6 10.8 10.9 10.2 10.1 2012 8.7 10.8 14.8 14.1 13.8 2013 22.6 26.7 26.2 24.5 2014 37.1 36.2 33.8 2015 33.9 29.2 2016 26.2 Total $ 143.4 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2010 $ — $ 0.2 $ 0.6 $ 1.1 $ 2.0 $ 2.8 $ 3.7 2011 0.2 0.8 1.6 3.4 5.4 6.9 2012 0.4 1.1 2.6 5.8 8.2 2013 1.5 3.2 7.0 11.3 2014 1.9 4.6 9.9 2015 0.8 5.2 2016 1.8 Total $ 47.0 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 96.4 As of December 31, 2016 Incurred IBNR & Expected Accident Losses & ALAE, Development on Year Net of Reinsurance Reported Claims 2010 $ 5.8 $ 1.1 2011 10.1 2.1 2012 13.8 3.6 2013 24.5 7.3 2014 33.8 13.8 2015 29.2 17.8 2016 26.2 21.5 (1) Information presented for calendar years prior to 2016 is required supplementary information and is unaudited. Syndicate 1200 Professional Products (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2010 $ 15.2 $ 12.5 $ 12.4 $ 11.0 $ 9.9 $ 9.2 $ 9.3 2011 18.7 20.5 18.1 15.1 14.3 14.4 2012 13.7 13.6 13.8 13.7 13.8 2013 22.4 22.3 22.4 22.0 2014 34.5 35.5 35.9 2015 37.1 36.7 2016 33.2 Total $ 165.3 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2010 $ 0.1 $ 0.9 $ 1.9 $ 2.9 $ 3.7 $ 5.0 $ 6.3 2011 1.0 2.4 4.1 6.4 8.1 10.4 2012 0.6 1.8 4.2 5.6 8.0 2013 1.6 3.6 7.0 11.5 2014 1.6 6.3 14.5 2015 2.2 8.1 2016 2.0 Total $ 60.8 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 104.5 As of December 31, 2016 Incurred IBNR & Expected Accident Losses & ALAE, Development on Year Net of Reinsurance Reported Claims 2010 $ 9.3 $ 1.9 2011 14.4 3.1 2012 13.8 3.3 2013 22.0 7.0 2014 35.9 13.1 2015 36.7 20.4 2016 33.2 28.7 (1) Information presented for calendar years prior to 2016 is required supplementary information and is unaudited. Syndicate 1200 Property Products (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2010 $ 50.4 $ 57.9 $ 54.3 $ 53.8 $ 51.1 $ 50.9 $ 50.3 2011 107.3 112.6 106.8 94.2 92.4 91.7 2012 88.4 88.1 92.5 91.6 90.5 2013 83.2 79.1 78.1 76.5 2014 69.5 64.1 65.4 2015 54.9 64.9 2016 72.1 Total $ 511.4 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2010 $ 1.8 $ 19.4 $ 27.8 $ 33.6 $ 35.6 $ 39.8 $ 41.3 2011 23.2 46.8 61.4 73.1 78.9 80.7 2012 29.3 47.5 62.6 73.6 76.0 2013 44.2 56.5 68.9 73.0 2014 29.3 51.3 57.3 2015 22.8 42.6 2016 38.8 Total $ 409.7 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 101.7 As of December 31, 2016 Incurred IBNR & Expected Accident Losses & ALAE, Development on Year Net of Reinsurance Reported Claims 2010 $ 50.3 $ 12.8 2011 91.7 23.6 2012 90.5 23.7 2013 76.5 20.1 2014 65.4 16.1 2015 64.9 17.3 2016 72.1 36.4 (1) Information presented for calendar years prior to 2016 is required supplementary information and is unaudited. Syndicate 1200 Claim Frequency Information Cumulative claim frequency information has been excluded from the Syndicate 1200 Casualty, Professional and Property incurred and paid claims development tables above due to the impracticability of obtaining such information at the level required for meaningful disaggregated disclosure. Syndicate 1200 measures claim frequency based on the number of reported claims by individual claimant at a coverage level for non-bordereaux reporting, which is consistent with market practices for insurance business sourced through open market channels. For claims reported on a bordereaux for business sourced through channels such as Lloyd’s authorized coverholders, which constitutes approximately half of the business written in Syndicate 1200, the number of reported claims is measured by bordereaux report at a coverage level. This method of tracking and analyzing bordereaux-reported claims is consistent with common industry practice within the Lloyd’s market. The information for both bordereaux and non-bordereaux claims may be pooled dependent on the class of business and analyzed in the aggregate to determine the ultimate cost of settling the claims by line of business and Lloyd’s year of account. Due to our methodology of establishing ultimate liabilities for Syndicate 1200 claims, there is not a reasonable way to disaggregate the IBNR reserves and expected development on reported claims between bordereaux and non-bordereaux business for separate disclosure. The reconciliation of the net incurred and paid development tables to the liability for unpaid losses and LAE in our Consolidated Balance Sheets is as follows: (in millions) As of December 31, 2016 Liabilities for unpaid losses and ALAE: Excess and Surplus Lines - Casualty products $ 792.6 Commercial Specialty - Casualty products 374.2 Commercial Specialty - Professional products 83.6 International Specialty - Casualty products 54.5 International Specialty - Professional products 30.2 International Specialty - Property products 63.5 Syndicate 1200 - Casualty products 96.4 Syndicate 1200 - Professional products 104.5 Syndicate 1200 - Property products 101.7 Run-off Lines 203.3 Other lines 227.1 Total liabilities for unpaid losses and ALAE, net of reinsurance 2,131.6 Reinsurance recoverables on unpaid losses and LAE: Excess and Surplus Lines - Casualty products 261.0 Commercial Specialty - Casualty products 239.6 Commercial Specialty - Professional products 51.5 International Specialty - Casualty products 115.2 International Specialty - Professional products 39.0 International Specialty - Property products 18.6 Syndicate 1200 - Casualty products 54.3 Syndicate 1200 - Professional products 59.9 Syndicate 1200 - Property products 58.9 Run-off Lines 96.7 Other lines 175.9 Total reinsurance recoverables on unpaid losses and LAE 1,170.6 Unallocated loss adjustment expenses 68.0 Unamortized reserve discount (19.4 ) Gross liability for unpaid losses and LAE $ 3,350.8 Other lines in the table above is comprised of products within our four operating segments which are not individually significant for separate disaggregated disclosure. Claims Duration The following table provides supplementary unaudited information about the annual percentage payout of incurred losses and ALAE, net of reinsurance, as of December 31, 2016: Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance (1) Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Excess and Surplus Lines - Casualty products 8.4% 18.7% 19.4% 16.3% 11.7% 8.1% N/A Commercial Specialty - Casualty products 14.6% 20.7% 18.4% 15.7% 9.7% 6.6% N/A Commercial Specialty - Professional products 9.6% 23.9% 29.8% 14.6% 6.4% 5.1% N/A International Specialty - Casualty products 11.5% 12.8% 17.5% 14.7% 10.5% 8.4% N/A International Specialty - Professional products 6.5% 17.2% 23.6% 15.4% 11.8% 10.2% N/A International Specialty - Property products 16.8% 41.2% 23.5% 9.9% 4.1% 2.0% N/A Syndicate 1200 - Casualty products 3.7% 7.6% 13.2% 20.4% 21.8% 11.0% 7.1% Syndicate 1200 - Professional products 4.3% 9.3% 15.0% 15.7% 14.7% 16.6% 7.3% Syndicate 1200 - Property products 38.4% 24.7% 15.1% 10.9% 5.0% 2.5% 1.3% (1) The average annual percentage payout is calculated from a paid losses and ALAE development pattern based on an actuarial analysis of the paid losses and ALAE movements by accident year for each disaggregation category. The paid losses and ALAE development pattern provides the expected percentage of ultimate losses and ALAE to be paid in each year. The pattern considers all accident years included in the claims development tables . Information About Amounts Reported at Present Value We discount certain workers compensation liabilities for unpaid losses and LAE within our Commercial Specialty and Run-off Lines segments. The discounted Commercial Specialty liabilities relate to all non-ALAE workers compensation liabilities within one of our insurance subsidiaries. In Run-off Lines, we discount certain pension-type liabilities for unpaid losses and LAE. The following tables provide information about these

Run-off Lines

Run-off Lines	12 Months Ended
	Dec. 31, 2016
Discontinued Operations And Disposal Groups [Abstract]
Run-off Lines	6 . Run-off Lines We have discontinued active underwriting of certain lines of business, including those lines that were previously recorded in Argo Group’s Risk Management segment. All current activity within these lines is related to the management of claims and other administrative functions. Also included in Run-off Lines are other liability reserves, which include exposure to claims for asbestos and environmental liabilities written in past years. The other liability reserves are often characterized by long elapsed periods between the occurrence of a claim and ultimate payment to resolve the claim. We use a specialized staff dedicated to administer and settle these claims. The following table presents our gross reserves for Run-off Lines as of December 31: December 31, (in millions) 2016 2015 Asbestos and Environmental: Reinsurance assumed $ 28.4 $ 34.6 Other 20.0 11.8 Total Asbestos and Environmental 48.4 46.4 Risk management 236.9 252.2 Run-off reinsurance lines 1.9 3.0 Other run-off lines 3.7 4.7 Total Run-off Lines $ 290.9 $ 306.3 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) 2016 2015 2014 Direct written Case reserves $ 2.8 $ 2.0 $ 2.5 Unallocated loss adjustment expense ("ULAE") 0.5 0.5 1.0 Incurred but not reported ("IBNR") 12.1 8.2 7.6 Total direct written reserves 15.4 10.7 11.1 Assumed domestic Case reserves 10.5 12.2 13.2 ULAE 0.8 0.8 1.6 IBNR 10.5 13.7 15.8 Total assumed domestic reserves 21.8 26.7 30.6 Assumed London Case reserves 3.3 4.0 4.7 ULAE — — 0.2 IBNR 1.4 1.4 1.2 Total assumed London reserves 4.7 5.4 6.1 Total asbestos reserves $ 41.9 $ 42.8 $ 47.8 The following table presents our results for Run-off Lines: For the Years Ended December 31, (in millions) 2016 2015 2014 Asbestos and Environmental: Reinsurance assumed $ (1.3 ) $ (1.0 ) $ (8.3 ) Other (9.6 ) (3.4 ) (5.0 ) Total Asbestos and Environmental (10.9 ) (4.4 ) (13.3 ) Risk management (13.1 ) (8.2 ) (15.5 ) Run-off reinsurance lines 0.1 2.0 (1.5 ) Other run-off lines (1.2 ) (3.5 ) (0.7 ) Total Run-off Lines $ (25.1 ) $ (14.1 ) $ (31.0 ) 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 utilizing a variety of methods which rely on historical claim reporting and average claim cost information. We apply greatest weight to the method that projects future calendar period claims and average claim costs because it best captures the unique claim characteristics of our underlying exposures. Although management has recorded its best estimate of loss reserves, due to the uncertainties of estimation of liability that may arise as discussed herein, further deterioration of claims could occur in the future. Please see Note 5

Junior Subordinated Debentures

Junior Subordinated Debentures	12 Months Ended
	Dec. 31, 2016
Junior Subordinated Debentures [Member]
Junior Subordinated Debentures	7. Junior Subordinated Debentures Through a series of trusts, that are wholly-owned subsidiaries (non-consolidated), we issued debt. The debentures are variable with the rate being reset quarterly and subject to certain interest rate ceilings. Interest payments are payable quarterly. The debentures are all unsecured and are subordinated to other indebtedness. At December 31, 2016 and 2015, all debentures were eligible for redemption subject to certain terms and conditions at a price equal to 100% of the principal plus accrued and unpaid interest. 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. A summary of our outstanding junior subordinated debentures is presented below: (in millions) Issue Date Trust Preferred Pools Maturity Rate Structure Interest Rate at December 31, 2016 Amount Argo Group 05/15/2003 PXRE Capital Statutory Trust II 05/15/2033 3M LIBOR + 4.10% 5.00% $ 18.1 11/06/2003 PXRE Capital Trust VI 09/30/2033 3M LIBOR + 3.90% 4.90% 10.3 Argo Group US 05/15/2003 Argonaut Group Statutory Trust I 05/15/2033 3M LIBOR + 4.10% 5.00% 15.5 12/16/2003 Argonaut Group Statutory Trust III 01/08/2034 3M LIBOR + 4.10% 4.98% 12.3 04/29/2004 Argonaut Group Statutory Trust IV 04/29/2034 3M LIBOR + 3.85% 4.76% 13.4 05/26/2004 Argonaut Group Statutory Trust V 05/24/2034 3M LIBOR + 3.85% 4.77% 12.3 05/12/2004 Argonaut Group Statutory Trust VI 05/12/2034 3M LIBOR + 3.80% 4.79% 13.4 09/17/2004 Argonaut Group Statutory Trust VII 12/15/2034 3M LIBOR + 3.60% 4.56% 15.5 09/22/2004 Argonaut Group Statutory Trust VIII 09/22/2034 3M LIBOR + 3.55% 4.55% 15.5 10/22/2004 Argonaut Group Statutory Trust IX 12/15/2034 3M LIBOR + 3.60% 4.56% 15.5 09/15/2005 Argonaut Group Statutory Trust X 09/15/2035 3M LIBOR + 3.40% 4.36% 30.9 Total Outstanding $ 172.7 (in millions) Issue Date Trust Preferred Pools Maturity Rate Structure Interest Rate at December 31, 2015 Amount Argo Group 05/15/2003 PXRE Capital Statutory Trust II 05/15/2033 3M LIBOR + 4.10% 4.46% $ 18.1 11/06/2003 PXRE Capital Trust VI 09/30/2033 3M LIBOR + 3.90% 4.51% 10.3 Argo Group US 05/15/2003 Argonaut Group Statutory Trust I 05/15/2033 3M LIBOR + 4.10% 4.46% 15.5 12/16/2003 Argonaut Group Statutory Trust III 01/08/2034 3M LIBOR + 4.10% 4.42% 12.3 04/29/2004 Argonaut Group Statutory Trust IV 04/29/2034 3M LIBOR + 3.85% 4.21% 13.4 05/26/2004 Argonaut Group Statutory Trust V 05/24/2034 3M LIBOR + 3.85% 4.23% 12.3 05/12/2004 Argonaut Group Statutory Trust VI 05/12/2034 3M LIBOR + 3.80% 4.33% 13.4 09/17/2004 Argonaut Group Statutory Trust VII 12/15/2034 3M LIBOR + 3.60% 4.11% 15.5 09/22/2004 Argonaut Group Statutory Trust VIII 09/22/2034 3M LIBOR + 3.55% 4.14% 15.5 10/22/2004 Argonaut Group Statutory Trust IX 12/15/2034 3M LIBOR + 3.60% 4.11% 15.5 09/15/2005 Argonaut Group Statutory Trust X 09/15/2035 3M LIBOR + 3.40% 3.91% 30.9 Total Outstanding $ 172.7

Other Indebtedness

Other Indebtedness	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Other Indebtedness	8. Other Indebtedness Floating Rate Loan Stock This debt was assumed through the acquisition of Syndicate 1200. These notes are unsecured. At December 31, 2016 and 2015, all notes were eligible for redemption subject to certain terms and conditions at a price equal to 100% of the principal plus accrued and unpaid interest. Interest on the U.S. Dollar and Euro notes is due semiannually and quarterly, respectively. A summary of the notes outstanding at December 31, 2016 and 2015 is presented below: (in millions) Issue Date Currency Maturity Rate Structure Interest Rate at December 31, 2016 Amount 12/08/2004 U.S. Dollar 11/15/2034 6 month LIBOR + 4.2% 5.18% $ 6.5 09/06/2005 Euro 08/22/2035 3 month LIBOR + 4.0% 3.70% 12.8 10/31/2006 U.S. Dollar 01/15/2036 6 month LIBOR + 4.0% 4.98% 10.0 10/31/2006 Euro 11/22/2036 3 month LIBOR + 4.0% 3.70% 11.2 06/08/2007 Euro 09/15/2037 3 month LIBOR + 3.9% 3.58% 14.3 $ 54.8 (in millions) Issue Date Currency Maturity Rate Structure Interest Rate at December 31, 2015 Amount 12/08/2004 U.S. Dollar 11/15/2034 6 month LIBOR + 4.2% 4.66% $ 6.5 09/06/2005 Euro 08/22/2035 3 month LIBOR + 4.0% 3.91% 12.7 10/31/2006 U.S. Dollar 01/15/2036 6 month LIBOR + 4.0% 4.46% 10.0 10/31/2006 Euro 11/22/2036 3 month LIBOR + 4.0% 3.91% 11.1 06/08/2007 Euro 09/15/2037 3 month LIBOR + 3.9% 3.86% 14.3 $ 54.6 No principal payments have been made since the acquisition of Syndicate 1200. The floating rate loan stock denominated in Euros fluctuates due to foreign currency translation. The outstanding balance on these loans was $ million and 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 (“Credit Agreement”) with JPMorgan Chase Bank, N.A., as administrative agent. The Credit Agreement replaced and terminated the previous $150.0 million Credit Agreement. The 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 Credit Agreement. Borrowings under the 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 Credit Agreement. The 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 Credit Agreement. Lenders holding at least a majority of the loans and commitments under the Credit Agreement may elect to accelerate the maturity of the loans and/or terminate the commitments under the Credit Agreement upon the occurrence and during the continuation of an event of default. Included in the Credit Agreement is a provision that allows up to $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 Credit Agreement. At December 31, 2016 and 2015, there were no borrowings outstanding and $0.2 million in LOCs against the Credit Facility. On January 31, 2017, Argo Group drew $125.0 million under this credit facility to help fund the acquisition of Maybrooke, which will bear interest at the one-month LIBOR rate plus 1.625%. See Note 2, “Subsequent Events,” for additional information related to the acquisition. Other Debt As part of the ARIS Title Insurance Corporation (“ARIS”) acquisition, at December 31, 2016 and 2015, we had a note payable for $0.6

Disclosures about Fair Value of

Disclosures about Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Disclosures about Fair Value of Financial Instruments	9. Disclosures about Fair Value of Financial Instruments Cash. The carrying amount approximates fair value. Investment securities and short-term investments . See Note 3, “Investments,” for additional information. Premiums receivable and reinsurance recoverables on paid losses. The carrying value of current receivables approximates fair value. At December 31, 2016 and 2015, the carrying values of premiums receivable over 90 days were $14.3 million and $10.0 million, respectively. Included in “Reinsurance recoverables” in our Consolidated Balance Sheets at December 31, 2016 and 2015, are amounts that are due from trade capital providers associated with the operations of Syndicate 1200. Upon settlement, the receivable is offset against the liability also reflected in our accompanying Consolidated Balance Sheets. At December 31, 2016 and 2015, the payable was in excess of the receivable. Of our reinsurance recoverables on paid losses, excluding amounts attributable to Syndicate 1200’s trade capital providers, at December 31, 2016 and 2015, the carrying values over 90 days were $11.2 million and $7.1 million, respectively. Our methodology for establishing our allowances for doubtful accounts includes specifically identifying all potential uncollectible balances regardless of aging. At December 31, 2016 and 2015, the allowance for doubtful accounts for premiums receivable was $2.7 million and $3.5 million, respectively, and the allowance for doubtful accounts for reinsurance recoverables on paid losses was $2.1 million and $2.2 million, respectively. Premiums receivable over 90 days were secured by collateral in the amount of $0.1 million and $0.2 million at December 31, 2016 and 2015, respectively. Reinsurance recoverables on paid losses over 90 days were secured by collateral in the amount of $0.6 million and $0.7 million at December 31, 2016 and 2015, respectively. Debt. At December 31, 2016 and 2015, 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: December 31, 2016 December 31, 2015 (in millions) Carrying Amount Fair Value Carrying Amount Fair Value Junior subordinated debentures $ 172.7 $ 162.4 $ 172.7 $ 166.5 Senior unsecured fixed rate notes 139.5 139.3 139.3 141.8 Other indebtedness: Floating rate loan stock 54.8 51.5 54.6 52.7 Note payable 0.6 0.6 0.6 0.6 $ 367.6 $ 353.8 $ 367.2 $ 361.6

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Shareholders' Equity	10. Shareholders’ Equity On February 21, 2017, our Board of Directors declared a quarterly cash dividend in the amount of $0.27 on each share of common stock outstanding. The cash dividend will be paid on March 15, 2017 to shareholders of record at the close of business on March 3, 2017. On May 3, 2016, our Board of Directors declared a 10% stock dividend, payable on June 15, 2016, to shareholders of record at the close of business on June 1, 2016. As a result of the stock dividend, 2,735,542 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. As a result of the stock dividend, 2,554,506 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. During 2016, our Board of Directors declared quarterly cash dividends totaling $0.86 on each share of common stock outstanding to our shareholders of record. For the year ended December 31, 2016, we paid cash dividends totaling $26.6 million to our shareholders. During 2015, our Board of Directors declared quarterly cash dividends totaling $0.80 on each share of common stock outstanding or $0.73 on each share outstanding adjusted for the 2016 stock dividend to our shareholders of record. For the year ended December 31, 2015, we paid cash dividends totaling $22.7 million to our shareholders. During 2014, our Board of Directors declared quarterly cash dividends totaling $0.69 on each share of common stock outstanding or $0.57 on each share outstanding adjusted for the 2016 and 2015 stock dividends to our shareholders of record. For the year ended December 31, 2014, we paid cash dividends totaling $18.2 million to our shareholders. We are authorized to issue 30 million shares of $1.00 par value preferred shares. As of December 31, 2016 and 2015, no preferred shares were issued and outstanding. On May 3, 2016, our Board of Directors authorized the repurchase of up to $150.0 million of our common shares (“2016 Repurchase Authorization”). The 2016 Repurchase Authorization supersedes all the previous Repurchase Authorizations. As of December 31, 2016, availability under the 2016 Repurchase Authorization for future repurchases of our common shares was $130.3 million. For the year ended December 31, 2016 and 2015, we repurchased 847,111 common shares and 575,155 common shares, respectively for $47.1 million and $29.7 million, respectively. A summary of common shares repurchased in 2016 is shown below: Repurchase Type Date Trading Plan Initiated 2016 Purchase Period Number of Shares Repurchased Average Price of Shares Repurchased Total Cost (in millions) Repurchase Authorization Year 10b5-1 Trading Plan 12/16/2015 01/04/2016-02/11/2016 266,538 $ 55.59 $ 14.8 2013 10b5-1 Trading Plan 03/16/2016 03/16/2016-05/02/2016 162,893 $ 55.62 9.1 2013 10b5-1 Trading Plan 06/16/2016 06/24/2016-06/28/2016 14,774 $ 49.78 0.7 2016 10b5-1 Trading Plan 09/15/2016 09/19/2016-11/2/2016 43,062 $ 55.23 2.4 2016 Open Market N/A 01/01/2016-05/02/2016 64,464 $ 54.14 3.5 2013 Open Market N/A 05/03/2016-09/30/2016 295,380 $ 56.38 16.6 2016 Total 847,111 $ 55.64 $ 47.1 At December 31, 2016, we had the following authorized, unissued common shares reserved for future issuance: Reserve Name Shares Reserved 2014 Long-Term Incentive Plan 3,848,430 2016 Employee Share Purchase Plan 526,543 Total 4,374,973

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Accumulated Other Comprehensive Income (Loss)	11. 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 Translation Adjustments Unrealized Holding Gains on Securities Defined Benefit Pension Plans Total Balance, January 1, 2015 $ (15.6 ) $ 130.7 $ (7.0 ) $ 108.1 Other comprehensive (loss) income before reclassifications (6.0 ) (89.8 ) 0.1 (95.7 ) Amounts reclassified from accumulated other comprehensive (loss) income — (0.9 ) — (0.9 ) Net current-period other comprehensive (loss) income (6.0 ) (90.7 ) 0.1 (96.6 ) Balance, December 31, 2015 (21.6 ) 40.0 (6.9 ) 11.5 Other comprehensive (loss) income before reclassifications 4.0 42.4 (0.2 ) 46.2 Amounts reclassified from accumulated other comprehensive (loss) income — (10.0 ) — (10.0 ) Net current-period other comprehensive (loss) income 4.0 32.4 (0.2 ) 36.2 Balance, December 31, 2016 $ (17.6 ) $ 72.4 $ (7.1 ) $ 47.7 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) 2016 2015 2014 Unrealized gains and losses on securities: Net realized investment gains $ (23.2 ) $ (7.2 ) $ (30.6 ) Provision for income taxes 13.2 6.3 9.9 Net of taxes $ (10.0 ) $ (0.9 ) $ (20.7 )

Net Income Per Common Share

Net Income Per Common Share	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Net Income Per Common Share	12. 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) 2016 2015 2014 Net income $ 146.7 $ 163.2 $ 183.2 Weighted average common shares outstanding - basic 30,166,440 30,769,089 31,559,422 Effect of dilutive securities: Equity compensation awards 679,270 616,371 574,796 Weighted average common shares outstanding - diluted 30,845,710 31,385,460 32,134,218 Net income per common share: Basic $ 4.86 $ 5.31 $ 5.80 Diluted $ 4.75 $ 5.20 $ 5.70 Excluded from the weighted average common shares outstanding calculation at December 31, 2016, 2015 and 2014 are 10,028,755 shares, 9,181,644 shares and 8,606,489 shares, respectively, which are held as treasury shares. The shares are excluded as of their repurchase date. In 2016 and 2015, there were no anti-dilutive shares of common stock to be excluded from the computation of diluted net income per common share. 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 expired or will expire at varying times from 2015 through 2021.

Share-based Compensation

Share-based Compensation	12 Months Ended
	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-based Compensation	13. 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, 2016 2015 2014 Risk-free rate of return 1.00% to 2.02% 1.44% to 1.81% 1.53% to 1.77% Expected dividend yields 1.62% to 1.70% 1.46% to 1.60% 1.49% to 1.55% Expected award life (years) 4.50 to 4.61 4.62 to 4.71 4.67 to 4.85 Expected volatility 18.73% to 19.70% 20.04% to 22.09% 22.84% to 25.46% All outstanding awards were adjusted to reflect the 10% stock dividend, resulting in a 10% increase to the number of awards outstanding and a 9.09% reduction in the exercise price. 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 $19.8 million ($15.5 million, net of tax), $29.1 million ($23.7 million, net of tax) and $19.6 million ($16.2 million, net of tax) for the years ended December 31, 2016, 2015 and 2014, 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 provided 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, 1.5 million 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 restricted share activity as of December 31, 2016 and changes during the year then ended is as follows: Shares Weighted-Average Grant Date Fair Value Outstanding at January 1, 2016 514,742 $ 36.87 Granted 287,227 $ 50.84 Vested and issued (71,177 ) $ 32.75 Expired or forfeited (28,762 ) $ 44.49 Outstanding at December 31, 2016 702,030 $ 42.69 As of December 31, 2016, there was $18.6 million of total unrecognized compensation cost related to restricted share compensation arrangements granted by Argo Group. The weighted-average period over which this unrecognized expense is expected to be recognized is 2.2 years. The total fair value of shares vested during the year ended December 31, 2016 was $2.3 million. A summary of stock-settled SARs activity as of December 31, 2016 and changes during the year then ended is as follows: Shares Weighted-Average Exercise Price Outstanding at January 1, 2016 1,438,146 $ 29.52 Granted 542 $ 36.71 Converted from cash-settled SARs 944,046 $ 41.21 Exercised (251,134 ) $ 24.46 Expired or forfeited (148,905 ) $ 41.93 Outstanding at December 31, 2016 1,982,695 $ 34.80 Vested or expected to vest as of end of year 1,808,016 $ 20.19 Exercisable at end of year 851,491 $ 30.02 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, 2016, 251,134 stock-settled SARs were exercised resulting in 141,418 shares being issued. As of December 31, 2016, there was $7.9 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 1.9 years. Aggregate intrinsic value of the stock-settled SARs at December 31, 2016 was $61.7 million. A summary of cash-settled SARs activity as of December 31, 2016 and changes during the year then ended is as follows: Shares Weighted-Average Exercise Price Outstanding at January 1, 2016 2,220,560 $ 35.53 Granted 540 $ 36.71 Converted to stock-settled SARs (1) (864,036 ) $ 41.21 Exercised (742,424 ) $ 30.70 Expired or forfeited (114,154 ) $ 39.03 Outstanding at December 31, 2016 500,486 $ 32.08 Vested or expected to vest as of end of year 480,891 $ 32.13 Exercisable at end of year 373,655 $ 32.44 (1) The converted shares were not adjusted for the 10% stock dividend because the conversion occurred prior to the stock dividend record date. 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, 2016, 742,424 cash-settled SARs were exercised resulting in $19.0 million in cash payments. As of December 31, 2016, there was $0.6 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 0.2 years. Aggregate intrinsic value of the cash-settled SARs at December 31, 2016 was $16.9 million. The liability for cash-settled SARs was $18.6 million and $31.0 million at December 31, 2016 and 2015, respectively. Included in the total shares outstanding at December 31, 2016 are 447,410 restricted shares whose vesting is contingent on the employee meeting defined performance conditions. Employees have a specified time period in which to meet the performance condition (typically 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 $0.1 million, $0.2 million, and $0.5 million for the years ended December 31, 2016, 2015 and 2014, respectively. For the year ended December 31, 2016, cash payments paid for vested awards under this plan were negligible. Cash payments paid for vested awards under this plan totaled $0.3 million for the year ended December 31, 2015. Employees Share Purchase Plans We have established an employee stock purchase plan for eligible employees (Argo Group’s 2007 Employee Share Purchase Plan). Under this plan, newly issued shares of our common stock may be purchased over an offering period of three months at 85% of the lower of the market value on the first day of the offering period or on the designated purchase date at the end of the offering period. We have also established a Save As You Earn Plan for our United Kingdom employees (Argo Group’s Save As You Earn Plan). Under this plan, newly issued shares of 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, 2016, 2015 and 2014 was $0.3 million, $0.4 million and $0.3 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 $0.9 million, $0.9 million and $0.7 million for the years ended December 31, 2016, 2015 and 2014, respectively. The liability for remaining distributions under the Directors Plan was $5.3 million and $4.5 million at December 31, 2016 and 2015, respectively.

Underwriting, Acquisition and I

Underwriting, Acquisition and Insurance Expenses	12 Months Ended
	Dec. 31, 2016
Underwriting Acquisition And Insurance Expenses [Abstract]
Underwriting, Acquisition and Insurance Expenses	14. Underwriting, Acquisition and Insurance Expenses Underwriting, acquisition and insurance expenses were as follows: For the Years Ended December 31, (in millions) 2016 2015 2014 Commissions $ 234.0 $ 232.2 $ 231.1 General expenses 292.1 295.6 285.8 Premium taxes, boards and bureaus 25.2 9.8 25.5 551.3 537.6 542.4 Net deferral of policy acquisition costs (4.3 ) (0.9 ) (5.4 ) Total underwriting, acquisition and insurance expenses $ 547.0 $ 536.7 $ 537.0 Included in general expenses for the years ended December 31, 2016, 2015 and 2014 is $19.8 million, $29.1 million and $19.6 million, respectively, of expense for our equity-related compensation. The increase in premium taxes, boards and bureaus for the year ended December 31, 2016 as compared to the year ended December 31, 2015 was primarily due to a decline in the accrual for premium taxes and other assessments due to a change in accounting estimate in the first quarter of 2015.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	15. 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. Seven of the United Kingdom subsidiaries are deemed to be engaged in business in the United States, and therefore, are subject to United States corporate tax in respect of a proportion of their United States underwriting business only. Relief is available against the United Kingdom tax liabilities in respect of overseas taxes paid that arise from the underwriting business. Our United Kingdom subsidiaries file separate United Kingdom income tax returns. We have subsidiaries based in the United States that are subject to United States tax laws. Under current law, these subsidiaries are taxed at the applicable corporate tax rates. Our United States subsidiaries 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) 2016 2015 2014 Current tax provision $ 36.3 $ 6.0 $ 5.2 Deferred tax provision related to: Future tax deductions (1.8 ) 10.9 58.4 Valuation allowance change 0.7 (2.6 ) (30.8 ) Income tax provision $ 35.2 $ 14.3 $ 32.8 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, 2016, 2015 and 2014, pre-tax income (loss) attributable to our operations and the operations’ effective tax rates were as follows: (in millions) 2016 2015 2014 Pre-Tax Income (Loss) Effective Tax Rate Pre-Tax Income (Loss) Effective Tax Rate Pre-Tax Income (Loss) Effective Tax Rate Bermuda $ 99.6 0.0 % $ 94.3 0.0 % $ 102.8 0.0 % United States 115.2 29.2 % 64.8 19.9 % 98.0 28.1 % United Kingdom (34.8 ) 1.2 % 21.3 (4.7 %) 21.5 24.8 % Belgium (0.1 ) 23.2 % — (1) 237.0 % — (1) 63.8 % Brazil 0.6 0.0 % (3.2 ) 0.0 % (2.2 ) 0.0 % United Arab Emirates — (1) 0.0 % 0.2 0.0 % (0.9 ) 0.0 % Ireland (2) (0.2 ) 5.0 % (0.1 ) 5.0 % (1.1 ) 0.0 % Malta 1.6 0.3 % 0.1 0.0 % (2.2 ) 0.0 % Switzerland — (1) 0.0 % 0.1 20.5 % 0.1 17.6 % Pre-tax income $ 181.9 $ 177.5 $ 216.0 (1) Pre-tax income for the respective year was less than $0.1 million. (2) Effective tax rate of 5 percent on intercompany dividends of $40.0 million for the year ended December 31, 2016. Dividends eliminated in consolidation. 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) 2016 2015 2014 Income tax provision at expected rate $ 34.1 $ 25.8 $ 37.2 Tax effect of: Tax-exempt interest (3.3 ) (4.2 ) (4.5 ) Dividends received deduction (2.2 ) (2.3 ) (2.3 ) Valuation allowance change 0.7 (2.6 ) (30.8 ) Other permanent adjustments, net 0.4 0.3 (0.7 ) Adjustment for prior year tax return (0.9 ) (0.6 ) (0.9 ) United States state tax expense — (2.5 ) 2.5 PXRE Reinsurance capital loss carryforward — — 29.8 Other foreign adjustments 0.2 (0.3 ) 0.7 Foreign tax credit utilization (1.5 ) (2.1 ) 0.1 Deferred tax rate reduction — — (0.4 ) Foreign exchange adjustments 5.3 (0.1 ) 1.7 Foreign withholding taxes 2.4 2.9 0.4 Income tax provision $ 35.2 $ 14.3 $ 32.8 Income tax provision - Foreign $ (0.4 ) $ (1.1 ) $ 5.2 Income tax provision - United States, Federal 33.2 16.4 23.3 Income tax (benefit) provision - United States, State — (3.9 ) 3.9 Foreign withholding tax 2.4 2.9 0.4 Income tax provision $ 35.2 $ 14.3 $ 32.8 The consolidated provision for income taxes for the year ended December 31, 2016 was affected by a $1.5 million decrease to taxes related to prior period adjustments in the United Kingdom, a $5.3 million increase for the foreign exchange adjustment on translation in the UK and Brazil, and an increase of $2.0 million in withholding taxes paid on an intercompany dividend payment. The consolidated provision for income taxes for the year ended December 31, 2015 was affected by a $2.1 million decrease to taxes related to foreign tax credit utilization in the United Kingdom, a $2.5 million decrease in tax related to the reversal of an estimated state tax accrual, and an increase of $2.5 million in withholding taxes paid on an intercompany dividend payment. 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. 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, 2016 and 2015 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 $0.5 million and decreased $29.4 million for the years ended December 31, 2016 and 2015, respectively. December 31, (in millions) 2016 2015 Deferred tax assets: Losses and loss adjustment expense reserve discounting $ 21.1 $ 23.4 Unearned premiums 29.1 26.6 Allowance for bad debt 1.6 1.6 Accrual for contingent commissions 0.3 0.3 Net operating loss carryforward 17.1 17.8 Impairment of investment values 8.6 9.6 United States amortization of intangible assets 5.3 4.9 Accrued bonus 7.4 7.0 Accrued vacation 1.7 1.6 Stock option expense 8.1 10.1 Brazil operating losses 8.3 5.9 Malta operating losses 1.3 1.8 Other 23.6 15.9 Deferred tax assets, gross 133.5 126.5 Deferred tax liabilities: Unrealized gains on equity securities (39.1 ) (40.1 ) Unrealized gains on fixed maturities and other investment securities (3.9 ) (0.4 ) Deferred acquisition costs (22.2 ) (20.4 ) United States amortization of intangible assets (3.8 ) (3.6 ) United Kingdom underwriting losses (5.4 ) (9.7 ) United Kingdom amortization of intangible assets (1.2 ) (1.8 ) Deferred gain on like-kind exchange (13.3 ) (13.3 ) Depreciable fixed asset (21.0 ) (18.0 ) Unrealized Gain on Limited Partnership Interests (17.6 ) (11.0 ) Other (6.6 ) (9.0 ) Deferred tax liabilities, gross (134.1 ) (127.3 ) Deferred tax assets, net before valuation allowance $ (0.6 ) $ (0.8 ) Valuation allowance (23.5 ) (22.8 ) Deferred tax liabilities, net $ (24.1 ) $ (23.6 ) Net deferred tax liabilities - Foreign $ (6.6 ) $ (11.7 ) Net deferred tax liabilities - United States (17.5 ) (11.9 ) Deferred tax liabilities, net $ (24.1 ) $ (23.6 ) 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 future taxable income sufficient to recover tax benefits that cannot be recovered from taxes paid in the carryback period, generally two years for net operating losses and three years for capital losses, for our United States operations. At December 31, 2016, we had a total net deferred tax liability of $0.6 million prior to any valuation allowance. Management has determined that a valuation allowance is required for a portion of the tax-effected net operating loss carryforward included as part of the United States consolidated group of $15.8 million generated from PXRE Corporation and for the tax effected net operating loss carryforward of $1.0 million from ARIS. The valuation allowances have been established pursuant to Internal Revenue Code Section 382 limits regarding the application of net operating loss carryforwards following an ownership change. The loss carryforwards available per year are $2.8 million, as required by Internal Revenue Code Section 382. Furthermore, due to cumulative losses incurred 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 $23.5 million is required as of December 31, 2016 of which $13.9 million relates to the PXRE Corporation and ARIS loss carryforwards, $8.3 million relates to Brazil operations, and $1.3 million relates to Malta operations. During the year ended December 31, 2016, the valuation allowance was reduced by $1.0 million pertaining to PXRE Corporation and ARIS loss carryforwards, increased by $2.3 million pertaining to our Brazil operations and decreased by $0.6 million pertaining to our Malta operations. Of the PXRE Corporation net operating loss carryforwards, $14.3 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. 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, 2016, 2015 and 2014. Our United States subsidiaries are no longer subject to U.S. federal and state income tax examinations by tax authorities for years before 2013. Our United Kingdom subsidiaries are no longer subject to United Kingdom income tax examinations by Her Majesty’s Revenue and Customs for years before 2014.

Pension Benefits and Savings Pl

Pension Benefits and Savings Plans	12 Months Ended
	Dec. 31, 2016
Compensation And Retirement Disclosure [Abstract]
Pension Benefits and Savings Plans	16. Pension Benefits and Savings Plans 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) 2016 2015 Change in plan assets Fair value of plan assets at beginning of year $ 17.5 $ 19.2 Actual return on plan assets 0.7 (0.1 ) Employer contributions 0.2 0.2 Settlements and benefits paid (1.7 ) (1.8 ) Fair value of plan assets at end of year $ 16.7 $ 17.5 (in millions) 2016 2015 Change in projected benefit obligation Projected benefit obligation at beginning of year $ 23.1 $ 25.8 Interest cost 0.8 0.8 Actuarial loss (gain) 0.4 (1.6 ) Settlements and benefits paid (1.7 ) (1.9 ) Projected benefit obligation at end of year $ 22.6 $ 23.1 As of December 31, 2016 and 2015, the qualified pension plan was underfunded by $3.7 million and $3.4 million, respectively. The non-qualified pension plans were unfunded by $2.2 million $2.3 million at December 31, 2016 and 2015, respectively. 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: 2016 2015 Weighted average discount rate 3.44% 3.48% 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, 2016 2015 2014 Weighted average discount rate 3.62% 3.55% 4.39% 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 2016, 2015 and 2014, the expected return on plan assets was ascertained using multiple factors that include market conditions, long-term return forecasts provided by several asset management companies, and the composition of the portfolio. Net periodic benefit costs were $0.1 million, $0.1 million and $0.5 million for the years ended December 31, 2016, 2015 and 2014, respectively. We estimate that $0.4 million of unrecognized actuarial loss will be amortized from accumulated other comprehensive gain into net periodic benefit cost during 2017. Over the next five years, we expect our annual payments under the pensions plan not to exceed $2.2 million per year. 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 and $2.3 million at December 31, 2016 and 2015, respectively. 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, 2016, the target allocations were 48% fixed income and short-term liquidity; and 52% 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, 2016 was 50.5% fixed maturity investments, short-term investments and cash; and 49.5% equity investments, of which 39.2% and 10.3% 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 (Level 1). For the years ended December 31, 2016 and 2015, assets with a fair value of $15.8 million and $17.4 million, respectively, were valued using Level 1 fair value measurements. Short-term investment fund : Fair value is determined based on the net asset values provided by the plan trustee (Level 2). For the years ended December 31, 2016 and 2015, assets with a fair value of $0.9 million and $0.1 million, respectively, were valued using Level 2 fair value measurements. 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. 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, 2017. 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 $6.0 million, $6.3 million and $7.1 million in 2016, 2015 and 2014, respectively.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	17. 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 $93.4 million related to our limited partnership investments at December 31, 2016. These commitments will be funded as required by the partnership agreements which can be called to be fulfilled at any time, not to exceed thirteen years.

Leases

Leases	12 Months Ended
	Dec. 31, 2016
Leases [Abstract]
Leases	18. 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, 2016, the future minimum payments under non-cancelable operating leases are as follows: (in millions) Amount Due 2017 $ 11.3 2018 9.5 2019 8.2 2020 5.9 2021 5.2 Thereafter 5.9 Total $ 46.0 We incurred lease expense of $12.2 million, $14.2 million and $14.7 million for the years ended December 31, 2016, 2015 and 2014, respectively.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Segment Information	19. 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. Transactions between segments are reported in the segment that initiated the transaction. Based on management’s evaluation of the Argo Pro platform’s shift in primary distribution channels and mix of admitted versus non-admitted business, we have reclassified Argo Pro’s results of operations and identifiable assets from the Excess and Surplus Lines segment to the Commercial Specialty segment effective January 1, 2016, as the current makeup of the platform more closely aligns with our Commercial Specialty segment. The results of operations and identifiable assets for prior periods have been reclassified to conform to the current presentation. In evaluating the operating performance of our segments, we focus on core underwriting and investing results before the consideration of realized gains or losses from the sales of investments. Realized investment gains are reported as a component of the Corporate and Other segment, as decisions regarding the acquisition and disposal of securities reside with the corporate investment function and are not under the control of the individual business segments. Identifiable assets by segment are those assets used in the operation of each segment. Revenue and income (loss) before income taxes for each segment were as follows: For the Years Ended December 31, (in millions) 2016 2015 2014 Revenue: Earned premiums Excess and Surplus Lines $ 485.3 $ 471.2 $ 444.6 Commercial Specialty 364.2 344.2 332.5 International Specialty 154.5 146.4 144.8 Syndicate 1200 406.4 409.7 414.6 Run-off Lines 0.4 0.4 1.6 Total earned premiums 1,410.8 1,371.9 1,338.1 Net investment income Excess and Surplus Lines 45.2 32.3 43.2 Commercial Specialty 26.7 19.9 25.6 International Specialty 16.8 11.4 11.3 Syndicate 1200 11.9 8.9 10.9 Run-off Lines 11.3 8.1 12.0 Corporate and Other 3.2 8.0 3.1 Total net investment income 115.1 88.6 106.1 Fee and other income 24.5 22.2 20.7 Net realized investment and other gains 26.1 24.1 74.5 Total revenue $ 1,576.5 $ 1,506.8 $ 1,539.4 For the Years Ended December 31, (in millions) 2016 2015 2014 Income (loss) before income taxes Excess and Surplus Lines $ 88.4 $ 81.4 $ 103.4 Commercial Specialty 86.0 43.0 24.8 International Specialty 38.2 29.0 23.8 Syndicate 1200 13.4 35.4 45.2 Run-off Lines (15.2 ) (7.4 ) (20.7 ) Total segment income before taxes 210.8 181.4 176.5 Corporate and Other (55.0 ) (28.0 ) (35.0 ) Net realized investment and other gains 26.1 24.1 74.5 Total income before income taxes $ 181.9 $ 177.5 $ 216.0 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) 2016 2015 2014 Bermuda $ 112.6 $ 103.4 $ 101.5 Brazil 39.2 43.1 44.3 Malta 2.1 1.9 2.1 United Kingdom 406.9 407.4 411.7 United States 850.0 816.1 778.5 Total earned premiums $ 1,410.8 $ 1,371.9 $ 1,338.1 The following table represents identifiable assets: December 31, (in millions) 2016 2015 Excess and Surplus Lines $ 2,259.3 $ 2,174.8 Commercial Specialty 1,701.9 1,511.7 International Specialty 970.6 877.2 Syndicate 1200 1,386.3 1,216.5 Run-off Lines 537.0 558.4 Corporate and Other 349.9 287.0 Total $ 7,205.0 $ 6,625.6 Included in total assets at December 31, 2016 and 2015 are $630.4 million and $377.1 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 Accumulated Amortization (in millions) 2016 2015 2016 2015 Excess and Surplus Lines $ 68.4 $ 68.4 $ — $ — Commercial Specialty 55.1 55.1 3.7 6.3 Syndicate 1200 28.7 28.7 64.0 67.0 Total $ 152.2 $ 152.2 $ 67.7 $ 73.3

Statutory Accounting Principles

Statutory Accounting Principles	12 Months Ended
	Dec. 31, 2016
Statutory Accounting Principles [Abstract]
Statutory Accounting Principles	20. 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) 2016 2015 Bermuda $ 1,510.8 $ 1,243.2 United Kingdom (2) 216.6 232.8 United States 886.7 854.5 (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) 2016 2015 2014 Bermuda $ 149.4 $ 182.2 $ 128.2 United Kingdom (2) 1.8 34.8 28.7 United States 99.0 94.4 117.7 (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 material restrictions on dividend payments that may be made to our shareholders at December 31, 2016. Argo Re is the direct subsidiary of Argo Group, and therefore, has direct dividend paying capabilities to the parent. As of December 31, 2016, 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, 2016 and 2015, the minimum statutory capital and surplus required to be maintained by Argo Re was $362.1 million and $345.9 million, respectively. Argo Re is generally prohibited from declaring or paying, in any financial year, dividends of more than 25% of its total statutory capital and surplus (as shown on its previous financial year’s statutory balance sheet) unless it files (at least seven days before payment of such dividends) with the Bermuda Monetary Authority (“BMA”) an affidavit signed by at least two directors (one of whom must be a Bermuda resident director if any of the insurer’s directors are resident in Bermuda) and the principal representative stating that it will continue to meet its solvency margin and minimum liquidity ratio. Argo Re may not reduce its total statutory capital by 15% or more, as set out in its previous year’s financial statements, unless it has received the prior approval of the BMA. Based on these regulatory restrictions, the maximum amount available for payment of dividends to Argo Group by Argo Re during 2017 without prior regulatory approval is $377.7 million. In 2016, 2015 and 2014, Argo Re paid cash dividends to Argo Group of $41.0 million, $41.0 million and $40.9 million, respectively. The proceeds of the dividends were used to repay intercompany balances related primarily to dividend and interest payments and other corporate expenses. Our U.S. insurance subsidiaries file financial statements prepared in accordance with statutory accounting principles prescribed or permitted by insurance regulatory authorities of the state in which they are 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 is 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 2016, Argo Group US received an ordinary dividend in the amount of $18.1 million in cash from Rockwood. In December 2016, Argo Group US received an ordinary dividend of $41.6 million from Argonaut Insurance Company. In March 2016, Argo Group US received an ordinary dividend of $35.0 million, in the form of $19.9 million in cash and $15.1 million in securities, from Colony 2016. Argo Group US did not receive dividends from its subsidiaries in 2015. 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. Argonaut Insurance Company is a direct subsidiary of Argo Group US and is regulated by the Illinois Division of Insurance. During 2017, Argonaut Insurance Company may be permitted to pay dividends of up to $80.0 million without approval from the Illinois Division of Insurance. 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 $11.3 million without approval from the Pennsylvania Department of Insurance during 2017. Each department of insurance may require prior approval for the payment of all dividends, based on business and regulatory conditions of the insurance companies. During 2016 we realigned our internal ownership structure so that Colony became a direct subsidiary of Argonaut Insurance Company. Prior to 2016, Colony had been a direct subsidiary of Argo Group US. Dividend payments from Syndicate 1200 to its immediate parent are not restricted by regulatory authority. Dividend payments will be subject to the earnings, operations, financial condition, capital and general business requirements of 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 3, “Investments” and Note 19, “Segment Information” for further discussion.

Insurance Assessments

Insurance Assessments	12 Months Ended
	Dec. 31, 2016
Insurance [Abstract]
Insurance Assessments	21. 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 $4.7 million and $4.1 million at December 31, 2016 and 2015, respectively.

Transactions with Related Parti

Transactions with Related Parties	12 Months Ended
	Dec. 31, 2016
Related Party Transactions [Abstract]
Transactions with Related Parties	22. 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. As of December 31, 2016, the surety bonds were still outstanding. Per the Surety unit’s standard requirements in connection with the issuance of surety bonds, Kinetica and Mr. Woods, in his personal capacity, among others, executed our Surety unit’s standard form of indemnity agreement holding our Surety unit harmless against any and all losses and expenses incurred resulting from the issuance of the surety bonds.

Unaudited Quarterly Financial D

Unaudited Quarterly Financial Data	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Unaudited Quarterly Financial Data	23. Unaudited Quarterly Financial Data The following tables represent unaudited quarterly financial data for the years ended December 31, 2016 and 2015. 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 3rd Quarter 4th Quarter Year 2016 Total revenue $ 370.1 $ 384.3 $ 416.7 $ 405.4 $ 1,576.5 Net income before income taxes 33.1 39.6 62.2 47.0 181.9 Net income 27.7 30.9 55.2 32.9 146.7 Net income per common share : Basic* $ 0.91 $ 1.03 $ 1.84 $ 1.10 $ 4.86 Diluted* $ 0.89 $ 1.00 $ 1.80 $ 1.07 $ 4.75 Comprehensive income (loss) $ 56.5 $ 59.7 $ 57.3 $ 9.4 $ 182.9 (in millions, except per share amounts) 1st Quarter 2nd 3rd Quarter 4th Quarter Year 2015 Total revenue $ 376.0 $ 377.2 $ 380.2 $ 373.4 $ 1,506.8 Net income before income taxes 62.4 34.7 36.2 44.2 177.5 Net income 58.8 27.9 35.3 41.2 163.2 Net income per common share : Basic* $ 1.90 $ 0.91 $ 1.15 $ 1.34 $ 5.31 Diluted* $ 1.87 $ 0.89 $ 1.13 $ 1.31 $ 5.20 Comprehensive income $ 36.8 $ 18.9 $ (18.3 ) $ 29.2 $ 66.6 * 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.

Senior Unsecured Fixed Rate Not

Senior Unsecured Fixed Rate Notes	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Senior Unsecured Fixed Rate Notes	24. Senior Unsecured Fixed Rate Notes In September 2012, Argo Group (the “Parent Guarantor”), through its subsidiary Argo Group US (the “Subsidiary Issuer”), issued $143,750,000 aggregate principal amount of the Subsidiary Issuer’s 6.5% Senior Notes due September 15, 2042 (the “Notes”). The Notes are unsecured and unsubordinated obligations of the Subsidiary Issuer and rank equally in right of payment with all of the Subsidiary Issuer’s other unsecured and unsubordinated debt. The Notes are guaranteed on a full and unconditional senior unsecured basis by the Parent Guarantor. The Notes may be redeemed, for cash, in whole or in part, on or after September 15, 2017, at the Subsidiary Issuer’s option, at any time and from time to time, prior to maturity at a redemption price equal to 100% of the principal amount of the Notes to be redeemed, plus accrued but unpaid interest on the principal amount being redeemed to, but not including, the redemption date. In accordance with ASU 2015-03, “Simplifying the Presentation of Debt Issuance Costs” (Topic 835), we present the unamortized debt issuance costs in the balance sheet as a direct deduction from the carrying value of the debt liability. At December 31, 2016 and 2015, the Notes consisted of the following: (in millions) December 31, 2016 December 31, 2015 Senior unsecured fixed rate notes Principal $ 143.8 $ 143.8 Less: unamortized debt issuance costs (4.3 ) (4.5 ) Senior unsecured fixed rate notes, less unamortized debt issuance costs $ 139.5 $ 139.3 In accordance with Article 10 of SEC Regulation S-X, we have elected to present condensed consolidating financial information in lieu of separate financial statements for the Subsidiary Issuer. The following tables present condensed consolidating financial information at December 31, 2016 and 2015 and for the three years ended December 31, 2016, 2015 and 2014 of the Parent Guarantor and the Subsidiary Issuer. The Subsidiary Issuer is an indirect wholly-owned subsidiary of the Parent Guarantor. Investments in subsidiaries are accounted for by the Parent Guarantor under the equity method for purposes of the supplemental consolidating presentation. Earnings of subsidiaries are reflected in the Parent Guarantor’s investment accounts and earnings. The Parent Guarantor fully and unconditionally guarantees certain of the debt of the Subsidiary Issuer. Condensed consolidating financial information of the Subsidiary Issuer is presented on a consolidated basis and consists principally of the net assets, results of operations and cash flows of operating insurance company subsidiaries. CONDENSED CONSOLIDATING BALANCE SHEET DECEMBER 31, 2016 (in millions) Argo Group International Holdings, Ltd (Parent Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Assets Investments $ 2.2 $ 2,834.2 $ 1,487.9 $ — $ 4,324.3 Cash — 53.7 32.3 — 86.0 Accrued investment income — 16.0 4.7 — 20.7 Premiums receivable — 204.9 258.9 — 463.8 Reinsurance recoverables — 1,348.4 37.2 — 1,385.6 Goodwill and other intangible assets, net — 127.1 92.8 — 219.9 Deferred acquisition costs, net — 63.5 75.6 — 139.1 Ceded unearned premiums — 168.9 133.9 — 302.8 Other assets 8.7 168.0 86.1 — 262.8 Intercompany note receivable — 50.2 (50.2 ) — — Investments in subsidiaries 1,834.4 — — (1,834.4 ) — Total assets $ 1,845.3 $ 5,034.9 $ 2,159.2 $ (1,834.4 ) $ 7,205.0 Liabilities and Shareholders' Equity Reserves for losses and loss adjustment expenses $ — $ 2,322.4 $ 1,028.4 $ — $ 3,350.8 Unearned premiums — 580.0 390.0 — 970.0 Funds held and ceded reinsurance payable, net — 750.2 (206.5 ) — 543.7 Long-term debt 28.4 284.4 54.8 — 367.6 Current income taxes payable, net — 8.5 (0.4 ) — 8.1 Deferred tax liabilities, net — 17.6 6.5 — 24.1 Accrued underwriting expenses and other liabilities 13.7 92.0 42.3 — 148.0 Due to affiliates 10.5 1.8 (1.8 ) (10.5 ) — Total liabilities 52.6 4,056.9 1,313.3 (10.5 ) 5,412.3 Total shareholders' equity 1,792.7 978.0 845.9 (1,823.9 ) 1,792.7 Total liabilities and shareholders' equity $ 1,845.3 $ 5,034.9 $ 2,159.2 $ (1,834.4 ) $ 7,205.0 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING BALANCE SHEET DECEMBER 31, 2015 (in millions) Argo Group International Holdings, Ltd (Parent Guarantor) Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Assets Investments $ 6.2 $ 2,761.0 $ 1,348.5 $ — $ 4,115.7 Cash — 88.8 32.9 — 121.7 Accrued investment income — 16.4 5.2 — 21.6 Premiums receivable — 166.4 238.1 — 404.5 Reinsurance recoverables — 1,212.2 (91.1 ) — 1,121.1 Goodwill and other intangible assets, net — 129.8 95.7 — 225.5 Current income taxes receivable, net — 4.7 6.9 — 11.6 Deferred acquisition costs, net — 58.2 74.2 — 132.4 Ceded unearned premiums — 125.8 125.0 — 250.8 Other assets 8.2 151.7 60.8 — 220.7 Intercompany note receivable — 49.8 (49.8 ) — — Investments in subsidiaries 1,715.9 — — (1,715.9 ) — Total assets $ 1,730.3 $ 4,764.8 $ 1,846.4 $ (1,715.9 ) $ 6,625.6 Liabilities and Shareholders' Equity Reserves for losses and loss adjustment expenses $ — $ 2,194.1 $ 929.5 $ — $ 3,123.6 Unearned premiums — 501.5 385.2 — 886.7 Funds held and ceded reinsurance payable, net — 702.6 (312.6 ) — 390.0 Long-term debt 28.4 284.2 54.6 — 367.2 Deferred tax liabilities, net — 11.9 11.7 — 23.6 Accrued underwriting expenses and other liabilities 16.3 95.4 54.7 — 166.4 Due to affiliates 17.5 2.3 (2.3 ) (17.5 ) — Total liabilities 62.2 3,792.0 1,120.8 (17.5 ) 4,957.5 Total shareholders' equity 1,668.1 972.8 725.6 (1,698.4 ) 1,668.1 Total liabilities and shareholders' equity $ 1,730.3 $ 4,764.8 $ 1,846.4 $ (1,715.9 ) $ 6,625.6 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF INCOME FOR THE YEAR ENDED DECEMBER 31, 2016 (in millions) Argo Group International Holdings, Ltd (Parent Guarantor) Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Premiums and other revenue: Earned premiums $ — $ 497.3 $ 913.5 $ — $ 1,410.8 Net investment income 37.2 78.9 40.0 (41.0 ) 115.1 Fee and other income — 21.4 3.1 — 24.5 Net realized investment and other gains 0.6 50.0 (24.5 ) — 26.1 Total revenue 37.8 647.6 932.1 (41.0 ) 1,576.5 Expenses: Losses and loss adjustment expenses — 290.4 519.7 — 810.1 Underwriting, acquisition and insurance expenses 12.8 204.4 329.8 — 547.0 Interest expense 1.4 15.8 2.4 — 19.6 Fee and other expense — 21.7 0.7 — 22.4 Foreign currency exchange loss (gains) — 0.2 (4.7 ) — (4.5 ) Total expenses 14.2 532.5 847.9 — 1,394.6 Income before income taxes 23.6 115.1 84.2 (41.0 ) 181.9 Provision for income taxes — 33.6 1.6 — 35.2 Net income before equity in earnings of subsidiaries 23.6 81.5 82.6 (41.0 ) 146.7 Equity in undistributed earnings of subsidiaries 123.1 — — (123.1 ) — Net income $ 146.7 $ 81.5 $ 82.6 $ (164.1 ) $ 146.7 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF INCOME FOR THE YEAR ENDED DECEMBER 31, 2015 (in millions) Argo Group International Holdings, Ltd (Parent Guarantor) Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Premiums and other revenue: Earned premiums $ — $ 497.3 $ 874.6 $ — $ 1,371.9 Net investment income 40.1 59.0 30.5 (41.0 ) 88.6 Fee and other income — 19.0 3.2 — 22.2 Net realized investment and other gains — 31.8 (7.7 ) — 24.1 Total revenue 40.1 607.1 900.6 (41.0 ) 1,506.8 Expenses: Losses and loss adjustment expenses — 304.2 461.9 — 766.1 Underwriting, acquisition and insurance expenses 19.0 198.4 319.3 — 536.7 Interest expense 1.5 15.3 2.2 — 19.0 Fee and other expense — 23.3 2.5 — 25.8 Foreign currency exchange loss (gains) — 1.0 (19.3 ) — (18.3 ) Total expenses 20.5 542.2 766.6 — 1,329.3 Income before income taxes 19.6 64.9 134.0 (41.0 ) 177.5 Provision for income taxes — 12.9 1.4 — 14.3 Net income before equity in earnings of subsidiaries 19.6 52.0 132.6 (41.0 ) 163.2 Equity in undistributed earnings of subsidiaries 143.6 — — (143.6 ) — Net income $ 163.2 $ 52.0 $ 132.6 $ (184.6 ) $ 163.2 (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, 2014 (in millions) Argo Group International Holdings, Ltd (Parent Guarantor) Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Premiums and other revenue: Earned premiums $ — $ 461.0 $ 877.1 $ — $ 1,338.1 Net investment income 40.5 76.2 (10.6 ) — 106.1 Fee and other income — 17.6 3.1 — 20.7 Net realized investment and other gains 2.0 67.4 7.1 (2.0 ) 74.5 Total revenue 42.5 622.2 876.7 (2.0 ) 1,539.4 Expenses: Losses and loss adjustment expenses — 285.6 461.8 — 747.4 Underwriting, acquisition and insurance expenses 17.3 199.9 319.8 — 537.0 Interest expense 2.3 15.2 2.7 (0.3 ) 19.9 Fee and other expense — 20.0 3.5 — 23.5 Foreign currency exchange gain — 0.4 (8.2 ) — (7.8 ) Impairment of intangible assets — 3.4 — — 3.4 Total expenses 19.6 524.5 779.6 (0.3 ) 1,323.4 Income before income taxes 22.9 97.7 97.1 (1.7 ) 216.0 Provision for income taxes — 27.5 5.3 — 32.8 Net income before equity in earnings of subsidiaries 22.9 70.2 91.8 (1.7 ) 183.2 Equity in undistributed earnings of 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 CASH FLOWS FOR YEAR ENDED DECEMBER 31, 2016 (in millions) Argo Group International Holdings, Ltd (Parent Guarantor) Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Net cash flows from operating activities $ 26.5 $ 71.7 $ 83.2 $ — $ 181.4 Cash flows from investing activities: Proceeds from sales of investments — 1,035.9 407.6 — 1,443.5 Maturities and mandatory calls of fixed maturity investments — 543.2 459.5 — 1,002.7 Purchases of investments — (1,450.0 ) (930.5 ) — (2,380.5 ) Change in short-term investments and foreign regulatory deposits (0.9 ) (138.1 ) (56.2 ) — (195.2 ) Settlements of foreign currency exchange forward contracts — — (5.4 ) — (5.4 ) Purchases of fixed assets and other, net — (11.3 ) 1.1 — (10.2 ) Cash used in investing activities (0.9 ) (20.3 ) (123.9 ) — (145.1 ) Cash flows from financing activities: Activity under stock incentive plans 1.0 — — — 1.0 Repurchase of Company's common shares — (47.1 ) — — (47.1 ) Excess tax expense from share-based payment arrangements — 0.6 — — 0.6 Payment of cash dividend to common shareholders (26.6 ) — — — (26.6 ) Intercompany cash dividend — (40.0 ) 40.0 — — Cash provided by (used in) financing activities (25.6 ) (86.5 ) 40.0 — (72.1 ) Effect of exchange rate changes on cash — — 0.1 — 0.1 Change in cash — (35.1 ) (0.6 ) — (35.7 ) Cash, beginning of year — 88.8 32.9 — 121.7 Cash, end of year $ — $ 53.7 $ 32.3 $ — $ 86.0 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS FOR YEAR ENDED DECEMBER 31, 2015 (in millions) Argo Group International Holdings, Ltd (Parent Guarantor) Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Net cash flows from operating activities $ 32.7 $ 116.4 $ 133.5 $ — $ 282.6 Cash flows from investing activities: Proceeds from sales of investments — 631.1 336.8 — 967.9 Maturities and mandatory calls of fixed maturity investments — 681.8 162.1 — 843.9 Purchases of investments — (1,384.5 ) (649.6 ) — (2,034.1 ) Change in short-term investments and foreign regulatory deposits 0.9 14.9 33.8 — 49.6 Settlements of foreign currency exchange forward contracts 1.5 — (11.6 ) — (10.1 ) Issuance of intercompany note, net — 7.5 (7.5 ) — — Redemption of PXRE Capital Trust V — 18.0 (18.0 ) — — Purchases of fixed assets and other, net 3.8 (16.6 ) 2.0 — (10.8 ) Cash provided by (used in) investing activities 6.2 (47.8 ) (152.0 ) $ — (193.6 ) Cash flows from financing activities: Redemption of PXRE Capital Trust V (18.0 ) — 18.0 — — Activity under stock incentive plans 1.8 — — — 1.8 Repurchase of Company's common shares — (29.7 ) — — (29.7 ) Excess tax expense from share-based payment arrangements — 0.6 — — 0.6 Payment of cash dividend to common shareholders (22.7 ) — — — (22.7 ) Cash provided by (used in) financing activities (38.9 ) (29.1 ) 18.0 $ — (50.0 ) Effect of exchange rate changes on cash — — 1.7 — 1.7 Change in cash — 39.5 1.2 — 40.7 Cash, beginning of year — 49.3 31.7 — 81.0 Cash, end of year $ — $ 88.8 $ 32.9 $ — $ 121.7 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS FOR YEAR ENDED DECEMBER 31, 2014 (in millions) Argo Group International Holdings, Ltd (Parent Guarantor) Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total 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 — 1,262.0 Maturities and mandatory calls of fixed maturity investments — 192.1 130.9 — 323.0 Purchases of investments — (1,126.1 ) (610.7 ) — (1,736.8 ) Change in short-term investments and foreign regulatory deposits 0.5 76.0 20.0 — 96.5 Settlements of foreign currency exchange 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 in 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 benefit from share-based payment arrangements — 0.1 — — 0.1 Payment of cash dividend to common shareholders (18.2 ) — — — (18.2 ) Cash used in 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 $ — $ 81.0 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations.

Schedule II Condensed Financial

Schedule II Condensed Financial Information of Registrant	12 Months Ended
	Dec. 31, 2016
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, 2016 2015 Assets Other investments $ 0.3 $ 5.2 Short-term investments 1.9 1.0 Investment in subsidiaries 1,834.4 1,715.9 Other assets 8.7 8.2 Total assets $ 1,845.3 $ 1,730.3 Liabilities and Shareholders' Equity Junior subordinated debentures $ 28.4 $ 28.4 Accrued underwriting expenses and other liabilities 13.7 16.3 Due to subsidiaries 10.5 17.5 Total liabilities 52.6 62.2 Shareholders' equity 1,792.7 1,668.1 Total liabilities and shareholders' equity $ 1,845.3 $ 1,730.3 STATEMENTS OF INCOME For the Years Ended December 31, 2016 2015 2014 Revenue: Net investment income (1) $ 37.2 $ 40.1 $ 40.5 Net realized investment and other gains 0.6 — 2.0 Total revenue 37.8 40.1 42.5 Expenses: Interest expense 1.4 1.5 2.3 Other expenses 12.8 19.0 17.3 Total expenses 14.2 20.5 19.6 Net income before equity in earnings of subsidiaries (2) 23.6 19.6 22.9 Equity in undistributed earnings of subsidiaries 123.1 143.6 160.3 Net income $ 146.7 $ 163.2 $ 183.2 (1) For the years ended December 31, 2016, 2015 and 2014, net investment income includes intercompany dividends of $41.0 million, $41.0 million and $40.9 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, 2016 2015 2014 Cash flows from operating activities: Net income $ 146.7 $ 163.2 $ 183.2 Adjustments to reconcile net income to net cash provided by (used in) operating activities: Amortization and depreciation 0.2 0.2 — Share-based payments expense 4.2 8.2 5.7 Net realized investment and other gains (0.6 ) — (2.0 ) Undistributed earnings of subsidiaries (123.1 ) (143.6 ) (160.3 ) Change in: Prepaid assets (0.2 ) 0.2 2.0 Accrued underwriting expenses 0.9 (2.4 ) (2.2 ) Due to subsidiaries (0.6 ) 12.5 (0.6 ) Interest on intercompany note payable — — 0.3 Other, net (1.0 ) (5.6 ) (0.4 ) Cash provided by operating activities 26.5 32.7 25.7 Cash flows from investing activities: Change in short-term investments (0.9 ) 0.9 0.5 Settlements of foreign currency exchange forward contracts — 1.5 1.3 Purchases of fixed assets and other, net — 3.8 (7.0 ) Cash (used in) provided by investing activities (0.9 ) 6.2 (5.2 ) Cash flows from financing activities: Borrowings under intercompany note payable, net — — (6.9 ) Activity under stock incentive plans 1.0 1.8 4.6 Redemption of PXRE Capital Trust V — (18.0 ) — Payment of cash dividend to common shareholders (26.6 ) (22.7 ) (18.2 ) Cash used in financing activities (25.6 ) (38.9 ) (20.5 ) Change in cash — — — Cash, beginning of year — — — Cash, end of year $ — $ — $ —

Schedule III Supplemental Insur

Schedule III Supplemental Insurance Information	12 Months Ended
	Dec. 31, 2016
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, 2016, 2015 AND 2014 (in millions) Segment DAC (a) Reserves for Losses and Loss Adjustment Expenses (b) UPR (c) Premium Revenue (d) Net Investment Income (l) Loss & LAE (e) Amortization (Deferral) DAC (f) (2) Other Operating Expenses (3) Net Premiums Written (g) Year Ended December 31, 2016 Excess and Surplus Lines $ 34.1 $ 1,112.8 $ 256.4 $ 485.3 $ 45.2 $ 286.4 $ 1.6 $ 148.3 $ 489.4 Commercial Specialty 29.4 915.6 319.0 364.2 26.7 181.1 (6.7 ) 127.3 394.1 International Specialty 1.3 374.0 114.9 154.5 16.8 83.3 0.7 46.3 153.5 Syndicate 1200 74.3 657.5 279.7 406.4 11.9 240.7 0.1 164.0 402.9 Run-off Lines — 290.9 — 0.4 11.3 18.6 — 6.9 0.3 Corporate and Other — — — — 3.2 — — 58.5 — Total $ 139.1 $ 3,350.8 $ 970.0 $ 1,410.8 $ 115.1 $ 810.1 $ (4.3 ) $ 551.3 $ 1,440.2 Year Ended December 31, 2015 Excess and Surplus Lines $ 35.7 $ 1,094.3 $ 245.1 $ 471.2 $ 32.3 $ 267.8 $ (0.5 ) $ 149.1 $ 485.6 Commercial Specialty 22.7 794.3 256.1 344.2 19.9 203.3 1.5 109.3 352.9 International Specialty 2.1 313.1 113.9 146.4 11.4 74.5 (2.1 ) 53.4 158.1 Syndicate 1200 71.9 615.6 271.6 409.7 8.9 211.9 0.2 168.9 405.1 Run-off Lines — 306.3 — 0.4 8.1 8.6 — 5.9 0.4 Corporate and Other — — — — 8.0 — — 51.0 — Total $ 132.4 $ 3,123.6 $ 886.7 $ 1,371.9 $ 88.6 $ 766.1 $ (0.9 ) $ 537.6 $ 1,402.1 Year Ended December 31, 2014 Excess and Surplus Lines $ 35.2 $ 1,075.2 $ 233.5 $ 444.6 $ 43.2 $ 233.8 $ 1.0 $ 143.6 $ 443.7 Commercial Specialty 24.2 742.4 214.3 332.5 25.6 203.3 (3.4 ) 123.9 345.2 International Specialty 0.7 299.2 115.6 144.8 11.3 76.4 1.6 51.2 152.2 Syndicate 1200 64.5 607.1 253.8 414.6 10.9 209.5 (4.6 ) 171.9 425.2 Run-off Lines — 318.5 — 1.6 12.0 24.4 — 8.2 1.6 Corporate and Other — — — — 3.1 — — 43.6 — Total $ 124.6 $ 3,042.4 $ 817.2 $ 1,338.1 $ 106.1 $ 747.4 $ (5.4 ) $ 542.4 $ 1,367.9 (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 Qualif

Schedule V Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2016
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 Beginning of Year Charged Cost and Expense Capital Loss Carryforward Net Operating Loss Carryforward Charged to Other Accounts Deductions Balance at End Year Ended December 31, 2016 Deducted from assets: Valuation allowance for deferred tax asset $ 22.8 $ (1.0 ) $ — $ — $ 1.7 $ — $ 23.5 Year Ended December 31, 2015 Deducted from assets: Valuation allowance for deferred tax asset $ 25.4 $ (1.0 ) $ — $ — $ (1.6 ) $ — $ 22.8 Year Ended December 31, 2014 Deducted from assets: Valuation allowance for deferred tax asset $ 56.2 $ (30.7 ) $ — $ — $ (0.1 ) $ — $ 25.4

Schedule VI Supplemental Inform

Schedule VI Supplemental Information for Property-Casualty Insurance Companies	12 Months Ended
	Dec. 31, 2016
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, 2016 2015 2014 Deferred acquisition costs $ 139.1 $ 132.4 $ 124.6 Reserves for losses and loss adjustment expenses $ 3,350.8 $ 3,123.6 $ 3,042.4 Unamortized discount in reserves for losses $ 19.4 $ 21.5 $ 23.7 Unearned premiums $ 970.0 $ 886.7 $ 817.2 Premiums earned $ 1,410.8 $ 1,371.9 $ 1,338.1 Net investment income $ 115.1 $ 88.6 $ 106.1 Losses and loss adjustment expenses incurred: Current year $ 843.4 $ 798.5 $ 785.1 Prior years (33.3 ) (32.4 ) (37.7 ) Losses and loss adjustment expenses incurred $ 810.1 $ 766.1 $ 747.4 Deferral of policy acquisition costs (1) $ (4.3 ) $ (0.9 ) $ (5.4 ) Paid losses and loss adjustment expenses, net of reinsurance $ 716.5 $ 733.5 $ 736.7 Gross premiums written $ 2,164.8 $ 2,012.1 $ 1,905.4 (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 Acco37

Business and Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Business	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) UC (“Argo Ireland”). Argo Underwriting Agency Limited (“Syndicate 1200”) is a subsidiary of Argo International Holdings, Ltd. Argo Re, Ltd. (“Argo Re”), a Bermuda based company, is the parent of both Argo Ireland and Argo International Holdings, Ltd. Argo Re is directly owned by Argo Group. We conduct our ongoing business through four segments. Excess and Surplus Lines products are underwritten by Colony Insurance Company (“Colony”). Commercial Specialty consists of the following operations: Argo Insurance, Rockwood Casualty Insurance Company (“Rockwood”), Argo Pro, 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 Argo Underwriting Agency Limited based in London, on behalf of one underwriting syndicate under the Lloyd’s of London (“Lloyd’s”) global franchise. Our Run-off Lines
Basis of Presentation and Use of Estimates	Basis of Presentation and Use of Estimates The consolidated financial statements of Argo Group and its subsidiaries have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenues and expenses during the reporting period. The major estimates reflected in our consolidated financial statements include, but are not limited to, reserves for losses and loss adjustment expenses; reinsurance recoverables, including the reinsurance recoverables allowance for doubtful accounts; estimates of written and earned premiums; reinsurance premium receivable; fair value of investments and assessment of potential impairment; valuation of goodwill and other 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. We have evaluated our investment in our twelve statutory trusts (collectively, the “Trusts”) and two charitable foundations (collectively, the “Foundations”) under the Financial Accounting Standards Board’s (“FASB’s”) provisions for consolidation of variable interest entities under Accounting Standards Codification (“ASC”) Topic 810-10, “Consolidation,” as amended. We determined that the Trusts and Foundations are 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 ASC Topic 810-10, 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. During the first quarter of 2016, we evaluated our accounting for income from our alternative investment portfolio and determined that as we manage these investments to appreciate in value on a quarter-to-quarter basis, it is more appropriate to classify the change in value as net investment income as opposed to realized investment gains (losses). As a result, net investment income for the year ended December 31, 2016 includes $23.9 million related to the appreciation of our alternative investment portfolio. Net investment income and net realized investment and other gains for the years ended December 31, 2015 and 2014 have been reclassified to reflect the current presentation. Specifically, net investment income for the years ended December 31, 2015 and 2014 include increases of $3.0 million and $19.5 million, respectively, related to the alternative investment portfolio, and net realized investment and other gains were decreased by the same amounts for the respective years. Additionally, beginning in 2016, we began presenting “Fee and other income” and “Fee and other expense” as separate financial statement line items. The presentation for prior years’ financial statements has been reclassified to conform to the current presentation.
Stock Dividend	Stock Dividends On May 3, 2016, our Board of Directors declared a 10% stock dividend, payable on June 15, 2016, to shareholders of record at the close of business on June 1, 2016. As a result of the stock dividend, 2,735,542 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. As a result of the stock dividend, 2,554,506 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.
Cash	Cash Cash consists of cash deposited in banks, generally in concentration and operating accounts. Interest-bearing cash accounts are classified as short-term investments.
Investments	Investments Investments in fixed maturities at December 31, 2016 and 2015 include bonds and structured securities. Equity securities include common stocks, preferred stocks and mutual funds. Other investments consist of foreign regulatory deposits, hedge funds, private equity funds, private equity direct investments, 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 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 in income during the period, but rather are recognized as a separate component of shareholders’ equity until realized. Fair value of these investments is estimated using prices obtained from third-party pricing services, where available. For securities where we were unable to obtain fair values from a pricing service or broker, fair values were estimated using information obtained from investment advisors. We performed several processes to ascertain the reasonableness of these investment values by 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, 2016 than 1% of Changes in the value of other investments consisting of hedge funds, private equity funds, private equity direct investments and voluntary pools are principally recognized to income during the period using the equity method of accounting. Our foreign regulatory deposits are assets held in trust in jurisdictions where there is a legal and regulatory requirement to maintain funds locally in order to protect policyholders. Lloyd’s is the appointed investment manager for the funds. The underlying assets are invested in government securities, agency securities and corporate bonds whose values are obtained from Lloyd’s. Foreign currency future contracts held by us are valued by our counterparties using market driven foreign currency 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	Receivables Premiums receivable, representing amounts due from insureds, are presented net of an allowance for doubtful accounts. The allowances for doubtful accounts were $2.7 million and $3.5 million at December 31, 2016 and 2015, 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 $2.1 million and $3.2 million at December 31, 2016 and 2015, 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) 2016 2015 2014 Premiums receivable $ 1.1 $ 1.0 $ 1.1 Reinsurance recoverables — 0.2 0.5 Net written off $ 1.1 $ 1.2 $ 1.6 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	Earned Premiums Premium revenue is recognized ratably over the policy period. Premiums that have yet to be earned are reported as “Unearned premiums” in our Consolidated Balance Sheets. Unearned premium balances include cessions to reinsurers including trade capital providers, while the earned premium recognized in our Consolidated Statements of Income excludes amounts relating to trade capital providers. The trade capital providers’ quota share amount is included in “Ceded reinsurance payable, net”. Assumed reinstatement premiums that reinstate coverage are written and earned at the time the associated loss event occurs. The original premium is earned over the remaining exposure period of the contract. Reinstatement premiums are estimated based upon contract terms for reported losses and estimated for incurred but not reported losses.
Retrospectively Rated Policies	Retrospectively Rated 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 $5.7 million and $6.5 million at December 31, 2016 and 2015, respectively. The estimated amount included in premiums receivables for additional premiums due under retrospectively rated policies was $0.1 million and $0.1 at December 31, 2016 and 2015, respectively.
Deferred Acquisition Costs	Deferred Acquisition Costs Policy acquisition costs, which include commissions, premium taxes, fees and certain other costs of underwriting policies, are deferred, when such class of policies are profitable, and amortized over the same period in which the related premiums are earned. To qualify for capitalization, the policy acquisition cost must be directly related to the successful acquisition of an insurance contract. Anticipated investment income is considered in determining whether the deferred acquisition costs are recoverable and whether a premium deficiency exists. We continually review the methods of making such estimates and establishing the deferred costs with any adjustments made in the accounting period in which the adjustment arose. The 2016 and 2015 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	Reserves for Losses and Loss Adjustment Expenses Liabilities for unpaid losses and loss adjustment expenses include the accumulation of individual case estimates for claims reported as well as estimates of IBNR claims and estimates of claim settlement expenses. Reinsurance recoverables on unpaid claims and claim expenses represent estimates of the portion of such liabilities that will be recoverable from reinsurers. Amounts recoverable from reinsurers are recognized as assets at the same time and in a manner consistent with the unpaid claims liabilities associated with the reinsurance policy.
Reinsurance	Reinsurance In the normal course of business, our insurance and reinsurance subsidiaries 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 Goodwill and intangible assets are allocated to the segment in which the results of operations for the acquired company are reported (see Note 19, “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 goodwill impairment test. Based on prior goodwill impairment testing, we determined the performance of the quantitative impairment test was required for 2016. The first step of the quantitative test 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, 2016, 2015 and 2014, all of our reporting units passed Step 1 of the goodwill impairment analysis as the fair value of each reporting unit were in excess of their carrying values. Therefore, Step 2 of the goodwill impairment analysis was not required. Any future 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: December 31, 2016 December 31, 2015 (in millions) Gross Carrying Amount Accumulated Amortization Gross Carrying Amount Accumulated Amortization Lloyd's capacity $ 60.5 n/a $ 60.5 n/a Distribution network 45.5 38.5 45.5 33.2 Additional Lloyd's capacity 4.8 4.8 4.8 4.6 Other 1.4 1.2 1.6 1.3 $ 112.2 $ 44.5 $ 112.4 $ 39.1 The weighted average useful life by category at December 31, 2016 was 9.3 years for the distribution network, 5.0 years for the additional Lloyd’s capacity and 8.7 years for other. The weighted average useful life for all categories was 8.9 years at December 31, 2016. During the years ended December 31, 2016, 2015 and 2014, amortization expense was $5.5 million, $7.5 million and $5.6 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, 2017, 2018 and 2019 is $4.7 million, $2.1 million and $0.4 million, respectively. There is no estimated amortization expense for either of the years ended December 31, 2020 and 2021.
Property and Equipment	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 nine years. The accumulated depreciation for property and equipment was $101.6 million and $85.1 million at December 31, 2016 and 2015, respectively. The net book value of our property and equipment at December 31, 2016 and 2015 was $142.2 million and $133.1 million, respectively. The depreciation expense at December 31, 2016, 2015 and 2014 was $20.9 million, $17.5 million and $15.1 million, respectively.
Derivative Instruments	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.
Share-Based Payments	Share-Based Payments Compensation expense for share-based payments is recognized based on the measurement-date fair value for awards that will settle in shares. 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 13, “Share-based Compensation” for related disclosures.
Foreign Currency Exchange Gain (Loss)	Foreign Currency Exchange Gain (Loss) The U.S. Dollar is the functional currency of all but 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, 2016 and 2015, the foreign currency translation adjustments were a loss of $17.6 million and $21.6 million, respectively.
Income Taxes	Income Taxes Deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates in effect for the year in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in net income in the period in which the change is enacted. We recognize potential accrued interest and penalties within our global operations in “Interest expense” and “Underwriting, acquisition and insurance expenses,” respectively, in our Consolidated Statements of Income.
Supplemental Cash Flow Information	Supplemental Cash Flow Information Income taxes paid. We paid income taxes of $16.6 million, $10.9 million and $23.7 million in 2016, 2015 and 2014, respectively. Income taxes recovered. We recovered income taxes of $0.5 million, $11.7 million and $0.1 million in 2016, 2015 and 2014, respectively. Interest paid as follows: For the Years Ended December 31, (in millions) 2016 2015 2014 Senior unsecured fixed rate notes $ 9.3 $ 9.3 $ 9.3 Junior subordinated debentures 7.7 7.0 7.6 Other indebtedness 2.3 2.4 2.8 Total interest paid $ 19.3 $ 18.7 $ 19.7 Non-cash operating activities transactions. 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 were held in escrow and recorded as a receivable within “Other assets” in our Consolidated Balance Sheet at December 31, 2014.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In December 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-19, “Technical Corrections and Improvements.” ASU 2016-19 clarifies guidance, corrects errors and makes minor improvements affecting a variety of topics in the FASB Accounting Standards Codification. We have adopted this ASU, effective immediately, and it does not have an impact on our financial results or disclosures. In October 2016, the FASB issued ASU 2016-16, “Intra-Entity Transfers of Assets Other Than Inventory” (Topic 740). ASU 2016-16 requires entities to recognize current and deferred income tax resulting from an intra-entity asset transfer when the transfer occurs. Prior to issuance of this ASU, U.S. GAAP did not allow recognition of income tax consequences until the asset had been sold to a third party. ASU 2016-16 requires adoption through a cumulative-effect adjustment to the balance sheet as of the beginning of the fiscal year of adoption with early adoption permitted. The ASU is effective in annual periods beginning after December 15, 2017, including interim periods therein. We are currently evaluating the impact that this ASU will have on our financial results and disclosures, but do not anticipate that any such potential impact would be material. In August 2016, the FASB issued ASU 2016-15, “Classification of Certain Cash Receipts and Cash Payments” (Topic 230). ASU 2016-15 will reduce diversity in practice on how eight specific cash receipts and payments are classified on the statement of cash flows. The ASU is effective for fiscal years beginning after December 15, 2017, including interim periods within those years. We anticipate that this ASU will have no net effect on our consolidated statements of cash flows, but will likely have an immaterial impact on the classification of specific cash receipts and payments within the statement. In June 2016, the FASB issued ASU 2016-13, “Measurement of Credit Losses on Financial Instruments” (Topic 326). ASU 2016-13 requires organizations to estimate credit losses on certain types of financial instruments, including receivables and available-for-sale debt securities, by introducing an approach based on expected losses. The expected loss approach will require entities to incorporate considerations of historical information, current information and reasonable and supportable forecasts. The ASU is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. The ASU requires a modified retrospective transition method and early adoption is permitted. We are currently evaluating the impact that the adoption of the ASU will have on our financial results and disclosures, but do not anticipate that any such potential impact would be material. In March 2016, the FASB issued ASU 2016-09, “Improvements to Employee Share-Based Payment Accounting” (Topic 718). ASU 2016-09 simplifies the accounting for share-based payment award transactions including income tax consequences, classification of awards as either equity or liabilities, classification on the statement of cash flows, and accounting for forfeitures. The ASU is effective for fiscal years beginning after December 15, 2016, and interim periods within those fiscal years. We have adopted this ASU as of January 1, 2017, and for presentation purposes, the incremental tax windfall or shortfall associated with these events will be classified as a cash inflow from operating activity as compared with a financing activity, as previously required, beginning with our quarterly report on Form 10-Q for the period ended March 31, 2017. In February 2016, the FASB issued ASU 2016-02, “Leases” (Topic 842). ASU 2016-02 requires organizations that lease assets to recognize on the balance sheet the assets and liabilities for the rights and obligations created by those leases. Additionally, the ASU modifies current guidance for lessors' accounting. The ASU is effective for interim and annual reporting periods beginning on or after January 1, 2019, with early adoption permitted. We do not anticipate that this ASU will have a material impact on our results of operations, but we anticipate an increase to the value of our assets and liabilities related to leases, with no material impact to equity. In January 2016, the FASB issued ASU 2016-01, “Recognition and Measurement of Financial Assets and Financial Liabilities” (Subtopic 825-10). ASU 2016-01 will require equity investments that are not consolidated or accounted for under the equity method of accounting to be measured at fair value with changes in fair value recognized in net income. This ASU will also require us to assess the ability to realize our deferred tax assets (“DTAs”) related to an available-for-sale debt security in combination with our other DTAs. The ASU will be effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. While we continue to evaluate the impact of this ASU, we anticipate the standard will increase the volatility of our consolidated statements of income, resulting from the remeasurement of our equity investments. In May 2015, the FASB issued ASU 2015-09, “Disclosures about Short-Duration Contracts” (Topic 944). ASU 2015-09 requires additional disclosures for unpaid claim liabilities and claim adjustment expenses for short-duration insurance contracts (i.e., coverage provided for a fixed period of short duration, typically a year or less). The ASU will require tables showing incurred and paid claims development information by accident year for the number of years claims typically remain outstanding, but not more than 10 years, including a reconciliation of this information to the statement of financial position. This ASU is effective for annual periods beginning after December 15, 2015 and interim periods within annual periods after December 15, 2016. We have adopted the ASU as of the effective date, and it has increased the volume and level of detail in our financial disclosures around reserves for losses and loss adjustment expenses in our financial statements. See Note 5, “Reserves for Losses and Loss Adjustment Expenses,” for additional information regarding this disclosure. In August 2014, the FASB issued ASU 2014-15, “Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern” (Subtopic 205-40). ASU 2014-15 requires entities to disclose whether there are conditions and events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the financial statements are issued. Management is also required to evaluate and disclose whether it plans to alleviate the doubt. The ASU will apply to both annual and interim reporting periods. The standard is effective for annual periods ending after December 15, 2016 and interim periods within annual periods beginning after December 15, 2016. We have adopted this ASU as of the effective date, and the adoption does not warrant the disclosure of conditions or events impacting our ability to continue as a going concern. In May 2014, the FASB issued ASU 2014-09, “Revenue from Contracts with Customers” (Topic 606), which replaces most existing U.S. GAAP revenue recognition guidance and permits the use of either the retrospective or cumulative effect transition method. In August 2015, “Deferral of the Effective Date” (Topic 606), deferred the effective date of this guidance to interim and annual reporting periods beginning after December 15, 2017. Early adoption is permitted for fiscal years, and interim reporting periods within those years, beginning after December 15, 2016. Subsequently, in 2016, the FASB issued implementation guidance related to ASU 2014-09, including: • ASU 2016-08, “Principal versus Agent Considerations (Reporting Revenue Gross versus Net)” (Topic 606), which is intended to provide further clarification on the application of the principal versus agent implementation; • ASU 2016-10, “Identifying Performance Obligations and Licensing” (Topic 606), which is intended to clarify the guidance for identifying promised goods or services in a contract with a customer; • ASU 2016-11, “Rescission of SEC Guidance Because of Accounting Standards Updates 2014-09 and 2014-16 Pursuant to Staff Announcements at the March 3, 2016 EITF Meeting” (Topic 605 & 815); • ASU 2016-12, “Narrow-Scope Improvements and Practical Expedients” (Topic 606), which amends certain aspects of ASU 2014-09 to address certain implementation issues; and • ASU 2016-20, “Technical Corrections and Improvements” (Topic 606), provides additional guidance for quantitative and qualitative disclosures in certain cases, and makes 12 additional technical corrections and improvements to the new revenue standard. 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 continue to evaluate what impact this ASU will have on our financial results and disclosures and which adoption method to apply, but do not anticipate such impact being material based on the limited revenue streams subject to the ASU. Accounting Standards Retrospectively Adopted in 2016 In April 2015, the FASB issued ASU 2015-03, “Simplifying the Presentation of Debt Issuance Costs,” which amends the guidance in Accounting Standards Codification Topic 835-30 “Interest – Imputation of Interest.” ASU 2015-03 requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. For public business entities, the guidance was effective for annual and interim periods beginning after December 15, 2015. We adopted this ASU effective January 1, 2016 and adjusted our prior period balances to reflect the adoption of this guidance. As of December 31, 2015, we reported $4.5 million of unamortized debt issuance costs related to our senior unsecured fixed rate notes. The effects of the retrospective application of ASU 2015-03 on individual financial statement line items in our Consolidated Balance Sheets were as follows: December 31, 2015 (in millions) As Previously Reported As Adjusted Effect of Change Other assets $ 225.2 $ 220.7 $ (4.5 ) Senior unsecured fixed rate notes 143.8 139.3 (4.5 ) The effects of the retrospective application of this ASU on individual financial statement line items in our Consolidated Statements of Cash Flows were as follows: For the Years Ended December 31, 2015 (in millions) As Previously Reported As Adjusted Effect of Change Cash flows from operating activities: Amortization of debt issuance costs $ — $ 0.2 $ 0.2 Other, net $ 0.6 $ 0.4 $ (0.2 ) For the Years Ended December 31, 2014 (in millions) As Previously Reported As Adjusted Effect of Change Cash flows from operating activities: Amortization of debt issuance costs $ — $ 0.2 $ 0.2 Other, net $ 28.0 $ 27.8 $ (0.2 )

Business and Significant Acco38

Business and Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2016
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) 2016 2015 2014 Premiums receivable $ 1.1 $ 1.0 $ 1.1 Reinsurance recoverables — 0.2 0.5 Net written off $ 1.1 $ 1.2 $ 1.6
Intangible Assets And Accumulated Amortization	The following table presents our intangible assets and accumulated amortization at December 31: December 31, 2016 December 31, 2015 (in millions) Gross Carrying Amount Accumulated Amortization Gross Carrying Amount Accumulated Amortization Lloyd's capacity $ 60.5 n/a $ 60.5 n/a Distribution network 45.5 38.5 45.5 33.2 Additional Lloyd's capacity 4.8 4.8 4.8 4.6 Other 1.4 1.2 1.6 1.3 $ 112.2 $ 44.5 $ 112.4 $ 39.1
Supplemental Cash Flow Information	Interest paid as follows: For the Years Ended December 31, (in millions) 2016 2015 2014 Senior unsecured fixed rate notes $ 9.3 $ 9.3 $ 9.3 Junior subordinated debentures 7.7 7.0 7.6 Other indebtedness 2.3 2.4 2.8 Total interest paid $ 19.3 $ 18.7 $ 19.7
Effects of Retrospective Application of ASU 2015-03 on Individual Financial Statement Line Items	The effects of the retrospective application of ASU 2015-03 on individual financial statement line items in our Consolidated Balance Sheets were as follows: December 31, 2015 (in millions) As Previously Reported As Adjusted Effect of Change Other assets $ 225.2 $ 220.7 $ (4.5 ) Senior unsecured fixed rate notes 143.8 139.3 (4.5 ) The effects of the retrospective application of this ASU on individual financial statement line items in our Consolidated Statements of Cash Flows were as follows: For the Years Ended December 31, 2015 (in millions) As Previously Reported As Adjusted Effect of Change Cash flows from operating activities: Amortization of debt issuance costs $ — $ 0.2 $ 0.2 Other, net $ 0.6 $ 0.4 $ (0.2 ) For the Years Ended December 31, 2014 (in millions) As Previously Reported As Adjusted Effect of Change Cash flows from operating activities: Amortization of debt issuance costs $ — $ 0.2 $ 0.2 Other, net $ 28.0 $ 27.8 $ (0.2 )

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2016
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: December 31, 2016 (in millions) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Fixed maturities U.S. Governments $ 275.1 $ 0.6 $ 4.5 $ 271.2 Foreign Governments 244.2 1.1 8.0 237.3 Obligations of states and political subdivisions 375.7 8.9 1.8 382.8 Corporate bonds 1,316.9 23.3 19.5 1,320.7 Commercial mortgage-backed securities 154.9 0.4 1.6 153.7 Residential mortgage-backed securities 174.8 3.7 1.7 176.8 Asset-backed securities 127.6 0.1 2.1 125.6 Collateralized loan obligations 269.6 3.8 9.1 264.3 Total fixed maturities 2,938.8 41.9 48.3 2,932.4 Equity securities 335.2 117.9 5.7 447.4 Other investments 531.6 7.5 0.1 539.0 Short-term investments 405.5 — — 405.5 Total investments $ 4,211.1 $ 167.3 $ 54.1 $ 4,324.3 December 31, 2015 (in millions) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Fixed maturities U.S. Governments $ 207.9 $ 0.7 $ 0.7 $ 207.9 Foreign Governments 263.1 0.8 20.8 243.1 Obligations of states and political subdivisions 467.6 20.7 0.3 488.0 Corporate bonds 1,355.1 13.6 48.8 1,319.9 Commercial mortgage-backed securities 151.5 0.3 1.6 150.2 Residential mortgage-backed securities 167.8 5.8 0.5 173.1 Asset-backed securities 131.1 0.3 2.9 128.5 Collateralized loan obligations 226.9 0.9 11.2 216.6 Total fixed maturities 2,971.0 43.1 86.8 2,927.3 Equity securities 349.7 131.5 17.3 463.9 Other investments 506.9 6.9 0.1 513.7 Short-term investments 211.2 — 0.4 210.8 Total investments $ 4,038.8 $ 181.5 $ 104.6 $ 4,115.7
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, 2016, by contractual maturity, were as follows: (in millions) Amortized Cost Fair Value Due in one year or less $ 266.9 $ 262.1 Due after one year through five years 1,237.9 1,239.9 Due after five years through ten years 545.9 547.0 Thereafter 161.2 163.0 Structured securities 726.9 720.4 Total $ 2,938.8 $ 2,932.4
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, 2016 and 2015 were as follows: December 31, 2016 (in millions) Carrying Value Unfunded Commitments Investment Type Hedge funds $ 180.9 $ — Private equity 179.0 93.4 Long only funds 170.7 — Other investments 8.4 — Total other invested assets $ 539.0 $ 93.4 December 31, 2015 (in millions) Carrying Value Unfunded Commitments Investment Type Hedge funds $ 146.9 $ — Private equity 144.1 90.2 Long only funds 211.0 — Other investments 11.7 — Total other invested assets $ 513.7 $ 90.2
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: December 31, 2016 Less Than One Year One Year or Greater Total (in millions) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Fixed maturities U.S. Governments $ 183.4 $ 4.5 $ — $ — $ 183.4 $ 4.5 Foreign Governments 201.2 8.0 — — 201.2 8.0 Obligations of states and political subdivisions 72.6 1.7 1.8 0.1 74.4 1.8 Corporate bonds 490.5 17.7 50.6 1.8 541.1 19.5 Commercial mortgage-backed securities 70.6 1.5 7.1 0.1 77.7 1.6 Residential mortgage-backed securities (2) 87.5 1.7 4.4 — 91.9 1.7 Asset-backed securities 69.7 1.4 8.2 0.7 77.9 2.1 Collateralized loan obligations 122.5 8.6 16.9 0.5 139.4 9.1 Total fixed maturities 1,298.0 45.1 89.0 3.2 1,387.0 48.3 Equity securities 62.1 5.7 — — 62.1 5.7 Other investments 0.3 0.1 — — 0.3 0.1 Short-term investments (1) 4.8 — — — 4.8 — Total $ 1,365.2 $ 50.9 $ 89.0 $ 3.2 $ 1,454.2 $ 54.1 December 31, 2015 Less Than One Year One Year or Greater Total (in millions) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Fixed maturities U.S. Governments (2) $ 138.3 $ 0.7 $ 0.4 $ — $ 138.7 $ 0.7 Foreign Governments 217.6 20.7 2.5 0.1 220.1 20.8 Obligations of states and political subdivisions (1) 9.3 — 8.8 0.3 18.1 0.3 Corporate bonds 844.7 41.1 77.8 7.7 922.5 48.8 Commercial mortgage-backed securities 108.1 1.3 9.8 0.3 117.9 1.6 Residential mortgage-backed securities (2) 52.1 0.5 1.5 — 53.6 0.5 Asset-backed securities 108.2 2.6 6.9 0.3 115.1 2.9 Collateralized loan obligations 183.4 10.7 13.1 0.5 196.5 11.2 Total fixed maturities 1,661.7 77.6 120.8 9.2 1,782.5 86.8 Equity securities 112.4 17.3 — — 112.4 17.3 Other investments 0.3 0.1 — — 0.3 0.1 Short-term investments 5.8 0.4 — — 5.8 0.4 Total $ 1,780.2 $ 95.4 $ 120.8 $ 9.2 $ 1,901.0 $ 104.6 (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 Recognized Other-than-temporary Losses on Fixed Maturities and Equity Portfolios	We recognized other-than-temporary losses on our fixed maturities and equity portfolios as follows: For the Years Ended December 31, (in millions) 2016 2015 2014 Other-than-temporary impairment: Obligations of states and political subdivisions $ — $ — $ (0.6 ) Corporate bonds (1.7 ) (2.2 ) (0.6 ) Equity securities (8.5 ) (9.7 ) (1.1 ) Other-than-temporary impairment losses $ (10.2 ) $ (11.9 ) $ (2.3 )
Schedule of Investment Income and Expenses	Investment income and expenses were as follows: For the Years Ended December 31, (in millions) 2016 2015 2014 Investment income: Interest on fixed maturities $ 88.9 $ 78.2 $ 76.3 Dividends on equity securities 15.6 16.3 15.8 Income on alternative investments 29.9 10.0 24.5 Income on short-term and other investments 0.4 0.2 0.3 Other — — 4.2 Investment income 134.8 104.7 121.1 Investment expenses (19.7 ) (16.1 ) (15.0 ) Net investment income $ 115.1 $ 88.6 $ 106.1
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) 2016 2015 2014 Realized gains Fixed maturities $ 21.5 $ 12.3 $ 17.0 Equity securities 57.5 40.5 29.2 Other investments 47.5 37.6 16.9 Short-term investments 0.5 1.2 0.1 Other assets 1.2 — 2.0 Gain on sale of real estate holdings — 0.3 43.3 Gross realized investment and other gains 128.2 91.9 108.5 Realized losses Fixed maturities (35.9 ) (23.5 ) (12.2 ) Equity securities (9.7 ) (6.6 ) (0.6 ) Other investments (46.0 ) (24.0 ) (13.4 ) Short-term investments (0.3 ) (1.8 ) (0.9 ) Other assets — — (4.6 ) Other-than-temporary impairment losses on fixed maturities (1.7 ) (2.2 ) (1.2 ) Other-than-temporary impairment losses on equity securities (8.5 ) (9.7 ) (1.1 ) Gross realized investment and other losses (102.1 ) (67.8 ) (34.0 ) Net realized investment and other gains before income taxes 26.1 24.1 74.5 Income tax expense (11.6 ) (10.0 ) (27.8 ) Net realized investment and other gains, net of income taxes $ 14.5 $ 14.1 $ 46.7
Schedule of Changes in Unrealized Appreciation (Depreciation)	Changes in unrealized appreciation (depreciation) related to investments are summarized as follows: For the Years Ended December 31, (in millions) 2016 2015 2014 Change in unrealized gains (losses) Fixed maturities $ 36.5 $ (65.3 ) $ (30.5 ) Equity securities (2.6 ) (64.1 ) (8.4 ) Other investments 0.6 1.5 2.5 Short-term investments 0.4 (0.4 ) — Net unrealized investment and other gains (losses) before income taxes 34.9 (128.3 ) (36.4 ) Income tax benefit (2.4 ) 37.6 3.1 Net unrealized investment and other gains (losses), net of income taxes $ 32.5 $ (90.7 ) $ (33.3 )
Schedule of Fair Value of Foreign Currency Exchange Forward Contracts	The fair value of our foreign currency exchange forward contracts as of December 31 was as follows: (in millions) December 31, 2016 December 31, 2015 Operational currency exposure (1) $ — $ 5.2 Asset manager investment exposure 0.7 2.9 Total return strategy 3.3 (0.8 ) $ 4.0 $ 7.3
Schedule of Realized Gains and Losses of Investment on Foreign Currency Exchange Forward Contracts	The following table presents our gross investment realized gains and losses on our foreign currency exchange forward contracts: For the Years Ended December 31, (in millions) 2016 2015 2014 Realized gains Global catastrophe (1) $ — $ 0.5 $ 4.6 Operational currency exposure 10.9 26.1 4.6 Asset manager investment exposure 9.0 8.5 6.0 Total return strategy 25.6 1.4 — Gross realized investment gains 45.5 36.5 15.2 Realized losses Global catastrophe — (2.3 ) (4.9 ) Operational currency exposure (18.0 ) (12.9 ) (2.2 ) Asset manager investment exposure (4.5 ) (2.3 ) (2.4 ) Total return strategy (21.0 ) (3.8 ) — Gross realized investment losses (43.5 ) (21.3 ) (9.5 ) Net realized investment gains on foreign currency exchange forward contracts $ 2.0 $ 15.2 $ 5.7 (1)
Schedule of Restricted Assets	The following table presents our components of restricted assets at December 31, 2016 (in millions) December 31, 2016 December 31, 2015 Securities on deposit for regulatory and other purposes $ 168.7 $ 192.8 Securities pledged as collateral for letters of credit 35.9 35.0 Securities on deposit supporting Lloyd’s business 161.8 202.5 Total restricted investments $ 366.4 $ 430.3
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 (in millions) December 31, 2016 Level 1 (a) Level 2 (b) Level 3 (c) Fixed maturities U.S. Governments $ 271.2 $ 228.0 $ 43.2 $ — Foreign Governments 237.3 — 237.3 — Obligations of states and political subdivisions 382.8 — 382.8 — Corporate bonds 1,320.7 — 1,318.7 2.0 Commercial mortgage-backed securities 153.7 — 153.7 — Residential mortgage-backed securities 176.8 — 176.8 — Asset-backed securities 125.6 — 125.6 — Collateralized loan obligations 264.3 — 264.3 — Total fixed maturities 2,932.4 228.0 2,702.4 2.0 Equity securities 447.4 444.9 2.1 0.4 Other investments 95.5 — 95.5 — Short-term investments 405.5 375.1 30.4 — $ 3,880.8 $ 1,048.0 $ 2,830.4 $ 2.4 (a) Quoted prices in active markets for identical assets (b) Significant other observable inputs (c) Significant unobservable inputs Fair Value Measurements at Reporting Date Using (in millions) December 31, 2015 Level 1 (a) Level 2 (b) Level 3 (c) Fixed maturities U.S. Governments $ 207.9 $ 150.4 $ 57.5 $ — Foreign Governments 243.1 — 243.1 — Obligations of states and political subdivisions 488.0 — 488.0 — Corporate bonds 1,319.9 — 1,319.9 — Commercial mortgage-backed securities 150.2 — 150.2 — Residential mortgage-backed securities 173.1 — 173.1 — Asset-backed securities 128.5 — 128.5 — Collateralized loan obligations 216.6 — 216.6 — Total fixed maturities 2,927.3 150.4 2,776.9 — Equity securities 463.9 457.6 5.6 0.7 Other investments 97.2 — 97.2 — Short-term investments 210.8 203.6 7.2 — $ 3,699.2 $ 811.6 $ 2,886.9 $ 0.7 (a) Quoted prices in active markets for identical assets (b) Significant other observable inputs (c) Significant unobservable inputs
Schedule of Reconciliation of Beginning and Ending Balances for Investments Categorized as Level 3	A reconciliation of the beginning and ending balances for the investments categorized as Level 3 are as follows: Fair Value Measurements Using Observable Inputs (Level 3) (in millions) Credit Financial Equity Securities Total Beginning balance, January 1, 2016 $ — $ 0.7 $ 0.7 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) — — — Purchases, issuances, sales, and settlements: Purchases 2.0 — 2.0 Issuances — — — Sales — (0.3 ) (0.3 ) Settlements — — — Ending balance, December 31, 2016 $ 2.0 $ 0.4 $ 2.4 Amount of total gains or losses for the year included in net income (loss) attributable to the change in unrealized gains or losses relating to assets still held at December 31, 2016 $ — $ — $ — (in millions) Credit Financial Equity Securities Total Beginning balance, January 1, 2015 $ — $ 0.9 $ 0.9 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) — — — Purchases, issuances, sales, and settlements: Purchases — — — Issuances — — — Sales — (0.2 ) (0.2 ) Settlements — — — Ending balance, December 31, 2015 $ — $ 0.7 $ 0.7 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, 2015 $ — $ — $ —

Reinsurance (Tables)

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2016
Insurance [Abstract]
Schedule of Reinsurance Premiums	Premiums were as follows: For the Years Ended December 31, (in millions) 2016 2015 2014 Direct written premiums $ 1,792.5 $ 1,651.4 $ 1,585.5 Reinsurance ceded to other companies (724.6 ) (610.0 ) (537.5 ) Reinsurance assumed from other companies 372.3 360.7 319.9 Net written premiums $ 1,440.2 $ 1,402.1 $ 1,367.9 Direct earned premiums $ 1,722.8 $ 1,602.2 $ 1,551.8 Reinsurance ceded to other companies (675.8 ) (563.7 ) (524.8 ) Reinsurance assumed from other companies 363.8 333.4 311.1 Net earned premiums $ 1,410.8 $ 1,371.9 $ 1,338.1 Percentage of reinsurance assumed to net earned premiums 25.8 % 24.3 % 23.2 %

Reserves for Losses and Loss 41

Reserves for Losses and Loss Adjustment Expenses (Tables)	12 Months Ended
	Dec. 31, 2016
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) 2016 2015 2014 Net reserves beginning of the year $ 2,133.3 $ 2,137.1 $ 2,107.6 Add: Losses and LAE incurred during current calendar year, net of reinsurance: Current accident year 843.4 798.5 785.1 Prior accident years (33.3 ) (32.4 ) (37.7 ) Losses and LAE incurred during calendar year, net of reinsurance 810.1 766.1 747.4 Deduct: Losses and LAE payments made during current calendar year, net of reinsurance: Current accident year 178.9 169.0 185.9 Prior accident years 537.6 564.5 550.8 Losses and LAE payments made during current calendar year, net of reinsurance: 716.5 733.5 736.7 Change in participation interest (1) (36.3 ) (1.2 ) 37.8 Foreign exchange adjustments (10.4 ) (35.2 ) (19.0 ) Net reserves - end of year 2,180.2 2,133.3 2,137.1 Add: Reinsurance recoverables on unpaid losses and LAE, end of year 1,170.6 990.3 905.3 Gross reserves - end of year $ 3,350.8 $ 3,123.6 $ 3,042.4 (1) Amount represents (decrease) increase in reserves due to change in our Syndicate 1200 participation.
Impact from (Favorable) Unfavorable Development of Prior Accident Years’ Loss and LAE Reserves on Each Reporting Segment	The impact from the (favorable) unfavorable development of prior accident years’ losses and LAE reserves on each reporting segment is presented below: For the Years Ended December 31, (in millions) 2016 2015 2014 Excess and Surplus Lines $ (13.2 ) $ (25.5 ) $ (38.9 ) Commercial Specialty (22.7 ) 2.5 (1.7 ) International Specialty (11.0 ) (7.7 ) (0.4 ) Syndicate 1200 (5.0 ) (10.3 ) (21.1 ) Run-off Lines 18.6 8.6 24.4 Total favorable prior-year development $ (33.3 ) $ (32.4 ) $ (37.7 )
Summary of Reconciliation of Net Incurred and Paid Development to Liability for Unpaid Losses and LAE in Consolidated Balance Sheets	The reconciliation of the net incurred and paid development tables to the liability for unpaid losses and LAE in our Consolidated Balance Sheets is as follows: (in millions) As of December 31, 2016 Liabilities for unpaid losses and ALAE: Excess and Surplus Lines - Casualty products $ 792.6 Commercial Specialty - Casualty products 374.2 Commercial Specialty - Professional products 83.6 International Specialty - Casualty products 54.5 International Specialty - Professional products 30.2 International Specialty - Property products 63.5 Syndicate 1200 - Casualty products 96.4 Syndicate 1200 - Professional products 104.5 Syndicate 1200 - Property products 101.7 Run-off Lines 203.3 Other lines 227.1 Total liabilities for unpaid losses and ALAE, net of reinsurance 2,131.6 Reinsurance recoverables on unpaid losses and LAE: Excess and Surplus Lines - Casualty products 261.0 Commercial Specialty - Casualty products 239.6 Commercial Specialty - Professional products 51.5 International Specialty - Casualty products 115.2 International Specialty - Professional products 39.0 International Specialty - Property products 18.6 Syndicate 1200 - Casualty products 54.3 Syndicate 1200 - Professional products 59.9 Syndicate 1200 - Property products 58.9 Run-off Lines 96.7 Other lines 175.9 Total reinsurance recoverables on unpaid losses and LAE 1,170.6 Unallocated loss adjustment expenses 68.0 Unamortized reserve discount (19.4 ) Gross liability for unpaid losses and LAE $ 3,350.8
Schedule of Supplementary Unaudited Information About Annual Percentage Payout of Incurred Losses and ALAE, Net of Reinsurance	The following table provides supplementary unaudited information about the annual percentage payout of incurred losses and ALAE, net of reinsurance, as of December 31, 2016: Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance (1) Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Excess and Surplus Lines - Casualty products 8.4% 18.7% 19.4% 16.3% 11.7% 8.1% N/A Commercial Specialty - Casualty products 14.6% 20.7% 18.4% 15.7% 9.7% 6.6% N/A Commercial Specialty - Professional products 9.6% 23.9% 29.8% 14.6% 6.4% 5.1% N/A International Specialty - Casualty products 11.5% 12.8% 17.5% 14.7% 10.5% 8.4% N/A International Specialty - Professional products 6.5% 17.2% 23.6% 15.4% 11.8% 10.2% N/A International Specialty - Property products 16.8% 41.2% 23.5% 9.9% 4.1% 2.0% N/A Syndicate 1200 - Casualty products 3.7% 7.6% 13.2% 20.4% 21.8% 11.0% 7.1% Syndicate 1200 - Professional products 4.3% 9.3% 15.0% 15.7% 14.7% 16.6% 7.3% Syndicate 1200 - Property products 38.4% 24.7% 15.1% 10.9% 5.0% 2.5% 1.3% (1) The average annual percentage payout is calculated from a paid losses and ALAE development pattern based on an actuarial analysis of the paid losses and ALAE movements by accident year for each disaggregation category. The paid losses and ALAE development pattern provides the expected percentage of ultimate losses and ALAE to be paid in each year. The pattern considers all accident years included in the claims development tables .
Schedule of Information About Discounted Liabilities For Unpaid Losses and LAE	The following tables provide information about these discounted liabilities for unpaid losses and LAE: Carrying Amount of Reserves for Losses & LAE Aggregate Amount of Discount As of December 31, As of December 31, (in millions, except discount percentages) 2016 2015 2014 2016 2015 2014 Commercial Specialty - Casualty products $ 121.1 $ 121.6 $ 114.4 $ 10.3 $ 10.3 $ 9.5 Run-off Lines 184.5 193.7 204.1 9.1 11.2 14.2 Total $ 305.6 $ 315.3 $ 318.5 $ 19.4 $ 21.5 $ 23.7 Interest Accretion (1) Discount Rate For the Years Ended December 31, As of December 31, 2016 2015 2014 2016 2015 2014 Commercial Specialty - Casualty products $ 1.9 $ 1.1 $ 2.1 2.25% 2.25% 2.25% Run-off Lines 2.1 3.1 2.1 3.50% 3.50% 3.50% Total $ 4.0 $ 4.2 $ 4.2 (1) Interest accretion is recorded in the line item “Losses and loss adjustment expenses” in our Consolidated Statements of Income.
Excess and Surplus Lines [Member] | Casualty Products [Member]
Summary of Information About Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	The following tables provide information about incurred and cumulative paid losses and allocated loss adjustment expenses (“ALAE”), net of reinsurance. The following tables also include IBNR reserves plus expected development on reported claims and the cumulative number of reported claims as of December 31, 2016. Excess and Surplus Lines Casualty Products (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 202.9 $ 206.0 $ 205.8 $ 200.0 $ 193.5 $ 192.8 2012 189.6 196.0 189.7 183.6 184.4 2013 217.9 222.6 224.3 227.2 2014 213.0 215.1 213.1 2015 232.3 237.0 2016 246.5 Total $ 1,301.0 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 17.6 $ 53.8 $ 91.0 $ 122.9 $ 146.6 $ 162.4 2012 17.2 52.8 89.1 120.8 142.4 2013 17.6 60.2 100.4 135.2 2014 15.0 52.2 95.9 2015 16.5 51.9 2016 17.4 Total $ 605.2 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 96.8 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 792.6 As of December 31, 2016 Incurred IBNR & Expected Cumulative Accident Losses & ALAE, Development on Number of Year Net of Reinsurance Reported Claims Reported Claims (2) 2011 $ 192.8 $ 21.1 8,324 2012 184.4 26.5 7,222 2013 227.2 51.5 7,016 2014 213.1 69.9 5,978 2015 237.0 131.2 5,035 2016 246.5 190.8 3,605 (1) Information presented for calendar years prior to 2016 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured at a coverage level by occurrence. Reported occurrences that do not result in a liability are included as reported claims.
Commercial Specialty [Member] | Casualty Products [Member]
Summary of Information About Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	Commercial Specialty Casualty Products (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 140.6 $ 155.1 $ 159.0 $ 157.5 $ 158.2 $ 154.0 2012 140.3 146.3 149.7 152.2 151.5 2013 126.6 133.2 135.1 133.2 2014 115.5 118.6 116.9 2015 102.6 106.7 2016 95.9 Total $ 758.2 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 23.1 $ 57.5 $ 85.9 $ 111.3 $ 126.1 $ 135.1 2012 20.1 51.0 80.7 105.3 120.8 2013 18.9 49.4 73.6 93.6 2014 17.4 38.4 58.7 2015 16.4 35.0 2016 11.1 Total $ 454.3 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 70.3 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 374.2 As of December 31, 2016 Incurred IBNR & Expected Cumulative Accident Losses & ALAE, Development on Number of Year Net of Reinsurance Reported Claims Reported Claims (2) 2011 $ 154.0 $ 9.1 28,462 2012 151.5 15.3 24,078 2013 133.2 16.9 19,117 2014 116.9 29.1 16,577 2015 106.7 40.5 13,758 2016 95.9 55.6 9,720 (1) Information presented for calendar years prior to 2016 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims.
Commercial Specialty [Member] | Professional Products [Member]
Summary of Information About Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	Commercial Specialty Professional Products (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 35.0 $ 35.0 $ 35.0 $ 32.5 $ 28.2 $ 26.9 2012 27.8 28.3 28.6 25.8 24.0 2013 20.9 21.5 21.1 19.0 2014 22.4 22.4 26.0 2015 29.9 29.5 2016 44.2 Total $ 169.6 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 3.2 $ 11.8 $ 17.8 $ 22.0 $ 24.0 $ 25.4 2012 2.3 8.6 16.9 19.9 21.4 2013 1.9 6.3 10.9 14.2 2014 2.3 5.4 15.1 2015 1.8 8.3 2016 2.4 Total $ 86.8 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 0.8 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 83.6 As of December 31, 2016 Incurred IBNR & Expected Cumulative Accident Losses & ALAE, Development on Number of Year Net of Reinsurance Reported Claims Reported Claims (2) 2011 $ 26.9 $ 0.7 815 2012 24.0 1.7 634 2013 19.0 1.6 611 2014 26.0 3.3 978 2015 29.5 11.7 1,647 2016 44.2 38.8 2,392 (1) Information presented for calendar years prior to 2016 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims.
International Specialty [Member] | Casualty Products [Member]
Summary of Information About Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	International Specialty Casualty Products (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 6.6 $ 6.6 $ 6.6 $ 4.4 $ 2.2 $ 1.6 2012 7.4 7.4 7.4 5.7 4.5 2013 9.1 9.5 9.6 9.6 2014 10.7 11.0 10.7 2015 12.6 15.3 2016 15.3 Total $ 57.0 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ — $ — $ — $ — $ — $ — 2012 — — — 0.1 0.1 2013 0.4 0.8 0.9 0.9 2014 0.3 0.7 0.8 2015 0.3 0.6 2016 0.5 Total $ 2.9 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 0.4 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 54.5 As of December 31, 2016 Incurred IBNR & Expected Cumulative Accident Losses & ALAE, Development on Number of Year Net of Reinsurance Reported Claims Reported Claims (2) 2011 $ 1.6 $ 1.6 1,416 2012 4.5 4.4 1,395 2013 9.6 8.5 1,416 2014 10.7 6.7 1,989 2015 15.3 6.3 2,487 2016 15.3 14.5 2,531 (1) Information presented for calendar years prior to 2016 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims.
International Specialty [Member] | Professional Products [Member]
Summary of Information About Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	International Specialty Professional Products (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 3.2 $ 3.2 $ 3.2 $ 2.3 $ 1.3 $ 0.8 2012 3.5 3.5 3.4 2.7 2.7 2013 5.8 6.4 6.2 4.9 2014 8.2 8.1 7.6 2015 10.8 10.8 2016 11.0 Total $ 37.8 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ — $ — $ — $ — $ — $ — 2012 — — — — 1.5 2013 0.5 0.9 1.4 1.4 2014 0.7 1.3 1.7 2015 1.3 2.1 2016 0.9 Total $ 7.6 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 30.2 As of December 31, 2016 Incurred IBNR & Expected Cumulative Accident Losses & ALAE, Development on Number of Year Net of Reinsurance Reported Claims Reported Claims (2) 2011 $ 0.8 $ 0.8 789 2012 2.7 1.2 986 2013 4.9 3.2 1,124 2014 7.6 4.7 1,275 2015 10.8 7.5 1,305 2016 11.0 8.7 1,315 (1) Information presented for calendar years prior to 2016 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims.
International Specialty [Member] | Property Products [Member]
Summary of Information About Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	International Specialty Property Products (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 114.9 $ 102.9 $ 105.0 $ 102.9 $ 102.2 $ 102.1 2012 47.3 51.5 50.5 51.7 46.5 2013 33.9 35.7 35.1 33.3 2014 28.0 28.2 26.2 2015 28.2 24.5 2016 45.5 Total $ 278.1 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2011 $ 39.9 $ 65.1 $ 86.2 $ 93.7 $ 96.0 $ 97.2 2012 12.4 31.2 40.7 49.7 44.1 2013 4.9 18.7 28.5 30.8 2014 3.3 13.7 20.3 2015 4.6 11.8 2016 14.8 Total $ 219.0 Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance 4.4 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 63.5 As of December 31, 2016 Incurred IBNR & Expected Cumulative Accident Losses & ALAE, Development on Number of Year Net of Reinsurance Reported Claims Reported Claims (2) 2011 $ 102.1 $ — 400 2012 46.5 0.9 299 2013 33.3 0.8 351 2014 26.2 2.6 339 2015 24.5 5.5 443 2016 45.5 19.5 742 (1) Information presented for calendar years prior to 2016 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims.
Syndicate 1200 [Member] | Casualty Products [Member]
Summary of Information About Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	Syndicate 1200 Casualty Products (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2010 $ 5.7 $ 4.8 $ 4.5 $ 6.1 $ 5.9 $ 5.8 $ 5.8 2011 8.0 8.6 10.8 10.9 10.2 10.1 2012 8.7 10.8 14.8 14.1 13.8 2013 22.6 26.7 26.2 24.5 2014 37.1 36.2 33.8 2015 33.9 29.2 2016 26.2 Total $ 143.4 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2010 $ — $ 0.2 $ 0.6 $ 1.1 $ 2.0 $ 2.8 $ 3.7 2011 0.2 0.8 1.6 3.4 5.4 6.9 2012 0.4 1.1 2.6 5.8 8.2 2013 1.5 3.2 7.0 11.3 2014 1.9 4.6 9.9 2015 0.8 5.2 2016 1.8 Total $ 47.0 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 96.4 As of December 31, 2016 Incurred IBNR & Expected Accident Losses & ALAE, Development on Year Net of Reinsurance Reported Claims 2010 $ 5.8 $ 1.1 2011 10.1 2.1 2012 13.8 3.6 2013 24.5 7.3 2014 33.8 13.8 2015 29.2 17.8 2016 26.2 21.5 (1) Information presented for calendar years prior to 2016 is required supplementary information and is unaudited.
Syndicate 1200 [Member] | Professional Products [Member]
Summary of Information About Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	Syndicate 1200 Professional Products (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2010 $ 15.2 $ 12.5 $ 12.4 $ 11.0 $ 9.9 $ 9.2 $ 9.3 2011 18.7 20.5 18.1 15.1 14.3 14.4 2012 13.7 13.6 13.8 13.7 13.8 2013 22.4 22.3 22.4 22.0 2014 34.5 35.5 35.9 2015 37.1 36.7 2016 33.2 Total $ 165.3 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2010 $ 0.1 $ 0.9 $ 1.9 $ 2.9 $ 3.7 $ 5.0 $ 6.3 2011 1.0 2.4 4.1 6.4 8.1 10.4 2012 0.6 1.8 4.2 5.6 8.0 2013 1.6 3.6 7.0 11.5 2014 1.6 6.3 14.5 2015 2.2 8.1 2016 2.0 Total $ 60.8 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 104.5 As of December 31, 2016 Incurred IBNR & Expected Accident Losses & ALAE, Development on Year Net of Reinsurance Reported Claims 2010 $ 9.3 $ 1.9 2011 14.4 3.1 2012 13.8 3.3 2013 22.0 7.0 2014 35.9 13.1 2015 36.7 20.4 2016 33.2 28.7 (1) Information presented for calendar years prior to 2016 is required supplementary information and is unaudited.
Syndicate 1200 [Member] | Property Products [Member]
Summary of Information About Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	Syndicate 1200 Property Products (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2010 $ 50.4 $ 57.9 $ 54.3 $ 53.8 $ 51.1 $ 50.9 $ 50.3 2011 107.3 112.6 106.8 94.2 92.4 91.7 2012 88.4 88.1 92.5 91.6 90.5 2013 83.2 79.1 78.1 76.5 2014 69.5 64.1 65.4 2015 54.9 64.9 2016 72.1 Total $ 511.4 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, Year 2010 (1) 2011 (1) 2012 (1) 2013 (1) 2014 (1) 2015 (1) 2016 2010 $ 1.8 $ 19.4 $ 27.8 $ 33.6 $ 35.6 $ 39.8 $ 41.3 2011 23.2 46.8 61.4 73.1 78.9 80.7 2012 29.3 47.5 62.6 73.6 76.0 2013 44.2 56.5 68.9 73.0 2014 29.3 51.3 57.3 2015 22.8 42.6 2016 38.8 Total $ 409.7 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 101.7 As of December 31, 2016 Incurred IBNR & Expected Accident Losses & ALAE, Development on Year Net of Reinsurance Reported Claims 2010 $ 50.3 $ 12.8 2011 91.7 23.6 2012 90.5 23.7 2013 76.5 20.1 2014 65.4 16.1 2015 64.9 17.3 2016 72.1 36.4 (1) Information presented for calendar years prior to 2016 is required supplementary information and is unaudited.

Run-off Lines (Tables)

Run-off Lines (Tables)	12 Months Ended
	Dec. 31, 2016
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) 2016 2015 Asbestos and Environmental: Reinsurance assumed $ 28.4 $ 34.6 Other 20.0 11.8 Total Asbestos and Environmental 48.4 46.4 Risk management 236.9 252.2 Run-off reinsurance lines 1.9 3.0 Other run-off lines 3.7 4.7 Total Run-off Lines $ 290.9 $ 306.3
Total Gross Reserves for Asbestos Exposure	The following table represents the total gross reserves for our asbestos exposure: December 31, (in millions) 2016 2015 2014 Direct written Case reserves $ 2.8 $ 2.0 $ 2.5 Unallocated loss adjustment expense ("ULAE") 0.5 0.5 1.0 Incurred but not reported ("IBNR") 12.1 8.2 7.6 Total direct written reserves 15.4 10.7 11.1 Assumed domestic Case reserves 10.5 12.2 13.2 ULAE 0.8 0.8 1.6 IBNR 10.5 13.7 15.8 Total assumed domestic reserves 21.8 26.7 30.6 Assumed London Case reserves 3.3 4.0 4.7 ULAE — — 0.2 IBNR 1.4 1.4 1.2 Total assumed London reserves 4.7 5.4 6.1 Total asbestos reserves $ 41.9 $ 42.8 $ 47.8
Run Off Lines [Member]
Results for Run-Off Lines	The following table presents our results for Run-off Lines: For the Years Ended December 31, (in millions) 2016 2015 2014 Asbestos and Environmental: Reinsurance assumed $ (1.3 ) $ (1.0 ) $ (8.3 ) Other (9.6 ) (3.4 ) (5.0 ) Total Asbestos and Environmental (10.9 ) (4.4 ) (13.3 ) Risk management (13.1 ) (8.2 ) (15.5 ) Run-off reinsurance lines 0.1 2.0 (1.5 ) Other run-off lines (1.2 ) (3.5 ) (0.7 ) Total Run-off Lines $ (25.1 ) $ (14.1 ) $ (31.0 )

Junior Subordinated Debentures

Junior Subordinated Debentures (Tables)	12 Months Ended
	Dec. 31, 2016
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 Rate Structure Interest Rate at December 31, 2016 Amount Argo Group 05/15/2003 PXRE Capital Statutory Trust II 05/15/2033 3M LIBOR + 4.10% 5.00% $ 18.1 11/06/2003 PXRE Capital Trust VI 09/30/2033 3M LIBOR + 3.90% 4.90% 10.3 Argo Group US 05/15/2003 Argonaut Group Statutory Trust I 05/15/2033 3M LIBOR + 4.10% 5.00% 15.5 12/16/2003 Argonaut Group Statutory Trust III 01/08/2034 3M LIBOR + 4.10% 4.98% 12.3 04/29/2004 Argonaut Group Statutory Trust IV 04/29/2034 3M LIBOR + 3.85% 4.76% 13.4 05/26/2004 Argonaut Group Statutory Trust V 05/24/2034 3M LIBOR + 3.85% 4.77% 12.3 05/12/2004 Argonaut Group Statutory Trust VI 05/12/2034 3M LIBOR + 3.80% 4.79% 13.4 09/17/2004 Argonaut Group Statutory Trust VII 12/15/2034 3M LIBOR + 3.60% 4.56% 15.5 09/22/2004 Argonaut Group Statutory Trust VIII 09/22/2034 3M LIBOR + 3.55% 4.55% 15.5 10/22/2004 Argonaut Group Statutory Trust IX 12/15/2034 3M LIBOR + 3.60% 4.56% 15.5 09/15/2005 Argonaut Group Statutory Trust X 09/15/2035 3M LIBOR + 3.40% 4.36% 30.9 Total Outstanding $ 172.7 (in millions) Issue Date Trust Preferred Pools Maturity Rate Structure Interest Rate at December 31, 2015 Amount Argo Group 05/15/2003 PXRE Capital Statutory Trust II 05/15/2033 3M LIBOR + 4.10% 4.46% $ 18.1 11/06/2003 PXRE Capital Trust VI 09/30/2033 3M LIBOR + 3.90% 4.51% 10.3 Argo Group US 05/15/2003 Argonaut Group Statutory Trust I 05/15/2033 3M LIBOR + 4.10% 4.46% 15.5 12/16/2003 Argonaut Group Statutory Trust III 01/08/2034 3M LIBOR + 4.10% 4.42% 12.3 04/29/2004 Argonaut Group Statutory Trust IV 04/29/2034 3M LIBOR + 3.85% 4.21% 13.4 05/26/2004 Argonaut Group Statutory Trust V 05/24/2034 3M LIBOR + 3.85% 4.23% 12.3 05/12/2004 Argonaut Group Statutory Trust VI 05/12/2034 3M LIBOR + 3.80% 4.33% 13.4 09/17/2004 Argonaut Group Statutory Trust VII 12/15/2034 3M LIBOR + 3.60% 4.11% 15.5 09/22/2004 Argonaut Group Statutory Trust VIII 09/22/2034 3M LIBOR + 3.55% 4.14% 15.5 10/22/2004 Argonaut Group Statutory Trust IX 12/15/2034 3M LIBOR + 3.60% 4.11% 15.5 09/15/2005 Argonaut Group Statutory Trust X 09/15/2035 3M LIBOR + 3.40% 3.91% 30.9 Total Outstanding $ 172.7

Other Indebtedness (Tables)

Other Indebtedness (Tables)	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Schedule of Floating Rate Loan Stock, Notes Outstanding	A summary of the notes outstanding at December 31, 2016 and 2015 is presented below: (in millions) Issue Date Currency Maturity Rate Structure Interest Rate at December 31, 2016 Amount 12/08/2004 U.S. Dollar 11/15/2034 6 month LIBOR + 4.2% 5.18% $ 6.5 09/06/2005 Euro 08/22/2035 3 month LIBOR + 4.0% 3.70% 12.8 10/31/2006 U.S. Dollar 01/15/2036 6 month LIBOR + 4.0% 4.98% 10.0 10/31/2006 Euro 11/22/2036 3 month LIBOR + 4.0% 3.70% 11.2 06/08/2007 Euro 09/15/2037 3 month LIBOR + 3.9% 3.58% 14.3 $ 54.8 (in millions) Issue Date Currency Maturity Rate Structure Interest Rate at December 31, 2015 Amount 12/08/2004 U.S. Dollar 11/15/2034 6 month LIBOR + 4.2% 4.66% $ 6.5 09/06/2005 Euro 08/22/2035 3 month LIBOR + 4.0% 3.91% 12.7 10/31/2006 U.S. Dollar 01/15/2036 6 month LIBOR + 4.0% 4.46% 10.0 10/31/2006 Euro 11/22/2036 3 month LIBOR + 4.0% 3.91% 11.1 06/08/2007 Euro 09/15/2037 3 month LIBOR + 3.9% 3.86% 14.3 $ 54.6

Disclosures about Fair Value 45

Disclosures about Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Summary of Company's Financial Instruments Whose Carrying Amount Did Not Equal Fair Value	A summary of our financial instruments whose carrying value did not equal fair value is shown below: December 31, 2016 December 31, 2015 (in millions) Carrying Amount Fair Value Carrying Amount Fair Value Junior subordinated debentures $ 172.7 $ 162.4 $ 172.7 $ 166.5 Senior unsecured fixed rate notes 139.5 139.3 139.3 141.8 Other indebtedness: Floating rate loan stock 54.8 51.5 54.6 52.7 Note payable 0.6 0.6 0.6 0.6 $ 367.6 $ 353.8 $ 367.2 $ 361.6

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Schedule of Repurchase of Shares	A summary of common shares repurchased in 2016 is shown below: Repurchase Type Date Trading Plan Initiated 2016 Purchase Period Number of Shares Repurchased Average Price of Shares Repurchased Total Cost (in millions) Repurchase Authorization Year 10b5-1 Trading Plan 12/16/2015 01/04/2016-02/11/2016 266,538 $ 55.59 $ 14.8 2013 10b5-1 Trading Plan 03/16/2016 03/16/2016-05/02/2016 162,893 $ 55.62 9.1 2013 10b5-1 Trading Plan 06/16/2016 06/24/2016-06/28/2016 14,774 $ 49.78 0.7 2016 10b5-1 Trading Plan 09/15/2016 09/19/2016-11/2/2016 43,062 $ 55.23 2.4 2016 Open Market N/A 01/01/2016-05/02/2016 64,464 $ 54.14 3.5 2013 Open Market N/A 05/03/2016-09/30/2016 295,380 $ 56.38 16.6 2016 Total 847,111 $ 55.64 $ 47.1
Schedule of Authorized and Unissued Common Shares Reserved	At December 31, 2016, we had the following authorized, unissued common shares reserved for future issuance: Reserve Name Shares Reserved 2014 Long-Term Incentive Plan 3,848,430 2016 Employee Share Purchase Plan 526,543 Total 4,374,973

Accumulated Other Comprehensi47

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2016
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 Translation Adjustments Unrealized Holding Gains on Securities Defined Benefit Pension Plans Total Balance, January 1, 2015 $ (15.6 ) $ 130.7 $ (7.0 ) $ 108.1 Other comprehensive (loss) income before reclassifications (6.0 ) (89.8 ) 0.1 (95.7 ) Amounts reclassified from accumulated other comprehensive (loss) income — (0.9 ) — (0.9 ) Net current-period other comprehensive (loss) income (6.0 ) (90.7 ) 0.1 (96.6 ) Balance, December 31, 2015 (21.6 ) 40.0 (6.9 ) 11.5 Other comprehensive (loss) income before reclassifications 4.0 42.4 (0.2 ) 46.2 Amounts reclassified from accumulated other comprehensive (loss) income — (10.0 ) — (10.0 ) Net current-period other comprehensive (loss) income 4.0 32.4 (0.2 ) 36.2 Balance, December 31, 2016 $ (17.6 ) $ 72.4 $ (7.1 ) $ 47.7
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) 2016 2015 2014 Unrealized gains and losses on securities: Net realized investment gains $ (23.2 ) $ (7.2 ) $ (30.6 ) Provision for income taxes 13.2 6.3 9.9 Net of taxes $ (10.0 ) $ (0.9 ) $ (20.7 )

Net Income Per Common Share (Ta

Net Income Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2016
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) 2016 2015 2014 Net income $ 146.7 $ 163.2 $ 183.2 Weighted average common shares outstanding - basic 30,166,440 30,769,089 31,559,422 Effect of dilutive securities: Equity compensation awards 679,270 616,371 574,796 Weighted average common shares outstanding - diluted 30,845,710 31,385,460 32,134,218 Net income per common share: Basic $ 4.86 $ 5.31 $ 5.80 Diluted $ 4.75 $ 5.20 $ 5.70

Share-based Compensation (Table

Share-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Fair Value Assumptions	The following table summarizes the assumptions we used: For the Years Ended December 31, 2016 2015 2014 Risk-free rate of return 1.00% to 2.02% 1.44% to 1.81% 1.53% to 1.77% Expected dividend yields 1.62% to 1.70% 1.46% to 1.60% 1.49% to 1.55% Expected award life (years) 4.50 to 4.61 4.62 to 4.71 4.67 to 4.85 Expected volatility 18.73% to 19.70% 20.04% to 22.09% 22.84% to 25.46%
Summary of Restricted Share Activity	A summary of restricted share activity as of December 31, 2016 and changes during the year then ended is as follows: Shares Weighted-Average Grant Date Fair Value Outstanding at January 1, 2016 514,742 $ 36.87 Granted 287,227 $ 50.84 Vested and issued (71,177 ) $ 32.75 Expired or forfeited (28,762 ) $ 44.49 Outstanding at December 31, 2016 702,030 $ 42.69
Summary of Stock-Settled SARs Activity	A summary of stock-settled SARs activity as of December 31, 2016 and changes during the year then ended is as follows: Shares Weighted-Average Exercise Price Outstanding at January 1, 2016 1,438,146 $ 29.52 Granted 542 $ 36.71 Converted from cash-settled SARs 944,046 $ 41.21 Exercised (251,134 ) $ 24.46 Expired or forfeited (148,905 ) $ 41.93 Outstanding at December 31, 2016 1,982,695 $ 34.80 Vested or expected to vest as of end of year 1,808,016 $ 20.19 Exercisable at end of year 851,491 $ 30.02
Summary of Cash-Settled SARs Activity	A summary of cash-settled SARs activity as of December 31, 2016 and changes during the year then ended is as follows: Shares Weighted-Average Exercise Price Outstanding at January 1, 2016 2,220,560 $ 35.53 Granted 540 $ 36.71 Converted to stock-settled SARs (1) (864,036 ) $ 41.21 Exercised (742,424 ) $ 30.70 Expired or forfeited (114,154 ) $ 39.03 Outstanding at December 31, 2016 500,486 $ 32.08 Vested or expected to vest as of end of year 480,891 $ 32.13 Exercisable at end of year 373,655 $ 32.44

Underwriting, Acquisition and50

Underwriting, Acquisition and Insurance Expenses (Tables)	12 Months Ended
	Dec. 31, 2016
Underwriting Acquisition And Insurance Expenses [Abstract]
Underwriting, Acquisition and Insurance Expenses	Underwriting, acquisition and insurance expenses were as follows: For the Years Ended December 31, (in millions) 2016 2015 2014 Commissions $ 234.0 $ 232.2 $ 231.1 General expenses 292.1 295.6 285.8 Premium taxes, boards and bureaus 25.2 9.8 25.5 551.3 537.6 542.4 Net deferral of policy acquisition costs (4.3 ) (0.9 ) (5.4 ) Total underwriting, acquisition and insurance expenses $ 547.0 $ 536.7 $ 537.0

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Tax Provision (Benefit)	Our income tax provision includes the following components: For the Years Ended December 31, (in millions) 2016 2015 2014 Current tax provision $ 36.3 $ 6.0 $ 5.2 Deferred tax provision related to: Future tax deductions (1.8 ) 10.9 58.4 Valuation allowance change 0.7 (2.6 ) (30.8 ) Income tax provision $ 35.2 $ 14.3 $ 32.8
Schedule of Pre-Tax Income (Loss) and Effective Income Tax Rates	For the years ended December 31, 2016, 2015 and 2014, pre-tax income (loss) attributable to our operations and the operations’ effective tax rates were as follows: (in millions) 2016 2015 2014 Pre-Tax Income (Loss) Effective Tax Rate Pre-Tax Income (Loss) Effective Tax Rate Pre-Tax Income (Loss) Effective Tax Rate Bermuda $ 99.6 0.0 % $ 94.3 0.0 % $ 102.8 0.0 % United States 115.2 29.2 % 64.8 19.9 % 98.0 28.1 % United Kingdom (34.8 ) 1.2 % 21.3 (4.7 %) 21.5 24.8 % Belgium (0.1 ) 23.2 % — (1) 237.0 % — (1) 63.8 % Brazil 0.6 0.0 % (3.2 ) 0.0 % (2.2 ) 0.0 % United Arab Emirates — (1) 0.0 % 0.2 0.0 % (0.9 ) 0.0 % Ireland (2) (0.2 ) 5.0 % (0.1 ) 5.0 % (1.1 ) 0.0 % Malta 1.6 0.3 % 0.1 0.0 % (2.2 ) 0.0 % Switzerland — (1) 0.0 % 0.1 20.5 % 0.1 17.6 % Pre-tax income $ 181.9 $ 177.5 $ 216.0 (1) Pre-tax income for the respective year was less than $0.1 million. (2) Effective tax rate of 5 percent on intercompany dividends of $40.0 million for the year ended December 31, 2016. Dividends eliminated in consolidation.
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) 2016 2015 2014 Income tax provision at expected rate $ 34.1 $ 25.8 $ 37.2 Tax effect of: Tax-exempt interest (3.3 ) (4.2 ) (4.5 ) Dividends received deduction (2.2 ) (2.3 ) (2.3 ) Valuation allowance change 0.7 (2.6 ) (30.8 ) Other permanent adjustments, net 0.4 0.3 (0.7 ) Adjustment for prior year tax return (0.9 ) (0.6 ) (0.9 ) United States state tax expense — (2.5 ) 2.5 PXRE Reinsurance capital loss carryforward — — 29.8 Other foreign adjustments 0.2 (0.3 ) 0.7 Foreign tax credit utilization (1.5 ) (2.1 ) 0.1 Deferred tax rate reduction — — (0.4 ) Foreign exchange adjustments 5.3 (0.1 ) 1.7 Foreign withholding taxes 2.4 2.9 0.4 Income tax provision $ 35.2 $ 14.3 $ 32.8 Income tax provision - Foreign $ (0.4 ) $ (1.1 ) $ 5.2 Income tax provision - United States, Federal 33.2 16.4 23.3 Income tax (benefit) provision - United States, State — (3.9 ) 3.9 Foreign withholding tax 2.4 2.9 0.4 Income tax provision $ 35.2 $ 14.3 $ 32.8
Schedule of Deferred Tax Assets and Liabilities	December 31, (in millions) 2016 2015 Deferred tax assets: Losses and loss adjustment expense reserve discounting $ 21.1 $ 23.4 Unearned premiums 29.1 26.6 Allowance for bad debt 1.6 1.6 Accrual for contingent commissions 0.3 0.3 Net operating loss carryforward 17.1 17.8 Impairment of investment values 8.6 9.6 United States amortization of intangible assets 5.3 4.9 Accrued bonus 7.4 7.0 Accrued vacation 1.7 1.6 Stock option expense 8.1 10.1 Brazil operating losses 8.3 5.9 Malta operating losses 1.3 1.8 Other 23.6 15.9 Deferred tax assets, gross 133.5 126.5 Deferred tax liabilities: Unrealized gains on equity securities (39.1 ) (40.1 ) Unrealized gains on fixed maturities and other investment securities (3.9 ) (0.4 ) Deferred acquisition costs (22.2 ) (20.4 ) United States amortization of intangible assets (3.8 ) (3.6 ) United Kingdom underwriting losses (5.4 ) (9.7 ) United Kingdom amortization of intangible assets (1.2 ) (1.8 ) Deferred gain on like-kind exchange (13.3 ) (13.3 ) Depreciable fixed asset (21.0 ) (18.0 ) Unrealized Gain on Limited Partnership Interests (17.6 ) (11.0 ) Other (6.6 ) (9.0 ) Deferred tax liabilities, gross (134.1 ) (127.3 ) Deferred tax assets, net before valuation allowance $ (0.6 ) $ (0.8 ) Valuation allowance (23.5 ) (22.8 ) Deferred tax liabilities, net $ (24.1 ) $ (23.6 ) Net deferred tax liabilities - Foreign $ (6.6 ) $ (11.7 ) Net deferred tax liabilities - United States (17.5 ) (11.9 ) Deferred tax liabilities, net $ (24.1 ) $ (23.6 )

Pension Benefits and Savings 52

Pension Benefits and Savings Plans (Tables)	12 Months Ended
	Dec. 31, 2016
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) 2016 2015 Change in plan assets Fair value of plan assets at beginning of year $ 17.5 $ 19.2 Actual return on plan assets 0.7 (0.1 ) Employer contributions 0.2 0.2 Settlements and benefits paid (1.7 ) (1.8 ) Fair value of plan assets at end of year $ 16.7 $ 17.5
Schedule of Change in Projected Benefit Obligation	(in millions) 2016 2015 Change in projected benefit obligation Projected benefit obligation at beginning of year $ 23.1 $ 25.8 Interest cost 0.8 0.8 Actuarial loss (gain) 0.4 (1.6 ) Settlements and benefits paid (1.7 ) (1.9 ) Projected benefit obligation at end of year $ 22.6 $ 23.1
Schedule of Assumptions to Determine Benefit Obligations	Assumptions used to determine benefit obligations at December 31 were as follows: 2016 2015 Weighted average discount rate 3.44% 3.48% 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, 2016 2015 2014 Weighted average discount rate 3.62% 3.55% 4.39% 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

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2016
Leases [Abstract]
Schedule of Future Minimum Payments Under Non-Cancelable Operating Leases	At December 31, 2016, the future minimum payments under non-cancelable operating leases are as follows: (in millions) Amount Due 2017 $ 11.3 2018 9.5 2019 8.2 2020 5.9 2021 5.2 Thereafter 5.9 Total $ 46.0

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2016
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) 2016 2015 2014 Revenue: Earned premiums Excess and Surplus Lines $ 485.3 $ 471.2 $ 444.6 Commercial Specialty 364.2 344.2 332.5 International Specialty 154.5 146.4 144.8 Syndicate 1200 406.4 409.7 414.6 Run-off Lines 0.4 0.4 1.6 Total earned premiums 1,410.8 1,371.9 1,338.1 Net investment income Excess and Surplus Lines 45.2 32.3 43.2 Commercial Specialty 26.7 19.9 25.6 International Specialty 16.8 11.4 11.3 Syndicate 1200 11.9 8.9 10.9 Run-off Lines 11.3 8.1 12.0 Corporate and Other 3.2 8.0 3.1 Total net investment income 115.1 88.6 106.1 Fee and other income 24.5 22.2 20.7 Net realized investment and other gains 26.1 24.1 74.5 Total revenue $ 1,576.5 $ 1,506.8 $ 1,539.4 For the Years Ended December 31, (in millions) 2016 2015 2014 Income (loss) before income taxes Excess and Surplus Lines $ 88.4 $ 81.4 $ 103.4 Commercial Specialty 86.0 43.0 24.8 International Specialty 38.2 29.0 23.8 Syndicate 1200 13.4 35.4 45.2 Run-off Lines (15.2 ) (7.4 ) (20.7 ) Total segment income before taxes 210.8 181.4 176.5 Corporate and Other (55.0 ) (28.0 ) (35.0 ) Net realized investment and other gains 26.1 24.1 74.5 Total income before income taxes $ 181.9 $ 177.5 $ 216.0
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) 2016 2015 2014 Bermuda $ 112.6 $ 103.4 $ 101.5 Brazil 39.2 43.1 44.3 Malta 2.1 1.9 2.1 United Kingdom 406.9 407.4 411.7 United States 850.0 816.1 778.5 Total earned premiums $ 1,410.8 $ 1,371.9 $ 1,338.1
Identifiable Assets	The following table represents identifiable assets: December 31, (in millions) 2016 2015 Excess and Surplus Lines $ 2,259.3 $ 2,174.8 Commercial Specialty 1,701.9 1,511.7 International Specialty 970.6 877.2 Syndicate 1200 1,386.3 1,216.5 Run-off Lines 537.0 558.4 Corporate and Other 349.9 287.0 Total $ 7,205.0 $ 6,625.6
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 Accumulated Amortization (in millions) 2016 2015 2016 2015 Excess and Surplus Lines $ 68.4 $ 68.4 $ — $ — Commercial Specialty 55.1 55.1 3.7 6.3 Syndicate 1200 28.7 28.7 64.0 67.0 Total $ 152.2 $ 152.2 $ 67.7 $ 73.3

Statutory Accounting Principl55

Statutory Accounting Principles (Tables)	12 Months Ended
	Dec. 31, 2016
Statutory Accounting Principles [Abstract]
Schedule Of Statutory Net Income And Capital And Surplus [Table Text Block]	The statutory capital and surplus for our principal operating subsidiaries was as follows: Statutory capital and surplus (1) December 31, (in millions) 2016 2015 Bermuda $ 1,510.8 $ 1,243.2 United Kingdom (2) 216.6 232.8 United States 886.7 854.5 (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) 2016 2015 2014 Bermuda $ 149.4 $ 182.2 $ 128.2 United Kingdom (2) 1.8 34.8 28.7 United States 99.0 94.4 117.7 (1) Such amounts include ownership interests in affiliate insurance and reinsurance subsidiaries. (2) In U.S. Dollars

Unaudited Quarterly Financial56

Unaudited Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data	(in millions, except per share amounts) 1st Quarter 2nd 3rd Quarter 4th Quarter Year 2016 Total revenue $ 370.1 $ 384.3 $ 416.7 $ 405.4 $ 1,576.5 Net income before income taxes 33.1 39.6 62.2 47.0 181.9 Net income 27.7 30.9 55.2 32.9 146.7 Net income per common share : Basic* $ 0.91 $ 1.03 $ 1.84 $ 1.10 $ 4.86 Diluted* $ 0.89 $ 1.00 $ 1.80 $ 1.07 $ 4.75 Comprehensive income (loss) $ 56.5 $ 59.7 $ 57.3 $ 9.4 $ 182.9 (in millions, except per share amounts) 1st Quarter 2nd 3rd Quarter 4th Quarter Year 2015 Total revenue $ 376.0 $ 377.2 $ 380.2 $ 373.4 $ 1,506.8 Net income before income taxes 62.4 34.7 36.2 44.2 177.5 Net income 58.8 27.9 35.3 41.2 163.2 Net income per common share : Basic* $ 1.90 $ 0.91 $ 1.15 $ 1.34 $ 5.31 Diluted* $ 1.87 $ 0.89 $ 1.13 $ 1.31 $ 5.20 Comprehensive income $ 36.8 $ 18.9 $ (18.3 ) $ 29.2 $ 66.6 * 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.

Senior Unsecured Fixed Rate N57

Senior Unsecured Fixed Rate Notes (Tables)	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Schedule Of Unamortized Debt Issuance Costs Deducted From Carrying Value Of Debt Liability	At December 31, 2016 and 2015, the Notes consisted of the following: (in millions) December 31, 2016 December 31, 2015 Senior unsecured fixed rate notes Principal $ 143.8 $ 143.8 Less: unamortized debt issuance costs (4.3 ) (4.5 ) Senior unsecured fixed rate notes, less unamortized debt issuance costs $ 139.5 $ 139.3
Condensed Consolidating Balance Sheet	CONDENSED CONSOLIDATING BALANCE SHEET DECEMBER 31, 2016 (in millions) Argo Group International Holdings, Ltd (Parent Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Assets Investments $ 2.2 $ 2,834.2 $ 1,487.9 $ — $ 4,324.3 Cash — 53.7 32.3 — 86.0 Accrued investment income — 16.0 4.7 — 20.7 Premiums receivable — 204.9 258.9 — 463.8 Reinsurance recoverables — 1,348.4 37.2 — 1,385.6 Goodwill and other intangible assets, net — 127.1 92.8 — 219.9 Deferred acquisition costs, net — 63.5 75.6 — 139.1 Ceded unearned premiums — 168.9 133.9 — 302.8 Other assets 8.7 168.0 86.1 — 262.8 Intercompany note receivable — 50.2 (50.2 ) — — Investments in subsidiaries 1,834.4 — — (1,834.4 ) — Total assets $ 1,845.3 $ 5,034.9 $ 2,159.2 $ (1,834.4 ) $ 7,205.0 Liabilities and Shareholders' Equity Reserves for losses and loss adjustment expenses $ — $ 2,322.4 $ 1,028.4 $ — $ 3,350.8 Unearned premiums — 580.0 390.0 — 970.0 Funds held and ceded reinsurance payable, net — 750.2 (206.5 ) — 543.7 Long-term debt 28.4 284.4 54.8 — 367.6 Current income taxes payable, net — 8.5 (0.4 ) — 8.1 Deferred tax liabilities, net — 17.6 6.5 — 24.1 Accrued underwriting expenses and other liabilities 13.7 92.0 42.3 — 148.0 Due to affiliates 10.5 1.8 (1.8 ) (10.5 ) — Total liabilities 52.6 4,056.9 1,313.3 (10.5 ) 5,412.3 Total shareholders' equity 1,792.7 978.0 845.9 (1,823.9 ) 1,792.7 Total liabilities and shareholders' equity $ 1,845.3 $ 5,034.9 $ 2,159.2 $ (1,834.4 ) $ 7,205.0 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING BALANCE SHEET DECEMBER 31, 2015 (in millions) Argo Group International Holdings, Ltd (Parent Guarantor) Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Assets Investments $ 6.2 $ 2,761.0 $ 1,348.5 $ — $ 4,115.7 Cash — 88.8 32.9 — 121.7 Accrued investment income — 16.4 5.2 — 21.6 Premiums receivable — 166.4 238.1 — 404.5 Reinsurance recoverables — 1,212.2 (91.1 ) — 1,121.1 Goodwill and other intangible assets, net — 129.8 95.7 — 225.5 Current income taxes receivable, net — 4.7 6.9 — 11.6 Deferred acquisition costs, net — 58.2 74.2 — 132.4 Ceded unearned premiums — 125.8 125.0 — 250.8 Other assets 8.2 151.7 60.8 — 220.7 Intercompany note receivable — 49.8 (49.8 ) — — Investments in subsidiaries 1,715.9 — — (1,715.9 ) — Total assets $ 1,730.3 $ 4,764.8 $ 1,846.4 $ (1,715.9 ) $ 6,625.6 Liabilities and Shareholders' Equity Reserves for losses and loss adjustment expenses $ — $ 2,194.1 $ 929.5 $ — $ 3,123.6 Unearned premiums — 501.5 385.2 — 886.7 Funds held and ceded reinsurance payable, net — 702.6 (312.6 ) — 390.0 Long-term debt 28.4 284.2 54.6 — 367.2 Deferred tax liabilities, net — 11.9 11.7 — 23.6 Accrued underwriting expenses and other liabilities 16.3 95.4 54.7 — 166.4 Due to affiliates 17.5 2.3 (2.3 ) (17.5 ) — Total liabilities 62.2 3,792.0 1,120.8 (17.5 ) 4,957.5 Total shareholders' equity 1,668.1 972.8 725.6 (1,698.4 ) 1,668.1 Total liabilities and shareholders' equity $ 1,730.3 $ 4,764.8 $ 1,846.4 $ (1,715.9 ) $ 6,625.6 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations.
Condensed Consolidating Statement of Income	CONDENSED CONSOLIDATING STATEMENT OF INCOME FOR THE YEAR ENDED DECEMBER 31, 2016 (in millions) Argo Group International Holdings, Ltd (Parent Guarantor) Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Premiums and other revenue: Earned premiums $ — $ 497.3 $ 913.5 $ — $ 1,410.8 Net investment income 37.2 78.9 40.0 (41.0 ) 115.1 Fee and other income — 21.4 3.1 — 24.5 Net realized investment and other gains 0.6 50.0 (24.5 ) — 26.1 Total revenue 37.8 647.6 932.1 (41.0 ) 1,576.5 Expenses: Losses and loss adjustment expenses — 290.4 519.7 — 810.1 Underwriting, acquisition and insurance expenses 12.8 204.4 329.8 — 547.0 Interest expense 1.4 15.8 2.4 — 19.6 Fee and other expense — 21.7 0.7 — 22.4 Foreign currency exchange loss (gains) — 0.2 (4.7 ) — (4.5 ) Total expenses 14.2 532.5 847.9 — 1,394.6 Income before income taxes 23.6 115.1 84.2 (41.0 ) 181.9 Provision for income taxes — 33.6 1.6 — 35.2 Net income before equity in earnings of subsidiaries 23.6 81.5 82.6 (41.0 ) 146.7 Equity in undistributed earnings of subsidiaries 123.1 — — (123.1 ) — Net income $ 146.7 $ 81.5 $ 82.6 $ (164.1 ) $ 146.7 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF INCOME FOR THE YEAR ENDED DECEMBER 31, 2015 (in millions) Argo Group International Holdings, Ltd (Parent Guarantor) Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Premiums and other revenue: Earned premiums $ — $ 497.3 $ 874.6 $ — $ 1,371.9 Net investment income 40.1 59.0 30.5 (41.0 ) 88.6 Fee and other income — 19.0 3.2 — 22.2 Net realized investment and other gains — 31.8 (7.7 ) — 24.1 Total revenue 40.1 607.1 900.6 (41.0 ) 1,506.8 Expenses: Losses and loss adjustment expenses — 304.2 461.9 — 766.1 Underwriting, acquisition and insurance expenses 19.0 198.4 319.3 — 536.7 Interest expense 1.5 15.3 2.2 — 19.0 Fee and other expense — 23.3 2.5 — 25.8 Foreign currency exchange loss (gains) — 1.0 (19.3 ) — (18.3 ) Total expenses 20.5 542.2 766.6 — 1,329.3 Income before income taxes 19.6 64.9 134.0 (41.0 ) 177.5 Provision for income taxes — 12.9 1.4 — 14.3 Net income before equity in earnings of subsidiaries 19.6 52.0 132.6 (41.0 ) 163.2 Equity in undistributed earnings of subsidiaries 143.6 — — (143.6 ) — Net income $ 163.2 $ 52.0 $ 132.6 $ (184.6 ) $ 163.2 (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, 2014 (in millions) Argo Group International Holdings, Ltd (Parent Guarantor) Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Premiums and other revenue: Earned premiums $ — $ 461.0 $ 877.1 $ — $ 1,338.1 Net investment income 40.5 76.2 (10.6 ) — 106.1 Fee and other income — 17.6 3.1 — 20.7 Net realized investment and other gains 2.0 67.4 7.1 (2.0 ) 74.5 Total revenue 42.5 622.2 876.7 (2.0 ) 1,539.4 Expenses: Losses and loss adjustment expenses — 285.6 461.8 — 747.4 Underwriting, acquisition and insurance expenses 17.3 199.9 319.8 — 537.0 Interest expense 2.3 15.2 2.7 (0.3 ) 19.9 Fee and other expense — 20.0 3.5 — 23.5 Foreign currency exchange gain — 0.4 (8.2 ) — (7.8 ) Impairment of intangible assets — 3.4 — — 3.4 Total expenses 19.6 524.5 779.6 (0.3 ) 1,323.4 Income before income taxes 22.9 97.7 97.1 (1.7 ) 216.0 Provision for income taxes — 27.5 5.3 — 32.8 Net income before equity in earnings of subsidiaries 22.9 70.2 91.8 (1.7 ) 183.2 Equity in undistributed earnings of 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 Cash Flows	CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS FOR YEAR ENDED DECEMBER 31, 2016 (in millions) Argo Group International Holdings, Ltd (Parent Guarantor) Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Net cash flows from operating activities $ 26.5 $ 71.7 $ 83.2 $ — $ 181.4 Cash flows from investing activities: Proceeds from sales of investments — 1,035.9 407.6 — 1,443.5 Maturities and mandatory calls of fixed maturity investments — 543.2 459.5 — 1,002.7 Purchases of investments — (1,450.0 ) (930.5 ) — (2,380.5 ) Change in short-term investments and foreign regulatory deposits (0.9 ) (138.1 ) (56.2 ) — (195.2 ) Settlements of foreign currency exchange forward contracts — — (5.4 ) — (5.4 ) Purchases of fixed assets and other, net — (11.3 ) 1.1 — (10.2 ) Cash used in investing activities (0.9 ) (20.3 ) (123.9 ) — (145.1 ) Cash flows from financing activities: Activity under stock incentive plans 1.0 — — — 1.0 Repurchase of Company's common shares — (47.1 ) — — (47.1 ) Excess tax expense from share-based payment arrangements — 0.6 — — 0.6 Payment of cash dividend to common shareholders (26.6 ) — — — (26.6 ) Intercompany cash dividend — (40.0 ) 40.0 — — Cash provided by (used in) financing activities (25.6 ) (86.5 ) 40.0 — (72.1 ) Effect of exchange rate changes on cash — — 0.1 — 0.1 Change in cash — (35.1 ) (0.6 ) — (35.7 ) Cash, beginning of year — 88.8 32.9 — 121.7 Cash, end of year $ — $ 53.7 $ 32.3 $ — $ 86.0 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS FOR YEAR ENDED DECEMBER 31, 2015 (in millions) Argo Group International Holdings, Ltd (Parent Guarantor) Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total Net cash flows from operating activities $ 32.7 $ 116.4 $ 133.5 $ — $ 282.6 Cash flows from investing activities: Proceeds from sales of investments — 631.1 336.8 — 967.9 Maturities and mandatory calls of fixed maturity investments — 681.8 162.1 — 843.9 Purchases of investments — (1,384.5 ) (649.6 ) — (2,034.1 ) Change in short-term investments and foreign regulatory deposits 0.9 14.9 33.8 — 49.6 Settlements of foreign currency exchange forward contracts 1.5 — (11.6 ) — (10.1 ) Issuance of intercompany note, net — 7.5 (7.5 ) — — Redemption of PXRE Capital Trust V — 18.0 (18.0 ) — — Purchases of fixed assets and other, net 3.8 (16.6 ) 2.0 — (10.8 ) Cash provided by (used in) investing activities 6.2 (47.8 ) (152.0 ) $ — (193.6 ) Cash flows from financing activities: Redemption of PXRE Capital Trust V (18.0 ) — 18.0 — — Activity under stock incentive plans 1.8 — — — 1.8 Repurchase of Company's common shares — (29.7 ) — — (29.7 ) Excess tax expense from share-based payment arrangements — 0.6 — — 0.6 Payment of cash dividend to common shareholders (22.7 ) — — — (22.7 ) Cash provided by (used in) financing activities (38.9 ) (29.1 ) 18.0 $ — (50.0 ) Effect of exchange rate changes on cash — — 1.7 — 1.7 Change in cash — 39.5 1.2 — 40.7 Cash, beginning of year — 49.3 31.7 — 81.0 Cash, end of year $ — $ 88.8 $ 32.9 $ — $ 121.7 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations. CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS FOR YEAR ENDED DECEMBER 31, 2014 (in millions) Argo Group International Holdings, Ltd (Parent Guarantor) Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) Other Subsidiaries and Eliminations (1) Consolidating Adjustments (2) Total 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 — 1,262.0 Maturities and mandatory calls of fixed maturity investments — 192.1 130.9 — 323.0 Purchases of investments — (1,126.1 ) (610.7 ) — (1,736.8 ) Change in short-term investments and foreign regulatory deposits 0.5 76.0 20.0 — 96.5 Settlements of foreign currency exchange 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 in 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 benefit from share-based payment arrangements — 0.1 — — 0.1 Payment of cash dividend to common shareholders (18.2 ) — — — (18.2 ) Cash used in 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 $ — $ 81.0 (1) Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations. (2) Includes all Argo Group parent company eliminations.

Business and Significant Acco58

Business and Significant Accounting Policies - Additional Information (Detail) $ in Millions	May 03, 2016shares	Feb. 17, 2015shares	Dec. 31, 2016USD ($)TrustInstitution	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Business And Significant Accounting Policies [Line Items]
Percentage of contractual participation			100.00%
Number of Statutory Trusts | Trust			12
Number of Charitable Foundations | Institution			2
Net investment income			$ 115.1	$ 88.6	$ 106.1
Stock dividend declared	10.00%	10.00%	10.00%	10.00%
Additional stock issued as dividend | shares	2,735,542	2,554,506
Dividends declaration date	May 3, 2016	Feb. 17, 2015
Dividends payable date	Jun. 15, 2016	Mar. 16, 2015
Dividend payable, date of record	Jun. 1, 2016	Mar. 2, 2015
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			$ 2.7	$ 3.5
Reinsurance recoverables, allowance for doubtful accounts			2.1	3.2
Estimated liability for return of premiums			5.7	6.5
Estimated amount of premiums receivables due			$ 0.1	0.1
Goodwill, Written off related to sale of operating unit					1.6
Indefinite-lived Intangible assets written-off					1.8
Weighted average useful life			8 years 10 months 24 days
Amortization expense			$ 5.5	7.5	5.6
Estimated amortization expense for 2017			4.7
Estimated amortization expense for 2018			2.1
Estimated amortization expense for 2019			0.4
Estimated amortization expense for 2020			0
Estimated amortization expense for 2021			0
Accumulated depreciation for property and equipment			101.6	85.1
Net book value of property and equipment			142.2	133.1
Depreciation expense			20.9	17.5	15.1
Foreign currency translation adjustment			17.6	21.6
Income taxes paid			16.6	10.9	23.7
Income taxes recovered			0.5	11.7	0.1
Proceeds from sale of real estate					43.3
Unamortized debt issuance costs related to senior unsecured fixed rate notes			$ 4.3	4.5
Accounting Standards Update 2015-03 [Member]
Business And Significant Accounting Policies [Line Items]
Unamortized debt issuance costs related to senior unsecured fixed rate notes				4.5
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			39 years
Distribution Network [Member]
Business And Significant Accounting Policies [Line Items]
Weighted average useful life			9 years 3 months 18 days
Additional Lloyd's Capacity [Member]
Business And Significant Accounting Policies [Line Items]
Weighted average useful life			5 years
Other [Member]
Business And Significant Accounting Policies [Line Items]
Weighted average useful life			8 years 8 months 12 days
Alternative Investment Portfolio [Member]
Business And Significant Accounting Policies [Line Items]
Net investment income			$ 23.9
Increases in net investment income				3	19.5
Decrease in net realized investment income and other gains				$ (3)	$ (19.5)

Business and Significant Acco59

Business and Significant Accounting Policies - Summary of Receivables (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Premiums receivable	$ 1.1	$ 1	$ 1.1
Reinsurance recoverables	0	0.2	0.5
Net written off	$ 1.1	$ 1.2	$ 1.6

Business and Significant Acco60

Business and Significant Accounting Policies - Intangible Assets and Accumulated Amortization (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 112.2	$ 112.4
Accumulated Amortization	44.5	39.1
Lloyd's Capacity [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	60.5	60.5
Accumulated Amortization	0	0
Distribution Network [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	45.5	45.5
Accumulated Amortization	38.5	33.2
Additional Lloyd's Capacity [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	4.8	4.8
Accumulated Amortization	4.8	4.6
Other [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	1.4	1.6
Accumulated Amortization	$ 1.2	$ 1.3

Business and Significant Acco61

Business and Significant Accounting Policies - Schedule of Interest Paid (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Disclosure - Business and Significant Accounting Policies - Supplemental Cash Flow Information - Schedule of Interest Paid (Detail) [Line Items]
Total interest paid	$ 19.3	$ 18.7	$ 19.7
Senior Unsecured Fixed Rate Notes [Member]
Disclosure - Business and Significant Accounting Policies - Supplemental Cash Flow Information - Schedule of Interest Paid (Detail) [Line Items]
Total interest paid	9.3	9.3	9.3
Junior Subordinated Debentures [Member]
Disclosure - Business and Significant Accounting Policies - Supplemental Cash Flow Information - Schedule of Interest Paid (Detail) [Line Items]
Total interest paid	7.7	7	7.6
Other Indebtedness [Member]
Disclosure - Business and Significant Accounting Policies - Supplemental Cash Flow Information - Schedule of Interest Paid (Detail) [Line Items]
Total interest paid	$ 2.3	$ 2.4	$ 2.8

Business and Significant Acco62

Business and Significant Accounting Policies - Effects of Retrospective Application of ASU 2015-03 on Individual Financial Statement Line Items in Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Debt Issuance Cost [Abstract]
Other assets	$ 262.8	$ 220.7
Senior unsecured fixed rate notes	$ 139.5	139.3
Accounting Standards Update 2015-03 [Member] | As Previously Reported [Member] | Other Assets [Member]
Debt Issuance Cost [Abstract]
Other assets		225.2
Accounting Standards Update 2015-03 [Member] | As Previously Reported [Member] | Senior Notes [Member]
Debt Issuance Cost [Abstract]
Senior unsecured fixed rate notes		143.8
Accounting Standards Update 2015-03 [Member] | Scenario Adjustment [Member] | Other Assets [Member]
Debt Issuance Cost [Abstract]
Other assets		220.7
Accounting Standards Update 2015-03 [Member] | Scenario Adjustment [Member] | Senior Notes [Member]
Debt Issuance Cost [Abstract]
Senior unsecured fixed rate notes		139.3
Accounting Standards Update 2015-03 [Member] | Restatement Adjustment [Member] | Other Assets [Member]
Debt Issuance Cost [Abstract]
Other assets		(4.5)
Accounting Standards Update 2015-03 [Member] | Restatement Adjustment [Member] | Senior Notes [Member]
Debt Issuance Cost [Abstract]
Senior unsecured fixed rate notes		$ (4.5)

Business and Significant Acco63

Business and Significant Accounting Policies - Effects of Retrospective Application of ASU on Individual Financial Statement Line Items in Consolidated Statement of Cash Flows (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Amortization of debt issuance costs	$ 0.2	$ 0.2	$ 0.2
Other, net	$ (49.1)	0.4	27.8
Accounting Standards Update 2015-03 [Member] | As Previously Reported [Member]
Cash flows from operating activities:
Amortization of debt issuance costs		0	0
Other, net		0.6	28
Accounting Standards Update 2015-03 [Member] | Scenario Adjustment [Member]
Cash flows from operating activities:
Amortization of debt issuance costs		0.2	0.2
Other, net		0.4	27.8
Accounting Standards Update 2015-03 [Member] | Restatement Adjustment [Member]
Cash flows from operating activities:
Amortization of debt issuance costs		0.2	0.2
Other, net		$ (0.2)	$ (0.2)

Subsequent Event - Additional I

Subsequent Event - Additional Information (Detail) - USD ($) $ in Millions	Feb. 06, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Subsequent Event [Line Items]
Acquisition related costs		$ 547	$ 536.7	$ 537
Maybrooke [Member]
Subsequent Event [Line Items]
Acquisition related costs		$ 0.4
Maybrooke [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Business acquisition effective date	Feb. 6, 2017
Purchase price paid	$ 235.3

Investments - Schedule of Amort

Investments - Schedule of Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Fair Value of Investments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Schedule of Invested Assets [Line Items]
Amortized Cost	$ 2,938.8	$ 2,971
Fair Value	2,932.4	2,927.3
Amortized Cost	335.2	349.7
Fair Value	447.4	463.9
Invested Assets Amortized Cost	4,211.1	4,038.8
Investments Gross Unrealized Gains	167.3	181.5
Investments Gross Unrealized losses	54.1	104.6
Total investments	4,324.3	4,115.7
Fixed Maturities [Member]
Schedule of Invested Assets [Line Items]
Amortized Cost	2,938.8	2,971
Gross Unrealized Gains	41.9	43.1
Gross Unrealized Losses	48.3	86.8
Fair Value	2,932.4	2,927.3
Fixed Maturities [Member] | Collateralized Loan Obligations [Member]
Schedule of Invested Assets [Line Items]
Amortized Cost	269.6	226.9
Gross Unrealized Gains	3.8	0.9
Gross Unrealized Losses	9.1	11.2
Fair Value	264.3	216.6
Fixed Maturities [Member] | Residential Mortgage-backed Securities [Member]
Schedule of Invested Assets [Line Items]
Amortized Cost	174.8	167.8
Gross Unrealized Gains	3.7	5.8
Gross Unrealized Losses	1.7	0.5
Fair Value	176.8	173.1
Fixed Maturities [Member] | U.S. Governments [Member]
Schedule of Invested Assets [Line Items]
Amortized Cost	275.1	207.9
Gross Unrealized Gains	0.6	0.7
Gross Unrealized Losses	4.5	0.7
Fair Value	271.2	207.9
Fixed Maturities [Member] | Foreign Governments [Member]
Schedule of Invested Assets [Line Items]
Amortized Cost	244.2	263.1
Gross Unrealized Gains	1.1	0.8
Gross Unrealized Losses	8	20.8
Fair Value	237.3	243.1
Fixed Maturities [Member] | Obligations of States and Political Subdivisions [Member]
Schedule of Invested Assets [Line Items]
Amortized Cost	375.7	467.6
Gross Unrealized Gains	8.9	20.7
Gross Unrealized Losses	1.8	0.3
Fair Value	382.8	488
Fixed Maturities [Member] | Corporate Bonds [Member]
Schedule of Invested Assets [Line Items]
Amortized Cost	1,316.9	1,355.1
Gross Unrealized Gains	23.3	13.6
Gross Unrealized Losses	19.5	48.8
Fair Value	1,320.7	1,319.9
Fixed Maturities [Member] | Commercial Mortgage-backed Securities [Member]
Schedule of Invested Assets [Line Items]
Amortized Cost	154.9	151.5
Gross Unrealized Gains	0.4	0.3
Gross Unrealized Losses	1.6	1.6
Fair Value	153.7	150.2
Fixed Maturities [Member] | Asset-backed Securities [Member]
Schedule of Invested Assets [Line Items]
Amortized Cost	127.6	131.1
Gross Unrealized Gains	0.1	0.3
Gross Unrealized Losses	2.1	2.9
Fair Value	125.6	128.5
Equity Securities [Member]
Schedule of Invested Assets [Line Items]
Amortized Cost	335.2	349.7
Gross Unrealized Gains	117.9	131.5
Gross Unrealized Losses	5.7	17.3
Fair Value	447.4	463.9
Other Investments [Member]
Schedule of Invested Assets [Line Items]
Invested Assets Amortized Cost	531.6	506.9
Investments Gross Unrealized Gains	7.5	6.9
Investments Gross Unrealized losses	0.1	0.1
Total investments	539	513.7
Short-Term Investments [Member]
Schedule of Invested Assets [Line Items]
Invested Assets Amortized Cost	405.5	211.2
Investments Gross Unrealized Gains	0	0
Investments Gross Unrealized losses	0	0.4
Total investments	$ 405.5	$ 210.8

Investments - Additional Inform

Investments - Additional Information (Detail)	Dec. 31, 2016USD ($)Security	Dec. 31, 2015USD ($)
Schedule Of Investments [Line Items]
Fair value of investments, assets managed on behalf of the trade capital providers	$ 131,900,000	$ 95,300,000
Number of securities in an unrealized loss position, total | Security	7,401
Number of securities in an unrealized loss position for less than one year | Security	2,194
Number of securities in an unrealized loss position for a period of one year or greater | Security	182
Transfers between Level 1 and Level 2 securities	$ 0	0
Transfers between Level 2 and Level 1 securities	0	$ 0
Fixed Maturities Term Loan [Member]
Schedule Of Investments [Line Items]
Own term loan fixed maturity level 3 value	$ 2,000,000

Investments - Schedule of Amo67

Investments - Schedule of Amortized Cost and Fair Values of Fixed Maturity Investments, by Contractual Maturity (Detail) $ in Millions	Dec. 31, 2016USD ($)
Investments Debt And Equity Securities [Abstract]
Amortized Cost, Due in one year or less	$ 266.9
Amortized Cost, Due after one year through five years	1,237.9
Amortized Cost, Due after five years through ten years	545.9
Amortized Cost, Thereafter	161.2
Amortized Cost, Structured securities	726.9
Amortized Cost, Total	2,938.8
Fair Value, Due in one year or less	262.1
Fair Value, Due after one year through five years	1,239.9
Fair Value, Due after five years through ten years	547
Fair Value, Thereafter	163
Fair Value, Structured securities	720.4
Fair Value, Total	$ 2,932.4

Investments - Schedule of Carry

Investments - Schedule of Carrying Value and Unfunded Investment Commitments of Other Invested Assets Portfolio (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Investments [Line Items]
Carrying Value	$ 4,324.3	$ 4,115.7
Hedge funds [Member]
Schedule Of Investments [Line Items]
Carrying Value	180.9	146.9
Unfunded Commitments	0	0
Private equity [Member]
Schedule Of Investments [Line Items]
Carrying Value	179	144.1
Unfunded Commitments	93.4	90.2
Long only funds [Member]
Schedule Of Investments [Line Items]
Carrying Value	170.7	211
Unfunded Commitments	0	0
Other Investments [Member]
Schedule Of Investments [Line Items]
Carrying Value	8.4	11.7
Unfunded Commitments	0	0
Other Invested Assets [Member]
Schedule Of Investments [Line Items]
Carrying Value	539	513.7
Unfunded Commitments	$ 93.4	$ 90.2

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 ($) $ in Millions		Dec. 31, 2016		Dec. 31, 2015
Schedule Of Investments [Line Items]
Fair Value, Less Than One Year		$ 1,365.2		$ 1,780.2
Unrealized Losses, Less Than One Year		50.9		95.4
Fair Value, One Year or Greater		89		120.8
Unrealized Losses, One Year or Greater		3.2		9.2
Fair Value, Total		1,454.2		1,901
Unrealized Losses, Total		54.1		104.6
Fixed Maturities [Member]
Schedule Of Investments [Line Items]
Fair Value, Less Than One Year		1,298		1,661.7
Unrealized Losses, Less Than One Year		45.1		77.6
Fair Value, One Year or Greater		89		120.8
Unrealized Losses, One Year or Greater		3.2		9.2
Fair Value, Total		1,387		1,782.5
Unrealized Losses, Total		48.3		86.8
Fixed Maturities [Member] | Collateralized Loan Obligations [Member]
Schedule Of Investments [Line Items]
Fair Value, Less Than One Year		122.5		183.4
Unrealized Losses, Less Than One Year		8.6		10.7
Fair Value, One Year or Greater		16.9		13.1
Unrealized Losses, One Year or Greater		0.5		0.5
Fair Value, Total		139.4		196.5
Unrealized Losses, Total		9.1		11.2
Fixed Maturities [Member] | Residential Mortgage-backed Securities [Member]
Schedule Of Investments [Line Items]
Fair Value, Less Than One Year	[1]	87.5		52.1
Unrealized Losses, Less Than One Year	[1]	1.7		0.5
Fair Value, One Year or Greater	[1]	4.4		1.5
Unrealized Losses, One Year or Greater	[1]	0		0
Fair Value, Total	[1]	91.9		53.6
Unrealized Losses, Total	[1]	1.7		0.5
Fixed Maturities [Member] | U.S. Governments [Member]
Schedule Of Investments [Line Items]
Fair Value, Less Than One Year		183.4		138.3	[1]
Unrealized Losses, Less Than One Year		4.5		0.7	[1]
Fair Value, One Year or Greater		0		0.4	[1]
Unrealized Losses, One Year or Greater		0		0	[1]
Fair Value, Total		183.4		138.7	[1]
Unrealized Losses, Total		4.5		0.7	[1]
Fixed Maturities [Member] | Foreign Governments [Member]
Schedule Of Investments [Line Items]
Fair Value, Less Than One Year		201.2		217.6
Unrealized Losses, Less Than One Year		8		20.7
Fair Value, One Year or Greater		0		2.5
Unrealized Losses, One Year or Greater		0		0.1
Fair Value, Total		201.2		220.1
Unrealized Losses, Total		8		20.8
Fixed Maturities [Member] | Obligations of States and Political Subdivisions [Member]
Schedule Of Investments [Line Items]
Fair Value, Less Than One Year		72.6		9.3	[2]
Unrealized Losses, Less Than One Year		1.7		0	[2]
Fair Value, One Year or Greater		1.8		8.8	[2]
Unrealized Losses, One Year or Greater		0.1		0.3	[2]
Fair Value, Total		74.4		18.1	[2]
Unrealized Losses, Total		1.8		0.3	[2]
Fixed Maturities [Member] | Corporate Bonds [Member]
Schedule Of Investments [Line Items]
Fair Value, Less Than One Year		490.5		844.7
Unrealized Losses, Less Than One Year		17.7		41.1
Fair Value, One Year or Greater		50.6		77.8
Unrealized Losses, One Year or Greater		1.8		7.7
Fair Value, Total		541.1		922.5
Unrealized Losses, Total		19.5		48.8
Fixed Maturities [Member] | Commercial Mortgage-backed Securities [Member]
Schedule Of Investments [Line Items]
Fair Value, Less Than One Year		70.6		108.1
Unrealized Losses, Less Than One Year		1.5		1.3
Fair Value, One Year or Greater		7.1		9.8
Unrealized Losses, One Year or Greater		0.1		0.3
Fair Value, Total		77.7		117.9
Unrealized Losses, Total		1.6		1.6
Fixed Maturities [Member] | Asset-backed Securities [Member]
Schedule Of Investments [Line Items]
Fair Value, Less Than One Year		69.7		108.2
Unrealized Losses, Less Than One Year		1.4		2.6
Fair Value, One Year or Greater		8.2		6.9
Unrealized Losses, One Year or Greater		0.7		0.3
Fair Value, Total		77.9		115.1
Unrealized Losses, Total		2.1		2.9
Equity Securities [Member]
Schedule Of Investments [Line Items]
Fair Value, Less Than One Year		62.1		112.4
Unrealized Losses, Less Than One Year		5.7		17.3
Fair Value, One Year or Greater		0		0
Unrealized Losses, One Year or Greater		0		0
Fair Value, Total		62.1		112.4
Unrealized Losses, Total		5.7		17.3
Other Investments [Member]
Schedule Of Investments [Line Items]
Fair Value, Less Than One Year		0.3		0.3
Unrealized Losses, Less Than One Year		0.1		0.1
Fair Value, One Year or Greater		0		0
Unrealized Losses, One Year or Greater		0		0
Fair Value, Total		0.3		0.3
Unrealized Losses, Total		0.1		0.1
Short-Term Investments [Member]
Schedule Of Investments [Line Items]
Fair Value, Less Than One Year		4.8	[2]	5.8
Unrealized Losses, Less Than One Year		0	[2]	0.4
Fair Value, One Year or Greater		0	[2]	0
Unrealized Losses, One Year or Greater		0	[2]	0
Fair Value, Total		4.8	[2]	5.8
Unrealized Losses, Total		$ 0	[2]	$ 0.4
[1]	Unrealized losses one year or greater are less than $0.1 million.
[2]	Unrealized losses less than one year are less than $0.1 million.

Investments - Schedule of Agi70

Investments - Schedule of Aging of Unrealized Losses on Company's Investments in Fixed Maturities, Equity Securities and Other Investments (Parenthetical) (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Investments Debt And Equity Securities [Abstract]
Unrealized losses less than one year	$ 0.1	$ 0.1
Unrealized losses one year or greater	$ 0.1	$ 0.1

Investments - Schedule of Recog

Investments - Schedule of Recognized Other-than-temporary Losses on Fixed Maturities and Equity Portfolios (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other-than-temporary impairment:
Other-than-temporary impairment losses	$ (10.2)	$ (11.9)	$ (2.3)
Obligations of States and Political Subdivisions [Member]
Other-than-temporary impairment:
Other-than-temporary impairment losses	0	0	(0.6)
Corporate Bonds [Member]
Other-than-temporary impairment:
Other-than-temporary impairment losses	(1.7)	(2.2)	(0.6)
Equity Securities [Member]
Other-than-temporary impairment:
Other-than-temporary impairment losses	$ (8.5)	$ (9.7)	$ (1.1)

Investments - Schedule of Inves

Investments - Schedule of Investment Income and Expenses (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Amortized Cost And Fair Value Debt Securities [Abstract]
Interest on fixed maturities	$ 88.9	$ 78.2	$ 76.3
Dividends on equity securities	15.6	16.3	15.8
Income on alternative investments	29.9	10	24.5
Income on short-term and other investments	0.4	0.2	0.3
Other	0	0	4.2
Investment income	134.8	104.7	121.1
Investment expenses	(19.7)	(16.1)	(15)
Net investment income	$ 115.1	$ 88.6	$ 106.1

Investments - Schedule of Compa

Investments - Schedule of Company's Gross Realized Investment Gains (Losses) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Investments [Line Items]
Gross realized investment and other gains	$ 128.2	$ 91.9	$ 108.5
Gross realized investment and other losses	(102.1)	(67.8)	(34)
Net realized investment and other gains	26.1	24.1	74.5
Income tax expense	(11.6)	(10)	(27.8)
Net realized investment and other gains, net of income taxes	14.5	14.1	46.7
Fixed Maturities [Member]
Schedule Of Investments [Line Items]
Gross realized investment and other gains	21.5	12.3	17
Gross realized investment and other losses	(35.9)	(23.5)	(12.2)
Equity Securities [Member]
Schedule Of Investments [Line Items]
Gross realized investment and other gains	57.5	40.5	29.2
Gross realized investment and other losses	(9.7)	(6.6)	(0.6)
Other Investments [Member]
Schedule Of Investments [Line Items]
Gross realized investment and other gains	47.5	37.6	16.9
Gross realized investment and other losses	(46)	(24)	(13.4)
Short-Term Investments [Member]
Schedule Of Investments [Line Items]
Gross realized investment and other gains	0.5	1.2	0.1
Gross realized investment and other losses	(0.3)	(1.8)	(0.9)
Other Assets [Member]
Schedule Of Investments [Line Items]
Gross realized investment and other gains	1.2	0	2
Gross realized investment and other losses	0	0	(4.6)
Real Estate Holdings [Member]
Schedule Of Investments [Line Items]
Gross realized investment and other gains	0	0.3	43.3
Other-Than-Temporary Impairment Losses on Fixed Maturities [Member]
Schedule Of Investments [Line Items]
Gross realized investment and other losses	(1.7)	(2.2)	(1.2)
Other-Than-Temporary Impairment Losses on Equity Securities [Member]
Schedule Of Investments [Line Items]
Gross realized investment and other losses	$ (8.5)	$ (9.7)	$ (1.1)

Investments - Schedule of Chang

Investments - Schedule of Changes in Unrealized Appreciation (Depreciation) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Investments [Line Items]
Net unrealized investment and other gains (losses) before income taxes	$ 34.9	$ (128.3)	$ (36.4)
Income tax benefit	(2.4)	37.6	3.1
Net unrealized investment and other gains (losses), net of income taxes	32.5	(90.7)	(33.3)
Fixed Maturities [Member]
Schedule Of Investments [Line Items]
Net unrealized investment and other gains (losses) before income taxes	36.5	(65.3)	(30.5)
Equity Securities [Member]
Schedule Of Investments [Line Items]
Net unrealized investment and other gains (losses) before income taxes	(2.6)	(64.1)	(8.4)
Other Investments [Member]
Schedule Of Investments [Line Items]
Net unrealized investment and other gains (losses) before income taxes	0.6	1.5	2.5
Short-Term Investments [Member]
Schedule Of Investments [Line Items]
Net unrealized investment and other gains (losses) before income taxes	$ 0.4	$ (0.4)	$ 0

Investments - Schedule of Fair

Investments - Schedule of Fair Value of Foreign Currency Exchange Forward Contracts (Detail) - Foreign Currency Exchange Forward Contracts [Member] - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Schedule Of Investments [Line Items]
Fair value of foreign currency exchange forward contracts		$ 4	$ 7.3
Operational Currency Exposure [Member]
Schedule Of Investments [Line Items]
Fair value of foreign currency exchange forward contracts	[1]	0	5.2
Asset Manager Investment Exposure [Member]
Schedule Of Investments [Line Items]
Fair value of foreign currency exchange forward contracts		0.7	2.9
Total return strategy [Member]
Schedule Of Investments [Line Items]
Fair value of foreign currency exchange forward contracts		$ 3.3	$ (0.8)
[1]	CAD currency exposure less than $0.1 million.

Investments - Schedule of Fai76

Investments - Schedule of Fair Value of Foreign Currency Exchange Forward Contracts (Parenthetical) (Detail) - Foreign Currency Exchange Forward Contracts [Member] - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Investments [Line Items]
Fair value of foreign currency exchange forward contracts	$ 4,000,000	$ 7,300,000
Canadian Dollar (CAD) [Member] | Currency Exposure [Member] | Maximum [Member]
Schedule Of Investments [Line Items]
Fair value of foreign currency exchange forward contracts	$ 100,000	$ 100,000

Investments - Schedule of Reali

Investments - Schedule of Realized Gains and Losses of Investment on Foreign Currency Exchange Forward Contracts (Detail) - Foreign Currency Exchange Forward Contracts [Member] - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Investments [Line Items]
Realized gains from foreign currency exchange forward contracts		$ 45.5	$ 36.5	$ 15.2
Realized losses from foreign currency exchange forward contracts		(43.5)	(21.3)	(9.5)
Net realized investment gains on foreign currency exchange forward contracts		2	15.2	5.7
Global Catastrophe [Member]
Schedule Of Investments [Line Items]
Realized gains from foreign currency exchange forward contracts	[1]	0	0.5	4.6
Realized losses from foreign currency exchange forward contracts		0	(2.3)	(4.9)
Operational Currency Exposure [Member]
Schedule Of Investments [Line Items]
Realized gains from foreign currency exchange forward contracts		10.9	26.1	4.6
Realized losses from foreign currency exchange forward contracts		(18)	(12.9)	(2.2)
Asset Manager Investment Exposure [Member]
Schedule Of Investments [Line Items]
Realized gains from foreign currency exchange forward contracts		9	8.5	6
Realized losses from foreign currency exchange forward contracts		(4.5)	(2.3)	(2.4)
Total return strategy [Member]
Schedule Of Investments [Line Items]
Realized gains from foreign currency exchange forward contracts		25.6	1.4	0
Realized losses from foreign currency exchange forward contracts		$ (21)	$ (3.8)	$ 0
[1]	Global Catastrophe program ended 2015

Investments - Components of Res

Investments - Components of Restricted Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Securities on deposit supporting Lloyd’s business	$ 161.8	$ 202.5
Total restricted investments	366.4	430.3
Securities Deposits For Regulatory and Other Purposes.
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Securities on deposit for regulatory and other purposes	168.7	192.8
Securities Pledged as Collateral [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Securities pledged as collateral for letters of credit	$ 35.9	$ 35

Investments - Financial Assets

Investments - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments		$ 4,324.3	$ 4,115.7
Other Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments		539	513.7
Short-Term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments		405.5	210.8
Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments		3,880.8	3,699.2
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[1]	1,048	811.6
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[2]	2,830.4	2,886.9
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[3]	2.4	0.7
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments		2,932.4	2,927.3
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Collateralized Loan Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments		264.3	216.6
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Residential Mortgage-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments		176.8	173.1
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[1]	228	150.4
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Collateralized Loan Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[1]	0	0
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Residential Mortgage-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[1]	0	0
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[2]	2,702.4	2,776.9
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Collateralized Loan Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[2]	264.3	216.6
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Residential Mortgage-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[2]	176.8	173.1
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[3]	2	0
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Collateralized Loan Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[3]	0	0
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Residential Mortgage-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[3]	0	0
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | U.S. Governments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments		271.2	207.9
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | U.S. Governments [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[1]	228	150.4
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | U.S. Governments [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[2]	43.2	57.5
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | U.S. Governments [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[3]	0	0
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Foreign Governments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments		237.3	243.1
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Foreign Governments [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[1]	0	0
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Foreign Governments [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[2]	237.3	243.1
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Foreign Governments [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[3]	0	0
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments		382.8	488
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Obligations of States and Political Subdivisions [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[1]	0	0
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Obligations of States and Political Subdivisions [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[2]	382.8	488
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Obligations of States and Political Subdivisions [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[3]	0	0
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Corporate Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments		1,320.7	1,319.9
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Corporate Bonds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[1]	0	0
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Corporate Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[2]	1,318.7	1,319.9
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Corporate Bonds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[3]	2	0
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Commercial Mortgage-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments		153.7	150.2
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Commercial Mortgage-backed Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[1]	0	0
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Commercial Mortgage-backed Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[2]	153.7	150.2
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Commercial Mortgage-backed Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[3]	0	0
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Asset-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments		125.6	128.5
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Asset-backed Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[1]	0	0
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Asset-backed Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[2]	125.6	128.5
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Asset-backed Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[3]	0	0
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments		447.4	463.9
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[1]	444.9	457.6
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[2]	2.1	5.6
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[3]	0.4	0.7
Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments		95.5	97.2
Fair Value, Measurements, Recurring [Member] | Other Investments [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[1]	0	0
Fair Value, Measurements, Recurring [Member] | Other Investments [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[2]	95.5	97.2
Fair Value, Measurements, Recurring [Member] | Other Investments [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[3]	0	0
Fair Value, Measurements, Recurring [Member] | Short-Term Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments		405.5	210.8
Fair Value, Measurements, Recurring [Member] | Short-Term Investments [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[1]	375.1	203.6
Fair Value, Measurements, Recurring [Member] | Short-Term Investments [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[2]	30.4	7.2
Fair Value, Measurements, Recurring [Member] | Short-Term Investments [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	[3]	$ 0	$ 0
[1]	Quoted prices in active markets for identical assets
[2]	Significant other observable inputs
[3]	Significant unobservable inputs

Investments - Schedule of Recon

Investments - Schedule of Reconciliation of Beginning and Ending Balances for Investments Categorized as Level 3 (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 0.7	$ 0.9
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	2	0
Issuances	0	0
Sales	(0.3)	(0.2)
Settlements	0	0
Ending balance	2.4	0.7
Amount of total gains or losses for the year included in net income (loss) attributable to the change in unrealized gains or losses relating to assets still held at end of period	0	0
Credit-Financial [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	0	0
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	2	0
Issuances	0	0
Sales	0	0
Settlements	0	0
Ending balance	2	0
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	0.7	0.9
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	(0.3)	(0.2)
Settlements	0	0
Ending balance	0.4	0.7
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

Reinsurance - Additional Inform

Reinsurance - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reinsurance Disclosures [Abstract]
Reinsurance recoverables, allowance for doubtful accounts	$ 2.1	$ 3.2
Amount of collateral under reinsurance agreement	492.6	421.6
Paid loss recoverables in insurance recoverables	215	130.8
Losses and loss adjustment expenses	810.1	766.1	$ 747.4
Net of amounts ceded to reinsurers	$ 419.3	$ 284.6	$ 246.6

Reinsurance - Schedule of Reins

Reinsurance - Schedule of Reinsurance Premium (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Premiums Written And Earned [Abstract]
Direct written premiums	$ 1,792.5	$ 1,651.4	$ 1,585.5
Reinsurance ceded to other companies	(724.6)	(610)	(537.5)
Reinsurance assumed from other companies	372.3	360.7	319.9
Net written premiums	1,440.2	1,402.1	1,367.9
Direct earned premiums	1,722.8	1,602.2	1,551.8
Reinsurance ceded to other companies	(675.8)	(563.7)	(524.8)
Reinsurance assumed from other companies	363.8	333.4	311.1
Net earned premiums	$ 1,410.8	$ 1,371.9	$ 1,338.1
Percentage of reinsurance assumed to net earned premiums	25.80%	24.30%	23.20%

Reserves for Losses and Loss 83

Reserves for Losses and Loss Adjustment Expenses - Reinsurance Recoverables (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Liability for Claims and Claims Adjustment Expense [Abstract]
Net reserves beginning of the year		$ 2,133.3	$ 2,137.1	$ 2,107.6
Losses and LAE incurred during current calendar year, net of reinsurance:
Current accident year		843.4	798.5	785.1
Prior accident years		(33.3)	(32.4)	(37.7)
Losses and LAE incurred during calendar year, net of reinsurance		810.1	766.1	747.4
Current accident year		178.9	169	185.9
Prior accident years		537.6	564.5	550.8
Losses and LAE payments made during current calendar year, net of reinsurance:		716.5	733.5	736.7
Change in participation interest	[1]	(36.3)	(1.2)	37.8
Foreign exchange adjustments		(10.4)	(35.2)	(19)
Net reserves - end of year		2,180.2	2,133.3	2,137.1
Reinsurance recoverables on unpaid losses and LAE, end of year		(1,170.6)	(990.3)	(905.3)
Reserves for losses and loss adjustment expenses		$ 3,350.8	$ 3,123.6	$ 3,042.4
[1]	Amount represents (decrease) increase in reserves due to change in our Syndicate 1200 participation.

Reserves for Losses and Loss 84

Reserves for Losses and Loss Adjustment Expenses - Impact from (Favorable) Unfavorable Development of Prior Accident Years' Loss and LAE Reserves on Each Reporting Segment (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total favorable prior-year development	$ (33.3)	$ (32.4)	$ (37.7)
Excess and Surplus Lines [Member]
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total favorable prior-year development	(13.2)	(25.5)	(38.9)
Commercial Specialty [Member]
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total favorable prior-year development	(22.7)	2.5	(1.7)
International Specialty [Member]
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total favorable prior-year development	(11)	(7.7)	(0.4)
Syndicate 1200 [Member]
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total favorable prior-year development	(5)	(10.3)	(21.1)
Run Off Lines [Member]
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total favorable prior-year development	$ 18.6	$ 8.6	$ 24.4

Reserves for Losses and Loss 85

Reserves for Losses and Loss Adjustment Expenses - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016Segment
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Claims remain outstanding period	10 years
Number of operating segments	4
Run Off Lines [Member] | Maximum [Member]
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Percentage of gross reserves for losses	9.00%

Reserves for Losses and Loss 86

Reserves for Losses and Loss Adjustment Expenses - Summary of Information about Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance, Excess and Surplus Lines Casualty Products (Detail) $ in Millions		Dec. 31, 2016USD ($)Claim	Dec. 31, 2015USD ($)	[1]	Dec. 31, 2014USD ($)	[1]	Dec. 31, 2013USD ($)	[1]	Dec. 31, 2012USD ($)	[1]	Dec. 31, 2011USD ($)	[1]
Claims Development [Line Items]
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance		$ 2,131.6
Excess and Surplus Lines [Member] | Casualty Products [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		1,301
Cumulative Paid Losses & ALAE, Net of Reinsurance		605.2
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance		96.8
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance		792.6
Excess and Surplus Lines [Member] | Casualty Products [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		192.8	$ 193.5		$ 200		$ 205.8		$ 206		$ 202.9
Cumulative Paid Losses & ALAE, Net of Reinsurance		162.4	146.6		122.9		91		53.8		$ 17.6
IBNR & Expected Development on Reported Claims		$ 21.1
Cumulative Number of Reported Claims | Claim	[2]	8,324
Excess and Surplus Lines [Member] | Casualty Products [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 184.4	183.6		189.7		196		189.6
Cumulative Paid Losses & ALAE, Net of Reinsurance		142.4	120.8		89.1		52.8		$ 17.2
IBNR & Expected Development on Reported Claims		$ 26.5
Cumulative Number of Reported Claims | Claim	[2]	7,222
Excess and Surplus Lines [Member] | Casualty Products [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 227.2	224.3		222.6		217.9
Cumulative Paid Losses & ALAE, Net of Reinsurance		135.2	100.4		60.2		$ 17.6
IBNR & Expected Development on Reported Claims		$ 51.5
Cumulative Number of Reported Claims | Claim	[2]	7,016
Excess and Surplus Lines [Member] | Casualty Products [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 213.1	215.1		213
Cumulative Paid Losses & ALAE, Net of Reinsurance		95.9	52.2		$ 15
IBNR & Expected Development on Reported Claims		$ 69.9
Cumulative Number of Reported Claims | Claim	[2]	5,978
Excess and Surplus Lines [Member] | Casualty Products [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 237	232.3
Cumulative Paid Losses & ALAE, Net of Reinsurance		51.9	$ 16.5
IBNR & Expected Development on Reported Claims		$ 131.2
Cumulative Number of Reported Claims | Claim	[2]	5,035
Excess and Surplus Lines [Member] | Casualty Products [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 246.5
Cumulative Paid Losses & ALAE, Net of Reinsurance		17.4
IBNR & Expected Development on Reported Claims		$ 190.8
Cumulative Number of Reported Claims | Claim	[2]	3,605
[1]	Information presented for calendar years prior to 2016 is required supplementary information and is unaudited.
[2]	The cumulative number of reported claims is measured at a coverage level by occurrence. Reported occurrences that do not result in a liability are included as reported claims.

Reserves for Losses and Loss 87

Reserves for Losses and Loss Adjustment Expenses - Summary of Information about Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance, Commercial Specialty Casualty Products (Detail) $ in Millions		Dec. 31, 2016USD ($)Claim	Dec. 31, 2015USD ($)	[1]	Dec. 31, 2014USD ($)	[1]	Dec. 31, 2013USD ($)	[1]	Dec. 31, 2012USD ($)	[1]	Dec. 31, 2011USD ($)	[1]
Claims Development [Line Items]
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance		$ 2,131.6
Commercial Specialty [Member] | Casualty Products [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		758.2
Cumulative Paid Losses & ALAE, Net of Reinsurance		454.3
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance		70.3
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance		374.2
Commercial Specialty [Member] | Casualty Products [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		154	$ 158.2		$ 157.5		$ 159		$ 155.1		$ 140.6
Cumulative Paid Losses & ALAE, Net of Reinsurance		135.1	126.1		111.3		85.9		57.5		$ 23.1
IBNR & Expected Development on Reported Claims		$ 9.1
Cumulative Number of Reported Claims | Claim	[2]	28,462
Commercial Specialty [Member] | Casualty Products [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 151.5	152.2		149.7		146.3		140.3
Cumulative Paid Losses & ALAE, Net of Reinsurance		120.8	105.3		80.7		51		$ 20.1
IBNR & Expected Development on Reported Claims		$ 15.3
Cumulative Number of Reported Claims | Claim	[2]	24,078
Commercial Specialty [Member] | Casualty Products [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 133.2	135.1		133.2		126.6
Cumulative Paid Losses & ALAE, Net of Reinsurance		93.6	73.6		49.4		$ 18.9
IBNR & Expected Development on Reported Claims		$ 16.9
Cumulative Number of Reported Claims | Claim	[2]	19,117
Commercial Specialty [Member] | Casualty Products [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 116.9	118.6		115.5
Cumulative Paid Losses & ALAE, Net of Reinsurance		58.7	38.4		$ 17.4
IBNR & Expected Development on Reported Claims		$ 29.1
Cumulative Number of Reported Claims | Claim	[2]	16,577
Commercial Specialty [Member] | Casualty Products [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 106.7	102.6
Cumulative Paid Losses & ALAE, Net of Reinsurance		35	$ 16.4
IBNR & Expected Development on Reported Claims		$ 40.5
Cumulative Number of Reported Claims | Claim	[2]	13,758
Commercial Specialty [Member] | Casualty Products [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 95.9
Cumulative Paid Losses & ALAE, Net of Reinsurance		11.1
IBNR & Expected Development on Reported Claims		$ 55.6
Cumulative Number of Reported Claims | Claim	[2]	9,720
[1]	Information presented for calendar years prior to 2016 is required supplementary information and is unaudited.
[2]	The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims.

Reserves for Losses and Loss 88

Reserves for Losses and Loss Adjustment Expenses - Summary of Information about Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance, Commercial Specialty Professional Products (Detail) $ in Millions		Dec. 31, 2016USD ($)Claim	Dec. 31, 2015USD ($)	[1]	Dec. 31, 2014USD ($)	[1]	Dec. 31, 2013USD ($)	[1]	Dec. 31, 2012USD ($)	[1]	Dec. 31, 2011USD ($)	[1]
Claims Development [Line Items]
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance		$ 2,131.6
Commercial Specialty [Member] | Professional Products [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		169.6
Cumulative Paid Losses & ALAE, Net of Reinsurance		86.8
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance		0.8
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance		83.6
Commercial Specialty [Member] | Professional Products [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		26.9	$ 28.2		$ 32.5		$ 35		$ 35		$ 35
Cumulative Paid Losses & ALAE, Net of Reinsurance		25.4	24		22		17.8		11.8		$ 3.2
IBNR & Expected Development on Reported Claims		$ 0.7
Cumulative Number of Reported Claims | Claim	[2]	815
Commercial Specialty [Member] | Professional Products [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 24	25.8		28.6		28.3		27.8
Cumulative Paid Losses & ALAE, Net of Reinsurance		21.4	19.9		16.9		8.6		$ 2.3
IBNR & Expected Development on Reported Claims		$ 1.7
Cumulative Number of Reported Claims | Claim	[2]	634
Commercial Specialty [Member] | Professional Products [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 19	21.1		21.5		20.9
Cumulative Paid Losses & ALAE, Net of Reinsurance		14.2	10.9		6.3		$ 1.9
IBNR & Expected Development on Reported Claims		$ 1.6
Cumulative Number of Reported Claims | Claim	[2]	611
Commercial Specialty [Member] | Professional Products [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 26	22.4		22.4
Cumulative Paid Losses & ALAE, Net of Reinsurance		15.1	5.4		$ 2.3
IBNR & Expected Development on Reported Claims		$ 3.3
Cumulative Number of Reported Claims | Claim	[2]	978
Commercial Specialty [Member] | Professional Products [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 29.5	29.9
Cumulative Paid Losses & ALAE, Net of Reinsurance		8.3	$ 1.8
IBNR & Expected Development on Reported Claims		$ 11.7
Cumulative Number of Reported Claims | Claim	[2]	1,647
Commercial Specialty [Member] | Professional Products [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 44.2
Cumulative Paid Losses & ALAE, Net of Reinsurance		2.4
IBNR & Expected Development on Reported Claims		$ 38.8
Cumulative Number of Reported Claims | Claim	[2]	2,392
[1]	Information presented for calendar years prior to 2016 is required supplementary information and is unaudited.
[2]	The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims.

Reserves for Losses and Loss 89

Reserves for Losses and Loss Adjustment Expenses - Summary of Information about Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance, International Specialty Casualty Products (Detail) $ in Millions		Dec. 31, 2016USD ($)Claim	Dec. 31, 2015USD ($)	[1]	Dec. 31, 2014USD ($)	[1]	Dec. 31, 2013USD ($)	[1]	Dec. 31, 2012USD ($)	[1]	Dec. 31, 2011USD ($)	[1]
Claims Development [Line Items]
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance		$ 2,131.6
International Specialty [Member] | Casualty Products [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		57
Cumulative Paid Losses & ALAE, Net of Reinsurance		2.9
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance		0.4
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance		54.5
International Specialty [Member] | Casualty Products [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		1.6	$ 2.2		$ 4.4		$ 6.6		$ 6.6		$ 6.6
Cumulative Paid Losses & ALAE, Net of Reinsurance		0	0		0		0		0		$ 0
IBNR & Expected Development on Reported Claims		$ 1.6
Cumulative Number of Reported Claims | Claim	[2]	1,416
International Specialty [Member] | Casualty Products [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 4.5	5.7		7.4		7.4		7.4
Cumulative Paid Losses & ALAE, Net of Reinsurance		0.1	0.1		0		0		$ 0
IBNR & Expected Development on Reported Claims		$ 4.4
Cumulative Number of Reported Claims | Claim	[2]	1,395
International Specialty [Member] | Casualty Products [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 9.6	9.6		9.5		9.1
Cumulative Paid Losses & ALAE, Net of Reinsurance		0.9	0.9		0.8		$ 0.4
IBNR & Expected Development on Reported Claims		$ 8.5
Cumulative Number of Reported Claims | Claim	[2]	1,416
International Specialty [Member] | Casualty Products [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 10.7	11		10.7
Cumulative Paid Losses & ALAE, Net of Reinsurance		0.8	0.7		$ 0.3
IBNR & Expected Development on Reported Claims		$ 6.7
Cumulative Number of Reported Claims | Claim	[2]	1,989
International Specialty [Member] | Casualty Products [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 15.3	12.6
Cumulative Paid Losses & ALAE, Net of Reinsurance		0.6	$ 0.3
IBNR & Expected Development on Reported Claims		$ 6.3
Cumulative Number of Reported Claims | Claim	[2]	2,487
International Specialty [Member] | Casualty Products [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 15.3
Cumulative Paid Losses & ALAE, Net of Reinsurance		0.5
IBNR & Expected Development on Reported Claims		$ 14.5
Cumulative Number of Reported Claims | Claim	[2]	2,531
[1]	Information presented for calendar years prior to 2016 is required supplementary information and is unaudited.
[2]	The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims.

Reserves for Losses and Loss 90

Reserves for Losses and Loss Adjustment Expenses - Summary of Information about Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance, International Specialty Professional (Detail) $ in Millions		Dec. 31, 2016USD ($)Contract	Dec. 31, 2015USD ($)	[1]	Dec. 31, 2014USD ($)	[1]	Dec. 31, 2013USD ($)	[1]	Dec. 31, 2012USD ($)	[1]	Dec. 31, 2011USD ($)	[1]
Claims Development [Line Items]
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance		$ 2,131.6
International Specialty [Member] | Professional Products [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		37.8
Cumulative Paid Losses & ALAE, Net of Reinsurance		7.6
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance		30.2
International Specialty [Member] | Professional Products [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		0.8	$ 1.3		$ 2.3		$ 3.2		$ 3.2		$ 3.2
Cumulative Paid Losses & ALAE, Net of Reinsurance		0	0		0		0		0		$ 0
IBNR & Expected Development on Reported Claims		$ 0.8
Cumulative Number of Reported Claims | Contract	[2]	789
International Specialty [Member] | Professional Products [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 2.7	2.7		3.4		3.5		3.5
Cumulative Paid Losses & ALAE, Net of Reinsurance		1.5	0		0		0		$ 0
IBNR & Expected Development on Reported Claims		$ 1.2
Cumulative Number of Reported Claims | Contract	[2]	986
International Specialty [Member] | Professional Products [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 4.9	6.2		6.4		5.8
Cumulative Paid Losses & ALAE, Net of Reinsurance		1.4	1.4		0.9		$ 0.5
IBNR & Expected Development on Reported Claims		$ 3.2
Cumulative Number of Reported Claims | Contract	[2]	1,124
International Specialty [Member] | Professional Products [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 7.6	8.1		8.2
Cumulative Paid Losses & ALAE, Net of Reinsurance		1.7	1.3		$ 0.7
IBNR & Expected Development on Reported Claims		$ 4.7
Cumulative Number of Reported Claims | Contract	[2]	1,275
International Specialty [Member] | Professional Products [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 10.8	10.8
Cumulative Paid Losses & ALAE, Net of Reinsurance		2.1	$ 1.3
IBNR & Expected Development on Reported Claims		$ 7.5
Cumulative Number of Reported Claims | Contract	[2]	1,305
International Specialty [Member] | Professional Products [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 11
Cumulative Paid Losses & ALAE, Net of Reinsurance		0.9
IBNR & Expected Development on Reported Claims		$ 8.7
Cumulative Number of Reported Claims | Contract	[2]	1,315
[1]	Information presented for calendar years prior to 2016 is required supplementary information and is unaudited.
[2]	The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims.

Reserves for Losses and Loss 91

Reserves for Losses and Loss Adjustment Expenses - Summary of Information about Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance, International Specialty Property Products (Detail) $ in Millions		Dec. 31, 2016USD ($)Claim	Dec. 31, 2015USD ($)	[1]	Dec. 31, 2014USD ($)	[1]	Dec. 31, 2013USD ($)	[1]	Dec. 31, 2012USD ($)	[1]	Dec. 31, 2011USD ($)	[1]
Claims Development [Line Items]
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance		$ 2,131.6
International Specialty [Member] | Property Products [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		278.1
Cumulative Paid Losses & ALAE, Net of Reinsurance		219
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance		4.4
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance		63.5
International Specialty [Member] | Property Products [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		102.1	$ 102.2		$ 102.9		$ 105		$ 102.9		$ 114.9
Cumulative Paid Losses & ALAE, Net of Reinsurance		97.2	96		93.7		86.2		65.1		$ 39.9
IBNR & Expected Development on Reported Claims		$ 0
Cumulative Number of Reported Claims | Claim	[2]	400
International Specialty [Member] | Property Products [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 46.5	51.7		50.5		51.5		47.3
Cumulative Paid Losses & ALAE, Net of Reinsurance		44.1	49.7		40.7		31.2		$ 12.4
IBNR & Expected Development on Reported Claims		$ 0.9
Cumulative Number of Reported Claims | Claim	[2]	299
International Specialty [Member] | Property Products [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 33.3	35.1		35.7		33.9
Cumulative Paid Losses & ALAE, Net of Reinsurance		30.8	28.5		18.7		$ 4.9
IBNR & Expected Development on Reported Claims		$ 0.8
Cumulative Number of Reported Claims | Claim	[2]	351
International Specialty [Member] | Property Products [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 26.2	28.2		28
Cumulative Paid Losses & ALAE, Net of Reinsurance		20.3	13.7		$ 3.3
IBNR & Expected Development on Reported Claims		$ 2.6
Cumulative Number of Reported Claims | Claim	[2]	339
International Specialty [Member] | Property Products [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 24.5	28.2
Cumulative Paid Losses & ALAE, Net of Reinsurance		11.8	$ 4.6
IBNR & Expected Development on Reported Claims		$ 5.5
Cumulative Number of Reported Claims | Claim	[2]	443
International Specialty [Member] | Property Products [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance		$ 45.5
Cumulative Paid Losses & ALAE, Net of Reinsurance		14.8
IBNR & Expected Development on Reported Claims		$ 19.5
Cumulative Number of Reported Claims | Claim	[2]	742
[1]	Information presented for calendar years prior to 2016 is required supplementary information and is unaudited.
[2]	The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims.

Reserves for Losses and Loss 92

Reserves for Losses and Loss Adjustment Expenses - Summary of Information about Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance, Syndicate 1200 Casualty Products (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	[1]	Dec. 31, 2014	[1]	Dec. 31, 2013	[1]	Dec. 31, 2012	[1]	Dec. 31, 2011	[1]	Dec. 31, 2010	[1]
Claims Development [Line Items]
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	$ 2,131.6
Syndicate 1200 [Member] | Casualty Products [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	143.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	47
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	96.4
Syndicate 1200 [Member] | Casualty Products [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	5.8	$ 5.8		$ 5.9		$ 6.1		$ 4.5		$ 4.8		$ 5.7
Cumulative Paid Losses & ALAE, Net of Reinsurance	3.7	2.8		2		1.1		0.6		0.2		$ 0
IBNR & Expected Development on Reported Claims	1.1
Syndicate 1200 [Member] | Casualty Products [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	10.1	10.2		10.9		10.8		8.6		8
Cumulative Paid Losses & ALAE, Net of Reinsurance	6.9	5.4		3.4		1.6		0.8		$ 0.2
IBNR & Expected Development on Reported Claims	2.1
Syndicate 1200 [Member] | Casualty Products [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	13.8	14.1		14.8		10.8		8.7
Cumulative Paid Losses & ALAE, Net of Reinsurance	8.2	5.8		2.6		1.1		$ 0.4
IBNR & Expected Development on Reported Claims	3.6
Syndicate 1200 [Member] | Casualty Products [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	24.5	26.2		26.7		22.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	11.3	7		3.2		$ 1.5
IBNR & Expected Development on Reported Claims	7.3
Syndicate 1200 [Member] | Casualty Products [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	33.8	36.2		37.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	9.9	4.6		$ 1.9
IBNR & Expected Development on Reported Claims	13.8
Syndicate 1200 [Member] | Casualty Products [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	29.2	33.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	5.2	$ 0.8
IBNR & Expected Development on Reported Claims	17.8
Syndicate 1200 [Member] | Casualty Products [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	26.2
Cumulative Paid Losses & ALAE, Net of Reinsurance	1.8
IBNR & Expected Development on Reported Claims	$ 21.5
[1]	Information presented for calendar years prior to 2016 is required supplementary information and is unaudited.

Reserves for Losses and Loss 93

Reserves for Losses and Loss Adjustment Expenses - Summary of Information about Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance, Syndicate 1200 Professional Products (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	[1]	Dec. 31, 2014	[1]	Dec. 31, 2013	[1]	Dec. 31, 2012	[1]	Dec. 31, 2011	[1]	Dec. 31, 2010	[1]
Claims Development [Line Items]
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	$ 2,131.6
Syndicate 1200 [Member] | Professional Products [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	165.3
Cumulative Paid Losses & ALAE, Net of Reinsurance	60.8
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	104.5
Syndicate 1200 [Member] | Professional Products [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	9.3	$ 9.2		$ 9.9		$ 11		$ 12.4		$ 12.5		$ 15.2
Cumulative Paid Losses & ALAE, Net of Reinsurance	6.3	5		3.7		2.9		1.9		0.9		$ 0.1
IBNR & Expected Development on Reported Claims	1.9
Syndicate 1200 [Member] | Professional Products [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	14.4	14.3		15.1		18.1		20.5		18.7
Cumulative Paid Losses & ALAE, Net of Reinsurance	10.4	8.1		6.4		4.1		2.4		$ 1
IBNR & Expected Development on Reported Claims	3.1
Syndicate 1200 [Member] | Professional Products [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	13.8	13.7		13.8		13.6		13.7
Cumulative Paid Losses & ALAE, Net of Reinsurance	8	5.6		4.2		1.8		$ 0.6
IBNR & Expected Development on Reported Claims	3.3
Syndicate 1200 [Member] | Professional Products [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	22	22.4		22.3		22.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	11.5	7		3.6		$ 1.6
IBNR & Expected Development on Reported Claims	7
Syndicate 1200 [Member] | Professional Products [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	35.9	35.5		34.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	14.5	6.3		$ 1.6
IBNR & Expected Development on Reported Claims	13.1
Syndicate 1200 [Member] | Professional Products [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	36.7	37.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	8.1	$ 2.2
IBNR & Expected Development on Reported Claims	20.4
Syndicate 1200 [Member] | Professional Products [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	33.2
Cumulative Paid Losses & ALAE, Net of Reinsurance	2
IBNR & Expected Development on Reported Claims	$ 28.7
[1]	Information presented for calendar years prior to 2016 is required supplementary information and is unaudited.

Reserves for Losses and Loss 94

Reserves for Losses and Loss Adjustment Expenses - Summary of Information about Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance, Syndicate 1200 Property Products (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	[1]	Dec. 31, 2014	[1]	Dec. 31, 2013	[1]	Dec. 31, 2012	[1]	Dec. 31, 2011	[1]	Dec. 31, 2010	[1]
Claims Development [Line Items]
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	$ 2,131.6
Syndicate 1200 [Member] | Property Products [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	511.4
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	101.7
Cumulative Paid Losses & ALAE, Net of Reinsurance	409.7
Syndicate 1200 [Member] | Property Products [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	50.3	$ 50.9		$ 51.1		$ 53.8		$ 54.3		$ 57.9		$ 50.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	41.3	39.8		35.6		33.6		27.8		19.4		$ 1.8
IBNR & Expected Development on Reported Claims	12.8
Syndicate 1200 [Member] | Property Products [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	91.7	92.4		94.2		106.8		112.6		107.3
Cumulative Paid Losses & ALAE, Net of Reinsurance	80.7	78.9		73.1		61.4		46.8		$ 23.2
IBNR & Expected Development on Reported Claims	23.6
Syndicate 1200 [Member] | Property Products [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	90.5	91.6		92.5		88.1		88.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	76	73.6		62.6		47.5		$ 29.3
IBNR & Expected Development on Reported Claims	23.7
Syndicate 1200 [Member] | Property Products [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	76.5	78.1		79.1		83.2
Cumulative Paid Losses & ALAE, Net of Reinsurance	73	68.9		56.5		$ 44.2
IBNR & Expected Development on Reported Claims	20.1
Syndicate 1200 [Member] | Property Products [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	65.4	64.1		69.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	57.3	51.3		$ 29.3
IBNR & Expected Development on Reported Claims	16.1
Syndicate 1200 [Member] | Property Products [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	64.9	54.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	42.6	$ 22.8
IBNR & Expected Development on Reported Claims	17.3
Syndicate 1200 [Member] | Property Products [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	72.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	38.8
IBNR & Expected Development on Reported Claims	$ 36.4
[1]	Information presented for calendar years prior to 2016 is required supplementary information and is unaudited.

Reserves for Losses and Loss 95

Reserves for Losses and Loss Adjustment Expenses - Summary of Reconciliation of Net Incurred and Paid Development to Liability for Unpaid Losses and LAE in Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	$ 2,131.6
Total reinsurance recoverables on unpaid losses and LAE	1,170.6
Unallocated loss adjustment expenses	68
Unamortized reserve discount	(19.4)	$ (21.5)	$ (23.7)
Gross liability for unpaid losses and LAE	3,350.8	3,123.6	3,042.4
Other Lines [Member]
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	227.1
Total reinsurance recoverables on unpaid losses and LAE	175.9
Excess and Surplus Lines [Member] | Casualty Products [Member]
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	792.6
Total reinsurance recoverables on unpaid losses and LAE	261
Commercial Specialty [Member] | Casualty Products [Member]
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	374.2
Total reinsurance recoverables on unpaid losses and LAE	239.6
Unamortized reserve discount	(10.3)	(10.3)	(9.5)
Commercial Specialty [Member] | Professional Products [Member]
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	83.6
Total reinsurance recoverables on unpaid losses and LAE	51.5
International Specialty [Member] | Casualty Products [Member]
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	54.5
Total reinsurance recoverables on unpaid losses and LAE	115.2
International Specialty [Member] | Professional Products [Member]
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	30.2
Total reinsurance recoverables on unpaid losses and LAE	39
International Specialty [Member] | Property Products [Member]
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	63.5
Total reinsurance recoverables on unpaid losses and LAE	18.6
Syndicate 1200 [Member] | Casualty Products [Member]
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	96.4
Total reinsurance recoverables on unpaid losses and LAE	54.3
Syndicate 1200 [Member] | Professional Products [Member]
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	104.5
Total reinsurance recoverables on unpaid losses and LAE	59.9
Syndicate 1200 [Member] | Property Products [Member]
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	101.7
Total reinsurance recoverables on unpaid losses and LAE	58.9
Run Off Lines [Member]
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	203.3
Total reinsurance recoverables on unpaid losses and LAE	96.7
Unamortized reserve discount	$ (9.1)	$ (11.2)	$ (14.2)

Reserves for Losses and Loss 96

Reserves for Losses and Loss Adjustment Expenses - Schedule of Supplementary Unaudited Information About Annual Percentage Payout of Incurred Losses and ALAE, Net of Reinsurance (Detail)	Dec. 31, 2016	[1]
Excess and Surplus Lines [Member] | Casualty Products [Member]
Shortduration Insurance Contracts Historical Claims Duration [Line Items]
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 1	8.40%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 2	18.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 3	19.40%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 4	16.30%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 5	11.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 6	8.10%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 7	0.00%
Commercial Specialty [Member] | Casualty Products [Member]
Shortduration Insurance Contracts Historical Claims Duration [Line Items]
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 1	14.60%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 2	20.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 3	18.40%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 4	15.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 5	9.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 6	6.60%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 7	0.00%
Commercial Specialty [Member] | Professional Products [Member]
Shortduration Insurance Contracts Historical Claims Duration [Line Items]
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 1	9.60%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 2	23.90%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 3	29.80%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 4	14.60%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 5	6.40%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 6	5.10%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 7	0.00%
International Specialty [Member] | Casualty Products [Member]
Shortduration Insurance Contracts Historical Claims Duration [Line Items]
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 1	11.50%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 2	12.80%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 3	17.50%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 4	14.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 5	10.50%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 6	8.40%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 7	0.00%
International Specialty [Member] | Professional Products [Member]
Shortduration Insurance Contracts Historical Claims Duration [Line Items]
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 1	6.50%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 2	17.20%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 3	23.60%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 4	15.40%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 5	11.80%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 6	10.20%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 7	0.00%
International Specialty [Member] | Property Products [Member]
Shortduration Insurance Contracts Historical Claims Duration [Line Items]
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 1	16.80%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 2	41.20%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 3	23.50%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 4	9.90%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 5	4.10%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 6	2.00%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 7	0.00%
Syndicate 1200 [Member] | Casualty Products [Member]
Shortduration Insurance Contracts Historical Claims Duration [Line Items]
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 1	3.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 2	7.60%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 3	13.20%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 4	20.40%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 5	21.80%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 6	11.00%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 7	7.10%
Syndicate 1200 [Member] | Professional Products [Member]
Shortduration Insurance Contracts Historical Claims Duration [Line Items]
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 1	4.30%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 2	9.30%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 3	15.00%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 4	15.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 5	14.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 6	16.60%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 7	7.30%
Syndicate 1200 [Member] | Property Products [Member]
Shortduration Insurance Contracts Historical Claims Duration [Line Items]
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 1	38.40%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 2	24.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 3	15.10%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 4	10.90%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 5	5.00%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 6	2.50%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance,Year 7	1.30%
[1]	The average annual percentage payout is calculated from a paid losses and ALAE development pattern based on an actuarial analysis of the paid losses and ALAE movements by accident year for each disaggregation category. The paid losses and ALAE development pattern provides the expected percentage of ultimate losses and ALAE to be paid in each year. The pattern considers all accident years included in the claims development tables.

Reserves for Losses and Loss 97

Reserves for Losses and Loss Adjustment Expenses - Schedule of Information About Discounted Liabilities For Unpaid Losses and LAE (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shortduration Insurance Contracts Discounted Liabilities [Line Items]
Carrying Amount of Reserves for Losses & LAE		$ 305.6	$ 315.3	$ 318.5
Aggregate Amount of Discount		19.4	21.5	23.7
Interest Accretion	[1]	4	4.2	4.2
Commercial Specialty [Member] | Casualty Products [Member]
Shortduration Insurance Contracts Discounted Liabilities [Line Items]
Carrying Amount of Reserves for Losses & LAE		121.1	121.6	114.4
Aggregate Amount of Discount		10.3	10.3	9.5
Interest Accretion	[1]	$ 1.9	$ 1.1	$ 2.1
Discount Rate		2.25%	2.25%	2.25%
Run Off Lines [Member]
Shortduration Insurance Contracts Discounted Liabilities [Line Items]
Carrying Amount of Reserves for Losses & LAE		$ 184.5	$ 193.7	$ 204.1
Aggregate Amount of Discount		9.1	11.2	14.2
Interest Accretion	[1]	$ 2.1	$ 3.1	$ 2.1
Discount Rate		3.50%	3.50%	3.50%
[1]	Interest accretion is recorded in the line item “Losses and loss adjustment expenses” in our Consolidated Statements of Income

Run-Off Lines - Gross Reserves

Run-Off Lines - Gross Reserves for Run-Off Lines (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	$ 48.4	$ 46.4
Total Run-off Lines	290.9	306.3
Reinsurance Assumed [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	28.4	34.6
Other [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	20	11.8
Risk Management [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Run-off Lines	236.9	252.2
Run-Off Reinsurance Lines [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Run-off Lines	1.9	3
Other Run-Off Lines [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Run-off Lines	$ 3.7	$ 4.7

Run-Off Lines - Total Gross Res

Run-Off Lines - Total Gross Reserves for Asbestos Exposure (Detail) - Asbestos and Environmental Claims [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total direct written reserves	$ 15.4	$ 10.7	$ 11.1
Total asbestos reserves	41.9	42.8	47.8
Case Reserves [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total direct written reserves	2.8	2	2.5
ULAE [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total direct written reserves	0.5	0.5	1
IBNR [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total direct written reserves	12.1	8.2	7.6
Assumed domestic [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total assumed reserves	21.8	26.7	30.6
Assumed domestic [Member] | Case Reserves [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total assumed reserves	10.5	12.2	13.2
Assumed domestic [Member] | ULAE [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total assumed reserves	0.8	0.8	1.6
Assumed domestic [Member] | IBNR [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total assumed reserves	10.5	13.7	15.8
Assumed London [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total assumed reserves	4.7	5.4	6.1
Assumed London [Member] | Case Reserves [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total assumed reserves	3.3	4	4.7
Assumed London [Member] | ULAE [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total assumed reserves	0	0	0.2
Assumed London [Member] | IBNR [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total assumed reserves	$ 1.4	$ 1.4	$ 1.2

Run-Off Lines - Results for Run

Run-Off Lines - Results for Run-Off Lines (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	$ (10.9)	$ (4.4)	$ (13.3)
Total Run-off Lines	(25.1)	(14.1)	(31)
Reinsurance Assumed [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	(1.3)	(1)	(8.3)
Other [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	(9.6)	(3.4)	(5)
Risk Management [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Run-off Lines	(13.1)	(8.2)	(15.5)
Run-Off Reinsurance Lines [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Run-off Lines	0.1	2	(1.5)
Other Run-Off Lines [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total Run-off Lines	$ (1.2)	$ (3.5)	$ (0.7)

Junior Subordinated Debentur101

Junior Subordinated Debentures - Additional Information (Detail) - USD ($)	Jul. 16, 2014	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Junior subordinated debentures	$ 20,000,000	$ 172,700,000	$ 172,700,000
Junior Subordinated Debentures [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage		100.00%	100.00%
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

Junior Subordinated Debentur102

Junior Subordinated Debentures - Schedule of Junior Subordinated Debentures (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Jul. 16, 2014
Debt Instrument [Line Items]
Junior subordinated debentures, Amount	$ 172,700,000	$ 172,700,000	$ 20,000,000
Argo Group [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Amount	$ 28,400,000	$ 28,400,000
PXRE Capital Statutory Trust II [Member] | Argo Group [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	May 15, 2003	May 15, 2003
Junior subordinated debentures, Maturity date	May 15, 2033	May 15, 2033
Junior subordinated debentures, Rate Structure	2016 and 2015: 3M LIBOR + 4.10%
Junior subordinated debentures, interest rate stated percentage	5.00%	4.46%
Junior subordinated debentures, Amount	$ 18,100,000	$ 18,100,000
PXRE Capital Trust VI [Member] | Argo Group [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	Nov. 6, 2003	Nov. 6, 2003
Junior subordinated debentures, Maturity date	Sep. 30, 2033	Sep. 30, 2033
Junior subordinated debentures, Rate Structure	2016 and 2015: 3M LIBOR + 3.90%
Junior subordinated debentures, interest rate stated percentage	4.90%	4.51%
Junior subordinated debentures, Amount	$ 10,300,000	$ 10,300,000
Argonaut Group Statutory Trust I [Member] | Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	May 15, 2003	May 15, 2003
Junior subordinated debentures, Maturity date	May 15, 2033	May 15, 2033
Junior subordinated debentures, Rate Structure	2016 and 2015: 3M LIBOR + 4.10%
Junior subordinated debentures, interest rate stated percentage	5.00%	4.46%
Junior subordinated debentures, Amount	$ 15,500,000	$ 15,500,000
Argonaut Group Statutory Trust III [Member] | Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	Dec. 16, 2003	Dec. 16, 2003
Junior subordinated debentures, Maturity date	Jan. 8, 2034	Jan. 8, 2034
Junior subordinated debentures, Rate Structure	2016 and 2015: 3M LIBOR + 4.10%
Junior subordinated debentures, interest rate stated percentage	4.98%	4.42%
Junior subordinated debentures, Amount	$ 12,300,000	$ 12,300,000
Argonaut Group Statutory Trust IV [Member] | Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	Apr. 29, 2004	Apr. 29, 2004
Junior subordinated debentures, Maturity date	Apr. 29, 2034	Apr. 29, 2034
Junior subordinated debentures, Rate Structure	2016 and 2015: 3M LIBOR + 3.85%
Junior subordinated debentures, interest rate stated percentage	4.76%	4.21%
Junior subordinated debentures, Amount	$ 13,400,000	$ 13,400,000
Argonaut Group Statutory Trust V [Member] | Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	May 26, 2004	May 26, 2004
Junior subordinated debentures, Maturity date	May 24, 2034	May 24, 2034
Junior subordinated debentures, Rate Structure	2016 and 2015: 3M LIBOR + 3.85%
Junior subordinated debentures, interest rate stated percentage	4.77%	4.23%
Junior subordinated debentures, Amount	$ 12,300,000	$ 12,300,000
Argonaut Group Statutory Trust VI [Member] | Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	May 12, 2004	May 12, 2004
Junior subordinated debentures, Maturity date	May 12, 2034	May 12, 2034
Junior subordinated debentures, Rate Structure	2016 and 2015: 3M LIBOR + 3.80%
Junior subordinated debentures, interest rate stated percentage	4.79%	4.33%
Junior subordinated debentures, Amount	$ 13,400,000	$ 13,400,000
Argonaut Group Statutory Trust VII [Member] | Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	Sep. 17, 2004	Sep. 17, 2004
Junior subordinated debentures, Maturity date	Dec. 15, 2034	Dec. 15, 2034
Junior subordinated debentures, Rate Structure	2016 and 2015: 3M LIBOR + 3.60%
Junior subordinated debentures, interest rate stated percentage	4.56%	4.11%
Junior subordinated debentures, Amount	$ 15,500,000	$ 15,500,000
Argonaut Group Statutory Trust VIII [Member] | Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	Sep. 22, 2004	Sep. 22, 2004
Junior subordinated debentures, Maturity date	Sep. 22, 2034	Sep. 22, 2034
Junior subordinated debentures, Rate Structure	2016 and 2015: 3M LIBOR + 3.55%
Junior subordinated debentures, interest rate stated percentage	4.55%	4.14%
Junior subordinated debentures, Amount	$ 15,500,000	$ 15,500,000
Argonaut Group Statutory Trust IX [Member] | Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	Oct. 22, 2004	Oct. 22, 2004
Junior subordinated debentures, Maturity date	Dec. 15, 2034	Dec. 15, 2034
Junior subordinated debentures, Rate Structure	2016 and 2015: 3M LIBOR + 3.60%
Junior subordinated debentures, interest rate stated percentage	4.56%	4.11%
Junior subordinated debentures, Amount	$ 15,500,000	$ 15,500,000
Argonaut Group Statutory Trust X [Member] | Argo Group US [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	Sep. 15, 2005	Sep. 15, 2005
Junior subordinated debentures, Maturity date	Sep. 15, 2035	Sep. 15, 2035
Junior subordinated debentures, Rate Structure	2016 and 2015: 3M LIBOR + 3.40%
Junior subordinated debentures, interest rate stated percentage	4.36%	3.91%
Junior subordinated debentures, Amount	$ 30,900,000	$ 30,900,000

Other Indebtedness - Additional

Other Indebtedness - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Jan. 31, 2017	Mar. 07, 2014
Debt Instrument [Line Items]
Floating rate loan stock denominated in Euros	$ 38,300,000	$ 38,100,000
Maybrooke [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Rate Structure	one-month LIBOR rate plus 1.625%.
Maybrooke [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, interest rate stated percentage			1.625%
Revolving Credit Facility | Maybrooke [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Drew under credit facility to fund the acquisition			$ 125,000,000
Credit Agreement [Member] | Revolving Credit Facility | J P Morgan Chase Bank
Debt Instrument [Line Items]
Letter of credit facility amount				$ 175,000,000
Revolving credit facility maturity date	Mar. 7, 2018
Credit Agreement [Member] | Letter Of Credit | J P Morgan Chase Bank
Debt Instrument [Line Items]
Letter of credit facility amount	$ 17,500,000
Letter of credit facility amount	$ 0	$ 200,000		200,000
Previous Credit Agreement [Member] | Revolving Credit Facility
Debt Instrument [Line Items]
Letter of credit facility amount				150,000,000
Maximum borrowing capacity under revolving credit facility before amendment				$ 150,000,000
Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%	100.00%
Other Debt - Note Payable [Member]
Debt Instrument [Line Items]
Note payable as part of ARIS acquisition	$ 600,000	$ 600,000
Debt instrument maturity date	Apr. 1, 2019
Debt instrument, interest rate terms	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.
Other Debt - Note Payable [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Variable interest rate of note payable, above 30-day LIBOR	2.00%

Other Indebtedness - Schedule o

Other Indebtedness - Schedule of Floating Rate Loan Stock, Notes Outstanding (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Other indebtedness, Amount	$ 54.8	$ 54.6
Floating Rate Loan Stock, U.S. Dollar, Start Year 2004 [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	Dec. 8, 2004	Dec. 8, 2004
Debt instrument maturity date	Nov. 15, 2034	Nov. 15, 2034
Other indebtedness, Rate Structure	2016 and 2015: 6 month LIBOR + 4.2%
Junior subordinated debentures, interest rate stated percentage	5.18%	4.66%
Other indebtedness, Amount	$ 6.5	$ 6.5
Floating Rate Loan Stock, Euro, Start Year 2005 [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	Sep. 6, 2005	Sep. 6, 2005
Debt instrument maturity date	Aug. 22, 2035	Aug. 22, 2035
Other indebtedness, Rate Structure	2016 and 2015: 3 month LIBOR + 4.0%
Junior subordinated debentures, interest rate stated percentage	3.70%	3.91%
Other indebtedness, Amount	$ 12.8	$ 12.7
Floating Rate Loan Stock, U.S. Dollar, Start Year 2006 [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	Oct. 31, 2006	Oct. 31, 2006
Debt instrument maturity date	Jan. 15, 2036	Jan. 15, 2036
Other indebtedness, Rate Structure	2016 and 2015: 6 month LIBOR + 4.0%
Junior subordinated debentures, interest rate stated percentage	4.98%	4.46%
Other indebtedness, Amount	$ 10	$ 10
Floating Rate Loan Stock, Euro, Start Year 2006 [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	Oct. 31, 2006	Oct. 31, 2006
Debt instrument maturity date	Nov. 22, 2036	Nov. 22, 2036
Other indebtedness, Rate Structure	2016 and 2015: 3 month LIBOR + 4.0%
Junior subordinated debentures, interest rate stated percentage	3.70%	3.91%
Other indebtedness, Amount	$ 11.2	$ 11.1
Floating Rate Loan Stock, Euro, Start Year 2007 [Member]
Debt Instrument [Line Items]
Junior subordinated debentures, Issue date	Jun. 8, 2007	Jun. 8, 2007
Debt instrument maturity date	Sep. 15, 2037	Sep. 15, 2037
Other indebtedness, Rate Structure	2016 and 2015: 3 month LIBOR + 3.9%
Junior subordinated debentures, interest rate stated percentage	3.58%	3.86%
Other indebtedness, Amount	$ 14.3	$ 14.3

Disclosures about Fair Value105

Disclosures about Fair Value of Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Financial Instruments Owned and Pledged as Collateral [Line Items]
Premiums receivable	$ 463.8	$ 404.5
Reinsurance recoverables	1,385.6	1,121.1
Premiums receivable, allowance for doubtful accounts	2.7	3.5
Reinsurance recoverables, allowance for doubtful accounts	2.1	3.2
Over 90 Days [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Premiums receivable	14.3	10
Reinsurance recoverables	11.2	7.1
Reinsurance recoverables, allowance for doubtful accounts	2.1	2.2
Premiums receivables, secured by collateral	0.1	0.2
Reinsurance recoverables, secured by collateral	$ 0.6	$ 0.7

Disclosures about Fair Value106

Disclosures about Fair Value of Financial Instruments - Summary of Company's Financial Instruments Whose Carrying Amount Did Not Equal Fair Value (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	$ 367.6	$ 367.2
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	353.8	361.6
Junior Subordinated Debentures [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	172.7	172.7
Junior Subordinated Debentures [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	162.4	166.5
Senior Unsecured Fixed Rate Notes [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	139.5	139.3
Senior Unsecured Fixed Rate Notes [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	139.3	141.8
Other Indebtedness [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	54.8	54.6
Other Indebtedness [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	51.5	52.7
Other Indebtedness [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	0.6	0.6
Other Indebtedness [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Instruments	$ 0.6	$ 0.6

Shareholders Equity - Additiona

Shareholders Equity - Additional Information (Detail) - USD ($)	Feb. 21, 2017	May 03, 2016	Feb. 17, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class Of Stock [Line Items]
Dividends declared per common share				$ 0.86	$ 0.73	$ 0.57
Dividends declaration date		May 3, 2016	Feb. 17, 2015
Dividends payable date		Jun. 15, 2016	Mar. 16, 2015
Dividend payable, date of record		Jun. 1, 2016	Mar. 2, 2015
Stock dividend declared		10.00%	10.00%	10.00%	10.00%
Additional stock issued as dividend		2,735,542	2,554,506
Cash dividends paid - common shares, total				$ 26,600,000	$ 22,700,000	$ 18,200,000
Preferred shares, authorized				30,000,000
Preferred shares, par value				$ 1
Preferred shares, issued				0	0
Preferred shares, outstanding				0	0
Common shares repurchased on open market				847,111	575,155	1,048,144
Common shares repurchased on open market, total cost				$ 47,100,000	$ 29,700,000	$ 50,800,000
2016 Repurchase Authorization [Member]
Class Of Stock [Line Items]
Total number of shares authorized for purchase, Value		$ 150,000,000		$ 130,300,000
Common shares repurchased on open market				847,111	575,155
Common shares repurchased on open market, total cost				$ 47,100,000	$ 29,700,000
Before 2016 Adjustment Stock Dividend [Member]
Class Of Stock [Line Items]
Dividends declared per common share					$ 0.80
Before 2016 and 2015 Adjustment Stock Dividend [Member]
Class Of Stock [Line Items]
Dividends declared per common share						$ 0.69
Subsequent Event [Member]
Class Of Stock [Line Items]
Dividends declared per common share	$ 0.27
Dividends declaration date	Feb. 21, 2017
Dividends payable date	Mar. 15, 2017
Dividend payable, date of record	Mar. 3, 2017

Shareholders Equity - Schedule

Shareholders Equity - Schedule of Repurchase of Shares (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity Class Of Treasury Stock [Line Items]
Common shares repurchased on open market	847,111	575,155	1,048,144
Average Price of Shares Repurchased	$ 55.64	$ 51.58	$ 48.48
Total Cost (in millions)	$ 47.1	$ 29.7	$ 50.8
10b5-1 Trading Plan Initiated In 12/16/2015 [Member]
Equity Class Of Treasury Stock [Line Items]
Date Trading Plan Initiated	Dec. 16, 2015
Trading Plan Purchase Period Start Date	Jan. 4, 2016
Common shares repurchased on open market	266,538
Average Price of Shares Repurchased	$ 55.59
Total Cost (in millions)	$ 14.8
Repurchase Authorization Year	2,013
Trading Plan Purchase Period End Date	Feb. 11, 2016
10b5-1 Trading Plan Initiated In 03/16/2016 [Member]
Equity Class Of Treasury Stock [Line Items]
Date Trading Plan Initiated	Mar. 16, 2016
Trading Plan Purchase Period Start Date	Mar. 16, 2016
Common shares repurchased on open market	162,893
Average Price of Shares Repurchased	$ 55.62
Total Cost (in millions)	$ 9.1
Repurchase Authorization Year	2,013
Trading Plan Purchase Period End Date	May 2, 2016
10b5-1 Trading Plan Initiated In 06/16/2016 [Member]
Equity Class Of Treasury Stock [Line Items]
Date Trading Plan Initiated	Jun. 16, 2016
Trading Plan Purchase Period Start Date	Jun. 24, 2016
Common shares repurchased on open market	14,774
Average Price of Shares Repurchased	$ 49.78
Total Cost (in millions)	$ 0.7
Repurchase Authorization Year	2,016
Trading Plan Purchase Period End Date	Jun. 28, 2016
10b5-1 Trading Plan Initiated In 09/15/2016 [Member]
Equity Class Of Treasury Stock [Line Items]
Date Trading Plan Initiated	Sep. 15, 2016
Trading Plan Purchase Period Start Date	Sep. 19, 2016
Common shares repurchased on open market	43,062
Average Price of Shares Repurchased	$ 55.23
Total Cost (in millions)	$ 2.4
Repurchase Authorization Year	2,016
Trading Plan Purchase Period End Date	Nov. 2, 2016
Open Market Repurchase Authorization Two Thousand And Sixteen [Member]
Equity Class Of Treasury Stock [Line Items]
Trading Plan Purchase Period Start Date	May 3, 2016
Common shares repurchased on open market	295,380
Average Price of Shares Repurchased	$ 56.38
Total Cost (in millions)	$ 16.6
Repurchase Authorization Year	2,016
Trading Plan Purchase Period End Date	Sep. 30, 2016
Open Market Repurchase Authorization Two Thousand And Thirteen [Member]
Equity Class Of Treasury Stock [Line Items]
Trading Plan Purchase Period Start Date	Jan. 1, 2016
Common shares repurchased on open market	64,464
Average Price of Shares Repurchased	$ 54.14
Total Cost (in millions)	$ 3.5
Repurchase Authorization Year	2,013
Trading Plan Purchase Period End Date	May 2, 2016

Shareholders' Equity - Schedule

Shareholders' Equity - Schedule of Authorized and Unissued Common Shares Reserved (Detail)	Dec. 31, 2016shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Shares Reserved	4,374,973
2014 Long-Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Shares Reserved	3,848,430
2016 Employee Share Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Shares Reserved	526,543

Accumulated Other Comprehens110

Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Beginning Balance	$ 11.5	$ 108.1
Other comprehensive (loss) income before reclassifications	46.2	(95.7)
Amounts reclassified from accumulated other comprehensive (loss) income	(10)	(0.9)
Other comprehensive income (loss), net of tax	36.2	(96.6)	$ (39.7)
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Ending Balance	47.7	11.5	108.1
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Beginning Balance	(21.6)	(15.6)
Other comprehensive (loss) income before reclassifications	4	(6)
Amounts reclassified from accumulated other comprehensive (loss) income	0	0
Other comprehensive income (loss), net of tax	4	(6)
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Ending Balance	(17.6)	(21.6)	(15.6)
Unrealized Holding Gains on Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Beginning Balance	40	130.7
Other comprehensive (loss) income before reclassifications	42.4	(89.8)
Amounts reclassified from accumulated other comprehensive (loss) income	(10)	(0.9)
Other comprehensive income (loss), net of tax	32.4	(90.7)
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Ending Balance	72.4	40	130.7
Defined Benefit Pension Plans
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Beginning Balance	(6.9)	(7)
Other comprehensive (loss) income before reclassifications	(0.2)	0.1
Amounts reclassified from accumulated other comprehensive (loss) income	0	0
Other comprehensive income (loss), net of tax	(0.2)	0.1
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Ending Balance	$ (7.1)	$ (6.9)	$ (7)

Accumulated Other Comprehens111

Accumulated Other Comprehensive Income (Loss) - Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Unrealized gains and losses on securities:
Reclassification adjustment for gains included in net income	$ (23.2)	$ (7.2)	$ (30.6)
Provision for income taxes	13.2	6.3	9.9
Net of taxes	(10)	(0.9)
Unrealized Holding Gains on Securities
Unrealized gains and losses on securities:
Net of taxes	(10)	(0.9)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Holding Gains on Securities
Unrealized gains and losses on securities:
Reclassification adjustment for gains included in net income	(23.2)	(7.2)	(30.6)
Provision for income taxes	13.2	6.3	9.9
Net of taxes	$ (10)	$ (0.9)	$ (20.7)

Net Income Per Common Share - N

Net Income Per Common Share - Net Income Per Common Share on Basic and Diluted Basis (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 32.9		$ 55.2		$ 30.9		$ 27.7		$ 41.2		$ 35.3		$ 27.9		$ 58.8		$ 146.7		$ 163.2		$ 183.2
Weighted average common shares outstanding - basic																	30,166,440		30,769,089		31,559,422
Effect of dilutive securities:
Equity compensation awards																	679,270		616,371		574,796
Weighted average common shares outstanding - diluted																	30,845,710		31,385,460		32,134,218
Net income per common share - basic	$ 1.10	[1]	$ 1.84	[1]	$ 1.03	[1]	$ 0.91	[1]	$ 1.34	[1]	$ 1.15	[1]	$ 0.91	[1]	$ 1.90	[1]	$ 4.86	[1]	$ 5.31	[1]	$ 5.80
Net income per common share - diluted	$ 1.07	[1]	$ 1.80	[1]	$ 1	[1]	$ 0.89	[1]	$ 1.31	[1]	$ 1.13	[1]	$ 0.89	[1]	$ 1.87	[1]	$ 4.75	[1]	$ 5.20	[1]	$ 5.70
[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.

Net Income Per Common Share - A

Net Income Per Common Share - Additional Information (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Treasury shares, shares	10,028,755	9,181,644	8,606,489
Antidilutive securities excluded from computation of diluted net income per share, shares	0	0	1,700

Share-based Compensation - Addi

Share-based Compensation - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	May 03, 2016	Feb. 17, 2015
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
Stock dividend declared	10.00%	10.00%		10.00%	10.00%
Percentage increase in number of awards outstanding due to stock dividend	10.00%
Reduction in exercise price of awards outstanding due to stock dividend	9.09%
Share-based payment expense	$ 19.8	$ 29.1	$ 19.6
Share-based payments expense, net of tax	$ 15.5	$ 23.7	$ 16.2

Share-based Compensation - Fair

Share-based Compensation - Fair Value Assumptions (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free rate of return, minimum	1.00%	1.44%	1.53%
Expected volatility, minimum	18.73%	20.04%	22.84%
Risk-free rate of return, maximum	2.02%	1.81%	1.77%
Expected volatility, maximum	19.70%	22.09%	25.46%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yields	1.62%	1.46%	1.49%
Expected award life (years)	4 years 6 months	4 years 7 months 13 days	4 years 8 months 1 day
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yields	1.70%	1.60%	1.55%
Expected award life (years)	4 years 7 months 10 days	4 years 8 months 16 days	4 years 10 months 6 days

Share-Based Compensation - 2014

Share-Based Compensation - 2014 Long-Term Incentive Plan - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	May 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	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		4,374,973
Share-based compensation arrangement by share-based payment award, award vesting period, years		5 years	5 years
Share-based payment expense		$ 19.8	$ 29.1	$ 19.6
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee service share-based compensation, unrecognized compensation costs on non-vested awards		18.6
Employee service share-based compensation, unrecognized compensation costs weighted-average period, years			2 years 2 months 12 days
Share-based compensation arrangement by share-based payment award, total fair value of shares vested		$ 2.3
Employee service share-based compensation, cash paid to exercise of stock options			$ 0.3
Share based compensation arrangement by share based payment award options, outstanding		702,030	514,742
Share-based payment expense		$ 0.1	$ 0.2	$ 0.5
Restricted Stock Units (RSUs) [Member] | Performance Condition [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement by share based payment award options, outstanding		447,410
Restricted Stock Units (RSUs) [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period, years		24 months
Restricted Stock Units (RSUs) [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period, years		48 months
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		$ 7.9
Employee service share-based compensation, unrecognized compensation costs weighted-average period, years		1 year 10 months 24 days
Exercised, shares		251,134
Share based compensation arrangement by share based payment award, shares issued		141,418
Share based compensation arrangement by share based payment award options exercises, intrinsic value		$ 61.7
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
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		$ 0.6
Employee service share-based compensation, unrecognized compensation costs weighted-average period, years		2 months 12 days
Exercised, shares		742,424
Share based compensation arrangement by share based payment award options exercises, intrinsic value		$ 16.9
Employee service share-based compensation, cash paid to exercise of stock options		19
Liability for stock awards		$ 18.6	$ 31
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
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	1,500,000
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

Share-based Compensation - Summ

Share-based Compensation - Summary of Restricted Share Activity (Detail) - Restricted Stock Units (RSUs) [Member]	12 Months Ended
	Dec. 31, 2016$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Outstanding at January 1, 2016 | shares	514,742
Granted, Shares | shares	287,227
Vested and issued, Shares | shares	(71,177)
Expired or forfeited, Shares | shares	(28,762)
Shares, Outstanding at December 31, 2016 | shares	702,030
Weighted-Average Grant Date Fair Value, Outstanding at January 1, 2016 | $ / shares	$ 36.87
Granted, Weighted-Average Grant Date Fair Value | $ / shares	50.84
Vested and issued, Weighted-Average Grant Date Fair Value | $ / shares	32.75
Expired or forfeited, Weighted-Average Grant Date Fair Value | $ / shares	44.49
Weighted-Average Grant Date Fair Value, Outstanding at December 31, 2016 | $ / shares	$ 42.69

Share-based Compensation - S118

Share-based Compensation - Summary of Stock-Settled SARs Activity (Detail) - Stock-Settled SARs Activity [Member]	12 Months Ended
	Dec. 31, 2016$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Outstanding at January 1, 2016 | shares	1,438,146
Granted, Shares | shares	542
Converted from cash-settled SARs | shares	944,046
Exercised, Shares | shares	(251,134)
Expired or forfeited, Shares | shares	(148,905)
Shares, Outstanding at December 31, 2016 | shares	1,982,695
Vested or expected to vest as of year end, Shares | shares	1,808,016
Exercisable at end of year, Shares | shares	851,491
Weighted-Average Exercise Price, Outstanding at January 1, 2016 | $ / shares	$ 29.52
Granted, Weighted-Average Exercise Price | $ / shares	36.71
Converted from cash-settled SARs | $ / shares	41.21
Exercised, Weighted-Average Exercise Price | $ / shares	24.46
Expired or forfeited, Weighted-Average Exercise Price | $ / shares	41.93
Weighted-Average Exercise Price, Outstanding at December 31, 2016 | $ / shares	34.80
Vested or expected to vest as of year end, Weighted-Average Exercise Price | $ / shares	20.19
Exercisable at end of year, Weighted-Average Exercise Price | $ / shares	$ 30.02

Share-based Compensation - S119

Share-based Compensation - Summary of Cash-Settled SARs Activity (Detail) - Cash-Settled SARs Activity [Member]	12 Months Ended
	Dec. 31, 2016$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Outstanding at January 1, 2016 | shares	2,220,560
Granted, Shares | shares	540
Converted to stock-settled SARs | shares	(864,036)	[1]
Exercised, Shares | shares	(742,424)
Expired or forfeited, Shares | shares	(114,154)
Shares, Outstanding at December 31, 2016 | shares	500,486
Vested or expected to vest as of year end, Shares | shares	480,891
Exercisable at end of year, Shares | shares	373,655
Weighted-Average Exercise Price, Outstanding at January 1, 2016 | $ / shares	$ 35.53
Granted, Weighted-Average Exercise Price | $ / shares	36.71
Converted to stock-settled SARs | $ / shares	41.21	[1]
Exercised, Weighted-Average Exercise Price | $ / shares	30.70
Expired or forfeited, Weighted-Average Exercise Price | $ / shares	39.03
Weighted-Average Exercise Price, Outstanding at December 31, 2016 | $ / shares	32.08
Vested or expected to vest as of year end, Weighted-Average Exercise Price | $ / shares	32.13
Exercisable at end of year, Weighted-Average Exercise Price | $ / shares	$ 32.44
[1]	The converted shares were not adjusted for the 10% stock dividend because the conversion occurred prior to the stock dividend record date.

Share-Based Compensation - Empl

Share-Based Compensation - Employees Share Purchase Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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 payment expense	$ 19.8	$ 29.1	$ 19.6
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
Earn Plan [Member]
Schedule Of Share Repurchase Programs [Line Items]
Share-based compensation arrangement by share-based payment award, discount from market price	85.00%
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	3 years
Earn Plan [Member] | Maximum [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 payment expense	$ 0.3	$ 0.4	$ 0.3

Share-Based Compensation - Defe

Share-Based Compensation - Deferred Compensation Plan for Non-Employee Directors - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
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 payment expense	$ 19.8	$ 29.1	$ 19.6
2007 Plan [Member]
Schedule Of Share Repurchase Programs [Line Items]
Share-based compensation arrangement by share-based payment award, discount from market price				50.00%
Deferred compensation arrangement with individual, interest rate	Two percent above the prime rate
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 payment expense	$ 0.9	0.9	$ 0.7
Liability for stock awards	$ 5.3	$ 4.5
Directors Plan Remaining Distributions Period [Member]
Schedule Of Share Repurchase Programs [Line Items]
Deferred compensation arrangement with individual, distributions period, months				6 months

Underwriting, Acquisition an122

Underwriting, Acquisition and Insurance Expenses - Underwriting, Acquisition and Insurance Expenses (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Underwriting Acquisition And Insurance Expenses [Abstract]
Commissions	$ 234	$ 232.2	$ 231.1
General expenses	292.1	295.6	285.8
Premium taxes, boards and bureaus	25.2	9.8	25.5
Underwriting, acquisition and insurance expenses, total	551.3	537.6	542.4
Net deferral of policy acquisition costs	(4.3)	(0.9)	(5.4)
Total underwriting, acquisition and insurance expenses	$ 547	$ 536.7	$ 537

Underwriting, Acquisition an123

Underwriting, Acquisition and Insurance Expenses - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Underwriting Acquisition And Insurance Expenses [Abstract]
Share-based payments expense	$ 19.8	$ 29.1	$ 19.6

Income Taxes - Income Tax Provi

Income Taxes - Income Tax Provision (Benefit) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Current tax provision	$ 36.3	$ 6	$ 5.2
Future tax deductions	(1.8)	10.9	58.4
Increase (decrease) in valuation allowance	0.7	(2.6)	(30.8)
Income tax provision	$ 35.2	$ 14.3	$ 32.8

Income Taxes - Schedule of Pre-

Income Taxes - Schedule of Pre-Tax Income (Loss) and Effective Income Tax Rates (Detail) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)		$ 47	$ 62.2	$ 39.6	$ 33.1	$ 44.2	$ 36.2	$ 34.7	$ 62.4	$ 181.9		$ 177.5		$ 216
Effective Tax Rate										0.00%		0.00%		0.00%
Bermuda [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)										$ 99.6		$ 94.3		$ 102.8
Effective Tax Rate										0.00%		0.00%		0.00%
United States [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)										$ 115.2		$ 64.8		$ 98
Effective Tax Rate										29.20%		19.90%		28.10%
United Kingdom [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)										$ (34.8)		$ 21.3		$ 21.5
Effective Tax Rate										1.20%		(4.70%)		24.80%
Belgium [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)										$ (0.1)		$ 0	[1]	$ 0	[1]
Effective Tax Rate										23.20%		237.00%		63.80%
Brazil [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)										$ 0.6		$ (3.2)		$ (2.2)
Effective Tax Rate										0.00%		0.00%		0.00%
United Arab Emirates [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)										$ 0	[1]	$ 0.2		$ (0.9)
Effective Tax Rate										0.00%		0.00%		0.00%
Ireland [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	[2]									$ (0.2)		$ (0.1)		$ (1.1)
Effective Tax Rate	[2]									5.00%		5.00%		0.00%
Malta [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)										$ 1.6		$ 0.1		$ (2.2)
Effective Tax Rate										0.30%		0.00%		0.00%
Switzerland [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)										$ 0	[1]	$ 0.1		$ 0.1
Effective Tax Rate										0.00%		20.50%		17.60%
[1]	Pre-tax income for the respective year was less than $0.1 million.
[2]	Effective tax rate of 5 percent on intercompany dividends of $40.0 million for the year ended December 31, 2016. Dividends eliminated in consolidation.

Income Taxes - Schedule of P126

Income Taxes - Schedule of Pre-Tax Income (Loss) and Effective Income Tax Rates (Parenthetical) (Detail) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)		$ 47	$ 62.2	$ 39.6	$ 33.1	$ 44.2	$ 36.2	$ 34.7	$ 62.4	$ 181.9	$ 177.5		$ 216
Effective tax rate percent on intercompany dividends										0.00%	0.00%		0.00%
Intercompany dividends										$ 2.2	$ 2.3		$ 2.3
Belgium [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)										$ (0.1)	$ 0	[1]	$ 0	[1]
Effective tax rate percent on intercompany dividends										23.20%	237.00%		63.80%
Ireland [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	[2]									$ (0.2)	$ (0.1)		$ (1.1)
Effective tax rate percent on intercompany dividends	[2]									5.00%	5.00%		0.00%
Intercompany dividends										$ 40
Maximum [Member] | Belgium [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)										$ 0.1	$ 0.1		$ 0.1
[1]	Pre-tax income for the respective year was less than $0.1 million.
[2]	Effective tax rate of 5 percent on intercompany dividends of $40.0 million for the year ended December 31, 2016. Dividends eliminated in consolidation.

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Difference Between Provision for Income Taxes and Expected Tax Provision at Weighted Average Tax Rate (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income tax provision at expected rate	$ 34.1	$ 25.8	$ 37.2
Tax-exempt interest	(3.3)	(4.2)	(4.5)
Dividends received deduction	(2.2)	(2.3)	(2.3)
Increase (decrease) in valuation allowance	0.7	(2.6)	(30.8)
Other permanent adjustments, net	0.4	0.3	(0.7)
Adjustment for prior year tax return	(0.9)	(0.6)	(0.9)
United States state tax expense	0	(2.5)	2.5
PXRE Reinsurance capital loss carryforward	0	0	29.8
Other foreign adjustments	0.2	(0.3)	0.7
Foreign tax credit utilization	(1.5)	(2.1)	0.1
Deferred tax rate reduction	0	0	(0.4)
Foreign exchange adjustments	5.3	(0.1)	1.7
Foreign withholding taxes	2.4	2.9	0.4
Income tax provision	35.2	14.3	32.8
Income tax provision - Foreign	(0.4)	(1.1)	5.2
Income tax provision - United States, Federal	33.2	16.4	23.3
Income tax (benefit) provision - United States, State	0	(3.9)	3.9
Foreign withholding tax	$ 2.4	$ 2.9	$ 0.4

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes Disclosure [Line Items]
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions			$ 1,300,000
Foreign exchange adjustments, increase			1,000,000
Increase withholding taxes paid	$ 2,000,000	$ 2,500,000
Foreign tax credit utilization	(1,500,000)	(2,100,000)	100,000
Decrease in tax related to reversal of estimated state tax accrual		2,500,000
Deferred tax rate reduction	0	0	(400,000)
Deferred tax increased (decreased) balance	$ 500,000	(29,400,000)
Net operating losses carryback period	2 years
Capital losses carryback period	3 years
Total net deferred tax liabilities	$ 600,000
Net operating loss carryforward	15,800,000
Loss carryforwards per year	2,800,000
Valuation allowance	23,500,000	22,800,000
Increase (decrease) in valuation allowance	(700,000)	2,600,000	30,800,000
Unrecognized tax benefits	0	0	0
December 31, 2025 [Member]
Income Taxes Disclosure [Line Items]
Loss carryforwards, amounts expiring if not utilized	14,300,000
December 31, 2027 [Member]
Income Taxes Disclosure [Line Items]
Loss carryforwards, amounts expiring if not utilized	1,500,000
ARIS [Member]
Income Taxes Disclosure [Line Items]
Net operating loss carryforward	1,000,000
ARIS [Member] | December 31, 2027 [Member]
Income Taxes Disclosure [Line Items]
Loss carryforwards, amounts expiring if not utilized	200,000
ARIS [Member] | December 31, 2028 [Member]
Income Taxes Disclosure [Line Items]
Loss carryforwards, amounts expiring if not utilized	400,000
ARIS [Member] | December 31, 2029 [Member]
Income Taxes Disclosure [Line Items]
Loss carryforwards, amounts expiring if not utilized	400,000
PXRE Reinsurance Company [Member]
Income Taxes Disclosure [Line Items]
Increase of recognized benefit			29,800,000
Valuation allowance	13,900,000
Increase (decrease) in valuation allowance	(1,000,000)
United Kingdom [Member]
Income Taxes Disclosure [Line Items]
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	1,500,000
Foreign tax credit utilization		$ 2,100,000
Deferred tax rate reduction			$ (400,000)
United Kingdom and Brazil [Member]
Income Taxes Disclosure [Line Items]
Foreign exchange adjustments, increase	5,300,000
Malta [Member]
Income Taxes Disclosure [Line Items]
Valuation allowance	1,300,000
Increase (decrease) in valuation allowance	(600,000)
Brazil [Member]
Income Taxes Disclosure [Line Items]
Valuation allowance	8,300,000
Increase (decrease) in valuation allowance	$ 2,300,000

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Income Tax Examination [Line Items]
Losses and loss adjustment expense reserve discounting	$ 21.1	$ 23.4
Unearned premiums	29.1	26.6
Allowance for bad debt	1.6	1.6
Accrual for contingent commissions	0.3	0.3
Net operating loss carryforward	17.1	17.8
Impairment of investment values	8.6	9.6
United States amortization of intangible assets	5.3	4.9
Accrued bonus	7.4	7
Accrued vacation	1.7	1.6
Stock option expense	8.1	10.1
Other	23.6	15.9
Deferred tax assets, gross	133.5	126.5
Unrealized gains on equity securities	(39.1)	(40.1)
Unrealized gains on fixed maturities and other investment securities	(3.9)	(0.4)
Deferred acquisition costs	(22.2)	(20.4)
United States amortization of intangible assets	(3.8)	(3.6)
United Kingdom underwriting losses	(5.4)	(9.7)
United Kingdom amortization of intangible assets	(1.2)	(1.8)
Deferred gain on like-kind exchange	(13.3)	(13.3)
Depreciable fixed asset	(21)	(18)
Unrealized Gain on Limited Partnership Interests	(17.6)	(11)
Other	(6.6)	(9)
Deferred tax liabilities, gross	(134.1)	(127.3)
Deferred tax assets, net before valuation allowance	(0.6)	(0.8)
Valuation allowance	(23.5)	(22.8)
Deferred tax liabilities, net	(24.1)	(23.6)
Net deferred tax liabilities - Foreign	(6.6)	(11.7)
Net deferred tax liabilities - United States	(17.5)	(11.9)
Brazil [Member]
Income Tax Examination [Line Items]
Operating losses	8.3	5.9
Malta [Member]
Income Tax Examination [Line Items]
Operating losses	$ 1.3	$ 1.8

Pension Benefits and Savings130

Pension Benefits and Savings Plans - Schedule of Change in Plan Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Fair value of plan assets at beginning of year	$ 17.5	$ 19.2
Actual return on plan assets	0.7	(0.1)
Employer contributions	0.2	0.2
Settlements and benefits paid	(1.7)	(1.8)
Fair value of plan assets at end of year	$ 16.7	$ 17.5

Pension Benefits and Savings131

Pension Benefits and Savings Plans - Schedule of Change in Projected Benefit Obligation (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Projected benefit obligation at beginning of year	$ 23.1	$ 25.8
Interest cost	0.8	0.8
Actuarial loss (gain)	0.4	(1.6)
Settlements and benefits paid	(1.7)	(1.9)
Projected benefit obligation at end of year	$ 22.6	$ 23.1

Pension Benefits and Savings132

Pension Benefits and Savings Plans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 100,000	$ 100,000	$ 500,000
Unrecognized actuarial loss	400,000
Maximum expected annual payments under the pensions plan	2,200,000
Defined benefit plans with accumulated benefit obligations in excess of plan assets	2,200,000	2,300,000
Fair value of plan assets	16,700,000	17,500,000	19,200,000
Mutual Funds | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	15,800,000	17,400,000
Short-Term Investments [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	900,000	100,000
Qualified Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Amount of pension related to plan	3,700,000	3,400,000
Non- Qualified Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Amount of pension related to plan	2,200,000	2,300,000
Fair value of plan assets	$ 0	0
Target Thresholds [Member] | Fixed Income Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Allocation Percentage	48.00%
Target Thresholds [Member] | Equity Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Allocation Percentage	52.00%
Actual Asset Allocation [Member] | Fixed Income Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Allocation Percentage	50.50%
Actual Asset Allocation [Member] | United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Allocation Percentage	39.20%
Actual Asset Allocation [Member] | Equity Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Allocation Percentage	49.50%
Actual Asset Allocation [Member] | Foreign Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Allocation Percentage	10.30%
Employee Savings Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer towards savings plan	$ 6,000,000	$ 6,300,000	$ 7,100,000

Pension Benefits and Savings133

Pension Benefits and Savings Plans - Schedule of Assumptions to Determine Benefit Obligations (Detail)	Dec. 31, 2016	Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Weighted average discount rate	3.44%	3.48%
Expected rate of increase in future compensation levels	0.00%	0.00%

Pension Benefits and Savings134

Pension Benefits and Savings Plans - Schedule of Assumptions to Determine Net Periodic Benefit Cost (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Compensation And Retirement Disclosure [Abstract]
Weighted average discount rate	3.62%	3.55%	4.39%
Expected return on plan assets	6.00%	6.00%	6.00%
Expected rate of increase in future compensation levels	0.00%	0.00%	0.00%

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
Commitments And Contingencies [Line Items]
Contractual commitments related to its limited partnership investments	$ 93.4
Maximum [Member]
Commitments And Contingencies [Line Items]
Contractual commitments period	13 years

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Payments Under Non-Cancelable Operating Leases (Detail) $ in Millions	Dec. 31, 2016USD ($)
Leases [Abstract]
2,017	$ 11.3
2,018	9.5
2,019	8.2
2,020	5.9
2,021	5.2
Thereafter	5.9
Total	$ 46

Lease - Additional Information

Lease - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Leases [Abstract]
Operating leases expense	$ 12.2	$ 14.2	$ 14.7

Segment Information - Additiona

Segment Information - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)Segment	Dec. 31, 2016USD ($)
Segment Reporting [Abstract]
Number of reportable segments | Segment	4
Assets associated with trade capital providers | $	$ 377.1	$ 630.4

Segment Information - Revenue a

Segment Information - Revenue and Income (Loss) Before Income Taxes for Each Segment (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Earned premiums									$ 1,410.8	$ 1,371.9	$ 1,338.1
Net investment income									115.1	88.6	106.1
Fee and other income									24.5	22.2	20.7
Net realized investment and other gains									26.1	24.1	74.5
Total revenue	$ 405.4	$ 416.7	$ 384.3	$ 370.1	$ 373.4	$ 380.2	$ 377.2	$ 376	1,576.5	1,506.8	1,539.4
Income (loss) before income taxes	$ 47	$ 62.2	$ 39.6	$ 33.1	$ 44.2	$ 36.2	$ 34.7	$ 62.4	181.9	177.5	216
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net investment income									3.2	8	3.1
Income (loss) before income taxes									(55)	(28)	(35)
Operating Segments [Members]
Segment Reporting Information [Line Items]
Income (loss) before income taxes									210.8	181.4	176.5
Excess and Surplus Lines [Member]
Segment Reporting Information [Line Items]
Earned premiums									485.3	471.2	444.6
Net investment income									45.2	32.3	43.2
Excess and Surplus Lines [Member] | Operating Segments [Members]
Segment Reporting Information [Line Items]
Income (loss) before income taxes									88.4	81.4	103.4
Commercial Specialty [Member]
Segment Reporting Information [Line Items]
Earned premiums									364.2	344.2	332.5
Net investment income									26.7	19.9	25.6
Commercial Specialty [Member] | Operating Segments [Members]
Segment Reporting Information [Line Items]
Income (loss) before income taxes									86	43	24.8
International Specialty [Member]
Segment Reporting Information [Line Items]
Earned premiums									154.5	146.4	144.8
Net investment income									16.8	11.4	11.3
International Specialty [Member] | Operating Segments [Members]
Segment Reporting Information [Line Items]
Income (loss) before income taxes									38.2	29	23.8
Syndicate 1200 [Member]
Segment Reporting Information [Line Items]
Earned premiums									406.4	409.7	414.6
Net investment income									11.9	8.9	10.9
Syndicate 1200 [Member] | Operating Segments [Members]
Segment Reporting Information [Line Items]
Income (loss) before income taxes									13.4	35.4	45.2
Run Off Lines [Member]
Segment Reporting Information [Line Items]
Earned premiums									0.4	0.4	1.6
Net investment income									11.3	8.1	12
Run Off Lines [Member] | Operating Segments [Members]
Segment Reporting Information [Line Items]
Income (loss) before income taxes									$ (15.2)	$ (7.4)	$ (20.7)

Segment Information - Schedule

Segment Information - Schedule of Earned Premiums by Geographic Location (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	$ 1,410.8	$ 1,371.9	$ 1,338.1
Bermuda [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	112.6	103.4	101.5
Brazil [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	39.2	43.1	44.3
Malta [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	2.1	1.9	2.1
United Kingdom [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	406.9	407.4	411.7
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	$ 850	$ 816.1	$ 778.5

Segment Information - Identifia

Segment Information - Identifiable Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	$ 7,205	$ 6,625.6
Excess and Surplus Lines [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	2,259.3	2,174.8
Commercial Specialty [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	1,701.9	1,511.7
International Specialty [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	970.6	877.2
Syndicate 1200 [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	1,386.3	1,216.5
Run Off Lines [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	537	558.4
Corporate and Other [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	$ 349.9	$ 287

Segment Information - Schedu142

Segment Information - Schedule of Goodwill and Intangible Assets Net of Accumulated Amortization (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Goodwill	$ 152.2	$ 152.2
Intangible assets, net of accumulated amortization	67.7	73.3
Excess and Surplus Lines [Member]
Segment Reporting Information [Line Items]
Goodwill	68.4	68.4
Intangible assets, net of accumulated amortization	0	0
Commercial Specialty [Member]
Segment Reporting Information [Line Items]
Goodwill	55.1	55.1
Intangible assets, net of accumulated amortization	3.7	6.3
Syndicate 1200 [Member]
Segment Reporting Information [Line Items]
Goodwill	28.7	28.7
Intangible assets, net of accumulated amortization	$ 64	$ 67

Statutory Accounting Principle

Statutory Accounting Principle - Statutory Capital and Surplus for Principal Operating Subsidiaries (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Bermuda [Member]
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	$ 1,510.8	$ 1,243.2
United Kingdom [Member]
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	216.6	232.8
United States [Member]
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	$ 886.7	$ 854.5

Statutory Accounting Princip144

Statutory Accounting Principles - Statutory Net Income (Loss) for Principal Operating Subsidiaries (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Bermuda [Member]
Statutory Accounting Practices [Line Items]
Statutory net income (loss)	$ 149.4	$ 182.2	$ 128.2
United Kingdom [Member]
Statutory Accounting Practices [Line Items]
Statutory net income (loss)	1.8	34.8	28.7
United States [Member]
Statutory Accounting Practices [Line Items]
Statutory net income (loss)	$ 99	$ 94.4	$ 117.7

Statutory Accounting Princip145

Statutory Accounting Principles - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Agro Re [Member]
Statutory Accounting Practices [Line Items]
Maximum permissible limit for dividend	25.00%			25.00%
Reduction in total statutory capital				15.00%
Maximum permitted amount of dividends				$ 377.7
Cash dividends				41	$ 41	$ 40.9
Rockwood Casualty Insurance Company [Member]
Statutory Accounting Practices [Line Items]
Cash dividends	$ 18.1					20
Rockwood Casualty Insurance Company [Member] | Scenario Forecast [Member]
Statutory Accounting Practices [Line Items]
Maximum permitted amount of dividends			$ 11.3
Argonaut Insurance Company [Member]
Statutory Accounting Practices [Line Items]
Cash dividends						0.1
Dividends, Securities						48.7
Value of ordinary dividends	41.6					48.8
Argonaut Insurance Company [Member] | Scenario Forecast [Member]
Statutory Accounting Practices [Line Items]
Maximum permitted amount of dividends			$ 80
Colony Insurance Company [Member]
Statutory Accounting Practices [Line Items]
Cash dividends		$ 19.9				0.2
Dividends, Securities		15.1				55
Value of ordinary dividends		$ 35
Value of extraordinary dividends						$ 55.2
Minimum [Member]
Statutory Accounting Practices [Line Items]
Minimum statutory capital and surplus balance	$ 362.1			$ 362.1	$ 345.9

Insurance Assessments - Additio

Insurance Assessments - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Insurance [Abstract]
Insurance assessments on current insolvencies	$ 4.7	$ 4.1

Transactions with Related Pa147

Transactions with Related Parties - Additional Information (Detail) - Kinetica [Member] $ in Millions	Dec. 31, 2016USD ($)
Schedule Of Other Related Party Transactions [Line Items]
Surety bonds issued	$ 13
Percentage of investment ownership	10.00%

Unaudited Quarterly Financia148

Unaudited Quarterly Financial Data - Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 405.4		$ 416.7		$ 384.3		$ 370.1		$ 373.4		$ 380.2		$ 377.2		$ 376		$ 1,576.5		$ 1,506.8		$ 1,539.4
Net income before income taxes	47		62.2		39.6		33.1		44.2		36.2		34.7		62.4		181.9		177.5		216
Net income	$ 32.9		$ 55.2		$ 30.9		$ 27.7		$ 41.2		$ 35.3		$ 27.9		$ 58.8		$ 146.7		$ 163.2		$ 183.2
Net income per common share:
Basic	$ 1.10	[1]	$ 1.84	[1]	$ 1.03	[1]	$ 0.91	[1]	$ 1.34	[1]	$ 1.15	[1]	$ 0.91	[1]	$ 1.90	[1]	$ 4.86	[1]	$ 5.31	[1]	$ 5.80
Diluted	$ 1.07	[1]	$ 1.80	[1]	$ 1	[1]	$ 0.89	[1]	$ 1.31	[1]	$ 1.13	[1]	$ 0.89	[1]	$ 1.87	[1]	$ 4.75	[1]	$ 5.20	[1]	$ 5.70
Comprehensive income (loss)	$ 9.4		$ 57.3		$ 59.7		$ 56.5		$ 29.2		$ (18.3)		$ 18.9		$ 36.8		$ 182.9		$ 66.6		$ 143.5
[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.

Senior Unsecured Fixed Rate 149

Senior Unsecured Fixed Rate Notes - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Equity Method Investments [Line Items]
Principal amount of senior note		$ 143,800,000	$ 143,800,000
Senior Unsecured Fixed Rate Notes [Member]
Schedule Of Equity Method Investments [Line Items]
Principal amount of senior note	$ 143,750,000
Debt instrument interest rate stated percentage	6.50%
Debt instrument maturity date		Sep. 15, 2042
Initial maturity date		Sep. 15, 2017
Debt Instrument, Redemption Price, Percentage	100.00%

Senior Unsecured Fixed Rate 150

Senior Unsecured Fixed Rate Notes - Schedule Of Unamortized Debt Issuance Costs Deducted From Carrying Value Of Debt Liability (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
Principal	$ 143.8	$ 143.8
Less: unamortized debt issuance costs	(4.3)	(4.5)
Senior unsecured fixed rate notes, less unamortized debt issuance costs	$ 139.5	$ 139.3

Senior Unsecured Fixed Rate 151

Senior Unsecured Fixed Rate Notes - Condensed Consolidating Balance Sheet (Detail) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Assets
Investments		$ 4,324.3	$ 4,115.7
Cash		86	121.7	$ 81	$ 157.4
Accrued investment income		20.7	21.6
Premiums receivable		463.8	404.5
Reinsurance recoverables		1,385.6	1,121.1
Goodwill and other intangible assets, net		219.9	225.5
Current income taxes receivable, net		0	11.6
Deferred acquisition costs, net		139.1	132.4
Ceded unearned premiums		302.8	250.8
Other assets		262.8	220.7
Intercompany note receivable		0	0
Investments in subsidiaries		0	0
Total assets		7,205	6,625.6
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses		3,350.8	3,123.6	3,042.4
Unearned premiums		970	886.7
Funds held and ceded reinsurance payable, net		543.7	390
Long-term debt		367.6	367.2
Current income taxes payable, net		8.1	0
Deferred tax liabilities, net		24.1	23.6
Accrued underwriting expenses and other liabilities		148	166.4
Due to affiliates		0	0
Total liabilities		5,412.3	4,957.5
Total shareholders' equity		1,792.7	1,668.1	1,646.7	1,563
Total liabilities and shareholders' equity		7,205	6,625.6
Argo Group International Holdings, Ltd (Parent Guarantor) [Member]
Assets
Investments		2.2	6.2
Cash		0	0	0	0
Accrued investment income		0	0
Premiums receivable		0	0
Reinsurance recoverables		0	0
Goodwill and other intangible assets, net		0	0
Current income taxes receivable, net			0
Deferred acquisition costs, net		0	0
Ceded unearned premiums		0	0
Other assets		8.7	8.2
Intercompany note receivable		0	0
Investments in subsidiaries		1,834.4	1,715.9
Total assets		1,845.3	1,730.3
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses		0	0
Unearned premiums		0	0
Funds held and ceded reinsurance payable, net		0	0
Long-term debt		28.4	28.4
Current income taxes payable, net		0
Deferred tax liabilities, net		0	0
Accrued underwriting expenses and other liabilities		13.7	16.3
Due to affiliates		10.5	17.5
Total liabilities		52.6	62.2
Total shareholders' equity		1,792.7	1,668.1
Total liabilities and shareholders' equity		1,845.3	1,730.3
Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) [Member]
Assets
Investments		2,834.2	2,761
Cash		53.7	88.8	49.3	132.1
Accrued investment income		16	16.4
Premiums receivable		204.9	166.4
Reinsurance recoverables		1,348.4	1,212.2
Goodwill and other intangible assets, net		127.1	129.8
Current income taxes receivable, net			4.7
Deferred acquisition costs, net		63.5	58.2
Ceded unearned premiums		168.9	125.8
Other assets		168	151.7
Intercompany note receivable		50.2	49.8
Investments in subsidiaries		0	0
Total assets		5,034.9	4,764.8
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses		2,322.4	2,194.1
Unearned premiums		580	501.5
Funds held and ceded reinsurance payable, net		750.2	702.6
Long-term debt		284.4	284.2
Current income taxes payable, net		8.5
Deferred tax liabilities, net		17.6	11.9
Accrued underwriting expenses and other liabilities		92	95.4
Due to affiliates		1.8	2.3
Total liabilities		4,056.9	3,792
Total shareholders' equity		978	972.8
Total liabilities and shareholders' equity		5,034.9	4,764.8
Other Subsidiaries and Eliminations [Member]
Assets
Investments	[1]	1,487.9	1,348.5
Cash	[1]	32.3	32.9	31.7	25.3
Accrued investment income	[1]	4.7	5.2
Premiums receivable	[1]	258.9	238.1
Reinsurance recoverables	[1]	37.2	(91.1)
Goodwill and other intangible assets, net	[1]	92.8	95.7
Current income taxes receivable, net	[1]		6.9
Deferred acquisition costs, net	[1]	75.6	74.2
Ceded unearned premiums	[1]	133.9	125
Other assets	[1]	86.1	60.8
Intercompany note receivable	[1]	(50.2)	(49.8)
Investments in subsidiaries	[1]	0	0
Total assets	[1]	2,159.2	1,846.4
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	[1]	1,028.4	929.5
Unearned premiums	[1]	390	385.2
Funds held and ceded reinsurance payable, net	[1]	(206.5)	(312.6)
Long-term debt	[1]	54.8	54.6
Current income taxes payable, net	[1]	(0.4)
Deferred tax liabilities, net	[1]	6.5	11.7
Accrued underwriting expenses and other liabilities	[1]	42.3	54.7
Due to affiliates	[1]	(1.8)	(2.3)
Total liabilities	[1]	1,313.3	1,120.8
Total shareholders' equity	[1]	845.9	725.6
Total liabilities and shareholders' equity	[1]	2,159.2	1,846.4
Consolidating Adjustments [Member]
Assets
Investments	[2]	0	0
Cash	[2]	0	0	$ 0	$ 0
Accrued investment income	[2]	0	0
Premiums receivable	[2]	0	0
Reinsurance recoverables	[2]	0	0
Goodwill and other intangible assets, net	[2]	0	0
Current income taxes receivable, net	[2]		0
Deferred acquisition costs, net	[2]	0	0
Ceded unearned premiums	[2]	0	0
Other assets	[2]	0	0
Intercompany note receivable	[2]	0	0
Investments in subsidiaries	[2]	(1,834.4)	(1,715.9)
Total assets	[2]	(1,834.4)	(1,715.9)
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	[2]	0	0
Unearned premiums	[2]	0	0
Funds held and ceded reinsurance payable, net	[2]	0	0
Long-term debt	[2]	0	0
Current income taxes payable, net	[2]	0
Deferred tax liabilities, net	[2]	0	0
Accrued underwriting expenses and other liabilities	[2]	0	0
Due to affiliates	[2]	(10.5)	(17.5)
Total liabilities	[2]	(10.5)	(17.5)
Total shareholders' equity	[2]	(1,823.9)	(1,698.4)
Total liabilities and shareholders' equity	[2]	$ (1,834.4)	$ (1,715.9)
[1]	Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations.
[2]	Includes all Argo Group parent company eliminations.

Senior Unsecured Fixed Rate 152

Senior Unsecured Fixed Rate Notes - Condensed Consolidating Statement of Income (Detail) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Premiums and other revenue:
Earned premiums										$ 1,410.8	$ 1,371.9	$ 1,338.1
Net investment income										115.1	88.6	106.1
Fee and other income										24.5	22.2	20.7
Net realized investment and other gains										26.1	24.1	74.5
Total revenue		$ 405.4	$ 416.7	$ 384.3	$ 370.1	$ 373.4	$ 380.2	$ 377.2	$ 376	1,576.5	1,506.8	1,539.4
Expenses:
Losses and loss adjustment expenses										810.1	766.1	747.4
Underwriting, acquisition and insurance expenses										547	536.7	537
Interest expense										19.6	19	19.9
Fee and other expense										22.4	25.8	23.5
Foreign currency exchange gain										(4.5)	(18.3)	(7.8)
Impairment of intangible assets										0	0	3.4
Total expenses										1,394.6	1,329.3	1,323.4
Income before income taxes		47	62.2	39.6	33.1	44.2	36.2	34.7	62.4	181.9	177.5	216
Provision for income taxes										35.2	14.3	32.8
Net income before equity in earnings of subsidiaries										146.7	163.2	183.2
Equity in undistributed earnings of subsidiaries										0	0	0
Net income		$ 32.9	$ 55.2	$ 30.9	$ 27.7	$ 41.2	$ 35.3	$ 27.9	$ 58.8	146.7	163.2	183.2
Argo Group International Holdings, Ltd (Parent Guarantor) [Member]
Premiums and other revenue:
Earned premiums										0	0	0
Net investment income										37.2	40.1	40.5
Fee and other income										0	0	0
Net realized investment and other gains										0.6	0	2
Total revenue										37.8	40.1	42.5
Expenses:
Losses and loss adjustment expenses										0	0	0
Underwriting, acquisition and insurance expenses										12.8	19	17.3
Interest expense										1.4	1.5	2.3
Fee and other expense										0	0	0
Foreign currency exchange gain										0	0	0
Impairment of intangible assets												0
Total expenses										14.2	20.5	19.6
Income before income taxes										23.6	19.6	22.9
Provision for income taxes										0	0	0
Net income before equity in earnings of subsidiaries										23.6	19.6	22.9
Equity in undistributed earnings of subsidiaries										123.1	143.6	160.3
Net income										146.7	163.2	183.2
Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) [Member]
Premiums and other revenue:
Earned premiums										497.3	497.3	461
Net investment income										78.9	59	76.2
Fee and other income										21.4	19	17.6
Net realized investment and other gains										50	31.8	67.4
Total revenue										647.6	607.1	622.2
Expenses:
Losses and loss adjustment expenses										290.4	304.2	285.6
Underwriting, acquisition and insurance expenses										204.4	198.4	199.9
Interest expense										15.8	15.3	15.2
Fee and other expense										21.7	23.3	20
Foreign currency exchange gain										0.2	1	0.4
Impairment of intangible assets												3.4
Total expenses										532.5	542.2	524.5
Income before income taxes										115.1	64.9	97.7
Provision for income taxes										33.6	12.9	27.5
Net income before equity in earnings of subsidiaries										81.5	52	70.2
Equity in undistributed earnings of subsidiaries										0	0	0
Net income										81.5	52	70.2
Other Subsidiaries and Eliminations [Member]
Premiums and other revenue:
Earned premiums	[1]									913.5	874.6	877.1
Net investment income	[1]									40	30.5	(10.6)
Fee and other income	[1]									3.1	3.2	3.1
Net realized investment and other gains	[1]									(24.5)	(7.7)	7.1
Total revenue	[1]									932.1	900.6	876.7
Expenses:
Losses and loss adjustment expenses	[1]									519.7	461.9	461.8
Underwriting, acquisition and insurance expenses	[1]									329.8	319.3	319.8
Interest expense	[1]									2.4	2.2	2.7
Fee and other expense	[1]									0.7	2.5	3.5
Foreign currency exchange gain	[1]									(4.7)	(19.3)	(8.2)
Impairment of intangible assets	[1]											0
Total expenses	[1]									847.9	766.6	779.6
Income before income taxes	[1]									84.2	134	97.1
Provision for income taxes	[1]									1.6	1.4	5.3
Net income before equity in earnings of subsidiaries	[1]									82.6	132.6	91.8
Equity in undistributed earnings of subsidiaries	[1]									0	0	0
Net income	[1]									82.6	132.6	91.8
Consolidating Adjustments [Member]
Premiums and other revenue:
Earned premiums	[2]									0	0	0
Net investment income	[2]									(41)	(41)	0
Fee and other income	[2]									0	0	0
Net realized investment and other gains	[2]									0	0	(2)
Total revenue	[2]									(41)	(41)	(2)
Expenses:
Losses and loss adjustment expenses	[2]									0	0	0
Underwriting, acquisition and insurance expenses	[2]									0	0	0
Interest expense	[2]									0	0	(0.3)
Fee and other expense	[2]									0	0	0
Foreign currency exchange gain	[2]									0	0	0
Impairment of intangible assets	[2]											0
Total expenses	[2]									0	0	(0.3)
Income before income taxes	[2]									(41)	(41)	(1.7)
Provision for income taxes	[2]									0	0	0
Net income before equity in earnings of subsidiaries	[2]									(41)	(41)	(1.7)
Equity in undistributed earnings of subsidiaries	[2]									(123.1)	(143.6)	(160.3)
Net income	[2]									$ (164.1)	$ (184.6)	$ (162)
[1]	Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations.
[2]	Includes all Argo Group parent company eliminations.

Senior Unsecured Fixed Rate 153

Senior Unsecured Fixed Rate Notes - Condensed Consolidating Statement of Cash Flows (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities		$ 181.4	$ 282.6	$ 130.5
Cash flows from investing activities:
Proceeds from sales of investments		1,443.5	967.9	1,262
Maturities and mandatory calls of fixed maturity investments		1,002.7	843.9	323
Purchases of investments		(2,380.5)	(2,034.1)	(1,736.8)
Change in short-term investments and foreign regulatory deposits		(195.2)	49.6	96.5
Settlements of foreign currency exchange forward contracts		(5.4)	(10.1)	(1.1)
Issuance of intercompany note, net			0	0
Redemption of PXRE Capital Trust V			0
Purchases of fixed assets and other, net		(10.2)	(10.8)	(64.9)
Cash used in investing activities		(145.1)	(193.6)	(121.3)
Cash flows from financing activities:
Borrowings under intercompany note, net		0		0
Activity under stock incentive plans		1	1.8	4.6
Redemption of trust preferred securities, net		0	0	(18)
Payment on note payable		0	0	(0.1)
Repurchase of Company's common shares		(47.1)	(29.7)	(50.8)
Excess tax benefit from share-based payment arrangements		0.6	0.6	0.1
Payment of cash dividends to common shareholders		(26.6)	(22.7)	(18.2)
Intercompany cash dividend		0
Cash used in financing activities		(72.1)	(50)	(82.4)
Effect of exchange rate changes on cash		0.1	1.7	(3.2)
Change in cash		(35.7)	40.7	(76.4)
Cash, beginning of year		121.7	81	157.4
Cash, end of year		86	121.7	81
Argo Group International Holdings, Ltd (Parent Guarantor) [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities		26.5	32.7	25.7
Cash flows from investing activities:
Proceeds from sales of investments		0	0	0
Maturities and mandatory calls of fixed maturity investments		0	0	0
Purchases of investments		0	0	0
Change in short-term investments and foreign regulatory deposits		(0.9)	0.9	0.5
Settlements of foreign currency exchange forward contracts		0	1.5	1.3
Issuance of intercompany note, net			0	0
Redemption of PXRE Capital Trust V			0
Purchases of fixed assets and other, net		0	3.8	(7)
Cash used in investing activities		(0.9)	6.2	(5.2)
Cash flows from financing activities:
Borrowings under intercompany note, net		0		(6.9)
Activity under stock incentive plans		1	1.8	4.6
Redemption of trust preferred securities, net		0	(18)	0
Payment on note payable		0		0
Repurchase of Company's common shares		0	0	0
Excess tax benefit from share-based payment arrangements		0	0	0
Payment of cash dividends to common shareholders		(26.6)	(22.7)	(18.2)
Intercompany cash dividend		0
Cash used in financing activities		(25.6)	(38.9)	(20.5)
Effect of exchange rate changes on cash		0	0	0
Change in cash		0	0	0
Cash, beginning of year		0	0	0
Cash, end of year		0	0	0
Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities		71.7	116.4	43.2
Cash flows from investing activities:
Proceeds from sales of investments		1,035.9	631.1	803.8
Maturities and mandatory calls of fixed maturity investments		543.2	681.8	192.1
Purchases of investments		(1,450)	(1,384.5)	(1,126.1)
Change in short-term investments and foreign regulatory deposits		(138.1)	14.9	76
Settlements of foreign currency exchange forward contracts		0	0	0
Issuance of intercompany note, net			7.5	14.5
Redemption of PXRE Capital Trust V			18
Purchases of fixed assets and other, net		(11.3)	(16.6)	(35.5)
Cash used in investing activities		(20.3)	(47.8)	(75.2)
Cash flows from financing activities:
Borrowings under intercompany note, net		0		0
Activity under stock incentive plans		0	0	0
Redemption of trust preferred securities, net		0	0	0
Payment on note payable		0		(0.1)
Repurchase of Company's common shares		(47.1)	(29.7)	(50.8)
Excess tax benefit from share-based payment arrangements		0.6	0.6	0.1
Payment of cash dividends to common shareholders		0	0	0
Intercompany cash dividend		(40)
Cash used in financing activities		(86.5)	(29.1)	(50.8)
Effect of exchange rate changes on cash		0	0	0
Change in cash		(35.1)	39.5	(82.8)
Cash, beginning of year		88.8	49.3	132.1
Cash, end of year		53.7	88.8	49.3
Other Subsidiaries and Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities	[1]	83.2	133.5	37.2
Cash flows from investing activities:
Proceeds from sales of investments	[1]	407.6	336.8	458.2
Maturities and mandatory calls of fixed maturity investments	[1]	459.5	162.1	130.9
Purchases of investments	[1]	(930.5)	(649.6)	(610.7)
Change in short-term investments and foreign regulatory deposits	[1]	(56.2)	33.8	20
Settlements of foreign currency exchange forward contracts	[1]	(5.4)	(11.6)	(2.4)
Issuance of intercompany note, net	[1]		(7.5)	(7.6)
Redemption of PXRE Capital Trust V	[1]		(18)
Purchases of fixed assets and other, net	[1]	1.1	2	(16)
Cash used in investing activities	[1]	(123.9)	(152)	(27.6)
Cash flows from financing activities:
Borrowings under intercompany note, net	[1]	0		0
Activity under stock incentive plans	[1]	0	0	0
Redemption of trust preferred securities, net	[1]	0	18	0
Payment on note payable	[1]	0		0
Repurchase of Company's common shares	[1]	0	0	0
Excess tax benefit from share-based payment arrangements	[1]	0	0	0
Payment of cash dividends to common shareholders	[1]	0	0	0
Intercompany cash dividend	[1]	40
Cash used in financing activities	[1]	40	18	0
Effect of exchange rate changes on cash	[1]	0.1	1.7	(3.2)
Change in cash	[1]	(0.6)	1.2	6.4
Cash, beginning of year	[1]	32.9	31.7	25.3
Cash, end of year	[1]	32.3	32.9	31.7
Consolidating Adjustments [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash flows from operating activities	[2]	0	0	24.4
Cash flows from investing activities:
Proceeds from sales of investments	[2]	0	0	0
Maturities and mandatory calls of fixed maturity investments	[2]	0	0	0
Purchases of investments	[2]	0	0	0
Change in short-term investments and foreign regulatory deposits	[2]	0	0	0
Settlements of foreign currency exchange forward contracts	[2]	0	0	0
Issuance of intercompany note, net	[2]		0	(6.9)
Redemption of PXRE Capital Trust V	[2]		0
Purchases of fixed assets and other, net	[2]	0	0	(6.4)
Cash used in investing activities	[2]	0	0	(13.3)
Cash flows from financing activities:
Borrowings under intercompany note, net	[2]	0		6.9
Activity under stock incentive plans	[2]	0	0	0
Redemption of trust preferred securities, net	[2]	0	0	(18)
Payment on note payable	[2]	0		0
Repurchase of Company's common shares	[2]	0	0	0
Excess tax benefit from share-based payment arrangements	[2]	0	0	0
Payment of cash dividends to common shareholders	[2]	0	0	0
Intercompany cash dividend	[2]	0
Cash used in financing activities	[2]	0	0	(11.1)
Effect of exchange rate changes on cash	[2]	0	0	0
Change in cash	[2]	0	0	0
Cash, beginning of year	[2]	0	0	0
Cash, end of year	[2]	$ 0	$ 0	$ 0
[1]	Includes all other subsidiaries of Argo Group International Holdings, Ltd. and all intercompany eliminations.
[2]	Includes all Argo Group parent company eliminations.

Schedule II - Schedule of Balan

Schedule II - Schedule of Balance Sheets (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jul. 16, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Other investments	$ 539,000,000	$ 513,700,000
Short-term investments	405,500,000	210,800,000
Investment in subsidiaries	0	0
Other assets	262,800,000	220,700,000
Total assets	7,205,000,000	6,625,600,000
Junior subordinated debentures, Amount	172,700,000	172,700,000		$ 20,000,000
Accrued underwriting expenses and other liabilities	148,000,000	166,400,000
Due to subsidiaries	0	0
Total liabilities	5,412,300,000	4,957,500,000
Shareholders' equity	1,792,700,000	1,668,100,000	$ 1,646,700,000		$ 1,563,000,000
Total liabilities and shareholders' equity	7,205,000,000	6,625,600,000
Argo Group International Holdings, Ltd (Parent Guarantor) [Member]
Condensed Financial Statements, Captions [Line Items]
Other investments	300,000	5,200,000
Short-term investments	1,900,000	1,000,000
Investment in subsidiaries	1,834,400,000	1,715,900,000
Other assets	8,700,000	8,200,000
Total assets	1,845,300,000	1,730,300,000
Junior subordinated debentures, Amount	28,400,000	28,400,000
Accrued underwriting expenses and other liabilities	13,700,000	16,300,000
Due to subsidiaries	10,500,000	17,500,000
Total liabilities	52,600,000	62,200,000
Shareholders' equity	1,792,700,000	1,668,100,000
Total liabilities and shareholders' equity	$ 1,845,300,000	$ 1,730,300,000

Schedule II - Schedule of State

Schedule II - Schedule of Statements of Income (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Net investment income									$ 115.1	$ 88.6	$ 106.1
Net realized investment and other gains									26.1	24.1	74.5
Total revenue	$ 405.4	$ 416.7	$ 384.3	$ 370.1	$ 373.4	$ 380.2	$ 377.2	$ 376	1,576.5	1,506.8	1,539.4
Interest expense									19.6	19	19.9
Other expenses									547	536.7	537
Net income before equity in earnings of subsidiaries									146.7	163.2	183.2
Equity in undistributed earnings of subsidiaries									0	0	0
Net income	$ 32.9	$ 55.2	$ 30.9	$ 27.7	$ 41.2	$ 35.3	$ 27.9	$ 58.8	146.7	163.2	183.2
Argo Group International Holdings, Ltd (Parent Guarantor) [Member]
Condensed Financial Statements, Captions [Line Items]
Net investment income									37.2	40.1	40.5
Net realized investment and other gains									0.6	0	2
Total revenue									37.8	40.1	42.5
Interest expense									1.4	1.5	2.3
Other expenses									12.8	19	17.3
Total expenses									14.2	20.5	19.6
Net income before equity in earnings of subsidiaries									23.6	19.6	22.9
Equity in undistributed earnings of subsidiaries									123.1	143.6	160.3
Net income									$ 146.7	$ 163.2	$ 183.2

Schedule II - Schedule of St156

Schedule II - Schedule of Statements of Income (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Argo Group International Holdings, Ltd (Parent Guarantor) [Member]
Condensed Financial Statements, Captions [Line Items]
Intercompany dividend	$ 41	$ 41	$ 40.9

Schedule II - Schedule of St157

Schedule II - Schedule of Statements of Cash Flows (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Net income	$ 32.9	$ 55.2	$ 30.9	$ 27.7	$ 41.2	$ 35.3	$ 27.9	$ 58.8	$ 146.7	$ 163.2	$ 183.2
Amortization and depreciation									35.4	38.7	37.2
Share-based payments expense									19.8	29.1	19.6
Net realized investment and other gains									(26.1)	(24.1)	(74.5)
Undistributed earnings of subsidiaries									0	0	0
Accrued underwriting expenses									(18.9)	(24.6)	11.7
Other, net									(49.1)	0.4	27.8
Cash provided by operating activities									181.4	282.6	130.5
Change in short-term investments									(193.9)	46.1	75.3
Settlements of foreign currency exchange forward contracts									(5.4)	(10.1)	(1.1)
Purchases of fixed assets and other, net									(10.2)	(10.8)	(64.9)
Cash used in investing activities									(145.1)	(193.6)	(121.3)
Activity under stock incentive plans									1	1.8	4.6
Redemption of trust preferred securities, net									0	0	(18)
Payment of cash dividends to common shareholders									(26.6)	(22.7)	(18.2)
Cash used in financing activities									(72.1)	(50)	(82.4)
Change in cash									(35.7)	40.7	(76.4)
Cash, beginning of year				121.7				81	121.7	81	157.4
Cash, end of year	86				121.7				86	121.7	81
Argo Group International Holdings, Ltd (Parent Guarantor) [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									146.7	163.2	183.2
Amortization and depreciation									0.2	0.2	0
Share-based payments expense									4.2	8.2	5.7
Net realized investment and other gains									(0.6)	0	(2)
Undistributed earnings of subsidiaries									(123.1)	(143.6)	(160.3)
Prepaid assets									(0.2)	0.2	2
Accrued underwriting expenses									0.9	(2.4)	(2.2)
Due to subsidiaries									(0.6)	12.5	(0.6)
Interest on intercompany note payable									0	0	0.3
Other, net									(1)	(5.6)	(0.4)
Cash provided by operating activities									26.5	32.7	25.7
Change in short-term investments									(0.9)	0.9	0.5
Settlements of foreign currency exchange forward contracts									0	1.5	1.3
Purchases of fixed assets and other, net									0	3.8	(7)
Cash used in investing activities									(0.9)	6.2	(5.2)
Borrowings under intercompany note payable, net									0	0	(6.9)
Activity under stock incentive plans									1	1.8	4.6
Redemption of trust preferred securities, net									0	(18)	0
Payment of cash dividends to common shareholders									(26.6)	(22.7)	(18.2)
Cash used in financing activities									(25.6)	(38.9)	(20.5)
Change in cash									0	0	0
Cash, beginning of year				$ 0				$ 0	0	0	0
Cash, end of year	$ 0				$ 0				$ 0	$ 0	$ 0

Schedule III - Supplemental Ins

Schedule III - Supplemental Insurance Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplementary Insurance Information By Segment [Line Items]
Deferred acquisition costs	$ 139.1	$ 132.4	$ 124.6
Reserves for Losses and Loss Adjustment Expenses	3,350.8	3,123.6	3,042.4
Unearned Premiums	970	886.7	817.2
Earned premiums	1,410.8	1,371.9	1,338.1
Net investment income	115.1	88.6	106.1
Benefits, Claims and Claim Adjustment Expenses	810.1	766.1	747.4
Amortization (Deferral) of Deferred Acquisition Costs	(4.3)	(0.9)	(5.4)
Other Insurance Expenses	551.3	537.6	542.4
Net Premiums Written	1,440.2	1,402.1	1,367.9
Excess and Surplus Lines [Member]
Supplementary Insurance Information By Segment [Line Items]
Deferred acquisition costs	34.1	35.7	35.2
Reserves for Losses and Loss Adjustment Expenses	1,112.8	1,094.3	1,075.2
Unearned Premiums	256.4	245.1	233.5
Earned premiums	485.3	471.2	444.6
Net investment income	45.2	32.3	43.2
Benefits, Claims and Claim Adjustment Expenses	286.4	267.8	233.8
Amortization (Deferral) of Deferred Acquisition Costs	1.6	(0.5)	1
Other Insurance Expenses	148.3	149.1	143.6
Net Premiums Written	489.4	485.6	443.7
Commercial Specialty [Member]
Supplementary Insurance Information By Segment [Line Items]
Deferred acquisition costs	29.4	22.7	24.2
Reserves for Losses and Loss Adjustment Expenses	915.6	794.3	742.4
Unearned Premiums	319	256.1	214.3
Earned premiums	364.2	344.2	332.5
Net investment income	26.7	19.9	25.6
Benefits, Claims and Claim Adjustment Expenses	181.1	203.3	203.3
Amortization (Deferral) of Deferred Acquisition Costs	(6.7)	1.5	(3.4)
Other Insurance Expenses	127.3	109.3	123.9
Net Premiums Written	394.1	352.9	345.2
International Specialty [Member]
Supplementary Insurance Information By Segment [Line Items]
Deferred acquisition costs	1.3	2.1	0.7
Reserves for Losses and Loss Adjustment Expenses	374	313.1	299.2
Unearned Premiums	114.9	113.9	115.6
Earned premiums	154.5	146.4	144.8
Net investment income	16.8	11.4	11.3
Benefits, Claims and Claim Adjustment Expenses	83.3	74.5	76.4
Amortization (Deferral) of Deferred Acquisition Costs	0.7	(2.1)	1.6
Other Insurance Expenses	46.3	53.4	51.2
Net Premiums Written	153.5	158.1	152.2
Syndicate 1200 [Member]
Supplementary Insurance Information By Segment [Line Items]
Deferred acquisition costs	74.3	71.9	64.5
Reserves for Losses and Loss Adjustment Expenses	657.5	615.6	607.1
Unearned Premiums	279.7	271.6	253.8
Earned premiums	406.4	409.7	414.6
Net investment income	11.9	8.9	10.9
Benefits, Claims and Claim Adjustment Expenses	240.7	211.9	209.5
Amortization (Deferral) of Deferred Acquisition Costs	0.1	0.2	(4.6)
Other Insurance Expenses	164	168.9	171.9
Net Premiums Written	402.9	405.1	425.2
Run Off Lines [Member]
Supplementary Insurance Information By Segment [Line Items]
Deferred acquisition costs	0	0	0
Reserves for Losses and Loss Adjustment Expenses	290.9	306.3	318.5
Unearned Premiums	0	0	0
Earned premiums	0.4	0.4	1.6
Net investment income	11.3	8.1	12
Benefits, Claims and Claim Adjustment Expenses	18.6	8.6	24.4
Amortization (Deferral) of Deferred Acquisition Costs	0	0	0
Other Insurance Expenses	6.9	5.9	8.2
Net Premiums Written	0.3	0.4	1.6
Corporate and Other [Member]
Supplementary Insurance Information By Segment [Line Items]
Deferred acquisition costs	0	0	0
Reserves for Losses and Loss Adjustment Expenses	0	0	0
Unearned Premiums	0	0	0
Earned premiums	0	0	0
Net investment income	3.2	8	3.1
Benefits, Claims and Claim Adjustment Expenses	0	0	0
Amortization (Deferral) of Deferred Acquisition Costs	0	0	0
Other Insurance Expenses	58.5	51	43.6
Net Premiums Written	$ 0	$ 0	$ 0

Schedule V - Valuation and Qual

Schedule V - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Valuation And Qualifying Accounts [Abstract]
Valuation allowance for deferred tax asset, Balance at Beginning of Year	$ 22.8	$ 25.4	$ 56.2
Valuation allowance for deferred tax asset, Charged to Cost and Expense	(1)	(1)	(30.7)
Valuation allowance for deferred tax asset, Capital Loss Carryforward	0	0	0
Valuation allowance for deferred tax asset, Net Operating Loss Carryforward	0	0	0
Valuation allowance for deferred tax asset, Charged to Other Accounts	1.7	(1.6)	(0.1)
Valuation allowance for deferred tax asset, Deductions	0	0	0
Valuation allowance for deferred tax asset, Balance at End of Year	$ 23.5	$ 22.8	$ 25.4

Schedule VI - Supplemental Info

Schedule VI - Supplemental Information for Property-Casualty Insurance Companies (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Information For Property Casualty Insurance Underwriters [Abstract]
Deferred acquisition costs	$ 139.1	$ 132.4	$ 124.6
Reserves for losses and loss adjustment expenses	3,350.8	3,123.6	3,042.4
Unamortized discount in reserves for losses	19.4	21.5	23.7
Unearned premiums	970	886.7	817.2
Premiums earned	1,410.8	1,371.9	1,338.1
Net investment income	115.1	88.6	106.1
Losses and loss adjustment expenses incurred: Current Year	843.4	798.5	785.1
Prior accident years	(33.3)	(32.4)	(37.7)
Losses and loss adjustment expenses incurred	810.1	766.1	747.4
Amortization (Deferral) of Deferred Acquisition Costs	(4.3)	(0.9)	(5.4)
Paid losses and loss adjustment expenses, net of reinsurance	716.5	733.5	736.7
Gross premiums written	$ 2,164.8	$ 2,012.1	$ 1,905.4