Markel (MKL) 10-K28 Feb 142013 FY Annual reportFinancial data

Company Profile

Document_And_Entity_Informatio

Document And Entity Information (USD $)	12 Months Ended
Document And Entity Information (USD $)	Dec. 31, 2013	Feb. 10, 2014	Jun. 30, 2013
Document And Entity Information [Abstract]	'	'	'
Document Type	'10-K	'	'
Amendment Flag	'false	'	'
Document Period End Date	31-Dec-13	'	'
Document Fiscal Year Focus	'2013	'	'
Document Fiscal Period Focus	'FY	'	'
Entity Registrant Name	'MARKEL CORP	'	'
Entity Central Index Key	'0001096343	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Filer Category	'Large Accelerated Filer	'	'
Entity Common Stock, Shares Outstanding	'	13,985,396	'
Entity Well-known Seasoned Issuer	'Yes	'	'
Entity Voluntary Filers	'No	'	'
Entity Current Reporting Status	'Yes	'	'
Entity Public Float	'	'	$7,085,000,000

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
ASSETS	'	'
Fixed maturities (amortized cost of $10,129,141 in 2013 and $4,562,278 in 2012)	$10,142,536	$4,979,283
Equity securities (cost of $1,566,553 in 2013 and $1,387,305 in 2012)	3,251,798	2,406,951
Short-term investments (estimated fair value approximates cost)	1,452,288	973,330
Total Investments	14,846,622	8,359,564
Cash and cash equivalents	1,978,526	863,766
Restricted cash and cash equivalents	786,926	109,415
Receivables	1,141,773	413,883
Reinsurance recoverable on unpaid losses	1,854,414	778,774
Reinsurance recoverable on paid losses	102,002	51,145
Deferred policy acquisition costs	260,967	157,465
Prepaid reinsurance premiums	383,559	110,332
Goodwill	967,717	674,930
Intangible assets	565,083	374,295
Other assets	1,067,922	663,019
Total Assets	23,955,511	12,556,588
LIABILITIES AND EQUITY	'	'
Unpaid losses and loss adjustment expenses	10,262,056	5,371,426
Life and annuity benefits	1,486,574	0
Unearned premiums	2,127,115	1,000,261
Payables to insurance and reinsurance companies	295,496	103,212
Senior long-term debt and other debt (estimated fair value of $2,372,000 in 2013 and $1,688,000 in 2012)	2,256,227	1,492,550
Other liabilities	777,850	613,897
Total Liabilities	17,205,318	8,581,346
Redeemable noncontrolling interests	72,183	86,225
Commitments and contingencies	'	'
Shareholders' equity:	'	'
Common stock	3,288,863	908,980
Retained earnings	2,294,909	2,068,340
Accumulated other comprehensive income	1,089,805	911,337
Total Shareholders' Equity	6,673,577	3,888,657
Noncontrolling interests	4,433	360
Total Equity	6,678,010	3,889,017
Total Liabilities and Equity	$23,955,511	$12,556,588

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Statement of Financial Position [Abstract]	'	'
Fixed maturities, amortized cost	$10,129,141	$4,562,278
Equity securities, cost	1,566,553	1,387,305
Senior long-term debt and other debt, estimated fair value	$2,372,000	$1,688,000

Consolidated_Statements_Of_Inc

Consolidated Statements Of Income And Comprehensive Income (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
OPERATING REVENUES	'	'	'
Earned premiums	$3,231,616	$2,147,128	$1,979,340
Net investment income	317,373	282,107	263,676
Net realized investment gains:	'	'	'
Other-than-temporary impairment losses	-4,706	-12,078	-14,250
Other-than-temporary impairment losses recognized in other comprehensive income	0	0	-5,946
Other-than-temporary impairment losses recognized in net income	-4,706	-12,078	-20,196
Net realized investment gains, excluding other-than-temporary impairment losses	67,858	43,671	56,053
Net realized investment gains	63,152	31,593	35,857
Other revenues	710,942	539,284	351,077
Total Operating Revenues	4,323,083	3,000,112	2,629,950
OPERATING EXPENSES	'	'	'
Losses and loss adjustment expenses	1,816,273	1,154,068	1,209,986
Underwriting, acquisition and insurance expenses	1,312,312	929,472	810,179
Amortization of intangible assets	55,223	33,512	24,291
Other expenses	663,528	478,248	309,046
Total Operating Expenses	3,847,336	2,595,300	2,353,502
Operating Income	475,747	404,812	276,448
Interest expense	114,004	92,762	86,252
Income Before Income Taxes	361,743	312,050	190,196
Income tax expense	77,898	53,802	41,710
Net Income	283,845	258,248	148,486
Net income attributable to noncontrolling interests	2,824	4,863	6,460
Net Income to Shareholders	281,021	253,385	142,026
OTHER COMPREHENSIVE INCOME	'	'	'
Net holding gains arising during the period	225,545	266,425	141,839
Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period	-141	-160	3,943
Reclassification adjustments for net gains included in net income	-40,830	-24,051	-22,341
Change in net unrealized gains on investments, net of taxes	184,574	242,214	123,441
Change in foreign currency translation adjustments, net of taxes	-10,143	1,534	-4,191
Change in net actuarial pension loss, net of taxes	4,065	6,664	-9,459
Total Other Comprehensive Income	178,496	250,412	109,791
Comprehensive Income	462,341	508,660	258,277
Comprehensive income attributable to noncontrolling interests	2,852	4,858	6,424
Comprehensive Income to Shareholders	$459,489	$503,802	$251,853
NET INCOME PER SHARE	'	'	'
Basic (dollars per share)	$22.57	$25.96	$14.66
Diluted (dollars per share)	$22.48	$25.89	$14.60

Consolidated_Statements_Of_Cha

Consolidated Statements Of Changes In Equity (USD $)	Total	Total Equity [Member]	Total Shareholders' Equity [Member]	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Noncontrolling Interests [Member]	Redeemable Noncontrolling Interests [Member]
In Thousands, except Share data	Total	Total Equity [Member]	Total Shareholders' Equity [Member]	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Noncontrolling Interests [Member]	Redeemable Noncontrolling Interests [Member]
Balance, redeemable noncontrolling interests at Dec. 31, 2010	'	'	'	'	'	'	'	$15,298
Balance at Dec. 31, 2010	'	3,172,394	3,171,523	884,457	1,735,973	551,093	871	'
Balance, shares at Dec. 31, 2010	'	'	'	9,718,000	'	'	'	'
Net income (loss)	148,486	141,836	142,026	'	142,026	0	-190	6,650
Other comprehensive income (loss)	109,791	109,827	109,827	'	0	109,827	0	-36
Comprehensive Income	258,277	251,663	251,853	'	'	'	-190	6,614
Issuance of common stock	'	1,182	1,182	1,182	0	0	0	0
Issuance of common stock, shares	'	'	'	16,000	'	'	'	'
Repurchase of common stock	'	-42,913	-42,913	0	-42,913	0	0	0
Repurchase of common stock, shares	'	'	'	-113,000	'	'	'	'
Restricted stock awards expensed	'	5,818	5,818	5,818	0	0	0	0
Restricted stock awards expensed, shares	'	'	'	0	'	'	'	'
Acquisitions	'	0	0	0	0	0	0	62,189
Acquisitions, shares	'	'	'	0	'	'	'	'
Adjustment of redeemable noncontrolling interests	0	'	'	'	'	'	'	'
Other	'	-29	50	50	0	0	-79	-9,870
Other, shares	'	'	'	0	'	'	'	'
Balance, redeemable noncontrolling interests at Dec. 31, 2011	'	'	'	'	'	'	'	74,231
Balance at Dec. 31, 2011	'	3,388,115	3,387,513	891,507	1,835,086	660,920	602	'
Balance, shares at Dec. 31, 2011	'	'	'	9,621,000	'	'	'	'
Net income (loss)	258,248	253,123	253,385	'	253,385	0	-262	5,125
Other comprehensive income (loss)	250,412	250,417	250,417	'	0	250,417	0	-5
Comprehensive Income	508,660	503,540	503,802	'	'	'	-262	5,120
Issuance of common stock	'	9,145	9,145	9,145	0	0	0	0
Issuance of common stock, shares	'	'	'	47,000	'	'	'	'
Repurchase of common stock	'	-16,873	-16,873	0	-16,873	0	0	0
Repurchase of common stock, shares	'	'	'	-39,000	'	'	'	'
Restricted stock awards expensed	'	6,462	6,462	6,462	0	0	0	0
Restricted stock awards expensed, shares	'	'	'	0	'	'	'	'
Acquisitions	'	0	0	0	0	0	0	15,055
Acquisitions, shares	'	'	'	0	'	'	'	'
Adjustment of redeemable noncontrolling interests	3,100	-3,101	-3,101	0	-3,101	0	0	3,101
Adjustment of redeemable noncontrolling interests, shares	'	'	'	0	'	'	'	'
Purchase of noncontrolling interest	'	'	1,430	1,430	0	0	'	'
Purchase of noncontrolling interest	'	'	'	'	'	'	0	-3,573
Purchase of noncontrolling interest	'	1,430	'	'	'	'	'	'
Purchase of noncontrolling interest, shares	'	'	'	0	'	'	'	'
Other	'	299	279	436	-157	0	20	-7,709
Other, shares	'	'	'	0	'	'	'	'
Balance, redeemable noncontrolling interests at Dec. 31, 2012	86,225	'	'	'	'	'	'	86,225
Balance at Dec. 31, 2012	3,889,017	3,889,017	3,888,657	908,980	2,068,340	911,337	360	'
Balance, shares at Dec. 31, 2012	'	'	'	9,629,000	'	'	'	'
Net income (loss)	283,845	280,063	281,021	'	281,021	0	-958	3,782
Other comprehensive income (loss)	178,496	178,468	178,468	'	0	178,468	0	28
Comprehensive Income	462,341	458,531	459,489	'	'	'	-958	3,810
Issuance of common stock	'	24,518	24,518	24,518	0	0	0	0
Issuance of common stock, shares	'	'	'	71,000	'	'	'	'
Repurchase of common stock	'	-57,388	-57,388	0	-57,388	0	0	0
Repurchase of common stock, shares	'	'	'	-109,000	'	'	'	'
Restricted stock awards expensed	'	25,239	25,239	25,239	0	0	0	0
Restricted stock awards expensed, shares	'	'	'	-3,000	'	'	'	'
Acquisitions, shares	'	'	'	4,398,000	'	'	'	'
Acquisition of Alterra	'	2,330,199	2,330,199	2,330,199	0	0	0	0
Adjustment of redeemable noncontrolling interests	-2,000	1,963	1,963	0	1,963	0	0	-1,963
Adjustment of redeemable noncontrolling interests, shares	'	'	'	0	'	'	'	'
Purchase of noncontrolling interest	'	'	-136	-136	0	0	'	'
Purchase of noncontrolling interest	'	'	'	'	'	'	0	-11,716
Purchase of noncontrolling interest	'	-136	'	'	'	'	'	'
Purchase of noncontrolling interest, shares	'	'	'	0	'	'	'	'
Other	'	6,067	1,036	63	973	0	5,031	-4,173
Other, shares	'	'	'	0	'	'	'	'
Balance, redeemable noncontrolling interests at Dec. 31, 2013	72,183	'	'	'	'	'	'	72,183
Balance at Dec. 31, 2013	$6,678,010	$6,678,010	$6,673,577	$3,288,863	$2,294,909	$1,089,805	$4,433	'
Balance, shares at Dec. 31, 2013	'	'	'	13,986,000	'	'	'	'

Consolidated_Statements_Of_Cas

Consolidated Statements Of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
OPERATING ACTIVITIES	'	'	'
Net income	$283,845	$258,248	$148,486
Adjustments to reconcile net income to net cash provided by operating activities:	'	'	'
Deferred income tax expense	4,050	37,648	5,649
Depreciation and amortization	190,066	87,326	70,572
Net realized investment gains	-63,152	-31,593	-35,857
Decrease (increase) in receivables	142,065	-36,590	-10,745
Decrease (increase) in deferred policy acquisition costs	-103,704	37,209	-5,891
Increase (decrease) in unpaid losses and loss adjustment expenses, net	290,130	-28,052	57,000
Decrease in life and annuity benefits	-40,235	0	0
Increase in unearned premiums, net	97,249	71,073	59,612
Increase (decrease) in payables to insurance and reinsurance companies	-150,764	19,190	-3,665
Increase (decrease) in income taxes payable	81,995	-9,909	28,036
Other	13,976	-12,017	-1,879
Net Cash Provided By Operating Activities	745,521	392,533	311,318
INVESTING ACTIVITIES	'	'	'
Proceeds from sales of fixed maturities and equity securities	879,564	336,548	288,046
Proceeds from maturities, calls and prepayments of fixed maturities	1,475,938	510,697	343,502
Cost of fixed maturities and equity securities purchased	-1,651,397	-426,439	-713,102
Net change in short-term investments	-470,423	-428,292	-216,972
Proceeds from sales of equity method investments	313,557	0	0
Cost of equity method investments	-38,018	-40,650	-9,880
Change in restricted cash and cash equivalents	-263,014	-37,642	-16,795
Additions to property and equipment	-47,725	-45,519	-60,132
Acquisitions, net of cash acquired	-12,198	-243,675	-120,102
Other	1,103	-2,158	14,329
Net Cash Provided (Used) By Investing Activities	187,387	-377,130	-491,106
FINANCING ACTIVITIES	'	'	'
Additions to senior long-term debt and other debt	547,214	492,792	336,181
Repayment and retirement of senior long-term debt and other debt	-321,978	-313,790	-90,557
Repurchases of common stock	-57,388	-16,873	-42,913
Issuance of common stock	24,518	9,145	1,182
Purchase of redeemable noncontrolling interests	-11,852	-2,143	0
Distributions to noncontrolling interests	-5,124	-7,684	-9,259
Other	-23	-19,485	-45
Net Cash Provided By Financing Activities	175,367	141,962	194,589
Effect of foreign currency rate changes on cash and cash equivalents	6,485	3,142	-1,823
Increase in cash and cash equivalents	1,114,760	160,507	12,978
Cash and cash equivalents at beginning of year	863,766	703,259	690,281
CASH AND CASH EQUIVALENTS AT END OF YEAR	$1,978,526	$863,766	$703,259

Summary_Of_Significant_Account

Summary Of Significant Accounting Policies	12 Months Ended
Summary Of Significant Accounting Policies	Dec. 31, 2013
Accounting Policies [Abstract]	'
Summary Of Significant Accounting Policies	'
	Summary of Significant Accounting Policies

	Markel Corporation is a diverse financial holding company serving a variety of niche markets. Markel Corporation's principal business markets and underwrites specialty insurance products. Through its wholly-owned subsidiary, Markel Ventures, Inc. (Markel Ventures), Markel Corporation also owns interests in various industrial and service businesses that operate outside of the specialty insurance marketplace.

	On May 1, 2013 (the Acquisition Date), Markel Corporation completed the acquisition of 100% of the issued and outstanding common stock of Alterra Capital Holdings Limited (Alterra) pursuant to an agreement dated December 18, 2012 which provided for the merger of Alterra with one of Markel Corporation's subsidiaries. Total purchase consideration was $3.3 billion. Alterra was a Bermuda-headquartered global enterprise providing diversified specialty insurance and reinsurance products to corporations, public entities and other property and casualty insurers.

	a)Basis of Presentation. The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (U.S. GAAP) and include the accounts of Markel Corporation and its subsidiaries (the Company). All significant intercompany balances and transactions have been eliminated in consolidation. The consolidated financial statements include the results of operations and cash flows of Alterra from the Acquisition Date to December 31, 2013 and not in any prior periods, except with respect to the Supplemental Pro Forma Information included in note 2. The Company consolidates the results of its Markel Ventures subsidiaries on a one-month lag. Certain prior year amounts have been reclassified to conform to the current presentation, including the separate presentation of restricted cash and cash equivalents on the consolidated balance sheets and corresponding change in cash flows from investing activities on the consolidated statements of cash flows.

	b)Use of Estimates. The preparation of financial statements in accordance with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities. Management periodically reviews its estimates and assumptions. Quarterly reviews include evaluating the adequacy of reserves for unpaid losses and loss adjustment expenses, life and annuity reinsurance benefit reserves, litigation contingencies, the reinsurance allowance for doubtful accounts and income tax liabilities, as well as analyzing the recoverability of deferred tax assets, estimating reinsurance premiums written and earned and evaluating the investment portfolio for other-than-temporary declines in estimated fair value. Estimates and assumptions for goodwill and intangible assets are reviewed in conjunction with an acquisition and goodwill and indefinite-lived intangible assets are reassessed at least annually for impairment. Actual results may differ materially from the estimates and assumptions used in preparing the consolidated financial statements.

	c)Investments. Available-for-sale investments are recorded at estimated fair value. Unrealized gains and losses on investments, net of deferred income taxes, are included in accumulated other comprehensive income in shareholders' equity. The Company completes a detailed analysis each quarter to assess whether the decline in the fair value of any investment below its cost basis is deemed other-than-temporary.

	Premiums and discounts are amortized or accreted over the lives of the related fixed maturities as an adjustment to the yield using the effective interest method. Dividend and interest income are recognized when earned. Realized investment gains or losses are included in earnings. Realized gains or losses from sales of investments are derived using the first-in, first-out method.

	Investments accounted for under the equity method of accounting are recorded at cost within other assets on the consolidated balance sheets and subsequently increased or decreased by the Company's proportionate share of the net income or loss of the investee. The Company records its proportionate share of net income or loss of the investee in net investment income. The Company records its proportionate share of other comprehensive income or loss of the investee as a component of other comprehensive income. Dividends or other equity distributions are recorded as a reduction of the investment. The Company reviews equity method investments for impairment when events or circumstances indicate that a decline in the fair value of the investment below its carrying value is other-than-temporary.

	d)Cash and Cash Equivalents. The Company considers all investments with original maturities of 90 days or less to be cash equivalents. The carrying value of the Company's cash and cash equivalents and restricted cash and cash equivalents approximates fair value.

	e)Receivables. Receivables include amounts receivable from agents, brokers and insureds, which represent premiums that are both currently due and amounts not yet due on insurance and reinsurance policies. Premiums for insurance policies are generally due at inception. Premiums for reinsurance policies generally become due over the period of coverage based on the policy terms. The Company monitors the credit risk associated with premiums receivable, taking into consideration the fact that in certain instances credit risk may be reduced by the Company's right to offset loss obligations or unearned premiums against premiums receivable. Amounts deemed uncollectible are charged to net income in the period they are determined. Changes in the estimate of reinsurance premiums written will result in an adjustment to premiums receivable in the period they are determined.

	f)Reinsurance Recoverables. Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability associated with the reinsured business. Allowances are established for amounts deemed uncollectible and reinsurance recoverables are recorded net of these allowances. The Company evaluates the financial condition of its reinsurers and monitors concentration risk to minimize its exposure to significant losses from individual reinsurers.

	g)Deferred Policy Acquisition Costs. Costs directly related to the acquisition of insurance premiums are deferred and amortized over the related policy period, generally one year. Concurrent with the adoption of Financial Accounting Standards Board (FASB) Accounting Standards Update (ASU) No. 2010-26, Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts, effective January 1, 2012, the Company only defers acquisition costs incurred that are related directly to the successful acquisition of new or renewal insurance contracts, including commissions to agents and brokers and premium taxes. Commissions received related to reinsurance premiums ceded are netted against broker commissions in determining acquisition costs eligible for deferral. To the extent that future policy revenues on existing policies are not adequate to cover related costs and expenses, deferred policy acquisition costs are charged to earnings. The Company does not consider anticipated investment income in determining whether a premium deficiency exists.

	h)Goodwill and Intangible Assets. Goodwill and intangible assets are recorded as a result of business acquisitions. Goodwill represents the excess of the amount paid to acquire a business over the net fair value of assets acquired and liabilities assumed at the date of acquisition. Indefinite-lived and other intangible assets are recorded at fair value as of the acquisition date. The determination of the fair value of certain assets acquired and liabilities assumed involves significant judgment and the use of valuation models and other estimates, which require assumptions that are inherently subjective. Goodwill and indefinite-lived intangible assets are tested for impairment at least annually. The Company completes an annual test during the fourth quarter of each year based upon the results of operations through September 30. Intangible assets with definite lives are amortized using the straight-line method over their estimated useful lives, generally five to 20 years, and are reviewed for impairment when events or circumstances indicate that their carrying value may not be recoverable.

	i)Property and Equipment. Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization of property and equipment are calculated using the straight-line method over the estimated useful lives (generally, the life of the lease for leasehold improvements, ten to 40 years for buildings, seven to 40 years for land improvements, three to ten years for furniture and equipment and three to 25 years for other property and equipment).

	j)Redeemable Noncontrolling Interests. The Company owns controlling interests in various companies through its Markel Ventures operations. Under the terms of certain of the acquisition and related agreements, the Company has the option to acquire the remaining equity interests and the remaining equity interests have the option to sell their interests to the Company in the future. The redemption value of the remaining equity interests is generally based on the respective company's earnings in specified periods preceding the redemption date. The redeemable noncontrolling interests generally become redeemable through 2018.

	The Company recognizes changes in the redemption value that exceed the carrying value of redeemable noncontrolling interests to retained earnings as if the balance sheet date were also the redemption date. Changes in the redemption value also result in an adjustment to net income to shareholders in the calculation of basic and diluted net income per share. The adjustment recorded to retained earnings during 2013 and 2012 was a decrease of $2.0 million and an increase of $3.1 million, respectively. There were no adjustments recorded to retained earnings in 2011 because the redemption values of the redeemable noncontrolling interests were less than or approximated their carrying values.

	k)Income Taxes. The Company records deferred income taxes to reflect the net tax effect of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and their tax bases. Deferred tax assets are reduced by a valuation allowance when management believes it is more likely than not that some, or all, of the deferred tax assets will not be realized. The Company recognizes the tax benefit from an uncertain tax position taken or expected to be taken in income tax returns only if it is more likely than not that the tax position will be sustained upon examination by tax authorities, based on the technical merits of the position. Tax positions that meet the more likely than not threshold are then measured using a probability weighted approach, whereby the largest amount of tax benefit that is greater than 50% likely of being realized upon ultimate settlement is recognized. The Company recognizes interest and penalties related to uncertain tax positions in income tax expense.

	l)Unpaid Losses and Loss Adjustment Expenses. Unpaid losses and loss adjustment expenses on our property and casualty insurance business are based on evaluations of reported claims and estimates for losses and loss adjustment expenses incurred but not reported. Estimates for losses and loss adjustment expenses incurred but not reported are based on reserve development studies, among other things. The Company does not discount reserves for losses and loss adjustment expenses to reflect estimated present value, except for reserves assumed in connection with an acquisition, which are recorded at fair value at the acquisition date. Recorded reserves are estimates, and the ultimate liability may be greater or less than the estimates.

	m)Life and Annuity Benefits. Prior to its acquisition by the Company, Alterra entered into long duration reinsurance contracts for life and annuity benefits which subject the Company to mortality, longevity and morbidity risks. The assumptions used to determine policy benefit reserves were determined at the Acquisition Date and are generally locked-in for the life of the contract unless an unlocking event occurs. To the extent existing policy reserves, together with the present value of future gross premiums and expected investment income earned thereon, are not adequate to cover the present value of future benefits, settlement and maintenance costs, the locked-in assumptions are revised to current best estimate assumptions and a charge to earnings for life and annuity benefits is recognized at that time. Because of the assumptions and estimates used in establishing reserves for life and annuity benefit obligations and the long-term nature of these reinsurance contracts, the ultimate liability may be greater or less than the estimates.

	Results attributable to the run-off of life and annuity reinsurance business are included in other revenues and other expenses in the Company's consolidated statements of income and comprehensive income and as part of the Company's Other Insurance (Discontinued Lines) segment.

	n)Revenue Recognition.

	Property and Casualty Premiums

	Insurance premiums are generally earned on a pro rata basis over the policy period, typically one year. The cost of reinsurance ceded is initially recorded as prepaid reinsurance premiums and is amortized over the reinsurance contract period in proportion to the amount of insurance protection provided. Premiums ceded are netted against premiums written.

	Assumed reinsurance premiums are recorded at the inception of each contract based upon contract terms and information received from cedents and brokers and are earned on a pro rata basis over the coverage period, or for multi-year contracts, in proportion with the underlying risk exposure to the extent there is variability in the exposure through the coverage period. Changes in reinsurance premium estimates are expected and may result in significant adjustments in any period. These estimates change over time as additional information regarding changes in underlying exposures is obtained. Any subsequent differences arising on such estimates are recorded as premiums written in the period they are determined. The Company uses the periodic method to account for assumed reinsurance from foreign reinsurers. The Company's foreign reinsurers provide sufficient information to record foreign assumed business in the same manner as the Company records assumed business from United States reinsurers.

	Certain contracts that the Company writes provide for reinstatement of coverage. Reinstatement premiums are the premiums for the restoration of the insurance or reinsurance limit of a contract to its full amount after a loss occurrence by the insured or reinsured. The Company accrues for reinstatement premiums resulting from losses recorded. Such accruals are based upon contractual terms and management judgment is involved with respect to the amount of losses recorded. Changes in estimates of losses recorded on contracts with reinstatement premium features will result in changes in reinstatement premiums based on contractual terms. Reinstatement premiums are recognized at the time losses are recorded and are earned on a pro-rata basis over the coverage period.

	Other Revenues

	Other revenues primarily relate to the Company's Markel Ventures operations and consist of revenues from the sale of manufactured products and service revenues. Revenues from manufactured products are generally recognized at the time title transfers to the customer, which occurs at the point of shipment or delivery to the customer, depending on the terms of the sales arrangement. Revenues from services are generally recognized as the services are performed. Services provided pursuant to a contract are recognized either over the contract period or upon completion of the elements specified in the contract, depending on the terms of the contract.

	o)Stock-based Compensation. Stock-based compensation expense is recognized as part of underwriting, acquisition and insurance expenses over the requisite service period. Stock-based compensation expense, net of taxes, was $18.4 million in 2013, $4.4 million in 2012 and $4.0 million in 2011. See note 12.

	p)Foreign Currency Translation. The functional currencies of the Company's foreign operations are the currencies in which the majority of their business is transacted. Assets and liabilities of foreign operations are translated into the United States Dollar using the exchange rates in effect at the balance sheet date. Revenues and expenses of foreign operations are translated using the average exchange rate for the period. Gains or losses from translating the financial statements of foreign operations are included, net of taxes, in shareholders' equity as a component of accumulated other comprehensive income. Gains and losses arising from transactions denominated in a foreign currency, other than a functional currency, are included in net income.

	The Company manages its exposure to foreign currency risk primarily by matching assets and liabilities denominated in the same currency. To the extent that assets and liabilities in foreign currencies are not matched, the Company is exposed to foreign currency risk. For functional currencies, the related exchange rate fluctuations are reflected in other comprehensive income. The cumulative foreign currency translation adjustment, net of taxes, was a loss of $11.2 million and $1.1 million at December 31, 2013 and 2012, respectively.

	q)Derivative Financial Instruments. Derivative instruments, including derivative instruments resulting from hedging activities, are measured at fair value and recognized as either assets or liabilities on the consolidated balance sheets. The changes in fair value of derivatives are recognized in earnings unless the derivative is designated as a hedge and qualifies for hedge accounting.

	The Company's foreign currency forward contracts are generally designated and qualified as hedges of a net investment in a foreign operation. The effective portion of the change in fair value resulting from these hedges is reported in currency translation adjustments as part of other comprehensive income. The ineffective portion of the change in fair value is recognized in earnings.

r)Comprehensive Income. Comprehensive income represents all changes in equity that result from recognized transactions and other economic events during the period. Other comprehensive income refers to revenues, expenses, gains and losses that under U.S. GAAP are included in comprehensive income but excluded from net income, such as unrealized gains or losses on investments, foreign currency translation adjustments and changes in net actuarial pension loss.

s)Net Income Per Share. Basic net income per share is computed by dividing adjusted net income to shareholders by the weighted average number of common shares outstanding during the year. Unvested share-based compensation awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid) are considered participating awards and are included in the computation of net income per share. Non-participating unvested share-based compensation awards are excluded from the computation of net income per share. Diluted net income per share is computed by dividing adjusted net income to shareholders by the weighted average number of common shares and dilutive potential common shares outstanding during the year. See note 12(b).

t)Recent Accounting Pronouncements. Effective January 1, 2013, the Company adopted FASB ASU No. 2013-02, Reporting Amounts Reclassified Out of Accumulated Other Comprehensive Income, which amends FASB Accounting Standards Codification (ASC) 220, Comprehensive Income, to improve the reporting of reclassifications out of accumulated other comprehensive income. ASU No. 2013-02 requires information about reclassifications out of accumulated other comprehensive income to be reported in one place, by component. The guidance also requires disclosure of the effect of significant reclassifications out of accumulated other comprehensive income on the respective line items in net income if the amount being reclassified is required under U.S. GAAP to be reclassified in its entirety to net income. For other amounts that are not required to be reclassified in their entirety to net income, an entity is required to cross-reference to other disclosures required under U.S. GAAP that provide additional detail about those amounts. The adoption of this guidance did not have an impact on the Company's financial position, results of operations or cash flows. The Company has included the additional disclosures required by ASU No. 2013-02 in note 13.

In July 2013, the FASB issued ASU No. 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists. ASU No. 2013-11 requires that a liability related to an unrecognized tax benefit be offset against a deferred tax asset for a net operating loss carryforward, a similar tax loss or a tax credit carryforward if such settlement is required or expected in the event the uncertain tax position is disallowed. In that case, the liability associated with the unrecognized tax benefit is presented in the financial statements as a reduction to the related deferred tax asset for a net operating loss carryforward, a similar tax loss or a tax credit carryforward. Otherwise, the unrecognized tax benefit should be presented in the financial statements as a liability and should not be combined with deferred tax assets. ASU No. 2013-11 becomes effective for the Company during the first quarter of 2014. The adoption of this ASU is not expected to impact the Company's financial position, results of operations or cash flows.

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2013
Acquisitions [Abstract]	'
Acquisitions	'
	Acquisitions

	Acquisition of Alterra

	a)Overview. On May 1, 2013, the Company completed the acquisition of 100% of the the issued and outstanding common stock of Alterra pursuant to an agreement dated December 18, 2012 (the Merger Agreement) which provided for the merger of Alterra with one of the Company's subsidiaries. Alterra was a Bermuda-headquartered global enterprise providing diversified specialty property and casualty insurance and reinsurance products to corporations, public entities and other property and casualty insurers. The acquisition of Alterra creates additional size and scale, providing additional insurance and investment opportunities for the Company. As a result of the acquisition of Alterra, the Company formed a new operating segment, the Alterra segment. Results attributable to Alterra's property and casualty insurance and reinsurance business are included in the Alterra segment. Alterra also offered life and annuity reinsurance products. In 2010, Alterra ceased writing life and annuity reinsurance contracts and placed this business into run-off. Results attributable to the run-off of life and annuity reinsurance business are included in the Company's Other Insurance (Discontinued Lines) segment. See note 20 for further discussion of the Company's operating segments.

	Pursuant to the terms of the Merger Agreement, on the Acquisition Date, equity holders of Alterra received, in exchange for each share of Alterra common stock held (other than restricted shares that did not vest in connection with the transaction), (1) 0.04315 shares of the Company's common stock and (2) $10.00 in cash. Equity holders of Alterra received total consideration of $3.3 billion, consisting of cash consideration of $964.3 million and stock consideration of 4.3 million shares of the Company's common stock.

	Following the acquisition, the Company's board of directors consists of all ten members from its pre-acquisition board of directors and two additional members who were designated by Alterra and approved by the Company's Nominating/Corporate Governance Committee.

	b)Purchase Price. The Company's total purchase price for Alterra as of the Acquisition Date was calculated as follows:



	(in thousands, except per share amounts)
	Shares of Alterra common stock outstanding as of the Acquisition Date	96,433

	Exchange ratio per the Merger Agreement	0.04315

	Markel share issuance to Alterra shareholders	4,161


	Shares of Alterra restricted stock outstanding as of the Acquisition Date	2,239

	Incentive award ratio per the Merger Agreement	0.06252

	Markel restricted stock issuance to Alterra restricted stock holders	140


	Multiplied by Markel's weighted average stock price on April 30, 2013 (1)	$	529.59


	Markel share and restricted stock issuance consideration, net of taxes	$	2,267,648


	Alterra common shares outstanding as of the Acquisition Date that received cash consideration	96,433

	Multiplied by cash price per share component per the Merger Agreement	$	10

	Markel cash consideration	$	964,330


	Fair value of Markel warrant issuance to Alterra warrant holders as of the Acquisition Date	$	73,685

	Fair value of Markel stock option issuance to Alterra stock option holders as of the Acquisition Date, net of taxes	$	12,335

	Fair value of partially vested Markel restricted stock unit issuance as of the Acquisition Date, net of taxes	$	6,867

	Unrecognized compensation on unvested restricted stock and restricted stock units	$	(20,572	)
	Total acquisition consideration	$	3,304,293


	-1	The fair value of the shares issued by the Company was calculated as the weighted average price of the Company's stock on April 30, 2013, the day preceding the Acquisition Date.

	As part of the consideration, the Company issued replacement warrants, options and restricted stock awards to holders of Alterra warrants, options and restricted stock awards. The acquisition consideration related to the options, restricted stock and restricted stock units issued was net of income taxes of $1.9 million, $10.1 million and $0.7 million, respectively. See note 12 for additional information about the equity awards issued in connection with the acquisition.

	c)Fair Value of Net Assets Acquired and Liabilities Assumed. The purchase price was allocated to the acquired assets and liabilities of Alterra based on estimated fair values at the Acquisition Date. The Company recognized goodwill of $295.7 million, all of which was recorded within the Alterra segment and is primarily attributable to Alterra's assembled workforce and synergies that are expected to result upon integration of Alterra into the Company's insurance operations and investing activities. None of the goodwill that was recorded is deductible for income tax purposes. The Company also recognized indefinite lived intangible assets of $37.5 million and other intangible assets of $170.0 million, which will be amortized over a weighted average period of 17 years.

	The following table summarizes the fair values of the assets acquired and liabilities assumed at the Acquisition Date.


	(dollars in thousands)
	ASSETS
Investments	$	6,407,841

Cash and cash equivalents	1,036,274

Restricted cash and cash equivalents	414,497

Receivables	866,388

Reinsurance recoverable on unpaid losses	1,169,084

Reinsurance recoverable on paid losses	80,672

Prepaid reinsurance premiums	317,445

Other assets	859,884

LIABILITIES
Unpaid losses and loss adjustment expenses	4,719,461

Life and annuity benefits	1,477,482

Unearned premiums	1,075,610

Payables to insurance and reinsurance companies	342,858

Senior long-term debt	512,463

Other liabilities	223,108

Net assets	2,801,103

Goodwill	295,690

Intangible assets	207,500

Acquisition date fair value	$	3,304,293


An explanation of the significant adjustments for fair value and the related impact on amortization is as follows:

•	Investments - Fixed maturity investments acquired include a net increase of $223.1 million to adjust the historical carrying amount of Alterra's investments to their estimated fair value as of the Acquisition Date. The difference in the historical amortized cost of the fixed maturity investments acquired and their estimated fair value as of the Acquisition Date, $495.5 million, represents incremental premium that will be amortized to net investment income over the term of the underlying securities. The amount of the unamortized incremental premium as of December 31, 2013 was $398.1 million, which will be amortized over a weighted average remaining term of approximately five years. The decrease in the unamortized incremental premium is due to amortization expense of $58.3 million and sales of securities.

•	Intangible assets - Establish the estimated fair value of intangible assets related to Alterra (see below for further detail).

•	Unearned Premiums - Unearned premiums acquired include a decrease of $176.3 million to adjust the carrying value of Alterra's historical unearned premiums to fair value as of the Acquisition Date. The adjustment consists of the present value of the expected underwriting profit within the unearned premiums liability less costs to service the related policies and a risk premium. This adjustment will be amortized to underwriting, acquisition and insurance expenses over a weighted average period of approximately one year, as the contracts for business in-force as of the Acquisition Date expire.

•	Unpaid losses and loss adjustment expenses - Unpaid losses and loss adjustment expenses acquired include an increase of $120.8 million to adjust the carrying value of Alterra's historical unpaid losses and loss adjustment expenses, net of related reinsurance recoverable, to fair value as of the Acquisition Date. The estimated fair value consists of the present value of the expected net loss and loss adjustment expense payments plus a risk premium. This adjustment, plus the $26.5 million unamortized fair value adjustment included in Alterra's historical unpaid losses and loss adjustment expenses, will be amortized to losses and loss adjustment expenses over a weighted average period of approximately five years, based on the estimated payout pattern of net reserves as of the Acquisition Date. As of December 31, 2013, the unamortized fair value adjustment included in unpaid losses and loss adjustment expenses was $136.5 million, which will be amortized over a weighted average remaining period of approximately four years.


•	Life and Annuity Benefits - Life and annuity benefits acquired include an increase of $329.6 million to adjust the carrying value of Alterra's historical life and annuity benefits to fair value as of the Acquisition Date. The estimated fair value consists of the present value of the expected net life and annuity benefit payments plus a risk premium. See note 10 for detail regarding accounting for life and annuity benefits.

•	Senior long-term debt - Senior long-term debt acquired includes an increase of $71.9 million to adjust the carrying value of Alterra's senior long-term debt to its estimated fair value based on prevailing interest rates and other factors as of the Acquisition Date. This adjustment will be amortized to interest expense over the term of the notes. See note 11. As of December 31, 2013, the unamortized premium on the acquired senior long-term debt was $66.1 million.

The following table summarizes the intangible assets recorded in connection with the acquisition, and as of December 31, 2013.



(dollars in thousands)	Amount				Economic
					Useful Life
Customer relationships	$	132,000			18 years

Broker relationships	19,000				18 years

Technology	18,000				Ten years

Trade names	1,000				One year

Lloyd's syndicate capacity	12,000				Indefinite

Insurance licenses	25,500				Indefinite

Intangible assets, before amortization, as of the Acquisition Date	207,500

Amortization (from the Acquisition Date through December 31, 2013)	7,785

Net intangible assets as of December 31, 2013	$	199,715


Customer relationships represent policyholder relationships and the network of insurance companies through which Alterra conducted its operations. The fair value of customer relationships and broker relationships was estimated using the income approach. Critical inputs into the valuation model for customer relationships and broker relationships include estimates of expected premium and attrition rates, and discounting at a weighted average cost of capital. Technology represents the intangible asset related to Alterra's internally developed software and was valued using the income approach.

The fair value of Lloyd's syndicate capacity and insurance licenses was estimated using the market approach. Lloyd's syndicate capacity represents Alterra's authorized premium income limit to write insurance business in the Lloyd's of London (Lloyd's) insurance market. The Lloyd's capacity is renewed annually at no cost to the Company or may be freely purchased or sold, subject to Lloyd's approval. The ability to write insurance business within the syndicate capacity is indefinite with the premium income limit being set annually by the Company, subject to Lloyd's approval.

d)Income Taxes. As a result of the acquisition, Alterra and its non-U.S. subsidiaries became controlled foreign corporations subject to U.S. income tax at a statutory rate of 35%. The acquisition was taxable to U.S. shareholders of Alterra, and Markel has elected to treat it as an asset acquisition under section 338(g) of the U.S. Internal Revenue Code of 1986 (IRC), as amended.

Effective May 1, 2013, the Company made an IRC section 953(d) election with respect to Markel Bermuda Limited (Markel Bermuda, formerly known as Alterra Bermuda Limited), a wholly-owned subsidiary of Alterra. As a result of the 953(d) election, Markel Bermuda is treated as a domestic corporation for U.S. tax purposes and, accordingly, is required to record deferred taxes at the 35% statutory U.S. rate.

As part of the allocation of the purchase price, the Company recorded net deferred tax assets of $310.1 million. Of this amount, $343.9 million represents deferred tax assets related to accrued losses and loss adjustment expenses and life and annuity benefits, which were partially offset by deferred tax liabilities of $64.6 million related to the estimated fair value of the intangible assets recorded. Other net deferred tax assets recorded primarily relate to differences between financial reporting and tax bases of the acquired assets and liabilities as of the Acquisition Date. At December 31, 2013, earnings of Alterra's foreign subsidiaries are considered reinvested indefinitely, consistent with the Company's other foreign subsidiaries, and no provision for deferred U.S. income tax has been recorded. As of December 31, 2013, the allocation of the purchase price reflects an increase of $54.3 million in the amount recorded for net deferred tax assets from the allocation initially reported at June 30, 2013 and a corresponding reduction in the amount recorded for goodwill.

e)Transaction and Acquisition-Related Costs. The following table summarizes transaction and acquisition-related costs incurred by the Company in connection with the acquisition, all of which were included in underwriting, acquisition and insurance expenses in the consolidated statements of income and comprehensive income.



(dollars in thousands)	Year Ended
	31-Dec-13
Transaction costs	$	15,981

Acquisition-related costs:
Severance costs	31,734

Stay bonuses	14,804

Acceleration of Alterra long-term incentive compensation awards and restricted stock awards	12,621

Total transaction and acquisition-related costs	$	75,140


Transaction costs primarily consist of due diligence, legal and investment banking costs. Per the terms of the Merger Agreement, transaction costs attributable to Alterra were recorded and paid by Alterra prior to the Acquisition Date ($23.0 million) and are not included within the Company's consolidated statements of income and comprehensive income.

In connection with the acquisition, Alterra instituted a retention plan for certain employees under which Alterra committed to the payment of stay bonuses to such employees one year from the Acquisition Date, provided they remain employed with the Company through that date. Payments may be accelerated for certain qualifying employment terminations.

Prior to its acquisition by the Company, Alterra granted long term incentive awards to certain employees to be paid in the form of cash on March 1, 2016, provided they remain employed with the Company on that date. Payments may be accelerated prior to March 1, 2016 for certain qualifying employment terminations. Additionally, as part of the purchase consideration, the Company issued replacement restricted stock awards to holders of Alterra restricted stock awards. As a result of separations made in connection with the acquisition, the Company recognized expense totaling $12.6 million related to the acceleration of certain of these awards during the year ended December 31, 2013.

f)Financial Results. The following table summarizes the results of Alterra since the Acquisition Date that have been included within the Company's consolidated statements of income and comprehensive income.



(dollars in thousands)	Year Ended
	December 31, 2013
Operating revenues	$	912,387

Net loss to shareholders	$	(93,074	)

g)Supplemental Pro Forma Information (unaudited). Alterra's results have been included in the Company's Consolidated Financial Statements from the Acquisition Date to December 31, 2013. The following table presents unaudited pro forma consolidated information for the years ended December 31, 2013 and 2012 and assumes the Company's acquisition of Alterra occurred on January 1, 2012. The pro forma financial information is presented for informational purposes only and does not necessarily reflect the results that would have occurred had the acquisition taken place on January 1, 2012, nor is it necessarily indicative of future results. Significant adjustments used to determine pro forma results include amortization of intangible assets and amortization of fair value adjustments discussed in c) above, and the corresponding income tax effects. The Company also excluded certain charges from the pro forma results, including transaction costs incurred by the Company ($16.0 million) and Alterra ($23.0 million) totaling $39.0 million for the year ended December 31, 2013, severance costs attributable to the acquisition totaling $31.7 million for the year ended December 31, 2013, and stay bonuses of $14.8 million for the year ended December 31, 2013. The acceleration of compensation expense during the year ended December 31, 2013 related to Alterra's long-term incentive compensation awards and restricted stock awards was attributable to the acquisition; however, the incremental expense recognized during the period only represents a timing difference in the recognition of expense. Therefore, it was not excluded from the pro forma underwriting results.



	Unaudited
	Consolidated Pro Forma
	Years Ended December 31,
(in thousands, except per share amounts)	2013				2012
Earned premiums	$	3,680,220			$	3,509,834

Operating revenues	4,899,628				4,561,107

Net income to shareholders	422,829				308,496


U.S. GAAP combined ratio (1)	95		%		99		%

Basic net income per share	$	30.33			$	21.79

Diluted net income per share	$	30.19			$	21.71


Weighted average common shares outstanding:
Basic	14,007				14,014

Diluted	14,069				14,065


-1	The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums.

Acquisition of Essentia

On January 1, 2013, the Company completed its acquisition of 100% of the outstanding shares of Essentia Insurance Company (Essentia), a company that underwrites insurance exclusively for Hagerty Insurance Agency and Hagerty Classic Marine Insurance Agency (collectively, Hagerty) throughout the United States. Hagerty offers insurance for classic cars, vintage boats, motorcycles and related automotive collectibles. The Company recognized intangible assets of $35.4 million associated with this acquisition, which includes $25.0 million of customer relationships to be amortized over a weighted average period of six years. Results attributable to this acquisition are included in the Specialty Admitted segment.

On January 1, 2014, Hagerty exercised its option to purchase 9.9% of the outstanding shares of Essentia, which reduced the Company's ownership interest in Essentia to 90.1%.

Acquisition of Abbey Protection

On January 17, 2014, the Company completed its acquisition of 100% of the issued and to be issued share capital of Abbey Protection plc (Abbey), an integrated specialty insurance and consultancy group headquartered in London. Abbey's business is focused on the underwriting and sale of insurance products to small and medium-sized enterprises and affinity groups in the United Kingdom providing protection against legal expenses and professional fees incurred as a result of legal actions or investigations by tax authorities, as well as providing a range of complementary legal, professional and reinsurance services.

Total consideration for this acquisition was $190.0 million, all of which was cash consideration. The purchase price allocation for Abbey will be completed in the first quarter of 2014.

Investments

Investments	12 Months Ended
	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]	'
Investments	'
	Investments

	a)The following tables summarize the Company's available-for-sale investments.



		December 31, 2013
	(dollars in thousands)	Amortized			Gross			Gross				Unrealized Other-				Estimated
		Cost			Unrealized			Unrealized				Than-Temporary				Fair
					Holding			Holding				Impairment Losses				Value
					Gains			Losses
	Fixed maturities:
	U.S. Treasury securities and obligations of U.S. government agencies	$	1,215,522		$	9,051		$	(30,342	)		$	—			$	1,194,231

	Obligations of states, municipalities and political subdivisions	2,986,758			116,341			(27,384		)		—				3,075,715

	Foreign governments	1,484,818			30,647			(54,411		)		—				1,461,054

	Commercial mortgage-backed securities	379,555			62			(11,796		)		—				367,821

	Residential mortgage-backed securities	875,902			13,046			(16,442		)		(2,258		)		870,248

	Asset-backed securities	189,646			257			(1,614		)		—				188,289

	Corporate bonds	2,996,940			54,777			(61,650		)		(4,889		)		2,985,178

	Total fixed maturities	10,129,141			224,181			(203,639		)		(7,147		)		10,142,536

	Equity securities:
	Insurance, banks and other financial institutions	422,975			592,112			(4		)		—				1,015,083

	Industrial, consumer and all other	1,143,578			1,094,251			(1,114		)		—				2,236,715

	Total equity securities	1,566,553			1,686,363			(1,118		)		—				3,251,798

	Short-term investments	1,452,270			18			—				—				1,452,288

	Investments, available-for-sale	$	13,147,964		$	1,910,562		$	(204,757	)		$	(7,147	)		$	14,846,622


		December 31, 2012
	(dollars in thousands)	Amortized			Gross			Gross				Unrealized Other-				Estimated
		Cost			Unrealized			Unrealized				Than-Temporary				Fair
					Holding			Holding				Impairment Losses				Value
					Gains			Losses
	Fixed maturities:
	U.S. Treasury securities and obligations of U.S. government agencies	$	297,663		$	19,844		$	—			$	—			$	317,507

	Obligations of states, municipalities and political subdivisions	2,586,867			245,057			(362		)		—				2,831,562

	Foreign governments	503,844			52,764			—				—				556,608

	Residential mortgage-backed securities	202,644			14,996			(5		)		(2,258		)		215,377

	Asset-backed securities	13,828			517			—				—				14,345

	Corporate bonds	957,432			93,395			(121		)		(6,822		)		1,043,884

	Total fixed maturities	4,562,278			426,573			(488		)		(9,080		)		4,979,283

	Equity securities:
	Insurance, banks and other financial institutions	508,771			389,434			(138		)		—				898,067

Industrial, consumer and all other	878,534			637,783			(7,433		)		—				1,508,884

Total equity securities	1,387,305			1,027,217			(7,571		)		—				2,406,951

Short-term investments	973,318			26			(14		)		—				973,330

Investments, available-for-sale	$	6,922,901		$	1,453,816		$	(8,073	)		$	(9,080	)		$	8,359,564


b)The following tables summarize gross unrealized investment losses by the length of time that securities have continuously been in an unrealized loss position.



	December 31, 2013
	Less than 12 months						12 months or longer								Total
(dollars in thousands)	Estimated			Gross			Estimated				Gross				Estimated			Gross
	Fair			Unrealized			Fair				Unrealized				Fair			Unrealized
	Value			Holding and			Value				Holding and				Value			Holding and
				Other-Than-							Other-Than-							Other-Than-
				Temporary							Temporary							Temporary
				Impairment							Impairment							Impairment
				Losses							Losses							Losses
Fixed maturities:
U.S. Treasury securities and obligations of U.S. government agencies	$	587,929		$	(30,342	)	$	—			$	—			$	587,929		$	(30,342	)

Obligations of states, municipalities and political subdivisions	513,608			(27,238		)	3,512				(146		)		517,120			(27,384		)

Foreign governments	950,040			(54,411		)	—				—				950,040			(54,411		)

Commercial mortgage-backed securities	357,737			(11,796		)	—				—				357,737			(11,796		)

Residential mortgage-backed securities	437,675			(18,700		)	—				—				437,675			(18,700		)

Asset-backed securities	142,011			(1,614		)	—				—				142,011			(1,614		)

Corporate bonds	1,817,737			(66,539		)	—				—				1,817,737			(66,539		)

Total fixed maturities	4,806,737			(210,640		)	3,512				(146		)		4,810,249			(210,786		)

Equity securities:
Insurance, banks and other financial institutions	144			(4		)	—				—				144			(4		)

Industrial, consumer and all other	20,943			(714		)	27,735				(400		)		48,678			(1,114		)

Total equity securities	21,087			(718		)	27,735				(400		)		48,822			(1,118		)

Total	$	4,827,824		$	(211,358	)	$	31,247			$	(546	)		$	4,859,071		$	(211,904	)


At December 31, 2013, the Company held 1,364 securities with a total estimated fair value of $4.9 billion and gross unrealized losses of $211.9 million. Of these 1,364 securities, nine securities had been in a continuous unrealized loss position for one year or longer and had a total estimated fair value of $31.2 million and gross unrealized losses of $0.5 million. Of these securities, eight securities were fixed maturities and one was an equity security. The Company does not intend to sell or believe it will be required to sell these fixed maturities before recovery of their amortized cost. The Company has the ability and intent to hold the equity security for a period of time sufficient to allow for the anticipated recovery of its fair value.



	December 31, 2012
	Less than 12 months						12 months or longer								Total
(dollars in thousands)	Estimated			Gross			Estimated				Gross				Estimated			Gross
	Fair			Unrealized			Fair				Unrealized				Fair			Unrealized
	Value			Holding and			Value				Holding and				Value			Holding and
				Other-Than-							Other-Than-							Other-Than-
				Temporary							Temporary							Temporary
				Impairment							Impairment							Impairment
				Losses							Losses							Losses
Fixed maturities:
Obligations of states, municipalities and political subdivisions	$	2,833		$	(46	)	$	3,616			$	(316	)		$	6,449		$	(362	)

Residential mortgage-backed securities	364			(2,260		)	201				(3		)		565			(2,263		)

Corporate bonds	—			(6,822		)	3,860				(121		)		3,860			(6,943		)

Total fixed maturities	3,197			(9,128		)	7,677				(440		)		10,874			(9,568		)

Equity securities:
Insurance, banks and other financial institutions	2,431			(138		)	—				—				2,431			(138		)

Industrial, consumer and all other	82,109			(7,310		)	1,983				(123		)		84,092			(7,433		)

Total equity securities	84,540			(7,448		)	1,983				(123		)		86,523			(7,571		)

Short-term investments	228,820			(14		)	—				—				228,820			(14		)

Total	$	316,557		$	(16,590	)	$	9,660			$	(563	)		$	326,217		$	(17,153	)


At December 31, 2012, the Company held 35 securities with a total estimated fair value of $326.2 million and gross unrealized losses of $17.2 million. Of these 35 securities, ten securities had been in a continuous unrealized loss position for one year or longer and had a total estimated fair value of $9.7 million and gross unrealized losses of $0.6 million. Of these securities, eight securities were fixed maturities and two were equity securities.

The Company completes a detailed analysis each quarter to assess whether the decline in the fair value of any investment below its cost basis is deemed other-than-temporary. All securities with unrealized losses are reviewed. The Company considers many factors in completing its quarterly review of securities with unrealized losses for other-than-temporary impairment, including the length of time and the extent to which fair value has been below cost and the financial condition and near-term prospects of the issuer. For equity securities, the ability and intent to hold the security for a period of time sufficient to allow for anticipated recovery is considered. For fixed maturities, the Company considers whether it intends to sell the security or if it is more likely than not that it will be required to sell the security before recovery, the implied yield-to-maturity, the credit quality of the issuer and the ability to recover all amounts outstanding when contractually due.

For equity securities, a decline in fair value that is considered to be other-than-temporary is recognized in net income based on the fair value of the security at the time of assessment, resulting in a new cost basis for the security. For fixed maturities where the Company intends to sell the security or it is more likely than not that the Company will be required to sell the security before recovery of its amortized cost, a decline in fair value is considered to be other-than-temporary and is recognized in net income based on the fair value of the security at the time of assessment, resulting in a new cost basis for the security. If the decline in fair value of a fixed maturity below its amortized cost is considered to be other-than-temporary based upon other considerations, the Company compares the estimated present value of the cash flows expected to be collected to the amortized cost of the security. The extent to which the estimated present value of the cash flows expected to be collected is less than the amortized cost of the security represents the credit-related portion of the other-than-temporary impairment, which is recognized in net income, resulting in a new cost basis for the security. Any remaining decline in fair value represents the non-credit portion of the other-than-temporary impairment, which is recognized in other comprehensive income. The discount rate used to calculate the estimated present value of the cash flows expected to be collected is the effective interest rate implicit for the security at the date of purchase.

When assessing whether it intends to sell a fixed maturity or if it is likely to be required to sell a fixed maturity before recovery of its amortized cost, the Company evaluates facts and circumstances including decisions to reposition the investment portfolio, potential sales of investments to meet cash flow needs and, ultimately, current market prices. Additional information on the methodology and significant inputs, by security type, that the Company used to determine the amount of credit loss recognized on fixed maturities with declines in fair value below amortized cost that were considered to be other-than-temporary is provided below.

Residential / Commercial mortgage-backed securities. For mortgage-backed securities, credit impairment is assessed by estimating future cash flows from the underlying mortgage loans and interest payments. The cash flow estimate incorporates actual cash flows from the mortgage-backed securities through the current period and then projects the remaining cash flows using a number of assumptions, including prepayment rates, default rates, recovery rates on foreclosed properties and loss severity assumptions. Management develops specific assumptions using market data and internal estimates, as well as estimates from rating agencies and other third party sources. Default rates are estimated by considering current underlying mortgage loan performance and expectations of future performance. Estimates of future cash flows are discounted to present value. If the present value of expected cash flows is less than the amortized cost, the Company recognizes the estimated credit loss in net income.

Corporate bonds and obligations of states, municipalities and political subdivisions. For corporate bonds and obligations of states, municipalities and political subdivisions, credit impairment is assessed by evaluating the underlying issuer. As part of this assessment, the Company analyzes various factors, including the following:


•	fundamentals of the issuer, including current and projected operating results, current liquidity position and ability to raise capital;

•	fundamentals of the industry in which the issuer operates;

•	expectations of defaults and recovery rates;

•	changes in ratings by rating agencies;

•	other relevant market considerations; and

•	receipt of interest payments.

Default probabilities and recovery rates from rating agencies are key factors used in calculating the credit loss. Additional research of the industry and issuer is completed to determine if there is any current information that may affect the fixed maturity or its issuer in a negative manner and require an adjustment to the cash flow assumptions.

c)The amortized cost and estimated fair value of fixed maturities at December 31, 2013 are shown below by contractual maturity.



(dollars in thousands)	Amortized			Estimated
	Cost			Fair Value
Due in one year or less	$	885,726		$	891,654

Due after one year through five years	2,891,314			2,947,173

Due after five years through ten years	2,217,759			2,254,169

Due after ten years	2,689,239			2,623,182

	8,684,038			8,716,178

Commercial mortgage-backed securities	379,555			367,821

Residential mortgage-backed securities	875,902			870,248

Asset-backed securities	189,646			188,289

Total fixed maturities	$	10,129,141		$	10,142,536


Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties, and the lenders may have the right to put the securities back to the borrower. Based on expected maturities, the estimated average duration of fixed maturities was 4.8 years.

d)The following table presents the components of net investment income.



	Years Ended December 31,
(dollars in thousands)	2013			2012			2011
Interest:
Municipal bonds (tax-exempt)	$	82,308		$	90,316		$	94,457

Municipal bonds (taxable)	28,041			22,663			23,277

Other taxable bonds	134,377			107,270			117,242

Short-term investments, including overnight deposits	3,573			2,755			2,484

Dividends on equity securities	48,641			50,416			35,996

Change in fair value of credit default swap	10,460			16,641			(4,103		)

Income from equity method investments	21,898			1,961			584

Other	355			(41		)	1,551

	329,653			291,981			271,488

Investment expenses	(12,280		)	(9,874		)	(7,812		)
Net investment income	$	317,373		$	282,107		$	263,676


e)The following table summarizes the activity for credit losses recognized in net income on fixed maturities where other-than-temporary impairment was identified and a portion of the other-than-temporary impairment was included in other comprehensive income.



	Years Ended December 31,
(dollars in thousands)	2013			2012			2011
Cumulative credit loss, beginning of year	$	21,370		$	21,370		$	10,307

Additions:
Other-than-temporary impairment losses not previously recognized	—			—			875

Increases related to other-than-temporary impairment losses previously recognized	—			—			10,203

Total additions	—			—			11,078

Reductions:
Sales or maturities of fixed maturities on which credit losses were recognized	(8,622		)	—			(15		)

Cumulative credit loss, end of year	$	12,748		$	21,370		$	21,370


f)The following table presents net realized investment gains and the change in net unrealized gains on investments.



	Years Ended December 31,
(dollars in thousands)	2013			2012			2011
Realized gains:
Sales of fixed maturities	$	13,772		$	18,337		$	17,035

Sales of equity securities	73,592			29,578			36,863

Other	5,940			749			2,626

Total realized gains	93,304			48,664			56,524

Realized losses:
Sales of fixed maturities	(25,168		)	(563		)	(410		)
Sales of equity securities	(278		)	(342		)	(61		)
Other-than-temporary impairments	(4,706		)	(12,078		)	(20,196		)
Other	—			(4,088		)	—

Total realized losses	(30,152		)	(17,071		)	(20,667		)
Net realized investment gains	$	63,152		$	31,593		$	35,857

Change in net unrealized gains on investments:
Fixed maturities	$	(403,610	)	$	51,783		$	190,976

Equity securities	665,599			302,013			(8,250		)

Short-term investments	6			12			(4		)

Net increase	$	261,995		$	353,808		$	182,722


g)The following table presents other-than-temporary impairment losses recognized in net income and included in net realized investment gains by investment type.



	Years Ended December 31,
(dollars in thousands)	2013			2012			2011
Fixed maturities:
Obligations of states, municipalities and political subdivisions	$	(1,242	)	$	—		$	—

Residential mortgage-backed securities	(640		)	—			(11,078		)

Total fixed maturities	(1,882		)	—			(11,078		)

Equity securities:
Insurance, banks and other financial institutions	—			(10,336		)	(4,251		)

Industrial, consumer and all other	(2,824		)	(1,742		)	(4,867		)
Total equity securities	(2,824		)	(12,078		)	(9,118		)
Total	$	(4,706	)	$	(12,078	)	$	(20,196	)

h)As of December 31, 2013 and December 31, 2012, the Company had restricted assets totaling $6.1 billion and $1.4 billion, respectively. Restricted assets held in trust or on deposit for the benefit of policyholders or ceding companies or to support underwriting activities were $5.2 billion and $1.3 billion as of December 31, 2013 and December 31, 2012, respectively, of which $3.7 billion at December 31, 2013 was attributable to Alterra. Additionally, the Company has pledged investments and cash and cash equivalents totaling $695.1 million and $23.2 million as of December 31, 2013 and December 31, 2012, respectively, as security for letters of credit that have been issued by various banks on behalf of the Company, of which $645.4 million at December 31, 2013 was attributable to Alterra.

Total restricted assets are included on the Company's consolidated balance sheets as follows.



(dollars in thousands)	December 31, 2013			December 31, 2012
Investments, available-for-sale	$	5,225,701		$	1,262,755

Restricted cash and cash equivalents	786,926			109,415

Other assets	76,752			—

Total	$	6,089,379		$	1,372,170


i)At December 31, 2013 and December 31, 2012, investments in U.S. Treasury securities and obligations of U.S. government agencies were the only investments in any one issuer that exceeded 10% of shareholders' equity.

At December 31, 2013, the Company's ten largest equity holdings represented $1.5 billion, or 46%, of the equity portfolio. Investments in the property and casualty insurance industry represented $568.3 million, or 17%, of the equity portfolio at December 31, 2013. Investments in the property and casualty insurance industry included a $371.1 million investment in the common stock of Berkshire Hathaway Inc.

Receivables

Receivables	12 Months Ended
	Dec. 31, 2013
Receivables [Abstract]	'
Receivables	'
	Receivables

	The following table presents the components of receivables.



		December 31,
	(dollars in thousands)	2013			2012
	Amounts receivable from agents, brokers and insureds	$	1,058,021		$	332,570

	Trade accounts receivable	85,203			73,512

	Employee stock loans receivable (see note 12(c))	12,822			11,413

	Other	5,420			12,982

		1,161,466			430,477

	Allowance for doubtful receivables	(19,693		)	(16,594		)
	Receivables	$	1,141,773		$	413,883

Deferred_Policy_Acquisition_Co

Deferred Policy Acquisition Costs	12 Months Ended
	Dec. 31, 2013
Deferred Policy Acquisition Costs Disclosures [Abstract]	'
Deferred Policy Acquisition Costs	'
	Deferred Policy Acquisition Costs

	The following table presents the amounts of policy acquisition costs deferred and amortized.



		Years Ended December 31,
	(dollars in thousands)	2013			2012			2011
	Balance, beginning of year	$	157,465		$	194,674		$	188,783

	Policy acquisition costs deferred	575,417			390,900			485,345

	Amortization of policy acquisition costs	(471,915		)	(428,109		)	(479,454		)
	Deferred policy acquisition costs	$	260,967		$	157,465		$	194,674


	The following table presents the components of underwriting, acquisition and insurance expenses.



		Years Ended December 31,
	(dollars in thousands)	2013			2012			2011
	Transaction costs and other acquisition-related expenses (1)	$	75,140		$	—		$	—

	Prospective adoption of FASB ASU No. 2010-26 (2)	—			43,093			—

	Other amortization of policy acquisition costs	471,915			385,016			479,454

	Other operating expenses	765,257			501,363			330,725

	Underwriting, acquisition and insurance expenses	$	1,312,312		$	929,472		$	810,179


	(1)	In connection with the acquisition of Alterra, the Company incurred transaction costs of $16.0 million for the year ended December 31, 2013, which primarily consist of due diligence, legal and investment banking costs. Additionally, the Company incurred severance costs of $31.7 million, stay bonuses of $14.8 million and other compensation costs totaling $12.6 million related to the acceleration of certain long-term incentive compensation awards and restricted stock awards that were granted by Alterra prior to the acquisition.

	(2)	Effective January 1, 2012, the Company prospectively adopted FASB ASU No. 2010-26, Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts. At December 31, 2011, deferred policy acquisition costs included $43.1 million of costs that no longer met the criteria for deferral as of January 1, 2012 and were recognized into income during 2012, consistent with policy terms.

Property_And_Equipment

Property And Equipment	12 Months Ended
	Dec. 31, 2013
Property, Plant and Equipment [Abstract]	'
Property And Equipment	'
	Property and Equipment

	The following table presents the components of property and equipment, which are included in other assets on the consolidated balance sheets.



		December 31,
	(dollars in thousands)	2013			2012
	Land	$	48,036		$	45,199

	Buildings	59,307			53,767

	Leasehold improvements	68,363			55,626

	Land improvements	57,673			51,512

	Furniture and equipment	217,528			211,354

	Other	104,690			85,714

		555,597			503,172

	Accumulated depreciation and amortization	(207,688		)	(172,943		)
	Property and equipment	$	347,909		$	330,229


	Depreciation and amortization expense of property and equipment was $51.5 million, $36.0 million and $24.2 million for the years ended December 31, 2013, 2012 and 2011, respectively.

	The Company does not own any material properties. The Company leases substantially all of the facilities used by its insurance operations and certain furniture and equipment under operating leases. The Company's Markel Ventures operations own certain of their facilities and lease others.

Goodwill_And_Intangible_Assets

Goodwill And Intangible Assets	12 Months Ended
	Dec. 31, 2013
Goodwill and Intangible Assets Disclosure [Abstract]	'
Goodwill And Intangible Assets	'
	Goodwill and Intangible Assets

	The following table presents the components of goodwill.



	(dollars in thousands)	Excess and		Specialty			London			Alterra			Other(1)			Total
		Surplus Lines		Admitted			Insurance			Segment
		Segment		Segment			Market
							Segment
	January 1, 2012	$	81,770	$	64,914		$	309,064		$	—		$	151,813		$	607,561

	Acquisitions	—		26,140			—			—			40,888			67,028

	Foreign currency movements and other adjustments	—		—			596			—			(255		)	341

	December 31, 2012	$	81,770	$	91,054		$	309,660		$	—		$	192,446		$	674,930

	Acquisitions (see note 2)	—		—			—			295,690			1,185			296,875

	Foreign currency movements and other adjustments	—		—			(2,088		)	—			(2,000		)	(4,088		)

	31-Dec-13	$	81,770	$	91,054		$	307,572		$	295,690		$	191,631		$	967,717


	(1)	Amounts included in Other above are related to the Company's Markel Ventures operations.

	Goodwill and indefinite-lived intangible assets are tested for impairment at least annually. The Company completes an annual test during the fourth quarter of each year based upon the results of operations through September 30. There were no impairment losses recognized during 2013 or 2012.

	The following table presents the components of intangible assets with a net carrying amount.



		December 31,
		2013					2012
	(dollars in thousands)	Gross		Accumulated			Gross			Accumulated
		Carrying		Amortization			Carrying			Amortization
		Amount					Amount
	Customer relationships	$	298,886	$	(43,286	)	$	171,591		$	(29,955	)

	Broker relationships	178,693		(23,255		)	135,867			(12,317		)

	Trade names	65,880		(12,666		)	75,781			(9,075		)

	Technology	56,429		(16,222		)	40,109			(11,785		)

	Insurance licenses	40,185		(133		)	4,300			(67		)

	Lloyd's syndicate capacity	12,000		—			—			—

	Other	14,197		(5,625		)	14,558			(4,712		)

	Total	$	666,270	$	(101,187	)	$	442,206		$	(67,911	)


	Amortization of intangible assets was $55.2 million, $33.5 million and $24.3 million for the years ended December 31, 2013, 2012 and 2011, respectively. Amortization of intangible assets is estimated to be $45.7 million for 2014, $44.7 million for 2015, $41.8 million for 2016, $40.4 million for 2017 and $40.2 million for 2018. Indefinite-lived intangible assets were $58.0 million at December 31, 2013 and $10.1 million at December 31, 2012.

	In 2013, the Company acquired $247.0 million of intangible assets. The definite-lived intangible assets acquired are expected to be amortized over a weighted average period of 15.5 years. The definite-lived intangible assets acquired during 2013 include customer relationships, broker relationships, trade names and technology, which are expected to be amortized over a weighted average period of 18.0, 11.2, 4.5 and 10.0 years, respectively.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	Income Taxes

	Income before income taxes includes the following components.



		Years Ended December 31,
	(dollars in thousands)	2013				2012				2011
	Domestic operations	$	325,133			$	126,466			$	200,446

	Foreign operations	36,610				185,584				(10,250		)

	Income before income taxes	$	361,743			$	312,050			$	190,196


	Income tax expense includes the following components.



		Years Ended December 31,
	(dollars in thousands)	2013				2012				2011
	Current:
	Domestic	$	50,683			$	14,340			$	35,721

	Foreign	23,165				1,814				340

	Total current tax expense	73,848				16,154				36,061

	Deferred:
	Domestic	23,906				(3,734		)		436

	Foreign	(19,856		)		41,382				5,213

	Total deferred tax expense	4,050				37,648				5,649

	Income tax expense	$	77,898			$	53,802			$	41,710


	Foreign income tax expense (benefit) includes United States tax expense (benefit) on foreign operations.

	State income tax expense is not material to the consolidated financial statements.

	The Company made income tax payments of $35.7 million, $30.0 million and $35.0 million in 2013, 2012 and 2011, respectively. Current income taxes payable were $84.2 million and $2.2 million at December 31, 2013 and 2012, respectively, and were included in other liabilities on the consolidated balance sheets.

	Reconciliations of the United States corporate income tax rate to the effective tax rate on income before income taxes are presented in the following table.



		Years Ended December 31,
		2013			2012			2011
	United States corporate tax rate	35	%		35	%		35	%
	Tax-exempt investment income	(9	)		(12	)		(18	)
	Uncertain tax positions	—			—			(2	)

	Foreign operations	(4	)		(5	)		6

	Other	—			(1	)		1

	Effective tax rate	22	%		17	%		22	%

	The following table presents the components of domestic and foreign deferred tax assets and liabilities.



	December 31,
(dollars in thousands)	2013				2012
Assets:
Differences between financial reporting and tax bases	$	139,357			$	81,305

Unpaid losses and loss adjustment expenses	283,365				122,217

Life and annuity benefits	161,209				—

Unearned premiums recognized for income tax purposes	76,862				42,938

Other-than-temporary impairments not yet deductible for income tax purposes	34,978				40,450

Net operating loss carryforwards	43,010				7,388

Tax credit carryforwards	33,773				41,387

Total gross deferred tax assets	772,554				335,685

Liabilities:
Differences between financial reporting and tax bases	46,699				33,323

Deferred policy acquisition costs	65,543				36,039

Net unrealized gains on investments	459,015				406,295

Amortization of goodwill and other intangible assets	97,580				28,931

Total gross deferred tax liabilities	668,837				504,588

Net deferred tax asset (liability)	$	103,717			$	(168,903	)


The net deferred tax asset at December 31, 2013 was included in other assets on the consolidated balance sheet. The net deferred tax liability at December 31, 2012 was included in other liabilities on the consolidated balance sheet.

At December 31, 2013, the Company had tax credit carryforwards of $33.8 million. The earliest any of these credits will expire is 2019.

At December 31, 2013, the Company had net operating losses of $73.1 million that can be used to offset future income that is taxable in the United States from Markel Capital Limited, a wholly owned United Kingdom subsidiary. The Company's ability to use these losses in the United States expires between the years 2021 and 2032. At December 31, 2013, the Company had net operating losses of $81.6 million that can be used to offset future income that is taxable in the United States. The Company's ability to use these losses in the United States expires between the years 2027 and 2033.

The Company estimates that it will realize $668.8 million of the gross deferred tax assets, including net operating losses, recorded at December 31, 2013 through the reversal of existing temporary differences attributable to the gross deferred tax liabilities. The Company believes that it is more likely than not that it will realize $103.7 million of gross deferred tax assets by generating future taxable income and by using prudent and feasible tax planning strategies if future taxable income is not sufficient.

At December 31, 2013, the Company had unrecognized tax benefits of $18.2 million. If recognized, $15.9 million of these tax benefits would decrease the annual effective tax rate. The Company does not currently anticipate any significant changes in unrecognized tax benefits during 2014.

The following table presents a reconciliation of unrecognized tax benefits.


	Years Ended December 31,
(dollars in thousands)	2013				2012
Unrecognized tax benefits, beginning of year	$	18,870			$	19,586

Increases based upon tax positions taken during the current year	—				888

Increases for tax positions taken in prior years	—				218

Decreases for tax positions taken in prior years	—				(764		)

Lapse of statute of limitations	(651		)		(1,058		)
Unrecognized tax benefits, end of year	$	18,219			$	18,870


At December 31, 2013, earnings of the Company's foreign subsidiaries, with the exception of our Bermuda subsidiaries, are considered reinvested indefinitely and no provision for deferred United States income taxes has been recorded. It is not practicable to determine the amount of unrecorded deferred tax liabilities associated with such earnings due to the complexity of this calculation.

The Company is subject to income tax in the United States and in foreign jurisdictions. With few exceptions, the Company is no longer subject to income tax examination by tax authorities for years ended before January 1, 2010.

Unpaid_Losses_And_Loss_Adjustm

Unpaid Losses And Loss Adjustment Expenses	12 Months Ended
	Dec. 31, 2013
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]	'
Unpaid Losses And Loss Adjustment Expenses	'
	Unpaid Losses and Loss Adjustment Expenses

	a)The following table presents a reconciliation of consolidated beginning and ending reserves for losses and loss adjustment expenses.



		Years Ended December 31,
	(dollars in thousands)	2013				2012				2011
	Net reserves for losses and loss adjustment expenses, beginning of year	$	4,592,652			$	4,607,767			$	4,600,316

	Foreign currency movements, commutations and other	(780		)		30,359				(7,496		)

	Adjusted net reserves for losses and loss adjustment expenses, beginning of year	4,591,872				4,638,126				4,592,820

	Incurred losses and loss adjustment expenses:
	Current year	2,227,402				1,553,070				1,563,993

	Prior years	(411,129		)		(399,002		)		(354,007		)
	Total incurred losses and loss adjustment expenses	1,816,273				1,154,068				1,209,986

	Payments:
	Current year	670,928				268,745				291,837

	Prior years	906,302				931,955				898,318

	Total payments	1,577,230				1,200,700				1,190,155

	Effect of foreign currency rate changes	(7,915		)		1,158				(4,884		)

	Net reserves for losses and loss adjustment expenses of acquired insurance companies	3,584,642				—				—

	Net reserves for losses and loss adjustment expenses, end of year	8,407,642				4,592,652				4,607,767

	Reinsurance recoverable on unpaid losses	1,854,414				778,774				791,102

	Gross reserves for losses and loss adjustment expenses, end of year	$	10,262,056			$	5,371,426			$	5,398,869


	Beginning of year net reserves for losses and loss adjustment expenses are adjusted, when applicable, for the impact of changes in foreign currency rates, commutations and other items. In 2013, beginning of year net reserves for losses and loss adjustment expenses were increased by a movement of $0.7 million in foreign currency rates of exchange, which was more than offset by commutations. In 2012, beginning of year net reserves for losses and loss adjustment expenses were increased by a movement of $23.4 million in foreign currency rates of exchange. In 2011, beginning of year net reserves for losses and loss adjustment expenses were decreased by a movement of $14.1 million in foreign currency rates of exchange, which was offset in part by increases for other items including commutations.

	As a result of the acquisition of Alterra, the Company recorded net reserves for losses and loss adjustment expenses of $3.6 billion as of the Acquisition Date. These reserves were recorded at fair value as part of the Company's purchase accounting. See note 2 for a discussion of the Company's acquisition of Alterra.

	In 2013, incurred losses and loss adjustment expenses included $411.1 million of favorable development on prior years' loss reserves, which was primarily due to $293.9 million of loss reserve redundancies experienced in the London Insurance Market segment and on the professional and products liability and casualty programs within the Excess and Surplus Lines segment as actual claims reporting patterns on prior accident years have been more favorable than the Company's actuarial analyses initially anticipated. The favorable development on prior years' loss reserves in 2013 was partially offset by $30.1 million of adverse development in prior years' loss reserves on asbestos and environmental (A&E) exposures.

	During the third quarter of each of the past three years, the Company completed an in-depth, actuarial review of its A&E exposures. Over the past few years, the number of A&E claims reported each year across the property and casualty industry has been on the decline. However, at the same time, the likelihood of making an indemnity payment has risen, thus increasing the average cost per reported claim. During our 2012 annual review, we reduced our estimate of the ultimate claims count, while increasing our estimate of the number of claims that would ultimately be closed with an indemnity payment. During our 2013 annual review, our expectation of the severity of the outcome of known claims increased. As a result, prior years' loss reserves for A&E exposures were increased by $28.4 million in 2013 and $31.1 million in 2012. During the 2011 review, the Company determined that no adjustment to loss reserves was necessary.

	Current year incurred losses and loss adjustment expenses for 2012 included $99.6 million of estimated net losses related to Hurricane Sandy. Current year incurred losses and loss adjustment expenses for 2011 included $150.9 million of estimated net losses related to the Thai floods, Hurricane Irene, U.S. tornadoes, Japanese earthquake and tsunami, Australian floods and New Zealand earthquakes. The estimated net losses on these natural catastrophes in 2012 and 2011 were net of estimated reinsurance recoverables of $77.6 million and $36.3 million, respectively.

	In 2012, incurred losses and loss adjustment expenses included $399.0 million of favorable development on prior years' loss reserves, which was primarily due to $336.7 million of loss reserve redundancies experienced in the London Insurance Market segment and on the professional and products liability and casualty programs within the Excess and Surplus Lines segment as actual claims reporting patterns on prior accident years have been more favorable than the Company's actuarial analyses initially anticipated. The favorable development on prior years' loss reserves in 2012 was partially offset by $38.2 million of adverse development in prior years' loss reserves on A&E exposures.

	In 2011, incurred losses and loss adjustment expenses included $354.0 million of favorable development on prior years' loss reserves, which was primarily due to $265.8 million of loss reserve redundancies experienced in the London Insurance Market segment and on the professional and products liability programs within the Excess and Surplus Lines segment as actual claims reporting patterns on prior accident years have been more favorable than the Company's actuarial analyses initially anticipated.

	Inherent in the Company's reserving practices is the desire to establish loss reserves that are more likely redundant than deficient. As such, the Company seeks to establish loss reserves that will ultimately prove to be adequate. As part of the Company's acquisition of insurance operations, to the extent the reserving philosophy of the acquired business differs from the Company's reserving philosophy, the post-acquisition loss reserves will be built until total loss reserves are consistent with the Company's target level of confidence. Furthermore, the Company's philosophy is to price its insurance products to make an underwriting profit. Management continually attempts to improve its loss estimation process by refining its ability to analyze loss development patterns, claim payments and other information, but uncertainty remains regarding the potential for adverse development of estimated ultimate liabilities.

	The Company uses a variety of techniques to establish the liabilities for unpaid losses and loss adjustment expenses, all of which involve significant judgments and assumptions. These techniques include detailed statistical analysis of past claim reporting, settlement activity, claim frequency and severity, policyholder loss experience, industry loss experience and changes in market conditions, policy forms and exposures. Greater judgment may be required when new product lines are introduced or when there have been changes in claims handling practices, as the statistical data available may be insufficient. The Company's estimates reflect implicit and explicit assumptions regarding the potential effects of external factors, including economic and social inflation, judicial decisions, changes in law, general economic conditions and recent trends in these factors. In some of the Company's markets, and where the Company acts as a reinsurer, the timing and amount of information reported about underlying claims are in the control of third parties. There is often a time lag between cedents establishing case reserves and re-estimating their reserves, and notifying the Company of the new or revised case reserves. This can also affect estimates and require re-estimation as new information becomes available.

	The Company believes the process of evaluating past experience, adjusted for the effects of current developments and anticipated trends, is an appropriate basis for predicting future events. Management currently believes the Company's gross and net reserves, including the reserves for A&E exposures, are adequate. However, there is no precise method for evaluating the impact of any significant factor on the adequacy of reserves, and actual results will differ from original estimates.

	b)The Company's exposure to A&E claims results from policies written by acquired insurance operations before their acquisitions by the Company. The Company's exposure to A&E claims originated from umbrella, excess and commercial general liability (CGL) insurance policies and assumed reinsurance contracts that were written on an occurrence basis from the 1970s to mid-1980s. Exposure also originated from claims-made policies that were designed to cover environmental risks provided that all other terms and conditions of the policy were met.

	A&E claims include property damage and clean-up costs related to pollution, as well as personal injury allegedly arising from exposure to hazardous materials. After 1986, the Company began underwriting CGL coverage with pollution exclusions, and in some lines of business the Company began using a claims-made form. These changes significantly reduced the Company's exposure to future A&E claims on post-1986 business.

	The following table provides a reconciliation of beginning and ending A&E reserves for losses and loss adjustment expenses, which are a component of consolidated unpaid losses and loss adjustment expenses. Amounts included in the following table are presented before consideration of reinsurance allowances.



	Years Ended December 31,
(dollars in thousands)	2013				2012				2011
Net reserves for A&E losses and loss adjustment expenses, beginning of year	$	260,791			$	244,772			$	216,034

Commutations and other	(5,067		)		(897		)		36,271

Adjusted net reserves for A&E losses and loss adjustment expenses, beginning of year	255,724				243,875				252,305

Incurred losses and loss adjustment expenses	30,128				38,179				(134		)

Payments	(13,658		)		(21,263		)		(7,399		)
Net reserves for A&E losses and loss adjustment expenses, end of year	272,194				260,791				244,772

Reinsurance recoverable on unpaid losses	100,784				100,063				89,391

Gross reserves for A&E losses and loss adjustment expenses, end of year	$	372,978			$	360,854			$	334,163


Commutations and other for the year ended December 31, 2011 included a $40.0 million adjustment related to commutations completed by Markel International, which involved the termination of ceded reinsurance contracts. The adjustment was made with respect to commuted recoverables where the amount of the balance due from reinsurers was offset in full by a provision within the reinsurance allowance. The adjustment reduced the reinsurance recoverable on unpaid losses with a corresponding reduction to the reinsurance allowance for doubtful accounts. Accordingly, there was no impact on the reinsurance recoverable on unpaid losses or on net reserves for A&E losses and loss adjustment expenses, net of the reinsurance allowance, for any period presented. See note 16 for further discussion of the corresponding reduction to the reinsurance allowance.

At December 31, 2013, asbestos-related reserves were $284.3 million and $206.6 million on a gross and net basis, respectively. Net reserves for reported claims and net incurred but not reported reserves for A&E exposures were $165.3 million and $106.9 million, respectively, at December 31, 2013. Inception-to-date net paid losses and loss adjustment expenses for A&E related exposures totaled $398.0 million at December 31, 2013, which includes $79.1 million of litigation-related expense.

The Company's reserves for losses and loss adjustment expenses related to A&E exposures represent management's best estimate of ultimate settlement values. A&E reserves are monitored by management, and the Company's statistical analysis of these reserves is reviewed by the Company's independent actuaries. A&E exposures are subject to significant uncertainty due to potential loss severity and frequency resulting from the uncertain and unfavorable legal climate. A&E reserves could be subject to increases in the future; however, management believes the Company's gross and net A&E reserves at December 31, 2013 are adequate.

Life_And_Annuity_Benefits

Life And Annuity Benefits	12 Months Ended
	Dec. 31, 2013
Liability for Future Policy Benefits [Abstract]	'
Life And Annuity Benefits	'
	Life and Annuity Benefits

	The following table presents life and annuity benefits as of December 31, 2013:



		(dollars in thousands)
	Life	$	190,765

	Annuities	1,194,558

	Accident and health	101,251

		$	1,486,574


	Life and annuity benefits are compiled on a reinsurance contract-by-contract basis and are discounted using standard actuarial techniques and cash flow models. Since the development of the life and annuity reinsurance reserves is based upon cash flow projection models, the Company must make estimates and assumptions based on cedent experience, industry mortality tables, and expense and investment experience, including a provision for adverse deviation. The assumptions used to determine policy benefit reserves were determined at the Acquisition Date and are generally locked-in for the life of the contract unless an unlocking event occurs. To the extent existing policy reserves, together with the present value of future gross premiums and expected investment income earned thereon, are not adequate to cover the present value of future benefits, settlement and maintenance costs, the locked-in assumptions are revised to current best estimate assumptions and a charge to earnings for life and annuity benefits is recognized at that time.

	Because of the assumptions and estimates used in establishing the Company's reserves for life and annuity benefit obligations and the long-term nature of these reinsurance contracts, the ultimate liability may be greater or less than the estimates. The average discount rate for the life and annuity benefit reserves was 2.3% as of December 31, 2013.
	As of December 31, 2013, the largest life and annuity benefits reserve for a single contract was 34.8% of the total.
	No annuities included in life and annuity benefits in the consolidated balance sheet are subject to discretionary withdrawal.

Senior_LongTerm_Debt_And_Other

Senior Long-Term Debt And Other Debt	12 Months Ended
	Dec. 31, 2013
Debt Disclosure [Abstract]	'
Senior Long-Term Debt And Other Debt	'
	Senior Long-Term Debt and Other Debt

	The following table summarizes the Company's senior long-term debt and other debt.



		December 31,
	(dollars in thousands)	2013		2012
	6.80% unsecured senior notes, due February 15, 2013, interest payable semi-annually, net of unamortized discount of $45 in 2012	$	—	$	246,619

	7.20% unsecured senior notes, due April 14, 2017, interest payable semi-annually, net of unamortized premium of $4,822 in 2013	95,451		—

	7.125% unsecured senior notes, due September 30, 2019, interest payable semi-annually, net of unamortized discount of $1,626 in 2013 and $1,909 in 2012	348,374		348,091

	6.25% unsecured senior notes, due September 30, 2020, interest payable semi-annually, net of unamortized premium of $61,273 in 2013	411,273		—

	5.35% unsecured senior notes, due June 1, 2021, interest payable semi-annually, net of unamortized discount of $1,531 in 2013 and $1,738 in 2012	248,469		248,262

	4.90% unsecured senior notes, due July 1, 2022, interest payable semi-annually, net of unamortized discount of $2,374 in 2013 and $2,653 in 2012	347,626		347,347

	3.625% unsecured senior notes, due March 30, 2023, interest payable semi-annually, net of unamortized discount of $1,860 in 2013	248,140		—

	7.35% unsecured senior notes, due August 15, 2034, interest payable semi-annually, net of unamortized discount of $2,185 in 2013 and $2,291 in 2012	197,815		197,710

	5.0% unsecured senior notes, due March 30, 2043, interest payable semi-annually, net of unamortized discount of $6,551 in 2013	243,449		—

	Other debt, at various interest rates ranging from 2.5% to 6.5%	115,630		104,521

	Senior long-term debt and other debt	$	2,256,227	$	1,492,550


	On July 2, 2012, the Company issued $350 million of 4.90% unsecured senior notes due July 1, 2022. Net proceeds to the Company were $347.2 million. On August 1, 2012, the Company used a portion of these proceeds to redeem its 7.50% unsecured senior debentures due August 22, 2046 at a redemption price equal to 100% of their principal amount, or $150 million. This redemption resulted in a loss of $4.1 million, which is reflected in net realized investment gains. The proceeds from the July 2012 issuance were also used to pre-fund the repayment of the Company's 6.80% unsecured senior notes due February 15, 2013.

	On February 15, 2013, the Company repaid its 6.80% unsecured senior notes ($246.7 million principal amount outstanding at December 31, 2012).

	On March 8, 2013, the Company issued $250 million of 3.625% unsecured senior notes due March 30, 2023 and $250 million of 5.0% unsecured senior notes due March 30, 2043. Net proceeds to the Company were approximately $491.2 million, to be used for general corporate purposes.

	On April 16, 2007, Alterra USA Holdings Limited (Alterra USA), a wholly-owned indirect subsidiary of Alterra, privately issued $100 million of 7.20% unsecured senior notes due April 14, 2017 (the 7.20% unsecured senior notes). The 7.20% unsecured senior notes are Alterra USA's senior unsecured obligations and rank equally in right of payment with all existing and future senior unsecured indebtedness of Alterra USA. The 7.20% unsecured senior notes are fully and unconditionally guaranteed by Alterra. The principal amount of the 7.20% unsecured senior notes outstanding as of the Acquisition Date was $90.6 million. As of the Acquisition Date, the 7.20% unsecured senior notes were recorded at their estimated fair value of $95.8 million.

	On September 27, 2010, Alterra Finance LLC, a wholly-owned indirect subsidiary of Alterra, issued $350 million of 6.25% unsecured senior notes due September 30, 2020 (the 6.25% unsecured senior notes). The 6.25% unsecured senior notes are Alterra Finance LLC's senior unsecured obligations and rank equally in right of payment with all of Alterra Finance LLC's future unsecured and unsubordinated indebtedness and rank senior to all of Alterra Finance LLC's future subordinated indebtedness. The 6.25% unsecured senior notes are fully and unconditionally guaranteed by Alterra on a senior unsecured basis. The guarantee ranks equally with all of Alterra's existing and future unsecured and unsubordinated indebtedness and ranks senior to all of Alterra's future subordinated indebtedness. As of the Acquisition Date, the 6.25% unsecured senior notes were recorded at their estimated fair value of $416.6 million.

	Alterra Finance LLC is a finance subsidiary and has no independent activities, assets or operations other than in connection with the 6.25% unsecured senior notes.

	The Company's 7.35% unsecured senior notes due August 15, 2034 are not redeemable. The Company's other unsecured senior notes are redeemable by the Company at any time, subject to payment of a make-whole premium to the noteholders. None of the Company's senior long-term debt is subject to any sinking fund requirements.

	The Company's other debt is primarily associated with its Markel Ventures operations and is non-recourse to the holding company. The debt of the Company's Markel Ventures subsidiaries generally is secured by the assets of those subsidiaries. ParkLand Ventures, Inc. (ParkLand), a subsidiary of the Company, has formed subsidiaries for the purpose of acquiring and financing real estate (the real estate subsidiaries). The assets of the real estate subsidiaries, which are not material to the Company, are consolidated in accordance with U.S. GAAP but are not available to satisfy the debt and other obligations of the Company or any affiliates other than the real estate subsidiaries.

	The estimated fair value based on quoted market prices of the Company's senior long-term debt and other debt was $2.4 billion and $1.7 billion at December 31, 2013 and 2012, respectively.

	The following table summarizes the future principal payments due at maturity on senior long-term debt and other debt as of December 31, 2013.



	Years Ending December 31,	(dollars in
		thousands)
	2014	$	28,795

	2015	6,102

	2016	11,822

	2017	105,987

2018	2,278

2019 and thereafter	2,051,275

Total principal payments	$	2,206,259

Net unamortized premium	49,968

Senior long-term debt and other debt	$	2,256,227


The Company also maintains a revolving credit facility for working capital and other general corporate purposes that expires September 2015. Effective July 12, 2013, the capacity of the Company's revolving credit facility was increased from $150 million to $300 million, as previously provided for by the terms of the revolving credit facility. The Company may select from two interest rate options for balances outstanding under the revolving credit facility and pays a commitment fee (0.25% at December 31, 2013) on the unused portion of the facility based on the Company's debt to equity leverage ratio as calculated under the agreement. At December 31, 2013 and 2012, the Company had no borrowings outstanding under the revolving credit facility.

Alterra and Markel Bermuda are party to a $900 million secured credit facility (the senior credit facility), which expires on December 15, 2015. The senior credit facility provides for secured letters of credit to be issued for the account of Alterra, Markel Bermuda and certain other subsidiaries of Alterra and for loans to Alterra and Markel Bermuda. Loans under the senior credit facility are subject to a sublimit of $250 million. Subject to certain conditions and at the request of Alterra, the aggregate commitments of the lenders under the senior credit facility may be increased up to a total of $1.4 billion. The Company pays a fee of 0.40% for outstanding letters of credit under the senior credit facility and a commitment fee of 0.125% on the total unused portion of the senior credit facility. At December 31, 2013, the Company had no borrowings outstanding under the senior credit facility. At December 31, 2013, $472.3 million of letters of credit were issued and outstanding under the senior credit facility.

At December 31, 2013, the Company was in compliance with all covenants contained in its revolving credit facility and senior credit facility. To the extent that the Company is not in compliance with its covenants, the Company's access to these credit facilities could be restricted.

The Company paid $114.5 million, $92.9 million and $84.1 million in interest on its senior long-term debt and other debt during the years ended December 31, 2013, 2012 and 2011, respectively.

Shareholders_Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2013
Stockholders' Equity Note [Abstract]	'
Shareholders' Equity	'
	Shareholders' Equity

	a)The Company had 50,000,000 shares of no par value common stock authorized of which 13,985,620 shares and 9,629,160 shares were issued and outstanding at December 31, 2013 and 2012, respectively. The Company also has 10,000,000 shares of no par value preferred stock authorized, none of which was issued or outstanding at December 31, 2013 or 2012.

	During 2013, the Company repurchased 77,693 shares of common stock at a cost of $40.9 million under a share repurchase program that was approved by the Company's Board of Directors in November 2010 (the 2010 Program). As of December 31, 2013, the Company had repurchased 232,535 shares of common stock at a cost of $101.4 million under the 2010 Program. In November 2013, the Board of Directors approved a new share repurchase program that provides for the repurchase of up to $300 million of common stock (the 2013 Program) to replace the 2010 Program. The 2013 Program has no expiration date but may be terminated by the Board of Directors at any time. As of December 31, 2013, the Company had not repurchased any shares of common stock under the 2013 Program.

	b)Net income per share was determined by dividing adjusted net income to shareholders by the applicable weighted average shares outstanding. Unvested share-based compensation awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid) are considered participating awards and are included in the computation of net income per share. Non-participating unvested share-based compensation awards are excluded from the computation of net income per share. Diluted net income per share is computed by dividing adjusted net income to shareholders by the weighted average number of common shares and dilutive potential common shares outstanding during the year. Average closing common stock market prices are used to calculate the dilutive effect attributable to restricted stock.



		Years Ended December 31,
	(in thousands, except per share amounts)	2013				2012			2011
	Net income to shareholders	$	281,021			$	253,385		$	142,026

	Adjustment of redeemable noncontrolling interests	1,963				(3,101		)	—

	Adjusted net income to shareholders	$	282,984			$	250,284		$	142,026


	Basic common shares outstanding	12,538				9,640			9,686

	Dilutive potential common shares from conversion of options	12				6			20

	Dilutive potential common shares from conversion of non-participating restricted stock	36				20			20

	Diluted shares outstanding	12,586				9,666			9,726

	Basic net income per share	$	22.57			$	25.96		$	14.66

	Diluted net income per share	$	22.48			$	25.89		$	14.6


	c)The Company's Employee Stock Purchase and Bonus Plan provides a method for employees and directors to purchase shares of the Company's common stock on the open market. The plan encourages share ownership by providing for the award of bonus shares to participants equal to 10% of the net increase in the number of shares owned under the plan in a given year, excluding shares acquired through the plan's loan program component. Under the loan program, the Company offers subsidized unsecured loans so participants may purchase shares and awards bonus shares equal to 5% of the shares purchased with a loan. The Company has authorized 100,000 shares for purchase under this plan, of which 33,454 and 46,889 shares were available for purchase at December 31, 2013 and 2012, respectively. At December 31, 2013 and 2012, loans outstanding under the plan, which are included in receivables on the consolidated balance sheets, totaled $12.8 million and $11.4 million, respectively.

	d)In April 2012, the Company adopted the 2012 Equity Incentive Compensation Plan (2012 Compensation Plan), which replaced the Markel Corporation Omnibus Incentive Plan (Omnibus Incentive Plan). The 2012 Compensation Plan provides for grants and awards of restricted stock, restricted stock units, performance grants, and other stock based awards to employees and directors and is administered by the Compensation Committee of the Company's Board of Directors (Compensation Committee). At December 31, 2013, there were 146,768 shares reserved for issuance under the 2012 Compensation Plan.

	Restricted stock units are awarded to certain associates and executive officers based upon meeting performance conditions determined by the Compensation Committee. These awards generally vest at the end of the fifth year following the year for which the Compensation Committee determines performance conditions have been met. At the end of the vesting period, recipients are entitled to receive one share of the Company's common stock for each vested restricted stock unit. During 2013, the Company awarded 13,648 restricted stock units to associates and executive officers based on performance conditions being met.

	Restricted stock units also are awarded to associates and executive officers to assist the Company in securing or retaining the services of key employees. In May 2013, the Compensation Committee awarded 31,669 restricted stock units to certain associates and executive officers to assist the Company in retaining the services of key employees. The restricted stock units had a grant-date fair value of $16.6 million. The awards vest over a three year period and entitle the recipient to receive one share of the Company's common stock for each vested restricted stock unit. Also during 2013, the Company awarded 1,833 restricted stock units to associates and executive officers as a hiring or retention incentive. These awards generally vest over a three-year period and entitle the recipient to receive one share of the Company's common stock for each vested restricted stock unit.

	During 2013, the Company awarded 1,710 shares of restricted stock to its non-employee directors. The shares awarded to non-employee directors will vest in 2014.

	The following table summarizes nonvested share-based awards.


		Number			Weighted Average
		of Awards			Grant-Date
					Fair Value
	Nonvested awards at January 1, 2013	55,580			$	388.58

	Granted	48,860			517.24

	Vested	(5,729	)		428.78

	Nonvested awards at December 31, 2013	98,711			$	449.93


	The fair value of the Company's share-based awards issued under the Omnibus Incentive Plan was determined based on the average price of the Company's common shares on the grant date. The fair value of the Company's share-based awards granted under the 2012 Compensation Plan is determined based on the closing price of the Company's common shares on the grant date. The weighted average grant-date fair value of the Company's share-based awards granted in 2013, 2012 and 2011 was $517.24, $412.04 and $408.60, respectively. As of December 31, 2013, unrecognized compensation cost related to nonvested share-based awards was $25.3 million, which is expected to be recognized over a weighted average period of 2.5 years. The fair value of the Company's share-based awards that vested during 2013, 2012 and 2011 was $2.5 million, $4.7 million and $5.3 million, respectively.

	e)In connection with the acquisition of Aspen Holdings, Inc. in October 2010, the Company provided for the conversion of options issued under the Aspen Holdings, Inc. 2008 Stock Option Plan and the Aspen Holdings, Inc. 2008 Stock Option Plan for Non-Employee Directors (the Aspen Option Plans) into options to purchase 58,116 of the Company's common shares. No further options are available for issuance under the Aspen Option Plans. The options issued were fully vested and exercisable upon conversion and expire ten years from the original date of issue or sooner upon the recipient's termination of employment or death. The options issued had a weighted average exercise price of $225.94 and a grant-date fair value of $157.15.

	The following table summarizes additional information with respect to these options.


	Number			Weighted				Weighted Average	Intrinsic Value
	of			Average				Remaining	(in millions)
	Shares			Exercise Price				Contractual Term
								(years)
Outstanding and exercisable, January 1, 2013	5,678			$	225.83

Exercised	957			$	204.83

Outstanding and exercisable, December 31, 2013	4,721			$	230.08			4.4	$	1.7


During 2013, 957 options were exercised under the Aspen Option Plans, resulting in cash proceeds of $0.2 million and a current tax benefit of $0.1 million. The intrinsic value of options exercised in 2013 was $0.3 million. During 2012, 39,183 options were exercised under the Aspen Option Plans, resulting in cash proceeds of $9.1 million and a current tax benefit of $2.5 million. The intrinsic value of options exercised in 2012 was $7.1 million. During 2011, 5,660 options were exercised under the Aspen Option Plans, resulting in cash proceeds of $1.2 million and a current tax benefit of $0.4 million. The intrinsic value of options exercised in 2011 was $1.1 million.

f)In May 2013, in connection with the acquisition of Alterra, the Company issued 101,875 replacement options and 154,103 restricted stock awards to holders of Alterra options and restricted stock awards. The replacement options and restricted stock awards were issued under the terms and conditions of the Alterra Capital Holdings Limited 2008 Stock Incentive Plan, the Alterra Capital Holdings Limited 2006 Equity Incentive Plan and the Alterra Capital Holdings Limited 2000 Stock Incentive Plan (collectively, the Alterra Equity Award Plans). No further options or restricted stock awards are available for issuance under the Alterra Equity Award Plans.

The replacement options issued were fully vested and exercisable as of the Acquisition Date and had a weighted average exercise price of $398.96 and a grant-date fair value of $140.08, which was included in the acquisition consideration. The fair value of the options was estimated on the grant date using the Black-Scholes option pricing model. Assumptions used in the pricing model included an expected annual volatility of 19.04%, a risk-free rate of approximately 0.20% and an expected term of approximately two years. The expected annual volatility was based on the historical volatility of the Company's stock and other factors. The risk-free rate was based on the U.S. Treasury yield curve, with a remaining term equal to the expected term assumption at the grant date. The expected term of the options granted represents the period of time that the options were expected to be outstanding at the grant date.

The following table summarizes additional information with respect to these options.


	Number			Weighted				Weighted Average	Intrinsic Value
	of			Average				Remaining	(in millions)
	Shares			Exercise Price				Contractual Term
								(years)
Outstanding and exercisable, May 1, 2013	101,875			$	398.96

Exercised	65,934			$	391.64

Outstanding and exercisable, December 31, 2013	35,941			$	412.39			2.6	$	6


From the Acquisition Date through December 31, 2013, 65,934 options were exercised under the Alterra Equity Award Plans, resulting in cash proceeds of $24.3 million and a current tax benefit of $0.8 million. The intrinsic value of options exercised in 2013 was $9.4 million.

The replacement restricted stock awards issued by the Company had a grant date fair value of $81.6 million, or $529.59 per share. The awards were partially vested as of the Acquisition Date and had a weighted average remaining service period of approximately one year. As a result, $61.0 million was recognized as part of the Acquisition Consideration and $20.6 million will be recognized as compensation expense over the remaining service period of the awards. The fair value of the replacement restricted stock awards was determined based on the weighted average price of the Company's stock on April 30, 2013, the day preceding the Acquisition Date. The following table summarizes activity related to these nonvested restricted stock awards.



	Number			Weighted Average
	of Awards			Grant-Date
				Fair Value
Nonvested awards issued on May 1, 2013	154,103			$	529.59

Vested	(77,941	)		529.59

Forfeited	(7,751	)		529.59

Nonvested awards at December 31, 2013	68,411			$	529.59


The Company recognized compensation expense totaling $12.7 million during the year ended December 31, 2013 related to these restricted stock awards. As of December 31, 2013, unrecognized compensation cost related to the nonvested restricted stock awards was $4.6 million, which is expected to be recognized over a weighted average period of less than one year. The fair value of the restricted stock awards that vested during 2013 was $41.3 million.

g)In accordance with the terms of the Merger Agreement, the Company also assumed outstanding warrants to purchase Alterra common stock. Holders of the warrants had the option to surrender them for consideration specified in the Merger Agreement, which included cash and registered shares of the Company's common stock, or to have them remain outstanding as "Company Converted Warrants," in which case the holders would be entitled to a combination of cash and unregistered shares of the Company's common stock upon exercise of the warrants. The warrants of all warrant holders who elected to exercise in conjunction with the Acquisition Date were considered to have been exercised on May 1, 2013. The Company issued 225,529 Company Converted Warrants with a fair value of $73.7 million to Alterra warrant holders who elected not to surrender their warrants in connection with the merger. Three holders who elected to have their warrants remain outstanding subsequently exercised a total of 225,499 warrants and received a total of 100,115 shares of the Company's common stock under the cashless exercise provision of the warrants. As of December 31, 2013, the Company had outstanding warrants to purchase 30 shares of its common stock.

Other_Comprehensive_Income

Other Comprehensive Income	12 Months Ended
	Dec. 31, 2013
Other Comprehensive Income (Loss), Tax [Abstract]	'
Other Comprehensive Income	'
	Other Comprehensive Income

	Other comprehensive income includes net holding gains arising during the period, changes in unrealized other-than-temporary impairment losses on fixed maturities arising during the period and reclassification adjustments for net gains included in net income. Other comprehensive income also includes changes in foreign currency translation adjustments and changes in net actuarial pension loss.

	The following table presents the change in accumulated other comprehensive income by component, net of taxes and noncontrolling interests.



	(dollars in thousands)	Unrealized				Foreign				Net Actuarial			Total
		Holding Gains				Currency				Pension Loss
		on Available-for-
		Sale Securities
	31-Dec-10	$	581,278			$	1,541			$	(31,726	)	$	551,093

	Other comprehensive income (loss) before reclassifications	145,782				(4,155		)		(10,890		)	130,737

	Amounts reclassified from accumulated other comprehensive income	(22,341		)		—				1,431			(20,910		)

	Total other comprehensive income (loss)	123,441				(4,155		)		(9,459		)	109,827

	31-Dec-11	$	704,719			$	(2,614	)		$	(41,185	)	$	660,920

	Other comprehensive income before reclassifications	266,265				1,539				4,670			272,474

	Amounts reclassified from accumulated other comprehensive income	(24,051		)		—				1,994			(22,057		)

	Total other comprehensive income	242,214				1,539				6,664			250,417

	31-Dec-12	$	946,933			$	(1,075	)		$	(34,521	)	$	911,337

	Other comprehensive income (loss) before reclassifications	225,404				(10,171		)		2,517			217,750

	Amounts reclassified from accumulated other comprehensive income	(40,830		)		—				1,548			(39,282		)

	Total other comprehensive income (loss)	184,574				(10,171		)		4,065			178,468

	31-Dec-13	$	1,131,507			$	(11,246	)		$	(30,456	)	$	1,089,805


	The following table summarizes the tax expense (benefit) associated with each component of other comprehensive income.



		Years Ended December 31,
	(dollars in thousands)	2013				2012				2011
	Change in net unrealized gains on investments:
	Net holding gains arising during the period	$	93,837			$	122,524			$	68,064

	Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period	(34		)		(49		)		2,107

	Reclassification adjustments for net gains included in net income	(16,382		)		(10,881		)		(10,890		)
	Change in net unrealized gains on investments	77,421				111,594				59,281

	Change in foreign currency translation adjustments	(1,619		)		(446		)		250

	Change in net actuarial pension loss	1,015				1,991				(3,153		)

	Total	$	76,817			$	113,139			$	56,378


	The following table presents the details of amounts reclassified from accumulated other comprehensive income into income, by component.


	Years Ended December 31,
(dollars in thousands)	2013				2012				2011
Unrealized holding gains on available-for-sale securities:
Other-than-temporary impairment losses	$	(4,706	)		$	(12,078	)		$	(20,196	)
Net realized investment gains, excluding other-than-temporary impairment losses	61,918				47,010				53,427

Total before taxes	57,212				34,932				33,231

Income taxes	(16,382		)		(10,881		)		(10,890		)
Reclassification of unrealized holding gains, net of taxes	$	40,830			$	24,051			$	22,341


Net actuarial pension loss:
Underwriting, acquisition and insurance expenses	$	(1,934	)		$	(2,590	)		$	(1,908	)
Income taxes	386				596				477

Reclassification of net actuarial pension loss, net of taxes	$	(1,548	)		$	(1,994	)		$	(1,431	)

Derivatives

Derivatives	12 Months Ended
Derivatives	Dec. 31, 2013
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Derivatives	'
	Derivatives

	The Company is a party to a credit default swap agreement, under which third party credit risk is transferred from a counterparty to the Company. The Company entered into the credit default swap agreement for investment purposes. At both December 31, 2013 and 2012, the notional amount of the credit default swap was $33.1 million, which represented the Company's aggregate exposure to losses if specified credit events involving third party reference entities occur. These third party reference entities are specified under the terms of the agreement and represent a portfolio of names upon which the Company has assumed credit risk from the counterparty. The Company's exposure to loss from any one reference entity is limited to $20.0 million. The credit default swap has a scheduled termination date of December 2014.

	The credit default swap is accounted for as a derivative instrument and is recorded at fair value with any changes in fair value recorded in net investment income. At December 31, 2013 and 2012, the credit default swap had a fair value of $2.2 million and $12.7 million, respectively. The fair value of the credit default swap is included in other liabilities on the consolidated balance sheets. Net investment income in 2013 and 2012 included favorable changes in the fair value of the credit default swap of $10.5 million and $16.6 million, respectively. Net investment income in 2011 included an adverse change in the fair value of the credit default swap of $4.1 million.

	Since entering into the credit default swap agreement, the Company has paid $16.9 million to settle its obligations related to credit events. These payments reduced the Company's liability related to its credit default swap.

	The fair value of the credit default swap is determined by the Company using a Gaussian copula valuation model, a market standard model for valuing credit default swaps. The fair value is dependent upon several inputs, including changes in interest rates, credit spreads, expected default rates, changes in credit quality, future expected recovery rates and other market factors. The significant unobservable inputs used in the fair value measurement of the credit default swap are expected default rates and future expected recovery rates. The Company determines these unobservable inputs based upon default rates and recovery rates used to price similar credit default swap indices. A significant increase in expected default rates in isolation results in a significantly higher fair value measurement, while a significant decrease in expected default rates results in a significantly lower fair value measurement. A significant increase in future expected recovery rates in isolation results in a significantly lower fair value measurement, while a significant decrease in future expected recovery rates results in a significantly higher fair value measurement. Generally, a change in the assumption used for expected default rates is accompanied by a directionally opposite change in future expected recovery rates. The fair value measurement of the credit default swap at December 31, 2013 included expected default rates ranging between less than 1% and 4%, with a weighted-average expected default rate of less than 1%, and future expected recovery rates ranging between 20% and 40%, with a weighted-average future expected recovery rate of 39%. The fair value measurement of the credit default swap at December 31, 2012 included expected default rates ranging between 1% and 43%, with a weighted-average expected default rate of 3%, and future expected recovery rates ranging between 20% and 40%, with a weighted-average future expected recovery rate of 39%.

	The Company's valuation policies and procedures for the credit default swap are determined by an internal investment manager with oversight provided by the Company's Chief Financial Officer and Chief Investment Officer. Fair value measurements are analyzed quarterly to ensure the change in fair value from prior periods is reasonable relative to recent market trends. Additionally, the reported fair value of the credit default swap is compared to results from similar valuation models.

	See note 15 for further discussion of the Company's credit default swap.

	The Company had no other material derivative instruments at December 31, 2013.

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2013
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'
	Fair Value Measurements

	FASB ASC 820-10, Fair Value Measurements and Disclosures, establishes a three-level hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The fair value hierarchy gives the highest priority to quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3). If the inputs used to measure the assets or liabilities fall within different levels of the hierarchy, the classification is based on the lowest level input that is significant to the fair value measurement of the asset or liability.

	Classification of assets and liabilities within the hierarchy considers the markets in which the assets and liabilities are traded and the reliability and transparency of the assumptions used to determine fair value. The hierarchy requires the use of observable market data when available. The levels of the hierarchy are defined as follows:

	Level 1 - Inputs to the valuation methodology are quoted prices (unadjusted) for identical assets or liabilities traded in active markets.

	Level 2 - Inputs to the valuation methodology include quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability and market-corroborated inputs.

	Level 3 - Inputs to the valuation methodology are unobservable for the asset or liability and are significant to the fair value measurement.

	In accordance with FASB ASC 820, the Company determines fair value based on 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. In determining fair value, the Company uses various methods, including the market, income and cost approaches. The Company uses valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs. The following section describes the valuation methodologies used by the Company to measure assets and liabilities at fair value, including an indication of the level within the fair value hierarchy in which each asset or liability is generally classified.

	Investments available-for-sale. Investments available-for-sale are recorded at fair value on a recurring basis and include fixed maturities, equity securities and short-term investments. Short-term investments include certificates of deposit, commercial paper, discount notes and treasury bills with original maturities of one year or less. Fair value for investments available-for-sale is determined by the Company after considering various sources of information, including information provided by a third party pricing service. The pricing service provides prices for substantially all of the Company's fixed maturities and equity securities. In determining fair value, the Company generally does not adjust the prices obtained from the pricing service. The Company obtains an understanding of the pricing service's valuation methodologies and related inputs, which include, but are not limited to, reported trades, benchmark yields, issuer spreads, bids, offers, duration, credit ratings, estimated cash flows and prepayment speeds. The Company validates prices provided by the pricing service by reviewing prices from other pricing sources and analyzing pricing data in certain instances.

	The Company has evaluated the various types of securities in its investment portfolio to determine an appropriate fair value hierarchy level based upon trading activity and the observability of market inputs. Level 1 investments include those traded on an active exchange, such as the New York Stock Exchange. Level 2 investments include U.S. Treasury securities and obligations of U.S. government agencies, municipal bonds, foreign government bonds, commercial mortgage-backed securities, residential mortgage-backed securities, asset-backed securities and corporate debt securities.

	Fair value for investments available-for-sale is measured based upon quoted prices in active markets, if available. Due to variations in trading volumes and the lack of quoted market prices, fixed maturities are classified as Level 2 investments. The fair value of fixed maturities is normally derived through recent reported trades for identical or similar securities, making adjustments through the reporting date based upon available market observable data described above. If there are no recent reported trades, the fair value of fixed maturities may be derived through the use of matrix pricing or model processes, where future cash flow expectations are developed based upon collateral performance and discounted at an estimated market rate. Significant inputs used to determine the fair value of obligations of states, municipalities and political subdivisions, corporate bonds and obligations of foreign governments include reported trades, benchmark yields, issuer spreads, bids, offers, credit information and estimated cash flows. Significant inputs used to determine the fair value of commercial mortgage-backed securities, residential mortgage-backed securities and asset-backed securities include the type of underlying assets, benchmark yields, prepayment speeds, collateral information, tranche type and volatility, estimated cash flows, credit information, default rates, recovery rates, issuer spreads and the year of issue.

	Derivatives. Derivatives are recorded at fair value on a recurring basis and include a credit default swap. The fair value of the credit default swap is measured by the Company using an external valuation model. See note 14 for a discussion of the valuation model for the credit default swap, including the key inputs and assumptions used in the model and a description of the valuation processes used by the Company. Due to the significance of unobservable inputs required in measuring the fair value of the credit default swap, the credit default swap has been classified as Level 3 within the fair value hierarchy.

	Senior long-term debt and other debt. Senior long-term debt and other debt is carried at amortized cost with the estimated fair value disclosed on the consolidated balance sheets. Senior long-term debt and other debt is classified as Level 2 within the fair value hierarchy due to variations in trading volumes and the lack of quoted market prices. Fair value for senior long-term debt and other debt is generally derived through recent reported trades for identical securities, making adjustments through the reporting date, if necessary, based upon available market observable data including U.S. Treasury securities and implied credit spreads. Significant inputs used to determine the fair value of senior long-term debt and other debt include reported trades, benchmark yields, issuer spreads, bids and offers.

	The following tables present the balances of assets and liabilities measured at fair value on a recurring basis by level within the fair value hierarchy.



		December 31, 2013
	(dollars in thousands)	Level 1			Level 2			Level 3			Total
	Assets:
	Investments available-for-sale:
	Fixed maturities:
	U.S. Treasury securities and obligations of U.S. government agencies	$	—		$	1,194,231		$	—		$	1,194,231

	Obligations of states, municipalities and political subdivisions	—			3,075,715			—			3,075,715

	Foreign governments	—			1,461,054			—			1,461,054

	Commercial mortgage-backed securities	—			367,821			—			367,821

	Residential mortgage-backed securities	—			870,248			—			870,248

	Asset-backed securities	—			188,289			—			188,289

	Corporate bonds	—			2,985,178			—			2,985,178

	Total fixed maturities	—			10,142,536			—			10,142,536

	Equity securities:
	Insurance, banks and other financial institutions	1,015,083			—			—			1,015,083

	Industrial, consumer and all other	2,236,715			—			—			2,236,715

	Total equity securities	3,251,798			—			—			3,251,798

	Short-term investments	1,312,561			139,727			—			1,452,288

	Total investments available-for-sale	$	4,564,359		$	10,282,263		$	—		$	14,846,622

	Liabilities:
	Derivative contracts	$	—		$	—		$	2,230		$	2,230




	December 31, 2012
(dollars in thousands)	Level 1			Level 2			Level 3			Total
Assets:
Investments available-for-sale:
Fixed maturities:
U.S. Treasury securities and obligations of U.S. government agencies	$	—		$	317,507		$	—		$	317,507

Obligations of states, municipalities and political subdivisions	—			2,831,562			—			2,831,562

Foreign governments	—			556,608			—			556,608

Residential mortgage-backed securities	—			215,377			—			215,377

Asset-backed securities	—			14,345			—			14,345

Corporate bonds	—			1,043,884			—			1,043,884

Total fixed maturities	—			4,979,283			—			4,979,283

Equity securities:
Insurance, banks and other financial institutions	898,067			—			—			898,067

Industrial, consumer and all other	1,508,884			—			—			1,508,884

Total equity securities	2,406,951			—			—			2,406,951

Short-term investments	888,758			84,572			—			973,330

Total investments available-for-sale	$	3,295,709		$	5,063,855		$	—		$	8,359,564

Liabilities:
Derivative contracts	$	—		$	—		$	12,690		$	12,690


The following table summarizes changes in Level 3 liabilities measured at fair value on a recurring basis.



(dollars in thousands)	2013			2012
Derivatives, beginning of period	$	12,690		$	29,331

Total gains included in:
Net income	(10,460		)	(16,641		)
Other comprehensive income	—			—

Transfers into Level 3	—			—

Transfers out of Level 3	—			—

Derivatives, end of period	$	2,230		$	12,690

Net unrealized gains included in net income relating to liabilities held at December 31, 2013 and 2012 (1)	$	10,460		$	16,641


(1)	Included in net investment income in the consolidated statements of income and comprehensive income.

There were no transfers into or out of Level 1 and Level 2 during 2013 or 2012. Except as disclosed in note 2, the Company did not have any assets or liabilities measured at fair value on a non-recurring basis during the years ended December 31, 2013 and 2012.

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2013
Reinsurance Disclosures [Abstract]	'
Reinsurance	'
	Reinsurance

	The Company uses reinsurance and retrocessional reinsurance to manage its net retention on individual risks and overall exposure to losses while providing it with the ability to offer policies with sufficient limits to meet policyholder needs. As part of the Company's underwriting philosophy, the Company has historically sought to offer products with limits that did not require significant reinsurance. Following the acquisition of Alterra, the Company now has certain insurance and reinsurance products that have typically required higher levels of reinsurance. In a reinsurance transaction, an insurance company transfers, or cedes, all or part of its exposure in return for a portion of the premium. In a retrocessional reinsurance transaction, a reinsurance company transfers, or cedes, all or part of its exposure in return for a portion of the premium. The ceding of insurance does not legally discharge the Company from its primary liability for the full amount of the policies, and the Company will be required to pay the loss and bear collection risk if the reinsurer fails to meet its obligations under the reinsurance or retrocessional agreement.

	A credit risk exists with ceded reinsurance to the extent that any reinsurer is unable to meet the obligations assumed under the reinsurance or retrocessional contracts. Allowances are established for amounts deemed uncollectible. The Company evaluates the financial condition of its reinsurers and monitors concentration of credit risk arising from its exposure to individual reinsurers. At December 31, 2013 and 2012, balances recoverable from the Company's ten largest reinsurers, by group, represented approximately 62% and 74%, respectively, of the reinsurance recoverable on paid and unpaid losses, before considering reinsurance allowances. At December 31, 2013, the Company's largest reinsurance balance was due from the Fairfax Financial Group and represented 10% of the reinsurance recoverable on paid and unpaid losses, before considering reinsurance allowances.

	To further reduce credit exposure to reinsurance recoverable balances, the Company has received collateral, including letters of credit and trust accounts, from certain reinsurers. Collateral related to these reinsurance agreements is available, without restriction, when the Company pays losses covered by the reinsurance agreements.

	The following table summarizes the Company's reinsurance allowance for doubtful accounts.



		Years Ended December 31,
	(dollars in thousands)	2013			2012			2011
	Reinsurance allowance, beginning of year	$	71,148		$	69,067		$	155,190

	Additions	13,621			24,179			8,504

	Deductions	(8,559		)	(22,098		)	(94,627		)
	Reinsurance allowance, end of year	$	76,210		$	71,148		$	69,067


	Deductions for the year ended December 31, 2011 included a $78.5 million adjustment related to commutations completed by Markel International, which involved the termination of ceded reinsurance contracts. Of the total adjustment, $40.0 million related to reinsurance recoverables on losses and loss adjustment expenses for A&E related exposures. The adjustment had no impact on the reinsurance recoverable on unpaid losses, net of the reinsurance allowance, for any period presented.

	Management believes the Company's reinsurance allowance for doubtful accounts is adequate at December 31, 2013; however, the deterioration in the credit quality of existing reinsurers or disputes over reinsurance and retrocessional contracts could result in additional charges.

	The following table summarizes the effect of reinsurance and retrocessional reinsurance on premiums written and earned.



		Years Ended December 31,
		2013						2012						2011
	(dollars in thousands)	Written			Earned			Written			Earned			Written			Earned
	Direct	$	3,143,957		$	2,947,812		$	2,115,353		$	2,057,735		$	1,957,397		$	1,873,512

	Assumed	776,269			1,016,853			398,328			376,186			333,854			338,183

	Ceded	(683,543		)	(733,049		)	(299,555		)	(286,793		)	(249,413		)	(232,355		)
	Net premiums	$	3,236,683		$	3,231,616		$	2,214,126		$	2,147,128		$	2,041,838		$	1,979,340


	Incurred losses and loss adjustment expenses were net of reinsurance recoverables (ceded incurred losses and loss adjustment expenses) of $269.4 million, $165.8 million and $159.8 million for the years ended December 31, 2013, 2012 and 2011, respectively.

	The percentage of ceded earned premiums to gross earned premiums was 18%, 12% and 11% for the years ended December 31, 2013, 2012 and 2011, respectively.

Commitments_And_Contingencies

Commitments And Contingencies	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Commitments And Contingencies	'
	Commitments and Contingencies

	a)The Company leases substantially all of its facilities and certain furniture and equipment under noncancelable operating leases with remaining terms up to 21 years.

	The following table summarizes the Company's minimum annual rental commitments, excluding taxes, insurance and other operating costs payable directly by the Company, for noncancelable operating leases at December 31, 2013.



	Years Ending December 31,	(dollars in
		thousands)
	2014	$	32,783

	2015	29,114

	2016	22,977

	2017	27,955

	2018	26,440

	2019 and thereafter	160,454

	Total	$	299,723


	Rental expense was $35.3 million, $28.1 million and $25.8 million for the years ended December 31, 2013, 2012 and 2011, respectively.

	b)On August 8, 2013, the Company, through its wholly-owned subsidiary, Alterra Holdings Limited, and several other third-party investors, executed a subscription agreement with New Point VI Limited (New Point VI) to purchase common shares of New Point VI. New Point VI is the holding company of New Point Re VI Limited, a Bermuda-domiciled reinsurance company that offers fully-collateralized retrocessional reinsurance to the property reinsurance catastrophe market, incepting between January 1, 2014 and December 31, 2014. Following execution of the subscription agreement and subsequent issuance of common shares, the Company holds approximately 34% of the issued and outstanding common shares of New Point VI. The Company's initial commitment under the subscription agreement with New Point VI was $75.0 million. As of December 31, 2013, the Company's total capital contributions to New Point VI totaled $7.8 million, which reduced its commitment under the subscription agreement to $67.2 million. During February 2014, the Company invested an additional $6.5 million under the subscription agreement.

	c)Contingencies arise in the normal course of the Company's operations and are not expected to have a material impact on the Company's financial condition or results of operations.

Related_Party_Transactions

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2013
Related Party Transactions [Abstract]	'
Related Party Transactions	'
	Related Party Transactions

	The Company engages in certain related party transactions in the normal course of business. These transactions are at arm's length and are not material to the Company's consolidated financial statements.

Statutory_Financial_Informatio

Statutory Financial Information	12 Months Ended
	Dec. 31, 2013
Statutory Financial Information [Abstract]	'
Statutory Financial Information	'
	Statutory Financial Information

	a) Statutory capital and surplus and statutory net income (loss) for the Company's wholly-owned insurance and reinsurance subsidiaries as of December 31, 2013 and 2012 and for the years ended December 31, 2013, 2012 and 2011, respectively, is summarized below.


		Statutory Capital and Surplus
	(dollars in thousands)	2013			2012
	United States	$	2,399,356		$	1,455,077

	United Kingdom	$	517,571		$	485,043

	Bermuda	$	1,503,004		N/A

	Other	$	171,410		N/A


	As of December 31, 2013, the amount of statutory capital and surplus necessary to satisfy regulatory requirements is not significant in relation to actual statutory capital and surplus.



		Statutory Net Income (Loss)
		Years Ended December 31,
	(dollars in thousands)	2013			2012		2011
	United States	$	235,009		$	127,179	$	180,744

	United Kingdom	$	117,020		$	82,573	$	18,386

	Bermuda	$	93,953		N/A		N/A

	Other	$	(12,617	)	N/A		N/A


	United States

	The laws of the domicile states of the Company's domestic insurance and reinsurance subsidiaries govern the amount of dividends that may be paid to the Company. Generally, statutes in the domicile states of the Company's domestic insurance and reinsurance subsidiaries require prior approval for payment of extraordinary as opposed to ordinary dividends. At December 31, 2013, the Company's domestic insurance and reinsurance subsidiaries could pay up to $296.9 million during the following 12 months under the ordinary dividend regulations.

	In converting from U.S. statutory accounting principles to U.S. GAAP, typical adjustments include deferral of policy acquisition costs, differences in the calculation of deferred income taxes and the inclusion of net unrealized gains or losses relating to fixed maturities in shareholders' equity. The Company does not use any permitted statutory accounting practices that are different from prescribed statutory accounting practices which impact statutory capital and surplus.
	United Kingdom
	The Company's United Kingdom insurance subsidiaries are authorized by the Prudential Regulation Authority (PRA) and regulated by both the PRA and the Financial Conduct Authority (FCA). The PRA oversees compliance with established periodic auditing and reporting requirements, minimum solvency margins and individual capital assessment requirements and dividend restrictions, while both the PRA and the FCA oversee compliance with risk assessment reviews and various other requirements. The ability of Markel International Insurance Company Limited to pay dividends is limited by applicable PRA requirements, which require 14 days advance notice to the PRA of the intention to declare and pay a dividend. Markel Syndicate Management Limited, the manager of the Company's syndicates at Lloyd's, is required to satisfy the solvency requirements of Lloyd's. In addition, the Company's United Kingdom subsidiaries must comply with the United Kingdom Companies Act of 2006, which provides that dividends may only be paid out of profits available for that purpose. As of December 31, 2013, earnings of the Company's United Kingdom subsidiaries are considered reinvested indefinitely for U.S. income tax purposes and will not be made available for distributions to the holding company.
	Bermuda

	Markel Bermuda is subject to enhanced capital requirements in addition to minimum solvency and liquidity requirements. The enhanced capital requirement is determined by reference to a risk-based capital model that determines a control threshold for statutory capital and surplus by taking into account the risk characteristics of different aspects of the insurer's business. At December 31, 2013, Markel Bermuda satisfied both the enhanced capital requirements and the minimum solvency and liquidity requirements.

	Under the Bermuda Insurance Act, Markel Bermuda is prohibited from paying or declaring dividends during a fiscal year if it is in breach of its enhanced capital requirement, solvency margin or minimum liquidity ratio or if the declaration or payment of the dividend would cause a breach. If an insurer fails to meet its solvency margin or minimum liquidity ratio on the last day of any financial year, it is prohibited from declaring or paying any dividends during the next financial year without the approval of the Bermuda Monetary Authority (BMA). Further, Markel Bermuda is prohibited from declaring or paying in any financial year dividends of more than 25% of its total statutory capital and surplus as set forth in its previous year's statutory balance sheet unless it files with the BMA an affidavit stating that it will continue to meet its solvency margin and minimum liquidity ratio. Markel Bermuda must obtain the BMA's prior approval for a reduction by 15% or more of the total statutory capital as set forth in its previous year's financial statements. In addition, as a long-term insurer, Markel Bermuda may not declare or pay a dividend to any person other than a policyholder unless the value of the assets in its long-term business fund exceeds the liabilities of its long-term business by the amount of the dividend and at least the prescribed minimum solvency margin. As of December 31, 2013, Markel Bermuda could pay up to $375.8 million during the following 12 months without making any additional filings with the BMA.
	Other Jurisdictions
	The Company's other foreign subsidiaries are subject to capital and solvency requirements in their respective jurisdictions of domicile that govern their ability to declare and pay dividends. As of December 31, 2013, earnings of our foreign subsidiaries are considered reinvested indefinitely for U.S. income tax purposes and will not be made available for distributions to the holding company.

	b) Lloyd's sets the corporate members' required capital annually based on each syndicates' business plans, rating environment, reserving environment and input arising from Lloyd's discussions with, inter alia, regulatory and rating agencies. Such required capital is referred to as Funds at Lloyd's (FAL), and comprises cash and investments. The amount of cash and investments held as FAL as of December 31, 2013 was $972.5 million. The amount which the Company provides as FAL is not available for distribution to the holding company. The Company's corporate members may also be required to maintain funds under the control of Lloyd's in excess of their capital requirements and such funds also may not be available for distribution to the holding company.

Segment_Reporting_Disclosures

Segment Reporting Disclosures	12 Months Ended
	Dec. 31, 2013
Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract]	'
Segment Reporting Disclosures	'
	Segment Reporting Disclosures

	The Company historically operated in three segments of the specialty insurance marketplace: the Excess and Surplus Lines, the Specialty Admitted and the London Insurance Market segments. The Company considers many factors, including the nature of its insurance products, production sources, distribution strategies and regulatory environment in determining how to aggregate operating segments.

	As a result of the acquisition of Alterra, the Company formed a new operating segment, effective May 1, 2013. The Alterra segment is comprised of all of the active property and casualty operations of the former Alterra companies, which provide specialty insurance and reinsurance products worldwide. During 2013, results attributable to Alterra were separately evaluated by management.

	For purposes of segment reporting, the Other Insurance (Discontinued Lines) segment includes lines of business that have been discontinued prior to, or in conjunction with, acquisitions. Alterra previously offered life and annuity reinsurance products. In 2010, Alterra ceased writing life and annuity reinsurance contracts and placed this business into run-off. Results attributable to the run-off of life and annuity reinsurance business are included in the Company's Other Insurance (Discontinued Lines) segment.

	All investing activities related to the Company's insurance operations are included in the Investing segment.

	The Company's Markel Ventures operations primarily consist of controlling interests in various industrial and service businesses. For purposes of segment reporting, the Company's Markel Ventures operations are not considered to be a reportable operating segment.

	The following table summarizes the Company's gross written premiums by country. Gross written premiums are attributed to individual countries based upon location of risk.



		Years Ended December 31,
	(dollars in thousands)	2013				% of			2012				% of			2011				% of
						Total							Total							Total
	United States	$	2,934,868			75	%		$	1,768,011			70	%		$	1,590,238			69	%

	United Kingdom	245,143				6			147,891				6			139,349				6

	Canada	128,420				3			120,542				5			126,434				6

	Other countries	611,795				16			477,237				19			435,230				19

	Total	$	3,920,226			100	%		$	2,513,681			100	%		$	2,291,251			100	%


	Most of the Company's gross written premiums are placed through insurance and reinsurance brokers. The top three independent brokers accounted for approximately 19% of consolidated gross premiums written for the year ended December 31, 2013 and approximately 40% of gross premiums written in the Alterra segment.

	Segment profit for the Investing segment is measured by net investment income and net realized investment gains or losses. Segment profit or loss for each of the Company's operating segments is measured by underwriting profit or loss. The property and casualty insurance industry commonly defines underwriting profit or loss as earned premiums net of losses and loss adjustment expenses and underwriting, acquisition and insurance expenses. Underwriting profit or loss does not replace operating income or net income computed in accordance with U.S. GAAP as a measure of profitability. Underwriting profit or loss provides a basis for management to evaluate the Company's underwriting performance. Segment profit or loss for the Company's operating segments also includes other revenues and other expenses, primarily related to the run-off of managing general agent operations that were discontinued in conjunction with acquisitions. Other revenues and other expenses in the Other Insurance (Discontinued Lines) segment are comprised of the results attributable to the run-off of life and annuity reinsurance business.

	For management reporting purposes, the Company allocates assets to its underwriting, investing and Markel Ventures operations. Underwriting assets are all assets not specifically allocated to the Investing segment or to the Company's Markel Ventures operations. Underwriting and investing assets are not allocated to the Excess and Surplus Lines, Specialty Admitted, London Insurance Market, Alterra or Other Insurance (Discontinued Lines) segments since the Company does not manage its assets by operating segment. The Company does not allocate capital expenditures for long-lived assets to any of its operating segments for management reporting purposes.


	a)	The following tables summarize the Company's segment disclosures.



		Year Ended December 31, 2013
	(dollars in thousands)	Excess and				Specialty				London				Alterra				Other				Investing			Consolidated
		Surplus				Admitted				Insurance								Insurance
		Lines								Market								(Discontinued
																		Lines)
	Gross premium volume	$	1,070,520			$	899,996			$	914,480			$	1,035,190			$	40			$	—		$	3,920,226

	Net written premiums	911,870				855,381				792,158				677,233				41				—			3,236,683


	Earned premiums	856,629				744,993				781,637				848,317				40				—			3,231,616

	Losses and loss adjustment expenses	(341,661		)		(410,068		)		(386,416		)		(647,546		)		(30,582		)		—			(1,816,273		)

	Transaction costs and other acquisition-related expenses (1)	—				—				—				(75,140		)		—				—			(75,140		)

	Amortization of policy acquisition costs	(147,996		)		(137,181		)		(149,191		)		(37,547		)		—				—			(471,915		)

	Other operating expenses	(195,464		)		(176,346		)		(150,537		)		(243,022		)		112				—			(765,257		)

	Underwriting profit (loss)	171,508				21,398				95,493				(154,938		)		(30,430		)		—			103,031

Net investment income	—				—				—				—				—				317,373			317,373

Net realized investment gains	—				—				—				—				—				63,152			63,152

Other revenues (insurance)	—				13,648				5,002				4,714				1,130				—			24,494

Other expenses (insurance)	—				(17,087		)		(5,065		)		—				(28,126		)		—			(50,278		)

Segment profit (loss)	$	171,508			$	17,959			$	95,430			$	(150,224	)		$	(57,426	)		$	380,525		$	457,772

Other revenues (Markel Ventures)																								686,448

Other expenses (Markel Ventures)																								(613,250		)
Amortization of intangible assets																								(55,223		)
Interest expense																								(114,004		)
Income before income taxes																								$	361,743

U.S. GAAP combined ratio (2)	80		%		97		%		88		%		118		%		NM			(3)				97		%


(1)	In connection with the acquisition of Alterra, the Company incurred transaction costs of $16.0 million for the year ended December 31, 2013, which primarily consist of due diligence, legal and investment banking costs. Additionally, the Company incurred severance costs of $31.7 million, stay bonuses of $14.8 million and other compensation costs totaling $12.6 million related to the acceleration of certain long-term incentive compensation awards and restricted stock awards that were granted by Alterra prior to the acquisition.

(2)	The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums.

(3)	NM — Ratio is not meaningful.



	Year Ended December 31, 2012
(dollars in thousands)	Excess and				Specialty				London				Other				Investing				Consolidated
	Surplus				Admitted				Insurance				Insurance
	Lines								Market				(Discontinued
													Lines)
Gross premium volume	$	956,273			$	669,692			$	887,720			$	(4	)		$	—			$	2,513,681

Net written premiums	811,601				628,147				774,383				(5		)		—				2,214,126


Earned premiums	793,159				588,758				765,216				(5		)		—				2,147,128

Losses and loss adjustment expenses	(388,793		)		(381,870		)		(362,330		)		(21,075		)		—				(1,154,068		)

Prospective adoption of FASB ASU No. 2010-26 (1)	(17,456		)		(13,577		)		(12,060		)		—				—				(43,093		)

Other amortization of policy acquisition costs	(135,573		)		(96,770		)		(152,673		)		—				—				(385,016		)

Other operating expenses	(201,196		)		(143,377		)		(156,587		)		(203		)		—				(501,363		)

Underwriting profit (loss)	50,141				(46,836		)		81,566				(21,283		)		—				63,588

Net investment income	—				—				—				—				282,107				282,107

Net realized investment gains	—				—				—				—				31,593				31,593

Other revenues (insurance)	—				44,968				4,964				—				—				49,932

Other expenses (insurance)	—				(41,425		)		(3,867		)		—				—				(45,292		)

Segment profit (loss)	$	50,141			$	(43,293	)		$	82,663			$	(21,283	)		$	313,700			$	381,928

Other revenues (Markel Ventures)																					489,352

Other expenses (Markel Ventures)																					(432,956		)
Amortization of intangible assets																					(33,512		)
Interest expense																					(92,762		)
Income before income taxes																					$	312,050

U.S. GAAP combined ratio(2)	94		%		108		%		89		%		NM			(3)					97		%


(1)	Effective January 1, 2012, the Company prospectively adopted FASB ASU No. 2010-26, Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts. At December 31, 2011, deferred policy acquisition costs included $43.1 million of costs that no longer met the criteria for deferral as of January 1, 2012 and were recognized into income during 2012, consistent with policy terms.

(2)	The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums.

(3)	NM — Ratio is not meaningful.



	Year Ended December 31, 2011
(dollars in thousands)	Excess and				Specialty				London				Other				Investing				Consolidated
	Surplus				Admitted				Insurance				Insurance
	Lines								Market				(Discontinued
													Lines)
Gross premium volume	$	893,427			$	572,392			$	825,301			$	131			$	—			$	2,291,251

Net written premiums	772,279				543,213				726,359				(13		)		—				2,041,838


Earned premiums	756,306				527,293				695,753				(12		)		—				1,979,340

Losses and loss adjustment expenses	(318,583		)		(364,144		)		(531,625		)		4,366				—				(1,209,986		)

Amortization of policy acquisition costs	(172,269		)		(129,731		)		(177,454		)		—				—				(479,454		)

Other operating expenses	(156,419		)		(78,509		)		(96,149		)		352				—				(330,725		)

Underwriting profit (loss)	109,035				(45,091		)		(109,475		)		4,706				—				(40,825		)

Net investment income	—				—				—				—				263,676				263,676

Net realized investment gains	—				—				—				—				35,857				35,857

Other revenues (insurance)	—				33,545				—				—				—				33,545

Other expenses (insurance)	—				(33,722		)		—				—				—				(33,722		)

Segment profit (loss)	$	109,035			$	(45,268	)		$	(109,475	)		$	4,706			$	299,533			$	258,531

Other revenues (Markel Ventures)																					317,532

Other expenses (Markel Ventures)																					(275,324		)
Amortization of intangible assets																					(24,291		)
Interest expense																					(86,252		)
Income before income taxes																					$	190,196

U.S. GAAP combined ratio(1)	86		%		109		%		116		%		NM			(2)					102		%


(1)	The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums.

(2)	NM — Ratio is not meaningful.

b)The following table summarizes deferred policy acquisition costs, unearned premiums and unpaid losses and loss adjustment expenses by segment.



(dollars in thousands)	Deferred Policy				Unearned				Unpaid Losses and
	Acquisition Costs				Premiums				Loss Adjustment Expenses
December 31, 2013
Excess and Surplus Lines	$	69,849			$	469,148			$	1,998,359

Specialty Admitted	77,118				391,606				878,564

London Insurance Market	53,420				321,383				1,909,612

Alterra	60,580				944,978				4,996,722

Other Insurance (Discontinued Lines)	—				—				478,799

Total	$	260,967			$	2,127,115			$	10,262,056

December 31, 2012
Excess and Surplus Lines	$	59,158			$	410,731			$	2,152,253

Specialty Admitted	43,810				280,811				796,093

London Insurance Market	54,497				308,719				1,958,249

Other Insurance (Discontinued Lines)	—				—				464,831

Total	$	157,465			$	1,000,261			$	5,371,426


c)The following table summarizes segment earned premiums by major product grouping.



(dollars in thousands)	Property				Casualty				Professional				Workers'				Other				Consolidated
									Liability				Compensation
Year Ended December 31, 2013
Excess and Surplus Lines	$	115,773			$	253,195			$	208,732			$	—			$	278,929			$	856,629

Specialty Admitted	230,068				232,868				—				253,347				28,710				744,993

London Insurance Market	230,278				124,843				176,302				—				250,214				781,637

Alterra	215,488				172,736				165,934				31,347				262,812				848,317

Other Insurance (Discontinued Lines)	—				—				—				—				40				40

Earned premiums	$	791,607			$	783,642			$	550,968			$	284,694			$	820,705			$	3,231,616

Year Ended December 31, 2012
Excess and Surplus Lines	$	109,607			$	227,880			$	189,199			$	—			$	266,473			$	793,159

Specialty Admitted	148,311				163,955				—				242,021				34,471				588,758

London Insurance Market	259,571				126,441				162,554				—				216,650				765,216

Other Insurance (Discontinued Lines)	—				—				—				—				(5		)		(5		)

Earned premiums	$	517,489			$	518,276			$	351,753			$	242,021			$	517,589			$	2,147,128

Year Ended December 31, 2011
Excess and Surplus Lines	$	103,406			$	214,565			$	197,131			$	—			$	241,204			$	756,306

Specialty Admitted	135,077				140,805				—				200,797				50,614				527,293

London Insurance Market	231,798				117,062				173,101				—				173,792				695,753

Other Insurance (Discontinued Lines)	—				—				—				—				(12		)		(12		)

Earned premiums	$	470,281			$	472,432			$	370,232			$	200,797			$	465,598			$	1,979,340


The Company does not manage products at this level of aggregation. The Company offers a diverse portfolio of products and manages these products in logical groupings within each operating segment.

d)The following table reconciles segment assets to the Company's consolidated balance sheets.



	December 31,
(dollars in thousands)	2013				2012				2011
Segment assets:
Investing	$	17,550,332			$	9,277,697			$	8,692,391

Underwriting	5,468,731				2,387,305				2,209,431

Total segment assets	23,019,063				11,665,002				10,901,822

Markel Ventures operations	936,448				891,586				630,281

Total assets	$	23,955,511			$	12,556,588			$	11,532,103


e) Beginning in 2014, the Company will monitor and report its ongoing underwriting operations in the following three segments: U.S. Insurance, International Insurance and Global Reinsurance. The U.S. Insurance segment will include all direct business and facultative placements written by the Company's insurance subsidiaries domiciled in the United States. The International Insurance segment will include all direct business and facultative placements written by the Company's insurance subsidiaries domiciled outside of the United States, including the Company's syndicates at Lloyd's. The Global Reinsurance segment will include all treaty reinsurance written across the Company. Results for lines of business discontinued prior to, or in conjunction with, acquisitions will continue to be reported as the Other Insurance (Discontinued Lines) segment.

Other_Revenues_And_Other_Expen

Other Revenues And Other Expenses	12 Months Ended
	Dec. 31, 2013
Other Income and Expenses [Abstract]	'
Other Revenues And Other Expenses	'
	Other Revenues and Other Expenses

	The following table summarizes the components of other revenues and other expenses.



		Years Ended December 31,
		2013				2012				2011
	(dollars in thousands)	Other		Other		Other		Other		Other		Other
		Revenues		Expenses		Revenues		Expenses		Revenues		Expenses
	Insurance:
	Managing general agent operations	$	17,399	$	20,382	$	48,056	$	43,069	$	31,136	$	30,728

	Life and annuity	1,130		28,126		—		—		—		—

	Other	5,965		1,770		1,876		2,223		2,409		2,994

		24,494		50,278		49,932		45,292		33,545		33,722

	Markel Ventures:
	Manufacturing	495,138		437,712		366,886		328,484		214,668		192,503

	Non-Manufacturing	191,310		175,538		122,466		104,472		102,864		82,821

		686,448		613,250		489,352		432,956		317,532		275,324

	Total	$	710,942	$	663,528	$	539,284	$	478,248	$	351,077	$	309,046


	The Company's Markel Ventures operations primarily consist of controlling interests in various industrial and service businesses and are viewed by management as separate and distinct from the Company's insurance operations. While each of the companies is operated independently from one another, management aggregates financial results into two industry groups: manufacturing and non-manufacturing.

	The financial results of the companies in which the Company owns controlling interests have been consolidated in our financial statements. The financial results of those companies in which the Company owns a noncontrolling interest are accounted for under the equity method of accounting.

	The increase in other revenues and other expenses attributable to Markel Ventures in each of the years presented was primarily due to acquisitions.

Employee_Benefit_Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2013
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]	'
Employee Benefit Plans	'
	Employee Benefit Plans

	a)The Company maintains defined contribution plans for employees of its United States insurance operations in accordance with Section 401(k) of the IRC. Employees of the Company's Markel Ventures subsidiaries are provided post-retirement benefits under separate plans. The Company also provides various defined contribution plans for employees of its international insurance operations, which are in line with local market terms and conditions of employment. Expenses relating to the Company's defined contribution plans, including the defined contribution plans of Alterra effective May 1, 2013, were $24.3 million, $19.1 million and $17.8 million in 2013, 2012 and 2011, respectively.

	b)The Terra Nova Pension Plan is a defined benefit plan which covers Markel International employees who meet the eligibility conditions set out in the plan. The plan has been closed to new participants since 2001. The cost of providing pensions for employees is charged to earnings over the average working life of employees according to actuarial recommendations. Final benefits are based on the employee's years of credited service and the higher of pensionable compensation received in the calendar year preceding retirement or the best average pensionable compensation received in any three consecutive years in the ten years preceding retirement. Effective April 1, 2012, employees are no longer accruing benefits for future service in the Terra Nova Pension Plan. The Company uses December 31 as the measurement date for the Terra Nova Pension Plan.

	The following table summarizes the funded status of the Terra Nova Pension Plan and the amounts recognized on the accompanying consolidated balance sheets of the Company.



		Years Ended December 31,
	(dollars in thousands)	2013				2012
	Change in projected benefit obligation:
	Projected benefit obligation at beginning of period	$	151,327			$	141,163

	Service cost	—				361

	Interest cost	6,533				6,815

	Participant contributions	—				81

	Benefits paid	(3,542		)		(2,938		)
	Actuarial loss (gain)	5,459				(601		)

	Effect of foreign currency rate changes	3,233				6,446

	Projected benefit obligation at end of year	$	163,010			$	151,327

	Change in plan assets:
	Fair value of plan assets at beginning of period	$	164,090			$	139,325

	Actual gain on plan assets	19,430				15,251

	Employer contributions	5,338				5,737

	Participant contributions	—				81

	Benefits paid	(3,542		)		(2,938		)
	Effect of foreign currency rate changes	4,121				6,634

	Fair value of plan assets at end of year	$	189,437			$	164,090

	Funded status of the plan	$	26,427			$	12,763

	Net actuarial pension loss	42,941				48,021

	Total	$	69,368			$	60,784


	Net actuarial pension loss is recognized as a component of accumulated other comprehensive income, net of a tax benefit of $12.4 million and $13.5 million in 2013 and 2012, respectively. The asset for pension benefits, also referred to as the funded status of the plan, at December 31, 2013 and December 31, 2012 was included in other assets on the consolidated balance sheet.

	The following table summarizes the components of net periodic benefit cost (income) and the weighted average assumptions for the Terra Nova Pension Plan.



		Years Ended December 31,
	(dollars in thousands)	2013				2012				2011
	Components of net periodic benefit cost (income):
	Service cost	$	—			$	361			$	1,357

	Interest cost	6,533				6,815				7,115

	Expected return on plan assets	(10,825		)		(9,788		)		(9,834		)
Amortization of net actuarial pension loss	1,934				2,590				1,908

Net periodic benefit cost (income)	$	(2,358	)		$	(22	)		$	546

Weighted average assumptions as of December 31:
Discount rate	4.7		%		4.5		%		4.8		%
Expected return on plan assets	6.6		%		6.6		%		6.6		%
Rate of compensation increase	3.2		%		3.1		%		3.2		%

The projected benefit obligation and the net periodic benefit cost (income) are determined by independent actuaries using assumptions provided by the Company. In determining the discount rate, the Company uses the current yield on high-quality, fixed-income investments that have maturities corresponding to the anticipated timing of estimated defined benefit payments. The Company's discount rate approximates a bond yield from a published index that includes "AA" rated corporate bonds with maturities of 15 years or more. The expected return on plan assets is estimated based upon the anticipated average yield on plan assets and reflects expected changes in the allocation of plan assets. Asset returns reflect management's belief that 4.5% is a reasonable rate of return to anticipate for fixed maturities given current market conditions and future expectations. In addition, the expected return on plan assets includes an assumption that equity securities will outperform fixed maturities by approximately 3.5% over the long term. The rate of compensation increase is based upon historical experience and management's expectation of future compensation.

Management's discount rate and rate of compensation increase assumptions at December 31, 2013 were used to calculate the Company's projected benefit obligation. Management's discount rate, expected return on plan assets and rate of compensation increase assumptions at December 31, 2012 were used to calculate the net periodic benefit income for 2013. The Company estimates that net periodic benefit income in 2014 will include an expense of $1.6 million resulting from the amortization of the net actuarial pension loss included as a component of accumulated other comprehensive income at December 31, 2013.

The fair values of each of the plan's assets are measured using quoted prices in active markets for identical assets, which represent Level 1 inputs within the fair value hierarchy established in FASB ASC 820-10. The following table summarizes the fair value of plan assets as of December 31, 2013 and 2012.



	December 31,
(dollars in thousands)	2013				2012
Plan assets:
Fixed maturity index funds	$	70,997			$	64,357

Equity security index funds	118,431				99,727

Cash and cash equivalents	9				6

Total	$	189,437			$	164,090


The Company's target asset allocation for the plan is 54% equity securities and 46% fixed maturities. At December 31, 2013, the actual allocation of assets in the plan was 63% equity securities and 37% fixed maturities. At December 31, 2012, the actual allocation of plan assets was 61% equity securities and 39% fixed maturities.

Investments are managed by a third-party investment manager. Equity securities are invested in two index funds that are allocated 25% to shares of United Kingdom companies and 75% to companies in other markets. The primary objective of investing in these funds is to earn rates of return that are consistently in excess of inflation. Investing in equity securities, historically, has provided rates of return that are higher than investments in fixed maturities. As the Company's obligations under this pension plan are expected to be paid out over a period in excess of 30 years, the Company primarily invests in equity securities. Fixed maturity investments are allocated between five index funds, two that include United Kingdom government securities, one that includes securities issued by other foreign governments and two that include United Kingdom corporate securities. The assets in these funds are invested to meet the Company's obligations for current pensioners and those individuals nearing retirement. The plan does not invest in the Company's common shares.

At December 31, 2013 and 2012, the fair value of plan assets exceeded the plan's accumulated benefit obligation of $146.0 million and $133.5 million, respectively. The Company expects to make plan contributions of $5.6 million in 2014.

The benefits expected to be paid in each year from 2014 to 2018 are $3.8 million, $3.9 million, $4.0 million, $4.1 million and $4.2 million, respectively. The aggregate benefits expected to be paid in the five years from 2019 to 2023 are $22.5 million. The expected benefits to be paid are based on the same assumptions used to measure the Company's projected benefit obligation at December 31, 2013 and include estimated future employee service.

c)AMF Bakery Systems (AMF), one of the Company's Markel Ventures subsidiaries, participated in a multiemployer defined benefit pension plan, Regime de retraite patronal-syndical (Quebec) de l'A.I.M. (Quebec pension plan no. 26467). The multiemployer plan covered approximately 90 union employees within the Canadian operations of AMF. In December 2011, AMF gave notice to the trustees of the multiemployer plan of its intent to withdraw. As a result, AMF established a liability of $2.0 million for its obligations under the multiemployer plan. During the year ended December 31, 2012, a $2.4 million payment, which represented approximately 95% of AMF's determined deficit payment, was remitted to the plan. The withdrawal report was approved by the Regie des rentes du Quebec in December 2013, and AMF paid $0.1 million to settle its remaining obligations under the multiemployer plan.

Markel_Corporation_Parent_Comp

Markel Corporation (Parent Company Only) Financial Information	12 Months Ended
	Dec. 31, 2013
Condensed Financial Information of Parent Company Only Disclosure [Abstract]	'
Markel Corporation (Parent Company Only) Financial Information	'
	Markel Corporation (Parent Company Only) Financial Information

	The following parent company only condensed financial information reflects the financial position, results of operations and cash flows of Markel Corporation.

	CONDENSED BALANCE SHEETS



		December 31,
		2013			2012
		(dollars in thousands)
	ASSETS
	Investments, available-for-sale, at estimated fair value:
	Fixed maturities (amortized cost of $66,154 in 2013 and $80,631 in 2012)	$	67,363		$	84,158

	Equity securities (cost of $197,549 in 2013 and $270,157 in 2012)	392,123			426,409

	Short-term investments (estimated fair value approximates cost)	654,971			664,986

	Total Investments	1,114,457			1,175,553

	Cash and cash equivalents	207,352			237,816

	Restricted cash and cash equivalents	1,010			662

	Receivables	14,326			13,994

	Investments in consolidated subsidiaries	6,826,790			3,656,577

	Notes receivable from subsidiaries	168,611			173,913

	Income taxes receivable	5,320			6,623

	Net deferred tax asset	—			6,595

	Other assets	102,193			99,107

	Total Assets	$	8,440,059		$	5,370,840

	LIABILITIES AND SHAREHOLDERS' EQUITY
	Senior long-term debt	$	1,633,873		$	1,388,029

	Net deferred tax liability	40,443			—

	Other liabilities	92,166			94,154

	Total Liabilities	1,766,482			1,482,183

	Total Shareholders' Equity	6,673,577			3,888,657

	Total Liabilities and Shareholders' Equity	$	8,440,059		$	5,370,840


	CONDENSED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME



		Years Ended December 31,
		2013			2012			2011
		(dollars in thousands)
	REVENUES
	Net investment income	$	21,946		$	30,619		$	12,629

Dividends on common stock of consolidated subsidiaries	806,233			337,585			330,462

Net realized investment gains (losses):
Other-than-temporary impairment losses	(15		)	(38		)	(7,676		)
Net realized investment gains, excluding other-than-temporary impairment losses	67,232			14,926			7,417

Net realized investment gains (losses)	67,217			14,888			(259		)

Other	1			3			13

Total Revenues	895,397			383,095			342,845

EXPENSES
Interest expense	92,743			87,391			78,830

Other expenses	2,617			1,166			4,572

Total Expenses	95,360			88,557			83,402

Income Before Equity in Undistributed Earnings of Consolidated Subsidiaries and Income Taxes	800,037			294,538			259,443

Equity in undistributed earnings of consolidated subsidiaries	(520,323		)	(61,663		)	(144,348		)
Income tax benefit	(1,307		)	(20,510		)	(26,931		)
Net Income to Shareholders	$	281,021		$	253,385		$	142,026

OTHER COMPREHENSIVE INCOME TO SHAREHOLDERS
Change in net unrealized gains on investments, net of taxes:
Net holding gains arising during the period	$	66,623		$	10,897		$	675

Consolidated subsidiaries' net holding gains arising during the period	158,922			255,528			141,164

Consolidated subsidiaries' change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period	(141		)	(160		)	3,943

Reclassification adjustments for net gains (losses) included in net income to shareholders	(43,220		)	11,847			735

Consolidated subsidiaries' reclassification adjustments for net gains (losses) included in net income to shareholders	2,390			(35,898		)	(23,076		)

Change in net unrealized gains on investments, net of taxes	184,574			242,214			123,441

Change in foreign currency translation adjustments, net of taxes	(2,670		)	(242		)	314

Consolidated subsidiaries' change in foreign currency translation adjustments, net of taxes	(7,501		)	1,781			(4,469		)

Consolidated subsidiaries' change in net actuarial pension loss, net of taxes	4,065			6,664			(9,459		)

Total Other Comprehensive Income to Shareholders	178,468			250,417			109,827

Comprehensive Income to Shareholders	$	459,489		$	503,802		$	251,853


CONDENSED STATEMENTS OF CASH FLOWS



	Years Ended December 31,
	2013			2012			2011
	(dollars in thousands)
OPERATING ACTIVITIES
Net income to shareholders	$	281,021		$	253,385		$	142,026

Adjustments to reconcile net income to shareholders to net cash provided by operating activities	186,574			(153,773		)	102,714

Net Cash Provided By Operating Activities	467,595			99,612			244,740

INVESTING ACTIVITIES
Proceeds from sales of fixed maturities and equity securities	142,259			149,314			50,322

Proceeds from maturities, calls and prepayments of fixed maturities	2,819			64,340			46,522

Cost of fixed maturities and equity securities purchased	(23,412		)	(89,569		)	(92,287		)
Net change in short-term investments	260,247			(214,820		)	(179,823		)

Decrease in notes receivable due from subsidiaries	5,302			116,797			7,401

Capital contributions to subsidiaries	(67,878		)	(198,349		)	(179,403		)
Acquisitions	(1,017,988		)	(100,409		)	—

Cost of equity method investments	(5,291		)	(38,250		)	—

Change in restricted cash and cash equivalents	(348		)	(204		)	(326		)
Additions to property and equipment	(3,653		)	(9,437		)	(16,927		)
Other	3,207			(4,369		)	12,175

Net Cash Used By Investing Activities	(704,736		)	(324,956		)	(352,346		)
FINANCING ACTIVITIES
Additions to senior long-term debt	491,235			347,207			247,935

Repayment and retirement of senior long-term debt	(246,665		)	(157,359		)	—

Repurchases of common stock	(57,388		)	(16,873		)	(42,913		)
Issuance of common stock	24,518			9,145			1,182

Other	(5,023		)	436			50

Net Cash Provided By Financing Activities	206,677			182,556			206,254

Increase (decrease) in cash and cash equivalents	(30,464		)	(42,788		)	98,648

Cash and cash equivalents at beginning of year	237,816			280,604			181,956

CASH AND CASH EQUIVALENTS AT END OF YEAR	$	207,352		$	237,816		$	280,604

Quarterly_Financial_Informatio

Quarterly Financial Information	12 Months Ended
	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]	'
Quarterly Financial Information	'
	Quarterly Financial Information (unaudited)

	The following table presents the unaudited quarterly results of consolidated operations for 2013, 2012 and 2011.



		Quarters Ended
	(dollars in thousands, except per share amounts)	Mar. 31			30-Jun				Sept. 30				Dec. 31
	2013
	Operating revenues	$	819,864		$	1,031,769			$	1,191,665			$	1,279,785

	Net income	89,263			28,676				66,967				98,939

	Net income to shareholders	88,902			27,756				65,599				98,764

	Comprehensive income (loss) to shareholders	257,684			(149,054		)		144,409				206,450

	Net income per share:
	Basic	$	9.53		$	2.24			$	4.69			$	6.98

	Diluted	9.5			2.24				4.67				6.95

	Common stock price ranges:
	High	$	510.05		$	546.94			$	549.09			$	582.59

	Low	434.98			501.76				506.64				511.06

	2012
	Operating revenues	$	733,135		$	693,247			$	765,775			$	807,955

	Net income	57,713			90,768				51,674				58,093

	Net income to shareholders	57,253			89,687				49,653				56,792

	Comprehensive income to shareholders	205,945			73,416				147,454				76,987

	Net income per share:
	Basic	$	5.94		$	8.44			$	5.33			$	6.25

	Diluted	5.92			8.42				5.32				6.23

	Common stock price ranges:
	High	$	451.9		$	453.5			$	459.9			$	502.2

	Low	398.65			421				420				425.17

	2011
	Operating revenues	$	621,594		$	647,168			$	676,088			$	685,100

	Net income	9,861			31,649				54,669				52,307

	Net income to shareholders	8,272			30,314				53,264				50,176

	Comprehensive income (loss) to shareholders	24,738			96,045				(52,626		)		183,696

	Net income per share:
	Basic	$	0.85		$	3.12			$	5.5			$	5.21

	Diluted	0.85			3.11				5.48				5.19

	Common stock price ranges:
	High	$	422.83		$	430.26			$	403.21			$	419.1

Low	379.44			386.81				346.15				337.5

Summary_Of_Significant_Account1

Summary Of Significant Accounting Policies (Policy)	12 Months Ended
Summary Of Significant Accounting Policies (Policy)	Dec. 31, 2013
Accounting Policies [Abstract]	'
Basis of Presentation	'
Basis of Presentation	Basis of Presentation. The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (U.S. GAAP) and include the accounts of Markel Corporation and its subsidiaries (the Company). All significant intercompany balances and transactions have been eliminated in consolidation. The consolidated financial statements include the results of operations and cash flows of Alterra from the Acquisition Date to December 31, 2013 and not in any prior periods, except with respect to the Supplemental Pro Forma Information included in note 2. The Company consolidates the results of its Markel Ventures subsidiaries on a one-month lag. Certain prior year amounts have been reclassified to conform to the current presentation, including the separate presentation of restricted cash and cash equivalents on the consolidated balance sheets and corresponding change in cash flows from investing activities on the consolidated statements of cash flows.
Use of Estimates	'
Use of Estimates	Use of Estimates. The preparation of financial statements in accordance with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities. Management periodically reviews its estimates and assumptions. Quarterly reviews include evaluating the adequacy of reserves for unpaid losses and loss adjustment expenses, life and annuity reinsurance benefit reserves, litigation contingencies, the reinsurance allowance for doubtful accounts and income tax liabilities, as well as analyzing the recoverability of deferred tax assets, estimating reinsurance premiums written and earned and evaluating the investment portfolio for other-than-temporary declines in estimated fair value. Estimates and assumptions for goodwill and intangible assets are reviewed in conjunction with an acquisition and goodwill and indefinite-lived intangible assets are reassessed at least annually for impairment. Actual results may differ materially from the estimates and assumptions used in preparing the consolidated financial statements.
Investments	'
	Investments. Available-for-sale investments are recorded at estimated fair value. Unrealized gains and losses on investments, net of deferred income taxes, are included in accumulated other comprehensive income in shareholders' equity. The Company completes a detailed analysis each quarter to assess whether the decline in the fair value of any investment below its cost basis is deemed other-than-temporary.

	Premiums and discounts are amortized or accreted over the lives of the related fixed maturities as an adjustment to the yield using the effective interest method. Dividend and interest income are recognized when earned. Realized investment gains or losses are included in earnings. Realized gains or losses from sales of investments are derived using the first-in, first-out method.

	Investments accounted for under the equity method of accounting are recorded at cost within other assets on the consolidated balance sheets and subsequently increased or decreased by the Company's proportionate share of the net income or loss of the investee. The Company records its proportionate share of net income or loss of the investee in net investment income. The Company records its proportionate share of other comprehensive income or loss of the investee as a component of other comprehensive income. Dividends or other equity distributions are recorded as a reduction of the investment. The Company reviews equity method investments for impairment when events or circumstances indicate that a decline in the fair value of the investment below its carrying value is other-than-temporary.
Cash and Cash Equivalents	'
Cash and Cash Equivalents	Cash and Cash Equivalents. The Company considers all investments with original maturities of 90 days or less to be cash equivalents. The carrying value of the Company's cash and cash equivalents and restricted cash and cash equivalents approximates fair value.
Receivables	'
Receivables	Receivables. Receivables include amounts receivable from agents, brokers and insureds, which represent premiums that are both currently due and amounts not yet due on insurance and reinsurance policies. Premiums for insurance policies are generally due at inception. Premiums for reinsurance policies generally become due over the period of coverage based on the policy terms. The Company monitors the credit risk associated with premiums receivable, taking into consideration the fact that in certain instances credit risk may be reduced by the Company's right to offset loss obligations or unearned premiums against premiums receivable. Amounts deemed uncollectible are charged to net income in the period they are determined. Changes in the estimate of reinsurance premiums written will result in an adjustment to premiums receivable in the period they are determined.
Reinsurance Recoverables	'
Reinsurance Recoverables	Reinsurance Recoverables. Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability associated with the reinsured business. Allowances are established for amounts deemed uncollectible and reinsurance recoverables are recorded net of these allowances. The Company evaluates the financial condition of its reinsurers and monitors concentration risk to minimize its exposure to significant losses from individual reinsurers.
Deferred Policy Acquisition Costs	'
Deferred Policy Acquisition Costs	Deferred Policy Acquisition Costs. Costs directly related to the acquisition of insurance premiums are deferred and amortized over the related policy period, generally one year. Concurrent with the adoption of Financial Accounting Standards Board (FASB) Accounting Standards Update (ASU) No. 2010-26, Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts, effective January 1, 2012, the Company only defers acquisition costs incurred that are related directly to the successful acquisition of new or renewal insurance contracts, including commissions to agents and brokers and premium taxes. Commissions received related to reinsurance premiums ceded are netted against broker commissions in determining acquisition costs eligible for deferral. To the extent that future policy revenues on existing policies are not adequate to cover related costs and expenses, deferred policy acquisition costs are charged to earnings. The Company does not consider anticipated investment income in determining whether a premium deficiency exists.
Goodwill and Intangible Assets	'
Goodwill and Intangible Assets	Goodwill and Intangible Assets. Goodwill and intangible assets are recorded as a result of business acquisitions. Goodwill represents the excess of the amount paid to acquire a business over the net fair value of assets acquired and liabilities assumed at the date of acquisition. Indefinite-lived and other intangible assets are recorded at fair value as of the acquisition date. The determination of the fair value of certain assets acquired and liabilities assumed involves significant judgment and the use of valuation models and other estimates, which require assumptions that are inherently subjective. Goodwill and indefinite-lived intangible assets are tested for impairment at least annually. The Company completes an annual test during the fourth quarter of each year based upon the results of operations through September 30. Intangible assets with definite lives are amortized using the straight-line method over their estimated useful lives, generally five to 20 years, and are reviewed for impairment when events or circumstances indicate that their carrying value may not be recoverable.
Property and Equipment	'
Property and Equipment	Property and Equipment. Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization of property and equipment are calculated using the straight-line method over the estimated useful lives (generally, the life of the lease for leasehold improvements, ten to 40 years for buildings, seven to 40 years for land improvements, three to ten years for furniture and equipment and three to 25 years for other property and equipment).
Redeemable Noncontrolling Interests	'
	Redeemable Noncontrolling Interests. The Company owns controlling interests in various companies through its Markel Ventures operations. Under the terms of certain of the acquisition and related agreements, the Company has the option to acquire the remaining equity interests and the remaining equity interests have the option to sell their interests to the Company in the future. The redemption value of the remaining equity interests is generally based on the respective company's earnings in specified periods preceding the redemption date. The redeemable noncontrolling interests generally become redeemable through 2018.

	The Company recognizes changes in the redemption value that exceed the carrying value of redeemable noncontrolling interests to retained earnings as if the balance sheet date were also the redemption date. Changes in the redemption value also result in an adjustment to net income to shareholders in the calculation of basic and diluted net income per share. The adjustment recorded to retained earnings during 2013 and 2012 was a decrease of $2.0 million and an increase of $3.1 million, respectively. There were no adjustments recorded to retained earnings in 2011 because the redemption values of the redeemable noncontrolling interests were less than or approximated their carrying values.
Income Taxes	'
Income Taxes	Income Taxes. The Company records deferred income taxes to reflect the net tax effect of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and their tax bases. Deferred tax assets are reduced by a valuation allowance when management believes it is more likely than not that some, or all, of the deferred tax assets will not be realized. The Company recognizes the tax benefit from an uncertain tax position taken or expected to be taken in income tax returns only if it is more likely than not that the tax position will be sustained upon examination by tax authorities, based on the technical merits of the position. Tax positions that meet the more likely than not threshold are then measured using a probability weighted approach, whereby the largest amount of tax benefit that is greater than 50% likely of being realized upon ultimate settlement is recognized. The Company recognizes interest and penalties related to uncertain tax positions in income tax expense.
Unpaid Losses and Loss Adjustment Expenses	'
Unpaid Losses and Loss Adjustment Expenses	Unpaid Losses and Loss Adjustment Expenses. Unpaid losses and loss adjustment expenses on our property and casualty insurance business are based on evaluations of reported claims and estimates for losses and loss adjustment expenses incurred but not reported. Estimates for losses and loss adjustment expenses incurred but not reported are based on reserve development studies, among other things. The Company does not discount reserves for losses and loss adjustment expenses to reflect estimated present value, except for reserves assumed in connection with an acquisition, which are recorded at fair value at the acquisition date. Recorded reserves are estimates, and the ultimate liability may be greater or less than the estimates.
Life and Annuity Benefits	'
	Life and Annuity Benefits. Prior to its acquisition by the Company, Alterra entered into long duration reinsurance contracts for life and annuity benefits which subject the Company to mortality, longevity and morbidity risks. The assumptions used to determine policy benefit reserves were determined at the Acquisition Date and are generally locked-in for the life of the contract unless an unlocking event occurs. To the extent existing policy reserves, together with the present value of future gross premiums and expected investment income earned thereon, are not adequate to cover the present value of future benefits, settlement and maintenance costs, the locked-in assumptions are revised to current best estimate assumptions and a charge to earnings for life and annuity benefits is recognized at that time. Because of the assumptions and estimates used in establishing reserves for life and annuity benefit obligations and the long-term nature of these reinsurance contracts, the ultimate liability may be greater or less than the estimates.

	Results attributable to the run-off of life and annuity reinsurance business are included in other revenues and other expenses in the Company's consolidated statements of income and comprehensive income and as part of the Company's Other Insurance (Discontinued Lines) segment.
Revenue Recognition	'
	Revenue Recognition.

	Property and Casualty Premiums

	Insurance premiums are generally earned on a pro rata basis over the policy period, typically one year. The cost of reinsurance ceded is initially recorded as prepaid reinsurance premiums and is amortized over the reinsurance contract period in proportion to the amount of insurance protection provided. Premiums ceded are netted against premiums written.

	Assumed reinsurance premiums are recorded at the inception of each contract based upon contract terms and information received from cedents and brokers and are earned on a pro rata basis over the coverage period, or for multi-year contracts, in proportion with the underlying risk exposure to the extent there is variability in the exposure through the coverage period. Changes in reinsurance premium estimates are expected and may result in significant adjustments in any period. These estimates change over time as additional information regarding changes in underlying exposures is obtained. Any subsequent differences arising on such estimates are recorded as premiums written in the period they are determined. The Company uses the periodic method to account for assumed reinsurance from foreign reinsurers. The Company's foreign reinsurers provide sufficient information to record foreign assumed business in the same manner as the Company records assumed business from United States reinsurers.

	Certain contracts that the Company writes provide for reinstatement of coverage. Reinstatement premiums are the premiums for the restoration of the insurance or reinsurance limit of a contract to its full amount after a loss occurrence by the insured or reinsured. The Company accrues for reinstatement premiums resulting from losses recorded. Such accruals are based upon contractual terms and management judgment is involved with respect to the amount of losses recorded. Changes in estimates of losses recorded on contracts with reinstatement premium features will result in changes in reinstatement premiums based on contractual terms. Reinstatement premiums are recognized at the time losses are recorded and are earned on a pro-rata basis over the coverage period.

	Other Revenues

	Other revenues primarily relate to the Company's Markel Ventures operations and consist of revenues from the sale of manufactured products and service revenues. Revenues from manufactured products are generally recognized at the time title transfers to the customer, which occurs at the point of shipment or delivery to the customer, depending on the terms of the sales arrangement. Revenues from services are generally recognized as the services are performed. Services provided pursuant to a contract are recognized either over the contract period or upon completion of the elements specified in the contract, depending on the terms of the contract.
Stock-based Compensation	'
Stock-based Compensation	Stock-based Compensation. Stock-based compensation expense is recognized as part of underwriting, acquisition and insurance expenses over the requisite service period. Stock-based compensation expense, net of taxes, was $18.4 million in 2013, $4.4 million in 2012 and $4.0 million in 2011. See note 12.
Foreign Currency Translation	'
	Foreign Currency Translation. The functional currencies of the Company's foreign operations are the currencies in which the majority of their business is transacted. Assets and liabilities of foreign operations are translated into the United States Dollar using the exchange rates in effect at the balance sheet date. Revenues and expenses of foreign operations are translated using the average exchange rate for the period. Gains or losses from translating the financial statements of foreign operations are included, net of taxes, in shareholders' equity as a component of accumulated other comprehensive income. Gains and losses arising from transactions denominated in a foreign currency, other than a functional currency, are included in net income.

	The Company manages its exposure to foreign currency risk primarily by matching assets and liabilities denominated in the same currency. To the extent that assets and liabilities in foreign currencies are not matched, the Company is exposed to foreign currency risk. For functional currencies, the related exchange rate fluctuations are reflected in other comprehensive income. The cumulative foreign currency translation adjustment, net of taxes, was a loss of $11.2 million and $1.1 million at December 31, 2013 and 2012, respectively.
Derivative Financial Instruments	'
	Derivative Financial Instruments. Derivative instruments, including derivative instruments resulting from hedging activities, are measured at fair value and recognized as either assets or liabilities on the consolidated balance sheets. The changes in fair value of derivatives are recognized in earnings unless the derivative is designated as a hedge and qualifies for hedge accounting.

	The Company's foreign currency forward contracts are generally designated and qualified as hedges of a net investment in a foreign operation. The effective portion of the change in fair value resulting from these hedges is reported in currency translation adjustments as part of other comprehensive income. The ineffective portion of the change in fair value is recognized in earnings.
Comprehensive Income	'
Comprehensive Income	Comprehensive Income. Comprehensive income represents all changes in equity that result from recognized transactions and other economic events during the period. Other comprehensive income refers to revenues, expenses, gains and losses that under U.S. GAAP are included in comprehensive income but excluded from net income, such as unrealized gains or losses on investments, foreign currency translation adjustments and changes in net actuarial pension loss.
Net Income Per Share	'
Net Income Per Share	Net Income Per Share. Basic net income per share is computed by dividing adjusted net income to shareholders by the weighted average number of common shares outstanding during the year. Unvested share-based compensation awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid) are considered participating awards and are included in the computation of net income per share. Non-participating unvested share-based compensation awards are excluded from the computation of net income per share. Diluted net income per share is computed by dividing adjusted net income to shareholders by the weighted average number of common shares and dilutive potential common shares outstanding during the year. See note 12(b).
Recent Accounting Pronouncements	'
	Recent Accounting Pronouncements. Effective January 1, 2013, the Company adopted FASB ASU No. 2013-02, Reporting Amounts Reclassified Out of Accumulated Other Comprehensive Income, which amends FASB Accounting Standards Codification (ASC) 220, Comprehensive Income, to improve the reporting of reclassifications out of accumulated other comprehensive income. ASU No. 2013-02 requires information about reclassifications out of accumulated other comprehensive income to be reported in one place, by component. The guidance also requires disclosure of the effect of significant reclassifications out of accumulated other comprehensive income on the respective line items in net income if the amount being reclassified is required under U.S. GAAP to be reclassified in its entirety to net income. For other amounts that are not required to be reclassified in their entirety to net income, an entity is required to cross-reference to other disclosures required under U.S. GAAP that provide additional detail about those amounts. The adoption of this guidance did not have an impact on the Company's financial position, results of operations or cash flows. The Company has included the additional disclosures required by ASU No. 2013-02 in note 13.

	In July 2013, the FASB issued ASU No. 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists. ASU No. 2013-11 requires that a liability related to an unrecognized tax benefit be offset against a deferred tax asset for a net operating loss carryforward, a similar tax loss or a tax credit carryforward if such settlement is required or expected in the event the uncertain tax position is disallowed. In that case, the liability associated with the unrecognized tax benefit is presented in the financial statements as a reduction to the related deferred tax asset for a net operating loss carryforward, a similar tax loss or a tax credit carryforward. Otherwise, the unrecognized tax benefit should be presented in the financial statements as a liability and should not be combined with deferred tax assets. ASU No. 2013-11 becomes effective for the Company during the first quarter of 2014. The adoption of this ASU is not expected to impact the Company's financial position, results of operations or cash flows.

Acquisitions_Tables

Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2013
Acquisitions [Abstract]	'
Calculation Of Total Purchase Price	'
	The Company's total purchase price for Alterra as of the Acquisition Date was calculated as follows:



	(in thousands, except per share amounts)
	Shares of Alterra common stock outstanding as of the Acquisition Date	96,433

	Exchange ratio per the Merger Agreement	0.04315

	Markel share issuance to Alterra shareholders	4,161


	Shares of Alterra restricted stock outstanding as of the Acquisition Date	2,239

	Incentive award ratio per the Merger Agreement	0.06252

	Markel restricted stock issuance to Alterra restricted stock holders	140


	Multiplied by Markel's weighted average stock price on April 30, 2013 (1)	$	529.59


	Markel share and restricted stock issuance consideration, net of taxes	$	2,267,648


	Alterra common shares outstanding as of the Acquisition Date that received cash consideration	96,433

	Multiplied by cash price per share component per the Merger Agreement	$	10

	Markel cash consideration	$	964,330


	Fair value of Markel warrant issuance to Alterra warrant holders as of the Acquisition Date	$	73,685

	Fair value of Markel stock option issuance to Alterra stock option holders as of the Acquisition Date, net of taxes	$	12,335

	Fair value of partially vested Markel restricted stock unit issuance as of the Acquisition Date, net of taxes	$	6,867

	Unrecognized compensation on unvested restricted stock and restricted stock units	$	(20,572	)
	Total acquisition consideration	$	3,304,293


	-1	The fair value of the shares issued by the Company was calculated as the weighted average price of the Company's stock on April 30, 2013, the day preceding the Acquisition Date.
Summary Of Fair Value Of Assets Acquired And Liabilities Assumed	'
	The following table summarizes the fair values of the assets acquired and liabilities assumed at the Acquisition Date.


	(dollars in thousands)
	ASSETS
	Investments	$	6,407,841

	Cash and cash equivalents	1,036,274

	Restricted cash and cash equivalents	414,497

	Receivables	866,388

	Reinsurance recoverable on unpaid losses	1,169,084

	Reinsurance recoverable on paid losses	80,672

	Prepaid reinsurance premiums	317,445

	Other assets	859,884

	LIABILITIES
	Unpaid losses and loss adjustment expenses	4,719,461

	Life and annuity benefits	1,477,482

	Unearned premiums	1,075,610

	Payables to insurance and reinsurance companies	342,858

	Senior long-term debt	512,463

	Other liabilities	223,108

	Net assets	2,801,103

	Goodwill	295,690

	Intangible assets	207,500

	Acquisition date fair value	$	3,304,293

Summary Of Net Intangible Assets Acquired	'
	The following table summarizes the intangible assets recorded in connection with the acquisition, and as of December 31, 2013.



	(dollars in thousands)	Amount			Economic
					Useful Life
	Customer relationships	$	132,000		18 years

	Broker relationships	19,000			18 years

	Technology	18,000			Ten years

	Trade names	1,000			One year

	Lloyd's syndicate capacity	12,000			Indefinite

	Insurance licenses	25,500			Indefinite

	Intangible assets, before amortization, as of the Acquisition Date	207,500

	Amortization (from the Acquisition Date through December 31, 2013)	7,785

	Net intangible assets as of December 31, 2013	$	199,715

Summary Of Transaction And Acquisition-Related Costs	'
	The following table summarizes transaction and acquisition-related costs incurred by the Company in connection with the acquisition, all of which were included in underwriting, acquisition and insurance expenses in the consolidated statements of income and comprehensive income.



	(dollars in thousands)	Year Ended
		31-Dec-13
	Transaction costs	$	15,981

	Acquisition-related costs:
	Severance costs	31,734

	Stay bonuses	14,804

	Acceleration of Alterra long-term incentive compensation awards and restricted stock awards	12,621

	Total transaction and acquisition-related costs	$	75,140

Summary Of Results Of Operations	'
	The following table summarizes the results of Alterra since the Acquisition Date that have been included within the Company's consolidated statements of income and comprehensive income.



	(dollars in thousands)	Year Ended
		December 31, 2013
	Operating revenues	$	912,387

	Net loss to shareholders	$	(93,074	)
Unaudited Pro Forma Consolidated Financial Information	'
	The following table presents unaudited pro forma consolidated information for the years ended December 31, 2013 and 2012 and assumes the Company's acquisition of Alterra occurred on January 1, 2012. The pro forma financial information is presented for informational purposes only and does not necessarily reflect the results that would have occurred had the acquisition taken place on January 1, 2012, nor is it necessarily indicative of future results. Significant adjustments used to determine pro forma results include amortization of intangible assets and amortization of fair value adjustments discussed in c) above, and the corresponding income tax effects. The Company also excluded certain charges from the pro forma results, including transaction costs incurred by the Company ($16.0 million) and Alterra ($23.0 million) totaling $39.0 million for the year ended December 31, 2013, severance costs attributable to the acquisition totaling $31.7 million for the year ended December 31, 2013, and stay bonuses of $14.8 million for the year ended December 31, 2013. The acceleration of compensation expense during the year ended December 31, 2013 related to Alterra's long-term incentive compensation awards and restricted stock awards was attributable to the acquisition; however, the incremental expense recognized during the period only represents a timing difference in the recognition of expense. Therefore, it was not excluded from the pro forma underwriting results.



		Unaudited
		Consolidated Pro Forma
		Years Ended December 31,
	(in thousands, except per share amounts)	2013			2012
	Earned premiums	$	3,680,220		$	3,509,834

	Operating revenues	4,899,628			4,561,107

	Net income to shareholders	422,829			308,496


	U.S. GAAP combined ratio (1)	95		%	99		%

	Basic net income per share	$	30.33		$	21.79

	Diluted net income per share	$	30.19		$	21.71


	Weighted average common shares outstanding:
	Basic	14,007			14,014

	Diluted	14,069			14,065


	-1	The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums.

Investments_Tables

Investments (Tables)	12 Months Ended
	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]	'
Available-For-Sale Investments	'
	The following tables summarize the Company's available-for-sale investments.



		December 31, 2013
	(dollars in thousands)	Amortized				Gross				Gross				Unrealized Other-				Estimated
		Cost				Unrealized				Unrealized				Than-Temporary				Fair
						Holding				Holding				Impairment Losses				Value
						Gains				Losses
	Fixed maturities:
	U.S. Treasury securities and obligations of U.S. government agencies	$	1,215,522			$	9,051			$	(30,342	)		$	—			$	1,194,231

	Obligations of states, municipalities and political subdivisions	2,986,758				116,341				(27,384		)		—				3,075,715

	Foreign governments	1,484,818				30,647				(54,411		)		—				1,461,054

	Commercial mortgage-backed securities	379,555				62				(11,796		)		—				367,821

	Residential mortgage-backed securities	875,902				13,046				(16,442		)		(2,258		)		870,248

	Asset-backed securities	189,646				257				(1,614		)		—				188,289

	Corporate bonds	2,996,940				54,777				(61,650		)		(4,889		)		2,985,178

	Total fixed maturities	10,129,141				224,181				(203,639		)		(7,147		)		10,142,536

	Equity securities:
	Insurance, banks and other financial institutions	422,975				592,112				(4		)		—				1,015,083

	Industrial, consumer and all other	1,143,578				1,094,251				(1,114		)		—				2,236,715

	Total equity securities	1,566,553				1,686,363				(1,118		)		—				3,251,798

	Short-term investments	1,452,270				18				—				—				1,452,288

	Investments, available-for-sale	$	13,147,964			$	1,910,562			$	(204,757	)		$	(7,147	)		$	14,846,622


		December 31, 2012
	(dollars in thousands)	Amortized				Gross				Gross				Unrealized Other-				Estimated
		Cost				Unrealized				Unrealized				Than-Temporary				Fair
						Holding				Holding				Impairment Losses				Value
						Gains				Losses
	Fixed maturities:
	U.S. Treasury securities and obligations of U.S. government agencies	$	297,663			$	19,844			$	—			$	—			$	317,507

	Obligations of states, municipalities and political subdivisions	2,586,867				245,057				(362		)		—				2,831,562

	Foreign governments	503,844				52,764				—				—				556,608

	Residential mortgage-backed securities	202,644				14,996				(5		)		(2,258		)		215,377

	Asset-backed securities	13,828				517				—				—				14,345

	Corporate bonds	957,432				93,395				(121		)		(6,822		)		1,043,884

	Total fixed maturities	4,562,278				426,573				(488		)		(9,080		)		4,979,283

	Equity securities:
	Insurance, banks and other financial institutions	508,771				389,434				(138		)		—				898,067

	Industrial, consumer and all other	878,534				637,783				(7,433		)		—				1,508,884

Total equity securities	1,387,305				1,027,217				(7,571		)		—				2,406,951

Short-term investments	973,318				26				(14		)		—				973,330

Investments, available-for-sale	$	6,922,901			$	1,453,816			$	(8,073	)		$	(9,080	)		$	8,359,564

Summary Of Gross Unrealized Investment Losses By Length Of Time That Securities Have Continuously Been In An Unrealized Loss Position	'
	The following tables summarize gross unrealized investment losses by the length of time that securities have continuously been in an unrealized loss position.



		December 31, 2013
		Less than 12 months								12 months or longer								Total
	(dollars in thousands)	Estimated				Gross				Estimated				Gross				Estimated			Gross
		Fair				Unrealized				Fair				Unrealized				Fair			Unrealized
		Value				Holding and				Value				Holding and				Value			Holding and
						Other-Than-								Other-Than-							Other-Than-
						Temporary								Temporary							Temporary
						Impairment								Impairment							Impairment
						Losses								Losses							Losses
	Fixed maturities:
	U.S. Treasury securities and obligations of U.S. government agencies	$	587,929			$	(30,342	)		$	—			$	—			$	587,929		$	(30,342	)

	Obligations of states, municipalities and political subdivisions	513,608				(27,238		)		3,512				(146		)		517,120			(27,384		)

	Foreign governments	950,040				(54,411		)		—				—				950,040			(54,411		)

	Commercial mortgage-backed securities	357,737				(11,796		)		—				—				357,737			(11,796		)

	Residential mortgage-backed securities	437,675				(18,700		)		—				—				437,675			(18,700		)

	Asset-backed securities	142,011				(1,614		)		—				—				142,011			(1,614		)

	Corporate bonds	1,817,737				(66,539		)		—				—				1,817,737			(66,539		)

	Total fixed maturities	4,806,737				(210,640		)		3,512				(146		)		4,810,249			(210,786		)

	Equity securities:
	Insurance, banks and other financial institutions	144				(4		)		—				—				144			(4		)

	Industrial, consumer and all other	20,943				(714		)		27,735				(400		)		48,678			(1,114		)

	Total equity securities	21,087				(718		)		27,735				(400		)		48,822			(1,118		)

	Total	$	4,827,824			$	(211,358	)		$	31,247			$	(546	)		$	4,859,071		$	(211,904	)



		December 31, 2012
		Less than 12 months								12 months or longer								Total
	(dollars in thousands)	Estimated				Gross				Estimated				Gross				Estimated			Gross
		Fair				Unrealized				Fair				Unrealized				Fair			Unrealized
		Value				Holding and				Value				Holding and				Value			Holding and
						Other-Than-								Other-Than-							Other-Than-
						Temporary								Temporary							Temporary
						Impairment								Impairment							Impairment
						Losses								Losses							Losses
	Fixed maturities:
	Obligations of states, municipalities and political subdivisions	$	2,833			$	(46	)		$	3,616			$	(316	)		$	6,449		$	(362	)

	Residential mortgage-backed securities	364				(2,260		)		201				(3		)		565			(2,263		)

	Corporate bonds	—				(6,822		)		3,860				(121		)		3,860			(6,943		)

	Total fixed maturities	3,197				(9,128		)		7,677				(440		)		10,874			(9,568		)

	Equity securities:
	Insurance, banks and other financial institutions	2,431				(138		)		—				—				2,431			(138		)

	Industrial, consumer and all other	82,109				(7,310		)		1,983				(123		)		84,092			(7,433		)

Total equity securities	84,540				(7,448		)		1,983				(123		)		86,523			(7,571		)

Short-term investments	228,820				(14		)		—				—				228,820			(14		)

Total	$	316,557			$	(16,590	)		$	9,660			$	(563	)		$	326,217		$	(17,153	)

Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturities By Contractual Maturity	'
	The amortized cost and estimated fair value of fixed maturities at December 31, 2013 are shown below by contractual maturity.



	(dollars in thousands)	Amortized				Estimated
		Cost				Fair Value
	Due in one year or less	$	885,726			$	891,654

	Due after one year through five years	2,891,314				2,947,173

	Due after five years through ten years	2,217,759				2,254,169

	Due after ten years	2,689,239				2,623,182

		8,684,038				8,716,178

	Commercial mortgage-backed securities	379,555				367,821

	Residential mortgage-backed securities	875,902				870,248

	Asset-backed securities	189,646				188,289

	Total fixed maturities	$	10,129,141			$	10,142,536

Components Of Net Investment Income	'
	The following table presents the components of net investment income.



		Years Ended December 31,
	(dollars in thousands)	2013				2012				2011
	Interest:
	Municipal bonds (tax-exempt)	$	82,308			$	90,316			$	94,457

	Municipal bonds (taxable)	28,041				22,663				23,277

	Other taxable bonds	134,377				107,270				117,242

	Short-term investments, including overnight deposits	3,573				2,755				2,484

	Dividends on equity securities	48,641				50,416				35,996

	Change in fair value of credit default swap	10,460				16,641				(4,103		)

	Income from equity method investments	21,898				1,961				584

	Other	355				(41		)		1,551

		329,653				291,981				271,488

	Investment expenses	(12,280		)		(9,874		)		(7,812		)
	Net investment income	$	317,373			$	282,107			$	263,676

Summary Of Activity For Credit Losses	'
	The following table summarizes the activity for credit losses recognized in net income on fixed maturities where other-than-temporary impairment was identified and a portion of the other-than-temporary impairment was included in other comprehensive income.



		Years Ended December 31,
	(dollars in thousands)	2013				2012				2011
	Cumulative credit loss, beginning of year	$	21,370			$	21,370			$	10,307

	Additions:
	Other-than-temporary impairment losses not previously recognized	—				—				875

	Increases related to other-than-temporary impairment losses previously recognized	—				—				10,203

	Total additions	—				—				11,078

	Reductions:
	Sales or maturities of fixed maturities on which credit losses were recognized	(8,622		)		—				(15		)

	Cumulative credit loss, end of year	$	12,748			$	21,370			$	21,370

Summary Of Net Realized Investment Gains And The Change In Net Unrealized Gains On Investments	'
	The following table presents net realized investment gains and the change in net unrealized gains on investments.



		Years Ended December 31,
	(dollars in thousands)	2013				2012				2011
	Realized gains:
	Sales of fixed maturities	$	13,772			$	18,337			$	17,035

	Sales of equity securities	73,592				29,578				36,863

	Other	5,940				749				2,626

	Total realized gains	93,304				48,664				56,524

	Realized losses:
	Sales of fixed maturities	(25,168		)		(563		)		(410		)
	Sales of equity securities	(278		)		(342		)		(61		)
	Other-than-temporary impairments	(4,706		)		(12,078		)		(20,196		)
	Other	—				(4,088		)		—

	Total realized losses	(30,152		)		(17,071		)		(20,667		)
	Net realized investment gains	$	63,152			$	31,593			$	35,857

	Change in net unrealized gains on investments:
	Fixed maturities	$	(403,610	)		$	51,783			$	190,976

	Equity securities	665,599				302,013				(8,250		)

	Short-term investments	6				12				(4		)

	Net increase	$	261,995			$	353,808			$	182,722

Summary Of Other-Than-Temporary Impairment Losses Recognized In Net Income And In Net Realized Investment Gains By Investment Type	'
	The following table presents other-than-temporary impairment losses recognized in net income and included in net realized investment gains by investment type.



		Years Ended December 31,
	(dollars in thousands)	2013				2012				2011
	Fixed maturities:
	Obligations of states, municipalities and political subdivisions	$	(1,242	)		$	—			$	—

	Residential mortgage-backed securities	(640		)		—				(11,078		)

	Total fixed maturities	(1,882		)		—				(11,078		)

	Equity securities:
	Insurance, banks and other financial institutions	—				(10,336		)		(4,251		)

	Industrial, consumer and all other	(2,824		)		(1,742		)		(4,867		)
	Total equity securities	(2,824		)		(12,078		)		(9,118		)
	Total	$	(4,706	)		$	(12,078	)		$	(20,196	)
Schedule Of Restricted Assets	'
	Total restricted assets are included on the Company's consolidated balance sheets as follows.



	(dollars in thousands)	December 31, 2013				December 31, 2012
	Investments, available-for-sale	$	5,225,701			$	1,262,755

	Restricted cash and cash equivalents	786,926				109,415

	Other assets	76,752				—

	Total	$	6,089,379			$	1,372,170

Receivables_Tables

Receivables (Tables)	12 Months Ended
	Dec. 31, 2013
Receivables [Abstract]	'
Components Of Receivables	'
	The following table presents the components of receivables.



		December 31,
	(dollars in thousands)	2013			2012
	Amounts receivable from agents, brokers and insureds	$	1,058,021		$	332,570

	Trade accounts receivable	85,203			73,512

	Employee stock loans receivable (see note 12(c))	12,822			11,413

	Other	5,420			12,982

		1,161,466			430,477

	Allowance for doubtful receivables	(19,693		)	(16,594		)
	Receivables	$	1,141,773		$	413,883

Deferred_Policy_Acquisition_Co1

Deferred Policy Acquisition Costs (Tables)	12 Months Ended
	Dec. 31, 2013
Deferred Policy Acquisition Costs Disclosures [Abstract]	'
Amounts Of Policy Acquisition Costs Acquired, Deferred And Amortized	'
	The following table presents the amounts of policy acquisition costs deferred and amortized.



		Years Ended December 31,
	(dollars in thousands)	2013			2012			2011
	Balance, beginning of year	$	157,465		$	194,674		$	188,783

	Policy acquisition costs deferred	575,417			390,900			485,345

	Amortization of policy acquisition costs	(471,915		)	(428,109		)	(479,454		)
	Deferred policy acquisition costs	$	260,967		$	157,465		$	194,674

Components Of Underwriting, Acquisition And Insurance Expenses	'
	The following table presents the components of underwriting, acquisition and insurance expenses.



		Years Ended December 31,
	(dollars in thousands)	2013			2012			2011
	Transaction costs and other acquisition-related expenses (1)	$	75,140		$	—		$	—

	Prospective adoption of FASB ASU No. 2010-26 (2)	—			43,093			—

	Other amortization of policy acquisition costs	471,915			385,016			479,454

	Other operating expenses	765,257			501,363			330,725

	Underwriting, acquisition and insurance expenses	$	1,312,312		$	929,472		$	810,179


	(1)	In connection with the acquisition of Alterra, the Company incurred transaction costs of $16.0 million for the year ended December 31, 2013, which primarily consist of due diligence, legal and investment banking costs. Additionally, the Company incurred severance costs of $31.7 million, stay bonuses of $14.8 million and other compensation costs totaling $12.6 million related to the acceleration of certain long-term incentive compensation awards and restricted stock awards that were granted by Alterra prior to the acquisition.

	(2)	Effective January 1, 2012, the Company prospectively adopted FASB ASU No. 2010-26, Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts. At December 31, 2011, deferred policy acquisition costs included $43.1 million of costs that no longer met the criteria for deferral as of January 1, 2012 and were recognized into income during 2012, consistent with policy terms.

Property_And_Equipment_Tables

Property And Equipment (Tables)	12 Months Ended
	Dec. 31, 2013
Property, Plant and Equipment [Abstract]	'
Components Of Property And Equipment	'
	The following table presents the components of property and equipment, which are included in other assets on the consolidated balance sheets.



		December 31,
	(dollars in thousands)	2013			2012
	Land	$	48,036		$	45,199

	Buildings	59,307			53,767

	Leasehold improvements	68,363			55,626

	Land improvements	57,673			51,512

	Furniture and equipment	217,528			211,354

	Other	104,690			85,714

		555,597			503,172

	Accumulated depreciation and amortization	(207,688		)	(172,943		)
	Property and equipment	$	347,909		$	330,229

Goodwill_And_Intangible_Assets1

Goodwill And Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2013
Goodwill and Intangible Assets Disclosure [Abstract]	'
Components Of Goodwill	'
	The following table presents the components of goodwill.



	(dollars in thousands)	Excess and		Specialty			London			Alterra			Other(1)			Total
		Surplus Lines		Admitted			Insurance			Segment
		Segment		Segment			Market
							Segment
	January 1, 2012	$	81,770	$	64,914		$	309,064		$	—		$	151,813		$	607,561

	Acquisitions	—		26,140			—			—			40,888			67,028

	Foreign currency movements and other adjustments	—		—			596			—			(255		)	341

	December 31, 2012	$	81,770	$	91,054		$	309,660		$	—		$	192,446		$	674,930

	Acquisitions (see note 2)	—		—			—			295,690			1,185			296,875

	Foreign currency movements and other adjustments	—		—			(2,088		)	—			(2,000		)	(4,088		)

	31-Dec-13	$	81,770	$	91,054		$	307,572		$	295,690		$	191,631		$	967,717


	(1)	Amounts included in Other above are related to the Company's Markel Ventures operations.
Components Of Intangible Assets	'
	The following table presents the components of intangible assets with a net carrying amount.



		December 31,
		2013					2012
	(dollars in thousands)	Gross		Accumulated			Gross			Accumulated
		Carrying		Amortization			Carrying			Amortization
		Amount					Amount
	Customer relationships	$	298,886	$	(43,286	)	$	171,591		$	(29,955	)

	Broker relationships	178,693		(23,255		)	135,867			(12,317		)

	Trade names	65,880		(12,666		)	75,781			(9,075		)

	Technology	56,429		(16,222		)	40,109			(11,785		)

	Insurance licenses	40,185		(133		)	4,300			(67		)

	Lloyd's syndicate capacity	12,000		—			—			—

	Other	14,197		(5,625		)	14,558			(4,712		)

	Total	$	666,270	$	(101,187	)	$	442,206		$	(67,911	)

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
Components Of Income Before Income Taxes	'
	Income before income taxes includes the following components.



		Years Ended December 31,
	(dollars in thousands)	2013				2012				2011
	Domestic operations	$	325,133			$	126,466			$	200,446

	Foreign operations	36,610				185,584				(10,250		)

	Income before income taxes	$	361,743			$	312,050			$	190,196

Components Of Income Tax Expense	'
	Income tax expense includes the following components.



		Years Ended December 31,
	(dollars in thousands)	2013				2012				2011
	Current:
	Domestic	$	50,683			$	14,340			$	35,721

	Foreign	23,165				1,814				340

	Total current tax expense	73,848				16,154				36,061

	Deferred:
	Domestic	23,906				(3,734		)		436

	Foreign	(19,856		)		41,382				5,213

	Total deferred tax expense	4,050				37,648				5,649

	Income tax expense	$	77,898			$	53,802			$	41,710

Reconciliations Of United States Corporate Income Tax Rate To Effective Tax Rate On Income Before Income Taxes	'
	Reconciliations of the United States corporate income tax rate to the effective tax rate on income before income taxes are presented in the following table.



		Years Ended December 31,
		2013			2012			2011
	United States corporate tax rate	35	%		35	%		35	%
	Tax-exempt investment income	(9	)		(12	)		(18	)
	Uncertain tax positions	—			—			(2	)

	Foreign operations	(4	)		(5	)		6

	Other	—			(1	)		1

	Effective tax rate	22	%		17	%		22	%
Components Of Domestic And Foreign Deferred Tax Assets And Liabilities	'
	The following table presents the components of domestic and foreign deferred tax assets and liabilities.



		December 31,
	(dollars in thousands)	2013				2012
	Assets:
	Differences between financial reporting and tax bases	$	139,357			$	81,305

	Unpaid losses and loss adjustment expenses	283,365				122,217

	Life and annuity benefits	161,209				—

	Unearned premiums recognized for income tax purposes	76,862				42,938

	Other-than-temporary impairments not yet deductible for income tax purposes	34,978				40,450

	Net operating loss carryforwards	43,010				7,388

	Tax credit carryforwards	33,773				41,387

	Total gross deferred tax assets	772,554				335,685

	Liabilities:
	Differences between financial reporting and tax bases	46,699				33,323

	Deferred policy acquisition costs	65,543				36,039

	Net unrealized gains on investments	459,015				406,295

	Amortization of goodwill and other intangible assets	97,580				28,931

	Total gross deferred tax liabilities	668,837				504,588

	Net deferred tax asset (liability)	$	103,717			$	(168,903	)

Reconciliation Of Beginning And Ending Unrecognized Tax Benefits	'
	The following table presents a reconciliation of unrecognized tax benefits.


		Years Ended December 31,
	(dollars in thousands)	2013				2012
	Unrecognized tax benefits, beginning of year	$	18,870			$	19,586

	Increases based upon tax positions taken during the current year	—				888

	Increases for tax positions taken in prior years	—				218

	Decreases for tax positions taken in prior years	—				(764		)

	Lapse of statute of limitations	(651		)		(1,058		)
	Unrecognized tax benefits, end of year	$	18,219			$	18,870

Unpaid_Losses_And_Loss_Adjustm1

Unpaid Losses And Loss Adjustment Expenses (Tables)	12 Months Ended
	Dec. 31, 2013
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]	'
Reconciliation Of Consolidated Reserves For Losses And Loss Adjustment Expenses	'
	The following table presents a reconciliation of consolidated beginning and ending reserves for losses and loss adjustment expenses.



		Years Ended December 31,
	(dollars in thousands)	2013			2012			2011
	Net reserves for losses and loss adjustment expenses, beginning of year	$	4,592,652		$	4,607,767		$	4,600,316

	Foreign currency movements, commutations and other	(780		)	30,359			(7,496		)

	Adjusted net reserves for losses and loss adjustment expenses, beginning of year	4,591,872			4,638,126			4,592,820

	Incurred losses and loss adjustment expenses:
	Current year	2,227,402			1,553,070			1,563,993

	Prior years	(411,129		)	(399,002		)	(354,007		)
	Total incurred losses and loss adjustment expenses	1,816,273			1,154,068			1,209,986

	Payments:
	Current year	670,928			268,745			291,837

	Prior years	906,302			931,955			898,318

	Total payments	1,577,230			1,200,700			1,190,155

	Effect of foreign currency rate changes	(7,915		)	1,158			(4,884		)

	Net reserves for losses and loss adjustment expenses of acquired insurance companies	3,584,642			—			—

	Net reserves for losses and loss adjustment expenses, end of year	8,407,642			4,592,652			4,607,767

	Reinsurance recoverable on unpaid losses	1,854,414			778,774			791,102

	Gross reserves for losses and loss adjustment expenses, end of year	$	10,262,056		$	5,371,426		$	5,398,869

Reconciliation Of Asbestos And Environmental Reserves For Losses And Loss Adjustment Expenses	'
	The following table provides a reconciliation of beginning and ending A&E reserves for losses and loss adjustment expenses, which are a component of consolidated unpaid losses and loss adjustment expenses. Amounts included in the following table are presented before consideration of reinsurance allowances.



		Years Ended December 31,
	(dollars in thousands)	2013			2012			2011
	Net reserves for A&E losses and loss adjustment expenses, beginning of year	$	260,791		$	244,772		$	216,034

	Commutations and other	(5,067		)	(897		)	36,271

	Adjusted net reserves for A&E losses and loss adjustment expenses, beginning of year	255,724			243,875			252,305

	Incurred losses and loss adjustment expenses	30,128			38,179			(134		)

	Payments	(13,658		)	(21,263		)	(7,399		)
	Net reserves for A&E losses and loss adjustment expenses, end of year	272,194			260,791			244,772

	Reinsurance recoverable on unpaid losses	100,784			100,063			89,391

	Gross reserves for A&E losses and loss adjustment expenses, end of year	$	372,978		$	360,854		$	334,163

Life_And_Annuity_Benefits_Tabl

Life And Annuity Benefits (Tables)	12 Months Ended
	Dec. 31, 2013
Liability for Future Policy Benefits [Abstract]	'
Schedule Of Life And Annuity Benefits	'
	The following table presents life and annuity benefits as of December 31, 2013:



		(dollars in thousands)
	Life	$	190,765

	Annuities	1,194,558

	Accident and health	101,251

		$	1,486,574

Senior_LongTerm_Debt_And_Other1

Senior Long-Term Debt And Other Debt (Tables)	12 Months Ended
	Dec. 31, 2013
Debt Disclosure [Abstract]	'
Summary Of Senior Long-Term Debt And Other Debt	'
	The following table summarizes the Company's senior long-term debt and other debt.



		December 31,
	(dollars in thousands)	2013		2012
	6.80% unsecured senior notes, due February 15, 2013, interest payable semi-annually, net of unamortized discount of $45 in 2012	$	—	$	246,619

	7.20% unsecured senior notes, due April 14, 2017, interest payable semi-annually, net of unamortized premium of $4,822 in 2013	95,451		—

	7.125% unsecured senior notes, due September 30, 2019, interest payable semi-annually, net of unamortized discount of $1,626 in 2013 and $1,909 in 2012	348,374		348,091

	6.25% unsecured senior notes, due September 30, 2020, interest payable semi-annually, net of unamortized premium of $61,273 in 2013	411,273		—

	5.35% unsecured senior notes, due June 1, 2021, interest payable semi-annually, net of unamortized discount of $1,531 in 2013 and $1,738 in 2012	248,469		248,262

	4.90% unsecured senior notes, due July 1, 2022, interest payable semi-annually, net of unamortized discount of $2,374 in 2013 and $2,653 in 2012	347,626		347,347

	3.625% unsecured senior notes, due March 30, 2023, interest payable semi-annually, net of unamortized discount of $1,860 in 2013	248,140		—

	7.35% unsecured senior notes, due August 15, 2034, interest payable semi-annually, net of unamortized discount of $2,185 in 2013 and $2,291 in 2012	197,815		197,710

	5.0% unsecured senior notes, due March 30, 2043, interest payable semi-annually, net of unamortized discount of $6,551 in 2013	243,449		—

	Other debt, at various interest rates ranging from 2.5% to 6.5%	115,630		104,521

	Senior long-term debt and other debt	$	2,256,227	$	1,492,550

Summary Of Future Principal Payments Due At Maturity On Senior Long-Term Debt And Other Debt	'
	The following table summarizes the future principal payments due at maturity on senior long-term debt and other debt as of December 31, 2013.



	Years Ending December 31,	(dollars in
		thousands)
	2014	$	28,795

	2015	6,102

	2016	11,822

	2017	105,987

	2018	2,278

	2019 and thereafter	2,051,275

	Total principal payments	$	2,206,259

	Net unamortized premium	49,968

	Senior long-term debt and other debt	$	2,256,227

Shareholders_Equity_Tables

Shareholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Schedule Of Net Income Per Share	'
	Net income per share was determined by dividing adjusted net income to shareholders by the applicable weighted average shares outstanding. Unvested share-based compensation awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid) are considered participating awards and are included in the computation of net income per share. Non-participating unvested share-based compensation awards are excluded from the computation of net income per share. Diluted net income per share is computed by dividing adjusted net income to shareholders by the weighted average number of common shares and dilutive potential common shares outstanding during the year. Average closing common stock market prices are used to calculate the dilutive effect attributable to restricted stock.



		Years Ended December 31,
	(in thousands, except per share amounts)	2013			2012				2011
	Net income to shareholders	$	281,021		$	253,385			$	142,026

	Adjustment of redeemable noncontrolling interests	1,963			(3,101		)		—

	Adjusted net income to shareholders	$	282,984		$	250,284			$	142,026


	Basic common shares outstanding	12,538			9,640				9,686

	Dilutive potential common shares from conversion of options	12			6				20

	Dilutive potential common shares from conversion of non-participating restricted stock	36			20				20

	Diluted shares outstanding	12,586			9,666				9,726

	Basic net income per share	$	22.57		$	25.96			$	14.66

	Diluted net income per share	$	22.48		$	25.89			$	14.6

2012 Compensation Plan [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Summary Of Nonvested Share-Based Awards	'
	The following table summarizes nonvested share-based awards.


		Number		Weighted Average
		of Awards		Grant-Date
				Fair Value
	Nonvested awards at January 1, 2013	55,580		$	388.58

	Granted	48,860		517.24

	Vested	(5,729	)	428.78

	Nonvested awards at December 31, 2013	98,711		$	449.93

Aspen Option Plans [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Summary Of Options	'
	The following table summarizes additional information with respect to these options.


		Number		Weighted				Weighted Average		Intrinsic Value
		of		Average				Remaining		(in millions)
		Shares		Exercise Price				Contractual Term
								(years)
	Outstanding and exercisable, January 1, 2013	5,678		$	225.83

	Exercised	957		$	204.83

	Outstanding and exercisable, December 31, 2013	4,721		$	230.08			4.4		$	1.7

Alterra Equity Award Plans [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Summary Of Options	'
	The following table summarizes additional information with respect to these options.


		Number		Weighted				Weighted Average		Intrinsic Value
		of		Average				Remaining		(in millions)
		Shares		Exercise Price				Contractual Term
								(years)
	Outstanding and exercisable, May 1, 2013	101,875		$	398.96

	Exercised	65,934		$	391.64

	Outstanding and exercisable, December 31, 2013	35,941		$	412.39			2.6		$	6

Summary Of Nonvested Share-Based Awards	'
	The following table summarizes activity related to these nonvested restricted stock awards.



		Number		Weighted Average
		of Awards		Grant-Date
				Fair Value
	Nonvested awards issued on May 1, 2013	154,103		$	529.59

	Vested	(77,941	)	529.59

	Forfeited	(7,751	)	529.59

	Nonvested awards at December 31, 2013	68,411		$	529.59

Other_Comprehensive_Income_Tab

Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2013
Other Comprehensive Income (Loss), Tax [Abstract]	'
Change In Accumulated Other Comprehensive Income By Component, Net Of Taxes	'
	The following table presents the change in accumulated other comprehensive income by component, net of taxes and noncontrolling interests.



	(dollars in thousands)	Unrealized			Foreign			Net Actuarial			Total
		Holding Gains			Currency			Pension Loss
		on Available-for-
		Sale Securities
	31-Dec-10	$	581,278		$	1,541		$	(31,726	)	$	551,093

	Other comprehensive income (loss) before reclassifications	145,782			(4,155		)	(10,890		)	130,737

	Amounts reclassified from accumulated other comprehensive income	(22,341		)	—			1,431			(20,910		)

	Total other comprehensive income (loss)	123,441			(4,155		)	(9,459		)	109,827

	31-Dec-11	$	704,719		$	(2,614	)	$	(41,185	)	$	660,920

	Other comprehensive income before reclassifications	266,265			1,539			4,670			272,474

	Amounts reclassified from accumulated other comprehensive income	(24,051		)	—			1,994			(22,057		)

	Total other comprehensive income	242,214			1,539			6,664			250,417

	31-Dec-12	$	946,933		$	(1,075	)	$	(34,521	)	$	911,337

	Other comprehensive income (loss) before reclassifications	225,404			(10,171		)	2,517			217,750

	Amounts reclassified from accumulated other comprehensive income	(40,830		)	—			1,548			(39,282		)

	Total other comprehensive income (loss)	184,574			(10,171		)	4,065			178,468

	31-Dec-13	$	1,131,507		$	(11,246	)	$	(30,456	)	$	1,089,805

Summary Of Tax Expense (Benefit) Of Other Comprehensive Income	'
	The following table summarizes the tax expense (benefit) associated with each component of other comprehensive income.



		Years Ended December 31,
	(dollars in thousands)	2013			2012			2011
	Change in net unrealized gains on investments:
	Net holding gains arising during the period	$	93,837		$	122,524		$	68,064

	Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period	(34		)	(49		)	2,107

	Reclassification adjustments for net gains included in net income	(16,382		)	(10,881		)	(10,890		)
	Change in net unrealized gains on investments	77,421			111,594			59,281

	Change in foreign currency translation adjustments	(1,619		)	(446		)	250

	Change in net actuarial pension loss	1,015			1,991			(3,153		)

	Total	$	76,817		$	113,139		$	56,378

Reclassifications From Accumulated Other Comprehensive Income Into Income, By Component	'
	The following table presents the details of amounts reclassified from accumulated other comprehensive income into income, by component.


		Years Ended December 31,
	(dollars in thousands)	2013			2012			2011
	Unrealized holding gains on available-for-sale securities:
	Other-than-temporary impairment losses	$	(4,706	)	$	(12,078	)	$	(20,196	)
	Net realized investment gains, excluding other-than-temporary impairment losses	61,918			47,010			53,427

	Total before taxes	57,212			34,932			33,231

	Income taxes	(16,382		)	(10,881		)	(10,890		)
	Reclassification of unrealized holding gains, net of taxes	$	40,830		$	24,051		$	22,341


	Net actuarial pension loss:
	Underwriting, acquisition and insurance expenses	$	(1,934	)	$	(2,590	)	$	(1,908	)
	Income taxes	386			596			477

	Reclassification of net actuarial pension loss, net of taxes	$	(1,548	)	$	(1,994	)	$	(1,431	)

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2013
Fair Value Disclosures [Abstract]	'
Balances Of Assets And Liabilities Measured At Fair Value On A Recurring Basis	'
	The following tables present the balances of assets and liabilities measured at fair value on a recurring basis by level within the fair value hierarchy.



		December 31, 2013
	(dollars in thousands)	Level 1				Level 2				Level 3			Total
	Assets:
	Investments available-for-sale:
	Fixed maturities:
	U.S. Treasury securities and obligations of U.S. government agencies	$	—			$	1,194,231			$	—		$	1,194,231

	Obligations of states, municipalities and political subdivisions	—				3,075,715				—			3,075,715

	Foreign governments	—				1,461,054				—			1,461,054

	Commercial mortgage-backed securities	—				367,821				—			367,821

	Residential mortgage-backed securities	—				870,248				—			870,248

	Asset-backed securities	—				188,289				—			188,289

	Corporate bonds	—				2,985,178				—			2,985,178

	Total fixed maturities	—				10,142,536				—			10,142,536

	Equity securities:
	Insurance, banks and other financial institutions	1,015,083				—				—			1,015,083

	Industrial, consumer and all other	2,236,715				—				—			2,236,715

	Total equity securities	3,251,798				—				—			3,251,798

	Short-term investments	1,312,561				139,727				—			1,452,288

	Total investments available-for-sale	$	4,564,359			$	10,282,263			$	—		$	14,846,622

	Liabilities:
	Derivative contracts	$	—			$	—			$	2,230		$	2,230




		December 31, 2012
	(dollars in thousands)	Level 1				Level 2				Level 3			Total
	Assets:
	Investments available-for-sale:
	Fixed maturities:
	U.S. Treasury securities and obligations of U.S. government agencies	$	—			$	317,507			$	—		$	317,507

	Obligations of states, municipalities and political subdivisions	—				2,831,562				—			2,831,562

	Foreign governments	—				556,608				—			556,608

	Residential mortgage-backed securities	—				215,377				—			215,377

	Asset-backed securities	—				14,345				—			14,345

	Corporate bonds	—				1,043,884				—			1,043,884

	Total fixed maturities	—				4,979,283				—			4,979,283

	Equity securities:
	Insurance, banks and other financial institutions	898,067				—				—			898,067

Industrial, consumer and all other	1,508,884				—				—			1,508,884

Total equity securities	2,406,951				—				—			2,406,951

Short-term investments	888,758				84,572				—			973,330

Total investments available-for-sale	$	3,295,709			$	5,063,855			$	—		$	8,359,564

Liabilities:
Derivative contracts	$	—			$	—			$	12,690		$	12,690

Summary Of Changes In Level 3 Liabilities Measured At Fair Value On A Recurring Basis	'
	The following table summarizes changes in Level 3 liabilities measured at fair value on a recurring basis.



	(dollars in thousands)	2013				2012
	Derivatives, beginning of period	$	12,690			$	29,331

	Total gains included in:
	Net income	(10,460		)		(16,641		)
	Other comprehensive income	—				—

	Transfers into Level 3	—				—

	Transfers out of Level 3	—				—

	Derivatives, end of period	$	2,230			$	12,690

	Net unrealized gains included in net income relating to liabilities held at December 31, 2013 and 2012 (1)	$	10,460			$	16,641


	(1)	Included in net investment income in the consolidated statements of income and comprehensive income.

Reinsurance_Tables

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2013
Reinsurance Disclosures [Abstract]	'
Reinsurance Allowance For Doubtful Accounts	'
	The following table summarizes the Company's reinsurance allowance for doubtful accounts.



		Years Ended December 31,
	(dollars in thousands)	2013			2012			2011
	Reinsurance allowance, beginning of year	$	71,148		$	69,067		$	155,190

	Additions	13,621			24,179			8,504

	Deductions	(8,559		)	(22,098		)	(94,627		)
	Reinsurance allowance, end of year	$	76,210		$	71,148		$	69,067

Effect Of Reinsurance On Premiums Written And Earned	'
	The following table summarizes the effect of reinsurance and retrocessional reinsurance on premiums written and earned.



		Years Ended December 31,
		2013						2012						2011
	(dollars in thousands)	Written			Earned			Written			Earned			Written			Earned
	Direct	$	3,143,957		$	2,947,812		$	2,115,353		$	2,057,735		$	1,957,397		$	1,873,512

	Assumed	776,269			1,016,853			398,328			376,186			333,854			338,183

	Ceded	(683,543		)	(733,049		)	(299,555		)	(286,793		)	(249,413		)	(232,355		)
	Net premiums	$	3,236,683		$	3,231,616		$	2,214,126		$	2,147,128		$	2,041,838		$	1,979,340

Commitments_And_Contingencies_

Commitments And Contingencies (Tables)	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Minimum Annual Rental Commitments	'
	The following table summarizes the Company's minimum annual rental commitments, excluding taxes, insurance and other operating costs payable directly by the Company, for noncancelable operating leases at December 31, 2013.



	Years Ending December 31,	(dollars in
		thousands)
	2014	$	32,783

	2015	29,114

	2016	22,977

	2017	27,955

	2018	26,440

	2019 and thereafter	160,454

	Total	$	299,723

Statutory_Financial_Informatio1

Statutory Financial Information (Tables)	12 Months Ended
	Dec. 31, 2013
Statutory Financial Information [Abstract]	'
Actual Statutory Capital And Surplus	'


		Statutory Capital and Surplus
	(dollars in thousands)	2013			2012
	United States	$	2,399,356		$	1,455,077

	United Kingdom	$	517,571		$	485,043

	Bermuda	$	1,503,004		N/A

	Other	$	171,410		N/A

Statutory Net Income (Loss)	'


		Statutory Net Income (Loss)
		Years Ended December 31,
	(dollars in thousands)	2013			2012		2011
	United States	$	235,009		$	127,179	$	180,744

	United Kingdom	$	117,020		$	82,573	$	18,386

	Bermuda	$	93,953		N/A		N/A

	Other	$	(12,617	)	N/A		N/A

Segment_Reporting_Disclosures_

Segment Reporting Disclosures (Tables)	12 Months Ended
	Dec. 31, 2013
Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract]	'
Summary Of Gross Written Premiums By Country	'
	The following table summarizes the Company's gross written premiums by country. Gross written premiums are attributed to individual countries based upon location of risk.



		Years Ended December 31,
	(dollars in thousands)	2013				% of			2012				% of			2011				% of
						Total							Total							Total
	United States	$	2,934,868			75	%		$	1,768,011			70	%		$	1,590,238			69	%

	United Kingdom	245,143				6			147,891				6			139,349				6

	Canada	128,420				3			120,542				5			126,434				6

	Other countries	611,795				16			477,237				19			435,230				19

	Total	$	3,920,226			100	%		$	2,513,681			100	%		$	2,291,251			100	%

Company's Segment Disclosures	'
	The following tables summarize the Company's segment disclosures.



		Year Ended December 31, 2013
	(dollars in thousands)	Excess and				Specialty				London				Alterra				Other				Investing			Consolidated
		Surplus				Admitted				Insurance								Insurance
		Lines								Market								(Discontinued
																		Lines)
	Gross premium volume	$	1,070,520			$	899,996			$	914,480			$	1,035,190			$	40			$	—		$	3,920,226

	Net written premiums	911,870				855,381				792,158				677,233				41				—			3,236,683


	Earned premiums	856,629				744,993				781,637				848,317				40				—			3,231,616

	Losses and loss adjustment expenses	(341,661		)		(410,068		)		(386,416		)		(647,546		)		(30,582		)		—			(1,816,273		)

	Transaction costs and other acquisition-related expenses (1)	—				—				—				(75,140		)		—				—			(75,140		)

	Amortization of policy acquisition costs	(147,996		)		(137,181		)		(149,191		)		(37,547		)		—				—			(471,915		)

	Other operating expenses	(195,464		)		(176,346		)		(150,537		)		(243,022		)		112				—			(765,257		)

	Underwriting profit (loss)	171,508				21,398				95,493				(154,938		)		(30,430		)		—			103,031

	Net investment income	—				—				—				—				—				317,373			317,373

	Net realized investment gains	—				—				—				—				—				63,152			63,152

	Other revenues (insurance)	—				13,648				5,002				4,714				1,130				—			24,494

	Other expenses (insurance)	—				(17,087		)		(5,065		)		—				(28,126		)		—			(50,278		)

	Segment profit (loss)	$	171,508			$	17,959			$	95,430			$	(150,224	)		$	(57,426	)		$	380,525		$	457,772

	Other revenues (Markel Ventures)																								686,448

	Other expenses (Markel Ventures)																								(613,250		)
	Amortization of intangible assets																								(55,223		)
	Interest expense																								(114,004		)
	Income before income taxes																								$	361,743

	U.S. GAAP combined ratio (2)	80		%		97		%		88		%		118		%		NM			(3)				97		%


	(1)	In connection with the acquisition of Alterra, the Company incurred transaction costs of $16.0 million for the year ended December 31, 2013, which primarily consist of due diligence, legal and investment banking costs. Additionally, the Company incurred severance costs of $31.7 million, stay bonuses of $14.8 million and other compensation costs totaling $12.6 million related to the acceleration of certain long-term incentive compensation awards and restricted stock awards that were granted by Alterra prior to the acquisition.

	(2)	The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums.

	(3)	NM — Ratio is not meaningful.



		Year Ended December 31, 2012
	(dollars in thousands)	Excess and				Specialty				London				Other				Investing				Consolidated
		Surplus				Admitted				Insurance				Insurance
		Lines								Market				(Discontinued
														Lines)
	Gross premium volume	$	956,273			$	669,692			$	887,720			$	(4	)		$	—			$	2,513,681

	Net written premiums	811,601				628,147				774,383				(5		)		—				2,214,126


Earned premiums	793,159				588,758				765,216				(5		)		—				2,147,128

Losses and loss adjustment expenses	(388,793		)		(381,870		)		(362,330		)		(21,075		)		—				(1,154,068		)

Prospective adoption of FASB ASU No. 2010-26 (1)	(17,456		)		(13,577		)		(12,060		)		—				—				(43,093		)

Other amortization of policy acquisition costs	(135,573		)		(96,770		)		(152,673		)		—				—				(385,016		)

Other operating expenses	(201,196		)		(143,377		)		(156,587		)		(203		)		—				(501,363		)

Underwriting profit (loss)	50,141				(46,836		)		81,566				(21,283		)		—				63,588

Net investment income	—				—				—				—				282,107				282,107

Net realized investment gains	—				—				—				—				31,593				31,593

Other revenues (insurance)	—				44,968				4,964				—				—				49,932

Other expenses (insurance)	—				(41,425		)		(3,867		)		—				—				(45,292		)

Segment profit (loss)	$	50,141			$	(43,293	)		$	82,663			$	(21,283	)		$	313,700			$	381,928

Other revenues (Markel Ventures)																					489,352

Other expenses (Markel Ventures)																					(432,956		)
Amortization of intangible assets																					(33,512		)
Interest expense																					(92,762		)
Income before income taxes																					$	312,050

U.S. GAAP combined ratio(2)	94		%		108		%		89		%		NM			(3)					97		%


(1)	Effective January 1, 2012, the Company prospectively adopted FASB ASU No. 2010-26, Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts. At December 31, 2011, deferred policy acquisition costs included $43.1 million of costs that no longer met the criteria for deferral as of January 1, 2012 and were recognized into income during 2012, consistent with policy terms.

(2)	The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums.

(3)	NM — Ratio is not meaningful.



	Year Ended December 31, 2011
(dollars in thousands)	Excess and				Specialty				London				Other				Investing				Consolidated
	Surplus				Admitted				Insurance				Insurance
	Lines								Market				(Discontinued
													Lines)
Gross premium volume	$	893,427			$	572,392			$	825,301			$	131			$	—			$	2,291,251

Net written premiums	772,279				543,213				726,359				(13		)		—				2,041,838


Earned premiums	756,306				527,293				695,753				(12		)		—				1,979,340

Losses and loss adjustment expenses	(318,583		)		(364,144		)		(531,625		)		4,366				—				(1,209,986		)

Amortization of policy acquisition costs	(172,269		)		(129,731		)		(177,454		)		—				—				(479,454		)

Other operating expenses	(156,419		)		(78,509		)		(96,149		)		352				—				(330,725		)

Underwriting profit (loss)	109,035				(45,091		)		(109,475		)		4,706				—				(40,825		)

Net investment income	—				—				—				—				263,676				263,676

Net realized investment gains	—				—				—				—				35,857				35,857

Other revenues (insurance)	—				33,545				—				—				—				33,545

Other expenses (insurance)	—				(33,722		)		—				—				—				(33,722		)

Segment profit (loss)	$	109,035			$	(45,268	)		$	(109,475	)		$	4,706			$	299,533			$	258,531

Other revenues (Markel Ventures)																					317,532

Other expenses (Markel Ventures)																					(275,324		)
Amortization of intangible assets																					(24,291		)
Interest expense																					(86,252		)
Income before income taxes																					$	190,196

U.S. GAAP combined ratio(1)	86		%		109		%		116		%		NM			(2)					102		%


(1)	The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums.

(2)	NM — Ratio is not meaningful.
Summary Of Deferred Policy Acquisition Costs, Unearned Premiums And Unpaid Losses And Loss Adjustment Expenses	'
	The following table summarizes deferred policy acquisition costs, unearned premiums and unpaid losses and loss adjustment expenses by segment.



	(dollars in thousands)	Deferred Policy				Unearned				Unpaid Losses and
		Acquisition Costs				Premiums				Loss Adjustment Expenses
	December 31, 2013
	Excess and Surplus Lines	$	69,849			$	469,148			$	1,998,359

	Specialty Admitted	77,118				391,606				878,564

	London Insurance Market	53,420				321,383				1,909,612

	Alterra	60,580				944,978				4,996,722

	Other Insurance (Discontinued Lines)	—				—				478,799

	Total	$	260,967			$	2,127,115			$	10,262,056

	December 31, 2012
	Excess and Surplus Lines	$	59,158			$	410,731			$	2,152,253

	Specialty Admitted	43,810				280,811				796,093

	London Insurance Market	54,497				308,719				1,958,249

	Other Insurance (Discontinued Lines)	—				—				464,831

	Total	$	157,465			$	1,000,261			$	5,371,426

Summary Of Segment Earned Premiums	'
	The following table summarizes segment earned premiums by major product grouping.



	(dollars in thousands)	Property				Casualty				Professional				Workers'				Other				Consolidated
										Liability				Compensation
	Year Ended December 31, 2013
	Excess and Surplus Lines	$	115,773			$	253,195			$	208,732			$	—			$	278,929			$	856,629

	Specialty Admitted	230,068				232,868				—				253,347				28,710				744,993

	London Insurance Market	230,278				124,843				176,302				—				250,214				781,637

	Alterra	215,488				172,736				165,934				31,347				262,812				848,317

	Other Insurance (Discontinued Lines)	—				—				—				—				40				40

	Earned premiums	$	791,607			$	783,642			$	550,968			$	284,694			$	820,705			$	3,231,616

	Year Ended December 31, 2012
	Excess and Surplus Lines	$	109,607			$	227,880			$	189,199			$	—			$	266,473			$	793,159

	Specialty Admitted	148,311				163,955				—				242,021				34,471				588,758

	London Insurance Market	259,571				126,441				162,554				—				216,650				765,216

	Other Insurance (Discontinued Lines)	—				—				—				—				(5		)		(5		)

	Earned premiums	$	517,489			$	518,276			$	351,753			$	242,021			$	517,589			$	2,147,128

	Year Ended December 31, 2011
	Excess and Surplus Lines	$	103,406			$	214,565			$	197,131			$	—			$	241,204			$	756,306

	Specialty Admitted	135,077				140,805				—				200,797				50,614				527,293

	London Insurance Market	231,798				117,062				173,101				—				173,792				695,753

	Other Insurance (Discontinued Lines)	—				—				—				—				(12		)		(12		)

	Earned premiums	$	470,281			$	472,432			$	370,232			$	200,797			$	465,598			$	1,979,340

Segment Assets To The Company's Consolidated Balance Sheets	'
	The following table reconciles segment assets to the Company's consolidated balance sheets.



		December 31,
	(dollars in thousands)	2013				2012				2011
	Segment assets:
	Investing	$	17,550,332			$	9,277,697			$	8,692,391

	Underwriting	5,468,731				2,387,305				2,209,431

	Total segment assets	23,019,063				11,665,002				10,901,822

	Markel Ventures operations	936,448				891,586				630,281

	Total assets	$	23,955,511			$	12,556,588			$	11,532,103

Other_Revenues_And_Other_Expen1

Other Revenues And Other Expenses (Tables)	12 Months Ended
	Dec. 31, 2013
Other Income and Expenses [Abstract]	'
Summary Of Other Revenues And Other Expenses By Component	'
	The following table summarizes the components of other revenues and other expenses.



		Years Ended December 31,
		2013				2012				2011
	(dollars in thousands)	Other		Other		Other		Other		Other		Other
		Revenues		Expenses		Revenues		Expenses		Revenues		Expenses
	Insurance:
	Managing general agent operations	$	17,399	$	20,382	$	48,056	$	43,069	$	31,136	$	30,728

	Life and annuity	1,130		28,126		—		—		—		—

	Other	5,965		1,770		1,876		2,223		2,409		2,994

		24,494		50,278		49,932		45,292		33,545		33,722

	Markel Ventures:
	Manufacturing	495,138		437,712		366,886		328,484		214,668		192,503

	Non-Manufacturing	191,310		175,538		122,466		104,472		102,864		82,821

		686,448		613,250		489,352		432,956		317,532		275,324

	Total	$	710,942	$	663,528	$	539,284	$	478,248	$	351,077	$	309,046

Employee_Benefit_Plans_Tables

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2013
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]	'
Funded Status Of The Terra Nova Pension Plan	'
	The following table summarizes the funded status of the Terra Nova Pension Plan and the amounts recognized on the accompanying consolidated balance sheets of the Company.



		Years Ended December 31,
	(dollars in thousands)	2013			2012
	Change in projected benefit obligation:
	Projected benefit obligation at beginning of period	$	151,327		$	141,163

	Service cost	—			361

	Interest cost	6,533			6,815

	Participant contributions	—			81

	Benefits paid	(3,542		)	(2,938		)
	Actuarial loss (gain)	5,459			(601		)

	Effect of foreign currency rate changes	3,233			6,446

	Projected benefit obligation at end of year	$	163,010		$	151,327

	Change in plan assets:
	Fair value of plan assets at beginning of period	$	164,090		$	139,325

	Actual gain on plan assets	19,430			15,251

	Employer contributions	5,338			5,737

	Participant contributions	—			81

	Benefits paid	(3,542		)	(2,938		)
	Effect of foreign currency rate changes	4,121			6,634

	Fair value of plan assets at end of year	$	189,437		$	164,090

	Funded status of the plan	$	26,427		$	12,763

	Net actuarial pension loss	42,941			48,021

	Total	$	69,368		$	60,784

Schedule Of Net Periodic Benefit Cost And Weighted Average Assumptions	'
	The following table summarizes the components of net periodic benefit cost (income) and the weighted average assumptions for the Terra Nova Pension Plan.



		Years Ended December 31,
	(dollars in thousands)	2013			2012			2011
	Components of net periodic benefit cost (income):
	Service cost	$	—		$	361		$	1,357

	Interest cost	6,533			6,815			7,115

	Expected return on plan assets	(10,825		)	(9,788		)	(9,834		)
	Amortization of net actuarial pension loss	1,934			2,590			1,908

	Net periodic benefit cost (income)	$	(2,358	)	$	(22	)	$	546

	Weighted average assumptions as of December 31:
	Discount rate	4.7		%	4.5		%	4.8		%
	Expected return on plan assets	6.6		%	6.6		%	6.6		%
	Rate of compensation increase	3.2		%	3.1		%	3.2		%
Summary Of Fair Value Of Plan Assets	'
	The following table summarizes the fair value of plan assets as of December 31, 2013 and 2012.



		December 31,
	(dollars in thousands)	2013			2012
	Plan assets:
	Fixed maturity index funds	$	70,997		$	64,357

	Equity security index funds	118,431			99,727

	Cash and cash equivalents	9			6

	Total	$	189,437		$	164,090

Markel_Corporation_Parent_Comp1

Markel Corporation (Parent Company Only) Financial Information (Tables)	12 Months Ended
	Dec. 31, 2013
Condensed Financial Information of Parent Company Only Disclosure [Abstract]	'
Schedule Of Condensed Balance Sheets	'
	CONDENSED BALANCE SHEETS



		December 31,
		2013			2012
		(dollars in thousands)
	ASSETS
	Investments, available-for-sale, at estimated fair value:
	Fixed maturities (amortized cost of $66,154 in 2013 and $80,631 in 2012)	$	67,363		$	84,158

	Equity securities (cost of $197,549 in 2013 and $270,157 in 2012)	392,123			426,409

	Short-term investments (estimated fair value approximates cost)	654,971			664,986

	Total Investments	1,114,457			1,175,553

	Cash and cash equivalents	207,352			237,816

	Restricted cash and cash equivalents	1,010			662

	Receivables	14,326			13,994

	Investments in consolidated subsidiaries	6,826,790			3,656,577

	Notes receivable from subsidiaries	168,611			173,913

	Income taxes receivable	5,320			6,623

	Net deferred tax asset	—			6,595

	Other assets	102,193			99,107

	Total Assets	$	8,440,059		$	5,370,840

	LIABILITIES AND SHAREHOLDERS' EQUITY
	Senior long-term debt	$	1,633,873		$	1,388,029

	Net deferred tax liability	40,443			—

	Other liabilities	92,166			94,154

	Total Liabilities	1,766,482			1,482,183

	Total Shareholders' Equity	6,673,577			3,888,657

	Total Liabilities and Shareholders' Equity	$	8,440,059		$	5,370,840

Schedule Of Condensed Statements Of Income And Comprehensive Income	'
	CONDENSED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME



		Years Ended December 31,
		2013			2012			2011
		(dollars in thousands)
	REVENUES
	Net investment income	$	21,946		$	30,619		$	12,629

	Dividends on common stock of consolidated subsidiaries	806,233			337,585			330,462

	Net realized investment gains (losses):
	Other-than-temporary impairment losses	(15		)	(38		)	(7,676		)
	Net realized investment gains, excluding other-than-temporary impairment losses	67,232			14,926			7,417

	Net realized investment gains (losses)	67,217			14,888			(259		)

	Other	1			3			13

	Total Revenues	895,397			383,095			342,845

	EXPENSES
	Interest expense	92,743			87,391			78,830

	Other expenses	2,617			1,166			4,572

	Total Expenses	95,360			88,557			83,402

	Income Before Equity in Undistributed Earnings of Consolidated Subsidiaries and Income Taxes	800,037			294,538			259,443

	Equity in undistributed earnings of consolidated subsidiaries	(520,323		)	(61,663		)	(144,348		)
	Income tax benefit	(1,307		)	(20,510		)	(26,931		)
	Net Income to Shareholders	$	281,021		$	253,385		$	142,026

	OTHER COMPREHENSIVE INCOME TO SHAREHOLDERS
	Change in net unrealized gains on investments, net of taxes:
	Net holding gains arising during the period	$	66,623		$	10,897		$	675

	Consolidated subsidiaries' net holding gains arising during the period	158,922			255,528			141,164

	Consolidated subsidiaries' change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period	(141		)	(160		)	3,943

	Reclassification adjustments for net gains (losses) included in net income to shareholders	(43,220		)	11,847			735

	Consolidated subsidiaries' reclassification adjustments for net gains (losses) included in net income to shareholders	2,390			(35,898		)	(23,076		)

	Change in net unrealized gains on investments, net of taxes	184,574			242,214			123,441

	Change in foreign currency translation adjustments, net of taxes	(2,670		)	(242		)	314

	Consolidated subsidiaries' change in foreign currency translation adjustments, net of taxes	(7,501		)	1,781			(4,469		)

	Consolidated subsidiaries' change in net actuarial pension loss, net of taxes	4,065			6,664			(9,459		)

	Total Other Comprehensive Income to Shareholders	178,468			250,417			109,827

	Comprehensive Income to Shareholders	$	459,489		$	503,802		$	251,853

Schedule Of Condensed Statements Of Cash Flows	'
	CONDENSED STATEMENTS OF CASH FLOWS



		Years Ended December 31,
		2013			2012			2011
		(dollars in thousands)
	OPERATING ACTIVITIES
	Net income to shareholders	$	281,021		$	253,385		$	142,026

	Adjustments to reconcile net income to shareholders to net cash provided by operating activities	186,574			(153,773		)	102,714

	Net Cash Provided By Operating Activities	467,595			99,612			244,740

	INVESTING ACTIVITIES
	Proceeds from sales of fixed maturities and equity securities	142,259			149,314			50,322

	Proceeds from maturities, calls and prepayments of fixed maturities	2,819			64,340			46,522

	Cost of fixed maturities and equity securities purchased	(23,412		)	(89,569		)	(92,287		)
	Net change in short-term investments	260,247			(214,820		)	(179,823		)

	Decrease in notes receivable due from subsidiaries	5,302			116,797			7,401

	Capital contributions to subsidiaries	(67,878		)	(198,349		)	(179,403		)
	Acquisitions	(1,017,988		)	(100,409		)	—

	Cost of equity method investments	(5,291		)	(38,250		)	—

	Change in restricted cash and cash equivalents	(348		)	(204		)	(326		)
	Additions to property and equipment	(3,653		)	(9,437		)	(16,927		)
	Other	3,207			(4,369		)	12,175

	Net Cash Used By Investing Activities	(704,736		)	(324,956		)	(352,346		)
	FINANCING ACTIVITIES
	Additions to senior long-term debt	491,235			347,207			247,935

	Repayment and retirement of senior long-term debt	(246,665		)	(157,359		)	—

	Repurchases of common stock	(57,388		)	(16,873		)	(42,913		)
	Issuance of common stock	24,518			9,145			1,182

	Other	(5,023		)	436			50

	Net Cash Provided By Financing Activities	206,677			182,556			206,254

	Increase (decrease) in cash and cash equivalents	(30,464		)	(42,788		)	98,648

	Cash and cash equivalents at beginning of year	237,816			280,604			181,956

	CASH AND CASH EQUIVALENTS AT END OF YEAR	$	207,352		$	237,816		$	280,604

Quarterly_Financial_Informatio1

Quarterly Financial Information (Tables)	12 Months Ended
	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]	'
Quarterly Results Of Consolidated Operations	'
	The following table presents the unaudited quarterly results of consolidated operations for 2013, 2012 and 2011.



		Quarters Ended
	(dollars in thousands, except per share amounts)	Mar. 31		30-Jun			Sept. 30			Dec. 31
	2013
	Operating revenues	$	819,864	$	1,031,769		$	1,191,665		$	1,279,785

	Net income	89,263		28,676			66,967			98,939

	Net income to shareholders	88,902		27,756			65,599			98,764

	Comprehensive income (loss) to shareholders	257,684		(149,054		)	144,409			206,450

	Net income per share:
	Basic	$	9.53	$	2.24		$	4.69		$	6.98

	Diluted	9.5		2.24			4.67			6.95

	Common stock price ranges:
	High	$	510.05	$	546.94		$	549.09		$	582.59

	Low	434.98		501.76			506.64			511.06

	2012
	Operating revenues	$	733,135	$	693,247		$	765,775		$	807,955

	Net income	57,713		90,768			51,674			58,093

	Net income to shareholders	57,253		89,687			49,653			56,792

	Comprehensive income to shareholders	205,945		73,416			147,454			76,987

	Net income per share:
	Basic	$	5.94	$	8.44		$	5.33		$	6.25

	Diluted	5.92		8.42			5.32			6.23

	Common stock price ranges:
	High	$	451.9	$	453.5		$	459.9		$	502.2

	Low	398.65		421			420			425.17

	2011
	Operating revenues	$	621,594	$	647,168		$	676,088		$	685,100

	Net income	9,861		31,649			54,669			52,307

	Net income to shareholders	8,272		30,314			53,264			50,176

	Comprehensive income (loss) to shareholders	24,738		96,045			(52,626		)	183,696

	Net income per share:
	Basic	$	0.85	$	3.12		$	5.5		$	5.21

	Diluted	0.85		3.11			5.48			5.19

	Common stock price ranges:
	High	$	422.83	$	430.26		$	403.21		$	419.1

	Low	379.44		386.81			346.15			337.5

Summary_Of_Significant_Account2

Summary Of Significant Accounting Policies (Narrative) (Details) (USD $)	12 Months Ended			6 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jun. 30, 2013
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	May 1, 2013 Alterra Capital Holdings [Member]
Summary of Significant Accounting Policies [Line Items]	'	'	'	'
Percentage of issued and outstanding common stock acquired	'	'	'	100.00%
Total purchase consideration	'	'	'	$3,304,293,000
Deferred policy acquisition cost amortization period	'1 year	'	'	'
Adjustment of redeemable noncontrolling interests	-2,000,000	3,100,000	0	'
Tax benefit greater than 50%	50.00%	'	'	'
Insurance premiums revenue recognition period	'1 year	'	'	'
Stock-based compensation expense, net of taxes	18,400,000	4,400,000	4,000,000	'
Cumulative foreign currency translation loss	($11,200,000)	($1,100,000)	'	'

Recovered_Sheet1

Summary of Significant Accounting Policies (Cash and Cash Equivalents) (Details) (Maximum [Member], Cash And Cash Equivalents [Member])	12 Months Ended
	Dec. 31, 2013
Maximum [Member] \| Cash And Cash Equivalents [Member]	'
Cash and Cash Equivalents [Line Items]	'
Investment maturity period	'90 days

Recovered_Sheet2

Summary of Significant Accounting Policies (Goodwill and Intangible Assets) (Details)	12 Months Ended
	Dec. 31, 2013
Minimum [Member]	'
Finite-Lived Intangible Assets [Line Items]	'
Intangible assets, estimated useful life	'5 years
Maximum [Member]	'
Finite-Lived Intangible Assets [Line Items]	'
Intangible assets, estimated useful life	'20 years

Recovered_Sheet3

Summary of Significant Accounting Policies (Property and Equipment) (Details)	12 Months Ended
	Dec. 31, 2013
Building [Member] \| Minimum [Member]	'
Property, Plant and Equipment [Line Items]	'
Property and equipment, estimated useful life	'10 years
Building [Member] \| Maximum [Member]	'
Property, Plant and Equipment [Line Items]	'
Property and equipment, estimated useful life	'40 years
Land Improvements [Member] \| Minimum [Member]	'
Property, Plant and Equipment [Line Items]	'
Property and equipment, estimated useful life	'7 years
Land Improvements [Member] \| Maximum [Member]	'
Property, Plant and Equipment [Line Items]	'
Property and equipment, estimated useful life	'40 years
Furniture And Equipment [Member] \| Minimum [Member]	'
Property, Plant and Equipment [Line Items]	'
Property and equipment, estimated useful life	'3 years
Furniture And Equipment [Member] \| Maximum [Member]	'
Property, Plant and Equipment [Line Items]	'
Property and equipment, estimated useful life	'10 years
Other Property And Equipment [Member] \| Minimum [Member]	'
Property, Plant and Equipment [Line Items]	'
Property and equipment, estimated useful life	'3 years
Other Property And Equipment [Member] \| Maximum [Member]	'
Property, Plant and Equipment [Line Items]	'
Property and equipment, estimated useful life	'25 years

Acquisitions_Narrative_Details

Acquisitions (Narrative) (Details) (USD $)

12 Months Ended

6 Months Ended

12 Months Ended

1 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Mar. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2013

Dec. 31, 2013

Jun. 30, 2013

Dec. 31, 2013

Jun. 30, 2013

Dec. 31, 2013

Jan. 17, 2014

Customer Relationships [Member]

January 1 Essentia Insurance Company [Member]

May 1, 2013 Alterra Capital Holdings [Member]

Pre-Acquisition Board Of Directors [Member]

Additional Alterra Board Of Directors [Member]

Abbey Protection plc [Member]

Subsequent Event [Member]

Customer Relationships [Member]

directors

Subsequent Event [Member]

Schedule of Asset and Business Acquisitions, by Acquisition [Line Items]

Percentage acquired

100.00%

Number of Markel Corporation shares issued for each outstanding share of Alterra common stock

0.04315

Cash paid for each oustanding share of Alterra common stock

$10

Total purchase consideration

$3,304,293,000

$190,000,000

Cash consideration

964,330,000

190,000,000

Stock consideration, shares

4,300,000

Number of board of directors

Options issued, taxes

1,900,000

Restricted stock issued, taxes

10,100,000

Restricted stock units issued, taxes

700,000

Goodwill recognized

295,690,000

Goodwill, tax deductible

Indefinite-lived intangible assets

37,500,000

Finite-lived intangible assets

170,000,000

132,000,000

Definite-lived intangible assets, weighted-average amortization period

'15 years 6 months 6 days

'17 years 11 months 20 days

'6 years

'17 years

'18 years

Investments acquired, adjustment to fair value

223,100,000

Investments acquired, incremental premium to be amortized to net investment income

495,500,000

Investments, unamortized incremental premium

398,100,000

Investments, unamortized incremental premium weighted average amortization period, years

'5 years

Investments, amortization expense on incremental premium

58,300,000

Unearned premiums acquired, adjustment to fair value

-176,300,000

Unearned premiums, weighted average amortization period, years

'1 year

Unpaid losses and loss adjustment expenses acquired, adjustment to fair value

120,800,000

Unpaid losses and loss adjustment expenses acquired pre acquisition adjustment, unamortized balance

26,500,000

Unpaid losses and loss adjustment expenses, weighted average amortization period, years

'5 years

Unpaid losses and loss adjustment expenses, unamortized fair value adjustment

136,500,000

Unpaid losses and loss adjustment expenses, unamortized fair value adjustment weighted average amortization period, years

'4 years

Life and annuity benefits acquired, adjustment to fair value

329,600,000

Senior long-term debt acquired, adjustment to fair value

71,900,000

Senior long-term debt acquired, unamortized premium

66,100,000

United States corporate tax rate

35.00%

Net deferred tax assets recognized

310,100,000

Deferred tax assets recognized, accrued losses and loss adjustment expenses and life and annuity benefits

343,900,000

Deferred tax liabilities recognized, intangible assets

64,600,000

Provision for United States income taxes on earnings of the Company's foreign subsidiaries

Deferred tax assets, increase in allocation of purchase price

54,300,000

Pro forma transaction costs, Alterra

23,000,000

Acceleration of Alterra long-term incentive compensation awards and restricted stock awards

12,621,000

[1]

Transaction costs

15,981,000

[1]

Pro forma transaction costs, total

39,000,000

Other acquisition related costs, severance costs

31,734,000

[1]

Other acquisition related costs, stay bonuses

14,804,000

[1]

Percentage of outstanding shares acquired

100.00%

Other intangible assets recognized, asset acquisition

$35,400,000

$25,000,000

Percentage of outstanding shares of Essentia purchased by Hagerty due to the exercise of options

9.90%

Company's ownership interest in Essentia

90.10%

[1]

In connection with the acquisition of Alterra, the Company incurred transaction costs of $16.0 million for the year ended December 31, 2013, which primarily consist of due diligence, legal and investment banking costs. Additionally, the Company incurred severance costs of $31.7 million, stay bonuses of $14.8 million and other compensation costs totaling $12.6 million related to the acceleration of certain long-term incentive compensation awards and restricted stock awards that were granted by Alterra prior to the acquisition.

Acquisitions_Calculation_Of_To

Acquisitions (Calculation Of Total Purchase Price) (Details) (May 1, 2013 Alterra Capital Holdings [Member], USD $)	6 Months Ended
In Thousands, except Share data, unless otherwise specified	Jun. 30, 2013
Business Acquisition [Line Items]	'
Exchange ratio per the Merger Agreement	0.04315
Markel share issuance to Alterra shareholders	4,300,000
Incentive award ratio per the Merger Agreement	0.06252
Multiplied by Markel's weighted average stock price on April 30, 2013	$529.59	[1]
Markel share and restricted stock issuance consideration, net of taxes	$2,267,648
Alterra common shares outstanding as of the Acquisition Date that received cash consideration	96,433,000
Multiplied by cash price per share component per the Merger Agreement	$10
Markel cash consideration	964,330
Fair value of Markel warrant issuance to Alterra warrant holders as of the Acquisition Date	73,685
Fair value of Markel stock option issuance to Alterra stock option holders as of the Acquisition Date, net of taxes	12,335
Fair value of partially vested Markel restricted stock unit issuance as of the Acquisition Date, net of taxes	6,867
Unrecognized compensation on unvested restricted stock and restricted stock units	-20,572
Total acquisition consideration	$3,304,293
Common Stock [Member]	'
Business Acquisition [Line Items]	'
Shares of Alterra stock outstanding as of the Acquisition Date	96,433,000
Markel share issuance to Alterra shareholders	4,161,000
Restricted Stock [Member]	'
Business Acquisition [Line Items]	'
Shares of Alterra stock outstanding as of the Acquisition Date	2,239,000
Markel share issuance to Alterra shareholders	140,000

[1]	The fair value of the shares issued by the Company was calculated as the weighted average price of the Company's stock on April 30, 2013, the day preceding the Acquisition Date.

Acquisitions_Summary_Of_Fair_V

Acquisitions (Summary Of Fair Value Of Assets Acquired And Liabilities Assumed) (Details) (May 1, 2013 Alterra Capital Holdings [Member], USD $)	Jun. 30, 2013
In Thousands, unless otherwise specified	Jun. 30, 2013
May 1, 2013 Alterra Capital Holdings [Member]	'
ASSETS	'
Investments	$6,407,841
Cash and cash equivalents	1,036,274
Restricted cash and cash equivalents	414,497
Receivables	866,388
Reinsurance recoverable on unpaid losses	1,169,084
Reinsurance recoverable on paid losses	80,672
Prepaid reinsurance premiums	317,445
Other assets	859,884
LIABILITIES	'
Unpaid losses and loss adjustment expenses	4,719,461
Life and annuity benefits	1,477,482
Unearned premiums	1,075,610
Payables to insurance and reinsurance companies	342,858
Senior long-term debt	512,463
Other liabilities	223,108
Net assets	2,801,103
Goodwill	295,690
Intangible assets	207,500
Acquisition date fair value	$3,304,293

Acquisitions_Summary_Of_Net_In

Acquisitions (Summary Of Net Intangible Assets Acquired) (Details) (USD $)

12 Months Ended

8 Months Ended

12 Months Ended

In Thousands, unless otherwise specified

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Jun. 30, 2013

Dec. 31, 2013

Jun. 30, 2013

Dec. 31, 2013

Jun. 30, 2013

Dec. 31, 2013

Jun. 30, 2013

Dec. 31, 2013

Jun. 30, 2013

Dec. 31, 2013

Jun. 30, 2013

Dec. 31, 2013

Jun. 30, 2013

Customer Relationships [Member]

Broker Relationships [Member]

Technology [Member]

Trade Names [Member]

May 1, 2013 Alterra Capital Holdings [Member]

Lloyd's Syndicate Capacity [Member]

Insurance Licenses [Member]

Customer Relationships [Member]

Broker Relationships [Member]

Technology [Member]

Trade Names [Member]

Schedule of Intangible Assets [Line Items]

Finite-lived intangible assets

$170,000

$132,000

$19,000

$18,000

$1,000

Indefinite-lived intangible assets

37,500

12,000

25,500

Economic useful lives of finite-lived intangible assets, years

'15 years 6 months 6 days

'17 years 11 months 20 days

'11 years 2 months 5 days

'10 years

'4 years 5 months 28 days

'17 years

'18 years

'10 years

'1 year

Economic useful lives of indefinite-lived intangible assets, years

'Indefinite

Intangible assets, before amortization, as of the Acquisition Date

207,500

Amortization (from the Acquisition Date through December 31, 2013)

55,223

33,512

24,291

7,785

Net intangible assets as of December 31, 2013

$565,083

$374,295

$199,715

Acquisitions_Summary_Of_Transa

Acquisitions (Summary Of Transaction And Acquisition-Related Costs) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
Acquisitions [Abstract]	'		'	'
Transaction costs	$15,981	[1]	'	'
Severance costs	31,734	[1]	'	'
Stay bonuses	14,804	[1]	'	'
Acceleration of Alterra long-term incentive compensation awards and restricted stock awards	12,621	[1]	'	'
Total transaction and acquisition-related costs	$75,140	[1],[2]	$0	$0

[1]	In connection with the acquisition of Alterra, the Company incurred transaction costs of $16.0 million for the year ended December 31, 2013, which primarily consist of due diligence, legal and investment banking costs. Additionally, the Company incurred severance costs of $31.7 million, stay bonuses of $14.8 million and other compensation costs totaling $12.6 million related to the acceleration of certain long-term incentive compensation awards and restricted stock awards that were granted by Alterra prior to the acquisition.
[2]	In connection with the acquisition of Alterra, the Company incurred transaction costs of $16.0 million for the year ended DecemberB 31, 2013, which primarily consist of due diligence, legal and investment banking costs. Additionally, the Company incurred severance costs of $31.7 million, stay bonuses of $14.8 million and other compensation costs totaling $12.6 million related to the acceleration of certain long-term incentive compensation awards and restricted stock awards that were granted by Alterra prior to the acquisition.

Acquisitions_Summary_Of_Result

Acquisitions (Summary Of Results Of Operations) (Details) (USD $)

3 Months Ended

12 Months Ended

8 Months Ended

In Thousands, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2011

Sep. 30, 2011

Jun. 30, 2011

Mar. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

May 1, 2013 Alterra Capital Holdings [Member]

Business Acquisition [Line Items]

Operating revenues

$1,279,785

$1,191,665

$1,031,769

$819,864

$807,955

$765,775

$693,247

$733,135

$685,100

$676,088

$647,168

$621,594

$4,323,083

$3,000,112

$2,629,950

$912,387

Net loss to shareholders

$98,764

$65,599

$27,756

$88,902

$56,792

$49,653

$89,687

$57,253

$50,176

$53,264

$30,314

$8,272

$281,021

$253,385

$142,026

($93,074)

Acquisitions_Unaudited_Pro_For

Acquisitions (Unaudited Pro Forma Consolidated Financial Information) (Details) (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Acquisitions [Abstract]	'		'
Earned premiums	$3,680,220		$3,509,834
Operating revenues	4,899,628		4,561,107
Net income to shareholders	$422,829		$308,496
U.S. GAAP combined ratio	95.00%	[1]	99.00%	[1]
Basic net income per share	$30.33		$21.79
Diluted net income per share	$30.19		$21.71
Weighted average common shares outstanding, basic	14,007		14,014
Weighted average common shares outstanding, diluted	14,069		14,065

[1]	The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums.

Investments_Narrative_Details

Investments (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
	securities	securities
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities in unrealized loss position, number of positions	1,364	35
Available-for-sale securities, estimated fair value	$4,859,071,000	$326,217,000
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-211,904,000	-17,153,000
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end	9	10
Available-for-sale securities, estimated fair value, 12 months or longer	31,247,000	9,660,000
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-546,000	-563,000
Estimated average duration of the fixed maturities	'4 years 9 months 15 days	'
Restricted assets	6,089,379,000	1,372,170,000
Percentage threshold of shareholders' equity used to define concentration of investments	10.00%	10.00%
Ten largest equity holdings	1,500,000,000	'
Ten largest equity holdings, percentage of equity portfolio	46.00%	'
Investments in property and casualty	568,300,000	'
Investments in property and casualty, percentage of equity portfolio	17.00%	'
Berkshire Hathaway Inc. [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Investments in property and casualty	371,100,000	'
Held In Trust Or On Deposit [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Restricted assets	5,200,000,000	1,300,000,000
Held In Trust Or On Deposit [Member] \| Alterra Capital Holdings [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Restricted assets	3,700,000,000	'
Cash And Cash Equivalents And Securities Pledged As Collateral [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Restricted assets	695,100,000	23,200,000
Cash And Cash Equivalents And Securities Pledged As Collateral [Member] \| Alterra Capital Holdings [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Restricted assets	645,400,000	'
Fixed Maturities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value	4,810,249,000	10,874,000
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-210,786,000	-9,568,000
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end	8	8
Available-for-sale securities, estimated fair value, 12 months or longer	3,512,000	7,677,000
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-146,000	-440,000
Equity Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value	48,822,000	86,523,000
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-1,118,000	-7,571,000
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end	1	2
Available-for-sale securities, estimated fair value, 12 months or longer	27,735,000	1,983,000
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	($400,000)	($123,000)

Investments_AvailableForSale_I

Investments (Available-For-Sale Investments) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	$13,147,964	$6,922,901
Available-for-sale investments, gross unrealized holding gains	1,910,562	1,453,816
Available-for-sale investments, gross unrealized holding losses	-204,757	-8,073
Available-for-sale investments, unrealized other-than-temporary impairment losses	-7,147	-9,080
Available-for-sale investments, estimated fair value	14,846,622	8,359,564
U.S. Treasury Securities And Obligations Of U.S. Government Agencies [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	1,215,522	297,663
Available-for-sale investments, gross unrealized holding gains	9,051	19,844
Available-for-sale investments, gross unrealized holding losses	-30,342	0
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	1,194,231	317,507
Obligations Of States, Municipalities And Political Subdivisions [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	2,986,758	2,586,867
Available-for-sale investments, gross unrealized holding gains	116,341	245,057
Available-for-sale investments, gross unrealized holding losses	-27,384	-362
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	3,075,715	2,831,562
Foreign Governments [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	1,484,818	503,844
Available-for-sale investments, gross unrealized holding gains	30,647	52,764
Available-for-sale investments, gross unrealized holding losses	-54,411	0
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	1,461,054	556,608
Commercial Mortgage-Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	379,555	'
Available-for-sale investments, gross unrealized holding gains	62	'
Available-for-sale investments, gross unrealized holding losses	-11,796	'
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	'
Available-for-sale investments, estimated fair value	367,821	'
Residential Mortgage-Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	875,902	202,644
Available-for-sale investments, gross unrealized holding gains	13,046	14,996
Available-for-sale investments, gross unrealized holding losses	-16,442	-5
Available-for-sale investments, unrealized other-than-temporary impairment losses	-2,258	-2,258
Available-for-sale investments, estimated fair value	870,248	215,377
Asset-Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	189,646	13,828
Available-for-sale investments, gross unrealized holding gains	257	517
Available-for-sale investments, gross unrealized holding losses	-1,614	0
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	188,289	14,345
Corporate Bonds [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	2,996,940	957,432
Available-for-sale investments, gross unrealized holding gains	54,777	93,395
Available-for-sale investments, gross unrealized holding losses	-61,650	-121
Available-for-sale investments, unrealized other-than-temporary impairment losses	-4,889	-6,822
Available-for-sale investments, estimated fair value	2,985,178	1,043,884
Total Fixed Maturities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	10,129,141	4,562,278
Available-for-sale investments, gross unrealized holding gains	224,181	426,573
Available-for-sale investments, gross unrealized holding losses	-203,639	-488
Available-for-sale investments, unrealized other-than-temporary impairment losses	-7,147	-9,080
Available-for-sale investments, estimated fair value	10,142,536	4,979,283
Insurance, Banks And Other Financial Institutions [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	422,975	508,771
Available-for-sale investments, gross unrealized holding gains	592,112	389,434
Available-for-sale investments, gross unrealized holding losses	-4	-138
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	1,015,083	898,067
Industrial, Consumer And All Other [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	1,143,578	878,534
Available-for-sale investments, gross unrealized holding gains	1,094,251	637,783
Available-for-sale investments, gross unrealized holding losses	-1,114	-7,433
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	2,236,715	1,508,884
Total Equity Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	1,566,553	1,387,305
Available-for-sale investments, gross unrealized holding gains	1,686,363	1,027,217
Available-for-sale investments, gross unrealized holding losses	-1,118	-7,571
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	3,251,798	2,406,951
Short-Term Investments [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	1,452,270	973,318
Available-for-sale investments, gross unrealized holding gains	18	26
Available-for-sale investments, gross unrealized holding losses	0	-14
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	$1,452,288	$973,330

Investments_Summary_Of_Gross_U

Investments (Summary Of Gross Unrealized Investment Losses By Length Of Time That Securities Have Continuously Been In An Unrealized Loss Position) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	$4,827,824	$316,557
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-211,358	-16,590
Available-for-sale securities, estimated fair value, 12 months or longer	31,247	9,660
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-546	-563
Available-for-sale securities, estimated fair value	4,859,071	326,217
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-211,904	-17,153
U.S. Treasury Securities And Obligations Of U.S. Government Agencies [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	587,929	'
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-30,342	'
Available-for-sale securities, estimated fair value, 12 months or longer	0	'
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	0	'
Available-for-sale securities, estimated fair value	587,929	'
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-30,342	'
Obligations Of States, Municipalities And Political Subdivisions [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	513,608	2,833
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-27,238	-46
Available-for-sale securities, estimated fair value, 12 months or longer	3,512	3,616
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-146	-316
Available-for-sale securities, estimated fair value	517,120	6,449
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-27,384	-362
Foreign Governments [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	950,040	'
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-54,411	'
Available-for-sale securities, estimated fair value, 12 months or longer	0	'
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	0	'
Available-for-sale securities, estimated fair value	950,040	'
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-54,411	'
Commercial Mortgage-Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	357,737	'
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-11,796	'
Available-for-sale securities, estimated fair value, 12 months or longer	0	'
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	0	'
Available-for-sale securities, estimated fair value	357,737	'
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-11,796	'
Residential Mortgage-Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	437,675	364
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-18,700	-2,260
Available-for-sale securities, estimated fair value, 12 months or longer	0	201
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	0	-3
Available-for-sale securities, estimated fair value	437,675	565
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-18,700	-2,263
Asset-Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	142,011	'
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-1,614	'
Available-for-sale securities, estimated fair value, 12 months or longer	0	'
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	0	'
Available-for-sale securities, estimated fair value	142,011	'
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-1,614	'
Corporate Bonds [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	1,817,737	0
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-66,539	-6,822
Available-for-sale securities, estimated fair value, 12 months or longer	0	3,860
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	0	-121
Available-for-sale securities, estimated fair value	1,817,737	3,860
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-66,539	-6,943
Total Fixed Maturities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	4,806,737	3,197
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-210,640	-9,128
Available-for-sale securities, estimated fair value, 12 months or longer	3,512	7,677
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-146	-440
Available-for-sale securities, estimated fair value	4,810,249	10,874
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-210,786	-9,568
Insurance, Banks And Other Financial Institutions [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	144	2,431
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-4	-138
Available-for-sale securities, estimated fair value, 12 months or longer	0	0
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	0	0
Available-for-sale securities, estimated fair value	144	2,431
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-4	-138
Industrial, Consumer And All Other [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	20,943	82,109
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-714	-7,310
Available-for-sale securities, estimated fair value, 12 months or longer	27,735	1,983
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-400	-123
Available-for-sale securities, estimated fair value	48,678	84,092
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-1,114	-7,433
Total Equity Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	21,087	84,540
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-718	-7,448
Available-for-sale securities, estimated fair value, 12 months or longer	27,735	1,983
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-400	-123
Available-for-sale securities, estimated fair value	48,822	86,523
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-1,118	-7,571
Short-Term Investments [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	'	228,820
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	'	-14
Available-for-sale securities, estimated fair value, 12 months or longer	'	0
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	'	0
Available-for-sale securities, estimated fair value	'	228,820
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	'	($14)

Investments_Schedule_Of_Amorti

Investments (Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturities By Contractual Maturity) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]	'	'
Due in one year or less, amortized cost	$885,726	'
Due after one year through five years, amortized cost	2,891,314	'
Due after five years through ten years, amortized cost	2,217,759	'
Due after ten years, amortized cost	2,689,239	'
Amortized cost, sub-total	8,684,038	'
Fixed maturities, amortized cost	10,129,141	4,562,278
Due in one year or less, estimated fair value	891,654	'
Due after one year through five years, estimated fair value	2,947,173	'
Due after five years through ten years, estimated fair value	2,254,169	'
Due after ten years, estimated fair value	2,623,182	'
Estimated fair value, sub-total	8,716,178	'
Fixed maturities, estimated fair value	10,142,536	4,979,283
Commercial Mortgage-Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized cost	379,555	'
Estimated fair value	367,821	'
Residential Mortgage-Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized cost	875,902	'
Estimated fair value	870,248	'
Asset-Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized cost	189,646	'
Estimated fair value	$188,289	'

Investments_Components_Of_Net_

Investments (Components Of Net Investment Income) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule of Investment Income, Reported Amounts, by Category [Line Items]	'	'	'
Municipal bonds (tax-exempt)	$82,308	$90,316	$94,457
Short-term investments, including overnight deposits	3,573	2,755	2,484
Dividends on equity securities	48,641	50,416	35,996
Change in fair value of credit default swap	10,460	16,641	-4,103
Income from equity method investments	21,898	1,961	584
Other	355	-41	1,551
Total investment income	329,653	291,981	271,488
Investment expenses	-12,280	-9,874	-7,812
Net investment income	317,373	282,107	263,676
Taxable Municipal Bonds [Member]	'	'	'
Schedule of Investment Income, Reported Amounts, by Category [Line Items]	'	'	'
Taxable bonds	28,041	22,663	23,277
Other Taxable Bonds [Member]	'	'	'
Schedule of Investment Income, Reported Amounts, by Category [Line Items]	'	'	'
Taxable bonds	$134,377	$107,270	$117,242

Investments_Summary_Of_Activit

Investments (Summary Of Activity For Credit Losses) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]	'	'	'
Cumulative credit loss, beginning of year	$21,370	$21,370	$10,307
Other-than-temporary impairment losses not previously recognized	0	0	875
Increases related to other-than-temporary impairment losses previously recognized	0	0	10,203
Total additions	0	0	11,078
Sales or maturities of fixed maturities on which credit losses were recognized	-8,622	0	-15
Cumulative credit loss, end of year	$12,748	$21,370	$21,370

Investments_Summary_Of_Net_Rea

Investments (Summary Of Net Realized Investment Gains And The Change In Net Unrealized Gains On Investments) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Gain (Loss) on Investments [Line Items]	'	'	'
Realized gains	$93,304	$48,664	$56,524
Realized losses	-30,152	-17,071	-20,667
Other-than-temporary impairment losses recognized in net income	-4,706	-12,078	-20,196
Net realized investment gains	63,152	31,593	35,857
Change in net unrealized gains on investments	261,995	353,808	182,722
Sales Of Fixed Maturities [Member]	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'
Realized gains	13,772	18,337	17,035
Realized losses	-25,168	-563	-410
Sales Of Equity Securities [Member]	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'
Realized gains	73,592	29,578	36,863
Realized losses	-278	-342	-61
Other [Member]	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'
Realized gains	5,940	749	2,626
Realized losses	0	-4,088	0
Fixed Maturities [Member]	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'
Change in net unrealized gains on investments	-403,610	51,783	190,976
Equity Securities [Member]	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'
Change in net unrealized gains on investments	665,599	302,013	-8,250
Short-Term Investments [Member]	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'
Change in net unrealized gains on investments	$6	$12	($4)

Investments_Summary_Of_OtherTh

Investments (Summary Of Other-Than-Temporary Impairment Losses Recognized In Net Income And In Net Realized Investment Gains By Investment Type) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'
Other-than-temporary impairment losses recognized in net income	($4,706)	($12,078)	($20,196)
Fixed Maturities [Member]	'	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'
Other-than-temporary impairment losses recognized in net income	-1,882	0	-11,078
Equity Securities [Member]	'	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'
Other-than-temporary impairment losses recognized in net income	-2,824	-12,078	-9,118
Obligations Of States, Municipalities And Political Subdivisions [Member] \| Fixed Maturities [Member]	'	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'
Other-than-temporary impairment losses recognized in net income	-1,242	0	0
Residential Mortgage-Backed Securities [Member] \| Fixed Maturities [Member]	'	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'
Other-than-temporary impairment losses recognized in net income	-640	0	-11,078
Insurance, Banks And Other Financial Institutions [Member] \| Equity Securities [Member]	'	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'
Other-than-temporary impairment losses recognized in net income	0	-10,336	-4,251
Industrial, Consumer And All Other [Member] \| Equity Securities [Member]	'	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'
Other-than-temporary impairment losses recognized in net income	($2,824)	($1,742)	($4,867)

Investments_Schedule_Of_Restri

Investments (Schedule Of Restricted Assets) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]	'	'
Investments, available-for-sale	$5,225,701	$1,262,755
Restricted cash and cash equivalents	786,926	109,415
Other assets	76,752	0
Total	$6,089,379	$1,372,170

Receivables_Components_Of_Rece

Receivables (Components Of Receivables) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Receivables [Abstract]	'	'
Amounts receivable from agents, brokers and insureds	$1,058,021	$332,570
Trade accounts receivable	85,203	73,512
Employee stock loans receivable (see note 12(c))	12,822	11,413
Other	5,420	12,982
Receivables, gross	1,161,466	430,477
Allowance for doubtful receivables	-19,693	-16,594
Receivables	$1,141,773	$413,883

Deferred_Policy_Acquisition_Co2

Deferred Policy Acquisition Costs (Amounts Of Policy Acquisition Costs Acquired, Deferred And Amortized) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]	'	'	'
Balance, beginning of year	$157,465	$194,674	$188,783
Policy acquisition costs deferred	575,417	390,900	485,345
Amortization of policy acquisition costs	-471,915	-428,109	-479,454
Deferred policy acquisition costs	$260,967	$157,465	$194,674

Deferred_Policy_Acquisition_Co3

Deferred Policy Acquisition Costs (Components Of Underwriting, Acquisition And Insurance Expenses) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Deferred Policy Acquisition Costs Disclosures [Abstract]	'		'		'
Transaction costs and other acquisition-related expenses	$75,140	[1],[2]	$0		$0
Transaction costs	15,981	[2]	'		'
Other acquisition related costs, severance costs	31,734	[2]	'		'
Other acquisition related costs, stay bonuses	14,804	[2]	'		'
Other acquisition related costs, other compensation costs	12,621	[2]	'		'
Prospective adoption of FASB ASU No. 2010-26	0		43,093	[3]	0
Other amortization of policy acquisition costs	471,915		385,016		479,454
Other operating expenses	765,257		501,363		330,725
Underwriting, acquisition and insurance expenses	$1,312,312		$929,472		$810,179

[1]	In connection with the acquisition of Alterra, the Company incurred transaction costs of $16.0 million for the year ended DecemberB 31, 2013, which primarily consist of due diligence, legal and investment banking costs. Additionally, the Company incurred severance costs of $31.7 million, stay bonuses of $14.8 million and other compensation costs totaling $12.6 million related to the acceleration of certain long-term incentive compensation awards and restricted stock awards that were granted by Alterra prior to the acquisition.
[2]	In connection with the acquisition of Alterra, the Company incurred transaction costs of $16.0 million for the year ended December 31, 2013, which primarily consist of due diligence, legal and investment banking costs. Additionally, the Company incurred severance costs of $31.7 million, stay bonuses of $14.8 million and other compensation costs totaling $12.6 million related to the acceleration of certain long-term incentive compensation awards and restricted stock awards that were granted by Alterra prior to the acquisition.
[3]	Effective January 1, 2012, the Company prospectively adopted FASB ASU No. 2010-26, Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts. At December 31, 2011, deferred policy acquisition costs included $43.1 million of costs that no longer met the criteria for deferral as of January 1, 2012 and were recognized into income during 2012, consistent with policy terms.

Property_And_Equipment_Compone

Property And Equipment (Components Of Property And Equipment) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Abstract]	'	'	'
Land	$48,036,000	$45,199,000	'
Buildings	59,307,000	53,767,000	'
Leasehold improvements	68,363,000	55,626,000	'
Land improvements	57,673,000	51,512,000	'
Furniture and equipment	217,528,000	211,354,000	'
Other	104,690,000	85,714,000	'
Property and equipment, gross	555,597,000	503,172,000	'
Accumulated depreciation and amortization	-207,688,000	-172,943,000	'
Property and equipment	347,909,000	330,229,000	'
Depreciation and amortization expense of property and equipment	$51,500,000	$36,000,000	$24,200,000

Goodwill_And_Intangible_Assets2

Goodwill And Intangible Assets (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Goodwill And Intangible Assets [Line Items]	'	'	'
Goodwill impairment	$0	$0	'
Amortization of intangible assets	55,223,000	33,512,000	24,291,000
Estimated amortization of intangible assets for 2014	45,700,000	'	'
Estimated amortization of intangible assets for 2015	44,700,000	'	'
Estimated amortization of intangible assets for 2016	41,800,000	'	'
Estimated amortization of intangible assets for 2017	40,400,000	'	'
Estimated amortization of intangible assets for 2018	40,200,000	'	'
Indefinite-lived intangible assets	58,000,000	10,100,000	'
Intangible assets acquired during period	$247,000,000	'	'
Definite-lived intangible assets, weighted-average amortization period	'15 years 6 months 6 days	'	'
Customer Relationships [Member]	'	'	'
Goodwill And Intangible Assets [Line Items]	'	'	'
Definite-lived intangible assets, weighted-average amortization period	'17 years 11 months 20 days	'	'
Broker Relationships [Member]	'	'	'
Goodwill And Intangible Assets [Line Items]	'	'	'
Definite-lived intangible assets, weighted-average amortization period	'11 years 2 months 5 days	'	'
Trade Names [Member]	'	'	'
Goodwill And Intangible Assets [Line Items]	'	'	'
Definite-lived intangible assets, weighted-average amortization period	'4 years 5 months 28 days	'	'
Technology [Member]	'	'	'
Goodwill And Intangible Assets [Line Items]	'	'	'
Definite-lived intangible assets, weighted-average amortization period	'10 years	'	'

Goodwill_And_Intangible_Assets3

Goodwill And Intangible Assets (Components Of Goodwill) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Goodwill [Line Items]	'		'
Goodwill, beginning balance	$674,930		$607,561
Acquisitions	296,875		67,028
Foreign currency movements and other adjustments	-4,088		341
Goodwill, ending balance	967,717		674,930
Excess And Surplus Lines Segment [Member]	'		'
Goodwill [Line Items]	'		'
Goodwill, beginning balance	81,770		81,770
Acquisitions	0		0
Foreign currency movements and other adjustments	0		0
Goodwill, ending balance	81,770		81,770
Specialty Admitted Segment [Member]	'		'
Goodwill [Line Items]	'		'
Goodwill, beginning balance	91,054		64,914
Acquisitions	0		26,140
Foreign currency movements and other adjustments	0		0
Goodwill, ending balance	91,054		91,054
London Insurance Market Segment [Member]	'		'
Goodwill [Line Items]	'		'
Goodwill, beginning balance	309,660		309,064
Acquisitions	0		0
Foreign currency movements and other adjustments	-2,088		596
Goodwill, ending balance	307,572		309,660
Alterra Segment [Member]	'		'
Goodwill [Line Items]	'		'
Goodwill, beginning balance	0		0
Acquisitions	295,690		0
Foreign currency movements and other adjustments	0		0
Goodwill, ending balance	295,690		0
Other [Member]	'		'
Goodwill [Line Items]	'		'
Goodwill, beginning balance	192,446	[1]	151,813	[1]
Acquisitions	1,185	[1]	40,888	[1]
Foreign currency movements and other adjustments	-2,000	[1]	-255	[1]
Goodwill, ending balance	$191,631	[1]	$192,446	[1]

[1]	Amounts included in Other above are related to the Company's Markel Ventures operations.

Goodwill_And_Intangible_Assets4

Goodwill And Intangible Assets (Components Of Intangible Assets) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Indefinite-Lived And Finite-Lived Intangible Assets [Line Items]	'	'
Intangible assets, gross carrying amount	$666,270	$442,206
Intangible assets, accumulated amortization	-101,187	-67,911
Customer Relationships [Member]	'	'
Schedule of Indefinite-Lived And Finite-Lived Intangible Assets [Line Items]	'	'
Intangible assets, gross carrying amount	298,886	171,591
Intangible assets, accumulated amortization	-43,286	-29,955
Broker Relationships [Member]	'	'
Schedule of Indefinite-Lived And Finite-Lived Intangible Assets [Line Items]	'	'
Intangible assets, gross carrying amount	178,693	135,867
Intangible assets, accumulated amortization	-23,255	-12,317
Trade Names [Member]	'	'
Schedule of Indefinite-Lived And Finite-Lived Intangible Assets [Line Items]	'	'
Intangible assets, gross carrying amount	65,880	75,781
Intangible assets, accumulated amortization	-12,666	-9,075
Technology [Member]	'	'
Schedule of Indefinite-Lived And Finite-Lived Intangible Assets [Line Items]	'	'
Intangible assets, gross carrying amount	56,429	40,109
Intangible assets, accumulated amortization	-16,222	-11,785
Insurance Licenses [Member]	'	'
Schedule of Indefinite-Lived And Finite-Lived Intangible Assets [Line Items]	'	'
Intangible assets, gross carrying amount	40,185	4,300
Intangible assets, accumulated amortization	-133	-67
Lloyd's Syndicate Capacity [Member]	'	'
Schedule of Indefinite-Lived And Finite-Lived Intangible Assets [Line Items]	'	'
Intangible assets, gross carrying amount	12,000	0
Intangible assets, accumulated amortization	0	0
Other [Member]	'	'
Schedule of Indefinite-Lived And Finite-Lived Intangible Assets [Line Items]	'	'
Intangible assets, gross carrying amount	14,197	14,558
Intangible assets, accumulated amortization	($5,625)	($4,712)

Income_Taxes_Narrative_Details

Income Taxes (Narrative) (Details) (USD $)	12 Months Ended
Income Taxes (Narrative) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Line Items]	'	'	'
Income tax payments	$35,700,000	$30,000,000	$35,000,000
Income taxes payable	84,200,000	2,200,000	'
Tax credit carryforwards	33,773,000	41,387,000	'
Tax credit, expiration date	31-Dec-19	'	'
Net operating loss carryforwards	81,600,000	'	'
Estimated gross deferred tax assets including net operating losses realized through reversal of existing temporary differences attributable to gross deferred tax liabilities	668,800,000	'	'
Estimated gross deferred tax assets realized by generating future taxable income	103,700,000	'	'
Unrecognized tax benefits	18,219,000	18,870,000	19,586,000
Unrecognized tax benefits decrease on effective tax rate	15,900,000	'	'
Provision for United States income taxes on earnings of the Company's foreign subsidiaries	0	'	'
Minimum [Member]	'	'	'
Income Tax Disclosure [Line Items]	'	'	'
Operating loss carryforwards, expiration date	31-Dec-27	'	'
Maximum [Member]	'	'	'
Income Tax Disclosure [Line Items]	'	'	'
Operating loss carryforwards, expiration date	31-Dec-33	'	'
Markel Capital Limited [Member]	'	'	'
Income Tax Disclosure [Line Items]	'	'	'
Net operating loss carryforwards	$73,100,000	'	'
Markel Capital Limited [Member] \| Minimum [Member]	'	'	'
Income Tax Disclosure [Line Items]	'	'	'
Operating loss carryforwards, expiration date	31-Dec-21	'	'
Markel Capital Limited [Member] \| Maximum [Member]	'	'	'
Income Tax Disclosure [Line Items]	'	'	'
Operating loss carryforwards, expiration date	31-Dec-32	'	'

Income_Taxes_Components_Of_Inc

Income Taxes (Components Of Income Before Income Taxes) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]	'	'	'
Domestic operations	$325,133	$126,466	$200,446
Foreign operations	36,610	185,584	-10,250
Income Before Income Taxes	$361,743	$312,050	$190,196

Income_Taxes_Components_Of_Inc1

Income Taxes (Components Of Income Tax Expense) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]	'	'	'
Domestic, current	$50,683	$14,340	$35,721
Foreign, current	23,165	1,814	340
Total current tax expense	73,848	16,154	36,061
Domestic, deferred	23,906	-3,734	436
Foreign, deferred	-19,856	41,382	5,213
Total deferred tax expense	4,050	37,648	5,649
Income tax expense	$77,898	$53,802	$41,710

Income_Taxes_Reconciliations_O

Income Taxes (Reconciliations Of United States Corporate Income Tax Rate To Effective Tax Rate On Income Before Income Taxes) (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]	'	'	'
United States corporate tax rate	35.00%	35.00%	35.00%
Tax-exempt investment income	-9.00%	-12.00%	-18.00%
Uncertain tax positions	0.00%	0.00%	-2.00%
Foreign operations	-4.00%	-5.00%	6.00%
Other	0.00%	-1.00%	1.00%
Effective tax rate	22.00%	17.00%	22.00%

Income_Taxes_Components_Of_Dom

Income Taxes (Components Of Domestic And Foreign Deferred Tax Assets And Liabilities) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]	'	'
Differences between financial reporting and tax bases	$139,357	$81,305
Unpaid losses and loss adjustment expenses	283,365	122,217
Life and annuity benefits	161,209	0
Unearned premiums recognized for income tax purposes	76,862	42,938
Other-than-temporary impairments not yet deductible for income tax purposes	34,978	40,450
Net operating loss carryforwards	43,010	7,388
Tax credit carryforwards	33,773	41,387
Total gross deferred tax assets	772,554	335,685
Differences between financial reporting and tax bases	46,699	33,323
Deferred policy acquisition costs	65,543	36,039
Net unrealized gains on investments	459,015	406,295
Amortization of goodwill and other intangible assets	97,580	28,931
Total gross deferred tax liabilities	668,837	504,588
Net deferred tax asset	103,717	'
Net deferred tax liability	'	($168,903)

Income_Taxes_Reconciliation_Of

Income Taxes (Reconciliation Of Beginning And Ending Unrecognized Tax Benefits) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]	'	'
Unrecognized tax benefits, beginning of year	$18,870	$19,586
Increases based upon tax positions taken during the current year	0	888
Increases for tax positions taken in prior years	0	218
Decreases for tax positions taken in prior years	0	-764
Lapse of statute of limitations	-651	-1,058
Unrecognized tax benefits, end of year	$18,219	$18,870

Unpaid_Losses_And_Loss_Adjustm2

Unpaid Losses And Loss Adjustment Expenses (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'	'
Increase (decrease) in reserves for losses and loss adjustment expenses due to movement in foreign currency rates of exchange	$700,000	$23,400,000	($14,100,000)	'
Net reserves for losses and loss adjustment expenses of acquired insurance companies	3,584,642,000	0	0	'
Favorable development on prior years' loss reserves	-411,129,000	-399,002,000	-354,007,000	'
Prior years' development on asbestos and environmental exposures	30,128,000	38,179,000	-134,000	'
Liability for asbestos and environmental claims net incurred loss annual claim review	28,400,000	31,100,000	0	'
Incurred losses and loss adjustment expenses, current year	2,227,402,000	1,553,070,000	1,563,993,000	'
Reinsurance recoverables	269,400,000	165,800,000	159,800,000	'
Impact on the reinsurance recoverable	0	0	0	'
Asbestos-related reserves, gross loss incurred	372,978,000	360,854,000	334,163,000	'
Asbestos-related reserves, net loss incurred	272,194,000	260,791,000	244,772,000	216,034,000
Asbestos and environmental net reserves for reported claims	165,300,000	'	'	'
Asbestos and environmental reserves incurred but not reported, net	106,900,000	'	'	'
Liability for asbestos and environmental claims, net claims paid since inception	398,000,000	'	'	'
Liability for asbestos and environmental claims, net litigation paid since inception	79,100,000	'	'	'
Markel International Commutations [Member]	'	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'	'
Commutation adjustments related to termination of ceded reinsurance contracts	'	'	40,000,000	'
Hurricane Sandy [Member]	'	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'	'
Incurred losses and loss adjustment expenses, current year	'	99,600,000	'	'
Reinsurance recoverables	'	77,600,000	'	'
2011 Natural Catastrophes [Member]	'	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'	'
Incurred losses and loss adjustment expenses, current year	'	'	150,900,000	'
Reinsurance recoverables	'	'	36,300,000	'
Asbestos [Member]	'	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'	'
Asbestos-related reserves, gross loss incurred	284,300,000	'	'	'
Asbestos-related reserves, net loss incurred	206,600,000	'	'	'
London Insurance Market Segment And Professional And Products Liability And Casualty Programs Within Excess And Surplus Lines Segment [Member]	'	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'	'
Favorable development on prior years' loss reserves	293,900,000	336,700,000	'	'
London Insurance Market Segment And Professional And Products Liability Programs Within Excess And Surplus Lines Segment [Member]	'	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]	'	'	'	'
Favorable development on prior years' loss reserves	'	'	$265,800,000	'

Unpaid_Losses_And_Loss_Adjustm3

Unpaid Losses And Loss Adjustment Expenses (Reconciliation Of Consolidated Reserves For Losses And Loss Adjustment Expenses) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]	'	'	'
Net reserves for losses and loss adjustment expenses, beginning of year	$4,592,652	$4,607,767	$4,600,316
Foreign currency movements, commutations and other	-780	30,359	-7,496
Adjusted net reserves for losses and loss adjustment expenses, beginning of year	4,591,872	4,638,126	4,592,820
Incurred losses and loss adjustment expenses, current year	2,227,402	1,553,070	1,563,993
Incurred losses and loss adjustment expenses, prior years	-411,129	-399,002	-354,007
Total incurred losses and loss adjustment expenses	1,816,273	1,154,068	1,209,986
Payments, current year	670,928	268,745	291,837
Payments, prior years	906,302	931,955	898,318
Total payments	1,577,230	1,200,700	1,190,155
Effect of foreign currency rate changes	-7,915	1,158	-4,884
Net reserves for losses and loss adjustment expenses of acquired insurance companies	3,584,642	0	0
Net reserves for losses and loss adjustment expenses, end of year	8,407,642	4,592,652	4,607,767
Reinsurance recoverable on unpaid losses	1,854,414	778,774	791,102
Gross reserves for losses and loss adjustment expenses, end of year	$10,262,056	$5,371,426	$5,398,869

Unpaid_Losses_And_Loss_Adjustm4

Unpaid Losses And Loss Adjustment Expenses (Reconciliation Of Consolidated A&E Reserves For Losses And Loss Adjustment Expenses) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]	'	'	'
Net reserves for A&E losses and loss adjustment expenses, beginning of year	$260,791	$244,772	$216,034
Commutations and other	-5,067	-897	36,271
Adjusted net reserves for A&E losses and loss adjustment expenses, beginning of year	255,724	243,875	252,305
Incurred losses and loss adjustment expenses	30,128	38,179	-134
Payments	-13,658	-21,263	-7,399
Net reserves for A&E losses and loss adjustment expenses, end of year	272,194	260,791	244,772
Reinsurance recoverable on unpaid losses	100,784	100,063	89,391
Gross reserves for A&E losses and loss adjustment expenses, end of year	$372,978	$360,854	$334,163

Life_And_Annuity_Benefits_Narr

Life And Annuity Benefits (Narrative) (Details) (USD $)	Dec. 31, 2013
In Millions, unless otherwise specified	Dec. 31, 2013
Liability for Future Policy Benefits [Abstract]	'
Average reserve valuation rate	2.30%
Life and annuity benefits reserve single contract concentration	34.80%
Annuities included in life and annuity benefits subject to discretionary withdrawal	$0

Life_And_Annuity_Benefits_Sche

Life And Annuity Benefits (Schedule Of Life And Annuity Benefits) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Liability for Future Policy Benefits [Abstract]	'	'
Life	$190,765	'
Annuities	1,194,558	'
Accident and health	101,251	'
Total life and annuity benefits	$1,486,574	$0

Senior_LongTerm_Debt_And_Other2

Senior Long-Term Debt And Other Debt (Narrative) (Details) (USD $)

12 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Jul. 02, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Mar. 08, 2013

Dec. 31, 2013

Mar. 08, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Jun. 30, 2013

Dec. 31, 2013

Jun. 30, 2013

Apr. 16, 2007

Dec. 31, 2013

Jun. 30, 2013

Sep. 27, 2010

Dec. 31, 2013

4.90% Unsecured Senior Notes [Member]

7.50% Unsecured Senior Debentures [Member]

6.80% Unsecured Senior Notes [Member]

3.625% Unsecured Senior Notes [Member]

5.0% Unsecured Senior Notes [Member]

3.625% And 5.0% Unsecured Senior Notes [Member]

7.20% Unsecured Senior Notes [Member]

6.25% Unsecured Senior Notes [Member]

7.35% Unsecured Senior Notes [Member]

Revolving Credit Facility [Member]

May 1, 2013 Alterra Capital Holdings [Member]

option

7.20% Unsecured Senior Notes [Member]

6.25% Unsecured Senior Notes [Member]

Senior Credit Facility [Member]

Debt Instrument [Line Items]

Debt instrument, face amount

$350,000,000

$150,000,000

$250,000,000

$100,000,000

$350,000,000

Debt instrument, interest rate

4.90%

7.50%

6.80%

3.63%

5.00%

7.20%

6.25%

7.35%

7.20%

6.25%

Net proceeds from issuance of debt

347,200,000

491,200,000

Debt instrument, redemption price, percentage of face amount

100.00%

Loss on extinguishment of debt

-4,100,000

Debt instrument, principal amount outstanding

246,700,000

90,600,000

Debt instrument, estimated fair value

512,463,000

95,800,000

416,600,000

Senior long-term debt and other debt, estimated fair value

2,372,000,000

1,688,000,000

Line of credit facility, previous capacity available

150,000,000

Line of credit facility, capacity available

300,000,000

250,000,000

Number of interest rate options on revolving credit facility

Line of credit facility, unused capacity, commitment fee, percent

0.25%

0.13%

Borrowings outstanding under the facility

Credit facility, maximum capacity

900,000,000

Credit facility, potential increased maxiumum capacity

1,400,000,000

Line of credit facility, outstanding balance fee, percent

0.40%

Credit facility, letters of credit issued and outstanding

472,300,000

Interest on senior long-term debt and other debt

$114,500,000

$92,900,000

$84,100,000

Senior_LongTerm_Debt_And_Other3

Senior Long-Term Debt And Other Debt (Summary Of Senior Long-Term Debt And Other Debt) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]	'	'
Senior long-term debt and other debt	$2,256,227	$1,492,550
6.80% Unsecured Senior Notes [Member]	'	'
Debt Instrument [Line Items]	'	'
Unsecured senior notes	0	246,619
Debt instrument, interest rate	6.80%	6.80%
Debt instrument, unamortized discount	0	45
7.20% Unsecured Senior Notes [Member]	'	'
Debt Instrument [Line Items]	'	'
Unsecured senior notes	95,451	0
Debt instrument, interest rate	7.20%	'
Debt Instrument, unamortized premium	4,822	'
7.125% Unsecured Senior Notes [Member]	'	'
Debt Instrument [Line Items]	'	'
Unsecured senior notes	348,374	348,091
Debt instrument, interest rate	7.13%	7.13%
Debt instrument, unamortized discount	1,626	1,909
6.25% Unsecured Senior Notes [Member]	'	'
Debt Instrument [Line Items]	'	'
Unsecured senior notes	411,273	0
Debt instrument, interest rate	6.25%	'
Debt Instrument, unamortized premium	61,273	'
5.35% Unsecured Senior Notes [Member]	'	'
Debt Instrument [Line Items]	'	'
Unsecured senior notes	248,469	248,262
Debt instrument, interest rate	5.35%	5.35%
Debt instrument, unamortized discount	1,531	1,738
4.90% Unsecured Senior Notes [Member]	'	'
Debt Instrument [Line Items]	'	'
Unsecured senior notes	347,626	347,347
Debt instrument, interest rate	4.90%	4.90%
Debt instrument, unamortized discount	2,374	2,653
3.625% Unsecured Senior Notes [Member]	'	'
Debt Instrument [Line Items]	'	'
Unsecured senior notes	248,140	0
Debt instrument, interest rate	3.63%	'
Debt instrument, unamortized discount	1,860	'
7.35% Unsecured Senior Notes [Member]	'	'
Debt Instrument [Line Items]	'	'
Unsecured senior notes	197,815	197,710
Debt instrument, interest rate	7.35%	7.35%
Debt instrument, unamortized discount	2,185	2,291
5.0% Unsecured Senior Notes [Member]	'	'
Debt Instrument [Line Items]	'	'
Unsecured senior notes	243,449	0
Debt instrument, interest rate	5.00%	'
Debt instrument, unamortized discount	6,551	'
Subsidiary And Other Debt [Member]	'	'
Debt Instrument [Line Items]	'	'
Senior long-term debt and other debt	$115,630	$104,521
Debt instrument, interest rate, percentage rate range, minimum	2.50%	'
Debt instrument, interest rate, percentage rate range, maximum	6.50%	'

Senior_LongTerm_Debt_And_Other4

Senior Long-Term Debt And Other Debt (Summary Of Future Principal Payments Due At Maturity On Senior Long-Term Debt And Other Debt) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Debt Disclosure [Abstract]	'	'
2014	$28,795	'
2015	6,102	'
2016	11,822	'
2017	105,987	'
2018	2,278	'
2019 and thereafter	2,051,275	'
Total principal payments	2,206,259	'
Net unamortized premium	49,968	'
Senior long-term debt and other debt	$2,256,227	$1,492,550

Shareholders_Equity_Narrative_

Shareholders' Equity (Narrative) (Details) (USD $)

Dec. 31, 2013

Dec. 31, 2012

Jun. 30, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

31-May-13

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

31-May-13

Dec. 31, 2013

31-May-13

Dec. 31, 2013

May 1, 2013 Alterra Capital Holdings [Member]

Warrant [Member]

November 2010 Share Repurchase Program [Member]

November 2013 Share Repurchase Program [Member]

Employee Stock Purchase And Bonus Plan [Member]

2012 Compensation Plan [Member]

Aspen Option Plans [Member]

Alterra Equity Award Plans [Member]

May 1, 2013 Alterra Capital Holdings [Member]

Restricted Stock Units (RSUs) [Member]

Stock Options [Member]

Restricted Stock Units (RSUs) [Member]

Stock Options [Member]

warrant_holders

Non-Employee Directors [Member]

Performance Based [Member]

Retention [Member]

Rentention And Hiring [Member]

Associates And Executive Officers [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Common stock, shares authorized

50,000,000

Common stock, par value

Common stock, shares issued

13,985,620

9,629,160

Common stock, shares outstanding

13,985,620

9,629,160

Preferred stock, shares authorized

10,000,000

Preferred stock, par value

Preferred stock, shares issued

Preferred stock, shares outstanding

Number of common stock shares repurchased

77,693

Stock repurchased value

$40,900,000

Cumulative number of common stock shares repurchased

232,535

Cumulative stock repurchased value

101,400,000

Board of Directors approved the repurchase of common stock under a share repurchase program, maximum

300,000,000

Bonus calculation percentage based on the value of stocks acquired by employees

10.00%

Percentage of bonus shares award to loan program participants

5.00%

Shares authorized under Employee Stock Purchase and Bonus Plan

100,000

Shares available for purchase

33,454

46,889

Loans outstanding under Employee Stock Purchase and Bonus Plan

12,800,000

11,400,000

Shares available for issuance

146,768

Number of shares of common stock issuable for each vested restricted stock unit

Number of restricted stock units awarded

48,860

1,710

13,648

31,669

1,833

Restricted stock units, grant date fair value

16,600,000

81,600,000

Restricted stock awards, vesting period

'5 years

'3 years

Restricted stock awards, year awards vest

'2014

Weighted average grant-date fair value, share-based awards

$517.24

$412.04

$408.60

$529.59

Unrecognized compensation cost related to nonvested share-based awards

25,300,000

Weighted average remaining service period of share-based awards

'2 years 6 months

'1 year

Fair value of the vested share-based awards

2,500,000

4,700,000

5,300,000

41,300,000

Number of awards issued in connection with acquisition

58,116

154,103

101,875

Expiration period of options

'10 years

Weighted average exercise price of options issued

$225.94

$398.96

Weighted average grant-date fair value of options

$157.15

$140.08

Number of options exercised under option plans

957

39,183

5,660

65,934

Cash proceeds resulting from exercise of stock options

200,000

9,100,000

1,200,000

24,300,000

Current tax benefits resulting from exercise of stock options

100,000

2,500,000

400,000

800,000

Intrinsic value of options exercised

300,000

7,100,000

1,100,000

9,400,000

Expected annual volatility, assumption used in pricing model

19.04%

Risk-free rate, assumption used in pricing model

0.20%

Expected term, assumption used in pricing model

'2 years

Recognized compensation expense related to vested restricted stock awards as of the acquisition date

-61,000,000

Unrecognized compensation on unvested restricted stock and restricted stock units

-20,572,000

-20,600,000

Recognized compensation expense related to restricted stock awards

12,700,000

Unrecognized compensation cost related to nonvested restricted stock awards

4,600,000

Number of Company Converted Warrants issued

225,529

Fair value of Company Converted Warrants

$73,700,000

Number of warrant holders who elected to have their warrants remain outstanding

Number of Company Converted Warrants exercised

225,499

Number of shares of the Company's common stock warrant holders received under the cashless exercise provision of warrants

100,115

Number of shares of the Company's common stock available for purchase related to outstanding warrants

Shareholders_Equity_Schedule_O

Shareholders' Equity (Schedule Of Net Income Per Share) (Details) (USD $)

3 Months Ended

12 Months Ended

In Thousands, except Per Share data, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2011

Sep. 30, 2011

Jun. 30, 2011

Mar. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Earnings Per Share [Line Items]

Net income to shareholders

$98,764

$65,599

$27,756

$88,902

$56,792

$49,653

$89,687

$57,253

$50,176

$53,264

$30,314

$8,272

$281,021

$253,385

$142,026

Adjustment of redeemable noncontrolling interests

1,963

-3,101

Adjusted net income to shareholders

$282,984

$250,284

$142,026

Basic common shares outstanding

12,538

9,640

9,686

Diluted shares outstanding

12,586

9,666

9,726

Basic net income per share (dollars per share)

$6.98

$4.69

$2.24

$9.53

$6.25

$5.33

$8.44

$5.94

$5.21

$5.50

$3.12

$0.85

$22.57

$25.96

$14.66

Diluted net income per share (dollars per share)

$6.95

$4.67

$2.24

$9.50

$6.23

$5.32

$8.42

$5.92

$5.19

$5.48

$3.11

$0.85

$22.48

$25.89

$14.60

Stock Options [Member]

Earnings Per Share [Line Items]

Dilutive potential common shares

Restricted Stock Units (RSUs) [Member]

Earnings Per Share [Line Items]

Dilutive potential common shares

Shareholders_Equity_Summary_Of

Shareholders' Equity (Summary Of Nonvested Share-Based Awards) (Details) (Restricted Stock Units (RSUs) [Member], USD $)	12 Months Ended			8 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013
	2012 Compensation Plan [Member]	2012 Compensation Plan [Member]	2012 Compensation Plan [Member]	Alterra Equity Award Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]	'	'	'	'
Number of awards, nonvested awards, beginning balance	55,580	'	'	154,103
Number of awards, granted	48,860	'	'	'
Number of awards, vested	-5,729	'	'	-77,941
Number of awards, forfeited	'	'	'	-7,751
Number of awards, nonvested awards, ending balance	98,711	55,580	'	68,411
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]	'	'	'	'
Weighted average grant-date fair value, nonvested awards, beginning balance	$388.58	'	'	$529.59
Weighted average grant-date fair value, granted	$517.24	$412.04	$408.60	$529.59
Weighted average grant-date fair value, vested	$428.78	'	'	$529.59
Weighted average grant-date fair value, forfeited	'	'	'	$529.59
Weighted average grant-date fair value, nonvested awards, ending balance	$449.93	$388.58	'	$529.59

Shareholders_Equity_Summary_Of1

Shareholders' Equity (Summary Of Options) (Details) (Stock Options [Member], USD $)	12 Months Ended			8 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013
	Aspen Option Plans [Member]	Aspen Option Plans [Member]	Aspen Option Plans [Member]	Alterra Equity Award Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]	'	'	'	'
Outstanding and exercisable, beginning balance, number of shares	5,678	'	'	101,875
Exercised, number of shares	957	39,183	5,660	65,934
Outstanding and exercisable, ending balance, number of shares	4,721	5,678	'	35,941
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]	'	'	'	'
Outstanding and exercisable, begining balance, weighted average exercise price (dollars per share)	$225.83	'	'	$398.96
Exercised, weighted average exercise price (dollars per share)	$204.83	'	'	$391.64
Outstanding and exercisable, ending balance, weighted average exercise price (dollars per share)	$230.08	$225.83	'	$412.39
Outstanding and exercisable, December 31, 2013, weighted average remaining contractual term	'4 years 5 months	'	'	'2 years 7 months
Outstanding and exercisable, December 31, 2013, intrinsic value	$1.70	'	'	$6

Other_Comprehensive_Income_Cha

Other Comprehensive Income (Change In Accumulated Other Comprehensive Income By Component, Net Of Taxes And Noncontrolling Interests) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'
Accumulated other comprehensive income, beginning balance	$911,337	$660,920	$551,093
Other comprehensive income (loss) before reclassifications	217,750	272,474	130,737
Amounts reclassified from accumulated other comprehensive income	-39,282	-22,057	-20,910
Total other comprehensive income (loss)	178,468	250,417	109,827
Accumulated other comprehensive income, ending balance	1,089,805	911,337	660,920
Unrealized Holding Gains On Available-For-Sale Securities [Member]	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'
Accumulated other comprehensive income, beginning balance	946,933	704,719	581,278
Other comprehensive income (loss) before reclassifications	225,404	266,265	145,782
Amounts reclassified from accumulated other comprehensive income	-40,830	-24,051	-22,341
Total other comprehensive income (loss)	184,574	242,214	123,441
Accumulated other comprehensive income, ending balance	1,131,507	946,933	704,719
Foreign Currency [Member]	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'
Accumulated other comprehensive income, beginning balance	-1,075	-2,614	1,541
Other comprehensive income (loss) before reclassifications	-10,171	1,539	-4,155
Amounts reclassified from accumulated other comprehensive income	0	0	0
Total other comprehensive income (loss)	-10,171	1,539	-4,155
Accumulated other comprehensive income, ending balance	-11,246	-1,075	-2,614
Net Actuarial Pension Loss [Member]	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'
Accumulated other comprehensive income, beginning balance	-34,521	-41,185	-31,726
Other comprehensive income (loss) before reclassifications	2,517	4,670	-10,890
Amounts reclassified from accumulated other comprehensive income	1,548	1,994	1,431
Total other comprehensive income (loss)	4,065	6,664	-9,459
Accumulated other comprehensive income, ending balance	($30,456)	($34,521)	($41,185)

Other_Comprehensive_Income_Sch

Other Comprehensive Income (Schedule Of Tax Expense (Benefit) Of Other Comprehensive Income) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Other Comprehensive Income (Loss), Tax [Abstract]	'	'	'
Net holding gains arising during the period	$93,837	$122,524	$68,064
Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period	-34	-49	2,107
Reclassification adjustments for net gains included in net income	-16,382	-10,881	-10,890
Change in net unrealized gains on investments	77,421	111,594	59,281
Change in foreign currency translation adjustments	-1,619	-446	250
Change in net actuarial pension loss	1,015	1,991	-3,153
Total	$76,817	$113,139	$56,378

Other_Comprehensive_Income_Amo

Other Comprehensive Income (Amounts Reclassified From Accumulated Other Comprehensive Income Into Income, By Component) (Details) (USD $)

3 Months Ended

12 Months Ended

In Thousands, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2011

Sep. 30, 2011

Jun. 30, 2011

Mar. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]

Other-than-temporary impairment losses recognized in net income

($4,706)

($12,078)

($20,196)

Net realized investment gains, excluding other-than-temporary impairment losses

67,858

43,671

56,053

Income Before Income Taxes

361,743

312,050

190,196

Underwriting, acquisition and insurance expenses

-1,312,312

-929,472

-810,179

Income Taxes

-77,898

-53,802

-41,710

Net Income

98,939

66,967

28,676

89,263

58,093

51,674

90,768

57,713

52,307

54,669

31,649

9,861

283,845

258,248

148,486

Reclassification Out Of Accumulated Other Comprehensive Income [Member] | Unrealized Holding Gains On Available-For-Sale Securities [Member]

Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]

Other-than-temporary impairment losses recognized in net income

-4,706

-12,078

-20,196

Net realized investment gains, excluding other-than-temporary impairment losses

61,918

47,010

53,427

Income Before Income Taxes

57,212

34,932

33,231

Income Taxes

-16,382

-10,881

-10,890

Net Income

40,830

24,051

22,341

Reclassification Out Of Accumulated Other Comprehensive Income [Member] | Net Actuarial Pension Loss [Member]

Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]

Underwriting, acquisition and insurance expenses

-1,934

-2,590

-1,908

Income Taxes

386

596

477

Net Income

($1,548)

($1,994)

($1,431)

Derivatives_Narrative_Details

Derivatives (Narrative) (Details) (USD $)	12 Months Ended
Derivatives (Narrative) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]	'	'	'
Credit default swap, notional value	$33,100,000	$33,100,000	'
Credit default swap, exposure to loss, maximum per reference entity	20,000,000	'	'
Credit default swap, fair value	2,200,000	12,700,000	'
Gain (loss) on derivative instrument recognized in earnings	10,460,000	16,641,000	-4,103,000
Derivative credit risk settlement payments	$16,900,000	'	'
Weighted-average expected default rate	0.35%	3.00%	'
Weighted-average future expected recovery rate	39.00%	39.00%	'
Minimum [Member]	'	'	'
Derivatives, Fair Value [Line Items]	'	'	'
Expected default rate	0.02%	1.00%	'
Future expected recovery rate	20.00%	20.00%	'
Maximum [Member]	'	'	'
Derivatives, Fair Value [Line Items]	'	'	'
Expected default rate	4.00%	43.00%	'
Future expected recovery rate	40.00%	40.00%	'

Fair_Value_Measurements_Narrat

Fair Value Measurements (Narrative) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fair value, level 1 to level 2 transfers, amount	$0	$0
Fair value, level 2 to level 1 transfers, amount	0	0
Assets measured at fair value on a non-recurring basis	0	0
Liabilities measured at fair value on a non-recurring basis	$0	$0
Short-Term Investments [Member] \| Maximum [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Investment maturity period	'1 year	'

Fair_Value_Measurements_Balanc

Fair Value Measurements (Balances Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	$10,142,536	$4,979,283
Equity securities	3,251,798	2,406,951
Short-term investments	1,452,288	973,330
Derivative contracts	2,200	12,700
Fair Value, Measurements, Recurring [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	10,142,536	4,979,283
Equity securities	3,251,798	2,406,951
Short-term investments	1,452,288	973,330
Total investments available-for-sale	14,846,622	8,359,564
Derivative contracts	2,230	12,690
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	0	0
Equity securities	3,251,798	2,406,951
Short-term investments	1,312,561	888,758
Total investments available-for-sale	4,564,359	3,295,709
Derivative contracts	0	0
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	10,142,536	4,979,283
Equity securities	0	0
Short-term investments	139,727	84,572
Total investments available-for-sale	10,282,263	5,063,855
Derivative contracts	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	0	0
Equity securities	0	0
Short-term investments	0	0
Total investments available-for-sale	0	0
Derivative contracts	2,230	12,690
Fair Value, Measurements, Recurring [Member] \| U.S. Treasury Securities And Obligations Of U.S. Government Agencies [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	1,194,231	317,507
Fair Value, Measurements, Recurring [Member] \| U.S. Treasury Securities And Obligations Of U.S. Government Agencies [Member] \| Level 1 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] \| U.S. Treasury Securities And Obligations Of U.S. Government Agencies [Member] \| Level 2 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	1,194,231	317,507
Fair Value, Measurements, Recurring [Member] \| U.S. Treasury Securities And Obligations Of U.S. Government Agencies [Member] \| Level 3 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Obligations Of States, Municipalities And Political Subdivisions [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	3,075,715	2,831,562
Fair Value, Measurements, Recurring [Member] \| Obligations Of States, Municipalities And Political Subdivisions [Member] \| Level 1 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Obligations Of States, Municipalities And Political Subdivisions [Member] \| Level 2 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	3,075,715	2,831,562
Fair Value, Measurements, Recurring [Member] \| Obligations Of States, Municipalities And Political Subdivisions [Member] \| Level 3 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Foreign Governments [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	1,461,054	556,608
Fair Value, Measurements, Recurring [Member] \| Foreign Governments [Member] \| Level 1 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Foreign Governments [Member] \| Level 2 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	1,461,054	556,608
Fair Value, Measurements, Recurring [Member] \| Foreign Governments [Member] \| Level 3 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Commercial Mortgage-Backed Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	367,821	'
Fair Value, Measurements, Recurring [Member] \| Commercial Mortgage-Backed Securities [Member] \| Level 1 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	0	'
Fair Value, Measurements, Recurring [Member] \| Commercial Mortgage-Backed Securities [Member] \| Level 2 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	367,821	'
Fair Value, Measurements, Recurring [Member] \| Commercial Mortgage-Backed Securities [Member] \| Level 3 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	0	'
Fair Value, Measurements, Recurring [Member] \| Residential Mortgage-Backed Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	870,248	215,377
Fair Value, Measurements, Recurring [Member] \| Residential Mortgage-Backed Securities [Member] \| Level 1 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Residential Mortgage-Backed Securities [Member] \| Level 2 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	870,248	215,377
Fair Value, Measurements, Recurring [Member] \| Residential Mortgage-Backed Securities [Member] \| Level 3 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Asset-Backed Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	188,289	14,345
Fair Value, Measurements, Recurring [Member] \| Asset-Backed Securities [Member] \| Level 1 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Asset-Backed Securities [Member] \| Level 2 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	188,289	14,345
Fair Value, Measurements, Recurring [Member] \| Asset-Backed Securities [Member] \| Level 3 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Corporate Bonds [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	2,985,178	1,043,884
Fair Value, Measurements, Recurring [Member] \| Corporate Bonds [Member] \| Level 1 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Corporate Bonds [Member] \| Level 2 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	2,985,178	1,043,884
Fair Value, Measurements, Recurring [Member] \| Corporate Bonds [Member] \| Level 3 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Fixed maturities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Insurance, Banks And Other Financial Institutions [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Equity securities	1,015,083	898,067
Fair Value, Measurements, Recurring [Member] \| Insurance, Banks And Other Financial Institutions [Member] \| Level 1 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Equity securities	1,015,083	898,067
Fair Value, Measurements, Recurring [Member] \| Insurance, Banks And Other Financial Institutions [Member] \| Level 2 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Equity securities	0	0
Fair Value, Measurements, Recurring [Member] \| Insurance, Banks And Other Financial Institutions [Member] \| Level 3 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Equity securities	0	0
Fair Value, Measurements, Recurring [Member] \| Industrial, Consumer And All Other [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Equity securities	2,236,715	1,508,884
Fair Value, Measurements, Recurring [Member] \| Industrial, Consumer And All Other [Member] \| Level 1 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Equity securities	2,236,715	1,508,884
Fair Value, Measurements, Recurring [Member] \| Industrial, Consumer And All Other [Member] \| Level 2 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Equity securities	0	0
Fair Value, Measurements, Recurring [Member] \| Industrial, Consumer And All Other [Member] \| Level 3 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Equity securities	$0	$0

Fair_Value_Measurements_Summar

Fair Value Measurements (Summary Of Changes In Level 3 Liabilities Measured At Fair Value On A Recurring Basis) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Fair Value Disclosures [Abstract]	'		'
Derivatives, beginning of period	$12,690		$29,331
Total gains included in net income	-10,460		-16,641
Total gains included in other comprehensive income	0		0
Transfers into Level 3	0		0
Transfers out of Level 3	0		0
Derivatives, end of period	2,230		12,690
Net unrealized gains included in net income relating to liabilities held at December 31, 2013 and 2012	$10,460	[1]	$16,641	[1]

[1]	Included in net investment income in the consolidated statements of income and comprehensive income.

Reinsurance_Narrative_Details

Reinsurance (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
	reinsurer	reinsurer	Dec. 31, 2011
Reinsurance Disclosures [Line Items]	'	'	'
Number of largest company reinsurers	10	10	'
Impact on the reinsurance recoverable on unpaid losses, net	$0	$0	$0
Reinsurance recoverables	269,400,000	165,800,000	159,800,000
Percentage of ceded earned premiums to gross earned premiums	18.00%	12.00%	11.00%
Ten Largest Reinsurers [Member]	'	'	'
Reinsurance Disclosures [Line Items]	'	'	'
Recoverable balances as a percentage of the total balance	62.00%	74.00%	'
Fairfax Financial Group [Member]	'	'	'
Reinsurance Disclosures [Line Items]	'	'	'
Recoverable balances as a percentage of the total balance	10.00%	'	'
Markel International Commutations [Member]	'	'	'
Reinsurance Disclosures [Line Items]	'	'	'
Valuation allowances and reserves, deductions	'	'	78,500,000
Commutation adjustments related to termination of ceded reinsurance contracts	'	'	$40,000,000

Reinsurance_Reinsurance_Allowa

Reinsurance (Reinsurance Allowance For Doubtful Accounts) (Details) (Allowance For Reinsurance Recoverable [Member], USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Allowance For Reinsurance Recoverable [Member]	'	'	'
Valuation and Qualifying Accounts Disclosure [Line Items]	'	'	'
Reinsurance allowance, beginning of year	$71,148	$69,067	$155,190
Additions	13,621	24,179	8,504
Deductions	-8,559	-22,098	-94,627
Reinsurance allowance, end of year	$76,210	$71,148	$69,067

Reinsurance_Effect_Of_Reinsura

Reinsurance (Effect Of Reinsurance On Premiums Written And Earned) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reinsurance Disclosures [Abstract]	'	'	'
Direct premiums written	$3,143,957	$2,115,353	$1,957,397
Direct premiums earned	2,947,812	2,057,735	1,873,512
Assumed premiums written	776,269	398,328	333,854
Assumed premiums earned	1,016,853	376,186	338,183
Ceded premiums written	-683,543	-299,555	-249,413
Ceded premiums earned	-733,049	-286,793	-232,355
Net premiums written	3,236,683	2,214,126	2,041,838
Net premiums earned	$3,231,616	$2,147,128	$1,979,340

Commitments_And_Contingencies_1

Commitments And Contingencies (Narrative) (Details) (USD $)	12 Months Ended					1 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013	Sep. 30, 2013	Feb. 28, 2014
				New Point VI Limited [Member]	New Point VI Limited [Member]	New Point VI Limited [Member]
						Subsequent Event [Member]
Other Commitments [Line Items]	'	'	'	'	'	'
Maximum remaining term of noncancelable operating leases	'21 years	'	'	'	'	'
Rental expense	$35.30	$28.10	$25.80	'	'	'
Percentage of issued and outstanding common shares	'	'	'	34.00%	'	'
Capital contribution under subscription agreement	'	'	'	7.8	'	'
Commitment under subscription agreement	'	'	'	67.2	75	'
Additional investment under subscription agreement	'	'	'	'	'	$6.50

Commitments_And_Contingencies_2

Commitments And Contingencies (Minimum Annual Rental Commitments) (Details) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]	'
2014	$32,783
2015	29,114
2016	22,977
2017	27,955
2018	26,440
2019 and thereafter	160,454
Total	$299,723

Statutory_Financial_Informatio2

Statutory Financial Information (Narrative) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013
Statutory Accounting Practices [Line Items]	'
Amount of cash and investments held as funds at Lloyd's	972.5
United States [Member]	'
Statutory Accounting Practices [Line Items]	'
Amount available for dividend payment	296.9
United Kingdom [Member]	'
Statutory Accounting Practices [Line Items]	'
Advance notice to declare and pay dividend under PRA	'14 days
Bermuda [Member]	'
Statutory Accounting Practices [Line Items]	'
Amount available for dividend payment	375.8

Statutory_Financial_Informatio3

Statutory Financial Information (Actual Statutory Capital And Surplus) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
United States [Member]	'	'
Statutory Accounting Practices [Line Items]	'	'
Actual statutory capital and surplus	$2,399,356	$1,455,077
United Kingdom [Member]	'	'
Statutory Accounting Practices [Line Items]	'	'
Actual statutory capital and surplus	517,571	485,043
Bermuda [Member]	'	'
Statutory Accounting Practices [Line Items]	'	'
Actual statutory capital and surplus	1,503,004	'
Other Countries [Member]	'	'
Statutory Accounting Practices [Line Items]	'	'
Actual statutory capital and surplus	$171,410	'

Statutory_Financial_Informatio4

Statutory Financial Information (Statutory Net Income (Loss)) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
United States [Member]	'	'	'
Statutory Accounting Practices [Line Items]	'	'	'
Statutory net income (loss)	$235,009	$127,179	$180,744
United Kingdom [Member]	'	'	'
Statutory Accounting Practices [Line Items]	'	'	'
Statutory net income (loss)	117,020	82,573	18,386
Bermuda [Member]	'	'	'
Statutory Accounting Practices [Line Items]	'	'	'
Statutory net income (loss)	93,953	'	'
Other Countries [Member]	'	'	'
Statutory Accounting Practices [Line Items]	'	'	'
Statutory net income (loss)	($12,617)	'	'

Segment_Reporting_Disclosures_1

Segment Reporting Disclosures (Narrative) (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
	segment	Dec. 31, 2012	Dec. 31, 2011
Revenue, Major Customer [Line Items]	'	'	'
Number of segments of the specialty insurance marketplace in which the Company historically operated	3	'	'
Percentage of gross premiums written	100.00%	100.00%	100.00%
Subsequent Event [Member]	'	'	'
Revenue, Major Customer [Line Items]	'	'	'
Number of operating segments beginning in 2014	3	'	'
Top Three Independent Brokers [Member]	'	'	'
Revenue, Major Customer [Line Items]	'	'	'
Percentage of gross premiums written	19.00%	'	'
Top Three Independent Brokers [Member] \| Alterra [Member]	'	'	'
Revenue, Major Customer [Line Items]	'	'	'
Percentage of gross premiums written	40.00%	'	'

Segment_Reporting_Disclosures_2

Segment Reporting Disclosures (Summary Of Gross Written Premiums By Country) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]	'	'	'
Gross written premiums	$3,920,226	$2,513,681	$2,291,251
Percentage of gross premiums written	100.00%	100.00%	100.00%
United States [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Gross written premiums	2,934,868	1,768,011	1,590,238
Percentage of gross premiums written	75.00%	70.00%	69.00%
United Kingdom [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Gross written premiums	245,143	147,891	139,349
Percentage of gross premiums written	6.00%	6.00%	6.00%
Canada [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Gross written premiums	128,420	120,542	126,434
Percentage of gross premiums written	3.00%	5.00%	6.00%
Other Countries [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Gross written premiums	$611,795	$477,237	$435,230
Percentage of gross premiums written	16.00%	19.00%	19.00%

Segment_Reporting_Disclosures_3

Segment Reporting Disclosures (Company's Segment Disclosures) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Segment Reporting Information [Line Items]	'		'		'
Gross premium volume	$3,920,226		$2,513,681		$2,291,251
Net written premiums	3,236,683		2,214,126		2,041,838
Earned premiums	3,231,616		2,147,128		1,979,340
Losses and loss adjustment expenses	-1,816,273		-1,154,068		-1,209,986
Transaction costs and other acquisition-related expenses	-75,140	[1],[2]	0		0
Transaction costs	-15,981	[2]	'		'
Other acquisition related costs, severance costs	-31,734	[2]	'		'
Other acquisition related costs, stay bonuses	-14,804	[2]	'		'
Other acquisition related costs, other compensation costs	-12,621	[2]	'		'
Amortization of policy acquisition costs	-471,915		-428,109		-479,454
Prospective adoption of FASB ASU No. 2010-26	0		-43,093	[3]	0
Other amortization of policy acquisition costs	-471,915		-385,016		-479,454
Other operating expenses	-765,257		-501,363		-330,725
Underwriting profit (loss)	103,031		63,588		-40,825
Net investment income	317,373		282,107		263,676
Net realized investment gains	63,152		31,593		35,857
Other revenues (insurance)	24,494		49,932		33,545
Other expenses (insurance)	-50,278		-45,292		-33,722
Segment profit (loss)	457,772		381,928		258,531
Other revenues (Markel Ventures)	686,448		489,352		317,532
Other expenses (Markel Ventures)	-613,250		-432,956		-275,324
Amortization of intangible assets	-55,223		-33,512		-24,291
Interest expense	-114,004		-92,762		-86,252
Income Before Income Taxes	361,743		312,050		190,196
U.S. GAAP combined ratio	97.00%	[4]	97.00%	[4]	102.00%	[4]
Excess And Surplus Lines [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Gross premium volume	1,070,520		956,273		893,427
Net written premiums	911,870		811,601		772,279
Earned premiums	856,629		793,159		756,306
Losses and loss adjustment expenses	-341,661		-388,793		-318,583
Transaction costs and other acquisition-related expenses	0	[1]	'		'
Amortization of policy acquisition costs	-147,996		'		-172,269
Prospective adoption of FASB ASU No. 2010-26	'		-17,456	[3]	'
Other amortization of policy acquisition costs	'		-135,573		'
Other operating expenses	-195,464		-201,196		-156,419
Underwriting profit (loss)	171,508		50,141		109,035
Net investment income	0		0		0
Net realized investment gains	0		0		0
Other revenues (insurance)	0		0		0
Other expenses (insurance)	0		0		0
Segment profit (loss)	171,508		50,141		109,035
U.S. GAAP combined ratio	80.00%	[4]	94.00%	[4]	86.00%	[4]
Specialty Admitted [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Gross premium volume	899,996		669,692		572,392
Net written premiums	855,381		628,147		543,213
Earned premiums	744,993		588,758		527,293
Losses and loss adjustment expenses	-410,068		-381,870		-364,144
Transaction costs and other acquisition-related expenses	0	[1]	'		'
Amortization of policy acquisition costs	-137,181		'		-129,731
Prospective adoption of FASB ASU No. 2010-26	'		-13,577	[3]	'
Other amortization of policy acquisition costs	'		-96,770		'
Other operating expenses	-176,346		-143,377		-78,509
Underwriting profit (loss)	21,398		-46,836		-45,091
Net investment income	0		0		0
Net realized investment gains	0		0		0
Other revenues (insurance)	13,648		44,968		33,545
Other expenses (insurance)	-17,087		-41,425		-33,722
Segment profit (loss)	17,959		-43,293		-45,268
U.S. GAAP combined ratio	97.00%	[4]	108.00%	[4]	109.00%	[4]
London Insurance Market [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Gross premium volume	914,480		887,720		825,301
Net written premiums	792,158		774,383		726,359
Earned premiums	781,637		765,216		695,753
Losses and loss adjustment expenses	-386,416		-362,330		-531,625
Transaction costs and other acquisition-related expenses	0	[1]	'		'
Amortization of policy acquisition costs	-149,191		'		-177,454
Prospective adoption of FASB ASU No. 2010-26	'		-12,060	[3]	'
Other amortization of policy acquisition costs	'		-152,673		'
Other operating expenses	-150,537		-156,587		-96,149
Underwriting profit (loss)	95,493		81,566		-109,475
Net investment income	0		0		0
Net realized investment gains	0		0		0
Other revenues (insurance)	5,002		4,964		0
Other expenses (insurance)	-5,065		-3,867		0
Segment profit (loss)	95,430		82,663		-109,475
U.S. GAAP combined ratio	88.00%	[4]	89.00%	[4]	116.00%	[4]
Alterra [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Gross premium volume	1,035,190		'		'
Net written premiums	677,233		'		'
Earned premiums	848,317		'		'
Losses and loss adjustment expenses	-647,546		'		'
Transaction costs and other acquisition-related expenses	-75,140	[1]	'		'
Amortization of policy acquisition costs	-37,547		'		'
Other operating expenses	-243,022		'		'
Underwriting profit (loss)	-154,938		'		'
Net investment income	0		'		'
Net realized investment gains	0		'		'
Other revenues (insurance)	4,714		'		'
Other expenses (insurance)	0		'		'
Segment profit (loss)	-150,224		'		'
U.S. GAAP combined ratio	118.00%	[4]	'		'
Other Insurance (Discontinued Lines) [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Gross premium volume	40		-4		131
Net written premiums	41		-5		-13
Earned premiums	40		-5		-12
Losses and loss adjustment expenses	-30,582		-21,075		4,366
Transaction costs and other acquisition-related expenses	0	[1]	'		'
Amortization of policy acquisition costs	0		'		0
Prospective adoption of FASB ASU No. 2010-26	'		0	[3]	'
Other amortization of policy acquisition costs	'		0		'
Other operating expenses	112		-203		352
Underwriting profit (loss)	-30,430		-21,283		4,706
Net investment income	0		0		0
Net realized investment gains	0		0		0
Other revenues (insurance)	1,130		0		0
Other expenses (insurance)	-28,126		0		0
Segment profit (loss)	-57,426		-21,283		4,706
U.S. GAAP combined ratio - not meaniningful	'NM	[4],[5]	'NM	[4],[6]	'NM	[4],[6]
Investing [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Gross premium volume	0		0		0
Net written premiums	0		0		0
Earned premiums	0		0		0
Losses and loss adjustment expenses	0		0		0
Transaction costs and other acquisition-related expenses	0	[1]	'		'
Amortization of policy acquisition costs	0		'		0
Prospective adoption of FASB ASU No. 2010-26	'		0	[3]	'
Other amortization of policy acquisition costs	'		0		'
Other operating expenses	0		0		0
Underwriting profit (loss)	0		0		0
Net investment income	317,373		282,107		263,676
Net realized investment gains	63,152		31,593		35,857
Other revenues (insurance)	0		0		0
Other expenses (insurance)	0		0		0
Segment profit (loss)	$380,525		$313,700		$299,533

[1]	In connection with the acquisition of Alterra, the Company incurred transaction costs of $16.0 million for the year ended DecemberB 31, 2013, which primarily consist of due diligence, legal and investment banking costs. Additionally, the Company incurred severance costs of $31.7 million, stay bonuses of $14.8 million and other compensation costs totaling $12.6 million related to the acceleration of certain long-term incentive compensation awards and restricted stock awards that were granted by Alterra prior to the acquisition.
[2]	In connection with the acquisition of Alterra, the Company incurred transaction costs of $16.0 million for the year ended December 31, 2013, which primarily consist of due diligence, legal and investment banking costs. Additionally, the Company incurred severance costs of $31.7 million, stay bonuses of $14.8 million and other compensation costs totaling $12.6 million related to the acceleration of certain long-term incentive compensation awards and restricted stock awards that were granted by Alterra prior to the acquisition.
[3]	Effective January 1, 2012, the Company prospectively adopted FASB ASU No. 2010-26, Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts. At December 31, 2011, deferred policy acquisition costs included $43.1 million of costs that no longer met the criteria for deferral as of January 1, 2012 and were recognized into income during 2012, consistent with policy terms.
[4]	The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums.
[5]	NM b Ratio is not meaningful
[6]	NM b Ratio is not meaningful.

Segment_Reporting_Disclosures_4

Segment Reporting Disclosures (Summary Of Deferred Policy Acquisition Costs, Unearned Premiums And Unpaid Losses And Loss Adjustment Expenses) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]	'	'	'	'
Deferred policy acquisition costs	$260,967	$157,465	$194,674	$188,783
Unearned premiums	2,127,115	1,000,261	'	'
Unpaid losses and loss adjustment expenses	10,262,056	5,371,426	'	'
Excess And Surplus Lines [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Deferred policy acquisition costs	69,849	59,158	'	'
Unearned premiums	469,148	410,731	'	'
Unpaid losses and loss adjustment expenses	1,998,359	2,152,253	'	'
Specialty Admitted [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Deferred policy acquisition costs	77,118	43,810	'	'
Unearned premiums	391,606	280,811	'	'
Unpaid losses and loss adjustment expenses	878,564	796,093	'	'
London Insurance Market [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Deferred policy acquisition costs	53,420	54,497	'	'
Unearned premiums	321,383	308,719	'	'
Unpaid losses and loss adjustment expenses	1,909,612	1,958,249	'	'
Alterra [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Deferred policy acquisition costs	60,580	'	'	'
Unearned premiums	944,978	'	'	'
Unpaid losses and loss adjustment expenses	4,996,722	'	'	'
Other Insurance (Discontinued Lines) [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Deferred policy acquisition costs	0	0	'	'
Unearned premiums	0	0	'	'
Unpaid losses and loss adjustment expenses	$478,799	$464,831	'	'

Segment_Reporting_Disclosures_5

Segment Reporting Disclosures (Summary Of Segment Earned Premiums) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	$3,231,616	$2,147,128	$1,979,340
Excess And Surplus Lines [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	856,629	793,159	756,306
Specialty Admitted [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	744,993	588,758	527,293
London Insurance Market [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	781,637	765,216	695,753
Alterra [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	848,317	'	'
Other Insurance (Discontinued Lines) [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	40	-5	-12
Property [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	791,607	517,489	470,281
Property [Member] \| Excess And Surplus Lines [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	115,773	109,607	103,406
Property [Member] \| Specialty Admitted [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	230,068	148,311	135,077
Property [Member] \| London Insurance Market [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	230,278	259,571	231,798
Property [Member] \| Alterra [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	215,488	'	'
Property [Member] \| Other Insurance (Discontinued Lines) [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	0	0	0
Casualty [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	783,642	518,276	472,432
Casualty [Member] \| Excess And Surplus Lines [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	253,195	227,880	214,565
Casualty [Member] \| Specialty Admitted [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	232,868	163,955	140,805
Casualty [Member] \| London Insurance Market [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	124,843	126,441	117,062
Casualty [Member] \| Alterra [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	172,736	'	'
Casualty [Member] \| Other Insurance (Discontinued Lines) [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	0	0	0
Professional Liability [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	550,968	351,753	370,232
Professional Liability [Member] \| Excess And Surplus Lines [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	208,732	189,199	197,131
Professional Liability [Member] \| Specialty Admitted [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	0	0	0
Professional Liability [Member] \| London Insurance Market [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	176,302	162,554	173,101
Professional Liability [Member] \| Alterra [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	165,934	'	'
Professional Liability [Member] \| Other Insurance (Discontinued Lines) [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	0	0	0
Workers' Compensation [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	284,694	242,021	200,797
Workers' Compensation [Member] \| Excess And Surplus Lines [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	0	0	0
Workers' Compensation [Member] \| Specialty Admitted [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	253,347	242,021	200,797
Workers' Compensation [Member] \| London Insurance Market [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	0	0	0
Workers' Compensation [Member] \| Alterra [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	31,347	'	'
Workers' Compensation [Member] \| Other Insurance (Discontinued Lines) [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	0	0	0
Other [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	820,705	517,589	465,598
Other [Member] \| Excess And Surplus Lines [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	278,929	266,473	241,204
Other [Member] \| Specialty Admitted [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	28,710	34,471	50,614
Other [Member] \| London Insurance Market [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	250,214	216,650	173,792
Other [Member] \| Alterra [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	262,812	'	'
Other [Member] \| Other Insurance (Discontinued Lines) [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Earned premiums	$40	($5)	($12)

Segment_Reporting_Disclosures_6

Segment Reporting Disclosures (Segment Assets To The Company's Consolidated Balance Sheets) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]	'	'	'
Assets	$23,955,511	$12,556,588	$11,532,103
Markel Ventures Operations [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Assets	936,448	891,586	630,281
Segment Assets [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Assets	23,019,063	11,665,002	10,901,822
Segment Assets [Member] \| Investing [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Assets	17,550,332	9,277,697	8,692,391
Segment Assets [Member] \| Underwriting [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Assets	$5,468,731	$2,387,305	$2,209,431

Other_Revenues_And_Other_Expen2

Other Revenues And Other Expenses (Summary Of Other Revenues And Other Expenses By Component) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Other Revenues and Other Expenses [Line Items]	'	'	'
Other revenues	$710,942	$539,284	$351,077
Other expenses	663,528	478,248	309,046
Insurance Operations [Member]	'	'	'
Other Revenues and Other Expenses [Line Items]	'	'	'
Other revenues	24,494	49,932	33,545
Other expenses	50,278	45,292	33,722
Markel Ventures Operations [Member]	'	'	'
Other Revenues and Other Expenses [Line Items]	'	'	'
Other revenues	686,448	489,352	317,532
Other expenses	613,250	432,956	275,324
Managing General Agent Operations [Member] \| Insurance Operations [Member]	'	'	'
Other Revenues and Other Expenses [Line Items]	'	'	'
Other revenues	17,399	48,056	31,136
Other expenses	20,382	43,069	30,728
Life And Annuity [Member] \| Insurance Operations [Member]	'	'	'
Other Revenues and Other Expenses [Line Items]	'	'	'
Other revenues	1,130	0	0
Other expenses	28,126	0	0
Other [Member] \| Insurance Operations [Member]	'	'	'
Other Revenues and Other Expenses [Line Items]	'	'	'
Other revenues	5,965	1,876	2,409
Other expenses	1,770	2,223	2,994
Manufacturing [Member] \| Markel Ventures Operations [Member]	'	'	'
Other Revenues and Other Expenses [Line Items]	'	'	'
Other revenues	495,138	366,886	214,668
Other expenses	437,712	328,484	192,503
Non-Manufacturing [Member] \| Markel Ventures Operations [Member]	'	'	'
Other Revenues and Other Expenses [Line Items]	'	'	'
Other revenues	191,310	122,466	102,864
Other expenses	$175,538	$104,472	$82,821

Employee_Benefit_Plans_Narrati

Employee Benefit Plans (Narrative) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
	funds
	employee
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Expenses relating to defined contribution plans	$24.30	$19.10	$17.80
Consecutive number of years	'3 years	'	'
Number of years preceding retirement	'10 years	'	'
Tax benefit of the net actuarial pension loss recognized as a component of accumulated other comprehensive income	12.4	13.5	'
Percentage of reasonable rate of return on fixed maturities	4.50%	'	'
Expected rate at which equity securities outperform fixed maturities in plan assets	3.50%	'	'
Amortization of the net actuarial pension loss included as a component of accumulated other comprehensive income	1.6	'	'
Number of equity security index funds	2	'	'
Percentage of equity securities invested in UK companies	25.00%	'	'
Percentage of equity securities invested in other markets	75.00%	'	'
Pension plan obligations, maturity period	'30 years	'	'
Number of fixed maturity index funds	5	'	'
Accumulated benefit obligation	146	133.5	'
Expected plan contributions in 2014	5.6	'	'
Expected benefits to be paid in 2014	3.8	'	'
Expected benefits to be paid in 2015	3.9	'	'
Expected benefits to be paid in 2016	4	'	'
Expected benefits to be paid in 2017	4.1	'	'
Expected benefits to be paid in 2018	4.2	'	'
Aggregate benefits expected to be paid from 2019 to 2023	22.5	'	'
Union employees covered by multiemployer plan, number of employees	90	'	'
Multiemployer plan, withdrawal obligation	'	'	2
Multiemployer plan, withdrawal obligation payment	$0.10	$2.40	'
Multiemployer plan, percentage of determined deficit payment	'	95.00%	'
United Kingdom [Member] \| Foreign Governments [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Number of fixed maturity index funds	2	'	'
United Kingdom [Member] \| Corporate Securities [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Number of fixed maturity index funds	2	'	'
Other Foreign Government Securities [Member] \| Foreign Governments [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Number of fixed maturity index funds	1	'	'
Equity Securities [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Target asset allocation, percent	54.00%	'	'
Actual asset allocation, percent	63.00%	61.00%	'
Fixed Maturities [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Target asset allocation, percent	46.00%	'	'
Actual asset allocation, percent	37.00%	39.00%	'
Minimum [Member] \| Corporate Bond [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Investment maturity period	'15 years	'	'

Employee_Benefit_Plans_Schedul

Employee Benefit Plans (Schedule Of Amounts Recognized On The Consolidated Balance Sheets) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan, Change in Projected Benefit Obligation and Plan Assets [Roll Forward]	'	'	'
Fair value of plan assets at beginning of period	$164,090	'	'
Service cost	0	361	1,357
Interest cost	6,533	6,815	7,115
Fair value of plan assets at end of year	189,437	164,090	'
Funded status of the plan	26,427	12,763	'
Net actuarial pension loss	42,941	48,021	'
Total	69,368	60,784	'
Change In Projected Benefit Obligation [Member]	'	'	'
Defined Benefit Plan, Change in Projected Benefit Obligation and Plan Assets [Roll Forward]	'	'	'
Projected benefit obligation at beginning of period	151,327	141,163	'
Service cost	0	361	'
Interest cost	6,533	6,815	'
Participant contributions	0	81	'
Benefits paid	-3,542	-2,938	'
Actuarial loss (gain)	5,459	-601	'
Effect of foreign currency rate changes	3,233	6,446	'
Projected benefit obligation at end of year	163,010	151,327	'
Change In Plan Assets [Member]	'	'	'
Defined Benefit Plan, Change in Projected Benefit Obligation and Plan Assets [Roll Forward]	'	'	'
Fair value of plan assets at beginning of period	164,090	139,325	'
Actual gain on plan assets	19,430	15,251	'
Employer contributions	5,338	5,737	'
Participant contributions	0	81	'
Benefits paid	-3,542	-2,938	'
Effect of foreign currency rate changes	4,121	6,634	'
Fair value of plan assets at end of year	$189,437	$164,090	'

Employee_Benefit_Plans_Schedul1

Employee Benefit Plans (Schedule Of Net Periodic Benefit Cost And Weighted Average Assumptions) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]	'	'	'
Service cost	$0	$361	$1,357
Interest cost	6,533	6,815	7,115
Expected return on plan assets	-10,825	-9,788	-9,834
Amortization of net actuarial pension loss	1,934	2,590	1,908
Net periodic benefit cost (income)	($2,358)	($22)	$546
Discount rate	4.70%	4.50%	4.80%
Expected return on plan assets, percent	6.60%	6.60%	6.60%
Rate of compensation increase	3.20%	3.10%	3.20%

Employee_Benefit_Plans_Summary

Employee Benefit Plans (Summary Of Fair Value Of Plan Assets) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]	'	'
Plan assets	$189,437	$164,090
Fixed Maturities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Plan assets	70,997	64,357
Equity Securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Plan assets	118,431	99,727
Cash And Cash Equivalents [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Plan assets	$9	$6

Markel_Corporation_Parent_Comp2

Markel Corporation (Parent Company Only) Financial Information (Schedule Of Condensed Balance Sheets) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed Financial Statements, Captions [Line Items]	'	'	'	'
Fixed maturities	$10,142,536	$4,979,283	'	'
Equity securities	3,251,798	2,406,951	'	'
Short-term investments (estimated fair value approximates cost)	1,452,288	973,330	'	'
Total Investments	14,846,622	8,359,564	'	'
Cash and cash equivalents	1,978,526	863,766	703,259	690,281
Restricted cash and cash equivalents	786,926	109,415	'	'
Net deferred tax asset	103,717	'	'	'
Other assets	1,067,922	663,019	'	'
Total Assets	23,955,511	12,556,588	11,532,103	'
Net deferred tax liability	'	168,903	'	'
Other liabilities	777,850	613,897	'	'
Total Liabilities	17,205,318	8,581,346	'	'
Total Shareholders' Equity	6,673,577	3,888,657	'	'
Total Liabilities and Equity	23,955,511	12,556,588	'	'
Parent Company [Member]	'	'	'	'
Condensed Financial Statements, Captions [Line Items]	'	'	'	'
Fixed maturities	67,363	84,158	'	'
Equity securities	392,123	426,409	'	'
Short-term investments (estimated fair value approximates cost)	654,971	664,986	'	'
Total Investments	1,114,457	1,175,553	'	'
Cash and cash equivalents	207,352	237,816	280,604	181,956
Restricted cash and cash equivalents	1,010	662	'	'
Receivables	14,326	13,994	'	'
Investments in consolidated subsidiaries	6,826,790	3,656,577	'	'
Notes receivable from subsidiaries	168,611	173,913	'	'
Income taxes receivable	5,320	6,623	'	'
Net deferred tax asset	0	6,595	'	'
Other assets	102,193	99,107	'	'
Total Assets	8,440,059	5,370,840	'	'
Senior long-term debt	1,633,873	1,388,029	'	'
Net deferred tax liability	40,443	0	'	'
Other liabilities	92,166	94,154	'	'
Total Liabilities	1,766,482	1,482,183	'	'
Total Shareholders' Equity	6,673,577	3,888,657	'	'
Total Liabilities and Equity	$8,440,059	$5,370,840	'	'

Markel_Corporation_Parent_Comp3

Markel Corporation (Parent Company Only) Financial Information (Schedule of Condensed Balance Sheets - Parentheticals) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]	'	'
Fixed maturities, amortized cost	$10,129,141	$4,562,278
Equity securities, cost	1,566,553	1,387,305
Parent Company [Member]	'	'
Condensed Financial Statements, Captions [Line Items]	'	'
Fixed maturities, amortized cost	66,154	80,631
Equity securities, cost	$197,549	$270,157

Markel_Corporation_Parent_Comp4

Markel Corporation (Parent Company Only) Financial Information (Schedule Of Condensed Statements Of Income And Comprehensive Income) (Details) (USD $)

3 Months Ended

12 Months Ended

In Thousands, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2011

Sep. 30, 2011

Jun. 30, 2011

Mar. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Condensed Financial Statements, Captions [Line Items]

Net investment income

$317,373

$282,107

$263,676

Other-than-temporary impairment losses

-4,706

-12,078

-20,196

Net realized investment gains, excluding other-than-temporary impairment losses

67,858

43,671

56,053

Net realized investment gains

63,152

31,593

35,857

Other

710,942

539,284

351,077

Total Operating Revenues

1,279,785

1,191,665

1,031,769

819,864

807,955

765,775

693,247

733,135

685,100

676,088

647,168

621,594

4,323,083

3,000,112

2,629,950

Interest expense

114,004

92,762

86,252

Other expenses

663,528

478,248

309,046

Total Operating Expenses

3,847,336

2,595,300

2,353,502

Income tax benefit

77,898

53,802

41,710

Net Income to Shareholders

98,764

65,599

27,756

88,902

56,792

49,653

89,687

57,253

50,176

53,264

30,314

8,272

281,021

253,385

142,026

Net holding gains arising during the period

225,545

266,425

141,839

Reclassification adjustments for net gains (losses) included in net income to shareholders

-40,830

-24,051

-22,341

Change in net unrealized gains on investments, net of taxes

184,574

242,214

123,441

Change in foreign currency translation adjustments, net of taxes

-10,143

1,534

-4,191

Total Other Comprehensive Income

178,496

250,412

109,791

Comprehensive Income to Shareholders

206,450

144,409

-149,054

257,684

76,987

147,454

73,416

205,945

183,696

-52,626

96,045

24,738

459,489

503,802

251,853

Parent Company [Member]

Condensed Financial Statements, Captions [Line Items]

Net investment income

21,946

30,619

12,629

Dividends on common stock of consolidated subsidiaries

806,233

337,585

330,462

Other-than-temporary impairment losses

-15

-38

-7,676

Net realized investment gains, excluding other-than-temporary impairment losses

67,232

14,926

7,417

Net realized investment gains

67,217

14,888

-259

Other

Total Operating Revenues

895,397

383,095

342,845

Interest expense

92,743

87,391

78,830

Other expenses

2,617

1,166

4,572

Total Operating Expenses

95,360

88,557

83,402

Income Before Equity in Undistributed Earnings of Consolidated Subsidiaries and Income Taxes

800,037

294,538

259,443

Equity in undistributed earnings of consolidated subsidiaries

-520,323

-61,663

-144,348

Income tax benefit

-1,307

-20,510

-26,931

Net Income to Shareholders

281,021

253,385

142,026

Net holding gains arising during the period

66,623

10,897

675

Consolidated subsidiaries' net holding gains arising during the period

158,922

255,528

141,164

Consolidated subsidiaries' change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period

-141

-160

3,943

Reclassification adjustments for net gains (losses) included in net income to shareholders

-43,220

11,847

735

Consolidated subsidiaries' reclassification adjustments for net gains (losses) included in net income to shareholders

2,390

-35,898

-23,076

Change in net unrealized gains on investments, net of taxes

184,574

242,214

123,441

Change in foreign currency translation adjustments, net of taxes

-2,670

-242

314

Consolidated subsidiaries' change in foreign currency translation adjustments, net of taxes

-7,501

1,781

-4,469

Consolidated subsidiaries' change in net actuarial pension loss, net of taxes

4,065

6,664

-9,459

Total Other Comprehensive Income

178,468

250,417

109,827

Comprehensive Income to Shareholders

$459,489

$503,802

$251,853

Markel_Corporation_Parent_Comp5

Markel Corporation (Parent Company Only) Financial Information (Schedule Of Condensed Statements Of Cash Flows) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]	'	'	'
Net income to shareholders	$281,021	$253,385	$142,026
Net Cash Provided By Operating Activities	745,521	392,533	311,318
Proceeds from sales of fixed maturities and equity securities	879,564	336,548	288,046
Proceeds from maturities, calls and prepayments of fixed maturities	1,475,938	510,697	343,502
Cost of fixed maturities and equity securities purchased	-1,651,397	-426,439	-713,102
Net change in short-term investments	-470,423	-428,292	-216,972
Cost of equity method investments	-38,018	-40,650	-9,880
Change in restricted cash and cash equivalents	-263,014	-37,642	-16,795
Additions to property and equipment	-47,725	-45,519	-60,132
Other	1,103	-2,158	14,329
Net Cash Provided (Used) By Investing Activities	187,387	-377,130	-491,106
Additions to senior long-term debt	547,214	492,792	336,181
Repurchases of common stock	-57,388	-16,873	-42,913
Issuance of common stock	24,518	9,145	1,182
Other	-23	-19,485	-45
Net Cash Provided By Financing Activities	175,367	141,962	194,589
Increase in cash and cash equivalents	1,114,760	160,507	12,978
Cash and cash equivalents at beginning of year	863,766	703,259	690,281
CASH AND CASH EQUIVALENTS AT END OF YEAR	1,978,526	863,766	703,259
Parent Company [Member]	'	'	'
Condensed Financial Statements, Captions [Line Items]	'	'	'
Net income to shareholders	281,021	253,385	142,026
Adjustments to reconcile net income to shareholders to net cash provided by operating activities	186,574	-153,773	102,714
Net Cash Provided By Operating Activities	467,595	99,612	244,740
Proceeds from sales of fixed maturities and equity securities	142,259	149,314	50,322
Proceeds from maturities, calls and prepayments of fixed maturities	2,819	64,340	46,522
Cost of fixed maturities and equity securities purchased	-23,412	-89,569	-92,287
Net change in short-term investments	260,247	-214,820	-179,823
Decrease in notes receivable due from subsidiaries	5,302	116,797	7,401
Capital contributions to subsidiaries	-67,878	-198,349	-179,403
Acquisitions	-1,017,988	-100,409	0
Cost of equity method investments	-5,291	-38,250	0
Change in restricted cash and cash equivalents	-348	-204	-326
Additions to property and equipment	-3,653	-9,437	-16,927
Other	3,207	-4,369	12,175
Net Cash Provided (Used) By Investing Activities	-704,736	-324,956	-352,346
Additions to senior long-term debt	491,235	347,207	247,935
Repayments and retirement of senior long-term debt	-246,665	-157,359	0
Repurchases of common stock	-57,388	-16,873	-42,913
Issuance of common stock	24,518	9,145	1,182
Other	-5,023	436	50
Net Cash Provided By Financing Activities	206,677	182,556	206,254
Increase in cash and cash equivalents	-30,464	-42,788	98,648
Cash and cash equivalents at beginning of year	237,816	280,604	181,956
CASH AND CASH EQUIVALENTS AT END OF YEAR	$207,352	$237,816	$280,604

Quarterly_Financial_Informatio2

Quarterly Financial Information (Details) (USD $)	3 Months Ended												12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information Disclosure [Abstract]	'	'	'	'	'	'	'	'	'	'	'	'	'	'	'
Operating revenues	$1,279,785	$1,191,665	$1,031,769	$819,864	$807,955	$765,775	$693,247	$733,135	$685,100	$676,088	$647,168	$621,594	$4,323,083	$3,000,112	$2,629,950
Net income	98,939	66,967	28,676	89,263	58,093	51,674	90,768	57,713	52,307	54,669	31,649	9,861	283,845	258,248	148,486
Net income to shareholders	98,764	65,599	27,756	88,902	56,792	49,653	89,687	57,253	50,176	53,264	30,314	8,272	281,021	253,385	142,026
Comprehensive income (loss) to shareholders	$206,450	$144,409	($149,054)	$257,684	$76,987	$147,454	$73,416	$205,945	$183,696	($52,626)	$96,045	$24,738	$459,489	$503,802	$251,853
Basic net income per share (dollars per share)	$6.98	$4.69	$2.24	$9.53	$6.25	$5.33	$8.44	$5.94	$5.21	$5.50	$3.12	$0.85	$22.57	$25.96	$14.66
Diluted net income per share (dollars per share)	$6.95	$4.67	$2.24	$9.50	$6.23	$5.32	$8.42	$5.92	$5.19	$5.48	$3.11	$0.85	$22.48	$25.89	$14.60
Common stock price, high (dollars per share)	$582.59	$549.09	$546.94	$510.05	$502.20	$459.90	$453.50	$451.90	$419.10	$403.21	$430.26	$422.83	'	'	'
Common stock price, low (dollars per share)	$511.06	$506.64	$501.76	$434.98	$425.17	$420	$421	$398.65	$337.50	$346.15	$386.81	$379.44	'	'	'