Markel (MKL) 10-Q 7 May 14 2014 Q1 Quarterly report Financial data

Document_And_Entity_Informatio

Document And Entity Information	3 Months Ended
	Mar. 31, 2014	Apr. 30, 2014
Document And Entity Information [Abstract]	'	'
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	31-Mar-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q1	'
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	'	13,969,287

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
ASSETS	'	'
Fixed maturities (amortized cost of $10,074,531 in 2014 and $10,129,141 in 2013)	$10,236,737	$10,142,536
Equity securities (cost of $1,647,953 in 2014 and $1,566,553 in 2013)	3,399,651	3,251,798
Short-term investments (estimated fair value approximates cost)	1,348,231	1,452,288
Total Investments	14,984,619	14,846,622
Cash and cash equivalents	2,151,420	1,978,526
Restricted cash and cash equivalents	634,029	786,926
Receivables	1,403,644	1,141,773
Reinsurance recoverable on unpaid losses	1,869,403	1,854,414
Reinsurance recoverable on paid losses	78,741	102,002
Deferred policy acquisition costs	334,593	260,967
Prepaid reinsurance premiums	379,621	383,559
Goodwill	1,019,770	967,717
Intangible assets	687,982	565,083
Other assets	909,170	1,067,922
Total Assets	24,452,992	23,955,511
LIABILITIES AND EQUITY	'	'
Unpaid losses and loss adjustment expenses	10,369,020	10,262,056
Life and annuity benefits	1,483,606	1,486,574
Unearned premiums	2,364,784	2,127,115
Payables to insurance and reinsurance companies	355,032	295,496
Senior long-term debt and other debt (estimated fair value of $2,428,000 in 2014 and $2,372,000 in 2013)	2,255,824	2,256,227
Other liabilities	663,625	777,850
Total Liabilities	17,491,891	17,205,318
Redeemable noncontrolling interests	52,915	72,183
Commitments and contingencies	'	'
Shareholders' equity:	'	'
Common stock	3,302,301	3,288,863
Retained earnings	2,365,469	2,294,909
Accumulated other comprehensive income	1,232,362	1,089,805
Total Shareholders' Equity	6,900,132	6,673,577
Noncontrolling interests	8,054	4,433
Total Equity	6,908,186	6,678,010
Total Liabilities and Equity	$24,452,992	$23,955,511

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Statement of Financial Position [Abstract]	'	'
Fixed maturities, amortized cost	$10,074,531	$10,129,141
Equity securities, cost	1,647,953	1,566,553
Senior long-term debt and other debt, estimated fair value	$2,428,000	$2,372,000

Consolidated_Statements_Of_Inc

Consolidated Statements Of Income And Comprehensive Income (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
OPERATING REVENUES	'	'
Earned premiums	$949,375	$564,587
Net investment income	86,715	64,617
Net realized investment gains	17,394	17,917
Other revenues	186,171	172,743
Total Operating Revenues	1,239,655	819,864
OPERATING EXPENSES	'	'
Losses and loss adjustment expenses	542,303	287,896
Underwriting, acquisition and insurance expenses	355,505	228,673
Amortization of intangible assets	13,999	9,615
Other expenses	182,168	152,317
Total Operating Expenses	1,093,975	678,501
Operating Income	145,680	141,363
Interest expense	29,699	23,574
Income Before Income Taxes	115,981	117,789
Income tax expense	28,480	28,526
Net Income	87,501	89,263
Net income (loss) attributable to noncontrolling interests	-215	361
Net Income to Shareholders	87,716	88,902
OTHER COMPREHENSIVE INCOME	'	'
Net holding gains arising during the period	147,296	181,599
Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period	-20	249
Reclassification adjustments for net gains included in net income	-5,944	-12,255
Change in net unrealized gains on investments, net of taxes	141,332	169,593
Change in foreign currency translation adjustments, net of taxes	913	-1,181
Change in net actuarial pension loss, net of taxes	319	370
Total Other Comprehensive Income	142,564	168,782
Comprehensive Income	230,065	258,045
Comprehensive income (loss) attributable to noncontrolling interests	-208	361
Comprehensive Income to Shareholders	$230,273	$257,684
NET INCOME PER SHARE	'	'
Basic (in dollars per share)	$6.28	$9.53
Diluted (in dollars per share)	$6.25	$9.50

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
Balance at Dec. 31, 2012	'	$3,889,017	$3,888,657	$908,980	$2,068,340	$911,337	$360	'
Balance, redeemable noncontrolling interests at Dec. 31, 2012	'	'	'	'	'	'	'	86,225
Net income (loss)	89,263	88,454	88,902	'	88,902	0	-448	809
Other comprehensive income	168,782	168,782	168,782	'	0	168,782	0	0
Comprehensive Income	258,045	257,236	257,684	'	'	'	-448	809
Issuance of common stock	'	19	19	19	0	0	0	0
Restricted stock units expensed	'	2,583	2,583	2,583	0	0	0	0
Adjustment of redeemable noncontrolling interests	'	2,886	2,886	0	2,886	0	0	-2,886
Purchase of noncontrolling interest	'	'	-283	-283	0	0	'	'
Purchase of noncontrolling interest	'	'	'	'	'	'	0	-8,157
Purchase of noncontrolling interest	'	-283	'	'	'	'	'	'
Other	'	4,963	-37	31	-68	0	5,000	-1,490
Balance, redeemable noncontrolling interests at Mar. 31, 2013	'	'	'	'	'	'	'	74,501
Balance at Mar. 31, 2013	'	4,156,421	4,151,509	911,330	2,160,060	1,080,119	4,912	'
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, redeemable noncontrolling interests at Dec. 31, 2013	72,183	'	'	'	'	'	'	72,183
Net income (loss)	87,501	87,392	87,716	'	87,716	0	-324	109
Other comprehensive income	142,564	142,557	142,557	'	0	142,557	0	7
Comprehensive Income	230,065	229,949	230,273	'	'	'	-324	116
Issuance of common stock	'	4,363	4,363	4,363	0	0	0	0
Repurchase of common stock	'	-17,282	-17,282	0	-17,282	0	0	0
Restricted stock units expensed	'	8,421	8,421	8,421	0	0	0	0
Adjustment of redeemable noncontrolling interests	'	117	117	0	117	0	0	-117
Purchase of noncontrolling interest	'	'	647	647	0	0	'	'
Purchase of noncontrolling interest	'	'	'	'	'	'	0	-18,405
Purchase of noncontrolling interest	'	647	'	'	'	'	'	'
Other	'	3,961	16	7	9	0	3,945	-862
Balance, redeemable noncontrolling interests at Mar. 31, 2014	52,915	'	'	'	'	'	'	52,915
Balance at Mar. 31, 2014	$6,908,186	$6,908,186	$6,900,132	$3,302,301	$2,365,469	$1,232,362	$8,054	'

Condensed_Consolidated_Stateme

Condensed Consolidated Statements Of Cash Flows (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
OPERATING ACTIVITIES	'	'
Net income	$87,501	$89,263
Adjustments to reconcile net income to net cash provided by operating activities	-65,084	-33,709
Net Cash Provided By Operating Activities	22,417	55,554
INVESTING ACTIVITIES	'	'
Proceeds from sales of fixed maturities and equity securities	660,447	52,834
Proceeds from maturities, calls and prepayments of fixed maturities	440,891	120,711
Cost of fixed maturities and equity securities purchased	-1,114,736	-62,775
Net change in short-term investments	130,557	-410,662
Proceeds from sales of equity method investments	82,518	0
Cost of equity method investments	-8,050	0
Change in restricted cash and cash equivalents	152,897	12,317
Additions to property and equipment	-10,725	-14,442
Acquisitions, net of cash acquired	-153,735	-36,531
Other	384	-2,438
Net Cash Provided (Used) By Investing Activities	180,448	-340,986
FINANCING ACTIVITIES	'	'
Additions to senior long-term debt and other debt	10,120	507,969
Repayment and retirement of senior long-term debt and other debt	-8,608	-268,522
Repurchases of common stock	-17,282	-169
Issuance of common stock	4,363	19
Purchase of redeemable noncontrolling interests	-17,758	-8,440
Distributions to noncontrolling interests	-1,168	-2,032
Other	-609	2,364
Net Cash Provided (Used) By Financing Activities	-30,942	231,189
Effect of foreign currency rate changes on cash and cash equivalents	971	-7,546
Increase (decrease) in cash and cash equivalents	172,894	-61,789
Cash and cash equivalents at beginning of period	1,978,526	863,766
CASH AND CASH EQUIVALENTS AT END OF PERIOD	$2,151,420	$801,977

Basis_Of_Presentation

Basis Of Presentation	3 Months Ended
	Mar. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Basis Of Presentation	'
	Basis of Presentation
	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 and programs. 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 (the Merger Agreement) 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.
	The consolidated balance sheet as of March 31, 2014 and the related consolidated statements of income and comprehensive income, changes in equity and cash flows for the three months ended March 31, 2014 and 2013 are unaudited. In the opinion of management, all adjustments necessary for fair presentation of such consolidated financial statements have been included. Such adjustments consist only of normal, recurring items. Interim results are not necessarily indicative of results of operations for the entire year. The consolidated balance sheet as of December 31, 2013 was derived from Markel Corporation's audited annual consolidated financial statements.
	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. 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.
	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. Actual results may differ materially from the estimates and assumptions used in preparing the consolidated financial statements.
	The consolidated financial statements and notes are presented as permitted by Form 10-Q and do not contain certain information included in the Company's annual consolidated financial statements and notes. Readers are urged to review the Company's 2013 Annual Report on Form 10-K for a more complete description of the Company's business and accounting policies.

Recent_Accounting_Pronouncemen

Recent Accounting Pronouncements	3 Months Ended
	Mar. 31, 2014
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]	'
Recent Accounting Pronouncements	'
	Recent Accounting Pronouncements
	Effective January 1, 2014, the Company adopted Financial Accounting Standards Board (FASB) Accounting Standards Update (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. The adoption of this guidance did not have an impact on the Company's financial position, results of operations or cash flows.

Acquisitions

Acquisitions	3 Months Ended
	Mar. 31, 2014
Business Combinations [Abstract]	'
Acquisitions	'
	Acquisitions
	Acquisition of Alterra
	a)Overview. On May 1, 2013, the Company completed the acquisition of 100% of the issued and outstanding common stock of Alterra. Results attributable to Alterra's property and casualty insurance and reinsurance business are included in each of the Company's underwriting segments, which were redefined during the first quarter of 2014. See note 6. Previously, 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 Alterra's life and annuity reinsurance business are included in the Company's Other Insurance (Discontinued Lines) segment. See note 6 for further discussion of the Company's reportable 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.
	b)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, of which $107.8 million is included in the U.S. Insurance segment, $89.8 million is included in the International Insurance segment and $98.1 million is included in the Reinsurance segment. 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 are being amortized over a weighted average period of 17 years.
	As part of the purchase price allocation, the Company adjusted the historical carrying value of the acquired assets and liabilities based on estimated fair values at the Acquisition Date. An explanation of the significant adjustments for fair value that are being amortized to net income 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 is being amortized to net investment income over the term of the underlying securities.  The amount of the unamortized incremental premium as of March 31, 2014 was $299.9 million. The decrease in the unamortized incremental premium since the Acquisition Date is due to amortization expense of $76.7 million, including $18.4 million recorded during the first quarter of 2014, and sales of securities.
	•	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, is being 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 March 31, 2014, the unamortized fair value adjustment included in unpaid losses and loss adjustment expenses was $131.0 million.
	•	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 is being amortized to interest expense over the term of the notes. As of March 31, 2014, the unamortized premium on the acquired senior long-term debt was $63.9 million.
	Acquisition of Abbey Protection
	On January 17, 2014, the Company completed its acquisition of 100% of the 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 and professional consulting services. Premiums associated with Abbey's insurance operations for 2013 were in excess of $60 million. Results attributable to Abbey's insurance operations are included in the International Insurance segment. Results attributable to Abbey's consultancy operations are reported with the Company's non-insurance operations, which are not included in a reportable segment.
	Total consideration for this acquisition was $190.7 million, all of which was cash consideration. The purchase price was allocated to the acquired assets and liabilities based on estimated fair values on January 17, 2014. The Company recognized goodwill of $52.8 million, of which $37.5 million was allocated to the International Insurance segment and $15.3 million was allocated to the Company's non-insurance operations. None of the goodwill recognized is expected to be deductible for income tax purposes. The goodwill is primarily attributable to Abbey's assembled workforce and synergies that are expected to result upon integration of Abbey into the Company's insurance operations. The Company also recognized other intangible assets of $130.6 million, including $119.9 million of customer relationships and $10.7 million of trade names. These intangible assets are expected to be amortized over 20 years and 14 years, respectively.

Investments

Investments	3 Months Ended
	Mar. 31, 2014
Investments, Debt and Equity Securities [Abstract]	'
Investments	'
	Investments
	a)The following tables summarize the Company's available-for-sale investments.
		March 31, 2014
	(dollars in thousands)	Amortized			Gross			Gross			Unrealized			Estimated
		Cost			Unrealized			Unrealized			Other-Than-			Fair
					Holding			Holding			Temporary			Value
					Gains			Losses			Impairment
											Losses
	Fixed maturities:
	U.S. Treasury securities and obligations of U.S. government agencies	$	780,801		$	8,446		$	(15,434	)	$	—		$	773,813
	Obligations of states, municipalities and political subdivisions	3,509,045			154,545			(14,683		)	—			3,648,907
	Foreign governments	1,548,401			40,642			(19,458		)	—			1,569,585
	Commercial mortgage-backed securities	354,194			1,010			(4,143		)	—			351,061
	Residential mortgage-backed securities	963,494			13,272			(15,181		)	(2,258		)	959,327
	Asset-backed securities	184,342			385			(1,383		)	—			183,344
	Corporate bonds	2,734,254			50,409			(31,903		)	(2,060		)	2,750,700
	Total fixed maturities	10,074,531			268,709			(102,185		)	(4,318		)	10,236,737
	Equity securities:
	Insurance, banks and other financial institutions	443,079			621,467			(17		)	—			1,064,529
	Industrial, consumer and all other	1,204,874			1,131,301			(1,053		)	—			2,335,122
	Total equity securities	1,647,953			1,752,768			(1,070		)	—			3,399,651
	Short-term investments	1,348,212			19			—			—			1,348,231
	Investments, available-for-sale	$	13,070,696		$	2,021,496		$	(103,255	)	$	(4,318	)	$	14,984,619
		December 31, 2013
	(dollars in thousands)	Amortized			Gross			Gross			Unrealized			Estimated
		Cost			Unrealized			Unrealized			Other-Than-			Fair
					Holding			Holding			Temporary			Value
					Gains			Losses			Impairment
											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
	b)The following tables summarize gross unrealized investment losses by the length of time that securities have continuously been in an unrealized loss position.
		March 31, 2014
		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	$	342,593		$	(15,422	)	$	4,337		$	(12	)	$	346,930	$	(15,434	)
	Obligations of states, municipalities and political subdivisions	439,805			(14,526		)	4,582			(157		)	444,387		(14,683		)
	Foreign governments	734,180			(19,458		)	—			—			734,180		(19,458		)
	Commercial mortgage-backed securities	206,242			(4,143		)	—			—			206,242		(4,143		)
	Residential mortgage-backed securities	508,762			(17,439		)	—			—			508,762		(17,439		)
	Asset-backed securities	85,100			(1,383		)	—			—			85,100		(1,383		)
	Corporate bonds	1,234,155			(33,963		)	—			—			1,234,155		(33,963		)
	Total fixed maturities	3,550,837			(106,334		)	8,919			(169		)	3,559,756		(106,503		)
Equity securities:
Insurance, banks and other financial institutions	781			(17		)	—			—			781		(17		)
Industrial, consumer and all other	32,639			(1,053		)	—			—			32,639		(1,053		)
Total equity securities	33,420			(1,070		)	—			—			33,420		(1,070		)
Total	$	3,584,257		$	(107,404	)	$	8,919		$	(169	)	$	3,593,176	$	(107,573	)
At March 31, 2014, the Company held 1,058 securities with a total estimated fair value of $3.6 billion and gross unrealized losses of $107.6 million. Of these 1,058 securities, 11 securities had been in a continuous unrealized loss position for one year or longer and had a total estimated fair value of $8.9 million and gross unrealized losses of $0.2 million. All 11 securities were fixed maturities. The Company does not intend to sell or believe it will be required to sell these fixed maturities before recovery of their amortized cost.
	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 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.
c)The amortized cost and estimated fair value of fixed maturities at March 31, 2014 are shown below by contractual maturity.
(dollars in thousands)	Amortized			Estimated
	Cost			Fair Value
Due in one year or less	$	783,252		$	790,476
Due after one year through five years	2,404,376			2,460,982
Due after five years through ten years	2,167,719			2,236,464
Due after ten years	3,217,154			3,255,083
	8,572,501			8,743,005
Commercial mortgage-backed securities	354,194			351,061
Residential mortgage-backed securities	963,494			959,327
Asset-backed securities	184,342			183,344
Total fixed maturities	$	10,074,531		$	10,236,737
d)The following table presents the components of net investment income.
	Three Months Ended March 31,
(dollars in thousands)	2014			2013
Interest:
Municipal bonds (tax-exempt)	$	23,104		$	21,448
Municipal bonds (taxable)	8,996			5,703
Other taxable bonds	35,744			21,332
Short-term investments, including overnight deposits	1,474			670
Dividends on equity securities	16,856			12,781
Change in fair value of credit default swap	1,160			3,290
Income from equity method investments	3,583			1,990
Other	19			62
	90,936			67,276
Investment expenses	(4,221		)	(2,659		)
Net investment income	$	86,715		$	64,617
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.
	Three Months Ended March 31,
(dollars in thousands)	2014			2013
Cumulative credit loss, beginning balance	$	12,748		$	21,370
Additions:
Other-than-temporary impairment losses not previously recognized	—			—
Increases related to other-than-temporary impairment losses previously recognized	—			—
Total additions	—			—
Reductions:
Sales or maturities of fixed maturities on which credit losses were recognized	(13		)	—
Cumulative credit loss, ending balance	$	12,735		$	21,370
f)The following table presents net realized investment gains and the change in net unrealized gains on investments.
	Three Months Ended March 31,
(dollars in thousands)	2014			2013
Realized gains:
Sales of fixed maturities	$	4,583		$	287
Sales of equity securities	12,145			17,921
Other	9,955			—
Total realized gains	26,683			18,208
Realized losses:
Sales of fixed maturities	(8,484		)	(138		)
Sales of equity securities	(146		)	(153		)
Other	(659		)	—
Total realized losses	(9,289		)	(291		)
Net realized investment gains	$	17,394		$	17,917
Change in net unrealized gains on investments:
Fixed maturities	$	148,811		$	(31,348	)
Equity securities	66,453			280,895
Short-term investments	1			5
Net increase	$	215,265		$	249,552
g)There were no writedowns for other-than-temporary declines in the estimated fair value of investments for the three months ended March 31, 2014 and 2013.

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2014
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. 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. At both March 31, 2014 and December 31, 2013, 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. The credit default swap has a scheduled termination date of December 2014.
	The fair value of the credit default swap is measured by the Company on a recurring basis using an external valuation model. 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.
		March 31, 2014
	(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	$	—		$	773,813		$	—	$	773,813
	Obligations of states, municipalities and political subdivisions	—			3,648,907			—		3,648,907
	Foreign governments	—			1,569,585			—		1,569,585
	Commercial mortgage-backed securities	—			351,061			—		351,061
	Residential mortgage-backed securities	—			959,327			—		959,327
	Asset-backed securities	—			183,344			—		183,344
	Corporate bonds	—			2,750,700			—		2,750,700
	Total fixed maturities	—			10,236,737			—		10,236,737
	Equity securities:
	Insurance, banks and other financial institutions	1,064,529			—			—		1,064,529
	Industrial, consumer and all other	2,335,122			—			—		2,335,122
	Total equity securities	3,399,651			—			—		3,399,651
	Short-term investments	1,209,462			138,769			—		1,348,231
	Total investments available-for-sale	$	4,609,113		$	10,375,506		$	—	$	14,984,619
	Liabilities:
	Derivative contracts	$	—		$	—		$	1,070	$	1,070
		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
	The following table summarizes changes in Level 3 liabilities measured at fair value on a recurring basis.
		Three Months Ended March 31,
	(dollars in thousands)	2014			2013
	Derivatives, beginning of period	$	2,230		$	12,690
	Total gains included in:
	Net income	(1,160		)	(3,290		)
	Other comprehensive income	—			—
Transfers into Level 3	—			—
Transfers out of Level 3	—			—
Derivatives, end of period	$	1,070		$	9,400
Net unrealized gains included in net income relating to liabilities held at March 31, 2014 and 2013 (1)	$	1,160		$	3,290
(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 the three months ended March 31, 2014 and 2013. Except as disclosed in note 3, the Company did not have any assets or liabilities measured at fair value on a non-recurring basis during the three months ended March 31, 2014 and 2013.

Segment_Reporting_Disclosures

Segment Reporting Disclosures	3 Months Ended
	Mar. 31, 2014
Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract]	'
Segment Reporting Disclosures	'
	Segment Reporting Disclosures
	In conjunction with the continued integration of Alterra into the Company's insurance operations, during the first quarter of 2014, the Company changed the way it aggregates and monitors its ongoing underwriting results. Effective January 1, 2014, the Company monitors and reports its ongoing underwriting operations in the following three segments: U.S. Insurance, International Insurance and Reinsurance. In determining how to aggregate and monitor its underwriting results, the Company considers many factors, including the geographic location and regulatory environment of the insurance entity underwriting the risk, the nature of the insurance product sold, the type of account written and the type of customer served. The U.S. Insurance segment includes all direct business and facultative placements written by the Company's insurance subsidiaries domiciled in the United States. The International Insurance segment includes all direct business and facultative placements written by the Company's insurance subsidiaries domiciled outside of the United States, including the Company's syndicate at Lloyd's of London. The Reinsurance segment includes all treaty reinsurance written across the Company. Results for lines of business discontinued prior to, or in conjunction with, acquisitions, including the results attributable to the run-off of life and annuity reinsurance business previously written by Alterra, will continue to be reported in the Other Insurance (Discontinued Lines) segment. All investing activities related to the Company's insurance operations are included in the Investing segment.
	The Company's non-insurance operations include the Company's Markel Ventures operations, which primarily consist of controlling interests in various industrial and service businesses. The Company's non-insurance operations also include the results of the Company's legal and professional consulting services, which were acquired through the acquisition of Abbey in January 2014. For purposes of segment reporting, the Company's non-insurance operations are not considered to be a reportable 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 underwriting 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 underwriting 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 non-insurance operations. Underwriting assets are all assets not specifically allocated to the Investing segment or to the Company's non-insurance operations. Underwriting and investing assets are not allocated to the U.S. Insurance, International Insurance, Reinsurance or Other Insurance (Discontinued Lines) segments since the Company does not manage its assets by underwriting segment. The Company does not allocate capital expenditures for long-lived assets to any of its underwriting segments for management reporting purposes.
	a)The following tables summarize the Company's segment disclosures. The segment disclosures for the prior period have been revised to be consistent with the new segment structure.
		Three Months Ended March 31, 2014
	(dollars in thousands)	U.S.			International			Reinsurance			Other				Investing		Consolidated
		Insurance			Insurance						Insurance
											(Discontinued
											Lines)
	Gross premium volume	$	575,233		$	294,236		$	489,961		$	327			$	—	$	1,359,757
	Net written premiums	474,054			229,120			435,997			140				—		1,139,311
	Earned premiums	483,735			222,147			243,315			178				—		949,375
	Losses and loss adjustment expenses:
	Current accident year	(312,413		)	(163,379		)	(173,900		)	—				—		(649,692		)
	Prior accident years	43,554			42,297			28,200			(6,662		)		—		107,389
	Underwriting, acquisition and insurance expenses	(193,529		)	(80,009		)	(81,972		)	5				—		(355,505		)
	Underwriting profit (loss)	21,347			21,056			15,643			(6,479		)		—		51,567
	Net investment income	—			—			—			—				86,715		86,715
	Net realized investment gains	—			—			—			—				17,394		17,394
	Other revenues (insurance)	2,110			7,348			2,136			43				—		11,637
	Other expenses (insurance)	(1,647		)	(3,595		)	—			(8,615		)		—		(13,857		)
	Segment profit (loss)	$	21,810		$	24,809		$	17,779		$	(15,051	)		$	104,109	$	153,456
	Other revenues (non-insurance)																174,534
	Other expenses (non-insurance)																(168,311		)
	Amortization of intangible assets																(13,999		)
	Interest expense																(29,699		)
	Income before income taxes																$	115,981
	U.S. GAAP combined ratio (1)	96		%	91		%	94		%	NM			(2)			95		%
	(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.
		Three Months Ended March 31, 2013
	(dollars in thousands)	U.S.			International			Reinsurance			Other				Investing		Consolidated
		Insurance			Insurance						Insurance
											(Discontinued
											Lines)
	Gross premium volume	$	445,264		$	235,875		$	62,140		$	21			$	—	$	743,300
	Net written premiums	401,549			201,677			59,741			21				—		662,988
	Earned premiums	355,141			178,192			31,233			21				—		564,587
	Losses and loss adjustment expenses:
	Current accident year	(234,671		)	(120,862		)	(17,205		)	—				—		(372,738		)
	Prior accident years	62,404			23,000			(979		)	417				—		84,842
	Underwriting, acquisition and insurance expenses	(150,783		)	(69,774		)	(8,204		)	88				—		(228,673		)
	Underwriting profit (loss)	32,091			10,556			4,845			526				—		48,018
	Net investment income	—			—			—			—				64,617		64,617
	Net realized investment gains	—			—			—			—				17,917		17,917
	Other revenues (insurance)	7,263			3,962			—			—				—		11,225
	Other expenses (insurance)	(6,197		)	(1,358		)	—			—				—		(7,555		)
	Segment profit (loss)	$	33,157		$	13,160		$	4,845		$	526			$	82,534	$	134,222
	Other revenues (non-insurance)																161,518
	Other expenses (non-insurance)																(144,762		)
	Amortization of intangible assets																(9,615		)
	Interest expense																(23,574		)
	Income before income taxes																$	117,789
	U.S. GAAP combined ratio (1)	91		%	94		%	84		%	NM			(2)			91		%
	(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 reconciles segment assets to the Company's consolidated balance sheets.
	(dollars in thousands)	March 31, 2014			December 31, 2013
	Segment assets:
	Investing	$	17,709,901		$	17,550,332
	Underwriting	5,771,517			5,468,731
Total segment assets	23,481,418			23,019,063
Non-insurance operations	971,574			936,448
Total assets	$	24,452,992		$	23,955,511

Goodwill

Goodwill	3 Months Ended
	Mar. 31, 2014
Goodwill [Abstract]	'
Goodwill	'
	Goodwill
	As described in note 6, effective January 1, 2014, the Company redefined its segments. As a result, goodwill was reallocated as of December 31, 2013 using a relative fair value allocation approach. The following table presents the components of goodwill by reportable segment.
	(dollars in thousands)	U.S.		International			Reinsurance		Other(1)		Total
		Insurance		Insurance
	31-Dec-13	$	280,579	$	372,764		$	122,745	$	191,629	$	967,717
	Acquisitions	—		37,530			—		15,258		52,788
	Foreign currency movements and other adjustments	—		(835		)	—		100		(735		)
	31-Mar-14	$	280,579	$	409,459		$	122,745	$	206,987	$	1,019,770
	(1)	Amounts included in Other are related to the Company's non-insurance operations, which are not included in a reportable segment.

Other_Revenues_And_Other_Expen

Other Revenues And Other Expenses	3 Months Ended
	Mar. 31, 2014
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.
		Three Months Ended March 31,
		2014				2013
	(dollars in thousands)	Other		Other		Other		Other
		Revenues		Expenses		Revenues		Expenses
	Insurance:
	Managing general agent operations	$	9,178	$	4,881	$	10,937	$	7,164
	Life and annuity	43		8,615		—		—
	Other	2,416		361		288		391
		11,637		13,857		11,225		7,555
	Non-Insurance:
	Markel Ventures: Manufacturing	100,611		95,889		128,576		115,184
	Markel Ventures: Non-Manufacturing	70,595		65,511		32,942		29,578
	Abbey: Consulting services	3,328		6,911		—		—
		174,534		168,311		161,518		144,762
	Total	$	186,171	$	182,168	$	172,743	$	152,317
	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.
	Effective January 17, 2014, the Company's non-insurance operations include the results of the legal and professional consulting services attributable to Abbey.

Reinsurance

Reinsurance	3 Months Ended
	Mar. 31, 2014
Reinsurance Disclosures [Abstract]	'
Reinsurance	'
	Reinsurance
	The following table summarizes the effect of reinsurance and retrocessional reinsurance on premiums written and earned.
		Three Months Ended March 31,
		2014						2013
	(dollars in thousands)	Written			Earned			Written			Earned
	Direct	$	795,311		$	828,292		$	597,419		$	538,142
	Assumed	564,446			347,699			145,881			102,127
	Ceded	(220,446		)	(226,616		)	(80,312		)	(75,682		)
	Net premiums	$	1,139,311		$	949,375		$	662,988		$	564,587
	The percentage of ceded earned premiums to gross earned premiums was 19% and 12%, respectively, for the three months ended March 31, 2014 and 2013.
	Incurred losses and loss adjustment expenses for the three months ended March 31, 2014 were net of reinsurance recoverables (ceded incurred losses and loss adjustment expenses) of $97.6 million.

Net_Income_Per_Share

Net Income Per Share	3 Months Ended
	Mar. 31, 2014
Earnings Per Share [Abstract]	'
Net Income Per Share	'
	Net Income per Share
	Net income per share was determined by dividing adjusted net income to shareholders by the applicable weighted average shares outstanding. 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 period.
		Three Months Ended March 31,
	(in thousands, except per share amounts)	2014		2013
	Net income to shareholders	$	87,716	$	88,902
	Adjustment of redeemable noncontrolling interests	117		2,886
	Adjusted net income to shareholders	$	87,833	$	91,788
	Basic common shares outstanding	13,995		9,636
	Dilutive potential common shares from conversion of options	11		3
	Dilutive potential common shares from conversion of restricted stock	52		27
	Diluted shares outstanding	14,058		9,666
	Basic net income per share	$	6.28	$	9.53
	Diluted net income per share	$	6.25	$	9.5

Other_Comprehensive_Income

Other Comprehensive Income	3 Months Ended
	Mar. 31, 2014
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, for the three months ended March 31, 2014 and 2013.
	(dollars in thousands)	Unrealized Holding Gains on Available-for-Sale Securities			Foreign Currency			Net Actuarial Pension Loss			Total
	31-Dec-12	$	946,933		$	(1,075	)	$	(34,521	)	$	911,337
	Other comprehensive income (loss) before reclassifications	181,848			(1,181		)	—			180,667
	Amounts reclassified from accumulated other comprehensive income	(12,255		)	—			370			(11,885		)
	Total other comprehensive income (loss)	169,593			(1,181		)	370			168,782
	31-Mar-13	$	1,116,526		$	(2,256	)	$	(34,151	)	$	1,080,119
	31-Dec-13	$	1,131,507		$	(11,246	)	$	(30,456	)	$	1,089,805
	Other comprehensive income before reclassifications	147,276			906			—			148,182
	Amounts reclassified from accumulated other comprehensive income	(5,944		)	—			319			(5,625		)
	Total other comprehensive income	141,332			906			319			142,557
	31-Mar-14	$	1,272,839		$	(10,340	)	$	(30,137	)	$	1,232,362
	The following table summarizes the tax expense associated with each component of other comprehensive income.
		Three Months Ended March 31,
	(dollars in thousands)	2014			2013
	Change in net unrealized gains on investments:
	Net holding gains arising during the period	$	75,523		$	85,546
	Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period	564			75
	Reclassification adjustments for net gains included in net income	(2,154		)	(5,662		)
	Change in net unrealized gains on investments	73,933			79,959
	Change in foreign currency translation adjustments	342			38
	Change in net actuarial pension loss	80			110
	Total	$	74,355		$	80,107
	The following table presents the details of amounts reclassified from accumulated other comprehensive income into income, by component.
		Three Months Ended March 31,
	(dollars in thousands)	2014			2013
	Unrealized holding gains on available-for-sale securities:
	Net realized investment gains	$	8,098		$	17,917
	Income taxes	(2,154		)	(5,662		)
	Reclassification of unrealized holding gains, net of taxes	$	5,944		$	12,255
	Net actuarial pension loss:
	Underwriting, acquisition and insurance expenses	$	(399	)	$	(480	)
	Income taxes	80			110
	Reclassification of net actuarial pension loss, net of taxes	$	(319	)	$	(370	)

Contingencies

Contingencies	3 Months Ended
	Mar. 31, 2014
Loss Contingency [Abstract]	'
Contingencies	'
	Contingencies
	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.

Investments_Tables

Investments (Tables)	3 Months Ended
	Mar. 31, 2014
Investments, Debt and Equity Securities [Abstract]	'
Available-For-Sale Investments	'
	The following tables summarize the Company's available-for-sale investments.
		March 31, 2014
	(dollars in thousands)	Amortized			Gross			Gross			Unrealized			Estimated
		Cost			Unrealized			Unrealized			Other-Than-			Fair
					Holding			Holding			Temporary			Value
					Gains			Losses			Impairment
											Losses
	Fixed maturities:
	U.S. Treasury securities and obligations of U.S. government agencies	$	780,801		$	8,446		$	(15,434	)	$	—		$	773,813
	Obligations of states, municipalities and political subdivisions	3,509,045			154,545			(14,683		)	—			3,648,907
	Foreign governments	1,548,401			40,642			(19,458		)	—			1,569,585
	Commercial mortgage-backed securities	354,194			1,010			(4,143		)	—			351,061
	Residential mortgage-backed securities	963,494			13,272			(15,181		)	(2,258		)	959,327
	Asset-backed securities	184,342			385			(1,383		)	—			183,344
	Corporate bonds	2,734,254			50,409			(31,903		)	(2,060		)	2,750,700
	Total fixed maturities	10,074,531			268,709			(102,185		)	(4,318		)	10,236,737
	Equity securities:
	Insurance, banks and other financial institutions	443,079			621,467			(17		)	—			1,064,529
	Industrial, consumer and all other	1,204,874			1,131,301			(1,053		)	—			2,335,122
	Total equity securities	1,647,953			1,752,768			(1,070		)	—			3,399,651
	Short-term investments	1,348,212			19			—			—			1,348,231
	Investments, available-for-sale	$	13,070,696		$	2,021,496		$	(103,255	)	$	(4,318	)	$	14,984,619
		December 31, 2013
	(dollars in thousands)	Amortized			Gross			Gross			Unrealized			Estimated
		Cost			Unrealized			Unrealized			Other-Than-			Fair
					Holding			Holding			Temporary			Value
					Gains			Losses			Impairment
											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
Summary Of Gross Unrealized Investment Losses By 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	)
	The following tables summarize gross unrealized investment losses by the length of time that securities have continuously been in an unrealized loss position.
		March 31, 2014
		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	$	342,593		$	(15,422	)	$	4,337		$	(12	)	$	346,930	$	(15,434	)
	Obligations of states, municipalities and political subdivisions	439,805			(14,526		)	4,582			(157		)	444,387		(14,683		)
	Foreign governments	734,180			(19,458		)	—			—			734,180		(19,458		)
	Commercial mortgage-backed securities	206,242			(4,143		)	—			—			206,242		(4,143		)
	Residential mortgage-backed securities	508,762			(17,439		)	—			—			508,762		(17,439		)
	Asset-backed securities	85,100			(1,383		)	—			—			85,100		(1,383		)
	Corporate bonds	1,234,155			(33,963		)	—			—			1,234,155		(33,963		)
	Total fixed maturities	3,550,837			(106,334		)	8,919			(169		)	3,559,756		(106,503		)
	Equity securities:
	Insurance, banks and other financial institutions	781			(17		)	—			—			781		(17		)
	Industrial, consumer and all other	32,639			(1,053		)	—			—			32,639		(1,053		)
	Total equity securities	33,420			(1,070		)	—			—			33,420		(1,070		)
	Total	$	3,584,257		$	(107,404	)	$	8,919		$	(169	)	$	3,593,176	$	(107,573	)
Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturities By Contractual Maturity Date	'
	The amortized cost and estimated fair value of fixed maturities at March 31, 2014 are shown below by contractual maturity.
	(dollars in thousands)	Amortized			Estimated
		Cost			Fair Value
	Due in one year or less	$	783,252		$	790,476
	Due after one year through five years	2,404,376			2,460,982
	Due after five years through ten years	2,167,719			2,236,464
	Due after ten years	3,217,154			3,255,083
		8,572,501			8,743,005
	Commercial mortgage-backed securities	354,194			351,061
	Residential mortgage-backed securities	963,494			959,327
	Asset-backed securities	184,342			183,344
	Total fixed maturities	$	10,074,531		$	10,236,737
Components Of Net Investment Income	'
	The following table presents the components of net investment income.
		Three Months Ended March 31,
	(dollars in thousands)	2014			2013
	Interest:
	Municipal bonds (tax-exempt)	$	23,104		$	21,448
	Municipal bonds (taxable)	8,996			5,703
	Other taxable bonds	35,744			21,332
	Short-term investments, including overnight deposits	1,474			670
	Dividends on equity securities	16,856			12,781
	Change in fair value of credit default swap	1,160			3,290
	Income from equity method investments	3,583			1,990
	Other	19			62
		90,936			67,276
	Investment expenses	(4,221		)	(2,659		)
	Net investment income	$	86,715		$	64,617
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.
		Three Months Ended March 31,
	(dollars in thousands)	2014			2013
	Cumulative credit loss, beginning balance	$	12,748		$	21,370
	Additions:
	Other-than-temporary impairment losses not previously recognized	—			—
	Increases related to other-than-temporary impairment losses previously recognized	—			—
	Total additions	—			—
	Reductions:
	Sales or maturities of fixed maturities on which credit losses were recognized	(13		)	—
	Cumulative credit loss, ending balance	$	12,735		$	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.
		Three Months Ended March 31,
	(dollars in thousands)	2014			2013
	Realized gains:
	Sales of fixed maturities	$	4,583		$	287
	Sales of equity securities	12,145			17,921
	Other	9,955			—
	Total realized gains	26,683			18,208
	Realized losses:
	Sales of fixed maturities	(8,484		)	(138		)
	Sales of equity securities	(146		)	(153		)
	Other	(659		)	—
	Total realized losses	(9,289		)	(291		)
	Net realized investment gains	$	17,394		$	17,917
	Change in net unrealized gains on investments:
	Fixed maturities	$	148,811		$	(31,348	)
	Equity securities	66,453			280,895
	Short-term investments	1			5
	Net increase	$	215,265		$	249,552

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2014
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.
		March 31, 2014
	(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	$	—		$	773,813		$	—	$	773,813
	Obligations of states, municipalities and political subdivisions	—			3,648,907			—		3,648,907
	Foreign governments	—			1,569,585			—		1,569,585
	Commercial mortgage-backed securities	—			351,061			—		351,061
	Residential mortgage-backed securities	—			959,327			—		959,327
	Asset-backed securities	—			183,344			—		183,344
	Corporate bonds	—			2,750,700			—		2,750,700
	Total fixed maturities	—			10,236,737			—		10,236,737
	Equity securities:
	Insurance, banks and other financial institutions	1,064,529			—			—		1,064,529
	Industrial, consumer and all other	2,335,122			—			—		2,335,122
	Total equity securities	3,399,651			—			—		3,399,651
	Short-term investments	1,209,462			138,769			—		1,348,231
	Total investments available-for-sale	$	4,609,113		$	10,375,506		$	—	$	14,984,619
	Liabilities:
	Derivative contracts	$	—		$	—		$	1,070	$	1,070
		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
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.
		Three Months Ended March 31,
	(dollars in thousands)	2014			2013
	Derivatives, beginning of period	$	2,230		$	12,690
	Total gains included in:
	Net income	(1,160		)	(3,290		)
	Other comprehensive income	—			—
	Transfers into Level 3	—			—
	Transfers out of Level 3	—			—
	Derivatives, end of period	$	1,070		$	9,400
	Net unrealized gains included in net income relating to liabilities held at March 31, 2014 and 2013 (1)	$	1,160		$	3,290
	(1)	Included in net investment income in the consolidated statements of income and comprehensive income.

Segment_Reporting_Disclosures_

Segment Reporting Disclosures (Tables)	3 Months Ended
	Mar. 31, 2014
Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract]	'
Company's Segment Disclosures	'
	The following tables summarize the Company's segment disclosures. The segment disclosures for the prior period have been revised to be consistent with the new segment structure.
		Three Months Ended March 31, 2014
	(dollars in thousands)	U.S.			International			Reinsurance			Other				Investing		Consolidated
		Insurance			Insurance						Insurance
											(Discontinued
											Lines)
	Gross premium volume	$	575,233		$	294,236		$	489,961		$	327			$	—	$	1,359,757
	Net written premiums	474,054			229,120			435,997			140				—		1,139,311
	Earned premiums	483,735			222,147			243,315			178				—		949,375
	Losses and loss adjustment expenses:
	Current accident year	(312,413		)	(163,379		)	(173,900		)	—				—		(649,692		)
	Prior accident years	43,554			42,297			28,200			(6,662		)		—		107,389
	Underwriting, acquisition and insurance expenses	(193,529		)	(80,009		)	(81,972		)	5				—		(355,505		)
	Underwriting profit (loss)	21,347			21,056			15,643			(6,479		)		—		51,567
	Net investment income	—			—			—			—				86,715		86,715
	Net realized investment gains	—			—			—			—				17,394		17,394
	Other revenues (insurance)	2,110			7,348			2,136			43				—		11,637
	Other expenses (insurance)	(1,647		)	(3,595		)	—			(8,615		)		—		(13,857		)
	Segment profit (loss)	$	21,810		$	24,809		$	17,779		$	(15,051	)		$	104,109	$	153,456
	Other revenues (non-insurance)																174,534
	Other expenses (non-insurance)																(168,311		)
	Amortization of intangible assets																(13,999		)
	Interest expense																(29,699		)
	Income before income taxes																$	115,981
	U.S. GAAP combined ratio (1)	96		%	91		%	94		%	NM			(2)			95		%
	(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.
		Three Months Ended March 31, 2013
	(dollars in thousands)	U.S.			International			Reinsurance			Other				Investing		Consolidated
		Insurance			Insurance						Insurance
											(Discontinued
											Lines)
	Gross premium volume	$	445,264		$	235,875		$	62,140		$	21			$	—	$	743,300
	Net written premiums	401,549			201,677			59,741			21				—		662,988
	Earned premiums	355,141			178,192			31,233			21				—		564,587
	Losses and loss adjustment expenses:
	Current accident year	(234,671		)	(120,862		)	(17,205		)	—				—		(372,738		)
	Prior accident years	62,404			23,000			(979		)	417				—		84,842
	Underwriting, acquisition and insurance expenses	(150,783		)	(69,774		)	(8,204		)	88				—		(228,673		)
	Underwriting profit (loss)	32,091			10,556			4,845			526				—		48,018
	Net investment income	—			—			—			—				64,617		64,617
	Net realized investment gains	—			—			—			—				17,917		17,917
	Other revenues (insurance)	7,263			3,962			—			—				—		11,225
	Other expenses (insurance)	(6,197		)	(1,358		)	—			—				—		(7,555		)
	Segment profit (loss)	$	33,157		$	13,160		$	4,845		$	526			$	82,534	$	134,222
	Other revenues (non-insurance)																161,518
	Other expenses (non-insurance)																(144,762		)
	Amortization of intangible assets																(9,615		)
	Interest expense																(23,574		)
	Income before income taxes																$	117,789
	U.S. GAAP combined ratio (1)	91		%	94		%	84		%	NM			(2)			91		%
	(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.
Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets	'
	The following table reconciles segment assets to the Company's consolidated balance sheets.
	(dollars in thousands)	March 31, 2014			December 31, 2013
	Segment assets:
	Investing	$	17,709,901		$	17,550,332
	Underwriting	5,771,517			5,468,731
	Total segment assets	23,481,418			23,019,063
	Non-insurance operations	971,574			936,448
	Total assets	$	24,452,992		$	23,955,511

Goodwill_Tables

Goodwill (Tables)	3 Months Ended
	Mar. 31, 2014
Goodwill [Abstract]	'
Components Of Goodwill	'
	The following table presents the components of goodwill by reportable segment.
	(dollars in thousands)	U.S.		International			Reinsurance		Other(1)		Total
		Insurance		Insurance
	31-Dec-13	$	280,579	$	372,764		$	122,745	$	191,629	$	967,717
	Acquisitions	—		37,530			—		15,258		52,788
	Foreign currency movements and other adjustments	—		(835		)	—		100		(735		)
	31-Mar-14	$	280,579	$	409,459		$	122,745	$	206,987	$	1,019,770
	(1)	Amounts included in Other are related to the Company's non-insurance operations, which are not included in a reportable segment.

Other_Revenues_And_Other_Expen1

Other Revenues And Other Expenses (Tables)	3 Months Ended
	Mar. 31, 2014
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.
		Three Months Ended March 31,
		2014				2013
	(dollars in thousands)	Other		Other		Other		Other
		Revenues		Expenses		Revenues		Expenses
	Insurance:
	Managing general agent operations	$	9,178	$	4,881	$	10,937	$	7,164
	Life and annuity	43		8,615		—		—
	Other	2,416		361		288		391
		11,637		13,857		11,225		7,555
	Non-Insurance:
	Markel Ventures: Manufacturing	100,611		95,889		128,576		115,184
	Markel Ventures: Non-Manufacturing	70,595		65,511		32,942		29,578
	Abbey: Consulting services	3,328		6,911		—		—
		174,534		168,311		161,518		144,762
	Total	$	186,171	$	182,168	$	172,743	$	152,317

Reinsurance_Tables

Reinsurance (Tables)	3 Months Ended
	Mar. 31, 2014
Reinsurance Disclosures [Abstract]	'
Effect Of Reinsurance On Premiums Written And Earned	'
	The following table summarizes the effect of reinsurance and retrocessional reinsurance on premiums written and earned.
		Three Months Ended March 31,
		2014						2013
	(dollars in thousands)	Written			Earned			Written			Earned
	Direct	$	795,311		$	828,292		$	597,419		$	538,142
	Assumed	564,446			347,699			145,881			102,127
	Ceded	(220,446		)	(226,616		)	(80,312		)	(75,682		)
	Net premiums	$	1,139,311		$	949,375		$	662,988		$	564,587

Net_Income_Per_Share_Tables

Net Income Per Share (Tables)	3 Months Ended
	Mar. 31, 2014
Earnings Per Share [Abstract]	'
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. 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 period.
		Three Months Ended March 31,
	(in thousands, except per share amounts)	2014		2013
	Net income to shareholders	$	87,716	$	88,902
	Adjustment of redeemable noncontrolling interests	117		2,886
	Adjusted net income to shareholders	$	87,833	$	91,788
	Basic common shares outstanding	13,995		9,636
	Dilutive potential common shares from conversion of options	11		3
	Dilutive potential common shares from conversion of restricted stock	52		27
	Diluted shares outstanding	14,058		9,666
	Basic net income per share	$	6.28	$	9.53
	Diluted net income per share	$	6.25	$	9.5

Other_Comprehensive_Income_Tab

Other Comprehensive Income (Tables)	3 Months Ended
	Mar. 31, 2014
Other Comprehensive Income (Loss), Tax [Abstract]	'
Change In Accumulated Other Comprehensive Income By Component, Net Of Taxes And Noncontrolling Interest	'
	The following table presents the change in accumulated other comprehensive income by component, net of taxes and noncontrolling interests, for the three months ended March 31, 2014 and 2013.
	(dollars in thousands)	Unrealized Holding Gains on Available-for-Sale Securities			Foreign Currency			Net Actuarial Pension Loss			Total
	31-Dec-12	$	946,933		$	(1,075	)	$	(34,521	)	$	911,337
	Other comprehensive income (loss) before reclassifications	181,848			(1,181		)	—			180,667
	Amounts reclassified from accumulated other comprehensive income	(12,255		)	—			370			(11,885		)
	Total other comprehensive income (loss)	169,593			(1,181		)	370			168,782
	31-Mar-13	$	1,116,526		$	(2,256	)	$	(34,151	)	$	1,080,119
	31-Dec-13	$	1,131,507		$	(11,246	)	$	(30,456	)	$	1,089,805
	Other comprehensive income before reclassifications	147,276			906			—			148,182
	Amounts reclassified from accumulated other comprehensive income	(5,944		)	—			319			(5,625		)
	Total other comprehensive income	141,332			906			319			142,557
	31-Mar-14	$	1,272,839		$	(10,340	)	$	(30,137	)	$	1,232,362
Summary Of Tax Expense Of Other Comprehensive Income	'
	The following table summarizes the tax expense associated with each component of other comprehensive income.
		Three Months Ended March 31,
	(dollars in thousands)	2014			2013
	Change in net unrealized gains on investments:
	Net holding gains arising during the period	$	75,523		$	85,546
	Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period	564			75
	Reclassification adjustments for net gains included in net income	(2,154		)	(5,662		)
	Change in net unrealized gains on investments	73,933			79,959
	Change in foreign currency translation adjustments	342			38
	Change in net actuarial pension loss	80			110
	Total	$	74,355		$	80,107
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.
		Three Months Ended March 31,
	(dollars in thousands)	2014			2013
	Unrealized holding gains on available-for-sale securities:
	Net realized investment gains	$	8,098		$	17,917
	Income taxes	(2,154		)	(5,662		)
	Reclassification of unrealized holding gains, net of taxes	$	5,944		$	12,255
	Net actuarial pension loss:
	Underwriting, acquisition and insurance expenses	$	(399	)	$	(480	)
	Income taxes	80			110
	Reclassification of net actuarial pension loss, net of taxes	$	(319	)	$	(370	)

Basis_Of_Presentation_Narrativ

Basis Of Presentation (Narrative) (Details) (May 1, 2013 Alterra Capital Holdings [Member], USD $)	6 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2013
May 1, 2013 Alterra Capital Holdings [Member]	'
Business Acquisition [Line Items]	'
Percentage of issued and outstanding common stock acquired	100.00%
Total purchase consideration	$3,300

Acquisitions_Narrative_Details

Acquisitions (Narrative) (Details) (USD $)

3 Months Ended

6 Months Ended

11 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

12 Months Ended

In Millions, except Share data, unless otherwise specified

Mar. 31, 2014

Jun. 30, 2013

Mar. 31, 2014

Jun. 30, 2013

Jun. 30, 2013

Jun. 30, 2013

Mar. 31, 2014

Jan. 17, 2014

Mar. 31, 2014

Jan. 17, 2014

Mar. 31, 2014

Jan. 17, 2014

Dec. 31, 2013

Jan. 17, 2014

Jan. 17, 2014

May 1, 2013 Alterra Capital Holdings [Member]

May 1, 2013 Alterra Capital Holdings [Member]

May 1, 2013 Alterra Capital Holdings [Member]

May 1, 2013 Alterra Capital Holdings [Member]

May 1, 2013 Alterra Capital Holdings [Member]

May 1, 2013 Alterra Capital Holdings [Member]

January 17, 2014 Abbey Protection plc [Member]

January 17, 2014 Abbey Protection plc [Member]

January 17, 2014 Abbey Protection plc [Member]

January 17, 2014 Abbey Protection plc [Member]

January 17, 2014 Abbey Protection plc [Member]

January 17, 2014 Abbey Protection plc [Member]

January 17, 2014 Abbey Protection plc [Member]

January 17, 2014 Abbey Protection plc [Member]

January 17, 2014 Abbey Protection plc [Member]

U.S. Insurance Segment [Member]

International Insurance Segment [Member]

Reinsurance Segment [Member]

Customer Relationships [Member]

Customer Relationships [Member]

Trade Names [Member]

Trade Names [Member]

Minimum [Member]

International Insurance Segment [Member]

Non-Insurance Operations [Member]

Business Acquisition [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage acquired

'

100.00%

'

'

'

'

'

100.00%

'

'

'

'

'

'

'

Number of Markel Corporation shares issued for each outstanding share of Alterra common stock

'

0.04315

'

'

'

'

'

'

'

'

'

'

'

'

'

Cash paid for each outstanding share of Alterra common stock

'

$10

'

'

'

'

'

'

'

'

'

'

'

'

'

Total purchase consideration

'

$3,300

'

'

'

'

$190.70

'

'

'

'

'

'

'

'

Cash consideration

'

964.3

'

'

'

'

190.7

'

'

'

'

'

'

'

'

Stock consideration, shares

'

4,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Goodwill recognized

'

295.7

'

107.8

89.8

98.1

'

52.8

'

'

'

'

'

37.5

15.3

Goodwill, expected tax deductible

'

0

'

'

'

'

'

0

'

'

'

'

'

'

'

Indefinite lived intangible assets

'

37.5

'

'

'

'

'

'

'

'

'

'

'

'

'

Other intangible assets

'

170

'

'

'

'

'

130.6

'

119.9

'

10.7

'

'

'

Other intangible assets, weighted average amortization period, years

'17 years

'

'

'

'

'

'

'

'20 years

'

'14 years

'

'

'

'

Investments acquired, adjustment to fair value

'

223.1

'

'

'

'

'

'

'

'

'

'

'

'

'

Investments acquired, incremental premium to be amortized to net investment income

'

495.5

'

'

'

'

'

'

'

'

'

'

'

'

'

Investments, unamortized incremental premium

299.9

'

299.9

'

'

'

'

'

'

'

'

'

'

'

'

Investments, amortization expense on incremental premium

18.4

'

76.7

'

'

'

'

'

'

'

'

'

'

'

'

Unpaid losses and loss adjustment expenses acquired, adjustment to fair value

'

120.8

'

'

'

'

'

'

'

'

'

'

'

'

'

Unpaid losses and loss adjustment expenses acquired pre acquisition adjustment, unamortized balance

'

26.5

'

'

'

'

'

'

'

'

'

'

'

'

'

Unpaid losses and loss adjustment expenses, weighted average amortization period, years

'5 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Unpaid losses and loss adjustment expenses, unamortized fair value adjustment

131

'

131

'

'

'

'

'

'

'

'

'

'

'

'

Senior long-term debt acquired, adjustment to fair value

'

71.9

'

'

'

'

'

'

'

'

'

'

'

'

'

Senior long-term debt acquired, unamortized premium

63.9

'

63.9

'

'

'

'

'

'

'

'

'

'

'

'

Premiums under management

'

'

'

'

'

'

'

'

'

'

'

'

$60

'

'

Investments_Narrative_Details

Investments (Narrative) (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	securities	securities
Schedule of Investments [Line Items]	'	'
Available-for-sale securities in unrealized loss position, number of positions	1,058	1,364
Available-for-sale securities, estimated fair value	$3,593,176	$4,859,071
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-107,573	-211,904
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end	11	9
Available-for-sale securities, estimated fair value, 12 months or longer	8,919	31,247
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-169	-546
Fixed Maturities [Member]	'	'
Schedule of Investments [Line Items]	'	'
Available-for-sale securities, estimated fair value	3,559,756	4,810,249
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-106,503	-210,786
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end	11	8
Available-for-sale securities, estimated fair value, 12 months or longer	8,919	3,512
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-169	-146
Equity Securities [Member]	'	'
Schedule of Investments [Line Items]	'	'
Available-for-sale securities, estimated fair value	33,420	48,822
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-1,070	-1,118
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end	'	1
Available-for-sale securities, estimated fair value, 12 months or longer	0	27,735
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	$0	($400)

Investments_AvailableForSale_I

Investments (Available-For-Sale Investments) (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	$13,070,696	$13,147,964
Available-for-sale investments, gross unrealized holding gains	2,021,496	1,910,562
Available-for-sale investments, gross unrealized holding losses	-103,255	-204,757
Available-for-sale investments, unrealized other-than-temporary impairment losses	-4,318	-7,147
Total investments, available-for-sale	14,984,619	14,846,622
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	780,801	1,215,522
Available-for-sale investments, gross unrealized holding gains	8,446	9,051
Available-for-sale investments, gross unrealized holding losses	-15,434	-30,342
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Total investments, available-for-sale	773,813	1,194,231
Obligations Of States, Municipalities And Political Subdivisions [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	3,509,045	2,986,758
Available-for-sale investments, gross unrealized holding gains	154,545	116,341
Available-for-sale investments, gross unrealized holding losses	-14,683	-27,384
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Total investments, available-for-sale	3,648,907	3,075,715
Foreign Governments [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	1,548,401	1,484,818
Available-for-sale investments, gross unrealized holding gains	40,642	30,647
Available-for-sale investments, gross unrealized holding losses	-19,458	-54,411
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Total investments, available-for-sale	1,569,585	1,461,054
Commercial Mortgage-Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	354,194	379,555
Available-for-sale investments, gross unrealized holding gains	1,010	62
Available-for-sale investments, gross unrealized holding losses	-4,143	-11,796
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Total investments, available-for-sale	351,061	367,821
Residential Mortgage-Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	963,494	875,902
Available-for-sale investments, gross unrealized holding gains	13,272	13,046
Available-for-sale investments, gross unrealized holding losses	-15,181	-16,442
Available-for-sale investments, unrealized other-than-temporary impairment losses	-2,258	-2,258
Total investments, available-for-sale	959,327	870,248
Asset-Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	184,342	189,646
Available-for-sale investments, gross unrealized holding gains	385	257
Available-for-sale investments, gross unrealized holding losses	-1,383	-1,614
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Total investments, available-for-sale	183,344	188,289
Corporate Bonds [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	2,734,254	2,996,940
Available-for-sale investments, gross unrealized holding gains	50,409	54,777
Available-for-sale investments, gross unrealized holding losses	-31,903	-61,650
Available-for-sale investments, unrealized other-than-temporary impairment losses	-2,060	-4,889
Total investments, available-for-sale	2,750,700	2,985,178
Total Fixed Maturities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	10,074,531	10,129,141
Available-for-sale investments, gross unrealized holding gains	268,709	224,181
Available-for-sale investments, gross unrealized holding losses	-102,185	-203,639
Available-for-sale investments, unrealized other-than-temporary impairment losses	-4,318	-7,147
Total investments, available-for-sale	10,236,737	10,142,536
Insurance, Banks And Other Financial Institutions [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	443,079	422,975
Available-for-sale investments, gross unrealized holding gains	621,467	592,112
Available-for-sale investments, gross unrealized holding losses	-17	-4
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Total investments, available-for-sale	1,064,529	1,015,083
Industrial, Consumer And All Other [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	1,204,874	1,143,578
Available-for-sale investments, gross unrealized holding gains	1,131,301	1,094,251
Available-for-sale investments, gross unrealized holding losses	-1,053	-1,114
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Total investments, available-for-sale	2,335,122	2,236,715
Total Equity Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	1,647,953	1,566,553
Available-for-sale investments, gross unrealized holding gains	1,752,768	1,686,363
Available-for-sale investments, gross unrealized holding losses	-1,070	-1,118
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Total investments, available-for-sale	3,399,651	3,251,798
Short-Term Investments [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale investments, amortized cost	1,348,212	1,452,270
Available-for-sale investments, gross unrealized holding gains	19	18
Available-for-sale investments, gross unrealized holding losses	0	0
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Total investments, available-for-sale	$1,348,231	$1,452,288

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 $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	$3,584,257	$4,827,824
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-107,404	-211,358
Available-for-sale securities, estimated fair value, 12 months or longer	8,919	31,247
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-169	-546
Available-for-sale securities, estimated fair value	3,593,176	4,859,071
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-107,573	-211,904
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	342,593	587,929
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-15,422	-30,342
Available-for-sale securities, estimated fair value, 12 months or longer	4,337	0
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-12	0
Available-for-sale securities, estimated fair value	346,930	587,929
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-15,434	-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	439,805	513,608
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-14,526	-27,238
Available-for-sale securities, estimated fair value, 12 months or longer	4,582	3,512
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-157	-146
Available-for-sale securities, estimated fair value	444,387	517,120
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-14,683	-27,384
Foreign Governments [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	734,180	950,040
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-19,458	-54,411
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	734,180	950,040
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-19,458	-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	206,242	357,737
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-4,143	-11,796
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	206,242	357,737
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-4,143	-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	508,762	437,675
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-17,439	-18,700
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	508,762	437,675
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-17,439	-18,700
Asset-Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	85,100	142,011
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-1,383	-1,614
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	85,100	142,011
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-1,383	-1,614
Corporate Bonds [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	1,234,155	1,817,737
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-33,963	-66,539
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	1,234,155	1,817,737
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-33,963	-66,539
Total Fixed Maturities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	3,550,837	4,806,737
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-106,334	-210,640
Available-for-sale securities, estimated fair value, 12 months or longer	8,919	3,512
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-169	-146
Available-for-sale securities, estimated fair value	3,559,756	4,810,249
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-106,503	-210,786
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	781	144
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-17	-4
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	781	144
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-17	-4
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	32,639	20,943
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-1,053	-714
Available-for-sale securities, estimated fair value, 12 months or longer	0	27,735
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	0	-400
Available-for-sale securities, estimated fair value	32,639	48,678
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-1,053	-1,114
Total Equity Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Available-for-sale securities, estimated fair value, less than 12 months	33,420	21,087
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-1,070	-718
Available-for-sale securities, estimated fair value, 12 months or longer	0	27,735
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	0	-400
Available-for-sale securities, estimated fair value	33,420	48,822
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	($1,070)	($1,118)

Investments_Schedule_Of_Amorti

Investments (Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturities By Contractual Maturity Date) (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]	'	'
Due in one year or less, amortized cost	$783,252	'
Due after one year through five years, amortized cost	2,404,376	'
Due after five years through ten years, amortized cost	2,167,719	'
Due after ten years, amortized cost	3,217,154	'
Amortized cost, sub-total	8,572,501	'
Total fixed maturities, amortized cost	10,074,531	10,129,141
Due in one year or less, estimated fair value	790,476	'
Due after one year through five years, estimated fair value	2,460,982	'
Due after five years through ten years, estimated fair value	2,236,464	'
Due after ten years, estimated fair value	3,255,083	'
Estimated fair value, sub-total	8,743,005	'
Total fixed maturities, estimated fair value	10,236,737	10,142,536
Commercial Mortgage-Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Fixed maturities, amortized cost	354,194	'
Fixed maturities, estimated fair value	351,061	'
Residential Mortgage-Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Fixed maturities, amortized cost	963,494	'
Fixed maturities, estimated fair value	959,327	'
Asset-Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Fixed maturities, amortized cost	184,342	'
Fixed maturities, estimated fair value	$183,344	'

Investments_Components_Of_Net_

Investments (Components Of Net Investment Income) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Schedule of Investment Income, Reported Amounts, by Category [Line Items]	'	'
Municipal bonds (tax-exempt)	$23,104	$21,448
Short-term investments, including overnight deposits	1,474	670
Dividends on equity securities	16,856	12,781
Change in fair value of credit default swap	1,160	3,290
Income from equity method investments	3,583	1,990
Other	19	62
Total investment income	90,936	67,276
Investment expenses	-4,221	-2,659
Net investment income	86,715	64,617
Taxable Municipal Bonds [Member]	'	'
Schedule of Investment Income, Reported Amounts, by Category [Line Items]	'	'
Taxable bonds	8,996	5,703
Other Taxable Bonds [Member]	'	'
Schedule of Investment Income, Reported Amounts, by Category [Line Items]	'	'
Taxable bonds	$35,744	$21,332

Investments_Summary_Of_Activit

Investments (Summary Of Activity For Credit Losses) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]	'	'
Cumulative credit loss, beginning balance	$12,748	$21,370
Other-than-temporary impairment losses not previously recognized	0	0
Increases related to other-than-temporary impairment losses previously recognized	0	0
Total additions	0	0
Sales or maturities of fixed maturities on which credit losses were recognized	-13	0
Cumulative credit loss, ending balance	$12,735	$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 $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Gain (Loss) on Investments [Line Items]	'	'
Realized gains	$26,683	$18,208
Realized losses	-9,289	-291
Net realized investment gains	17,394	17,917
Change in net unrealized gains on investments	215,265	249,552
Sales Of Fixed Maturities [Member]	'	'
Gain (Loss) on Investments [Line Items]	'	'
Realized gains	4,583	287
Realized losses	-8,484	-138
Sales Of Equity Securities [Member]	'	'
Gain (Loss) on Investments [Line Items]	'	'
Realized gains	12,145	17,921
Realized losses	-146	-153
Other [Member]	'	'
Gain (Loss) on Investments [Line Items]	'	'
Realized gains	9,955	0
Realized losses	-659	0
Fixed Maturities [Member]	'	'
Gain (Loss) on Investments [Line Items]	'	'
Change in net unrealized gains on investments	148,811	-31,348
Equity Securities [Member]	'	'
Gain (Loss) on Investments [Line Items]	'	'
Change in net unrealized gains on investments	66,453	280,895
Short-Term Investments [Member]	'	'
Gain (Loss) on Investments [Line Items]	'	'
Change in net unrealized gains on investments	$1	$5

Investments_Summary_Of_OtherTh

Investments (Summary Of Other-Than-Temporary Impairment Losses Recognized In Net Income And In Net Realized Investment Gains (Losses) By Investment Type) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Investments, Debt and Equity Securities [Abstract]	'	'
Write-downs for other-than-temporary declines in estimated fair value of investments	$0	$0

Fair_Value_Measurements_Narrat

Fair Value Measurements (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Fair Value Disclosures [Abstract]	'	'	'
Credit default swap, notional value	$33,100,000	'	$33,100,000
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 nonrecurring basis	0	0	'
Liabilities measured at fair value on a nonrecurring basis	$0	$0	'

Fair_Value_Measurements_Balanc

Fair Value Measurements (Balances Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total fixed maturities	$10,236,737	$10,142,536
Total equity securities	3,399,651	3,251,798
Short-term investments	1,348,231	1,452,288
Fair Value, Measurements, Recurring [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total fixed maturities	10,236,737	10,142,536
Total equity securities	3,399,651	3,251,798
Short-term investments	1,348,231	1,452,288
Available-for-sale investments, estimated fair value	14,984,619	14,846,622
Derivative contracts	1,070	2,230
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total fixed maturities	0	0
Total equity securities	3,399,651	3,251,798
Short-term investments	1,209,462	1,312,561
Available-for-sale investments, estimated fair value	4,609,113	4,564,359
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]	'	'
Total fixed maturities	10,236,737	10,142,536
Total equity securities	0	0
Short-term investments	138,769	139,727
Available-for-sale investments, estimated fair value	10,375,506	10,282,263
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]	'	'
Total fixed maturities	0	0
Total equity securities	0	0
Short-term investments	0	0
Available-for-sale investments, estimated fair value	0	0
Derivative contracts	1,070	2,230
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]	'	'
Total fixed maturities	773,813	1,194,231
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]	'	'
Total fixed maturities	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]	'	'
Total fixed maturities	773,813	1,194,231
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]	'	'
Total fixed maturities	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]	'	'
Total fixed maturities	3,648,907	3,075,715
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]	'	'
Total fixed maturities	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]	'	'
Total fixed maturities	3,648,907	3,075,715
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]	'	'
Total fixed maturities	0	0
Fair Value, Measurements, Recurring [Member] | Foreign Governments [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total fixed maturities	1,569,585	1,461,054
Fair Value, Measurements, Recurring [Member] | Foreign Governments [Member] | Level 1 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total fixed maturities	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]	'	'
Total fixed maturities	1,569,585	1,461,054
Fair Value, Measurements, Recurring [Member] | Foreign Governments [Member] | Level 3 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total fixed maturities	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]	'	'
Total fixed maturities	351,061	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]	'	'
Total fixed maturities	0	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]	'	'
Total fixed maturities	351,061	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]	'	'
Total fixed maturities	0	0
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total fixed maturities	959,327	870,248
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]	'	'
Total fixed maturities	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]	'	'
Total fixed maturities	959,327	870,248
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]	'	'
Total fixed maturities	0	0
Fair Value, Measurements, Recurring [Member] | Asset-Backed Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total fixed maturities	183,344	188,289
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]	'	'
Total fixed maturities	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]	'	'
Total fixed maturities	183,344	188,289
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]	'	'
Total fixed maturities	0	0
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total fixed maturities	2,750,700	2,985,178
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Level 1 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total fixed maturities	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]	'	'
Total fixed maturities	2,750,700	2,985,178
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Level 3 [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total fixed maturities	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]	'	'
Total equity securities	1,064,529	1,015,083
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]	'	'
Total equity securities	1,064,529	1,015,083
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]	'	'
Total 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]	'	'
Total 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]	'	'
Total equity securities	2,335,122	2,236,715
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]	'	'
Total equity securities	2,335,122	2,236,715
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]	'	'
Total 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]	'	'
Total 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 $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Fair Value Disclosures [Abstract]	'		'
Derivatives, beginning of period	$2,230		$12,690
Total gains included in net income	-1,160		-3,290
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	1,070		9,400
Net unrealized gains included in net income relating to liabilities held at March 31, 2014 and 2013	$1,160	[1]	$3,290	[1]
[1]	Included in net investment income in the consolidated statements of income and comprehensive income.

Segment_Reporting_Disclosures_1

Segment Reporting Disclosures (Company's Segment Disclosures) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
	segment
Segment Reporting Information [Line Items]	'		'
Number of reportable ongoing underwriting segments	3		'
Gross premium volume	$1,359,757		$743,300
Net written premiums	1,139,311		662,988
Earned premiums	949,375		564,587
Losses and loss adjustment expenses, current accident year	-649,692		-372,738
Losses and loss adjustment expenses, prior accident years	107,389		84,842
Underwriting, acquisition and insurance expenses	-355,505		-228,673
Underwriting profit (loss)	51,567		48,018
Net investment income	86,715		64,617
Net realized investment gains	17,394		17,917
Other revenues (insurance)	11,637		11,225
Other expenses (insurance)	-13,857		-7,555
Segment profit (loss)	153,456		134,222
Other revenues (non-insurance)	174,534		161,518
Other expenses (non-insurance)	-168,311		-144,762
Amortization of intangible assets	-13,999		-9,615
Interest expense	-29,699		-23,574
Income Before Income Taxes	115,981		117,789
U.S. GAAP combined ratio	95.00%	[1]	91.00%	[1]
U.S. Insurance [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Gross premium volume	575,233		445,264
Net written premiums	474,054		401,549
Earned premiums	483,735		355,141
Losses and loss adjustment expenses, current accident year	-312,413		-234,671
Losses and loss adjustment expenses, prior accident years	43,554		62,404
Underwriting, acquisition and insurance expenses	-193,529		-150,783
Underwriting profit (loss)	21,347		32,091
Net investment income	0		0
Net realized investment gains	0		0
Other revenues (insurance)	2,110		7,263
Other expenses (insurance)	-1,647		-6,197
Segment profit (loss)	21,810		33,157
U.S. GAAP combined ratio	96.00%	[1]	91.00%	[1]
International Insurance [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Gross premium volume	294,236		235,875
Net written premiums	229,120		201,677
Earned premiums	222,147		178,192
Losses and loss adjustment expenses, current accident year	-163,379		-120,862
Losses and loss adjustment expenses, prior accident years	42,297		23,000
Underwriting, acquisition and insurance expenses	-80,009		-69,774
Underwriting profit (loss)	21,056		10,556
Net investment income	0		0
Net realized investment gains	0		0
Other revenues (insurance)	7,348		3,962
Other expenses (insurance)	-3,595		-1,358
Segment profit (loss)	24,809		13,160
U.S. GAAP combined ratio	91.00%	[1]	94.00%	[1]
Reinsurance [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Gross premium volume	489,961		62,140
Net written premiums	435,997		59,741
Earned premiums	243,315		31,233
Losses and loss adjustment expenses, current accident year	-173,900		-17,205
Losses and loss adjustment expenses, prior accident years	28,200		-979
Underwriting, acquisition and insurance expenses	-81,972		-8,204
Underwriting profit (loss)	15,643		4,845
Net investment income	0		0
Net realized investment gains	0		0
Other revenues (insurance)	2,136		0
Other expenses (insurance)	0		0
Segment profit (loss)	17,779		4,845
U.S. GAAP combined ratio	94.00%	[1]	84.00%	[1]
Other Insurance (Discontinued Lines) [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Gross premium volume	327		21
Net written premiums	140		21
Earned premiums	178		21
Losses and loss adjustment expenses, current accident year	0		0
Losses and loss adjustment expenses, prior accident years	-6,662		417
Underwriting, acquisition and insurance expenses	5		88
Underwriting profit (loss)	-6,479		526
Net investment income	0		0
Net realized investment gains	0		0
Other revenues (insurance)	43		0
Other expenses (insurance)	-8,615		0
Segment profit (loss)	-15,051		526
U.S. GAAP combined ratio - not meaniningful	'NM	[1],[2]	'NM	[1],[2]
Investing [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Gross premium volume	0		0
Net written premiums	0		0
Earned premiums	0		0
Losses and loss adjustment expenses, current accident year	0		0
Losses and loss adjustment expenses, prior accident years	0		0
Underwriting, acquisition and insurance expenses	0		0
Underwriting profit (loss)	0		0
Net investment income	86,715		64,617
Net realized investment gains	17,394		17,917
Other revenues (insurance)	0		0
Other expenses (insurance)	0		0
Segment profit (loss)	$104,109		$82,534
[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 b Ratio is not meaningful.

Segment_Reporting_Disclosures_2

Segment Reporting Disclosures (Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Segment Reporting Information [Line Items]	'	'
Assets	$24,452,992	$23,955,511
Non-Insurance Operations [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	971,574	936,448
Segment Assets [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	23,481,418	23,019,063
Segment Assets [Member] | Investing [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	17,709,901	17,550,332
Segment Assets [Member] | Underwriting [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	$5,771,517	$5,468,731

Goodwill_Components_Of_Goodwil

Goodwill (Components Of Goodwill) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014
Goodwill [Line Items]	'
Goodwill, beginning balance	$967,717
Acquisitions	52,788
Foreign currency movements and other adjustments	-735
Goodwill, ending balance	1,019,770
U.S. Insurance [Member]	'
Goodwill [Line Items]	'
Goodwill, beginning balance	280,579
Acquisitions	0
Foreign currency movements and other adjustments	0
Goodwill, ending balance	280,579
International Insurance [Member]	'
Goodwill [Line Items]	'
Goodwill, beginning balance	372,764
Acquisitions	37,530
Foreign currency movements and other adjustments	-835
Goodwill, ending balance	409,459
Reinsurance [Member]	'
Goodwill [Line Items]	'
Goodwill, beginning balance	122,745
Acquisitions	0
Foreign currency movements and other adjustments	0
Goodwill, ending balance	122,745
Other [Member]	'
Goodwill [Line Items]	'
Goodwill, beginning balance	191,629	[1]
Acquisitions	15,258	[1]
Foreign currency movements and other adjustments	100	[1]
Goodwill, ending balance	$206,987	[1]
[1]	Amounts included in Other are related to the Company's non-insurance operations, which are not included in a reportable segment.

Other_Revenues_And_Other_Expen2

Other Revenues And Other Expenses (Summary Of Other Revenues And Other Expenses By Component) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Other Revenues and Other Expenses [Line Items]	'	'
Other revenues	$186,171	$172,743
Other expenses	182,168	152,317
Insurance Operations [Member]	'	'
Other Revenues and Other Expenses [Line Items]	'	'
Other revenues	11,637	11,225
Other expenses	13,857	7,555
Non-Insurance Operations [Member]	'	'
Other Revenues and Other Expenses [Line Items]	'	'
Other revenues	174,534	161,518
Other expenses	168,311	144,762
Managing General Agent Operations [Member] | Insurance Operations [Member]	'	'
Other Revenues and Other Expenses [Line Items]	'	'
Other revenues	9,178	10,937
Other expenses	4,881	7,164
Life And Annuity [Member] | Insurance Operations [Member]	'	'
Other Revenues and Other Expenses [Line Items]	'	'
Other revenues	43	0
Other expenses	8,615	0
Other [Member] | Insurance Operations [Member]	'	'
Other Revenues and Other Expenses [Line Items]	'	'
Other revenues	2,416	288
Other expenses	361	391
Manufacturing [Member] | Non-Insurance Operations [Member] | Markel Ventures Operations [Member]	'	'
Other Revenues and Other Expenses [Line Items]	'	'
Other revenues	100,611	128,576
Other expenses	95,889	115,184
Non-Manufacturing [Member] | Non-Insurance Operations [Member] | Markel Ventures Operations [Member]	'	'
Other Revenues and Other Expenses [Line Items]	'	'
Other revenues	70,595	32,942
Other expenses	65,511	29,578
Consulting Services [Member] | Non-Insurance Operations [Member] | Abbey Protection plc [Member]	'	'
Other Revenues and Other Expenses [Line Items]	'	'
Other revenues	3,328	0
Other expenses	$6,911	$0

Reinsurance_Narrative_Details

Reinsurance (Narrative) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Reinsurance Disclosures [Abstract]	'	'
Percentage of ceded earned premiums to gross earned premiums	19.00%	12.00%
Reinsurance recoverables	$97.60	'

Reinsurance_Effect_Of_Reinsura

Reinsurance (Effect Of Reinsurance On Premiums Written And Earned) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Reinsurance Disclosures [Abstract]	'	'
Direct premiums written	$795,311	$597,419
Direct premiums earned	828,292	538,142
Assumed premiums written	564,446	145,881
Assumed premiums earned	347,699	102,127
Ceded premiums written	-220,446	-80,312
Ceded premiums earned	-226,616	-75,682
Net premiums written	1,139,311	662,988
Net premiums earned	$949,375	$564,587

Net_Income_Per_Share_Schedule_

Net Income Per Share (Schedule Of Net Income Per Share) (Details) (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share [Line Items]	'	'
Net income to shareholders	$87,716	$88,902
Adjustment of redeemable noncontrolling interests	117	2,886
Adjusted net income to shareholders	$87,833	$91,788
Basic common shares outstanding	13,995	9,636
Diluted shares outstanding	14,058	9,666
Basic net income per share	$6.28	$9.53
Diluted net income per share	$6.25	$9.50
Stock Options [Member]	'	'
Earnings Per Share [Line Items]	'	'
Dilutive potential common shares	11	3
Restricted Stock Units (RSUs) [Member]	'	'
Earnings Per Share [Line Items]	'	'
Dilutive potential common shares	52	27

Other_Comprehensive_Income_Cha

Other Comprehensive Income (Change In Accumulated Other Comprehensive Income By Component, Net Of Taxes And Noncontrolling Interest) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Accumulated Other Comprehensive Income [Line Items]	'	'
Accumulated other comprehensive income, beginning balance	$1,089,805	$911,337
Other comprehensive income (loss) before reclassifications	148,182	180,667
Amounts reclassified from accumulated other comprehensive income	-5,625	-11,885
Total other comprehensive income (loss)	142,557	168,782
Accumulated other comprehensive income, ending balance	1,232,362	1,080,119
Unrealized Holding Gains On Available-For-Sale Securities [Member]	'	'
Accumulated Other Comprehensive Income [Line Items]	'	'
Accumulated other comprehensive income, beginning balance	1,131,507	946,933
Other comprehensive income (loss) before reclassifications	147,276	181,848
Amounts reclassified from accumulated other comprehensive income	-5,944	-12,255
Total other comprehensive income (loss)	141,332	169,593
Accumulated other comprehensive income, ending balance	1,272,839	1,116,526
Foreign Currency [Member]	'	'
Accumulated Other Comprehensive Income [Line Items]	'	'
Accumulated other comprehensive income, beginning balance	-11,246	-1,075
Other comprehensive income (loss) before reclassifications	906	-1,181
Amounts reclassified from accumulated other comprehensive income	0	0
Total other comprehensive income (loss)	906	-1,181
Accumulated other comprehensive income, ending balance	-10,340	-2,256
Net Actuarial Pension Loss [Member]	'	'
Accumulated Other Comprehensive Income [Line Items]	'	'
Accumulated other comprehensive income, beginning balance	-30,456	-34,521
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	319	370
Total other comprehensive income (loss)	319	370
Accumulated other comprehensive income, ending balance	($30,137)	($34,151)

Other_Comprehensive_Income_Sum

Other Comprehensive Income (Summary Of Tax Expense Of Other Comprehensive Income) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Other Comprehensive Income (Loss), Tax [Abstract]	'	'
Net holding gains arising during the period	$75,523	$85,546
Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period	564	75
Reclassification adjustments for net gains included in net income	-2,154	-5,662
Change in net unrealized gains on investments	73,933	79,959
Change in foreign currency translation adjustments	342	38
Change in net actuarial pension loss	80	110
Total	$74,355	$80,107

Other_Comprehensive_Income_Rec

Other Comprehensive Income (Reclassifications From Accumulated Other Comprehensive Income Into Income, By Component) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]	'	'
Net realized investment gains	$17,394	$17,917
Underwriting, acquisition and insurance expenses	-355,505	-228,673
Income taxes	-28,480	-28,526
Net Income	87,501	89,263
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]	'	'
Net realized investment gains	8,098	17,917
Income taxes	-2,154	-5,662
Net Income	5,944	12,255
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	-399	-480
Income taxes	80	110
Net Income	($319)	($370)