Markel (MKL) 10-Q 6 May 15 2015 Q1 Quarterly report Financial data

Document_And_Entity_Informatio

Document And Entity Information	3 Months Ended
	Mar. 31, 2015	Apr. 29, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	FALSE
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Entity Registrant Name	MARKEL CORP
Entity Central Index Key	1096343
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		13,945,734

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
ASSETS
Fixed maturities (amortized cost of $9,371,731 in 2015 and $9,929,137 in 2014)	$9,971,814	$10,422,882
Equity securities (cost of $2,096,586 in 2015 and $1,951,658 in 2014)	4,340,849	4,137,576
Short-term investments (estimated fair value approximates cost)	1,731,872	1,594,849
Total Investments	16,044,535	16,155,307
Cash and cash equivalents	1,958,087	1,960,169
Restricted cash and cash equivalents	550,610	522,225
Receivables	1,193,405	1,135,217
Reinsurance recoverable on unpaid losses	1,949,974	1,868,669
Reinsurance recoverable on paid losses	113,816	102,206
Deferred policy acquisition costs	369,632	353,410
Prepaid reinsurance premiums	365,496	365,458
Goodwill	1,039,911	1,049,115
Intangible assets	680,357	702,747
Other assets	987,566	985,834
Total Assets	25,253,389	25,200,357
LIABILITIES AND EQUITY
Unpaid losses and loss adjustment expenses	10,280,037	10,404,152
Life and annuity benefits	1,189,140	1,305,818
Unearned premiums	2,316,508	2,245,690
Payables to insurance and reinsurance companies	286,102	276,122
Senior long-term debt and other debt (estimated fair value of $2,525,000 in 2015 and $2,493,000 in 2014)	2,249,554	2,253,594
Other liabilities	999,542	1,051,931
Total Liabilities	17,320,883	17,537,307
Redeemable noncontrolling interests	55,108	61,048
Commitments and contingencies
Shareholders' equity:
Common stock	3,320,323	3,308,395
Retained earnings	2,753,963	2,581,866
Accumulated other comprehensive income	1,795,372	1,704,557
Total Shareholders' Equity	7,869,658	7,594,818
Noncontrolling interests	7,740	7,184
Total Equity	7,877,398	7,602,002
Total Liabilities and Equity	$25,253,389	$25,200,357

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Statement of Financial Position [Abstract]
Fixed maturities, amortized cost	$9,371,731	$9,929,137
Equity securities, cost	2,096,586	1,951,658
Senior long-term debt and other debt, estimated fair value	$2,525,000	$2,493,000

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, 2015	Mar. 31, 2014
OPERATING REVENUES
Earned premiums	$943,650	$949,375
Net investment income	92,875	86,715
Other-than-temporary impairment losses	-5,092	0
Net realized investment gains, excluding other-than-temporary impairment losses	10,663	17,394
Net realized investment gains	5,571	17,394
Other revenues	260,058	186,171
Total Operating Revenues	1,302,154	1,239,655
OPERATING EXPENSES
Losses and loss adjustment expenses	446,995	542,303
Underwriting, acquisition and insurance expenses	340,685	355,505
Amortization of intangible assets	14,640	13,999
Other expenses	231,001	182,168
Total Operating Expenses	1,033,321	1,093,975
Operating Income	268,833	145,680
Interest expense	29,312	29,699
Income Before Income Taxes	239,521	115,981
Income tax expense	45,515	28,480
Net Income	194,006	87,501
Net income (loss) attributable to noncontrolling interests	3,014	-215
Net Income to Shareholders	190,992	87,716
OTHER COMPREHENSIVE INCOME
Net holding gains arising during the period	121,022	147,296
Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period	167	-20
Reclassification adjustments for net gains included in net income	-9,053	-5,944
Change in net unrealized gains on investments, net of taxes	112,136	141,332
Change in foreign currency translation adjustments, net of taxes	-21,814	913
Change in net actuarial pension loss, net of taxes	463	319
Total Other Comprehensive Income	90,785	142,564
Comprehensive Income (Loss)	284,791	230,065
Comprehensive income (loss) attributable to noncontrolling interests	2,984	-208
Comprehensive Income to Shareholders	$281,807	$230,273
NET INCOME PER SHARE
Basic (in dollars per share)	$13.57	$6.28
Diluted (in dollars per share)	$13.49	$6.25

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, redeemable noncontrolling interests at Dec. 31, 2013								$72,183
Balance at Dec. 31, 2013		6,678,010	6,673,577	3,288,863	2,294,909	1,089,805	4,433
Balance, shares at Dec. 31, 2013				13,986
Net income (loss)	87,501	87,392	87,716		87,716	0	-324	109
Other comprehensive income (loss)	142,564	142,557	142,557		0	142,557	0	7
Comprehensive Income (Loss)	230,065	229,949	230,273				-324	116
Issuance of common stock		4,363	4,363	4,363	0	0	0	0
Issuance of common stock, shares				22
Repurchase of common stock		-17,282	-17,282	0	-17,282	0	0	0
Repurchase of common stock, shares				-39
Restricted stock units expensed		8,421	8,421	8,421	0	0	0	0
Restricted stock units expensed, shares				0
Adjustment of redeemable noncontrolling interests		117	117	0	117	0	0	-117
Adjustment of redeemable noncontrolling interests, shares				0
Purchase of noncontrolling interest		647	647	647	0	0	0	-18,405
Purchase of noncontrolling interest, shares				0
Other		3,961	16	7	9	0	3,945	-862
Other, shares				0
Balance, redeemable noncontrolling interests at Mar. 31, 2014								52,915
Balance at Mar. 31, 2014		6,908,186	6,900,132	3,302,301	2,365,469	1,232,362	8,054
Balance, shares at Mar. 31, 2014				13,969
Balance, redeemable noncontrolling interests at Dec. 31, 2014	61,048							61,048
Balance at Dec. 31, 2014	7,602,002	7,602,002	7,594,818	3,308,395	2,581,866	1,704,557	7,184
Balance, shares at Dec. 31, 2014				13,962
Net income (loss)	194,006	191,503	190,992		190,992	0	511	2,503
Other comprehensive income (loss)	90,785	90,815	90,815		0	90,815	0	-30
Comprehensive Income (Loss)	284,791	282,318	281,807				511	2,473
Issuance of common stock		429	429	429	0	0	0	0
Issuance of common stock, shares				5
Repurchase of common stock		-17,548	-17,548	0	-17,548	0	0	0
Repurchase of common stock, shares				-21
Restricted stock units expensed		10,632	10,632	10,632	0	0	0	0
Restricted stock units expensed, shares				0
Adjustment of redeemable noncontrolling interests		-1,347	-1,347	0	-1,347	0	0	1,347
Adjustment of redeemable noncontrolling interests, shares				0
Purchase of noncontrolling interest		-903	-903	-903	0	0	0	-8,609
Purchase of noncontrolling interest, shares				0
Other		1,815	1,770	1,770	0	0	45	-1,151
Other, shares				0
Balance, redeemable noncontrolling interests at Mar. 31, 2015	55,108							55,108
Balance at Mar. 31, 2015	$7,877,398	$7,877,398	$7,869,658	$3,320,323	$2,753,963	$1,795,372	$7,740
Balance, shares at Mar. 31, 2015				13,946

Condensed_Consolidated_Stateme

Condensed Consolidated Statements Of Cash Flows (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
OPERATING ACTIVITIES
Net income	$194,006	$87,501
Adjustments to reconcile net income to net cash provided by operating activities	-171,174	-65,084
Net Cash Provided By Operating Activities	22,832	22,417
INVESTING ACTIVITIES
Proceeds from sales of fixed maturities and equity securities	71,721	660,447
Proceeds from maturities, calls and prepayments of fixed maturities	388,522	440,891
Cost of fixed maturities and equity securities purchased	-232,551	-1,114,736
Net change in short-term investments	-146,545	130,557
Proceeds from sales of equity method investments	15,003	82,518
Cost of equity method investments	-600	-8,050
Change in restricted cash and cash equivalents	-40,841	152,897
Additions to property and equipment	-23,606	-10,725
Acquisitions, net of cash acquired	0	-153,735
Other	-441	384
Net Cash Provided By Investing Activities	30,662	180,448
FINANCING ACTIVITIES
Additions to senior long-term debt and other debt	27,711	10,120
Repayment of senior long-term debt and other debt	-29,160	-8,608
Repurchases of common stock	-17,548	-17,282
Issuance of common stock	429	4,363
Purchase of noncontrolling interests	-10,314	-17,758
Distributions to noncontrolling interests	-1,159	-1,168
Other	-3,407	-609
Net Cash Used By Financing Activities	-33,448	-30,942
Effect of foreign currency rate changes on cash and cash equivalents	-22,128	971
Increase (decrease) in cash and cash equivalents	-2,082	172,894
Cash and cash equivalents at beginning of period	1,960,169	1,978,526
CASH AND CASH EQUIVALENTS AT END OF PERIOD	$1,958,087	$2,151,420

Basis_Of_Presentation

Basis Of Presentation	3 Months Ended
	Mar. 31, 2015
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.
	The consolidated balance sheet as of March 31, 2015 and the related consolidated statements of income and comprehensive income, changes in equity and cash flows for the three months ended March 31, 2015 and 2014 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, 2014 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 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 2014 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, 2015
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements
	In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers (Topic 606), which creates a new comprehensive revenue recognition standard that will serve as a single source of revenue guidance for all companies in all industries. The guidance applies to all companies that either enter into contracts with customers to transfer goods or services or enter into contracts for the transfer of nonfinancial assets, unless those contracts are within the scope of other standards, such as insurance contracts. ASU No. 2014-09's core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In doing so, companies will need to use more judgment and make more estimates than under the current guidance. These may include identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. ASU No. 2014-09 becomes effective for the Company during the first quarter of 2017 and may be applied retrospectively or under a modified retrospective method where the cumulative effect is recognized at the date of initial application. Early application is not permitted. On April 29, 2015, the FASB proposed a one-year deferral of the effective date for ASU 2014-09. Early application would be permitted for all entities, but not before the original effective date for public business entities. The Company is currently evaluating ASU No. 2014-09 to determine the potential impact that adopting this standard will have on its consolidated financial statements. Adoption of this ASU is not expected to have a significant impact on the Company's insurance operations, but will impact the Company's non-insurance operations.
	In February 2015, the FASB issued ASU No. 2015-02, Consolidation (Topic 810): Amendments to the Consolidation Analysis, which changes the way reporting enterprises evaluate whether (a) they should consolidate limited partnerships and similar entities, (b) fees paid to a decision maker or service provider are variable interests in a variable interest entity (VIE), and (c) variable interests in a VIE held by related parties of the reporting enterprise require the reporting enterprise to consolidate the VIE. It also eliminates the VIE consolidation model based on majority exposure to variability that applied to certain investment companies and similar entities. The ASU also significantly changes how to evaluate voting rights for entities that are not similar to limited partnerships when determining whether the entity is a VIE, which may affect entities for which the decision making rights are conveyed through a contractual arrangement. ASU No. 2015-02 becomes effective for the Company during the first quarter of 2016 and may be applied retrospectively or under a modified retrospective method where the cumulative-effect adjustment to retained earnings is recognized as of the beginning of the fiscal year of adoption. Reporting enterprises may also restate previously issued financial statements for one or more years with a cumulative-effect adjustment to retained earnings as of the beginning of the first year restated. Early adoption is allowed. The Company is currently evaluating ASU No. 2015-02 to determine the potential impact that adopting this standard will have on its consolidated financial statements.

Investments

Investments	3 Months Ended
	Mar. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Investments	Investments
	a)The following tables summarize the Company's available-for-sale investments.
		March 31, 2015
	(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	$	612,368		$	17,212		$	(764	)	$	—		$	628,816
	Obligations of states, municipalities and political subdivisions	3,956,064			251,023			(2,661		)	—			4,204,426
	Foreign governments	1,336,176			213,901			(191		)	—			1,549,886
	Commercial mortgage-backed securities	408,016			8,861			(1,255		)	—			415,622
	Residential mortgage-backed securities	920,185			44,219			(1,774		)	(2,258		)	960,372
	Asset-backed securities	77,341			73			(295		)	—			77,119
	Corporate bonds	2,061,581			78,801			(3,198		)	(1,611		)	2,135,573
	Total fixed maturities	9,371,731			614,090			(10,138		)	(3,869		)	9,971,814
	Equity securities:
	Insurance, banks and other financial institutions	588,140			798,628			(1,740		)	—			1,385,028
	Industrial, consumer and all other	1,508,446			1,458,816			(11,441		)	—			2,955,821
	Total equity securities	2,096,586			2,257,444			(13,181		)	—			4,340,849
	Short-term investments	1,731,862			13			(3		)	—			1,731,872
	Investments, available-for-sale	$	13,200,179		$	2,871,547		$	(23,322	)	$	(3,869	)	$	16,044,535
		December 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	$	662,462		$	12,963		$	(2,163	)	$	—		$	673,262
	Obligations of states, municipalities and political subdivisions	4,075,748			245,158			(3,359		)	—			4,317,547
	Foreign governments	1,458,255			154,707			(1,041		)	—			1,611,921
	Commercial mortgage-backed securities	427,904			5,325			(2,602		)	—			430,627
	Residential mortgage-backed securities	954,263			34,324			(3,482		)	(2,258		)	982,847
	Asset-backed securities	100,073			99			(682		)	—			99,490
	Corporate bonds	2,250,432			69,016			(10,441		)	(1,819		)	2,307,188
	Total fixed maturities	9,929,137			521,592			(23,770		)	(4,077		)	10,422,882
	Equity securities:
	Insurance, banks and other financial institutions	523,739			789,717			(1,531		)	—			1,311,925
	Industrial, consumer and all other	1,427,919			1,403,566			(5,834		)	—			2,825,651
	Total equity securities	1,951,658			2,193,283			(7,365		)	—			4,137,576
	Short-term investments	1,594,819			36			(6		)	—			1,594,849
	Investments, available-for-sale	$	13,475,614		$	2,714,911		$	(31,141	)	$	(4,077	)	$	16,155,307
	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, 2015
		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	$	5,716		$	(3	)	$	125,651		$	(761	)	$	131,367	$	(764	)
	Obligations of states, municipalities and political subdivisions	95,257			(547		)	61,394			(2,114		)	156,651		(2,661		)
	Foreign governments	16,965			(68		)	44,204			(123		)	61,169		(191		)
	Commercial mortgage-backed securities	51,673			(157		)	107,698			(1,098		)	159,371		(1,255		)
	Residential mortgage-backed securities	3,726			(2,277		)	167,295			(1,755		)	171,021		(4,032		)
	Asset-backed securities	10,147			(17		)	45,378			(278		)	55,525		(295		)
	Corporate bonds	74,273			(1,742		)	373,451			(3,067		)	447,724		(4,809		)
	Total fixed maturities	257,757			(4,811		)	925,071			(9,196		)	1,182,828		(14,007		)
	Equity securities:
Insurance, banks and other financial institutions	16,810			(1,740		)	—			—			16,810		(1,740		)
Industrial, consumer and all other	158,284			(11,441		)	—			—			158,284		(11,441		)
Total equity securities	175,094			(13,181		)	—			—			175,094		(13,181		)
Short-term investments	440,985			(3		)	—			—			440,985		(3		)
Total	$	873,836		$	(17,995	)	$	925,071		$	(9,196	)	$	1,798,907	$	(27,191	)
At March 31, 2015, the Company held 424 securities with a total estimated fair value of $1.8 billion and gross unrealized losses of $27.2 million. Of these 424 securities, 281 securities had been in a continuous unrealized loss position for one year or longer and had a total estimated fair value of $925.1 million and gross unrealized losses of $9.2 million. All 281 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, 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	$	108,250		$	(62	)	$	163,359		$	(2,101	)	$	271,609	$	(2,163	)
Obligations of states, municipalities and political subdivisions	58,583			(542		)	92,441			(2,817		)	151,024		(3,359		)
Foreign governments	18,856			(386		)	56,217			(655		)	75,073		(1,041		)
Commercial mortgage-backed securities	45,931			(210		)	147,558			(2,392		)	193,489		(2,602		)
Residential mortgage-backed securities	9,613			(2,285		)	207,374			(3,455		)	216,987		(5,740		)
Asset-backed securities	30,448			(20		)	45,160			(662		)	75,608		(682		)
Corporate bonds	141,176			(2,263		)	621,821			(9,997		)	762,997		(12,260		)
Total fixed maturities	412,857			(5,768		)	1,333,930			(22,079		)	1,746,787		(27,847		)
Equity securities:
Insurance, banks and other financial institutions	16,219			(1,531		)	—			—			16,219		(1,531		)
Industrial, consumer and all other	86,062			(5,834		)	—			—			86,062		(5,834		)
Total equity securities	102,281			(7,365		)	—			—			102,281		(7,365		)
Short-term investments	181,964			(6		)	—			—			181,964		(6		)
Total	$	697,102		$	(13,139	)	$	1,333,930		$	(22,079	)	$	2,031,032	$	(35,218	)
At December 31, 2014, the Company held 552 securities with a total estimated fair value of $2.0 billion and gross unrealized losses of $35.2 million. Of these 552 securities, 396 securities had been in a continuous unrealized loss position for one year or longer and had a total estimated fair value of $1.3 billion and gross unrealized losses of $22.1 million. All 396 securities were fixed maturities.
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, 2015 are shown below by contractual maturity.
(dollars in thousands)	Amortized			Estimated
	Cost			Fair Value
Due in one year or less	$	617,588		$	620,740
Due after one year through five years	1,904,996			1,962,240
Due after five years through ten years	1,925,821			2,054,347
Due after ten years	3,517,784			3,881,374
	7,966,189			8,518,701
Commercial mortgage-backed securities	408,016			415,622
Residential mortgage-backed securities	920,185			960,372
Asset-backed securities	77,341			77,119
Total fixed maturities	$	9,371,731		$	9,971,814
d)The following table presents the components of net investment income.
	Three Months Ended March 31,
(dollars in thousands)	2015			2014
Interest:
Municipal bonds (tax-exempt)	$	25,852		$	23,104
Municipal bonds (taxable)	14,100			8,996
Other taxable bonds	35,138			35,744
Short-term investments, including overnight deposits	1,251			1,474
Dividends on equity securities	19,024			16,856
Income from equity method investments	1,344			3,583
Other	61			1,179
	96,770			90,936
Investment expenses	(3,895		)	(4,221		)
Net investment income	$	92,875		$	86,715
e)Cumulative 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 were $10.7 million at March 31, 2015 and $12.7 million at December 31, 2014.
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)	2015			2014
Realized gains:
Sales of fixed maturities	$	1,586		$	4,583
Sales of equity securities	15,957			12,145
Other	1,307			9,955
Total realized gains	18,850			26,683
Realized losses:
Sales of fixed maturities	(142		)	(8,484		)
Sales of equity securities	(160		)	(146		)
Other-than-temporary impairments	(5,092		)	—
Other	(7,885		)	(659		)
Total realized losses	(13,279		)	(9,289		)
Net realized investment gains	$	5,571		$	17,394
Change in net unrealized gains on investments:
Fixed maturities	$	106,338		$	148,811
Equity securities	58,345			66,453
Short-term investments	(20		)	1
Net increase	$	164,663		$	215,265
Other-than-temporary impairment losses recognized in net income and included in net realized investment gains included losses attributable to equity securities totaling $5.1 million for the three months ended March 31, 2015. There were no writedowns for other-than-temporary declines in the estimated fair value of investments for the three months ended March 31, 2014.

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2015
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.
	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, 2015
	(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	$	—	$	628,816	$	—	$	628,816
	Obligations of states, municipalities and political subdivisions	—		4,204,426		—		4,204,426
	Foreign governments	—		1,549,886		—		1,549,886
	Commercial mortgage-backed securities	—		415,622		—		415,622
	Residential mortgage-backed securities	—		960,372		—		960,372
	Asset-backed securities	—		77,119		—		77,119
	Corporate bonds	—		2,135,573		—		2,135,573
	Total fixed maturities	—		9,971,814		—		9,971,814
	Equity securities:
	Insurance, banks and other financial institutions	1,385,028		—		—		1,385,028
	Industrial, consumer and all other	2,955,821		—		—		2,955,821
	Total equity securities	4,340,849		—		—		4,340,849
	Short-term investments	1,618,657		113,215		—		1,731,872
	Total investments available-for-sale	$	5,959,506	$	10,085,029	$	—	$	16,044,535
		December 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	$	—	$	673,262	$	—	$	673,262
	Obligations of states, municipalities and political subdivisions	—		4,317,547		—		4,317,547
	Foreign governments	—		1,611,921		—		1,611,921
	Commercial mortgage-backed securities	—		430,627		—		430,627
	Residential mortgage-backed securities	—		982,847		—		982,847
	Asset-backed securities	—		99,490		—		99,490
	Corporate bonds	—		2,307,188		—		2,307,188
	Total fixed maturities	—		10,422,882		—		10,422,882
	Equity securities:
	Insurance, banks and other financial institutions	1,311,925		—		—		1,311,925
	Industrial, consumer and all other	2,825,651		—		—		2,825,651
	Total equity securities	4,137,576		—		—		4,137,576
	Short-term investments	1,469,975		124,874		—		1,594,849
	Total investments available-for-sale	$	5,607,551	$	10,547,756	$	—	$	16,155,307
	There were no transfers into or out of Level 1 and Level 2 during the three months ended March 31, 2015 and 2014.
	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, 2015 and 2014.

Segment_Reporting_Disclosures

Segment Reporting Disclosures	3 Months Ended
	Mar. 31, 2015
Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract]
Segment Reporting Disclosures	Segment Reporting Disclosures
	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, are 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. 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.
		Three Months Ended March 31, 2015
	(dollars in thousands)	U.S.			International			Reinsurance			Other				Investing		Consolidated
		Insurance			Insurance						Insurance
											(Discontinued
											Lines)
	Gross premium volume	$	585,365		$	289,227		$	377,837		$	44			$	—	$	1,252,473
	Net written premiums	496,169			222,708			316,212			341				—		1,035,430
	Earned premiums	514,554			205,961			222,754			381				—		943,650
	Losses and loss adjustment expenses:
	Current accident year	(316,757		)	(148,844		)	(148,740		)	—				—		(614,341		)
	Prior accident years	67,581			76,650			26,387			(3,272		)		—		167,346
	Underwriting, acquisition and insurance expenses	(185,260		)	(78,794		)	(76,553		)	(78		)		—		(340,685		)
	Underwriting profit (loss)	80,118			54,973			23,848			(2,969		)		—		155,970
	Net investment income	—			—			—			—				92,875		92,875
	Net realized investment gains	—			—			—			—				5,571		5,571
	Other revenues (insurance)	1,402			5,387			423			(23		)		—		7,189
	Other expenses (insurance)	(905		)	(1,404		)	—			(7,349		)		—		(9,658		)
	Segment profit (loss)	$	80,615		$	58,956		$	24,271		$	(10,341	)		$	98,446	$	251,947
	Other revenues (non-insurance)																252,869
	Other expenses (non-insurance)																(221,343		)
	Amortization of intangible assets																(14,640		)
	Interest expense																(29,312		)
	Income before income taxes																$	239,521
	U.S. GAAP combined ratio (1)	84		%	73		%	89		%	NM			(2)			83		%
	(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, 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.
	b)	The following table reconciles segment assets to the Company's consolidated balance sheets.
	(dollars in thousands)	March 31, 2015			December 31, 2014
	Segment assets:
	Investing	$	18,450,247		$	18,531,150
	Underwriting	5,584,980			5,422,445
	Total segment assets	24,035,227			23,953,595
Non-insurance operations	1,218,162			1,246,762
Total assets	$	25,253,389		$	25,200,357

Other_Revenues_And_Other_Expen

Other Revenues And Other Expenses	3 Months Ended
	Mar. 31, 2015
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,
		2015					2014
	(dollars in thousands)	Other			Other		Other		Other
		Revenues			Expenses		Revenues		Expenses
	Insurance:
	Managing general agent operations	$	5,870		$	2,309	$	9,178	$	4,881
	Life and annuity	(23		)	7,349		43		8,615
	Other	1,342			—		2,416		361
		7,189			9,658		11,637		13,857
	Non-Insurance:
	Markel Ventures: Manufacturing	177,762			151,800		100,611		95,889
	Markel Ventures: Non-Manufacturing	67,681			63,830		70,595		65,511
	Other	7,426			5,713		3,328		6,911
		252,869			221,343		174,534		168,311
	Total	$	260,058		$	231,001	$	186,171	$	182,168
	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.

Reinsurance

Reinsurance	3 Months Ended
	Mar. 31, 2015
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,
		2015						2014
	(dollars in thousands)	Written			Earned			Written			Earned
	Direct	$	801,580		$	844,570		$	795,311		$	828,292
	Assumed	450,893			312,835			564,446			347,699
	Ceded	(217,043		)	(213,755		)	(220,446		)	(226,616		)
	Net premiums	$	1,035,430		$	943,650		$	1,139,311		$	949,375
	The percentage of ceded earned premiums to gross earned premiums was 18% and 19%, respectively, for the three months ended March 31, 2015 and 2014. The percentage of assumed earned premiums to net earned premiums was 33% and 37%, respectively, for the three months ended March 31, 2015 and 2014.
	Incurred losses and loss adjustment expenses were net of reinsurance recoverables (ceded incurred losses and loss adjustment expenses) of $88.8 million and $97.6 million, respectively, for the three months ended March 31, 2015 and 2014.
	On March 9, 2015, the Company completed a retrospective reinsurance transaction to cede a portfolio of policies comprised of liabilities arising from asbestos and environmental exposures that originated before 1992 in exchange for payments totaling $89.0 million, which included cash paid at closing of $69.9 million. At the time of the transaction, reserves for unpaid losses and loss adjustment expenses on the policies ceded totaled $94.1 million, resulting in a deferred gain of $5.1 million which will be recognized in earnings in future periods in proportion to actual reinsurance recoveries received pursuant to the transaction. The ceded reserves represented approximately 35% of our net asbestos and environmental reserves for losses and loss adjustment expenses as of December 31, 2014.

Income_Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes
	The estimated annual effective tax rate was 19% and 25% for the three months ended March 31, 2015 and 2014, respectively. For the three months ended March 31, 2015, the estimated annual effective tax rate differs from the U.S. statutory tax rate of 35% primarily as a result of tax-exempt investment income and foreign tax credits for foreign taxes paid. In previous periods, foreign taxes paid were not available for use as tax credits against the Company's U.S. provision for income taxes. Based on the Company's estimated earnings from foreign operations in 2015, the Company expects that significant foreign taxes paid, both in the current period and prior periods, will be available for use as credits against its U.S. provision for income taxes in 2015. For the three months ended March 31, 2014, the estimated annual effective tax rate differs from the U.S. statutory tax rate of 35% primarily as a result of tax-exempt investment income. The decrease in the estimated annual effective tax rate in 2015 compared to 2014 was primarily due to the impact of the foreign tax credits described above.

Net_Income_Per_Share

Net Income Per Share	3 Months Ended
	Mar. 31, 2015
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)	2015			2014
	Net income to shareholders	$	190,992		$	87,716
	Adjustment of redeemable noncontrolling interests	(1,347		)	117
	Adjusted net income to shareholders	$	189,645		$	87,833
	Basic common shares outstanding	13,972			13,995
	Dilutive potential common shares from conversion of options	10			11
	Dilutive potential common shares from conversion of restricted stock	81			52
	Diluted shares outstanding	14,063			14,058
	Basic net income per share	$	13.57		$	6.28
	Diluted net income per share	$	13.49		$	6.25

Other_Comprehensive_Income

Other Comprehensive Income	3 Months Ended
	Mar. 31, 2015
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, 2015 and 2014.
	(dollars in thousands)	Unrealized Holding Gains on Available-for-Sale Securities			Foreign Currency			Net Actuarial Pension Loss			Total
	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
	31-Dec-14	$	1,793,254		$	(43,491	)	$	(45,206	)	$	1,704,557
	Other comprehensive income (loss) before reclassifications	121,189			(21,784		)	—			99,405
	Amounts reclassified from accumulated other comprehensive income	(9,053		)	—			463			(8,590		)
	Total other comprehensive income (loss)	112,136			(21,784		)	463			90,815
	31-Mar-15	$	1,905,390		$	(65,275	)	$	(44,743	)	$	1,795,372
	The following table summarizes the tax expense (benefit) associated with each component of other comprehensive income.
		Three Months Ended March 31,
	(dollars in thousands)	2015			2014
	Change in net unrealized gains on investments:
	Net holding gains arising during the period	$	55,582		$	75,523
	Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period	41			564
	Reclassification adjustments for net gains included in net income	(3,096		)	(2,154		)
	Change in net unrealized gains on investments	52,527			73,933
	Change in foreign currency translation adjustments	(1,039		)	342
	Change in net actuarial pension loss	116			80
	Total	$	51,604		$	74,355
	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)	2015			2014
	Unrealized holding gains on available-for-sale securities:
	Other-than-temporary impairment losses	$	(5,092	)	$	—
	Net realized investment gains, excluding other-than-temporary impairment losses	17,241			8,098
	Total before taxes	12,149			8,098
	Income taxes	(3,096		)	(2,154		)
	Reclassification of unrealized holding gains, net of taxes	$	9,053		$	5,944
	Net actuarial pension loss:
	Underwriting, acquisition and insurance expenses	$	(579	)	$	(399	)
	Income taxes	116			80
	Reclassification of net actuarial pension loss, net of taxes	$	(463	)	$	(319	)

Contingencies

Contingencies	3 Months Ended
	Mar. 31, 2015
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, 2015
Investments, Debt and Equity Securities [Abstract]
Available-For-Sale Investments	The following tables summarize the Company's available-for-sale investments.
		March 31, 2015
	(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	$	612,368		$	17,212		$	(764	)	$	—		$	628,816
	Obligations of states, municipalities and political subdivisions	3,956,064			251,023			(2,661		)	—			4,204,426
	Foreign governments	1,336,176			213,901			(191		)	—			1,549,886
	Commercial mortgage-backed securities	408,016			8,861			(1,255		)	—			415,622
	Residential mortgage-backed securities	920,185			44,219			(1,774		)	(2,258		)	960,372
	Asset-backed securities	77,341			73			(295		)	—			77,119
	Corporate bonds	2,061,581			78,801			(3,198		)	(1,611		)	2,135,573
	Total fixed maturities	9,371,731			614,090			(10,138		)	(3,869		)	9,971,814
	Equity securities:
	Insurance, banks and other financial institutions	588,140			798,628			(1,740		)	—			1,385,028
	Industrial, consumer and all other	1,508,446			1,458,816			(11,441		)	—			2,955,821
	Total equity securities	2,096,586			2,257,444			(13,181		)	—			4,340,849
	Short-term investments	1,731,862			13			(3		)	—			1,731,872
	Investments, available-for-sale	$	13,200,179		$	2,871,547		$	(23,322	)	$	(3,869	)	$	16,044,535
		December 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	$	662,462		$	12,963		$	(2,163	)	$	—		$	673,262
	Obligations of states, municipalities and political subdivisions	4,075,748			245,158			(3,359		)	—			4,317,547
	Foreign governments	1,458,255			154,707			(1,041		)	—			1,611,921
	Commercial mortgage-backed securities	427,904			5,325			(2,602		)	—			430,627
	Residential mortgage-backed securities	954,263			34,324			(3,482		)	(2,258		)	982,847
	Asset-backed securities	100,073			99			(682		)	—			99,490
	Corporate bonds	2,250,432			69,016			(10,441		)	(1,819		)	2,307,188
	Total fixed maturities	9,929,137			521,592			(23,770		)	(4,077		)	10,422,882
	Equity securities:
	Insurance, banks and other financial institutions	523,739			789,717			(1,531		)	—			1,311,925
	Industrial, consumer and all other	1,427,919			1,403,566			(5,834		)	—			2,825,651
	Total equity securities	1,951,658			2,193,283			(7,365		)	—			4,137,576
	Short-term investments	1,594,819			36			(6		)	—			1,594,849
	Investments, available-for-sale	$	13,475,614		$	2,714,911		$	(31,141	)	$	(4,077	)	$	16,155,307
Summary Of Gross Unrealized Investment Losses By Length Of Time That Securities Have Continuously Been In An Unrealized Loss Position
		December 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	$	108,250		$	(62	)	$	163,359		$	(2,101	)	$	271,609	$	(2,163	)
	Obligations of states, municipalities and political subdivisions	58,583			(542		)	92,441			(2,817		)	151,024		(3,359		)
	Foreign governments	18,856			(386		)	56,217			(655		)	75,073		(1,041		)
	Commercial mortgage-backed securities	45,931			(210		)	147,558			(2,392		)	193,489		(2,602		)
	Residential mortgage-backed securities	9,613			(2,285		)	207,374			(3,455		)	216,987		(5,740		)
	Asset-backed securities	30,448			(20		)	45,160			(662		)	75,608		(682		)
	Corporate bonds	141,176			(2,263		)	621,821			(9,997		)	762,997		(12,260		)
	Total fixed maturities	412,857			(5,768		)	1,333,930			(22,079		)	1,746,787		(27,847		)
	Equity securities:
	Insurance, banks and other financial institutions	16,219			(1,531		)	—			—			16,219		(1,531		)
	Industrial, consumer and all other	86,062			(5,834		)	—			—			86,062		(5,834		)
	Total equity securities	102,281			(7,365		)	—			—			102,281		(7,365		)
	Short-term investments	181,964			(6		)	—			—			181,964		(6		)
	Total	$	697,102		$	(13,139	)	$	1,333,930		$	(22,079	)	$	2,031,032	$	(35,218	)
	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, 2015
		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	$	5,716		$	(3	)	$	125,651		$	(761	)	$	131,367	$	(764	)
	Obligations of states, municipalities and political subdivisions	95,257			(547		)	61,394			(2,114		)	156,651		(2,661		)
	Foreign governments	16,965			(68		)	44,204			(123		)	61,169		(191		)
	Commercial mortgage-backed securities	51,673			(157		)	107,698			(1,098		)	159,371		(1,255		)
	Residential mortgage-backed securities	3,726			(2,277		)	167,295			(1,755		)	171,021		(4,032		)
	Asset-backed securities	10,147			(17		)	45,378			(278		)	55,525		(295		)
	Corporate bonds	74,273			(1,742		)	373,451			(3,067		)	447,724		(4,809		)
	Total fixed maturities	257,757			(4,811		)	925,071			(9,196		)	1,182,828		(14,007		)
	Equity securities:
	Insurance, banks and other financial institutions	16,810			(1,740		)	—			—			16,810		(1,740		)
	Industrial, consumer and all other	158,284			(11,441		)	—			—			158,284		(11,441		)
	Total equity securities	175,094			(13,181		)	—			—			175,094		(13,181		)
	Short-term investments	440,985			(3		)	—			—			440,985		(3		)
	Total	$	873,836		$	(17,995	)	$	925,071		$	(9,196	)	$	1,798,907	$	(27,191	)
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, 2015 are shown below by contractual maturity.
	(dollars in thousands)	Amortized			Estimated
		Cost			Fair Value
	Due in one year or less	$	617,588		$	620,740
	Due after one year through five years	1,904,996			1,962,240
	Due after five years through ten years	1,925,821			2,054,347
	Due after ten years	3,517,784			3,881,374
		7,966,189			8,518,701
	Commercial mortgage-backed securities	408,016			415,622
	Residential mortgage-backed securities	920,185			960,372
	Asset-backed securities	77,341			77,119
	Total fixed maturities	$	9,371,731		$	9,971,814
Components Of Net Investment Income	The following table presents the components of net investment income.
		Three Months Ended March 31,
	(dollars in thousands)	2015			2014
	Interest:
	Municipal bonds (tax-exempt)	$	25,852		$	23,104
	Municipal bonds (taxable)	14,100			8,996
	Other taxable bonds	35,138			35,744
	Short-term investments, including overnight deposits	1,251			1,474
	Dividends on equity securities	19,024			16,856
	Income from equity method investments	1,344			3,583
	Other	61			1,179
		96,770			90,936
	Investment expenses	(3,895		)	(4,221		)
	Net investment income	$	92,875		$	86,715
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)	2015			2014
	Realized gains:
	Sales of fixed maturities	$	1,586		$	4,583
	Sales of equity securities	15,957			12,145
	Other	1,307			9,955
	Total realized gains	18,850			26,683
	Realized losses:
	Sales of fixed maturities	(142		)	(8,484		)
	Sales of equity securities	(160		)	(146		)
	Other-than-temporary impairments	(5,092		)	—
	Other	(7,885		)	(659		)
	Total realized losses	(13,279		)	(9,289		)
	Net realized investment gains	$	5,571		$	17,394
	Change in net unrealized gains on investments:
	Fixed maturities	$	106,338		$	148,811
	Equity securities	58,345			66,453
	Short-term investments	(20		)	1
	Net increase	$	164,663		$	215,265

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2015
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, 2015
	(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	$	—	$	628,816	$	—	$	628,816
	Obligations of states, municipalities and political subdivisions	—		4,204,426		—		4,204,426
	Foreign governments	—		1,549,886		—		1,549,886
	Commercial mortgage-backed securities	—		415,622		—		415,622
	Residential mortgage-backed securities	—		960,372		—		960,372
	Asset-backed securities	—		77,119		—		77,119
	Corporate bonds	—		2,135,573		—		2,135,573
	Total fixed maturities	—		9,971,814		—		9,971,814
	Equity securities:
	Insurance, banks and other financial institutions	1,385,028		—		—		1,385,028
	Industrial, consumer and all other	2,955,821		—		—		2,955,821
	Total equity securities	4,340,849		—		—		4,340,849
	Short-term investments	1,618,657		113,215		—		1,731,872
	Total investments available-for-sale	$	5,959,506	$	10,085,029	$	—	$	16,044,535
		December 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	$	—	$	673,262	$	—	$	673,262
	Obligations of states, municipalities and political subdivisions	—		4,317,547		—		4,317,547
	Foreign governments	—		1,611,921		—		1,611,921
	Commercial mortgage-backed securities	—		430,627		—		430,627
	Residential mortgage-backed securities	—		982,847		—		982,847
	Asset-backed securities	—		99,490		—		99,490
	Corporate bonds	—		2,307,188		—		2,307,188
	Total fixed maturities	—		10,422,882		—		10,422,882
	Equity securities:
	Insurance, banks and other financial institutions	1,311,925		—		—		1,311,925
	Industrial, consumer and all other	2,825,651		—		—		2,825,651
	Total equity securities	4,137,576		—		—		4,137,576
	Short-term investments	1,469,975		124,874		—		1,594,849
	Total investments available-for-sale	$	5,607,551	$	10,547,756	$	—	$	16,155,307

Segment_Reporting_Disclosures_

Segment Reporting Disclosures (Tables)	3 Months Ended
	Mar. 31, 2015
Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract]
Company's Segment Disclosures	The following tables summarize the Company's segment disclosures.
		Three Months Ended March 31, 2015
	(dollars in thousands)	U.S.			International			Reinsurance			Other				Investing		Consolidated
		Insurance			Insurance						Insurance
											(Discontinued
											Lines)
	Gross premium volume	$	585,365		$	289,227		$	377,837		$	44			$	—	$	1,252,473
	Net written premiums	496,169			222,708			316,212			341				—		1,035,430
	Earned premiums	514,554			205,961			222,754			381				—		943,650
	Losses and loss adjustment expenses:
	Current accident year	(316,757		)	(148,844		)	(148,740		)	—				—		(614,341		)
	Prior accident years	67,581			76,650			26,387			(3,272		)		—		167,346
	Underwriting, acquisition and insurance expenses	(185,260		)	(78,794		)	(76,553		)	(78		)		—		(340,685		)
	Underwriting profit (loss)	80,118			54,973			23,848			(2,969		)		—		155,970
	Net investment income	—			—			—			—				92,875		92,875
	Net realized investment gains	—			—			—			—				5,571		5,571
	Other revenues (insurance)	1,402			5,387			423			(23		)		—		7,189
	Other expenses (insurance)	(905		)	(1,404		)	—			(7,349		)		—		(9,658		)
	Segment profit (loss)	$	80,615		$	58,956		$	24,271		$	(10,341	)		$	98,446	$	251,947
	Other revenues (non-insurance)																252,869
	Other expenses (non-insurance)																(221,343		)
	Amortization of intangible assets																(14,640		)
	Interest expense																(29,312		)
	Income before income taxes																$	239,521
	U.S. GAAP combined ratio (1)	84		%	73		%	89		%	NM			(2)			83		%
	(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, 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.
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, 2015			December 31, 2014
	Segment assets:
	Investing	$	18,450,247		$	18,531,150
	Underwriting	5,584,980			5,422,445
	Total segment assets	24,035,227			23,953,595
	Non-insurance operations	1,218,162			1,246,762
	Total assets	$	25,253,389		$	25,200,357

Other_Revenues_And_Other_Expen1

Other Revenues And Other Expenses (Tables)	3 Months Ended
	Mar. 31, 2015
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,
		2015					2014
	(dollars in thousands)	Other			Other		Other		Other
		Revenues			Expenses		Revenues		Expenses
	Insurance:
	Managing general agent operations	$	5,870		$	2,309	$	9,178	$	4,881
	Life and annuity	(23		)	7,349		43		8,615
	Other	1,342			—		2,416		361
		7,189			9,658		11,637		13,857
	Non-Insurance:
	Markel Ventures: Manufacturing	177,762			151,800		100,611		95,889
	Markel Ventures: Non-Manufacturing	67,681			63,830		70,595		65,511
	Other	7,426			5,713		3,328		6,911
		252,869			221,343		174,534		168,311
	Total	$	260,058		$	231,001	$	186,171	$	182,168

Reinsurance_Tables

Reinsurance (Tables)	3 Months Ended
	Mar. 31, 2015
Reinsurance Disclosures [Abstract]
Effect Of Reinsurance And Retrocessional 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,
		2015						2014
	(dollars in thousands)	Written			Earned			Written			Earned
	Direct	$	801,580		$	844,570		$	795,311		$	828,292
	Assumed	450,893			312,835			564,446			347,699
	Ceded	(217,043		)	(213,755		)	(220,446		)	(226,616		)
	Net premiums	$	1,035,430		$	943,650		$	1,139,311		$	949,375

Net_Income_Per_Share_Tables

Net Income Per Share (Tables)	3 Months Ended
	Mar. 31, 2015
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)	2015			2014
	Net income to shareholders	$	190,992		$	87,716
	Adjustment of redeemable noncontrolling interests	(1,347		)	117
	Adjusted net income to shareholders	$	189,645		$	87,833
	Basic common shares outstanding	13,972			13,995
	Dilutive potential common shares from conversion of options	10			11
	Dilutive potential common shares from conversion of restricted stock	81			52
	Diluted shares outstanding	14,063			14,058
	Basic net income per share	$	13.57		$	6.28
	Diluted net income per share	$	13.49		$	6.25

Other_Comprehensive_Income_Tab

Other Comprehensive Income (Tables)	3 Months Ended
	Mar. 31, 2015
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, 2015 and 2014.
	(dollars in thousands)	Unrealized Holding Gains on Available-for-Sale Securities			Foreign Currency			Net Actuarial Pension Loss			Total
	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
	31-Dec-14	$	1,793,254		$	(43,491	)	$	(45,206	)	$	1,704,557
	Other comprehensive income (loss) before reclassifications	121,189			(21,784		)	—			99,405
	Amounts reclassified from accumulated other comprehensive income	(9,053		)	—			463			(8,590		)
	Total other comprehensive income (loss)	112,136			(21,784		)	463			90,815
	31-Mar-15	$	1,905,390		$	(65,275	)	$	(44,743	)	$	1,795,372
Summary Of Tax Expense (Benefit) Of Other Comprehensive Income	The following table summarizes the tax expense (benefit) associated with each component of other comprehensive income.
		Three Months Ended March 31,
	(dollars in thousands)	2015			2014
	Change in net unrealized gains on investments:
	Net holding gains arising during the period	$	55,582		$	75,523
	Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period	41			564
	Reclassification adjustments for net gains included in net income	(3,096		)	(2,154		)
	Change in net unrealized gains on investments	52,527			73,933
	Change in foreign currency translation adjustments	(1,039		)	342
	Change in net actuarial pension loss	116			80
	Total	$	51,604		$	74,355
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)	2015			2014
	Unrealized holding gains on available-for-sale securities:
	Other-than-temporary impairment losses	$	(5,092	)	$	—
	Net realized investment gains, excluding other-than-temporary impairment losses	17,241			8,098
	Total before taxes	12,149			8,098
	Income taxes	(3,096		)	(2,154		)
	Reclassification of unrealized holding gains, net of taxes	$	9,053		$	5,944
	Net actuarial pension loss:
	Underwriting, acquisition and insurance expenses	$	(579	)	$	(399	)
	Income taxes	116			80
	Reclassification of net actuarial pension loss, net of taxes	$	(463	)	$	(319	)

Investments_Narrative_Details

Investments (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
	securities		securities
Schedule of Investments [Line Items]
Available-for-sale securities in unrealized loss position, number of positions	424		552
Available-for-sale securities, estimated fair value	$1,798,907,000		$2,031,032,000
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-27,191,000		-35,218,000
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end	281		396
Available-for-sale securities, estimated fair value, 12 months or longer	925,071,000		1,333,930,000
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-9,196,000		-22,079,000
Cumulative credit losses recognized in net income	10,700,000		12,700,000
Other-than-temporary impairment losses recognized in net income	-5,092,000	0
Fixed Maturities [Member]
Schedule of Investments [Line Items]
Available-for-sale securities, estimated fair value	1,182,828,000		1,746,787,000
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-14,007,000		-27,847,000
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end	281		396
Available-for-sale securities, estimated fair value, 12 months or longer	925,071,000		1,333,930,000
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-9,196,000		-22,079,000
Equity Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale securities, estimated fair value	175,094,000		102,281,000
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-13,181,000		-7,365,000
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
Other-than-temporary impairment losses recognized in net income	($5,100,000)

Investments_AvailableForSale_I

Investments (Available-For-Sale Investments) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	$13,200,179	$13,475,614
Available-for-sale investments, gross unrealized holding gains	2,871,547	2,714,911
Available-for-sale investments, gross unrealized holding losses	-23,322	-31,141
Available-for-sale investments, unrealized other-than-temporary impairment losses	-3,869	-4,077
Available-for-sale investments, estimated fair value	16,044,535	16,155,307
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	612,368	662,462
Available-for-sale investments, gross unrealized holding gains	17,212	12,963
Available-for-sale investments, gross unrealized holding losses	-764	-2,163
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	628,816	673,262
Obligations Of States, Municipalities And Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	3,956,064	4,075,748
Available-for-sale investments, gross unrealized holding gains	251,023	245,158
Available-for-sale investments, gross unrealized holding losses	-2,661	-3,359
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	4,204,426	4,317,547
Foreign Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	1,336,176	1,458,255
Available-for-sale investments, gross unrealized holding gains	213,901	154,707
Available-for-sale investments, gross unrealized holding losses	-191	-1,041
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	1,549,886	1,611,921
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	408,016	427,904
Available-for-sale investments, gross unrealized holding gains	8,861	5,325
Available-for-sale investments, gross unrealized holding losses	-1,255	-2,602
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	415,622	430,627
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	920,185	954,263
Available-for-sale investments, gross unrealized holding gains	44,219	34,324
Available-for-sale investments, gross unrealized holding losses	-1,774	-3,482
Available-for-sale investments, unrealized other-than-temporary impairment losses	-2,258	-2,258
Available-for-sale investments, estimated fair value	960,372	982,847
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	77,341	100,073
Available-for-sale investments, gross unrealized holding gains	73	99
Available-for-sale investments, gross unrealized holding losses	-295	-682
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	77,119	99,490
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	2,061,581	2,250,432
Available-for-sale investments, gross unrealized holding gains	78,801	69,016
Available-for-sale investments, gross unrealized holding losses	-3,198	-10,441
Available-for-sale investments, unrealized other-than-temporary impairment losses	-1,611	-1,819
Available-for-sale investments, estimated fair value	2,135,573	2,307,188
Total Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	9,371,731	9,929,137
Available-for-sale investments, gross unrealized holding gains	614,090	521,592
Available-for-sale investments, gross unrealized holding losses	-10,138	-23,770
Available-for-sale investments, unrealized other-than-temporary impairment losses	-3,869	-4,077
Available-for-sale investments, estimated fair value	9,971,814	10,422,882
Insurance, Banks And Other Financial Institutions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	588,140	523,739
Available-for-sale investments, gross unrealized holding gains	798,628	789,717
Available-for-sale investments, gross unrealized holding losses	-1,740	-1,531
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	1,385,028	1,311,925
Industrial, Consumer And All Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	1,508,446	1,427,919
Available-for-sale investments, gross unrealized holding gains	1,458,816	1,403,566
Available-for-sale investments, gross unrealized holding losses	-11,441	-5,834
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	2,955,821	2,825,651
Total Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	2,096,586	1,951,658
Available-for-sale investments, gross unrealized holding gains	2,257,444	2,193,283
Available-for-sale investments, gross unrealized holding losses	-13,181	-7,365
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	4,340,849	4,137,576
Short-Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	1,731,862	1,594,819
Available-for-sale investments, gross unrealized holding gains	13	36
Available-for-sale investments, gross unrealized holding losses	-3	-6
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	$1,731,872	$1,594,849

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, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	$873,836	$697,102
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-17,995	-13,139
Available-for-sale securities, estimated fair value, 12 months or longer	925,071	1,333,930
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-9,196	-22,079
Available-for-sale securities, estimated fair value	1,798,907	2,031,032
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-27,191	-35,218
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	5,716	108,250
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-3	-62
Available-for-sale securities, estimated fair value, 12 months or longer	125,651	163,359
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-761	-2,101
Available-for-sale securities, estimated fair value	131,367	271,609
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-764	-2,163
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	95,257	58,583
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-547	-542
Available-for-sale securities, estimated fair value, 12 months or longer	61,394	92,441
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-2,114	-2,817
Available-for-sale securities, estimated fair value	156,651	151,024
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-2,661	-3,359
Foreign Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	16,965	18,856
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-68	-386
Available-for-sale securities, estimated fair value, 12 months or longer	44,204	56,217
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-123	-655
Available-for-sale securities, estimated fair value	61,169	75,073
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-191	-1,041
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	51,673	45,931
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-157	-210
Available-for-sale securities, estimated fair value, 12 months or longer	107,698	147,558
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-1,098	-2,392
Available-for-sale securities, estimated fair value	159,371	193,489
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-1,255	-2,602
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	3,726	9,613
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-2,277	-2,285
Available-for-sale securities, estimated fair value, 12 months or longer	167,295	207,374
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-1,755	-3,455
Available-for-sale securities, estimated fair value	171,021	216,987
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-4,032	-5,740
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	10,147	30,448
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-17	-20
Available-for-sale securities, estimated fair value, 12 months or longer	45,378	45,160
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-278	-662
Available-for-sale securities, estimated fair value	55,525	75,608
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-295	-682
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	74,273	141,176
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-1,742	-2,263
Available-for-sale securities, estimated fair value, 12 months or longer	373,451	621,821
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-3,067	-9,997
Available-for-sale securities, estimated fair value	447,724	762,997
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-4,809	-12,260
Total Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	257,757	412,857
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-4,811	-5,768
Available-for-sale securities, estimated fair value, 12 months or longer	925,071	1,333,930
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	-9,196	-22,079
Available-for-sale securities, estimated fair value	1,182,828	1,746,787
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-14,007	-27,847
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	16,810	16,219
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-1,740	-1,531
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	16,810	16,219
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-1,740	-1,531
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	158,284	86,062
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-11,441	-5,834
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	158,284	86,062
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-11,441	-5,834
Total Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	175,094	102,281
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-13,181	-7,365
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	175,094	102,281
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	-13,181	-7,365
Short-Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	440,985	181,964
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	-3	-6
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	440,985	181,964
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	($3)	($6)

Investments_Schedule_Of_Amorti

Investments (Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturities By Contractual Maturity Date) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, amortized cost	$617,588
Due after one year through five years, amortized cost	1,904,996
Due after five years through ten years, amortized cost	1,925,821
Due after ten years, amortized cost	3,517,784
Amortized cost, sub-total	7,966,189
Total fixed maturities, amortized cost	9,371,731	9,929,137
Due in one year or less, estimated fair value	620,740
Due after one year through five years, estimated fair value	1,962,240
Due after five years through ten years, estimated fair value	2,054,347
Due after ten years, estimated fair value	3,881,374
Estimated fair value, sub-total	8,518,701
Total fixed maturities, estimated fair value	9,971,814	10,422,882
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, amortized cost	408,016
Fixed maturities, estimated fair value	415,622
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, amortized cost	920,185
Fixed maturities, estimated fair value	960,372
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, amortized cost	77,341
Fixed maturities, estimated fair value	$77,119

Investments_Components_Of_Net_

Investments (Components Of Net Investment Income) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Municipal bonds (tax-exempt)	$25,852	$23,104
Short-term investments, including overnight deposits	1,251	1,474
Dividends on equity securities	19,024	16,856
Income from equity method investments	1,344	3,583
Other	61	1,179
Total investment income	96,770	90,936
Investment expenses	-3,895	-4,221
Net investment income	92,875	86,715
Taxable Municipal Bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	14,100	8,996
Other Taxable Bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	$35,138	$35,744

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, 2015	Mar. 31, 2014
Gain (Loss) on Investments [Line Items]
Realized gains	$18,850	$26,683
Realized losses	-13,279	-9,289
Other-than-temporary impairment losses recognized in net income	-5,092	0
Net realized investment gains	5,571	17,394
Change in net unrealized gains on investments	164,663	215,265
Sales Of Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Realized gains	1,586	4,583
Realized losses	-142	-8,484
Sales Of Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Realized gains	15,957	12,145
Realized losses	-160	-146
Other [Member]
Gain (Loss) on Investments [Line Items]
Realized gains	1,307	9,955
Realized losses	-7,885	-659
Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Change in net unrealized gains on investments	106,338	148,811
Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Other-than-temporary impairment losses recognized in net income	-5,100
Change in net unrealized gains on investments	58,345	66,453
Short-Term Investments [Member]
Gain (Loss) on Investments [Line Items]
Change in net unrealized gains on investments	($20)	$1

Fair_Value_Measurements_Narrat

Fair Value Measurements (Narrative) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Fair Value Disclosures [Abstract]
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, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	$9,971,814	$10,422,882
Total equity securities	4,340,849	4,137,576
Short-term investments	1,731,872	1,594,849
Available-for-sale investments, estimated fair value	16,044,535	16,155,307
Fixed Maturities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	9,971,814	10,422,882
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]
Available-for-sale investments, estimated fair value	628,816	673,262
Obligations Of States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	4,204,426	4,317,547
Foreign Governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	1,549,886	1,611,921
Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	415,622	430,627
Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	960,372	982,847
Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	77,119	99,490
Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	2,135,573	2,307,188
Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	4,340,849	4,137,576
Insurance, Banks And Other Financial Institutions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	1,385,028	1,311,925
Industrial, Consumer And All Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	2,955,821	2,825,651
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	9,971,814	10,422,882
Total equity securities	4,340,849	4,137,576
Short-term investments	1,731,872	1,594,849
Available-for-sale investments, estimated fair value	16,044,535	16,155,307
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	4,340,849	4,137,576
Short-term investments	1,618,657	1,469,975
Available-for-sale investments, estimated fair value	5,959,506	5,607,551
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	9,971,814	10,422,882
Total equity securities	0	0
Short-term investments	113,215	124,874
Available-for-sale investments, estimated fair value	10,085,029	10,547,756
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
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	628,816	673,262
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	628,816	673,262
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	4,204,426	4,317,547
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	4,204,426	4,317,547
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	1,549,886	1,611,921
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	1,549,886	1,611,921
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	415,622	430,627
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	415,622	430,627
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	960,372	982,847
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	960,372	982,847
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	77,119	99,490
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	77,119	99,490
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	2,135,573	2,307,188
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	2,135,573	2,307,188
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	1,385,028	1,311,925
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	1,385,028	1,311,925
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	2,955,821	2,825,651
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	2,955,821	2,825,651
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

Segment_Reporting_Disclosures_1

Segment Reporting Disclosures (Company's Segment Disclosures) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
	segment
Segment Reporting Information [Line Items]
Number of reportable ongoing underwriting segments	3
Gross premium volume	$1,252,473		$1,359,757
Net written premiums	1,035,430		1,139,311
Earned premiums	943,650		949,375
Losses and loss adjustment expenses, current accident year	-614,341		-649,692
Losses and loss adjustment expenses, prior accident years	167,346		107,389
Underwriting, acquisition and insurance expenses	-340,685		-355,505
Underwriting profit (loss)	155,970		51,567
Net investment income	92,875		86,715
Net realized investment gains	5,571		17,394
Other revenues (insurance)	7,189		11,637
Other expenses (insurance)	-9,658		-13,857
Segment profit (loss)	251,947		153,456
Other revenues (non-insurance)	252,869		174,534
Other expenses (non-insurance)	-221,343		-168,311
Amortization of intangible assets	-14,640		-13,999
Interest expense	-29,312		-29,699
Income Before Income Taxes	239,521		115,981
U.S. GAAP combined ratio	83.00%	[1]	95.00%	[1]
U.S. Insurance [Member]
Segment Reporting Information [Line Items]
Gross premium volume	585,365		575,233
Net written premiums	496,169		474,054
Earned premiums	514,554		483,735
Losses and loss adjustment expenses, current accident year	-316,757		-312,413
Losses and loss adjustment expenses, prior accident years	67,581		43,554
Underwriting, acquisition and insurance expenses	-185,260		-193,529
Underwriting profit (loss)	80,118		21,347
Net investment income	0		0
Net realized investment gains	0		0
Other revenues (insurance)	1,402		2,110
Other expenses (insurance)	-905		-1,647
Segment profit (loss)	80,615		21,810
U.S. GAAP combined ratio	84.00%	[1]	96.00%	[1]
International Insurance [Member]
Segment Reporting Information [Line Items]
Gross premium volume	289,227		294,236
Net written premiums	222,708		229,120
Earned premiums	205,961		222,147
Losses and loss adjustment expenses, current accident year	-148,844		-163,379
Losses and loss adjustment expenses, prior accident years	76,650		42,297
Underwriting, acquisition and insurance expenses	-78,794		-80,009
Underwriting profit (loss)	54,973		21,056
Net investment income	0		0
Net realized investment gains	0		0
Other revenues (insurance)	5,387		7,348
Other expenses (insurance)	-1,404		-3,595
Segment profit (loss)	58,956		24,809
U.S. GAAP combined ratio	73.00%	[1]	91.00%	[1]
Reinsurance [Member]
Segment Reporting Information [Line Items]
Gross premium volume	377,837		489,961
Net written premiums	316,212		435,997
Earned premiums	222,754		243,315
Losses and loss adjustment expenses, current accident year	-148,740		-173,900
Losses and loss adjustment expenses, prior accident years	26,387		28,200
Underwriting, acquisition and insurance expenses	-76,553		-81,972
Underwriting profit (loss)	23,848		15,643
Net investment income	0		0
Net realized investment gains	0		0
Other revenues (insurance)	423		2,136
Other expenses (insurance)	0		0
Segment profit (loss)	24,271		17,779
U.S. GAAP combined ratio	89.00%	[1]	94.00%	[1]
Other Insurance (Discontinued Lines) [Member]
Segment Reporting Information [Line Items]
Gross premium volume	44		327
Net written premiums	341		140
Earned premiums	381		178
Losses and loss adjustment expenses, current accident year	0		0
Losses and loss adjustment expenses, prior accident years	-3,272		-6,662
Underwriting, acquisition and insurance expenses	-78		5
Underwriting profit (loss)	-2,969		-6,479
Net investment income	0		0
Net realized investment gains	0		0
Other revenues (insurance)	-23		43
Other expenses (insurance)	-7,349		-8,615
Segment profit (loss)	-10,341		-15,051
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	92,875		86,715
Net realized investment gains	5,571		17,394
Other revenues (insurance)	0		0
Other expenses (insurance)	0		0
Segment profit (loss)	$98,446		$104,109
[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, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Segment Reporting Information [Line Items]
Assets	$25,253,389	$25,200,357
Non-Insurance Operations [Member]
Segment Reporting Information [Line Items]
Assets	1,218,162	1,246,762
Segment Assets [Member]
Segment Reporting Information [Line Items]
Assets	24,035,227	23,953,595
Segment Assets [Member] | Investing [Member]
Segment Reporting Information [Line Items]
Assets	18,450,247	18,531,150
Segment Assets [Member] | Underwriting [Member]
Segment Reporting Information [Line Items]
Assets	$5,584,980	$5,422,445

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, 2015	Mar. 31, 2014
Other Revenues and Other Expenses [Line Items]
Other revenues	$260,058	$186,171
Other expenses	231,001	182,168
Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	7,189	11,637
Other expenses	9,658	13,857
Non-Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	252,869	174,534
Other expenses	221,343	168,311
Managing General Agent Operations [Member] | Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	5,870	9,178
Other expenses	2,309	4,881
Life And Annuity [Member] | Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	-23	43
Other expenses	7,349	8,615
Other Insurance [Member] | Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	1,342	2,416
Other expenses	0	361
Manufacturing [Member] | Non-Insurance Operations [Member] | Markel Ventures Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	177,762	100,611
Other expenses	151,800	95,889
Non-Manufacturing [Member] | Non-Insurance Operations [Member] | Markel Ventures Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	67,681	70,595
Other expenses	63,830	65,511
Other Non-Insurance [Member] | Non-Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	7,426	3,328
Other expenses	$5,713	$6,911

Reinsurance_Narrative_Details

Reinsurance (Narrative) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 09, 2015	Dec. 31, 2014
Reinsurance Disclosures [Abstract]
Percentage of ceded earned premiums to gross earned premiums	18.00%	19.00%
Percentage of assumed earned premiums to net earned premiums	33.00%	37.00%
Reinsurance recoverables	$88.80	$97.60
Total payment under retrospective reinsurance transaction on ceded asbestos and environmental policies			89
Cash paid at closing under retrospective reinsurance transaction on ceded asbestos and environmental policies			69.9
Cumulative amount of reserves for losses and loss adjustment expenses on ceded asbestos and environmental policies			94.1
Deferred gain under retrospective reinsurance transaction on ceded asbestos and environmental policies			$5.10
Approximate percentage of ceded reserves under retrospective reinsurance transaction to net asbestos and environmental reserves for losses and loss adjustment expenses				35.00%

Reinsurance_Effect_Of_Reinsura

Reinsurance (Effect Of Reinsurance And Retrocessional Reinsurance On Premiums Written And Earned) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Reinsurance Disclosures [Abstract]
Direct premiums written	$801,580	$795,311
Direct premiums earned	844,570	828,292
Assumed premiums written	450,893	564,446
Assumed premiums earned	312,835	347,699
Ceded premiums written	-217,043	-220,446
Ceded premiums earned	-213,755	-226,616
Net premiums written	1,035,430	1,139,311
Net premiums earned	$943,650	$949,375

Income_Taxes_Narrative_Details

Income Taxes (Narrative) (Details)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Income Tax Disclosure [Abstract]
Effective tax rate	19.00%	25.00%
U.S. statutory tax rate	35.00%	35.00%

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, 2015	Mar. 31, 2014
Earnings Per Share [Line Items]
Net income to shareholders	$190,992	$87,716
Adjustment of redeemable noncontrolling interests	-1,347	117
Adjusted net income to shareholders	$189,645	$87,833
Basic common shares outstanding	13,972	13,995
Diluted shares outstanding	14,063	14,058
Basic net income per share	$13.57	$6.28
Diluted net income per share	$13.49	$6.25
Stock Options [Member]
Earnings Per Share [Line Items]
Dilutive potential common shares	10	11
Restricted Stock Units (RSUs) [Member]
Earnings Per Share [Line Items]
Dilutive potential common shares	81	52

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, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income, beginning balance	$1,704,557	$1,089,805
Other comprehensive income (loss) before reclassifications	99,405	148,182
Amounts reclassified from accumulated other comprehensive income	-8,590	-5,625
Total other comprehensive income (loss)	90,815	142,557
Accumulated other comprehensive income, ending balance	1,795,372	1,232,362
Unrealized Holding Gains On Available-For-Sale Securities [Member]
Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income, beginning balance	1,793,254	1,131,507
Other comprehensive income (loss) before reclassifications	121,189	147,276
Amounts reclassified from accumulated other comprehensive income	-9,053	-5,944
Total other comprehensive income (loss)	112,136	141,332
Accumulated other comprehensive income, ending balance	1,905,390	1,272,839
Foreign Currency [Member]
Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income, beginning balance	-43,491	-11,246
Other comprehensive income (loss) before reclassifications	-21,784	906
Amounts reclassified from accumulated other comprehensive income	0	0
Total other comprehensive income (loss)	-21,784	906
Accumulated other comprehensive income, ending balance	-65,275	-10,340
Net Actuarial Pension Loss [Member]
Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income, beginning balance	-45,206	-30,456
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	463	319
Total other comprehensive income (loss)	463	319
Accumulated other comprehensive income, ending balance	($44,743)	($30,137)

Other_Comprehensive_Income_Sum

Other Comprehensive Income (Summary Of Tax Expense (Benefit) Of Other Comprehensive Income) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Other Comprehensive Income (Loss), Tax [Abstract]
Net holding gains arising during the period	$55,582	$75,523
Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period	41	564
Reclassification adjustments for net gains included in net income	-3,096	-2,154
Change in net unrealized gains on investments	52,527	73,933
Change in foreign currency translation adjustments	-1,039	342
Change in net actuarial pension loss	116	80
Total	$51,604	$74,355

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, 2015	Mar. 31, 2014
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses recognized in net income	($5,092)	$0
Net realized investment gains, excluding other-than-temporary impairment losses	10,663	17,394
Income Before Income Taxes	239,521	115,981
Underwriting, acquisition and insurance expenses	-340,685	-355,505
Income taxes	-45,515	-28,480
Net Income	194,006	87,501
Reclassification Out Of Accumulated Other Comprehensive Income [Member] | Unrealized Holding Gains On Available-For-Sale Securities [Member]
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses recognized in net income	-5,092	0
Net realized investment gains, excluding other-than-temporary impairment losses	17,241	8,098
Income Before Income Taxes	12,149	8,098
Income taxes	-3,096	-2,154
Net Income	9,053	5,944
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	-579	-399
Income taxes	116	80
Net Income	($463)	($319)