Markel (MKL) 10-Q 30 Oct 18 2018 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 23, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Entity Registrant Name	MARKEL CORP
Entity Central Index Key	1,096,343
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		13,884,649

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
ASSETS
Fixed maturities, available-for-sale (amortized cost of $9,946,656 in 2018 and $9,551,153 in 2017)	$ 9,952,053	$ 9,940,670
Equity securities, available-for-sale (cost of $2,667,661 in 2017)	0	5,967,847
Equity securities (cost of $2,871,203 in 2018)	6,549,848	0
Short-term investments, available-for-sale (estimated fair value approximates cost)	1,918,691	2,160,974
Total Investments	18,420,592	18,069,491
Cash and cash equivalents	2,347,040	2,198,459
Restricted cash and cash equivalents	279,902	302,387
Receivables	1,817,637	1,567,453
Reinsurance recoverable on unpaid losses	4,836,271	4,619,336
Reinsurance recoverable on paid losses	137,364	126,054
Deferred policy acquisition costs	518,853	465,569
Prepaid reinsurance premiums	1,361,044	1,099,757
Goodwill	1,783,784	1,777,464
Intangible assets	1,241,108	1,355,681
Other assets	1,214,710	1,223,365
Total Assets	33,958,305	32,805,016
LIABILITIES AND EQUITY
Unpaid losses and loss adjustment expenses	13,888,489	13,584,281
Life and annuity benefits	1,028,696	1,072,112
Unearned premiums	3,816,249	3,308,779
Payables to insurance and reinsurance companies	453,132	324,304
Senior long-term debt and other debt (estimated fair value of $3,037,000 in 2018 and $3,351,000 in 2017)	2,993,243	3,099,230
Other liabilities	1,839,603	1,748,460
Total Liabilities	24,019,412	23,137,166
Redeemable noncontrolling interests	158,739	166,269
Commitments and contingencies
Shareholders' equity:
Common stock	3,392,322	3,381,834
Retained earnings	6,576,562	3,776,743
Accumulated other comprehensive income (loss)	(184,892)	2,345,571
Total Shareholders' Equity	9,783,992	9,504,148
Noncontrolling interests	(3,838)	(2,567)
Total Equity	9,780,154	9,501,581
Total Liabilities and Equity	$ 33,958,305	$ 32,805,016

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Fixed maturities, available-for-sale amortized cost	$ 9,946,656	$ 9,551,153
Equity securities, available-for-sale cost		2,667,661
Equity securities, cost	2,871,203
Senior long-term debt and other debt, estimated fair value	$ 3,037,000	$ 3,351,000

Consolidated Statements Of Inco

Consolidated Statements Of Income (Loss) And Comprehensive Income (Loss) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017
OPERATING REVENUES
Earned premiums		$ 1,185,323		$ 1,099,862		$ 3,484,528		$ 3,116,038
Net investment income		106,307		104,489		319,710		304,156
Other-than-temporary impairment losses		0		(3,444)		0		(7,261)
Net realized investment gains (losses), excluding other-than-temporary impairment losses		(496)		11,814		(9,084)		31,826
Change in fair value of equity securities	[1]	426,571		(48,377)		417,410		(26,080)
Net investment gains (losses)		426,075		(40,007)		408,326		(1,515)
Other revenues		518,244		341,804		1,585,869		980,713
Total Operating Revenues		2,235,949		1,506,148		5,798,433		4,399,392
OPERATING EXPENSES
Losses and loss adjustment expenses		736,846		1,075,432		1,951,142		2,210,129
Underwriting, acquisition and insurance expenses		441,961		396,972		1,317,921		1,171,520
Amortization of intangible assets	[2]	27,795		18,654		86,259		53,450
Other expenses		473,742	[3]	344,996	[4]	1,471,215	[5]	926,385	[6]
Total Operating Expenses		1,680,344		1,836,054		4,826,537		4,361,484
Operating Income (Loss)		555,605		(329,906)		971,896		37,908
Interest expense		37,961		31,814		114,722		97,013
Net foreign exchange gains		(1,383)		(1,772)		(65,427)		(2,746)
Income (Loss) Before Income Taxes		519,027		(359,948)		922,601		(56,359)
Income tax expense (benefit)		109,999		(98,913)		299,580		(17,791)
Net Income (Loss)		409,028		(261,035)		623,021		(38,568)
Net income (loss) attributable to noncontrolling interests		(410)		(1,894)		(342)		1,044
Net Income (Loss) to Shareholders		409,438		(259,141)		623,363		(39,612)
OTHER COMPREHENSIVE INCOME (LOSS)
Net holding gains (losses) arising during the period		(91,002)		227,447		(306,069)		577,796
Reclassification adjustments for net gains (losses) included in net income (loss)		10,573		(5,207)		5,496		(14,598)
Change in net unrealized gains (losses) on available-for-sale investments, net of taxes		(80,429)		222,240		(300,573)		563,198
Change in foreign currency translation adjustments, net of taxes		(14,471)		16,263		(19,968)		19,770
Change in net actuarial pension loss, net of taxes		509		773		1,741		2,391
Total Other Comprehensive Income (Loss)		(94,391)		239,276		(318,800)		585,359
Comprehensive Income (Loss)		314,637		(21,759)		304,221		546,791
Comprehensive income (loss) attributable to noncontrolling interests		(469)		(1,890)		(382)		1,064
Comprehensive Income (Loss) to Shareholders		$ 315,106		$ (19,869)		$ 304,603		$ 545,727
NET INCOME (LOSS) PER SHARE
Basic (in dollars per share)	[7]	$ 28.56		$ (18.82)		$ 44.29		$ (4.52)
Diluted (in dollars per share)	[7]	$ 28.50		$ (18.82)		$ 44.21		$ (4.52)
[1]	Effective January 1, 2018, the Company adopted ASU No. 2016-01. As a result, equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income; rather, all changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 2.
[2]	Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to any other reportable segments.
[3]	Other expenses for the Markel Ventures segment include depreciation expense of $13.0 million for the quarter ended September 30, 2018.
[4]	Other expenses for the Markel Ventures segment include depreciation expense of $9.7 million for the quarter ended September 30, 2017.
[5]	Other expenses for the Markel Ventures segment include depreciation expense of $38.5 million for the nine months ended September 30, 2018.
[6]	Other expenses for the Markel Ventures segment include depreciation expense of $28.7 million for the nine months ended September 30, 2017.
[7]	Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income, rather, changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 2.

Consolidated Statements Of Chan

Consolidated Statements Of Changes In Equity - USD ($) $ in Thousands	Total	Total Equity [Member]	Total Shareholders' Equity [Member]	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interests [Member]	Redeemable Noncontrolling Interests [Member]
Balance at Dec. 31, 2016		$ 8,467,411	$ 8,460,927	$ 3,368,666	$ 3,526,395	$ 1,565,866	$ 6,484
Balance, shares at Dec. 31, 2016				13,955,000
Balance, redeemable noncontrolling interests at Dec. 31, 2016								$ 73,678
Net income (loss)	$ (38,568)	(40,105)	(39,612)		(39,612)	0	(493)	1,537
Other comprehensive income (loss)	585,359	585,339	585,339		0	585,339	0	20
Comprehensive Income (Loss)	546,791	545,234	545,727				(493)	1,557
Issuance of common stock		359	359	$ 359	0	0	0	0
Issuance of common stock, shares				24,000
Repurchase of common stock		(84,436)	(84,436)	$ 0	(84,436)	0	0	0
Repurchase of common stock, shares				(85,000)
Restricted stock units expensed		13,389	13,389	$ 13,389	0	0	0	0
Restricted stock units expensed, shares				0
Acquisition of Costa Farms		0	0	$ 0	0	0	0	66,600
Acquisition of Costa Farms, shares				0
Adjustment of redeemable noncontrolling interests		(23,582)	(23,582)	$ 0	(23,582)	0	0	23,582
Adjustment of redeemable noncontrolling interests, shares				0
Purchase of noncontrolling interest		(11,019)	(2,910)	$ (2,910)	0	0	(8,109)	(6,179)
Purchase of noncontrolling interest, shares				0
Other		(512)	(589)	$ (348)	(241)	0	77	(5,928)
Other, shares				0
Balance at Sep. 30, 2017		8,906,844	8,908,885	$ 3,379,156	3,378,524	2,151,205	(2,041)
Balance, shares at Sep. 30, 2017				13,894,000
Balance, redeemable noncontrolling interests at Sep. 30, 2017								153,310
Balance at Dec. 31, 2017	9,501,581	9,501,581	9,504,148	$ 3,381,834	3,776,743	2,345,571	(2,567)
Balance, shares at Dec. 31, 2017				13,904,000
Balance, redeemable noncontrolling interests at Dec. 31, 2017	166,269							166,269
Cumulative effect of adoption of ASU No. 2014-09, net of taxes	300	325	325	$ 0	325	0	0	0
Cumulative effect of adoption of ASU No. 2014-09, shares				0
Cumulative effect of adoption of ASU No. 2016-01, net of taxes	(2,613,242)	0	0	$ 0	2,613,242	(2,613,242)	0	0
Cumulative effect of adoption of ASU No. 2016-01, shares				0
Cumulative effect of adoption of ASU No. 2018-02	401,539	0	0	$ 0	(401,539)	401,539	0	0
Cumulative effect of adoption of ASU 2018-02, shares				0
Net income (loss)	623,021	622,094	623,363		623,363	0	(1,269)	927
Other comprehensive income (loss)	(318,800)	(318,760)	(318,760)		0	(318,760)	0	(40)
Comprehensive Income (Loss)	304,221	303,659	304,928				(1,269)	887
Issuance of common stock		2	2	$ 2	0	0	0	0
Issuance of common stock, shares				8,000
Repurchase of common stock	$ (27,800)	(30,829)	(30,829)	$ 0	(30,829)	0	0	0
Repurchase of common stock, shares	(24,584)			(28,000)
Restricted stock units expensed		15,521	15,521	$ 15,521	0	0	0	0
Restricted stock units expensed, shares				0
Adjustment of redeemable noncontrolling interests		(6,621)	(6,621)	$ 0	(6,621)	0	0	6,621
Adjustment of redeemable noncontrolling interests, shares				0
Purchase of noncontrolling interest		(4,986)	(4,986)	$ (4,986)	0	0	0	(7,104)
Purchase of noncontrolling interest, shares				0
Other		1,827	1,829	$ (49)	1,878	0	(2)	(7,934)
Other, shares				0
Balance at Sep. 30, 2018	$ 9,780,154	$ 9,780,154	$ 9,783,992	$ 3,392,322	$ 6,576,562	$ (184,892)	$ (3,838)
Balance, shares at Sep. 30, 2018				13,884,000
Balance, redeemable noncontrolling interests at Sep. 30, 2018	$ 158,739							$ 158,739

Condensed Consolidated Statemen

Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
OPERATING ACTIVITIES
Net income (loss)	$ 623,021	$ (38,568)
Adjustments to reconcile net income (loss) to net cash provided by operating activities	140,155	637,271
Net Cash Provided By Operating Activities	763,176	598,703
INVESTING ACTIVITIES
Proceeds from sales of fixed maturities and equity securities	361,768	360,327
Proceeds from maturities, calls and prepayments of fixed maturities	459,517	948,756
Cost of fixed maturities and equity securities purchased	(1,409,263)	(1,162,438)
Net change in short-term investments	257,288	406,138
Additions to property and equipment	(78,886)	(50,099)
Acquisitions, net of cash acquired	(11,314)	(592,045)
Other	(32,325)	(4,864)
Net Cash Used By Investing Activities	(453,215)	(94,225)
FINANCING ACTIVITIES
Additions to senior long-term debt and other debt	145,813	42,638
Repayment of senior long-term debt and other debt	(246,049)	(224,516)
Repurchases of common stock	(30,829)	(84,436)
Purchase of noncontrolling interests	(13,523)	(18,068)
Distributions to noncontrolling interests	(7,964)	(5,929)
Other	(19,217)	(9,004)
Net Cash Used By Financing Activities	(171,769)	(299,315)
Effect of foreign currency rate changes on cash, cash equivalents, restricted cash and restricted cash equivalents	(12,096)	65,338
Increase in cash, cash equivalents, restricted cash and restricted cash equivalents	126,096	270,501
Cash, cash equivalents, restricted cash and restricted cash equivalents at beginning of period	2,500,846	2,085,164
CASH, CASH EQUIVALENTS, RESTRICTED CASH AND RESTRICTED CASH EQUIVALENTS AT END OF PERIOD	$ 2,626,942	$ 2,355,665

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Summary Of Significant Accounting Policies	Summary of Significant Accounting Policies Markel Corporation is a diverse financial holding company serving a variety of niche markets. Markel Corporation's principal business markets and underwrites specialty insurance products and programs. Through its wholly-owned subsidiary, Markel Ventures, Inc. (Markel Ventures), Markel Corporation also owns interests in various businesses that operate outside of the specialty insurance marketplace. a) Basis of Presentation. The consolidated balance sheet as of September 30, 2018 and the related consolidated statements of income (loss) and comprehensive income (loss) for the quarters and nine months ended September 30, 2018 and 2017 , and the consolidated statements of changes in equity and cash flows for the nine months ended September 30, 2018 and 2017 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, 2017 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 consolidated subsidiaries, as well as any variable interest entities (VIEs) that meet the requirements for consolidation (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, with the exception of significant transactions or events that occur during the intervening period. 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 2017 Annual Report on Form 10-K for a more complete description of the Company's business and accounting policies. b) Foreign Currency Transactions. The U.S. Dollar is the Company’s reporting currency and the primary functional currency of its foreign underwriting operations. The functional currencies of the Company's other foreign operations are the currencies of the primary economic environments in which the majority of their business is transacted. Foreign currency transaction gains and losses are the result of exchange rate changes on transactions denominated in currencies other than the functional currency at each foreign entity. Monetary assets and liabilities are remeasured to the functional currency at current exchange rates, with resulting gains and losses included in net foreign exchange losses (gains) within net income. Non-monetary assets and liabilities are remeasured to the functional currency at historic exchange rates. Available-for-sale securities are recorded at fair value with resulting gains and losses, including the portion attributable to movements in exchange rates, included in the change in net unrealized gains on available-for-sale investments, net of taxes within other comprehensive income. While we attempt to naturally hedge our exposure to foreign currency fluctuations by matching assets and liabilities in currency, there is a financial statement mismatch between the gains or losses recorded in net income related to insurance reserves denominated in non-functional currencies and the gains or losses recorded in other comprehensive income related to the available-for-sale securities supporting the reserves. Assets and liabilities of foreign operations denominated in a functional currency other than the U.S. Dollar are translated into the U.S. Dollar at current exchange rates, with resulting gains or losses included, net of taxes, in the change in foreign currency translation adjustments within other comprehensive income. Historically, the Company also designated certain additional currencies, including the British Pound Sterling, the Euro, and the Canadian Dollar, as functional currencies within its foreign underwriting operations that were deemed to contain distinct and separable operations in those foreign economic environments. However, over time the Company’s foreign underwriting operations have evolved and are now managed on a global basis. Effective January 1, 2018, management reassessed its functional currency determination as required by Financial Accounting Standards Board (FASB) Accounting Standards Codification (ASC) 830, Foreign Currency Matters , and concluded that its foreign underwriting operations have evolved to function as an extension, or integral component, of the Company’s global underwriting operations, and are no longer deemed to contain distinct and separable operations. As a result, more foreign currency denominated transactions are designated as non-functional, with related remeasurement gains and losses included in net income. The change in the Company’s functional currency determination has been applied on a prospective basis in accordance with ASC 830. Therefore, any translation gains and losses that were previously recorded in accumulated other comprehensive income through December 31, 2017 remain unchanged as of September 30, 2018. c) Revenue Recognition. Effective January 1, 2018, the Company adopted FASB Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers (Topic 606), and related amendments, which created a new comprehensive revenue recognition standard, ASC 606, that serves as a single source of revenue guidance for all contracts with customers to transfer goods or services or contracts for the transfer of nonfinancial assets, unless those contracts are within the scope of other standards, such as insurance contracts. ASC 606 is not applicable to the Company's insurance premium revenues or revenues from its investment portfolio but is applicable to most of the Company's other revenues, as described below. See note 2 for further discussion of the impact of adopting this standard. Other revenues primarily relate to the Company's Markel Ventures segment and consist of revenues from the sale of products and services. Revenues are recognized when, or as, control of the promised goods or services is transferred to the Company's customers, in an amount that reflects the consideration the Company expects to be entitled to in exchange for those goods or services. All contracts with customers either have an original expected length of one year or less or the Company recognizes revenue at the amount for which it has a right to invoice for the products delivered or services performed. Certain customers may receive volume rebates or credits for products and services, which are accounted for as variable consideration. The Company estimates these amounts based on the expected amount to be provided to the customer and reduces revenues recognized by a corresponding amount. The Company does not expect significant changes to its estimates of variable consideration over the term of the contracts. Payment terms for products and services vary by the type of product or service offered and the location of the customer, and payment is typically received at or shortly after the point of sale. For certain products, the Company requires partial payment in the form of a deposit before the products are delivered to the customer, which is included in other liabilities on the Company's consolidated balance sheet. Product revenues are primarily generated from the sale of ornamental plants, equipment used in baking systems, portable dredges, over the road transportation equipment, flooring for the trucking industry, and residential homes. Most of the Company's product revenues are recognized when the products are shipped to the customer or the products arrive at the agreed upon destination with the end customer. Some of the Company's contracts include multiple performance obligations. For such arrangements, revenues are allocated to each performance obligation based on the relative standalone selling price, which is derived from amounts stated in the contract. Service revenues are primarily generated by delivering healthcare services, retail intelligence, consulting services and investment management services. Service revenues are generally recognized over the term of the contracts based on hours incurred or as services are provided. Investment management fee income is recognized over the period in which investment management services are provided and is calculated and recognized monthly based on the net asset value of the accounts managed. In connection with the investment management services provided, the Company is also entitled to participate, on a fixed-percentage basis, in any net income generated in excess of an agreed-upon threshold as established by the underlying investment management agreements. In general, net income is calculated at the end of each calendar year and performance fees are payable annually. Performance fee income is recognized at the conclusion of the contractual performance period, when the uncertainty related to performance has been resolved.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements Effective January 1, 2018, the Company adopted ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) and several other ASU’s that were issued as amendments to ASU No. 2014-09, which apply to all contracts with customers to transfer goods or services or for the transfer of nonfinancial assets, unless those contracts are within the scope of other standards. ASU No. 2014-09's core principle is that a company recognizes 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 adopting this standard, the Company is required to use more judgment and make more estimates than under the previous guidance, including 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. The Company adopted ASU No. 2014-09 using the modified retrospective method. Prior periods were not restated and a cumulative-effect adjustment of applying the new standard to all open contracts at January 1, 2018 was $0.3 million , and is included as an adjustment to 2018 beginning retained earnings. The Company's other revenues for the quarter and nine months ended September 30, 2018 and its receivables, other assets and other liabilities as of September 30, 2018 were not materially different from the amounts that would have been recognized under the previous guidance. ASU No. 2014-09 also requires expanded revenue disclosures which are included in note 8 . Effective January 1, 2018, the Company adopted ASU No. 2016-01, Financial Instruments (Topic 825): Recognition and Measurement of Financial Assets and Financial Liabilities . As a result of adoption of this ASU, equity instruments that do not result in consolidation and are not accounted for under the equity method are measured at fair value and any changes in fair value are recognized in net income. Previously, the Company’s equity securities were classified as available-for-sale and changes in fair value were recorded in other comprehensive income. Upon adoption of this ASU, cumulative net unrealized gains on equity securities of $2.6 billion , net of deferred income taxes of $684.4 million , were reclassified from accumulated other comprehensive income into retained earnings. Prior periods have not been restated to conform to the current presentation. See note 4(e) for details regarding the change in net unrealized gains on equity securities included in net income for the quarter and nine months ended September 30, 2018 and included in other comprehensive income for the quarter and nine months ended September 30, 2017. Effective January 1, 2018, the Company early adopted ASU No. 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. The ASU provides an option to reclassify tax effects remaining in accumulated other comprehensive income as a result of the Tax Cuts and Jobs Act (TCJA) to retained earnings. Upon enactment of the TCJA, the U.S. corporate tax rate was reduced from 35% to 21% and the Company's U.S. deferred tax balances were remeasured to the lower enacted U.S. corporate tax rate. U.S. GAAP requires the effects of changes in tax rates and laws on deferred tax balances to be recorded as a component of income tax expense in the period of enactment, even if the assets and liabilities relate to items of accumulated other comprehensive income. As a result of adopting the ASU, the Company reclassified $401.5 million of previously recognized deferred taxes from accumulated other comprehensive income into retained earnings as of January 1, 2018. The following ASUs relate to topics relevant to the Company's operations and were adopted effective January 1, 2018. These ASUs did not have a material impact on the Company’s financial position, results of operations or cash flows: • ASU No. 2016-16, Income Taxes (Topic 740): Intra-entity Transfers of Assets Other Than Inventory • ASU No. 2017-07, Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost • ASU No. 2017-09, Stock Compensation (Topic 718): Scope of Modification Accounting In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) . The ASU requires lessees to record most leases on their balance sheets as a lease liability with a corresponding right-of-use asset, but continue to recognize the related leasing expense within net income. The FASB subsequently issued ASUs with improvements to the guidance, including ASU No. 2018-11, Leases (Topic 842): Targeted Improvements , which provides entities with an additional transition method to apply the new standard. Under the new optional transition method, an entity initially applies ASC 842 at the adoption date and recognizes a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. The ASUs become effective for the Company during the first quarter of 2019 and will be applied using a modified retrospective approach. The Company intends to elect the new transition method permitted by ASU No. 2018-11. The Company's future minimum lease payments, which represent minimum annual rental commitments excluding taxes, insurance and other operating costs for noncancelable operating leases, and which will be subject to this new guidance, totaled $311.7 million at December 31, 2017 . Adoption of this standard will impact the Company’s consolidated balance sheets but is not expected to have a material impact on the Company’s results of operations or cash flows. The Company is currently evaluating ASU No. 2016-02 to determine the magnitude of the impact that adopting this standard will have on its consolidated financial statements. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The ASU replaces the current incurred loss model used to measure impairment losses with an expected loss model for trade, reinsurance, and other receivables as well as financial instruments measured at amortized cost. For available-for-sale debt securities, which are measured at fair value, the ASU requires entities to record impairments as an allowance, rather than a reduction of the amortized cost, as is currently required under the other-than-temporary impairment model. ASU No. 2016-13 becomes effective for the Company during the first quarter of 2020 and will be applied using a modified retrospective approach through a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. The Company is currently evaluating ASU No. 2016-13 to determine the potential impact that adopting this standard will have on its consolidated financial statements. Application of the new expected loss model for measuring impairment losses will not impact the Company's investment portfolio, none of which is measured at amortized cost, but will impact the Company's other financial assets, including its reinsurance recoverables. Upon adoption of this ASU, any impairment losses on the Company's available-for-sale debt securities will be recorded as an allowance, subject to reversal, rather than as a reduction in amortized cost. In August 2018, the FASB issued ASU No. 2018-12, Financial Services-Insurance (Topic 944): Targeted Improvements to the Accounting for Long-Duration Contracts. The ASU requires insurance entities with long duration contracts to: (1) review and, if there is a change, update the assumptions used to measure cash flows at least annually, as well as update the discount rate assumption at each reporting date; (2) measure all market risk benefits associated with deposit (or account balance) contracts at fair value; and (3) disclose liability rollforwards and information about significant inputs, judgments, assumptions and methods used in measurement, including changes thereto and the effect of those changes on measurement. ASU No. 2018-12 becomes effective for the Company during the first quarter of 2021. The ASU will, among other things, impact the discount rate used in estimating reserves for the Company’s life and annuity reinsurance portfolio, which is in runoff. Currently, the discount rate assumption is locked-in for the life of the contracts, unless there is a loss recognition event. The Company is currently evaluating ASU No. 2018-12 to determine the impact that adopting this standard will have on its consolidated financial statements. In August 2018, the FASB issued ASU No. 2018-15, Intangibles-Goodwill and Other- Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. The ASU aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software and hosting arrangements that include an internal-use software license. The ASU requires an entity to expense the capitalized implementation costs of a hosting arrangement that is a service contract over the term of the hosting arrangement. Currently, such costs are generally expensed as incurred. ASU No. 2018-15 becomes effective for the Company during the first quarter of 2020 and may be applied on a prospective or retrospective basis. Early adoption is permitted. The Company is currently evaluating ASU No. 2018-15 to determine the impact that adopting this standard will have on its consolidated financial statements. The following ASUs are relevant to the Company's operations and are not yet effective. These ASUs are not expected to have a material impact on the Company's financial position, results of operations or cash flows: • ASU No. 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities • ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement • ASU No. 2018-14, Compensation—Retirement Benefits—Defined Benefit Plans—General (Subtopic 715-20): Disclosure Framework—Changes to the Disclosure Requirements for Defined Benefit Plans

Acquisitions

Acquisitions	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Acquisitions	Acquisitions State National Acquisition In November 2017, the Company completed its acquisition of 100% of the issued and outstanding common stock of State National Companies, Inc. (State National). Results attributable to State National's collateral protection insurance coverages are included in the Insurance segment, which was redefined during the first quarter of 2018. Results attributable to State National's program services (fronting) business are not included in a reportable segment. Total consideration for this acquisition was $918.8 million , all of which was cash consideration. As of December 31, 2017, the purchase price was preliminarily allocated to the acquired assets and liabilities of State National based on estimated fair value at the acquisition date. During the first quarter of 2018, the Company completed the process of determining the fair value of the assets and liabilities acquired with State National. The Company recognized goodwill of $379.2 million , none of which is expected to be deductible for income tax purposes. The Company also recognized indefinite lived intangible assets of $32.0 million and other intangible assets of $338.5 million , which are being amortized over a weighted average period of 13 years . The following table summarizes the intangible assets recorded in connection with the acquisition, and as of September 30, 2018 . (dollars in thousands) Amount Economic Useful Life Customer relationships $ 289,000 13 years Trade names 22,500 13 years Technology 27,000 Nine years Insurance licenses 32,000 Indefinite Intangible assets, before amortization, as of the acquisition date 370,500 Amortization (from the acquisition date through September 30, 2018) 25,407 Net intangible assets as of September 30, 2018 $ 345,093 Nephila Acquisition In August 2018, the Company entered into a definitive agreement to acquire all of the outstanding shares of Nephila Holdings Limited (Nephila), a Bermuda-based investment manager offering a broad range of investment products, including insurance-linked securities, catastrophe bonds, insurance swaps and weather derivatives. Nephila has more than $12 billion of assets under management and generates revenue primarily through management and incentive fees. Total consideration for this acquisition is estimated to be $975.0 million , all of which is expected to be paid in cash. Upon completion of the transaction, Nephila will continue to operate as a separate business unit and its operating results will not be included in a reportable segment. See note 6 for further discussion of the Company's reportable segments. The transaction remains subject to customary closing conditions and is expected to close in the fourth quarter of 2018. Brahmin Acquisition In October 2018, the Company acquired 90% of Brahmin Leather Works (Brahmin), a Massachusetts-based privately held creator of fashion leather handbags. Total consideration for the acquisition was $194.0 million , which included cash consideration of $173.3 million . Total consideration also includes the estimated fair value of contingent consideration the Company expects to pay based on Brahmin’s earnings as defined in the purchase agreement, for the period of 2019 through 2021. The purchase price allocation for Brahmin will be performed in the fourth quarter of 2018. Results attributable to Brahmin will be included within the Company’s Markel Ventures segment.

Investments

Investments	9 Months Ended
	Sep. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Investments	Investments a) The following tables summarize the Company's available-for-sale investments. Commercial and residential mortgage-backed securities include securities issued by U.S. government-sponsored enterprises and U.S. government agencies. September 30, 2018 (dollars in thousands) Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Unrealized Other-Than- Temporary Impairment Losses Estimated Fair Value Fixed maturities: U.S. Treasury securities $ 241,485 $ 20 $ (3,360 ) $ — $ 238,145 U.S. government-sponsored enterprises 359,348 3,612 (8,081 ) — 354,879 Obligations of states, municipalities and political subdivisions 4,289,636 73,456 (50,246 ) — 4,312,846 Foreign governments 1,463,626 105,158 (17,047 ) — 1,551,737 Commercial mortgage-backed securities 1,672,438 13 (70,603 ) — 1,601,848 Residential mortgage-backed securities 898,169 1,058 (31,136 ) — 868,091 Asset-backed securities 24,819 — (309 ) — 24,510 Corporate bonds 997,135 20,351 (17,489 ) — 999,997 Total fixed maturities 9,946,656 203,668 (198,271 ) — 9,952,053 Short-term investments 1,918,495 649 (453 ) — 1,918,691 Investments, available-for-sale $ 11,865,151 $ 204,317 $ (198,724 ) $ — $ 11,870,744 December 31, 2017 (dollars in thousands) Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Unrealized Other-Than- Temporary Impairment Losses Estimated Fair Value Fixed maturities: U.S. Treasury securities $ 162,378 $ 54 $ (1,819 ) $ — $ 160,613 U.S. government-sponsored enterprises 352,455 11,883 (818 ) — 363,520 Obligations of states, municipalities and political subdivisions 4,381,358 193,120 (7,916 ) — 4,566,562 Foreign governments 1,341,628 150,010 (2,410 ) — 1,489,228 Commercial mortgage-backed securities 1,244,777 6,108 (16,559 ) — 1,234,326 Residential mortgage-backed securities 846,916 14,115 (4,863 ) — 856,168 Asset-backed securities 34,942 8 (222 ) — 34,728 Corporate bonds 1,186,699 51,563 (2,737 ) — 1,235,525 Total fixed maturities 9,551,153 426,861 (37,344 ) — 9,940,670 Equity securities: (1) Insurance, banks and other financial institutions 899,324 1,209,162 (5,453 ) — 2,103,033 Industrial, consumer and all other 1,768,337 2,110,959 (14,482 ) — 3,864,814 Total equity securities 2,667,661 3,320,121 (19,935 ) — 5,967,847 Short-term investments 2,161,017 26 (69 ) — 2,160,974 Investments, available-for-sale $ 14,379,831 $ 3,747,008 $ (57,348 ) $ — $ 18,069,491 (1) Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale. Prior periods have not been restated to conform to the current presentation. See note 2. b) The following tables summarize gross unrealized investment losses on available-for-sale investments by the length of time that securities have continuously been in an unrealized loss position. September 30, 2018 Less than 12 months 12 months or longer Total (dollars in thousands) Estimated Fair Value Gross Unrealized Holding and Other-Than- Temporary Impairment Losses Estimated Fair Value Gross Unrealized Holding and Other-Than- Temporary Impairment Losses Estimated Fair Value Gross Unrealized Holding and Other-Than- Temporary Impairment Losses Fixed maturities: U.S. Treasury securities $ 120,072 $ (1,338 ) $ 117,487 $ (2,022 ) $ 237,559 $ (3,360 ) U.S. government-sponsored enterprises 117,344 (4,545 ) 93,453 (3,536 ) 210,797 (8,081 ) Obligations of states, municipalities and political subdivisions 1,384,033 (26,815 ) 411,317 (23,431 ) 1,795,350 (50,246 ) Foreign governments 455,170 (9,425 ) 84,395 (7,622 ) 539,565 (17,047 ) Commercial mortgage-backed securities 1,049,350 (29,512 ) 550,006 (41,091 ) 1,599,356 (70,603 ) Residential mortgage-backed securities 665,021 (22,760 ) 128,067 (8,376 ) 793,088 (31,136 ) Asset-backed securities 10,493 (147 ) 13,964 (162 ) 24,457 (309 ) Corporate bonds 411,153 (12,506 ) 134,322 (4,983 ) 545,475 (17,489 ) Total fixed maturities 4,212,636 (107,048 ) 1,533,011 (91,223 ) 5,745,647 (198,271 ) Short-term investments 1,792,510 (453 ) — — 1,792,510 (453 ) Total $ 6,005,146 $ (107,501 ) $ 1,533,011 $ (91,223 ) $ 7,538,157 $ (198,724 ) At September 30, 2018 , the Company held 1,221 fixed maturities with a total estimated fair value of $7.5 billion and gross unrealized losses of $198.7 million . Of these 1,221 securities, 284 securities had been in a continuous unrealized loss position for one year or longer and had a total estimated fair value of $1.5 billion and gross unrealized losses of $91.2 million . 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, 2017 Less than 12 months 12 months or longer Total (dollars in thousands) Estimated Fair Value Gross Unrealized Holding and Other-Than- Temporary Impairment Losses Estimated Fair Value Gross Unrealized Holding and Other-Than- Temporary Impairment Losses Estimated Fair Value Gross Unrealized Holding and Other-Than- Temporary Impairment Losses Fixed maturities: U.S. Treasury securities $ 78,756 $ (659 ) $ 78,298 $ (1,160 ) $ 157,054 $ (1,819 ) U.S. government-sponsored enterprises 11,593 (79 ) 89,194 (739 ) 100,787 (818 ) Obligations of states, municipalities and political subdivisions 80,654 (789 ) 404,814 (7,127 ) 485,468 (7,916 ) Foreign governments 31,752 (452 ) 63,406 (1,958 ) 95,158 (2,410 ) Commercial mortgage-backed securities 253,936 (1,980 ) 481,216 (14,579 ) 735,152 (16,559 ) Residential mortgage-backed securities 157,508 (1,345 ) 148,960 (3,518 ) 306,468 (4,863 ) Asset-backed securities 14,263 (123 ) 15,165 (99 ) 29,428 (222 ) Corporate bonds 149,345 (863 ) 187,754 (1,874 ) 337,099 (2,737 ) Total fixed maturities 777,807 (6,290 ) 1,468,807 (31,054 ) 2,246,614 (37,344 ) Equity securities: (1) Insurance, banks and other financial institutions 60,848 (4,843 ) 1,291 (610 ) 62,139 (5,453 ) Industrial, consumer and all other 78,552 (11,798 ) 11,243 (2,684 ) 89,795 (14,482 ) Total equity securities 139,400 (16,641 ) 12,534 (3,294 ) 151,934 (19,935 ) Short-term investments 369,104 (69 ) — — 369,104 (69 ) Total $ 1,286,311 $ (23,000 ) $ 1,481,341 $ (34,348 ) $ 2,767,652 $ (57,348 ) (1) Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale. Prior periods have not been restated to conform to the current presentation. See note 2. At December 31, 2017 , the Company held 739 securities with a total estimated fair value of $2.8 billion and gross unrealized losses of $57.3 million . Of these 739 securities, 272 securities had been in a continuous unrealized loss position for one year or longer and had a total estimated fair value of $1.5 billion and gross unrealized losses of $34.3 million . Of these securities, 258 securities were fixed maturities and 14 were equity securities. The Company completes a detailed analysis each quarter to assess whether the decline in the fair value of any investment below its cost basis is deemed other-than-temporary. All available-for-sale 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 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 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. Prior to the adoption of ASU No. 2016-01, equity securities were considered available-for-sale and were included in the analysis of other than temporary impairments. For equity securities, the ability and intent to hold the security for a period of time sufficient to allow for anticipated recovery was considered. A decline in fair value of equity securities that was considered to be other-than-temporary was 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. c) The amortized cost and estimated fair value of fixed maturities at September 30, 2018 are shown below by contractual maturity. (dollars in thousands) Amortized Cost Estimated Fair Value Due in one year or less $ 213,805 $ 212,952 Due after one year through five years 1,426,784 1,433,680 Due after five years through ten years 1,884,581 1,902,186 Due after ten years 3,826,060 3,908,786 7,351,230 7,457,604 Commercial mortgage-backed securities 1,672,438 1,601,848 Residential mortgage-backed securities 898,169 868,091 Asset-backed securities 24,819 24,510 Total fixed maturities $ 9,946,656 $ 9,952,053 d) The following table presents the components of net investment income. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2018 2017 2018 2017 Interest: Municipal bonds (tax-exempt) $ 19,588 $ 21,486 $ 60,810 $ 66,616 Municipal bonds (taxable) 18,634 17,732 54,487 53,030 Other taxable bonds 40,932 36,337 117,949 107,521 Short-term investments, including overnight deposits 13,719 7,779 36,224 18,562 Dividends on equity securities 21,721 21,467 66,202 61,090 Income (loss) from equity method investments (3,556 ) 4,239 (3,268 ) 10,634 Other 255 (315 ) 242 (520 ) 111,293 108,725 332,646 316,933 Investment expenses (4,986 ) (4,236 ) (12,936 ) (12,777 ) Net investment income $ 106,307 $ 104,489 $ 319,710 $ 304,156 e) The following table presents net investment gains (losses) and the change in net unrealized gains (losses) on available-for-sale investments. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2018 2017 2018 2017 Realized gains: Sales of fixed maturities $ 2,916 $ 3,426 $ 3,748 $ 4,189 Sales of equity securities (1) — 9,276 — 25,806 Sales of short-term investments 1,447 8 1,624 19 Other 171 1,121 1,008 5,960 Total realized gains 4,534 13,831 6,380 35,974 Realized losses: Sales of fixed maturities (1,003 ) (657 ) (2,652 ) (1,265 ) Sales of equity securities (1) — (578 ) — (1,791 ) Sales of short-term investments (3,997 ) (207 ) (10,044 ) (499 ) Other-than-temporary impairments — (3,444 ) — (7,261 ) Other (30 ) (575 ) (2,768 ) (593 ) Total realized losses (5,030 ) (5,461 ) (15,464 ) (11,409 ) Net realized investment gains (losses) (496 ) 8,370 (9,084 ) 24,565 Change in fair value of equity securities: (1) Change in fair value of equity securities sold during the period (1) 151 — 10,230 — Change in fair value of equity securities held at the end of the period 426,420 (48,377 ) 407,180 (26,080 ) Change in fair value of equity securities (1) 426,571 (48,377 ) 417,410 (26,080 ) Net investment gains (losses) $ 426,075 $ (40,007 ) $ 408,326 $ (1,515 ) Change in net unrealized gains (losses) on available-for-sale investments included in other comprehensive income: Fixed maturities $ (103,083 ) $ 20,428 $ (384,176 ) $ 104,488 Equity securities (1) — 308,324 — 731,748 Short-term investments 1,417 16 239 22 Net increase (decrease) $ (101,666 ) $ 328,768 $ (383,937 ) $ 836,258 (1) Effective January 1, 2018, the Company adopted ASU No. 2016-01. As a result, equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income; rather, all changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 2.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements 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 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 and equity securities. Equity securities and available-for-sale investments are recorded at fair value on a recurring basis. Available-for-sale investments include fixed maturities 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 and equity securities are 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, U.S. government-sponsored enterprises, municipal bonds, foreign government bonds, commercial mortgage-backed securities, residential mortgage-backed securities, asset-backed securities and corporate debt securities. Level 3 investments include the Company's investments in insurance-linked securities funds (ILS Funds) that are not traded on an active exchange, as further described in note 11 , and are valued using unobservable inputs. Fair value for investments available-for-sale and equity securities 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. Due to the significance of unobservable inputs required in measuring the fair value of the Company's investments in the ILS Funds, these investments are classified as Level 3 within the fair value hierarchy. Changes in fair value of the ILS Funds are included in the change in fair value of equity securities in net income. The fair value of the securities are derived using their reported net asset value (NAV) as the primary input, as well as other observable and unobservable inputs as deemed necessary by management. Management has obtained an understanding of the inputs, assumptions, process, and controls used to determine NAV, which is calculated by an independent third party. Unobservable inputs to the NAV calculations include assumptions around premium earnings patterns and loss reserve estimates for the underlying securitized reinsurance contracts in which the ILS Funds invest. Generally, the Company's investments in the ILS Funds are redeemable annually as of January 1 st of each calendar year. However, in years with significant loss events on the underlying securitized reinsurance contracts, certain investments may be restricted from redemption for up to three years. The Company's valuation policies and procedures for Level 3 investments are determined by management. Fair value measurements are analyzed quarterly to ensure the change in fair value from prior periods is reasonable relative to management's understanding of the underlying investments, recent market trends and external market data, which includes the price of a comparable security and an insurance-linked security index. 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 measured at fair value on a recurring basis by level within the fair value hierarchy. September 30, 2018 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments: Fixed maturities, available-for-sale: U.S. Treasury securities $ — $ 238,145 $ — $ 238,145 U.S. government-sponsored enterprises — 354,879 — 354,879 Obligations of states, municipalities and political subdivisions — 4,312,846 — 4,312,846 Foreign governments — 1,551,737 — 1,551,737 Commercial mortgage-backed securities — 1,601,848 — 1,601,848 Residential mortgage-backed securities — 868,091 — 868,091 Asset-backed securities — 24,510 — 24,510 Corporate bonds — 999,997 — 999,997 Total fixed maturities, available-for-sale — 9,952,053 — 9,952,053 Equity securities: Insurance, banks and other financial institutions 2,110,953 — 122,093 2,233,046 Industrial, consumer and all other 4,316,802 — — 4,316,802 Total equity securities 6,427,755 — 122,093 6,549,848 Short-term investments, available-for-sale 1,825,777 92,914 — 1,918,691 Total investments $ 8,253,532 $ 10,044,967 $ 122,093 $ 18,420,592 December 31, 2017 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments available-for-sale: Fixed maturities: U.S. Treasury securities $ — $ 160,613 $ — $ 160,613 U.S. government-sponsored enterprises — 363,520 — 363,520 Obligations of states, municipalities and political subdivisions — 4,566,562 — 4,566,562 Foreign governments — 1,489,228 — 1,489,228 Commercial mortgage-backed securities — 1,234,326 — 1,234,326 Residential mortgage-backed securities — 856,168 — 856,168 Asset-backed securities — 34,728 — 34,728 Corporate bonds — 1,235,525 — 1,235,525 Total fixed maturities — 9,940,670 — 9,940,670 Equity securities: (1) Insurance, banks and other financial institutions 1,934,224 — 168,809 2,103,033 Industrial, consumer and all other 3,864,814 — — 3,864,814 Total equity securities 5,799,038 — 168,809 5,967,847 Short-term investments 2,065,749 95,225 — 2,160,974 Total investments available-for-sale (1) $ 7,864,787 $ 10,035,895 $ 168,809 $ 18,069,491 (1) Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale. Prior periods have not been restated to conform to the current presentation. See note 2. The following table summarizes changes in Level 3 investments measured at fair value on a recurring basis. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2018 2017 2018 2017 Equity securities, beginning of period $ 119,675 $ 183,913 $ 168,809 $ 191,203 Purchases — 49,000 28,900 56,250 Sales — — (34,653 ) (26,674 ) Total gains (losses) included in net income (loss) 2,418 (51,639 ) (40,963 ) (39,505 ) Transfers into Level 3 — — — — Transfers out of Level 3 — — — — Equity securities, end of period $ 122,093 $ 181,274 $ 122,093 $ 181,274 Change in fair value of equity securities included in net income (loss) relating to assets held at September 30, 2018 and 2017 $ 2,418 $ (51,639 ) $ (40,963 ) $ (39,505 ) Net realized investment losses for the nine months ended September 30, 2018 included losses of $41.0 million on the Company’s investment in the ILS Funds. Net realized investment losses for the quarter and nine months ended September 30, 2017 included losses of $51.6 million and $39.5 million , respectively, on the Company's investment in the ILS Funds. In 2018 and 2017, these losses resulted from decreases in the NAV of the ILS Funds. There were no transfers into or out of Level 1 and Level 2 during the quarter and nine months ended September 30, 2018 and 2017 . The Company did not have any assets or liabilities measured at fair value on a non-recurring basis during the nine months ended September 30, 2018 and 2017 .

Segment Reporting Disclosures

Segment Reporting Disclosures	9 Months Ended
	Sep. 30, 2018
Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract]
Segment Reporting Disclosures	Segment Reporting Disclosures In conjunction with the Company's continued growth and diversification, beginning in the first quarter of 2018 the Company's chief operating decision maker changed the way it reviews the Company's ongoing underwriting results. Effective January 1, 2018, the Company's chief operating decision maker reviews the Company's ongoing underwriting operations on a global basis in the following two segments: Insurance and Reinsurance. In determining how to allocate resources and assess the performance of its underwriting results, management considers many factors, including the nature of the insurance product sold, the type of account written and the type of customer served. The Insurance segment includes all direct business and facultative placements written across the Company. The Reinsurance segment includes all treaty reinsurance written across the Company. All investing activities related to the Company's underwriting operations are included in the Investing segment. Also during the first quarter of 2018, the Company's chief operating decision maker changed the way it assesses the performance of and allocates resources to its Markel Ventures operations. Historically, the Company’s chief operating decision maker reviewed and assessed the performance of each Markel Ventures business separately with no single business being individually significant. Following the continued growth in the Company’s Markel Ventures operations, effective in the first quarter of 2018, the chief operating decision maker reviews and assesses Markel Ventures’ performance in the aggregate, as a single operating segment. The Markel Ventures segment primarily consists of controlling interests in a diverse portfolio of businesses that operate in various industries. The following table summarizes revenue from the Markel Ventures segment by major product grouping. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2018 2017 2018 2017 Markel Ventures: Products $ 362,577 $ 233,895 $ 1,129,036 $ 648,134 Services 106,694 98,853 311,048 285,146 Total Markel Ventures $ 469,271 $ 332,748 $ 1,440,084 $ 933,280 The Company's other operations include the results of the Company's legal and professional consulting services and the results of the Company's investment management services attributable to Markel CATCo Investment Management Ltd. Also included in the Company's other operations are results attributable to the run-off of acquired managing general agent operations and underwriting results for lines of business discontinued prior to, or in conjunction with, acquisitions, including run-off of life and annuity reinsurance business, which are monitored separately from the Company's ongoing underwriting operations. Effective November 17, 2017, the Company's other operations also include the results of the program services business acquired as part of the State National transaction. For purposes of segment reporting, none of the Company's other operations are considered to be reportable segments. Segment profit for each of the Company's underwriting segments is measured by underwriting profit. The property and casualty insurance industry commonly defines underwriting profit as earned premiums net of losses and loss adjustment expenses and underwriting, acquisition and insurance expenses. Underwriting profit 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 for the Investing segment is measured by net investment income and net investment gains. Segment profit for the Markel Ventures segment is measured by operating income. For management reporting purposes, the Company allocates assets to its underwriting, investing, Markel Ventures, and other operations. Underwriting assets are all assets not specifically allocated to the Investing or Markel Ventures segments, or to the Company's other operations. Underwriting and investing assets are not allocated to the Insurance and Reinsurance segments since the Company does not manage its assets by underwriting segment. The Company does not allocate capital expenditures for long-lived assets to either of its underwriting segments for management reporting purposes. a) The following tables summarize the Company's segment disclosures. Prior year amounts have been recast for consistency with the current year presentation. Quarter Ended September 30, 2018 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures Other (1) Consolidated Gross premium volume $ 1,248,150 $ 234,360 $ — $ — $ 561,261 $ 2,043,771 Net written premiums 1,021,684 195,349 — — (762 ) 1,216,271 Earned premiums 961,062 225,277 — — (1,016 ) 1,185,323 Losses and loss adjustment expenses: Current accident year (674,529 ) (186,505 ) — — 48 (860,986 ) Prior accident years 111,117 12,681 — — 342 124,140 Amortization of policy acquisition costs (182,857 ) (58,991 ) — — — (241,848 ) Other operating expenses (172,340 ) (26,125 ) — — (1,648 ) (200,113 ) Underwriting profit (loss) 42,453 (33,663 ) — — (2,274 ) 6,516 Net investment income — — 106,164 143 — 106,307 Net investment gains — — 426,075 — — 426,075 Other revenues — — — 469,271 48,973 518,244 Other expenses (2) — — — (436,642 ) (37,100 ) (473,742 ) Amortization of intangible assets (3) — — — (9,139 ) (18,656 ) (27,795 ) Segment profit (loss) $ 42,453 $ (33,663 ) $ 532,239 $ 23,633 $ (9,057 ) $ 555,605 Interest expense (37,961 ) Net foreign exchange gains 1,383 Income before income taxes $ 519,027 U.S. GAAP combined ratio (4) 96 % 115 % NM (5) 99 % (1) Other segment profit (loss) represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. (2) Other expenses for the Markel Ventures segment include depreciation expense of $13.0 million for the quarter ended September 30, 2018 . (3) Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to any other reportable segments. (4) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (5) NM - Ratio is not meaningful Quarter Ended September 30, 2017 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures Other (1) Consolidated Gross premium volume $ 1,098,237 $ 230,077 $ — $ — $ (186 ) $ 1,328,128 Net written premiums 908,296 189,636 — — (178 ) 1,097,754 Earned premiums 840,439 259,601 — — (178 ) 1,099,862 Losses and loss adjustment expenses: Current accident year (808,243 ) (418,297 ) — — — (1,226,540 ) Prior accident years 128,353 21,164 — — 1,591 151,108 Amortization of policy acquisition costs (177,383 ) (53,440 ) — — — (230,823 ) Other operating expenses (142,667 ) (23,402 ) — — (80 ) (166,149 ) Underwriting profit (loss) (159,501 ) (214,374 ) — — 1,333 (372,542 ) Net investment income — — 104,387 102 — 104,489 Net investment losses — — (40,007 ) — — (40,007 ) Other revenues — — — 332,748 9,056 341,804 Other expenses (2) — — — (319,317 ) (25,679 ) (344,996 ) Amortization of intangible assets (3) — — — (6,917 ) (11,737 ) (18,654 ) Segment profit (loss) $ (159,501 ) $ (214,374 ) $ 64,380 $ 6,616 $ (27,027 ) $ (329,906 ) Interest expense (31,814 ) Net foreign exchange gains 1,772 Loss before income taxes $ (359,948 ) U.S. GAAP combined ratio (4) 119 % 183 % NM (5) 134 % (1) Other segment profit (loss) represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. (2) Other expenses for the Markel Ventures segment include depreciation expense of $9.7 million for the quarter ended September 30, 2017 . (3) Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to any other reportable segments. (4) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (5) NM - Ratio is not meaningful Nine Months Ended September 30, 2018 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures Other (1) Consolidated Gross premium volume $ 3,575,340 $ 935,498 $ — $ — $ 1,577,250 $ 6,088,088 Net written premiums 2,935,789 795,136 — — 754 3,731,679 Earned premiums 2,782,107 702,854 — — (433 ) 3,484,528 Losses and loss adjustment expenses: Current accident year (1,855,190 ) (485,678 ) — — — (2,340,868 ) Prior accident years 369,775 18,135 — — 1,816 389,726 Amortization of policy acquisition costs (554,185 ) (178,818 ) — — — (733,003 ) Other operating expenses (523,239 ) (59,433 ) — — (2,246 ) (584,918 ) Underwriting profit (loss) 219,268 (2,940 ) — — (863 ) 215,465 Net investment income — — 319,253 457 — 319,710 Net investment gains — — 408,326 — — 408,326 Other revenues — — — 1,440,084 145,785 1,585,869 Other expenses (2) — — — (1,350,780 ) (120,435 ) (1,471,215 ) Amortization of intangible assets (3) — — — (29,332 ) (56,927 ) (86,259 ) Segment profit (loss) $ 219,268 $ (2,940 ) $ 727,579 $ 60,429 $ (32,440 ) $ 971,896 Interest expense (114,722 ) Net foreign exchange gains 65,427 Income before income taxes $ 922,601 U.S. GAAP combined ratio (4) 92 % 100 % NM (5) 94 % (1) Other segment profit (loss) represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. (2) Other expenses for the Markel Ventures segment include depreciation expense of $38.5 million for the nine months ended September 30, 2018 . (3) Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to any other reportable segments. (4) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (5) NM - Ratio is not meaningful Nine Months Ended September 30, 2017 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures Other (1) Consolidated Gross premium volume $ 3,120,512 $ 1,025,716 $ — $ — $ (185 ) $ 4,146,043 Net written premiums 2,596,099 899,698 — — (157 ) 3,495,640 Earned premiums 2,401,477 714,718 — — (157 ) 3,116,038 Losses and loss adjustment expenses: Current accident year (1,839,378 ) (710,093 ) — — — (2,549,471 ) Prior accident years 353,767 (22,248 ) — — 7,823 339,342 Amortization of policy acquisition costs (485,460 ) (163,385 ) — — — (648,845 ) Other operating expenses (452,544 ) (69,752 ) — — (379 ) (522,675 ) Underwriting profit (loss) (22,138 ) (250,760 ) — — 7,287 (265,611 ) Net investment income — — 303,951 205 — 304,156 Net investment losses — — (1,515 ) — — (1,515 ) Other revenues — — — 933,280 47,433 980,713 Other expenses (2) — — — (841,674 ) (84,711 ) (926,385 ) Amortization of intangible assets (3) — — — (20,777 ) (32,673 ) (53,450 ) Segment profit (loss) $ (22,138 ) $ (250,760 ) $ 302,436 $ 71,034 $ (62,664 ) $ 37,908 Interest expense (97,013 ) Net foreign exchange gains 2,746 Loss before income taxes $ (56,359 ) U.S. GAAP combined ratio (4) 101 % 135 % NM (5) 108 % (1) Other segment profit (loss) represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. (2) Other expenses for the Markel Ventures segment include depreciation expense of $28.7 million for the nine months ended September 30, 2017 . (3) Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to any other reportable segments. (4) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (5) NM - Ratio is not meaningful b) The following table reconciles segment assets to the Company's consolidated balance sheets. (dollars in thousands) September 30, 2018 December 31, 2017 Segment assets: Investing $ 20,956,369 $ 20,317,160 Underwriting 6,501,069 6,828,048 Markel Ventures 2,027,782 1,900,728 Total segment assets 29,485,220 29,045,936 Other operations 4,473,085 3,759,080 Total assets $ 33,958,305 $ 32,805,016

Unpaid Losses And Loss Adjustme

Unpaid Losses And Loss Adjustment Expenses	9 Months Ended
	Sep. 30, 2018
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Unpaid Losses And Loss Adjustment Expenses	Unpaid Losses and Loss Adjustment Expenses The following table presents a reconciliation of consolidated beginning and ending reserves for losses and loss adjustment expenses. Nine Months Ended September 30, (dollars in thousands) 2018 2017 Net reserves for losses and loss adjustment expenses, beginning of year $ 8,964,945 $ 8,108,717 Foreign currency movements (35,754 ) 158,360 Adjusted net reserves for losses and loss adjustment expenses, beginning of year 8,929,191 8,267,077 Incurred losses and loss adjustment expenses: Current accident year 2,340,868 2,549,471 Prior accident years (389,740 ) (335,494 ) Total incurred losses and loss adjustment expenses 1,951,128 2,213,977 Payments: Current accident year 390,245 342,055 Prior accident years 1,438,224 1,185,689 Total payments 1,828,469 1,527,744 Effect of foreign currency rate changes 368 10,582 Net reserves for losses and loss adjustment expenses of acquired insurance companies — 12,702 Net reserves for losses and loss adjustment expenses, end of period 9,052,218 8,976,594 Reinsurance recoverable on unpaid losses 4,836,271 2,466,554 Gross reserves for losses and loss adjustment expenses, end of period $ 13,888,489 $ 11,443,148 Effective March 31, 2017, reserves of $69.1 million , were formally transferred to a third party by way of a Part VII transfer pursuant to the Financial Services and Markets Act 2000 of the United Kingdom. Upon completion of the transfer in the first quarter of 2017, the Company recognized a previously deferred gain of $3.9 million , which is included in losses and loss adjustment expenses on the consolidated statement of income (loss) and comprehensive income (loss) for the nine months ended September 30, 2017 . This amount is excluded from the prior years' incurred losses and loss adjustment expenses for the nine months ended September 30, 2017 in the above table as the deferred gain was included in other liabilities on the consolidated balance sheet as of December 31, 2016, rather than unpaid losses and loss adjustment expenses. For the nine months ended September 30, 2018 , incurred losses and loss adjustment expenses included $389.7 million of favorable development on prior years' loss reserves, which included $312.2 million of favorable development on the Company's general liability, professional liability, worker's compensation and marine and energy product lines within the Insurance segment, and surety and marine and energy product lines within the Reinsurance segment. Underwriting results for the nine months ended September 30, 2018 included $75.7 million of underwriting loss from Hurricane Florence and Typhoon Jebi (2018 Catastrophes). The underwriting loss on the 2018 Catastrophes was comprised of $77.8 million of estimated net losses and loss adjustment expenses partially offset by $2.1 million of net assumed reinstatement premiums. The estimated net losses and loss adjustment expenses on the 2018 Catastrophes for the nine months ended September 30, 2018 were net of estimated ceded losses of $28.6 million . For the nine months ended September 30, 2017 , incurred losses and loss adjustment expenses included $335.5 million of favorable development on prior years' loss reserves, which included $302.5 million of favorable development on the Company's general liability, professional liability, marine and energy, personal lines business and worker's compensation product lines within the Insurance segment and property and whole account product lines within the Reinsurance segment. Favorable development for the nine months ended September 30, 2017 were partially offset by $85.0 million of adverse development resulting from a decrease in the discount rate, known as the Ogden Rate, used to calculate lump sum awards in U.K. bodily injury cases. Underwriting results for the nine months ended September 30, 2017 included $503.0 million of underwriting loss from Hurricanes Harvey, Irma and Maria as well as the earthquakes in Mexico (2017 Catastrophes). The underwriting loss on the 2017 Catastrophes was comprised of $521.2 million of estimated net losses and loss adjustment expenses partially offset by $18.2 million of net assumed reinstatement premiums. The estimated net losses and loss adjustment expenses on the 2017 Catastrophes for the nine months ended September 30, 2017 were net of estimated ceded losses of $464.4 million . During the nine months ended September 30, 2017 , the Company recorded net reserves for losses and loss adjustment expenses of $12.7 million as a result of the acquisition of SureTec.

Other Revenues

Other Revenues	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Other Revenues	Other Revenues The amount of revenues from contracts with customers included in other revenues on the consolidated statements of income (loss) and comprehensive income (loss) is $472.2 million and $319.0 million for the quarters ended September 30, 2018 and 2017 , respectively, and $1.5 billion and $911.0 million for the nine months ended September 30, 2018 and 2017 , respectively. The following tables disaggregate revenues from contracts with customers by type. Quarter Ended September 30, 2018 2017 (dollars in thousands) Markel Ventures Other Total Markel Ventures Other Total Products $ 350,981 $ — $ 350,981 $ 222,280 $ — $ 222,280 Services 95,071 7,841 102,912 88,082 7,381 95,463 Investment management — 18,258 18,258 — 1,248 1,248 Total revenues from contracts with customers 446,052 26,099 472,151 310,362 8,629 318,991 Program services — 22,478 22,478 — — — Other 23,219 396 23,615 22,386 427 22,813 Total Other Revenues $ 469,271 $ 48,973 $ 518,244 $ 332,748 $ 9,056 $ 341,804 Nine Months Ended September 30, 2018 2017 (dollars in thousands) Markel Ventures Other Total Markel Ventures Other Total Products $ 1,095,461 $ — $ 1,095,461 $ 611,852 $ — $ 611,852 Services 276,548 25,737 302,285 253,311 25,915 279,226 Investment management — 52,965 52,965 — 19,884 19,884 Total revenues from contracts with customers 1,372,009 78,702 1,450,711 865,163 45,799 910,962 Program services — 65,810 65,810 — — — Other 68,075 1,273 69,348 68,117 1,634 69,751 Total Other Revenues $ 1,440,084 $ 145,785 $ 1,585,869 $ 933,280 $ 47,433 $ 980,713 The following table presents receivables and customer deposits related to our contracts with customers. (dollars in thousands) September 30, 2018 December 31, 2017 Receivables $ 208,117 $ 176,865 Customer deposits 60,220 61,546

Reinsurance

Reinsurance	9 Months Ended
	Sep. 30, 2018
Reinsurance Disclosures [Abstract]
Reinsurance	Reinsurance The following tables summarize the effect of reinsurance and retrocessional reinsurance on premiums written and earned. Quarter Ended September 30, 2018 2017 (dollars in thousands) Direct Assumed Ceded Net Premiums Direct Assumed Ceded Net Premiums Underwriting: Written $ 1,207,605 $ 274,898 $ (266,788 ) $ 1,215,715 $ 1,035,705 $ 292,423 $ (230,374 ) $ 1,097,754 Earned 1,113,763 313,378 (242,120 ) 1,185,021 966,735 356,529 (223,402 ) 1,099,862 Program Services: Written 529,958 31,310 (560,712 ) 556 — — — — Earned 480,694 13,046 (493,438 ) 302 — — — — Consolidated: Written 1,737,563 306,208 (827,500 ) 1,216,271 1,035,705 292,423 (230,374 ) 1,097,754 Earned $ 1,594,457 $ 326,424 $ (735,558 ) $ 1,185,323 $ 966,735 $ 356,529 $ (223,402 ) $ 1,099,862 Nine Months Ended September 30, 2018 2017 (dollars in thousands) Direct Assumed Ceded Net Premiums Direct Assumed Ceded Net Premiums Underwriting: Written $ 3,429,666 $ 1,081,171 $ (781,126 ) $ 3,729,711 $ 2,932,022 $ 1,214,021 $ (650,403 ) $ 3,495,640 Earned 3,221,946 965,586 (703,785 ) 3,483,747 2,743,970 976,636 (604,568 ) 3,116,038 Program Services: Written 1,537,412 39,839 (1,575,283 ) 1,968 — — — — Earned 1,374,443 16,784 (1,390,446 ) 781 — — — — Consolidated: Written 4,967,078 1,121,010 (2,356,409 ) 3,731,679 2,932,022 1,214,021 (650,403 ) 3,495,640 Earned $ 4,596,389 $ 982,370 $ (2,094,231 ) $ 3,484,528 $ 2,743,970 $ 976,636 $ (604,568 ) $ 3,116,038 Substantially all of the premium written and earned in the Company's fee-based program services business, which was acquired as part of the State National acquisition in November 2017, for the quarter and nine months ended September 30, 2018 was ceded to third parties. The percentage of ceded earned premiums to gross earned premiums was 38% for both the quarter and nine months ended September 30, 2018 , and 17% and 16% for the quarter and nine months ended September 30, 2017 , respectively. The percentage of assumed earned premiums to net earned premiums was 28% for both the quarter and nine months ended September 30, 2018 , and 32% and 31% , for the quarter and nine months ended September 30, 2017 , respectively. Substantially all of the incurred losses and loss adjustment expenses in the Company's program services business, which totaled $329.9 million and $959.5 million for the quarter and nine months ended September 30, 2018 , respectively, were ceded to third parties. Incurred losses and loss adjustment expenses for the Company's underwriting operations were net of ceded incurred losses and loss adjustment expenses of $171.1 million and $540.1 million for the quarters ended September 30, 2018 and 2017 , respectively, and $394.9 million and $748.7 million for the nine months ended September 30, 2018 and 2017 , respectively. Ceded incurred losses and loss adjustment expenses for both the quarter and nine months ended September 30, 2018 included estimated ceded losses on the 2018 Catastrophes of $28.6 million . Ceded incurred losses and loss adjustment expenses for both the quarter and nine months ended September 30, 2017 included estimated ceded losses on the 2017 Catastrophes of $464.4 million .

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The effective tax rate was 32% for both the nine months ended September 30, 2018 and 2017 . During the first quarter of 2018, the Company decided to make the election to have two of its most significant U.K. subsidiaries treated as domestic corporations for U.S. tax purposes. As a result, during the nine months ended September 30, 2018, the Company recorded a $102.0 million provision for deferred U.S. income taxes on the book and tax basis differences attributable to those subsidiaries, which added 11% to the effective tax rate. The Company continues to be indefinitely reinvested in its other foreign subsidiaries, with the exception of certain Bermuda-based subsidiaries. The Company uses the estimated annual effective tax rate method for calculating its tax provision in interim periods. This method applies the Company's best estimate of the effective tax rate expected for the full year to year-to-date earnings before income taxes. Certain items, including those deemed to be unusual, infrequent or that cannot be reliably estimated (discrete items), are excluded from the estimated annual effective tax rate and the related tax expense or benefit is reported in the same period as the related item. The Company's estimated annual effective tax rate, which excludes the tax attributable to the change in tax status of the two U.K. subsidiaries, was 20% and 28% for the nine months ended September 30, 2018 and 2017 , respectively. For the nine months ended September 30, 2018 and 2017 , the estimated annual effective tax rate differs from the U.S. statutory tax rate of 21% and 35% , respectively, primarily as a result of tax-exempt investment income. The decrease in the estimated annual effective tax rate in 2018 compared to 2017 was primarily attributable to the TCJA, which reduced the U.S. corporate tax rate from 35% to 21% , partially offset by the impact of having higher pre-tax income for the nine months ended September 30, 2018, which reduced the net favorable impact of certain tax adjustments.

Variable Interest Entities

Variable Interest Entities	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Variable Interest Entities	Variable Interest Entities Markel CATCo Investment Management Ltd. (MCIM), a wholly-owned consolidated subsidiary of the Company, is an insurance-linked securities investment fund manager and insurance manager headquartered in Bermuda. Results attributable to MCIM are not included in a reportable segment. MCIM manages a mutual fund company and reinsurance company, both of which were organized under Bermuda law. The mutual fund company issues multiple classes of nonvoting, redeemable preference shares to investors through its funds (the Funds) and the Funds are primarily invested in nonvoting shares of the reinsurance company. The underwriting results of the reinsurance company are attributed to the Funds through the issuance of nonvoting preference shares. The Funds and the reinsurance company are considered VIEs, as their preference shareholders have no voting rights. MCIM has the power to direct the activities that most significantly impact the economic performance of these entities, but does not have a variable interest in any of the entities. Except as described below, the Company is not the primary beneficiary of the Funds or the reinsurance company, as the Company's involvement is generally limited to that of an investment or insurance manager, receiving fees that are at market and commensurate with the level of effort required. Investment management fees earned by the Company from unconsolidated Funds were $18.3 million and $1.2 million for the quarters ended September 30, 2018 and 2017 , respectively, and $53.0 million and $19.9 million for the nine months ended September 30, 2018 and 2017 , respectively. The Company is the sole investor in one of the Funds, the Markel Diversified Fund, and consolidates that fund as its primary beneficiary. The Company also holds an investment in another one of the Funds ( $27.4 million as of September 30, 2018 ) but does not have the obligation to absorb losses or right to receive benefits from the VIE that could potentially be significant to the VIE, and therefore does not consolidate that Fund. As of September 30, 2018 , total assets of the Markel Diversified Fund were $96.1 million and total liabilities were $25.1 million . As of December 31, 2017 , total assets of the Markel Diversified Fund were $170.3 million and total liabilities were $62.7 million . The assets of the Markel Diversified Fund are available for use only by the Markel Diversified Fund, and are not available for use by the Company. Total assets of the Markel Diversified Fund include an investment in one of the unconsolidated Funds totaling $94.7 million as of September 30, 2018 and $168.2 million as of December 31, 2017 , which represents 2% of the outstanding preference shares of that fund as of September 30, 2018 and 7% as of December 31, 2017 . This investment is included in equity securities on the Company's consolidated balance sheets. At September 30, 2018 and December 31, 2017 , total liabilities of the Markel Diversified Fund included a $24.9 million and $62.5 million note payable, delivered as part of the consideration provided for its investment. The Company repaid $37.5 million of the note payable in January 2018. Other than the note payable, any liabilities held by the Markel Diversified Fund have no recourse to the Company's general credit. The Company also holds an investment in CATCo Reinsurance Opportunities Fund Ltd. (CROF), a limited liability closed-end fund listed on the London and Bermuda Stock Exchanges, which is not a VIE. This investment is included in equity securities on the Company's consolidated balance sheets. CROF is managed by MCIM and invests substantially all of its assets in one of the unconsolidated Funds. At September 30, 2018 and December 31, 2017 , the fair value of the Company's investment in CROF was $11.7 million and $20.5 million , respectively. The Company's exposure to risk from the unconsolidated Funds and the reinsurance company is generally limited to its investment and any earned but uncollected fees. The Company has not issued any investment performance guarantees to these VIEs or their investors. As of September 30, 2018 , total investment and insurance assets under management of MCIM for unconsolidated VIEs were $6.6 billion , which includes funds held that will be used to settle claims for incurred losses.

Shareholders' Equity

Shareholders' Equity	9 Months Ended
	Sep. 30, 2018
Stockholders' Equity Note [Abstract]
Shareholders' Equity	Shareholders' Equity a) In May 2018, the Company’s Board of Directors approved a new share repurchase program (the 2018 Program) to replace the previous share repurchase program that was approved by the Board of Directors in November 2013 (the 2013 Program). The 2018 Program provides for the repurchase of up to $300 million of common stock and has no expiration date but may be terminated by the Board of Directors at any time. During the nine months ended September 30, 2018 , the Company repurchased an aggregate of 24,584 shares of common stock at a cost of $27.8 million , including 15,509 shares repurchased under the 2013 Program at a cost of $17.6 million , and 9,075 shares repurchased under the 2018 Program at a cost of $10.2 million . In total, the Company repurchased 199,244 shares of common stock under the 2013 Program at a cost of $175.6 million . b) Net income (loss) per share was determined by dividing adjusted net income (loss) to shareholders by the applicable weighted average shares outstanding. Diluted net income (loss) per share is computed by dividing adjusted net income (loss) to shareholders by the weighted average number of common shares and dilutive potential common shares outstanding during the period. Quarter Ended September 30, Nine Months Ended September 30, (in thousands, except per share amounts) 2018 2017 2018 2017 Net income (loss) to shareholders $ 409,438 $ (259,141 ) $ 623,363 $ (39,612 ) Adjustment of redeemable noncontrolling interests (12,035 ) (3,298 ) (6,621 ) (23,582 ) Adjusted net income (loss) to shareholders $ 397,403 $ (262,439 ) $ 616,742 $ (63,194 ) Basic common shares outstanding 13,917 13,947 13,925 13,974 Dilutive potential common shares from conversion of options — 1 — 2 Dilutive potential common shares from conversion of restricted stock units and restricted stock 26 42 24 42 Diluted shares outstanding 13,943 13,990 13,949 14,018 Basic net income (loss) per share (1) $ 28.56 $ (18.82 ) $ 44.29 $ (4.52 ) Diluted net income (loss) per share (1) $ 28.50 $ (18.82 ) $ 44.21 $ (4.52 ) (1) Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income, rather, changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 2.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 2018
Other Comprehensive Income (Loss), Tax [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) Other comprehensive income (loss) includes net holding gains (losses) on available-for-sale investments 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 (losses) included in net income (loss). Other comprehensive income (loss) 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 (loss) by component, net of taxes and noncontrolling interests, for the nine months ended September 30, 2018 and 2017 . (dollars in thousands) Unrealized Holding Gains (Losses) on Available-for-Sale Securities Foreign Currency Net Actuarial Pension Loss Total December 31, 2016 $ 1,714,930 $ (84,406 ) $ (64,658 ) $ 1,565,866 Other comprehensive income before reclassifications 577,796 19,750 — 597,546 Amounts reclassified from accumulated other comprehensive income (14,598 ) — 2,391 (12,207 ) Total other comprehensive income 563,198 19,750 2,391 585,339 September 30, 2017 $ 2,278,128 $ (64,656 ) $ (62,267 ) $ 2,151,205 December 31, 2017 $ 2,477,973 $ (74,003 ) $ (58,399 ) $ 2,345,571 Cumulative effect of adoption of ASU No. 2016-01 (2,615,734 ) 2,492 — (2,613,242 ) Cumulative effect of adoption of ASU No. 2018-02 401,539 — — 401,539 Other comprehensive income (loss) before reclassifications (306,069 ) (19,928 ) 1,741 (324,256 ) Amounts reclassified from accumulated other comprehensive loss (1) 5,496 — — 5,496 Total other comprehensive income (loss) (2,514,768 ) (17,436 ) 1,741 (2,530,463 ) September 30, 2018 $ (36,795 ) $ (91,439 ) $ (56,658 ) $ (184,892 ) (1) Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income, rather, changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 2. The following table summarizes the tax expense (benefit) associated with each component of other comprehensive income (loss). Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2018 2017 2018 2017 Change in net unrealized gains (losses) on available-for-sale investments: (1) Net holding gains (losses) arising during the period $ (24,047 ) $ 109,338 $ (84,825 ) $ 278,266 Reclassification adjustments for net gains (losses) included in net income (loss) 2,810 (2,810 ) 1,461 (5,206 ) Change in net unrealized gains (losses) on available-for-sale investments (21,237 ) 106,528 (83,364 ) 273,060 Change in foreign currency translation adjustments 6,594 656 3,072 153 Change in net actuarial pension loss 135 159 463 492 Total $ (14,508 ) $ 107,343 $ (79,829 ) $ 273,705 (1) Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income, rather, changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 2. The following table presents the details of amounts reclassified from accumulated other comprehensive income (loss) into net income (loss), by component. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2018 2017 2018 2017 Unrealized holding gains (losses) on available-for-sale investments: (1) Other-than-temporary impairment losses $ — $ (3,444 ) $ — $ (7,261 ) Net realized investment gains (losses), excluding other-than-temporary impairment losses (13,383 ) 11,461 (6,957 ) 27,065 Total before income taxes (13,383 ) 8,017 (6,957 ) 19,804 Income taxes 2,810 (2,810 ) 1,461 (5,206 ) Reclassification of unrealized holding gains (losses), net of taxes $ (10,573 ) $ 5,207 $ (5,496 ) $ 14,598 Net actuarial pension loss: Underwriting, acquisition and insurance expenses $ (644 ) $ (932 ) $ (2,204 ) $ (2,883 ) Income taxes 135 159 463 492 Reclassification of net actuarial pension loss, net of taxes $ (509 ) $ (773 ) $ (1,741 ) $ (2,391 ) (1) Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income, rather, changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 2.

Contingencies

Contingencies	9 Months Ended
	Sep. 30, 2018
Loss Contingency [Abstract]
Contingencies	Contingencies Aspen Holdings. In October 2010, the Company completed its acquisition of Aspen Holdings, Inc. (Aspen). As part of the consideration for that acquisition, Aspen shareholders received contingent value rights (CVRs). Based on a valuation of the CVRs as of their December 31, 2017 maturity date, we paid $9.9 million to the CVR holders on June 5, 2018, which represents 90% of the undisputed portion of the final amount the Company believes it is required to pay under the CVR agreement. Prior to the December 31, 2017 maturity date, the CVR holder representative, Thomas Yeransian, had disputed the Company's estimation of the value of the CVRs. On September 15, 2016, Mr. Yeransian filed a suit alleging, among other things, that the Company is in default under the CVR agreement. The holder representative seeks: $47.3 million in damages, which represents the unadjusted value of the CVRs; plus interest ( $13.4 million through September 30, 2018 ) and default interest (up to an additional $11.5 million through September 30, 2018 , depending on the date any default occurred); and an unspecified amount of punitive damages, costs, and attorneys’ fees. Management believes the holder representative’s suit to be without merit and will vigorously defend against it. Further, management believes that any material loss resulting from the holder representative’s suit to be remote. Markel Ventures. The Company has been reviewing events at one of its Markel Ventures products businesses. Since becoming aware of a matter late in the first quarter of 2018 related to the business's manufacture of products, the Company has conducted an investigation, reviewing the business's operations and developing remediation plans. Upon completion of its review during the second quarter of 2018, the Company recorded an expense of $33.5 million in its results of operations. This amount represented management’s best estimate of amounts currently considered probable including: remediation costs associated with the manufacture of products, costs associated with the investigation of this matter, a write down of inventory on hand and settlement costs related to pre-existing litigation. The Company also recorded an impairment charge of $14.9 million during the second quarter of 2018 which reduced the carrying value of intangible assets at this reporting unit to zero . Final resolution of this matter could ultimately result in additional remediation and other costs, the amount of which cannot be estimated at this time, but which could have a material impact on the Company’s income before income taxes. However, management does not expect this matter ultimately will have a material adverse effect on the Company’s results of operations or financial condition. If a determination is made that additional costs associated with this matter are considered probable, these additional costs will be recognized as an expense in the Company's results of operations. In addition, 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.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2018
Subsequent Events [Abstract]
Subsequent Events [Text Block]	Subsequent Events In early October 2018, the Gulf Coast and southeastern regions of the United States sustained losses from Hurricane Michael. Based on information currently available, the Company estimates its range of net incurred losses on this event is between $60 million and $120 million before income taxes. This estimated range of losses was derived based on initial industry loss estimates, policy level reviews and direct contact with insureds and brokers when possible. However, the Company is still gathering preliminary loss data and few losses have been reported at this time. Potential losses associated with business interruption are also not yet clear. The Company continues to closely monitor reported claims and will refine its initial estimate of losses, which will be recorded in the fourth quarter of 2018, as the actual level of claims becomes more certain.

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation. The consolidated balance sheet as of September 30, 2018 and the related consolidated statements of income (loss) and comprehensive income (loss) for the quarters and nine months ended September 30, 2018 and 2017 , and the consolidated statements of changes in equity and cash flows for the nine months ended September 30, 2018 and 2017 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, 2017 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 consolidated subsidiaries, as well as any variable interest entities (VIEs) that meet the requirements for consolidation (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, with the exception of significant transactions or events that occur during the intervening period. 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 2017 Annual Report on Form 10-K for a more complete description of the Company's business and accounting policies.
Foreign Currency Transactions	Foreign Currency Transactions. The U.S. Dollar is the Company’s reporting currency and the primary functional currency of its foreign underwriting operations. The functional currencies of the Company's other foreign operations are the currencies of the primary economic environments in which the majority of their business is transacted. Foreign currency transaction gains and losses are the result of exchange rate changes on transactions denominated in currencies other than the functional currency at each foreign entity. Monetary assets and liabilities are remeasured to the functional currency at current exchange rates, with resulting gains and losses included in net foreign exchange losses (gains) within net income. Non-monetary assets and liabilities are remeasured to the functional currency at historic exchange rates. Available-for-sale securities are recorded at fair value with resulting gains and losses, including the portion attributable to movements in exchange rates, included in the change in net unrealized gains on available-for-sale investments, net of taxes within other comprehensive income. While we attempt to naturally hedge our exposure to foreign currency fluctuations by matching assets and liabilities in currency, there is a financial statement mismatch between the gains or losses recorded in net income related to insurance reserves denominated in non-functional currencies and the gains or losses recorded in other comprehensive income related to the available-for-sale securities supporting the reserves. Assets and liabilities of foreign operations denominated in a functional currency other than the U.S. Dollar are translated into the U.S. Dollar at current exchange rates, with resulting gains or losses included, net of taxes, in the change in foreign currency translation adjustments within other comprehensive income. Historically, the Company also designated certain additional currencies, including the British Pound Sterling, the Euro, and the Canadian Dollar, as functional currencies within its foreign underwriting operations that were deemed to contain distinct and separable operations in those foreign economic environments. However, over time the Company’s foreign underwriting operations have evolved and are now managed on a global basis. Effective January 1, 2018, management reassessed its functional currency determination as required by Financial Accounting Standards Board (FASB) Accounting Standards Codification (ASC) 830, Foreign Currency Matters , and concluded that its foreign underwriting operations have evolved to function as an extension, or integral component, of the Company’s global underwriting operations, and are no longer deemed to contain distinct and separable operations. As a result, more foreign currency denominated transactions are designated as non-functional, with related remeasurement gains and losses included in net income. The change in the Company’s functional currency determination has been applied on a prospective basis in accordance with ASC 830. Therefore, any translation gains and losses that were previously recorded in accumulated other comprehensive income through December 31, 2017 remain unchanged as of September 30, 2018.
Revenue Recognition	Revenue Recognition. Effective January 1, 2018, the Company adopted FASB Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers (Topic 606), and related amendments, which created a new comprehensive revenue recognition standard, ASC 606, that serves as a single source of revenue guidance for all contracts with customers to transfer goods or services or contracts for the transfer of nonfinancial assets, unless those contracts are within the scope of other standards, such as insurance contracts. ASC 606 is not applicable to the Company's insurance premium revenues or revenues from its investment portfolio but is applicable to most of the Company's other revenues, as described below. See note 2 for further discussion of the impact of adopting this standard. Other revenues primarily relate to the Company's Markel Ventures segment and consist of revenues from the sale of products and services. Revenues are recognized when, or as, control of the promised goods or services is transferred to the Company's customers, in an amount that reflects the consideration the Company expects to be entitled to in exchange for those goods or services. All contracts with customers either have an original expected length of one year or less or the Company recognizes revenue at the amount for which it has a right to invoice for the products delivered or services performed. Certain customers may receive volume rebates or credits for products and services, which are accounted for as variable consideration. The Company estimates these amounts based on the expected amount to be provided to the customer and reduces revenues recognized by a corresponding amount. The Company does not expect significant changes to its estimates of variable consideration over the term of the contracts. Payment terms for products and services vary by the type of product or service offered and the location of the customer, and payment is typically received at or shortly after the point of sale. For certain products, the Company requires partial payment in the form of a deposit before the products are delivered to the customer, which is included in other liabilities on the Company's consolidated balance sheet. Product revenues are primarily generated from the sale of ornamental plants, equipment used in baking systems, portable dredges, over the road transportation equipment, flooring for the trucking industry, and residential homes. Most of the Company's product revenues are recognized when the products are shipped to the customer or the products arrive at the agreed upon destination with the end customer. Some of the Company's contracts include multiple performance obligations. For such arrangements, revenues are allocated to each performance obligation based on the relative standalone selling price, which is derived from amounts stated in the contract. Service revenues are primarily generated by delivering healthcare services, retail intelligence, consulting services and investment management services. Service revenues are generally recognized over the term of the contracts based on hours incurred or as services are provided. Investment management fee income is recognized over the period in which investment management services are provided and is calculated and recognized monthly based on the net asset value of the accounts managed. In connection with the investment management services provided, the Company is also entitled to participate, on a fixed-percentage basis, in any net income generated in excess of an agreed-upon threshold as established by the underlying investment management agreements. In general, net income is calculated at the end of each calendar year and performance fees are payable annually. Performance fee income is recognized at the conclusion of the contractual performance period, when the uncertainty related to performance has been resolved.

Acquisitions (Tables)

Acquisitions (Tables)	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Summary Of Net Intangible Assets Acquired	The following table summarizes the intangible assets recorded in connection with the acquisition, and as of September 30, 2018 . (dollars in thousands) Amount Economic Useful Life Customer relationships $ 289,000 13 years Trade names 22,500 13 years Technology 27,000 Nine years Insurance licenses 32,000 Indefinite Intangible assets, before amortization, as of the acquisition date 370,500 Amortization (from the acquisition date through September 30, 2018) 25,407 Net intangible assets as of September 30, 2018 $ 345,093

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Available-For-Sale Investments	The following tables summarize the Company's available-for-sale investments. Commercial and residential mortgage-backed securities include securities issued by U.S. government-sponsored enterprises and U.S. government agencies. September 30, 2018 (dollars in thousands) Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Unrealized Other-Than- Temporary Impairment Losses Estimated Fair Value Fixed maturities: U.S. Treasury securities $ 241,485 $ 20 $ (3,360 ) $ — $ 238,145 U.S. government-sponsored enterprises 359,348 3,612 (8,081 ) — 354,879 Obligations of states, municipalities and political subdivisions 4,289,636 73,456 (50,246 ) — 4,312,846 Foreign governments 1,463,626 105,158 (17,047 ) — 1,551,737 Commercial mortgage-backed securities 1,672,438 13 (70,603 ) — 1,601,848 Residential mortgage-backed securities 898,169 1,058 (31,136 ) — 868,091 Asset-backed securities 24,819 — (309 ) — 24,510 Corporate bonds 997,135 20,351 (17,489 ) — 999,997 Total fixed maturities 9,946,656 203,668 (198,271 ) — 9,952,053 Short-term investments 1,918,495 649 (453 ) — 1,918,691 Investments, available-for-sale $ 11,865,151 $ 204,317 $ (198,724 ) $ — $ 11,870,744 December 31, 2017 (dollars in thousands) Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Unrealized Other-Than- Temporary Impairment Losses Estimated Fair Value Fixed maturities: U.S. Treasury securities $ 162,378 $ 54 $ (1,819 ) $ — $ 160,613 U.S. government-sponsored enterprises 352,455 11,883 (818 ) — 363,520 Obligations of states, municipalities and political subdivisions 4,381,358 193,120 (7,916 ) — 4,566,562 Foreign governments 1,341,628 150,010 (2,410 ) — 1,489,228 Commercial mortgage-backed securities 1,244,777 6,108 (16,559 ) — 1,234,326 Residential mortgage-backed securities 846,916 14,115 (4,863 ) — 856,168 Asset-backed securities 34,942 8 (222 ) — 34,728 Corporate bonds 1,186,699 51,563 (2,737 ) — 1,235,525 Total fixed maturities 9,551,153 426,861 (37,344 ) — 9,940,670 Equity securities: (1) Insurance, banks and other financial institutions 899,324 1,209,162 (5,453 ) — 2,103,033 Industrial, consumer and all other 1,768,337 2,110,959 (14,482 ) — 3,864,814 Total equity securities 2,667,661 3,320,121 (19,935 ) — 5,967,847 Short-term investments 2,161,017 26 (69 ) — 2,160,974 Investments, available-for-sale $ 14,379,831 $ 3,747,008 $ (57,348 ) $ — $ 18,069,491 (1) Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale. Prior periods have not been restated to conform to the current presentation. See note 2.
Summary Of Gross Unrealized Investment Losses By Length Of Time That Securities Have Continuously Been In An Unrealized Loss Position	December 31, 2017 Less than 12 months 12 months or longer Total (dollars in thousands) Estimated Fair Value Gross Unrealized Holding and Other-Than- Temporary Impairment Losses Estimated Fair Value Gross Unrealized Holding and Other-Than- Temporary Impairment Losses Estimated Fair Value Gross Unrealized Holding and Other-Than- Temporary Impairment Losses Fixed maturities: U.S. Treasury securities $ 78,756 $ (659 ) $ 78,298 $ (1,160 ) $ 157,054 $ (1,819 ) U.S. government-sponsored enterprises 11,593 (79 ) 89,194 (739 ) 100,787 (818 ) Obligations of states, municipalities and political subdivisions 80,654 (789 ) 404,814 (7,127 ) 485,468 (7,916 ) Foreign governments 31,752 (452 ) 63,406 (1,958 ) 95,158 (2,410 ) Commercial mortgage-backed securities 253,936 (1,980 ) 481,216 (14,579 ) 735,152 (16,559 ) Residential mortgage-backed securities 157,508 (1,345 ) 148,960 (3,518 ) 306,468 (4,863 ) Asset-backed securities 14,263 (123 ) 15,165 (99 ) 29,428 (222 ) Corporate bonds 149,345 (863 ) 187,754 (1,874 ) 337,099 (2,737 ) Total fixed maturities 777,807 (6,290 ) 1,468,807 (31,054 ) 2,246,614 (37,344 ) Equity securities: (1) Insurance, banks and other financial institutions 60,848 (4,843 ) 1,291 (610 ) 62,139 (5,453 ) Industrial, consumer and all other 78,552 (11,798 ) 11,243 (2,684 ) 89,795 (14,482 ) Total equity securities 139,400 (16,641 ) 12,534 (3,294 ) 151,934 (19,935 ) Short-term investments 369,104 (69 ) — — 369,104 (69 ) Total $ 1,286,311 $ (23,000 ) $ 1,481,341 $ (34,348 ) $ 2,767,652 $ (57,348 ) (1) Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale. Prior periods have not been restated to conform to the current presentation. See note 2. The following tables summarize gross unrealized investment losses on available-for-sale investments by the length of time that securities have continuously been in an unrealized loss position. September 30, 2018 Less than 12 months 12 months or longer Total (dollars in thousands) Estimated Fair Value Gross Unrealized Holding and Other-Than- Temporary Impairment Losses Estimated Fair Value Gross Unrealized Holding and Other-Than- Temporary Impairment Losses Estimated Fair Value Gross Unrealized Holding and Other-Than- Temporary Impairment Losses Fixed maturities: U.S. Treasury securities $ 120,072 $ (1,338 ) $ 117,487 $ (2,022 ) $ 237,559 $ (3,360 ) U.S. government-sponsored enterprises 117,344 (4,545 ) 93,453 (3,536 ) 210,797 (8,081 ) Obligations of states, municipalities and political subdivisions 1,384,033 (26,815 ) 411,317 (23,431 ) 1,795,350 (50,246 ) Foreign governments 455,170 (9,425 ) 84,395 (7,622 ) 539,565 (17,047 ) Commercial mortgage-backed securities 1,049,350 (29,512 ) 550,006 (41,091 ) 1,599,356 (70,603 ) Residential mortgage-backed securities 665,021 (22,760 ) 128,067 (8,376 ) 793,088 (31,136 ) Asset-backed securities 10,493 (147 ) 13,964 (162 ) 24,457 (309 ) Corporate bonds 411,153 (12,506 ) 134,322 (4,983 ) 545,475 (17,489 ) Total fixed maturities 4,212,636 (107,048 ) 1,533,011 (91,223 ) 5,745,647 (198,271 ) Short-term investments 1,792,510 (453 ) — — 1,792,510 (453 ) Total $ 6,005,146 $ (107,501 ) $ 1,533,011 $ (91,223 ) $ 7,538,157 $ (198,724 )
Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturity Securities By Contractual Maturity Date	The amortized cost and estimated fair value of fixed maturities at September 30, 2018 are shown below by contractual maturity. (dollars in thousands) Amortized Cost Estimated Fair Value Due in one year or less $ 213,805 $ 212,952 Due after one year through five years 1,426,784 1,433,680 Due after five years through ten years 1,884,581 1,902,186 Due after ten years 3,826,060 3,908,786 7,351,230 7,457,604 Commercial mortgage-backed securities 1,672,438 1,601,848 Residential mortgage-backed securities 898,169 868,091 Asset-backed securities 24,819 24,510 Total fixed maturities $ 9,946,656 $ 9,952,053
Components Of Net Investment Income	The following table presents the components of net investment income. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2018 2017 2018 2017 Interest: Municipal bonds (tax-exempt) $ 19,588 $ 21,486 $ 60,810 $ 66,616 Municipal bonds (taxable) 18,634 17,732 54,487 53,030 Other taxable bonds 40,932 36,337 117,949 107,521 Short-term investments, including overnight deposits 13,719 7,779 36,224 18,562 Dividends on equity securities 21,721 21,467 66,202 61,090 Income (loss) from equity method investments (3,556 ) 4,239 (3,268 ) 10,634 Other 255 (315 ) 242 (520 ) 111,293 108,725 332,646 316,933 Investment expenses (4,986 ) (4,236 ) (12,936 ) (12,777 ) Net investment income $ 106,307 $ 104,489 $ 319,710 $ 304,156
Summary Of Net Investment Gains (Losses) And The Change In Net Unrealized Gains On Investments	The following table presents net investment gains (losses) and the change in net unrealized gains (losses) on available-for-sale investments. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2018 2017 2018 2017 Realized gains: Sales of fixed maturities $ 2,916 $ 3,426 $ 3,748 $ 4,189 Sales of equity securities (1) — 9,276 — 25,806 Sales of short-term investments 1,447 8 1,624 19 Other 171 1,121 1,008 5,960 Total realized gains 4,534 13,831 6,380 35,974 Realized losses: Sales of fixed maturities (1,003 ) (657 ) (2,652 ) (1,265 ) Sales of equity securities (1) — (578 ) — (1,791 ) Sales of short-term investments (3,997 ) (207 ) (10,044 ) (499 ) Other-than-temporary impairments — (3,444 ) — (7,261 ) Other (30 ) (575 ) (2,768 ) (593 ) Total realized losses (5,030 ) (5,461 ) (15,464 ) (11,409 ) Net realized investment gains (losses) (496 ) 8,370 (9,084 ) 24,565 Change in fair value of equity securities: (1) Change in fair value of equity securities sold during the period (1) 151 — 10,230 — Change in fair value of equity securities held at the end of the period 426,420 (48,377 ) 407,180 (26,080 ) Change in fair value of equity securities (1) 426,571 (48,377 ) 417,410 (26,080 ) Net investment gains (losses) $ 426,075 $ (40,007 ) $ 408,326 $ (1,515 ) Change in net unrealized gains (losses) on available-for-sale investments included in other comprehensive income: Fixed maturities $ (103,083 ) $ 20,428 $ (384,176 ) $ 104,488 Equity securities (1) — 308,324 — 731,748 Short-term investments 1,417 16 239 22 Net increase (decrease) $ (101,666 ) $ 328,768 $ (383,937 ) $ 836,258 (1) Effective January 1, 2018, the Company adopted ASU No. 2016-01. As a result, equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income; rather, all changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 2.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Balances Of Assets Measured At Fair Value On A Recurring Basis	The following tables present the balances of assets measured at fair value on a recurring basis by level within the fair value hierarchy. September 30, 2018 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments: Fixed maturities, available-for-sale: U.S. Treasury securities $ — $ 238,145 $ — $ 238,145 U.S. government-sponsored enterprises — 354,879 — 354,879 Obligations of states, municipalities and political subdivisions — 4,312,846 — 4,312,846 Foreign governments — 1,551,737 — 1,551,737 Commercial mortgage-backed securities — 1,601,848 — 1,601,848 Residential mortgage-backed securities — 868,091 — 868,091 Asset-backed securities — 24,510 — 24,510 Corporate bonds — 999,997 — 999,997 Total fixed maturities, available-for-sale — 9,952,053 — 9,952,053 Equity securities: Insurance, banks and other financial institutions 2,110,953 — 122,093 2,233,046 Industrial, consumer and all other 4,316,802 — — 4,316,802 Total equity securities 6,427,755 — 122,093 6,549,848 Short-term investments, available-for-sale 1,825,777 92,914 — 1,918,691 Total investments $ 8,253,532 $ 10,044,967 $ 122,093 $ 18,420,592 December 31, 2017 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments available-for-sale: Fixed maturities: U.S. Treasury securities $ — $ 160,613 $ — $ 160,613 U.S. government-sponsored enterprises — 363,520 — 363,520 Obligations of states, municipalities and political subdivisions — 4,566,562 — 4,566,562 Foreign governments — 1,489,228 — 1,489,228 Commercial mortgage-backed securities — 1,234,326 — 1,234,326 Residential mortgage-backed securities — 856,168 — 856,168 Asset-backed securities — 34,728 — 34,728 Corporate bonds — 1,235,525 — 1,235,525 Total fixed maturities — 9,940,670 — 9,940,670 Equity securities: (1) Insurance, banks and other financial institutions 1,934,224 — 168,809 2,103,033 Industrial, consumer and all other 3,864,814 — — 3,864,814 Total equity securities 5,799,038 — 168,809 5,967,847 Short-term investments 2,065,749 95,225 — 2,160,974 Total investments available-for-sale (1) $ 7,864,787 $ 10,035,895 $ 168,809 $ 18,069,491 (1) Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale. Prior periods have not been restated to conform to the current presentation. See note 2.
Summary Of Changes In Level 3 Investments Measured At Fair Value On A Recurring Basis	The following table summarizes changes in Level 3 investments measured at fair value on a recurring basis. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2018 2017 2018 2017 Equity securities, beginning of period $ 119,675 $ 183,913 $ 168,809 $ 191,203 Purchases — 49,000 28,900 56,250 Sales — — (34,653 ) (26,674 ) Total gains (losses) included in net income (loss) 2,418 (51,639 ) (40,963 ) (39,505 ) Transfers into Level 3 — — — — Transfers out of Level 3 — — — — Equity securities, end of period $ 122,093 $ 181,274 $ 122,093 $ 181,274 Change in fair value of equity securities included in net income (loss) relating to assets held at September 30, 2018 and 2017 $ 2,418 $ (51,639 ) $ (40,963 ) $ (39,505 )

Segment Reporting Disclosures (

Segment Reporting Disclosures (Tables)	9 Months Ended
	Sep. 30, 2018
Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract]
Summary Of Revenue From The Markel Ventures Segment By Major Product Grouping	The following table summarizes revenue from the Markel Ventures segment by major product grouping. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2018 2017 2018 2017 Markel Ventures: Products $ 362,577 $ 233,895 $ 1,129,036 $ 648,134 Services 106,694 98,853 311,048 285,146 Total Markel Ventures $ 469,271 $ 332,748 $ 1,440,084 $ 933,280
Company's Segment Disclosures	The following tables summarize the Company's segment disclosures. Prior year amounts have been recast for consistency with the current year presentation. Quarter Ended September 30, 2018 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures Other (1) Consolidated Gross premium volume $ 1,248,150 $ 234,360 $ — $ — $ 561,261 $ 2,043,771 Net written premiums 1,021,684 195,349 — — (762 ) 1,216,271 Earned premiums 961,062 225,277 — — (1,016 ) 1,185,323 Losses and loss adjustment expenses: Current accident year (674,529 ) (186,505 ) — — 48 (860,986 ) Prior accident years 111,117 12,681 — — 342 124,140 Amortization of policy acquisition costs (182,857 ) (58,991 ) — — — (241,848 ) Other operating expenses (172,340 ) (26,125 ) — — (1,648 ) (200,113 ) Underwriting profit (loss) 42,453 (33,663 ) — — (2,274 ) 6,516 Net investment income — — 106,164 143 — 106,307 Net investment gains — — 426,075 — — 426,075 Other revenues — — — 469,271 48,973 518,244 Other expenses (2) — — — (436,642 ) (37,100 ) (473,742 ) Amortization of intangible assets (3) — — — (9,139 ) (18,656 ) (27,795 ) Segment profit (loss) $ 42,453 $ (33,663 ) $ 532,239 $ 23,633 $ (9,057 ) $ 555,605 Interest expense (37,961 ) Net foreign exchange gains 1,383 Income before income taxes $ 519,027 U.S. GAAP combined ratio (4) 96 % 115 % NM (5) 99 % (1) Other segment profit (loss) represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. (2) Other expenses for the Markel Ventures segment include depreciation expense of $13.0 million for the quarter ended September 30, 2018 . (3) Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to any other reportable segments. (4) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (5) NM - Ratio is not meaningful Quarter Ended September 30, 2017 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures Other (1) Consolidated Gross premium volume $ 1,098,237 $ 230,077 $ — $ — $ (186 ) $ 1,328,128 Net written premiums 908,296 189,636 — — (178 ) 1,097,754 Earned premiums 840,439 259,601 — — (178 ) 1,099,862 Losses and loss adjustment expenses: Current accident year (808,243 ) (418,297 ) — — — (1,226,540 ) Prior accident years 128,353 21,164 — — 1,591 151,108 Amortization of policy acquisition costs (177,383 ) (53,440 ) — — — (230,823 ) Other operating expenses (142,667 ) (23,402 ) — — (80 ) (166,149 ) Underwriting profit (loss) (159,501 ) (214,374 ) — — 1,333 (372,542 ) Net investment income — — 104,387 102 — 104,489 Net investment losses — — (40,007 ) — — (40,007 ) Other revenues — — — 332,748 9,056 341,804 Other expenses (2) — — — (319,317 ) (25,679 ) (344,996 ) Amortization of intangible assets (3) — — — (6,917 ) (11,737 ) (18,654 ) Segment profit (loss) $ (159,501 ) $ (214,374 ) $ 64,380 $ 6,616 $ (27,027 ) $ (329,906 ) Interest expense (31,814 ) Net foreign exchange gains 1,772 Loss before income taxes $ (359,948 ) U.S. GAAP combined ratio (4) 119 % 183 % NM (5) 134 % (1) Other segment profit (loss) represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. (2) Other expenses for the Markel Ventures segment include depreciation expense of $9.7 million for the quarter ended September 30, 2017 . (3) Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to any other reportable segments. (4) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (5) NM - Ratio is not meaningful Nine Months Ended September 30, 2018 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures Other (1) Consolidated Gross premium volume $ 3,575,340 $ 935,498 $ — $ — $ 1,577,250 $ 6,088,088 Net written premiums 2,935,789 795,136 — — 754 3,731,679 Earned premiums 2,782,107 702,854 — — (433 ) 3,484,528 Losses and loss adjustment expenses: Current accident year (1,855,190 ) (485,678 ) — — — (2,340,868 ) Prior accident years 369,775 18,135 — — 1,816 389,726 Amortization of policy acquisition costs (554,185 ) (178,818 ) — — — (733,003 ) Other operating expenses (523,239 ) (59,433 ) — — (2,246 ) (584,918 ) Underwriting profit (loss) 219,268 (2,940 ) — — (863 ) 215,465 Net investment income — — 319,253 457 — 319,710 Net investment gains — — 408,326 — — 408,326 Other revenues — — — 1,440,084 145,785 1,585,869 Other expenses (2) — — — (1,350,780 ) (120,435 ) (1,471,215 ) Amortization of intangible assets (3) — — — (29,332 ) (56,927 ) (86,259 ) Segment profit (loss) $ 219,268 $ (2,940 ) $ 727,579 $ 60,429 $ (32,440 ) $ 971,896 Interest expense (114,722 ) Net foreign exchange gains 65,427 Income before income taxes $ 922,601 U.S. GAAP combined ratio (4) 92 % 100 % NM (5) 94 % (1) Other segment profit (loss) represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. (2) Other expenses for the Markel Ventures segment include depreciation expense of $38.5 million for the nine months ended September 30, 2018 . (3) Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to any other reportable segments. (4) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (5) NM - Ratio is not meaningful Nine Months Ended September 30, 2017 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures Other (1) Consolidated Gross premium volume $ 3,120,512 $ 1,025,716 $ — $ — $ (185 ) $ 4,146,043 Net written premiums 2,596,099 899,698 — — (157 ) 3,495,640 Earned premiums 2,401,477 714,718 — — (157 ) 3,116,038 Losses and loss adjustment expenses: Current accident year (1,839,378 ) (710,093 ) — — — (2,549,471 ) Prior accident years 353,767 (22,248 ) — — 7,823 339,342 Amortization of policy acquisition costs (485,460 ) (163,385 ) — — — (648,845 ) Other operating expenses (452,544 ) (69,752 ) — — (379 ) (522,675 ) Underwriting profit (loss) (22,138 ) (250,760 ) — — 7,287 (265,611 ) Net investment income — — 303,951 205 — 304,156 Net investment losses — — (1,515 ) — — (1,515 ) Other revenues — — — 933,280 47,433 980,713 Other expenses (2) — — — (841,674 ) (84,711 ) (926,385 ) Amortization of intangible assets (3) — — — (20,777 ) (32,673 ) (53,450 ) Segment profit (loss) $ (22,138 ) $ (250,760 ) $ 302,436 $ 71,034 $ (62,664 ) $ 37,908 Interest expense (97,013 ) Net foreign exchange gains 2,746 Loss before income taxes $ (56,359 ) U.S. GAAP combined ratio (4) 101 % 135 % NM (5) 108 % (1) Other segment profit (loss) represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. (2) Other expenses for the Markel Ventures segment include depreciation expense of $28.7 million for the nine months ended September 30, 2017 . (3) Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to any other reportable segments. (4) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (5) NM - 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) September 30, 2018 December 31, 2017 Segment assets: Investing $ 20,956,369 $ 20,317,160 Underwriting 6,501,069 6,828,048 Markel Ventures 2,027,782 1,900,728 Total segment assets 29,485,220 29,045,936 Other operations 4,473,085 3,759,080 Total assets $ 33,958,305 $ 32,805,016

Unpaid Losses And Loss Adjust_2

Unpaid Losses And Loss Adjustment Expenses (Tables)	9 Months Ended
	Sep. 30, 2018
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Reconciliation Of Consolidated Reserves For Losses And Loss Adjustment Expenses	The following table presents a reconciliation of consolidated beginning and ending reserves for losses and loss adjustment expenses. Nine Months Ended September 30, (dollars in thousands) 2018 2017 Net reserves for losses and loss adjustment expenses, beginning of year $ 8,964,945 $ 8,108,717 Foreign currency movements (35,754 ) 158,360 Adjusted net reserves for losses and loss adjustment expenses, beginning of year 8,929,191 8,267,077 Incurred losses and loss adjustment expenses: Current accident year 2,340,868 2,549,471 Prior accident years (389,740 ) (335,494 ) Total incurred losses and loss adjustment expenses 1,951,128 2,213,977 Payments: Current accident year 390,245 342,055 Prior accident years 1,438,224 1,185,689 Total payments 1,828,469 1,527,744 Effect of foreign currency rate changes 368 10,582 Net reserves for losses and loss adjustment expenses of acquired insurance companies — 12,702 Net reserves for losses and loss adjustment expenses, end of period 9,052,218 8,976,594 Reinsurance recoverable on unpaid losses 4,836,271 2,466,554 Gross reserves for losses and loss adjustment expenses, end of period $ 13,888,489 $ 11,443,148

Other Revenues (Tables)

Other Revenues (Tables)	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Schedule Of Revenues From Contracts With Customers By Type	The following tables disaggregate revenues from contracts with customers by type. Quarter Ended September 30, 2018 2017 (dollars in thousands) Markel Ventures Other Total Markel Ventures Other Total Products $ 350,981 $ — $ 350,981 $ 222,280 $ — $ 222,280 Services 95,071 7,841 102,912 88,082 7,381 95,463 Investment management — 18,258 18,258 — 1,248 1,248 Total revenues from contracts with customers 446,052 26,099 472,151 310,362 8,629 318,991 Program services — 22,478 22,478 — — — Other 23,219 396 23,615 22,386 427 22,813 Total Other Revenues $ 469,271 $ 48,973 $ 518,244 $ 332,748 $ 9,056 $ 341,804 Nine Months Ended September 30, 2018 2017 (dollars in thousands) Markel Ventures Other Total Markel Ventures Other Total Products $ 1,095,461 $ — $ 1,095,461 $ 611,852 $ — $ 611,852 Services 276,548 25,737 302,285 253,311 25,915 279,226 Investment management — 52,965 52,965 — 19,884 19,884 Total revenues from contracts with customers 1,372,009 78,702 1,450,711 865,163 45,799 910,962 Program services — 65,810 65,810 — — — Other 68,075 1,273 69,348 68,117 1,634 69,751 Total Other Revenues $ 1,440,084 $ 145,785 $ 1,585,869 $ 933,280 $ 47,433 $ 980,713
Schedule Of Receivables And Customer Deposits Related To Contracts With Customers	The following table presents receivables and customer deposits related to our contracts with customers. (dollars in thousands) September 30, 2018 December 31, 2017 Receivables $ 208,117 $ 176,865 Customer deposits 60,220 61,546

Reinsurance (Tables)

Reinsurance (Tables)	9 Months Ended
	Sep. 30, 2018
Reinsurance Disclosures [Abstract]
Effect Of Reinsurance And Retrocessional Reinsurance On Premiums Written And Earned	The following tables summarize the effect of reinsurance and retrocessional reinsurance on premiums written and earned. Quarter Ended September 30, 2018 2017 (dollars in thousands) Direct Assumed Ceded Net Premiums Direct Assumed Ceded Net Premiums Underwriting: Written $ 1,207,605 $ 274,898 $ (266,788 ) $ 1,215,715 $ 1,035,705 $ 292,423 $ (230,374 ) $ 1,097,754 Earned 1,113,763 313,378 (242,120 ) 1,185,021 966,735 356,529 (223,402 ) 1,099,862 Program Services: Written 529,958 31,310 (560,712 ) 556 — — — — Earned 480,694 13,046 (493,438 ) 302 — — — — Consolidated: Written 1,737,563 306,208 (827,500 ) 1,216,271 1,035,705 292,423 (230,374 ) 1,097,754 Earned $ 1,594,457 $ 326,424 $ (735,558 ) $ 1,185,323 $ 966,735 $ 356,529 $ (223,402 ) $ 1,099,862 Nine Months Ended September 30, 2018 2017 (dollars in thousands) Direct Assumed Ceded Net Premiums Direct Assumed Ceded Net Premiums Underwriting: Written $ 3,429,666 $ 1,081,171 $ (781,126 ) $ 3,729,711 $ 2,932,022 $ 1,214,021 $ (650,403 ) $ 3,495,640 Earned 3,221,946 965,586 (703,785 ) 3,483,747 2,743,970 976,636 (604,568 ) 3,116,038 Program Services: Written 1,537,412 39,839 (1,575,283 ) 1,968 — — — — Earned 1,374,443 16,784 (1,390,446 ) 781 — — — — Consolidated: Written 4,967,078 1,121,010 (2,356,409 ) 3,731,679 2,932,022 1,214,021 (650,403 ) 3,495,640 Earned $ 4,596,389 $ 982,370 $ (2,094,231 ) $ 3,484,528 $ 2,743,970 $ 976,636 $ (604,568 ) $ 3,116,038

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2018
Stockholders' Equity Note [Abstract]
Schedule Of Net Income (Loss) Per Share	Net income (loss) per share was determined by dividing adjusted net income (loss) to shareholders by the applicable weighted average shares outstanding. Diluted net income (loss) per share is computed by dividing adjusted net income (loss) to shareholders by the weighted average number of common shares and dilutive potential common shares outstanding during the period. Quarter Ended September 30, Nine Months Ended September 30, (in thousands, except per share amounts) 2018 2017 2018 2017 Net income (loss) to shareholders $ 409,438 $ (259,141 ) $ 623,363 $ (39,612 ) Adjustment of redeemable noncontrolling interests (12,035 ) (3,298 ) (6,621 ) (23,582 ) Adjusted net income (loss) to shareholders $ 397,403 $ (262,439 ) $ 616,742 $ (63,194 ) Basic common shares outstanding 13,917 13,947 13,925 13,974 Dilutive potential common shares from conversion of options — 1 — 2 Dilutive potential common shares from conversion of restricted stock units and restricted stock 26 42 24 42 Diluted shares outstanding 13,943 13,990 13,949 14,018 Basic net income (loss) per share (1) $ 28.56 $ (18.82 ) $ 44.29 $ (4.52 ) Diluted net income (loss) per share (1) $ 28.50 $ (18.82 ) $ 44.21 $ (4.52 ) (1) Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income, rather, changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 2.

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2018
Other Comprehensive Income (Loss), Tax [Abstract]
Change In Accumulated Other Comprehensive Income (Loss) By Component, Net Of Taxes And Noncontrolling Interest	The following table presents the change in accumulated other comprehensive income (loss) by component, net of taxes and noncontrolling interests, for the nine months ended September 30, 2018 and 2017 . (dollars in thousands) Unrealized Holding Gains (Losses) on Available-for-Sale Securities Foreign Currency Net Actuarial Pension Loss Total December 31, 2016 $ 1,714,930 $ (84,406 ) $ (64,658 ) $ 1,565,866 Other comprehensive income before reclassifications 577,796 19,750 — 597,546 Amounts reclassified from accumulated other comprehensive income (14,598 ) — 2,391 (12,207 ) Total other comprehensive income 563,198 19,750 2,391 585,339 September 30, 2017 $ 2,278,128 $ (64,656 ) $ (62,267 ) $ 2,151,205 December 31, 2017 $ 2,477,973 $ (74,003 ) $ (58,399 ) $ 2,345,571 Cumulative effect of adoption of ASU No. 2016-01 (2,615,734 ) 2,492 — (2,613,242 ) Cumulative effect of adoption of ASU No. 2018-02 401,539 — — 401,539 Other comprehensive income (loss) before reclassifications (306,069 ) (19,928 ) 1,741 (324,256 ) Amounts reclassified from accumulated other comprehensive loss (1) 5,496 — — 5,496 Total other comprehensive income (loss) (2,514,768 ) (17,436 ) 1,741 (2,530,463 ) September 30, 2018 $ (36,795 ) $ (91,439 ) $ (56,658 ) $ (184,892 ) (1) Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income, rather, changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 2.
Summary Of Tax Expense (Benefit) Of Other Comprehensive Income (Loss)	The following table summarizes the tax expense (benefit) associated with each component of other comprehensive income (loss). Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2018 2017 2018 2017 Change in net unrealized gains (losses) on available-for-sale investments: (1) Net holding gains (losses) arising during the period $ (24,047 ) $ 109,338 $ (84,825 ) $ 278,266 Reclassification adjustments for net gains (losses) included in net income (loss) 2,810 (2,810 ) 1,461 (5,206 ) Change in net unrealized gains (losses) on available-for-sale investments (21,237 ) 106,528 (83,364 ) 273,060 Change in foreign currency translation adjustments 6,594 656 3,072 153 Change in net actuarial pension loss 135 159 463 492 Total $ (14,508 ) $ 107,343 $ (79,829 ) $ 273,705 (1) Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income, rather, changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 2.
Reclassifications From Accumulated Other Comprehensive Income (Loss) Into Income, By Component	The following table presents the details of amounts reclassified from accumulated other comprehensive income (loss) into net income (loss), by component. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2018 2017 2018 2017 Unrealized holding gains (losses) on available-for-sale investments: (1) Other-than-temporary impairment losses $ — $ (3,444 ) $ — $ (7,261 ) Net realized investment gains (losses), excluding other-than-temporary impairment losses (13,383 ) 11,461 (6,957 ) 27,065 Total before income taxes (13,383 ) 8,017 (6,957 ) 19,804 Income taxes 2,810 (2,810 ) 1,461 (5,206 ) Reclassification of unrealized holding gains (losses), net of taxes $ (10,573 ) $ 5,207 $ (5,496 ) $ 14,598 Net actuarial pension loss: Underwriting, acquisition and insurance expenses $ (644 ) $ (932 ) $ (2,204 ) $ (2,883 ) Income taxes 135 159 463 492 Reclassification of net actuarial pension loss, net of taxes $ (509 ) $ (773 ) $ (1,741 ) $ (2,391 ) (1) Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income, rather, changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 2.

Recent Accounting Pronounceme_2

Recent Accounting Pronouncements (Narrative) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of ASU No. 2014-09, net of taxes	$ 300
Cumulative effect of adoption of ASU No. 2016-01, net of taxes	$ (2,613,242)
U.S. statutory tax rate	21.00%	35.00%
Cumulative effect of adoption of ASU No. 2018-02	$ 401,539
Future minimum lease payments			$ 311,700
Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of ASU No. 2016-01, net of taxes	(2,600,000)
Deferred income taxes	$ 684,400

Acquisitions (Narrative) (Detai

Acquisitions (Narrative) (Details) - USD ($) $ in Millions	Oct. 01, 2018	Aug. 01, 2018	Nov. 17, 2017	Mar. 31, 2018
Nephila Holdings Limited [Member]
Business Acquisition [Line Items]
Percentage acquired		100.00%
Total consideration		$ 975
Cash consideration		975
Assets under management		$ 12,000
State National Companies, Inc. [Member]
Business Acquisition [Line Items]
Percentage acquired			100.00%
Total consideration			$ 918.8
Cash consideration			$ 918.8
Goodwill recognized				$ 379.2
Goodwill, tax deductible				0
Indefinite-lived intangible assets				32
Finite-lived intangible assets				$ 338.5
Definite-lived intangible assets, weighted-average amortization period				13 years
Brahmin [Member]
Business Acquisition [Line Items]
Percentage acquired	90.00%
Total consideration	$ 194
Cash consideration	$ 173.3

Acquisitions (Summary Of Net In

Acquisitions (Summary Of Net Intangible Assets Acquired) (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization (from the acquisition date through September 30, 2018)	[1]	$ 27,795		$ 18,654	$ 86,259	$ 53,450
Net intangible assets as of September 30, 2018		1,241,108			1,241,108		$ 1,355,681
State National Companies, Inc. [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets			$ 338,500
Indefinite-lived intangible assets			$ 32,000
Economic useful lives of finite-lived intangible assets, years			13 years
Intangible assets, before amortization, as of the acquisition date		370,500			370,500
Amortization (from the acquisition date through September 30, 2018)					25,407
Net intangible assets as of September 30, 2018		345,093			345,093
State National Companies, Inc. [Member] | Insurance Licenses [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets		32,000			$ 32,000
Economic useful lives of indefinite-lived intangible assets, years					Indefinite
State National Companies, Inc. [Member] | Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets		289,000			$ 289,000
Economic useful lives of finite-lived intangible assets, years					13 years
State National Companies, Inc. [Member] | Trade Names [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets		22,500			$ 22,500
Economic useful lives of finite-lived intangible assets, years					13 years
State National Companies, Inc. [Member] | Technology [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets		$ 27,000			$ 27,000
Economic useful lives of finite-lived intangible assets, years					9 years
[1]	Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to any other reportable segments.

Investments (Narrative) (Detail

Investments (Narrative) (Details) $ in Thousands		Sep. 30, 2018USD ($)securities	Dec. 31, 2017USD ($)securities
Schedule of Investments [Line Items]
Available-for-sale fixed maturity securities in unrealized loss position, number of positions | securities		1,221
Available-for-sale fixed maturity securities, estimated fair value		$ 7,538,157
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		$ (198,724)
Number of available-for-sale fixed maturity securities positions in a continuous unrealized loss position for one year or longer at period end | securities		284
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		$ 1,533,011
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(91,223)
Available-for-sale securities in unrealized loss position, number of positions | securities			739
Available-for-sale securities, estimated fair value			$ 2,767,652
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses			$ (57,348)
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end | securities			272
Available-for-sale securities, estimated fair value, 12 months or longer			$ 1,481,341
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer			(34,348)
Fixed Maturities [Member]
Schedule of Investments [Line Items]
Available-for-sale fixed maturity securities, estimated fair value		5,745,647	2,246,614
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(198,271)	(37,344)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		1,533,011	1,468,807
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		$ (91,223)	$ (31,054)
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end | securities			258
Equity Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale securities, estimated fair value	[1]		$ 151,934
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	[1]		$ (19,935)
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end | securities			14
Available-for-sale securities, estimated fair value, 12 months or longer	[1]		$ 12,534
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	[1]		$ (3,294)
[1]	Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale. Prior periods have not been restated to conform to the current presentation. See note 2.

Investments (Available-For-Sale

Investments (Available-For-Sale Investments) (Details) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		$ 9,946,656	$ 9,551,153
Available-for-sale investments, amortized cost		11,865,151	14,379,831
Available-for-sale investments, gross unrealized holding gains		204,317	3,747,008
Available-for-sale investments, gross unrealized holding losses		(198,724)	(57,348)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		9,952,053	9,940,670
Available-for-sale investments, estimated fair value		11,870,744	18,069,491
U.S. Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		241,485	162,378
Available-for-sale fixed maturity investments, gross unrealized holding gains		20	54
Available-for-sale fixed maturity investments, gross unrealized holding losses		(3,360)	(1,819)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		238,145	160,613
U.S. Government-Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		359,348	352,455
Available-for-sale fixed maturity investments, gross unrealized holding gains		3,612	11,883
Available-for-sale fixed maturity investments, gross unrealized holding losses		(8,081)	(818)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		354,879	363,520
Obligations Of States, Municipalities And Political Subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		4,289,636	4,381,358
Available-for-sale fixed maturity investments, gross unrealized holding gains		73,456	193,120
Available-for-sale fixed maturity investments, gross unrealized holding losses		(50,246)	(7,916)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		4,312,846	4,566,562
Foreign Governments [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		1,463,626	1,341,628
Available-for-sale fixed maturity investments, gross unrealized holding gains		105,158	150,010
Available-for-sale fixed maturity investments, gross unrealized holding losses		(17,047)	(2,410)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		1,551,737	1,489,228
Commercial Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		1,672,438	1,244,777
Available-for-sale fixed maturity investments, gross unrealized holding gains		13	6,108
Available-for-sale fixed maturity investments, gross unrealized holding losses		(70,603)	(16,559)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		1,601,848	1,234,326
Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		898,169	846,916
Available-for-sale fixed maturity investments, gross unrealized holding gains		1,058	14,115
Available-for-sale fixed maturity investments, gross unrealized holding losses		(31,136)	(4,863)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		868,091	856,168
Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		24,819	34,942
Available-for-sale fixed maturity investments, gross unrealized holding gains		0	8
Available-for-sale fixed maturity investments, gross unrealized holding losses		(309)	(222)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		24,510	34,728
Corporate Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		997,135	1,186,699
Available-for-sale fixed maturity investments, gross unrealized holding gains		20,351	51,563
Available-for-sale fixed maturity investments, gross unrealized holding losses		(17,489)	(2,737)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		999,997	1,235,525
Total Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		9,946,656	9,551,153
Available-for-sale fixed maturity investments, gross unrealized holding gains		203,668	426,861
Available-for-sale fixed maturity investments, gross unrealized holding losses		(198,271)	(37,344)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		9,952,053	9,940,670
Insurance, Banks And Other Financial Institutions [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale investments, amortized cost	[1]		899,324
Available-for-sale investments, gross unrealized holding gains	[1]		1,209,162
Available-for-sale investments, gross unrealized holding losses	[1]		(5,453)
Available-for-sale investments, unrealized other-than-temporary impairment losses	[1]		0
Available-for-sale investments, estimated fair value	[1]		2,103,033
Industrial, Consumer And All Other [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale investments, amortized cost	[1]		1,768,337
Available-for-sale investments, gross unrealized holding gains	[1]		2,110,959
Available-for-sale investments, gross unrealized holding losses	[1]		(14,482)
Available-for-sale investments, unrealized other-than-temporary impairment losses	[1]		0
Available-for-sale investments, estimated fair value	[1]		3,864,814
Equity Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale investments, amortized cost	[1]		2,667,661
Available-for-sale investments, gross unrealized holding gains	[1]		3,320,121
Available-for-sale investments, gross unrealized holding losses	[1]		(19,935)
Available-for-sale investments, unrealized other-than-temporary impairment losses	[1]		0
Available-for-sale investments, estimated fair value	[1]		5,967,847
Short-Term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale investments, amortized cost		1,918,495	2,161,017
Available-for-sale investments, gross unrealized holding gains		649	26
Available-for-sale investments, gross unrealized holding losses		(453)	(69)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale investments, estimated fair value		$ 1,918,691	$ 2,160,974
[1]	Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale. Prior periods have not been restated to conform to the current presentation. See note 2.

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 ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		$ 6,005,146
Available-for-sale securities, estimated fair value, less than 12 months			$ 1,286,311
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(107,501)
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months			(23,000)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		1,533,011
Available-for-sale securities, estimated fair value, 12 months or longer			1,481,341
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(91,223)
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer			(34,348)
Available-for-sale fixed maturity securities, estimated fair value		7,538,157
Available-for-sale securities, estimated fair value			2,767,652
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(198,724)
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses			(57,348)
U.S. Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		120,072	78,756
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(1,338)	(659)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		117,487	78,298
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(2,022)	(1,160)
Available-for-sale fixed maturity securities, estimated fair value		237,559	157,054
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(3,360)	(1,819)
U.S. Government-Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		117,344	11,593
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(4,545)	(79)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		93,453	89,194
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(3,536)	(739)
Available-for-sale fixed maturity securities, estimated fair value		210,797	100,787
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(8,081)	(818)
Obligations Of States, Municipalities And Political Subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		1,384,033	80,654
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(26,815)	(789)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		411,317	404,814
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(23,431)	(7,127)
Available-for-sale fixed maturity securities, estimated fair value		1,795,350	485,468
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(50,246)	(7,916)
Foreign Governments [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		455,170	31,752
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(9,425)	(452)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		84,395	63,406
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(7,622)	(1,958)
Available-for-sale fixed maturity securities, estimated fair value		539,565	95,158
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(17,047)	(2,410)
Commercial Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		1,049,350	253,936
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(29,512)	(1,980)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		550,006	481,216
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(41,091)	(14,579)
Available-for-sale fixed maturity securities, estimated fair value		1,599,356	735,152
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(70,603)	(16,559)
Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		665,021	157,508
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(22,760)	(1,345)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		128,067	148,960
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(8,376)	(3,518)
Available-for-sale fixed maturity securities, estimated fair value		793,088	306,468
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(31,136)	(4,863)
Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		10,493	14,263
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(147)	(123)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		13,964	15,165
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(162)	(99)
Available-for-sale fixed maturity securities, estimated fair value		24,457	29,428
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(309)	(222)
Corporate Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		411,153	149,345
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(12,506)	(863)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		134,322	187,754
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(4,983)	(1,874)
Available-for-sale fixed maturity securities, estimated fair value		545,475	337,099
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(17,489)	(2,737)
Total Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		4,212,636	777,807
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(107,048)	(6,290)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		1,533,011	1,468,807
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(91,223)	(31,054)
Available-for-sale fixed maturity securities, estimated fair value		5,745,647	2,246,614
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(198,271)	(37,344)
Insurance, Banks And Other Financial Institutions [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	[1]		60,848
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	[1]		(4,843)
Available-for-sale securities, estimated fair value, 12 months or longer	[1]		1,291
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	[1]		(610)
Available-for-sale securities, estimated fair value	[1]		62,139
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	[1]		(5,453)
Industrial, Consumer And All Other [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	[1]		78,552
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	[1]		(11,798)
Available-for-sale securities, estimated fair value, 12 months or longer	[1]		11,243
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	[1]		(2,684)
Available-for-sale securities, estimated fair value	[1]		89,795
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	[1]		(14,482)
Total Equity Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	[1]		139,400
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	[1]		(16,641)
Available-for-sale securities, estimated fair value, 12 months or longer	[1]		12,534
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	[1]		(3,294)
Available-for-sale securities, estimated fair value	[1]		151,934
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	[1]		(19,935)
Short-Term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		1,792,510	369,104
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(453)	(69)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		0	0
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		0	0
Available-for-sale fixed maturity securities, estimated fair value		1,792,510	369,104
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		$ (453)	$ (69)
[1]	Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale. Prior periods have not been restated to conform to the current presentation. See note 2.

Investments (Schedule Of Amorti

Investments (Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturity Securities By Contractual Maturity Date) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Due in one year or less, amortized cost	$ 213,805
Due after one year through five years, amortized cost	1,426,784
Due after five years through ten years, amortized cost	1,884,581
Due after ten years, amortized cost	3,826,060
Amortized cost, sub-total	7,351,230
Total fixed maturities, amortized cost	9,946,656	$ 9,551,153
Due in one year or less, estimated fair value	212,952
Due after one year through five years, estimated fair value	1,433,680
Due after five years through ten years, estimated fair value	1,902,186
Due after ten years, estimated fair value	3,908,786
Estimated fair value, sub-total	7,457,604
Total fixed maturities, estimated fair value	9,952,053	9,940,670
Commercial Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, amortized cost	1,672,438
Total fixed maturities, amortized cost	1,672,438	1,244,777
Fixed maturities, estimated fair value	1,601,848
Total fixed maturities, estimated fair value	1,601,848	1,234,326
Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, amortized cost	898,169
Total fixed maturities, amortized cost	898,169	846,916
Fixed maturities, estimated fair value	868,091
Total fixed maturities, estimated fair value	868,091	856,168
Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, amortized cost	24,819
Total fixed maturities, amortized cost	24,819	34,942
Fixed maturities, estimated fair value	24,510
Total fixed maturities, estimated fair value	$ 24,510	$ 34,728

Investments (Components Of Net

Investments (Components Of Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Municipal bonds (tax-exempt)	$ 19,588	$ 21,486	$ 60,810	$ 66,616
Short-term investments, including overnight deposits	13,719	7,779	36,224	18,562
Dividends on equity securities	21,721	21,467	66,202	61,090
Income (loss) from equity method investments	(3,556)	4,239	(3,268)	10,634
Other	255	(315)	242	(520)
Total investment income	111,293	108,725	332,646	316,933
Investment expenses	(4,986)	(4,236)	(12,936)	(12,777)
Net investment income	106,307	104,489	319,710	304,156
Taxable Municipal Bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	18,634	17,732	54,487	53,030
Other Taxable Bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	$ 40,932	$ 36,337	$ 117,949	$ 107,521

Investments (Summary Of Net Inv

Investments (Summary Of Net Investment Gains (Losses) And The Change In Net Unrealized Gains On Investments) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Gain (Loss) on Securities [Line Items]
Realized gains		$ 4,534	$ 13,831	$ 6,380	$ 35,974
Realized losses		(5,030)	(5,461)	(15,464)	(11,409)
Other-than-temporary impairment losses		0	(3,444)	0	(7,261)
Net realized investment gains (losses)		(496)		(9,084)
Net realized investment gains (losses)			8,370		24,565
Change in fair value of equity securities sold during the period	[1]	151	0	10,230	0
Change in fair value of equity securities held at the end of the period		426,420	(48,377)	407,180	(26,080)
Change in fair value of equity securities	[1]	426,571	(48,377)	417,410	(26,080)
Net investment gains (losses)		426,075	(40,007)	408,326	(1,515)
Change in net unrealized gains (losses) on available-for-sale investments included in other comprehensive income		(101,666)	328,768	(383,937)	836,258
Sales Of Fixed Maturities [Member]
Gain (Loss) on Securities [Line Items]
Realized gains		2,916	3,426	3,748	4,189
Realized losses		(1,003)	(657)	(2,652)	(1,265)
Sales Of Equity Securities [Member]
Gain (Loss) on Securities [Line Items]
Realized gains	[1]	0	9,276	0	25,806
Realized losses	[1]	0	(578)	0	(1,791)
Sales Of Short-Term Investments [Member]
Gain (Loss) on Securities [Line Items]
Realized gains		1,447	8	1,624	19
Realized losses		(3,997)	(207)	(10,044)	(499)
Sales Of Other Debt Obligations [Member]
Gain (Loss) on Securities [Line Items]
Realized gains		171	1,121	1,008	5,960
Realized losses		(30)	(575)	(2,768)	(593)
Short-Term Investments [Member]
Gain (Loss) on Securities [Line Items]
Change in net unrealized gains (losses) on available-for-sale investments included in other comprehensive income		1,417	16	239	22
Fixed Maturities [Member]
Gain (Loss) on Securities [Line Items]
Change in net unrealized gains (losses) on available-for-sale investments included in other comprehensive income		(103,083)	20,428	(384,176)	104,488
Equity Securities [Member]
Gain (Loss) on Securities [Line Items]
Change in net unrealized gains (losses) on available-for-sale investments included in other comprehensive income	[1]	$ 0	$ 308,324	$ 0	$ 731,748
[1]	Effective January 1, 2018, the Company adopted ASU No. 2016-01. As a result, equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income; rather, all changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 2.

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized investment losses	$ 2,418	$ (51,639)		$ (39,505)
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, level 1 to level 2 transfers, amount			$ 0	0
Fair value, level 2 to level 1 transfers, amount			0	0
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis	0	0	0	0
Liabilities measured at fair value on a nonrecurring basis	$ 0	0	0	0
Investment In ILS Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized investment losses		$ (51,600)	$ (40,963)	$ (39,500)

Fair Value Measurements (Balanc

Fair Value Measurements (Balances Of Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	$ 9,952,053	$ 9,940,670
Total equity securities	6,549,848	0
Short-term investments	1,918,691	2,160,974
Total Investments	18,420,592	18,069,491
Fixed Maturities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	9,952,053	9,940,670
U.S. Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	238,145	160,613
U.S. Government-Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	354,879	363,520
Obligations Of States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	4,312,846	4,566,562
Foreign Governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	1,551,737	1,489,228
Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	1,601,848	1,234,326
Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	868,091	856,168
Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	24,510	34,728
Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	999,997	1,235,525
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	9,952,053	9,940,670
Total equity securities	6,549,848	5,967,847	[1]
Short-term investments	1,918,691	2,160,974
Total Investments	18,420,592	18,069,491	[1]
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Total equity securities	6,427,755	5,799,038	[1]
Short-term investments	1,825,777	2,065,749
Total Investments	8,253,532	7,864,787	[1]
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	9,952,053	9,940,670
Total equity securities	0	0	[1]
Short-term investments	92,914	95,225
Total Investments	10,044,967	10,035,895	[1]
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Total equity securities	122,093	168,809	[1]
Short-term investments	0	0
Total Investments	122,093	168,809	[1]
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	238,145	160,613
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	238,145	160,613
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | U.S. Government-Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	354,879	363,520
Fair Value, Measurements, Recurring [Member] | U.S. Government-Sponsored Enterprises [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | U.S. Government-Sponsored Enterprises [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	354,879	363,520
Fair Value, Measurements, Recurring [Member] | U.S. Government-Sponsored Enterprises [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Obligations Of States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	4,312,846	4,566,562
Fair Value, Measurements, Recurring [Member] | Obligations Of States, Municipalities And Political Subdivisions [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Obligations Of States, Municipalities And Political Subdivisions [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	4,312,846	4,566,562
Fair Value, Measurements, Recurring [Member] | Obligations Of States, Municipalities And Political Subdivisions [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Foreign Governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	1,551,737	1,489,228
Fair Value, Measurements, Recurring [Member] | Foreign Governments [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Foreign Governments [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	1,551,737	1,489,228
Fair Value, Measurements, Recurring [Member] | Foreign Governments [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	1,601,848	1,234,326
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]
Available-for-sale fixed maturity investments, estimated fair value	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]
Available-for-sale fixed maturity investments, estimated fair value	1,601,848	1,234,326
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]
Available-for-sale fixed maturity investments, estimated fair value	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]
Available-for-sale fixed maturity investments, estimated fair value	868,091	856,168
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]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	868,091	856,168
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]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	24,510	34,728
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]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Asset-Backed Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	24,510	34,728
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]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	999,997	1,235,525
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	999,997	1,235,525
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Insurance, Banks And Other Financial Institutions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total equity securities	2,233,046	2,103,033	[1]
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	2,110,953	1,934,224	[1]
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	[1]
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	122,093	168,809	[1]
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	4,316,802	3,864,814	[1]
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	4,316,802	3,864,814	[1]
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	[1]
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	[1]
[1]	Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale. Prior periods have not been restated to conform to the current presentation. See note 2.

Fair Value Measurements (Summar

Fair Value Measurements (Summary Of Changes In Level 3 Investments Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Equity securities, beginning of period	$ 119,675	$ 183,913	$ 168,809	$ 191,203
Purchases	0	49,000	28,900	56,250
Sales	0	0	(34,653)	(26,674)
Total gains (losses) included in net income (loss)	2,418	(51,639)		(39,505)
Transfers into level 3	0	0	0	0
Transfers out of level 3	0	0	0	0
Equity securities, end of period	122,093	181,274	122,093	181,274
Change in fair value of equity securities included in net income (loss) relating to assets held at September 30, 2018 and 2017	$ 2,418	$ (51,639)	$ (40,963)	$ (39,505)

Segment Reporting Disclosures_2

Segment Reporting Disclosures (Summary Of Revenue From The Markel Ventures Segment By Major Product Grouping) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue from External Customer [Line Items]
Other revenues	$ 518,244	$ 341,804	$ 1,585,869	$ 980,713
Markel Ventures [Member]
Revenue from External Customer [Line Items]
Other revenues	469,271	332,748	1,440,084	933,280
Markel Ventures [Member] | Products [Member]
Revenue from External Customer [Line Items]
Other revenues	362,577	233,895	1,129,036	648,134
Markel Ventures [Member] | Services [Member]
Revenue from External Customer [Line Items]
Other revenues	$ 106,694	$ 98,853	$ 311,048	$ 285,146

Segment Reporting Disclosures_3

Segment Reporting Disclosures (Company's Segment Disclosures) (Details) $ in Thousands		3 Months Ended				9 Months Ended
		Sep. 30, 2018USD ($)		Sep. 30, 2017USD ($)		Sep. 30, 2018USD ($)segment		Sep. 30, 2017USD ($)
Segment Reporting Information [Line Items]
Number of reportable ongoing underwriting segments | segment						2
Gross premium volume		$ 2,043,771		$ 1,328,128		$ 6,088,088		$ 4,146,043
Net written premiums		1,216,271		1,097,754		3,731,679		3,495,640
Earned premiums		1,185,323		1,099,862		3,484,528		3,116,038
Losses and loss adjustment expenses, current accident year		(860,986)		(1,226,540)		(2,340,868)		(2,549,471)
Losses and loss adjustment expenses, prior accident years		124,140		151,108		389,726		339,342
Amortization of policy acquisition costs		(241,848)		(230,823)		(733,003)		(648,845)
Other operating expenses		(200,113)		(166,149)		(584,918)		(522,675)
Underwriting profit (loss)		6,516		(372,542)		215,465		(265,611)
Net investment income		106,307		104,489		319,710		304,156
Net investment gains (losses)		426,075		(40,007)		408,326		(1,515)
Other revenues		518,244		341,804		1,585,869		980,713
Other expenses		(473,742)	[1]	(344,996)	[2]	(1,471,215)	[3]	(926,385)	[4]
Amortization of intangible assets	[5]	(27,795)		(18,654)		(86,259)		(53,450)
Segment profit (loss)		555,605		(329,906)		971,896		37,908
Interest expense		(37,961)		(31,814)		(114,722)		(97,013)
Net foreign exchange gains		1,383		1,772		65,427		2,746
Income (Loss) Before Income Taxes		$ 519,027		$ (359,948)		$ 922,601		$ (56,359)
U.S. GAAP combined ratio	[6]	99.00%		134.00%		94.00%		108.00%
Insurance [Member]
Segment Reporting Information [Line Items]
Gross premium volume		$ 1,248,150		$ 1,098,237		$ 3,575,340		$ 3,120,512
Net written premiums		1,021,684		908,296		2,935,789		2,596,099
Earned premiums		961,062		840,439		2,782,107		2,401,477
Losses and loss adjustment expenses, current accident year		(674,529)		(808,243)		(1,855,190)		(1,839,378)
Losses and loss adjustment expenses, prior accident years		111,117		128,353		369,775		353,767
Amortization of policy acquisition costs		(182,857)		(177,383)		(554,185)		(485,460)
Other operating expenses		(172,340)		(142,667)		(523,239)		(452,544)
Underwriting profit (loss)		42,453		(159,501)		219,268		(22,138)
Net investment income		0		0		0		0
Net investment gains (losses)		0		0		0		0
Other revenues		0		0		0		0
Other expenses		0	[1]	0	[2]	0	[3]	0	[4]
Amortization of intangible assets	[5]	0		0		0		0
Segment profit (loss)		$ 42,453		$ (159,501)		$ 219,268		$ (22,138)
U.S. GAAP combined ratio	[6]	96.00%		119.00%		92.00%		101.00%
Reinsurance [Member]
Segment Reporting Information [Line Items]
Gross premium volume		$ 234,360		$ 230,077		$ 935,498		$ 1,025,716
Net written premiums		195,349		189,636		795,136		899,698
Earned premiums		225,277		259,601		702,854		714,718
Losses and loss adjustment expenses, current accident year		(186,505)		(418,297)		(485,678)		(710,093)
Losses and loss adjustment expenses, prior accident years		12,681		21,164		18,135		(22,248)
Amortization of policy acquisition costs		(58,991)		(53,440)		(178,818)		(163,385)
Other operating expenses		(26,125)		(23,402)		(59,433)		(69,752)
Underwriting profit (loss)		(33,663)		(214,374)		(2,940)		(250,760)
Net investment income		0		0		0		0
Net investment gains (losses)		0		0		0		0
Other revenues		0		0		0		0
Other expenses		0	[1]	0	[2]	0	[3]	0	[4]
Amortization of intangible assets	[5]	0		0		0		0
Segment profit (loss)		$ (33,663)		$ (214,374)		$ (2,940)		$ (250,760)
U.S. GAAP combined ratio	[6]	115.00%		183.00%		100.00%		135.00%
Investing [Member]
Segment Reporting Information [Line Items]
Gross premium volume		$ 0		$ 0		$ 0		$ 0
Net written premiums		0		0		0		0
Earned premiums		0		0		0		0
Losses and loss adjustment expenses, current accident year		0		0		0		0
Losses and loss adjustment expenses, prior accident years		0		0		0		0
Amortization of policy acquisition costs		0		0		0		0
Other operating expenses		0		0		0		0
Underwriting profit (loss)		0		0		0		0
Net investment income		106,164		104,387		319,253		303,951
Net investment gains (losses)		426,075		(40,007)		408,326		(1,515)
Other revenues		0		0		0		0
Other expenses		0	[1]	0	[2]	0	[3]	0	[4]
Amortization of intangible assets	[5]	0		0		0		0
Segment profit (loss)		532,239		64,380		727,579		302,436
Markel Ventures [Member]
Segment Reporting Information [Line Items]
Gross premium volume		0		0		0		0
Net written premiums		0		0		0		0
Earned premiums		0		0		0		0
Losses and loss adjustment expenses, current accident year		0		0		0		0
Losses and loss adjustment expenses, prior accident years		0		0		0		0
Amortization of policy acquisition costs		0		0		0		0
Other operating expenses		0		0		0		0
Underwriting profit (loss)		0		0		0		0
Net investment income		143		102		457		205
Net investment gains (losses)		0		0		0		0
Other revenues		469,271		332,748		1,440,084		933,280
Other expenses		(436,642)	[1]	(319,317)	[2]	(1,350,780)	[3]	(841,674)	[4]
Amortization of intangible assets	[5]	(9,139)		(6,917)		(29,332)		(20,777)
Segment profit (loss)		23,633		6,616		60,429		71,034
Depreciation expense		(13,000)	[1]	(9,700)	[2]	(38,500)	[3]	(28,700)	[4]
Other [Member]
Segment Reporting Information [Line Items]
Gross premium volume	[7]	561,261		(186)		1,577,250		(185)
Net written premiums	[7]	(762)		(178)		754		(157)
Earned premiums	[7]	(1,016)		(178)		(433)		(157)
Losses and loss adjustment expenses, current accident year	[7]	48		0		0		0
Losses and loss adjustment expenses, prior accident years	[7]	342		1,591		1,816		7,823
Amortization of policy acquisition costs	[7]	0		0		0		0
Other operating expenses	[7]	(1,648)		(80)		(2,246)		(379)
Underwriting profit (loss)	[7]	(2,274)		1,333		(863)		7,287
Net investment income	[7]	0		0		0		0
Net investment gains (losses)	[7]	0		0		0		0
Other revenues	[7]	48,973		9,056		145,785		47,433
Other expenses	[7]	(37,100)	[1]	(25,679)	[2]	(120,435)	[3]	(84,711)	[4]
Amortization of intangible assets	[5],[7]	(18,656)		(11,737)		(56,927)		(32,673)
Segment profit (loss)	[7]	$ (9,057)		$ (27,027)		$ (32,440)		$ (62,664)
U.S. GAAP combined ratio - not meaniningful	[6],[7],[8]	NM		NM		NM		NM
[1]	Other expenses for the Markel Ventures segment include depreciation expense of $13.0 million for the quarter ended September 30, 2018.
[2]	Other expenses for the Markel Ventures segment include depreciation expense of $9.7 million for the quarter ended September 30, 2017.
[3]	Other expenses for the Markel Ventures segment include depreciation expense of $38.5 million for the nine months ended September 30, 2018.
[4]	Other expenses for the Markel Ventures segment include depreciation expense of $28.7 million for the nine months ended September 30, 2017.
[5]	Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to any other reportable segments.
[6]	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.
[7]	Other segment profit (loss) represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment.
[8]	NM - Ratio is not meaningful

Segment Reporting Disclosures_4

Segment Reporting Disclosures (Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Assets	$ 33,958,305	$ 32,805,016
Other Operations [Member]
Segment Reporting Information [Line Items]
Assets	4,473,085	3,759,080
Segment Assets [Member]
Segment Reporting Information [Line Items]
Assets	29,485,220	29,045,936
Segment Assets [Member] | Investing [Member]
Segment Reporting Information [Line Items]
Assets	20,956,369	20,317,160
Segment Assets [Member] | Underwriting [Member]
Segment Reporting Information [Line Items]
Assets	6,501,069	6,828,048
Segment Assets [Member] | Markel Ventures [Member]
Segment Reporting Information [Line Items]
Assets	$ 2,027,782	$ 1,900,728

Unpaid Losses And Loss Adjust_3

Unpaid Losses And Loss Adjustment Expenses (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2017
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Ceded reserves for losses and loss adjustment expenses on asbestos and environmental policies transferred to a third party by way of a Part VII transfer					$ 69,100
Deferred gain related to the completion of the Part VII transfer				$ 3,900
Favorable (adverse) development on prior years' loss reserves			$ 389,740	335,494
Estimated net losses and loss adjustment expenses	$ 860,986	$ 1,226,540	2,340,868	2,549,471
Reinsurance recoverables	171,100	540,100	394,900	748,700
Net reserves for losses and loss adjustment expenses of acquired insurance companies			0	12,702
2018 Catastrophes [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Estimated net losses, net of assumed reinstatement premiums			75,700
Estimated net losses and loss adjustment expenses			77,800
Net assumed reinstatement premiums			2,100
Reinsurance recoverables	$ 28,600		28,600
2017 Catastrophes [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Estimated net losses, net of assumed reinstatement premiums				503,000
Estimated net losses and loss adjustment expenses				521,200
Net assumed reinstatement premiums				18,200
Reinsurance recoverables		$ 464,400		464,400
Gen Liability Prof Liability Workers Comp And Marine And Energy Insurance Segment Surety And Marine And Energy Reinsurance Segment [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable (adverse) development on prior years' loss reserves			$ 312,200
Gen Liability Prof Liability Marine And Energy Personal Lines And Workers Comp Insurance Segment Property And Whole Reins Segment [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable (adverse) development on prior years' loss reserves				302,500
Ogden Rate Change [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable (adverse) development on prior years' loss reserves				$ (85,000)

Unpaid Losses And Loss Adjust_4

Unpaid Losses And Loss Adjustment Expenses (Reconciliation Of Consolidated Reserves For Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Net reserves for losses and loss adjustment expenses, beginning of year			$ 8,964,945	$ 8,108,717
Foreign currency movements	$ (35,754)	$ 158,360	(35,754)	158,360
Adjusted net reserves for losses and loss adjustment expenses, beginning of year			8,929,191	8,267,077
Incurred losses and loss adjustment expenses, current accident year	860,986	1,226,540	2,340,868	2,549,471
Incurred losses and loss adjustment expenses, prior accident years			(389,740)	(335,494)
Total incurred losses and loss adjustment expenses			1,951,128	2,213,977
Payments, current accident year			390,245	342,055
Payments, prior accident years			1,438,224	1,185,689
Total payments			1,828,469	1,527,744
Effect of foreign currency rate changes			368	10,582
Net reserves for losses and loss adjustment expenses of acquired insurance companies			0	12,702
Net reserves for losses and loss adjustment expenses, end of period	9,052,218	8,976,594	9,052,218	8,976,594
Reinsurance recoverable on unpaid losses	4,836,271	2,466,554	4,836,271	2,466,554	$ 4,619,336
Gross reserves for losses and loss adjustment expenses, end of period	$ 13,888,489	$ 11,443,148	$ 13,888,489	$ 11,443,148

Other Revenues (Schedule Of Rev

Other Revenues (Schedule Of Revenues From Contracts With Customers By Type) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Other revenues	$ 518,244	$ 341,804	$ 1,585,869	$ 980,713
Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	472,151	318,991	1,450,711	910,962
Markel Ventures [Member]
Disaggregation of Revenue [Line Items]
Other revenues	469,271	332,748	1,440,084	933,280
Markel Ventures [Member] | Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	446,052	310,362	1,372,009	865,163
Other [Member]
Disaggregation of Revenue [Line Items]
Other revenues	48,973	9,056	145,785	47,433
Other [Member] | Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	26,099	8,629	78,702	45,799
Products [Member] | Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	350,981	222,280	1,095,461	611,852
Products [Member] | Markel Ventures [Member] | Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	350,981	222,280	1,095,461	611,852
Products [Member] | Other [Member] | Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	0	0	0	0
Services [Member] | Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	102,912	95,463	302,285	279,226
Services [Member] | Markel Ventures [Member] | Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	95,071	88,082	276,548	253,311
Services [Member] | Other [Member] | Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	7,841	7,381	25,737	25,915
Investment Management [Member] | Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	18,258	1,248	52,965	19,884
Investment Management [Member] | Markel Ventures [Member] | Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	0	0	0	0
Investment Management [Member] | Other [Member] | Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	18,258	1,248	52,965	19,884
Program Services [Member]
Disaggregation of Revenue [Line Items]
Other revenues	22,478	0	65,810	0
Program Services [Member] | Markel Ventures [Member]
Disaggregation of Revenue [Line Items]
Other revenues	0	0	0	0
Program Services [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other revenues	22,478	0	65,810	0
Other [Member]
Disaggregation of Revenue [Line Items]
Other revenues	23,615	22,813	69,348	69,751
Other [Member] | Markel Ventures [Member]
Disaggregation of Revenue [Line Items]
Other revenues	23,219	22,386	68,075	68,117
Other [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other revenues	$ 396	$ 427	$ 1,273	$ 1,634

Other Revenues (Schedule Of Rec

Other Revenues (Schedule Of Receivables And Customer Deposits Related To Contracts With Customers) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Other Revenue [Line Items]
Receivables	$ 1,817,637	$ 1,567,453
Contracts With Customers [Member]
Other Revenue [Line Items]
Receivables	208,117	176,865
Customer deposits	$ 60,220	$ 61,546

Reinsurance (Narrative) (Detail

Reinsurance (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Percentage of ceded earned premiums to gross earned premiums	38.00%	17.00%	38.00%	16.00%
Percentage of assumed earned premiums to net earned premiums	28.00%	32.00%	28.00%	31.00%
Reinsurance recoverables	$ 171.1	$ 540.1	$ 394.9	$ 748.7
2018 Catastrophes [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance recoverables	28.6		28.6
2017 Catastrophes [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance recoverables		$ 464.4		$ 464.4
Program Services [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance recoverables	$ 329.9		$ 959.5

Reinsurance (Effect Of Reinsura

Reinsurance (Effect Of Reinsurance And Retrocessional Reinsurance On Premiums Written And Earned) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Effects of Reinsurance [Line Items]
Direct premiums written	$ 1,737,563	$ 1,035,705	$ 4,967,078	$ 2,932,022
Direct premiums earned	1,594,457	966,735	4,596,389	2,743,970
Assumed premiums written	306,208	292,423	1,121,010	1,214,021
Assumed premiums earned	326,424	356,529	982,370	976,636
Ceded premiums written	(827,500)	(230,374)	(2,356,409)	(650,403)
Ceded premiums earned	(735,558)	(223,402)	(2,094,231)	(604,568)
Net premiums written	1,216,271	1,097,754	3,731,679	3,495,640
Net premiums earned	1,185,323	1,099,862	3,484,528	3,116,038
Underwriting [Member]
Effects of Reinsurance [Line Items]
Direct premiums written	1,207,605	1,035,705	3,429,666	2,932,022
Direct premiums earned	1,113,763	966,735	3,221,946	2,743,970
Assumed premiums written	274,898	292,423	1,081,171	1,214,021
Assumed premiums earned	313,378	356,529	965,586	976,636
Ceded premiums written	(266,788)	(230,374)	(781,126)	(650,403)
Ceded premiums earned	(242,120)	(223,402)	(703,785)	(604,568)
Net premiums written	1,215,715	1,097,754	3,729,711	3,495,640
Net premiums earned	1,185,021	1,099,862	3,483,747	3,116,038
Program Services [Member]
Effects of Reinsurance [Line Items]
Direct premiums written	529,958	0	1,537,412	0
Direct premiums earned	480,694	0	1,374,443	0
Assumed premiums written	31,310	0	39,839	0
Assumed premiums earned	13,046	0	16,784	0
Ceded premiums written	(560,712)	0	(1,575,283)	0
Ceded premiums earned	(493,438)	0	(1,390,446)	0
Net premiums written	556	0	1,968	0
Net premiums earned	$ 302	$ 0	$ 781	$ 0

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Effective tax rate	32.00%	32.00%
Provision for deferred U.S. income taxes	$ 102
Effective tax rate attributable to U.K. subsidiaries being taxed as domestic corporations	(11.00%)
Estimated annual effective tax rate	20.00%	28.00%
U.S. statutory tax rate	21.00%	35.00%

Variable Interest Entities (Nar

Variable Interest Entities (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds		$ 518,244	$ 341,804	$ 1,585,869	$ 980,713
Fair value of the Company's investment in CROF		6,549,848		6,549,848		$ 0
Fair value of the Company's investment in CROF		0		0		5,967,847
Total investment and insurance assets under management of MCIM for unconsolidated VIEs		6,600,000		6,600,000
Other Fund [Member]
Variable Interest Entity [Line Items]
Investment in one of the unconsolidated Funds		27,400		27,400
Markel Diversified Fund [Member]
Variable Interest Entity [Line Items]
Investment in one of the unconsolidated Funds		94,700		94,700		168,200
Total assets of the Markel Diversified Fund		96,100		96,100		170,300
Total liabilities of the Markel Diversified Fund		$ 25,100		$ 25,100		$ 62,700
Percentage of total assets of the Markel Diversified Fund invested in one of the unconsolidated Funds		2.00%		2.00%		7.00%
CATCo Reinsurance Opportunities Fund Ltd. (CROF) [Member]
Variable Interest Entity [Line Items]
Fair value of the Company's investment in CROF		$ 11,700		$ 11,700
Fair value of the Company's investment in CROF						$ 20,500
Other Debt [Member] | Markel Diversified Fund [Member]
Variable Interest Entity [Line Items]
Note payable included in total liabilities of the Markel Diversified Fund delivered as part of the consideration provided for its investment		24,900		24,900		$ 62,500
Repayment of note payable	$ 37,500
Revenue From Contracts With Customers [Member]
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds		472,151	318,991	1,450,711	910,962
Other [Member]
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds		48,973	9,056	145,785	47,433
Other [Member] | Revenue From Contracts With Customers [Member]
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds		26,099	8,629	78,702	45,799
Investment Management [Member] | Revenue From Contracts With Customers [Member]
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds		18,258	1,248	52,965	19,884
Investment Management [Member] | Other [Member] | Revenue From Contracts With Customers [Member]
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds		$ 18,258	$ 1,248	$ 52,965	$ 19,884

Shareholders' Equity (Narrative

Shareholders' Equity (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares repurchased | shares	24,584
Stock repurchased value	$ 27.8
November 2013 Share Repurchase Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares repurchased | shares	15,509
Stock repurchased value	$ 17.6
Cumulative number of common stock shares repurchased | shares	199,244
Cumulative stock repurchased value	$ 175.6
May 2018 Share Repurchase Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares repurchased | shares	9,075
Stock repurchased value	$ 10.2
Board of Directors approved the repurchase of common stock under a share repurchase program, maximum	$ 300

Shareholders' Equity (Schedule

Shareholders' Equity (Schedule Of Net Income (Loss) Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Line Items]
Net income (loss) to shareholders		$ 409,438	$ (259,141)	$ 623,363	$ (39,612)
Adjustment of redeemable noncontrolling interests		(12,035)	(3,298)	(6,621)	(23,582)
Adjusted net income (loss) to shareholders		$ 397,403	$ (262,439)	$ 616,742	$ (63,194)
Basic common shares outstanding		13,917	13,947	13,925	13,974
Diluted shares outstanding		13,943	13,990	13,949	14,018
Basic net income (loss) per share	[1]	$ 28.56	$ (18.82)	$ 44.29	$ (4.52)
Diluted net income (loss) per share	[1]	$ 28.50	$ (18.82)	$ 44.21	$ (4.52)
Stock Options [Member]
Earnings Per Share [Line Items]
Dilutive potential common shares		0	1	0	2
Restricted Stock Units (RSUs) [Member]
Earnings Per Share [Line Items]
Dilutive potential common shares		26	42	24	42
[1]	Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income, rather, changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 2.

Other Comprehensive Income (L_3

Other Comprehensive Income (Loss) (Change In Accumulated Other Comprehensive Income (Loss) By Component, Net Of Taxes And Noncontrolling Interest) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017
Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income, beginning balance	$ 2,345,571		$ 1,565,866
Cumulative effect of adoption of ASU No. 2016-01	(2,613,242)
Cumulative effect of adoption of ASU No. 2018-02	401,539
Other comprehensive income (loss) before reclassifications	(324,256)		597,546
Amounts reclassified from accumulated other comprehensive income (loss)	5,496	[1]	(12,207)
Total other comprehensive income (loss)	(2,530,463)		585,339
Accumulated other comprehensive income, ending balance	(184,892)		2,151,205
Unrealized Holding Gains On Available-For-Sale Securities [Member]
Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income, beginning balance	2,477,973		1,714,930
Cumulative effect of adoption of ASU No. 2016-01	(2,615,734)
Cumulative effect of adoption of ASU No. 2018-02	401,539
Other comprehensive income (loss) before reclassifications	(306,069)		577,796
Amounts reclassified from accumulated other comprehensive income (loss)	5,496	[1]	(14,598)
Total other comprehensive income (loss)	(2,514,768)		563,198
Accumulated other comprehensive income, ending balance	(36,795)		2,278,128
Foreign Currency [Member]
Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income, beginning balance	(74,003)		(84,406)
Cumulative effect of adoption of ASU No. 2016-01	2,492
Cumulative effect of adoption of ASU No. 2018-02	0
Other comprehensive income (loss) before reclassifications	(19,928)		19,750
Amounts reclassified from accumulated other comprehensive income (loss)	0	[1]	0
Total other comprehensive income (loss)	(17,436)		19,750
Accumulated other comprehensive income, ending balance	(91,439)		(64,656)
Net Actuarial Pension Loss [Member]
Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income, beginning balance	(58,399)		(64,658)
Cumulative effect of adoption of ASU No. 2016-01	0
Cumulative effect of adoption of ASU No. 2018-02	0
Other comprehensive income (loss) before reclassifications	1,741		0
Amounts reclassified from accumulated other comprehensive income (loss)	0	[1]	2,391
Total other comprehensive income (loss)	1,741		2,391
Accumulated other comprehensive income, ending balance	$ (56,658)		$ (62,267)
[1]	Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income, rather, changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 2.

Other Comprehensive Income (L_4

Other Comprehensive Income (Loss) (Summary Of Tax Expense (Benefit) Of Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other Comprehensive Income (Loss), Tax [Abstract]
Net holding gains (losses) arising during the period	[1]	$ (24,047)	$ 109,338	$ (84,825)	$ 278,266
Reclassification adjustments for net gains (losses) included in net income (loss)	[1]	2,810	(2,810)	1,461	(5,206)
Change in net unrealized gains (losses) on available-for-sale investments	[1]	(21,237)	106,528	(83,364)	273,060
Change in foreign currency translation adjustments		6,594	656	3,072	153
Change in net actuarial pension loss		135	159	463	492
Total		$ (14,508)	$ 107,343	$ (79,829)	$ 273,705
[1]	Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income, rather, changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 2.

Other Comprehensive Income (L_5

Other Comprehensive Income (Loss) (Reclassifications From Accumulated Other Comprehensive Income (Loss) Into Income, By Component) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses		$ 0	$ (3,444)	$ 0	$ (7,261)
Net realized investment gains (losses), excluding other-than-temporary impairment losses		(496)	11,814	(9,084)	31,826
Total before taxes		519,027	(359,948)	922,601	(56,359)
Underwriting, acquisition and insurance expenses		(441,961)	(396,972)	(1,317,921)	(1,171,520)
Income taxes		(109,999)	98,913	(299,580)	17,791
Net income (loss)		409,028	(261,035)	623,021	(38,568)
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	[1]	0	(3,444)	0	(7,261)
Net realized investment gains (losses), excluding other-than-temporary impairment losses	[1]	(13,383)	11,461	(6,957)	27,065
Total before taxes	[1]	(13,383)	8,017	(6,957)	19,804
Income taxes		2,810	(2,810)	1,461	(5,206)
Net income (loss)		(10,573)	5,207	(5,496)	14,598
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		(644)	(932)	(2,204)	(2,883)
Income taxes		135	159	463	492
Net income (loss)		$ (509)	$ (773)	$ (1,741)	$ (2,391)
[1]	Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income, rather, changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 2.

Contingencies (Narrative) (Deta

Contingencies (Narrative) (Details) - USD ($) $ in Thousands	Jun. 05, 2018	Sep. 30, 2018
Other [Member]
Loss Contingencies [Line Items]
Payment to CVR agreement holders	$ 9,900
Portion paid of the undisputed final amount required per the CVR agreement	90.00%
Markel Ventures [Member] | Industrial Products [Member]
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss		$ 33,500
Impairment charge		14,900
Carrying value following impairment charge		0
Damages [Member] | Thomas Yeransian v. Markel Corporation [Member]
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss		47,300
Interest [Member] | Thomas Yeransian v. Markel Corporation [Member]
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss		13,400
Default Interest [Member] | Thomas Yeransian v. Markel Corporation [Member]
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss		$ 11,500

Subsequent Events (Narrative) (

Subsequent Events (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Subsequent Event [Line Items]
Net incurred losses		$ 736,846	$ 1,075,432	$ 1,951,142	$ 2,210,129
Minimum [Member] | Hurricane [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Net incurred losses	$ 60,000
Maximum [Member] | Hurricane [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Net incurred losses	$ 120,000