Markel (MKL) 10-Q 31 Jul 18 2018 Q2 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Jul. 24, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2
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 Common Stock, Shares Outstanding		13,885,592

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
ASSETS
Fixed maturities, available-for-sale (amortized cost of $10,025,593 in 2018 and $9,551,153 in 2017)	$ 10,134,073	$ 9,940,670
Equity securities, available-for-sale (cost of $2,667,661 in 2017)	0	5,967,847
Equity securities (cost of $2,787,763 in 2018)	6,069,245	0
Short-term investments, available-for-sale (estimated fair value approximates cost)	1,947,585	2,160,974
Total Investments	18,150,903	18,069,491
Cash and cash equivalents	1,945,370	2,198,459
Restricted cash and cash equivalents	299,026	302,387
Receivables	1,944,751	1,567,453
Reinsurance recoverable on unpaid losses	4,739,259	4,619,336
Reinsurance recoverable on paid losses	90,649	126,054
Deferred policy acquisition costs	508,214	465,569
Prepaid reinsurance premiums	1,266,916	1,099,757
Goodwill	1,784,667	1,777,464
Intangible assets	1,269,520	1,355,681
Other assets	1,247,756	1,223,365
Total Assets	33,247,031	32,805,016
LIABILITIES AND EQUITY
Unpaid losses and loss adjustment expenses	13,628,941	13,584,281
Life and annuity benefits	1,033,461	1,072,112
Unearned premiums	3,695,040	3,308,779
Payables to insurance and reinsurance companies	422,423	324,304
Senior long-term debt and other debt (estimated fair value of $3,088,000 in 2018 and $3,351,000 in 2017)	3,024,306	3,099,230
Other liabilities	1,809,448	1,748,460
Total Liabilities	23,613,619	23,137,166
Redeemable noncontrolling interests	155,998	166,269
Commitments and contingencies
Shareholders' equity:
Common stock	3,387,121	3,381,834
Retained earnings	6,184,299	3,776,743
Accumulated other comprehensive income (loss)	(90,560)	2,345,571
Total Shareholders' Equity	9,480,860	9,504,148
Noncontrolling interests	(3,446)	(2,567)
Total Equity	9,477,414	9,501,581
Total Liabilities and Equity	$ 33,247,031	$ 32,805,016

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Fixed maturities, available-for-sale amortized cost	$ 10,025,593	$ 9,551,153
Equity securities, available-for-sale cost		2,667,661
Equity securities, cost	2,787,763
Senior long-term debt and other debt, estimated fair value	$ 3,088,000	$ 3,351,000

Consolidated Statements Of Inco

Consolidated Statements Of Income And Comprehensive Income (Loss) - USD ($) $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2018		Jun. 30, 2017		Jun. 30, 2018		Jun. 30, 2017
OPERATING REVENUES
Earned premiums		$ 1,148,184		$ 1,033,574		$ 2,299,205		$ 2,016,176
Net investment income		105,387		99,299		213,403		199,667
Other-than-temporary impairment losses		0		(604)		0		(3,817)
Net realized investment gains (losses), excluding other-than-temporary impairment losses		(7,642)		4,829		(8,588)		20,012
Change in fair value of equity securities	[1]	112,891		13,402		(9,161)		22,297
Net investment gains (losses)		105,249		17,627		(17,749)		38,492
Other revenues		628,193		330,993		1,067,625		638,909
Total Operating Revenues		1,987,013		1,481,493		3,562,484		2,893,244
OPERATING EXPENSES
Losses and loss adjustment expenses		599,178		522,978		1,214,296		1,134,697
Underwriting, acquisition and insurance expenses		451,570		401,270		875,960		774,548
Amortization of intangible assets	[2]	29,641		18,026		58,464		34,796
Other expenses		595,343	[3]	298,756	[4]	997,473	[5]	581,389	[6]
Total Operating Expenses		1,675,732		1,241,030		3,146,193		2,525,430
Operating Income		311,281		240,463		416,291		367,814
Interest expense		36,702		31,797		76,761		65,199
Net foreign exchange gains		(86,158)		(879)		(64,044)		(974)
Income Before Income Taxes		360,737		209,545		403,574		303,589
Income tax expense		81,150		58,118		189,581		81,122
Net Income		279,587		151,427		213,993		222,467
Net income attributable to noncontrolling interests		1,356		1,767		68		2,938
Net Income to Shareholders		278,231		149,660		213,925		219,529
OTHER COMPREHENSIVE INCOME (LOSS)
Net holding gains (losses) arising during the period		(98,145)		190,069		(215,067)		350,349
Reclassification adjustments for net gains included in net income		(5,891)		(222)		(5,077)		(9,391)
Change in net unrealized gains on available-for-sale investments, net of taxes		(104,036)		189,847		(220,144)		340,958
Change in foreign currency translation adjustments, net of taxes		(10,450)		1,962		(5,497)		3,507
Change in net actuarial pension loss, net of taxes		568		902		1,232		1,618
Total Other Comprehensive Income (Loss)		(113,918)		192,711		(224,409)		346,083
Comprehensive Income (Loss)		165,669		344,138		(10,416)		568,550
Comprehensive income attributable to noncontrolling interests		1,333		1,781		87		2,954
Comprehensive Income (Loss) to Shareholders		$ 164,336		$ 342,357		$ (10,503)		$ 565,596
NET INCOME PER SHARE
Basic (in dollars per share)	[7]	$ 20.01		$ 10.34		$ 15.75		$ 14.25
Diluted (in dollars per share)	[7]	$ 19.97		$ 10.31		$ 15.72		$ 14.20
[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 $12.8 million for the quarter ended June 30, 2018.
[4]	Other expenses for the Markel Ventures segment include depreciation expense of $9.6 million for the quarter ended June 30, 2017.
[5]	Other expenses for the Markel Ventures segment include depreciation expense of $25.5 million for the six months ended June 30, 2018.
[6]	Other expenses for the Markel Ventures segment include depreciation expense of $19.0 million for the six months ended June 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 ($) shares in Thousands, $ 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
Balance, redeemable noncontrolling interests at Dec. 31, 2016								$ 73,678
Net income (loss)	$ 222,467	219,222	219,529		219,529	0	(307)	3,245
Other comprehensive income (loss)	346,083	346,067	346,067		0	346,067	0	16
Comprehensive Income (Loss)	568,550	565,289	565,596				(307)	3,261
Issuance of common stock		359	359	$ 359	0	0	0	0
Issuance of common stock, shares				24
Repurchase of common stock		(59,194)	(59,194)	$ 0	(59,194)	0	0	0
Repurchase of common stock, shares				(61)
Restricted stock units expensed		10,568	10,568	$ 10,568	0	0	0	0
Restricted stock units expensed, shares				0
Adjustment of redeemable noncontrolling interests		(20,284)	(20,284)	$ 0	(20,284)	0	0	20,284
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		(614)	(653)	$ (453)	(200)	0	39	(4,353)
Other, shares				0
Balance at Jun. 30, 2017		8,952,516	8,954,409	$ 3,376,230	3,666,246	1,911,933	(1,893)
Balance, shares at Jun. 30, 2017				13,918
Balance, redeemable noncontrolling interests at Jun. 30, 2017								86,691
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
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)	213,993	213,015	213,925		213,925	0	(910)	978
Other comprehensive income (loss)	(224,409)	(224,428)	(224,428)		0	(224,428)	0	19
Comprehensive Income (Loss)	(10,416)	(11,088)	(10,178)				(910)	997
Issuance of common stock		2	2	$ 2	0	0	0	0
Issuance of common stock, shares				4
Repurchase of common stock		(24,257)	(24,257)	$ 0	(24,257)	0	0	0
Repurchase of common stock, shares				(22)
Restricted stock units expensed		12,229	12,229	$ 12,229	0	0	0	0
Restricted stock units expensed, shares				0
Adjustment of redeemable noncontrolling interests		5,414	5,414	$ 0	5,414	0	0	(5,414)
Adjustment of redeemable noncontrolling interests, shares				0
Purchase of noncontrolling interest		(5,586)	(5,586)	$ (5,586)	0	0	0	(39)
Purchase of noncontrolling interest, shares				0
Other		(881)	(912)	$ (1,358)	446	0	31	(5,815)
Other, shares				0
Balance at Jun. 30, 2018	9,477,414	$ 9,477,414	$ 9,480,860	$ 3,387,121	$ 6,184,299	$ (90,560)	$ (3,446)
Balance, shares at Jun. 30, 2018				13,886
Balance, redeemable noncontrolling interests at Jun. 30, 2018	$ 155,998							$ 155,998

Condensed Consolidated Statemen

Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
OPERATING ACTIVITIES
Net income	$ 213,993	$ 222,467
Adjustments to reconcile net income to net cash provided by operating activities	93,541	15,478
Net Cash Provided By Operating Activities	307,534	237,945
INVESTING ACTIVITIES
Proceeds from sales of fixed maturities and equity securities	234,442	262,518
Proceeds from maturities, calls and prepayments of fixed maturities	374,719	676,023
Cost of fixed maturities and equity securities purchased	(1,185,375)	(939,314)
Net change in short-term investments	220,428	677,968
Additions to property and equipment	(52,388)	(35,578)
Acquisitions, net of cash acquired	(7,804)	(202,033)
Other	(29,661)	(2,808)
Net Cash Provided (Used) By Investing Activities	(445,639)	436,776
FINANCING ACTIVITIES
Additions to senior long-term debt and other debt	109,113	29,898
Repayment of senior long-term debt and other debt	(180,158)	(139,564)
Repurchases of common stock	(24,257)	(59,194)
Purchase of noncontrolling interests	(7,058)	(18,068)
Distributions to noncontrolling interests	(5,815)	(4,345)
Other	(3,288)	(7,346)
Net Cash Used By Financing Activities	(111,463)	(198,619)
Effect of foreign currency rate changes on cash, cash equivalents, restricted cash and restricted cash equivalents	(6,882)	24,977
Increase (decrease) in cash, cash equivalents, restricted cash and restricted cash equivalents	(256,450)	501,079
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	$ 2,244,396	$ 2,586,243

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	6 Months Ended
	Jun. 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 June 30, 2018 and the related consolidated statements of income and comprehensive income (loss) for the quarters and six months ended June 30, 2018 and 2017 , and the consolidated statements of changes in equity and cash flows for the six months ended June 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 June 30, 2018. c) Revenue Recognition. Effective January 1, 2018, the Company adopted 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	6 Months Ended
	Jun. 30, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements Effective January 1, 2018, the Company adopted FASB 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 six months ended June 30, 2018 and its receivables, other assets and other liabilities as of June 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 FASB 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 six months ended June 30, 2018 and included in other comprehensive income (loss) for the quarter and six months ended June 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. 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. ASU No. 2016-02 becomes effective for the Company during the first quarter of 2019 and will be applied using a modified retrospective approach for leases that exist or are entered into after the beginning of the earliest comparative period in the financial statements. 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. The following ASU's relate to topics relevant to the Company's operations and were adopted effective January 1, 2018. These ASU's 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 The following ASU is relevant to the Company's operations and is not yet effective. This ASU is 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

Acquisitions

Acquisitions	6 Months Ended
	Jun. 30, 2018
Business Combinations [Abstract]
Acquisitions	Acquisitions 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. See note 6 for further discussion of the Company's reportable segments. 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 June 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 June 30, 2018) 18,478 Net intangible assets as of June 30, 2018 $ 352,022

Investments

Investments	6 Months Ended
	Jun. 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. June 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 $ 184,972 $ 23 $ (2,797 ) $ — $ 182,198 U.S. government-sponsored enterprises 360,192 5,719 (5,544 ) — 360,367 Obligations of states, municipalities and political subdivisions 4,379,175 107,644 (33,843 ) — 4,452,976 Foreign governments 1,454,335 113,963 (12,188 ) — 1,556,110 Commercial mortgage-backed securities 1,668,547 668 (58,319 ) — 1,610,896 Residential mortgage-backed securities 910,466 2,564 (20,875 ) — 892,155 Asset-backed securities 30,229 1 (455 ) — 29,775 Corporate bonds 1,037,677 25,776 (13,857 ) — 1,049,596 Total fixed maturities 10,025,593 256,358 (147,878 ) — 10,134,073 Short-term investments 1,948,806 203 (1,424 ) — 1,947,585 Investments, available-for-sale $ 11,974,399 $ 256,561 $ (149,302 ) $ — $ 12,081,658 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. June 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 $ 102,764 $ (1,397 ) $ 78,840 $ (1,400 ) $ 181,604 $ (2,797 ) U.S. government-sponsored enterprises 115,354 (2,714 ) 94,301 (2,830 ) 209,655 (5,544 ) Obligations of states, municipalities and political subdivisions 855,186 (15,141 ) 402,553 (18,702 ) 1,257,739 (33,843 ) Foreign governments 328,049 (6,714 ) 75,799 (5,474 ) 403,848 (12,188 ) Commercial mortgage-backed securities 962,732 (24,757 ) 497,169 (33,562 ) 1,459,901 (58,319 ) Residential mortgage-backed securities 590,710 (14,181 ) 126,355 (6,694 ) 717,065 (20,875 ) Asset-backed securities 14,389 (277 ) 14,316 (178 ) 28,705 (455 ) Corporate bonds 401,878 (9,366 ) 153,196 (4,491 ) 555,074 (13,857 ) Total fixed maturities 3,371,062 (74,547 ) 1,442,529 (73,331 ) 4,813,591 (147,878 ) Short-term investments 177,977 (1,424 ) — — 177,977 (1,424 ) Total $ 3,549,039 $ (75,971 ) $ 1,442,529 $ (73,331 ) $ 4,991,568 $ (149,302 ) At June 30, 2018 , the Company held 1,120 fixed maturities with a total estimated fair value of $5.0 billion and gross unrealized losses of $149.3 million . Of these 1,120 securities, 275 securities had been in a continuous unrealized loss position for one year or longer and had a total estimated fair value of $1.4 billion and gross unrealized losses of $73.3 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 June 30, 2018 are shown below by contractual maturity. (dollars in thousands) Amortized Cost Estimated Fair Value Due in one year or less $ 222,476 $ 221,579 Due after one year through five years 1,354,381 1,366,516 Due after five years through ten years 1,845,977 1,876,279 Due after ten years 3,993,517 4,136,873 7,416,351 7,601,247 Commercial mortgage-backed securities 1,668,547 1,610,896 Residential mortgage-backed securities 910,466 892,155 Asset-backed securities 30,229 29,775 Total fixed maturities $ 10,025,593 $ 10,134,073 d) The following table presents the components of net investment income. Quarter Ended June 30, Six Months Ended June 30, (dollars in thousands) 2018 2017 2018 2017 Interest: Municipal bonds (tax-exempt) $ 20,287 $ 22,758 $ 41,222 $ 45,130 Municipal bonds (taxable) 18,220 17,793 35,853 35,298 Other taxable bonds 39,548 36,296 77,017 71,184 Short-term investments, including overnight deposits 11,915 5,834 22,505 10,783 Dividends on equity securities 20,474 19,017 44,481 39,623 Income (loss) from equity method investments (1,490 ) 1,802 288 6,395 Other 97 24 (13 ) (205 ) 109,051 103,524 221,353 208,208 Investment expenses (3,664 ) (4,225 ) (7,950 ) (8,541 ) Net investment income $ 105,387 $ 99,299 $ 213,403 $ 199,667 e) The following table presents net investment gains (losses) and the change in net unrealized gains on available-for-sale investments. Quarter Ended June 30, Six Months Ended June 30, (dollars in thousands) 2018 2017 2018 2017 Realized gains on available-for-sale investments: Sales of fixed maturities $ 242 $ 554 $ 1,765 $ 757 Sales of equity securities (1) — 1,295 — 16,533 Other 810 4,259 891 4,826 Total realized gains 1,052 6,108 2,656 22,116 Realized losses on available-for-sale investments: Sales of fixed maturities (7,706 ) (412 ) (8,198 ) (602 ) Sales of equity securities (1) — (786 ) — (1,216 ) Other-than-temporary impairments — (604 ) — (3,817 ) Other (988 ) (81 ) (3,046 ) (286 ) Total realized losses (8,694 ) (1,883 ) (11,244 ) (5,921 ) Net realized investment gains (losses) (7,642 ) 4,225 (8,588 ) 16,195 Change in fair value of equity securities: (1) Change in fair value of equity securities sold during the period (1) 9,631 — 13,897 — Change in fair value of equity securities held at the end of the period 103,260 13,402 (23,058 ) 22,297 Change in fair value of equity securities (1) 112,891 13,402 (9,161 ) 22,297 Net investment gains (losses) $ 105,249 $ 17,627 $ (17,749 ) $ 38,492 Change in net unrealized gains on available-for-sale investments included in other comprehensive income: Fixed maturities $ (143,593 ) $ 79,413 $ (281,093 ) $ 84,060 Equity securities (1) — 204,372 — 423,424 Short-term investments 5,499 133 (1,178 ) 6 Net increase (decrease) $ (138,094 ) $ 283,918 $ (282,271 ) $ 507,490 (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	6 Months Ended
	Jun. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements FASB ASC 820-10, Fair Value Measurements and Disclosures, establishes a three-level hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The fair value hierarchy gives the highest priority to quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3). If the inputs used to measure the assets or liabilities fall within different levels of the hierarchy, the classification is based on the lowest level input that is significant to the fair value measurement of the asset or liability. Classification of assets and liabilities within the hierarchy considers the markets in which the assets and liabilities are traded and the reliability and transparency of the assumptions used to determine fair value. The hierarchy requires the use of observable market data when available. The levels of the hierarchy are defined as follows: Level 1 – Inputs to the valuation methodology are quoted prices (unadjusted) for identical assets or liabilities traded in active markets. Level 2 – Inputs to the valuation methodology include quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability and market-corroborated inputs. Level 3 – Inputs to the valuation methodology are unobservable for the asset or liability and are significant to the fair value measurement. In accordance with FASB ASC 820, the Company determines fair value based on the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. In determining fair value, the Company uses various methods, including the market, income and cost approaches. The Company uses valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs. The following section describes the valuation methodologies used by the Company to measure assets and liabilities at fair value, including an indication of the level within the fair value hierarchy in which each asset or liability is generally classified. Investments available-for-sale 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), as further described in note 11 , which are not traded on an active exchange 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. The Company's investments in the ILS Funds are redeemable annually as of January 1 st of each calendar year. 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. June 30, 2018 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments: Fixed maturities, available-for-sale: U.S. Treasury securities $ — $ 182,198 $ — $ 182,198 U.S. government-sponsored enterprises — 360,367 — 360,367 Obligations of states, municipalities and political subdivisions — 4,452,976 — 4,452,976 Foreign governments — 1,556,110 — 1,556,110 Commercial mortgage-backed securities — 1,610,896 — 1,610,896 Residential mortgage-backed securities — 892,155 — 892,155 Asset-backed securities — 29,775 — 29,775 Corporate bonds — 1,049,596 — 1,049,596 Total fixed maturities, available-for-sale — 10,134,073 — 10,134,073 Equity securities: Insurance, banks and other financial institutions 1,981,481 — 119,675 2,101,156 Industrial, consumer and all other 3,968,089 — — 3,968,089 Total equity securities 5,949,570 — 119,675 6,069,245 Short-term investments, available-for-sale 1,853,387 94,198 — 1,947,585 Total investments $ 7,802,957 $ 10,228,271 $ 119,675 $ 18,150,903 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 June 30, Six Months Ended June 30, (dollars in thousands) 2018 2017 2018 2017 Equity securities, beginning of period $ 151,398 $ 178,043 $ 168,809 $ 191,203 Purchases — 1,250 28,900 7,250 Sales (6,401 ) (1,303 ) (34,653 ) (26,674 ) Total gains (losses) included in net income (25,322 ) 5,923 (43,381 ) 12,134 Transfers into Level 3 — — — — Transfers out of Level 3 — — — — Equity securities, end of period $ 119,675 $ 183,913 $ 119,675 $ 183,913 Change in fair value of equity securities included in net income relating to assets held at June 30, 2018 and 2017 $ (25,322 ) $ 5,923 $ (43,381 ) $ 12,134 There were no transfers into or out of Level 1 and Level 2 during the quarter and six months ended June 30, 2018 and 2017 . The Company did not have any assets or liabilities measured at fair value on a non-recurring basis during the six months ended June 30, 2018 and 2017 .

Segment Reporting Disclosures

Segment Reporting Disclosures	6 Months Ended
	Jun. 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 June 30, Six Months Ended June 30, (dollars in thousands) 2018 2017 2018 2017 Markel Ventures: Products $ 472,323 $ 217,175 $ 766,459 $ 414,239 Services 106,433 96,422 204,354 186,293 Total Markel Ventures $ 578,756 $ 313,597 $ 970,813 $ 600,532 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 June 30, 2018 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures Other (1) Consolidated Gross premium volume $ 1,233,828 $ 208,805 $ — $ — $ 554,800 $ 1,997,433 Net written premiums 1,001,126 178,729 — — 751 1,180,606 Earned premiums 918,194 229,613 — — 377 1,148,184 Losses and loss adjustment expenses: Current accident year (610,634 ) (145,992 ) — — (48 ) (756,674 ) Prior accident years 139,485 18,525 — — (514 ) 157,496 Amortization of policy acquisition costs (191,843 ) (57,407 ) — — — (249,250 ) Other operating expenses (180,928 ) (21,178 ) — — (214 ) (202,320 ) Underwriting profit (loss) 74,274 23,561 — — (399 ) 97,436 Net investment income — — 105,195 192 — 105,387 Net investment gains — — 105,249 — — 105,249 Other revenues — — — 578,756 49,437 628,193 Other expenses (2) — — — (555,833 ) (39,510 ) (595,343 ) Amortization of intangible assets (3) — — — (10,096 ) (19,545 ) (29,641 ) Segment profit (loss) $ 74,274 $ 23,561 $ 210,444 $ 13,019 $ (10,017 ) $ 311,281 Interest expense (36,702 ) Net foreign exchange gains 86,158 Income before income taxes $ 360,737 U.S. GAAP combined ratio (4) 92 % 90 % NM (5) 92 % (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 $12.8 million for the quarter ended June 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 June 30, 2017 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures Other (1) Consolidated Gross premium volume $ 1,109,278 $ 247,902 $ — $ — $ (16 ) $ 1,357,164 Net written premiums 917,286 220,466 — — (95 ) 1,137,657 Earned premiums 804,189 229,480 — — (95 ) 1,033,574 Losses and loss adjustment expenses: Current accident year (538,399 ) (146,186 ) — — — (684,585 ) Prior accident years 132,528 28,151 — — 928 161,607 Amortization of policy acquisition costs (160,388 ) (53,086 ) — — — (213,474 ) Other operating expenses (163,480 ) (24,181 ) — — (135 ) (187,796 ) Underwriting profit 74,450 34,178 — — 698 109,326 Net investment income — — 99,239 60 — 99,299 Net realized investment gains — — 17,627 — — 17,627 Other revenues — — — 313,597 17,396 330,993 Other expenses (2) — — — (271,045 ) (27,711 ) (298,756 ) Amortization of intangible assets (3) — — — (6,956 ) (11,070 ) (18,026 ) Segment profit (loss) $ 74,450 $ 34,178 $ 116,866 $ 35,656 $ (20,687 ) $ 240,463 Interest expense (31,797 ) Net foreign exchange gains 879 Income before income taxes $ 209,545 U.S. GAAP combined ratio (4) 91 % 85 % NM (5) 89 % (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 $9.6 million for the quarter ended June 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 Six Months Ended June 30, 2018 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures Other (1) Consolidated Gross premium volume $ 2,327,190 $ 701,138 $ — $ — $ 1,015,989 $ 4,044,317 Net written premiums 1,914,105 599,787 — — 1,516 2,515,408 Earned premiums 1,821,045 477,577 — — 583 2,299,205 Losses and loss adjustment expenses: Current accident year (1,180,661 ) (299,173 ) — — (48 ) (1,479,882 ) Prior accident years 258,658 5,454 — — 1,474 265,586 Amortization of policy acquisition costs (371,328 ) (119,827 ) — — — (491,155 ) Other operating expenses (350,899 ) (33,308 ) — — (598 ) (384,805 ) Underwriting profit 176,815 30,723 — — 1,411 208,949 Net investment income — — 213,089 314 — 213,403 Net investment losses — — (17,749 ) — — (17,749 ) Other revenues — — — 970,813 96,812 1,067,625 Other expenses (2) — — — (914,138 ) (83,335 ) (997,473 ) Amortization of intangible assets (3) — — — (20,193 ) (38,271 ) (58,464 ) Segment profit (loss) $ 176,815 $ 30,723 $ 195,340 $ 36,796 $ (23,383 ) $ 416,291 Interest expense (76,761 ) Net foreign exchange gains 64,044 Income before income taxes $ 403,574 U.S. GAAP combined ratio (4) 90 % 94 % NM (5) 91 % (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 $25.5 million for the six months ended June 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 Six Months Ended June 30, 2017 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures Other (1) Consolidated Gross premium volume $ 2,022,275 $ 795,639 $ — $ — $ 1 $ 2,817,915 Net written premiums 1,687,803 710,062 — — 21 2,397,886 Earned premiums 1,561,038 455,117 — — 21 2,016,176 Losses and loss adjustment expenses: Current accident year (1,031,135 ) (291,796 ) — — — (1,322,931 ) Prior accident years 225,414 (43,412 ) — — 6,232 188,234 Amortization of policy acquisition costs (308,077 ) (109,945 ) — — — (418,022 ) Other operating expenses (309,877 ) (46,350 ) — — (299 ) (356,526 ) Underwriting profit (loss) 137,363 (36,386 ) — — 5,954 106,931 Net investment income — — 199,564 103 — 199,667 Net investment gains — — 38,492 — — 38,492 Other revenues — — — 600,532 38,377 638,909 Other expenses (2) — — — (522,357 ) (59,032 ) (581,389 ) Amortization of intangible assets (3) — — — (13,860 ) (20,936 ) (34,796 ) Segment profit (loss) $ 137,363 $ (36,386 ) $ 238,056 $ 64,418 $ (35,637 ) $ 367,814 Interest expense (65,199 ) Net foreign exchange gains 974 Income before income taxes $ 303,589 U.S. GAAP combined ratio (4) 91 % 108 % NM (5) 95 % (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 $19.0 million for the six months ended June 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) June 30, 2018 December 31, 2017 Segment assets: Investing $ 20,303,090 $ 20,317,160 Underwriting 6,955,342 6,828,048 Markel Ventures 1,936,966 1,900,728 Total segment assets 29,195,398 29,045,936 Other operations 4,051,633 3,759,080 Total assets $ 33,247,031 $ 32,805,016

Unpaid Losses And Loss Adjustme

Unpaid Losses And Loss Adjustment Expenses	6 Months Ended
	Jun. 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. Six Months Ended June 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 (20,554 ) 57,991 Adjusted net reserves for losses and loss adjustment expenses, beginning of year 8,944,391 8,166,708 Incurred losses and loss adjustment expenses: Current accident year 1,479,882 1,322,931 Prior accident years (265,613 ) (184,367 ) Total incurred losses and loss adjustment expenses 1,214,269 1,138,564 Payments: Current accident year 195,873 186,138 Prior accident years 1,073,004 829,126 Total payments 1,268,877 1,015,264 Effect of foreign currency rate changes (101 ) 2,333 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 8,889,682 8,305,043 Reinsurance recoverable on unpaid losses 4,739,259 2,007,652 Gross reserves for losses and loss adjustment expenses, end of period $ 13,628,941 $ 10,312,695 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 six months ended June 30, 2017 . This amount is excluded from the prior years' incurred losses and loss adjustment expenses for the six months ended June 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 six months ended June 30, 2018 , incurred losses and loss adjustment expenses included $265.6 million of favorable development on prior years' loss reserves, which included $211.9 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. For the six months ended June 30, 2017 , incurred losses and loss adjustment expenses included $184.4 million of favorable development on prior years' loss reserves, which included $195.7 million of loss reserve redundancies 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. Redundancies for the six months ended June 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 United Kingdom bodily injury cases. During the six months ended June 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	6 Months Ended
	Jun. 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 and comprehensive income (loss) is $581.4 million and $307.1 million for the quarters ended June 30, 2018 and 2017 , respectively, and $978.6 million and $592.0 million for the six months ended June 30, 2018 and 2017 , respectively. The following tables disaggregate revenues from contracts with customers by type. Quarter Ended June 30, 2018 2017 (dollars in thousands) Markel Ventures Other Total Markel Ventures Other Total Products $ 461,007 $ — $ 461,007 $ 204,839 $ — $ 204,839 Services 94,035 8,972 103,007 85,617 7,348 92,965 Investment management — 17,418 17,418 — 9,277 9,277 Total revenues from contracts with customers 555,042 26,390 581,432 290,456 16,625 307,081 Program services — 22,635 22,635 — — — Other 23,714 412 24,126 23,141 771 23,912 Total Other Revenues $ 578,756 $ 49,437 $ 628,193 $ 313,597 $ 17,396 $ 330,993 Six Months Ended June 30, 2018 2017 (dollars in thousands) Markel Ventures Other Total Markel Ventures Other Total Products $ 744,480 $ — $ 744,480 $ 389,572 $ — $ 389,572 Services 181,477 17,896 199,373 165,229 18,534 183,763 Investment management — 34,707 34,707 — 18,636 18,636 Total revenues from contracts with customers 925,957 52,603 978,560 554,801 37,170 591,971 Program services — 43,332 43,332 — — — Other 44,856 877 45,733 45,731 1,207 46,938 Total Other Revenues $ 970,813 $ 96,812 $ 1,067,625 $ 600,532 $ 38,377 $ 638,909 The following table presents receivables and customer deposits related to our contracts with customers. (dollars in thousands) June 30, 2018 December 31, 2017 Receivables $ 277,624 $ 176,865 Customer deposits 78,083 61,546

Reinsurance

Reinsurance	6 Months Ended
	Jun. 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 June 30, 2018 2017 (dollars in thousands) Direct Assumed Ceded Net Premiums Direct Assumed Ceded Net Premiums Underwriting: Written $ 1,182,683 $ 259,960 $ (262,781 ) $ 1,179,862 $ 1,046,833 $ 310,331 $ (219,507 ) $ 1,137,657 Earned 1,070,248 316,718 (239,152 ) 1,147,814 914,249 312,538 (193,213 ) 1,033,574 Program Services: Written 549,630 5,160 (554,046 ) 744 — — — — Earned 470,824 2,286 (472,740 ) 370 — — — — Consolidated: Written 1,732,313 265,120 (816,827 ) 1,180,606 1,046,833 310,331 (219,507 ) 1,137,657 Earned $ 1,541,072 $ 319,004 $ (711,892 ) $ 1,148,184 $ 914,249 $ 312,538 $ (193,213 ) $ 1,033,574 Six Months Ended June 30, 2018 2017 (dollars in thousands) Direct Assumed Ceded Net Premiums Direct Assumed Ceded Net Premiums Underwriting: Written $ 2,222,061 $ 806,273 $ (514,338 ) $ 2,513,996 $ 1,896,317 $ 921,598 $ (420,029 ) $ 2,397,886 Earned 2,108,183 652,208 (461,665 ) 2,298,726 1,777,235 620,107 (381,166 ) 2,016,176 Program Services: Written 1,007,454 8,529 (1,014,571 ) 1,412 — — — — Earned 893,749 3,738 (897,008 ) 479 — — — — Consolidated: Written 3,229,515 814,802 (1,528,909 ) 2,515,408 1,896,317 921,598 (420,029 ) 2,397,886 Earned $ 3,001,932 $ 655,946 $ (1,358,673 ) $ 2,299,205 $ 1,777,235 $ 620,107 $ (381,166 ) $ 2,016,176 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 six months ended June 30, 2018 was ceded to third parties. The percentage of ceded earned premiums to gross earned premiums was 38% and 37% for the quarter and six months ended June 30, 2018 , respectively, and 16% for the quarter and six months ended June 30, 2017 . The percentage of assumed earned premiums to net earned premiums was 28% and 29% for the quarter and six months ended June 30, 2018 , respectively, and 30% and 31% , for the quarter and six months ended June 30, 2017 , respectively. Substantially all of the incurred losses and loss adjustment expenses in the Company's program services business for the quarter and six months ended June 30, 2018 , which totaled $373.3 million and $629.6 million , respectively, were ceded to third parties. Incurred losses and loss adjustment expenses for the Company's underwriting operations were net of reinsurance recoverables (ceded incurred losses and loss adjustment expenses) of $52.0 million and $109.0 million for the quarters ended June 30, 2018 and 2017 , respectively, and $223.8 million and $208.6 million for the six months ended June 30, 2018 and 2017 , respectively.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The effective tax rate was 47% and 27% for the six months ended June 30, 2018 and 2017 , respectively. 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 six months ended June 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 25% 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 27% for the six months ended June 30, 2018 and 2017 , respectively. For the six months ended June 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 anticipating a smaller tax benefit from tax-exempt investment income in 2018 compared to 2017.

Variable Interest Entities

Variable Interest Entities	6 Months Ended
	Jun. 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 $17.4 million and $9.3 million for the quarters ended June 30, 2018 and 2017 , respectively, and $34.7 million and $18.6 million for the six months ended June 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 ( $26.4 million as of June 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 June 30, 2018 , total assets of the Markel Diversified Fund were $95.2 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 $93.2 million as of June 30, 2018 and $168.2 million as of December 31, 2017 , which represents 2% of the outstanding preference shares of that fund as of June 30, 2018 and 7% as of December 31, 2017 . This investment is included in equity securities on the Company's consolidated balance sheets. At June 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 June 30, 2018 and December 31, 2017 , the fair value of the Company's investment in CROF was $12.0 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 June 30, 2018 , total investment and insurance assets under management of MCIM for unconsolidated VIEs were $6.5 billion , which includes funds held that will be used to settle claims for incurred losses.

Shareholders' Equity

Shareholders' Equity	6 Months Ended
	Jun. 30, 2018
Stockholders' Equity Note [Abstract]
Shareholders' Equity	Shareholders' Equity a) During the six months ended June 30, 2018 , the Company repurchased 15,509 shares of common stock at a cost of $17.6 million under a share repurchase program that was approved by the Company’s Board of Directors in November 2013 (the 2013 Program). As of June 30, 2018 , the Company had repurchased 199,244 shares of common stock at a cost of $175.6 million under the 2013 Program. In May 2018, the Board of Directors approved a new share repurchase program that provides for the repurchase of up to $300 million of common stock (the 2018 Program) to replace the 2013 Program. The 2018 Program has no expiration date but may be terminated by the Board of Directors at any time. As of June 30, 2018 , the Company had repurchased 4,950 shares of common stock at a cost of $5.5 million under the 2018 Program. b) Net income per share was determined by dividing adjusted net income to shareholders by the applicable weighted average shares outstanding. Diluted net income per share is computed by dividing adjusted net income to shareholders by the weighted average number of common shares and dilutive potential common shares outstanding during the period. Quarter Ended June 30, Six Months Ended June 30, (in thousands, except per share amounts) 2018 2017 2018 2017 Net income to shareholders $ 278,231 $ 149,660 $ 213,925 $ 219,529 Adjustment of redeemable noncontrolling interests 363 (5,141 ) 5,414 (20,284 ) Adjusted net income to shareholders $ 278,594 $ 144,519 $ 219,339 $ 199,245 Basic common shares outstanding 13,925 13,977 13,929 13,987 Dilutive potential common shares from conversion of options — 2 — 2 Dilutive potential common shares from conversion of restricted stock units and restricted stock 25 40 24 43 Diluted shares outstanding 13,950 14,019 13,953 14,032 Basic net income per share (1) $ 20.01 $ 10.34 $ 15.75 $ 14.25 Diluted net income per share (1) $ 19.97 $ 10.31 $ 15.72 $ 14.20 (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)	6 Months Ended
	Jun. 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 included in net income. 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 six months ended June 30, 2018 and 2017 . (dollars in thousands) Unrealized Holding Gains 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 350,349 3,491 — 353,840 Amounts reclassified from accumulated other comprehensive income (9,391 ) — 1,618 (7,773 ) Total other comprehensive income 340,958 3,491 1,618 346,067 June 30, 2017 $ 2,055,888 $ (80,915 ) $ (63,040 ) $ 1,911,933 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 (215,067 ) (5,516 ) 1,232 (219,351 ) Amounts reclassified from accumulated other comprehensive loss (1) (5,077 ) — — (5,077 ) Total other comprehensive income (loss) (2,434,339 ) (3,024 ) 1,232 (2,436,131 ) June 30, 2018 $ 43,634 $ (77,027 ) $ (57,167 ) $ (90,560 ) (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 June 30, Six Months Ended June 30, (dollars in thousands) 2018 2017 2018 2017 Change in net unrealized gains on available-for-sale investments: (1) Net holding gains (losses) arising during the period $ (32,548 ) $ 93,935 $ (60,778 ) $ 168,928 Reclassification adjustments for net gains (losses) included in net income (1,566 ) 136 (1,349 ) (2,396 ) Change in net unrealized gains on available-for-sale investments (34,114 ) 94,071 (62,127 ) 166,532 Change in foreign currency translation adjustments (4,288 ) (466 ) (3,522 ) (503 ) Change in net actuarial pension loss 192 154 328 333 Total $ (38,210 ) $ 93,759 $ (65,321 ) $ 166,362 (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 income, by component. Quarter Ended June 30, Six Months Ended June 30, (dollars in thousands) 2018 2017 2018 2017 Unrealized holding gains on available-for-sale investments: (1) Other-than-temporary impairment losses $ — $ (604 ) $ — $ (3,817 ) Net realized investment gains, excluding other-than-temporary impairment losses 7,457 690 6,426 15,604 Total before taxes 7,457 86 6,426 11,787 Income taxes (1,566 ) 136 (1,349 ) (2,396 ) Reclassification of unrealized holding gains, net of taxes $ 5,891 $ 222 $ 5,077 $ 9,391 Net actuarial pension loss: Underwriting, acquisition and insurance expenses $ (760 ) $ (1,056 ) $ (1,560 ) $ (1,951 ) Income taxes 192 154 328 333 Reclassification of net actuarial pension loss, net of taxes $ (568 ) $ (902 ) $ (1,232 ) $ (1,618 ) (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	6 Months Ended
	Jun. 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), which are currently expected to result in the payment of additional cash consideration to CVR holders. Absent the litigation described below, the final amount to be paid to CVR holders would be determined after December 31, 2017, the CVR maturity date, based on, among other things, adjustments for the development of pre-acquisition loss reserves and loss sensitive profit commissions. The CVR holder representative, Thomas Yeransian, has 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 ( $12.7 million through June 30, 2018 ) and default interest (up to an additional $11.0 million through June 30, 2018 , depending on the date any default occurred ); and an unspecified amount of punitive damages, costs, and attorneys’ fees. At the initial hearing held February 21, 2017, the court stayed the proceedings and ordered the parties to discuss resolving the dispute pursuant to the independent CVR valuation procedure under the CVR agreement. The parties met on April 5, 2017, but were unsuccessful in reaching agreement on a process for resolving the dispute. The Company subsequently filed a motion to stay the litigation and compel arbitration, and, on July 31, 2017, the court issued an order granting that motion. Mr. Yeransian has filed a motion requesting that the court reconsider that order, and that motion is pending. 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 and that the contractual contingent consideration payments related to the CVRs will not have a material impact on the Company's liquidity. 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 for the period ended June 30, 2018. The amount recognized in the period represents 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 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.

Summary Of Significant Accoun21

Summary Of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation. The consolidated balance sheet as of June 30, 2018 and the related consolidated statements of income and comprehensive income (loss) for the quarters and six months ended June 30, 2018 and 2017 , and the consolidated statements of changes in equity and cash flows for the six months ended June 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 June 30, 2018.
Revenue Recognition	Revenue Recognition. Effective January 1, 2018, the Company adopted 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)	6 Months Ended
	Jun. 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 June 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 June 30, 2018) 18,478 Net intangible assets as of June 30, 2018 $ 352,022

Investments (Tables)

Investments (Tables)	6 Months Ended
	Jun. 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. June 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 $ 184,972 $ 23 $ (2,797 ) $ — $ 182,198 U.S. government-sponsored enterprises 360,192 5,719 (5,544 ) — 360,367 Obligations of states, municipalities and political subdivisions 4,379,175 107,644 (33,843 ) — 4,452,976 Foreign governments 1,454,335 113,963 (12,188 ) — 1,556,110 Commercial mortgage-backed securities 1,668,547 668 (58,319 ) — 1,610,896 Residential mortgage-backed securities 910,466 2,564 (20,875 ) — 892,155 Asset-backed securities 30,229 1 (455 ) — 29,775 Corporate bonds 1,037,677 25,776 (13,857 ) — 1,049,596 Total fixed maturities 10,025,593 256,358 (147,878 ) — 10,134,073 Short-term investments 1,948,806 203 (1,424 ) — 1,947,585 Investments, available-for-sale $ 11,974,399 $ 256,561 $ (149,302 ) $ — $ 12,081,658 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. June 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 $ 102,764 $ (1,397 ) $ 78,840 $ (1,400 ) $ 181,604 $ (2,797 ) U.S. government-sponsored enterprises 115,354 (2,714 ) 94,301 (2,830 ) 209,655 (5,544 ) Obligations of states, municipalities and political subdivisions 855,186 (15,141 ) 402,553 (18,702 ) 1,257,739 (33,843 ) Foreign governments 328,049 (6,714 ) 75,799 (5,474 ) 403,848 (12,188 ) Commercial mortgage-backed securities 962,732 (24,757 ) 497,169 (33,562 ) 1,459,901 (58,319 ) Residential mortgage-backed securities 590,710 (14,181 ) 126,355 (6,694 ) 717,065 (20,875 ) Asset-backed securities 14,389 (277 ) 14,316 (178 ) 28,705 (455 ) Corporate bonds 401,878 (9,366 ) 153,196 (4,491 ) 555,074 (13,857 ) Total fixed maturities 3,371,062 (74,547 ) 1,442,529 (73,331 ) 4,813,591 (147,878 ) Short-term investments 177,977 (1,424 ) — — 177,977 (1,424 ) Total $ 3,549,039 $ (75,971 ) $ 1,442,529 $ (73,331 ) $ 4,991,568 $ (149,302 )
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 June 30, 2018 are shown below by contractual maturity. (dollars in thousands) Amortized Cost Estimated Fair Value Due in one year or less $ 222,476 $ 221,579 Due after one year through five years 1,354,381 1,366,516 Due after five years through ten years 1,845,977 1,876,279 Due after ten years 3,993,517 4,136,873 7,416,351 7,601,247 Commercial mortgage-backed securities 1,668,547 1,610,896 Residential mortgage-backed securities 910,466 892,155 Asset-backed securities 30,229 29,775 Total fixed maturities $ 10,025,593 $ 10,134,073
Components Of Net Investment Income	The following table presents the components of net investment income. Quarter Ended June 30, Six Months Ended June 30, (dollars in thousands) 2018 2017 2018 2017 Interest: Municipal bonds (tax-exempt) $ 20,287 $ 22,758 $ 41,222 $ 45,130 Municipal bonds (taxable) 18,220 17,793 35,853 35,298 Other taxable bonds 39,548 36,296 77,017 71,184 Short-term investments, including overnight deposits 11,915 5,834 22,505 10,783 Dividends on equity securities 20,474 19,017 44,481 39,623 Income (loss) from equity method investments (1,490 ) 1,802 288 6,395 Other 97 24 (13 ) (205 ) 109,051 103,524 221,353 208,208 Investment expenses (3,664 ) (4,225 ) (7,950 ) (8,541 ) Net investment income $ 105,387 $ 99,299 $ 213,403 $ 199,667
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 on available-for-sale investments. Quarter Ended June 30, Six Months Ended June 30, (dollars in thousands) 2018 2017 2018 2017 Realized gains on available-for-sale investments: Sales of fixed maturities $ 242 $ 554 $ 1,765 $ 757 Sales of equity securities (1) — 1,295 — 16,533 Other 810 4,259 891 4,826 Total realized gains 1,052 6,108 2,656 22,116 Realized losses on available-for-sale investments: Sales of fixed maturities (7,706 ) (412 ) (8,198 ) (602 ) Sales of equity securities (1) — (786 ) — (1,216 ) Other-than-temporary impairments — (604 ) — (3,817 ) Other (988 ) (81 ) (3,046 ) (286 ) Total realized losses (8,694 ) (1,883 ) (11,244 ) (5,921 ) Net realized investment gains (losses) (7,642 ) 4,225 (8,588 ) 16,195 Change in fair value of equity securities: (1) Change in fair value of equity securities sold during the period (1) 9,631 — 13,897 — Change in fair value of equity securities held at the end of the period 103,260 13,402 (23,058 ) 22,297 Change in fair value of equity securities (1) 112,891 13,402 (9,161 ) 22,297 Net investment gains (losses) $ 105,249 $ 17,627 $ (17,749 ) $ 38,492 Change in net unrealized gains on available-for-sale investments included in other comprehensive income: Fixed maturities $ (143,593 ) $ 79,413 $ (281,093 ) $ 84,060 Equity securities (1) — 204,372 — 423,424 Short-term investments 5,499 133 (1,178 ) 6 Net increase (decrease) $ (138,094 ) $ 283,918 $ (282,271 ) $ 507,490 (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)	6 Months Ended
	Jun. 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. June 30, 2018 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments: Fixed maturities, available-for-sale: U.S. Treasury securities $ — $ 182,198 $ — $ 182,198 U.S. government-sponsored enterprises — 360,367 — 360,367 Obligations of states, municipalities and political subdivisions — 4,452,976 — 4,452,976 Foreign governments — 1,556,110 — 1,556,110 Commercial mortgage-backed securities — 1,610,896 — 1,610,896 Residential mortgage-backed securities — 892,155 — 892,155 Asset-backed securities — 29,775 — 29,775 Corporate bonds — 1,049,596 — 1,049,596 Total fixed maturities, available-for-sale — 10,134,073 — 10,134,073 Equity securities: Insurance, banks and other financial institutions 1,981,481 — 119,675 2,101,156 Industrial, consumer and all other 3,968,089 — — 3,968,089 Total equity securities 5,949,570 — 119,675 6,069,245 Short-term investments, available-for-sale 1,853,387 94,198 — 1,947,585 Total investments $ 7,802,957 $ 10,228,271 $ 119,675 $ 18,150,903 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 June 30, Six Months Ended June 30, (dollars in thousands) 2018 2017 2018 2017 Equity securities, beginning of period $ 151,398 $ 178,043 $ 168,809 $ 191,203 Purchases — 1,250 28,900 7,250 Sales (6,401 ) (1,303 ) (34,653 ) (26,674 ) Total gains (losses) included in net income (25,322 ) 5,923 (43,381 ) 12,134 Transfers into Level 3 — — — — Transfers out of Level 3 — — — — Equity securities, end of period $ 119,675 $ 183,913 $ 119,675 $ 183,913 Change in fair value of equity securities included in net income relating to assets held at June 30, 2018 and 2017 $ (25,322 ) $ 5,923 $ (43,381 ) $ 12,134

Segment Reporting Disclosures (

Segment Reporting Disclosures (Tables)	6 Months Ended
	Jun. 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 June 30, Six Months Ended June 30, (dollars in thousands) 2018 2017 2018 2017 Markel Ventures: Products $ 472,323 $ 217,175 $ 766,459 $ 414,239 Services 106,433 96,422 204,354 186,293 Total Markel Ventures $ 578,756 $ 313,597 $ 970,813 $ 600,532
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 June 30, 2018 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures Other (1) Consolidated Gross premium volume $ 1,233,828 $ 208,805 $ — $ — $ 554,800 $ 1,997,433 Net written premiums 1,001,126 178,729 — — 751 1,180,606 Earned premiums 918,194 229,613 — — 377 1,148,184 Losses and loss adjustment expenses: Current accident year (610,634 ) (145,992 ) — — (48 ) (756,674 ) Prior accident years 139,485 18,525 — — (514 ) 157,496 Amortization of policy acquisition costs (191,843 ) (57,407 ) — — — (249,250 ) Other operating expenses (180,928 ) (21,178 ) — — (214 ) (202,320 ) Underwriting profit (loss) 74,274 23,561 — — (399 ) 97,436 Net investment income — — 105,195 192 — 105,387 Net investment gains — — 105,249 — — 105,249 Other revenues — — — 578,756 49,437 628,193 Other expenses (2) — — — (555,833 ) (39,510 ) (595,343 ) Amortization of intangible assets (3) — — — (10,096 ) (19,545 ) (29,641 ) Segment profit (loss) $ 74,274 $ 23,561 $ 210,444 $ 13,019 $ (10,017 ) $ 311,281 Interest expense (36,702 ) Net foreign exchange gains 86,158 Income before income taxes $ 360,737 U.S. GAAP combined ratio (4) 92 % 90 % NM (5) 92 % (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 $12.8 million for the quarter ended June 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 June 30, 2017 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures Other (1) Consolidated Gross premium volume $ 1,109,278 $ 247,902 $ — $ — $ (16 ) $ 1,357,164 Net written premiums 917,286 220,466 — — (95 ) 1,137,657 Earned premiums 804,189 229,480 — — (95 ) 1,033,574 Losses and loss adjustment expenses: Current accident year (538,399 ) (146,186 ) — — — (684,585 ) Prior accident years 132,528 28,151 — — 928 161,607 Amortization of policy acquisition costs (160,388 ) (53,086 ) — — — (213,474 ) Other operating expenses (163,480 ) (24,181 ) — — (135 ) (187,796 ) Underwriting profit 74,450 34,178 — — 698 109,326 Net investment income — — 99,239 60 — 99,299 Net realized investment gains — — 17,627 — — 17,627 Other revenues — — — 313,597 17,396 330,993 Other expenses (2) — — — (271,045 ) (27,711 ) (298,756 ) Amortization of intangible assets (3) — — — (6,956 ) (11,070 ) (18,026 ) Segment profit (loss) $ 74,450 $ 34,178 $ 116,866 $ 35,656 $ (20,687 ) $ 240,463 Interest expense (31,797 ) Net foreign exchange gains 879 Income before income taxes $ 209,545 U.S. GAAP combined ratio (4) 91 % 85 % NM (5) 89 % (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 $9.6 million for the quarter ended June 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 Six Months Ended June 30, 2018 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures Other (1) Consolidated Gross premium volume $ 2,327,190 $ 701,138 $ — $ — $ 1,015,989 $ 4,044,317 Net written premiums 1,914,105 599,787 — — 1,516 2,515,408 Earned premiums 1,821,045 477,577 — — 583 2,299,205 Losses and loss adjustment expenses: Current accident year (1,180,661 ) (299,173 ) — — (48 ) (1,479,882 ) Prior accident years 258,658 5,454 — — 1,474 265,586 Amortization of policy acquisition costs (371,328 ) (119,827 ) — — — (491,155 ) Other operating expenses (350,899 ) (33,308 ) — — (598 ) (384,805 ) Underwriting profit 176,815 30,723 — — 1,411 208,949 Net investment income — — 213,089 314 — 213,403 Net investment losses — — (17,749 ) — — (17,749 ) Other revenues — — — 970,813 96,812 1,067,625 Other expenses (2) — — — (914,138 ) (83,335 ) (997,473 ) Amortization of intangible assets (3) — — — (20,193 ) (38,271 ) (58,464 ) Segment profit (loss) $ 176,815 $ 30,723 $ 195,340 $ 36,796 $ (23,383 ) $ 416,291 Interest expense (76,761 ) Net foreign exchange gains 64,044 Income before income taxes $ 403,574 U.S. GAAP combined ratio (4) 90 % 94 % NM (5) 91 % (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 $25.5 million for the six months ended June 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 Six Months Ended June 30, 2017 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures Other (1) Consolidated Gross premium volume $ 2,022,275 $ 795,639 $ — $ — $ 1 $ 2,817,915 Net written premiums 1,687,803 710,062 — — 21 2,397,886 Earned premiums 1,561,038 455,117 — — 21 2,016,176 Losses and loss adjustment expenses: Current accident year (1,031,135 ) (291,796 ) — — — (1,322,931 ) Prior accident years 225,414 (43,412 ) — — 6,232 188,234 Amortization of policy acquisition costs (308,077 ) (109,945 ) — — — (418,022 ) Other operating expenses (309,877 ) (46,350 ) — — (299 ) (356,526 ) Underwriting profit (loss) 137,363 (36,386 ) — — 5,954 106,931 Net investment income — — 199,564 103 — 199,667 Net investment gains — — 38,492 — — 38,492 Other revenues — — — 600,532 38,377 638,909 Other expenses (2) — — — (522,357 ) (59,032 ) (581,389 ) Amortization of intangible assets (3) — — — (13,860 ) (20,936 ) (34,796 ) Segment profit (loss) $ 137,363 $ (36,386 ) $ 238,056 $ 64,418 $ (35,637 ) $ 367,814 Interest expense (65,199 ) Net foreign exchange gains 974 Income before income taxes $ 303,589 U.S. GAAP combined ratio (4) 91 % 108 % NM (5) 95 % (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 $19.0 million for the six months ended June 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) June 30, 2018 December 31, 2017 Segment assets: Investing $ 20,303,090 $ 20,317,160 Underwriting 6,955,342 6,828,048 Markel Ventures 1,936,966 1,900,728 Total segment assets 29,195,398 29,045,936 Other operations 4,051,633 3,759,080 Total assets $ 33,247,031 $ 32,805,016

Unpaid Losses And Loss Adjust26

Unpaid Losses And Loss Adjustment Expenses (Tables)	6 Months Ended
	Jun. 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. Six Months Ended June 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 (20,554 ) 57,991 Adjusted net reserves for losses and loss adjustment expenses, beginning of year 8,944,391 8,166,708 Incurred losses and loss adjustment expenses: Current accident year 1,479,882 1,322,931 Prior accident years (265,613 ) (184,367 ) Total incurred losses and loss adjustment expenses 1,214,269 1,138,564 Payments: Current accident year 195,873 186,138 Prior accident years 1,073,004 829,126 Total payments 1,268,877 1,015,264 Effect of foreign currency rate changes (101 ) 2,333 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 8,889,682 8,305,043 Reinsurance recoverable on unpaid losses 4,739,259 2,007,652 Gross reserves for losses and loss adjustment expenses, end of period $ 13,628,941 $ 10,312,695

Other Revenues (Tables)

Other Revenues (Tables)	6 Months Ended
	Jun. 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 June 30, 2018 2017 (dollars in thousands) Markel Ventures Other Total Markel Ventures Other Total Products $ 461,007 $ — $ 461,007 $ 204,839 $ — $ 204,839 Services 94,035 8,972 103,007 85,617 7,348 92,965 Investment management — 17,418 17,418 — 9,277 9,277 Total revenues from contracts with customers 555,042 26,390 581,432 290,456 16,625 307,081 Program services — 22,635 22,635 — — — Other 23,714 412 24,126 23,141 771 23,912 Total Other Revenues $ 578,756 $ 49,437 $ 628,193 $ 313,597 $ 17,396 $ 330,993 Six Months Ended June 30, 2018 2017 (dollars in thousands) Markel Ventures Other Total Markel Ventures Other Total Products $ 744,480 $ — $ 744,480 $ 389,572 $ — $ 389,572 Services 181,477 17,896 199,373 165,229 18,534 183,763 Investment management — 34,707 34,707 — 18,636 18,636 Total revenues from contracts with customers 925,957 52,603 978,560 554,801 37,170 591,971 Program services — 43,332 43,332 — — — Other 44,856 877 45,733 45,731 1,207 46,938 Total Other Revenues $ 970,813 $ 96,812 $ 1,067,625 $ 600,532 $ 38,377 $ 638,909
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) June 30, 2018 December 31, 2017 Receivables $ 277,624 $ 176,865 Customer deposits 78,083 61,546

Reinsurance (Tables)

Reinsurance (Tables)	6 Months Ended
	Jun. 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 June 30, 2018 2017 (dollars in thousands) Direct Assumed Ceded Net Premiums Direct Assumed Ceded Net Premiums Underwriting: Written $ 1,182,683 $ 259,960 $ (262,781 ) $ 1,179,862 $ 1,046,833 $ 310,331 $ (219,507 ) $ 1,137,657 Earned 1,070,248 316,718 (239,152 ) 1,147,814 914,249 312,538 (193,213 ) 1,033,574 Program Services: Written 549,630 5,160 (554,046 ) 744 — — — — Earned 470,824 2,286 (472,740 ) 370 — — — — Consolidated: Written 1,732,313 265,120 (816,827 ) 1,180,606 1,046,833 310,331 (219,507 ) 1,137,657 Earned $ 1,541,072 $ 319,004 $ (711,892 ) $ 1,148,184 $ 914,249 $ 312,538 $ (193,213 ) $ 1,033,574 Six Months Ended June 30, 2018 2017 (dollars in thousands) Direct Assumed Ceded Net Premiums Direct Assumed Ceded Net Premiums Underwriting: Written $ 2,222,061 $ 806,273 $ (514,338 ) $ 2,513,996 $ 1,896,317 $ 921,598 $ (420,029 ) $ 2,397,886 Earned 2,108,183 652,208 (461,665 ) 2,298,726 1,777,235 620,107 (381,166 ) 2,016,176 Program Services: Written 1,007,454 8,529 (1,014,571 ) 1,412 — — — — Earned 893,749 3,738 (897,008 ) 479 — — — — Consolidated: Written 3,229,515 814,802 (1,528,909 ) 2,515,408 1,896,317 921,598 (420,029 ) 2,397,886 Earned $ 3,001,932 $ 655,946 $ (1,358,673 ) $ 2,299,205 $ 1,777,235 $ 620,107 $ (381,166 ) $ 2,016,176

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	6 Months Ended
	Jun. 30, 2018
Stockholders' Equity Note [Abstract]
Schedule Of Net Income Per Share	Net income per share was determined by dividing adjusted net income to shareholders by the applicable weighted average shares outstanding. Diluted net income per share is computed by dividing adjusted net income to shareholders by the weighted average number of common shares and dilutive potential common shares outstanding during the period. Quarter Ended June 30, Six Months Ended June 30, (in thousands, except per share amounts) 2018 2017 2018 2017 Net income to shareholders $ 278,231 $ 149,660 $ 213,925 $ 219,529 Adjustment of redeemable noncontrolling interests 363 (5,141 ) 5,414 (20,284 ) Adjusted net income to shareholders $ 278,594 $ 144,519 $ 219,339 $ 199,245 Basic common shares outstanding 13,925 13,977 13,929 13,987 Dilutive potential common shares from conversion of options — 2 — 2 Dilutive potential common shares from conversion of restricted stock units and restricted stock 25 40 24 43 Diluted shares outstanding 13,950 14,019 13,953 14,032 Basic net income per share (1) $ 20.01 $ 10.34 $ 15.75 $ 14.25 Diluted net income per share (1) $ 19.97 $ 10.31 $ 15.72 $ 14.20 (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 (L30

Other Comprehensive Income (Loss) (Tables)	6 Months Ended
	Jun. 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 six months ended June 30, 2018 and 2017 . (dollars in thousands) Unrealized Holding Gains 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 350,349 3,491 — 353,840 Amounts reclassified from accumulated other comprehensive income (9,391 ) — 1,618 (7,773 ) Total other comprehensive income 340,958 3,491 1,618 346,067 June 30, 2017 $ 2,055,888 $ (80,915 ) $ (63,040 ) $ 1,911,933 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 (215,067 ) (5,516 ) 1,232 (219,351 ) Amounts reclassified from accumulated other comprehensive loss (1) (5,077 ) — — (5,077 ) Total other comprehensive income (loss) (2,434,339 ) (3,024 ) 1,232 (2,436,131 ) June 30, 2018 $ 43,634 $ (77,027 ) $ (57,167 ) $ (90,560 ) (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 June 30, Six Months Ended June 30, (dollars in thousands) 2018 2017 2018 2017 Change in net unrealized gains on available-for-sale investments: (1) Net holding gains (losses) arising during the period $ (32,548 ) $ 93,935 $ (60,778 ) $ 168,928 Reclassification adjustments for net gains (losses) included in net income (1,566 ) 136 (1,349 ) (2,396 ) Change in net unrealized gains on available-for-sale investments (34,114 ) 94,071 (62,127 ) 166,532 Change in foreign currency translation adjustments (4,288 ) (466 ) (3,522 ) (503 ) Change in net actuarial pension loss 192 154 328 333 Total $ (38,210 ) $ 93,759 $ (65,321 ) $ 166,362 (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 income, by component. Quarter Ended June 30, Six Months Ended June 30, (dollars in thousands) 2018 2017 2018 2017 Unrealized holding gains on available-for-sale investments: (1) Other-than-temporary impairment losses $ — $ (604 ) $ — $ (3,817 ) Net realized investment gains, excluding other-than-temporary impairment losses 7,457 690 6,426 15,604 Total before taxes 7,457 86 6,426 11,787 Income taxes (1,566 ) 136 (1,349 ) (2,396 ) Reclassification of unrealized holding gains, net of taxes $ 5,891 $ 222 $ 5,077 $ 9,391 Net actuarial pension loss: Underwriting, acquisition and insurance expenses $ (760 ) $ (1,056 ) $ (1,560 ) $ (1,951 ) Income taxes 192 154 328 333 Reclassification of net actuarial pension loss, net of taxes $ (568 ) $ (902 ) $ (1,232 ) $ (1,618 ) (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 Pronounceme31

Recent Accounting Pronouncements (Narrative) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 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) - State National Companies, Inc. [Member] - USD ($) $ in Millions	Nov. 17, 2017	Mar. 31, 2018
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

Acquisitions (Summary Of Net In

Acquisitions (Summary Of Net Intangible Assets Acquired) (Details) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended
		Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization (from the acquisition date through June 30, 2018)	[1]	$ 29,641		$ 18,026	$ 58,464	$ 34,796
Net intangible assets as of June 30, 2018		1,269,520			1,269,520		$ 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 June 30, 2018)					18,478
Net intangible assets as of June 30, 2018		352,022			352,022
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		Jun. 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		1,120
Available-for-sale fixed maturity securities, estimated fair value		$ 4,991,568
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		$ (149,302)
Number of available-for-sale fixed maturity securities positions in a continuous unrealized loss position for one year or longer at period end | securities		275
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		$ 1,442,529
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(73,331)
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		4,813,591	2,246,614
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(147,878)	(37,344)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		1,442,529	1,468,807
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		$ (73,331)	$ (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		Jun. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		$ 10,025,593	$ 9,551,153
Available-for-sale investments, amortized cost		11,974,399	14,379,831
Available-for-sale investments, gross unrealized holding gains		256,561	3,747,008
Available-for-sale investments, gross unrealized holding losses		(149,302)	(57,348)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		10,134,073	9,940,670
Available-for-sale investments, estimated fair value		12,081,658	18,069,491
U.S. Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		184,972	162,378
Available-for-sale fixed maturity investments, gross unrealized holding gains		23	54
Available-for-sale fixed maturity investments, gross unrealized holding losses		(2,797)	(1,819)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		182,198	160,613
U.S. Government-Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		360,192	352,455
Available-for-sale fixed maturity investments, gross unrealized holding gains		5,719	11,883
Available-for-sale fixed maturity investments, gross unrealized holding losses		(5,544)	(818)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		360,367	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		4,379,175	4,381,358
Available-for-sale fixed maturity investments, gross unrealized holding gains		107,644	193,120
Available-for-sale fixed maturity investments, gross unrealized holding losses		(33,843)	(7,916)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		4,452,976	4,566,562
Foreign Governments [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		1,454,335	1,341,628
Available-for-sale fixed maturity investments, gross unrealized holding gains		113,963	150,010
Available-for-sale fixed maturity investments, gross unrealized holding losses		(12,188)	(2,410)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		1,556,110	1,489,228
Commercial Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		1,668,547	1,244,777
Available-for-sale fixed maturity investments, gross unrealized holding gains		668	6,108
Available-for-sale fixed maturity investments, gross unrealized holding losses		(58,319)	(16,559)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		1,610,896	1,234,326
Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		910,466	846,916
Available-for-sale fixed maturity investments, gross unrealized holding gains		2,564	14,115
Available-for-sale fixed maturity investments, gross unrealized holding losses		(20,875)	(4,863)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		892,155	856,168
Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		30,229	34,942
Available-for-sale fixed maturity investments, gross unrealized holding gains		1	8
Available-for-sale fixed maturity investments, gross unrealized holding losses		(455)	(222)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		29,775	34,728
Corporate Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		1,037,677	1,186,699
Available-for-sale fixed maturity investments, gross unrealized holding gains		25,776	51,563
Available-for-sale fixed maturity investments, gross unrealized holding losses		(13,857)	(2,737)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		1,049,596	1,235,525
Total Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity investments, amortized cost		10,025,593	9,551,153
Available-for-sale fixed maturity investments, gross unrealized holding gains		256,358	426,861
Available-for-sale fixed maturity investments, gross unrealized holding losses		(147,878)	(37,344)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale fixed maturity investments, estimated fair value		10,134,073	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		1,948,806	2,161,017
Available-for-sale investments, gross unrealized holding gains		203	26
Available-for-sale investments, gross unrealized holding losses		(1,424)	(69)
Available-for-sale investments, unrealized other-than-temporary impairment losses		0	0
Available-for-sale investments, estimated fair value		$ 1,947,585	$ 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		Jun. 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		$ 3,549,039
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		(75,971)
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		1,442,529
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		(73,331)
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		4,991,568
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		(149,302)
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		102,764	78,756
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(1,397)	(659)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		78,840	78,298
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(1,400)	(1,160)
Available-for-sale fixed maturity securities, estimated fair value		181,604	157,054
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(2,797)	(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		115,354	11,593
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(2,714)	(79)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		94,301	89,194
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(2,830)	(739)
Available-for-sale fixed maturity securities, estimated fair value		209,655	100,787
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(5,544)	(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		855,186	80,654
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(15,141)	(789)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		402,553	404,814
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(18,702)	(7,127)
Available-for-sale fixed maturity securities, estimated fair value		1,257,739	485,468
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(33,843)	(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		328,049	31,752
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(6,714)	(452)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		75,799	63,406
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(5,474)	(1,958)
Available-for-sale fixed maturity securities, estimated fair value		403,848	95,158
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(12,188)	(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		962,732	253,936
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(24,757)	(1,980)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		497,169	481,216
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(33,562)	(14,579)
Available-for-sale fixed maturity securities, estimated fair value		1,459,901	735,152
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(58,319)	(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		590,710	157,508
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(14,181)	(1,345)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		126,355	148,960
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(6,694)	(3,518)
Available-for-sale fixed maturity securities, estimated fair value		717,065	306,468
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(20,875)	(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		14,389	14,263
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(277)	(123)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		14,316	15,165
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(178)	(99)
Available-for-sale fixed maturity securities, estimated fair value		28,705	29,428
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(455)	(222)
Corporate Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		401,878	149,345
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(9,366)	(863)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		153,196	187,754
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(4,491)	(1,874)
Available-for-sale fixed maturity securities, estimated fair value		555,074	337,099
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(13,857)	(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		3,371,062	777,807
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(74,547)	(6,290)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		1,442,529	1,468,807
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer		(73,331)	(31,054)
Available-for-sale fixed maturity securities, estimated fair value		4,813,591	2,246,614
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		(147,878)	(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		177,977	369,104
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months		(1,424)	(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		177,977	369,104
Available-for-sale fixed maturity securities, gross unrealized holding and other-than-temporary impairment losses		$ (1,424)	$ (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	Jun. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Due in one year or less, amortized cost	$ 222,476
Due after one year through five years, amortized cost	1,354,381
Due after five years through ten years, amortized cost	1,845,977
Due after ten years, amortized cost	3,993,517
Amortized cost, sub-total	7,416,351
Total fixed maturities, amortized cost	10,025,593	$ 9,551,153
Due in one year or less, estimated fair value	221,579
Due after one year through five years, estimated fair value	1,366,516
Due after five years through ten years, estimated fair value	1,876,279
Due after ten years, estimated fair value	4,136,873
Estimated fair value, sub-total	7,601,247
Total fixed maturities, estimated fair value	10,134,073	9,940,670
Commercial Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, amortized cost	1,668,547
Total fixed maturities, amortized cost	1,668,547	1,244,777
Fixed maturities, estimated fair value	1,610,896
Total fixed maturities, estimated fair value	1,610,896	1,234,326
Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, amortized cost	910,466
Total fixed maturities, amortized cost	910,466	846,916
Fixed maturities, estimated fair value	892,155
Total fixed maturities, estimated fair value	892,155	856,168
Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, amortized cost	30,229
Total fixed maturities, amortized cost	30,229	34,942
Fixed maturities, estimated fair value	29,775
Total fixed maturities, estimated fair value	$ 29,775	$ 34,728

Investments (Components Of Net

Investments (Components Of Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Municipal bonds (tax-exempt)	$ 20,287	$ 22,758	$ 41,222	$ 45,130
Short-term investments, including overnight deposits	11,915	5,834	22,505	10,783
Dividends on equity securities	20,474	19,017	44,481	39,623
Income (loss) from equity method investments	(1,490)	1,802	288	6,395
Other	97	24	(13)	(205)
Total investment income	109,051	103,524	221,353	208,208
Investment expenses	(3,664)	(4,225)	(7,950)	(8,541)
Net investment income	105,387	99,299	213,403	199,667
Taxable Municipal Bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	18,220	17,793	35,853	35,298
Other Taxable Bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	$ 39,548	$ 36,296	$ 77,017	$ 71,184

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		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Gain (Loss) on Securities [Line Items]
Realized gains		$ 1,052	$ 6,108	$ 2,656	$ 22,116
Realized losses		(8,694)	(1,883)	(11,244)	(5,921)
Other-than-temporary impairment losses		0	(604)	0	(3,817)
Net realized investment gains (losses)		(7,642)		(8,588)
Net realized investment gains (losses)			4,225		16,195
Change in fair value of equity securities sold during the period	[1]	9,631	0	13,897	0
Change in fair value of equity securities held at the end of the period		103,260	13,402	(23,058)	22,297
Change in fair value of equity securities	[1]	112,891	13,402	(9,161)	22,297
Net investment gains (losses)		105,249	17,627	(17,749)	38,492
Change in net unrealized gains on available-for-sale investments included in other comprehensive income		(138,094)	283,918	(282,271)	507,490
Sales Of Fixed Maturities [Member]
Gain (Loss) on Securities [Line Items]
Realized gains		242	554	1,765	757
Realized losses		(7,706)	(412)	(8,198)	(602)
Sales Of Equity Securities [Member]
Gain (Loss) on Securities [Line Items]
Realized gains	[1]	0	1,295	0	16,533
Realized losses	[1]	0	(786)	0	(1,216)
Other [Member]
Gain (Loss) on Securities [Line Items]
Realized gains		810	4,259	891	4,826
Realized losses		(988)	(81)	(3,046)	(286)
Fixed Maturities [Member]
Gain (Loss) on Securities [Line Items]
Change in net unrealized gains on available-for-sale investments included in other comprehensive income		(143,593)	79,413	(281,093)	84,060
Equity Securities [Member]
Gain (Loss) on Securities [Line Items]
Change in net unrealized gains on available-for-sale investments included in other comprehensive income	[1]	0	204,372	0	423,424
Short-Term Investments [Member]
Gain (Loss) on Securities [Line Items]
Change in net unrealized gains on available-for-sale investments included in other comprehensive income		$ 5,499	$ 133	$ (1,178)	$ 6
[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	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
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
Liabilities measured at fair value on a nonrecurring basis	$ 0	$ 0

Fair Value Measurements (Balanc

Fair Value Measurements (Balances Of Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Thousands	Jun. 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	$ 10,134,073	$ 9,940,670
Total equity securities	6,069,245	0
Short-term investments	1,947,585	2,160,974
Total Investments	18,150,903	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	10,134,073	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	182,198	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	360,367	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	4,452,976	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	1,556,110	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	1,610,896	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	892,155	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	29,775	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	1,049,596	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	10,134,073	9,940,670
Total equity securities	6,069,245	5,967,847	[1]
Short-term investments	1,947,585	2,160,974
Total Investments	18,150,903	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	5,949,570	5,799,038	[1]
Short-term investments	1,853,387	2,065,749
Total Investments	7,802,957	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	10,134,073	9,940,670
Total equity securities	0	0	[1]
Short-term investments	94,198	95,225
Total Investments	10,228,271	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	119,675	168,809	[1]
Short-term investments	0	0
Total Investments	119,675	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	182,198	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	182,198	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	360,367	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	360,367	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	4,452,976	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	4,452,976	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	1,556,110	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	1,556,110	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	1,610,896	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	1,610,896	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	892,155	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	892,155	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	29,775	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	29,775	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	1,049,596	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	1,049,596	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	2,101,156	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	1,981,481	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	119,675	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	3,968,089	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	3,968,089	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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Fair Value Disclosures [Abstract]
Equity securities, beginning of period	$ 151,398	$ 178,043	$ 168,809	$ 191,203
Purchases	0	1,250	28,900	7,250
Sales	(6,401)	(1,303)	(34,653)	(26,674)
Total gains (losses) included in net income	(25,322)	5,923	(43,381)	12,134
Transfers into level 3	0	0	0	0
Transfers out of level 3	0	0	0	0
Equity securities, end of period	119,675	183,913	119,675	183,913
Change in fair value of equity securities included in net income relating to assets held at June 30, 2018 and 2017	$ (25,322)	$ 5,923	$ (43,381)	$ 12,134

Segment Reporting Disclosures43

Segment Reporting Disclosures (Summary Of Revenue From The Markel Ventures Segment By Major Product Grouping) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue from External Customer [Line Items]
Other revenues	$ 628,193	$ 330,993	$ 1,067,625	$ 638,909
Markel Ventures [Member]
Revenue from External Customer [Line Items]
Other revenues	578,756	313,597	970,813	600,532
Markel Ventures [Member] | Products [Member]
Revenue from External Customer [Line Items]
Other revenues	472,323	217,175	766,459	414,239
Markel Ventures [Member] | Services [Member]
Revenue from External Customer [Line Items]
Other revenues	$ 106,433	$ 96,422	$ 204,354	$ 186,293

Segment Reporting Disclosures44

Segment Reporting Disclosures (Company's Segment Disclosures) (Details) $ in Thousands		3 Months Ended					6 Months Ended
		Jun. 30, 2018USD ($)		Mar. 31, 2018segment	Jun. 30, 2017USD ($)		Jun. 30, 2018USD ($)		Jun. 30, 2017USD ($)
Segment Reporting Information [Line Items]
Number of reportable ongoing underwriting segments | segment				2
Gross premium volume		$ 1,997,433			$ 1,357,164		$ 4,044,317		$ 2,817,915
Net written premiums		1,180,606			1,137,657		2,515,408		2,397,886
Earned premiums		1,148,184			1,033,574		2,299,205		2,016,176
Losses and loss adjustment expenses, current accident year		(756,674)			(684,585)		(1,479,882)		(1,322,931)
Losses and loss adjustment expenses, prior accident years		157,496			161,607		265,586		188,234
Amortization of policy acquisition costs		(249,250)			(213,474)		(491,155)		(418,022)
Other operating expenses		(202,320)			(187,796)		(384,805)		(356,526)
Underwriting profit (loss)		97,436			109,326		208,949		106,931
Net investment income		105,387			99,299		213,403		199,667
Net investment gains (losses)		105,249			17,627		(17,749)		38,492
Other revenues		628,193			330,993		1,067,625		638,909
Other expenses		(595,343)	[1]		(298,756)	[2]	(997,473)	[3]	(581,389)	[4]
Amortization of intangible assets	[5]	(29,641)			(18,026)		(58,464)		(34,796)
Segment profit (loss)		311,281			240,463		416,291		367,814
Interest expense		(36,702)			(31,797)		(76,761)		(65,199)
Net foreign exchange gains		86,158			879		64,044		974
Income Before Income Taxes		$ 360,737			$ 209,545		$ 403,574		$ 303,589
U.S. GAAP combined ratio	[6]	92.00%			89.00%		91.00%		95.00%
Insurance [Member]
Segment Reporting Information [Line Items]
Gross premium volume		$ 1,233,828			$ 1,109,278		$ 2,327,190		$ 2,022,275
Net written premiums		1,001,126			917,286		1,914,105		1,687,803
Earned premiums		918,194			804,189		1,821,045		1,561,038
Losses and loss adjustment expenses, current accident year		(610,634)			(538,399)		(1,180,661)		(1,031,135)
Losses and loss adjustment expenses, prior accident years		139,485			132,528		258,658		225,414
Amortization of policy acquisition costs		(191,843)			(160,388)		(371,328)		(308,077)
Other operating expenses		(180,928)			(163,480)		(350,899)		(309,877)
Underwriting profit (loss)		74,274			74,450		176,815		137,363
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)		$ 74,274			$ 74,450		$ 176,815		$ 137,363
U.S. GAAP combined ratio	[6]	92.00%			91.00%		90.00%		91.00%
Reinsurance [Member]
Segment Reporting Information [Line Items]
Gross premium volume		$ 208,805			$ 247,902		$ 701,138		$ 795,639
Net written premiums		178,729			220,466		599,787		710,062
Earned premiums		229,613			229,480		477,577		455,117
Losses and loss adjustment expenses, current accident year		(145,992)			(146,186)		(299,173)		(291,796)
Losses and loss adjustment expenses, prior accident years		18,525			28,151		5,454		(43,412)
Amortization of policy acquisition costs		(57,407)			(53,086)		(119,827)		(109,945)
Other operating expenses		(21,178)			(24,181)		(33,308)		(46,350)
Underwriting profit (loss)		23,561			34,178		30,723		(36,386)
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)		$ 23,561			$ 34,178		$ 30,723		$ (36,386)
U.S. GAAP combined ratio	[6]	90.00%			85.00%		94.00%		108.00%
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		105,195			99,239		213,089		199,564
Net investment gains (losses)		105,249			17,627		(17,749)		38,492
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)		210,444			116,866		195,340		238,056
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		192			60		314		103
Net investment gains (losses)		0			0		0		0
Other revenues		578,756			313,597		970,813		600,532
Other expenses		(555,833)	[1]		(271,045)	[2]	(914,138)	[3]	(522,357)	[4]
Amortization of intangible assets	[5]	(10,096)			(6,956)		(20,193)		(13,860)
Segment profit (loss)		13,019			35,656		36,796		64,418
Depreciation expense		(12,800)	[1]		(9,600)	[2]	(25,500)	[3]	(19,000)	[4]
Other [Member]
Segment Reporting Information [Line Items]
Gross premium volume	[7]	554,800			(16)		1,015,989		1
Net written premiums	[7]	751			(95)		1,516		21
Earned premiums	[7]	377			(95)		583		21
Losses and loss adjustment expenses, current accident year	[7]	(48)			0		(48)		0
Losses and loss adjustment expenses, prior accident years	[7]	(514)			928		1,474		6,232
Amortization of policy acquisition costs	[7]	0			0		0		0
Other operating expenses	[7]	(214)			(135)		(598)		(299)
Underwriting profit (loss)	[7]	(399)			698		1,411		5,954
Net investment income	[7]	0			0		0		0
Net investment gains (losses)	[7]	0			0		0		0
Other revenues	[7]	49,437			17,396		96,812		38,377
Other expenses	[7]	(39,510)	[1]		(27,711)	[2]	(83,335)	[3]	(59,032)	[4]
Amortization of intangible assets	[5],[7]	(19,545)			(11,070)		(38,271)		(20,936)
Segment profit (loss)	[7]	$ (10,017)			$ (20,687)		$ (23,383)		$ (35,637)
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 $12.8 million for the quarter ended June 30, 2018.
[2]	Other expenses for the Markel Ventures segment include depreciation expense of $9.6 million for the quarter ended June 30, 2017.
[3]	Other expenses for the Markel Ventures segment include depreciation expense of $25.5 million for the six months ended June 30, 2018.
[4]	Other expenses for the Markel Ventures segment include depreciation expense of $19.0 million for the six months ended June 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 Disclosures45

Segment Reporting Disclosures (Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Assets	$ 33,247,031	$ 32,805,016
Other Operations [Member]
Segment Reporting Information [Line Items]
Assets	4,051,633	3,759,080
Segment Assets [Member]
Segment Reporting Information [Line Items]
Assets	29,195,398	29,045,936
Segment Assets [Member] | Investing [Member]
Segment Reporting Information [Line Items]
Assets	20,303,090	20,317,160
Segment Assets [Member] | Underwriting [Member]
Segment Reporting Information [Line Items]
Assets	6,955,342	6,828,048
Segment Assets [Member] | Markel Ventures [Member]
Segment Reporting Information [Line Items]
Assets	$ 1,936,966	$ 1,900,728

Unpaid Losses And Loss Adjust46

Unpaid Losses And Loss Adjustment Expenses (Narrative) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 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	$ 265,613	184,367
Net reserves for losses and loss adjustment expenses of acquired insurance companies	0	12,702
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	$ 211,900
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		195,700
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 Adjust47

Unpaid Losses And Loss Adjustment Expenses (Reconciliation Of Consolidated Reserves For Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 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	$ (20,554)	$ 57,991	(20,554)	57,991
Adjusted net reserves for losses and loss adjustment expenses, beginning of year			8,944,391	8,166,708
Incurred losses and loss adjustment expenses, current accident year	756,674	684,585	1,479,882	1,322,931
Incurred losses and loss adjustment expenses, prior accident years			(265,613)	(184,367)
Total incurred losses and loss adjustment expenses			1,214,269	1,138,564
Payments, current accident year			195,873	186,138
Payments, prior accident years			1,073,004	829,126
Total payments			1,268,877	1,015,264
Effect of foreign currency rate changes			(101)	2,333
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	8,889,682	8,305,043	8,889,682	8,305,043
Reinsurance recoverable on unpaid losses	4,739,259	2,007,652	4,739,259	2,007,652	$ 4,619,336
Gross reserves for losses and loss adjustment expenses, end of period	$ 13,628,941	$ 10,312,695	$ 13,628,941	$ 10,312,695

Other Revenues (Schedule Of Rev

Other Revenues (Schedule Of Revenues From Contracts With Customers By Type) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Other revenues	$ 628,193	$ 330,993	$ 1,067,625	$ 638,909
Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	581,432	307,081	978,560	591,971
Markel Ventures [Member]
Disaggregation of Revenue [Line Items]
Other revenues	578,756	313,597	970,813	600,532
Markel Ventures [Member] | Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	555,042	290,456	925,957	554,801
Other [Member]
Disaggregation of Revenue [Line Items]
Other revenues	49,437	17,396	96,812	38,377
Other [Member] | Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	26,390	16,625	52,603	37,170
Products [Member] | Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	461,007	204,839	744,480	389,572
Products [Member] | Markel Ventures [Member] | Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	461,007	204,839	744,480	389,572
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	103,007	92,965	199,373	183,763
Services [Member] | Markel Ventures [Member] | Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	94,035	85,617	181,477	165,229
Services [Member] | Other [Member] | Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	8,972	7,348	17,896	18,534
Investment Management [Member] | Revenue From Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	17,418	9,277	34,707	18,636
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	17,418	9,277	34,707	18,636
Program Services [Member]
Disaggregation of Revenue [Line Items]
Other revenues	22,635	0	43,332	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	22,635	0	43,332	0
Other [Member]
Disaggregation of Revenue [Line Items]
Other revenues	24,126	23,912	45,733	46,938
Other [Member] | Markel Ventures [Member]
Disaggregation of Revenue [Line Items]
Other revenues	23,714	23,141	44,856	45,731
Other [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other revenues	$ 412	$ 771	$ 877	$ 1,207

Other Revenues (Schedule Of Rec

Other Revenues (Schedule Of Receivables And Customer Deposits Related To Contracts With Customers) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Other Revenue [Line Items]
Receivables	$ 1,944,751	$ 1,567,453
Contracts With Customers [Member]
Other Revenue [Line Items]
Receivables	277,624	176,865
Customer deposits	$ 78,083	$ 61,546

Reinsurance (Narrative) (Detail

Reinsurance (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Percentage of ceded earned premiums to gross earned premiums	38.00%	16.00%	37.00%	16.00%
Percentage of assumed earned premiums to net earned premiums	28.00%	30.00%	29.00%	31.00%
Reinsurance recoverables	$ 52	$ 109	$ 223.8	$ 208.6
Program Services [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance recoverables	$ 373.3		$ 629.6

Reinsurance (Effect Of Reinsura

Reinsurance (Effect Of Reinsurance And Retrocessional Reinsurance On Premiums Written And Earned) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Effects of Reinsurance [Line Items]
Direct premiums written	$ 1,732,313	$ 1,046,833	$ 3,229,515	$ 1,896,317
Direct premiums earned	1,541,072	914,249	3,001,932	1,777,235
Assumed premiums written	265,120	310,331	814,802	921,598
Assumed premiums earned	319,004	312,538	655,946	620,107
Ceded premiums written	(816,827)	(219,507)	(1,528,909)	(420,029)
Ceded premiums earned	(711,892)	(193,213)	(1,358,673)	(381,166)
Net premiums written	1,180,606	1,137,657	2,515,408	2,397,886
Net premiums earned	1,148,184	1,033,574	2,299,205	2,016,176
Underwriting [Member]
Effects of Reinsurance [Line Items]
Direct premiums written	1,182,683	1,046,833	2,222,061	1,896,317
Direct premiums earned	1,070,248	914,249	2,108,183	1,777,235
Assumed premiums written	259,960	310,331	806,273	921,598
Assumed premiums earned	316,718	312,538	652,208	620,107
Ceded premiums written	(262,781)	(219,507)	(514,338)	(420,029)
Ceded premiums earned	(239,152)	(193,213)	(461,665)	(381,166)
Net premiums written	1,179,862	1,137,657	2,513,996	2,397,886
Net premiums earned	1,147,814	1,033,574	2,298,726	2,016,176
Program Services [Member]
Effects of Reinsurance [Line Items]
Direct premiums written	549,630	0	1,007,454	0
Direct premiums earned	470,824	0	893,749	0
Assumed premiums written	5,160	0	8,529	0
Assumed premiums earned	2,286	0	3,738	0
Ceded premiums written	(554,046)	0	(1,014,571)	0
Ceded premiums earned	(472,740)	0	(897,008)	0
Net premiums written	744	0	1,412	0
Net premiums earned	$ 370	$ 0	$ 479	$ 0

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Effective tax rate	47.00%	27.00%
Provision for deferred U.S. income taxes	$ 102
Effective tax rate attributable to U.K. subsidiaries being taxed as domestic corporations	(25.00%)
Estimated annual effective tax rate	20.00%	27.00%
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		6 Months Ended
	Jan. 31, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds		$ 628,193	$ 330,993	$ 1,067,625	$ 638,909
Fair value of the Company's investment in CROF		6,069,245		6,069,245		$ 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		6,500,000		6,500,000
Other Fund [Member]
Variable Interest Entity [Line Items]
Investment in one of the unconsolidated Funds		26,400		26,400
Markel Diversified Fund [Member]
Variable Interest Entity [Line Items]
Investment in one of the unconsolidated Funds		93,200		93,200		168,200
Total assets of the Markel Diversified Fund		95,200		95,200		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		$ 12,000		$ 12,000
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		581,432	307,081	978,560	591,971
Other [Member]
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds		49,437	17,396	96,812	38,377
Other [Member] | Revenue From Contracts With Customers [Member]
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds		26,390	16,625	52,603	37,170
Investment Management [Member] | Revenue From Contracts With Customers [Member]
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds		17,418	9,277	34,707	18,636
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		$ 17,418	$ 9,277	$ 34,707	$ 18,636

Shareholders' Equity (Narrative

Shareholders' Equity (Narrative) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018USD ($)shares
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	4,950
Stock repurchased value	$ 5.5
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 Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Line Items]
Net income to shareholders		$ 278,231	$ 149,660	$ 213,925	$ 219,529
Adjustment of redeemable noncontrolling interests		363	(5,141)	5,414	(20,284)
Adjusted net income to shareholders		$ 278,594	$ 144,519	$ 219,339	$ 199,245
Basic common shares outstanding		13,925	13,977	13,929	13,987
Diluted shares outstanding		13,950	14,019	13,953	14,032
Basic net income per share	[1]	$ 20.01	$ 10.34	$ 15.75	$ 14.25
Diluted net income per share	[1]	$ 19.97	$ 10.31	$ 15.72	$ 14.20
Stock Options [Member]
Earnings Per Share [Line Items]
Dilutive potential common shares		0	2	0	2
Restricted Stock Units (RSUs) [Member]
Earnings Per Share [Line Items]
Dilutive potential common shares		25	40	24	43
[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 (L56

Other Comprehensive Income (Loss) (Change In Accumulated Other Comprehensive Income (Loss) By Component, Net Of Taxes And Noncontrolling Interest) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018		Jun. 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	(219,351)		353,840
Amounts reclassified from accumulated other comprehensive income (loss)	(5,077)	[1]	(7,773)
Total other comprehensive income (loss)	(2,436,131)		346,067
Accumulated other comprehensive income, ending balance	(90,560)		1,911,933
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	(215,067)		350,349
Amounts reclassified from accumulated other comprehensive income (loss)	(5,077)	[1]	(9,391)
Total other comprehensive income (loss)	(2,434,339)		340,958
Accumulated other comprehensive income, ending balance	43,634		2,055,888
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	(5,516)		3,491
Amounts reclassified from accumulated other comprehensive income (loss)	0	[1]	0
Total other comprehensive income (loss)	(3,024)		3,491
Accumulated other comprehensive income, ending balance	(77,027)		(80,915)
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	1,232		0
Amounts reclassified from accumulated other comprehensive income (loss)	0	[1]	1,618
Total other comprehensive income (loss)	1,232		1,618
Accumulated other comprehensive income, ending balance	$ (57,167)		$ (63,040)
[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 (L57

Other Comprehensive Income (Loss) (Summary Of Tax Expense (Benefit) Of Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Other Comprehensive Income (Loss), Tax [Abstract]
Net holding gains (losses) arising during the period	[1]	$ (32,548)	$ 93,935	$ (60,778)	$ 168,928
Reclassification adjustments for net gains (losses) included in net income	[1]	(1,566)	136	(1,349)	(2,396)
Change in net unrealized gains on available-for-sale investments	[1]	(34,114)	94,071	(62,127)	166,532
Change in foreign currency translation adjustments		(4,288)	(466)	(3,522)	(503)
Change in net actuarial pension loss		192	154	328	333
Total		$ (38,210)	$ 93,759	$ (65,321)	$ 166,362
[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 (L58

Other Comprehensive Income (Loss) (Reclassifications From Accumulated Other Comprehensive Income (Loss) Into Income, By Component) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses		$ 0	$ (604)	$ 0	$ (3,817)
Net realized investment gains, excluding other-than-temporary impairment losses		(7,642)	4,829	(8,588)	20,012
Total before taxes		360,737	209,545	403,574	303,589
Underwriting, acquisition and insurance expenses		(451,570)	(401,270)	(875,960)	(774,548)
Income taxes		(81,150)	(58,118)	(189,581)	(81,122)
Net income		279,587	151,427	213,993	222,467
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	(604)	0	(3,817)
Net realized investment gains, excluding other-than-temporary impairment losses	[1]	7,457	690	6,426	15,604
Total before taxes	[1]	7,457	86	6,426	11,787
Income taxes		(1,566)	136	(1,349)	(2,396)
Net income		5,891	222	5,077	9,391
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		(760)	(1,056)	(1,560)	(1,951)
Income taxes		192	154	328	333
Net income		$ (568)	$ (902)	$ (1,232)	$ (1,618)
[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) $ in Thousands	3 Months Ended
	Jun. 30, 2018USD ($)
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	12,700
Default Interest [Member] | Thomas Yeransian v. Markel Corporation [Member]
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss	$ 11,000