Markel (MKL) 10-Q 25 Oct 17 2017 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Oct. 18, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q3
Entity Registrant Name	MARKEL CORP
Entity Central Index Key	1,096,343
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		13,891,901

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
ASSETS
Fixed maturities (amortized cost of $9,515,082 in 2017 and $9,591,734 in 2016)	$ 9,919,346	$ 9,891,510
Equity securities (cost of $2,713,805 in 2017 and $2,481,448 in 2016)	5,709,946	4,745,841
Short-term investments (estimated fair value approximates cost)	1,995,562	2,336,151
Total Investments	17,624,854	16,973,502
Cash and cash equivalents	2,076,266	1,738,747
Restricted cash and cash equivalents	279,399	346,417
Receivables	1,588,636	1,241,649
Reinsurance recoverable on unpaid losses	2,466,554	2,006,945
Reinsurance recoverable on paid losses	72,487	64,892
Deferred policy acquisition costs	506,294	392,410
Prepaid reinsurance premiums	352,676	299,923
Goodwill	1,425,789	1,142,248
Intangible assets	990,008	722,542
Other assets	1,136,448	946,024
Total Assets	28,519,411	25,875,299
LIABILITIES AND EQUITY
Unpaid losses and loss adjustment expenses	11,443,148	10,115,662
Life and annuity benefits	1,108,947	1,049,654
Unearned premiums	2,750,243	2,263,838
Payables to insurance and reinsurance companies	230,041	231,327
Senior long-term debt and other debt (estimated fair value of $2,686,000 in 2017 and $2,721,000 in 2016)	2,471,419	2,574,529
Other liabilities	1,455,459	1,099,200
Total Liabilities	19,459,257	17,334,210
Redeemable noncontrolling interests	153,310	73,678
Commitments and contingencies
Shareholders' equity:
Common stock	3,379,156	3,368,666
Retained earnings	3,378,524	3,526,395
Accumulated other comprehensive income	2,151,205	1,565,866
Total Shareholders' Equity	8,908,885	8,460,927
Noncontrolling interests	(2,041)	6,484
Total Equity	8,906,844	8,467,411
Total Liabilities and Equity	$ 28,519,411	$ 25,875,299

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Fixed maturities, amortized cost	$ 9,515,082	$ 9,591,734
Equity securities, cost	2,713,805	2,481,448
Senior long-term debt and other debt, estimated fair value	$ 2,686,000	$ 2,721,000

Consolidated Statements Of Inco

Consolidated Statements Of Income (Loss) And Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
OPERATING REVENUES
Earned premiums	$ 1,099,862	$ 974,244	$ 3,116,038	$ 2,882,789
Net investment income	104,489	93,147	304,156	279,437
Other-than-temporary impairment losses	(3,444)	0	(7,261)	(12,080)
Net realized investment gains (losses), excluding other-than-temporary impairment losses	(36,563)	27,416	5,746	77,916
Net realized investment gains (losses)	(40,007)	27,416	(1,515)	65,836
Other revenues	341,804	336,475	980,713	955,339
Total Operating Revenues	1,506,148	1,431,282	4,399,392	4,183,401
OPERATING EXPENSES
Losses and loss adjustment expenses	1,075,432	579,405	2,210,129	1,564,925
Underwriting, acquisition and insurance expenses	395,909	372,521	1,169,175	1,112,789
Amortization of intangible assets	18,654	17,010	53,450	51,474
Other expenses	344,287	309,713	925,984	862,715
Total Operating Expenses	1,834,282	1,278,649	4,358,738	3,591,903
Operating Income (Loss)	(328,134)	152,633	40,654	591,498
Interest expense	31,814	33,152	97,013	97,690
Loss on early extinguishment of debt	0	0	0	44,100
Income (Loss) Before Income Taxes	(359,948)	119,481	(56,359)	449,708
Income tax expense (benefit)	(98,913)	36,060	(17,791)	121,968
Net Income (Loss)	(261,035)	83,421	(38,568)	327,740
Net income (loss) attributable to noncontrolling interests	(1,894)	(375)	1,044	4,777
Net Income (Loss) to Shareholders	(259,141)	83,796	(39,612)	322,963
OTHER COMPREHENSIVE INCOME
Net holding gains arising during the period	227,447	23,098	577,796	411,394
Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period	0	(17)	0	(40)
Reclassification adjustments for net gains included in net income (loss)	(5,207)	(9,758)	(14,598)	(33,308)
Change in net unrealized gains on investments, net of taxes	222,240	13,323	563,198	378,046
Change in foreign currency translation adjustments, net of taxes	16,263	(8,349)	19,770	(6,141)
Change in net actuarial pension loss, net of taxes	773	390	2,391	1,247
Total Other Comprehensive Income	239,276	5,364	585,359	373,152
Comprehensive Income (Loss)	(21,759)	88,785	546,791	700,892
Comprehensive income (loss) attributable to noncontrolling interests	(1,890)	(376)	1,064	4,795
Comprehensive Income (Loss) to Shareholders	$ (19,869)	$ 89,161	$ 545,727	$ 696,097
NET INCOME (LOSS) PER SHARE
Basic (in dollars per share)	$ (18.82)	$ 5.62	$ (4.52)	$ 22.27
Diluted (in dollars per share)	$ (18.82)	$ 5.60	$ (4.52)	$ 22.16

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 [Member]	Noncontrolling Interests [Member]	Redeemable Noncontrolling Interests [Member]
Balance at Dec. 31, 2015		$ 7,840,609	$ 7,834,150	$ 3,342,357	$ 3,137,285	$ 1,354,508	$ 6,459
Balance, shares at Dec. 31, 2015				13,959
Balance, redeemable noncontrolling interests at Dec. 31, 2015								$ 62,958
Net income (loss)	$ 327,740	323,568	322,963		322,963	0	605	4,172
Other comprehensive income	373,152	373,134	373,134		0	373,134	0	18
Comprehensive Income (Loss)	700,892	696,702	696,097				605	4,190
Issuance of common stock		4,531	4,531	$ 4,531	0	0	0	0
Issuance of common stock, shares				48
Repurchase of common stock		(15,503)	(15,503)	$ 0	(15,503)	0	0	0
Repurchase of common stock, shares				(16)
Restricted stock units expensed		18,512	18,512	$ 18,512	0	0	0	0
Restricted stock units expensed, shares				0
Adjustment of redeemable noncontrolling interests		(10,909)	(10,909)	$ 0	(10,909)	0	0	10,909
Adjustment of redeemable noncontrolling interests, shares				0
Purchase of noncontrolling interest		350	350	$ 350	0	0	0	(3,517)
Purchase of noncontrolling interest, shares				0
Other		(17)	55	$ 0	55	0	(72)	(3,880)
Other, shares				0
Balance at Sep. 30, 2016		8,534,275	8,527,283	$ 3,365,750	3,433,891	1,727,642	6,992
Balance, shares at Sep. 30, 2016				13,991
Balance, redeemable noncontrolling interests at Sep. 30, 2016								70,660
Balance at Dec. 31, 2016	8,467,411	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							73,678
Net income (loss)	(38,568)	(40,105)	(39,612)		(39,612)	0	(493)	1,537
Other comprehensive income	585,359	585,339	585,339		0	585,339	0	20
Comprehensive Income (Loss)	546,791	545,234	545,727				(493)	1,557
Issuance of common stock		359	359	$ 359	0	0	0	0
Issuance of common stock, shares				24
Repurchase of common stock		(84,436)	(84,436)	$ 0	(84,436)	0	0	0
Repurchase of common stock, shares				(85)
Restricted stock units expensed		13,389	13,389	$ 13,389	0	0	0	0
Restricted stock units expensed, shares				0
Acquisition of Costa Farms		0	0	$ 0	0	0	0	66,600
Acquisition of Costa Farms, shares				0
Adjustment of redeemable noncontrolling interests		(23,582)	(23,582)	$ 0	(23,582)	0	0	23,582
Adjustment of redeemable noncontrolling interests, shares				0
Purchase of noncontrolling interest		(11,019)	(2,910)	$ (2,910)	0	0	(8,109)	(6,179)
Purchase of noncontrolling interest, shares				0
Other		(512)	(589)	$ (348)	(241)	0	77	(5,928)
Other, shares				0
Balance at Sep. 30, 2017	8,906,844	$ 8,906,844	$ 8,908,885	$ 3,379,156	$ 3,378,524	$ 2,151,205	$ (2,041)
Balance, shares at Sep. 30, 2017				13,894
Balance, redeemable noncontrolling interests at Sep. 30, 2017	$ 153,310							$ 153,310

Condensed Consolidated Statemen

Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
OPERATING ACTIVITIES
Net income (loss)	$ (38,568)	$ 327,740
Adjustments to reconcile net income (loss) to net cash provided by operating activities	637,271	(3,383)
Net Cash Provided By Operating Activities	598,703	324,357
INVESTING ACTIVITIES
Proceeds from sales of fixed maturities and equity securities	360,327	330,110
Proceeds from maturities, calls and prepayments of fixed maturities	948,756	734,010
Cost of fixed maturities and equity securities purchased	(1,162,438)	(1,728,396)
Net change in short-term investments	406,138	(340,742)
Proceeds from sales of equity method investments	2,938	9,325
Additions to property and equipment	(50,099)	(49,565)
Acquisitions, net of cash acquired	(592,045)	(5,762)
Other	(7,802)	(4,618)
Net Cash Used By Investing Activities	(94,225)	(1,055,638)
FINANCING ACTIVITIES
Additions to senior long-term debt and other debt	42,638	553,537
Repayment of senior long-term debt and other debt	(224,516)	(260,086)
Premiums and fees related to early extinguishment of debt	0	(43,691)
Repurchases of common stock	(84,436)	(15,503)
Issuance of common stock	359	4,531
Payment of contingent consideration	(5,018)	(14,219)
Purchase of noncontrolling interests	(18,068)	(3,167)
Distributions to noncontrolling interests	(5,929)	(3,931)
Other	(4,345)	(14,478)
Net Cash Provided (Used) By Financing Activities	(299,315)	202,993
Effect of foreign currency rate changes on cash, cash equivalents, restricted cash and restricted cash equivalents	65,338	(1,484)
Increase (decrease) in cash, cash equivalents, restricted cash and restricted cash equivalents	270,501	(529,772)
Cash, cash equivalents, restricted cash and restricted cash equivalents at beginning of period	2,085,164	3,070,141
CASH, CASH EQUIVALENTS, RESTRICTED CASH AND RESTRICTED CASH EQUIVALENTS AT END OF PERIOD	$ 2,355,665	$ 2,540,369

Basis Of Presentation

Basis Of Presentation	9 Months Ended
	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis Of Presentation	Basis of Presentation Markel Corporation is a diverse financial holding company serving a variety of niche markets. Markel Corporation's principal business markets and underwrites specialty insurance products and programs. Through its wholly-owned subsidiary, Markel Ventures, Inc. (Markel Ventures), Markel Corporation also owns interests in various businesses that operate outside of the specialty insurance marketplace. The consolidated balance sheet as of September 30, 2017 , the related consolidated statements of income (loss) and comprehensive income (loss) for the quarters and nine months ended September 30, 2017 and 2016 , and the consolidated statements of changes in equity and cash flows for the nine months ended September 30, 2017 and 2016 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, 2016 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 2016 Annual Report on Form 10-K for a more complete description of the Company's business and accounting policies.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2017
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements Effective for the year ended December 31, 2016, the Company adopted Financial Accounting Standards Board (FASB) Accounting Standards Update (ASU) No. 2015-09, Financial Services-Insurance (Topic 944): Disclosures about Short-Duration Contracts , which requires significant new disclosures for insurers relating to short-duration insurance contract claims and the unpaid claims liability rollforward for long and short-duration contracts on both an annual and interim basis. Interim period disclosures required by ASU No. 2015-09 include a tabular rollforward and related qualitative information for the liability for unpaid losses and loss adjustment expenses. The interim disclosures were required beginning in the first quarter of 2017 and have been included in note 7 . Effective January 1, 2017, the Company early adopted ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments , which is intended to reduce diversity in practice in how certain transactions are classified in the statement of cash flows. Some of the topics covered by the ASU include the classification of debt prepayment and extinguishment costs, contingent consideration payments made after a business combination and distributions from equity method investees. Upon adoption of this ASU, the Company made an accounting policy election to use the cumulative earnings approach for presenting distributions received from equity method investees, which is consistent with its existing approach. Under this approach, distributions up to the amount of cumulative equity in earnings recognized will be treated as returns on investment and presented in operating activities and those in excess of that amount will be treated as returns of investment and presented in financing activities. The provisions of ASU No. 2016-15 were adopted on a retrospective basis and did not impact the Company's financial position, results of operations or cash flows. Effective January 1, 2017, the Company early adopted ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash. The ASU requires that amounts generally described as restricted cash and restricted cash equivalents be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The Company previously presented changes in restricted cash and restricted cash equivalents on the statements of cash flows as an investing activity. The Company generally describes amounts held in trust or on deposit to support underwriting activities as well as amounts pledged as security for letters of credit as restricted cash or restricted cash equivalents. The provisions of ASU No. 2016-18 were adopted on a retrospective basis and did not impact the Company's financial position, results of operations or total comprehensive income. As a result of adoption of this ASU, investing cash inflows of $61.1 million attributed to the change in restricted cash for the nine months ended September 30, 2016 were reclassified out of investing activities. The Company's statements of cash flows now include restricted cash and restricted cash equivalents in the beginning-of-period and end-of-period total amounts for cash, cash equivalents, restricted cash and restricted cash equivalents. Effective January 1, 2017, the Company early adopted ASU No. 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business. The ASU changes the definition of a business to assist entities with evaluating when a set of transferred assets and activities is a business. The guidance provides a screen to determine when a set of assets and activities is not a business. The provisions of ASU No. 2017-01 were adopted on a prospective basis and did not have an impact on the Company's financial position, results of operations or cash flows. Effective January 1, 2017, the Company early adopted ASU No. 2017-04, Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment . The ASU eliminates Step 2 of the goodwill impairment test, which is performed by estimating the fair value of individual assets and liabilities of the reporting unit to calculate the implied fair value of goodwill. Instead, an entity will record a goodwill impairment charge based on the excess of a reporting unit's carrying value over its estimated fair value, not to exceed the carrying amount of goodwill. The provisions of ASU No. 2017-04 were adopted on a prospective basis and did not have an impact on the Company's financial position, results of operations or cash flows. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) , which creates a new comprehensive revenue recognition standard that will serve as a single source of revenue guidance for all companies in all industries. The guidance applies to all companies that either enter into contracts with customers to transfer goods or services or enter into contracts for the transfer of nonfinancial assets, unless those contracts are within the scope of other standards, such as insurance contracts. ASU No. 2014-09's core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In doing so, companies will need to use more judgment and make more estimates than under the current guidance. These may include identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. Several ASUs have also been issued as amendments to ASU No. 2014-09 and will be evaluated and adopted in conjunction with ASU No. 2014-09. ASU No. 2014-09 becomes effective for the Company during the first quarter of 2018 and will be applied using the modified retrospective method, whereby the cumulative effect of adoption will be recognized as an adjustment to retained earnings at the date of initial application. The adoption of this ASU will not impact the Company's insurance premium revenues or revenues from its investment portfolio, which totaled 77% of consolidated revenues for the year ended December 31, 2016, but will impact certain of the Company's other revenues, which are comprised of a diverse portfolio of contracts across various industries. Based on the Company’s evaluation of the impacted revenue streams, which was completed in the third quarter of 2017, the timing of the recognition of revenue and related costs may change with respect to certain contracts with customers, none of which are expected to have a material effect on the consolidated financial statements. For instance, revenues and costs for certain contracts may be recognized over time rather than when the product or service is delivered, as is the current practice. Additionally, the cumulative effect adjustment to retained earnings at the date of initial application is not expected to be material. The Company also expects to provide additional disclosures in the notes to the consolidated financial statements as required under the new guidance. In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments (Topic 825): Recognition and Measurement of Financial Assets and Financial Liabilities . The ASU significantly changes the income statement impact of equity investments and the recognition of changes in fair value of financial liabilities attributable to an entity's own credit risk when the fair value option is elected. The ASU requires equity instruments that do not result in consolidation and are not accounted for under the equity method to be measured at fair value and to recognize any changes in fair value in net income rather than other comprehensive income. ASU No. 2016-01 becomes effective for the Company during the first quarter of 2018 and will be applied using a cumulative-effect adjustment to retained earnings as of the beginning of the fiscal year of adoption. The provisions related to equity investments without a readily determinable fair value will be applied prospectively to equity investments as of the adoption date. The Company is currently evaluating ASU No. 2016-01 to determine the impact that adopting this standard will have on the consolidated financial statements. Adoption of this ASU is not expected to have a material impact on the Company's financial position, cash flows, or total comprehensive income, but will have a material impact on the Company's results of operations as changes in fair value of equity instruments will be presented in net income rather than other comprehensive income. As of September 30, 2017 , accumulated other comprehensive income included $2.0 billion of net unrealized gains on equity securities, net of taxes. See note 4(e) for details regarding the change in net unrealized gains on equity securities included in other comprehensive income for the quarters and nine months ended September 30, 2017 and 2016. 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 will be subject to this new guidance, totaled $234.3 million at December 31, 2016. The calculation of the lease liability and right-of-use asset requires further analysis of the underlying leases to determine which portions of the underlying lease payments are required to be included in the calculation. 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 the consolidated financial statements. Application of the new expected loss model for measuring impairment losses will not impact the Company's investment portfolio, all of which is considered available-for sale, 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, 2017. These ASU's did not have a material impact on the Company’s financial position, results of operations or cash flows: • ASU No. 2015-11, Inventory (Topic 330): Simplifying the Measurement of Inventory • ASU No. 2016-07, Investments - Equity Method and Joint Ventures (Topic 323): Simplifying the Transition to the Equity Method of Accounting • ASU No. 2016-17, Consolidation (Topic 810): Interests Held through Related Parties That Are under Common Control • ASU No. 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business The following ASU’s relate to topics relevant to the Company's operations and are not yet effective. These ASU's are not expected to 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. 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities • ASU No. 2017-09, Stock Compensation (Topic 718): Scope of Modification Accounting

Acquisitions

Acquisitions	9 Months Ended
	Sep. 30, 2017
Business Combinations [Abstract]
Acquisitions	Acquisitions SureTec Acquisition In April 2017, the Company completed the acquisition of SureTec Financial Corp. (SureTec), a Texas-based privately held surety company primarily offering contract, commercial and court bonds. Results attributable to this acquisition are included in the U.S. Insurance segment. Total consideration for this acquisition was $246.9 million , which included cash consideration of $225.6 million . Total consideration also includes the estimated fair value of contingent consideration the Company expects to pay based on SureTec's earnings, as defined in the merger agreement, for the years 2017 through 2020. The purchase price was allocated to the acquired assets and liabilities of SureTec based on estimated fair values on the acquisition date. The Company recognized goodwill of $70.4 million , which is primarily attributable to synergies that are expected to result upon integration of SureTec into the Company's insurance operations. None of the goodwill recognized is expected to be deductible for income tax purposes. The Company also recognized other intangible assets of $103.0 million , which includes $92.0 million of agent relationships to be amortized over a weighted average period of 15 years . Costa Farms Acquisition In August 2017, the Company acquired 81% of Costa Farms, a Florida-based privately held grower of house and garden plants. Total consideration for the purchase was $424.5 million , which included cash consideration of $395.2 million . Total consideration also includes the estimated fair value of contingent consideration the Company expects to pay based on Costa Farms' earnings, as defined in the purchase agreement, annually through 2021. The purchase price was preliminarily allocated to the acquired assets and liabilities of Costa Farms based on estimated fair values at the acquisition date. The Company preliminarily recognized goodwill of $201.0 million , which is primarily attributable to expected future earnings and cash flow potential of Costa Farms. The majority of the goodwill recognized is expected to be deductible for income tax purposes. The Company also recognized other intangible assets of $192.0 million , which includes $161.0 million of customer relationships and $31.0 million of trade names, which are expected to be amortized over a weighted average period of 17 years and nine years , respectively. The Company also preliminarily recognized redeemable non-controlling interests of $66.6 million . Results attributable to this acquisition are included with the Company's non-insurance operations, which are not included in a reportable segment. The Company has not completed the process of determining the fair value of the assets and liabilities acquired with Costa Farms. These valuations will be completed within the measurement period, which cannot exceed 12 months from the acquisition date. As a result, the fair value amounts recorded for these items are provisional estimates subject to adjustment. Once completed, any adjustments resulting from the valuations may impact the individual amounts recorded for assets acquired and liabilities assumed, the residual goodwill, and the fair value attributable to the noncontrolling equity interest holders. State National Acquisition In July 2017, the Company entered into a definitive merger agreement to acquire State National Companies, Inc. (State National). State National is a leading specialty provider of property and casualty insurance services that includes both fronting services and collateral protection insurance coverage. Under the merger agreement, State National stockholders will receive $21.00 cash for each outstanding share of State National common stock (other than restricted shares that do not vest in connection with the transaction). The aggregate merger consideration, which includes net cash payments for State National stock options and restricted stock, is estimated to be $919 million . The merger was approved by State National's stockholders on October 24, 2017. The transaction remains subject to customary closing conditions, including regulatory approvals, and is expected to close in the fourth quarter of 2017.

Investments

Investments	9 Months Ended
	Sep. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Investments	Investments a) The following tables summarize the Company's available-for-sale investments. Commercial and residential mortgage-backed securities include securities issued by U.S. government-sponsored enterprises and U.S. government agencies. September 30, 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 $ 129,631 $ 64 $ (859 ) $ — $ 128,836 U.S. government-sponsored enterprises 359,492 11,389 (1,240 ) — 369,641 Obligations of states, municipalities and political subdivisions 4,366,775 199,013 (12,789 ) — 4,552,999 Foreign governments 1,395,157 153,766 (3,601 ) — 1,545,322 Commercial mortgage-backed securities 1,195,384 8,353 (12,327 ) — 1,191,410 Residential mortgage-backed securities 799,872 19,269 (3,079 ) — 816,062 Asset-backed securities 20,221 7 (72 ) — 20,156 Corporate bonds 1,248,550 49,349 (2,979 ) — 1,294,920 Total fixed maturities 9,515,082 441,210 (36,946 ) — 9,919,346 Equity securities: Insurance, banks and other financial institutions 910,682 1,103,007 (3,418 ) — 2,010,271 Industrial, consumer and all other 1,803,123 1,908,012 (11,460 ) — 3,699,675 Total equity securities 2,713,805 3,011,019 (14,878 ) — 5,709,946 Short-term investments 1,995,489 87 (14 ) — 1,995,562 Investments, available-for-sale $ 14,224,376 $ 3,452,316 $ (51,838 ) $ — $ 17,624,854 December 31, 2016 (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 $ 259,379 $ 99 $ (894 ) $ — $ 258,584 U.S. government-sponsored enterprises 418,457 9,083 (4,328 ) — 423,212 Obligations of states, municipalities and political subdivisions 4,324,332 145,678 (41,805 ) — 4,428,205 Foreign governments 1,306,324 159,291 (2,153 ) — 1,463,462 Commercial mortgage-backed securities 1,055,947 3,953 (19,544 ) — 1,040,356 Residential mortgage-backed securities 779,503 18,749 (5,048 ) (2,258 ) 790,946 Asset-backed securities 27,494 2 (158 ) — 27,338 Corporate bonds 1,420,298 49,146 (9,364 ) (673 ) 1,459,407 Total fixed maturities 9,591,734 386,001 (83,294 ) (2,931 ) 9,891,510 Equity securities: Insurance, banks and other financial institutions 846,343 857,063 (5,596 ) — 1,697,810 Industrial, consumer and all other 1,635,105 1,421,080 (8,154 ) — 3,048,031 Total equity securities 2,481,448 2,278,143 (13,750 ) — 4,745,841 Short-term investments 2,336,100 57 (6 ) — 2,336,151 Investments, available-for-sale $ 14,409,282 $ 2,664,201 $ (97,050 ) $ (2,931 ) $ 16,973,502 b) The following tables summarize gross unrealized investment losses by the length of time that securities have continuously been in an unrealized loss position. September 30, 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 $ 102,240 $ (585 ) $ 23,609 $ (274 ) $ 125,849 $ (859 ) U.S. government-sponsored enterprises 102,957 (1,237 ) 1,744 (3 ) 104,701 (1,240 ) Obligations of states, municipalities and political subdivisions 525,844 (6,801 ) 143,119 (5,988 ) 668,963 (12,789 ) Foreign governments 135,018 (3,594 ) 7,158 (7 ) 142,176 (3,601 ) Commercial mortgage-backed securities 569,763 (12,071 ) 13,486 (256 ) 583,249 (12,327 ) Residential mortgage-backed securities 106,673 (1,501 ) 70,723 (1,578 ) 177,396 (3,079 ) Asset-backed securities 9,676 (38 ) 6,561 (34 ) 16,237 (72 ) Corporate bonds 266,040 (2,275 ) 69,916 (704 ) 335,956 (2,979 ) Total fixed maturities 1,818,211 (28,102 ) 336,316 (8,844 ) 2,154,527 (36,946 ) Equity securities: Insurance, banks and other financial institutions 23,636 (2,616 ) 1,099 (802 ) 24,735 (3,418 ) Industrial, consumer and all other 60,596 (8,333 ) 11,112 (3,127 ) 71,708 (11,460 ) Total equity securities 84,232 (10,949 ) 12,211 (3,929 ) 96,443 (14,878 ) Short-term investments 75,829 (14 ) — — 75,829 (14 ) Total $ 1,978,272 $ (39,065 ) $ 348,527 $ (12,773 ) $ 2,326,799 $ (51,838 ) At September 30, 2017 , the Company held 465 securities with a total estimated fair value of $2.3 billion and gross unrealized losses of $51.8 million . Of these 465 securities, 105 securities had been in a continuous unrealized loss position for one year or longer and had a total estimated fair value of $348.5 million and gross unrealized losses of $12.8 million . Of these securities, 90 securities were fixed maturities and 15 were equity securities. The Company does not intend to sell or believe it will be required to sell these fixed maturities before recovery of their amortized cost. The Company has the ability and intent to hold these equity securities for a period of time sufficient to allow for the anticipated recovery of their fair value. December 31, 2016 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 $ 122,950 $ (894 ) $ — $ — $ 122,950 $ (894 ) U.S. government-sponsored enterprises 220,333 (4,324 ) 7,618 (4 ) 227,951 (4,328 ) Obligations of states, municipalities and political subdivisions 1,004,947 (37,685 ) 31,723 (4,120 ) 1,036,670 (41,805 ) Foreign governments 68,887 (2,145 ) 5,005 (8 ) 73,892 (2,153 ) Commercial mortgage-backed securities 749,889 (19,091 ) 29,988 (453 ) 779,877 (19,544 ) Residential mortgage-backed securities 181,557 (4,987 ) 79,936 (2,319 ) 261,493 (7,306 ) Asset-backed securities 14,501 (106 ) 5,869 (52 ) 20,370 (158 ) Corporate bonds 494,573 (8,357 ) 93,790 (1,680 ) 588,363 (10,037 ) Total fixed maturities 2,857,637 (77,589 ) 253,929 (8,636 ) 3,111,566 (86,225 ) Equity securities: Insurance, banks and other financial institutions 8,808 (410 ) 37,973 (5,186 ) 46,781 (5,596 ) Industrial, consumer and all other 98,406 (4,772 ) 29,650 (3,382 ) 128,056 (8,154 ) Total equity securities 107,214 (5,182 ) 67,623 (8,568 ) 174,837 (13,750 ) Short-term investments 504,211 (6 ) — — 504,211 (6 ) Total $ 3,469,062 $ (82,777 ) $ 321,552 $ (17,204 ) $ 3,790,614 $ (99,981 ) At December 31, 2016 , the Company held 654 securities with a total estimated fair value of $3.8 billion and gross unrealized losses of $100.0 million . Of these 654 securities, 109 securities had been in a continuous unrealized loss position for one year or longer and had a total estimated fair value of $321.6 million and gross unrealized losses of $17.2 million . Of these securities, 93 securities were fixed maturities and 16 were equity securities. The Company completes a detailed analysis each quarter to assess whether the decline in the fair value of any investment below its cost basis is deemed other-than-temporary. All securities with unrealized losses are reviewed. The Company considers many factors in completing its quarterly review of securities with unrealized losses for other-than-temporary impairment, including the length of time and the extent to which fair value has been below cost and the financial condition and near-term prospects of the issuer. For equity securities, the ability and intent to hold the security for a period of time sufficient to allow for anticipated recovery is considered. For fixed maturities, the Company considers whether it intends to sell the security or if it is more likely than not that it will be required to sell the security before recovery, the implied yield-to-maturity, the credit quality of the issuer and the ability to recover all amounts outstanding when contractually due. For equity securities, a decline in fair value that is considered to be other-than-temporary is recognized in net income (loss) based on the fair value of the security at the time of assessment, resulting in a new cost basis for the security. For fixed maturities where the Company intends to sell the security or it is more likely than not that the Company will be required to sell the security before recovery of its amortized cost, a decline in fair value is considered to be other-than-temporary and is recognized in net income (loss) 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 (loss), resulting in a new cost basis for the security. Any remaining decline in fair value represents the non-credit portion of the other-than-temporary impairment, which is recognized in other comprehensive income. The discount rate used to calculate the estimated present value of the cash flows expected to be collected is the effective interest rate implicit for the security at the date of purchase. When assessing whether it intends to sell a fixed maturity or if it is likely to be required to sell a fixed maturity before recovery of its amortized cost, the Company evaluates facts and circumstances including decisions to reposition the investment portfolio, potential sales of investments to meet cash flow needs and, ultimately, current market prices. c) The amortized cost and estimated fair value of fixed maturities at September 30, 2017 are shown below by contractual maturity. (dollars in thousands) Amortized Cost Estimated Fair Value Due in one year or less $ 375,471 $ 377,672 Due after one year through five years 1,232,430 1,276,160 Due after five years through ten years 1,567,938 1,646,296 Due after ten years 4,323,766 4,591,590 7,499,605 7,891,718 Commercial mortgage-backed securities 1,195,384 1,191,410 Residential mortgage-backed securities 799,872 816,062 Asset-backed securities 20,221 20,156 Total fixed maturities $ 9,515,082 $ 9,919,346 d) The following table presents the components of net investment income. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2017 2016 2017 2016 Interest: Municipal bonds (tax-exempt) $ 21,486 $ 22,136 $ 66,616 $ 66,621 Municipal bonds (taxable) 17,732 16,710 53,030 48,820 Other taxable bonds 36,337 36,697 107,521 108,975 Short-term investments, including overnight deposits 7,779 2,878 18,562 7,823 Dividends on equity securities 21,467 17,308 61,090 51,718 Income from equity method investments 4,239 1,232 10,634 4,900 Other (315 ) (60 ) (520 ) 2,614 108,725 96,901 316,933 291,471 Investment expenses (4,236 ) (3,754 ) (12,777 ) (12,034 ) Net investment income $ 104,489 $ 93,147 $ 304,156 $ 279,437 e) The following table presents net realized investment gains (losses) and the change in net unrealized gains on investments. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2017 2016 2017 2016 Realized gains: Sales of fixed maturities $ 3,426 $ 3,698 $ 4,189 $ 4,658 Sales of equity securities 9,276 18,418 25,806 63,931 Other 1,129 423 5,979 1,117 Total realized gains 13,831 22,539 35,974 69,706 Realized losses: Sales of fixed maturities (663 ) (60 ) (1,271 ) (608 ) Sales of equity securities (578 ) (4,187 ) (1,791 ) (6,672 ) Other-than-temporary impairments (3,444 ) — (7,261 ) (12,080 ) Other (776 ) (55 ) (1,086 ) (2,972 ) Total realized losses (5,461 ) (4,302 ) (11,409 ) (22,332 ) Gains (losses) on securities measured at fair value through net income (loss) (48,377 ) 9,179 (26,080 ) 18,462 Net realized investment gains (losses) $ (40,007 ) $ 27,416 $ (1,515 ) $ 65,836 Change in net unrealized gains on investments included in other comprehensive income: Fixed maturities $ 20,428 $ (53,962 ) $ 104,488 $ 399,020 Equity securities 308,324 80,285 731,748 220,029 Short-term investments 16 58 22 23 Net increase $ 328,768 $ 26,381 $ 836,258 $ 619,072

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements FASB ASC 820-10, Fair Value Measurements and Disclosures, establishes a three-level hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The fair value hierarchy gives the highest priority to quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3). If the inputs used to measure the assets or liabilities fall within different levels of the hierarchy, the classification is based on the lowest level input that is significant to the fair value measurement of the asset or liability. Classification of assets and liabilities within the hierarchy considers the markets in which the assets and liabilities are traded and the reliability and transparency of the assumptions used to determine fair value. The hierarchy requires the use of observable market data when available. The levels of the hierarchy are defined as follows: Level 1 – Inputs to the valuation methodology are quoted prices (unadjusted) for identical assets or liabilities traded in active markets. Level 2 – Inputs to the valuation methodology include quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability and market-corroborated inputs. Level 3 – Inputs to the valuation methodology are unobservable for the asset or liability and are significant to the fair value measurement. In accordance with FASB ASC 820, the Company determines fair value based on the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. In determining fair value, the Company uses various methods, including the market, income and cost approaches. The Company uses valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs. The following section describes the valuation methodologies used by the Company to measure assets and liabilities at fair value, including an indication of the level within the fair value hierarchy in which each asset or liability is generally classified. Investments available-for-sale. Investments available-for-sale are recorded at fair value on a recurring basis and include fixed maturities, equity securities and short-term investments. Short-term investments include certificates of deposit, commercial paper, discount notes and treasury bills with original maturities of one year or less. Fair value for investments available-for-sale is determined by the Company after considering various sources of information, including information provided by a third party pricing service. The pricing service provides prices for substantially all of the Company's fixed maturities and equity securities. In determining fair value, the Company generally does not adjust the prices obtained from the pricing service. The Company obtains an understanding of the pricing service's valuation methodologies and related inputs, which include, but are not limited to, reported trades, benchmark yields, issuer spreads, bids, offers, duration, credit ratings, estimated cash flows and prepayment speeds. The Company validates prices provided by the pricing service by reviewing prices from other pricing sources and analyzing pricing data in certain instances. The Company has evaluated the various types of securities in its investment portfolio to determine an appropriate fair value hierarchy level based upon trading activity and the observability of market inputs. Level 1 investments include those traded on an active exchange, such as the New York Stock Exchange. Level 2 investments include U.S. Treasury securities, 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 12 , which are not traded on an active exchange and are valued using unobservable inputs. Fair value for investments available-for-sale is measured based upon quoted prices in active markets, if available. Due to variations in trading volumes and the lack of quoted market prices, fixed maturities are classified as Level 2 investments. The fair value of fixed maturities is normally derived through recent reported trades for identical or similar securities, making adjustments through the reporting date based upon available market observable data described above. If there are no recent reported trades, the fair value of fixed maturities may be derived through the use of matrix pricing or model processes, where future cash flow expectations are developed based upon collateral performance and discounted at an estimated market rate. Significant inputs used to determine the fair value of obligations of states, municipalities and political subdivisions, corporate bonds and obligations of foreign governments include reported trades, benchmark yields, issuer spreads, bids, offers, credit information and estimated cash flows. Significant inputs used to determine the fair value of commercial mortgage-backed securities, residential mortgage-backed securities and asset-backed securities include the type of underlying assets, benchmark yields, prepayment speeds, collateral information, tranche type and volatility, estimated cash flows, credit information, default rates, recovery rates, issuer spreads and the year of issue. 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 net realized gains (losses) in net income (loss). 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. Significant unobservable inputs used in the valuation of these investments include an adjustment to include the fair value of the equity that was issued by one of the ILS Funds in exchange for notes receivable, rather than cash, which is excluded from NAV. 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. September 30, 2017 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments available-for-sale: Fixed maturities: U.S. Treasury securities $ — $ 128,836 $ — $ 128,836 U.S. government-sponsored enterprises — 369,641 — 369,641 Obligations of states, municipalities and political subdivisions — 4,552,999 — 4,552,999 Foreign governments — 1,545,322 — 1,545,322 Commercial mortgage-backed securities — 1,191,410 — 1,191,410 Residential mortgage-backed securities — 816,062 — 816,062 Asset-backed securities — 20,156 — 20,156 Corporate bonds — 1,294,920 — 1,294,920 Total fixed maturities — 9,919,346 — 9,919,346 Equity securities: Insurance, banks and other financial institutions 1,828,997 — 181,274 2,010,271 Industrial, consumer and all other 3,699,675 — — 3,699,675 Total equity securities 5,528,672 — 181,274 5,709,946 Short-term investments 1,895,262 100,300 — 1,995,562 Total investments available-for-sale $ 7,423,934 $ 10,019,646 $ 181,274 $ 17,624,854 December 31, 2016 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments available-for-sale: Fixed maturities: U.S. Treasury securities $ — $ 258,584 $ — $ 258,584 U.S. government-sponsored enterprises — 423,212 — 423,212 Obligations of states, municipalities and political subdivisions — 4,428,205 — 4,428,205 Foreign governments — 1,463,462 — 1,463,462 Commercial mortgage-backed securities — 1,040,356 — 1,040,356 Residential mortgage-backed securities — 790,946 — 790,946 Asset-backed securities — 27,338 — 27,338 Corporate bonds — 1,459,407 — 1,459,407 Total fixed maturities — 9,891,510 — 9,891,510 Equity securities: Insurance, banks and other financial institutions 1,506,607 — 191,203 1,697,810 Industrial, consumer and all other 3,048,031 — — 3,048,031 Total equity securities 4,554,638 — 191,203 4,745,841 Short-term investments 2,255,898 80,253 — 2,336,151 Total investments available-for-sale $ 6,810,536 $ 9,971,763 $ 191,203 $ 16,973,502 The following table summarizes changes in Level 3 investments measured at fair value on a recurring basis. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2017 2016 2017 2016 Equity securities, beginning of period $ 183,913 $ 183,523 $ 191,203 $ — Purchases 49,000 — 56,250 195,250 Sales — — (26,674 ) (25,000 ) Total gains (losses) included in: Net income (loss) (51,639 ) 6,881 (39,505 ) 20,154 Other comprehensive income — — — — Transfers into Level 3 — — — — Transfers out of Level 3 — — — — Equity securities, end of period $ 181,274 $ 190,404 $ 181,274 $ 190,404 Net unrealized gains (losses) included in net income (loss) relating to assets held at September 30, 2017 and 2016 (1) $ (51,639 ) $ 6,881 $ (39,505 ) $ 20,154 (1) Included in net realized investment gains (losses) in the consolidated statements of income (loss) and comprehensive income (loss). Net realized investment losses for the quarter and nine months ended September 30, 2017 included losses of $51.6 million and $39.5 million , respectively, on the Company's investment in the ILS Funds as a result of a decrease in the NAV of the ILS Funds during the third quarter. There were no transfers into or out of Level 1 and Level 2 during the quarter and nine months ended September 30, 2017 and 2016 . Except as disclosed in note 3, the Company did not have any assets or liabilities measured at fair value on a non-recurring basis during the nine months ended September 30, 2017 and 2016 .

Segment Reporting Disclosures

Segment Reporting Disclosures	9 Months Ended
	Sep. 30, 2017
Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract]
Segment Reporting Disclosures	Segment Reporting Disclosures The Company monitors and reports its ongoing underwriting operations in the following three segments: U.S. Insurance, International Insurance and Reinsurance. In determining how to aggregate and monitor its underwriting results, the Company considers many factors, including the geographic location and regulatory environment of the insurance entity underwriting the risk, the nature of the insurance product sold, the type of account written and the type of customer served. The U.S. Insurance segment includes all direct business and facultative placements written by the Company's insurance subsidiaries domiciled in the United States. The International Insurance segment includes all direct business and facultative placements written by the Company's insurance subsidiaries domiciled outside of the United States, including the Company's syndicate at Lloyd's of London. The Reinsurance segment includes all treaty reinsurance written across the Company. Results for lines of business discontinued prior to, or in conjunction with, acquisitions, including the results attributable to the run-off of life and annuity reinsurance business, are reported in the Other Insurance (Discontinued Lines) segment. All investing activities related to the Company's insurance operations are included in the Investing segment. The Company's non-insurance operations include the Company's Markel Ventures operations, which primarily consist of controlling interests in various businesses that operate outside of the specialty insurance marketplace. The Company's non-insurance operations also 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. For purposes of segment reporting, the Company's non-insurance operations are not considered to be a reportable segment. Segment profit for the Investing segment is measured by net investment income and net realized investment gains. Segment profit or loss for each of the Company's underwriting segments is measured by underwriting profit or loss. The property and casualty insurance industry commonly defines underwriting profit or loss as earned premiums net of losses and loss adjustment expenses and underwriting, acquisition and insurance expenses. Underwriting profit or loss does not replace operating income or net income computed in accordance with U.S. GAAP as a measure of profitability. Underwriting profit or loss provides a basis for management to evaluate the Company's underwriting performance. Segment profit or loss for the Company's underwriting segments also includes other revenues and other expenses, primarily related to the run-off of managing general agent operations that were discontinued in conjunction with acquisitions. Other revenues and other expenses in the Other Insurance (Discontinued Lines) segment are comprised of the results attributable to the run-off of life and annuity reinsurance business. For management reporting purposes, the Company allocates assets to its underwriting, investing and non-insurance operations. Underwriting assets are all assets not specifically allocated to the Investing segment or to the Company's non-insurance operations. Underwriting and investing assets are not allocated to the U.S. Insurance, International Insurance, Reinsurance or Other Insurance (Discontinued Lines) segments since the Company does not manage its assets by underwriting segment. The Company does not allocate capital expenditures for long-lived assets to any of its underwriting segments for management reporting purposes. a) The following tables summarize the Company's segment disclosures. Quarter Ended September 30, 2017 (dollars in thousands) U.S. Insurance International Insurance Reinsurance Other Insurance (Discontinued Lines) Investing Consolidated Gross premium volume $ 778,323 $ 319,914 $ 230,077 $ (186 ) $ — $ 1,328,128 Net written premiums 653,970 254,326 189,636 (178 ) — 1,097,754 Earned premiums 600,294 240,145 259,601 (178 ) — 1,099,862 Losses and loss adjustment expenses: Current accident year (533,662 ) (274,581 ) (418,297 ) — — (1,226,540 ) Prior accident years 87,613 40,740 21,164 1,591 — 151,108 Amortization of policy acquisition costs (134,243 ) (43,140 ) (53,440 ) — — (230,823 ) Other operating expenses (90,350 ) (50,771 ) (23,885 ) (80 ) — (165,086 ) Underwriting profit (loss) (70,348 ) (87,607 ) (214,857 ) 1,333 — (371,479 ) Net investment income — — — — 104,489 104,489 Net realized investment losses — — — — (40,007 ) (40,007 ) Other revenues (insurance) 979 658 — 428 — 2,065 Other expenses (insurance) (162 ) (1,035 ) — (6,776 ) — (7,973 ) Segment profit (loss) $ (69,531 ) $ (87,984 ) $ (214,857 ) $ (5,015 ) $ 64,482 $ (312,905 ) Other revenues (non-insurance) 339,739 Other expenses (non-insurance) (336,314 ) Amortization of intangible assets (18,654 ) Interest expense (31,814 ) Loss before income taxes $ (359,948 ) U.S. GAAP combined ratio (1) 112 % 136 % 183 % NM (2) 134 % Quarter Ended September 30, 2016 (dollars in thousands) U.S. Insurance International Insurance Reinsurance Other Insurance (Discontinued Lines) Investing Consolidated Gross premium volume $ 663,196 $ 269,093 $ 196,948 $ 536 $ — $ 1,129,773 Net written premiums 562,215 209,656 157,043 469 — 929,383 Earned premiums 548,792 218,968 206,018 466 — 974,244 Losses and loss adjustment expenses: Current accident year (370,435 ) (159,812 ) (129,875 ) — — (660,122 ) Prior accident years 21,471 42,705 19,135 (2,594 ) — 80,717 Amortization of policy acquisition costs (115,504 ) (38,075 ) (48,294 ) — — (201,873 ) Other operating expenses (91,124 ) (44,716 ) (34,196 ) (612 ) — (170,648 ) Underwriting profit (loss) (6,800 ) 19,070 12,788 (2,740 ) — 22,318 Net investment income — — — — 93,147 93,147 Net realized investment gains — — — — 27,416 27,416 Other revenues (insurance) 1,285 419 — 466 — 2,170 Other expenses (insurance) (670 ) (677 ) — (4,232 ) — (5,579 ) Segment profit (loss) $ (6,185 ) $ 18,812 $ 12,788 $ (6,506 ) $ 120,563 $ 139,472 Other revenues (non-insurance) 334,305 Other expenses (non-insurance) (304,134 ) Amortization of intangible assets (17,010 ) Interest expense (33,152 ) Income before income taxes $ 119,481 U.S. GAAP combined ratio (1) 101 % 91 % 94 % NM (2) 98 % (1) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (2) NM – Ratio is not meaningful. Nine Months Ended September 30, 2017 (dollars in thousands) U.S. Insurance International Insurance Reinsurance Other Insurance (Discontinued Lines) Investing Consolidated Gross premium volume $ 2,171,481 $ 949,031 $ 1,025,716 $ (185 ) $ — $ 4,146,043 Net written premiums 1,829,528 766,571 899,698 (157 ) — 3,495,640 Earned premiums 1,727,871 673,606 714,718 (157 ) — 3,116,038 Losses and loss adjustment expenses: Current accident year (1,259,777 ) (579,601 ) (710,093 ) — — (2,549,471 ) Prior accident years 207,499 146,268 (22,248 ) 7,823 — 339,342 Amortization of policy acquisition costs (371,241 ) (114,219 ) (163,385 ) — — (648,845 ) Other operating expenses (292,409 ) (157,249 ) (70,293 ) (379 ) — (520,330 ) Underwriting profit (loss) 11,943 (31,195 ) (251,301 ) 7,287 — (263,266 ) Net investment income — — — — 304,156 304,156 Net realized investment losses — — — — (1,515 ) (1,515 ) Other revenues (insurance) 2,685 5,227 417 1,634 — 9,963 Other expenses (insurance) (1,005 ) (6,109 ) — (21,009 ) — (28,123 ) Segment profit (loss) $ 13,623 $ (32,077 ) $ (250,884 ) $ (12,088 ) $ 302,641 $ 21,215 Other revenues (non-insurance) 970,750 Other expenses (non-insurance) (897,861 ) Amortization of intangible assets (53,450 ) Interest expense (97,013 ) Loss before income taxes $ (56,359 ) U.S. GAAP combined ratio (1) 99 % 105 % 135 % NM (2) 108 % Nine Months Ended September 30, 2016 (dollars in thousands) U.S. Insurance International Insurance Reinsurance Other Insurance (Discontinued Lines) Investing Consolidated Gross premium volume $ 2,000,454 $ 879,078 $ 920,038 $ 515 $ — $ 3,800,085 Net written premiums 1,694,193 680,691 786,450 555 — 3,161,889 Earned premiums 1,614,588 637,365 630,151 685 — 2,882,789 Losses and loss adjustment expenses: Current accident year (1,038,860 ) (451,741 ) (413,044 ) — — (1,903,645 ) Prior accident years 126,457 111,359 90,140 10,764 — 338,720 Amortization of policy acquisition costs (336,093 ) (105,220 ) (138,895 ) — — (580,208 ) Other operating expenses (280,913 ) (162,739 ) (88,243 ) (686 ) — (532,581 ) Underwriting profit 85,179 29,024 80,109 10,763 — 205,075 Net investment income — — — — 279,437 279,437 Net realized investment gains — — — — 65,836 65,836 Other revenues (insurance) 3,662 5,149 — 1,407 — 10,218 Other expenses (insurance) (2,078 ) (4,368 ) — (19,432 ) — (25,878 ) Segment profit (loss) $ 86,763 $ 29,805 $ 80,109 $ (7,262 ) $ 345,273 $ 534,688 Other revenues (non-insurance) 945,121 Other expenses (non-insurance) (836,837 ) Amortization of intangible assets (51,474 ) Interest expense (97,690 ) Loss on early extinguishment of debt (44,100 ) Income before income taxes $ 449,708 U.S. GAAP combined ratio (1) 95 % 95 % 87 % NM (2) 93 % (1) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (2) NM – Ratio is not meaningful. b) The following table reconciles segment assets to the Company's consolidated balance sheets. (dollars in thousands) September 30, 2017 December 31, 2016 Segment assets: Investing $ 19,884,334 $ 19,029,584 Underwriting 6,528,093 5,397,696 Total segment assets 26,412,427 24,427,280 Non-insurance operations 2,106,984 1,448,019 Total assets $ 28,519,411 $ 25,875,299

Unpaid Losses And Loss Adjustme

Unpaid Losses And Loss Adjustment Expenses	9 Months Ended
	Sep. 30, 2017
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Unpaid Losses And Loss Adjustment Expenses	Unpaid Losses and Loss Adjustment Expenses The following table presents a reconciliation of consolidated beginning and ending reserves for losses and loss adjustment expenses. Nine Months Ended September 30, (dollars in thousands) 2017 2016 Net reserves for losses and loss adjustment expenses, beginning of year $ 8,108,717 $ 8,235,288 Foreign currency movements 158,360 (56,741 ) Adjusted net reserves for losses and loss adjustment expenses, beginning of year 8,267,077 8,178,547 Incurred losses and loss adjustment expenses: Current accident year 2,549,471 1,903,645 Prior accident years (335,494 ) (327,064 ) Total incurred losses and loss adjustment expenses 2,213,977 1,576,581 Payments: Current accident year 342,055 319,049 Prior accident years 1,185,689 1,219,755 Total payments 1,527,744 1,538,804 Effect of foreign currency rate changes 10,582 38 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 8,976,594 8,216,362 Reinsurance recoverable on unpaid losses 2,466,554 2,041,928 Gross reserves for losses and loss adjustment expenses, end of period $ 11,443,148 $ 10,258,290 In March 2015, the Company completed a retroactive reinsurance transaction to cede to a third party a portfolio of policies primarily comprised of liabilities arising from asbestos and environmental exposures that originated before 1992. Effective March 31, 2017, the related reserves, which totaled $69.1 million , were formally transferred to the third party by way of a Part VII transfer pursuant to the Financial Services and Markets Act 2000 of the United Kingdom. The Part VII transfer eliminates the uncertainty regarding the potential for adverse development of estimated ultimate liabilities on the underlying policies. Upon completion of the transfer in the first quarter of 2017, the Company recognized a previously deferred gain of $3.9 million , which is included in losses and loss adjustment expenses on the consolidated statement of income (loss) and comprehensive income (loss) for the nine months ended September 30, 2017 . This amount is excluded from the prior years' incurred losses and loss adjustment expenses for the nine months ended September 30, 2017 in the above table as the deferred gain was included in other liabilities on the consolidated balance sheet as of December 31, 2016, rather than unpaid losses and loss adjustment expenses. For the nine months ended September 30, 2016 , incurred losses and loss adjustment expenses in the above table exclude $11.7 million of favorable development on prior years loss reserves included in losses and loss adjustment expenses on the consolidated statement of income (loss) and comprehensive income (loss) related to the commutation of a property and casualty deposit contract, for which the underlying deposit liability was included in other liabilities on the consolidated balance sheet as of December 31, 2015, rather than unpaid losses and loss adjustment expenses. For the nine months ended September 30, 2017 , the Company recorded net reserves for losses and loss adjustment expenses of $12.7 million as a result of the acquisition of SureTec. Underwriting results for the nine months ended September 30, 2017 included $503.0 million of underwriting loss from Hurricanes Harvey, Irma and Maria as well as the earthquakes in Mexico (2017 Catastrophes). The underwriting loss on the 2017 Catastrophes was comprised of $521.2 million of estimated net losses and loss adjustment expenses and $18.2 million of net assumed reinstatement premiums. The estimated net losses and loss adjustment expenses on the 2017 Catastrophes for the nine months ended September 30, 2017 were net of estimated reinsurance recoverables of $464.4 million . For the nine months ended September 30, 2017 , incurred losses and loss adjustment expenses included $335.5 million of favorable development on prior years' loss reserves, which included $302.5 million of loss reserve redundancies on the Company's general liability, personal lines business and worker's compensation product lines within the U.S. Insurance segment, professional liability, general liability and marine and energy product lines within the International Insurance segment, and property and whole account product lines within the Reinsurance segment. Redundancies for the nine months ended September 30, 2017 were partially offset by $85.0 million of adverse development resulting from a decrease in the discount rate, known as the Ogden Rate, used to calculate lump sum awards in United Kingdom (U.K.) bodily injury cases. Effective March 20, 2017, the Ogden Rate decreased from plus 2.5% to minus 0.75% , which represents the first rate change since 2001. The effect of the rate change is most impactful to the Company's U.K. auto casualty exposures through reinsurance contracts written in the Reinsurance segment. In late 2014, the Company ceased writing auto reinsurance in the U.K. The reduction in the Ogden Rate increased the expected claims payments on these exposures, and management increased loss reserves accordingly. The Company's estimate of the ultimate cost of settling these claims is based on many factors, and is subject to increase or decrease as the effect of changes in these factors becomes known over time. For the nine months ended September 30, 2016 , incurred losses and loss adjustment expenses included $327.1 million of favorable development on prior years' loss reserves, which included $263.3 million of loss reserve redundancies on the Company's general liability, property and worker's compensation product lines within the U.S. Insurance segment, professional liability and marine and energy product lines within the International Insurance segment, and property and worker's compensation product lines within the Reinsurance segment. Redundancies for the nine months ended September 30, 2016 were partially offset by $71.4 million of adverse development on our specified medical and medical malpractice product lines within the U.S. Insurance segment.

Senior Long-Term Debt And Other

Senior Long-Term Debt And Other Debt	9 Months Ended
	Sep. 30, 2017
Debt Disclosure [Abstract]
Senior Long-Term Debt And Other Debt	Senior Long-Term Debt and Other Debt In April 2017, the Company repaid its 7.20% unsecured senior notes due April 14, 2017 ( $90.6 million principal outstanding at December 31, 2016). Also in 2017, the Company repaid $84.3 million of debt assumed in connection with acquisitions.

Other Revenues And Other Expens

Other Revenues And Other Expenses	9 Months Ended
	Sep. 30, 2017
Other Income and Expenses [Abstract]
Other Revenues And Other Expenses	Other Revenues and Other Expenses The following tables summarize the components of other revenues and other expenses. Quarter Ended September 30, 2017 2016 (dollars in thousands) Other Revenues Other Expenses Other Revenues Other Expenses Insurance: Managing general agent operations $ 1,637 $ 1,134 $ 1,704 $ 1,347 Life and annuity 428 6,776 466 4,232 Other — 63 — — 2,065 7,973 2,170 5,579 Non-Insurance: Markel Ventures: Manufacturing 195,535 173,174 203,909 171,595 Markel Ventures: Non-Manufacturing 137,213 145,434 117,433 115,529 Investment management 1,248 11,552 8,297 10,385 Other 5,743 6,154 4,666 6,625 339,739 336,314 334,305 304,134 Total $ 341,804 $ 344,287 $ 336,475 $ 309,713 Nine Months Ended September 30, 2017 2016 (dollars in thousands) Other Revenues Other Expenses Other Revenues Other Expenses Insurance: Managing general agent operations $ 7,912 $ 4,480 $ 8,811 $ 6,446 Life and annuity 1,634 21,009 1,407 19,432 Other 417 2,634 — — 9,963 28,123 10,218 25,878 Non-Insurance: Markel Ventures: Manufacturing 556,691 483,724 589,752 491,188 Markel Ventures: Non-Manufacturing 376,589 357,549 315,863 295,647 Investment management 19,884 37,682 22,820 31,151 Other 17,586 18,906 16,686 18,851 970,750 897,861 945,121 836,837 Total $ 980,713 $ 925,984 $ 955,339 $ 862,715 The Company's Markel Ventures operations primarily consist of controlling interests in various businesses that operate outside of the specialty insurance marketplace and are viewed by management as separate and distinct from the Company's insurance operations. While each of the businesses is operated independently from one another, management aggregates financial results into two industry groups: manufacturing and non-manufacturing.

Reinsurance

Reinsurance	9 Months Ended
	Sep. 30, 2017
Reinsurance Disclosures [Abstract]
Reinsurance	Reinsurance The following tables summarize the effect of reinsurance and retrocessional reinsurance on premiums written and earned. Quarter Ended September 30, 2017 2016 (dollars in thousands) Written Earned Written Earned Direct $ 1,035,705 $ 966,735 $ 888,009 $ 883,687 Assumed 292,423 356,529 241,764 292,951 Ceded (230,374 ) (223,402 ) (200,390 ) (202,394 ) Net premiums $ 1,097,754 $ 1,099,862 $ 929,383 $ 974,244 Nine Months Ended September 30, 2017 2016 (dollars in thousands) Written Earned Written Earned Direct $ 2,932,022 $ 2,743,970 $ 2,724,341 $ 2,617,074 Assumed 1,214,021 976,636 1,075,744 878,882 Ceded (650,403 ) (604,568 ) (638,196 ) (613,167 ) Net premiums $ 3,495,640 $ 3,116,038 $ 3,161,889 $ 2,882,789 The percentage of ceded earned premiums to gross earned premiums was 17% and 16% for the quarter and nine months ended September 30, 2017 , respectively, and 17% and 18% for the quarter and nine months ended September 30, 2016 , respectively. The percentage of assumed earned premiums to net earned premiums was 32% and 31% for the quarter and nine months ended September 30, 2017 , respectively, and 30% for both the quarter and nine months ended September 30, 2016 . Incurred losses and loss adjustment expenses were net of reinsurance recoverables (ceded incurred losses and loss adjustment expenses) of $540.1 million and $83.3 million for the quarters ended September 30, 2017 and 2016 , respectively, and $748.7 million and $289.4 million for the nine months ended September 30, 2017 and 2016 , respectively. Ceded incurred losses and loss adjustment expenses for both the quarter and nine months ended September 30, 2017 included ceded losses on the 2017 Catastrophes of $464.4 million .

Life And Annuity Benefits

Life And Annuity Benefits	9 Months Ended
	Sep. 30, 2017
Liability for Future Policy Benefits [Abstract]
Life And Annuity Benefits	Life and Annuity Benefits Life and annuity benefits are compiled on a reinsurance contract-by-contract basis and are discounted using standard actuarial techniques and cash flow models. Since the development of the life and annuity reinsurance reserves is based upon cash flow projection models, the Company must make estimates and assumptions based on cedent experience, industry mortality tables, and expense and investment experience, including a provision for adverse deviation. The assumptions used to determine policy benefit reserves are generally locked-in for the life of the contract unless an unlocking event occurs. Loss recognition testing is performed to determine if existing policy benefit reserves, together with the present value of future gross premiums and expected investment income earned thereon, are adequate to cover the present value of future benefits, settlement and maintenance costs. If the existing policy benefit reserves are not sufficient, the locked-in assumptions are revised to current best estimate assumptions and a charge to earnings for life and annuity benefits is recognized at that time. Life and annuity benefits are also adjusted to the extent unrealized gains on the investments supporting the policy benefit reserves would result in a reserve deficiency if those gains were realized. During the quarter and nine months ended September 30, 2016 , the Company recognized a reserve deficiency resulting from a decrease in the market yield on the investment portfolio supporting the policy benefit reserves by increasing life and annuity benefits by $9.6 million and $57.5 million , respectively, and decreasing the change in net unrealized holding gains included in other comprehensive income by a corresponding amount. No adjustment was required for the quarter or nine months ended September 30, 2017.

Variable Interest Entities

Variable Interest Entities	9 Months Ended
	Sep. 30, 2017
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 included with the Company's non-insurance operations, which 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 $1.2 million and $8.3 million for the quarters ended September 30, 2017 and 2016 , respectively, and $19.9 million and $22.8 million for the nine months ended September 30, 2017 and 2016 , respectively. The Company is the sole investor in one of the Funds, the Markel Diversified Fund, and consolidates that fund as its primary beneficiary. As of September 30, 2017 , total assets of the Markel Diversified Fund were $183.3 million and total liabilities were $62.8 million . As of December 31, 2016 , total assets of the Markel Diversified Fund were $166.8 million and total liabilities were $64.6 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 $180.7 million as of September 30, 2017 and $165.1 million as of December 31, 2016 , which represents 7% of the outstanding preference shares of that fund as of September 30, 2017 and 6% as of December 31, 2016 . This investment is included in equity securities (available-for-sale) on the Company's consolidated balance sheets. Total liabilities of the Markel Diversified Fund for both periods includes a $62.5 million note payable, delivered as part of the consideration provided for its investment. This note payable is included in senior long-term debt and other debt on the Company's consolidated balance sheets. Other than the note payable, any liabilities held by the Markel Diversified Fund have no recourse to the Company's general credit. The Company's exposure to risk from the unconsolidated Funds and reinsurance company is generally limited to its investment and any earned but uncollected fees. The Company has not issued any investment performance guarantees to these VIEs or their investors. As of September 30, 2017 , total investment and insurance assets under management of MCIM for unconsolidated VIEs were $4.5 billion , which includes funds held that will be used to settle claims for incurred losses.

Net Income (Loss) Per Share

Net Income (Loss) Per Share	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Net Income (Loss) Per Share	Net Income (Loss) per Share Net income (loss) per share was determined by dividing adjusted net income (loss) to shareholders by the applicable weighted average shares outstanding. Diluted net income (loss) per share is computed by dividing adjusted net income (loss) to shareholders by the weighted average number of common shares and dilutive potential common shares outstanding during the period. Quarter Ended September 30, Nine Months Ended September 30, (in thousands, except per share amounts) 2017 2016 2017 2016 Net income (loss) to shareholders $ (259,141 ) $ 83,796 $ (39,612 ) $ 322,963 Adjustment of redeemable noncontrolling interests (3,298 ) (4,928 ) (23,582 ) (10,909 ) Adjusted net income (loss) to shareholders $ (262,439 ) $ 78,868 $ (63,194 ) $ 312,054 Basic common shares outstanding 13,947 14,033 13,974 14,013 Dilutive potential common shares from conversion of options 1 3 2 4 Dilutive potential common shares from conversion of restricted stock 42 49 42 62 Diluted shares outstanding 13,990 14,085 14,018 14,079 Basic net income (loss) per share $ (18.82 ) $ 5.62 $ (4.52 ) $ 22.27 Diluted net income (loss) per share $ (18.82 ) $ 5.60 $ (4.52 ) $ 22.16

Other Comprehensive Income

Other Comprehensive Income	9 Months Ended
	Sep. 30, 2017
Other Comprehensive Income (Loss), Tax [Abstract]
Other Comprehensive Income	Other Comprehensive Income Other comprehensive income includes net holding gains arising during the period, changes in unrealized other-than-temporary impairment losses on fixed maturities arising during the period and reclassification adjustments for net gains included in net income (loss). Other comprehensive income also includes changes in foreign currency translation adjustments and changes in net actuarial pension loss. The following table presents the change in accumulated other comprehensive income by component, net of taxes and noncontrolling interests, for the nine months ended September 30, 2017 and 2016 . (dollars in thousands) Unrealized Holding Gains on Available-for-Sale Securities Foreign Currency Net Actuarial Pension Loss Total December 31, 2015 $ 1,472,762 $ (72,696 ) $ (45,558 ) $ 1,354,508 Other comprehensive income (loss) before reclassifications 411,354 (6,159 ) — 405,195 Amounts reclassified from accumulated other comprehensive income (33,308 ) — 1,247 (32,061 ) Total other comprehensive income (loss) 378,046 (6,159 ) 1,247 373,134 September 30, 2016 $ 1,850,808 $ (78,855 ) $ (44,311 ) $ 1,727,642 December 31, 2016 $ 1,714,930 $ (84,406 ) $ (64,658 ) $ 1,565,866 Other comprehensive income before reclassifications 577,796 19,750 — 597,546 Amounts reclassified from accumulated other comprehensive income (14,598 ) — 2,391 (12,207 ) Total other comprehensive income 563,198 19,750 2,391 585,339 September 30, 2017 $ 2,278,128 $ (64,656 ) $ (62,267 ) $ 2,151,205 The following table summarizes the tax expense (benefit) associated with each component of other comprehensive income. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2017 2016 2017 2016 Change in net unrealized gains on investments: Net holding gains arising during the period $ 109,338 $ 8,309 $ 278,266 $ 196,189 Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period — (3 ) — (9 ) Reclassification adjustments for net losses included in net income (loss) (2,810 ) (4,811 ) (5,206 ) (12,621 ) Change in net unrealized gains on investments 106,528 3,495 273,060 183,559 Change in foreign currency translation adjustments 656 2,847 153 1,152 Change in net actuarial pension loss 159 86 492 274 Total $ 107,343 $ 6,428 $ 273,705 $ 184,985 The following table presents the details of amounts reclassified from accumulated other comprehensive income into income, by component. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2017 2016 2017 2016 Unrealized holding gains on available-for-sale securities: Other-than-temporary impairment losses $ (3,444 ) $ — $ (7,261 ) $ (12,080 ) Net realized investment gains, excluding other-than-temporary impairment losses 11,461 14,569 27,065 58,009 Total before taxes 8,017 14,569 19,804 45,929 Income taxes (2,810 ) (4,811 ) (5,206 ) (12,621 ) Reclassification of unrealized holding gains, net of taxes $ 5,207 $ 9,758 $ 14,598 $ 33,308 Net actuarial pension loss: Underwriting, acquisition and insurance expenses $ (932 ) $ (476 ) $ (2,883 ) $ (1,521 ) Income taxes 159 86 492 274 Reclassification of net actuarial pension loss, net of taxes $ (773 ) $ (390 ) $ (2,391 ) $ (1,247 )

Contingencies

Contingencies	9 Months Ended
	Sep. 30, 2017
Loss Contingency [Abstract]
Contingencies	Contingencies 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 ( $11.1 million through September 30, 2017) and default interest (up to an additional $9.7 million through September 30, 2017, 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. 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. In addition, contingencies arise in the normal course of the Company's operations and are not expected to have a material impact on the Company's financial condition or results of operations.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2017
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events After the end of the third quarter of 2017, northern California sustained losses from several wildfires. Events are ongoing; however, with the information currently available, the Company has preliminarily estimated its range of net incurred losses on this event to be $40 million to $80 million before income taxes. This estimated range of losses was derived based on preliminary industry loss estimates, policy level reviews and direct contact with insureds and brokers when possible. However, the Company is still gathering loss data from policy holders and cedents and does not expect that all losses have been reported at this time. Potential losses associated with business interruption are also not yet clear. The Company continues to closely monitor reported claims to refine its estimate of losses, which will be recorded in the fourth quarter of 2017.

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Available-For-Sale Investments	The following tables summarize the Company's available-for-sale investments. Commercial and residential mortgage-backed securities include securities issued by U.S. government-sponsored enterprises and U.S. government agencies. September 30, 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 $ 129,631 $ 64 $ (859 ) $ — $ 128,836 U.S. government-sponsored enterprises 359,492 11,389 (1,240 ) — 369,641 Obligations of states, municipalities and political subdivisions 4,366,775 199,013 (12,789 ) — 4,552,999 Foreign governments 1,395,157 153,766 (3,601 ) — 1,545,322 Commercial mortgage-backed securities 1,195,384 8,353 (12,327 ) — 1,191,410 Residential mortgage-backed securities 799,872 19,269 (3,079 ) — 816,062 Asset-backed securities 20,221 7 (72 ) — 20,156 Corporate bonds 1,248,550 49,349 (2,979 ) — 1,294,920 Total fixed maturities 9,515,082 441,210 (36,946 ) — 9,919,346 Equity securities: Insurance, banks and other financial institutions 910,682 1,103,007 (3,418 ) — 2,010,271 Industrial, consumer and all other 1,803,123 1,908,012 (11,460 ) — 3,699,675 Total equity securities 2,713,805 3,011,019 (14,878 ) — 5,709,946 Short-term investments 1,995,489 87 (14 ) — 1,995,562 Investments, available-for-sale $ 14,224,376 $ 3,452,316 $ (51,838 ) $ — $ 17,624,854 December 31, 2016 (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 $ 259,379 $ 99 $ (894 ) $ — $ 258,584 U.S. government-sponsored enterprises 418,457 9,083 (4,328 ) — 423,212 Obligations of states, municipalities and political subdivisions 4,324,332 145,678 (41,805 ) — 4,428,205 Foreign governments 1,306,324 159,291 (2,153 ) — 1,463,462 Commercial mortgage-backed securities 1,055,947 3,953 (19,544 ) — 1,040,356 Residential mortgage-backed securities 779,503 18,749 (5,048 ) (2,258 ) 790,946 Asset-backed securities 27,494 2 (158 ) — 27,338 Corporate bonds 1,420,298 49,146 (9,364 ) (673 ) 1,459,407 Total fixed maturities 9,591,734 386,001 (83,294 ) (2,931 ) 9,891,510 Equity securities: Insurance, banks and other financial institutions 846,343 857,063 (5,596 ) — 1,697,810 Industrial, consumer and all other 1,635,105 1,421,080 (8,154 ) — 3,048,031 Total equity securities 2,481,448 2,278,143 (13,750 ) — 4,745,841 Short-term investments 2,336,100 57 (6 ) — 2,336,151 Investments, available-for-sale $ 14,409,282 $ 2,664,201 $ (97,050 ) $ (2,931 ) $ 16,973,502
Summary Of Gross Unrealized Investment Losses By Length Of Time That Securities Have Continuously Been In An Unrealized Loss Position	The following tables summarize gross unrealized investment losses by the length of time that securities have continuously been in an unrealized loss position. September 30, 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 $ 102,240 $ (585 ) $ 23,609 $ (274 ) $ 125,849 $ (859 ) U.S. government-sponsored enterprises 102,957 (1,237 ) 1,744 (3 ) 104,701 (1,240 ) Obligations of states, municipalities and political subdivisions 525,844 (6,801 ) 143,119 (5,988 ) 668,963 (12,789 ) Foreign governments 135,018 (3,594 ) 7,158 (7 ) 142,176 (3,601 ) Commercial mortgage-backed securities 569,763 (12,071 ) 13,486 (256 ) 583,249 (12,327 ) Residential mortgage-backed securities 106,673 (1,501 ) 70,723 (1,578 ) 177,396 (3,079 ) Asset-backed securities 9,676 (38 ) 6,561 (34 ) 16,237 (72 ) Corporate bonds 266,040 (2,275 ) 69,916 (704 ) 335,956 (2,979 ) Total fixed maturities 1,818,211 (28,102 ) 336,316 (8,844 ) 2,154,527 (36,946 ) Equity securities: Insurance, banks and other financial institutions 23,636 (2,616 ) 1,099 (802 ) 24,735 (3,418 ) Industrial, consumer and all other 60,596 (8,333 ) 11,112 (3,127 ) 71,708 (11,460 ) Total equity securities 84,232 (10,949 ) 12,211 (3,929 ) 96,443 (14,878 ) Short-term investments 75,829 (14 ) — — 75,829 (14 ) Total $ 1,978,272 $ (39,065 ) $ 348,527 $ (12,773 ) $ 2,326,799 $ (51,838 ) December 31, 2016 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 $ 122,950 $ (894 ) $ — $ — $ 122,950 $ (894 ) U.S. government-sponsored enterprises 220,333 (4,324 ) 7,618 (4 ) 227,951 (4,328 ) Obligations of states, municipalities and political subdivisions 1,004,947 (37,685 ) 31,723 (4,120 ) 1,036,670 (41,805 ) Foreign governments 68,887 (2,145 ) 5,005 (8 ) 73,892 (2,153 ) Commercial mortgage-backed securities 749,889 (19,091 ) 29,988 (453 ) 779,877 (19,544 ) Residential mortgage-backed securities 181,557 (4,987 ) 79,936 (2,319 ) 261,493 (7,306 ) Asset-backed securities 14,501 (106 ) 5,869 (52 ) 20,370 (158 ) Corporate bonds 494,573 (8,357 ) 93,790 (1,680 ) 588,363 (10,037 ) Total fixed maturities 2,857,637 (77,589 ) 253,929 (8,636 ) 3,111,566 (86,225 ) Equity securities: Insurance, banks and other financial institutions 8,808 (410 ) 37,973 (5,186 ) 46,781 (5,596 ) Industrial, consumer and all other 98,406 (4,772 ) 29,650 (3,382 ) 128,056 (8,154 ) Total equity securities 107,214 (5,182 ) 67,623 (8,568 ) 174,837 (13,750 ) Short-term investments 504,211 (6 ) — — 504,211 (6 ) Total $ 3,469,062 $ (82,777 ) $ 321,552 $ (17,204 ) $ 3,790,614 $ (99,981 )
Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturity Securities By Contractual Maturity Date	The amortized cost and estimated fair value of fixed maturities at September 30, 2017 are shown below by contractual maturity. (dollars in thousands) Amortized Cost Estimated Fair Value Due in one year or less $ 375,471 $ 377,672 Due after one year through five years 1,232,430 1,276,160 Due after five years through ten years 1,567,938 1,646,296 Due after ten years 4,323,766 4,591,590 7,499,605 7,891,718 Commercial mortgage-backed securities 1,195,384 1,191,410 Residential mortgage-backed securities 799,872 816,062 Asset-backed securities 20,221 20,156 Total fixed maturities $ 9,515,082 $ 9,919,346
Components Of Net Investment Income	The following table presents the components of net investment income. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2017 2016 2017 2016 Interest: Municipal bonds (tax-exempt) $ 21,486 $ 22,136 $ 66,616 $ 66,621 Municipal bonds (taxable) 17,732 16,710 53,030 48,820 Other taxable bonds 36,337 36,697 107,521 108,975 Short-term investments, including overnight deposits 7,779 2,878 18,562 7,823 Dividends on equity securities 21,467 17,308 61,090 51,718 Income from equity method investments 4,239 1,232 10,634 4,900 Other (315 ) (60 ) (520 ) 2,614 108,725 96,901 316,933 291,471 Investment expenses (4,236 ) (3,754 ) (12,777 ) (12,034 ) Net investment income $ 104,489 $ 93,147 $ 304,156 $ 279,437
Summary Of Net Realized Investment Gains (Losses) And The Change In Net Unrealized Gains On Investments	The following table presents net realized investment gains (losses) and the change in net unrealized gains on investments. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2017 2016 2017 2016 Realized gains: Sales of fixed maturities $ 3,426 $ 3,698 $ 4,189 $ 4,658 Sales of equity securities 9,276 18,418 25,806 63,931 Other 1,129 423 5,979 1,117 Total realized gains 13,831 22,539 35,974 69,706 Realized losses: Sales of fixed maturities (663 ) (60 ) (1,271 ) (608 ) Sales of equity securities (578 ) (4,187 ) (1,791 ) (6,672 ) Other-than-temporary impairments (3,444 ) — (7,261 ) (12,080 ) Other (776 ) (55 ) (1,086 ) (2,972 ) Total realized losses (5,461 ) (4,302 ) (11,409 ) (22,332 ) Gains (losses) on securities measured at fair value through net income (loss) (48,377 ) 9,179 (26,080 ) 18,462 Net realized investment gains (losses) $ (40,007 ) $ 27,416 $ (1,515 ) $ 65,836 Change in net unrealized gains on investments included in other comprehensive income: Fixed maturities $ 20,428 $ (53,962 ) $ 104,488 $ 399,020 Equity securities 308,324 80,285 731,748 220,029 Short-term investments 16 58 22 23 Net increase $ 328,768 $ 26,381 $ 836,258 $ 619,072

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Balances Of Assets Measured At Fair Value On A Recurring Basis	The following tables present the balances of assets measured at fair value on a recurring basis by level within the fair value hierarchy. September 30, 2017 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments available-for-sale: Fixed maturities: U.S. Treasury securities $ — $ 128,836 $ — $ 128,836 U.S. government-sponsored enterprises — 369,641 — 369,641 Obligations of states, municipalities and political subdivisions — 4,552,999 — 4,552,999 Foreign governments — 1,545,322 — 1,545,322 Commercial mortgage-backed securities — 1,191,410 — 1,191,410 Residential mortgage-backed securities — 816,062 — 816,062 Asset-backed securities — 20,156 — 20,156 Corporate bonds — 1,294,920 — 1,294,920 Total fixed maturities — 9,919,346 — 9,919,346 Equity securities: Insurance, banks and other financial institutions 1,828,997 — 181,274 2,010,271 Industrial, consumer and all other 3,699,675 — — 3,699,675 Total equity securities 5,528,672 — 181,274 5,709,946 Short-term investments 1,895,262 100,300 — 1,995,562 Total investments available-for-sale $ 7,423,934 $ 10,019,646 $ 181,274 $ 17,624,854 December 31, 2016 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments available-for-sale: Fixed maturities: U.S. Treasury securities $ — $ 258,584 $ — $ 258,584 U.S. government-sponsored enterprises — 423,212 — 423,212 Obligations of states, municipalities and political subdivisions — 4,428,205 — 4,428,205 Foreign governments — 1,463,462 — 1,463,462 Commercial mortgage-backed securities — 1,040,356 — 1,040,356 Residential mortgage-backed securities — 790,946 — 790,946 Asset-backed securities — 27,338 — 27,338 Corporate bonds — 1,459,407 — 1,459,407 Total fixed maturities — 9,891,510 — 9,891,510 Equity securities: Insurance, banks and other financial institutions 1,506,607 — 191,203 1,697,810 Industrial, consumer and all other 3,048,031 — — 3,048,031 Total equity securities 4,554,638 — 191,203 4,745,841 Short-term investments 2,255,898 80,253 — 2,336,151 Total investments available-for-sale $ 6,810,536 $ 9,971,763 $ 191,203 $ 16,973,502
Summary Of Changes In Level 3 Investments Measured At Fair Value On A Recurring Basis	The following table summarizes changes in Level 3 investments measured at fair value on a recurring basis. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2017 2016 2017 2016 Equity securities, beginning of period $ 183,913 $ 183,523 $ 191,203 $ — Purchases 49,000 — 56,250 195,250 Sales — — (26,674 ) (25,000 ) Total gains (losses) included in: Net income (loss) (51,639 ) 6,881 (39,505 ) 20,154 Other comprehensive income — — — — Transfers into Level 3 — — — — Transfers out of Level 3 — — — — Equity securities, end of period $ 181,274 $ 190,404 $ 181,274 $ 190,404 Net unrealized gains (losses) included in net income (loss) relating to assets held at September 30, 2017 and 2016 (1) $ (51,639 ) $ 6,881 $ (39,505 ) $ 20,154 (1) Included in net realized investment gains (losses) in the consolidated statements of income (loss) and comprehensive income (loss).

Segment Reporting Disclosures (

Segment Reporting Disclosures (Tables)	9 Months Ended
	Sep. 30, 2017
Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract]
Company's Segment Disclosures	The following tables summarize the Company's segment disclosures. Quarter Ended September 30, 2017 (dollars in thousands) U.S. Insurance International Insurance Reinsurance Other Insurance (Discontinued Lines) Investing Consolidated Gross premium volume $ 778,323 $ 319,914 $ 230,077 $ (186 ) $ — $ 1,328,128 Net written premiums 653,970 254,326 189,636 (178 ) — 1,097,754 Earned premiums 600,294 240,145 259,601 (178 ) — 1,099,862 Losses and loss adjustment expenses: Current accident year (533,662 ) (274,581 ) (418,297 ) — — (1,226,540 ) Prior accident years 87,613 40,740 21,164 1,591 — 151,108 Amortization of policy acquisition costs (134,243 ) (43,140 ) (53,440 ) — — (230,823 ) Other operating expenses (90,350 ) (50,771 ) (23,885 ) (80 ) — (165,086 ) Underwriting profit (loss) (70,348 ) (87,607 ) (214,857 ) 1,333 — (371,479 ) Net investment income — — — — 104,489 104,489 Net realized investment losses — — — — (40,007 ) (40,007 ) Other revenues (insurance) 979 658 — 428 — 2,065 Other expenses (insurance) (162 ) (1,035 ) — (6,776 ) — (7,973 ) Segment profit (loss) $ (69,531 ) $ (87,984 ) $ (214,857 ) $ (5,015 ) $ 64,482 $ (312,905 ) Other revenues (non-insurance) 339,739 Other expenses (non-insurance) (336,314 ) Amortization of intangible assets (18,654 ) Interest expense (31,814 ) Loss before income taxes $ (359,948 ) U.S. GAAP combined ratio (1) 112 % 136 % 183 % NM (2) 134 % Quarter Ended September 30, 2016 (dollars in thousands) U.S. Insurance International Insurance Reinsurance Other Insurance (Discontinued Lines) Investing Consolidated Gross premium volume $ 663,196 $ 269,093 $ 196,948 $ 536 $ — $ 1,129,773 Net written premiums 562,215 209,656 157,043 469 — 929,383 Earned premiums 548,792 218,968 206,018 466 — 974,244 Losses and loss adjustment expenses: Current accident year (370,435 ) (159,812 ) (129,875 ) — — (660,122 ) Prior accident years 21,471 42,705 19,135 (2,594 ) — 80,717 Amortization of policy acquisition costs (115,504 ) (38,075 ) (48,294 ) — — (201,873 ) Other operating expenses (91,124 ) (44,716 ) (34,196 ) (612 ) — (170,648 ) Underwriting profit (loss) (6,800 ) 19,070 12,788 (2,740 ) — 22,318 Net investment income — — — — 93,147 93,147 Net realized investment gains — — — — 27,416 27,416 Other revenues (insurance) 1,285 419 — 466 — 2,170 Other expenses (insurance) (670 ) (677 ) — (4,232 ) — (5,579 ) Segment profit (loss) $ (6,185 ) $ 18,812 $ 12,788 $ (6,506 ) $ 120,563 $ 139,472 Other revenues (non-insurance) 334,305 Other expenses (non-insurance) (304,134 ) Amortization of intangible assets (17,010 ) Interest expense (33,152 ) Income before income taxes $ 119,481 U.S. GAAP combined ratio (1) 101 % 91 % 94 % NM (2) 98 % (1) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (2) NM – Ratio is not meaningful. Nine Months Ended September 30, 2017 (dollars in thousands) U.S. Insurance International Insurance Reinsurance Other Insurance (Discontinued Lines) Investing Consolidated Gross premium volume $ 2,171,481 $ 949,031 $ 1,025,716 $ (185 ) $ — $ 4,146,043 Net written premiums 1,829,528 766,571 899,698 (157 ) — 3,495,640 Earned premiums 1,727,871 673,606 714,718 (157 ) — 3,116,038 Losses and loss adjustment expenses: Current accident year (1,259,777 ) (579,601 ) (710,093 ) — — (2,549,471 ) Prior accident years 207,499 146,268 (22,248 ) 7,823 — 339,342 Amortization of policy acquisition costs (371,241 ) (114,219 ) (163,385 ) — — (648,845 ) Other operating expenses (292,409 ) (157,249 ) (70,293 ) (379 ) — (520,330 ) Underwriting profit (loss) 11,943 (31,195 ) (251,301 ) 7,287 — (263,266 ) Net investment income — — — — 304,156 304,156 Net realized investment losses — — — — (1,515 ) (1,515 ) Other revenues (insurance) 2,685 5,227 417 1,634 — 9,963 Other expenses (insurance) (1,005 ) (6,109 ) — (21,009 ) — (28,123 ) Segment profit (loss) $ 13,623 $ (32,077 ) $ (250,884 ) $ (12,088 ) $ 302,641 $ 21,215 Other revenues (non-insurance) 970,750 Other expenses (non-insurance) (897,861 ) Amortization of intangible assets (53,450 ) Interest expense (97,013 ) Loss before income taxes $ (56,359 ) U.S. GAAP combined ratio (1) 99 % 105 % 135 % NM (2) 108 % Nine Months Ended September 30, 2016 (dollars in thousands) U.S. Insurance International Insurance Reinsurance Other Insurance (Discontinued Lines) Investing Consolidated Gross premium volume $ 2,000,454 $ 879,078 $ 920,038 $ 515 $ — $ 3,800,085 Net written premiums 1,694,193 680,691 786,450 555 — 3,161,889 Earned premiums 1,614,588 637,365 630,151 685 — 2,882,789 Losses and loss adjustment expenses: Current accident year (1,038,860 ) (451,741 ) (413,044 ) — — (1,903,645 ) Prior accident years 126,457 111,359 90,140 10,764 — 338,720 Amortization of policy acquisition costs (336,093 ) (105,220 ) (138,895 ) — — (580,208 ) Other operating expenses (280,913 ) (162,739 ) (88,243 ) (686 ) — (532,581 ) Underwriting profit 85,179 29,024 80,109 10,763 — 205,075 Net investment income — — — — 279,437 279,437 Net realized investment gains — — — — 65,836 65,836 Other revenues (insurance) 3,662 5,149 — 1,407 — 10,218 Other expenses (insurance) (2,078 ) (4,368 ) — (19,432 ) — (25,878 ) Segment profit (loss) $ 86,763 $ 29,805 $ 80,109 $ (7,262 ) $ 345,273 $ 534,688 Other revenues (non-insurance) 945,121 Other expenses (non-insurance) (836,837 ) Amortization of intangible assets (51,474 ) Interest expense (97,690 ) Loss on early extinguishment of debt (44,100 ) Income before income taxes $ 449,708 U.S. GAAP combined ratio (1) 95 % 95 % 87 % NM (2) 93 % (1) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (2) NM – Ratio is not meaningful.
Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets	The following table reconciles segment assets to the Company's consolidated balance sheets. (dollars in thousands) September 30, 2017 December 31, 2016 Segment assets: Investing $ 19,884,334 $ 19,029,584 Underwriting 6,528,093 5,397,696 Total segment assets 26,412,427 24,427,280 Non-insurance operations 2,106,984 1,448,019 Total assets $ 28,519,411 $ 25,875,299

Unpaid Losses And Loss Adjust26

Unpaid Losses And Loss Adjustment Expenses (Tables)	9 Months Ended
	Sep. 30, 2017
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Reconciliation Of Consolidated Reserves For Losses And Loss Adjustment Expenses	The following table presents a reconciliation of consolidated beginning and ending reserves for losses and loss adjustment expenses. Nine Months Ended September 30, (dollars in thousands) 2017 2016 Net reserves for losses and loss adjustment expenses, beginning of year $ 8,108,717 $ 8,235,288 Foreign currency movements 158,360 (56,741 ) Adjusted net reserves for losses and loss adjustment expenses, beginning of year 8,267,077 8,178,547 Incurred losses and loss adjustment expenses: Current accident year 2,549,471 1,903,645 Prior accident years (335,494 ) (327,064 ) Total incurred losses and loss adjustment expenses 2,213,977 1,576,581 Payments: Current accident year 342,055 319,049 Prior accident years 1,185,689 1,219,755 Total payments 1,527,744 1,538,804 Effect of foreign currency rate changes 10,582 38 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 8,976,594 8,216,362 Reinsurance recoverable on unpaid losses 2,466,554 2,041,928 Gross reserves for losses and loss adjustment expenses, end of period $ 11,443,148 $ 10,258,290

Other Revenues And Other Expe27

Other Revenues And Other Expenses (Tables)	9 Months Ended
	Sep. 30, 2017
Other Income and Expenses [Abstract]
Summary Of Other Revenues And Other Expenses By Component	The following tables summarize the components of other revenues and other expenses. Quarter Ended September 30, 2017 2016 (dollars in thousands) Other Revenues Other Expenses Other Revenues Other Expenses Insurance: Managing general agent operations $ 1,637 $ 1,134 $ 1,704 $ 1,347 Life and annuity 428 6,776 466 4,232 Other — 63 — — 2,065 7,973 2,170 5,579 Non-Insurance: Markel Ventures: Manufacturing 195,535 173,174 203,909 171,595 Markel Ventures: Non-Manufacturing 137,213 145,434 117,433 115,529 Investment management 1,248 11,552 8,297 10,385 Other 5,743 6,154 4,666 6,625 339,739 336,314 334,305 304,134 Total $ 341,804 $ 344,287 $ 336,475 $ 309,713 Nine Months Ended September 30, 2017 2016 (dollars in thousands) Other Revenues Other Expenses Other Revenues Other Expenses Insurance: Managing general agent operations $ 7,912 $ 4,480 $ 8,811 $ 6,446 Life and annuity 1,634 21,009 1,407 19,432 Other 417 2,634 — — 9,963 28,123 10,218 25,878 Non-Insurance: Markel Ventures: Manufacturing 556,691 483,724 589,752 491,188 Markel Ventures: Non-Manufacturing 376,589 357,549 315,863 295,647 Investment management 19,884 37,682 22,820 31,151 Other 17,586 18,906 16,686 18,851 970,750 897,861 945,121 836,837 Total $ 980,713 $ 925,984 $ 955,339 $ 862,715

Reinsurance (Tables)

Reinsurance (Tables)	9 Months Ended
	Sep. 30, 2017
Reinsurance Disclosures [Abstract]
Effect Of Reinsurance And Retrocessional Reinsurance On Premiums Written And Earned	The following tables summarize the effect of reinsurance and retrocessional reinsurance on premiums written and earned. Quarter Ended September 30, 2017 2016 (dollars in thousands) Written Earned Written Earned Direct $ 1,035,705 $ 966,735 $ 888,009 $ 883,687 Assumed 292,423 356,529 241,764 292,951 Ceded (230,374 ) (223,402 ) (200,390 ) (202,394 ) Net premiums $ 1,097,754 $ 1,099,862 $ 929,383 $ 974,244 Nine Months Ended September 30, 2017 2016 (dollars in thousands) Written Earned Written Earned Direct $ 2,932,022 $ 2,743,970 $ 2,724,341 $ 2,617,074 Assumed 1,214,021 976,636 1,075,744 878,882 Ceded (650,403 ) (604,568 ) (638,196 ) (613,167 ) Net premiums $ 3,495,640 $ 3,116,038 $ 3,161,889 $ 2,882,789

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Schedule Of Net Income (Loss) Per Share	Net income (loss) per share was determined by dividing adjusted net income (loss) to shareholders by the applicable weighted average shares outstanding. Diluted net income (loss) per share is computed by dividing adjusted net income (loss) to shareholders by the weighted average number of common shares and dilutive potential common shares outstanding during the period. Quarter Ended September 30, Nine Months Ended September 30, (in thousands, except per share amounts) 2017 2016 2017 2016 Net income (loss) to shareholders $ (259,141 ) $ 83,796 $ (39,612 ) $ 322,963 Adjustment of redeemable noncontrolling interests (3,298 ) (4,928 ) (23,582 ) (10,909 ) Adjusted net income (loss) to shareholders $ (262,439 ) $ 78,868 $ (63,194 ) $ 312,054 Basic common shares outstanding 13,947 14,033 13,974 14,013 Dilutive potential common shares from conversion of options 1 3 2 4 Dilutive potential common shares from conversion of restricted stock 42 49 42 62 Diluted shares outstanding 13,990 14,085 14,018 14,079 Basic net income (loss) per share $ (18.82 ) $ 5.62 $ (4.52 ) $ 22.27 Diluted net income (loss) per share $ (18.82 ) $ 5.60 $ (4.52 ) $ 22.16

Other Comprehensive Income (Tab

Other Comprehensive Income (Tables)	9 Months Ended
	Sep. 30, 2017
Other Comprehensive Income (Loss), Tax [Abstract]
Change In Accumulated Other Comprehensive Income By Component, Net Of Taxes And Noncontrolling Interest	The following table presents the change in accumulated other comprehensive income by component, net of taxes and noncontrolling interests, for the nine months ended September 30, 2017 and 2016 . (dollars in thousands) Unrealized Holding Gains on Available-for-Sale Securities Foreign Currency Net Actuarial Pension Loss Total December 31, 2015 $ 1,472,762 $ (72,696 ) $ (45,558 ) $ 1,354,508 Other comprehensive income (loss) before reclassifications 411,354 (6,159 ) — 405,195 Amounts reclassified from accumulated other comprehensive income (33,308 ) — 1,247 (32,061 ) Total other comprehensive income (loss) 378,046 (6,159 ) 1,247 373,134 September 30, 2016 $ 1,850,808 $ (78,855 ) $ (44,311 ) $ 1,727,642 December 31, 2016 $ 1,714,930 $ (84,406 ) $ (64,658 ) $ 1,565,866 Other comprehensive income before reclassifications 577,796 19,750 — 597,546 Amounts reclassified from accumulated other comprehensive income (14,598 ) — 2,391 (12,207 ) Total other comprehensive income 563,198 19,750 2,391 585,339 September 30, 2017 $ 2,278,128 $ (64,656 ) $ (62,267 ) $ 2,151,205
Summary Of Tax Expense (Benefit) Of Other Comprehensive Income	The following table summarizes the tax expense (benefit) associated with each component of other comprehensive income. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2017 2016 2017 2016 Change in net unrealized gains on investments: Net holding gains arising during the period $ 109,338 $ 8,309 $ 278,266 $ 196,189 Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period — (3 ) — (9 ) Reclassification adjustments for net losses included in net income (loss) (2,810 ) (4,811 ) (5,206 ) (12,621 ) Change in net unrealized gains on investments 106,528 3,495 273,060 183,559 Change in foreign currency translation adjustments 656 2,847 153 1,152 Change in net actuarial pension loss 159 86 492 274 Total $ 107,343 $ 6,428 $ 273,705 $ 184,985
Reclassifications From Accumulated Other Comprehensive Income Into Income, By Component	The following table presents the details of amounts reclassified from accumulated other comprehensive income into income, by component. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2017 2016 2017 2016 Unrealized holding gains on available-for-sale securities: Other-than-temporary impairment losses $ (3,444 ) $ — $ (7,261 ) $ (12,080 ) Net realized investment gains, excluding other-than-temporary impairment losses 11,461 14,569 27,065 58,009 Total before taxes 8,017 14,569 19,804 45,929 Income taxes (2,810 ) (4,811 ) (5,206 ) (12,621 ) Reclassification of unrealized holding gains, net of taxes $ 5,207 $ 9,758 $ 14,598 $ 33,308 Net actuarial pension loss: Underwriting, acquisition and insurance expenses $ (932 ) $ (476 ) $ (2,883 ) $ (1,521 ) Income taxes 159 86 492 274 Reclassification of net actuarial pension loss, net of taxes $ (773 ) $ (390 ) $ (2,391 ) $ (1,247 )

Recent Accounting Pronounceme31

Recent Accounting Pronouncements (Narrative) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2016	Sep. 30, 2017	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in restricted cash reclassified out of investing activities	$ 61,100
Insurance premium revenues and investment portfolio revenues as a percentage of consolidated revenues		77.00%
Net unrealized gains, net of taxes, included in accumulated other comprehensive income	$ 1,727,642	$ 1,565,866	$ 2,151,205	$ 1,354,508
Future minimum lease payments		$ 234,300
Equity Securities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net unrealized gains, net of taxes, included in accumulated other comprehensive income			$ 2,000,000

Acquisitions (Narrative) (Detai

Acquisitions (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	Aug. 31, 2017	Jul. 31, 2017	Apr. 30, 2017
SureTec Financial Corp [Member]
Business Acquisition [Line Items]
Total consideration			$ 246.9
Cash consideration			225.6
Goodwill recognized			70.4
Goodwill, tax deductible			0
Finite-lived and indefinite-lived intangible assets			103
SureTec Financial Corp [Member] | Agent Relationships [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets			$ 92
Definite-lived intangible assets, weighted-average amortization period			15 years
Costa Farms [Member]
Business Acquisition [Line Items]
Total consideration	$ 424.5
Cash consideration	395.2
Goodwill recognized	201
Finite-lived and indefinite-lived intangible assets	$ 192
Percentage acquired	81.00%
Redeemable non-controlling interests	$ 66.6
Costa Farms [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets	$ 161
Definite-lived intangible assets, weighted-average amortization period	17 years
Costa Farms [Member] | Trade Names [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets	$ 31
Definite-lived intangible assets, weighted-average amortization period	9 years
State National Companies, Inc. [Member]
Business Acquisition [Line Items]
Total consideration		$ 919
Cash State National stockholders will receive for each outstanding share of State National common stock		$ 21

Investments (Narrative) (Detail

Investments (Narrative) (Details) $ in Thousands	Sep. 30, 2017USD ($)securities	Dec. 31, 2016USD ($)securities
Schedule of Investments [Line Items]
Available-for-sale securities in unrealized loss position, number of positions | securities	465	654
Available-for-sale securities, estimated fair value	$ 2,326,799	$ 3,790,614
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	$ (51,838)	$ (99,981)
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end | securities	105	109
Available-for-sale securities, estimated fair value, 12 months or longer	$ 348,527	$ 321,552
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(12,773)	(17,204)
Fixed Maturities [Member]
Schedule of Investments [Line Items]
Available-for-sale securities, estimated fair value	2,154,527	3,111,566
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	$ (36,946)	$ (86,225)
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end | securities	90	93
Available-for-sale securities, estimated fair value, 12 months or longer	$ 336,316	$ 253,929
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(8,844)	(8,636)
Equity Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale securities, estimated fair value	96,443	174,837
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	$ (14,878)	$ (13,750)
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end | securities	15	16
Available-for-sale securities, estimated fair value, 12 months or longer	$ 12,211	$ 67,623
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	$ (3,929)	$ (8,568)

Investments (Available-For-Sale

Investments (Available-For-Sale Investments) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	$ 14,224,376	$ 14,409,282
Available-for-sale investments, gross unrealized holding gains	3,452,316	2,664,201
Available-for-sale investments, gross unrealized holding losses	(51,838)	(97,050)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	(2,931)
Available-for-sale investments, estimated fair value	17,624,854	16,973,502
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	129,631	259,379
Available-for-sale investments, gross unrealized holding gains	64	99
Available-for-sale investments, gross unrealized holding losses	(859)	(894)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	128,836	258,584
U.S. Government-Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	359,492	418,457
Available-for-sale investments, gross unrealized holding gains	11,389	9,083
Available-for-sale investments, gross unrealized holding losses	(1,240)	(4,328)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	369,641	423,212
Obligations Of States, Municipalities And Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	4,366,775	4,324,332
Available-for-sale investments, gross unrealized holding gains	199,013	145,678
Available-for-sale investments, gross unrealized holding losses	(12,789)	(41,805)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	4,552,999	4,428,205
Foreign Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	1,395,157	1,306,324
Available-for-sale investments, gross unrealized holding gains	153,766	159,291
Available-for-sale investments, gross unrealized holding losses	(3,601)	(2,153)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	1,545,322	1,463,462
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	1,195,384	1,055,947
Available-for-sale investments, gross unrealized holding gains	8,353	3,953
Available-for-sale investments, gross unrealized holding losses	(12,327)	(19,544)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	1,191,410	1,040,356
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	799,872	779,503
Available-for-sale investments, gross unrealized holding gains	19,269	18,749
Available-for-sale investments, gross unrealized holding losses	(3,079)	(5,048)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	(2,258)
Available-for-sale investments, estimated fair value	816,062	790,946
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	20,221	27,494
Available-for-sale investments, gross unrealized holding gains	7	2
Available-for-sale investments, gross unrealized holding losses	(72)	(158)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	20,156	27,338
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	1,248,550	1,420,298
Available-for-sale investments, gross unrealized holding gains	49,349	49,146
Available-for-sale investments, gross unrealized holding losses	(2,979)	(9,364)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	(673)
Available-for-sale investments, estimated fair value	1,294,920	1,459,407
Total Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	9,515,082	9,591,734
Available-for-sale investments, gross unrealized holding gains	441,210	386,001
Available-for-sale investments, gross unrealized holding losses	(36,946)	(83,294)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	(2,931)
Available-for-sale investments, estimated fair value	9,919,346	9,891,510
Insurance, Banks And Other Financial Institutions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	910,682	846,343
Available-for-sale investments, gross unrealized holding gains	1,103,007	857,063
Available-for-sale investments, gross unrealized holding losses	(3,418)	(5,596)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	2,010,271	1,697,810
Industrial, Consumer And All Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	1,803,123	1,635,105
Available-for-sale investments, gross unrealized holding gains	1,908,012	1,421,080
Available-for-sale investments, gross unrealized holding losses	(11,460)	(8,154)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	3,699,675	3,048,031
Total Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	2,713,805	2,481,448
Available-for-sale investments, gross unrealized holding gains	3,011,019	2,278,143
Available-for-sale investments, gross unrealized holding losses	(14,878)	(13,750)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	5,709,946	4,745,841
Short-Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	1,995,489	2,336,100
Available-for-sale investments, gross unrealized holding gains	87	57
Available-for-sale investments, gross unrealized holding losses	(14)	(6)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	$ 1,995,562	$ 2,336,151

Investments (Summary Of Gross U

Investments (Summary Of Gross Unrealized Investment Losses By Length Of Time That Securities Have Continuously Been In An Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	$ 1,978,272	$ 3,469,062
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(39,065)	(82,777)
Available-for-sale securities, estimated fair value, 12 months or longer	348,527	321,552
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(12,773)	(17,204)
Available-for-sale securities, estimated fair value	2,326,799	3,790,614
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(51,838)	(99,981)
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	102,240	122,950
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(585)	(894)
Available-for-sale securities, estimated fair value, 12 months or longer	23,609	0
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(274)	0
Available-for-sale securities, estimated fair value	125,849	122,950
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(859)	(894)
U.S. Government-Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	102,957	220,333
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(1,237)	(4,324)
Available-for-sale securities, estimated fair value, 12 months or longer	1,744	7,618
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(3)	(4)
Available-for-sale securities, estimated fair value	104,701	227,951
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(1,240)	(4,328)
Obligations Of States, Municipalities And Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	525,844	1,004,947
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(6,801)	(37,685)
Available-for-sale securities, estimated fair value, 12 months or longer	143,119	31,723
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(5,988)	(4,120)
Available-for-sale securities, estimated fair value	668,963	1,036,670
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(12,789)	(41,805)
Foreign Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	135,018	68,887
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(3,594)	(2,145)
Available-for-sale securities, estimated fair value, 12 months or longer	7,158	5,005
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(7)	(8)
Available-for-sale securities, estimated fair value	142,176	73,892
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(3,601)	(2,153)
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	569,763	749,889
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(12,071)	(19,091)
Available-for-sale securities, estimated fair value, 12 months or longer	13,486	29,988
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(256)	(453)
Available-for-sale securities, estimated fair value	583,249	779,877
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(12,327)	(19,544)
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	106,673	181,557
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(1,501)	(4,987)
Available-for-sale securities, estimated fair value, 12 months or longer	70,723	79,936
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(1,578)	(2,319)
Available-for-sale securities, estimated fair value	177,396	261,493
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(3,079)	(7,306)
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	9,676	14,501
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(38)	(106)
Available-for-sale securities, estimated fair value, 12 months or longer	6,561	5,869
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(34)	(52)
Available-for-sale securities, estimated fair value	16,237	20,370
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(72)	(158)
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	266,040	494,573
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(2,275)	(8,357)
Available-for-sale securities, estimated fair value, 12 months or longer	69,916	93,790
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(704)	(1,680)
Available-for-sale securities, estimated fair value	335,956	588,363
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(2,979)	(10,037)
Total Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	1,818,211	2,857,637
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(28,102)	(77,589)
Available-for-sale securities, estimated fair value, 12 months or longer	336,316	253,929
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(8,844)	(8,636)
Available-for-sale securities, estimated fair value	2,154,527	3,111,566
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(36,946)	(86,225)
Insurance, Banks And Other Financial Institutions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	23,636	8,808
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(2,616)	(410)
Available-for-sale securities, estimated fair value, 12 months or longer	1,099	37,973
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(802)	(5,186)
Available-for-sale securities, estimated fair value	24,735	46,781
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(3,418)	(5,596)
Industrial, Consumer And All Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	60,596	98,406
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(8,333)	(4,772)
Available-for-sale securities, estimated fair value, 12 months or longer	11,112	29,650
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(3,127)	(3,382)
Available-for-sale securities, estimated fair value	71,708	128,056
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(11,460)	(8,154)
Total Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	84,232	107,214
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(10,949)	(5,182)
Available-for-sale securities, estimated fair value, 12 months or longer	12,211	67,623
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(3,929)	(8,568)
Available-for-sale securities, estimated fair value	96,443	174,837
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(14,878)	(13,750)
Short-Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	75,829	504,211
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(14)	(6)
Available-for-sale securities, estimated fair value, 12 months or longer	0	0
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	0	0
Available-for-sale securities, estimated fair value	75,829	504,211
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	$ (14)	$ (6)

Investments (Schedule Of Amorti

Investments (Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturity Securities By Contractual Maturity Date) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, amortized cost	$ 375,471
Due after one year through five years, amortized cost	1,232,430
Due after five years through ten years, amortized cost	1,567,938
Due after ten years, amortized cost	4,323,766
Amortized cost, sub-total	7,499,605
Total fixed maturities, amortized cost	9,515,082	$ 9,591,734
Due in one year or less, estimated fair value	377,672
Due after one year through five years, estimated fair value	1,276,160
Due after five years through ten years, estimated fair value	1,646,296
Due after ten years, estimated fair value	4,591,590
Estimated fair value, sub-total	7,891,718
Total fixed maturities, estimated fair value	9,919,346	$ 9,891,510
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, amortized cost	1,195,384
Fixed maturities, estimated fair value	1,191,410
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, amortized cost	799,872
Fixed maturities, estimated fair value	816,062
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, amortized cost	20,221
Fixed maturities, estimated fair value	$ 20,156

Investments (Components Of Net

Investments (Components Of Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Municipal bonds (tax-exempt)	$ 21,486	$ 22,136	$ 66,616	$ 66,621
Short-term investments, including overnight deposits	7,779	2,878	18,562	7,823
Dividends on equity securities	21,467	17,308	61,090	51,718
Income from equity method investments	4,239	1,232	10,634	4,900
Other	(315)	(60)	(520)	2,614
Total investment income	108,725	96,901	316,933	291,471
Investment expenses	(4,236)	(3,754)	(12,777)	(12,034)
Net investment income	104,489	93,147	304,156	279,437
Taxable Municipal Bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	17,732	16,710	53,030	48,820
Other Taxable Bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	$ 36,337	$ 36,697	$ 107,521	$ 108,975

Investments (Summary Of Net Rea

Investments (Summary Of Net Realized Investment Gains (Losses) And The Change In Net Unrealized Gains On Investments) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Gain (Loss) on Investments [Line Items]
Realized gains	$ 13,831	$ 22,539	$ 35,974	$ 69,706
Realized losses	(5,461)	(4,302)	(11,409)	(22,332)
Gains (losses) on securities measured at fair value through net income (loss)	(48,377)	9,179	(26,080)	18,462
Other-than-temporary impairment losses recognized in net income	(3,444)	0	(7,261)	(12,080)
Net realized investment gains (losses)	(40,007)	27,416	(1,515)	65,836
Change in net unrealized gains on investments included in other comprehensive income	328,768	26,381	836,258	619,072
Sales Of Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Realized gains	3,426	3,698	4,189	4,658
Realized losses	(663)	(60)	(1,271)	(608)
Sales Of Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Realized gains	9,276	18,418	25,806	63,931
Realized losses	(578)	(4,187)	(1,791)	(6,672)
Other [Member]
Gain (Loss) on Investments [Line Items]
Realized gains	1,129	423	5,979	1,117
Realized losses	(776)	(55)	(1,086)	(2,972)
Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Change in net unrealized gains on investments included in other comprehensive income	20,428	(53,962)	104,488	399,020
Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Change in net unrealized gains on investments included in other comprehensive income	308,324	80,285	731,748	220,029
Short-Term Investments [Member]
Gain (Loss) on Investments [Line Items]
Change in net unrealized gains on investments included in other comprehensive income	$ 16	$ 58	$ 22	$ 23

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized investment gains (losses)	$ (51,639)	$ 6,881	$ (39,505)	$ 20,154
Fair value, level 1 to level 2 transfers, amount	0	0	0	0
Fair value, level 2 to level 1 transfers, amount	0	0	0	0
Assets measured at fair value on a nonrecurring basis	0	0	0	0
Liabilities measured at fair value on a nonrecurring basis	0	$ 0	0	$ 0
Investment in ILS Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized investment gains (losses)	$ (51,600)		$ (39,500)

Fair Value Measurements (Balanc

Fair Value Measurements (Balances Of Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	$ 9,919,346	$ 9,891,510
Total equity securities	5,709,946	4,745,841
Short-term investments	1,995,562	2,336,151
Available-for-sale investments, estimated fair value	17,624,854	16,973,502
Fixed Maturities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	9,919,346	9,891,510
U.S. Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	128,836	258,584
U.S. Government-Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	369,641	423,212
Obligations Of States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	4,552,999	4,428,205
Foreign Governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	1,545,322	1,463,462
Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	1,191,410	1,040,356
Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	816,062	790,946
Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	20,156	27,338
Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	1,294,920	1,459,407
Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	5,709,946	4,745,841
Insurance, Banks And Other Financial Institutions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	2,010,271	1,697,810
Industrial, Consumer And All Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments, estimated fair value	3,699,675	3,048,031
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	9,919,346	9,891,510
Total equity securities	5,709,946	4,745,841
Short-term investments	1,995,562	2,336,151
Available-for-sale investments, estimated fair value	17,624,854	16,973,502
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	0	0
Total equity securities	5,528,672	4,554,638
Short-term investments	1,895,262	2,255,898
Available-for-sale investments, estimated fair value	7,423,934	6,810,536
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	9,919,346	9,891,510
Total equity securities	0	0
Short-term investments	100,300	80,253
Available-for-sale investments, estimated fair value	10,019,646	9,971,763
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	0	0
Total equity securities	181,274	191,203
Short-term investments	0	0
Available-for-sale investments, estimated fair value	181,274	191,203
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	128,836	258,584
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]
Total fixed maturities	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]
Total fixed maturities	128,836	258,584
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]
Total fixed maturities	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]
Total fixed maturities	369,641	423,212
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]
Total fixed maturities	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]
Total fixed maturities	369,641	423,212
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]
Total fixed maturities	0	0
Fair Value, Measurements, Recurring [Member] | Obligations Of States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	4,552,999	4,428,205
Fair Value, Measurements, Recurring [Member] | Obligations Of States, Municipalities And Political Subdivisions [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	0	0
Fair Value, Measurements, Recurring [Member] | Obligations Of States, Municipalities And Political Subdivisions [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	4,552,999	4,428,205
Fair Value, Measurements, Recurring [Member] | Obligations Of States, Municipalities And Political Subdivisions [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	0	0
Fair Value, Measurements, Recurring [Member] | Foreign Governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	1,545,322	1,463,462
Fair Value, Measurements, Recurring [Member] | Foreign Governments [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	0	0
Fair Value, Measurements, Recurring [Member] | Foreign Governments [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	1,545,322	1,463,462
Fair Value, Measurements, Recurring [Member] | Foreign Governments [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	0	0
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	1,191,410	1,040,356
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	0	0
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	1,191,410	1,040,356
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	0	0
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	816,062	790,946
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	0	0
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	816,062	790,946
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	0	0
Fair Value, Measurements, Recurring [Member] | Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	20,156	27,338
Fair Value, Measurements, Recurring [Member] | Asset-Backed Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	0	0
Fair Value, Measurements, Recurring [Member] | Asset-Backed Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	20,156	27,338
Fair Value, Measurements, Recurring [Member] | Asset-Backed Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	0	0
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	1,294,920	1,459,407
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	0	0
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	1,294,920	1,459,407
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	0	0
Fair Value, Measurements, Recurring [Member] | Insurance, Banks And Other Financial Institutions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total equity securities	2,010,271	1,697,810
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	1,828,997	1,506,607
Fair Value, Measurements, Recurring [Member] | Insurance, Banks And Other Financial Institutions [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total equity securities	0	0
Fair Value, Measurements, Recurring [Member] | Insurance, Banks And Other Financial Institutions [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total equity securities	181,274	191,203
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	3,699,675	3,048,031
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	3,699,675	3,048,031
Fair Value, Measurements, Recurring [Member] | Industrial, Consumer And All Other [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total equity securities	0	0
Fair Value, Measurements, Recurring [Member] | Industrial, Consumer And All Other [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total equity securities	$ 0	$ 0

Fair Value Measurements (Summar

Fair Value Measurements (Summary Of Changes In Level 3 Investments Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value Disclosures [Abstract]
Equity securities, beginning of period		$ 183,913	$ 183,523	$ 191,203	$ 0
Purchases		49,000	0	56,250	195,250
Sales		0	0	(26,674)	(25,000)
Total gains (losses) included in net income (loss)		(51,639)	6,881	(39,505)	20,154
Total gains (losses) included in other comprehensive income		0	0	0	0
Transfers into level 3		0	0	0	0
Transfers out of level 3		0	0	0	0
Equity securities, end of period		181,274	190,404	181,274	190,404
Net unrealized gains (losses) included in net income (loss) relating to assets held at September 30, 2017 and 2016	[1]	$ (51,639)	$ 6,881	$ (39,505)	$ 20,154
[1]	Included in net realized investment gains (losses) in the consolidated statements of income (loss) and comprehensive income (loss).

Segment Reporting Disclosures42

Segment Reporting Disclosures (Company's Segment Disclosures) (Details) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)segment	Sep. 30, 2016USD ($)
Segment Reporting Information [Line Items]
Number of reportable ongoing underwriting segments | segment				3
Gross premium volume		$ 1,328,128	$ 1,129,773	$ 4,146,043	$ 3,800,085
Net written premiums		1,097,754	929,383	3,495,640	3,161,889
Earned premiums		1,099,862	974,244	3,116,038	2,882,789
Losses and loss adjustment expenses, current accident year		(1,226,540)	(660,122)	(2,549,471)	(1,903,645)
Losses and loss adjustment expenses, prior accident years		151,108	80,717	339,342	338,720
Amortization of policy acquisition costs		(230,823)	(201,873)	(648,845)	(580,208)
Other operating expenses		(165,086)	(170,648)	(520,330)	(532,581)
Underwriting profit (loss)		(371,479)	22,318	(263,266)	205,075
Net investment income		104,489	93,147	304,156	279,437
Net realized investment gains (losses)		(40,007)	27,416	(1,515)	65,836
Other revenues (insurance)		2,065	2,170	9,963	10,218
Other expenses (insurance)		(7,973)	(5,579)	(28,123)	(25,878)
Segment profit (loss)		(312,905)	139,472	21,215	534,688
Other revenues (non-insurance)		339,739	334,305	970,750	945,121
Other expenses (non-insurance)		(336,314)	(304,134)	(897,861)	(836,837)
Amortization of intangible assets		(18,654)	(17,010)	(53,450)	(51,474)
Interest expense		(31,814)	(33,152)	(97,013)	(97,690)
Loss on early extinguishment of debt		0	0	0	(44,100)
Income (Loss) Before Income Taxes		$ (359,948)	$ 119,481	$ (56,359)	$ 449,708
U.S. GAAP combined ratio	[1]	134.00%	98.00%	108.00%	93.00%
U.S. Insurance [Member]
Segment Reporting Information [Line Items]
Gross premium volume		$ 778,323	$ 663,196	$ 2,171,481	$ 2,000,454
Net written premiums		653,970	562,215	1,829,528	1,694,193
Earned premiums		600,294	548,792	1,727,871	1,614,588
Losses and loss adjustment expenses, current accident year		(533,662)	(370,435)	(1,259,777)	(1,038,860)
Losses and loss adjustment expenses, prior accident years		87,613	21,471	207,499	126,457
Amortization of policy acquisition costs		(134,243)	(115,504)	(371,241)	(336,093)
Other operating expenses		(90,350)	(91,124)	(292,409)	(280,913)
Underwriting profit (loss)		(70,348)	(6,800)	11,943	85,179
Net investment income		0	0	0	0
Net realized investment gains (losses)		0	0	0	0
Other revenues (insurance)		979	1,285	2,685	3,662
Other expenses (insurance)		(162)	(670)	(1,005)	(2,078)
Segment profit (loss)		$ (69,531)	$ (6,185)	$ 13,623	$ 86,763
U.S. GAAP combined ratio	[1]	112.00%	101.00%	99.00%	95.00%
International Insurance [Member]
Segment Reporting Information [Line Items]
Gross premium volume		$ 319,914	$ 269,093	$ 949,031	$ 879,078
Net written premiums		254,326	209,656	766,571	680,691
Earned premiums		240,145	218,968	673,606	637,365
Losses and loss adjustment expenses, current accident year		(274,581)	(159,812)	(579,601)	(451,741)
Losses and loss adjustment expenses, prior accident years		40,740	42,705	146,268	111,359
Amortization of policy acquisition costs		(43,140)	(38,075)	(114,219)	(105,220)
Other operating expenses		(50,771)	(44,716)	(157,249)	(162,739)
Underwriting profit (loss)		(87,607)	19,070	(31,195)	29,024
Net investment income		0	0	0	0
Net realized investment gains (losses)		0	0	0	0
Other revenues (insurance)		658	419	5,227	5,149
Other expenses (insurance)		(1,035)	(677)	(6,109)	(4,368)
Segment profit (loss)		$ (87,984)	$ 18,812	$ (32,077)	$ 29,805
U.S. GAAP combined ratio	[1]	136.00%	91.00%	105.00%	95.00%
Reinsurance [Member]
Segment Reporting Information [Line Items]
Gross premium volume		$ 230,077	$ 196,948	$ 1,025,716	$ 920,038
Net written premiums		189,636	157,043	899,698	786,450
Earned premiums		259,601	206,018	714,718	630,151
Losses and loss adjustment expenses, current accident year		(418,297)	(129,875)	(710,093)	(413,044)
Losses and loss adjustment expenses, prior accident years		21,164	19,135	(22,248)	90,140
Amortization of policy acquisition costs		(53,440)	(48,294)	(163,385)	(138,895)
Other operating expenses		(23,885)	(34,196)	(70,293)	(88,243)
Underwriting profit (loss)		(214,857)	12,788	(251,301)	80,109
Net investment income		0	0	0	0
Net realized investment gains (losses)		0	0	0	0
Other revenues (insurance)		0	0	417	0
Other expenses (insurance)		0	0	0	0
Segment profit (loss)		$ (214,857)	$ 12,788	$ (250,884)	$ 80,109
U.S. GAAP combined ratio	[1]	183.00%	94.00%	135.00%	87.00%
Other Insurance (Discontinued Lines) [Member]
Segment Reporting Information [Line Items]
Gross premium volume		$ (186)	$ 536	$ (185)	$ 515
Net written premiums		(178)	469	(157)	555
Earned premiums		(178)	466	(157)	685
Losses and loss adjustment expenses, current accident year		0	0	0	0
Losses and loss adjustment expenses, prior accident years		1,591	(2,594)	7,823	10,764
Amortization of policy acquisition costs		0	0	0	0
Other operating expenses		(80)	(612)	(379)	(686)
Underwriting profit (loss)		1,333	(2,740)	7,287	10,763
Net investment income		0	0	0	0
Net realized investment gains (losses)		0	0	0	0
Other revenues (insurance)		428	466	1,634	1,407
Other expenses (insurance)		(6,776)	(4,232)	(21,009)	(19,432)
Segment profit (loss)		$ (5,015)	$ (6,506)	$ (12,088)	$ (7,262)
U.S. GAAP combined ratio - not meaniningful	[1],[2]	NM	NM	NM	NM
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		104,489	93,147	304,156	279,437
Net realized investment gains (losses)		(40,007)	27,416	(1,515)	65,836
Other revenues (insurance)		0	0	0	0
Other expenses (insurance)		0	0	0	0
Segment profit (loss)		$ 64,482	$ 120,563	$ 302,641	$ 345,273
[1]	The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums.
[2]	NM – Ratio is not meaningful.

Segment Reporting Disclosures43

Segment Reporting Disclosures (Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Assets	$ 28,519,411	$ 25,875,299
Non-Insurance Operations [Member]
Segment Reporting Information [Line Items]
Assets	2,106,984	1,448,019
Segment Assets [Member]
Segment Reporting Information [Line Items]
Assets	26,412,427	24,427,280
Segment Assets [Member] | Investing [Member]
Segment Reporting Information [Line Items]
Assets	19,884,334	19,029,584
Segment Assets [Member] | Underwriting [Member]
Segment Reporting Information [Line Items]
Assets	$ 6,528,093	$ 5,397,696

Unpaid Losses And Loss Adjust44

Unpaid Losses And Loss Adjustment Expenses (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	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 development related to the commutation of a property and casualty deposit contract				$ 11,700
Net reserves for losses and loss adjustment expenses of acquired insurance companies			12,702	0
Estimated net losses and loss adjustment expenses	$ 1,226,540	$ 660,122	2,549,471	1,903,645
Reinsurance recoverables	540,100	$ 83,300	748,700	289,400
Favorable (adverse) development on prior years' loss reserves			$ 335,494	327,064
Previous Ogden discount rate, percent			2.50%
Current Ogden discount rate, percent			(0.75%)
Gen Liability Personal Lines And Workers Comp US Segment Prof Liability Gen Liability And Marine And Energy Intl Segment Property And Whole Acct Reins Segment [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable (adverse) development on prior years' loss reserves			$ 302,500
Ogden Rate Change [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable (adverse) development on prior years' loss reserves			(85,000)
Gen Liability Prop And Workers Comp US Segment Prof Liability And Marine And Energy Intl Segment Property And Workers Comp 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				263,300
Development On Specified Medical And Medical Malpractice [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable (adverse) development on prior years' loss reserves				$ (71,400)
2017 Catastrophes [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Estimated net losses, net of assumed reinstatement premiums			503,000
Estimated net losses and loss adjustment expenses			521,200
Net assumed reinstatement premiums			18,200
Reinsurance recoverables	$ 464,400		$ 464,400

Unpaid Losses And Loss Adjust45

Unpaid Losses And Loss Adjustment Expenses (Reconciliation Of Consolidated Reserves For Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Net reserves for losses and loss adjustment expenses, beginning of year			$ 8,108,717	$ 8,235,288
Foreign currency movements	$ 158,360	$ (56,741)	158,360	(56,741)
Adjusted net reserves for losses and loss adjustment expenses, beginning of year			8,267,077	8,178,547
Incurred losses and loss adjustment expenses, current accident year	1,226,540	660,122	2,549,471	1,903,645
Incurred losses and loss adjustment expenses, prior accident years			(335,494)	(327,064)
Total incurred losses and loss adjustment expenses			2,213,977	1,576,581
Payments, current accident year			342,055	319,049
Payments, prior accident years			1,185,689	1,219,755
Total payments			1,527,744	1,538,804
Effect of foreign currency rate changes			10,582	38
Net reserves for losses and loss adjustment expenses of acquired insurance companies			12,702	0
Net reserves for losses and loss adjustment expenses, end of period	8,976,594	8,216,362	8,976,594	8,216,362
Reinsurance recoverable on unpaid losses	2,466,554	2,041,928	2,466,554	2,041,928	$ 2,006,945
Gross reserves for losses and loss adjustment expenses, end of period	$ 11,443,148	$ 10,258,290	$ 11,443,148	$ 10,258,290

Senior Long-Term Debt And Oth46

Senior Long-Term Debt And Other Debt (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Apr. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Repayment of debt assumed in connection with acquisitions	$ 84.3
7.20% Unsecured Senior Notes Due April 14, 2017 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate		7.20%
Unsecured senior notes, principal outstanding			$ 90.6

Other Revenues And Other Expe47

Other Revenues And Other Expenses (Summary Of Other Revenues And Other Expenses By Component) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Other Revenues and Other Expenses [Line Items]
Other revenues	$ 341,804	$ 336,475	$ 980,713	$ 955,339
Other expenses	344,287	309,713	925,984	862,715
Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	2,065	2,170	9,963	10,218
Other expenses	7,973	5,579	28,123	25,878
Non-Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	339,739	334,305	970,750	945,121
Other expenses	336,314	304,134	897,861	836,837
Managing General Agent Operations [Member] | Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	1,637	1,704	7,912	8,811
Other expenses	1,134	1,347	4,480	6,446
Life And Annuity [Member] | Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	428	466	1,634	1,407
Other expenses	6,776	4,232	21,009	19,432
Other Insurance [Member] | Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	0	0	417	0
Other expenses	63	0	2,634	0
Manufacturing [Member] | Non-Insurance Operations [Member] | Markel Ventures Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	195,535	203,909	556,691	589,752
Other expenses	173,174	171,595	483,724	491,188
Non-Manufacturing [Member] | Non-Insurance Operations [Member] | Markel Ventures Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	137,213	117,433	376,589	315,863
Other expenses	145,434	115,529	357,549	295,647
Investment Management [Member] | Non-Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	1,248	8,297	19,884	22,820
Other expenses	11,552	10,385	37,682	31,151
Other Non-Insurance [Member] | Non-Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	5,743	4,666	17,586	16,686
Other expenses	$ 6,154	$ 6,625	$ 18,906	$ 18,851

Reinsurance (Narrative) (Detail

Reinsurance (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Percentage of ceded earned premiums to gross earned premiums	17.00%	17.00%	16.00%	18.00%
Percentage of assumed earned premiums to net earned premiums	32.00%	30.00%	31.00%	30.00%
Reinsurance recoverables	$ 540.1	$ 83.3	$ 748.7	$ 289.4
2017 Catastrophes [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reinsurance recoverables	$ 464.4		$ 464.4

Reinsurance (Effect Of Reinsura

Reinsurance (Effect Of Reinsurance And Retrocessional Reinsurance On Premiums Written And Earned) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reinsurance Disclosures [Abstract]
Direct premiums written	$ 1,035,705	$ 888,009	$ 2,932,022	$ 2,724,341
Direct premiums earned	966,735	883,687	2,743,970	2,617,074
Assumed premiums written	292,423	241,764	1,214,021	1,075,744
Assumed premiums earned	356,529	292,951	976,636	878,882
Ceded premiums written	(230,374)	(200,390)	(650,403)	(638,196)
Ceded premiums earned	(223,402)	(202,394)	(604,568)	(613,167)
Net premiums written	1,097,754	929,383	3,495,640	3,161,889
Net premiums earned	$ 1,099,862	$ 974,244	$ 3,116,038	$ 2,882,789

Life And Annuity Benefits (Narr

Life And Annuity Benefits (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Liability for Future Policy Benefits [Abstract]
Adjustment to life and annuity benefits	$ 0	$ 9.6	$ 0	$ 57.5

Variable Interest Entities (Nar

Variable Interest Entities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds	$ 341,804	$ 336,475	$ 980,713	$ 955,339
Total investment and insurance assets under management of MCIM for unconsolidated VIEs	4,500,000		4,500,000
Markel Diversified Fund [Member]
Variable Interest Entity [Line Items]
Total assets of the Markel Diversified Fund	183,300		183,300		$ 166,800
Total liabilities of the Markel Diversified Fund	62,800		62,800		64,600
Investment in one of the unconsolidated Funds	$ 180,700		$ 180,700		$ 165,100
Percentage of total assets of the Markel Diversified Fund invested in one of the unconsolidated Funds	7.00%		7.00%		6.00%
Note payable included in total liabilities of the Markel Diversified Fund delivered as part of the consideration provided for its investment	$ 62,500		$ 62,500		$ 62,500
Non-Insurance Operations [Member]
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds	339,739	334,305	970,750	945,121
Investment Management [Member] | Non-Insurance Operations [Member]
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds	$ 1,248	$ 8,297	$ 19,884	$ 22,820

Net Income (Loss) Per Share (Sc

Net Income (Loss) Per Share (Schedule Of Net Income (Loss) Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings (Loss) Per Share [Line Items]
Net income (loss) to shareholders	$ (259,141)	$ 83,796	$ (39,612)	$ 322,963
Adjustment of redeemable noncontrolling interests	(3,298)	(4,928)	(23,582)	(10,909)
Adjusted net income (loss) to shareholders	$ (262,439)	$ 78,868	$ (63,194)	$ 312,054
Basic common shares outstanding	13,947	14,033	13,974	14,013
Diluted shares outstanding	13,990	14,085	14,018	14,079
Basic net income (loss) per share	$ (18.82)	$ 5.62	$ (4.52)	$ 22.27
Diluted net income (loss) per share	$ (18.82)	$ 5.60	$ (4.52)	$ 22.16
Stock Options [Member]
Earnings (Loss) Per Share [Line Items]
Dilutive potential common shares	1	3	2	4
Restricted Stock Units (RSUs) [Member]
Earnings (Loss) Per Share [Line Items]
Dilutive potential common shares	42	49	42	62

Other Comprehensive Income (Cha

Other Comprehensive Income (Change In Accumulated Other Comprehensive Income By Component, Net Of Taxes And Noncontrolling Interest) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income, beginning balance	$ 1,565,866	$ 1,354,508
Other comprehensive income (loss) before reclassifications	597,546	405,195
Amounts reclassified from accumulated other comprehensive income	(12,207)	(32,061)
Total other comprehensive income (loss)	585,339	373,134
Accumulated other comprehensive income, ending balance	2,151,205	1,727,642
Unrealized Holding Gains On Available-For-Sale Securities [Member]
Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income, beginning balance	1,714,930	1,472,762
Other comprehensive income (loss) before reclassifications	577,796	411,354
Amounts reclassified from accumulated other comprehensive income	(14,598)	(33,308)
Total other comprehensive income (loss)	563,198	378,046
Accumulated other comprehensive income, ending balance	2,278,128	1,850,808
Foreign Currency [Member]
Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income, beginning balance	(84,406)	(72,696)
Other comprehensive income (loss) before reclassifications	19,750	(6,159)
Amounts reclassified from accumulated other comprehensive income	0	0
Total other comprehensive income (loss)	19,750	(6,159)
Accumulated other comprehensive income, ending balance	(64,656)	(78,855)
Net Actuarial Pension Loss [Member]
Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income, beginning balance	(64,658)	(45,558)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	2,391	1,247
Total other comprehensive income (loss)	2,391	1,247
Accumulated other comprehensive income, ending balance	$ (62,267)	$ (44,311)

Other Comprehensive Income (Sum

Other Comprehensive Income (Summary Of Tax Expense (Benefit) Of Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Other Comprehensive Income (Loss), Tax [Abstract]
Net holding gains arising during the period	$ 109,338	$ 8,309	$ 278,266	$ 196,189
Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period	0	(3)	0	(9)
Reclassification adjustments for net losses included in net income (loss)	(2,810)	(4,811)	(5,206)	(12,621)
Change in net unrealized gains on investments	106,528	3,495	273,060	183,559
Change in foreign currency translation adjustments	656	2,847	153	1,152
Change in net actuarial pension loss	159	86	492	274
Total	$ 107,343	$ 6,428	$ 273,705	$ 184,985

Other Comprehensive Income (Rec

Other Comprehensive Income (Reclassifications From Accumulated Other Comprehensive Income Into Income, By Component) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses recognized in net income	$ (3,444)	$ 0	$ (7,261)	$ (12,080)
Net realized investment gains, excluding other-than-temporary impairment losses	(36,563)	27,416	5,746	77,916
Income (Loss) Before Income Taxes	(359,948)	119,481	(56,359)	449,708
Underwriting, acquisition and insurance expenses	(395,909)	(372,521)	(1,169,175)	(1,112,789)
Income taxes	98,913	(36,060)	17,791	(121,968)
Net Income (Loss)	(261,035)	83,421	(38,568)	327,740
Reclassification Out Of Accumulated Other Comprehensive Income [Member] | Unrealized Holding Gains On Available-For-Sale Securities [Member]
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses recognized in net income	(3,444)	0	(7,261)	(12,080)
Net realized investment gains, excluding other-than-temporary impairment losses	11,461	14,569	27,065	58,009
Income (Loss) Before Income Taxes	8,017	14,569	19,804	45,929
Income taxes	(2,810)	(4,811)	(5,206)	(12,621)
Net Income (Loss)	5,207	9,758	14,598	33,308
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	(932)	(476)	(2,883)	(1,521)
Income taxes	159	86	492	274
Net Income (Loss)	$ (773)	$ (390)	$ (2,391)	$ (1,247)

Contingencies (Narrative) (Deta

Contingencies (Narrative) (Details) - Thomas Yeransian v. Markel Corporation [Member] $ in Millions	Sep. 30, 2017USD ($)
Damages [Member]
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss	$ 47.3
Interest [Member]
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss	11.1
Default Interest [Member]
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss	$ 9.7

Subsequent Events (Narrative) (

Subsequent Events (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 25, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Subsequent Event [Line Items]
Estimated net incurred losses		$ 1,075,432	$ 579,405	$ 2,210,129	$ 1,564,925
California Wildfires [Member] | Minimum [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Estimated net incurred losses	$ 40,000
California Wildfires [Member] | Maximum [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Estimated net incurred losses	$ 80,000