Markel (MKL) 10-K 24 Feb 17 2016 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2016	Feb. 06, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
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		13,955,617
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 12,978,000,000

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
ASSETS
Fixed maturities (amortized cost of $9,591,734 in 2016 and $9,038,158 in 2015)	$ 9,891,510	$ 9,394,468
Equity securities (cost of $2,481,448 in 2016 and $2,208,834 in 2015)	4,745,841	4,074,475
Short-term investments (estimated fair value approximates cost)	2,336,151	1,642,261
Total Investments	16,973,502	15,111,204
Cash and cash equivalents	1,738,747	2,630,009
Restricted cash and cash equivalents	346,417	440,132
Receivables	1,241,649	1,113,703
Reinsurance recoverable on unpaid losses	2,006,945	2,016,665
Reinsurance recoverable on paid losses	64,892	50,123
Deferred policy acquisition costs	392,410	352,756
Prepaid reinsurance premiums	299,923	322,362
Goodwill	1,142,248	1,167,844
Intangible assets	722,542	792,372
Other assets	946,024	941,945
Total Assets	25,875,299	24,939,115
LIABILITIES AND EQUITY
Unpaid losses and loss adjustment expenses	10,115,662	10,251,953
Life and annuity benefits	1,049,654	1,123,275
Unearned premiums	2,263,838	2,166,105
Payables to insurance and reinsurance companies	231,327	224,921
Senior long-term debt and other debt (estimated fair value of $2,721,000 in 2016 and $2,403,000 in 2015)	2,574,529	2,239,271
Other liabilities	1,099,200	1,030,023
Total Liabilities	17,334,210	17,035,548
Redeemable noncontrolling interests	73,678	62,958
Commitments and contingencies
Shareholders' equity:
Common stock	3,368,666	3,342,357
Retained earnings	3,526,395	3,137,285
Accumulated other comprehensive income	1,565,866	1,354,508
Total Shareholders' Equity	8,460,927	7,834,150
Noncontrolling interests	6,484	6,459
Total Equity	8,467,411	7,840,609
Total Liabilities and Equity	$ 25,875,299	$ 24,939,115

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Fixed maturities, amortized cost	$ 9,591,734	$ 9,038,158
Equity securities, cost	2,481,448	2,208,834
Senior long-term debt and other debt, estimated fair value	$ 2,721,000	$ 2,403,000

Consolidated Statements Of Inco

Consolidated Statements Of Income And Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
OPERATING REVENUES
Earned premiums	$ 3,865,870	$ 3,823,532	$ 3,840,912
Net investment income	373,230	353,213	363,230
Net realized investment gains:
Other-than-temporary impairment losses	(18,355)	(44,481)	(4,784)
Net realized investment gains, excluding other-than-temporary impairment losses	83,502	150,961	50,784
Net realized investment gains	65,147	106,480	46,000
Other revenues	1,307,779	1,086,758	883,525
Total Operating Revenues	5,612,026	5,369,983	5,133,667
OPERATING EXPENSES
Losses and loss adjustment expenses	2,050,744	1,938,745	2,202,467
Underwriting, acquisition and insurance expenses	1,498,590	1,455,080	1,460,882
Amortization of intangible assets	68,533	68,947	57,627
Other expenses	1,190,243	1,046,805	854,871
Total Operating Expenses	4,808,110	4,509,577	4,575,847
Operating Income	803,916	860,406	557,820
Interest expense	129,896	118,301	117,442
Loss on early extinguishment of debt	44,100	0	0
Income Before Income Taxes	629,920	742,105	440,378
Income tax expense	169,477	152,963	116,690
Net Income	460,443	589,142	323,688
Net income attributable to noncontrolling interests	4,754	6,370	2,506
Net Income to Shareholders	455,689	582,772	321,182
OTHER COMPREHENSIVE INCOME (LOSS)
Net holding gains (losses) arising during the period	275,661	(240,170)	687,735
Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period	35	160	173
Reclassification adjustments for net gains included in net income	(33,528)	(80,482)	(26,161)
Change in net unrealized gains on investments, net of taxes	242,168	(320,492)	661,747
Change in foreign currency translation adjustments, net of taxes	(11,704)	(29,278)	(32,241)
Change in net actuarial pension loss, net of taxes	(19,100)	(352)	(14,750)
Total Other Comprehensive Income (Loss)	211,364	(350,122)	614,756
Comprehensive Income	671,807	239,020	938,444
Comprehensive income attributable to noncontrolling interests	4,760	6,297	2,510
Comprehensive Income to Shareholders	$ 667,047	$ 232,723	$ 935,934
NET INCOME PER SHARE
Basic (dollars per share)	$ 31.41	$ 41.99	$ 22.38
Diluted (dollars per share)	$ 31.27	$ 41.74	$ 22.27

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, 2013		$ 6,678,010	$ 6,673,577	$ 3,288,863	$ 2,294,909	$ 1,089,805	$ 4,433
Balance, shares at Dec. 31, 2013				13,986
Balance, redeemable noncontrolling interests at Dec. 31, 2013								$ 72,183
Net income (loss)	$ 323,688	319,201	321,182		321,182	0	(1,981)	4,487
Other comprehensive income (loss)	614,756	614,752	614,752		0	614,752	0	4
Comprehensive Income	938,444	933,953	935,934				(1,981)	4,491
Issuance of common stock		5,691	5,691	$ 5,691	0	0	0	0
Issuance of common stock, shares				19
Repurchase of common stock		(26,053)	(26,053)	$ 0	(26,053)	0	0	0
Repurchase of common stock, shares				(43)
Restricted stock awards expensed		22,935	22,935	$ 22,935	0	0	0	0
Restricted stock awards expensed, shares				0
Adjustment of redeemable noncontrolling interests		(8,186)	(8,186)	$ 0	(8,186)	0	0	8,186
Adjustment of redeemable noncontrolling interests, shares				0
Purchase of noncontrolling interest		(9,352)	(10,257)	$ (10,257)	0	0	905	(18,566)
Purchase of noncontrolling interest, shares				0
Other		5,004	1,177	$ 1,163	14	0	3,827	(5,246)
Other, shares				0
Balance at Dec. 31, 2014		7,602,002	7,594,818	$ 3,308,395	2,581,866	1,704,557	7,184
Balance, shares at Dec. 31, 2014				13,962
Balance, redeemable noncontrolling interests at Dec. 31, 2014								61,048
Net income (loss)	589,142	581,784	582,772		582,772	0	(988)	7,358
Other comprehensive income (loss)	(350,122)	(350,049)	(350,049)		0	(350,049)	0	(73)
Comprehensive Income	239,020	231,735	232,723				(988)	7,285
Issuance of common stock		4,752	4,752	$ 4,752	0	0	0	0
Issuance of common stock, shares				34
Repurchase of common stock		(31,491)	(31,491)	$ 0	(31,491)	0	0	0
Repurchase of common stock, shares				(37)
Restricted stock awards expensed		24,129	24,129	$ 24,129	0	0	0	0
Restricted stock awards expensed, shares				0
Acquisition of CapTech		0	0	$ 0	0	0	0	13,817
Acquisition of CapTech, shares				0
Adjustment of redeemable noncontrolling interests		4,144	4,144	$ 0	4,144	0	0	(4,144)
Adjustment of redeemable noncontrolling interests, shares				0
Purchase of noncontrolling interest		(1,447)	(1,447)	$ (1,447)	0	0	0	(8,224)
Purchase of noncontrolling interest, shares				0
Other		6,785	6,522	$ 6,528	(6)	0	263	(6,824)
Other, shares				0
Balance at Dec. 31, 2015	7,840,609	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							62,958
Net income (loss)	460,443	455,788	455,689		455,689	0	99	4,655
Other comprehensive income (loss)	211,364	211,358	211,358		0	211,358	0	6
Comprehensive Income	671,807	667,146	667,047				99	4,661
Issuance of common stock		4,623	4,623	$ 4,623	0	0	0	0
Issuance of common stock, shares				54
Repurchase of common stock		(51,142)	(51,142)	$ 0	(51,142)	0	0	0
Repurchase of common stock, shares				(58)
Restricted stock awards expensed		21,336	21,336	$ 21,336	0	0	0	0
Restricted stock awards expensed, shares				0
Adjustment of redeemable noncontrolling interests		(15,472)	(15,472)	$ 0	(15,472)	0	0	15,472
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		(39)	35	$ 0	35	0	(74)	(5,896)
Other, shares				0
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

Consolidated Statements Of Cash

Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
OPERATING ACTIVITIES
Net income	$ 460,443	$ 589,142	$ 323,688
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred income tax expense (benefit)	63,358	(9,678)	84,543
Depreciation and amortization	194,147	200,987	203,580
Net realized investment gains	(65,147)	(106,480)	(46,000)
Loss on early extinguishment of debt	44,100	0	0
Decrease (increase) in receivables	(163,123)	5,604	21,148
Increase in deferred policy acquisition costs	(41,619)	(7,360)	(99,387)
Increase (decrease) in unpaid losses and loss adjustment expenses, net	(9,429)	(91,960)	249,873
Decrease in life and annuity benefits	(54,580)	(85,257)	(62,883)
Increase (decrease) in unearned premiums, net	134,593	(4,522)	147,840
Increase (decrease) in payables to insurance and reinsurance companies	11,582	(31,829)	(45,204)
Increase (decrease) in income taxes payable	(16,484)	27,817	(46,576)
Increase in accrued expenses	67,994	97,273	56,042
Decrease in other liabilities	(90,571)	(5,793)	(76,383)
Other	(641)	73,207	6,511
Net Cash Provided By Operating Activities	534,623	651,151	716,792
INVESTING ACTIVITIES
Proceeds from sales of fixed maturities and equity securities	365,822	538,978	1,286,871
Proceeds from maturities, calls and prepayments of fixed maturities	963,165	1,503,616	1,420,817
Cost of fixed maturities and equity securities purchased	(2,205,939)	(1,576,254)	(3,153,055)
Net change in short-term investments	(689,194)	(62,124)	(129,164)
Proceeds from sales of equity method investments	8,790	23,155	107,292
Cost of equity method investments	(8,576)	(21,849)	(16,081)
Change in restricted cash and cash equivalents	93,370	62,324	264,701
Additions to property and equipment	(63,674)	(79,755)	(82,132)
Acquisitions, net of cash acquired	(7,527)	(261,521)	(319,086)
Other	(1,348)	(797)	(2,368)
Net Cash Provided (Used) By Investing Activities	(1,545,111)	125,773	(622,205)
FINANCING ACTIVITIES
Additions to senior long-term debt and other debt	559,300	69,797	89,480
Repayment and retirement of senior long-term debt and other debt	(278,363)	(88,020)	(83,722)
Premiums and fees related to early extinguishment of debt	(43,691)	0	0
Repurchases of common stock	(51,142)	(31,491)	(26,053)
Issuance of common stock	4,623	4,752	5,691
Payment of contingent consideration	(14,219)	(9,263)	(2,766)
Purchase of redeemable noncontrolling interests	(3,167)	(12,474)	(25,918)
Distributions to noncontrolling interests	(5,949)	(6,287)	(5,245)
Other	(15,373)	(1,225)	(18,591)
Net Cash Provided (Used) By Financing Activities	152,019	(74,211)	(67,124)
Effect of foreign currency rate changes on cash and cash equivalents	(32,793)	(32,873)	(45,820)
Increase (decrease) in cash and cash equivalents	(891,262)	669,840	(18,357)
Cash and cash equivalents at beginning of year	2,630,009	1,960,169	1,978,526
CASH AND CASH EQUIVALENTS AT END OF YEAR	$ 1,738,747	$ 2,630,009	$ 1,960,169

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Summary Of Significant Accounting Policies	Summary of Significant Accounting Policies Markel Corporation is a diverse financial holding company serving a variety of niche markets. Markel Corporation's principal business markets and underwrites specialty insurance products. Through its wholly owned subsidiary, Markel Ventures, Inc. (Markel Ventures), Markel Corporation also owns interests in various industrial and service businesses that operate outside of the specialty insurance marketplace. a) Basis of Presentation. 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. Certain prior year amounts have been reclassified to conform to the current presentation. b) Use of Estimates. 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. Management periodically reviews its estimates and assumptions. Quarterly reviews include evaluating the adequacy of reserves for unpaid losses and loss adjustment expenses, life and annuity reinsurance benefit reserves, litigation contingencies, the reinsurance allowance for doubtful accounts and income tax liabilities, as well as analyzing the recoverability of deferred tax assets, estimating reinsurance premiums written and earned and evaluating the investment portfolio for other-than-temporary declines in estimated fair value. Estimates and assumptions for goodwill and intangible assets are reviewed in conjunction with an acquisition, and goodwill and indefinite-lived intangible assets are reassessed at least annually for impairment. Actual results may differ materially from the estimates and assumptions used in preparing the consolidated financial statements. c) Investments. Available-for-sale investments are recorded at estimated fair value. Unrealized gains and losses on investments, net of income taxes, are included in accumulated other comprehensive income in shareholders' equity. 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. Premiums and discounts are amortized or accreted over the lives of the related fixed maturities as an adjustment to the yield using the effective interest method. Dividend and interest income are recognized when earned. Realized investment gains or losses are included in earnings. Realized gains or losses from sales of investments are derived using the first-in, first-out method. The Company also has certain investments in fixed maturity and equity securities that are recorded at estimated fair value with changes in unrealized gains and losses recorded in net income. These fixed maturity and equity security investments totaled $41.4 million and $191.2 million , respectively, as of December 31, 2016 and are included in fixed maturities and equity securities in the consolidated balance sheets. Investments accounted for under the equity method of accounting are recorded at cost within other assets on the consolidated balance sheets and subsequently increased or decreased by the Company's proportionate share of the net income or loss of the investee. The Company records its proportionate share of net income or loss of the investee in net investment income. The Company records its proportionate share of other comprehensive income or loss of the investee as a component of other comprehensive income (loss). Dividends or other equity distributions are recorded as a reduction of the investment. The Company reviews equity method investments for impairment when events or circumstances indicate that a decline in the fair value of the investment below its carrying value is other-than-temporary. d) Cash and Cash Equivalents. The Company considers all investments with original maturities of 90 days or less to be cash equivalents. The carrying value of the Company's cash and cash equivalents and restricted cash and cash equivalents approximates fair value. e) Receivables. Receivables include amounts receivable from agents, brokers and insureds, which represent premiums that are both currently due and amounts not yet due on insurance and reinsurance policies. Premiums for insurance policies are generally due at inception. Premiums for reinsurance policies generally become due over the period of coverage based on the policy terms. The Company monitors the credit risk associated with premiums receivable, taking into consideration the fact that in certain instances credit risk may be reduced by the Company's right to offset loss obligations or unearned premiums against premiums receivable. Amounts deemed uncollectible are charged to net income in the period they are determined. Changes in the estimate of reinsurance premiums written will result in an adjustment to premiums receivable in the period they are determined. f) Reinsurance Recoverables. Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability associated with the reinsured business. Allowances are established for amounts deemed uncollectible and reinsurance recoverables are recorded net of these allowances. The Company evaluates the financial condition of its reinsurers and monitors concentration risk to minimize its exposure to significant losses from individual reinsurers. g) Deferred Policy Acquisition Costs. Costs directly related to the acquisition of insurance premiums are deferred and amortized over the related policy period, generally one year . The Company only defers acquisition costs incurred that are related directly to the successful acquisition of new or renewal insurance contracts, including commissions to agents and brokers and premium taxes. Commissions received related to reinsurance premiums ceded are netted against broker commissions in determining acquisition costs eligible for deferral. To the extent that future policy revenues on existing policies are not adequate to cover related costs and expenses, deferred policy acquisition costs are charged to earnings. The Company does not consider anticipated investment income in determining whether a premium deficiency exists. h) Goodwill and Intangible Assets. Goodwill and intangible assets are recorded as a result of business acquisitions. Goodwill represents the excess of the amount paid to acquire a business over the net fair value of assets acquired and liabilities assumed at the date of acquisition. Indefinite-lived and other intangible assets are recorded at fair value as of the acquisition date. The determination of the fair value of certain assets acquired and liabilities assumed involves significant judgment and the use of valuation models and other estimates, which require assumptions that are inherently subjective. Goodwill and indefinite-lived intangible assets are tested for impairment at least annually. The Company completes an annual test during the fourth quarter of each year based upon the results of operations through September 30. Intangible assets with definite lives are amortized using the straight-line method over their estimated useful lives, generally five to 20 years , and are reviewed for impairment when events or circumstances indicate that their carrying value may not be recoverable. i) Property and Equipment. Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization of property and equipment are calculated using the straight-line method over the estimated useful lives (generally, the lower of the life of the lease or the estimated useful life for leasehold improvements, ten to 40 years for buildings, seven to 40 years for land improvements, three to ten years for furniture and equipment and three to 25 years for other property and equipment). j) Redeemable Noncontrolling Interests. The Company owns controlling interests in various companies through its Markel Ventures operations. In some cases, the Company has the option to acquire the remaining equity interests, and the remaining equity interests have the option to sell their interests to the Company, in the future. The redemption value of the remaining equity interests is generally based on the respective company's earnings in specified periods preceding the redemption date. The redeemable noncontrolling interests generally become redeemable through 2020. The Company recognizes changes in the redemption value that exceed the carrying value of redeemable noncontrolling interests to retained earnings as if the balance sheet date were also the redemption date. Changes in the redemption value also result in an adjustment to net income to shareholders in the calculation of basic and diluted net income per share. The change in the redemption value of redeemable noncontrolling interests in 2016 , 2015 and 2014 resulted in an adjustment to retained earnings of a decrease of $15.5 million , an increase of $4.1 million , and a decrease of $8.2 million , respectively. k) Income Taxes. The Company records deferred income taxes to reflect the net tax effect of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and their tax bases. Deferred tax assets are reduced by a valuation allowance when management believes it is more likely than not that some, or all, of the deferred tax assets will not be realized. The Company recognizes the tax benefit from an uncertain tax position taken or expected to be taken in income tax returns only if it is more likely than not that the tax position will be sustained upon examination by tax authorities, based on the technical merits of the position. Tax positions that meet the more likely than not threshold are then measured using a probability weighted approach, whereby the largest amount of tax benefit that is greater than 50% likely of being realized upon ultimate settlement is recognized. The Company recognizes interest and penalties related to uncertain tax positions in income tax expense. l) Unpaid Losses and Loss Adjustment Expenses. Unpaid losses and loss adjustment expenses on our property and casualty insurance business are based on evaluations of reported claims and estimates for losses and loss adjustment expenses incurred but not reported. Estimates for losses and loss adjustment expenses incurred but not reported are based on reserve development studies, among other things. The Company does not discount reserves for losses and loss adjustment expenses to reflect estimated present value, except for reserves assumed in connection with an acquisition, which are recorded at fair value at the acquisition date. Recorded reserves are estimates, and the ultimate liability may be greater or less than the estimates. m) Life and Annuity Benefits. The Company previously acquired a block of long duration reinsurance contracts for life and annuity benefits which subject the Company to mortality, longevity and morbidity risks. The assumptions used to determine policy benefit reserves are generally locked-in for the life of the contract unless an unlocking event occurs. To the extent existing policy reserves, together with the present value of future gross premiums and expected investment income earned thereon, are not adequate to cover the present value of future benefits, settlement and maintenance costs, 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. Because of the assumptions and estimates used in establishing reserves for life and annuity benefit obligations and the long-term nature of these reinsurance contracts, the ultimate liability may be greater or less than the estimates. Results attributable to the run-off of life and annuity reinsurance business are included in other revenues and other expenses in the Company's consolidated statements of income and comprehensive income and as part of the Company's Other Insurance (Discontinued Lines) segment. n) Revenue Recognition. Property and Casualty Premiums Insurance premiums are generally earned on a pro rata basis over the policy period, typically one year . The cost of reinsurance ceded is initially recorded as prepaid reinsurance premiums and is amortized over the reinsurance contract period in proportion to the amount of insurance protection provided. Premiums ceded are netted against premiums written. Assumed reinsurance premiums are recorded at the inception of each contract based upon contract terms and information received from cedents and brokers and are earned on a pro rata basis over the coverage period, or for multi-year contracts, in proportion with the underlying risk exposure to the extent there is variability in the exposure through the coverage period. Changes in reinsurance premium estimates are expected and may result in significant adjustments in any period. These estimates change over time as additional information regarding changes in underlying exposures is obtained. Any subsequent differences arising on such estimates are recorded as premiums written in the period they are determined and are earned on a pro rata basis over the coverage period. The Company uses the periodic method to account for assumed reinsurance from foreign reinsurers. The Company's foreign reinsurers provide sufficient information to record foreign assumed business in the same manner as the Company records assumed business from United States reinsurers. Certain contracts that the Company writes provide for reinstatement of coverage. Reinstatement premiums are the premiums for the restoration of the insurance or reinsurance limit of a contract to its full amount after a loss occurrence by the insured or reinsured. The Company accrues for reinstatement premiums resulting from losses recorded. Such accruals are based upon contractual terms and management judgment is involved with respect to the amount of losses recorded. Changes in estimates of losses recorded on contracts with reinstatement premium features will result in changes in reinstatement premiums based on contractual terms. Reinstatement premiums are recognized at the time losses are recorded and are earned on a pro-rata basis over the coverage period. Other Revenues Other revenues primarily relate to the Company's Markel Ventures operations and consist of revenues from the sale of manufactured products and service revenues. Revenues from manufactured products are generally recognized at the time title transfers to the customer, which typically occurs at the point of shipment or delivery to the customer, depending on the terms of the sales arrangement. Revenues from services are generally recognized as the services are performed. Services provided pursuant to a contract are recognized either over the contract period or upon completion of the elements specified in the contract, depending on the terms of the contract. Investment management fee income is recognized over the period in which investment management services are provided and is calculated and billed monthly based on the net asset value of the accounts managed. Performance fee arrangements entitle the Company to participate, on a fixed-percentage basis, in any net income generated in excess of an agreed-upon threshold as established by the underlying investment management agreements. In general, net income is calculated at the end of each calendar year and performance fees are payable annually. Following the preferred method identified in the Accounting Standards Codification (ASC) Topic 605, Revenue Recognition , such performance fee income is recorded at the conclusion of the contractual performance period, when all contingencies are resolved. o) Stock-based Compensation. Stock-based compensation expense is generally recognized as part of underwriting, acquisition and insurance expenses over the requisite service period. Stock-based compensation expense, net of taxes, was $14.3 million in 2016 , $16.3 million in 2015 and $18.7 million in 2014 . See note 12 . p) Foreign Currency Translation. The functional currencies of the Company's foreign operations are the currencies in which the majority of their business is transacted. Assets and liabilities of foreign operations are translated into the United States Dollar using the exchange rates in effect at the balance sheet date. Revenues and expenses of foreign operations are translated using the average exchange rate for the period. Gains or losses from translating the financial statements of foreign operations denominated in a functional currency are included, net of taxes, in shareholders' equity as a component of accumulated other comprehensive income. Gains and losses arising from transactions denominated in a foreign currency other than a functional currency are included in net income. The Company manages its exposure to foreign currency risk primarily by matching assets, other than goodwill and intangible assets, and liabilities denominated in the same currency. To the extent that assets and liabilities in foreign currencies are not matched, the Company is exposed to foreign currency risk. For functional currencies, the related exchange rate fluctuations are reflected in other comprehensive income (loss). The cumulative foreign currency translation adjustment, net of taxes, was a loss of $84.4 million and $72.7 million at December 31, 2016 and 2015 , respectively. q) Derivative Financial Instruments. Derivative instruments, including derivative instruments resulting from hedging activities, are measured at fair value and recognized as either assets or liabilities on the consolidated balance sheets. The changes in fair value of derivatives are recognized in earnings unless the derivative is designated as a hedge and qualifies for hedge accounting. The Company's foreign currency forward contracts are generally designated and qualify as hedges of a net investment in a foreign operation. The effective portion of the change in fair value resulting from these hedges is reported in currency translation adjustments as part of other comprehensive income (loss). The ineffective portion of the change in fair value is recognized in earnings. r) Comprehensive Income. Comprehensive income represents all changes in equity that result from recognized transactions and other economic events during the period. Other comprehensive income (loss) refers to revenues, expenses, gains and losses that under U.S. GAAP are included in comprehensive income but excluded from net income, such as unrealized gains or losses on investments, foreign currency translation adjustments and changes in net actuarial pension loss. s) Net Income Per Share. Basic net income per share is computed by dividing adjusted net income to shareholders by the weighted average number of common shares outstanding during the year. Diluted net income per share is computed by dividing adjusted net income to shareholders by the weighted average number of common shares and dilutive potential common shares outstanding during the year. See note 12 (b). t) Variable Interest Entities. The Company determines whether it has relationships with entities defined as VIEs in accordance with ASC Topic 810, Consolidation . Under this guidance, a VIE is consolidated by the variable interest holder that is determined to be the primary beneficiary. An entity in which the Company holds a variable interest is a VIE if any of the following conditions exist: (a) the total equity investment at risk is not sufficient to permit the entity to finance its activities without additional subordinated financial support, (b) as a group, the holders of equity investment at risk lack either the direct or indirect ability through voting rights or similar rights to make decisions about an entity's activities that most significantly impact the entity's economic performance or the obligation to absorb the expected losses or right to receive the expected residual returns, or (c) the voting rights of some investors are disproportionate to their obligation to absorb the expected losses of the entity, their rights to receive the expected residual returns of the entity, or both and substantially all of the entity's activities either involve or are conducted on behalf of an investor with disproportionately few voting rights. The primary beneficiary is defined as the variable interest holder that is determined to have the controlling financial interest as a result of having both (a) the power to direct the activities of a VIE that most significantly impact the economic performance of the VIE and (b) the obligation to absorb losses or right to receive benefits from the VIE that could potentially be significant to the VIE. The Company determines whether an entity is a VIE at the inception of our variable interest in the entity and upon the occurrence of certain reconsideration events. The Company continually reassesses whether it is the primary beneficiary of VIEs in which it holds a variable interest. u) Recent Accounting Pronouncements. Effective January 1, 2016, the Company adopted Financial Accounting Standards Board (FASB) Accounting Standards Update (ASU) No. 2015-02, Consolidation (Topic 810): Amendments to the Consolidation Analysis , which changes the way reporting enterprises evaluate whether (a) they should consolidate limited partnerships and similar entities, (b) fees paid to a decision maker or service provider are variable interests in a VIE, and (c) variable interests in a VIE held by related parties of the reporting enterprise require the reporting enterprise to consolidate the VIE. It also eliminates the VIE consolidation model based on majority exposure to variability that applied to certain investment companies and similar entities. The ASU also significantly changes how to evaluate voting rights for entities that are not similar to limited partnerships when determining whether the entity is a VIE, which may affect entities for which the decision making rights are conveyed through a contractual arrangement. The adoption of this guidance did not result in any changes to our previous consolidation conclusions. Effective January 1, 2016, the Company adopted FASB ASU No. 2015-03, Interest-Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs . ASU No. 2015-03 requires that debt issuance costs related to a recognized debt liability be presented on the balance sheet as a direct deduction from the debt liability, similar to the presentation of debt discounts. The cost of issuing debt is no longer recorded as a separate asset on the balance sheet. The amortization of debt issuance costs continues to be included in interest expense. ASU No. 2015-03 was applied retrospectively to all periods presented. As a result, debt issuance costs totaling $2.2 million and $2.6 million were reclassified from other assets to senior long-term debt and other debt as of December 31, 2015 and December 31, 2014, respectively. The adoption of this ASU did not have an impact on the Company's results of operations or cash flows. Effective January 1, 2016, the Company adopted FASB ASU No. 2015-05, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer's Accounting for Fees Paid in a Cloud Computing Arrangement , which clarifies that software licenses contained in a cloud computing arrangement should be capitalized if the customer has the right to take possession of the software and the ability to run the software outside of the cloud computing arrangement. The adoption of this ASU did not have an impact on the Company's financial position, results of operations or cash flows. Effective January 1, 2016, the Company adopted FASB ASU No. 2015-16, Business Combinations (Topic 805): Simplifying the Accounting for Measurement-Period Adjustments . ASU No. 2015-16 eliminates the requirement to retrospectively adjust the financial statements for measurement-period adjustments that occur in periods after a business combination is consummated. The adoption of this ASU did not have an impact on the Company's financial position, results of operations or cash flows and will be applied on a prospective basis, as applicable. During the second quarter of 2016, the Company early adopted FASB ASU No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting , which changes several aspects of the accounting for share-based payment award transactions. Under the new guidance, all excess tax benefits or deficiencies associated with share-based payment award transactions are required to be recognized as an income tax benefit or expense in net income when the awards vest or are settled, with the corresponding cash flows recognized as an operating activity in the statement of cash flows. Excess tax benefits and deficiencies are no longer recognized in additional paid-in-capital. The new guidance also allows an employer to repurchase more of an employee's shares for tax witholding purposes without triggering liability accounting and to make a policy election to account for forfeitures as they occur, rather than estimating forfeitures upon issuance of the award. Upon adoption of ASU No. 2016-09, the Company elected to account for forfeitures as they occur, which had no impact on the consolidated financial statements. The provisions of ASU No. 2016-09 were adopted as of January 1, 2016 on a prospective basis and did not have a material impact on the Company's financial position, results of operations or cash flows. Effective for the year ended December 31, 2016, the Company adopted FASB ASU No. 2015-09, Financial Services-Insurance (Topic 944): Disclosures about Short-Duration Contracts . ASU No. 2015-09 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. The guidance requires annual tabular disclosure, on a disaggregated basis, of undiscounted incurred and paid claim and allocated claim adjustment expense development by accident year, net of reinsurance, for up to 10 years. Tables must also include the total incurred but not reported claims liabilities, plus expected development on reported claims, and claims frequency for each accident year. A description of estimation methodologies and any significant changes in methodologies and assumptions used to calculate the liability and frequency is also required. Based on the disaggregated claims information in the tables, disclosure of historical average annual percentage payout of incurred claims is also required. The ASU requires retrospective application by providing comparative disclosures for each period presented, other than those that are only required for the most recent reporting period. These new annual disclosures have been included in note 9. Interim period disclosures must include a tabular rollforward and related qualitative information for the liability for unpaid losses and loss adjustment expenses. The interim disclosures are required beginning in the first quarter of 2017. 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. ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Consideration (Reporting Revenue Gross versus Net), ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing, ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients and ASU No. 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers were all issued in 2016 as amendments to ASU No. 2014-09. These amendments will be evaluated and adopted in conjunction with ASU No. 2014-09. The Company expects to adopt ASU No. 2014-09 as of January 1, 2018 using the modified retrospective method, whereby the cumulative effect of adoption will be recognized 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 the Company's other revenues, which are primarily attributable to its non-insurance operations. The Company has completed an inventory of revenue streams from its non-insurance operations, which are comprised of a diverse portfolio of contracts across various industries, and is currently evaluating changes, if any, that will be necessary. The Company has not determined the full impact that adopting the new accounting guidance will have on its consolidated financial statements. In July 2015, the FASB issued ASU No. 2015-11, Inventory (Topic 330): Simplifying the Measurement of Inventory . The ASU changes the measurement principle for inventory from the lower of cost or market to lower of cost and net realizable value and eliminates the requirement to consider replacement cost or net realizable value less an approximately normal profit margin when measuring inventory. ASU No. 2015-11 becomes effective for the Company during the first quarter of 2017 and will be applied prospectively. Adoption of this ASU is not expected to have a material impact on the Company's financial position, results of operations or cash flows. 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 (loss). 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 (loss). As of December 31, 2016 , accumulated other comprehensive income included $1.5 billion of net unrealized gains on equity securities, net of taxes. See

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2016
Acquisitions [Abstract]
Acquisitions	Acquisitions CATCo Investment Management Acquisition In December 2015, the Company completed the acquisition of substantially all of the assets of CATCo Investment Management Ltd. (CATCo IM) and CATCo-Re Ltd. CATCo IM was a leading insurance-linked securities investment fund manager and reinsurance manager headquartered in Bermuda focused on building and managing highly diversified, collateralized retrocession and reinsurance portfolios covering global property catastrophe risks. Results attributable to Markel CATCo Investment Management Ltd. (MCIM), the wholly owned subsidiary formed in conjunction with this transaction, are included with the Company's non-insurance operations, which are not included in a reportable segment. Total consideration for the acquisition was $205.7 million , all of which was cash. The purchase price was allocated to the acquired assets and liabilities based on estimated fair values at the acquisition date. The Company recognized goodwill of $91.9 million , all of which is expected to be deductible for income tax purposes. The goodwill is primarily attributable to the Company's ability to achieve continued capital growth in excess of that which can be expected for the investment funds previously managed by CATCo IM. The Company also recognized other intangible assets of $113.0 million , primarily related to its investment management agreements. These intangible assets are expected to be amortized over a weighted average period of 14 years . In connection with the acquisition, the Company instituted performance incentive and retention arrangements for former CATCo employees, whom are now employed by MCIM. Pursuant to these agreements, the Company committed to the payment of performance bonuses derived from the results of the business in 2016 through 2018 and retention bonuses that will be paid annually over the three year period following the acquisition. The total amount of these payments is currently estimated to be $105 million , of which $33.2 million was recognized as compensation expense for the year ended December 31, 2016. The balance will be recognized in the consolidated financial statements as post-acquisition compensation expense over the remaining performance period and as services are provided. Markel Ventures Acquisitions In December 2015, the Company acquired 80% of the outstanding shares of CapTech Ventures, Inc. (CapTech), a privately held company headquartered in Richmond, Virginia. CapTech is a management and IT consulting firm, providing services and solutions to a wide array of customers. Under the terms of the acquisition agreement for CapTech, the Company has the option to acquire the remaining equity interests and the remaining equity interests have the option to sell their interests to the Company in the future. The redemption value of the remaining equity interests is generally based on CapTech's earnings in specified periods preceding the redemption date. Total consideration for the CapTech acquisition was $60.6 million . Total consideration included the estimated fair value of contingent consideration we expected to pay based on CapTech's earnings, as defined in the stock purchase agreement, through 2018. The purchase price was preliminarily allocated to the acquired assets and liabilities based on the estimated fair values at the acquisition date. During 2016, the Company completed the process of determining the fair value of the assets and liabilities acquired with CapTech. There were no material adjustments to the provisional estimates recorded as of December 31, 2015. The Company recognized goodwill of $50.6 million related to this acquisition, none of which is expected to be deductible for income tax purposes. The Company also recognized other intangible assets of $49.2 million , primarily related to customer relationships, and redeemable noncontrolling interests of $13.8 million . These intangible assets are expected to be amortized over a weighted average period of 14 years . Results attributable to this acquisition are included with the Company's non-insurance operations, which are not included in a reportable segment. In July 2014, the Company acquired 100% of the outstanding shares of Cottrell, Inc. (Cottrell), a privately held company headquartered in Gainesville, Georgia. Cottrell is a leading manufacturer of over-the-road car hauler equipment and related car hauler parts. In June and August 2014, ParkLand Ventures, Inc. (ParkLand) also completed the acquisition of several manufactured housing communities. Total consideration for these acquisitions was $187.0 million , which primarily consisted of cash consideration. Total consideration included the estimated fair value of contingent consideration we expected to pay based on Cottrell's earnings, as defined in the stock purchase agreement, in 2014 and 2015. The Company recognized goodwill of $38.7 million related to these acquisitions, the majority of which we expect to amortize for income tax purposes. The Company also recognized other intangible assets of $78.7 million , including $53.7 million of customer relationships and $13.0 million of trade names, which are expected to be amortized over a weighted average period of 17 years and 10 years , respectively. Results attributable to these acquisitions are included with the Company's non-insurance operations, which are not included in a reportable segment. Acquisition of Abbey Protection In January 2014, the Company completed its acquisition of 100% of the share capital of Abbey Protection plc (Abbey), an integrated specialty insurance and consultancy group headquartered in London. Abbey's business is focused on the underwriting and sale of insurance products to small and medium-sized enterprises and affinity groups in the United Kingdom providing protection against legal expenses and professional fees incurred as a result of legal actions or investigations by tax authorities, as well as providing a range of complementary legal and professional consulting services. Results attributable to Abbey's insurance operations are included in the International Insurance segment. Results attributable to Abbey's consultancy operations are reported with the Company's non-insurance operations, which are not included in a reportable segment. Total consideration for this acquisition was $190.7 million , all of which was cash consideration. The purchase price was allocated to the acquired assets and liabilities based on estimated fair values at the acquisition date. The Company recognized goodwill of $65.8 million , of which $43.0 million was allocated to the International Insurance segment and $22.8 million was allocated to the Company's non-insurance operations. None of the goodwill recognized is expected to be deductible for income tax purposes. The goodwill is primarily attributable to Abbey's assembled workforce and synergies that are expected to result upon integration of Abbey into the Company's insurance operations. The Company also recognized other intangible assets of $113.4 million , including $103.5 million of customer relationships and $9.9 million of trade names. These intangible assets are expected to be amortized over 20 years and 14 years , respectively. Subsequent Event On February 1, 2017, the Company entered into a definitive merger agreement to acquire SureTec Financial Corp. (SureTec) for approximately $250 million . SureTec is a Texas-based privately held surety company primarily offering contract, commercial and court bonds. The transaction is subject to customary closing conditions, including insurance regulatory approvals, and is expected to close in the first half of 2017. Upon completion of the acquisition, SureTec's operating results will be included in the Company's U.S. Insurance segment.

Investments

Investments	12 Months Ended
	Dec. 31, 2016
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. 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 maturity securities: U.S. Treasury $ 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 1,055,947 3,953 (19,544 ) — 1,040,356 Residential mortgage-backed 779,503 18,749 (5,048 ) (2,258 ) 790,946 Asset-backed 27,494 2 (158 ) — 27,338 Corporate 1,420,298 49,146 (9,364 ) (673 ) 1,459,407 Total fixed maturity securities 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 December 31, 2015 (dollars in thousands) Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Unrealized Other- Than-Temporary Impairment Losses Estimated Fair Value Fixed maturity securities: U.S. Treasury $ 310,370 $ 95 $ (1,048 ) $ — $ 309,417 U.S. government-sponsored enterprises 385,282 9,741 (3,733 ) — 391,290 Obligations of states, municipalities and political subdivisions 3,817,136 204,302 (8,225 ) — 4,013,213 Foreign governments 1,302,329 115,809 (1,681 ) — 1,416,457 Commercial mortgage-backed 657,670 6,867 (4,999 ) — 659,538 Residential mortgage-backed 837,964 22,563 (4,022 ) (2,258 ) 854,247 Asset-backed 36,462 15 (406 ) — 36,071 Corporate 1,690,945 41,123 (16,209 ) (1,624 ) 1,714,235 Total fixed maturity securities 9,038,158 400,515 (40,323 ) (3,882 ) 9,394,468 Equity securities: Insurance, banks and other financial institutions 651,002 690,271 (6,551 ) — 1,334,722 Industrial, consumer and all other 1,557,832 1,227,052 (45,131 ) — 2,739,753 Total equity securities 2,208,834 1,917,323 (51,682 ) — 4,074,475 Short-term investments 1,642,103 167 (9 ) — 1,642,261 Investments, available-for-sale $ 12,889,095 $ 2,318,005 $ (92,014 ) $ (3,882 ) $ 15,111,204 b) The following tables summarize gross unrealized investment losses by the length of time that securities have continuously been in an unrealized loss position. 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 maturity securities: U.S. Treasury $ 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 749,889 (19,091 ) 29,988 (453 ) 779,877 (19,544 ) Residential mortgage-backed 181,557 (4,987 ) 79,936 (2,319 ) 261,493 (7,306 ) Asset-backed 14,501 (106 ) 5,869 (52 ) 20,370 (158 ) Corporate 494,573 (8,357 ) 93,790 (1,680 ) 588,363 (10,037 ) Total fixed maturity securities 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 maturity securities and 16 were equity securities. The Company does not intend to sell or believe it will be required to sell these fixed maturity securities 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, 2015 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 maturity securities: U.S. Treasury $ 301,300 $ (962 ) $ 7,426 $ (86 ) $ 308,726 $ (1,048 ) U.S. government-sponsored enterprises 125,703 (2,686 ) 85,126 (1,047 ) 210,829 (3,733 ) Obligations of states, municipalities and political subdivisions 169,362 (4,864 ) 70,101 (3,361 ) 239,463 (8,225 ) Foreign governments 51,328 (249 ) 40,345 (1,432 ) 91,673 (1,681 ) Commercial mortgage-backed 289,058 (3,600 ) 95,843 (1,399 ) 384,901 (4,999 ) Residential mortgage-backed 78,814 (2,858 ) 137,100 (3,422 ) 215,914 (6,280 ) Asset-backed 6,228 (54 ) 24,315 (352 ) 30,543 (406 ) Corporate 470,694 (9,509 ) 343,737 (8,324 ) 814,431 (17,833 ) Total fixed maturity securities 1,492,487 (24,782 ) 803,993 (19,423 ) 2,296,480 (44,205 ) Equity securities: Insurance, banks and other financial institutions 63,873 (6,384 ) 6,247 (167 ) 70,120 (6,551 ) Industrial, consumer and all other 344,857 (44,879 ) 2,907 (252 ) 347,764 (45,131 ) Total equity securities 408,730 (51,263 ) 9,154 (419 ) 417,884 (51,682 ) Short-term investments 129,473 (9 ) — — 129,473 (9 ) Total $ 2,030,690 $ (76,054 ) $ 813,147 $ (19,842 ) $ 2,843,837 $ (95,896 ) At December 31, 2015 , the Company held 659 securities with a total estimated fair value of $2.8 billion and gross unrealized losses of $95.9 million . Of these 659 securities, 271 securities had been in a continuous unrealized loss position for one year or longer and had a total estimated fair value of $813.1 million and gross unrealized losses of $19.8 million . Of these securities, 264 securities were fixed maturity securities and seven 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 maturity securities, the Company considers whether it intends to sell the security or if it is more likely than not that it will be required to sell the security before recovery, the implied yield-to-maturity, the credit quality of the issuer and the ability to recover all amounts outstanding when contractually due. For equity securities, a decline in fair value that is considered to be other-than-temporary is recognized in net income based on the fair value of the security at the time of assessment, resulting in a new cost basis for the security. For fixed maturity securities where the Company intends to sell the security or it is more likely than not that the Company will be required to sell the security before recovery of its amortized cost, a decline in fair value is considered to be other-than-temporary and is recognized in net income based on the fair value of the security at the time of assessment, resulting in a new cost basis for the security. If the decline in fair value of a fixed maturity below its amortized cost is considered to be other-than-temporary based upon other considerations, the Company compares the estimated present value of the cash flows expected to be collected to the amortized cost of the security. The extent to which the estimated present value of the cash flows expected to be collected is less than the amortized cost of the security represents the credit-related portion of the other-than-temporary impairment, which is recognized in net income, resulting in a new cost basis for the security. Any remaining decline in fair value represents the non-credit portion of the other-than-temporary impairment, which is recognized in other comprehensive income (loss). 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 maturity securities at December 31, 2016 are shown below by contractual maturity. (dollars in thousands) Amortized Cost Estimated Fair Value Due in one year or less $ 798,529 $ 800,733 Due after one year through five years 1,210,130 1,252,152 Due after five years through ten years 1,582,373 1,659,755 Due after ten years 4,137,758 4,320,230 7,728,790 8,032,870 Commercial mortgage-backed 1,055,947 1,040,356 Residential mortgage-backed 779,503 790,946 Asset-backed 27,494 27,338 Total fixed maturity securities $ 9,591,734 $ 9,891,510 Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties, and the lenders may have the right to put the securities back to the borrower. Based on expected maturities, the estimated average duration of fixed maturity securities at December 31, 2016 was 6.3 years. d) The following table presents the components of net investment income. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Interest: Municipal bonds (tax-exempt) $ 88,654 $ 93,580 $ 98,262 Municipal bonds (taxable) 65,749 57,550 49,345 Other taxable bonds 144,752 138,763 152,789 Short-term investments, including overnight deposits 11,177 5,223 5,959 Dividends on equity securities 70,577 74,705 65,031 Income (loss) from equity method investments 6,852 (262 ) 4,766 Other 2,676 651 2,338 390,437 370,210 378,490 Investment expenses (17,207 ) (16,997 ) (15,260 ) Net investment income $ 373,230 $ 353,213 $ 363,230 e) Cumulative credit losses recognized in net income on fixed maturities where other-than-temporary impairment was identified and a portion of the other-than-temporary impairment was included in other comprehensive income (loss) were $10.7 million at December 31, 2016 and 2015 and $12.7 million at December 31, 2014 . f) The following table presents net realized investment gains and the change in net unrealized gains on investments. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Realized gains: Sales of fixed maturity securities $ 5,160 $ 3,073 $ 8,417 Sales of equity securities 70,177 156,987 51,356 Other 1,415 8,103 15,205 Total realized gains 76,752 168,163 74,978 Realized losses: Sales of fixed maturity securities (704 ) (4,598 ) (18,136 ) Sales of equity securities (6,988 ) (1,232 ) (802 ) Other-than-temporary impairments (18,355 ) (44,481 ) (4,784 ) Other (2,349 ) (486 ) (15,700 ) Total realized losses (28,396 ) (50,797 ) (39,422 ) Gains (losses) on securities measured at fair value through net income 16,791 (10,886 ) 10,444 Net realized investment gains $ 65,147 $ 106,480 $ 46,000 Change in net unrealized gains on investments included in other comprehensive income (loss): Fixed maturity securities $ (56,534 ) $ (137,435 ) $ 480,350 Equity securities 398,752 (320,277 ) 500,673 Short-term investments (107 ) 128 12 Net increase (decrease) $ 342,111 $ (457,584 ) $ 981,035 g) The following table presents other-than-temporary impairment losses recognized in net income and included in net realized investment gains by investment type. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Fixed maturity securities: Commercial mortgage-backed $ — $ — $ (61 ) Asset-backed — — (197 ) Corporate — — (46 ) Total fixed maturity securities — — (304 ) Equity securities: Insurance, banks and other financial institutions (7,586 ) (9,835 ) (341 ) Industrial, consumer and all other (10,769 ) (34,646 ) (4,139 ) Total equity securities (18,355 ) (44,481 ) (4,480 ) Total $ (18,355 ) $ (44,481 ) $ (4,784 ) h) The following table presents the components of restricted assets. December 31, (dollars in thousands) 2016 2015 Restricted assets held in trust or on deposit to support underwriting activities $ 4,059,336 $ 4,037,458 Investments and cash and cash equivalents pledged as security for letters of credit 355,616 745,744 Total $ 4,414,952 $ 4,783,202 Total restricted assets are included on the Company's consolidated balance sheets as follows. December 31, (dollars in thousands) 2016 2015 Investments, available-for-sale $ 4,068,535 $ 4,343,070 Restricted cash and cash equivalents 346,417 440,132 Total $ 4,414,952 $ 4,783,202 i) At December 31, 2016 and 2015 , investments in securities issued by the U.S. Treasury, U.S. government agencies and U.S. government-sponsored enterprises were the only investments in any one issuer that exceeded 10% of shareholders' equity. At December 31, 2016 , the Company's ten largest equity holdings represented $2.1 billion , or 44% , of the equity portfolio. Investments in the property and casualty insurance industry represented $1.0 billion , or 22% , of the equity portfolio at December 31, 2016 . Investments in the property and casualty insurance industry included a $511.3 million investment in the common stock of Berkshire Hathaway Inc.

Receivables

Receivables	12 Months Ended
	Dec. 31, 2016
Receivables [Abstract]
Receivables	Receivables The following table presents the components of receivables. December 31, (dollars in thousands) 2016 2015 Amounts receivable from agents, brokers and insureds $ 1,061,190 $ 983,510 Trade accounts receivable 123,341 119,558 Investment management and performance fees receivable 38,735 — Employee stock loans receivable (see note 12(c)) 20,171 16,900 Other 10,122 6,165 1,253,559 1,126,133 Allowance for doubtful receivables (11,910 ) (12,430 ) Receivables $ 1,241,649 $ 1,113,703

Deferred Policy Acquisition Cos

Deferred Policy Acquisition Costs	12 Months Ended
	Dec. 31, 2016
Deferred Policy Acquisition Costs Disclosures [Abstract]
Deferred Policy Acquisition Costs	Deferred Policy Acquisition Costs The following table presents the amounts of policy acquisition costs deferred and amortized. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Balance, beginning of year $ 352,756 $ 353,410 $ 260,967 Policy acquisition costs deferred 823,840 752,324 754,303 Amortization of policy acquisition costs (782,221 ) (744,964 ) (654,916 ) Foreign currency movements (1,965 ) (8,014 ) (6,944 ) Deferred policy acquisition costs $ 392,410 $ 352,756 $ 353,410 The following table presents the components of underwriting, acquisition and insurance expenses. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Amortization of policy acquisition costs $ 782,221 $ 744,964 $ 654,916 Other operating expenses 716,369 710,116 805,966 Underwriting, acquisition and insurance expenses $ 1,498,590 $ 1,455,080 $ 1,460,882

Property And Equipment

Property And Equipment	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Property And Equipment	Property and Equipment The following table presents the components of property and equipment, which are included in other assets on the consolidated balance sheets. December 31, (dollars in thousands) 2016 2015 Land $ 56,783 $ 56,408 Buildings 76,159 77,488 Leasehold improvements 95,898 104,003 Land improvements 74,040 71,585 Furniture and equipment 301,146 291,736 Other 162,385 134,939 766,411 736,159 Accumulated depreciation and amortization (354,009 ) (305,324 ) Property and equipment $ 412,402 $ 430,835 Depreciation and amortization expense of property and equipment was $64.8 million , $64.2 million and $51.2 million for the years ended December 31, 2016 , 2015 and 2014 , respectively. The Company does not own any individually material properties. The Company leases substantially all of the facilities used by its insurance operations and certain furniture and equipment under operating leases. The Company leases offices for the U.S. Insurance segment in Glen Allen, Virginia and in 24 other locations; the Company leases offices for the International Insurance segment in London, England and in 29 other locations; and the Company leases offices for the Reinsurance segment primarily in Summit, New Jersey and Hamilton, Bermuda. The Company's Markel Ventures operations own certain of their office, clinic, manufacturing, warehouse and distribution facilities and lease others. The Company believes these facilities are suitable and adequate for the Company's insurance and non-insurance operations.

Goodwill And Intangible Assets

Goodwill And Intangible Assets	12 Months Ended
	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill And Intangible Assets	Goodwill and Intangible Assets The following table presents the components of goodwill by reportable segment. (dollars in thousands) U.S. Insurance International Insurance Reinsurance Other (1) Total January 1, 2015 $ 280,579 $ 408,183 $ 122,745 $ 237,608 $ 1,049,115 Acquisitions (see note 2) — — — 146,659 146,659 Impairment loss — — — (14,880 ) (14,880 ) Foreign currency movements and other adjustments — (10,190 ) — (2,860 ) (13,050 ) December 31, 2015 (2) $ 280,579 $ 397,993 $ 122,745 $ 366,527 $ 1,167,844 Impairment loss — — — (18,723 ) (18,723 ) Foreign currency movements and other adjustments — (5,809 ) — (1,064 ) (6,873 ) December 31, 2016 (2) $ 280,579 $ 392,184 $ 122,745 $ 346,740 $ 1,142,248 (1) Amounts included in Other above are related to the Company's non-insurance operations, which are not included in a reportable segment. (2) Goodwill is net of accumulated impairment losses of $47.3 million and $28.6 million , as of December 31, 2016 and 2015, respectively, included in Other. Goodwill and indefinite-lived intangible assets are tested for impairment at least annually. The Company completes an annual test during the fourth quarter of each year based upon the results of operations through September 30. As part of our annual impairment test, during the fourth quarter of 2016, the Company recorded a goodwill impairment charge of $18.7 million to other expenses for one of our Markel Ventures industrial manufacturing reporting units, to reduce the carrying value of its goodwill to its implied fair value. Unfavorable market conditions, specifically declining oil prices from late 2014 through 2016 resulted in lower than expected earnings over a similar time period. The reporting unit's earnings are generally tied to infrastructure spending across global markets, a significant portion of which are influenced by the price of oil. To determine the value of the impairment loss, the Company estimated the fair value of the reporting unit primarily using an income approach based on a discounted cash flow model. While these cash flow projections yield positive cash flows and earnings in the long-term, they were insufficient to support the current carrying value of the reporting unit due to the unfavorable impact of current market conditions and recent trends on our shorter-term projections. Following the impairment charge in 2016, the carrying value of the reporting unit's goodwill is zero . During the fourth quarters of 2015 and 2014, the Company recorded goodwill impairment charges of $14.9 million and $13.7 million , respectively, to other expenses, for one of our Markel Ventures healthcare reporting units, to reduce the carrying value of its goodwill to its implied fair value. The reporting unit's operations consist of the planning, development and operation of behavioral health services in partnership with healthcare organizations and are reported in our non-insurance operations. In both periods, the Company determined the goodwill for the reporting unit was impaired as a result of lower than expected earnings and lower estimated future earnings. To determine the value of the impairment losses, the Company estimated the fair value of the reporting unit primarily using an income approach based on a discounted cash flow model. Following the impairment charge in 2015, the carrying value of the reporting unit's goodwill is zero . The following table presents the components of intangible assets with a net carrying amount. December 31, 2016 2015 (dollars in thousands) Gross Carrying Amount Accumulated Amortization Gross Carrying Amount Accumulated Amortization Customer relationships $ 460,327 $ (119,376 ) $ 481,547 $ (97,892 ) Broker relationships 183,092 (56,888 ) 182,626 (45,135 ) Trade names 100,966 (29,745 ) 103,681 (23,821 ) Investment management agreements 98,000 (7,000 ) 98,000 — Technology 54,408 (28,220 ) 54,241 (22,288 ) Insurance licenses 30,185 — 30,185 — Lloyd's syndicate capacity 12,000 — 12,000 — Other 34,172 (9,379 ) 30,496 (11,268 ) Total $ 973,150 $ (250,608 ) $ 992,776 $ (200,404 ) Amortization of intangible assets was $68.5 million , $68.9 million and $57.6 million for the years ended December 31, 2016 , 2015 and 2014 , respectively. Amortization of intangible assets is estimated to be $67.4 million for 2017 , $66.0 million for 2018 , $58.0 million for 2019 , $51.6 million for 2020 and $50.0 million for 2021 . Indefinite-lived intangible assets were $48.2 million at December 31, 2016 and December 31, 2015 .

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Income before income taxes includes the following components. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Domestic operations $ 288,905 $ 323,954 $ 240,279 Foreign operations 341,015 418,151 200,099 Income before income taxes $ 629,920 $ 742,105 $ 440,378 Income tax expense includes the following components. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Current: Domestic $ 57,916 $ 44,406 $ 7,573 Foreign 48,203 118,235 24,574 Total current tax expense 106,119 162,641 32,147 Deferred: Domestic 19,991 9,415 43,673 Foreign 43,367 (19,093 ) 40,870 Total deferred tax expense (benefit) 63,358 (9,678 ) 84,543 Income tax expense $ 169,477 $ 152,963 $ 116,690 Foreign income tax expense includes United States income tax expense on foreign operations, which includes United States income tax on the Company's Bermuda-based operations, certain of which have elected to be taxed as domestic corporations for United States tax purposes. State income tax expense is not material to the consolidated financial statements. The Company made income tax payments of $142.2 million , $132.5 million and $89.5 million in 2016 , 2015 and 2014 , respectively. Current income taxes payable were $46.4 million and $63.5 million at December 31, 2016 and 2015 , respectively, and were included in other liabilities on the consolidated balance sheets. Reconciliations of the United States corporate income tax rate to the effective tax rate on income before income taxes are presented in the following table. Years Ended December 31, 2016 2015 2014 United States corporate tax rate 35 % 35 % 35 % Tax-exempt investment income (6 ) (5 ) (9 ) Foreign tax credits (2 ) (8 ) (1 ) Foreign operations 1 (1 ) — Other (1 ) — 1 Effective tax rate 27 % 21 % 26 % The 2015 effective tax rate included an 8% income tax benefit related to tax credits for foreign taxes paid. In previous periods, certain foreign taxes paid were not available for use as tax credits against the Company's United States provision for income taxes. Based on the Company's earnings from foreign operations in 2015, significant foreign taxes paid, both in 2015 and prior periods, were used as credits against its United States provision for income taxes in 2015. Foreign tax credits of the magnitude recognized in 2015 are not expected in future periods. The following table presents the components of domestic and foreign deferred tax assets and liabilities. December 31, (dollars in thousands) 2016 2015 Assets: Unpaid losses and loss adjustment expenses $ 181,303 $ 212,012 Life and annuity benefits 135,075 156,950 Unearned premiums recognized for income tax purposes 121,852 102,076 Accrued incentive compensation 67,719 53,586 Investments, including other-than-temporary impairments 58,248 65,641 Net operating loss carryforwards 26,743 18,771 Tax credit carryforwards 23,037 18,158 Stock-based compensation 19,235 21,948 Other differences between financial reporting and tax bases 44,942 40,497 Total gross deferred tax assets 678,154 689,639 Less valuation allowance (18,781 ) (5,131 ) Total gross deferred tax assets, net of allowance 659,373 684,508 Liabilities: Net unrealized gains on investments 723,198 626,776 Deferred policy acquisition costs 128,302 88,036 Amortization of goodwill and other intangible assets 102,631 107,271 Other differences between financial reporting and tax bases 35,727 38,613 Total gross deferred tax liabilities 989,858 860,696 Net deferred tax liability $ 330,485 $ 176,188 The net deferred tax liability at December 31, 2016 and 2015 was included in other liabilities on the consolidated balance sheets. At December 31, 2016 , the Company had tax credit carryforwards of $23.0 million . The earliest any of these credits will expire is 2025 . At December 31, 2016 , the Company had net operating losses of $12.6 million that can be used to offset future taxable income in the United States from Markel Capital Limited, a wholly owned United Kingdom subsidiary. The Company's ability to use these losses in the United States expires between the years 2023 and 2033 . At December 31, 2016 , the Company also had net operating losses of $18.1 million that can be used to offset other future taxable income in the United States. The Company's ability to use these losses in the United States expires between the years 2028 and 2030 . At December 31, 2016 , certain branch operations in Europe and a wholly owned subsidiary in Brazil had net operating losses of $81.7 million that can be used to offset future income in their local jurisdictions. The Company's ability to use $20.4 million of these losses expires between the years 2020 and 2025 . The remaining losses are not subject to expiration. As discussed below, the deferred tax assets related to losses at the Company's European branches and Brazilian subsidiary are offset by valuation allowances. The Company believes that it is more likely than not that it will realize $659.4 million of gross deferred tax assets, including net operating losses at December 31, 2016 , through generating taxable income or the reversal of existing temporary differences attributable to the gross deferred tax liabilities. As a result of cumulative net operating losses in certain jurisdictions, the Company has a valuation allowance of $18.8 million at December 31, 2016 that offsets the deferred tax assets primarily related to losses incurred at European branches of one of the Company's wholly owned United Kingdom subsidiaries and at one of the Company's Brazilian subsidiaries. At December 31, 2016 , the Company had unrecognized tax benefits of $8.9 million . If recognized, $8.6 million of these tax benefits would decrease the annual effective tax rate. The Company does not currently anticipate any changes in unrecognized tax benefits during 2017 that would have a material impact on the Company's income tax provision. The following table presents a reconciliation of unrecognized tax benefits. Years Ended December 31, (dollars in thousands) 2016 2015 Unrecognized tax benefits, beginning of year $ 15,324 $ 17,700 Decreases for tax positions taken in prior years — (146 ) Lapse of statute of limitations (6,448 ) (606 ) Settlement with taxing authorities — (1,624 ) Unrecognized tax benefits, end of year $ 8,876 $ 15,324 With the exception of certain of our Bermuda subsidiaries, at December 31, 2016 , earnings of the Company's foreign subsidiaries not previously taxed in the United States are considered reinvested indefinitely and no provision for deferred United States income taxes has been recorded. If the Company's intentions with respect to reinvestment were to change, and earnings were to be repatriated to the United States, these foreign subsidiaries would be subject to tax in the United States less applicable foreign tax credits. As of December 31, 2016 , cumulative earnings of our foreign subsidiaries that are considered reinvested indefinitely and have not previously been subject to tax in the United States totaled approximately $615 million . The Company is subject to income tax in the United States and in foreign jurisdictions. With few exceptions, the Company is no longer subject to income tax examination by tax authorities for years ended before January 1, 2013. During the first quarter of 2016, the Internal Revenue Service completed its examination of the Company's 2012 United States federal income tax return. There were no adjustments to the Company's income tax liabilities as a result of this examination.

Unpaid Losses And Loss Adjustme

Unpaid Losses And Loss Adjustment Expenses	12 Months Ended
	Dec. 31, 2016
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Unpaid Losses And Loss Adjustment Expenses	Unpaid Losses and Loss Adjustment Expenses a) The following table presents a reconciliation of consolidated beginning and ending reserves for losses and loss adjustment expenses. In 2016, incurred losses and loss adjustment expenses in the following 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 and other 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. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Net reserves for losses and loss adjustment expenses, beginning of year $ 8,235,288 $ 8,535,483 $ 8,407,642 Foreign currency movements (129,692 ) (134,173 ) (137,385 ) Adjusted net reserves for losses and loss adjustment expenses, beginning of year 8,105,596 8,401,310 8,270,257 Incurred losses and loss adjustment expenses: Current year 2,555,902 2,566,545 2,638,012 Prior years (493,495 ) (627,800 ) (435,545 ) Total incurred losses and loss adjustment expenses 2,062,407 1,938,745 2,202,467 Payments: Current year 532,140 486,551 502,107 Prior years 1,529,206 1,423,286 1,436,851 Total payments 2,061,346 1,909,837 1,938,958 Effect of foreign currency rate changes 2,060 (17,281 ) (19,476 ) Net reserves for losses and loss adjustment expenses of acquired insurance companies — — 21,193 Reinsurance recoverable on retroactive reinsurance transactions — (177,649 ) — Net reserves for losses and loss adjustment expenses, end of year 8,108,717 8,235,288 8,535,483 Reinsurance recoverable on unpaid losses 2,006,945 2,016,665 1,868,669 Gross reserves for losses and loss adjustment expenses, end of year $ 10,115,662 $ 10,251,953 $ 10,404,152 On March 9, 2015, the Company completed a retroactive reinsurance transaction to cede a portfolio of policies primarily comprised of liabilities arising from asbestos and environmental (A&E) exposures that originated before 1992 in exchange for payments totaling $89.0 million , which included cash paid at closing of $69.9 million . At the time of the transaction, reserves for unpaid losses and loss adjustment expenses on the policies ceded totaled $94.1 million , resulting in a deferred gain of $5.1 million which will be recognized in earnings in proportion to actual reinsurance recoveries received pursuant to the transaction. On October 30, 2015, the Company completed a second retroactive reinsurance transaction to cede a portfolio of policies primarily comprised of liabilities arising from A&E exposures that originated before 1987 in exchange for cash payments totaling $86.5 million . The transaction provides up to $300 million of coverage for losses in excess of a $97.0 million retention on the ceded policies and 50% coverage on an additional $100 million of losses. The transaction is effective as of January 1, 2015, at which time reserves for unpaid losses and loss adjustment expenses on the policies ceded totaled $173.4 million . After considering the Company's retention on the ceded policies, ceded reserves for unpaid losses and loss adjustment expenses totaled $76.4 million , resulting in an underwriting loss of $10.1 million on the transaction. In 2016, incurred losses and loss adjustment expenses included $493.5 million of favorable development on prior years' loss reserves, which was due in part to $418.0 million of loss reserve redundancies on our long-tail casualty lines within the U.S. Insurance and International Insurance segments, our marine and energy product lines within the International Insurance segment, and our property product lines in the U.S. Insurance and Reinsurance segments, as actual claims reporting and development patterns on prior accident years have been more favorable than the Company's actuarial analyses initially anticipated. Redundancies in 2016 were partially offset by $71.2 million of adverse development on our specified medical and medical malpractice product lines within the U.S. Insurance segment. In 2015, incurred losses and loss adjustment expenses included $627.8 million of favorable development on prior years' loss reserves, which was due in part to $375.8 million of loss reserve redundancies on our general liability, workers' compensation, inland marine and brokerage property product lines within the U.S. Insurance segment and on our general liability, professional liability and marine and energy product lines within the International Insurance segment, as actual claims reporting patterns on prior accident years have been more favorable than the Company's actuarial analyses initially anticipated. In 2015, incurred losses and loss adjustment expenses also included $82.7 million of favorable development on prior years' loss reserves attributable to a decrease in the estimated volatility of our consolidated net reserves for unpaid losses and loss adjustment expenses as a result of ceding a significant portion of the Company's A&E exposures to a third party during 2015, as described above. As a result of this decrease in estimated volatility, the level of confidence in the Company's net reserves for unpaid losses and loss adjustment expenses increased. Therefore, management reduced prior years' loss reserves by $82.7 million in order to maintain a consolidated confidence level in a range consistent with the Company's historic levels. This reduction in prior years' loss reserves occurred across all three of the Company's ongoing underwriting segments. The favorable development on prior years' loss reserves in 2015 was partially offset by $25.4 million of adverse development on prior years' loss reserves for A&E exposures, of which $7.1 million is attributable to the underwriting loss on the retroactive reinsurance transaction described above. Following the October 2015 retroactive reinsurance transaction, the Company's actuaries increased their estimate of the ultimate losses on the remaining A&E claims and management increased prior years' loss reserves by $15.0 million . Without the diversification of a larger portfolio of loss reserves, there is greater uncertainty around the potential outcomes of the remaining claims, and management strengthened reserves accordingly. In 2014, the Company recorded net reserves for losses and loss adjustment expenses of $21.2 million as a result of the acquisition of Abbey. These reserves were recorded at fair value as part of the Company's purchase accounting. In 2014, incurred losses and loss adjustment expenses included $435.5 million of favorable development on prior years' loss reserves, which was due in part to $250.4 million of loss reserve redundancies on our long-tail casualty and professional liability lines within the U.S. Insurance segment and on our professional liability and marine and energy product lines within the International Insurance segment, as actual claims reporting patterns on prior accident years have been more favorable than the Company's actuarial analyses initially anticipated. The favorable development on prior years' loss reserves in 2014 was partially offset by $32.8 million of adverse development in prior years' loss reserves on A&E exposures. Once a year, generally during the third quarter, the Company completes an in-depth, actuarial review of its A&E exposures. During the annual review for 2014, the Company increased its expectation of the severity of the outcome of certain claims subject to litigation. As the ultimate outcome of known claims increases, the Company's expected ultimate closure value on unreported claims also increases. As a result, prior years' loss reserves for A&E exposures were increased by $27.2 million in 2014 . During the annual review for both 2016 and 2015, the Company determined that no adjustment to loss reserves was required. The Company uses a variety of techniques to establish the liabilities for unpaid losses and loss adjustment expenses based upon estimates of the ultimate amounts payable. The Company maintains reserves for specific claims incurred and reported (case reserves) and reserves for claims incurred but not reported (IBNR reserves), which include expected development on reported claims. The Company does not discount its reserves for losses and loss adjustment expenses to reflect estimated present value, except for reserves assumed in connection with an acquisition, which are recorded at fair value at the acquisition date. The fair value adjustment includes an adjustment to reflect the acquired reserves for losses and loss adjustment expenses at present value plus a risk premium, the net of which is amortized to losses and loss adjustment expenses within the consolidated statements of income. The amount of unamortized fair value adjustments included in unpaid losses and loss adjustment expenses as of December 31, 2016 and 2015 was $68.9 million and $91.0 million , respectively. As of any balance sheet date, all claims have not yet been reported, and some claims may not be reported for many years. As a result, the liability for unpaid losses and loss adjustment expenses includes significant estimates for incurred but not reported claims. There is normally a time lag between when a loss event occurs and when it is actually reported to the Company. The actuarial methods that the Company uses to estimate losses have been designed to address the lag in loss reporting as well as the delay in obtaining information that would allow the Company to more accurately estimate future payments. There is also a time lag between cedents establishing case reserves and re-estimating their reserves, and notifying the Company of the new or revised case reserves. As a result, the reporting lag is more pronounced in reinsurance contracts than in the insurance contracts due to the reliance on ceding companies to report their claims. On reinsurance transactions, the reporting lag will generally be 60 to 90 days after the end of a reporting period, but can be longer in some cases. Based on the experience of the Company's actuaries and management, loss development factors and trending techniques are selected to mitigate the difficulties caused by reporting lags. The loss development and trending factor selections are evaluated at least annually and updated using cedent specific and industry data. IBNR reserves are based on the estimated ultimate cost of settling claims, including the effects of inflation and other social and economic factors, using past experience adjusted for current trends and any other factors that would modify past experience. IBNR reserves, which include expected development on reported claims, are generally calculated by subtracting paid losses and loss adjustment expenses and case reserves from estimated ultimate losses and loss adjustment expenses. IBNR reserves were 67% of total unpaid losses and loss adjustment expenses at December 31, 2016 compared to 65% at December 31, 2015 In establishing liabilities for unpaid losses and loss adjustment expenses, the Company's actuaries estimate an ultimate loss ratio, by accident year or policy year, for each product line with input from underwriting and claims associates. For product lines in which loss reserves are established on a policy year basis, the Company has developed a methodology to convert from policy year to accident year for financial reporting purposes. In estimating an ultimate loss ratio for a particular line of business, the actuaries may use one or more actuarial reserving methods and select from these a single point estimate. To varying degrees, these methods include detailed statistical analysis of past claim reporting, settlement activity, claim frequency and severity, policyholder loss experience, industry loss experience and changes in market conditions, policy forms and exposures. Greater judgment may be required when new product lines are introduced or when there have been changes in claims handling practices, as the statistical data available may be insufficient. These estimates also reflect implicit and explicit assumptions regarding the potential effects of external factors, including economic and social inflation, judicial decisions, changes in law, general economic conditions and recent trends in these factors. Management believes the process of evaluating past experience, adjusted for the effects of current developments and anticipated trends, is an appropriate basis for predicting future events. Loss reserves are established at management's best estimate, which is generally higher than the corresponding actuarially calculated point estimate. The actuarial point estimate represents the actuaries' estimate of the most likely amount that will ultimately be paid to settle the loss reserves that are recorded at a particular point in time; however, there is inherent uncertainty in the point estimate as it is the expected value in a range of possible reserve estimates. In some cases, actuarial analyses, which are based on statistical analysis, cannot fully incorporate all of the subjective factors that affect development of losses. In other cases, management's perspective of these more subjective factors may differ from the actuarial perspective. Subjective factors where management's perspective may differ from that of the actuaries include: the credibility and timeliness of claims information received from third parties, economic and social inflation, judicial decisions, changes in law, changes in underwriting or claims handling practices, general economic conditions, the risk of moral hazard and other current and developing trends within the insurance and reinsurance markets, including the effects of competition. As a result, the actuarially calculated point estimates for each of line of business represents starting points for management's quarterly review of loss reserves. Inherent in the Company's reserving practices is the desire to establish loss reserves that are more likely redundant than deficient. As such, the Company seeks to establish loss reserves that will ultimately prove to be adequate. As part of the Company's acquisition of insurance operations, to the extent the reserving philosophy of the acquired business differs from the Company's reserving philosophy, the post-acquisition loss reserves will be strengthened until total loss reserves are consistent with the Company's target level of confidence. Furthermore, the Company's philosophy is to price its insurance products to make an underwriting profit. Management continually attempts to improve its loss estimation process by refining its ability to analyze loss development patterns, claim payments and other information, but uncertainty remains regarding the potential for adverse development of estimated ultimate liabilities. Following the completion of two retroactive reinsurance transactions in 2015, the Company has less variability in its consolidated loss reserves. Additionally, management continues to gain confidence in the actuarial projections on product lines previously written by Alterra Capital Holdings Limited (Alterra), which we acquired in 2013. As a result, management's best estimate of the current accident year ultimate loss ratios on various product lines across all three of the Company's ongoing underwriting segments decreased in 2016 compared to 2015. Management currently believes the Company's gross and net reserves are adequate. However, there is no precise method for evaluating the impact of any significant factor on the adequacy of reserves, and actual results will differ from original estimates. b) The following tables present loss development information, by accident year, for the Company's U.S. Insurance, International Insurance and Reinsurance segments, including cumulative incurred and paid losses and allocated loss adjustment expenses, net of reinsurance, as well as the corresponding amount of IBNR reserves as of December 31, 2016. This level of disaggregation is consistent with how the Company analyzes loss reserves for both internal and external reporting purposes. The loss development information for the years ended December 31, 2012 through 2015 is presented as supplementary information. For the Company's U.S. Insurance segment, the years presented in the tables comprise the majority of the period for which incurred losses typically remain outstanding. Incurred losses in the Company's International Insurance and Reinsurance segments, which generally include a larger proportion of long-tail business than the U.S. Insurance segment, generally remain outstanding more than five years; however, data prior to 2012 is not practically available by segment as a result of a change in the Company's reportable segments in 2014, which was most impactful on these two segments. Additionally, reserves for our international operations within these two segments are determined on a policy year basis and historical data prior to 2012 does not exist by accident year. All amounts included in the tables below related to transactions denominated in a foreign currency have been translated into United States Dollars using the exchange rates in effect at December 31, 2016. The tables below also include claim frequency information, by accident year, for each of the segments presented. The Company defines a claim as a single claim incident, per policy, which may include multiple claimants and multiple coverages on a single policy. Claim counts include claims closed without a payment as well as claims where the Company is monitoring to determine if an exposure exists, even if a reserve has not been established. In 2013, the Company completed the acquisition of Alterra, the results of which are included in each of the Company's reportable segments. Ultimate incurred losses and loss adjustment expenses, net of reinsurance for the year ended December 31, 2013 include outstanding liabilities for losses and loss adjustment expenses of Alterra as of the acquisition date, by accident year and not in any prior periods. Pre-acquisition data is not available by segment and accident year as a result of changes to the historical Alterra product line reporting structure that impacted each of the Company's reportable segments and the impact of significant intercompany reinsurance contracts. Additionally, Alterra reserves were historically determined on a policy year basis and pre-acquisition data does not exist in a format that can be used to determine accident year and segment. Following the acquisition, ongoing business attributable to Alterra was integrated with the Company's other insurance operations and is not separately tracked. U.S. Insurance Segment Ultimate Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance Total of Incurred-but-Not-Reported Liabilities, Net of Reinsurance Cumulative Number of Reported Claims Unaudited Year Ended December 31, (in thousands) Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 December 31, 2016 2012 $ 949,141 $ 985,721 $ 924,138 $ 924,621 $ 909,237 $ 117,333 106 2013 1,130,681 1,105,927 1,042,100 1,009,438 175,309 65 2014 1,278,116 1,140,685 1,116,093 290,827 56 2015 1,285,411 1,211,389 500,705 55 2016 1,319,731 781,984 49 Total $ 5,565,888 Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance Unaudited Year Ended December 31, Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 2012 $ 193,708 $ 401,773 $ 546,635 $ 644,658 $ 728,802 2013 222,890 443,392 594,558 725,782 2014 264,697 487,068 650,118 2015 260,121 514,497 2016 278,650 Total $ 2,897,849 All outstanding liabilities for unpaid losses and loss adjustment expenses before 2012, net of reinsurance 402,534 Total liabilities for unpaid losses and loss adjustment expenses, net of reinsurance $ 3,070,573 Ultimate incurred losses and allocated loss adjustment expenses for the year ended December 31, 2013 for the U.S. Insurance segment include $97.4 million and $149.9 million of losses and loss adjustment expenses on the 2012 and 2013 accident years, respectively, attributable to Alterra. Cumulative paid losses and allocated loss adjustment expenses for the year ended December 31, 2013 include $22.6 million and $23.2 million of paid losses and allocated loss adjustment expenses on the 2012 and 2013 accident years, respectively, attributable to the acquired Alterra reserves and post-acquisition Alterra business. Cumulative paid losses and allocated loss adjustment expenses and cumulative reported claims for the 2012 and 2013 accident years exclude any claims paid or closed prior to the acquisition. Cumulative reported claims for the 2012 and 2013 accident years include 65 thousand and 16 thousand , respectively, of claim counts associated with a personal lines product with high claim frequency and low claim severity that the Company stopped writing in 2013. The related net incurred losses and allocated loss adjustment expenses are not material to the U.S. Insurance segment. International Insurance Segment Ultimate Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance Total of Incurred-but-Not-Reported Liabilities, Net of Reinsurance Cumulative Number of Reported Claims Unaudited Year Ended December 31, (in thousands) Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 December 31, 2016 2012 $ 412,684 $ 616,641 $ 557,604 $ 495,641 $ 479,558 $ 87,383 18 2013 597,145 581,164 476,433 446,568 155,062 17 2014 577,454 545,954 502,708 149,455 16 2015 488,649 489,119 222,864 16 2016 543,959 279,320 13 Total $ 2,461,912 Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance Unaudited Year Ended December 31, Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 2012 $ 38,992 $ 163,805 $ 230,882 $ 289,517 $ 319,843 2013 47,887 126,699 182,173 220,625 2014 65,683 167,568 240,050 2015 61,556 148,037 2016 92,665 Total $ 1,021,220 All outstanding liabilities for unpaid losses and loss adjustment expenses before 2012, net of reinsurance 570,940 Total liabilities for unpaid losses and loss adjustment expenses, net of reinsurance $ 2,011,632 Ultimate incurred losses and allocated loss adjustment expenses for the year ended December 31, 2013 for the International Insurance segment include $158.0 million and $162.7 million of losses and loss adjustment expenses on the 2012 and 2013 accident years, respectively, attributable to Alterra. Cumulative paid losses and allocated loss adjustment expenses for the year ended December 31, 2013 include $14.0 million and $6.2 million of paid losses and allocated loss adjustment expenses on the 2012 and 2013 accident years, respectively, attributable to the acquired Alterra reserves and post-acquisition Alterra business. Cumulative paid losses and allocated loss adjustment expenses and cumulative reported claims for the 2012 and 2013 accident years exclude any claims paid or closed prior to the acquisition. Business contained within the Company's International Insurance segment includes business managed by other managing agents, coverholders and third party administrators, for which the Company is unable to obtain access to the underlying claim counts. As such, the claim count information for this business has been excluded from the total claim counts reported above. This business represents 4% of the cumulative incurred losses and allocated loss adjustment expenses, net of reinsurance, on the 2012 through 2016 accident years detailed above. Reinsurance Segment Ultimate Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance Total of Incurred-but-Not-Reported Liabilities, Net of Reinsurance Unaudited Year Ended December 31, (in thousands) Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 December 31, 2016 2012 $ 72,250 $ 545,939 $ 503,410 $ 482,836 $ 455,103 $ 137,778 2013 581,963 574,760 545,743 531,955 179,519 2014 575,479 565,252 536,274 209,246 2015 526,286 511,959 306,717 2016 529,518 382,407 Total $ 2,564,809 Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance Unaudited Year Ended December 31, Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 2012 $ 3,955 $ 64,209 $ 128,174 $ 183,321 $ 230,742 2013 71,182 154,494 209,256 268,052 2014 97,617 158,104 228,293 2015 63,963 134,530 2016 79,481 Total $ 941,098 All outstanding liabilities for unpaid losses and loss adjustment expenses before 2012, net of reinsurance 840,563 Total liabilities for unpaid losses and loss adjustment expenses, net of reinsurance $ 2,464,274 Ultimate incurred losses and allocated loss adjustment expenses for the year ended December 31, 2013 for the Reinsurance segment include $471.0 million and $531.8 million of losses and loss adjustment expenses on the 2012 and 2013 accident years, respectively, attributable to Alterra. Cumulative paid losses and allocated loss adjustment expenses for the year ended December 31, 2013 include $52.4 million and $68.6 million of paid losses and allocated loss adjustment expenses on the 2012 and 2013 accident years, respectively, attributable to the acquired Alterra reserves and post-acquisition Alterra business. Cumulative paid losses and allocated loss adjustment expenses for the 2012 and 2013 accident years exclude any claims paid prior to the acquisition. All of the business contained within the Company's Reinsurance segment represents treaty business that is assumed from other insurance or reinsurance companies, for which the Company does not have access to the underlying claim counts. Further, this business includes both quota share and excess of loss treaty reinsurance, through which only a portion of each reported claim results in losses to the Company. As such, the Company has excluded claim count information from the Reinsurance segment disclosures. The following table presents supplementary information about average historical claims duration as of December 31, 2016 based on the cumulative incurred and paid losses and allocated loss adjustment expenses presented above. Average Annual Percentage Payout of Incurred Losses by Age (in Years), Net of Reinsurance Unaudited 1 2 3 4 5 U.S. Insurance 21.9 % 21.4 % 15.2 % 11.9 % 9.3 % International Insurance 12.3 % 20.4 % 13.6 % 10.4 % 6.3 % Reinsurance 12.0 % 13.5 % 12.5 % 11.6 % 10.4 % The following table reconciles the net incurred and paid loss development tables, by segment, to the liability for losses and loss adjustment expenses in the consolidated balance sheet. (dollars in thousands) December 31, 2016 Net outstanding liabilities U.S. Insurance $ 3,070,573 International Insurance 2,011,632 Reinsurance 2,464,274 Other Insurance (Discontinued Lines) 281,562 Liabilities for unpaid losses and loss adjustment expenses, net of reinsurance 7,828,041 Reinsurance recoverable on unpaid losses U.S. Insurance 631,608 International Insurance 982,127 Reinsurance 140,629 Other Insurance (Discontinued Lines) 252,581 Total reinsurance recoverable on unpaid losses 2,006,945 Unallocated loss adjustment expenses 211,777 Unamortized fair value adjustments on acquired reserves for losses and loss adjustment expenses 68,899 280,676 Total gross liability for unpaid losses and loss adjustment expenses $ 10,115,662 c) The Company's exposure to A&E claims results from policies written by acquired insurance operations before their acquisition by the Company. The Company's exposure to A&E claims originated from umbrella, excess and commercial general liability (CGL) insurance policies and assumed reinsurance contracts that were written on an occurrence basis from the 1970s to mid-1980s. Exposure also originated from claims-made policies that were designed to cover environmental risks provided that all other terms and conditions of the policy were met. A&E claims include property damage and clean-up costs related to pollution, as well as personal injury allegedly arising from exposure to hazardous materials. After 1986, the Company began underwriting CGL coverage with pollution exclusions, and in some lines of business the Company began using a claims-made form. These changes significantly reduced the Company's exposure to future A&E claims on post-1986 business. The following table provides a reconciliation of beginning and ending A&E reserves for losses and loss adjustment expenses, which are a component of consolidated unpaid losses and loss adjustment expenses. Amounts included in the following table are presented before consideration of reinsurance allowances. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Net reserves for A&E losses and loss adjustment expenses, beginning of year $ 132,869 $ 287,723 $ 272,194 Incurred losses and loss adjustment expenses (5,277 ) 25,415 32,840 Payments (15,988 ) (20,628 ) (17,311 ) Reinsurance recoverable on retroactive reinsurance transactions — (159,641 ) — Net reserves for A&E losses and loss adjustment expenses, end of year 111,604 132,869 287,723 Reinsurance recoverable on unpaid losses 212,300 253,756 102,719 Gross reserves for A&E losses and loss adjustment expenses, end of year $ 323,904 $ 386,625 $ 390,442 At December 31, 2016 , asbestos-related reserves were $252.1 million and $90.0 million on a gross and net basis, respectively. Net reserves for reported claims for A&E exposures were $104.1 million at December 31, 2016 . Net incurred but not reported reserves for A&E exposures were $7.5 million at December 31, 2016 . Inception-to-date net paid losses and loss adjustment expenses for A&E related exposures totaled $612.0 million at December 31, 2016 , which includes $159.6 million of payments for two retroactive reinsurance transactions completed in 2015 and $93.6 million of litigation-related expense. As previously described, during 2015, the Company completed two retroactive reinsurance transactions to cede two portfolios of policies primarily comprised of liabilities arising from A&E exposures. At the time of the transactions, the reinsurance recoverable for the retroactive reinsurance coverages totaled $177.6 million , of which $159.6 million was attributable to A&E exposures. The Company's reserves for losses and loss adjustment expenses related to A&E exposures represent management's best estimate of ultimate settlement values. A&E reserves are monitored by management, and the Company's statistical analysis of these reserves is reviewed by the Company's independent actuaries. A&E exposures are subject to significant uncertainty due to potential loss severity and frequency resulting from the uncertain and unfavorable legal climate. A&E reserves could be subject to increases in the future; however, management believes the Company's gross and net A&E reserves at December 31, 2016 are adequate.

Life And Annuity Benefits

Life And Annuity Benefits	12 Months Ended
	Dec. 31, 2016
Liability for Future Policy Benefits [Abstract]
Life And Annuity Benefits	Life and Annuity Benefits The following table presents life and annuity benefits. December 31, (dollars in thousands) 2016 2015 Life $ 131,768 $ 142,068 Annuities 849,226 901,218 Accident and health 68,660 79,989 Total $ 1,049,654 $ 1,123,275 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. Because of the assumptions and estimates used in establishing the Company's reserves for life and annuity benefit obligations and the long-term nature of these reinsurance contracts, the ultimate liability may be greater or less than the estimates. The average discount rate for the life and annuity benefit reserves was 2.3% as of December 31, 2016 . As of December 31, 2016 , the largest life and annuity benefits reserve for a single contract was 32.9% of the total. No annuities included in life and annuity benefits in the consolidated balance sheet are subject to discretionary withdrawal. On April 24, 2015, the Company completed a novation that transferred its obligations under a reinsurance contract for life and annuity benefit policies to a third party in exchange for cash payments totaling $29.0 million , net of commissions. At the time of the transaction, reserves for life and annuity benefits on the novated reinsurance contract totaled $32.6 million , resulting in a gain of $3.6 million that was recorded as an offset to other expenses.

Senior Long-Term Debt And Other

Senior Long-Term Debt And Other Debt	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Senior Long-Term Debt And Other Debt	Senior Long-Term Debt and Other Debt The following table summarizes the Company's senior long-term debt and other debt. December 31, (dollars in thousands) 2016 2015 7.20% unsecured senior notes, due April 14, 2017, interest payable semi-annually, net of unamortized premium of $417 in 2016 and $1,808 in 2015 $ 91,046 $ 92,436 7.125% unsecured senior notes, due September 30, 2019, interest payable semi-annually, net of unamortized discount of $522 in 2016 and $1,060 in 2015 234,183 346,725 6.25% unsecured senior notes, due September 30, 2020, interest payable semi-annually, net of unamortized premium of $35,717 in 2016 and $44,519 in 2015 385,714 394,464 5.35% unsecured senior notes, due June 1, 2021, interest payable semi-annually, net of unamortized discount of $912 in 2016 and $1,119 in 2015 248,957 248,694 4.90% unsecured senior notes, due July 1, 2022, interest payable semi-annually, net of unamortized discount of $1,536 in 2016 and $1,815 in 2015 348,215 347,891 3.625% unsecured senior notes, due March 30, 2023, interest payable semi-annually, net of unamortized discount of $1,257 in 2016 and $1,458 in 2015 248,508 248,277 7.35% unsecured senior notes, due August 15, 2034, interest payable semi-annually, net of unamortized discount of $1,212 in 2016 and $1,972 in 2015 128,570 197,923 5.0% unsecured senior notes, due March 30, 2043, interest payable semi-annually, net of unamortized discount of $5,879 in 2016 and $6,103 in 2015 243,796 243,559 5.0% unsecured senior notes, due April 5, 2046, interest payable semi-annually, net of unamortized discount of $7,154 in 2016 491,943 — Other debt, at various interest rates ranging from 1.7% to 6.5% 153,597 119,302 Senior long-term debt and other debt $ 2,574,529 $ 2,239,271 The Company's 6.25% unsecured senior notes and the 7.20% unsecured senior notes were issued by Alterra Finance LLC and Alterra USA Holdings Limited, respectively, which are wholly owned indirect subsidiaries of the Company, and are guaranteed by Markel Corporation. All of the Company's other unsecured senior notes were issued by Markel Corporation. In the second quarter of 2016, the Company issued $500 million of 5.0% unsecured senior notes due April 5, 2046. Net proceeds to the Company were $493.1 million . The Company used a portion of these proceeds to purchase $70.2 million of principal on its 7.35% unsecured senior notes due 2034 and $108.8 million of principal on its 7.125% unsecured senior notes due 2019 through a tender offer at a total purchase price of $95.0 million and $126.4 million , respectively. The Company also expects to use the proceeds from this issuance to retire its 7.20% unsecured senior notes, when they come due April 14, 2017, and the remainder for general corporate purposes. In connection with the purchase, the Company recognized a loss on early extinguishment of debt of $44.1 million during the year ended December 31, 2016. The Company's 7.35% unsecured senior notes due August 15, 2034 are not redeemable. The Company's other unsecured senior notes are redeemable by the Company at any time, subject to payment of a make-whole premium to the noteholders. None of the Company's senior long-term debt is subject to any sinking fund requirements. The Company's other debt is primarily associated with its Markel Ventures operations and is non-recourse to the holding company. The debt of the Company's Markel Ventures subsidiaries generally is secured by the assets of those subsidiaries. ParkLand, a subsidiary of the Company, has formed subsidiaries for the purpose of acquiring and financing real estate (the real estate subsidiaries). The assets of certain real estate subsidiaries, which are not material to the Company, are consolidated in accordance with U.S. GAAP but are not available to satisfy the debt and other obligations of the Company or any affiliates other than those real estate subsidiaries. Other debt also includes a $62.5 million note payable delivered as part of the consideration provided for the investment held by the Markel Diversified Fund, as discussed in note 17. The estimated fair value of the Company's senior long-term debt and other debt was $2.7 billion and $2.4 billion at December 31, 2016 and 2015 , respectively. The following table summarizes the future principal payments due at maturity on senior long-term debt and other debt as of December 31, 2016 . Years Ending December 31, (dollars in thousands) 2017 $ 183,916 2018 6,365 2019 239,633 2020 359,332 2021 284,758 2022 and thereafter 1,485,404 Total principal payments $ 2,559,408 Net unamortized premium 17,662 Net unamortized debt issuance costs (2,541 ) Senior long-term debt and other debt $ 2,574,529 The Company maintains a revolving credit facility which provides $300 million of capacity for future acquisitions, investments, repurchases of capital stock of the Company and for general corporate purposes. At the Company's discretion, $200 million of the total capacity may be used for secured letters of credit. The Company may increase the capacity of the facility to $500 million subject to certain terms and conditions. The Company pays interest on balances outstanding under the facility and a utilization fee for letters of credit issued under the facility. The Company also pays a commitment fee ( 0.225% at December 31, 2016 ) on the unused portion of the facility based on the Company's debt to equity leverage ratio as calculated under the credit agreement. Markel Corporation, along with Alterra Finance LLC and Alterra USA Holdings Limited, guaranteed the Company's obligations under the facility. As a result, the Company's revolving credit facility ranks equally with the 6.25% unsecured senior notes and the 7.20% unsecured senior notes. At December 31, 2016 and 2015 , the Company had no borrowings outstanding under this revolving credit facility. This facility expires in August 2019. At December 31, 2016 , the Company was in compliance with all covenants contained in its revolving credit facility. To the extent that the Company is not in compliance with its covenants, the Company's access to the revolving credit facility could be restricted. The Company paid $135.4 million , $127.0 million and $125.8 million in interest on its senior long-term debt and other debt during the years ended December 31, 2016 , 2015 and 2014 , respectively.

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2016
Stockholders' Equity Note [Abstract]
Shareholders' Equity	Shareholders' Equity a) The Company had 50,000,000 shares of no par value common stock authorized of which 13,954,931 shares and 13,959,018 shares were issued and outstanding at December 31, 2016 and 2015 , respectively. The Company also has 10,000,000 shares of no par value preferred stock authorized, none of which was issued or outstanding at December 31, 2016 or 2015 . The Company's Board of Directors has approved the repurchase of up to $300 million of common stock under a share repurchase program (the Program). Under the Program, the Company may repurchase outstanding shares of common stock from time to time, primarily through open-market transactions. The Program has no expiration date but may be terminated by the Board of Directors at any time. As of December 31, 2016 , the Company had repurchased 96,345 shares of common stock at a cost of $70.7 million under the Program. b) Net income per share was determined by dividing adjusted net income to shareholders by the applicable weighted average shares outstanding. Basic shares outstanding include restricted stock units that are no longer subject to any contingencies for issuance, but for which the corresponding shares have not been issued. Diluted net income per share is computed by dividing adjusted net income to shareholders by the weighted average number of common shares and dilutive potential common shares outstanding during the year. Average closing common stock market prices are used to calculate the dilutive effect attributable to restricted stock. Years Ended December 31, (in thousands, except per share amounts) 2016 2015 2014 Net income to shareholders $ 455,689 $ 582,772 $ 321,182 Adjustment of redeemable noncontrolling interests (15,472 ) 4,144 (8,186 ) Adjusted net income to shareholders $ 440,217 $ 586,916 $ 312,996 Basic common shares outstanding 14,013 13,978 13,984 Dilutive potential common shares from conversion of options 4 9 11 Dilutive potential common shares from conversion of restricted stock 61 74 62 Diluted shares outstanding 14,078 14,061 14,057 Basic net income per share $ 31.41 $ 41.99 $ 22.38 Diluted net income per share $ 31.27 $ 41.74 $ 22.27 c) The Company's Employee Stock Purchase and Bonus Plan provides a method for employees and directors to purchase shares of the Company's common stock on the open market. The plan encourages share ownership by providing for the award of bonus shares to participants equal to 10% of the net increase in the number of shares owned under the plan in a given year, excluding shares acquired through the plan's loan program component. Under the loan program, the Company offers subsidized unsecured loans so participants may purchase shares and awards bonus shares equal to 5% of the shares purchased with a loan. In May 2016, the Company adopted the Markel Corporation 2016 Employee Stock Purchase and Bonus Plan which replaced the Company's prior Employee Stock Purchase and Bonus Plan. No shares have been issued under the prior Employee Stock Purchase and Bonus Plan since the effective date of the 2016 Employee Stock Purchase and Bonus Plan. The Company authorized 125,000 shares for purchase under the 2016 Employee Stock Purchase and Bonus Plan, of which 118,692 shares were available for purchase as of December 31, 2016 . As of December 31, 2015, 9,458 shares were available for purchase under the prior Employee Stock Purchase and Bonus Plan. At December 31, 2016 and 2015 , loans outstanding under the plans, which are included in receivables on the consolidated balance sheets, totaled $20.2 million and $16.9 million , respectively. d) In May 2016, the Company adopted the 2016 Equity Incentive Compensation Plan (2016 Compensation Plan), which replaced the 2012 Equity Incentive Compensation Plan (2012 Compensation Plan). In April 2012, the Company adopted the 2012 Compensation Plan, which replaced the Markel Corporation Omnibus Incentive Plan (Omnibus Incentive Plan). The 2016 Compensation Plan provides for grants and awards of restricted stock, restricted stock units, performance grants, and other stock based awards to employees and non-employee directors and is administered by the Compensation Committee of the Company's Board of Directors (Compensation Committee). No share-based awards have been issued under the 2012 Compensation Plan after the effective date of the 2016 Compensation Plan. At December 31, 2016 , there were 248,025 shares available for future awards under the 2016 Compensation Plan. Restricted stock units are awarded to certain associates and executive officers based upon meeting performance conditions determined by the Compensation Committee. These awards generally vest at the end of the third year following the year for which the Compensation Committee determines performance conditions have been met. At the end of the vesting period, recipients are entitled to receive one share of the Company's common stock for each vested restricted stock unit. During 2016 , the Company awarded 12,664 restricted stock units to associates and executive officers based on performance conditions being met. Restricted stock units also are awarded to associates to assist the Company in securing or retaining the services of key employees. During 2016 , the Company awarded 1,900 restricted stock units to associates as a hiring or retention incentive. The restricted stock units had a grant-date fair value of $1.7 million . These awards generally vest over a three -year period and entitle the recipient to receive one share of the Company's common stock for each vested restricted stock unit. During 2016 , the Company awarded 1,050 shares of restricted stock to its non-employee directors. The shares awarded to non-employee directors will vest in 2017 . The following table summarizes nonvested share-based awards. Number of Awards Weighted Average Grant-Date Fair Value Nonvested awards at January 1, 2016 103,883 $ 556.66 Granted 15,614 878.03 Vested (53,798 ) 554.62 Forfeited (81 ) 632.82 Nonvested awards at December 31, 2016 65,618 $ 634.71 The fair value of the Company's share-based awards issued under the Omnibus Incentive Plan was determined based on the average price of the Company's common shares on the grant date. The fair value of the Company's share-based awards granted under the 2012 Compensation Plan and 2016 Compensation Plan is determined based on the closing price of the Company's common shares on the grant date. The weighted average grant-date fair value of the Company's share-based awards granted in 2016 , 2015 and 2014 was $878.03 , $740.80 and $583.74 , respectively. As of December 31, 2016 , unrecognized compensation cost related to nonvested share-based awards was $10.7 million , which is expected to be recognized over a weighted average period of 1.6 years . The fair value of the Company's share-based awards that vested during 2016 , 2015 and 2014 was $29.8 million , $15.8 million and $4.2 million , respectively.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2016
Other Comprehensive Income (Loss), Tax [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) Other comprehensive income (loss) includes net holding gains (losses) arising during the period, changes in unrealized other-than-temporary impairment losses on fixed maturities arising during the period and reclassification adjustments for net gains included in net income. Other comprehensive income (loss) also includes changes in foreign currency translation adjustments and changes in net actuarial pension loss. The following table presents the change in accumulated other comprehensive income by component, net of taxes and noncontrolling interests. (dollars in thousands) Unrealized Holding Gains on Available-for- Sale Securities Foreign Currency Net Actuarial Pension Loss Total December 31, 2013 $ 1,131,507 $ (11,246 ) $ (30,456 ) $ 1,089,805 Other comprehensive income (loss) before reclassifications 687,908 (32,245 ) (16,516 ) 639,147 Amounts reclassified from accumulated other comprehensive income (26,161 ) — 1,766 (24,395 ) Total other comprehensive income (loss) 661,747 (32,245 ) (14,750 ) 614,752 December 31, 2014 $ 1,793,254 $ (43,491 ) $ (45,206 ) $ 1,704,557 Other comprehensive loss before reclassifications (240,010 ) (29,205 ) (2,482 ) (271,697 ) Amounts reclassified from accumulated other comprehensive income (80,482 ) — 2,130 (78,352 ) Total other comprehensive loss (320,492 ) (29,205 ) (352 ) (350,049 ) December 31, 2015 $ 1,472,762 $ (72,696 ) $ (45,558 ) $ 1,354,508 Other comprehensive income (loss) before reclassifications 275,696 (11,710 ) (20,700 ) 243,286 Amounts reclassified from accumulated other comprehensive income (33,528 ) — 1,600 (31,928 ) Total other comprehensive income (loss) 242,168 (11,710 ) (19,100 ) 211,358 December 31, 2016 $ 1,714,930 $ (84,406 ) $ (64,658 ) $ 1,565,866 The following table summarizes the tax expense (benefit) associated with each component of other comprehensive income (loss). Years Ended December 31, (dollars in thousands) 2016 2015 2014 Change in net unrealized gains on investments: Net holding gains (losses) arising during the period $ 112,399 $ (107,860 ) $ 328,564 Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period 6 35 614 Reclassification adjustments for net gains included in net income (12,462 ) (29,267 ) (9,890 ) Change in net unrealized gains on investments 99,943 (137,092 ) 319,288 Change in foreign currency translation adjustments 1,037 408 1,918 Change in net actuarial pension loss (4,192 ) (88 ) (3,687 ) Total $ 96,788 $ (136,772 ) $ 317,519 The following table presents the details of amounts reclassified from accumulated other comprehensive income into income, by component. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Unrealized holding gains on available-for-sale securities: Other-than-temporary impairment losses $ (18,355 ) $ (44,481 ) $ (4,784 ) Net realized investment gains, excluding other-than-temporary impairment losses 64,345 154,230 40,835 Total before taxes 45,990 109,749 36,051 Income taxes (12,462 ) (29,267 ) (9,890 ) Reclassification of unrealized holding gains, net of taxes $ 33,528 $ 80,482 $ 26,161 Net actuarial pension loss: Underwriting, acquisition and insurance expenses $ (1,951 ) $ (2,662 ) $ (2,084 ) Income taxes 351 532 318 Reclassification of net actuarial pension loss, net of taxes $ (1,600 ) $ (2,130 ) $ (1,766 )

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2016
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 maturity securities, 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 maturity securities 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 (the ILS Funds), as further described in note 17 , 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. 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. December 31, 2016 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments available-for-sale: Fixed maturity securities: U.S. Treasury $ — $ 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 — 1,040,356 — 1,040,356 Residential mortgage-backed — 790,946 — 790,946 Asset-backed — 27,338 — 27,338 Corporate — 1,459,407 — 1,459,407 Total fixed maturity securities — 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 December 31, 2015 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments available-for-sale: Fixed maturity securities: U.S. Treasury $ — $ 309,417 $ — $ 309,417 U.S. government-sponsored enterprises — 391,290 — 391,290 Obligations of states, municipalities and political subdivisions — 4,013,213 — 4,013,213 Foreign governments — 1,416,457 — 1,416,457 Commercial mortgage-backed — 659,538 — 659,538 Residential mortgage-backed — 854,247 — 854,247 Asset-backed — 36,071 — 36,071 Corporate — 1,714,235 — 1,714,235 Total fixed maturity securities — 9,394,468 — 9,394,468 Equity securities: Insurance, banks and other financial institutions 1,334,722 — — 1,334,722 Industrial, consumer and all other 2,739,753 — — 2,739,753 Total equity securities 4,074,475 — — 4,074,475 Short-term investments 1,529,924 112,337 — 1,642,261 Total investments available-for-sale $ 5,604,399 $ 9,506,805 $ — $ 15,111,204 The following table summarizes changes in Level 3 investments measured at fair value on a recurring basis. (dollars in thousands) 2016 2015 Equity securities, beginning of period $ — $ — Purchases 195,250 — Sales (25,000 ) — Total gains included in: Net income 20,953 — Other comprehensive income (loss) — — Transfers into Level 3 — — Transfers out of Level 3 — — Equity securities, end of period $ 191,203 $ — Net unrealized gains included in net income relating to assets held at December 31, 2016 and 2015 (1) $ 20,953 $ — (1) Included in net realized investment gains in the consolidated statements of income and comprehensive income. There were no transfers into or out of Level 1 and Level 2 during 2016 or 2015 . The Company did not have any assets or liabilities measured at fair value on a non-recurring basis during the years ended December 31, 2016 and 2015 .

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2016
Reinsurance Disclosures [Abstract]
Reinsurance	Reinsurance The Company uses reinsurance and retrocessional reinsurance to manage its net retention on individual risks and overall exposure to losses while providing it with the ability to offer policies with sufficient limits to meet policyholder needs. In reinsurance and retrocession transactions, an insurance or reinsurance company transfers, or cedes, all or part of its exposure in return for a portion of the premium. The ceding of insurance does not legally discharge the Company from its primary liability for the full amount of the policies, and the Company will be required to pay the loss and bear collection risk if the reinsurer fails to meet its obligations under the reinsurance or retrocessional agreement. A credit risk exists with ceded reinsurance to the extent that any reinsurer is unable to meet the obligations assumed under the reinsurance or retrocessional contracts. Allowances are established for amounts deemed uncollectible. The Company evaluates the financial condition of its reinsurers and monitors concentration of credit risk arising from its exposure to individual reinsurers. At December 31, 2016 and 2015 , balances recoverable from the Company's ten largest reinsurers, by group, represented approximately 67% and 68% , respectively, of the reinsurance recoverable on paid and unpaid losses, before considering reinsurance allowances. At December 31, 2016 , the Company's largest reinsurance balance was due from the Fairfax Financial Group and represented 15% of the reinsurance recoverable on paid and unpaid losses, before considering reinsurance allowances. To further reduce credit exposure to reinsurance recoverable balances, the Company has received collateral, including letters of credit and trust accounts, from certain reinsurers. Collateral related to these reinsurance agreements is available, without restriction, when the Company pays losses covered by the reinsurance agreements. The following table summarizes the Company's reinsurance allowance for doubtful accounts. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Reinsurance allowance, beginning of year $ 59,350 $ 59,813 $ 76,210 Additions 980 5,897 10,316 Deductions (23,560 ) (6,360 ) (26,713 ) Reinsurance allowance, end of year $ 36,770 $ 59,350 $ 59,813 Management believes the Company's reinsurance allowance for doubtful accounts is adequate at December 31, 2016 ; however, the deterioration in the credit quality of existing reinsurers or disputes over reinsurance and retrocessional contracts could result in additional charges. The following table summarizes the effect of reinsurance and retrocessional reinsurance on premiums written and earned. Years Ended December 31, 2016 2015 2014 (dollars in thousands) Written Earned Written Earned Written Earned Direct $ 3,560,635 $ 3,506,687 $ 3,474,510 $ 3,480,297 $ 3,478,273 $ 3,443,912 Assumed 1,236,010 1,176,205 1,158,402 1,194,772 1,327,240 1,298,371 Ceded (795,625 ) (817,022 ) (813,619 ) (851,537 ) (888,498 ) (901,371 ) Net premiums $ 4,001,020 $ 3,865,870 $ 3,819,293 $ 3,823,532 $ 3,917,015 $ 3,840,912 Incurred losses and loss adjustment expenses were net of reinsurance recoverables (ceded incurred losses and loss adjustment expenses) of $362.0 million , $330.7 million and $423.1 million for the years ended December 31, 2016 , 2015 and 2014 , respectively. The percentage of ceded earned premiums to gross earned premiums was 17% , 18% and 19% for the years ended December 31, 2016 , 2015 and 2014 , respectively. The percentage of assumed earned premiums to net earned premiums was 30% , 31% and 34% for the years ended December 31, 2016 , 2015 and 2014 , respectively. See note 9 of the notes to consolidated financial statements for information regarding two retroactive reinsurance transactions completed during 2015 to cede portfolios of policies primarily comprised of liabilities arising from A&E exposures.

Commitments And Contingencies

Commitments And Contingencies	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments And Contingencies	Commitments and Contingencies a) The Company leases substantially all of its facilities and certain furniture and equipment under noncancelable operating leases with remaining terms up to 18 years. The following table summarizes the Company's minimum annual rental commitments, excluding taxes, insurance and other operating costs payable directly by the Company, for noncancelable operating leases at December 31, 2016 . Years Ending December 31, (dollars in thousands) 2017 $ 34,449 2018 31,883 2019 29,270 2020 21,536 2021 21,140 2022 and thereafter 95,979 Total $ 234,257 Rental expense was $40.2 million , $44.3 million and $42.7 million for the years ended December 31, 2016 , 2015 and 2014 , respectively. b) 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.

Variable Interest Entities

Variable Interest Entities	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Variable Interest Entities	Variable Interest Entities In December 2015, the Company formed MCIM, a wholly owned consolidated subsidiary. MCIM 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. In December 2015, the Company also formed a mutual fund company and reinsurance company, both of which were organized under Bermuda law and are managed by MCIM. 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 for the year ended December 31, 2016 were $56.5 million . The Company is the sole investor in one of the Funds, the Markel Diversified Fund, and consolidates that fund as its primary beneficiary. The Company also holds an investment in another one of the Funds ( $26.1 million as of December 31, 2016 ) but does not have the obligation to absorb losses or right to receive benefits from the VIE that could potentially be significant to the VIE, and therefore does not consolidate that Fund. As of 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 $165.1 million as of December 31, 2016 , which represents 6% of the outstanding preference shares of that fund. This investment is included in equity securities (available-for-sale) on the Company's consolidated balance sheet. Total liabilities of the Markel Diversified Fund include 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 sheet. 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 December 31, 2016 , total investment and insurance assets under management of MCIM for unconsolidated VIEs were $3.4 billion .

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2016
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions The Company engages in certain related party transactions in the normal course of business. These transactions are at arm's length and are not material to the Company's consolidated financial statements. See note 17 for a discussion of the Company's related party transactions with unconsolidated VIEs.

Statutory Financial Information

Statutory Financial Information	12 Months Ended
	Dec. 31, 2016
Statutory Financial Information [Abstract]
Statutory Financial Information	Statutory Financial Information a) Statutory capital and surplus and statutory net income (loss) for the Company's insurance subsidiaries as of December 31, 2016 and 2015 and for the years ended December 31, 2016 , 2015 and 2014 , respectively, is summarized below. Statutory Capital and Surplus (dollars in thousands) 2016 2015 United States $ 2,761,454 $ 2,569,928 United Kingdom $ 682,477 $ 603,238 Bermuda $ 2,189,649 $ 1,964,844 Other $ 24,726 $ 17,305 As of December 31, 2016 , the amount of statutory capital and surplus necessary to satisfy regulatory requirements is not significant in relation to actual statutory capital and surplus. Statutory Net Income (Loss) Years Ended December 31, (dollars in thousands) 2016 2015 2014 United States $ 249,176 $ 291,783 $ 212,909 United Kingdom $ 77,909 $ 74,330 $ 73,697 Bermuda $ 132,442 $ 185,289 $ 110,401 Other $ (891 ) $ (3,181 ) $ 1,367 The Solvency II Directive that governs the calculation of statutory capital and surplus for the Company's United Kingdom insurance subsidiary does not provide requirements for the calculation of net income. Amounts presented in the table above have been calculated in accordance with United Kingdom GAAP. United States The laws of the domicile states of the Company's U.S. insurance subsidiaries govern the amount of dividends that may be paid to the Company. Generally, statutes in the domicile states of the Company's U.S. insurance subsidiaries require prior approval for payment of extraordinary, as opposed to ordinary, dividends. At December 31, 2016 , the Company's U.S. insurance subsidiaries could pay up to $330.4 million during the following 12 months under the ordinary dividend regulations. In converting from U.S. statutory accounting principles to U.S. GAAP, typical adjustments include deferral of policy acquisition costs, differences in the calculation of deferred income taxes and the inclusion of net unrealized gains or losses relating to fixed maturities in shareholders' equity. The Company does not use any permitted statutory accounting practices that are different from prescribed statutory accounting practices which impact statutory capital and surplus. United Kingdom The Company's United Kingdom insurance subsidiary, Markel International Insurance Company Limited (MIICL), and its Lloyd's managing agent, Markel Syndicate Management Limited (MSM), are authorized by the Prudential Regulation Authority (PRA) and regulated by both the PRA and the Financial Conduct Authority (FCA). The PRA oversees compliance with established periodic auditing and reporting requirements, minimum solvency margins and individual capital assessment requirements under the Solvency II Directive and imposes dividend restrictions, while both the PRA and the FCA oversee compliance with risk assessment reviews and various other requirements. MIICL is required to give advance notice to the PRA for any dividends from MIICL and any transaction or proposed transaction with a connected or related person. MSM is required to satisfy the solvency requirements of Lloyd's. In addition, the Company's United Kingdom subsidiaries must comply with the United Kingdom Companies Act of 2006, which provides that dividends may only be paid out of profits available for that purpose. As of December 31, 2016 , earnings of the Company's United Kingdom subsidiaries, to the extent not previously taxed in the United States, are considered reinvested indefinitely for U.S. income tax purposes and will not be made available for distributions to the holding company. Bermuda The Company's Bermuda insurance subsidiary, Markel Bermuda Limited (Markel Bermuda), is subject to enhanced capital requirements in addition to minimum solvency and liquidity requirements. The enhanced capital requirement is determined by reference to a risk-based capital model that determines a control threshold for statutory capital and surplus by taking into account the risk characteristics of different aspects of the insurer's business. At December 31, 2016 , Markel Bermuda satisfied both the enhanced capital requirements and the minimum solvency and liquidity requirements. Under the Bermuda Insurance Act, Markel Bermuda is prohibited from paying or declaring dividends during a fiscal year if it is in breach of its enhanced capital requirement, solvency margin or minimum liquidity ratio or if the declaration or payment of the dividend would cause a breach of those requirements. If an insurer fails to meet its solvency margin or minimum liquidity ratio on the last day of any financial year, it is prohibited from declaring or paying any dividends during the next financial year without the approval of the Bermuda Monetary Authority (BMA). Further, Markel Bermuda is prohibited from declaring or paying, in any financial year, dividends of more than 25% of its total statutory capital and surplus as set forth in its previous year's statutory balance sheet unless at least seven days before payment of those dividends it files with the BMA an affidavit stating that it will continue to meet its solvency margin and minimum liquidity ratio. Markel Bermuda must obtain the BMA's prior approval for a reduction by 15% or more of the total statutory capital as set forth in its previous year's financial statements. In addition, as a long-term insurer, Markel Bermuda may not declare or pay a dividend to any person other than a policyholder unless the value of the assets in its long-term business fund, as certified by Markel Bermuda's approved actuary, exceeds the liabilities of its long-term business. The amount of the dividend cannot exceed the aggregate of that excess and any other funds legally available for the payment of the dividend. As of December 31, 2016 , Markel Bermuda could pay up to $547.4 million during the following 12 months without making any additional filings with the BMA. Other Jurisdictions The Company's other foreign subsidiaries are subject to capital and solvency requirements in their respective jurisdictions of domicile that govern their ability to declare and pay dividends. As of December 31, 2016 , earnings of our foreign subsidiaries, to the extent not previously taxed in the United States, are considered reinvested indefinitely for U.S. income tax purposes and will not be made available for distributions to the holding company. b) Lloyd's sets the corporate members' required capital annually based on each syndicates' business plans, rating environment, reserving environment and input arising from Lloyd's discussions with, inter alia, regulatory and rating agencies. Such required capital is referred to as Funds at Lloyd's (FAL), and comprises cash and investments. The amount of cash and investments held as FAL as of December 31, 2016 was $784.9 million . The amount which the Company provides as FAL is not available for distribution to the holding company. The Company's corporate members may also be required to maintain funds under the control of Lloyd's in excess of their capital requirements and such funds also may not be available for distribution to the holding company.

Segment Reporting Disclosures

Segment Reporting Disclosures	12 Months Ended
	Dec. 31, 2016
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 reinsurance placements written by the Company's insurance subsidiaries domiciled in the United States. The International Insurance segment includes all direct business and facultative reinsurance 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 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 its Markel Ventures operations, which primarily consist of controlling interests in various industrial and service businesses. The Company's non-insurance operations also include the results of the Company's legal and professional consulting services, and, effective December 8, 2015, the results of the Company's investment management services attributable to MCIM. For purposes of segment reporting, the Company's non-insurance operations are not considered a reportable segment. The following table summarizes the Company's gross written premiums by country. Gross written premiums are attributed to individual countries based upon location of risk or cedent. Years Ended December 31, (dollars in thousands) 2016 % of Total 2015 % of Total 2014 % of Total United States $ 3,691,840 77 % $ 3,519,487 76 % $ 3,523,239 73 % United Kingdom 358,348 7 414,941 9 441,669 9 Canada 125,444 3 115,191 2 125,617 3 Other countries 621,013 13 583,293 13 714,988 15 Total $ 4,796,645 100 % $ 4,632,912 100 % $ 4,805,513 100 % Most of the Company's gross written premiums are placed through insurance and reinsurance brokers. During the years ended December 31, 2016 , 2015 and 2014 , the top three independent brokers accounted for approximately 28% , 27% and 28% of consolidated gross premiums written. During the years ended December 31, 2016 , 2015 and 2014 , the top three independent brokers accounted for approximately 40% , 42% and 41% , respectively, of gross premiums written in the International Insurance segment and 75% , 68% and 68% , respectively, of gross premiums written in the Reinsurance segment. Segment profit for the Investing segment is measured by net investment income and net realized investment gains or losses. Segment profit or loss for each of the Company's underwriting segments is measured by underwriting profit or loss. The property and casualty insurance industry commonly defines underwriting profit or loss as earned premiums net of losses and loss adjustment expenses and underwriting, acquisition and insurance expenses. Underwriting profit or loss does not replace operating income or net income computed in accordance with U.S. GAAP as a measure of profitability. Underwriting profit or loss provides a basis for management to evaluate the Company's underwriting performance. Segment profit or loss for the Company's underwriting segments also includes other revenues and other expenses, primarily related to the run-off of managing general agent operations that were discontinued in conjunction with acquisitions. Other revenues and other expenses in the Other Insurance (Discontinued Lines) segment are comprised of the results attributable to the run-off of life and annuity reinsurance business. For management reporting purposes, the Company allocates assets to its underwriting, investing and non-insurance operations. Underwriting assets are all assets not specifically allocated to the Investing segment or to the Company's non-insurance operations. Underwriting and investing assets are not allocated to the U.S. Insurance, International Insurance, Reinsurance or Other Insurance (Discontinued Lines) segments since the Company does not manage its assets by underwriting segment. The Company does not allocate capital expenditures for long-lived assets to any of its underwriting segments for management reporting purposes. a) The following tables summarize the Company's segment disclosures. Year Ended December 31, 2016 (dollars in thousands) U.S. Insurance International Insurance Reinsurance Other Insurance (Discontinued Lines) Investing Consolidated Gross premium volume $ 2,635,266 $ 1,119,815 $ 1,041,055 $ 509 $ — $ 4,796,645 Net written premiums 2,237,163 864,494 898,728 635 — 4,001,020 Earned premiums 2,175,332 853,512 836,264 762 — 3,865,870 Losses and loss adjustment expenses: Current accident year (1,403,589 ) (605,837 ) (546,476 ) — — (2,555,902 ) Prior accident years 204,881 164,713 125,514 10,050 — 505,158 Amortization of policy acquisition costs (446,649 ) (146,117 ) (189,455 ) — — (782,221 ) Other operating expenses (377,230 ) (219,066 ) (119,012 ) (1,061 ) — (716,369 ) Underwriting profit 152,745 47,205 106,835 9,751 — 316,536 Net investment income — — — — 373,230 373,230 Net realized investment gains — — — — 65,147 65,147 Other revenues (insurance) 7,143 5,560 — 1,891 — 14,594 Other expenses (insurance) (15,407 ) (5,712 ) — (26,504 ) — (47,623 ) Segment profit (loss) $ 144,481 $ 47,053 $ 106,835 $ (14,862 ) $ 438,377 $ 721,884 Other revenues (non-insurance) 1,293,185 Other expenses (non-insurance) (1,142,620 ) Amortization of intangible assets (68,533 ) Interest expense (129,896 ) Loss on early extinguishment of debt (44,100 ) Income before income taxes $ 629,920 U.S. GAAP combined ratio (1) 93 % 94 % 87 % NM (2) 92 % (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. Year Ended December 31, 2015 (dollars in thousands) U.S. Insurance International Insurance Reinsurance Other Insurance (Discontinued Lines) Investing Consolidated Gross premium volume $ 2,504,096 $ 1,164,866 $ 965,374 $ (1,424 ) $ — $ 4,632,912 Net written premiums 2,106,490 888,214 824,324 265 — 3,819,293 Earned premiums 2,105,212 879,426 838,543 351 — 3,823,532 Losses and loss adjustment expenses: Current accident year (1,367,159 ) (638,144 ) (561,242 ) — — (2,566,545 ) Prior accident years 298,967 248,834 97,860 (17,861 ) — 627,800 Amortization of policy acquisition costs (420,289 ) (142,657 ) (182,018 ) — — (744,964 ) Other operating expenses (378,563 ) (221,758 ) (106,863 ) (2,932 ) — (710,116 ) Underwriting profit (loss) 238,168 125,701 86,280 (20,442 ) — 429,707 Net investment income — — — — 353,213 353,213 Net realized investment gains — — — — 106,480 106,480 Other revenues (insurance) 3,331 7,790 593 617 — 12,331 Other expenses (insurance) (3,902 ) (5,717 ) (1,419 ) (29,057 ) — (40,095 ) Segment profit (loss) $ 237,597 $ 127,774 $ 85,454 $ (48,882 ) $ 459,693 $ 861,636 Other revenues (non-insurance) 1,074,427 Other expenses (non-insurance) (1,006,710 ) Amortization of intangible assets (68,947 ) Interest expense (118,301 ) Income before income taxes $ 742,105 U.S. GAAP combined ratio (1) 89 % 86 % 90 % NM (2) 89 % (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. Year Ended December 31, 2014 (dollars in thousands) U.S. Insurance International Insurance Reinsurance Other Insurance (Discontinued Lines) Investing Consolidated Gross premium volume $ 2,493,823 $ 1,200,403 $ 1,112,728 $ (1,441 ) $ — $ 4,805,513 Net written premiums 2,071,466 889,336 956,584 (371 ) — 3,917,015 Earned premiums 2,022,860 909,679 908,385 (12 ) — 3,840,912 Losses and loss adjustment expenses: Current accident year (1,340,129 ) (660,409 ) (637,474 ) — — (2,638,012 ) Prior accident years 216,557 166,615 79,951 (27,578 ) — 435,545 Amortization of policy acquisition costs (403,233 ) (141,394 ) (110,289 ) — — (654,916 ) Other operating expenses (396,737 ) (207,175 ) (201,673 ) (381 ) — (805,966 ) Underwriting profit (loss) 99,318 67,316 38,900 (27,971 ) — 177,563 Net investment income — — — — 363,230 363,230 Net realized investment gains — — — — 46,000 46,000 Other revenues (insurance) 2,478 21,827 2,696 1,631 — 28,632 Other expenses (insurance) (5,149 ) (18,706 ) (1,847 ) (37,132 ) — (62,834 ) Segment profit (loss) $ 96,647 $ 70,437 $ 39,749 $ (63,472 ) $ 409,230 $ 552,591 Other revenues (non-insurance) 854,893 Other expenses (non-insurance) (792,037 ) Amortization of intangible assets (57,627 ) Interest expense (117,442 ) Income before income taxes $ 440,378 U.S. GAAP combined ratio (1) 95 % 93 % 96 % NM (2) 95 % (1) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (2) NM — Ratio is not meaningful. b) The following table summarizes deferred policy acquisition costs, unearned premiums and unpaid losses and loss adjustment expenses by segment. (dollars in thousands) Deferred Policy Acquisition Costs Unearned Premiums Unpaid Losses and Loss Adjustment Expenses December 31, 2016 U.S. Insurance $ 176,348 $ 1,166,914 $ 3,849,541 International Insurance 51,948 445,183 3,062,725 Reinsurance 164,114 651,741 2,661,209 Other Insurance (Discontinued Lines) — — 542,187 Total $ 392,410 $ 2,263,838 $ 10,115,662 December 31, 2015 U.S. Insurance $ 162,289 $ 1,105,456 $ 3,720,429 International Insurance 48,913 467,158 3,140,000 Reinsurance 141,554 593,491 2,750,258 Other Insurance (Discontinued Lines) — — 641,266 Total $ 352,756 $ 2,166,105 $ 10,251,953 c) The following table summarizes segment earned premiums by major product grouping. Years Ended December 31, (dollars in thousands) 2016 2015 2014 U.S. Insurance: General liability $ 563,908 $ 522,358 $ 491,645 Professional liability 328,597 324,230 321,005 Property 270,026 264,232 266,019 Personal lines 364,843 325,811 299,442 Programs 263,783 277,829 244,216 Workers compensation 301,126 281,954 263,164 Other 83,049 108,798 137,369 Total U.S. Insurance 2,175,332 2,105,212 2,022,860 International Insurance: General liability 111,291 124,198 146,178 Professional liability 272,010 268,637 285,300 Property 87,294 85,152 76,691 Marine and energy 242,070 262,307 287,263 Other 140,847 139,132 114,247 Total International Insurance 853,512 879,426 909,679 Reinsurance: Property 288,771 265,373 270,461 Casualty 327,383 315,027 323,390 Auto 65,363 102,227 152,645 Other 154,747 155,916 161,889 Total Reinsurance 836,264 838,543 908,385 Other Insurance (Discontinued Lines) 762 351 (12 ) Total earned premiums $ 3,865,870 $ 3,823,532 $ 3,840,912 The Company does not manage products at this level of aggregation. The Company offers a diverse portfolio of products and manages these products in logical groupings within each operating segment. d) The following table reconciles segment assets to the Company's consolidated balance sheets. December 31, (dollars in thousands) 2016 2015 2014 Segment assets: Investing $ 19,029,584 $ 18,056,947 $ 18,531,150 Underwriting 5,397,696 5,385,126 5,420,624 Total segment assets 24,427,280 23,442,073 23,951,774 Non-insurance operations 1,448,019 1,497,042 1,245,986 Total assets $ 25,875,299 $ 24,939,115 $ 25,197,760

Other Revenues And Other Expens

Other Revenues And Other Expenses	12 Months Ended
	Dec. 31, 2016
Other Income and Expenses [Abstract]
Other Revenues And Other Expenses	Other Revenues and Other Expenses The following table summarizes the components of other revenues and other expenses. Years Ended December 31, 2016 2015 2014 (dollars in thousands) Other Revenues Other Expenses Other Revenues Other Expenses Other Revenues Other Expenses Insurance: Managing general agent operations $ 12,703 $ 21,119 $ 10,202 $ 9,619 $ 23,324 $ 22,527 Life and annuity 1,891 26,504 617 29,057 1,631 37,132 Other — — 1,512 1,419 3,677 3,175 14,594 47,623 12,331 40,095 28,632 62,834 Non-Insurance: Markel Ventures: Manufacturing 784,745 675,620 755,802 677,054 575,353 513,668 Markel Ventures: Non-Manufacturing 429,704 396,323 291,714 301,004 262,767 261,551 Investment management 56,455 46,190 — — — — Other 22,281 24,487 26,911 28,652 16,773 16,818 1,293,185 1,142,620 1,074,427 1,006,710 854,893 792,037 Total $ 1,307,779 $ 1,190,243 $ 1,086,758 $ 1,046,805 $ 883,525 $ 854,871 The Company's Markel Ventures operations primarily consist of controlling interests in various industrial and service businesses and are viewed by management as separate and distinct from the Company's insurance operations. While each of the businesses is operated independently from one another, management aggregates financial results into two industry groups: manufacturing and non-manufacturing.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2016
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]
Employee Benefit Plans	Employee Benefit Plans a) The Company maintains defined contribution plans for employees of its United States insurance operations in accordance with Section 401(k) of the U.S. Internal Revenue Code of 1986. Employees of the Company's Markel Ventures subsidiaries are provided post-retirement benefits under separate plans. The Company also provides various defined contribution plans for employees of its international insurance and non-insurance operations, which are in line with local market terms and conditions of employment. Expenses relating to the Company's defined contribution plans were $30.1 million , $27.7 million and $27.2 million in 2016 , 2015 and 2014 , respectively. b) The Terra Nova Pension Plan is a defined benefit plan which covers certain employees in our international insurance operations who meet the eligibility conditions set out in the plan. The plan has been closed to new participants since 2001. The cost of providing pensions for employees is charged to earnings over the average working life of employees according to actuarial recommendations. Final benefits are based on the employee's years of credited service and the higher of pensionable compensation received in the calendar year preceding retirement or the best average pensionable compensation received in any three consecutive years in the ten years preceding retirement. Effective April 1, 2012, employees are no longer accruing benefits for future service in the Terra Nova Pension Plan. The Company uses December 31 as the measurement date for the Terra Nova Pension Plan. The following table summarizes the funded status of the Terra Nova Pension Plan and the amounts recognized on the accompanying consolidated balance sheets of the Company. Years Ended December 31, (dollars in thousands) 2016 2015 Change in projected benefit obligation: Projected benefit obligation at beginning of period $ 170,005 $ 185,556 Interest cost 6,113 6,645 Plan settlements — (2,863 ) Benefits paid (3,322 ) (3,970 ) Actuarial loss (gain) 38,485 (6,051 ) Effect of foreign currency rate changes (32,663 ) (9,312 ) Projected benefit obligation at end of year $ 178,618 $ 170,005 Change in plan assets: Fair value of plan assets at beginning of period $ 186,727 $ 201,399 Actual gain on plan assets 22,367 2,246 Employer contributions 3,577 — Plan settlements — (2,766 ) Benefits paid (3,322 ) (3,970 ) Effect of foreign currency rate changes (33,705 ) (10,182 ) Fair value of plan assets at end of year $ 175,644 $ 186,727 Funded status of the plan $ (2,974 ) $ 16,722 Net actuarial pension loss 85,110 61,818 Total $ 82,136 $ 78,540 Net actuarial pension loss is recognized as a component of accumulated other comprehensive income, net of taxes. The asset or liability for pension benefits, also referred to as the funded status of the plan, at December 31, 2016 and 2015 was included in other assets on the consolidated balance sheets. The following table presents the changes in plan assets and projected benefit obligation recognized in accumulated other comprehensive income. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Net actuarial loss $ (25,243 ) $ (3,102 ) $ (20,521 ) Settlement loss recognized — 343 — Amortization of: Net actuarial loss 1,951 2,319 1,589 Prior service costs — — 495 Tax benefit 4,192 88 3,687 Total other comprehensive loss $ (19,100 ) $ (352 ) $ (14,750 ) The following table summarizes the components of net periodic benefit income and the weighted average assumptions for the Terra Nova Pension Plan. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Components of net periodic benefit income: Interest cost $ 6,113 $ 6,645 $ 7,572 Expected return on plan assets (9,124 ) (11,496 ) (12,812 ) Amortization of prior service cost — — 495 Amortization of net actuarial pension loss 1,951 2,319 1,589 Settlement loss recognized — 343 — Net periodic benefit income $ (1,060 ) $ (2,189 ) $ (3,156 ) Weighted average assumptions as of December 31: Discount rate 2.7 % 4.0 % 3.8 % Expected return on plan assets 4.5 % 5.4 % 6.0 % Rate of compensation increase 3.0 % 2.9 % 2.9 % The projected benefit obligation and the net periodic benefit income are determined by independent actuaries using assumptions provided by the Company. In determining the discount rate, the Company uses the current yield on high-quality, fixed maturity investments that have maturities corresponding to the anticipated timing of estimated defined benefit payments. The decrease in the weighted average discount rate from 2015 to 2016 is due to a decrease in the yields on securities used to determine the discount rate during 2016. The expected return on plan assets is estimated based upon the anticipated average yield on plan assets using asset return assumptions for each asset class, and the cross-correlations between the asset classes, over a specified projection horizon. The decrease in the weighted average expected return on plan assets from 2015 to 2016 is due to changes in market conditions during 2016 that impacted projected returns. The rate of compensation increase is based upon historical experience and management's expectation of future compensation. Management's discount rate and rate of compensation increase assumptions at December 31, 2016 were used to calculate the Company's projected benefit obligation. Management's discount rate, expected return on plan assets and rate of compensation increase assumptions at December 31, 2015 were used to calculate the net periodic benefit income for 2016 . The Company estimates that net periodic benefit cost in 2017 will include an expense of $3.5 million resulting from the amortization of the net actuarial pension loss included as a component of accumulated other comprehensive income at December 31, 2016 . The fair values of each of the plan's assets are measured using quoted prices in active markets for identical assets, which represent Level 1 inputs within the fair value hierarchy established in FASB ASC 820-10. The following table summarizes the fair value of plan assets as of December 31, 2016 and 2015 . December 31, (dollars in thousands) 2016 2015 Plan assets: Fixed maturity index funds $ 103,218 $ 107,033 Equity security index funds 72,419 79,686 Cash and cash equivalents 7 8 Total $ 175,644 $ 186,727 During 2014, the Company revised the target asset allocation and adjusted the investment balances to reduce risk while maintaining long-term return objectives. The Company's target asset allocation for the plan is 47% equity securities and 53% fixed maturities. At December 31, 2016 , the actual allocation of assets in the plan was 41% equity securities and 59% fixed maturities. At December 31, 2015 , the actual allocation of assets in the plan was 43% equity securities and 57% fixed maturities. Investments are managed by a third party investment manager. Equity securities are invested in an index fund where 30% is indexed to United Kingdom equities and 70% is indexed to other markets. Assets are also invested in a mutual fund with a diversified global portfolio of equities, investment grade debt, property and cash. The primary objective of investing in these funds is to earn rates of return that are consistently in excess of inflation. Investing in equity securities, historically, has provided rates of return that are higher than investments in fixed maturities. Fixed maturity investments are allocated between five mutual funds; two index funds that include United Kingdom government securities, one index fund that includes securities issued by other foreign governments, one mutual fund that includes investment grade corporate bonds from the United Kingdom and foreign markets and one index fund that includes United Kingdom corporate securities. The assets in these funds are invested to meet the Company's obligations for current pensioners and those individuals nearing retirement. The plan does not invest in the Company's common shares. At December 31, 2016 and 2015 , the fair value of plan assets exceeded the plan's accumulated benefit obligation of $175.1 million and $164.8 million , respectively. The Company expects to make plan contributions of $3.2 million in 2017 . The benefits expected to be paid in each year from 2017 to 2021 are $3.0 million , $3.1 million , $3.1 million , $3.2 million and $3.3 million , respectively. The aggregate benefits expected to be paid in the five years from 2022 to 2026 are $17.4 million . The expected benefits to be paid are based on the same assumptions used to measure the Company's projected benefit obligation at December 31, 2016 .

Markel Corporation (Parent Comp

Markel Corporation (Parent Company Only) Financial Information	12 Months Ended
	Dec. 31, 2016
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Markel Corporation (Parent Company Only) Financial Information	Markel Corporation (Parent Company Only) Financial Information The following parent company only condensed financial information reflects the financial position, results of operations and cash flows of Markel Corporation. CONDENSED BALANCE SHEETS December 31, 2016 2015 (dollars in thousands) ASSETS Investments, available-for-sale, at estimated fair value: Fixed maturities (amortized cost of $51,181 in 2016 and $35,475 in 2015) $ 52,234 $ 36,618 Equity securities (cost of $203,708 in 2016 and $204,289 in 2015) 367,156 311,405 Short-term investments (estimated fair value approximates cost) 1,729,400 755,619 Total Investments 2,148,790 1,103,642 Cash and cash equivalents 369,641 460,271 Restricted cash and cash equivalents 1,013 670 Receivables 20,477 17,200 Investments in consolidated subsidiaries 8,107,450 7,961,315 Notes receivable from subsidiaries 60,110 212,636 Other assets 97,364 89,747 Total Assets $ 10,804,845 $ 9,845,481 LIABILITIES AND SHAREHOLDERS' EQUITY Senior long-term debt $ 1,944,171 $ 1,633,068 Notes payable to subsidiaries 285,000 300,000 Income taxes payable 25,240 4,262 Net deferred tax liability 25,902 7,498 Other liabilities 63,605 66,503 Total Liabilities 2,343,918 2,011,331 Total Shareholders' Equity 8,460,927 7,834,150 Total Liabilities and Shareholders' Equity $ 10,804,845 $ 9,845,481 CONDENSED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME Years Ended December 31, 2016 2015 2014 (dollars in thousands) REVENUES Net investment income $ 9,561 $ 2,565 $ 5,354 Dividends on common stock of consolidated subsidiaries 349,622 187,496 217,121 Net realized investment gains: Other-than-temporary impairment losses (98 ) (3,455 ) (120 ) Net realized investment gains, excluding other-than-temporary impairment losses 1,166 75,000 3,873 Net realized investment gains 1,068 71,545 3,753 Total Revenues 360,251 261,606 226,228 EXPENSES Interest expense 116,013 95,620 94,097 Loss on early extinguishment of debt 44,100 — — Other expenses 13,076 11,287 2,685 Total Expenses 173,189 106,907 96,782 Income Before Equity in Undistributed Earnings of Consolidated Subsidiaries and Income Taxes 187,062 154,699 129,446 Equity in undistributed earnings of consolidated subsidiaries 196,615 407,489 163,341 Income tax benefit (72,012 ) (20,584 ) (28,395 ) Net Income to Shareholders $ 455,689 $ 582,772 $ 321,182 OTHER COMPREHENSIVE INCOME (LOSS) TO SHAREHOLDERS Change in net unrealized gains on investments, net of taxes: Net holding gains (losses) arising during the period $ 37,045 $ (41,861 ) $ 32,118 Consolidated subsidiaries' net holding gains (losses) arising during the period 238,616 (198,309 ) 655,617 Consolidated subsidiaries' change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period 35 160 173 Reclassification adjustments for net gains included in net income to shareholders (558 ) (45,273 ) (1,874 ) Consolidated subsidiaries' reclassification adjustments for net gains included in net income to shareholders (32,970 ) (35,209 ) (24,287 ) Change in net unrealized gains on investments, net of taxes 242,168 (320,492 ) 661,747 Change in foreign currency translation adjustments, net of taxes (1,326 ) 2,970 1,949 Consolidated subsidiaries' change in foreign currency translation adjustments, net of taxes (10,384 ) (32,175 ) (34,194 ) Consolidated subsidiaries' change in net actuarial pension loss, net of taxes (19,100 ) (352 ) (14,750 ) Total Other Comprehensive Income (Loss) to Shareholders 211,358 (350,049 ) 614,752 Comprehensive Income to Shareholders $ 667,047 $ 232,723 $ 935,934 CONDENSED STATEMENTS OF CASH FLOWS Years Ended December 31, 2016 2015 2014 (dollars in thousands) OPERATING ACTIVITIES Net income to shareholders $ 455,689 $ 582,772 $ 321,182 Adjustments to reconcile net income to shareholders to net cash provided by operating activities (120,564 ) (464,193 ) (218,396 ) Net Cash Provided By Operating Activities 335,125 118,579 102,786 INVESTING ACTIVITIES Proceeds from sales of fixed maturities and equity securities 1,831 100,633 9,306 Proceeds from maturities, calls and prepayments of fixed maturities 11,960 24,945 15,710 Cost of fixed maturities and equity securities purchased (29,110 ) (55,656 ) (687 ) Net change in short-term investments (970,364 ) 9,956 (109,728 ) Securities received from subsidiaries as dividends, repayment of notes receivable and return of capital 238,975 — 89,996 Return of capital from subsidiaries 21,021 — — Decrease in notes receivable due from subsidiaries 92,530 — 28,506 Capital contributions to subsidiaries — (228,578 ) (74,788 ) Cost of equity method investments (3,100 ) (13,164 ) — Change in restricted cash and cash equivalents (343 ) 289 51 Additions to property and equipment (584 ) (305 ) (342 ) Other (3,207 ) (376 ) (2,150 ) Net Cash Used By Investing Activities (640,391 ) (162,256 ) (44,126 ) FINANCING ACTIVITIES Additions to senior long-term debt 493,149 — — Increase in notes payable to subsidiaries — 285,000 — Repayment and retirement of senior long-term debt (183,343 ) (2,000 ) — Premiums and fees related to early extinguishment of debt (43,691 ) — — Repurchases of common stock (51,142 ) (31,491 ) (26,053 ) Issuance of common stock 4,623 4,752 5,691 Other (4,960 ) 3,985 (1,948 ) Net Cash Provided (Used) By Financing Activities 214,636 260,246 (22,310 ) Increase (decrease) in cash and cash equivalents (90,630 ) 216,569 36,350 Cash and cash equivalents at beginning of year 460,271 243,702 207,352 CASH AND CASH EQUIVALENTS AT END OF YEAR $ 369,641 $ 460,271 $ 243,702

Quarterly Financial Information

Quarterly Financial Information	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information	Quarterly Financial Information (unaudited) The following table presents the unaudited quarterly results of consolidated operations for 2016 , 2015 and 2014 . Quarters Ended (dollars in thousands, except per share amounts) Mar. 31 June 30 Sept. 30 Dec. 31 2016 Operating revenues $ 1,376,182 $ 1,375,937 $ 1,431,282 $ 1,428,625 Net income 163,646 80,673 83,421 132,703 Net income to shareholders 160,370 78,797 83,796 132,726 Comprehensive income (loss) to shareholders 396,994 209,942 89,161 (29,050 ) Net income per share: Basic $ 11.21 $ 5.44 $ 5.62 $ 9.14 Diluted 11.15 5.41 5.60 9.11 Common stock price ranges: High $ 895.03 $ 989.18 $ 961.78 $ 931.94 Low 805.03 880.01 909.84 811.05 2015 Operating revenues $ 1,302,154 $ 1,304,605 $ 1,342,764 $ 1,420,460 Net income 194,006 92,453 104,410 198,273 Net income to shareholders 190,992 91,369 102,519 197,892 Comprehensive income (loss) to shareholders 281,807 (132,925 ) (51,143 ) 134,984 Net income per share: Basic $ 13.57 $ 6.76 $ 7.43 $ 14.23 Diluted 13.49 6.72 7.39 14.14 Common stock price ranges: High $ 783.50 $ 821.00 $ 898.08 $ 937.91 Low 660.05 736.96 775.00 791.97 2014 Operating revenues $ 1,239,655 $ 1,258,971 $ 1,299,286 $ 1,335,755 Net income 87,501 41,141 76,824 118,222 Net income to shareholders 87,716 40,068 75,803 117,595 Comprehensive income to shareholders 230,273 250,588 36,502 418,571 Net income per share: Basic $ 6.28 $ 2.67 $ 5.33 $ 8.10 Diluted 6.25 2.66 5.30 8.05 Common stock price ranges: High $ 596.87 $ 655.75 $ 666.00 $ 707.36 Low 527.17 593.76 623.90 632.65

Summary Of Significant Accoun31

Summary Of Significant Accounting Policies (Policy)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation. 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. Certain prior year amounts have been reclassified to conform to the current presentation.
Use of Estimates	Use of Estimates. 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. Management periodically reviews its estimates and assumptions. Quarterly reviews include evaluating the adequacy of reserves for unpaid losses and loss adjustment expenses, life and annuity reinsurance benefit reserves, litigation contingencies, the reinsurance allowance for doubtful accounts and income tax liabilities, as well as analyzing the recoverability of deferred tax assets, estimating reinsurance premiums written and earned and evaluating the investment portfolio for other-than-temporary declines in estimated fair value. Estimates and assumptions for goodwill and intangible assets are reviewed in conjunction with an acquisition, and goodwill and indefinite-lived intangible assets are reassessed at least annually for impairment. Actual results may differ materially from the estimates and assumptions used in preparing the consolidated financial statements.
Investments	Investments. Available-for-sale investments are recorded at estimated fair value. Unrealized gains and losses on investments, net of income taxes, are included in accumulated other comprehensive income in shareholders' equity. 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. Premiums and discounts are amortized or accreted over the lives of the related fixed maturities as an adjustment to the yield using the effective interest method. Dividend and interest income are recognized when earned. Realized investment gains or losses are included in earnings. Realized gains or losses from sales of investments are derived using the first-in, first-out method. The Company also has certain investments in fixed maturity and equity securities that are recorded at estimated fair value with changes in unrealized gains and losses recorded in net income. These fixed maturity and equity security investments totaled $41.4 million and $191.2 million , respectively, as of December 31, 2016 and are included in fixed maturities and equity securities in the consolidated balance sheets. Investments accounted for under the equity method of accounting are recorded at cost within other assets on the consolidated balance sheets and subsequently increased or decreased by the Company's proportionate share of the net income or loss of the investee. The Company records its proportionate share of net income or loss of the investee in net investment income. The Company records its proportionate share of other comprehensive income or loss of the investee as a component of other comprehensive income (loss). Dividends or other equity distributions are recorded as a reduction of the investment. The Company reviews equity method investments for impairment when events or circumstances indicate that a decline in the fair value of the investment below its carrying value is other-than-temporary.
Cash and Cash Equivalents	Cash and Cash Equivalents. The Company considers all investments with original maturities of 90 days or less to be cash equivalents. The carrying value of the Company's cash and cash equivalents and restricted cash and cash equivalents approximates fair value.
Receivables	Receivables. Receivables include amounts receivable from agents, brokers and insureds, which represent premiums that are both currently due and amounts not yet due on insurance and reinsurance policies. Premiums for insurance policies are generally due at inception. Premiums for reinsurance policies generally become due over the period of coverage based on the policy terms. The Company monitors the credit risk associated with premiums receivable, taking into consideration the fact that in certain instances credit risk may be reduced by the Company's right to offset loss obligations or unearned premiums against premiums receivable. Amounts deemed uncollectible are charged to net income in the period they are determined. Changes in the estimate of reinsurance premiums written will result in an adjustment to premiums receivable in the period they are determined.
Reinsurance Recoverables	Reinsurance Recoverables. Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability associated with the reinsured business. Allowances are established for amounts deemed uncollectible and reinsurance recoverables are recorded net of these allowances. The Company evaluates the financial condition of its reinsurers and monitors concentration risk to minimize its exposure to significant losses from individual reinsurers.
Deferred Policy Acquisition Costs	Deferred Policy Acquisition Costs. Costs directly related to the acquisition of insurance premiums are deferred and amortized over the related policy period, generally one year . The Company only defers acquisition costs incurred that are related directly to the successful acquisition of new or renewal insurance contracts, including commissions to agents and brokers and premium taxes. Commissions received related to reinsurance premiums ceded are netted against broker commissions in determining acquisition costs eligible for deferral. To the extent that future policy revenues on existing policies are not adequate to cover related costs and expenses, deferred policy acquisition costs are charged to earnings. The Company does not consider anticipated investment income in determining whether a premium deficiency exists.
Goodwill and Intangible Assets	Goodwill and Intangible Assets. Goodwill and intangible assets are recorded as a result of business acquisitions. Goodwill represents the excess of the amount paid to acquire a business over the net fair value of assets acquired and liabilities assumed at the date of acquisition. Indefinite-lived and other intangible assets are recorded at fair value as of the acquisition date. The determination of the fair value of certain assets acquired and liabilities assumed involves significant judgment and the use of valuation models and other estimates, which require assumptions that are inherently subjective. Goodwill and indefinite-lived intangible assets are tested for impairment at least annually. The Company completes an annual test during the fourth quarter of each year based upon the results of operations through September 30. Intangible assets with definite lives are amortized using the straight-line method over their estimated useful lives, generally five to 20 years , and are reviewed for impairment when events or circumstances indicate that their carrying value may not be recoverable.
Property and Equipment	Property and Equipment. Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization of property and equipment are calculated using the straight-line method over the estimated useful lives (generally, the lower of the life of the lease or the estimated useful life for leasehold improvements, ten to 40 years for buildings, seven to 40 years for land improvements, three to ten years for furniture and equipment and three to 25 years for other property and equipment).
Redeemable Noncontrolling Interests	Redeemable Noncontrolling Interests. The Company owns controlling interests in various companies through its Markel Ventures operations. In some cases, the Company has the option to acquire the remaining equity interests, and the remaining equity interests have the option to sell their interests to the Company, in the future. The redemption value of the remaining equity interests is generally based on the respective company's earnings in specified periods preceding the redemption date. The redeemable noncontrolling interests generally become redeemable through 2020. The Company recognizes changes in the redemption value that exceed the carrying value of redeemable noncontrolling interests to retained earnings as if the balance sheet date were also the redemption date. Changes in the redemption value also result in an adjustment to net income to shareholders in the calculation of basic and diluted net income per share. The change in the redemption value of redeemable noncontrolling interests in 2016 , 2015 and 2014 resulted in an adjustment to retained earnings of a decrease of $15.5 million , an increase of $4.1 million , and a decrease of $8.2 million , respectively.
Income Taxes	Income Taxes. The Company records deferred income taxes to reflect the net tax effect of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and their tax bases. Deferred tax assets are reduced by a valuation allowance when management believes it is more likely than not that some, or all, of the deferred tax assets will not be realized. The Company recognizes the tax benefit from an uncertain tax position taken or expected to be taken in income tax returns only if it is more likely than not that the tax position will be sustained upon examination by tax authorities, based on the technical merits of the position. Tax positions that meet the more likely than not threshold are then measured using a probability weighted approach, whereby the largest amount of tax benefit that is greater than 50% likely of being realized upon ultimate settlement is recognized. The Company recognizes interest and penalties related to uncertain tax positions in income tax expense.
Unpaid Losses and Loss Adjustment Expenses	Unpaid Losses and Loss Adjustment Expenses. Unpaid losses and loss adjustment expenses on our property and casualty insurance business are based on evaluations of reported claims and estimates for losses and loss adjustment expenses incurred but not reported. Estimates for losses and loss adjustment expenses incurred but not reported are based on reserve development studies, among other things. The Company does not discount reserves for losses and loss adjustment expenses to reflect estimated present value, except for reserves assumed in connection with an acquisition, which are recorded at fair value at the acquisition date. Recorded reserves are estimates, and the ultimate liability may be greater or less than the estimates.
Life and Annuity Benefits	Life and Annuity Benefits. The Company previously acquired a block of long duration reinsurance contracts for life and annuity benefits which subject the Company to mortality, longevity and morbidity risks. The assumptions used to determine policy benefit reserves are generally locked-in for the life of the contract unless an unlocking event occurs. To the extent existing policy reserves, together with the present value of future gross premiums and expected investment income earned thereon, are not adequate to cover the present value of future benefits, settlement and maintenance costs, 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. Because of the assumptions and estimates used in establishing reserves for life and annuity benefit obligations and the long-term nature of these reinsurance contracts, the ultimate liability may be greater or less than the estimates. Results attributable to the run-off of life and annuity reinsurance business are included in other revenues and other expenses in the Company's consolidated statements of income and comprehensive income and as part of the Company's Other Insurance (Discontinued Lines) segment.
Revenue Recognition	Revenue Recognition. Property and Casualty Premiums Insurance premiums are generally earned on a pro rata basis over the policy period, typically one year . The cost of reinsurance ceded is initially recorded as prepaid reinsurance premiums and is amortized over the reinsurance contract period in proportion to the amount of insurance protection provided. Premiums ceded are netted against premiums written. Assumed reinsurance premiums are recorded at the inception of each contract based upon contract terms and information received from cedents and brokers and are earned on a pro rata basis over the coverage period, or for multi-year contracts, in proportion with the underlying risk exposure to the extent there is variability in the exposure through the coverage period. Changes in reinsurance premium estimates are expected and may result in significant adjustments in any period. These estimates change over time as additional information regarding changes in underlying exposures is obtained. Any subsequent differences arising on such estimates are recorded as premiums written in the period they are determined and are earned on a pro rata basis over the coverage period. The Company uses the periodic method to account for assumed reinsurance from foreign reinsurers. The Company's foreign reinsurers provide sufficient information to record foreign assumed business in the same manner as the Company records assumed business from United States reinsurers. Certain contracts that the Company writes provide for reinstatement of coverage. Reinstatement premiums are the premiums for the restoration of the insurance or reinsurance limit of a contract to its full amount after a loss occurrence by the insured or reinsured. The Company accrues for reinstatement premiums resulting from losses recorded. Such accruals are based upon contractual terms and management judgment is involved with respect to the amount of losses recorded. Changes in estimates of losses recorded on contracts with reinstatement premium features will result in changes in reinstatement premiums based on contractual terms. Reinstatement premiums are recognized at the time losses are recorded and are earned on a pro-rata basis over the coverage period. Other Revenues Other revenues primarily relate to the Company's Markel Ventures operations and consist of revenues from the sale of manufactured products and service revenues. Revenues from manufactured products are generally recognized at the time title transfers to the customer, which typically occurs at the point of shipment or delivery to the customer, depending on the terms of the sales arrangement. Revenues from services are generally recognized as the services are performed. Services provided pursuant to a contract are recognized either over the contract period or upon completion of the elements specified in the contract, depending on the terms of the contract. Investment management fee income is recognized over the period in which investment management services are provided and is calculated and billed monthly based on the net asset value of the accounts managed. Performance fee arrangements entitle the Company to participate, on a fixed-percentage basis, in any net income generated in excess of an agreed-upon threshold as established by the underlying investment management agreements. In general, net income is calculated at the end of each calendar year and performance fees are payable annually. Following the preferred method identified in the Accounting Standards Codification (ASC) Topic 605, Revenue Recognition , such performance fee income is recorded at the conclusion of the contractual performance period, when all contingencies are resolved.
Stock-based Compensation	Stock-based Compensation. Stock-based compensation expense is generally recognized as part of underwriting, acquisition and insurance expenses over the requisite service period. Stock-based compensation expense, net of taxes, was $14.3 million in 2016 , $16.3 million in 2015 and $18.7 million in 2014 . See note 12 .
Foreign Currency Translation	Foreign Currency Translation. The functional currencies of the Company's foreign operations are the currencies in which the majority of their business is transacted. Assets and liabilities of foreign operations are translated into the United States Dollar using the exchange rates in effect at the balance sheet date. Revenues and expenses of foreign operations are translated using the average exchange rate for the period. Gains or losses from translating the financial statements of foreign operations denominated in a functional currency are included, net of taxes, in shareholders' equity as a component of accumulated other comprehensive income. Gains and losses arising from transactions denominated in a foreign currency other than a functional currency are included in net income. The Company manages its exposure to foreign currency risk primarily by matching assets, other than goodwill and intangible assets, and liabilities denominated in the same currency. To the extent that assets and liabilities in foreign currencies are not matched, the Company is exposed to foreign currency risk. For functional currencies, the related exchange rate fluctuations are reflected in other comprehensive income (loss). The cumulative foreign currency translation adjustment, net of taxes, was a loss of $84.4 million and $72.7 million at December 31, 2016 and 2015 , respectively.
Derivative Financial Instruments	Derivative Financial Instruments. Derivative instruments, including derivative instruments resulting from hedging activities, are measured at fair value and recognized as either assets or liabilities on the consolidated balance sheets. The changes in fair value of derivatives are recognized in earnings unless the derivative is designated as a hedge and qualifies for hedge accounting. The Company's foreign currency forward contracts are generally designated and qualify as hedges of a net investment in a foreign operation. The effective portion of the change in fair value resulting from these hedges is reported in currency translation adjustments as part of other comprehensive income (loss). The ineffective portion of the change in fair value is recognized in earnings.
Comprehensive Income	Comprehensive Income. Comprehensive income represents all changes in equity that result from recognized transactions and other economic events during the period. Other comprehensive income (loss) refers to revenues, expenses, gains and losses that under U.S. GAAP are included in comprehensive income but excluded from net income, such as unrealized gains or losses on investments, foreign currency translation adjustments and changes in net actuarial pension loss.
Net Income Per Share	Net Income Per Share. Basic net income per share is computed by dividing adjusted net income to shareholders by the weighted average number of common shares outstanding during the year. Diluted net income per share is computed by dividing adjusted net income to shareholders by the weighted average number of common shares and dilutive potential common shares outstanding during the year. See note 12 (b).
Variable Interest Entities	Variable Interest Entities. The Company determines whether it has relationships with entities defined as VIEs in accordance with ASC Topic 810, Consolidation . Under this guidance, a VIE is consolidated by the variable interest holder that is determined to be the primary beneficiary. An entity in which the Company holds a variable interest is a VIE if any of the following conditions exist: (a) the total equity investment at risk is not sufficient to permit the entity to finance its activities without additional subordinated financial support, (b) as a group, the holders of equity investment at risk lack either the direct or indirect ability through voting rights or similar rights to make decisions about an entity's activities that most significantly impact the entity's economic performance or the obligation to absorb the expected losses or right to receive the expected residual returns, or (c) the voting rights of some investors are disproportionate to their obligation to absorb the expected losses of the entity, their rights to receive the expected residual returns of the entity, or both and substantially all of the entity's activities either involve or are conducted on behalf of an investor with disproportionately few voting rights. The primary beneficiary is defined as the variable interest holder that is determined to have the controlling financial interest as a result of having both (a) the power to direct the activities of a VIE that most significantly impact the economic performance of the VIE and (b) the obligation to absorb losses or right to receive benefits from the VIE that could potentially be significant to the VIE. The Company determines whether an entity is a VIE at the inception of our variable interest in the entity and upon the occurrence of certain reconsideration events. The Company continually reassesses whether it is the primary beneficiary of VIEs in which it holds a variable interest.
Recent Accounting Pronouncements	Recent Accounting Pronouncements. Effective January 1, 2016, the Company adopted Financial Accounting Standards Board (FASB) Accounting Standards Update (ASU) No. 2015-02, Consolidation (Topic 810): Amendments to the Consolidation Analysis , which changes the way reporting enterprises evaluate whether (a) they should consolidate limited partnerships and similar entities, (b) fees paid to a decision maker or service provider are variable interests in a VIE, and (c) variable interests in a VIE held by related parties of the reporting enterprise require the reporting enterprise to consolidate the VIE. It also eliminates the VIE consolidation model based on majority exposure to variability that applied to certain investment companies and similar entities. The ASU also significantly changes how to evaluate voting rights for entities that are not similar to limited partnerships when determining whether the entity is a VIE, which may affect entities for which the decision making rights are conveyed through a contractual arrangement. The adoption of this guidance did not result in any changes to our previous consolidation conclusions. Effective January 1, 2016, the Company adopted FASB ASU No. 2015-03, Interest-Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs . ASU No. 2015-03 requires that debt issuance costs related to a recognized debt liability be presented on the balance sheet as a direct deduction from the debt liability, similar to the presentation of debt discounts. The cost of issuing debt is no longer recorded as a separate asset on the balance sheet. The amortization of debt issuance costs continues to be included in interest expense. ASU No. 2015-03 was applied retrospectively to all periods presented. As a result, debt issuance costs totaling $2.2 million and $2.6 million were reclassified from other assets to senior long-term debt and other debt as of December 31, 2015 and December 31, 2014, respectively. The adoption of this ASU did not have an impact on the Company's results of operations or cash flows. Effective January 1, 2016, the Company adopted FASB ASU No. 2015-05, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer's Accounting for Fees Paid in a Cloud Computing Arrangement , which clarifies that software licenses contained in a cloud computing arrangement should be capitalized if the customer has the right to take possession of the software and the ability to run the software outside of the cloud computing arrangement. The adoption of this ASU did not have an impact on the Company's financial position, results of operations or cash flows. Effective January 1, 2016, the Company adopted FASB ASU No. 2015-16, Business Combinations (Topic 805): Simplifying the Accounting for Measurement-Period Adjustments . ASU No. 2015-16 eliminates the requirement to retrospectively adjust the financial statements for measurement-period adjustments that occur in periods after a business combination is consummated. The adoption of this ASU did not have an impact on the Company's financial position, results of operations or cash flows and will be applied on a prospective basis, as applicable. During the second quarter of 2016, the Company early adopted FASB ASU No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting , which changes several aspects of the accounting for share-based payment award transactions. Under the new guidance, all excess tax benefits or deficiencies associated with share-based payment award transactions are required to be recognized as an income tax benefit or expense in net income when the awards vest or are settled, with the corresponding cash flows recognized as an operating activity in the statement of cash flows. Excess tax benefits and deficiencies are no longer recognized in additional paid-in-capital. The new guidance also allows an employer to repurchase more of an employee's shares for tax witholding purposes without triggering liability accounting and to make a policy election to account for forfeitures as they occur, rather than estimating forfeitures upon issuance of the award. Upon adoption of ASU No. 2016-09, the Company elected to account for forfeitures as they occur, which had no impact on the consolidated financial statements. The provisions of ASU No. 2016-09 were adopted as of January 1, 2016 on a prospective basis and did not have a material impact on the Company's financial position, results of operations or cash flows. Effective for the year ended December 31, 2016, the Company adopted FASB ASU No. 2015-09, Financial Services-Insurance (Topic 944): Disclosures about Short-Duration Contracts . ASU No. 2015-09 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. The guidance requires annual tabular disclosure, on a disaggregated basis, of undiscounted incurred and paid claim and allocated claim adjustment expense development by accident year, net of reinsurance, for up to 10 years. Tables must also include the total incurred but not reported claims liabilities, plus expected development on reported claims, and claims frequency for each accident year. A description of estimation methodologies and any significant changes in methodologies and assumptions used to calculate the liability and frequency is also required. Based on the disaggregated claims information in the tables, disclosure of historical average annual percentage payout of incurred claims is also required. The ASU requires retrospective application by providing comparative disclosures for each period presented, other than those that are only required for the most recent reporting period. These new annual disclosures have been included in note 9. Interim period disclosures must include a tabular rollforward and related qualitative information for the liability for unpaid losses and loss adjustment expenses. The interim disclosures are required beginning in the first quarter of 2017. 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. ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Consideration (Reporting Revenue Gross versus Net), ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing, ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients and ASU No. 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers were all issued in 2016 as amendments to ASU No. 2014-09. These amendments will be evaluated and adopted in conjunction with ASU No. 2014-09. The Company expects to adopt ASU No. 2014-09 as of January 1, 2018 using the modified retrospective method, whereby the cumulative effect of adoption will be recognized 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 the Company's other revenues, which are primarily attributable to its non-insurance operations. The Company has completed an inventory of revenue streams from its non-insurance operations, which are comprised of a diverse portfolio of contracts across various industries, and is currently evaluating changes, if any, that will be necessary. The Company has not determined the full impact that adopting the new accounting guidance will have on its consolidated financial statements. In July 2015, the FASB issued ASU No. 2015-11, Inventory (Topic 330): Simplifying the Measurement of Inventory . The ASU changes the measurement principle for inventory from the lower of cost or market to lower of cost and net realizable value and eliminates the requirement to consider replacement cost or net realizable value less an approximately normal profit margin when measuring inventory. ASU No. 2015-11 becomes effective for the Company during the first quarter of 2017 and will be applied prospectively. Adoption of this ASU is not expected to have a material impact on the Company's financial position, results of operations or cash flows. 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 (loss). 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 (loss). As of December 31, 2016 , accumulated other comprehensive income included $1.5 billion of net unrealized gains on equity securities, net of taxes. See note 3(f) for details regarding the change in net unrealized gains on equity securities included in other comprehensive income (loss) for the years ended December 31, 2016 , 2015 and 2014 . In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) . The ASU requires lessees to record most leases on their balance sheets as a lease liability with a corresponding right-of-use asset, but continue to recognize the related leasing expense within net income. The guidance also eliminates real estate-specific provisions for all entities. For lessors, the guidance modifies the classification criteria and the accounting for sales-type and direct financing leases. ASU No. 2016-02 becomes effective for the Company during the first quarter of 2019 and will be applied under a modified retrospective approach for leases that exist or are entered into after the beginning of the earliest comparative period in the financial statements. See note 16 for details regarding the Company's minimum annual rental commitments payable directly by the Company for noncancelable operating leases at December 31, 2016 , which will be subject to this new guidance. The calculation of the lease liability and right-of-use asset requires further analysis of the underlying leases to determine which portion of the underlying lease payments are required to be included in the calculation. The Company is currently evaluating ASU No. 2016-02 to determine the potential impact that adopting this standard will have on its consolidated financial statements. In March 2016, the FASB issued ASU No. 2016-07, Investments - Equity Method and Joint Ventures (Topic 323): Simplifying the Transition to the Equity Method of Accounting. The ASU eliminates the requirement for an investor to retroactively apply the equity method when its increase in ownership interest or degree of influence in an investee triggers equity method accounting. ASU No. 2016-07 becomes effective for the Company during the first quarter of 2017 and will be applied prospectively. Early adoption is permitted. Adoption of this ASU is not expected to have an impact on the Company's financial position, results of operations or cash flows. 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. In August 2016, the FASB issued 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. ASU No. 2016-15 becomes effective for the Company during the first quarter of 2018 and will be applied using a retrospective transition approach. Early adoption is permitted. The Company is currently evaluating ASU No. 2016-15 to determine the potential impact that adopting this standard will have on the consolidated statements of cash flows. Adoption of this ASU will not impact the Company's financial position or results of operations and is not expected to have a material impact on the Company's consolidated statements of cash flows. In October 2016, the FASB issued ASU No. 2016-16, Income Taxes (Topic 740): Intra-entity Transfers of Assets Other Than Inventory , which will require companies to account for the income tax effects of intercompany transfers of assets other than inventory when the transfer occurs. Intercompany transfers of assets across tax jurisdictions may have cash tax consequences and may be taxable events as proscribed by the applicable tax jurisdiction. Currently, companies are prohibited from recognizing those tax effects until the asset has been sold to an outside party. The income tax effects of intercompany inventory transactions will continue to be deferred. ASU No. 2016-16 becomes effective for the Company during the first quarter of 2018 and will be applied using a modified retrospective transition approach. Early adoption is permitted. Adoption of this ASU will not impact the Company's cash flows and is not expected to have a material impact on the Company's financial position or results of operations. In October 2016, the FASB issued ASU No. 2016-17, Consolidation (Topic 810): Interests Held through Related Parties That Are under Common Control, which will require a single decision maker evaluating whether it is the primary beneficiary of a VIE to consider its indirect interests held by related parties that are under common control on a proportionate basis. Under the guidance the FASB issued last year, which was adopted by the Company effective January 1, 2016, the decision maker was required to consider those interests in their entirety. ASU No. 2016-17 becomes effective for the Company beginning in 2017 and will be applied retrospectively to 2016, the fiscal year in which the amendments in Update 2015-02 initially were applied, as described above. Adoption of this guidance is not expected to result in any changes to our previous consolidation conclusions. In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash. The ASU requires that a statement of cash flows explain the change during the period of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Amounts generally described as restricted cash and restricted cash equivalents should 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. Currently, changes in restricted cash and cash equivalents are presented as operating, investing or financing activities on the statement of cash flows. ASU No. 2016-18 becomes effective for the Company during the first quarter of 2018 and will be applied using a retrospective approach for each period presented. The Company currently presents changes in restricted cash and cash equivalents on the face of the statements of cash flows as an investing activity. Upon adoption of this ASU, the Company's statements of cash flows will include restricted cash and cash equivalents in the beginning-of-period and end-of-period total amounts for cash, cash equivalents and restricted cash and cash equivalents. Adoption of this ASU will not impact the Company's financial position, results of operations or total comprehensive income (loss). In January 2017, the FASB issued 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. ASU No. 2017-04 becomes effective for the Company during the first quarter of 2020 and will be applied prospectively. Early adoption is permitted. Adoption of this ASU is not expected to have a material impact on the Company's financial position, results of operations or cash flows.

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2016
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. 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 maturity securities: U.S. Treasury $ 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 1,055,947 3,953 (19,544 ) — 1,040,356 Residential mortgage-backed 779,503 18,749 (5,048 ) (2,258 ) 790,946 Asset-backed 27,494 2 (158 ) — 27,338 Corporate 1,420,298 49,146 (9,364 ) (673 ) 1,459,407 Total fixed maturity securities 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 December 31, 2015 (dollars in thousands) Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Unrealized Other- Than-Temporary Impairment Losses Estimated Fair Value Fixed maturity securities: U.S. Treasury $ 310,370 $ 95 $ (1,048 ) $ — $ 309,417 U.S. government-sponsored enterprises 385,282 9,741 (3,733 ) — 391,290 Obligations of states, municipalities and political subdivisions 3,817,136 204,302 (8,225 ) — 4,013,213 Foreign governments 1,302,329 115,809 (1,681 ) — 1,416,457 Commercial mortgage-backed 657,670 6,867 (4,999 ) — 659,538 Residential mortgage-backed 837,964 22,563 (4,022 ) (2,258 ) 854,247 Asset-backed 36,462 15 (406 ) — 36,071 Corporate 1,690,945 41,123 (16,209 ) (1,624 ) 1,714,235 Total fixed maturity securities 9,038,158 400,515 (40,323 ) (3,882 ) 9,394,468 Equity securities: Insurance, banks and other financial institutions 651,002 690,271 (6,551 ) — 1,334,722 Industrial, consumer and all other 1,557,832 1,227,052 (45,131 ) — 2,739,753 Total equity securities 2,208,834 1,917,323 (51,682 ) — 4,074,475 Short-term investments 1,642,103 167 (9 ) — 1,642,261 Investments, available-for-sale $ 12,889,095 $ 2,318,005 $ (92,014 ) $ (3,882 ) $ 15,111,204
Summary Of Gross Unrealized Investment Losses By Length Of Time That Securities Have Continuously Been In An Unrealized Loss Position	December 31, 2015 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 maturity securities: U.S. Treasury $ 301,300 $ (962 ) $ 7,426 $ (86 ) $ 308,726 $ (1,048 ) U.S. government-sponsored enterprises 125,703 (2,686 ) 85,126 (1,047 ) 210,829 (3,733 ) Obligations of states, municipalities and political subdivisions 169,362 (4,864 ) 70,101 (3,361 ) 239,463 (8,225 ) Foreign governments 51,328 (249 ) 40,345 (1,432 ) 91,673 (1,681 ) Commercial mortgage-backed 289,058 (3,600 ) 95,843 (1,399 ) 384,901 (4,999 ) Residential mortgage-backed 78,814 (2,858 ) 137,100 (3,422 ) 215,914 (6,280 ) Asset-backed 6,228 (54 ) 24,315 (352 ) 30,543 (406 ) Corporate 470,694 (9,509 ) 343,737 (8,324 ) 814,431 (17,833 ) Total fixed maturity securities 1,492,487 (24,782 ) 803,993 (19,423 ) 2,296,480 (44,205 ) Equity securities: Insurance, banks and other financial institutions 63,873 (6,384 ) 6,247 (167 ) 70,120 (6,551 ) Industrial, consumer and all other 344,857 (44,879 ) 2,907 (252 ) 347,764 (45,131 ) Total equity securities 408,730 (51,263 ) 9,154 (419 ) 417,884 (51,682 ) Short-term investments 129,473 (9 ) — — 129,473 (9 ) Total $ 2,030,690 $ (76,054 ) $ 813,147 $ (19,842 ) $ 2,843,837 $ (95,896 ) The following tables summarize gross unrealized investment losses by the length of time that securities have continuously been in an unrealized loss position. 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 maturity securities: U.S. Treasury $ 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 749,889 (19,091 ) 29,988 (453 ) 779,877 (19,544 ) Residential mortgage-backed 181,557 (4,987 ) 79,936 (2,319 ) 261,493 (7,306 ) Asset-backed 14,501 (106 ) 5,869 (52 ) 20,370 (158 ) Corporate 494,573 (8,357 ) 93,790 (1,680 ) 588,363 (10,037 ) Total fixed maturity securities 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	The amortized cost and estimated fair value of fixed maturity securities at December 31, 2016 are shown below by contractual maturity. (dollars in thousands) Amortized Cost Estimated Fair Value Due in one year or less $ 798,529 $ 800,733 Due after one year through five years 1,210,130 1,252,152 Due after five years through ten years 1,582,373 1,659,755 Due after ten years 4,137,758 4,320,230 7,728,790 8,032,870 Commercial mortgage-backed 1,055,947 1,040,356 Residential mortgage-backed 779,503 790,946 Asset-backed 27,494 27,338 Total fixed maturity securities $ 9,591,734 $ 9,891,510
Components Of Net Investment Income	The following table presents the components of net investment income. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Interest: Municipal bonds (tax-exempt) $ 88,654 $ 93,580 $ 98,262 Municipal bonds (taxable) 65,749 57,550 49,345 Other taxable bonds 144,752 138,763 152,789 Short-term investments, including overnight deposits 11,177 5,223 5,959 Dividends on equity securities 70,577 74,705 65,031 Income (loss) from equity method investments 6,852 (262 ) 4,766 Other 2,676 651 2,338 390,437 370,210 378,490 Investment expenses (17,207 ) (16,997 ) (15,260 ) Net investment income $ 373,230 $ 353,213 $ 363,230
Summary Of Net Realized Investment Gains And The Change In Net Unrealized Gains On Investments	The following table presents net realized investment gains and the change in net unrealized gains on investments. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Realized gains: Sales of fixed maturity securities $ 5,160 $ 3,073 $ 8,417 Sales of equity securities 70,177 156,987 51,356 Other 1,415 8,103 15,205 Total realized gains 76,752 168,163 74,978 Realized losses: Sales of fixed maturity securities (704 ) (4,598 ) (18,136 ) Sales of equity securities (6,988 ) (1,232 ) (802 ) Other-than-temporary impairments (18,355 ) (44,481 ) (4,784 ) Other (2,349 ) (486 ) (15,700 ) Total realized losses (28,396 ) (50,797 ) (39,422 ) Gains (losses) on securities measured at fair value through net income 16,791 (10,886 ) 10,444 Net realized investment gains $ 65,147 $ 106,480 $ 46,000 Change in net unrealized gains on investments included in other comprehensive income (loss): Fixed maturity securities $ (56,534 ) $ (137,435 ) $ 480,350 Equity securities 398,752 (320,277 ) 500,673 Short-term investments (107 ) 128 12 Net increase (decrease) $ 342,111 $ (457,584 ) $ 981,035
Summary of Other-Than-Temporary Impairment Losses Recognized In Net Income And In Net Realized Investment Gains By Investment Type	The following table presents other-than-temporary impairment losses recognized in net income and included in net realized investment gains by investment type. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Fixed maturity securities: Commercial mortgage-backed $ — $ — $ (61 ) Asset-backed — — (197 ) Corporate — — (46 ) Total fixed maturity securities — — (304 ) Equity securities: Insurance, banks and other financial institutions (7,586 ) (9,835 ) (341 ) Industrial, consumer and all other (10,769 ) (34,646 ) (4,139 ) Total equity securities (18,355 ) (44,481 ) (4,480 ) Total $ (18,355 ) $ (44,481 ) $ (4,784 )
Components Of Restricted Assets	The following table presents the components of restricted assets. December 31, (dollars in thousands) 2016 2015 Restricted assets held in trust or on deposit to support underwriting activities $ 4,059,336 $ 4,037,458 Investments and cash and cash equivalents pledged as security for letters of credit 355,616 745,744 Total $ 4,414,952 $ 4,783,202
Schedule Of Restricted Assets	Total restricted assets are included on the Company's consolidated balance sheets as follows. December 31, (dollars in thousands) 2016 2015 Investments, available-for-sale $ 4,068,535 $ 4,343,070 Restricted cash and cash equivalents 346,417 440,132 Total $ 4,414,952 $ 4,783,202

Receivables (Tables)

Receivables (Tables)	12 Months Ended
	Dec. 31, 2016
Receivables [Abstract]
Components Of Receivables	The following table presents the components of receivables. December 31, (dollars in thousands) 2016 2015 Amounts receivable from agents, brokers and insureds $ 1,061,190 $ 983,510 Trade accounts receivable 123,341 119,558 Investment management and performance fees receivable 38,735 — Employee stock loans receivable (see note 12(c)) 20,171 16,900 Other 10,122 6,165 1,253,559 1,126,133 Allowance for doubtful receivables (11,910 ) (12,430 ) Receivables $ 1,241,649 $ 1,113,703

Deferred Policy Acquisition C34

Deferred Policy Acquisition Costs (Tables)	12 Months Ended
	Dec. 31, 2016
Deferred Policy Acquisition Costs Disclosures [Abstract]
Amounts Of Policy Acquisition Costs Acquired, Deferred And Amortized	The following table presents the amounts of policy acquisition costs deferred and amortized. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Balance, beginning of year $ 352,756 $ 353,410 $ 260,967 Policy acquisition costs deferred 823,840 752,324 754,303 Amortization of policy acquisition costs (782,221 ) (744,964 ) (654,916 ) Foreign currency movements (1,965 ) (8,014 ) (6,944 ) Deferred policy acquisition costs $ 392,410 $ 352,756 $ 353,410
Components Of Underwriting, Acquisition And Insurance Expenses	The following table presents the components of underwriting, acquisition and insurance expenses. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Amortization of policy acquisition costs $ 782,221 $ 744,964 $ 654,916 Other operating expenses 716,369 710,116 805,966 Underwriting, acquisition and insurance expenses $ 1,498,590 $ 1,455,080 $ 1,460,882

Property And Equipment (Tables)

Property And Equipment (Tables)	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Components Of Property And Equipment	The following table presents the components of property and equipment, which are included in other assets on the consolidated balance sheets. December 31, (dollars in thousands) 2016 2015 Land $ 56,783 $ 56,408 Buildings 76,159 77,488 Leasehold improvements 95,898 104,003 Land improvements 74,040 71,585 Furniture and equipment 301,146 291,736 Other 162,385 134,939 766,411 736,159 Accumulated depreciation and amortization (354,009 ) (305,324 ) Property and equipment $ 412,402 $ 430,835

Goodwill And Intangible Assets

Goodwill And Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Components Of Goodwill	The following table presents the components of goodwill by reportable segment. (dollars in thousands) U.S. Insurance International Insurance Reinsurance Other (1) Total January 1, 2015 $ 280,579 $ 408,183 $ 122,745 $ 237,608 $ 1,049,115 Acquisitions (see note 2) — — — 146,659 146,659 Impairment loss — — — (14,880 ) (14,880 ) Foreign currency movements and other adjustments — (10,190 ) — (2,860 ) (13,050 ) December 31, 2015 (2) $ 280,579 $ 397,993 $ 122,745 $ 366,527 $ 1,167,844 Impairment loss — — — (18,723 ) (18,723 ) Foreign currency movements and other adjustments — (5,809 ) — (1,064 ) (6,873 ) December 31, 2016 (2) $ 280,579 $ 392,184 $ 122,745 $ 346,740 $ 1,142,248 (1) Amounts included in Other above are related to the Company's non-insurance operations, which are not included in a reportable segment. (2) Goodwill is net of accumulated impairment losses of $47.3 million and $28.6 million , as of December 31, 2016 and 2015, respectively, included in Other.
Components Of Intangible Assets	The following table presents the components of intangible assets with a net carrying amount. December 31, 2016 2015 (dollars in thousands) Gross Carrying Amount Accumulated Amortization Gross Carrying Amount Accumulated Amortization Customer relationships $ 460,327 $ (119,376 ) $ 481,547 $ (97,892 ) Broker relationships 183,092 (56,888 ) 182,626 (45,135 ) Trade names 100,966 (29,745 ) 103,681 (23,821 ) Investment management agreements 98,000 (7,000 ) 98,000 — Technology 54,408 (28,220 ) 54,241 (22,288 ) Insurance licenses 30,185 — 30,185 — Lloyd's syndicate capacity 12,000 — 12,000 — Other 34,172 (9,379 ) 30,496 (11,268 ) Total $ 973,150 $ (250,608 ) $ 992,776 $ (200,404 )

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Components Of Income Before Income Taxes	Income before income taxes includes the following components. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Domestic operations $ 288,905 $ 323,954 $ 240,279 Foreign operations 341,015 418,151 200,099 Income before income taxes $ 629,920 $ 742,105 $ 440,378
Components Of Income Tax Expense	Income tax expense includes the following components. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Current: Domestic $ 57,916 $ 44,406 $ 7,573 Foreign 48,203 118,235 24,574 Total current tax expense 106,119 162,641 32,147 Deferred: Domestic 19,991 9,415 43,673 Foreign 43,367 (19,093 ) 40,870 Total deferred tax expense (benefit) 63,358 (9,678 ) 84,543 Income tax expense $ 169,477 $ 152,963 $ 116,690
Reconciliations Of United States Corporate Income Tax Rate To Effective Tax Rate On Income Before Income Taxes	Reconciliations of the United States corporate income tax rate to the effective tax rate on income before income taxes are presented in the following table. Years Ended December 31, 2016 2015 2014 United States corporate tax rate 35 % 35 % 35 % Tax-exempt investment income (6 ) (5 ) (9 ) Foreign tax credits (2 ) (8 ) (1 ) Foreign operations 1 (1 ) — Other (1 ) — 1 Effective tax rate 27 % 21 % 26 %
Components Of Domestic And Foreign Deferred Tax Assets And Liabilities	The following table presents the components of domestic and foreign deferred tax assets and liabilities. December 31, (dollars in thousands) 2016 2015 Assets: Unpaid losses and loss adjustment expenses $ 181,303 $ 212,012 Life and annuity benefits 135,075 156,950 Unearned premiums recognized for income tax purposes 121,852 102,076 Accrued incentive compensation 67,719 53,586 Investments, including other-than-temporary impairments 58,248 65,641 Net operating loss carryforwards 26,743 18,771 Tax credit carryforwards 23,037 18,158 Stock-based compensation 19,235 21,948 Other differences between financial reporting and tax bases 44,942 40,497 Total gross deferred tax assets 678,154 689,639 Less valuation allowance (18,781 ) (5,131 ) Total gross deferred tax assets, net of allowance 659,373 684,508 Liabilities: Net unrealized gains on investments 723,198 626,776 Deferred policy acquisition costs 128,302 88,036 Amortization of goodwill and other intangible assets 102,631 107,271 Other differences between financial reporting and tax bases 35,727 38,613 Total gross deferred tax liabilities 989,858 860,696 Net deferred tax liability $ 330,485 $ 176,188
Reconciliation Of Beginning And Ending Unrecognized Tax Benefits	The following table presents a reconciliation of unrecognized tax benefits. Years Ended December 31, (dollars in thousands) 2016 2015 Unrecognized tax benefits, beginning of year $ 15,324 $ 17,700 Decreases for tax positions taken in prior years — (146 ) Lapse of statute of limitations (6,448 ) (606 ) Settlement with taxing authorities — (1,624 ) Unrecognized tax benefits, end of year $ 8,876 $ 15,324

Unpaid Losses And Loss Adjust38

Unpaid Losses And Loss Adjustment Expenses (Tables)	12 Months Ended
	Dec. 31, 2016
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. In 2016, incurred losses and loss adjustment expenses in the following 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 and other 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. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Net reserves for losses and loss adjustment expenses, beginning of year $ 8,235,288 $ 8,535,483 $ 8,407,642 Foreign currency movements (129,692 ) (134,173 ) (137,385 ) Adjusted net reserves for losses and loss adjustment expenses, beginning of year 8,105,596 8,401,310 8,270,257 Incurred losses and loss adjustment expenses: Current year 2,555,902 2,566,545 2,638,012 Prior years (493,495 ) (627,800 ) (435,545 ) Total incurred losses and loss adjustment expenses 2,062,407 1,938,745 2,202,467 Payments: Current year 532,140 486,551 502,107 Prior years 1,529,206 1,423,286 1,436,851 Total payments 2,061,346 1,909,837 1,938,958 Effect of foreign currency rate changes 2,060 (17,281 ) (19,476 ) Net reserves for losses and loss adjustment expenses of acquired insurance companies — — 21,193 Reinsurance recoverable on retroactive reinsurance transactions — (177,649 ) — Net reserves for losses and loss adjustment expenses, end of year 8,108,717 8,235,288 8,535,483 Reinsurance recoverable on unpaid losses 2,006,945 2,016,665 1,868,669 Gross reserves for losses and loss adjustment expenses, end of year $ 10,115,662 $ 10,251,953 $ 10,404,152
Ultimate Incurred Losses And Cumulative Paid Losses And Allocated Loss Adjustment Expenses, Net Of Reinsurance	The tables below also include claim frequency information, by accident year, for each of the segments presented. The Company defines a claim as a single claim incident, per policy, which may include multiple claimants and multiple coverages on a single policy. Claim counts include claims closed without a payment as well as claims where the Company is monitoring to determine if an exposure exists, even if a reserve has not been established. In 2013, the Company completed the acquisition of Alterra, the results of which are included in each of the Company's reportable segments. Ultimate incurred losses and loss adjustment expenses, net of reinsurance for the year ended December 31, 2013 include outstanding liabilities for losses and loss adjustment expenses of Alterra as of the acquisition date, by accident year and not in any prior periods. Pre-acquisition data is not available by segment and accident year as a result of changes to the historical Alterra product line reporting structure that impacted each of the Company's reportable segments and the impact of significant intercompany reinsurance contracts. Additionally, Alterra reserves were historically determined on a policy year basis and pre-acquisition data does not exist in a format that can be used to determine accident year and segment. Following the acquisition, ongoing business attributable to Alterra was integrated with the Company's other insurance operations and is not separately tracked. U.S. Insurance Segment Ultimate Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance Total of Incurred-but-Not-Reported Liabilities, Net of Reinsurance Cumulative Number of Reported Claims Unaudited Year Ended December 31, (in thousands) Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 December 31, 2016 2012 $ 949,141 $ 985,721 $ 924,138 $ 924,621 $ 909,237 $ 117,333 106 2013 1,130,681 1,105,927 1,042,100 1,009,438 175,309 65 2014 1,278,116 1,140,685 1,116,093 290,827 56 2015 1,285,411 1,211,389 500,705 55 2016 1,319,731 781,984 49 Total $ 5,565,888 Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance Unaudited Year Ended December 31, Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 2012 $ 193,708 $ 401,773 $ 546,635 $ 644,658 $ 728,802 2013 222,890 443,392 594,558 725,782 2014 264,697 487,068 650,118 2015 260,121 514,497 2016 278,650 Total $ 2,897,849 All outstanding liabilities for unpaid losses and loss adjustment expenses before 2012, net of reinsurance 402,534 Total liabilities for unpaid losses and loss adjustment expenses, net of reinsurance $ 3,070,573 Reinsurance Segment Ultimate Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance Total of Incurred-but-Not-Reported Liabilities, Net of Reinsurance Unaudited Year Ended December 31, (in thousands) Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 December 31, 2016 2012 $ 72,250 $ 545,939 $ 503,410 $ 482,836 $ 455,103 $ 137,778 2013 581,963 574,760 545,743 531,955 179,519 2014 575,479 565,252 536,274 209,246 2015 526,286 511,959 306,717 2016 529,518 382,407 Total $ 2,564,809 Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance Unaudited Year Ended December 31, Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 2012 $ 3,955 $ 64,209 $ 128,174 $ 183,321 $ 230,742 2013 71,182 154,494 209,256 268,052 2014 97,617 158,104 228,293 2015 63,963 134,530 2016 79,481 Total $ 941,098 All outstanding liabilities for unpaid losses and loss adjustment expenses before 2012, net of reinsurance 840,563 Total liabilities for unpaid losses and loss adjustment expenses, net of reinsurance $ 2,464,274 International Insurance Segment Ultimate Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance Total of Incurred-but-Not-Reported Liabilities, Net of Reinsurance Cumulative Number of Reported Claims Unaudited Year Ended December 31, (in thousands) Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 December 31, 2016 2012 $ 412,684 $ 616,641 $ 557,604 $ 495,641 $ 479,558 $ 87,383 18 2013 597,145 581,164 476,433 446,568 155,062 17 2014 577,454 545,954 502,708 149,455 16 2015 488,649 489,119 222,864 16 2016 543,959 279,320 13 Total $ 2,461,912 Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance Unaudited Year Ended December 31, Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 2012 $ 38,992 $ 163,805 $ 230,882 $ 289,517 $ 319,843 2013 47,887 126,699 182,173 220,625 2014 65,683 167,568 240,050 2015 61,556 148,037 2016 92,665 Total $ 1,021,220 All outstanding liabilities for unpaid losses and loss adjustment expenses before 2012, net of reinsurance 570,940 Total liabilities for unpaid losses and loss adjustment expenses, net of reinsurance $ 2,011,632
Average Annual Percentage Payout Of Incurred Losses By Age (in Years), Net Of Reinsurance	The following table presents supplementary information about average historical claims duration as of December 31, 2016 based on the cumulative incurred and paid losses and allocated loss adjustment expenses presented above. Average Annual Percentage Payout of Incurred Losses by Age (in Years), Net of Reinsurance Unaudited 1 2 3 4 5 U.S. Insurance 21.9 % 21.4 % 15.2 % 11.9 % 9.3 % International Insurance 12.3 % 20.4 % 13.6 % 10.4 % 6.3 % Reinsurance 12.0 % 13.5 % 12.5 % 11.6 % 10.4 %
Reconciliation Of Net Incurred And Paid Loss Development Tables, By Segment, To The Liability For Losses And Loss Adjustment Expenses In The Consolidated Balance Sheet	The following table reconciles the net incurred and paid loss development tables, by segment, to the liability for losses and loss adjustment expenses in the consolidated balance sheet. (dollars in thousands) December 31, 2016 Net outstanding liabilities U.S. Insurance $ 3,070,573 International Insurance 2,011,632 Reinsurance 2,464,274 Other Insurance (Discontinued Lines) 281,562 Liabilities for unpaid losses and loss adjustment expenses, net of reinsurance 7,828,041 Reinsurance recoverable on unpaid losses U.S. Insurance 631,608 International Insurance 982,127 Reinsurance 140,629 Other Insurance (Discontinued Lines) 252,581 Total reinsurance recoverable on unpaid losses 2,006,945 Unallocated loss adjustment expenses 211,777 Unamortized fair value adjustments on acquired reserves for losses and loss adjustment expenses 68,899 280,676 Total gross liability for unpaid losses and loss adjustment expenses $ 10,115,662
Reconciliation Of Asbestos And Environmental Reserves For Losses And Loss Adjustment Expenses	The following table provides a reconciliation of beginning and ending A&E reserves for losses and loss adjustment expenses, which are a component of consolidated unpaid losses and loss adjustment expenses. Amounts included in the following table are presented before consideration of reinsurance allowances. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Net reserves for A&E losses and loss adjustment expenses, beginning of year $ 132,869 $ 287,723 $ 272,194 Incurred losses and loss adjustment expenses (5,277 ) 25,415 32,840 Payments (15,988 ) (20,628 ) (17,311 ) Reinsurance recoverable on retroactive reinsurance transactions — (159,641 ) — Net reserves for A&E losses and loss adjustment expenses, end of year 111,604 132,869 287,723 Reinsurance recoverable on unpaid losses 212,300 253,756 102,719 Gross reserves for A&E losses and loss adjustment expenses, end of year $ 323,904 $ 386,625 $ 390,442

Life And Annuity Benefits (Tabl

Life And Annuity Benefits (Tables)	12 Months Ended
	Dec. 31, 2016
Liability for Future Policy Benefits [Abstract]
Schedule Of Life And Annuity Benefits	The following table presents life and annuity benefits. December 31, (dollars in thousands) 2016 2015 Life $ 131,768 $ 142,068 Annuities 849,226 901,218 Accident and health 68,660 79,989 Total $ 1,049,654 $ 1,123,275

Senior Long-Term Debt And Oth40

Senior Long-Term Debt And Other Debt (Tables)	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Summary Of Senior Long-Term Debt And Other Debt	The following table summarizes the Company's senior long-term debt and other debt. December 31, (dollars in thousands) 2016 2015 7.20% unsecured senior notes, due April 14, 2017, interest payable semi-annually, net of unamortized premium of $417 in 2016 and $1,808 in 2015 $ 91,046 $ 92,436 7.125% unsecured senior notes, due September 30, 2019, interest payable semi-annually, net of unamortized discount of $522 in 2016 and $1,060 in 2015 234,183 346,725 6.25% unsecured senior notes, due September 30, 2020, interest payable semi-annually, net of unamortized premium of $35,717 in 2016 and $44,519 in 2015 385,714 394,464 5.35% unsecured senior notes, due June 1, 2021, interest payable semi-annually, net of unamortized discount of $912 in 2016 and $1,119 in 2015 248,957 248,694 4.90% unsecured senior notes, due July 1, 2022, interest payable semi-annually, net of unamortized discount of $1,536 in 2016 and $1,815 in 2015 348,215 347,891 3.625% unsecured senior notes, due March 30, 2023, interest payable semi-annually, net of unamortized discount of $1,257 in 2016 and $1,458 in 2015 248,508 248,277 7.35% unsecured senior notes, due August 15, 2034, interest payable semi-annually, net of unamortized discount of $1,212 in 2016 and $1,972 in 2015 128,570 197,923 5.0% unsecured senior notes, due March 30, 2043, interest payable semi-annually, net of unamortized discount of $5,879 in 2016 and $6,103 in 2015 243,796 243,559 5.0% unsecured senior notes, due April 5, 2046, interest payable semi-annually, net of unamortized discount of $7,154 in 2016 491,943 — Other debt, at various interest rates ranging from 1.7% to 6.5% 153,597 119,302 Senior long-term debt and other debt $ 2,574,529 $ 2,239,271
Summary Of Future Principal Payments Due At Maturity On Senior Long-Term Debt And Other Debt	The following table summarizes the future principal payments due at maturity on senior long-term debt and other debt as of December 31, 2016 . Years Ending December 31, (dollars in thousands) 2017 $ 183,916 2018 6,365 2019 239,633 2020 359,332 2021 284,758 2022 and thereafter 1,485,404 Total principal payments $ 2,559,408 Net unamortized premium 17,662 Net unamortized debt issuance costs (2,541 ) Senior long-term debt and other debt $ 2,574,529

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2016
Stockholders' Equity Note [Abstract]
Schedule Of Net Income Per Share	Net income per share was determined by dividing adjusted net income to shareholders by the applicable weighted average shares outstanding. Basic shares outstanding include restricted stock units that are no longer subject to any contingencies for issuance, but for which the corresponding shares have not been issued. Diluted net income per share is computed by dividing adjusted net income to shareholders by the weighted average number of common shares and dilutive potential common shares outstanding during the year. Average closing common stock market prices are used to calculate the dilutive effect attributable to restricted stock. Years Ended December 31, (in thousands, except per share amounts) 2016 2015 2014 Net income to shareholders $ 455,689 $ 582,772 $ 321,182 Adjustment of redeemable noncontrolling interests (15,472 ) 4,144 (8,186 ) Adjusted net income to shareholders $ 440,217 $ 586,916 $ 312,996 Basic common shares outstanding 14,013 13,978 13,984 Dilutive potential common shares from conversion of options 4 9 11 Dilutive potential common shares from conversion of restricted stock 61 74 62 Diluted shares outstanding 14,078 14,061 14,057 Basic net income per share $ 31.41 $ 41.99 $ 22.38 Diluted net income per share $ 31.27 $ 41.74 $ 22.27
Summary Of Nonvested Share-Based Awards	The following table summarizes nonvested share-based awards. Number of Awards Weighted Average Grant-Date Fair Value Nonvested awards at January 1, 2016 103,883 $ 556.66 Granted 15,614 878.03 Vested (53,798 ) 554.62 Forfeited (81 ) 632.82 Nonvested awards at December 31, 2016 65,618 $ 634.71

Other Comprehensive Income (L42

Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2016
Other Comprehensive Income (Loss), Tax [Abstract]
Change In Accumulated Other Comprehensive Income By Component, Net Of Taxes And Noncontrolling Interests	The following table presents the change in accumulated other comprehensive income by component, net of taxes and noncontrolling interests. (dollars in thousands) Unrealized Holding Gains on Available-for- Sale Securities Foreign Currency Net Actuarial Pension Loss Total December 31, 2013 $ 1,131,507 $ (11,246 ) $ (30,456 ) $ 1,089,805 Other comprehensive income (loss) before reclassifications 687,908 (32,245 ) (16,516 ) 639,147 Amounts reclassified from accumulated other comprehensive income (26,161 ) — 1,766 (24,395 ) Total other comprehensive income (loss) 661,747 (32,245 ) (14,750 ) 614,752 December 31, 2014 $ 1,793,254 $ (43,491 ) $ (45,206 ) $ 1,704,557 Other comprehensive loss before reclassifications (240,010 ) (29,205 ) (2,482 ) (271,697 ) Amounts reclassified from accumulated other comprehensive income (80,482 ) — 2,130 (78,352 ) Total other comprehensive loss (320,492 ) (29,205 ) (352 ) (350,049 ) December 31, 2015 $ 1,472,762 $ (72,696 ) $ (45,558 ) $ 1,354,508 Other comprehensive income (loss) before reclassifications 275,696 (11,710 ) (20,700 ) 243,286 Amounts reclassified from accumulated other comprehensive income (33,528 ) — 1,600 (31,928 ) Total other comprehensive income (loss) 242,168 (11,710 ) (19,100 ) 211,358 December 31, 2016 $ 1,714,930 $ (84,406 ) $ (64,658 ) $ 1,565,866
Summary Of Tax Expense (Benefit) Of Other Comprehensive Income (Loss)	The following table summarizes the tax expense (benefit) associated with each component of other comprehensive income (loss). Years Ended December 31, (dollars in thousands) 2016 2015 2014 Change in net unrealized gains on investments: Net holding gains (losses) arising during the period $ 112,399 $ (107,860 ) $ 328,564 Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period 6 35 614 Reclassification adjustments for net gains included in net income (12,462 ) (29,267 ) (9,890 ) Change in net unrealized gains on investments 99,943 (137,092 ) 319,288 Change in foreign currency translation adjustments 1,037 408 1,918 Change in net actuarial pension loss (4,192 ) (88 ) (3,687 ) Total $ 96,788 $ (136,772 ) $ 317,519
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. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Unrealized holding gains on available-for-sale securities: Other-than-temporary impairment losses $ (18,355 ) $ (44,481 ) $ (4,784 ) Net realized investment gains, excluding other-than-temporary impairment losses 64,345 154,230 40,835 Total before taxes 45,990 109,749 36,051 Income taxes (12,462 ) (29,267 ) (9,890 ) Reclassification of unrealized holding gains, net of taxes $ 33,528 $ 80,482 $ 26,161 Net actuarial pension loss: Underwriting, acquisition and insurance expenses $ (1,951 ) $ (2,662 ) $ (2,084 ) Income taxes 351 532 318 Reclassification of net actuarial pension loss, net of taxes $ (1,600 ) $ (2,130 ) $ (1,766 )

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2016
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. December 31, 2016 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments available-for-sale: Fixed maturity securities: U.S. Treasury $ — $ 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 — 1,040,356 — 1,040,356 Residential mortgage-backed — 790,946 — 790,946 Asset-backed — 27,338 — 27,338 Corporate — 1,459,407 — 1,459,407 Total fixed maturity securities — 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 December 31, 2015 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments available-for-sale: Fixed maturity securities: U.S. Treasury $ — $ 309,417 $ — $ 309,417 U.S. government-sponsored enterprises — 391,290 — 391,290 Obligations of states, municipalities and political subdivisions — 4,013,213 — 4,013,213 Foreign governments — 1,416,457 — 1,416,457 Commercial mortgage-backed — 659,538 — 659,538 Residential mortgage-backed — 854,247 — 854,247 Asset-backed — 36,071 — 36,071 Corporate — 1,714,235 — 1,714,235 Total fixed maturity securities — 9,394,468 — 9,394,468 Equity securities: Insurance, banks and other financial institutions 1,334,722 — — 1,334,722 Industrial, consumer and all other 2,739,753 — — 2,739,753 Total equity securities 4,074,475 — — 4,074,475 Short-term investments 1,529,924 112,337 — 1,642,261 Total investments available-for-sale $ 5,604,399 $ 9,506,805 $ — $ 15,111,204
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. (dollars in thousands) 2016 2015 Equity securities, beginning of period $ — $ — Purchases 195,250 — Sales (25,000 ) — Total gains included in: Net income 20,953 — Other comprehensive income (loss) — — Transfers into Level 3 — — Transfers out of Level 3 — — Equity securities, end of period $ 191,203 $ — Net unrealized gains included in net income relating to assets held at December 31, 2016 and 2015 (1) $ 20,953 $ — (1) Included in net realized investment gains in the consolidated statements of income and comprehensive income.

Reinsurance (Tables)

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2016
Reinsurance Disclosures [Abstract]
Reinsurance Allowance For Doubtful Accounts	The following table summarizes the Company's reinsurance allowance for doubtful accounts. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Reinsurance allowance, beginning of year $ 59,350 $ 59,813 $ 76,210 Additions 980 5,897 10,316 Deductions (23,560 ) (6,360 ) (26,713 ) Reinsurance allowance, end of year $ 36,770 $ 59,350 $ 59,813
Effect Of Reinsurance And Retrocessional Reinsurance On Premiums Written And Earned	The following table summarizes the effect of reinsurance and retrocessional reinsurance on premiums written and earned. Years Ended December 31, 2016 2015 2014 (dollars in thousands) Written Earned Written Earned Written Earned Direct $ 3,560,635 $ 3,506,687 $ 3,474,510 $ 3,480,297 $ 3,478,273 $ 3,443,912 Assumed 1,236,010 1,176,205 1,158,402 1,194,772 1,327,240 1,298,371 Ceded (795,625 ) (817,022 ) (813,619 ) (851,537 ) (888,498 ) (901,371 ) Net premiums $ 4,001,020 $ 3,865,870 $ 3,819,293 $ 3,823,532 $ 3,917,015 $ 3,840,912

Commitments And Contingencies (

Commitments And Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Minimum Annual Rental Commitments	The following table summarizes the Company's minimum annual rental commitments, excluding taxes, insurance and other operating costs payable directly by the Company, for noncancelable operating leases at December 31, 2016 . Years Ending December 31, (dollars in thousands) 2017 $ 34,449 2018 31,883 2019 29,270 2020 21,536 2021 21,140 2022 and thereafter 95,979 Total $ 234,257

Statutory Financial Informati46

Statutory Financial Information (Tables)	12 Months Ended
	Dec. 31, 2016
Statutory Financial Information [Abstract]
Actual Statutory Capital And Surplus	Statutory capital and surplus and statutory net income (loss) for the Company's insurance subsidiaries as of December 31, 2016 and 2015 and for the years ended December 31, 2016 , 2015 and 2014 , respectively, is summarized below. Statutory Capital and Surplus (dollars in thousands) 2016 2015 United States $ 2,761,454 $ 2,569,928 United Kingdom $ 682,477 $ 603,238 Bermuda $ 2,189,649 $ 1,964,844 Other $ 24,726 $ 17,305
Statutory Net Income (Loss)	Statutory Net Income (Loss) Years Ended December 31, (dollars in thousands) 2016 2015 2014 United States $ 249,176 $ 291,783 $ 212,909 United Kingdom $ 77,909 $ 74,330 $ 73,697 Bermuda $ 132,442 $ 185,289 $ 110,401 Other $ (891 ) $ (3,181 ) $ 1,367

Segment Reporting Disclosures (

Segment Reporting Disclosures (Tables)	12 Months Ended
	Dec. 31, 2016
Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract]
Summary Of Gross Written Premiums By Country	The following table summarizes the Company's gross written premiums by country. Gross written premiums are attributed to individual countries based upon location of risk or cedent. Years Ended December 31, (dollars in thousands) 2016 % of Total 2015 % of Total 2014 % of Total United States $ 3,691,840 77 % $ 3,519,487 76 % $ 3,523,239 73 % United Kingdom 358,348 7 414,941 9 441,669 9 Canada 125,444 3 115,191 2 125,617 3 Other countries 621,013 13 583,293 13 714,988 15 Total $ 4,796,645 100 % $ 4,632,912 100 % $ 4,805,513 100 %
Company's Segment Disclosures	The following tables summarize the Company's segment disclosures. Year Ended December 31, 2016 (dollars in thousands) U.S. Insurance International Insurance Reinsurance Other Insurance (Discontinued Lines) Investing Consolidated Gross premium volume $ 2,635,266 $ 1,119,815 $ 1,041,055 $ 509 $ — $ 4,796,645 Net written premiums 2,237,163 864,494 898,728 635 — 4,001,020 Earned premiums 2,175,332 853,512 836,264 762 — 3,865,870 Losses and loss adjustment expenses: Current accident year (1,403,589 ) (605,837 ) (546,476 ) — — (2,555,902 ) Prior accident years 204,881 164,713 125,514 10,050 — 505,158 Amortization of policy acquisition costs (446,649 ) (146,117 ) (189,455 ) — — (782,221 ) Other operating expenses (377,230 ) (219,066 ) (119,012 ) (1,061 ) — (716,369 ) Underwriting profit 152,745 47,205 106,835 9,751 — 316,536 Net investment income — — — — 373,230 373,230 Net realized investment gains — — — — 65,147 65,147 Other revenues (insurance) 7,143 5,560 — 1,891 — 14,594 Other expenses (insurance) (15,407 ) (5,712 ) — (26,504 ) — (47,623 ) Segment profit (loss) $ 144,481 $ 47,053 $ 106,835 $ (14,862 ) $ 438,377 $ 721,884 Other revenues (non-insurance) 1,293,185 Other expenses (non-insurance) (1,142,620 ) Amortization of intangible assets (68,533 ) Interest expense (129,896 ) Loss on early extinguishment of debt (44,100 ) Income before income taxes $ 629,920 U.S. GAAP combined ratio (1) 93 % 94 % 87 % NM (2) 92 % (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. Year Ended December 31, 2015 (dollars in thousands) U.S. Insurance International Insurance Reinsurance Other Insurance (Discontinued Lines) Investing Consolidated Gross premium volume $ 2,504,096 $ 1,164,866 $ 965,374 $ (1,424 ) $ — $ 4,632,912 Net written premiums 2,106,490 888,214 824,324 265 — 3,819,293 Earned premiums 2,105,212 879,426 838,543 351 — 3,823,532 Losses and loss adjustment expenses: Current accident year (1,367,159 ) (638,144 ) (561,242 ) — — (2,566,545 ) Prior accident years 298,967 248,834 97,860 (17,861 ) — 627,800 Amortization of policy acquisition costs (420,289 ) (142,657 ) (182,018 ) — — (744,964 ) Other operating expenses (378,563 ) (221,758 ) (106,863 ) (2,932 ) — (710,116 ) Underwriting profit (loss) 238,168 125,701 86,280 (20,442 ) — 429,707 Net investment income — — — — 353,213 353,213 Net realized investment gains — — — — 106,480 106,480 Other revenues (insurance) 3,331 7,790 593 617 — 12,331 Other expenses (insurance) (3,902 ) (5,717 ) (1,419 ) (29,057 ) — (40,095 ) Segment profit (loss) $ 237,597 $ 127,774 $ 85,454 $ (48,882 ) $ 459,693 $ 861,636 Other revenues (non-insurance) 1,074,427 Other expenses (non-insurance) (1,006,710 ) Amortization of intangible assets (68,947 ) Interest expense (118,301 ) Income before income taxes $ 742,105 U.S. GAAP combined ratio (1) 89 % 86 % 90 % NM (2) 89 % (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. Year Ended December 31, 2014 (dollars in thousands) U.S. Insurance International Insurance Reinsurance Other Insurance (Discontinued Lines) Investing Consolidated Gross premium volume $ 2,493,823 $ 1,200,403 $ 1,112,728 $ (1,441 ) $ — $ 4,805,513 Net written premiums 2,071,466 889,336 956,584 (371 ) — 3,917,015 Earned premiums 2,022,860 909,679 908,385 (12 ) — 3,840,912 Losses and loss adjustment expenses: Current accident year (1,340,129 ) (660,409 ) (637,474 ) — — (2,638,012 ) Prior accident years 216,557 166,615 79,951 (27,578 ) — 435,545 Amortization of policy acquisition costs (403,233 ) (141,394 ) (110,289 ) — — (654,916 ) Other operating expenses (396,737 ) (207,175 ) (201,673 ) (381 ) — (805,966 ) Underwriting profit (loss) 99,318 67,316 38,900 (27,971 ) — 177,563 Net investment income — — — — 363,230 363,230 Net realized investment gains — — — — 46,000 46,000 Other revenues (insurance) 2,478 21,827 2,696 1,631 — 28,632 Other expenses (insurance) (5,149 ) (18,706 ) (1,847 ) (37,132 ) — (62,834 ) Segment profit (loss) $ 96,647 $ 70,437 $ 39,749 $ (63,472 ) $ 409,230 $ 552,591 Other revenues (non-insurance) 854,893 Other expenses (non-insurance) (792,037 ) Amortization of intangible assets (57,627 ) Interest expense (117,442 ) Income before income taxes $ 440,378 U.S. GAAP combined ratio (1) 95 % 93 % 96 % NM (2) 95 % (1) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (2) NM — Ratio is not meaningful.
Summary Of Deferred Policy Acquisition Costs, Unearned Premiums And Unpaid Losses And Loss Adjustment Expenses	The following table summarizes deferred policy acquisition costs, unearned premiums and unpaid losses and loss adjustment expenses by segment. (dollars in thousands) Deferred Policy Acquisition Costs Unearned Premiums Unpaid Losses and Loss Adjustment Expenses December 31, 2016 U.S. Insurance $ 176,348 $ 1,166,914 $ 3,849,541 International Insurance 51,948 445,183 3,062,725 Reinsurance 164,114 651,741 2,661,209 Other Insurance (Discontinued Lines) — — 542,187 Total $ 392,410 $ 2,263,838 $ 10,115,662 December 31, 2015 U.S. Insurance $ 162,289 $ 1,105,456 $ 3,720,429 International Insurance 48,913 467,158 3,140,000 Reinsurance 141,554 593,491 2,750,258 Other Insurance (Discontinued Lines) — — 641,266 Total $ 352,756 $ 2,166,105 $ 10,251,953
Summary Of Segment Earned Premiums By Product	The following table summarizes segment earned premiums by major product grouping. Years Ended December 31, (dollars in thousands) 2016 2015 2014 U.S. Insurance: General liability $ 563,908 $ 522,358 $ 491,645 Professional liability 328,597 324,230 321,005 Property 270,026 264,232 266,019 Personal lines 364,843 325,811 299,442 Programs 263,783 277,829 244,216 Workers compensation 301,126 281,954 263,164 Other 83,049 108,798 137,369 Total U.S. Insurance 2,175,332 2,105,212 2,022,860 International Insurance: General liability 111,291 124,198 146,178 Professional liability 272,010 268,637 285,300 Property 87,294 85,152 76,691 Marine and energy 242,070 262,307 287,263 Other 140,847 139,132 114,247 Total International Insurance 853,512 879,426 909,679 Reinsurance: Property 288,771 265,373 270,461 Casualty 327,383 315,027 323,390 Auto 65,363 102,227 152,645 Other 154,747 155,916 161,889 Total Reinsurance 836,264 838,543 908,385 Other Insurance (Discontinued Lines) 762 351 (12 ) Total earned premiums $ 3,865,870 $ 3,823,532 $ 3,840,912
Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets	The following table reconciles segment assets to the Company's consolidated balance sheets. December 31, (dollars in thousands) 2016 2015 2014 Segment assets: Investing $ 19,029,584 $ 18,056,947 $ 18,531,150 Underwriting 5,397,696 5,385,126 5,420,624 Total segment assets 24,427,280 23,442,073 23,951,774 Non-insurance operations 1,448,019 1,497,042 1,245,986 Total assets $ 25,875,299 $ 24,939,115 $ 25,197,760

Other Revenues And Other Expe48

Other Revenues And Other Expenses (Tables)	12 Months Ended
	Dec. 31, 2016
Other Income and Expenses [Abstract]
Summary Of Other Revenues And Other Expenses By Component	The following table summarizes the components of other revenues and other expenses. Years Ended December 31, 2016 2015 2014 (dollars in thousands) Other Revenues Other Expenses Other Revenues Other Expenses Other Revenues Other Expenses Insurance: Managing general agent operations $ 12,703 $ 21,119 $ 10,202 $ 9,619 $ 23,324 $ 22,527 Life and annuity 1,891 26,504 617 29,057 1,631 37,132 Other — — 1,512 1,419 3,677 3,175 14,594 47,623 12,331 40,095 28,632 62,834 Non-Insurance: Markel Ventures: Manufacturing 784,745 675,620 755,802 677,054 575,353 513,668 Markel Ventures: Non-Manufacturing 429,704 396,323 291,714 301,004 262,767 261,551 Investment management 56,455 46,190 — — — — Other 22,281 24,487 26,911 28,652 16,773 16,818 1,293,185 1,142,620 1,074,427 1,006,710 854,893 792,037 Total $ 1,307,779 $ 1,190,243 $ 1,086,758 $ 1,046,805 $ 883,525 $ 854,871

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2016
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]
Funded Status Of The Terra Nova Pension Plan	The following table summarizes the funded status of the Terra Nova Pension Plan and the amounts recognized on the accompanying consolidated balance sheets of the Company. Years Ended December 31, (dollars in thousands) 2016 2015 Change in projected benefit obligation: Projected benefit obligation at beginning of period $ 170,005 $ 185,556 Interest cost 6,113 6,645 Plan settlements — (2,863 ) Benefits paid (3,322 ) (3,970 ) Actuarial loss (gain) 38,485 (6,051 ) Effect of foreign currency rate changes (32,663 ) (9,312 ) Projected benefit obligation at end of year $ 178,618 $ 170,005 Change in plan assets: Fair value of plan assets at beginning of period $ 186,727 $ 201,399 Actual gain on plan assets 22,367 2,246 Employer contributions 3,577 — Plan settlements — (2,766 ) Benefits paid (3,322 ) (3,970 ) Effect of foreign currency rate changes (33,705 ) (10,182 ) Fair value of plan assets at end of year $ 175,644 $ 186,727 Funded status of the plan $ (2,974 ) $ 16,722 Net actuarial pension loss 85,110 61,818 Total $ 82,136 $ 78,540
Schedule of Defined Benefit Plan Amounts Recognized in Accumulated Other Comprehensive Income	The following table presents the changes in plan assets and projected benefit obligation recognized in accumulated other comprehensive income. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Net actuarial loss $ (25,243 ) $ (3,102 ) $ (20,521 ) Settlement loss recognized — 343 — Amortization of: Net actuarial loss 1,951 2,319 1,589 Prior service costs — — 495 Tax benefit 4,192 88 3,687 Total other comprehensive loss $ (19,100 ) $ (352 ) $ (14,750 )
Schedule Of Net Periodic Benefit Income And Weighted Average Assumptions	The following table summarizes the components of net periodic benefit income and the weighted average assumptions for the Terra Nova Pension Plan. Years Ended December 31, (dollars in thousands) 2016 2015 2014 Components of net periodic benefit income: Interest cost $ 6,113 $ 6,645 $ 7,572 Expected return on plan assets (9,124 ) (11,496 ) (12,812 ) Amortization of prior service cost — — 495 Amortization of net actuarial pension loss 1,951 2,319 1,589 Settlement loss recognized — 343 — Net periodic benefit income $ (1,060 ) $ (2,189 ) $ (3,156 ) Weighted average assumptions as of December 31: Discount rate 2.7 % 4.0 % 3.8 % Expected return on plan assets 4.5 % 5.4 % 6.0 % Rate of compensation increase 3.0 % 2.9 % 2.9 %
Summary Of Fair Value Of Plan Assets	The following table summarizes the fair value of plan assets as of December 31, 2016 and 2015 . December 31, (dollars in thousands) 2016 2015 Plan assets: Fixed maturity index funds $ 103,218 $ 107,033 Equity security index funds 72,419 79,686 Cash and cash equivalents 7 8 Total $ 175,644 $ 186,727

Markel Corporation (Parent Co50

Markel Corporation (Parent Company Only) Financial Information (Tables)	12 Months Ended
	Dec. 31, 2016
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Schedule Of Condensed Balance Sheets	CONDENSED BALANCE SHEETS December 31, 2016 2015 (dollars in thousands) ASSETS Investments, available-for-sale, at estimated fair value: Fixed maturities (amortized cost of $51,181 in 2016 and $35,475 in 2015) $ 52,234 $ 36,618 Equity securities (cost of $203,708 in 2016 and $204,289 in 2015) 367,156 311,405 Short-term investments (estimated fair value approximates cost) 1,729,400 755,619 Total Investments 2,148,790 1,103,642 Cash and cash equivalents 369,641 460,271 Restricted cash and cash equivalents 1,013 670 Receivables 20,477 17,200 Investments in consolidated subsidiaries 8,107,450 7,961,315 Notes receivable from subsidiaries 60,110 212,636 Other assets 97,364 89,747 Total Assets $ 10,804,845 $ 9,845,481 LIABILITIES AND SHAREHOLDERS' EQUITY Senior long-term debt $ 1,944,171 $ 1,633,068 Notes payable to subsidiaries 285,000 300,000 Income taxes payable 25,240 4,262 Net deferred tax liability 25,902 7,498 Other liabilities 63,605 66,503 Total Liabilities 2,343,918 2,011,331 Total Shareholders' Equity 8,460,927 7,834,150 Total Liabilities and Shareholders' Equity $ 10,804,845 $ 9,845,481
Schedule Of Condensed Statements Of Income And Comprehensive Income	CONDENSED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME Years Ended December 31, 2016 2015 2014 (dollars in thousands) REVENUES Net investment income $ 9,561 $ 2,565 $ 5,354 Dividends on common stock of consolidated subsidiaries 349,622 187,496 217,121 Net realized investment gains: Other-than-temporary impairment losses (98 ) (3,455 ) (120 ) Net realized investment gains, excluding other-than-temporary impairment losses 1,166 75,000 3,873 Net realized investment gains 1,068 71,545 3,753 Total Revenues 360,251 261,606 226,228 EXPENSES Interest expense 116,013 95,620 94,097 Loss on early extinguishment of debt 44,100 — — Other expenses 13,076 11,287 2,685 Total Expenses 173,189 106,907 96,782 Income Before Equity in Undistributed Earnings of Consolidated Subsidiaries and Income Taxes 187,062 154,699 129,446 Equity in undistributed earnings of consolidated subsidiaries 196,615 407,489 163,341 Income tax benefit (72,012 ) (20,584 ) (28,395 ) Net Income to Shareholders $ 455,689 $ 582,772 $ 321,182 OTHER COMPREHENSIVE INCOME (LOSS) TO SHAREHOLDERS Change in net unrealized gains on investments, net of taxes: Net holding gains (losses) arising during the period $ 37,045 $ (41,861 ) $ 32,118 Consolidated subsidiaries' net holding gains (losses) arising during the period 238,616 (198,309 ) 655,617 Consolidated subsidiaries' change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period 35 160 173 Reclassification adjustments for net gains included in net income to shareholders (558 ) (45,273 ) (1,874 ) Consolidated subsidiaries' reclassification adjustments for net gains included in net income to shareholders (32,970 ) (35,209 ) (24,287 ) Change in net unrealized gains on investments, net of taxes 242,168 (320,492 ) 661,747 Change in foreign currency translation adjustments, net of taxes (1,326 ) 2,970 1,949 Consolidated subsidiaries' change in foreign currency translation adjustments, net of taxes (10,384 ) (32,175 ) (34,194 ) Consolidated subsidiaries' change in net actuarial pension loss, net of taxes (19,100 ) (352 ) (14,750 ) Total Other Comprehensive Income (Loss) to Shareholders 211,358 (350,049 ) 614,752 Comprehensive Income to Shareholders $ 667,047 $ 232,723 $ 935,934
Schedule Of Condensed Statements Of Cash Flows	CONDENSED STATEMENTS OF CASH FLOWS Years Ended December 31, 2016 2015 2014 (dollars in thousands) OPERATING ACTIVITIES Net income to shareholders $ 455,689 $ 582,772 $ 321,182 Adjustments to reconcile net income to shareholders to net cash provided by operating activities (120,564 ) (464,193 ) (218,396 ) Net Cash Provided By Operating Activities 335,125 118,579 102,786 INVESTING ACTIVITIES Proceeds from sales of fixed maturities and equity securities 1,831 100,633 9,306 Proceeds from maturities, calls and prepayments of fixed maturities 11,960 24,945 15,710 Cost of fixed maturities and equity securities purchased (29,110 ) (55,656 ) (687 ) Net change in short-term investments (970,364 ) 9,956 (109,728 ) Securities received from subsidiaries as dividends, repayment of notes receivable and return of capital 238,975 — 89,996 Return of capital from subsidiaries 21,021 — — Decrease in notes receivable due from subsidiaries 92,530 — 28,506 Capital contributions to subsidiaries — (228,578 ) (74,788 ) Cost of equity method investments (3,100 ) (13,164 ) — Change in restricted cash and cash equivalents (343 ) 289 51 Additions to property and equipment (584 ) (305 ) (342 ) Other (3,207 ) (376 ) (2,150 ) Net Cash Used By Investing Activities (640,391 ) (162,256 ) (44,126 ) FINANCING ACTIVITIES Additions to senior long-term debt 493,149 — — Increase in notes payable to subsidiaries — 285,000 — Repayment and retirement of senior long-term debt (183,343 ) (2,000 ) — Premiums and fees related to early extinguishment of debt (43,691 ) — — Repurchases of common stock (51,142 ) (31,491 ) (26,053 ) Issuance of common stock 4,623 4,752 5,691 Other (4,960 ) 3,985 (1,948 ) Net Cash Provided (Used) By Financing Activities 214,636 260,246 (22,310 ) Increase (decrease) in cash and cash equivalents (90,630 ) 216,569 36,350 Cash and cash equivalents at beginning of year 460,271 243,702 207,352 CASH AND CASH EQUIVALENTS AT END OF YEAR $ 369,641 $ 460,271 $ 243,702

Quarterly Financial Informati51

Quarterly Financial Information (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Quarterly Results Of Consolidated Operations	The following table presents the unaudited quarterly results of consolidated operations for 2016 , 2015 and 2014 . Quarters Ended (dollars in thousands, except per share amounts) Mar. 31 June 30 Sept. 30 Dec. 31 2016 Operating revenues $ 1,376,182 $ 1,375,937 $ 1,431,282 $ 1,428,625 Net income 163,646 80,673 83,421 132,703 Net income to shareholders 160,370 78,797 83,796 132,726 Comprehensive income (loss) to shareholders 396,994 209,942 89,161 (29,050 ) Net income per share: Basic $ 11.21 $ 5.44 $ 5.62 $ 9.14 Diluted 11.15 5.41 5.60 9.11 Common stock price ranges: High $ 895.03 $ 989.18 $ 961.78 $ 931.94 Low 805.03 880.01 909.84 811.05 2015 Operating revenues $ 1,302,154 $ 1,304,605 $ 1,342,764 $ 1,420,460 Net income 194,006 92,453 104,410 198,273 Net income to shareholders 190,992 91,369 102,519 197,892 Comprehensive income (loss) to shareholders 281,807 (132,925 ) (51,143 ) 134,984 Net income per share: Basic $ 13.57 $ 6.76 $ 7.43 $ 14.23 Diluted 13.49 6.72 7.39 14.14 Common stock price ranges: High $ 783.50 $ 821.00 $ 898.08 $ 937.91 Low 660.05 736.96 775.00 791.97 2014 Operating revenues $ 1,239,655 $ 1,258,971 $ 1,299,286 $ 1,335,755 Net income 87,501 41,141 76,824 118,222 Net income to shareholders 87,716 40,068 75,803 117,595 Comprehensive income to shareholders 230,273 250,588 36,502 418,571 Net income per share: Basic $ 6.28 $ 2.67 $ 5.33 $ 8.10 Diluted 6.25 2.66 5.30 8.05 Common stock price ranges: High $ 596.87 $ 655.75 $ 666.00 $ 707.36 Low 527.17 593.76 623.90 632.65

Summary Of Significant Accoun52

Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Investments in fixed maturities recorded at estimated fair value with changes in unrealized gains and losses recorded in net income	$ 41,400
Investments in equity securities recorded at estimated fair value with changes in unrealized gains and losses recorded in net income	$ 191,200
Deferred policy acquisition cost amortization period	1 year
Adjustment of redeemable noncontrolling interests	$ (15,472)	$ 4,144	$ (8,186)
Tax benefit greater than 50%	50.00%
Insurance premiums revenue recognition period	1 year
Stock-based compensation expense, net of taxes	$ 14,300	16,300	$ 18,700
Cumulative foreign currency translation loss	$ (84,400)	$ (72,700)

Summary of Significant Accoun53

Summary of Significant Accounting Policies (Cash and Cash Equivalents) (Details)	12 Months Ended
	Dec. 31, 2016
Maximum [Member] | Cash And Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Investment maturity period	90 days

Summary of Significant Accoun54

Summary of Significant Accounting Policies (Goodwill and Intangible Assets) (Details)	12 Months Ended
	Dec. 31, 2016
Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, estimated useful life	5 years
Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, estimated useful life	20 years

Summary of Significant Accoun55

Summary of Significant Accounting Policies (Property and Equipment) (Details)	12 Months Ended
	Dec. 31, 2016
Building [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful life	10 years
Building [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful life	40 years
Land Improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful life	7 years
Land Improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful life	40 years
Furniture and Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful life	3 years
Furniture and Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful life	10 years
Other Property And Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful life	3 years
Other Property And Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful life	25 years

Summary Of Significant Accoun56

Summary Of Significant Accounting Policies (Recent Accounting Pronouncements) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net unrealized gains on equity securities, net of taxes, included in accumulated other comprehensive income	$ 1,565,866	$ 1,354,508	$ 1,704,557	$ 1,089,805
Accounting Standards Update 2015-03 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt issuance costs reclassified from other assets to senior long-term debt and other debt		$ 2,200	$ 2,600
Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Insurance premium revenues and investment portfolio revenues as a percentage of consolidated revenues	77.00%
Accounting Standards Update 2016-01 [Member] | Equity Securities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net unrealized gains on equity securities, net of taxes, included in accumulated other comprehensive income	$ 1,500,000

Acquisitions (Narrative) (Detai

Acquisitions (Narrative) (Details) - USD ($) $ in Millions	Feb. 01, 2017	Dec. 31, 2015	Jan. 31, 2014	Dec. 31, 2016	Dec. 31, 2014	Jul. 31, 2014
Markel CATCo IM [Member]
Schedule of Asset and Business Acquisitions, by Acquisition [Line Items]
Total purchase consideration		$ 205.7
Cash consideration		205.7
Goodwill recognized		91.9
Goodwill, tax deductible		91.9
Finite-lived intangible assets		$ 113
Definite-lived intangible assets, weighted-average amortization period		14 years
Estimated amount of performance and retention bonus payments				$ 105
Compensation expense recognized for performance and retention bonuses				$ 33.2
CapTech Ventures Inc [Member]
Schedule of Asset and Business Acquisitions, by Acquisition [Line Items]
Total purchase consideration		$ 60.6
Goodwill recognized		50.6
Goodwill, tax deductible		0
Finite-lived intangible assets		$ 49.2
Definite-lived intangible assets, weighted-average amortization period		14 years
Percentage acquired		80.00%
Redeemable noncontrolling interest		$ 13.8
Cottrell Inc [Member]
Schedule of Asset and Business Acquisitions, by Acquisition [Line Items]
Percentage acquired						100.00%
Non-Insurance Acquisitions [Member]
Schedule of Asset and Business Acquisitions, by Acquisition [Line Items]
Total purchase consideration					$ 187
Goodwill recognized					38.7
Finite-lived intangible assets					78.7
Non-Insurance Acquisitions [Member] | Customer Relationships [Member]
Schedule of Asset and Business Acquisitions, by Acquisition [Line Items]
Finite-lived intangible assets					$ 53.7
Definite-lived intangible assets, weighted-average amortization period					17 years
Non-Insurance Acquisitions [Member] | Trade Names [Member]
Schedule of Asset and Business Acquisitions, by Acquisition [Line Items]
Finite-lived intangible assets					$ 13
Definite-lived intangible assets, weighted-average amortization period					10 years
Abbey Protection plc [Member]
Schedule of Asset and Business Acquisitions, by Acquisition [Line Items]
Total purchase consideration			$ 190.7
Cash consideration			190.7
Goodwill recognized			65.8
Goodwill, tax deductible			0
Finite-lived intangible assets			$ 113.4
Percentage acquired			100.00%
Abbey Protection plc [Member] | Customer Relationships [Member]
Schedule of Asset and Business Acquisitions, by Acquisition [Line Items]
Finite-lived intangible assets			$ 103.5
Definite-lived intangible assets, weighted-average amortization period			20 years
Abbey Protection plc [Member] | Trade Names [Member]
Schedule of Asset and Business Acquisitions, by Acquisition [Line Items]
Finite-lived intangible assets			$ 9.9
Definite-lived intangible assets, weighted-average amortization period			14 years
Abbey Protection plc [Member] | International Insurance [Member]
Schedule of Asset and Business Acquisitions, by Acquisition [Line Items]
Goodwill recognized			$ 43
Abbey Protection plc [Member] | Non-Insurance Operations [Member]
Schedule of Asset and Business Acquisitions, by Acquisition [Line Items]
Goodwill recognized			$ 22.8
SureTec Financial Corp [Member] | Subsequent Event [Member]
Schedule of Asset and Business Acquisitions, by Acquisition [Line Items]
Total purchase consideration	$ 250

Investments (Narrative) (Detail

Investments (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)securities	Dec. 31, 2015USD ($)securities	Dec. 31, 2014USD ($)
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities in unrealized loss position, number of positions | securities	654	659
Available-for-sale securities, estimated fair value	$ 3,790,614	$ 2,843,837
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	$ (99,981)	$ (95,896)
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end | securities	109	271
Available-for-sale securities, estimated fair value, 12 months or longer	$ 321,552	$ 813,147
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	$ (17,204)	(19,842)
Estimated average duration of the fixed maturity securities	6 years 4 months
Cumulative credit loss recognized in income	$ 10,700	$ 10,700	$ 12,700
Percentage threshold of shareholders' equity used to define concentration of investments	10.00%	10.00%
Ten largest equity holdings	$ 2,100,000
Ten largest equity holdings, percentage of equity portfolio	44.00%
Investments in property and casualty	$ 1,000,000
Investments in property and casualty, percentage of equity portfolio	22.00%
Berkshire Hathaway Inc. [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments in property and casualty	$ 511,300
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value	3,111,566	$ 2,296,480
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	$ (86,225)	$ (44,205)
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end | securities	93	264
Available-for-sale securities, estimated fair value, 12 months or longer	$ 253,929	$ 803,993
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(8,636)	(19,423)
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value	174,837	417,884
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	$ (13,750)	$ (51,682)
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end | securities	16	7
Available-for-sale securities, estimated fair value, 12 months or longer	$ 67,623	$ 9,154
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	$ (8,568)	$ (419)

Investments (Available-For-Sale

Investments (Available-For-Sale Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	$ 14,409,282	$ 12,889,095
Available-for-sale investments, gross unrealized holding gains	2,664,201	2,318,005
Available-for-sale investments, gross unrealized holding losses	(97,050)	(92,014)
Available-for-sale investments, unrealized other-than-temporary impairment losses	(2,931)	(3,882)
Available-for-sale investments, estimated fair value	16,973,502	15,111,204
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	259,379	310,370
Available-for-sale investments, gross unrealized holding gains	99	95
Available-for-sale investments, gross unrealized holding losses	(894)	(1,048)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	258,584	309,417
U.S. Government-Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	418,457	385,282
Available-for-sale investments, gross unrealized holding gains	9,083	9,741
Available-for-sale investments, gross unrealized holding losses	(4,328)	(3,733)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	423,212	391,290
Obligations Of States, Municipalities And Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	4,324,332	3,817,136
Available-for-sale investments, gross unrealized holding gains	145,678	204,302
Available-for-sale investments, gross unrealized holding losses	(41,805)	(8,225)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	4,428,205	4,013,213
Foreign Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	1,306,324	1,302,329
Available-for-sale investments, gross unrealized holding gains	159,291	115,809
Available-for-sale investments, gross unrealized holding losses	(2,153)	(1,681)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	1,463,462	1,416,457
Commercial Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	1,055,947	657,670
Available-for-sale investments, gross unrealized holding gains	3,953	6,867
Available-for-sale investments, gross unrealized holding losses	(19,544)	(4,999)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	1,040,356	659,538
Residential Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	779,503	837,964
Available-for-sale investments, gross unrealized holding gains	18,749	22,563
Available-for-sale investments, gross unrealized holding losses	(5,048)	(4,022)
Available-for-sale investments, unrealized other-than-temporary impairment losses	(2,258)	(2,258)
Available-for-sale investments, estimated fair value	790,946	854,247
Asset-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	27,494	36,462
Available-for-sale investments, gross unrealized holding gains	2	15
Available-for-sale investments, gross unrealized holding losses	(158)	(406)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	27,338	36,071
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	1,420,298	1,690,945
Available-for-sale investments, gross unrealized holding gains	49,146	41,123
Available-for-sale investments, gross unrealized holding losses	(9,364)	(16,209)
Available-for-sale investments, unrealized other-than-temporary impairment losses	(673)	(1,624)
Available-for-sale investments, estimated fair value	1,459,407	1,714,235
Total Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	9,591,734	9,038,158
Available-for-sale investments, gross unrealized holding gains	386,001	400,515
Available-for-sale investments, gross unrealized holding losses	(83,294)	(40,323)
Available-for-sale investments, unrealized other-than-temporary impairment losses	(2,931)	(3,882)
Available-for-sale investments, estimated fair value	9,891,510	9,394,468
Insurance, Banks And Other Financial Institutions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	846,343	651,002
Available-for-sale investments, gross unrealized holding gains	857,063	690,271
Available-for-sale investments, gross unrealized holding losses	(5,596)	(6,551)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	1,697,810	1,334,722
Industrial, Consumer And All Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	1,635,105	1,557,832
Available-for-sale investments, gross unrealized holding gains	1,421,080	1,227,052
Available-for-sale investments, gross unrealized holding losses	(8,154)	(45,131)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	3,048,031	2,739,753
Total Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	2,481,448	2,208,834
Available-for-sale investments, gross unrealized holding gains	2,278,143	1,917,323
Available-for-sale investments, gross unrealized holding losses	(13,750)	(51,682)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	4,745,841	4,074,475
Short-Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, amortized cost	2,336,100	1,642,103
Available-for-sale investments, gross unrealized holding gains	57	167
Available-for-sale investments, gross unrealized holding losses	(6)	(9)
Available-for-sale investments, unrealized other-than-temporary impairment losses	0	0
Available-for-sale investments, estimated fair value	$ 2,336,151	$ 1,642,261

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	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	$ 3,469,062	$ 2,030,690
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(82,777)	(76,054)
Available-for-sale securities, estimated fair value, 12 months or longer	321,552	813,147
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(17,204)	(19,842)
Available-for-sale securities, estimated fair value	3,790,614	2,843,837
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(99,981)	(95,896)
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	122,950	301,300
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(894)	(962)
Available-for-sale securities, estimated fair value, 12 months or longer	0	7,426
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	0	(86)
Available-for-sale securities, estimated fair value	122,950	308,726
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(894)	(1,048)
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	220,333	125,703
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(4,324)	(2,686)
Available-for-sale securities, estimated fair value, 12 months or longer	7,618	85,126
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(4)	(1,047)
Available-for-sale securities, estimated fair value	227,951	210,829
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(4,328)	(3,733)
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	1,004,947	169,362
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(37,685)	(4,864)
Available-for-sale securities, estimated fair value, 12 months or longer	31,723	70,101
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(4,120)	(3,361)
Available-for-sale securities, estimated fair value	1,036,670	239,463
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(41,805)	(8,225)
Foreign Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	68,887	51,328
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(2,145)	(249)
Available-for-sale securities, estimated fair value, 12 months or longer	5,005	40,345
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(8)	(1,432)
Available-for-sale securities, estimated fair value	73,892	91,673
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(2,153)	(1,681)
Commercial Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	749,889	289,058
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(19,091)	(3,600)
Available-for-sale securities, estimated fair value, 12 months or longer	29,988	95,843
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(453)	(1,399)
Available-for-sale securities, estimated fair value	779,877	384,901
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(19,544)	(4,999)
Residential Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	181,557	78,814
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(4,987)	(2,858)
Available-for-sale securities, estimated fair value, 12 months or longer	79,936	137,100
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(2,319)	(3,422)
Available-for-sale securities, estimated fair value	261,493	215,914
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(7,306)	(6,280)
Asset-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	14,501	6,228
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(106)	(54)
Available-for-sale securities, estimated fair value, 12 months or longer	5,869	24,315
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(52)	(352)
Available-for-sale securities, estimated fair value	20,370	30,543
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(158)	(406)
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	494,573	470,694
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(8,357)	(9,509)
Available-for-sale securities, estimated fair value, 12 months or longer	93,790	343,737
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(1,680)	(8,324)
Available-for-sale securities, estimated fair value	588,363	814,431
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(10,037)	(17,833)
Total Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	2,857,637	1,492,487
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(77,589)	(24,782)
Available-for-sale securities, estimated fair value, 12 months or longer	253,929	803,993
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(8,636)	(19,423)
Available-for-sale securities, estimated fair value	3,111,566	2,296,480
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(86,225)	(44,205)
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	8,808	63,873
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(410)	(6,384)
Available-for-sale securities, estimated fair value, 12 months or longer	37,973	6,247
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(5,186)	(167)
Available-for-sale securities, estimated fair value	46,781	70,120
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(5,596)	(6,551)
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	98,406	344,857
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(4,772)	(44,879)
Available-for-sale securities, estimated fair value, 12 months or longer	29,650	2,907
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(3,382)	(252)
Available-for-sale securities, estimated fair value	128,056	347,764
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(8,154)	(45,131)
Total Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	107,214	408,730
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(5,182)	(51,263)
Available-for-sale securities, estimated fair value, 12 months or longer	67,623	9,154
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(8,568)	(419)
Available-for-sale securities, estimated fair value	174,837	417,884
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(13,750)	(51,682)
Short-Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	504,211	129,473
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(6)	(9)
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	504,211	129,473
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	$ (6)	$ (9)

Investments (Schedule Of Amorti

Investments (Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturity Securities By Contractual Maturity) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, amortized cost	$ 798,529
Due after one year through five years, amortized cost	1,210,130
Due after five years through ten years, amortized cost	1,582,373
Due after ten years, amortized cost	4,137,758
Amortized cost, sub-total	7,728,790
Fixed maturities, amortized cost	9,591,734	$ 9,038,158
Due in one year or less, estimated fair value	800,733
Due after one year through five years, estimated fair value	1,252,152
Due after five years through ten years, estimated fair value	1,659,755
Due after ten years, estimated fair value	4,320,230
Estimated fair value, sub-total	8,032,870
Fixed maturity securities, estimated fair value	9,891,510	$ 9,394,468
Commercial Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,055,947
Estimated fair value	1,040,356
Residential Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	779,503
Estimated fair value	790,946
Asset-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	27,494
Estimated fair value	$ 27,338

Investments (Components Of Net

Investments (Components Of Net Investment Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Municipal bonds (tax-exempt)	$ 88,654	$ 93,580	$ 98,262
Short-term investments, including overnight deposits	11,177	5,223	5,959
Dividends on equity securities	70,577	74,705	65,031
Income (loss) from equity method investments	6,852	(262)	4,766
Other	2,676	651	2,338
Total investment income	390,437	370,210	378,490
Investment expenses	(17,207)	(16,997)	(15,260)
Net investment income	373,230	353,213	363,230
Taxable Municipal Bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	65,749	57,550	49,345
Other Taxable Bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	$ 144,752	$ 138,763	$ 152,789

Investments (Summary Of Net Rea

Investments (Summary Of Net Realized Investment Gains And The Change In Net Unrealized Gains On Investments) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Gain (Loss) on Investments [Line Items]
Realized gains	$ 76,752	$ 168,163	$ 74,978
Realized losses	(28,396)	(50,797)	(39,422)
Other-than-temporary impairment losses recognized in net income	(18,355)	(44,481)	(4,784)
Gains (losses) on securities measured at fair value through net income	16,791	(10,886)	10,444
Net realized investment gains	65,147	106,480	46,000
Change in net unrealized gains on investments included in other comprehensive income (loss)	342,111	(457,584)	981,035
Sales Of Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Realized gains	5,160	3,073	8,417
Realized losses	(704)	(4,598)	(18,136)
Sales Of Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Realized gains	70,177	156,987	51,356
Realized losses	(6,988)	(1,232)	(802)
Other [Member]
Gain (Loss) on Investments [Line Items]
Realized gains	1,415	8,103	15,205
Realized losses	(2,349)	(486)	(15,700)
Fixed Maturity Securities [Member]
Gain (Loss) on Investments [Line Items]
Other-than-temporary impairment losses recognized in net income	0	0	(304)
Change in net unrealized gains on investments included in other comprehensive income (loss)	(56,534)	(137,435)	480,350
Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Other-than-temporary impairment losses recognized in net income	(18,355)	(44,481)	(4,480)
Change in net unrealized gains on investments included in other comprehensive income (loss)	398,752	(320,277)	500,673
Short-Term Investments [Member]
Gain (Loss) on Investments [Line Items]
Change in net unrealized gains on investments included in other comprehensive income (loss)	$ (107)	$ 128	$ 12

Investments (Summary Of Other-T

Investments (Summary Of Other-Than-Temporary Impairment Losses Recognized In Net Income And In Net Realized Investment Gains By Investment Type) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Other-than-temporary impairment losses recognized in net income	$ (18,355)	$ (44,481)	$ (4,784)
Commercial Mortgage-Backed [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Other-than-temporary impairment losses recognized in net income	0	0	(61)
Asset-Backed [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Other-than-temporary impairment losses recognized in net income	0	0	(197)
Corporate [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Other-than-temporary impairment losses recognized in net income	0	0	(46)
Fixed Maturity Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Other-than-temporary impairment losses recognized in net income	0	0	(304)
Insurance, Banks And Other Financial Institutions [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Other-than-temporary impairment losses recognized in net income	(7,586)	(9,835)	(341)
Industrial, Consumer And All Other [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Other-than-temporary impairment losses recognized in net income	(10,769)	(34,646)	(4,139)
Equity Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Other-than-temporary impairment losses recognized in net income	$ (18,355)	$ (44,481)	$ (4,480)

Investments Investments (Compon

Investments Investments (Components Of Restricted Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Components Of Restricted Assets [Line Items]
Restricted assets	$ 4,414,952	$ 4,783,202
Held In Trust Or On Deposit [Member]
Components Of Restricted Assets [Line Items]
Restricted assets	4,059,336	4,037,458
Cash And Cash Equivalents And Securities Pledged As Collateral [Member]
Components Of Restricted Assets [Line Items]
Restricted assets	$ 355,616	$ 745,744

Investments (Schedule Of Restri

Investments (Schedule Of Restricted Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Investments, available-for-sale	$ 4,068,535	$ 4,343,070
Restricted cash and cash equivalents	346,417	440,132
Total	$ 4,414,952	$ 4,783,202

Receivables (Components Of Rece

Receivables (Components Of Receivables) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Receivables [Abstract]
Amounts receivable from agents, brokers and insureds	$ 1,061,190	$ 983,510
Trade accounts receivable	123,341	119,558
Investment management and performance fees receivable	38,735	0
Employee stock loans receivable (see note 12(c))	20,171	16,900
Other	10,122	6,165
Receivables, gross	1,253,559	1,126,133
Allowance for doubtful receivables	(11,910)	(12,430)
Receivables	$ 1,241,649	$ 1,113,703

Deferred Policy Acquisition C68

Deferred Policy Acquisition Costs (Amounts Of Policy Acquisition Costs Acquired, Deferred And Amortized) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of year	$ 352,756	$ 353,410	$ 260,967
Policy acquisition costs deferred	823,840	752,324	754,303
Amortization of policy acquisition costs	(782,221)	(744,964)	(654,916)
Foreign currency movements	(1,965)	(8,014)	(6,944)
Deferred policy acquisition costs	$ 392,410	$ 352,756	$ 353,410

Deferred Policy Acquisition C69

Deferred Policy Acquisition Costs (Components Of Underwriting, Acquisition And Insurance Expenses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred Policy Acquisition Costs Disclosures [Abstract]
Amortization of policy acquisition costs	$ 782,221	$ 744,964	$ 654,916
Other operating expenses	716,369	710,116	805,966
Underwriting, acquisition and insurance expenses	$ 1,498,590	$ 1,455,080	$ 1,460,882

Property And Equipment (Compone

Property And Equipment (Components Of Property And Equipment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Land	$ 56,783	$ 56,408
Buildings	76,159	77,488
Leasehold improvements	95,898	104,003
Land improvements	74,040	71,585
Furniture and equipment	301,146	291,736
Other	162,385	134,939
Property and equipment, gross	766,411	736,159
Accumulated depreciation and amortization	(354,009)	(305,324)
Property and equipment	412,402	430,835
Depreciation and amortization expense of property and equipment	$ 64,800	$ 64,200	$ 51,200

Goodwill And Intangible Asset71

Goodwill And Intangible Assets (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Goodwill And Intangible Assets [Line Items]
Goodwill impairment	$ (18,723)	$ (14,880)
Carrying value following impairment charge	1,142,248	1,167,844	$ 1,049,115
Amortization of intangible assets	68,533	68,947	57,627
Estimated amortization of intangible assets for 2017	67,400
Estimated amortization of intangible assets for 2018	66,000
Estimated amortization of intangible assets for 2019	58,000
Estimated amortization of intangible assets for 2020	51,600
Estimated amortization of intangible assets for 2021	50,000
Indefinite-lived intangible assets	48,200	48,200
Markel Ventures Operations [Member] | Industrial Manufacturing [Member]
Goodwill And Intangible Assets [Line Items]
Goodwill impairment	(18,700)
Carrying value following impairment charge	$ 0
Markel Ventures Operations [Member] | Healthcare [Member]
Goodwill And Intangible Assets [Line Items]
Goodwill impairment		(14,900)	$ (13,700)
Carrying value following impairment charge		$ 0

Goodwill And Intangible Asset72

Goodwill And Intangible Assets (Components Of Goodwill) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015
Goodwill [Line Items]
Goodwill, beginning balance		$ 1,167,844		$ 1,049,115
Acquisitions (see note 2)				146,659
Impairment loss		(18,723)		(14,880)
Foreign currency movements and other adjustments		(6,873)		(13,050)
Goodwill, ending balance		1,142,248		1,167,844
U.S. Insurance [Member]
Goodwill [Line Items]
Goodwill, beginning balance		280,579		280,579
Acquisitions (see note 2)				0
Impairment loss		0		0
Foreign currency movements and other adjustments		0		0
Goodwill, ending balance		280,579		280,579
International Insurance [Member]
Goodwill [Line Items]
Goodwill, beginning balance		397,993		408,183
Acquisitions (see note 2)				0
Impairment loss		0		0
Foreign currency movements and other adjustments		(5,809)		(10,190)
Goodwill, ending balance		392,184		397,993
Reinsurance [Member]
Goodwill [Line Items]
Goodwill, beginning balance		122,745		122,745
Acquisitions (see note 2)				0
Impairment loss		0		0
Foreign currency movements and other adjustments		0		0
Goodwill, ending balance		122,745		122,745
Other [Member]
Goodwill [Line Items]
Goodwill, beginning balance	[1]	366,527	[2]	237,608
Acquisitions (see note 2)	[1]			146,659
Impairment loss	[1]	(18,723)		(14,880)
Foreign currency movements and other adjustments	[1]	(1,064)		(2,860)
Goodwill, ending balance	[1],[2]	346,740		366,527
Accumulated impairment losses	[2]	$ 47,300		$ 28,600
[1]	Amounts included in Other above are related to the Company's non-insurance operations, which are not included in a reportable segment.
[2]	Goodwill is net of accumulated impairment losses of $47.3 million and $28.6 million, as of December 31, 2016 and 2015, respectively, included in Other.

Goodwill And Intangible Asset73

Goodwill And Intangible Assets (Components Of Intangible Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Indefinite-Lived And Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross carrying amount	$ 973,150	$ 992,776
Intangible assets, accumulated amortization	(250,608)	(200,404)
Customer Relationships [Member]
Schedule of Indefinite-Lived And Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross carrying amount	460,327	481,547
Intangible assets, accumulated amortization	(119,376)	(97,892)
Broker Relationships [Member]
Schedule of Indefinite-Lived And Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross carrying amount	183,092	182,626
Intangible assets, accumulated amortization	(56,888)	(45,135)
Trade Names [Member]
Schedule of Indefinite-Lived And Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross carrying amount	100,966	103,681
Intangible assets, accumulated amortization	(29,745)	(23,821)
Investment Management Agreements [Member]
Schedule of Indefinite-Lived And Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross carrying amount	98,000	98,000
Intangible assets, accumulated amortization	(7,000)	0
Technology [Member]
Schedule of Indefinite-Lived And Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross carrying amount	54,408	54,241
Intangible assets, accumulated amortization	(28,220)	(22,288)
Insurance Licenses [Member]
Schedule of Indefinite-Lived And Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross carrying amount	30,185	30,185
Intangible assets, accumulated amortization	0	0
Lloyd's Syndicate Capacity [Member]
Schedule of Indefinite-Lived And Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross carrying amount	12,000	12,000
Intangible assets, accumulated amortization	0	0
Other [Member]
Schedule of Indefinite-Lived And Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross carrying amount	34,172	30,496
Intangible assets, accumulated amortization	$ (9,379)	$ (11,268)

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Line Items]
Income tax payments	$ 142,200,000	$ 132,500,000	$ 89,500,000
Income taxes payable	$ 46,400,000	$ 63,500,000
Income tax benefit related to tax credits for foreign taxes paid	2.00%	8.00%	1.00%
Tax credit carryforwards	$ 23,037,000	$ 18,158,000
Tax credit, expiration date	Dec. 31, 2025
Net operating loss carryforwards	$ 18,100,000
Estimated gross deferred tax assets including net operating losses realized through generating taxable income or reversal of existing temporary differences attributable to gross deferred tax liabilities	659,400,000
Valuation allowance	(18,781,000)	(5,131,000)
Unrecognized tax benefits	8,876,000	$ 15,324,000	$ 17,700,000
Unrecognized tax benefits decrease on effective tax rate	8,600,000
Provision for United States income taxes on earnings of the Company's foreign subsidiaries	0
Undistributed earnings of foreign subsidiaries	615,000,000
Adjustment to the Company's income tax liabilities as a result of IRS examination	$ 0
Earliest Tax Year [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2028
Latest Tax Year [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2030
Markel Capital Limited [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 12,600,000
Markel Capital Limited [Member] | Earliest Tax Year [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2023
Markel Capital Limited [Member] | Latest Tax Year [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2033
Certain Branch Operations In Europe And Wholly Owned Subsidiary In Brazil [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 81,700,000
Certain Branch Operations In Europe And Wholly Owned Subsidiary In Brazil [Member] | Earliest Tax Year [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2020
Certain Branch Operations In Europe And Wholly Owned Subsidiary In Brazil [Member] | Latest Tax Year [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforwards, expiration date	Dec. 31, 2025
Certain Branch Operations In Europe And Wholly Owned Subsidiary In Brazil [Member] | Subject To Expiration [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 20,400,000

Income Taxes (Components Of Inc

Income Taxes (Components Of Income Before Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Domestic operations	$ 288,905	$ 323,954	$ 240,279
Foreign operations	341,015	418,151	200,099
Income Before Income Taxes	$ 629,920	$ 742,105	$ 440,378

Income Taxes (Components Of I76

Income Taxes (Components Of Income Tax Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Domestic, current	$ 57,916	$ 44,406	$ 7,573
Foreign, current	48,203	118,235	24,574
Total current tax expense	106,119	162,641	32,147
Domestic, deferred	19,991	9,415	43,673
Foreign, deferred	43,367	(19,093)	40,870
Total deferred tax expense (benefit)	63,358	(9,678)	84,543
Income tax expense	$ 169,477	$ 152,963	$ 116,690

Income Taxes (Reconciliations O

Income Taxes (Reconciliations Of United States Corporate Income Tax Rate To Effective Tax Rate On Income Before Income Taxes) (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
United States corporate tax rate	35.00%	35.00%	35.00%
Tax-exempt investment income	(6.00%)	(5.00%)	(9.00%)
Foreign tax credits	(2.00%)	(8.00%)	(1.00%)
Foreign operations	1.00%	(1.00%)	0.00%
Other	(1.00%)	0.00%	1.00%
Effective tax rate	27.00%	21.00%	26.00%

Income Taxes (Components Of Dom

Income Taxes (Components Of Domestic And Foreign Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Unpaid losses and loss adjustment expenses	$ 181,303	$ 212,012
Life and annuity benefits	135,075	156,950
Unearned premiums recognized for income tax purposes	121,852	102,076
Accrued incentive compensation	67,719	53,586
Investments, including other-than-temporary impairments	58,248	65,641
Net operating loss carryforwards	26,743	18,771
Tax credit carryforwards	23,037	18,158
Stock-based compensation	19,235	21,948
Other differences between financial reporting and tax bases	44,942	40,497
Total gross deferred tax assets	678,154	689,639
Less valuation allowance	(18,781)	(5,131)
Total gross deferred tax assets, net of allowance	659,373	684,508
Net unrealized gains on investments	723,198	626,776
Deferred policy acquisition costs	128,302	88,036
Amortization of goodwill and other intangible assets	102,631	107,271
Other differences between financial reporting and tax bases	35,727	38,613
Total gross deferred tax liabilities	989,858	860,696
Net deferred tax liability	$ 330,485	$ 176,188

Income Taxes (Reconciliation Of

Income Taxes (Reconciliation Of Beginning And Ending Unrecognized Tax Benefits) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Unrecognized tax benefits, beginning of year	$ 15,324	$ 17,700
Decreases for tax positions taken in prior years	0	(146)
Lapse of statute of limitations	(6,448)	(606)
Settlement with taxing authorities	0	(1,624)
Unrecognized tax benefits, end of year	$ 8,876	$ 15,324

Unpaid Losses And Loss Adjust80

Unpaid Losses And Loss Adjustment Expenses (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Oct. 30, 2015	Mar. 09, 2015	Dec. 31, 2013	Dec. 31, 2012
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable development related to the commutation of a property and casualty deposit contract	$ (11,700)
Adverse (favorable) development on prior years' loss reserves	(493,495)	$ (627,800)	$ (435,545)
Prior years' adverse (favorable) development on asbestos and environmental exposures	(5,277)	25,415	32,840
Loss on retrospective reinsurance transaction recognized in losses and loss adjustment expenses		7,100
Increase in asbestos and environmental prior years’ loss reserves following the retroactive reinsurance transaction		15,000
Net reserves for losses and loss adjustment expenses of acquired insurance companies	0	0	21,193
Liability for asbestos and environmental claims net incurred loss annual claim review	0	0	27,200
Unamortized fair value adjustment included in unpaid losses and loss adjustment expenses	$ 68,900	$ 91,000
IBNR reserves as a percentage of total unpaid losses and loss adjustment expenses	67.00%	65.00%
Asbestos-related reserves, gross loss incurred	$ 323,904	$ 386,625	390,442
Asbestos-related reserves, net loss incurred	111,604	132,869	287,723			$ 272,194
Asbestos and environmental net reserves for reported claims	104,100
Asbestos and environmental reserves incurred but not reported, net	7,500
Liability for asbestos and environmental claims, net claims paid since inception	612,000
Reinsurance recoverable on retroactive reinsurance transactions attributable to A&E exposures	0	159,641	0
Liability for asbestos and environmental claims, net litigation paid since inception	93,600
Reinsurance recoverable on retroactive reinsurance transactions	0	177,649	0
U.S. Insurance [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	5,565,888
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	2,897,849
U.S. Insurance [Member] | 2012 Accident Year [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	909,237	924,621	924,138			985,721	$ 949,141
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	$ 728,802	644,658	546,635			401,773	193,708
Cumulative number of reported claims	106
U.S. Insurance [Member] | 2012 Accident Year [Member] | Alterra [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance						97,400
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance						22,600
U.S. Insurance [Member] | 2013 Accident Year [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 1,009,438	1,042,100	1,105,927			1,130,681
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	$ 725,782	594,558	443,392			222,890
Cumulative number of reported claims	65
U.S. Insurance [Member] | 2013 Accident Year [Member] | Alterra [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance						149,900
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance						23,200
International Insurance [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 2,461,912
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	1,021,220
International Insurance [Member] | 2012 Accident Year [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	479,558	495,641	557,604			616,641	412,684
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	$ 319,843	289,517	230,882			163,805	38,992
Cumulative number of reported claims	18
International Insurance [Member] | 2012 Accident Year [Member] | Alterra [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance						158,000
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance						14,000
International Insurance [Member] | 2013 Accident Year [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 446,568	476,433	581,164			597,145
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	$ 220,625	182,173	126,699			47,887
Cumulative number of reported claims	17
International Insurance [Member] | 2013 Accident Year [Member] | Alterra [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance						162,700
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance						6,200
International Insurance [Member] | 2012 To 2016 Accident Years [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Percentage of cumulative incurred losses and allocated loss adjustment expenses, net of reinsurance from managing agents	4.00%
Reinsurance [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 2,564,809
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	941,098
Reinsurance [Member] | 2012 Accident Year [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	455,103	482,836	503,410			545,939	72,250
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	230,742	183,321	128,174			64,209	$ 3,955
Reinsurance [Member] | 2012 Accident Year [Member] | Alterra [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance						471,000
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance						52,400
Reinsurance [Member] | 2013 Accident Year [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	531,955	545,743	574,760			581,963
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	268,052	209,256	154,494			71,182
Reinsurance [Member] | 2013 Accident Year [Member] | Alterra [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance						531,800
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance						$ 68,600
Impact Of Retroactive Reinsurance Transactions On Reserve Volatility [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Adverse (favorable) development on prior years' loss reserves		(82,700)
Asbestos [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Asbestos-related reserves, gross loss incurred	252,100
Asbestos-related reserves, net loss incurred	90,000
Long Tail Casualty U.S. Insurance And Intl Marine And Energy Intl And Property U.S. Insurance And Reinsurance Segments [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Adverse (favorable) development on prior years' loss reserves	(418,000)
Specified Medical And Medical Malpractice [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Adverse (favorable) development on prior years' loss reserves	$ 71,200
General Liability Workers Compensation Inland Marine And Brokerage Property Within U.S. Insurance Segment And General Liability Professional Liability And Marine And Energy Within International Segment [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Adverse (favorable) development on prior years' loss reserves		$ (375,800)
Long-Tail Casualty And Professional Liability Witihin U.S. Insurance Segment And Professional Liability And Marine And Energy International Segment [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Adverse (favorable) development on prior years' loss reserves			$ (250,400)
Personal Lines [Member] | U.S. Insurance [Member] | 2012 Accident Year [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Cumulative number of reported claims	65
Personal Lines [Member] | U.S. Insurance [Member] | 2013 Accident Year [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Cumulative number of reported claims	16
March 9, 2015 [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Total payment under retrospective reinsurance transaction on ceded asbestos and environmental policies					$ 89,000
Cash paid at closing under retrospective reinsurance transaction on ceded asbestos and environmental policies					69,900
Cumulative amount of reserves for losses and loss adjustment expenses on ceded asbestos and environmental policies					94,100
Deferred gain under retrospective reinsurance transaction on ceded asbestos and environmental policies					$ 5,100
October 30, 2015 [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Total payment under retrospective reinsurance transaction on ceded asbestos and environmental policies				$ 86,500
Cumulative amount of reserves for losses and loss adjustment expenses on ceded asbestos and environmental policies				173,400
Cumulative reserves for losses and loss adjustment expenses on ceded asbestos and environmental policies, net of retention				76,400
Loss on retrospective reinsurance transaction				$ 10,100

Unpaid Losses And Loss Adjust81

Unpaid Losses And Loss Adjustment Expenses (Reconciliation Of Consolidated Reserves For Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Net reserves for losses and loss adjustment expenses, beginning of year	$ 8,235,288	$ 8,535,483	$ 8,407,642
Foreign currency movements	(129,692)	(134,173)	(137,385)
Adjusted net reserves for losses and loss adjustment expenses, beginning of year	8,105,596	8,401,310	8,270,257
Incurred losses and loss adjustment expenses, current year	2,555,902	2,566,545	2,638,012
Incurred losses and loss adjustment expenses, prior years	(493,495)	(627,800)	(435,545)
Total incurred losses and loss adjustment expenses	2,062,407	1,938,745	2,202,467
Payments, current year	532,140	486,551	502,107
Payments, prior years	1,529,206	1,423,286	1,436,851
Total payments	2,061,346	1,909,837	1,938,958
Effect of foreign currency rate changes	2,060	(17,281)	(19,476)
Net reserves for losses and loss adjustment expenses of acquired insurance companies	0	0	21,193
Reinsurance recoverable on retroactive reinsurance transactions	0	(177,649)	0
Net reserves for losses and loss adjustment expenses, end of year	8,108,717	8,235,288	8,535,483
Reinsurance recoverable on unpaid losses	2,006,945	2,016,665	1,868,669
Gross reserves for losses and loss adjustment expenses, end of year	$ 10,115,662	$ 10,251,953	$ 10,404,152

Unpaid Losses And Loss Adjust82

Unpaid Losses And Loss Adjustment Expenses (Ultimate Incurred Losses And Cumulative Paid Losses And Allocated Loss Adjustment Expenses, Net Of Reinsurance) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Claims Development [Line Items]
Total liabilities for unpaid losses and loss adjustment expenses, net of reinsurance	$ 7,828,041
U.S. Insurance [Member]
Claims Development [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	5,565,888
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	2,897,849
All outstanding liabilities for unpaid losses and loss adjustment expenses before 2012, net of reinsurance	402,534
Total liabilities for unpaid losses and loss adjustment expenses, net of reinsurance	3,070,573
U.S. Insurance [Member] | 2012 Accident Year [Member]
Claims Development [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	909,237	$ 924,621	$ 924,138	$ 985,721	$ 949,141
Total of incurred-but-not-reported liabilities, net of reinsurance	$ 117,333
Cumulative number of reported claims	106
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	$ 728,802	644,658	546,635	401,773	193,708
U.S. Insurance [Member] | 2013 Accident Year [Member]
Claims Development [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	1,009,438	1,042,100	1,105,927	1,130,681
Total of incurred-but-not-reported liabilities, net of reinsurance	$ 175,309
Cumulative number of reported claims	65
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	$ 725,782	594,558	443,392	222,890
U.S. Insurance [Member] | 2014 Accident Year [Member]
Claims Development [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	1,116,093	1,140,685	1,278,116
Total of incurred-but-not-reported liabilities, net of reinsurance	$ 290,827
Cumulative number of reported claims	56
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	$ 650,118	487,068	264,697
U.S. Insurance [Member] | 2015 Accident Year [Member]
Claims Development [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	1,211,389	1,285,411
Total of incurred-but-not-reported liabilities, net of reinsurance	$ 500,705
Cumulative number of reported claims	55
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	$ 514,497	260,121
U.S. Insurance [Member] | 2016 Accident Year [Member]
Claims Development [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	1,319,731
Total of incurred-but-not-reported liabilities, net of reinsurance	$ 781,984
Cumulative number of reported claims	49
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	$ 278,650
International Insurance [Member]
Claims Development [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	2,461,912
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	1,021,220
All outstanding liabilities for unpaid losses and loss adjustment expenses before 2012, net of reinsurance	570,940
Total liabilities for unpaid losses and loss adjustment expenses, net of reinsurance	2,011,632
International Insurance [Member] | 2012 Accident Year [Member]
Claims Development [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	479,558	495,641	557,604	616,641	412,684
Total of incurred-but-not-reported liabilities, net of reinsurance	$ 87,383
Cumulative number of reported claims	18
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	$ 319,843	289,517	230,882	163,805	38,992
International Insurance [Member] | 2013 Accident Year [Member]
Claims Development [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	446,568	476,433	581,164	597,145
Total of incurred-but-not-reported liabilities, net of reinsurance	$ 155,062
Cumulative number of reported claims	17
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	$ 220,625	182,173	126,699	47,887
International Insurance [Member] | 2014 Accident Year [Member]
Claims Development [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	502,708	545,954	577,454
Total of incurred-but-not-reported liabilities, net of reinsurance	$ 149,455
Cumulative number of reported claims	16
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	$ 240,050	167,568	65,683
International Insurance [Member] | 2015 Accident Year [Member]
Claims Development [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	489,119	488,649
Total of incurred-but-not-reported liabilities, net of reinsurance	$ 222,864
Cumulative number of reported claims	16
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	$ 148,037	61,556
International Insurance [Member] | 2016 Accident Year [Member]
Claims Development [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	543,959
Total of incurred-but-not-reported liabilities, net of reinsurance	$ 279,320
Cumulative number of reported claims	13
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	$ 92,665
Reinsurance [Member]
Claims Development [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	2,564,809
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	941,098
All outstanding liabilities for unpaid losses and loss adjustment expenses before 2012, net of reinsurance	840,563
Total liabilities for unpaid losses and loss adjustment expenses, net of reinsurance	2,464,274
Reinsurance [Member] | 2012 Accident Year [Member]
Claims Development [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	455,103	482,836	503,410	545,939	72,250
Total of incurred-but-not-reported liabilities, net of reinsurance	137,778
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	230,742	183,321	128,174	64,209	$ 3,955
Reinsurance [Member] | 2013 Accident Year [Member]
Claims Development [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	531,955	545,743	574,760	581,963
Total of incurred-but-not-reported liabilities, net of reinsurance	179,519
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	268,052	209,256	154,494	$ 71,182
Reinsurance [Member] | 2014 Accident Year [Member]
Claims Development [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	536,274	565,252	575,479
Total of incurred-but-not-reported liabilities, net of reinsurance	209,246
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	228,293	158,104	$ 97,617
Reinsurance [Member] | 2015 Accident Year [Member]
Claims Development [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	511,959	526,286
Total of incurred-but-not-reported liabilities, net of reinsurance	306,717
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	134,530	$ 63,963
Reinsurance [Member] | 2016 Accident Year [Member]
Claims Development [Line Items]
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance	529,518
Total of incurred-but-not-reported liabilities, net of reinsurance	382,407
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	$ 79,481

Unpaid Losses And Loss Adjust83

Unpaid Losses And Loss Adjustment Expenses (Average Annual Percentage Payout Of Incurred Losses By Age (in Years), Net Of Reinsurance) (Details)	Dec. 31, 2016
U.S. Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Average annual percentage payout of incurred losses in year 1	21.90%
Average annual percentage payout of incurred losses in year 2	21.40%
Average annual percentage payout of incurred losses in year 3	15.20%
Average annual percentage payout of incurred losses in year 4	11.90%
Average annual percentage payout of incurred losses in year 5	9.30%
International Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Average annual percentage payout of incurred losses in year 1	12.30%
Average annual percentage payout of incurred losses in year 2	20.40%
Average annual percentage payout of incurred losses in year 3	13.60%
Average annual percentage payout of incurred losses in year 4	10.40%
Average annual percentage payout of incurred losses in year 5	6.30%
Reinsurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Average annual percentage payout of incurred losses in year 1	12.00%
Average annual percentage payout of incurred losses in year 2	13.50%
Average annual percentage payout of incurred losses in year 3	12.50%
Average annual percentage payout of incurred losses in year 4	11.60%
Average annual percentage payout of incurred losses in year 5	10.40%

Unpaid Losses And Loss Adjust84

Unpaid Losses And Loss Adjustment Expenses (Reconciliation Of Net Incurred And Paid Loss Development Tables, By Segment, To The Liability For Losses And Loss Adjustment Expenses In The Consolidated Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for for unpaid losses and loss adjustment expenses, net of reinsurance	$ 7,828,041
Reinsurance recoverable on unpaid losses	2,006,945
Unallocated loss adjustment expenses	211,777
Unamortized fair value adjustments on acquired reserves for losses and loss adjustment expenses	68,899
Total reconciling items	280,676
Liability for unpaid losses and loss adjustment expenses	10,115,662	$ 10,251,953	$ 10,404,152
U.S. Insurance [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for for unpaid losses and loss adjustment expenses, net of reinsurance	3,070,573
Reinsurance recoverable on unpaid losses	631,608
Liability for unpaid losses and loss adjustment expenses	3,849,541	3,720,429
International Insurance [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for for unpaid losses and loss adjustment expenses, net of reinsurance	2,011,632
Reinsurance recoverable on unpaid losses	982,127
Liability for unpaid losses and loss adjustment expenses	3,062,725	3,140,000
Reinsurance [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for for unpaid losses and loss adjustment expenses, net of reinsurance	2,464,274
Reinsurance recoverable on unpaid losses	140,629
Liability for unpaid losses and loss adjustment expenses	2,661,209	2,750,258
Other Insurance (Discontinued Lines) [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for for unpaid losses and loss adjustment expenses, net of reinsurance	281,562
Reinsurance recoverable on unpaid losses	252,581
Liability for unpaid losses and loss adjustment expenses	$ 542,187	$ 641,266

Unpaid Losses And Loss Adjust85

Unpaid Losses And Loss Adjustment Expenses (Reconciliation Of Consolidated A&E Reserves For Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Net reserves for A&E losses and loss adjustment expenses, beginning of year	$ 132,869	$ 287,723	$ 272,194
Incurred losses and loss adjustment expenses	(5,277)	25,415	32,840
Payments	(15,988)	(20,628)	(17,311)
Reinsurance recoverable on retroactive reinsurance transactions	0	(159,641)	0
Net reserves for A&E losses and loss adjustment expenses, end of year	111,604	132,869	287,723
Reinsurance recoverable on unpaid losses	212,300	253,756	102,719
Gross reserves for A&E losses and loss adjustment expenses, end of year	$ 323,904	$ 386,625	$ 390,442

Life And Annuity Benefits (Narr

Life And Annuity Benefits (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Apr. 24, 2015
Liability for Future Policy Benefits [Abstract]
Average reserve valuation rate	2.30%
Life and annuity benefits reserve single contract concentration	32.90%
Annuities included in life and annuity benefits subject to discretionary withdrawal	$ 0
Cash payments for life and annuity benefit policies transferred under novated reinsurance contract		$ 29,000
Reserves on novated life and annuity benefit reinsurance contract		32,600
Gain on novated life and annuity benefit reinsurance contract		$ 3,600

Life And Annuity Benefits (Sche

Life And Annuity Benefits (Schedule Of Life And Annuity Benefits) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Liability for Future Policy Benefits [Abstract]
Life	$ 131,768	$ 142,068
Annuities	849,226	901,218
Accident and health	68,660	79,989
Total life and annuity benefits	$ 1,049,654	$ 1,123,275

Senior Long-Term Debt And Oth88

Senior Long-Term Debt And Other Debt (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Loss on early extinguishment of debt		$ 44,100	$ 0	$ 0
Senior long-term debt and other debt, estimated fair value		2,721,000	2,403,000
Interest on senior long-term debt and other debt		135,400	127,000	$ 125,800
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, capacity available		300,000
Line of credit facility, potential increased maximum capacity		$ 500,000
Line of credit facility, unused capacity, commitment fee, percent		0.225%
Borrowings outstanding under the facility		$ 0	$ 0
Secured Letters Of Credit [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, capacity available		200,000
Markel Diversified Fund [Member]
Debt Instrument [Line Items]
Note payable included in total liabilities of the Markel Diversified Fund delivered as part of the consideration provided for its investment		$ 62,500
Unsecured Senior Notes [Member] | 7.20% Unsecured Senior Notes Due April 14, 2017 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate		7.20%	7.20%
Unsecured Senior Notes [Member] | 6.25% Unsecured Senior Notes Due September 30, 2020 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate		6.25%	6.25%
Unsecured Senior Notes [Member] | 5.0% Unsecured Senior Notes Due April 5, 2046 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 500,000
Debt instrument, interest rate	5.00%	5.00%
Net proceeds from issuance of unsecured senior notes	$ 493,100
Unsecured Senior Notes [Member] | 7.35% Unsecured Senior Notes Due August 15, 2034 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate	7.35%	7.35%	7.35%
Debt instrument, repurchased face amount	$ 70,200
Early repayment of senior debt	$ 95,000
Unsecured Senior Notes [Member] | 7.125% Unsecured Senior Notes Due September 30, 2019 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate	7.125%	7.125%	7.125%
Debt instrument, repurchased face amount	$ 108,800
Early repayment of senior debt	$ 126,400

Senior Long-Term Debt And Oth89

Senior Long-Term Debt And Other Debt (Summary Of Senior Long-Term Debt And Other Debt) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Senior long-term debt and other debt	$ 2,574,529		$ 2,239,271
Unsecured Senior Notes [Member] | 7.20% Unsecured Senior Notes Due April 14, 2017 [Member]
Debt Instrument [Line Items]
Unsecured senior notes	$ 91,046		$ 92,436
Debt instrument, interest rate	7.20%		7.20%
Debt Instrument, unamortized premium	$ 417		$ 1,808
Unsecured Senior Notes [Member] | 7.125% Unsecured Senior Notes Due September 30, 2019 [Member]
Debt Instrument [Line Items]
Unsecured senior notes	$ 234,183		$ 346,725
Debt instrument, interest rate	7.125%	7.125%	7.125%
Debt instrument, unamortized discount	$ 522		$ 1,060
Unsecured Senior Notes [Member] | 6.25% Unsecured Senior Notes Due September 30, 2020 [Member]
Debt Instrument [Line Items]
Unsecured senior notes	$ 385,714		$ 394,464
Debt instrument, interest rate	6.25%		6.25%
Debt Instrument, unamortized premium	$ 35,717		$ 44,519
Unsecured Senior Notes [Member] | 5.35% Unsecured Senior Notes Due June 1, 2021 [Member]
Debt Instrument [Line Items]
Unsecured senior notes	$ 248,957		$ 248,694
Debt instrument, interest rate	5.35%		5.35%
Debt instrument, unamortized discount	$ 912		$ 1,119
Unsecured Senior Notes [Member] | 4.90% Unsecured Senior Notes Due July 1, 2022 [Member]
Debt Instrument [Line Items]
Unsecured senior notes	$ 348,215		$ 347,891
Debt instrument, interest rate	4.90%		4.90%
Debt instrument, unamortized discount	$ 1,536		$ 1,815
Unsecured Senior Notes [Member] | 3.625% Unsecured Senior Notes Due March 30, 2023 [Member]
Debt Instrument [Line Items]
Unsecured senior notes	$ 248,508		$ 248,277
Debt instrument, interest rate	3.625%		3.625%
Debt instrument, unamortized discount	$ 1,257		$ 1,458
Unsecured Senior Notes [Member] | 7.35% Unsecured Senior Notes Due August 15, 2034 [Member]
Debt Instrument [Line Items]
Unsecured senior notes	$ 128,570		$ 197,923
Debt instrument, interest rate	7.35%	7.35%	7.35%
Debt instrument, unamortized discount	$ 1,212		$ 1,972
Unsecured Senior Notes [Member] | 5.0% Unsecured Senior Notes Due March 30, 2043 [Member]
Debt Instrument [Line Items]
Unsecured senior notes	$ 243,796		$ 243,559
Debt instrument, interest rate	5.00%		5.00%
Debt instrument, unamortized discount	$ 5,879		$ 6,103
Unsecured Senior Notes [Member] | 5.0% Unsecured Senior Notes Due April 5, 2046 [Member]
Debt Instrument [Line Items]
Unsecured senior notes	$ 491,943		0
Debt instrument, interest rate	5.00%	5.00%
Debt instrument, unamortized discount	$ 7,154
Other Debt [Member]
Debt Instrument [Line Items]
Senior long-term debt and other debt	$ 153,597		$ 119,302
Other Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate	1.70%
Other Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate	6.50%

Senior Long-Term Debt And Oth90

Senior Long-Term Debt And Other Debt (Summary Of Future Principal Payments Due At Maturity On Senior Long-Term Debt And Other Debt) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
2,017	$ 183,916
2,018	6,365
2,019	239,633
2,020	359,332
2,021	284,758
2022 and thereafter	1,485,404
Total principal payments	2,559,408
Net unamortized premium	17,662
Net unamortized debt issuance costs	(2,541)
Senior long-term debt and other debt	$ 2,574,529	$ 2,239,271

Shareholders' Equity (Narrative

Shareholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized	50,000,000	50,000,000
Common stock, par value	$ 0	$ 0
Common stock, shares issued	13,954,931	13,959,018
Common stock, shares outstanding	13,954,931	13,959,018
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, par value	$ 0	$ 0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
November 2013 Share Repurchase Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Board of Directors approved the repurchase of common stock under a share repurchase program, maximum	$ 300
Cumulative number of common stock shares repurchased	96,345
Cumulative stock repurchased value	$ 70.7
2016 Employee Stock Purchase And Bonus Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Bonus calculation percentage based on the value of stocks acquired by employees	10.00%
Percentage of bonus shares award to loan program participants	5.00%
Shares authorized under the 2016 Employee Stock Purchase and Bonus Plan	125,000
Number of shares available for purchase	118,692
Loans outstanding under 2016 Employee Stock Purchase and Bonus Plan	$ 20.2	$ 16.9
Employee Stock Purchase And Bonus Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued under the prior Employee Stock Purchase and Bonus Plan since the effective date of the 2016 Employee Stock Purchase and Bonus Plan	0
Number of shares available for purchase		9,458
2012 Compensation Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based awards issued under the 2012 Compensation Plan since the effective date of the 2016 Compensation Plan	0
2016 Compensation Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for future awards	248,025
2016 Compensation Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted stock units awarded	15,614
Weighted average grant-date fair value, share-based awards	$ 878.03	$ 740.80	$ 583.74
Unrecognized compensation cost related to nonvested share-based awards	$ 10.7
Weighted average remaining service period of share-based awards	1 year 7 months
Fair value of the vested share-based awards	$ 29.8	$ 15.8	$ 4.2
2016 Compensation Plan [Member] | Restricted Stock Units (RSUs) [Member] | Non-Employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted stock units awarded	1,050
Restricted stock awards, year awards vest	2,017
2016 Compensation Plan [Member] | Restricted Stock Units (RSUs) [Member] | Performance Based [Member] | Associates And Executive Officers [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock issuable for each vested restricted stock unit	1
Number of restricted stock units awarded	12,664
Restricted stock awards, vesting period	3 years
2016 Compensation Plan [Member] | Restricted Stock Units (RSUs) [Member] | Retention And Hiring [Member] | Associates And Executive Officers [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock issuable for each vested restricted stock unit	1
Number of restricted stock units awarded	1,900
Restricted stock units, grant date fair value	$ 1.7
Restricted stock awards, vesting period	3 years

Shareholders' Equity (Schedule

Shareholders' Equity (Schedule Of Net Income Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Line Items]
Net income to shareholders	$ 132,726	$ 83,796	$ 78,797	$ 160,370	$ 197,892	$ 102,519	$ 91,369	$ 190,992	$ 117,595	$ 75,803	$ 40,068	$ 87,716	$ 455,689	$ 582,772	$ 321,182
Adjustment of redeemable noncontrolling interests													(15,472)	4,144	(8,186)
Adjusted net income to shareholders													$ 440,217	$ 586,916	$ 312,996
Basic common shares outstanding													14,013	13,978	13,984
Diluted shares outstanding													14,078	14,061	14,057
Basic net income per share (dollars per share)	$ 9.14	$ 5.62	$ 5.44	$ 11.21	$ 14.23	$ 7.43	$ 6.76	$ 13.57	$ 8.10	$ 5.33	$ 2.67	$ 6.28	$ 31.41	$ 41.99	$ 22.38
Diluted net income per share (dollars per share)	$ 9.11	$ 5.60	$ 5.41	$ 11.15	$ 14.14	$ 7.39	$ 6.72	$ 13.49	$ 8.05	$ 5.30	$ 2.66	$ 6.25	$ 31.27	$ 41.74	$ 22.27
Stock Options [Member]
Earnings Per Share [Line Items]
Dilutive potential common shares													4	9	11
Restricted Stock Units (RSUs) [Member]
Earnings Per Share [Line Items]
Dilutive potential common shares													61	74	62

Shareholders' Equity (Summary O

Shareholders' Equity (Summary Of Nonvested Share-Based Awards) (Details) - 2016 Compensation Plan [Member] - Restricted Stock Units (RSUs) [Member] - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Number of awards, nonvested awards, beginning balance	103,883
Number of awards, granted	15,614
Number of awards, vested	(53,798)
Number of awards, forfeited	(81)
Number of awards, nonvested awards, ending balance	65,618	103,883
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Weighted average grant-date fair value, nonvested awards, beginning balance	$ 556.66
Weighted average grant-date fair value, granted	878.03	$ 740.80	$ 583.74
Weighted average grant-date fair value, vested	554.62
Weighted average grant-date fair value, forfeited	632.82
Weighted average grant-date fair value, nonvested awards, ending balance	$ 634.71	$ 556.66

Other Comprehensive Income (L94

Other Comprehensive Income (Loss) (Change In Accumulated Other Comprehensive Income By Component, Net Of Taxes And Noncontrolling Interests) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, beginning balance	$ 1,354,508	$ 1,704,557	$ 1,089,805
Other comprehensive income (loss) before reclassifications	243,286	(271,697)	639,147
Amounts reclassified from accumulated other comprehensive income	(31,928)	(78,352)	(24,395)
Total other comprehensive income (loss)	211,358	(350,049)	614,752
Accumulated other comprehensive income, ending balance	1,565,866	1,354,508	1,704,557
Unrealized Holding Gains On Available-For-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, beginning balance	1,472,762	1,793,254	1,131,507
Other comprehensive income (loss) before reclassifications	275,696	(240,010)	687,908
Amounts reclassified from accumulated other comprehensive income	(33,528)	(80,482)	(26,161)
Total other comprehensive income (loss)	242,168	(320,492)	661,747
Accumulated other comprehensive income, ending balance	1,714,930	1,472,762	1,793,254
Foreign Currency [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, beginning balance	(72,696)	(43,491)	(11,246)
Other comprehensive income (loss) before reclassifications	(11,710)	(29,205)	(32,245)
Amounts reclassified from accumulated other comprehensive income	0	0	0
Total other comprehensive income (loss)	(11,710)	(29,205)	(32,245)
Accumulated other comprehensive income, ending balance	(84,406)	(72,696)	(43,491)
Net Actuarial Pension Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, beginning balance	(45,558)	(45,206)	(30,456)
Other comprehensive income (loss) before reclassifications	(20,700)	(2,482)	(16,516)
Amounts reclassified from accumulated other comprehensive income	1,600	2,130	1,766
Total other comprehensive income (loss)	(19,100)	(352)	(14,750)
Accumulated other comprehensive income, ending balance	$ (64,658)	$ (45,558)	$ (45,206)

Other Comprehensive Income (L95

Other Comprehensive Income (Loss) (Schedule Of Tax Expense (Benefit) Of Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Comprehensive Income (Loss), Tax [Abstract]
Net holding gains (losses) arising during the period	$ 112,399	$ (107,860)	$ 328,564
Change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period	6	35	614
Reclassification adjustments for net gains included in net income	(12,462)	(29,267)	(9,890)
Change in net unrealized gains on investments	99,943	(137,092)	319,288
Change in foreign currency translation adjustments	1,037	408	1,918
Change in net actuarial pension loss	(4,192)	(88)	(3,687)
Total	$ 96,788	$ (136,772)	$ 317,519

Other Comprehensive Income (L96

Other Comprehensive Income (Loss) (Amounts Reclassified From Accumulated Other Comprehensive Income Into Income, By Component) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses recognized in net income													$ (18,355)	$ (44,481)	$ (4,784)
Net realized investment gains, excluding other-than-temporary impairment losses													83,502	150,961	50,784
Income Before Income Taxes													629,920	742,105	440,378
Underwriting, acquisition and insurance expenses													(1,498,590)	(1,455,080)	(1,460,882)
Income Taxes													(169,477)	(152,963)	(116,690)
Net Income	$ 132,703	$ 83,421	$ 80,673	$ 163,646	$ 198,273	$ 104,410	$ 92,453	$ 194,006	$ 118,222	$ 76,824	$ 41,141	$ 87,501	460,443	589,142	323,688
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													(18,355)	(44,481)	(4,784)
Net realized investment gains, excluding other-than-temporary impairment losses													64,345	154,230	40,835
Income Before Income Taxes													45,990	109,749	36,051
Income Taxes													(12,462)	(29,267)	(9,890)
Net Income													33,528	80,482	26,161
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													(1,951)	(2,662)	(2,084)
Income Taxes													351	532	318
Net Income													$ (1,600)	$ (2,130)	$ (1,766)

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, level 1 to level 2 transfers, amount	$ 0	$ 0
Fair value, level 2 to level 1 transfers, amount	0	0
Assets measured at fair value on a non-recurring basis	0	0
Liabilities measured at fair value on a non-recurring basis	$ 0	$ 0
Short-Term Investments [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment maturity period	1 year

Fair Value Measurements (Balanc

Fair Value Measurements (Balances Of Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	$ 9,891,510	$ 9,394,468
Equity securities	4,745,841	4,074,475
Short-term investments	2,336,151	1,642,261
Total investments available-for-sale	16,973,502	15,111,204
Fixed Maturity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	9,891,510	9,394,468
U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	258,584	309,417
U.S. Government-Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	423,212	391,290
Obligations Of States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	4,428,205	4,013,213
Foreign Governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	1,463,462	1,416,457
Commercial Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	1,040,356	659,538
Residential Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	790,946	854,247
Asset-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	27,338	36,071
Corporate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	1,459,407	1,714,235
Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	4,745,841	4,074,475
Insurance, Banks And Other Financial Institutions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	1,697,810	1,334,722
Industrial, Consumer And All Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	3,048,031	2,739,753
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	9,891,510	9,394,468
Equity securities	4,745,841	4,074,475
Short-term investments	2,336,151	1,642,261
Total investments available-for-sale	16,973,502	15,111,204
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	0	0
Equity securities	4,554,638	4,074,475
Short-term investments	2,255,898	1,529,924
Total investments available-for-sale	6,810,536	5,604,399
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	9,891,510	9,394,468
Equity securities	0	0
Short-term investments	80,253	112,337
Total investments available-for-sale	9,971,763	9,506,805
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	0	0
Equity securities	191,203	0
Short-term investments	0	0
Total investments available-for-sale	191,203	0
Fair Value, Measurements, Recurring [Member] | U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	258,584	309,417
Fair Value, Measurements, Recurring [Member] | U.S. Treasury [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | U.S. Treasury [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	258,584	309,417
Fair Value, Measurements, Recurring [Member] | U.S. Treasury [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | U.S. Government-Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	423,212	391,290
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]
Fixed maturity securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | U.S. Government-Sponsored Enterprises [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	423,212	391,290
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]
Fixed maturity securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Obligations Of States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	4,428,205	4,013,213
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]
Fixed maturity securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Obligations Of States, Municipalities And Political Subdivisions [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	4,428,205	4,013,213
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]
Fixed maturity securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Foreign Governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	1,463,462	1,416,457
Fair Value, Measurements, Recurring [Member] | Foreign Governments [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Foreign Governments [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	1,463,462	1,416,457
Fair Value, Measurements, Recurring [Member] | Foreign Governments [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	1,040,356	659,538
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	1,040,356	659,538
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	790,946	854,247
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	790,946	854,247
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Asset-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	27,338	36,071
Fair Value, Measurements, Recurring [Member] | Asset-Backed [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Asset-Backed [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	27,338	36,071
Fair Value, Measurements, Recurring [Member] | Asset-Backed [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Corporate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	1,459,407	1,714,235
Fair Value, Measurements, Recurring [Member] | Corporate [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Corporate [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	1,459,407	1,714,235
Fair Value, Measurements, Recurring [Member] | Corporate [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] | Insurance, Banks And Other Financial Institutions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	1,697,810	1,334,722
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]
Equity securities	1,506,607	1,334,722
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]
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]
Equity securities	191,203	0
Fair Value, Measurements, Recurring [Member] | Industrial, Consumer And All Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	3,048,031	2,739,753
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]
Equity securities	3,048,031	2,739,753
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]
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]
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		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Equity securities, beginning of period		$ 0	$ 0
Purchases		195,250	0
Sales		(25,000)	0
Total gains included in net income		20,953	0
Total gains included in other comprehensive income (loss)		0	0
Transfers into Level 3		0	0
Transfers out of Level 3		0	0
Equity securities, end of period		191,203	0
Net unrealized gains included in net income relating to assets held at December 31, 2016 and 2015	[1]	$ 20,953	$ 0
[1]	Included in net realized investment gains in the consolidated statements of income and comprehensive income.

Reinsurance (Narrative) (Detail

Reinsurance (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)reinsurer	Dec. 31, 2015USD ($)reinsurer	Dec. 31, 2014USD ($)
Reinsurance Disclosures [Line Items]
Number of largest company reinsurers | reinsurer	10	10
Reinsurance recoverables | $	$ 362	$ 330.7	$ 423.1
Percentage of ceded earned premiums to gross earned premiums	17.00%	18.00%	19.00%
Percentage of assumed earned premiums to net earned premiums	30.00%	31.00%	34.00%
Ten Largest Reinsurers [Member]
Reinsurance Disclosures [Line Items]
Recoverable balances as a percentage of the total balance	67.00%	68.00%
Fairfax Financial Group [Member]
Reinsurance Disclosures [Line Items]
Recoverable balances as a percentage of the total balance	15.00%

Reinsurance (Reinsurance Allowa

Reinsurance (Reinsurance Allowance For Doubtful Accounts) (Details) - Allowance For Reinsurance Recoverable [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Valuation and Qualifying Accounts Disclosure [Line Items]
Reinsurance allowance, beginning of year	$ 59,350	$ 59,813	$ 76,210
Additions	980	5,897	10,316
Deductions	(23,560)	(6,360)	(26,713)
Reinsurance allowance, end of year	$ 36,770	$ 59,350	$ 59,813

Reinsurance (Effect Of Reinsura

Reinsurance (Effect Of Reinsurance And Retrocessional Reinsurance On Premiums Written And Earned) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reinsurance Disclosures [Abstract]
Direct premiums written	$ 3,560,635	$ 3,474,510	$ 3,478,273
Direct premiums earned	3,506,687	3,480,297	3,443,912
Assumed premiums written	1,236,010	1,158,402	1,327,240
Assumed premiums earned	1,176,205	1,194,772	1,298,371
Ceded premiums written	(795,625)	(813,619)	(888,498)
Ceded premiums earned	(817,022)	(851,537)	(901,371)
Net premiums written	4,001,020	3,819,293	3,917,015
Net premiums earned	$ 3,865,870	$ 3,823,532	$ 3,840,912

Commitments And Contingencie103

Commitments And Contingencies (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Maximum remaining term of noncancelable operating leases	18 years
Rental expense	$ 40.2	$ 44.3	$ 42.7

Commitments And Contingencie104

Commitments And Contingencies (Minimum Annual Rental Commitments) (Details) $ in Thousands	Dec. 31, 2016USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,017	$ 34,449
2,018	31,883
2,019	29,270
2,020	21,536
2,021	21,140
2022 and thereafter	95,979
Total	$ 234,257

Variable Interest Entities (Nar

Variable Interest Entities (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds	$ 1,307,779	$ 1,086,758	$ 883,525
Total investment and insurance assets under management of MCIM for unconsolidated VIEs	3,400,000
Other Fund [Member]
Variable Interest Entity [Line Items]
Investment in one of the unconsolidated funds	26,100
Markel Diversified Fund [Member]
Variable Interest Entity [Line Items]
Investment in one of the unconsolidated funds	165,100
Total assets of the Markel Diversified Fund	166,800
Total liabilities of the Markel Diversified Fund	$ 64,600
Percentage of total assets of the Markel Diversified Fund invested in one of the unconsolidated Funds	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
Non-Insurance Operations [Member]
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds	1,293,185	1,074,427	854,893
Non-Insurance Operations [Member] | Investment Management [Member]
Variable Interest Entity [Line Items]
Investment management fees earned by the Company from unconsolidated Funds	$ 56,455	$ 0	$ 0

Statutory Financial Informat106

Statutory Financial Information (Narrative) (Details) $ in Millions	Dec. 31, 2016USD ($)
Statutory Accounting Practices [Line Items]
Amount of cash and investments held as funds at Lloyd's	$ 784.9
United States [Member]
Statutory Accounting Practices [Line Items]
Amount available for dividend payment	330.4
Bermuda [Member]
Statutory Accounting Practices [Line Items]
Amount available for dividend payment	$ 547.4

Statutory Financial Informat107

Statutory Financial Information (Actual Statutory Capital And Surplus) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
United States [Member]
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	$ 2,761,454	$ 2,569,928
United Kingdom [Member]
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	682,477	603,238
Bermuda [Member]
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	2,189,649	1,964,844
Other Countries [Member]
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	$ 24,726	$ 17,305

Statutory Financial Informat108

Statutory Financial Information (Statutory Net Income (Loss)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
United States [Member]
Statutory Accounting Practices [Line Items]
Statutory net income (loss)	$ 249,176	$ 291,783	$ 212,909
United Kingdom [Member]
Statutory Accounting Practices [Line Items]
Statutory net income (loss)	77,909	74,330	73,697
Bermuda [Member]
Statutory Accounting Practices [Line Items]
Statutory net income (loss)	132,442	185,289	110,401
Other Countries [Member]
Statutory Accounting Practices [Line Items]
Statutory net income (loss)	$ (891)	$ (3,181)	$ 1,367

Segment Reporting Disclosure109

Segment Reporting Disclosures (Narrative) (Details) - segment	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue, Major Customer [Line Items]
Number of reportable ongoing underwriting segments	3
Percentage of gross premiums written	100.00%	100.00%	100.00%
Top Three Independent Brokers [Member]
Revenue, Major Customer [Line Items]
Percentage of gross premiums written	28.00%	27.00%	28.00%
Top Three Independent Brokers [Member] | International Insurance [Member]
Revenue, Major Customer [Line Items]
Percentage of gross premiums written	40.00%	42.00%	41.00%
Top Three Independent Brokers [Member] | Reinsurance [Member]
Revenue, Major Customer [Line Items]
Percentage of gross premiums written	75.00%	68.00%	68.00%

Segment Reporting Disclosure110

Segment Reporting Disclosures (Summary Of Gross Written Premiums By Country) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Gross written premiums	$ 4,796,645	$ 4,632,912	$ 4,805,513
Percentage of gross premiums written	100.00%	100.00%	100.00%
United States [Member]
Segment Reporting Information [Line Items]
Gross written premiums	$ 3,691,840	$ 3,519,487	$ 3,523,239
Percentage of gross premiums written	77.00%	76.00%	73.00%
United Kingdom [Member]
Segment Reporting Information [Line Items]
Gross written premiums	$ 358,348	$ 414,941	$ 441,669
Percentage of gross premiums written	7.00%	9.00%	9.00%
Canada [Member]
Segment Reporting Information [Line Items]
Gross written premiums	$ 125,444	$ 115,191	$ 125,617
Percentage of gross premiums written	3.00%	2.00%	3.00%
Other Countries [Member]
Segment Reporting Information [Line Items]
Gross written premiums	$ 621,013	$ 583,293	$ 714,988
Percentage of gross premiums written	13.00%	13.00%	15.00%

Segment Reporting Disclosure111

Segment Reporting Disclosures (Company's Segment Disclosures) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Gross premium volume		$ 4,796,645	$ 4,632,912	$ 4,805,513
Net written premiums		4,001,020	3,819,293	3,917,015
Earned premiums		3,865,870	3,823,532	3,840,912
Losses and loss adjustment expenses, current accident year		(2,555,902)	(2,566,545)	(2,638,012)
Losses and loss adjustment expenses, prior accident years		505,158	627,800	435,545
Amortization of policy acquisition costs		(782,221)	(744,964)	(654,916)
Other operating expenses		(716,369)	(710,116)	(805,966)
Underwriting profit (loss)		316,536	429,707	177,563
Net investment income		373,230	353,213	363,230
Net realized investment gains		65,147	106,480	46,000
Other revenues (insurance)		14,594	12,331	28,632
Other expenses (insurance)		(47,623)	(40,095)	(62,834)
Segment profit (loss)		721,884	861,636	552,591
Other revenues (non-insurance)		1,293,185	1,074,427	854,893
Other expenses (non-insurance)		(1,142,620)	(1,006,710)	(792,037)
Amortization of intangible assets		(68,533)	(68,947)	(57,627)
Interest expense		(129,896)	(118,301)	(117,442)
Loss on early extinguishment of debt		(44,100)	0	0
Income Before Income Taxes		$ 629,920	$ 742,105	$ 440,378
U.S. GAAP combined ratio	[1]	92.00%	89.00%	95.00%
U.S. Insurance [Member]
Segment Reporting Information [Line Items]
Gross premium volume		$ 2,635,266	$ 2,504,096	$ 2,493,823
Net written premiums		2,237,163	2,106,490	2,071,466
Earned premiums		2,175,332	2,105,212	2,022,860
Losses and loss adjustment expenses, current accident year		(1,403,589)	(1,367,159)	(1,340,129)
Losses and loss adjustment expenses, prior accident years		204,881	298,967	216,557
Amortization of policy acquisition costs		(446,649)	(420,289)	(403,233)
Other operating expenses		(377,230)	(378,563)	(396,737)
Underwriting profit (loss)		152,745	238,168	99,318
Net investment income		0	0	0
Net realized investment gains		0	0	0
Other revenues (insurance)		7,143	3,331	2,478
Other expenses (insurance)		(15,407)	(3,902)	(5,149)
Segment profit (loss)		$ 144,481	$ 237,597	$ 96,647
U.S. GAAP combined ratio	[1]	93.00%	89.00%	95.00%
International Insurance [Member]
Segment Reporting Information [Line Items]
Gross premium volume		$ 1,119,815	$ 1,164,866	$ 1,200,403
Net written premiums		864,494	888,214	889,336
Earned premiums		853,512	879,426	909,679
Losses and loss adjustment expenses, current accident year		(605,837)	(638,144)	(660,409)
Losses and loss adjustment expenses, prior accident years		164,713	248,834	166,615
Amortization of policy acquisition costs		(146,117)	(142,657)	(141,394)
Other operating expenses		(219,066)	(221,758)	(207,175)
Underwriting profit (loss)		47,205	125,701	67,316
Net investment income		0	0	0
Net realized investment gains		0	0	0
Other revenues (insurance)		5,560	7,790	21,827
Other expenses (insurance)		(5,712)	(5,717)	(18,706)
Segment profit (loss)		$ 47,053	$ 127,774	$ 70,437
U.S. GAAP combined ratio	[1]	94.00%	86.00%	93.00%
Reinsurance [Member]
Segment Reporting Information [Line Items]
Gross premium volume		$ 1,041,055	$ 965,374	$ 1,112,728
Net written premiums		898,728	824,324	956,584
Earned premiums		836,264	838,543	908,385
Losses and loss adjustment expenses, current accident year		(546,476)	(561,242)	(637,474)
Losses and loss adjustment expenses, prior accident years		125,514	97,860	79,951
Amortization of policy acquisition costs		(189,455)	(182,018)	(110,289)
Other operating expenses		(119,012)	(106,863)	(201,673)
Underwriting profit (loss)		106,835	86,280	38,900
Net investment income		0	0	0
Net realized investment gains		0	0	0
Other revenues (insurance)		0	593	2,696
Other expenses (insurance)		0	(1,419)	(1,847)
Segment profit (loss)		$ 106,835	$ 85,454	$ 39,749
U.S. GAAP combined ratio	[1]	87.00%	90.00%	96.00%
Other Insurance (Discontinued Lines) [Member]
Segment Reporting Information [Line Items]
Gross premium volume		$ 509	$ (1,424)	$ (1,441)
Net written premiums		635	265	(371)
Earned premiums		762	351	(12)
Losses and loss adjustment expenses, current accident year		0	0	0
Losses and loss adjustment expenses, prior accident years		10,050	(17,861)	(27,578)
Amortization of policy acquisition costs		0	0	0
Other operating expenses		(1,061)	(2,932)	(381)
Underwriting profit (loss)		9,751	(20,442)	(27,971)
Net investment income		0	0	0
Net realized investment gains		0	0	0
Other revenues (insurance)		1,891	617	1,631
Other expenses (insurance)		(26,504)	(29,057)	(37,132)
Segment profit (loss)		$ (14,862)	$ (48,882)	$ (63,472)
U.S. GAAP combined ratio - not meaniningful	[1],[2]	NM	NM	NM
Investing [Member]
Segment Reporting Information [Line Items]
Gross premium volume		$ 0	$ 0	$ 0
Net written premiums		0	0	0
Earned premiums		0	0	0
Losses and loss adjustment expenses, current accident year		0	0	0
Losses and loss adjustment expenses, prior accident years		0	0	0
Amortization of policy acquisition costs		0	0	0
Other operating expenses		0	0	0
Underwriting profit (loss)		0	0	0
Net investment income		373,230	353,213	363,230
Net realized investment gains		65,147	106,480	46,000
Other revenues (insurance)		0	0	0
Other expenses (insurance)		0	0	0
Segment profit (loss)		$ 438,377	$ 459,693	$ 409,230
[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 Disclosure112

Segment Reporting Disclosures (Summary Of Deferred Policy Acquisition Costs, Unearned Premiums And Unpaid Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Deferred policy acquisition costs	$ 392,410	$ 352,756	$ 353,410	$ 260,967
Unearned premiums	2,263,838	2,166,105
Unpaid losses and loss adjustment expenses	10,115,662	10,251,953	$ 10,404,152
U.S. Insurance [Member]
Segment Reporting Information [Line Items]
Deferred policy acquisition costs	176,348	162,289
Unearned premiums	1,166,914	1,105,456
Unpaid losses and loss adjustment expenses	3,849,541	3,720,429
International Insurance [Member]
Segment Reporting Information [Line Items]
Deferred policy acquisition costs	51,948	48,913
Unearned premiums	445,183	467,158
Unpaid losses and loss adjustment expenses	3,062,725	3,140,000
Reinsurance [Member]
Segment Reporting Information [Line Items]
Deferred policy acquisition costs	164,114	141,554
Unearned premiums	651,741	593,491
Unpaid losses and loss adjustment expenses	2,661,209	2,750,258
Other Insurance (Discontinued Lines) [Member]
Segment Reporting Information [Line Items]
Deferred policy acquisition costs	0	0
Unearned premiums	0	0
Unpaid losses and loss adjustment expenses	$ 542,187	$ 641,266

Segment Reporting Disclosure113

Segment Reporting Disclosures (Summary Of Segment Earned Premiums By Product) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Earned premiums	$ 3,865,870	$ 3,823,532	$ 3,840,912
U.S. Insurance [Member]
Segment Reporting Information [Line Items]
Earned premiums	2,175,332	2,105,212	2,022,860
U.S. Insurance [Member] | General Liability [Member]
Segment Reporting Information [Line Items]
Earned premiums	563,908	522,358	491,645
U.S. Insurance [Member] | Professional Liability [Member]
Segment Reporting Information [Line Items]
Earned premiums	328,597	324,230	321,005
U.S. Insurance [Member] | Property [Member]
Segment Reporting Information [Line Items]
Earned premiums	270,026	264,232	266,019
U.S. Insurance [Member] | Personal Lines [Member]
Segment Reporting Information [Line Items]
Earned premiums	364,843	325,811	299,442
U.S. Insurance [Member] | Programs [Member]
Segment Reporting Information [Line Items]
Earned premiums	263,783	277,829	244,216
U.S. Insurance [Member] | Workers' Compensation [Member]
Segment Reporting Information [Line Items]
Earned premiums	301,126	281,954	263,164
U.S. Insurance [Member] | Other Products [Member]
Segment Reporting Information [Line Items]
Earned premiums	83,049	108,798	137,369
International Insurance [Member]
Segment Reporting Information [Line Items]
Earned premiums	853,512	879,426	909,679
International Insurance [Member] | General Liability [Member]
Segment Reporting Information [Line Items]
Earned premiums	111,291	124,198	146,178
International Insurance [Member] | Professional Liability [Member]
Segment Reporting Information [Line Items]
Earned premiums	272,010	268,637	285,300
International Insurance [Member] | Property [Member]
Segment Reporting Information [Line Items]
Earned premiums	87,294	85,152	76,691
International Insurance [Member] | Marine And Energy [Member]
Segment Reporting Information [Line Items]
Earned premiums	242,070	262,307	287,263
International Insurance [Member] | Other Products [Member]
Segment Reporting Information [Line Items]
Earned premiums	140,847	139,132	114,247
Reinsurance [Member]
Segment Reporting Information [Line Items]
Earned premiums	836,264	838,543	908,385
Reinsurance [Member] | Property [Member]
Segment Reporting Information [Line Items]
Earned premiums	288,771	265,373	270,461
Reinsurance [Member] | Casualty [Member]
Segment Reporting Information [Line Items]
Earned premiums	327,383	315,027	323,390
Reinsurance [Member] | Auto [Member]
Segment Reporting Information [Line Items]
Earned premiums	65,363	102,227	152,645
Reinsurance [Member] | Other Products [Member]
Segment Reporting Information [Line Items]
Earned premiums	154,747	155,916	161,889
Other Insurance (Discontinued Lines) [Member]
Segment Reporting Information [Line Items]
Earned premiums	$ 762	$ 351	$ (12)

Segment Reporting Disclosure114

Segment Reporting Disclosures (Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Assets	$ 25,875,299	$ 24,939,115	$ 25,197,760
Non-Insurance Operations [Member]
Segment Reporting Information [Line Items]
Assets	1,448,019	1,497,042	1,245,986
Segment Assets [Member]
Segment Reporting Information [Line Items]
Assets	24,427,280	23,442,073	23,951,774
Segment Assets [Member] | Investing [Member]
Segment Reporting Information [Line Items]
Assets	19,029,584	18,056,947	18,531,150
Segment Assets [Member] | Underwriting [Member]
Segment Reporting Information [Line Items]
Assets	$ 5,397,696	$ 5,385,126	$ 5,420,624

Other Revenues And Other Exp115

Other Revenues And Other Expenses (Summary Of Other Revenues And Other Expenses By Component) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Revenues and Other Expenses [Line Items]
Other revenues	$ 1,307,779	$ 1,086,758	$ 883,525
Other expenses	1,190,243	1,046,805	854,871
Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	14,594	12,331	28,632
Other expenses	47,623	40,095	62,834
Non-Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	1,293,185	1,074,427	854,893
Other expenses	1,142,620	1,006,710	792,037
Managing General Agent Operations [Member] | Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	12,703	10,202	23,324
Other expenses	21,119	9,619	22,527
Life And Annuity [Member] | Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	1,891	617	1,631
Other expenses	26,504	29,057	37,132
Other Insurance [Member] | Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	0	1,512	3,677
Other expenses	0	1,419	3,175
Manufacturing [Member] | Non-Insurance Operations [Member] | Markel Ventures Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	784,745	755,802	575,353
Other expenses	675,620	677,054	513,668
Non-Manufacturing [Member] | Non-Insurance Operations [Member] | Markel Ventures Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	429,704	291,714	262,767
Other expenses	396,323	301,004	261,551
Investment Management [Member] | Non-Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	56,455	0	0
Other expenses	46,190	0	0
Other Non-Insurance [Member] | Non-Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	22,281	26,911	16,773
Other expenses	$ 24,487	$ 28,652	$ 16,818

Employee Benefit Plans (Narrati

Employee Benefit Plans (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)fundsfund	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Defined Benefit Plan Disclosure [Line Items]
Expenses relating to defined contribution plans	$ 30.1	$ 27.7	$ 27.2
Consecutive number of years	3 years
Number of years preceding retirement	10 years
Amortization of the net actuarial pension loss included as a component of accumulated other comprehensive income	$ 3.5
Percentage of equity securities invested in UK companies	30.00%
Percentage of equity securities invested in other markets	70.00%
Number of fixed maturity mutual funds | funds	5
Accumulated benefit obligation	$ 175.1	$ 164.8
Expected plan contributions in 2017	3.2
Expected benefits to be paid in 2017	3
Expected benefits to be paid in 2018	3.1
Expected benefits to be paid in 2019	3.1
Expected benefits to be paid in 2020	3.2
Expected benefits to be paid in 2021	3.3
Aggregate benefits expected to be paid from 2022 to 2026	$ 17.4
United Kingdom [Member] | Foreign Governments [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of fixed maturity mutual funds | funds	2
United Kingdom [Member] | Corporate Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of fixed maturity mutual funds | funds	1
Other Foreign Governments [Member] | Foreign Governments [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of fixed maturity mutual funds | funds	1
United Kingdom And Other Foreign Governments [Member] | Corporate Bond Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of fixed maturity mutual funds | fund	1
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percent	47.00%
Actual asset allocation, percent	41.00%	43.00%
Fixed Maturity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percent	53.00%
Actual asset allocation, percent	59.00%	57.00%

Employee Benefit Plans (Schedul

Employee Benefit Plans (Schedule Of Amounts Recognized On The Consolidated Balance Sheets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of period	$ 170,005	$ 185,556
Interest cost	6,113	6,645	$ 7,572
Plan settlements	0	(2,863)
Benefits paid	(3,322)	(3,970)
Actuarial loss (gain)	38,485	(6,051)
Effect of foreign currency rate changes	(32,663)	(9,312)
Projected benefit obligation at end of year	178,618	170,005	185,556
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period	186,727	201,399
Actual gain on plan assets	22,367	2,246
Employer contributions	3,577	0
Plan settlements	0	(2,766)
Benefits paid	(3,322)	(3,970)
Effect of foreign currency rate changes	(33,705)	(10,182)
Fair value of plan assets at end of year	175,644	186,727	$ 201,399
Funded status of the plan	(2,974)	16,722
Net actuarial pension loss	85,110	61,818
Total	$ 82,136	$ 78,540

Employee Benefit Plans (Sche118

Employee Benefit Plans (Schedule of Defined Benefit Plan Amounts Recognized in Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Tax benefit	$ 4,192	$ 88	$ 3,687
Total other comprehensive income (loss)	211,358	(350,049)	614,752
Net Actuarial Pension Loss [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	(25,243)	(3,102)	(20,521)
Settlement loss recognized	0	343	0
Amortization of net actuarial loss	1,951	2,319	1,589
Amortization of prior service costs	0	0	495
Tax benefit	4,192	88	3,687
Total other comprehensive income (loss)	$ (19,100)	$ (352)	$ (14,750)

Employee Benefit Plans (Sche119

Employee Benefit Plans (Schedule Of Net Periodic Benefit Income And Weighted Average Assumptions) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]
Interest cost	$ 6,113	$ 6,645	$ 7,572
Expected return on plan assets	(9,124)	(11,496)	(12,812)
Amortization of prior service cost	0	0	495
Amortization of net actuarial pension loss	1,951	2,319	1,589
Settlement loss recognized	0	343	0
Net periodic benefit income	$ (1,060)	$ (2,189)	$ (3,156)
Discount rate	2.70%	4.00%	3.80%
Expected return on plan assets, percent	4.50%	5.40%	6.00%
Rate of compensation increase	3.00%	2.90%	2.90%

Employee Benefit Plans (Summary

Employee Benefit Plans (Summary Of Fair Value Of Plan Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 175,644	$ 186,727	$ 201,399
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	175,644	186,727
Level 1 [Member] | Fixed Maturity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	103,218	107,033
Level 1 [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	72,419	79,686
Level 1 [Member] | Cash And Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 7	$ 8

Markel Corporation (Parent C121

Markel Corporation (Parent Company Only) Financial Information (Schedule Of Condensed Balance Sheets) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Fixed maturities	$ 9,891,510	$ 9,394,468
Equity securities	4,745,841	4,074,475
Short-term investments (estimated fair value approximates cost)	2,336,151	1,642,261
Total Investments	16,973,502	15,111,204
Cash and cash equivalents	1,738,747	2,630,009	$ 1,960,169	$ 1,978,526
Restricted cash and cash equivalents	346,417	440,132
Other assets	946,024	941,945
Total Assets	25,875,299	24,939,115	25,197,760
Net deferred tax liability	330,485	176,188
Other liabilities	1,099,200	1,030,023
Total Liabilities	17,334,210	17,035,548
Total Shareholders' Equity	8,460,927	7,834,150
Total Liabilities and Equity	25,875,299	24,939,115
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Fixed maturities	52,234	36,618
Equity securities	367,156	311,405
Short-term investments (estimated fair value approximates cost)	1,729,400	755,619
Total Investments	2,148,790	1,103,642
Cash and cash equivalents	369,641	460,271	$ 243,702	$ 207,352
Restricted cash and cash equivalents	1,013	670
Receivables	20,477	17,200
Investments in consolidated subsidiaries	8,107,450	7,961,315
Notes receivable from subsidiaries	60,110	212,636
Other assets	97,364	89,747
Total Assets	10,804,845	9,845,481
Senior long-term debt	1,944,171	1,633,068
Notes payable to subsidiaries	285,000	300,000
Income taxes payable	25,240	4,262
Net deferred tax liability	25,902	7,498
Other liabilities	63,605	66,503
Total Liabilities	2,343,918	2,011,331
Total Shareholders' Equity	8,460,927	7,834,150
Total Liabilities and Equity	$ 10,804,845	$ 9,845,481

Markel Corporation (Parent C122

Markel Corporation (Parent Company Only) Financial Information (Schedule of Condensed Balance Sheets - Parenthetical) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Fixed maturities, amortized cost	$ 9,591,734	$ 9,038,158
Equity securities, cost	2,481,448	2,208,834
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Fixed maturities, amortized cost	51,181	35,475
Equity securities, cost	$ 203,708	$ 204,289

Markel Corporation (Parent C123

Markel Corporation (Parent Company Only) Financial Information (Schedule Of Condensed Statements Of Income And Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Net investment income													$ 373,230	$ 353,213	$ 363,230
Other-than-temporary impairment losses													(18,355)	(44,481)	(4,784)
Net realized investment gains, excluding other-than-temporary impairment losses													83,502	150,961	50,784
Net realized investment gains													65,147	106,480	46,000
Total Operating Revenues	$ 1,428,625	$ 1,431,282	$ 1,375,937	$ 1,376,182	$ 1,420,460	$ 1,342,764	$ 1,304,605	$ 1,302,154	$ 1,335,755	$ 1,299,286	$ 1,258,971	$ 1,239,655	5,612,026	5,369,983	5,133,667
Interest expense													129,896	118,301	117,442
Loss on early extinguishment of debt													44,100	0	0
Other expenses													1,190,243	1,046,805	854,871
Total Operating Expenses													4,808,110	4,509,577	4,575,847
Income tax benefit													169,477	152,963	116,690
Net Income to Shareholders	132,726	83,796	78,797	160,370	197,892	102,519	91,369	190,992	117,595	75,803	40,068	87,716	455,689	582,772	321,182
Net holding gains (losses) arising during the period													275,661	(240,170)	687,735
Reclassification adjustments for net gains included in net income to shareholders													(33,528)	(80,482)	(26,161)
Change in net unrealized gains on investments, net of taxes													242,168	(320,492)	661,747
Change in foreign currency translation adjustments, net of taxes													(11,704)	(29,278)	(32,241)
Total Other Comprehensive Income (Loss)													211,364	(350,122)	614,756
Comprehensive Income to Shareholders	$ (29,050)	$ 89,161	$ 209,942	$ 396,994	$ 134,984	$ (51,143)	$ (132,925)	$ 281,807	$ 418,571	$ 36,502	$ 250,588	$ 230,273	667,047	232,723	935,934
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net investment income													9,561	2,565	5,354
Dividends on common stock of consolidated subsidiaries													349,622	187,496	217,121
Other-than-temporary impairment losses													(98)	(3,455)	(120)
Net realized investment gains, excluding other-than-temporary impairment losses													1,166	75,000	3,873
Net realized investment gains													1,068	71,545	3,753
Total Operating Revenues													360,251	261,606	226,228
Interest expense													116,013	95,620	94,097
Loss on early extinguishment of debt													44,100	0	0
Other expenses													13,076	11,287	2,685
Total Operating Expenses													173,189	106,907	96,782
Income Before Equity in Undistributed Earnings of Consolidated Subsidiaries and Income Taxes													187,062	154,699	129,446
Equity in undistributed earnings of consolidated subsidiaries													196,615	407,489	163,341
Income tax benefit													(72,012)	(20,584)	(28,395)
Net Income to Shareholders													455,689	582,772	321,182
Net holding gains (losses) arising during the period													37,045	(41,861)	32,118
Consolidated subsidiaries' net holding gains (losses) arising during the period													238,616	(198,309)	655,617
Consolidated subsidiaries' change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period													35	160	173
Reclassification adjustments for net gains included in net income to shareholders													(558)	(45,273)	(1,874)
Consolidated subsidiaries' reclassification adjustments for net gains included in net income to shareholders													(32,970)	(35,209)	(24,287)
Change in net unrealized gains on investments, net of taxes													242,168	(320,492)	661,747
Change in foreign currency translation adjustments, net of taxes													(1,326)	2,970	1,949
Consolidated subsidiaries' change in foreign currency translation adjustments, net of taxes													(10,384)	(32,175)	(34,194)
Consolidated subsidiaries' change in net actuarial pension loss, net of taxes													(19,100)	(352)	(14,750)
Total Other Comprehensive Income (Loss)													211,358	(350,049)	614,752
Comprehensive Income to Shareholders													$ 667,047	$ 232,723	$ 935,934

Markel Corporation (Parent C124

Markel Corporation (Parent Company Only) Financial Information (Schedule Of Condensed Statements Of Cash Flows) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Net income to shareholders	$ 132,726	$ 83,796	$ 78,797	$ 160,370	$ 197,892	$ 102,519	$ 91,369	$ 190,992	$ 117,595	$ 75,803	$ 40,068	$ 87,716	$ 455,689	$ 582,772	$ 321,182
Net Cash Provided By Operating Activities													534,623	651,151	716,792
Proceeds from sales of fixed maturities and equity securities													365,822	538,978	1,286,871
Proceeds from maturities, calls and prepayments of fixed maturities													963,165	1,503,616	1,420,817
Cost of fixed maturities and equity securities purchased													(2,205,939)	(1,576,254)	(3,153,055)
Net change in short-term investments													(689,194)	(62,124)	(129,164)
Cost of equity method investments													(8,576)	(21,849)	(16,081)
Change in restricted cash and cash equivalents													93,370	62,324	264,701
Additions to property and equipment													(63,674)	(79,755)	(82,132)
Other													(1,348)	(797)	(2,368)
Net Cash Provided (Used) By Investing Activities													(1,545,111)	125,773	(622,205)
Additions to senior long-term debt													559,300	69,797	89,480
Premiums and fees related to early extinguishment of debt													(43,691)	0	0
Repurchases of common stock													(51,142)	(31,491)	(26,053)
Issuance of common stock													4,623	4,752	5,691
Other													(15,373)	(1,225)	(18,591)
Net Cash Provided (Used) By Financing Activities													152,019	(74,211)	(67,124)
Increase (decrease) in cash and cash equivalents													(891,262)	669,840	(18,357)
Cash and cash equivalents at beginning of year				2,630,009				1,960,169				1,978,526	2,630,009	1,960,169	1,978,526
CASH AND CASH EQUIVALENTS AT END OF YEAR	1,738,747				2,630,009				1,960,169				1,738,747	2,630,009	1,960,169
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net income to shareholders													455,689	582,772	321,182
Adjustments to reconcile net income to shareholders to net cash provided by operating activities													(120,564)	(464,193)	(218,396)
Net Cash Provided By Operating Activities													335,125	118,579	102,786
Proceeds from sales of fixed maturities and equity securities													1,831	100,633	9,306
Proceeds from maturities, calls and prepayments of fixed maturities													11,960	24,945	15,710
Cost of fixed maturities and equity securities purchased													(29,110)	(55,656)	(687)
Net change in short-term investments													(970,364)	9,956	(109,728)
Securities received from subsidiaries as dividends, repayment of notes receivable and return of capital													238,975	0	89,996
Return of capital from subsidiaries													21,021	0	0
Decrease in notes receivable due from subsidiaries													92,530	0	28,506
Capital contributions to subsidiaries													0	(228,578)	(74,788)
Cost of equity method investments													(3,100)	(13,164)	0
Change in restricted cash and cash equivalents													(343)	289	51
Additions to property and equipment													(584)	(305)	(342)
Other													(3,207)	(376)	(2,150)
Net Cash Provided (Used) By Investing Activities													(640,391)	(162,256)	(44,126)
Additions to senior long-term debt													493,149	0	0
Increase in notes payable to subsidiaries													0	285,000	0
Repayment and retirement of senior long-term debt													(183,343)	(2,000)	0
Premiums and fees related to early extinguishment of debt													(43,691)	0	0
Repurchases of common stock													(51,142)	(31,491)	(26,053)
Issuance of common stock													4,623	4,752	5,691
Other													(4,960)	3,985	(1,948)
Net Cash Provided (Used) By Financing Activities													214,636	260,246	(22,310)
Increase (decrease) in cash and cash equivalents													(90,630)	216,569	36,350
Cash and cash equivalents at beginning of year				$ 460,271				$ 243,702				$ 207,352	460,271	243,702	207,352
CASH AND CASH EQUIVALENTS AT END OF YEAR	$ 369,641				$ 460,271				$ 243,702				$ 369,641	$ 460,271	$ 243,702

Quarterly Financial Informat125

Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Operating revenues	$ 1,428,625	$ 1,431,282	$ 1,375,937	$ 1,376,182	$ 1,420,460	$ 1,342,764	$ 1,304,605	$ 1,302,154	$ 1,335,755	$ 1,299,286	$ 1,258,971	$ 1,239,655	$ 5,612,026	$ 5,369,983	$ 5,133,667
Net income	132,703	83,421	80,673	163,646	198,273	104,410	92,453	194,006	118,222	76,824	41,141	87,501	460,443	589,142	323,688
Net income to shareholders	132,726	83,796	78,797	160,370	197,892	102,519	91,369	190,992	117,595	75,803	40,068	87,716	455,689	582,772	321,182
Comprehensive income (loss) to shareholders	$ (29,050)	$ 89,161	$ 209,942	$ 396,994	$ 134,984	$ (51,143)	$ (132,925)	$ 281,807	$ 418,571	$ 36,502	$ 250,588	$ 230,273	$ 667,047	$ 232,723	$ 935,934
Basic net income per share (dollars per share)	$ 9.14	$ 5.62	$ 5.44	$ 11.21	$ 14.23	$ 7.43	$ 6.76	$ 13.57	$ 8.10	$ 5.33	$ 2.67	$ 6.28	$ 31.41	$ 41.99	$ 22.38
Diluted net income per share (dollars per share)	9.11	5.60	5.41	11.15	14.14	7.39	6.72	13.49	8.05	5.30	2.66	6.25	$ 31.27	$ 41.74	$ 22.27
Common stock price, high (dollars per share)	931.94	961.78	989.18	895.03	937.91	898.08	821	783.50	707.36	666	655.75	596.87
Common stock price, low (dollars per share)	$ 811.05	$ 909.84	$ 880.01	$ 805.03	$ 791.97	$ 775	$ 736.96	$ 660.05	$ 632.65	$ 623.90	$ 593.76	$ 527.17