W. R. Berkley (WRB) 10-K 27 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Feb. 23, 2015	Jun. 30, 2014
Document and Entity Information [Abstract]
Entity Registrant Name	BERKLEY W R CORP
Entity Central Index Key	11544
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Amendment Flag	FALSE
Entity Common Stock, Shares Outstanding		125,810,616
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$5,097,062,590

Consolidated_Statements_of_Inc

Consolidated Statements of Income (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
REVENUES:
Net premiums written	$5,996,947	$5,500,173	$4,898,539
Change in net unearned premiums	-252,529	-273,636	-225,023
Net premiums earned	5,744,418	5,226,537	4,673,516
Net investment income	600,885	544,291	586,763
Insurance service fees	117,443	107,513	103,133
Net investment gains:
Net realized gains on investment sales	254,852	127,586	201,451
Other-than-temporary impairments and change in valuation allowance	0	-6,042	9,014
Net investment gains	254,852	121,544	210,465
Revenues from wholly-owned investees	410,022	407,623	247,113
Other income	1,308	1,026	2,564
Total revenues	7,128,928	6,408,534	5,823,554
OPERATING COSTS AND EXPENSES:
Losses and loss expenses	3,490,567	3,197,024	2,948,479
Other operating costs and expenses	2,157,456	2,000,684	1,799,623
Expenses from wholly-owned investees	400,535	388,761	247,222
Interest expense	128,174	123,177	126,302
Total operating costs and expenses	6,176,732	5,709,646	5,121,626
Income before income taxes	952,196	698,888	701,928
Income Tax expense	-302,593	-193,587	-191,285
Net income before noncontrolling interests	649,603	505,301	510,643
Noncontrolling interests	-719	-5,376	-51
Net income to common stockholders	$648,884	$499,925	$510,592
NET INCOME PER SHARE:
Basic (dollars per share)	$5.07	$3.69	$3.72
Diluted (dollars per share)	$4.86	$3.55	$3.56

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Investments:
Fixed maturity securities	$12,705,160	$11,616,844
Equity securities available for sale	170,991	283,338
Arbitrage trading account	450,648	522,128
Loans receivable	322,012	343,583
Investment funds	1,211,401	1,067,495
Equity securities available for sale	731,612	715,242
Total investments	15,591,824	14,548,630
Cash and cash equivalents	674,441	839,738
Premiums and fees receivable	1,651,088	1,557,480
Due from reinsurers	1,503,441	1,533,103
Accrued investment income	120,367	118,329
Prepaid reinsurance premiums	395,748	367,803
Deferred policy acquisition costs	488,525	452,101
Property, furniture and equipment	332,098	339,448
Goodwill	150,944	110,146
Accrued investment income	371,034	304,936
Deferred federal and foreign income taxes	0	20,120
Current federal and foreign income taxes	67,623	24,737
Other assets	369,558	335,225
Total assets	21,716,691	20,551,796
Liabilities:
Reserves for losses and loss expenses	10,369,701	10,080,941
Unearned premiums	3,026,732	2,781,437
Due to reinsurers	237,270	276,755
Trading account securities sold but not yet purchased	106,079	162,278
Deferred federal and foreign income taxes	37,452	0
Other liabilities	859,736	848,749
Subordinated debentures	340,060	339,800
Senior notes and other debt	2,115,527	1,692,442
Total liabilities	17,092,557	16,182,402
Equity:
Preferred stock, par value $.10 per share: Authorized 5,000,000 shares; issued and outstanding - none	0	0
Common stock, par value $.20 per share: Authorized 500,000,000 shares, issued and outstanding, net of treasury shares, 132,233,167 and 136,017,732 shares, respectively	47,024	47,024
Additional paid-in capital	991,512	967,440
Retained earnings	5,732,410	5,265,015
Accumulated other comprehensive income	183,550	189,391
Treasury stock, at cost, 108,369,082 and 102,884,751 shares, respectively	-2,364,551	-2,132,835
Total common stockholders’ equity	4,589,945	4,336,035
Noncontrolling interests	34,189	33,359
Total equity	4,624,134	4,369,394
Total liabilities and equity	$21,716,691	$20,551,796

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Preferred stock, par value (dollars per share)	$0.10	$0.10
Preferred stock, authorized (shares)	5,000,000	5,000,000
Preferred stock, issued (shares)	0	0
Preferred stock, outstanding (shares)	0	0
Common stock, par value (dollars per share)	$0.20	$0.20
Common stock, authorized (shares)	500,000,000	500,000,000
Common stock, issued (shares)	126,748,836	132,233,167
Common stock, outstanding (shares)	126,748,836	132,233,167
Treasury stock, at cost (shares)	108,369,082	102,884,751

Consolidated_Statements_of_Sto

Consolidated Statements of Stockholders' Equity (USD $)	Total	Common stocks	Additional Paid In Capital	Retained Earnings	Accumulated Other Comprehensive Income	Unrealized Investment gains (losses)	Currency translation adjustments	Net pension asset	Treasury Stock	Noncontrolling Interests
In Thousands, unless otherwise specified
Beginning of period at Dec. 31, 2011		$47,024	$941,109	$4,491,162		$430,419	($61,239)	($14,329)	($1,880,790)	$7,526
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock options exercised and restricted units issued including tax benefit			-22,125
Restricted stock units expensed			25,728
Stock issued			454						581
Net income (loss)	510,643			510,592						51
Dividends				-183,947
Unrealized gains (losses) on securities not other-than-temporarily impaired	87,316					84,229
Unrealized gains on other-than-temporarily impaired securities						3,010
Net change in period	24,563						24,563
Net change in period	-1,022							-1,022
Stock exercised/vested									45,253
Stock repurchased									-134,455
Acquisition of noncontrolling interest										21,595
Other comprehensive income, net of tax	110,857									77
End of period at Dec. 31, 2012		47,024	945,166	4,817,807	465,631	517,658	-36,676	-15,351	-1,969,411	29,249
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock options exercised and restricted units issued including tax benefit			-1,143
Restricted stock units expensed			22,881
Stock issued			536						597
Net income (loss)	505,301			499,925						5,376
Dividends				-52,717
Unrealized gains (losses) on securities not other-than-temporarily impaired	-261,064					-261,791
Unrealized gains on other-than-temporarily impaired securities						699
Net change in period	-23,848						-23,848
Net change in period	8,700							8,700
Stock exercised/vested									2,452
Stock repurchased									-166,473
Acquisition of noncontrolling interest										-1,294
Other comprehensive income, net of tax	-276,212				-276,212		-23,848	8,700		28
End of period at Dec. 31, 2013	4,369,394	47,024	967,440	5,265,015	189,391	256,566	-60,524	-6,651	-2,132,835	33,359
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock options exercised and restricted units issued including tax benefit			-4,485
Restricted stock units expensed			27,966
Stock issued			591						594
Net income (loss)	649,603			648,884						719
Dividends				-181,489
Unrealized gains (losses) on securities not other-than-temporarily impaired	49,666					49,071
Unrealized gains on other-than-temporarily impaired securities						562
Net change in period	-62,125						-62,125
Net change in period	6,651							6,651
Stock exercised/vested									6,623
Stock repurchased									-238,933
Acquisition of noncontrolling interest										78
Other comprehensive income, net of tax	-5,808				-5,808		-62,125	6,651		33
End of period at Dec. 31, 2014	$4,624,134	$47,024	$991,512	$5,732,410	$183,550	$306,199	($122,649)	$0	($2,364,551)	$34,189

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net income before noncontrolling interests	$649,603	$505,301	$510,643
Other comprehensive income:
Change in unrealized translation adjustments	-62,125	-23,848	24,563
Change in unrealized investment gains (losses), net of taxes	49,666	-261,064	87,316
Change in unrecognized pension obligation, net of taxes	6,651	8,700	-1,022
Other comprehensive income (loss)	-5,808	-276,212	110,857
Comprehensive income	643,795	229,089	621,500
Comprehensive income to the noncontrolling interest	-752	-5,404	-128
Comprehensive income to common shareholders	$643,043	$223,685	$621,372

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
CASH FROM OPERATING ACTIVITIES:
Net income to common stockholders	$648,884	$499,925	$510,592
Adjustments to reconcile net income to net cash from operating activities:
Net investment gains	-254,852	-121,544	-210,465
Depreciation and amortization	88,836	103,090	103,419
Noncontrolling interests	719	5,376	51
Investment funds	-131,649	-67,712	-77,015
Stock incentive plans	28,068	23,784	26,763
Change in:
Arbitrage trading account	-50,817	-10,324	-1,424
Premiums and fees receivable	-104,174	-138,027	-228,756
Reinsurance accounts	-33,445	-171,263	-216,968
Deferred policy acquisition costs	-42,789	-52,124	-38,656
Increase (Decrease) in Income Taxes	-40,935	-45,613	5,914
Current Income Tax Expense (Benefit)	271,306	139,164	179,368
Deferred income taxes	30,812	56,281	13,240
Reserves for losses and loss expenses	376,617	372,002	406,763
Unearned premiums	277,826	323,160	279,986
Other	-58,254	42,787	102,014
Net cash from operating activities	734,847	819,798	675,458
CASH FLOWS USED IN INVESTING ACTIVITIES:
Proceeds from sale of fixed maturity securities	633,459	1,344,707	838,576
Proceeds from sale of equity securities	113,251	267,554	409,610
Distributions from (contributions to) investment funds	69,319	-236,580	77,930
Proceeds from maturities and prepayments of fixed maturity securities	2,605,839	2,718,156	2,291,105
Purchase of fixed maturity securities	-4,292,165	-4,198,135	-3,617,002
Purchase of equity securities	-31,207	-156,557	-284,991
Real estate purchased	-213,159	-107,352	-256,386
Proceeds from Sale of Buildings	343,723	0	0
Change in loans receivable	21,608	-30,974	-124,776
Net additions to property, furniture and equipment	-41,958	-63,150	-40,556
Change in balances due from security brokers	32,617	-26,155	-25,799
Proceeds from Sales of Business, Affiliate and Productive Assets	15,783
Payment for business purchased, net of cash acquired	-65,421	-56,878	-42,779
Net cash used in investing activities	-808,311	-545,364	-775,068
CASH FLOWS FROM (USED IN) FINANCING ACTIVITIES:
Net proceeds from issuance of debt	354,012	346,822	369,291
Net proceeds from stock options exercised	0	53	7,660
Repayment of senior notes and other debt	-3,700	-465,389	0
Cash dividends to common stockholders	-181,489	-52,717	-183,947
Purchase of common treasury shares	-238,933	-166,473	-127,663
Other	337	7,442	31,851
Net cash from (used in) financing activities	-69,773	-330,262	97,192
Net impact on cash due to change in foreign exchange rates	-22,060	-10,104	-3,654
Net decrease in cash and cash equivalents	-165,297	-65,932	-6,072
Cash and cash equivalents at beginning of year	839,738	905,670	911,742
Cash and cash equivalents at end of year	$674,441	$839,738	$905,670

Summary_of_Significant_Account

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies
	(A) Principles of consolidation and basis of presentation
	The consolidated financial statements, which include the accounts of W. R. Berkley Corporation and its subsidiaries (the "Company"), have been prepared on the basis of U.S. generally accepted accounting principles ("GAAP"). All significant intercompany transactions and balances have been eliminated. Reclassifications have been made in the 2013 and 2012 financial statements to conform to the presentation of the 2014 financial statements. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the revenues and expenses reflected during the reporting period. The most significant items on our balance sheet that involve a greater degree of accounting estimates that are subject to change in the future are the valuation of investments, other-than-temporary impairments, loss and loss adjustment expense reserves and premium estimates. Actual results could differ from those estimates.
	(B) Revenue recognition
	Insurance premiums are recognized as written at the inception of the policy. Reinsurance premiums are estimated based upon information received from ceding companies, and subsequent differences from such estimates are recorded in the period they are determined. Insurance and reinsurance premiums are primarily earned on a pro rata basis over the policy term. Fees for services are earned over the period that the services are provided.
	Audit premiums are recognized when they are reliably determinable. The change in accruals for earned but unbilled audit premiums increased net premiums written and premiums earned by $9 million, $12 million and $7 million in 2014, 2013 and 2012, respectively.
	Revenues from wholly-owned investees are derived from aircraft services provided to the general, commercial and military aviation markets. These services include (i) the distribution, manufacturing, repair and overhaul of aircraft parts and components, (ii) the sale of new and used aircraft, and (iii) avionics, fuel, maintenance, storage and charter services. Revenue is recognized upon the shipment of parts, the delivery of aircraft, the delivery of fuel, and upon completion of services.
	(C) Cash and cash equivalents
	Cash equivalents consist of funds invested in money market accounts and investments with an effective maturity of three months or less when purchased.
	(D) Investments
	Fixed maturity securities classified as available for sale are carried at estimated fair value, with unrealized gains and losses, net of applicable income taxes, excluded from earnings and reported as a component of comprehensive income and a separate component of stockholders' equity. Fixed maturity securities that the Company has the positive intent and ability to hold to maturity are classified as held to maturity and reported at amortized cost. Investment income from fixed maturity securities is recognized based on the constant effective yield method. Premiums and discounts on mortgage-backed securities are adjusted for the effects of actual and anticipated prepayments on a retrospective basis.
	Equity securities classified as available for sale are carried at estimated fair value, with unrealized gains and losses, net of applicable income taxes, excluded from earnings and reported as a component of comprehensive income and a separate component of stockholders' equity.
	Equity and fixed maturity securities that the Company purchased with the intent to sell in the near-term are classified as trading account securities and are reported at estimated fair value. Realized and unrealized gains and losses from trading activity are reported as net investment income and are recorded at the trade date. Short sales and short call options are presented as trading securities sold but not yet purchased. Unsettled trades and the net margin balances held by the clearing broker are presented as a trading account receivable from brokers and clearing organizations.
	Investment funds are carried under the equity method of accounting. For certain investment funds, the Company's share of the earnings or losses is reported on a one-quarter lag in order to facilitate the timely completion of the Company's consolidated financial statements.
	Loans receivable primarily represent commercial real estate mortgage loans and bank loans and are carried at amortized cost. The Company monitors the performance of its loans receivable and establishes an allowance for loan losses for loans where the Company determines it is probable that the contractual terms will not be met, with a corresponding charge to earnings. For loans that are evaluated individually and deemed to be impaired, the Company establishes a specific allowance based on a discounted cash flow analysis and comparable cost and sales methodologies, if appropriate. Individual loans that are not considered impaired and smaller-balance homogeneous loans are evaluated collectively and a general allowance is established if it is considered probable that a loss has been incurred.
	The accrual of interest on loans receivable is discontinued if the loan is 90 days past due based on the contractual terms of the loan unless the loan is adequately secured and in process of collection. In general, loans are placed on non-accrual status or charged off at an earlier date if collection of principal or interest is considered doubtful. Interest on these loans is accounted for on a cash basis until qualifying for return to accrual status. Loans are returned to accrual status when all principal and interest amounts contractually due are brought current and future payments are reasonably assured.
	Fair value is defined as “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.” Fair value of investments is determined based on a fair value hierarchy that prioritizes the use of observable inputs over the use of unobservable inputs and requires the use of observable inputs when available. (See Note 13 of the Notes to Consolidated Financial Statements.)
	Realized gains or losses represent the difference between the cost of securities sold and the proceeds realized upon sale and are recorded at the trade date. The Company uses primarily the first-in, first-out method to determine the cost of securities sold.
	The cost of securities is adjusted where appropriate to include a provision for a decline in value which is considered to be other than temporary. An other-than-temporary decline is considered to occur in investments where there has been a sustained reduction in fair value and where the Company does not expect to recover the cost basis of the investment prior to the time of sale or maturity. Since equity securities do not have a contractual cash flow or a maturity, the Company considers whether the price of an equity security is expected to recover within a reasonable period of time.
	For fixed maturity securities that the Company intends to sell or, more likely than not, would be required to sell, a decline in value below amortized cost is considered to be an other-than-temporary impairment (“OTTI”). The amount of OTTI is equal to the difference between amortized cost and fair value at the balance sheet date. For fixed maturity securities that the Company does not intend to sell or believes that it is more likely than not it would not be required to sell, a decline in value below amortized cost is considered to be an OTTI if the Company does not expect to recover the entire amortized cost basis of a security (i.e., the present value of cash flows expected to be collected is less than the amortized cost basis of the security). The portion of the decline in value considered to be a credit loss (i.e., the difference between the present value of cash flows expected to be collected and the amortized cost basis of the security) is recognized in earnings. The portion of the decline in value not considered to be a credit loss (i.e., the difference in the present value of cash flows expected to be collected and the fair value of the security) is recognized in other comprehensive income.
	Impairment assessments for structured securities, including mortgage-backed securities and asset-backed securities, collateralized debt obligations and corporate debt, are generally evaluated based on the performance of the underlying collateral under various economic and default scenarios that may involve subjective judgments and estimates by management. Modeling these securities involves various factors, such as projected default rates, the nature and realizable value of the collateral, if any, the ability of the issuer to make scheduled payments, historical performance and other relevant economic and performance factors. If an OTTI determination is made, a discounted cash flow analysis is used to ascertain the amount of the credit impairment.
	Real estate held for investment purposes is initially recorded at the purchase price, which is generally fair value, and is subsequently reported at cost less accumulated depreciation. Real estate taxes, interest and other costs incurred during development and construction are capitalized. Buildings are depreciated on a straight-line basis over the estimated useful lives of the building. Minimum rental income is recognized on a straight-line basis over the lease term. Income and expenses from real estate are reported as net investment income. The carrying value of real estate is reviewed for impairment and an impairment loss is recognized if the estimated undiscounted cash flows from the use and disposition of the property are less than the carrying value of the property.
	(E) Per share data
	The Company presents both basic and diluted net income per share (“EPS”) amounts. Basic EPS is calculated by dividing net income by weighted average number of common shares outstanding during the year. Diluted EPS is based upon the weighted average number of common and common equivalent shares outstanding during the year and is calculated using the treasury stock method for stock incentive plans. Common equivalent shares are excluded from the computation in periods in which they have an anti-dilutive effect. Stock options for which the exercise price exceeds the average market price over the period have an anti-dilutive effect on EPS and, accordingly, are excluded from the calculation.
	(F) Deferred policy acquisition costs
	Acquisition costs associated with the successful acquisition of new and renewed insurance and reinsurance contracts are deferred and amortized ratably over the terms of the related contracts. Ceding commissions received on reinsurance contracts are netted against acquisition costs and are recognized ratably over the life of the contract. Deferred policy acquisition costs are presented net of unearned ceding commissions. Deferred policy acquisition costs are comprised primarily of commissions, as well as employment-related underwriting costs and premium taxes. Deferred policy acquisition costs are reviewed to determine if they are recoverable from future income and, if not, are charged to expense. The recoverability of deferred policy acquisition costs is evaluated separately by each of our operating companies for each of their major lines of business. Future investment income is taken into account in measuring the recoverability of deferred policy acquisition costs.
	(G) Reserves for losses and loss expenses
	Reserves for losses and loss expenses are an accumulation of amounts determined on the basis of (1) evaluation of claims for business written directly by the Company; (2) estimates received from other companies for reinsurance assumed by the Company; and (3) estimates for losses incurred but not reported (based on Company and industry experience). These estimates are periodically reviewed and, as experience develops and new information becomes known, the reserves are adjusted as necessary. Such adjustments are reflected in the statements of income in the period in which they are determined. The Company discounts its reserves for excess and assumed workers' compensation claims using a risk-free or statutory rate. (See Note 14 of Notes to Consolidated Financial Statements.)
	(H) Reinsurance ceded
	The unearned portion of premiums ceded to reinsurers is reported as prepaid reinsurance premiums and earned ratably over the policy term. The estimated amounts of reinsurance recoverable on unpaid losses are reported as due from reinsurers. To the extent any reinsurer does not meet its obligations under reinsurance agreements, the Company must discharge its liability. Amounts due from reinsurers are reflected net of funds held where the right of offset is present. The Company has provided reserves for estimated uncollectible reinsurance.
	(I) Deposit accounting
	Contracts that do not meet the risk transfer requirements of GAAP are accounted for using the deposit accounting method. Under this method, an asset or liability is recognized at the inception of the contract based on consideration paid or received. The amount of the deposit asset or liability is adjusted at subsequent reporting dates using the interest method with a corresponding credit or charge to interest income or expense. Deposit liabilities for assumed reinsurance contracts were $68 million and $72 million at December 31, 2014 and 2013, respectively.
	(J) Federal and foreign income taxes
	The Company files a consolidated income tax return in the U.S. and foreign tax returns in countries where it has overseas operations. The Company's method of accounting for income taxes is the asset and liability method. Under this method, deferred tax assets and liabilities are measured using tax rates currently in effect or expected to apply in the years in which those temporary differences are expected to reverse. Interest and penalties, if any, are reported as income tax expense. The Company believes there are no tax positions that would require disclosure under GAAP. Deferred tax assets are reduced by a valuation allowance if it is more likely than not that all or a portion of the deferred tax assets will not be realized.
	(K) Foreign currency
	Gains and losses resulting from foreign currency transactions (transactions denominated in a currency other than the entity's functional currency) are reported on the statements of income as other operating costs and expenses. Unrealized gains or losses resulting from translating the results of non-U.S. dollar denominated operations are reported in accumulated other comprehensive income. Revenues and expenses denominated in currencies other than U.S. dollars are translated at the weighted average exchange rate during the year. Assets and liabilities are translated at the rate of exchange in effect at the balance sheet date.
	(L) Property, furniture and equipment
	Property, furniture and equipment are carried at cost less accumulated depreciation. Depreciation is calculated using the estimated useful lives of the respective assets. Depreciation expense was $44 million, $38 million and $38 million for 2014, 2013 and 2012, respectively.
	(M) Comprehensive income
	Comprehensive income encompasses all changes in stockholders' equity (except those arising from transactions with stockholders) and includes net income, net unrealized holding gains or losses on available for sale securities, unrealized foreign currency translation adjustments and changes in unrecognized pension obligations.
	(N) Goodwill and other intangible assets
	Goodwill and other intangible assets are tested for impairment on an annual basis and at interim periods where circumstances require. The Company's impairment test as of December 31, 2014 indicated that there were no impairment losses related to goodwill and other intangible assets. Intangible assets of $96 million and $72 million are included in other assets as of December 31, 2014 and 2013, respectively.
	(O) Stock options
	The costs resulting from all share-based payment transactions with employees are recognized in the consolidated financial statements using a fair-value-based measurement method.
	(P) Statements of cash flows
	Interest payments were $120 million, $125 million and $119 million in 2014, 2013 and 2012, respectively. Income taxes paid were $314 million, $186 million and $133 million in 2014, 2013 and 2012, respectively. Other non-cash items include acquisitions, unrealized investment gains and losses and pension expense. (See Note 2, Note 11 and Note 25 of Notes to Consolidated Financial Statements.)
	(Q) Recent accounting pronouncements
	In January 2014, the Financial Accounting Standards Board issued guidance relating to Accounting for Investments in Qualified Affordable Housing Projects. This guidance modified the amortization method on these investments and the statement of operations classification as pre-adoption amounts were presented in both pre-tax income and income tax expense while post adoption all impacts are recorded in income tax expense. The Company adopted this guidance effective January 1, 2014, and the impact of applying this guidance was immaterial.
	All recently issued but not yet effective accounting and reporting standards are either not applicable to the Company or are not expected to have a material impact on the Company.

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2014
Business Combinations [Abstract]
Acquisitions	Acquisitions / Dispositions
	In 2014, the Company acquired a specialty property and casualty insurance distribution company for $83 million. The fair values of the assets acquired and liabilities assumed have been estimated based on a valuation prepared by a third party. The estimated useful lives of the intangible assets acquired range from 7 years to 15 years, with approximately $10 million having an indefinite life.
	In 2012, the Company acquired a 49% interest in a worldwide supplier of after-market original equipment manufacturer (OEM) parts, systems and custom logistic support services for military aircraft operations for $43 million. In 2013, the Company acquired the remaining 51% of this business for $43 million. The estimated useful lives of the intangible assets acquired range from 2 years to 15 years, with approximately $3 million having an indefinite life.
	In 2014, the Company sold an aviation-related business for $16 million. The business had a net carrying value of $15 million, comprised of $7 million of goodwill, $6 million of other assets, $4 million of furniture and equipment and $2 million of liabilities.
	The following table summarizes the estimated fair value of net assets acquired and liabilities assumed for business combinations completed in 2014 and 2013:
	(In thousands)	2014			2013
	Cash and cash equivalents	$	17,457		$	3,911
	Real estate, furniture and equipment	669			898
	Goodwill and other intangibles assets	79,646			64,464
	Premium and service fee receivable	24,432			—
	Other assets	2,590			60,661
	Total assets acquired	124,794			129,934
	Deferred federal income tax	(7,107		)	—
	Debt	—			(27,612		)
	Other liabilities assumed	(34,809		)	(17,076		)
	Net assets acquired	$	82,878		$	85,246

Consolidated_Statement_of_Comp

Consolidated Statement of Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Consolidated Statement of Comprehensive Income (Loss)	Consolidated Statement of Comprehensive Income (Loss)
	The following table presents the components of the changes in accumulated other comprehensive income (loss) (AOCI) as of and for the year ended December 31, 2014:
	(In thousands)	Unrealized investment gains (losses)				Currency translation adjustments			Net pension asset				Accumulated other comprehensive income (loss)
	Changes in AOCI
	Beginning of period	$	256,566			$	(60,524	)	$	(6,651	)		$	189,391
	Other comprehensive income (loss) before reclassifications	98,294				(62,125		)	—				36,169
	Amounts reclassified from AOCI	(48,628		)		—			6,651				(41,977		)
	Other comprehensive income (loss)	49,666				(62,125		)	6,651				(5,808		)
	Unrealized investment gain related to non-controlling interest	(33		)		—			—				(33		)
	Ending balance	$	306,199			$	(122,649	)	$	—			$	183,550
	Amounts reclassified from AOCI
	Pre-tax	$	(74,812	)	-1	$	—		$	10,232		-3	$	(64,580	)
	Tax effect	26,184			-2	—			(3,581		)	-2	22,603
	After-tax amounts reclassified	$	(48,628	)		$	—		$	6,651			$	(41,977	)
	Other comprehensive income (loss)
	Pre-tax	$	72,889			$	(62,125	)	$	10,232			$	20,996
	Tax effect	(23,223		)		—			(3,581		)		(26,804		)
	Other comprehensive income (loss)	$	49,666			$	(62,125	)	$	6,651			$	(5,808	)
	The following table presents the components of the changes in accumulated other comprehensive income (loss) (AOCI) as of and for the year ended December 31, 2013:
	(In thousands)	Unrealized investment gains (losses)				Currency translation adjustments			Net pension asset				Accumulated other comprehensive income (loss)
	Changes in AOCI
	Beginning of period	$	517,658			$	(36,676	)	$	(15,351	)		$	465,631
	Other comprehensive income (loss) before reclassifications	(193,188		)		(23,848		)	—				(217,036		)
	Amounts reclassified from AOCI	(67,876		)		—			8,700				(59,176		)
	Other comprehensive income (loss)	(261,064		)		(23,848		)	8,700				(276,212		)
	Unrealized investment gain related to non-controlling interest	(28		)		—			—				(28		)
	Ending balance	$	256,566			$	(60,524	)	$	(6,651	)		$	189,391
	Amounts reclassified from AOCI
	Pre-tax	$	(104,425	)	-1	$	—		$	13,387		-3	$	(91,038	)
	Tax effect	36,549			-2	—			(4,687		)	-2	31,862
	After-tax amounts reclassified	$	(67,876	)		$	—		$	8,700			$	(59,176	)
	Other comprehensive income (loss)
	Pre-tax	$	(401,637	)		$	(23,848	)	$	13,387			$	(412,098	)
	Tax effect	140,573				—			(4,687		)		135,886
	Other comprehensive income (loss)	$	(261,064	)		$	(23,848	)	$	8,700			$	(276,212	)
	_______________
	(1) Net investment gains in the consolidated statements of income.
	(2) Income tax expense in the consolidated statements of income.
	(3) Other operating costs and expenses in the consolidated statements of income.

Investments_In_Fixed_Maturity_

Investments In Fixed Maturity Securities (Debt Securities)	12 Months Ended
	Dec. 31, 2012
Debt Securities
Schedule of Marketable Securities [Line Items]
Investments In Fixed Maturity Securities	Investments in Fixed Maturity Securities
	At December 31, 2014 and 2013, investments in fixed maturity securities were as follows:
	(In thousands)	Amortized		Gross		Gross			Fair		Carrying
		Cost		Unrealized		Unrealized			Value		Value
				Gains		Losses
	December 31, 2014
	Held to maturity:
	State and municipal	$	72,901	$	17,501	$	—		$	90,402	$	72,901
	Residential mortgage-backed securities	23,278		2,854		—			26,132		23,278
	Corporate	4,998		291		—			5,289		4,998
	Total held to maturity	101,177		20,646		—			121,823		101,177
	Available for sale:
	U.S. government and government agency	773,192		33,353		(3,157		)	803,388		803,388
	State and municipal	4,137,866		229,150		(4,020		)	4,362,996		4,362,996
	Mortgage-backed securities:
	Residential(1)	1,201,924		27,124		(9,449		)	1,219,599		1,219,599
	Commercial	74,479		1,610		(52		)	76,037		76,037
	Corporate	5,036,958		187,960		(24,781		)	5,200,137		5,200,137
	Foreign government	897,668		62,223		(18,065		)	941,826		941,826
	Total available for sale	12,122,087		541,420		(59,524		)	12,603,983		12,603,983
	Total investment in fixed maturity securities	$	12,223,264	$	562,066	$	(59,524	)	$	12,725,806	$	12,705,160
	December 31, 2013
	Held to maturity:
	State and municipal	$	68,929	$	11,172	$	—		$	80,101	$	68,929
	Residential mortgage-backed securities	27,393		3,311		—			30,704		27,393
	Corporate	4,998		417		—			5,415		4,998
	Total held to maturity	101,320		14,900		—			116,220		101,320
	Available for sale:
	U.S. government and government agency	858,319		34,522		(7,982		)	884,859		884,859
	State and municipal	4,085,791		162,330		(29,837		)	4,218,284		4,218,284
	Mortgage-backed securities:
	Residential(1)	1,248,693		25,895		(25,941		)	1,248,647		1,248,647
	Commercial	76,454		5,670		(988		)	81,136		81,136
	Corporate	4,076,585		156,256		(30,100		)	4,202,741		4,202,741
	Foreign government	844,469		51,674		(16,286		)	879,857		879,857
	Total available for sale	11,190,311		436,347		(111,134		)	11,515,524		11,515,524
	Total investment in fixed maturity securities	$	11,291,631	$	451,247	$	(111,134	)	$	11,631,744	$	11,616,844
	_______________________________________
	-1	Gross unrealized losses for mortgage-backed securities include $1,095,671 and $1,961,247, as of December 31, 2014 and 2013, respectively, related to the non-credit portion of OTTI recognized in other comprehensive income.
	The amortized cost and fair value of fixed maturity securities at December 31, 2014, by contractual maturity, are shown below. Actual maturities may differ from contractual maturities because certain issuers may have the right to call or prepay obligations.
	(In thousands)	Amortized		Fair Value
		Cost
	Due in one year or less	$	884,831	$	895,004
	Due after one year through five years	3,953,003		4,119,946
	Due after five years through ten years	3,600,155		3,790,402
	Due after ten years	2,485,594		2,598,686
	Mortgage-backed securities	1,299,681		1,321,768
	Total	$	12,223,264	$	12,725,806
	At December 31, 2014 and 2013, there were no investments, other than investments in United States government and government agency securities, which exceeded 10% of common stockholders’ equity. At December 31, 2014, investments with a carrying value of $1,151 million were on deposit in custodial or trust accounts, of which $906 million was on deposit with state insurance departments, $188 million was on deposit in support of the Company’s underwriting activities at Lloyd’s, $44 million was on deposit as security for reinsurance clients and $13 million was on deposit as security for letters of credit issued in support of the Company’s reinsurance operations.

Investments_In_Equity_Securiti

Investments In Equity Securities Available for Sale (Equity securities available for sale)	12 Months Ended
	Dec. 31, 2014
Equity securities available for sale
Schedule of Available-for-sale Securities [Line Items]
Investments in Equity Securities	Investments in Equity Securities Available for Sale
	At December 31, 2014 and 2013, investments in equity securities available for sale were as follows:
	(In thousands)	Cost		Gross		Gross			Fair		Carrying
				Unrealized		Unrealized			Value		Value
				Gains		Losses
	December 31, 2014
	Common stocks	$	69,870	$	11,929	$	(5,453	)	$	76,346	$	76,346
	Preferred stocks	90,425		8,385		(4,165		)	94,645		94,645
	Total	$	160,295	$	20,314	$	(9,618	)	$	170,991	$	170,991
	December 31, 2013
	Common stocks	$	118,536	$	42,239	$	—		$	160,775	$	160,775
	Preferred stocks	85,091		43,791		(6,319		)	122,563		122,563
	Total	$	203,627	$	86,030	$	(6,319	)	$	283,338	$	283,338

Arbitrage_Trading_Account

Arbitrage Trading Account	12 Months Ended
	Dec. 31, 2014
Trading Securities and Derivative Instruments [Abstract]
Arbitrage Trading Account	Arbitrage Trading Account
	At December 31, 2014 and 2013, the fair value and carrying value of the arbitrage trading account were $451 million and $522 million, respectively. The primary focus of the trading account is merger arbitrage. Merger arbitrage is the business of investing in the securities of publicly held companies which are the targets in announced tender offers and mergers. Arbitrage investing differs from other types of investing in its focus on transactions and events believed likely to bring about a change in value over a relatively short time period (usually four months or less). The Company believes that this makes arbitrage investments less vulnerable to changes in general financial market conditions.
	The Company uses put options, call options and swap contracts in order to mitigate the impact of potential changes in market conditions on the merger arbitrage trading account. These options and contracts are reported at fair value. As of December 31, 2014, the fair value of long option contracts outstanding was $8 million (notional amount of $133 million) and the fair value of short option contracts outstanding was $2 million (notional amount of $106 million). Other than with respect to the use of these trading account securities, the Company does not make use of derivatives.

Net_Investment_Income

Net Investment Income	12 Months Ended
	Dec. 31, 2014
Net Investment Income [Abstract]
Net Investment Income	Net Investment Income
	Net investment income consists of the following:
	(In thousands)	2014			2013			2012
	Investment income earned on:
	Fixed maturity securities, including cash and cash equivalents and loans receivable	$	439,489		$	442,287		$	479,035
	Equity securities available for sale	6,726			11,380			16,419
	Investment funds	131,649			67,712			77,015
	Arbitrage trading account	22,438			20,431			8,286
	Real estate	10,228			12,498			12,097
	Gross investment income	610,530			554,308			592,852
	Investment expense	(9,645		)	(10,017		)	(6,089		)
	Net investment income	$	600,885		$	544,291		$	586,763

Investment_Funds

Investment Funds	12 Months Ended
	Dec. 31, 2014
Equity Method Investments and Joint Ventures [Abstract]
Investment Funds	Investment Funds
	Investment funds consist of the following:
		Carrying Value				Income
		as of December 31,
	(In thousands)	2014		2013		2014		2013		2012
	Real estate	$	466,703	$	378,435	$	26,233	$	9,315	$	30,196
	Energy	152,056		155,026		12,797		29,739		33,146
	Hedged equity	282,335		271,575		10,760		7,655		5,912
	Other funds	310,307		262,459		81,859		21,003		7,761
	Total	$	1,211,401	$	1,067,495	$	131,649	$	67,712	$	77,015
	Other funds include private equity investments carried on the equity method of accounting, which includes a publicly traded common stock investment in HealthEquity, Inc. (HQY). Our ownership interest in HQY as of December 31, 2014 is 28.1%, with a fair value of $392 million and a carrying value of $45 million.

Real_Estate_Notes

Real Estate (Notes)	12 Months Ended
	Dec. 31, 2014
Real Estate [Abstract]
Real Estate	Real Estate
	Investment in real estate represents directly owned property held for investment, as follows:
		As of December 31,
	(In thousands)	2014		2013
	Properties in operation	$	196,980	$	283,393
	Properties under development	534,632		431,849
	Total	$	731,612	$	715,242
	In 2014, properties in operation included a long-term ground lease in Washington, D.C. and an office building in West Palm Beach, Florida. Properties in operation in 2013 included an office building located in London which was sold during 2014. Properties in operation are net of accumulated depreciation and amortization of $1,609,000 and $17,827,000 as of December 31, 2014 and 2013, respectively. Related depreciation expense was $4,808,000 and $7,474,000 for the years ended December 31, 2014 and 2013, respectively. Future minimum rental income expected on operating leases relating to properties in operation is $11,379,000 in 2015, $11,457,000 in 2016, $11,500,000 in 2017, $10,833,000 in 2018, $7,839,000 in 2019 and $336,653,000 thereafter.
	Properties under development represent the following: an office building in London, a mixed-use project in Washington D.C. and an office complex in New York City. The Company expects to fund further development costs for these projects with a combination of its own funds and external financing.

Loans_Receivable

Loans Receivable	12 Months Ended
	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable, Gross, Allowance, and Net [Abstract]
Loans Receivable	Loans Receivable
	Loans receivable are as follows:
		As of December 31,
	(In thousands)	2014		2013
	Amortized cost:
	Real estate loans	$	243,407	$	282,357
	Commercial loans	78,605		61,226
	Total	$	322,012	$	343,583
	Fair value:
	Real estate loans	$	245,112	$	284,017
	Commercial loans	80,107		62,729
	Total	$	325,219	$	346,746
	Valuation allowance:
	Specific	$	115	$	—
	General	2,371		2,087
	Total	$	2,486	$	2,087
		For the Year Ended December 31,
		2014		2013
	Increase in valuation allowance	$	398	$	308
	Loans receivable in non-accrual status as of December 31, 2014 was $14.2 million, primarily resulting from the transfer of such loans to held-for-sale.
	The Company monitors the performance of its loans receivable and assesses the ability of the borrower to pay principal and interest based upon loan structure, underlying property values, cash flow and related financial and operating performance of the property and market conditions. Loans receivable with a potential for default are further assessed using discounted cash flow analysis and comparable cost and sales methodologies, if appropriate.
	The real estate loans are secured by commercial real estate primarily located in Arizona, Illinois, Maryland, New York, North Carolina, Texas and Virginia. These loans generally earn interest at floating LIBOR-based interest rates and have maturities (inclusive of extension options) through August 2025. The commercial loans are with small business owners who have secured the related financing with the assets of the business. These loans generally earn interest on a fixed basis and have varying maturities not exceeding 10 years.
	The Company utilizes a risk rating system to assign a risk to each of its real estate loans. The loan rating system takes into consideration credit quality indicators including loan to value ratios, which compare the outstanding loan amount to the estimated value of the property, the borrower’s financial condition and performance with respect to loan terms, the Company’s position in the capital structure, and the overall leverage in the capital structure. Based on this rating system, none of the real estate loans were considered to be impaired at December 31, 2014, and accordingly, the Company determined that a specific valuation allowance was not required.

Realized_And_Unrealized_Invest

Realized And Unrealized Investment Gains and Losses	12 Months Ended
	Dec. 31, 2014
Realized and Unrealized Investment Gains (Losses) [Abstract]
Realized and Unrealized Investment Gains and Losses	Realized and Unrealized Investment Gains and Losses
	Realized and unrealized investment gains and losses are as follows:
	(In thousands)	2014			2013			2012
	Realized investment gains and losses:
	Fixed maturity securities:
	Gains	$	39,113		$	48,860		$	34,295
	Losses	(4,420		)	(14,670		)	(6,436		)
	Equity securities available for sale	38,296			70,235			97,300
	Investment funds	96,204			10,976			74,777
	Real estate	85,659			—			—
	Other gains	—			12,185			1,515
	Net realized gains on investments sales	254,852			127,586			201,451
	Net other-than-temporary impairments:
	Other-than-temporary impairments	—			(6,042		)	(4,984		)
	Decrease in valuation allowance	—			—			13,998
	Net other-than-temporary impairments	—			(6,042		)	9,014
	Total net investment gains	254,852			121,544			210,465
	Income tax expense	(89,198		)	(47,426		)	(73,663		)
		$	165,654		$	74,118		$	136,802
	Change in unrealized gains and losses of available for sales securities:
	Fixed maturity securities	$	155,765		$	(401,812	)	$	162,220
	Previously impaired fixed maturity securities	865			1,076			4,631
	Equity securities available for sale	(69,016		)	11,864			(33,199		)
	Investment funds	(14,725		)	(10,250		)	1,630
	Total change in unrealized gains	72,889			(399,122		)	135,282
	Income tax benefit (expense)	(23,223		)	138,058			(47,966		)
	Noncontrolling interests	(33		)	(28		)	(77		)
		$	49,633		$	(261,092	)	$	87,239

Securities_In_An_Unrealized_Lo

Securities In An Unrealized Loss Position	12 Months Ended
	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Securities In An Unrealized Loss Position	Securities in an Unrealized Loss Position
	The following table summarizes all securities in an unrealized loss position at December 31, 2014 and 2013 by the length of time those securities have been continuously in an unrealized loss position.
		Less Than 12 Months						12 Months or Greater				Total
	(In thousands)	Fair			Gross			Fair		Gross		Fair		Gross
		Value			Unrealized			Value		Unrealized		Value		Unrealized
					Losses					Losses				Losses
	December 31, 2014
	U.S. government and government agency	$	84,750		$	522		$	84,850	$	2,635	$	169,600	$	3,157
	State and municipal	158,594			631			150,284		3,389		308,878		4,020
	Mortgage-backed securities	75,739			332			312,922		9,169		388,661		9,501
	Corporate	1,586,238			8,697			214,628		16,084		1,800,866		24,781
	Foreign government	76,471			3,907			85,025		14,158		161,496		18,065
	Fixed maturity securities	1,981,792			14,089			847,709		45,435		2,829,501		59,524
	Common stocks	15,929			5,453			—		—		15,929		5,453
	Preferred stocks	27,126			1,139			22,648		3,026		49,774		4,165
	Equity securities available for sale	43,055			6,592			22,648		3,026		65,703		9,618
	Total	$	2,024,847		$	20,681		$	870,357	$	48,461	$	2,895,204	$	69,142
	December 31, 2013
	U.S. government and government agency	$	260,882		$	7,927		$	2,163	$	55	$	263,045	$	7,982
	State and municipal	899,613			24,503			87,345		5,334		986,958		29,837
	Mortgage-backed securities	578,603			17,964			140,648		8,965		719,251		26,929
	Corporate	1,013,373			17,066			105,074		13,034		1,118,447		30,100
	Foreign government	320,215			16,286			—		—		320,215		16,286
	Fixed maturity securities	3,072,686			83,746			335,230		27,388		3,407,916		111,134
	Common stocks	—			—			—		—		—		—
	Preferred stocks	13,291			513			19,868		5,806		33,159		6,319
	Equity securities available for sale	13,291			513			19,868		5,806		33,159		6,319
	Total	$	3,085,977		$	84,259		$	355,098	$	33,194	$	3,441,075	$	117,453
	Fixed Maturity Securities — A summary of the Company’s non-investment grade fixed maturity securities that were in an unrealized loss position at December 31, 2014 is presented in the table below:
	(Dollars in thousands)	Number of		Aggregate			Gross
		Securities		Fair Value			Unrealized
							Loss
	Mortgage-backed securities	9		$	28,537		$	1,699
	Corporate	10		24,528			742
	Foreign government	2		11,177			247
	Total	21		$	64,242		$	2,688
	For OTTI of fixed maturity securities that management does not intend to sell or, more likely than not, would not be required to sell, the portion of the decline in value considered to be due to credit factors is recognized in earnings and the portion of the decline in value considered to be due to non-credit factors is recognized in other comprehensive income.
	The Company has evaluated its fixed maturity securities in an unrealized loss position and believes the unrealized losses are due primarily to temporary market and sector-related factors rather than to issuer-specific factors. None of these securities are delinquent or in default on financial covenants. Based on its assessment of these issuers, the Company expects them to continue to meet their contractual payment obligations as they become due and does not consider any of these securities to be OTTI.
	Preferred Stocks – At December 31, 2014, there were six preferred stocks in an unrealized loss position, with an aggregate fair value of $49.8 million and a gross unrealized loss of $4.2 million. Four of these preferred stocks are rated non-investment grade, and none are delinquent. Management believes the unrealized losses are due primarily to market and sector related factors and does not consider these to be OTTI.
	Common Stocks – At December 31, 2014, there were two common stocks in an unrealized loss position, with an aggregate fair value of $15.9 million and a gross unrealized loss of $5.5 million. Based on management's view on the underlying securities, the Company does not consider the common stocks to be OTTI.

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements
	The Company’s fixed maturity, equity securities available for sale and its trading account securities are carried at fair value. Fair value is defined as “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.” The Company utilizes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for similar assets in active markets. Level 3 inputs are unobservable inputs for the asset or liability. Unobservable inputs may only be used to measure fair value to the extent that observable inputs are not available.
	Because many fixed maturity securities do not trade on a daily basis, the Company utilizes pricing models and processes which may include benchmark curves, benchmarking of like securities, sector groupings and matrix pricing. Market inputs used to evaluate securities include benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers and reference data. Quoted prices are often unavailable for recently issued securities, securities that are infrequently traded or securities that are only traded in private transactions. For publicly traded securities for which quoted prices are unavailable, the Company determines fair value based on independent broker quotations and other observable market data. For securities traded only in private negotiations, the Company determines fair value based primarily on the cost of such securities, which is adjusted to reflect prices of recent placements of securities of the same issuer, financial projections, credit quality and business developments of the issuer and other relevant information.
	The following tables present the assets and liabilities measured at fair value on a recurring basis as of December 31, 2014 and 2013 by level:
	(In thousands)	Total		Level 1			Level 2			Level 3
	December 31, 2014
	Assets:
	Fixed maturity securities available for sale:
	U.S. government and government agency	$	803,388	$	—		$	803,388		$	—
	State and municipal	4,362,996		—			4,362,996			—
	Mortgage-backed securities	1,295,636		—			1,295,636			—
	Corporate	5,200,137		—			5,179,372			20,765
	Foreign government	941,826		—			941,826			—
	Total fixed maturity securities available for sale	12,603,983		—			12,583,218			20,765
	Equity securities available for sale:
	Common stocks	76,346		65,605			—			10,741
	Preferred stocks	94,645		—			90,932			3,713
	Total equity securities available for sale	170,991		65,605			90,932			14,454
	Arbitrage trading account	450,648		295,047			154,881			720
	Total	$	13,225,622	$	360,652		$	12,829,031		$	35,939
	Liabilities:
	Securities sold but not yet purchased	$	106,079	$	106,074		$	5		$	—
	December 31, 2013
	Assets:
	Fixed maturity securities available for sale:
	U.S. government and government agency	$	884,859	$	—		$	884,859		$	—
	State and municipal	4,218,284		—			4,218,284			—
	Mortgage-backed securities	1,329,783		—			1,329,783			—
	Corporate	4,202,741		—			4,159,877			42,864
	Foreign government	879,857		—			879,857			—
	Total fixed maturity securities available for sale	11,515,524		—			11,472,660			42,864
	Equity securities available for sale:
	Common stocks	160,775		159,537			—			1,238
	Preferred stocks	122,563		—			118,811			3,752
	Total equity securities available for sale	283,338		159,537			118,811			4,990
	Arbitrage trading account	522,128		192,281			328,067			1,780
	Total	$	12,320,990	$	351,818		$	11,919,538		$	49,634
	Liabilities:
	Securities sold but not yet purchased	$	162,278	$	162,126		$	152		$	—
	There were no transfers between Levels 1 and 2 for the years ended December 31, 2014 and 2013.
	The following tables summarize changes in Level 3 assets and liabilities for the years ended December 31, 2014 and 2013:
		Gains (Losses) Included in:
	(In thousands)	Beginning Balance		Earnings			Other Comprehensive Income			Purchases		Sales			Paydowns/Maturities			In		Out			Ending Balance
	Year ended December 31, 2014
	Assets:
	Fixed maturity securities available for sale:
	Corporate	$	42,864	$	47		$	(3,711	)	$	238	$	(15,244	)	$	(3,429	)	$	—	$	—		$	20,765
	Total	42,864		47			(3,711		)	238		(15,244		)	(3,429		)	—		—			20,765
	Equity securities available for sale:
	Common stocks	1,238		—			(911		)	11,343		(929		)	—			—		—			10,741
	Preferred stocks	3,752		(17		)	—			3,430		(3,452		)	—			—		—			3,713
	Total	4,990		(17		)	(911		)	14,773		(4,381		)	—			—		—			14,454
	Arbitrage trading account	1,780		2,274			—			4,942		(14,073		)	—			9,064		(3,267		)	720
	Total	$	49,634	$	2,304		$	(4,622	)	$	19,953	$	(33,698	)	$	(3,429	)	$	9,064	$	(3,267	)	$	35,939
	Liabilities:
	Securities sold but not yet purchased	$	—	$	(20	)	$	—		$	31	$	(11	)	$	—		$	—	$	—		$	—
	Year ended December 31, 2013
	Assets:
	Fixed maturity securities available for sale:
	Corporate	$	59,065	$	677		$	309		$	170	$	(4,753	)	$	(12,604	)	$	—	$	—		$	42,864
	Total	59,065		677			309			170		(4,753		)	(12,604		)	—		—			42,864
	Equity securities available for sale:
	Common stocks	1,408		—			—			—		(170		)	—			—		—			1,238
	Preferred stocks	621		(299		)	—			3,430		—			—			—		—			3,752
Total	2,029		(299		)	—			3,430		(170		)	—			—		—			4,990
Arbitrage trading account	928		1,458			730			824		(853		)	—			22		(1,329		)	1,780
Total	$	62,022	$	1,836		$	1,039		$	4,424	$	(5,776	)	$	(12,604	)	$	22	$	(1,329	)	$	49,634
Liabilities:
Securities sold but not yet purchased	$	20	$	(4	)	$	—		$	4	$	(20	)	$	—		$	—	$	—		$	—
There were no significant transfers in or out of Level 3 during the years ended December 31, 2014 or 2013.
Fair Value of Financial Instruments
The following table presents the carrying amounts and estimated fair values of the Company’s financial instruments as of December 31, 2014 and 2013:
	2014					2013
(In thousands)	Carrying Value		Fair Value			Carrying Value			Fair Value
Assets:
Fixed maturity securities	$	12,705,160	$	12,725,806		$	11,616,844		$	11,631,744
Equity securities available for sale	170,991		170,991			283,338			283,338
Arbitrage trading account	450,648		450,648			522,128			522,128
Loans receivable	322,012		325,219			343,583			346,746
Cash and cash equivalents	674,441		674,441			839,738			839,738
Trading accounts receivable from brokers and clearing organizations	371,034		371,034			304,936			304,936
Due from broker	—		—			17,735			17,735
Liabilities:
Due to broker	23,133		23,133			8,273			8,273
Trading account securities sold but not yet purchased	106,079		106,079			162,278			162,278
Subordinated debentures	340,060		332,640			339,800			288,540
Senior notes and other debt	2,115,527		2,344,292			1,692,442			1,861,898
The estimated fair values of the Company’s fixed maturity securities, equity securities available for sale and arbitrage trading account securities are based on various valuation techniques. Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for similar assets in active markets. Level 3 inputs are unobservable inputs for the asset or liability. Unobservable inputs may only be used to measure fair value to the extent that observable inputs are not available. The fair value of loans receivable are estimated by using current institutional purchaser yield requirements for loans with similar credit characteristics, which is considered a Level 2 input. The fair value of the senior notes, other debt and the subordinated debentures is based on spreads for similar securities, which is considered a Level 2 input.

Reserves_For_Losses_And_Loss_E

Reserves For Losses And Loss Expenses	12 Months Ended
	Dec. 31, 2013
Insurance [Abstract]
Reserves For Losses And Loss Expenses	Reserves for Losses and Loss Expenses
	The table below provides a reconciliation of the beginning and ending reserve balances:
	(In thousands)	2014			2013			2012
	Net reserves at beginning of year	$	8,683,797		$	8,411,851		$	8,172,112
	Net provision for losses and loss expenses:
	Claims occuring during the current year(1)	3,495,825			3,221,393			2,997,995
	Decrease in estimates for claims occurring in prior years(2)(3)	(75,764		)	(78,810		)	(102,571		)
	Loss reserve discount accretion(4)	70,506			54,441			53,055
	Total	3,490,567			3,197,024			2,948,479
	Net payments for claims:
	Current year	898,944			822,787			698,834
	Prior year	2,216,283			2,055,284			2,010,101
	Total	3,115,227			2,878,071			2,708,935
	Foreign currency translation	(88,496		)	(47,007		)	195
	Net reserves at end of year	8,970,641			8,683,797			8,411,851
	Ceded reserve at end of year	1,399,060			1,397,144			1,339,235
	Gross reserves at end of year	$	10,369,701		$	10,080,941		$	9,751,086
	_______________________________________
	-1	Claims occurring during the current year are net of loss reserve discounts of $21,306,000, $22,680,000, and $26,078,000 in 2014, 2013 and 2012, respectively.
	-2	The decrease in estimates for claims occurring in prior years is net of loss reserve discount. On an undiscounted basis, the estimates for claims occurring in prior years decreased by $116,866,000, $77,430,000 and $100,667,000 in 2014, 2013 and 2012, respectively.
	-3	For certain retrospectively rated insurance polices and reinsurance agreements, reserve development is offset by additional or return premiums. Favorable reserve development, net of additional and return premiums, was $85 million, $98 million and $103 million in 2014, 2013 and 2012, respectively.
	-4	In 2014, the Company entered into a commutation agreement that resulted in a reduction in prior year workers' compensation reserves of $30 million on an undiscounted basis and $12 million on a discounted basis.
	For the year ended December 31, 2014, estimates for claims occurring in prior years (net of additional and return premiums) decreased by $85 million. The favorable reserve development in 2014 was primarily attributable to domestic other liability business for accident years 2006 through 2010, primarily related to excess and surplus lines casualty business. The changes in prior year loss reserve estimates are generally the result of ongoing analysis of recent loss development trends. Original estimates are increased or decreased as additional information becomes known regarding individual claims and aggregate claim trends.
	Favorable development in 2013 was primarily attributable to accident years 2006 through 2012 and included favorable development of $39 million for other liability business, $32 million for reinsurance assumed liability business, $22 million for workers’ compensation, $18 million for commercial property and $24 million for other lines of business. The 2013 favorable development was partially offset by unfavorable development of $23 million for commercial automobile business and $14 million for products liability business.
	Favorable reserve development in 2012 was primarily attributable to improved claim frequency (i.e., number of reported claims per unit of exposure), especially in the excess and surplus casualty business.
	Environmental and Asbestos — To date, known environmental and asbestos claims have not had a material impact on the Company’s operations, because its subsidiaries generally did not insure large industrial companies that are subject to significant environmental or asbestos exposures prior to 1986 when an absolute exclusion was incorporated into standard policy language.
	The Company’s net reserves for losses and loss adjustment expenses relating to asbestos and environmental claims was $36 million at December 31, 2014 and 2013. The Company’s gross reserves for losses and loss adjustment expenses relating to asbestos and environmental claims were $56 million and $59 million at December 31, 2014 and 2013, respectively. Increases in net incurred losses and loss expenses for reported asbestos and environmental claims were approximately $4 million, $5 million and $2 million in 2014, 2013 and 2012, respectively. Net paid losses and loss expenses for asbestos and environmental claims were approximately $3 million in 2014, $3 million in 2013 and $2 million in 2012. The estimation of these liabilities is subject to significantly greater than normal variation and uncertainty because it is difficult to make an actuarial estimate of these liabilities due to the absence of a generally accepted actuarial methodology for these exposures and the potential effect of significant unresolved legal matters, including coverage issues, as well as the cost of litigating the legal issues. Additionally, the determination of ultimate damages and the final allocation of such damages to financially responsible parties are highly uncertain.
	Discounting — The Company discounts its liabilities for excess and assumed workers’ compensation business because of the long period of time over which losses are paid. Discounting is intended to appropriately match losses and loss expenses to income earned on investment securities supporting the liabilities. The expected losses and loss expense payout pattern subject to discounting was derived from the Company’s loss payout experience. For non-proportional business, reserves for losses and loss expenses have been discounted using risk-free discount rates determined by reference to the U.S. Treasury yield curve. At December 31, 2014, the discount rates by year ranged from 2.0% to 6.5% with a weighted average discount rate of 4.2%. For proportional business, reserves for losses and loss expenses have been discounted at the statutory rate permitted by the Department of Insurance of the State of Delaware of 2%. The aggregate net discount, after reflecting the effects of ceded reinsurance, was $746 million, $837 million and $867 million at December 31, 2014, 2013 and 2012, respectively.

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2014
Reinsurance Disclosures [Abstract]
Reinsurance	Reinsurance
	The Company reinsures a portion of its insurance exposures in order to reduce its net liability on individual risks and catastrophe losses. Reinsurance coverage and retentions vary depending on the line of business, location of the risk and nature of loss. The Company’s reinsurance purchases include the following: property reinsurance treaties that reduce exposure to large individual property losses and catastrophe events; casualty reinsurance treaties that reduce its exposure to large individual casualty losses, workers’ compensation catastrophe losses and casualty losses involving multiple claimants or insureds; and facultative reinsurance that reduces exposure on individual policies or risks for losses that exceed treaty reinsurance capacity. Depending on the operating unit, the Company purchases specific additional reinsurance to supplement the above programs.
	The following is a summary of reinsurance financial information:
	(In thousands)	2014			2013			2012
	Written premiums:
	Direct	$	6,185,242		$	5,626,172		$	4,964,069
	Assumed	877,596			884,919			815,810
	Ceded	(1,065,891		)	(1,010,918		)	(881,340		)
	Total net written premiums	$	5,996,947		$	5,500,173		$	4,898,539
	Earned premiums:
	Direct	$	5,889,021		$	5,328,955		$	4,723,882
	Assumed	886,063			857,119			770,981
	Ceded	(1,030,666		)	(959,537		)	(821,347		)
	Total net earned premiums	$	5,744,418		$	5,226,537		$	4,673,516
	Ceded losses and loss expenses incurred	$	475,802		$	556,108		$	528,018
	Ceded commission earned	$	160,215		$	137,449		$	121,089
	The Company reinsures a portion of its exposures principally to reduce its net liability on individual risks and to protect against catastrophic losses. Estimated amounts due from reinsurers are reported net of reserves for uncollectible reinsurance of $1,144,000, $1,385,000 and $1,680,000 as of December 31, 2014, 2013 and 2012, respectively. The following table presents the amounts due from reinsurers as of December 31, 2014:
	(In thousands)
	Munich Re	$	141,489
	Allegany Grp	109,976
	Lloyd’s of London	101,308
	Swiss Re	97,300
	Partner Re	70,756
	Axis Capital	63,352
	Berkshire Hathaway	48,804
	Ace Group	44,215
	Everest Re	43,207
	Hannover Re Group	41,749
	Arch Capital Group	23,453
	Other reinsurers less than $20,000	212,270
	Subtotal	997,879
	Residual market pools	505,562
	Total	$	1,503,441

Indebtedness

Indebtedness (Senior Notes and Other Debt)	12 Months Ended
	Dec. 31, 2013
Senior Notes and Other Debt
Debt Instrument [Line Items]
Senior Notes And Other Debt	Indebtedness consisted of the following as of December 31, 2014 (the difference between the face value and the carrying value is unamortized discount):
	(In thousands)	Interest Rate	Face Value		2014 Carrying Value		2013 Carrying Value
	Senior notes due on:
	May 15, 2015	5.60%	$	200,000	$	199,930	$	199,744
	August 15, 2019	6.15%	150,000		149,342		149,199
	September 15, 2019	7.38%	300,000		298,800		298,546
	September 15, 2020	5.38%	300,000		298,074		297,738
	January 1, 2022	8.70%	76,503		76,048		76,004
	15-Mar-22	4.63%	350,000		346,999		346,581
	February 15, 2037	6.25%	250,000		247,566		247,457
	1-Aug-44	4.75%	350,000		344,545		—
	Subsidiary debt (1)	Various	153,549		154,223		77,173
	Total senior notes and other debt		$	2,130,052	$	2,115,527	$	1,692,442
	Subordinated debentures	5.63%	$	350,000	$	340,060	$	339,800
	_____________
	(1) Subsidiary debt is due as follows: $76 million in 2015, $33 million in 2016, $42 million in 2017 and $3 million thereafter.
	In 2013, the Company issued $350 million aggregate principal amount of 5.625% Subordinated Debentures due April 2053. At December 31, 2014, the carrying value of the debentures, net of unamortized discount, was $340 million.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes
	Income tax expense consists of:
	(In thousands)	Current			Deferred			Total
		Expense			Expense
	31-Dec-14
	Domestic	$	258,337		$	28,029		$	286,366
	Foreign	12,969			3,258			16,227
	Total expense	$	271,306		$	31,287		$	302,593
	31-Dec-13
	Domestic	$	116,802		$	47,370		$	164,172
	Foreign	22,362			7,053			29,415
	Total expense	$	139,164		$	54,423		$	193,587
	31-Dec-12
	Domestic	$	156,339		$	11,448		$	167,787
	Foreign	23,029			469			23,498
	Total expense	$	179,368		$	11,917		$	191,285
	Income before income taxes from domestic operations was $910 million, $598 million and $624 million for the years ended December 31, 2014, 2013 and 2012, respectively. Income before income taxes from foreign operations was $42 million, $101 million and $78 million for the years ended December 31, 2014, 2013 and 2012, respectively.
	A reconciliation of the income tax expense and the amounts computed by applying the Federal and foreign income tax rate of 35% to pre-tax income are as follows:
	(In thousands)	2014			2013			2012
	Computed “expected” tax expense	$	333,269		$	244,611		$	245,675
	Tax-exempt investment income	(38,757		)	(40,679		)	(50,665		)
	Change in valuation allowance	1,335			—			—
	Impact of foreign tax rates	6,239			(4,851		)	(5,234		)
	State and local taxes	2,375			2,906			(753		)
	Other, net	(1,868		)	(8,400		)	2,262
	Total expense	$	302,593		$	193,587		$	191,285
	At December 31, 2014 and 2013, the tax effects of differences that give rise to significant portions of the deferred tax asset and deferred tax liability are as follows:
	(In thousands)	2014			2013
	Deferred tax asset:
	Loss reserve discounting	$	77,216		$	87,394
	Unearned premiums	165,075			149,107
	Other-than-temporary impairments	45,367			49,483
	Restricted stock units	60,061			52,671
	Other	101,131			92,698
	Gross deferred tax asset	448,850			431,353
	Less valuation allowance	(1,335		)	—
	Deferred tax asset	447,515			431,353
	Deferred tax liability:
	Amortization of intangibles	22,747			11,886
	Deferred policy acquisition costs	152,001			136,635
	Unrealized investment gains	175,111			148,215
	Other	135,108			114,497
	Deferred tax liability	484,967			411,233
	Net deferred tax asset (liability)	$	(37,452	)	$	20,120
	The Company had current tax receivables of $67,623,000 and $24,737,000 at December 31, 2014 and 2013, respectively. At December 31, 2014, the Company had foreign net operating loss carryforwards of $559 thousand that expire beginning in 2015, $6 million that expire beginning in 2031, and an additional $12 million that have no expiration date. At December 31, 2014, the Company had a valuation allowance of $1,335,000, as compared to none at December 31, 2013. The Company has provided a valuation allowance against losses for certain foreign non-insurance related business. The statute of limitations has closed for the Company’s tax returns through December 31, 2010.
	The realization of the deferred tax asset is dependent upon the Company’s ability to generate sufficient taxable income in future periods. Based on historical results and the prospects for future current operations, management anticipates that it is more likely than not that future taxable income will be sufficient for the realization of this asset.

Dividends_From_Subsidiaries_An

Dividends From Subsidiaries And Statutory Financial Information	12 Months Ended
	Dec. 31, 2013
Insurance [Abstract]
Dividends From Subsidiaries And Statutory Financial Information (Unaudited)	Dividends from Subsidiaries and Statutory Financial Information
	The Company’s insurance subsidiaries are restricted by law as to the amount of dividends they may pay without the approval of regulatory authorities. The Company’s lead insurer, Berkley Insurance Company (BIC), directly or indirectly owns all of the Company’s other insurance companies. During 2015, the maximum amount of dividends that can be paid by BIC without such approval is approximately $631 million.
	BIC’s net income and statutory capital and surplus, as determined in accordance with statutory accounting practices (SAP), are as follows:
	(In thousands)	2014		2013		2012
	Net income	$	753,260	$	469,354	$	482,457
	Statutory capital and surplus	$	5,438,064	$	4,908,010	$	4,671,979
	The significant variances between SAP and GAAP are that for statutory purposes bonds are carried at amortized cost, acquisition costs are charged to income as incurred, deferred Federal income taxes are subject to limitations, excess and assumed workers’ compensation reserves are discounted at different discount rates and certain assets designated as “non-admitted assets” are charged against surplus. The Commissioner of Insurance of the State of Delaware has allowed BIC to discount non-tabular workers' compensation loss reserves, which is a permitted practice that differs from SAP. The effect of using this permitted practice was to increase BIC’s statutory capital and surplus by $251 million at December 31, 2014.
	The National Association of Insurance Commissioners (“NAIC”) has risk-based capital (“RBC”) requirements that require insurance companies to calculate and report information under a risk-based formula which measures statutory capital and surplus needs based on a regulatory definition of risk in a company’s mix of products and its balance sheet. This guidance is used to calculate two capital measurements: Total Adjusted Capital and RBC Authorized Control Level. Total Adjusted Capital is equal to the Company’s statutory capital and surplus excluding capital and surplus derived from the use of permitted practices that differ from statutory accounting practices. RBC Authorized Control Level is the capital level used by regulatory authorities to determine whether remedial action is required. Generally, no remedial action is required if Total Adjusted Capital is 200% or more of the RBC Authorized Control Level. At December 31, 2014, BIC’s Total Adjusted Capital of $5.187 billion was 465% of its RBC Authorized Control Level.
	See Note 4, Investments in Fixed Maturity Securities, for a description of assets held on deposit as security.

Common_Stockholders_Equity

Common Stockholders' Equity	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Common Stockholders' Equity	Common Stockholders’ Equity
	The weighted average number of shares used in the computation of net income per share was as follows:
		2014		2013		2012
	Basic	127,873,708		135,304,752		137,097,162
	Diluted	133,651,855		140,742,922		143,314,544
	Treasury shares have been excluded from average outstanding shares from the date of acquisition. The difference in calculating basic and diluted net income per share is attributable entirely to the dilutive effect of stock-based compensation plans.
	Changes in shares of common stock outstanding, net of treasury shares, are presented below. Shares of common stock issued and outstanding do not include shares related to unissued restricted stock units and unexercised stock options.
		2014		2013		2012
	Balance, beginning of year	132,233,167		136,017,732		137,520,019
	Shares issued	332,137		139,790		2,114,168
	Shares repurchased	(5,816,468	)	(3,924,355	)	-3,616,455
	Balance, end of year	126,748,836		132,233,167		136,017,732
	The amount of dividends paid is dependent upon factors such as the receipt of dividends from our subsidiaries, our results of operations, cash flow, financial condition and business needs, the capital and surplus requirements of our subsidiaries, and applicable insurance regulations that limit the amount of dividends that may be paid by our regulated insurance subsidiaries.

Fair_Value_Of_Financial_Instru

Fair Value Of Financial Instruments	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value Of Financial Instruments	Fair Value Measurements
	The Company’s fixed maturity, equity securities available for sale and its trading account securities are carried at fair value. Fair value is defined as “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.” The Company utilizes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for similar assets in active markets. Level 3 inputs are unobservable inputs for the asset or liability. Unobservable inputs may only be used to measure fair value to the extent that observable inputs are not available.
	Because many fixed maturity securities do not trade on a daily basis, the Company utilizes pricing models and processes which may include benchmark curves, benchmarking of like securities, sector groupings and matrix pricing. Market inputs used to evaluate securities include benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers and reference data. Quoted prices are often unavailable for recently issued securities, securities that are infrequently traded or securities that are only traded in private transactions. For publicly traded securities for which quoted prices are unavailable, the Company determines fair value based on independent broker quotations and other observable market data. For securities traded only in private negotiations, the Company determines fair value based primarily on the cost of such securities, which is adjusted to reflect prices of recent placements of securities of the same issuer, financial projections, credit quality and business developments of the issuer and other relevant information.
	The following tables present the assets and liabilities measured at fair value on a recurring basis as of December 31, 2014 and 2013 by level:
	(In thousands)	Total		Level 1			Level 2			Level 3
	December 31, 2014
	Assets:
	Fixed maturity securities available for sale:
	U.S. government and government agency	$	803,388	$	—		$	803,388		$	—
	State and municipal	4,362,996		—			4,362,996			—
	Mortgage-backed securities	1,295,636		—			1,295,636			—
	Corporate	5,200,137		—			5,179,372			20,765
	Foreign government	941,826		—			941,826			—
	Total fixed maturity securities available for sale	12,603,983		—			12,583,218			20,765
	Equity securities available for sale:
	Common stocks	76,346		65,605			—			10,741
	Preferred stocks	94,645		—			90,932			3,713
	Total equity securities available for sale	170,991		65,605			90,932			14,454
	Arbitrage trading account	450,648		295,047			154,881			720
	Total	$	13,225,622	$	360,652		$	12,829,031		$	35,939
	Liabilities:
	Securities sold but not yet purchased	$	106,079	$	106,074		$	5		$	—
	December 31, 2013
	Assets:
	Fixed maturity securities available for sale:
	U.S. government and government agency	$	884,859	$	—		$	884,859		$	—
	State and municipal	4,218,284		—			4,218,284			—
	Mortgage-backed securities	1,329,783		—			1,329,783			—
	Corporate	4,202,741		—			4,159,877			42,864
	Foreign government	879,857		—			879,857			—
	Total fixed maturity securities available for sale	11,515,524		—			11,472,660			42,864
	Equity securities available for sale:
	Common stocks	160,775		159,537			—			1,238
	Preferred stocks	122,563		—			118,811			3,752
	Total equity securities available for sale	283,338		159,537			118,811			4,990
	Arbitrage trading account	522,128		192,281			328,067			1,780
	Total	$	12,320,990	$	351,818		$	11,919,538		$	49,634
	Liabilities:
	Securities sold but not yet purchased	$	162,278	$	162,126		$	152		$	—
	There were no transfers between Levels 1 and 2 for the years ended December 31, 2014 and 2013.
	The following tables summarize changes in Level 3 assets and liabilities for the years ended December 31, 2014 and 2013:
		Gains (Losses) Included in:
	(In thousands)	Beginning Balance		Earnings			Other Comprehensive Income			Purchases		Sales			Paydowns/Maturities			In		Out			Ending Balance
	Year ended December 31, 2014
	Assets:
	Fixed maturity securities available for sale:
	Corporate	$	42,864	$	47		$	(3,711	)	$	238	$	(15,244	)	$	(3,429	)	$	—	$	—		$	20,765
	Total	42,864		47			(3,711		)	238		(15,244		)	(3,429		)	—		—			20,765
	Equity securities available for sale:
	Common stocks	1,238		—			(911		)	11,343		(929		)	—			—		—			10,741
	Preferred stocks	3,752		(17		)	—			3,430		(3,452		)	—			—		—			3,713
	Total	4,990		(17		)	(911		)	14,773		(4,381		)	—			—		—			14,454
	Arbitrage trading account	1,780		2,274			—			4,942		(14,073		)	—			9,064		(3,267		)	720
	Total	$	49,634	$	2,304		$	(4,622	)	$	19,953	$	(33,698	)	$	(3,429	)	$	9,064	$	(3,267	)	$	35,939
	Liabilities:
	Securities sold but not yet purchased	$	—	$	(20	)	$	—		$	31	$	(11	)	$	—		$	—	$	—		$	—
	Year ended December 31, 2013
	Assets:
	Fixed maturity securities available for sale:
	Corporate	$	59,065	$	677		$	309		$	170	$	(4,753	)	$	(12,604	)	$	—	$	—		$	42,864
	Total	59,065		677			309			170		(4,753		)	(12,604		)	—		—			42,864
	Equity securities available for sale:
	Common stocks	1,408		—			—			—		(170		)	—			—		—			1,238
	Preferred stocks	621		(299		)	—			3,430		—			—			—		—			3,752
Total	2,029		(299		)	—			3,430		(170		)	—			—		—			4,990
Arbitrage trading account	928		1,458			730			824		(853		)	—			22		(1,329		)	1,780
Total	$	62,022	$	1,836		$	1,039		$	4,424	$	(5,776	)	$	(12,604	)	$	22	$	(1,329	)	$	49,634
Liabilities:
Securities sold but not yet purchased	$	20	$	(4	)	$	—		$	4	$	(20	)	$	—		$	—	$	—		$	—
There were no significant transfers in or out of Level 3 during the years ended December 31, 2014 or 2013.
Fair Value of Financial Instruments
The following table presents the carrying amounts and estimated fair values of the Company’s financial instruments as of December 31, 2014 and 2013:
	2014					2013
(In thousands)	Carrying Value		Fair Value			Carrying Value			Fair Value
Assets:
Fixed maturity securities	$	12,705,160	$	12,725,806		$	11,616,844		$	11,631,744
Equity securities available for sale	170,991		170,991			283,338			283,338
Arbitrage trading account	450,648		450,648			522,128			522,128
Loans receivable	322,012		325,219			343,583			346,746
Cash and cash equivalents	674,441		674,441			839,738			839,738
Trading accounts receivable from brokers and clearing organizations	371,034		371,034			304,936			304,936
Due from broker	—		—			17,735			17,735
Liabilities:
Due to broker	23,133		23,133			8,273			8,273
Trading account securities sold but not yet purchased	106,079		106,079			162,278			162,278
Subordinated debentures	340,060		332,640			339,800			288,540
Senior notes and other debt	2,115,527		2,344,292			1,692,442			1,861,898
The estimated fair values of the Company’s fixed maturity securities, equity securities available for sale and arbitrage trading account securities are based on various valuation techniques. Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for similar assets in active markets. Level 3 inputs are unobservable inputs for the asset or liability. Unobservable inputs may only be used to measure fair value to the extent that observable inputs are not available. The fair value of loans receivable are estimated by using current institutional purchaser yield requirements for loans with similar credit characteristics, which is considered a Level 2 input. The fair value of the senior notes, other debt and the subordinated debentures is based on spreads for similar securities, which is considered a Level 2 input.

Lease_Obligations

Lease Obligations	12 Months Ended
	Dec. 31, 2014
Leases [Abstract]
Lease Obligations	Lease Obligations
	The Company and its subsidiaries use office space and equipment under leases expiring at various dates. These leases are considered operating leases for financial reporting purposes. Some of these leases have options to extend the length of the leases and contain clauses for cost of living, operating expense and real estate tax adjustments. Future minimum lease payments, without provision for sublease income, are: $41,210,000 in 2015; $36,547,000 in 2016; $32,336,000 in 2017; $27,012,000 in 2018; $23,344,000 in 2019 and $78,517,000 thereafter. Rental expense was $45,198,000, $44,752,000 and $38,179,000 for 2014, 2013 and 2012, respectively.

Commitments_Litigation_And_Con

Commitments, Litigation And Contingent Liabilities	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments, Litigation And Contingent Liabilities	Commitments, Litigation and Contingent Liabilities
	In the ordinary course of business, the Company is subject to disputes, litigation and arbitration arising from its insurance and reinsurance businesses. These matters are generally related to insurance and reinsurance claims and are considered in the establishment of loss and loss expense reserves. In addition, the Company may also become involved in legal actions which seek extra-contractual damages, punitive damages or penalties, including claims alleging bad faith in handling of insurance claims. The Company expects its ultimate liability with respect to such matters will not be material to its financial condition. However, adverse outcomes on such matters are possible, from time to time, and could be material to the Company’s results of operations in any particular financial reporting period.
	At December 31, 2014, the Company had commitments to invest up to $242 million in certain investment funds.

Stock_Incentive_Plan

Stock Incentive Plan	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Incentive Plan	Stock Incentive Plan
	The Company has not issued any stock options under its stock incentive plans since 2004, and there were no outstanding options at December 31, 2014. The following table summarizes stock option information:
			2013							2012
			Shares			Price(1)				Shares			Price(1)
	Outstanding at beginning of year		3,375			$	15.17			1,314,057			$	11.04
	Exercised		3,375			15.17				1,310,682			11.03
	Canceled		—			—				—			—
	Outstanding at year end		—			$	—			3,375			$	15.17
	_______________________________________
	-1	Weighted average exercise price.
	Pursuant to the stock incentive plan, the Company may issue restricted stock units (RSUs) to employees of the Company and its subsidiaries. The RSUs generally vest three to five years from the award date and are subject to other vesting and forfeiture provisions contained in the award agreement. The following table summarizes RSU information for the three years ended December 31, 2014:
		2014			2013			2012
	RSUs granted and unvested at beginning of period:	4,491,520			4,701,120			4,370,975
	Granted	1,154,950			108,400			2,161,220
	Vested	(81,500	)		(146,250	)		(1,704,625	)
	Cancelled	(234,525	)		(171,750	)		(126,450	)
	RSUs granted and unvested at end of period:	5,330,445			4,491,520			4,701,120
	Upon vesting, shares of the Company’s common stock equal to the number of vested RSUs are issued or deferred to a later date, depending on the terms of the specific award agreement. As of December 31, 2014, 3,417,918 RSUs had been deferred. Accordingly, we have not included in the issued and outstanding common stock any shares relating to RSUs that have been granted but remain unvested or to issued RSUs that are vested and have been deferred.
	The fair value of RSUs at the date of grant are recorded as unearned compensation, a component of stockholders’ equity, and expensed over the vesting period. Following is a summary of changes in unearned compensation for the three years ended December 31, 2014:
	(In thousands)	2014				2013				2012
	Unearned compensation at beginning of year	$	73,205			$	93,653			$	57,315
	RSUs granted, net of cancellations	51,575				4,406				73,255
	RSUs expensed	(27,966		)		(22,881		)		(25,728		)
	RSUs forfeitures	(8,799		)		(1,973		)		(11,189		)
	Unearned compensation at end of year	$	88,015			$	73,205			$	93,653

Compensation_Plans

Compensation Plans	12 Months Ended
	Dec. 31, 2014
Compensation Related Costs [Abstract]
Compensation Plans	Compensation Plans
	The Company and its subsidiaries have profit sharing plans in which substantially all employees participate. The plans provide for minimum annual contributions of 5% of eligible compensation; contributions above the minimum are discretionary and vary with each participating subsidiary’s profitability. Employees will become eligible to participate in the Plan on the first day of the calendar quarter following the first full calendar quarter after the Employee's date of hire provided the Employee has completed 250 hours of service during the calendar quarter. The plans provide that 40% of the contributions vest immediately and that the remaining 60% vest at varying percentages based upon years of service. Profit sharing expense was $38 million, $34 million, and $31 million in 2014, 2013 and 2012, respectively.
	The Company has a long-term incentive compensation plan ("LTIP") that provides for incentive compensation to key executives based on the growth in the company's book value per share over a five year period.
	The following table is a summary of the outstanding LTIP awards as of December 31, 2014:
		Units Outstanding		Maximum Value			Inception to date earned through December 31, 2014 on outstanding units
	2011 grant	175,100		$	43,775,000		$	27,307,000
	2013 grant	208,000		52,000,000			16,665,000
	2014 grant	220,000		22,000,000			3,663,000
	The following table summarizes the LTIP expense for each of the three years ended December 31, 2014:
	(In thousands)	2014				2013			2012
	2008 grant	$	—			$	—		$	4,283
	2011 grant	9,855				6,939			6,822
	2013 grant	9,493				7,231			—
	2014 grant	3,663				—			—
	Total	$	23,011			$	14,170		$	11,105

Retirement_Benefits

Retirement Benefits	12 Months Ended
	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Retirement Benefits	Retirement Benefits
	The Company and its chairman of the board and chief executive officer entered into an unfunded supplemental benefit agreement (SBA) in 2004. On March 28, 2013, the Company agreed to terminate and distribute the retirement benefit of the SBA. As a result, the Company distributed retirement benefits of $0.3 million and $4.6 million in 2013 and 2014, respectively. The final retirement benefit of $59.4 million, which is fully accrued at December 31, 2014, will be distributed during the first quarter of 2015. Net retirement benefit expense was $7,696,000, $13,357,000 and $9,994,000 in 2012, 2013 and 2014, respectively.

Supplemental_Financial_Stateme

Supplemental Financial Statement Information	12 Months Ended
	Dec. 31, 2014
Other Income and Expenses [Abstract]
Supplemental Financial Statement Data	Supplemental Financial Statement Data
	Other operating costs and expenses consist of the following:
	(In thousands)	2014			2013			2012
	Amortization of deferred policy acquisition costs	$	1,053,397		$	991,070		$	917,583
	Other underwriting expenses	843,133			780,058			675,163
	Service company expenses	102,726			88,662			84,986
	Net foreign currency gains	(27		)	(10,120		)	(6,092		)
	Other costs and expenses	158,227			151,014			127,983
	Total	$	2,157,456		$	2,000,684		$	1,799,623

Industry_Segments

Industry Segments	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Industry Segments	Industry Segments
	The Company’s reportable segments include the following three business segments, plus a corporate segment:
	•	Insurance-Domestic - commercial insurance business, including excess and surplus lines and admitted lines, primarily throughout the United States;
	•	Insurance-International - insurance business primarily in the United Kingdom, Continental Europe, South America, Canada, Scandinavia, and Australia; and
	•	Reinsurance-Global - reinsurance business on a facultative and treaty basis, primarily in the United States, United Kingdom, Continental Europe, Australia, and the Asia-Pacific Region.
	The accounting policies of the segments are the same as those described in the summary of significant accounting policies. Income tax expense and benefits are calculated based upon the Company’s overall effective tax rate.
	Summary financial information about the Company’s reporting segments is presented in the following table. Income (loss) before income taxes by segment includes allocated investment income. Identifiable assets by segment are those assets used in or allocated to the operation of each segment.
	Revenues
	(In thousands)	Earned		Investment		Other		Total		Pre-Tax			Net
		Premiums		Income						Income			Income
										(Loss)			(Loss)
	December 31, 2014:
	Insurance-Domestic	$	4,271,933	$	428,632	$	106,853	$	4,807,418	$	796,309		$	539,461
	Insurance-International	802,375		55,407		—		857,782		29,779			22,182
	Reinsurance-Global	670,110		88,821		—		758,931		115,677			79,720
	Corporate, other and eliminations(1)	—		28,025		421,920		449,945		(244,421		)	(158,133		)
	Net investment gains	—		—		254,852		254,852		254,852			165,654
	Consolidated	$	5,744,418	$	600,885	$	783,625	$	7,128,928	$	952,196		$	648,884
	December 31, 2013:
	Insurance-Domestic	$	3,782,416	$	404,280	$	107,517	$	4,294,213	$	648,740		$	449,981
	Insurance-International	723,151		47,039		—		770,190		56,922			40,292
	Reinsurance-Global	720,970		89,090		—		810,060		110,425			78,013
	Corporate, other and eliminations(1)	—		3,882		408,645		412,527		(238,743		)	(142,479		)
	Net investment gains	—		—		121,544		121,544		121,544			74,118
	Consolidated	$	5,226,537	$	544,291	$	637,706	$	6,408,534	$	698,888		$	499,925
	December 31, 2012:
	Insurance-Domestic	$	3,417,022	$	424,787	$	103,133	$	3,944,942	$	578,500		$	397,942
	Insurance-International	631,841		45,796		—		677,637		51,639			35,928
	Reinsurance-Global	624,653		106,932		—		731,585		103,690			72,916
	Corporate, other and eliminations(1)	—		9,248		249,677		258,925		(242,366		)	(132,996		)
	Net investment gains	—		—		210,465		210,465		210,465			136,802
	Consolidated	$	4,673,516	$	586,763	$	563,275	$	5,823,554	$	701,928		$	510,592
	Identifiable Assets
	(In thousands)	31-Dec-14		31-Dec-13
	Insurance-Domestic	$	16,065,409	$	15,247,807
	Insurance-International	1,879,438		1,516,310
	Reinsurance-Global	2,713,554		3,103,193
	Corporate, other and eliminations(1)	1,058,290		684,486
	Consolidated	$	21,716,691	$	20,551,796
	_______________________________________
	-1	Corporate, other and eliminations represent corporate revenues and expenses and other items that are not allocated to business segments.
	Net premiums earned by major line of business are as follows:
	(In thousands)	2014		2013		2012
	Insurance-Domestic
	Other liability	$	1,449,425	$	1,259,376	$	1,104,369
	Workers' compensation	1,126,704		995,047		869,042
	Short-tail lines	875,898		774,809		733,239
	Commercial automobile	526,344		486,759		455,988
	Professional liability	293,562		266,425		254,384
	Total Insurance-Domestic	4,271,933		3,782,416		3,417,022
	Insurance-International
	Other liability	92,411		65,528		44,065
	Workers' compensation	71,997		84,637		82,066
	Short-tail lines	415,123		336,814		276,599
	Commercial automobile	116,369		130,020		125,927
	Professional liability	106,475		106,152		103,184
	Total Insurance-International	802,375		723,151		631,841
	Reinsurance-Global
	Casualty	487,264		507,790		456,376
	Property	182,846		213,180		168,277
	Total Reinsurance-Global	670,110		720,970		624,653
	Total	$	5,744,418	$	5,226,537	$	4,673,516

Quarterly_Financial_Informatio

Quarterly Financial Information (Unaudited)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information (Unaudited)	Quarterly Financial Information (Unaudited)
	The following is a summary of quarterly financial data:
	(In thousands. except per share data)	2014
	Three months ended	March 31		June 30		September 30		December 31
	Revenues	$	1,706,906	$	1,796,989	$	1,840,605	$	1,784,428
	Net income	169,673		179,961		188,539		110,711
	Net income per share(1)
	Basic	1.31		1.41		1.48		0.87
	Diluted	1.25		1.35		1.42		0.83
		2013
	Three months ended	March 31		June 30		September 30		December 31
	Revenues	$	1,506,769	$	1,570,962	$	1,634,124	$	1,696,679
	Net income	116,615		115,957		136,974		130,379
	Net income per share(1)
	Basic	0.86		0.85		1.01		0.97
	Diluted	0.83		0.82		0.97		0.93
	_______________________________________
	-1	Net income per share (“EPS”) in each quarter is computed using the weighted-average number of shares outstanding during that quarter, while EPS for the full year is computed using the weighted-average number of shares outstanding during the year. Thus, the sum of the four quarters EPS does not necessarily equal the full-year EPS.

Schedule_II_Condensed_Financia

Schedule II - Condensed Financial Information of Registrant	12 Months Ended
	Dec. 31, 2012
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Schedule II - Condensed Financial Information of Registrant	Schedule II
	W. R. Berkley Corporation
	Condensed Financial Information of Registrant
	Balance Sheets (Parent Company)
		December 31,
	(In thousands)	2014			2013
	Assets:
	Cash and cash equivalents	$	90,693		$	17,315
	Fixed maturity securities available for sale at fair value (cost $272,283 and $61,084 at December 31, 2014 and 2013, respectively)	273,773			63,115
	Equity securities available for sale, at fair value (cost $3,738 in 2014 and $4,668 in 2013)	3,738			11,240
	Investment in subsidiaries	6,693,731			6,250,979
	Due from subsidiaries	—			13,648
	Deferred Federal income taxes	—			51,346
	Current Federal income taxes	62,882			17,540
	Property, furniture and equipment at cost, less accumulated depreciation	9,852			9,028
	Other assets	6,978			5,795
	Total assets	$	7,141,647		$	6,440,006
	Liabilities and stockholders’ equity
	Liabilities:
	Due to subsidiaries	$	87,540		$	—
	Other liabilities	162,648			148,903
	Deferred Federal income taxes	149			—
	Subordinated debentures	340,060			339,800
	Senior notes	1,961,305			1,615,268
	Total liabilities	2,551,702			2,103,971
	Stockholders’ equity:
	Preferred stock	—			—
	Common stock	47,024			47,024
	Additional paid-in capital	991,512			967,440
	Retained earnings (including accumulated undistributed net income of subsidiaries of $4,700,821 and $4,393,420 at December 31, 2014 and 2013, respectively)	5,732,410			5,265,015
	Accumulated other comprehensive income	183,550			189,391
	Treasury stock, at cost	(2,364,551		)	(2,132,835		)
	Total stockholders’ equity	4,589,945			4,336,035
	Total liabilities and stockholders’ equity	$	7,141,647		$	6,440,006
	________________
	See accompanying Report of Independent Registered Public Accounting Firm and note to condensed financial statements.
	Schedule II, Continued
	W. R. Berkley Corporation
	Condensed Financial Information of Registrant, Continued
	Statements of Income (Parent Company)
		Years Ended December 31,
	(In thousands)	2014			2013			2012
	Management fees and investment income including dividends from subsidiaries of $503,483, $269,626, and $25,968 for the years ended December 31, 2014, 2013 and 2012, respectively	$	515,775		$	277,223		$	29,961
	Net investment gains	5,487			24,550			71,130
	Other income	450			223			271
	Total revenues	521,712			301,996			101,362
	Operating costs and expense	148,288			122,562			133,326
	Interest expense	125,352			120,066			124,298
	Income (loss) before federal income taxes	248,072			59,368			(156,262		)
	Federal income taxes:
	Federal income taxes provided by subsidiaries on a separate return basis	366,721			225,845			132,379
	Federal income tax expense on a consolidated return basis	(273,310		)	(154,928		)	(160,226		)
	Net expense	93,411			70,917			(27,847		)
	Income (loss) before undistributed equity in net income of subsidiaries	341,483			130,285			(184,109		)
	Equity in undistributed net income of subsidiaries	307,401			369,640			694,701
	Net income	$	648,884		$	499,925		$	510,592
	________________
	See accompanying Report of Independent Registered Public Accounting Firm and note to condensed financial statements.
	Schedule II, Continued
	W. R. Berkley Corporation
	Condensed Financial Information of Registrant, Continued
	Statements of Cash Flows (Parent Company)
		Years Ended December 31,
	(In thousands)	2014			2013			2012
Cash flows (used in) from operating activities:
Net income	$	648,884		$	499,925		$	510,592
Adjustments to reconcile net income to net cash from operating activities:
Net investment gains	(5,487		)	(24,550		)	(71,130		)
Depreciation and amortization	2,916			10,397			5,624
Equity in undistributed earnings of subsidiaries	(307,401		)	(369,640		)	(694,701		)
Tax payments received from subsidiaries	462,809			77,305			125,046
Federal income taxes provided by subsidiaries on a separate return basis	(366,721		)	(225,845		)	(132,379		)
Stock incentive plans	28,068			23,784			26,763
Change in:
Federal income taxes	(15,239		)	21,866			44,423
Other assets	(364		)	(821		)	911
Other liabilities	(39,780		)	(15,470		)	28,017
Accrued investment income	(820		)	967			97
Other, net	—			—			(13		)
Net cash (used in) from operating activities	406,865			(2,082		)	(156,750		)
Cash from (used in) investing activities:
Proceeds from sales of fixed maturity securities	289,683			230,854			93,354
Proceeds from maturities and prepayments of fixed maturity securities	103,646			68,918			121,191
Proceeds from sales of equity securities	7,356			23,395			72,565
Cost of purchases of fixed maturity securities	(605,768		)	(79,132		)	(255,885		)
Cost of purchases of equity securities	—			(4,668		)	—
Cost of acquired companies	(82,879		)	—			—
Investments in and advances to subsidiaries, net	34,191			(58,454		)	(16,480		)
Change in balance due to security broker	(2,151		)	6,918			(4,767		)
Net additions to real estate, furniture & equipment	(1,615		)	(1,896		)	(1,857		)
Net cash from (used in) investing activities	(257,537		)	185,935			8,121
Cash from (used in) financing activities:
Net proceeds from issuance of senior notes	344,472			339,627			345,823
Net proceeds from stock options exercised	—			53			13,544
Repayment of senior notes	—			(450,000		)	—
Purchase of common treasury shares	(238,933		)	(166,473		)	(134,456		)
Cash dividends to common stockholders	(181,489		)	(52,717		)	(183,947		)
Net cash from (used in) financing activities	(75,950		)	(329,510		)	40,964
Net increase (decrease) in cash and cash equivalents	73,378			(145,657		)	(107,665		)
Cash and cash equivalents at beginning of year	17,315			162,972			270,637
Cash and cash equivalents at end of year	$	90,693		$	17,315		$	162,972
________________
See accompanying Report of Independent Registered Public Accounting Firm and note to condensed financial statements.
W. R. Berkley Corporation
Condensed Financial Information of Registrant,Continued
December 31, 2014
Note to Condensed Financial Statements (Parent Company)
The accompanying condensed financial statements should be read in conjunction with the notes to consolidated financial statements included elsewhere herein. Reclassifications have been made in the 2013 and 2012 financial statements as originally reported to conform them to the presentation of the 2014 financial statements.
The Company files a consolidated federal tax return with the results of its domestic insurance subsidiaries included on a statutory basis. Under present Company policy, federal income taxes payable by subsidiary companies on a separate-return basis are paid to W. R. Berkley Corporation, and the Company pays the tax due on a consolidated return basis.

Schedule_III_Supplementary_Ins

Schedule III - Supplementary Insurance Information	12 Months Ended
	Dec. 31, 2014
Supplementary Insurance Information [Abstract]
Schedule III - Supplementary Insurance Information	Schedule III
	W. R. Berkley Corporation and Subsidiaries
	Supplementary Insurance Information
	December 31, 2014, 2013 and 2012
	(In thousands)	Deferrred		Reserve for		Unearned		Net Premiums		Net		Loss and Loss		Amortization of		Other		Net
		Policy		Losses and		Premiums		Earned		Investment		Expenses		Deferred Policy		Operating Cost		Premiums
		Acquisition		Loss Expenses						Income				Acquisition		and Expenses		Written
		Cost												Cost
	December 31, 2014
	Insurance-Domestic	$	347,261	$	8,000,863	$	2,384,511	$	4,271,933	$	428,632	$	2,571,010	$	710,141	$	729,958	$	4,517,587
	Insurance-International	60,900		855,852		342,746		802,375		55,407		503,997		173,877		150,129		828,076
	Reinsurance-Global	80,364		1,512,986		299,475		670,110		88,821		415,560		169,379		58,315		651,284
	Corporate and adjustments	—		—		—		—		28,025		—		—		165,657		—
	Total	$	488,525	$	10,369,701	$	3,026,732	$	5,744,418	$	600,885	$	3,490,567	$	1,053,397	$	1,104,059	$	5,996,947
	December 31, 2013
	Insurance-Domestic	$	306,464	$	7,715,124	$	2,107,768	$	3,782,416	$	404,280	$	2,318,541	$	651,524	$	671,096	$	3,994,387
	Insurance-International	60,751		672,009		317,691		723,151		47,039		429,900		152,843		124,497		756,185
	Reinsurance-Global	84,886		1,693,808		355,978		720,970		89,090		448,583		186,703		64,567		749,601
	Corporate and adjustments	—		—		—		—		3,882		—		—		149,454		—
	Total	$	452,101	$	10,080,941	$	2,781,437	$	5,226,537	$	544,291	$	3,197,024	$	991,070	$	1,009,614	$	5,500,173
	December 31, 2012
	Insurance-Domestic	$	269,418	$	7,466,538	$	1,844,452	$	3,417,022	$	424,787	$	2,169,090	$	613,252	$	584,100	$	3,569,883
	Insurance-International	56,995		622,202		297,581		631,841		45,796		377,459		136,412		112,128		664,459
	Reinsurance-Global	77,634		1,662,346		332,814		624,653		106,932		401,930		167,919		58,044		664,197
	Corporate and adjustments	—		—		—		—		9,248		—		—		127,768		—
	Total	$	404,047	$	9,751,086	$	2,474,847	$	4,673,516	$	586,763	$	2,948,479	$	917,583	$	882,040	$	4,898,539
	See accompanying Report of Independent Registered Public Accounting Firm.

Schedule_IV_Reinsurance

Schedule IV - Reinsurance	12 Months Ended
	Dec. 31, 2014
Supplemental Schedule of Reinsurance Premiums for Insurance Companies [Abstract]
Schedule IV - Reinsurance	Schedule IV
	W. R. Berkley Corporation and Subsidiaries
	Reinsurance
	Years ended December 31, 2014, 2013 and 2012
		Premiums Written
	(In thousands, other than percentages)	Direct		Ceded		Assumed		Net		Percentage
		Amount		to Other		from Other		Amount		of Amount
				Companies		Companies				Assumed
										to Net
	Year ended December 31, 2014:
	Insurance-Domestic	$	5,214,849	$	866,092	$	168,830	$	4,517,587	3.7	%
	Insurance-International	927,799		156,195		56,472		828,076		6.8	%
	Reinsurance-Global	42,594		43,604		652,294		651,284		100.2	%
	Total	$	6,185,242	$	1,065,891	$	877,596	$	5,996,947	14.6	%
	Year ended December 31, 2013:
	Insurance-Domestic	$	4,699,348	$	809,368	$	104,407	$	3,994,387	2.6	%
	Insurance-International	887,027		142,591		11,749		756,185		1.6	%
	Reinsurance-Global	39,797		58,959		768,763		749,601		102.6	%
	Total	$	5,626,172	$	1,010,918	$	884,919	$	5,500,173	16.1	%
	Year ended December 31, 2012:
	Insurance-Domestic	$	4,133,960	$	691,284	$	127,207	$	3,569,883	3.6	%
	Insurance-International	798,750		137,598		3,307		664,459		0.5	%
	Reinsurance-Global	31,359		52,458		685,296		664,197		103.2	%
	Total	$	4,964,069	$	881,340	$	815,810	$	4,898,539	16.7	%
	See accompanying Report of Independent Registered Public Accounting Firm.

Schedule_V_Valuation_and_Quali

Schedule V - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2014
Valuation and Qualifying Accounts [Abstract]
Schedule V - Valuation and Qualifying Accounts	Schedule V
	W. R. Berkley Corporation and Subsidiaries
	Valuation and Qualifying Accounts
	Years ended December 31, 2014, 2013 and 2012
	(In thousands)	Opening		Additions-			Deduction-			Ending
		Balance		Charged to			Amounts			Balance
				Expense			Written Off
	Year ended December 31, 2014:
	Premiums and fees receivable	$	20,951	$	5,944		$	(5,449	)	$	21,446
	Due from reinsurers	1,385		301			(542		)	1,144
	Deferred federal and foreign income taxes	—		1,335			—			1,335
	Loan loss reserves	2,087		399			—			2,486
	Total	$	24,423	$	7,979		$	(5,991	)	$	26,411
	Year ended December 31, 2013:
	Premiums and fees receivable	$	22,919	$	3,133		$	(5,101	)	$	20,951
	Due from reinsurers	1,680		186			(481		)	1,385
	Loan loss reserves	5,620		308			(3,841		)	2,087
	Total	$	30,219	$	3,627		$	(9,423	)	$	24,423
	Year ended December 31, 2012:
	Premiums and fees receivable	$	17,666	$	9,598		$	(4,345	)	$	22,919
	Due from reinsurers	3,169		22			(1,511		)	1,680
	Loan loss reserves	19,805		(13,723		)	(462		)	5,620
	Total	$	40,640	$	(4,103	)	$	(6,318	)	$	30,219
	See accompanying Report of Independent Registered Public Accounting Firm.

Schedule_VI_Supplementary_Info

Schedule VI - Supplementary Information Concerning Property-Casualty Insurance Operations	12 Months Ended
	Dec. 31, 2014
Supplemental Information for Property, Casualty Insurance Underwriters [Abstract]
Schedule VI - Supplementary Information Concerning Property-Casualty Insurance Operations	Schedule VI
	W. R. Berkley Corporation and Subsidiaries
	Supplementary Information Concerning Property-Casualty Insurance Operations
	Years Ended December 31, 2014, 2013 and 2012
	(In thousands)	2014			2013			2012
	Deferred policy acquisition costs	$	488,525		$	452,101		$	404,047
	Reserves for losses and loss expenses	10,369,701			10,080,941			9,751,086
	Unearned premium	3,026,732			2,781,437			2,474,847
	Net premiums earned	5,744,418			5,226,537			4,673,516
	Net investment income	600,885			544,291			586,763
	Losses and loss expenses incurred:
	Current year	3,495,825			3,221,393			2,997,995
	Prior years	(75,764		)	(78,810		)	(102,571		)
	Loss reserve discount accretion	70,506			54,441			53,055
	Amortization of deferred policy acquisition costs	1,053,397			991,070			917,583
	Paid losses and loss expenses	3,115,227			2,878,071			2,708,935
	Net premiums written	5,996,947			5,500,173			4,898,539
	See accompanying Report of Independent Registered Public Accounting Firm.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Principles of consolidation and basis of presentation	Principles of consolidation and basis of presentation
	The consolidated financial statements, which include the accounts of W. R. Berkley Corporation and its subsidiaries (the "Company"), have been prepared on the basis of U.S. generally accepted accounting principles ("GAAP"). All significant intercompany transactions and balances have been eliminated. Reclassifications have been made in the 2013 and 2012 financial statements to conform to the presentation of the 2014 financial statements. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the revenues and expenses reflected during the reporting period. The most significant items on our balance sheet that involve a greater degree of accounting estimates that are subject to change in the future are the valuation of investments, other-than-temporary impairments, loss and loss adjustment expense reserves and premium estimates. Actual results could differ from those estimates.
Revenue recognition	Revenue recognition
	Insurance premiums are recognized as written at the inception of the policy. Reinsurance premiums are estimated based upon information received from ceding companies, and subsequent differences from such estimates are recorded in the period they are determined. Insurance and reinsurance premiums are primarily earned on a pro rata basis over the policy term. Fees for services are earned over the period that the services are provided.
	Audit premiums are recognized when they are reliably determinable. The change in accruals for earned but unbilled audit premiums increased net premiums written and premiums earned by $9 million, $12 million and $7 million in 2014, 2013 and 2012, respectively.
Cash and cash equivalents	Cash and cash equivalents
	Cash equivalents consist of funds invested in money market accounts and investments with an effective maturity of three months or less when purchased.
Investments	Investments
	Fixed maturity securities classified as available for sale are carried at estimated fair value, with unrealized gains and losses, net of applicable income taxes, excluded from earnings and reported as a component of comprehensive income and a separate component of stockholders' equity. Fixed maturity securities that the Company has the positive intent and ability to hold to maturity are classified as held to maturity and reported at amortized cost. Investment income from fixed maturity securities is recognized based on the constant effective yield method. Premiums and discounts on mortgage-backed securities are adjusted for the effects of actual and anticipated prepayments on a retrospective basis.
	Equity securities classified as available for sale are carried at estimated fair value, with unrealized gains and losses, net of applicable income taxes, excluded from earnings and reported as a component of comprehensive income and a separate component of stockholders' equity.
	Equity and fixed maturity securities that the Company purchased with the intent to sell in the near-term are classified as trading account securities and are reported at estimated fair value. Realized and unrealized gains and losses from trading activity are reported as net investment income and are recorded at the trade date. Short sales and short call options are presented as trading securities sold but not yet purchased. Unsettled trades and the net margin balances held by the clearing broker are presented as a trading account receivable from brokers and clearing organizations.
	Investment funds are carried under the equity method of accounting. For certain investment funds, the Company's share of the earnings or losses is reported on a one-quarter lag in order to facilitate the timely completion of the Company's consolidated financial statements.
	Loans receivable primarily represent commercial real estate mortgage loans and bank loans and are carried at amortized cost. The Company monitors the performance of its loans receivable and establishes an allowance for loan losses for loans where the Company determines it is probable that the contractual terms will not be met, with a corresponding charge to earnings. For loans that are evaluated individually and deemed to be impaired, the Company establishes a specific allowance based on a discounted cash flow analysis and comparable cost and sales methodologies, if appropriate. Individual loans that are not considered impaired and smaller-balance homogeneous loans are evaluated collectively and a general allowance is established if it is considered probable that a loss has been incurred.
	The accrual of interest on loans receivable is discontinued if the loan is 90 days past due based on the contractual terms of the loan unless the loan is adequately secured and in process of collection. In general, loans are placed on non-accrual status or charged off at an earlier date if collection of principal or interest is considered doubtful. Interest on these loans is accounted for on a cash basis until qualifying for return to accrual status. Loans are returned to accrual status when all principal and interest amounts contractually due are brought current and future payments are reasonably assured.
	Fair value is defined as “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.” Fair value of investments is determined based on a fair value hierarchy that prioritizes the use of observable inputs over the use of unobservable inputs and requires the use of observable inputs when available. (See Note 13 of the Notes to Consolidated Financial Statements.)
	Realized gains or losses represent the difference between the cost of securities sold and the proceeds realized upon sale and are recorded at the trade date. The Company uses primarily the first-in, first-out method to determine the cost of securities sold.
	The cost of securities is adjusted where appropriate to include a provision for a decline in value which is considered to be other than temporary. An other-than-temporary decline is considered to occur in investments where there has been a sustained reduction in fair value and where the Company does not expect to recover the cost basis of the investment prior to the time of sale or maturity. Since equity securities do not have a contractual cash flow or a maturity, the Company considers whether the price of an equity security is expected to recover within a reasonable period of time.
	For fixed maturity securities that the Company intends to sell or, more likely than not, would be required to sell, a decline in value below amortized cost is considered to be an other-than-temporary impairment (“OTTI”). The amount of OTTI is equal to the difference between amortized cost and fair value at the balance sheet date. For fixed maturity securities that the Company does not intend to sell or believes that it is more likely than not it would not be required to sell, a decline in value below amortized cost is considered to be an OTTI if the Company does not expect to recover the entire amortized cost basis of a security (i.e., the present value of cash flows expected to be collected is less than the amortized cost basis of the security). The portion of the decline in value considered to be a credit loss (i.e., the difference between the present value of cash flows expected to be collected and the amortized cost basis of the security) is recognized in earnings. The portion of the decline in value not considered to be a credit loss (i.e., the difference in the present value of cash flows expected to be collected and the fair value of the security) is recognized in other comprehensive income.
	Impairment assessments for structured securities, including mortgage-backed securities and asset-backed securities, collateralized debt obligations and corporate debt, are generally evaluated based on the performance of the underlying collateral under various economic and default scenarios that may involve subjective judgments and estimates by management. Modeling these securities involves various factors, such as projected default rates, the nature and realizable value of the collateral, if any, the ability of the issuer to make scheduled payments, historical performance and other relevant economic and performance factors. If an OTTI determination is made, a discounted cash flow analysis is used to ascertain the amount of the credit impairment.
	Real estate held for investment purposes is initially recorded at the purchase price, which is generally fair value, and is subsequently reported at cost less accumulated depreciation. Real estate taxes, interest and other costs incurred during development and construction are capitalized. Buildings are depreciated on a straight-line basis over the estimated useful lives of the building. Minimum rental income is recognized on a straight-line basis over the lease term. Income and expenses from real estate are reported as net investment income. The carrying value of real estate is reviewed for impairment and an impairment loss is recognized if the estimated undiscounted cash flows from the use and disposition of the property are less than the carrying value of the property.
Per share data	Per share data
	The Company presents both basic and diluted net income per share (“EPS”) amounts. Basic EPS is calculated by dividing net income by weighted average number of common shares outstanding during the year. Diluted EPS is based upon the weighted average number of common and common equivalent shares outstanding during the year and is calculated using the treasury stock method for stock incentive plans. Common equivalent shares are excluded from the computation in periods in which they have an anti-dilutive effect. Stock options for which the exercise price exceeds the average market price over the period have an anti-dilutive effect on EPS and, accordingly, are excluded from the calculation.
Deferred policy acquisition costs	Deferred policy acquisition costs
	Acquisition costs associated with the successful acquisition of new and renewed insurance and reinsurance contracts are deferred and amortized ratably over the terms of the related contracts. Ceding commissions received on reinsurance contracts are netted against acquisition costs and are recognized ratably over the life of the contract. Deferred policy acquisition costs are presented net of unearned ceding commissions. Deferred policy acquisition costs are comprised primarily of commissions, as well as employment-related underwriting costs and premium taxes. Deferred policy acquisition costs are reviewed to determine if they are recoverable from future income and, if not, are charged to expense. The recoverability of deferred policy acquisition costs is evaluated separately by each of our operating companies for each of their major lines of business. Future investment income is taken into account in measuring the recoverability of deferred policy acquisition costs.
Reserves for losses and loss expenses	Reserves for losses and loss expenses
	Reserves for losses and loss expenses are an accumulation of amounts determined on the basis of (1) evaluation of claims for business written directly by the Company; (2) estimates received from other companies for reinsurance assumed by the Company; and (3) estimates for losses incurred but not reported (based on Company and industry experience). These estimates are periodically reviewed and, as experience develops and new information becomes known, the reserves are adjusted as necessary. Such adjustments are reflected in the statements of income in the period in which they are determined. The Company discounts its reserves for excess and assumed workers' compensation claims using a risk-free or statutory rate.
Reinsurance ceded	Reinsurance ceded
	The unearned portion of premiums ceded to reinsurers is reported as prepaid reinsurance premiums and earned ratably over the policy term. The estimated amounts of reinsurance recoverable on unpaid losses are reported as due from reinsurers. To the extent any reinsurer does not meet its obligations under reinsurance agreements, the Company must discharge its liability. Amounts due from reinsurers are reflected net of funds held where the right of offset is present. The Company has provided reserves for estimated uncollectible reinsurance.
Deposit accounting	Deposit accounting
	Contracts that do not meet the risk transfer requirements of GAAP are accounted for using the deposit accounting method. Under this method, an asset or liability is recognized at the inception of the contract based on consideration paid or received. The amount of the deposit asset or liability is adjusted at subsequent reporting dates using the interest method with a corresponding credit or charge to interest income or expense.
Federal and foreign income taxes	Federal and foreign income taxes
	The Company files a consolidated income tax return in the U.S. and foreign tax returns in countries where it has overseas operations. The Company's method of accounting for income taxes is the asset and liability method. Under this method, deferred tax assets and liabilities are measured using tax rates currently in effect or expected to apply in the years in which those temporary differences are expected to reverse. Interest and penalties, if any, are reported as income tax expense. The Company believes there are no tax positions that would require disclosure under GAAP. Deferred tax assets are reduced by a valuation allowance if it is more likely than not that all or a portion of the deferred tax assets will not be realized.
Foreign currency	Foreign currency
	Gains and losses resulting from foreign currency transactions (transactions denominated in a currency other than the entity's functional currency) are reported on the statements of income as other operating costs and expenses. Unrealized gains or losses resulting from translating the results of non-U.S. dollar denominated operations are reported in accumulated other comprehensive income. Revenues and expenses denominated in currencies other than U.S. dollars are translated at the weighted average exchange rate during the year. Assets and liabilities are translated at the rate of exchange in effect at the balance sheet date.
Property, furniture and equipment	Property, furniture and equipment
	Property, furniture and equipment are carried at cost less accumulated depreciation. Depreciation is calculated using the estimated useful lives of the respective assets.
Comprehensive income	Comprehensive income
	Comprehensive income encompasses all changes in stockholders' equity (except those arising from transactions with stockholders) and includes net income, net unrealized holding gains or losses on available for sale securities, unrealized foreign currency translation adjustments and changes in unrecognized pension obligations.
Goodwill and other intangible assets	Goodwill and other intangible assets
	Goodwill and other intangible assets are tested for impairment on an annual basis and at interim periods where circumstances require.
Stock options	Stock options
	The costs resulting from all share-based payment transactions with employees are recognized in the consolidated financial statements using a fair-value-based measurement method.
Recent accounting pronouncements	Recent accounting pronouncements
	In January 2014, the Financial Accounting Standards Board issued guidance relating to Accounting for Investments in Qualified Affordable Housing Projects. This guidance modified the amortization method on these investments and the statement of operations classification as pre-adoption amounts were presented in both pre-tax income and income tax expense while post adoption all impacts are recorded in income tax expense. The Company adopted this guidance effective January 1, 2014, and the impact of applying this guidance was immaterial.
	All recently issued but not yet effective accounting and reporting standards are either not applicable to the Company or are not expected to have a material impact on the Company.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles

Acquisitions_Tables

Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2014
Business Combinations [Abstract]
Schedule of estimated fair value of net assets acquired and liabilities assumed
	(In thousands)	2014			2013
	Cash and cash equivalents	$	17,457		$	3,911
	Real estate, furniture and equipment	669			898
	Goodwill and other intangibles assets	79,646			64,464
	Premium and service fee receivable	24,432			—
	Other assets	2,590			60,661
	Total assets acquired	124,794			129,934
	Deferred federal income tax	(7,107		)	—
	Debt	—			(27,612		)
	Other liabilities assumed	(34,809		)	(17,076		)
	Net assets acquired	$	82,878		$	85,246

Consolidated_Statement_of_Comp1

Consolidated Statement of Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Components of Changes in Accumulated Other Comprehensive Income (Loss) (AOCI)	The following table presents the components of the changes in accumulated other comprehensive income (loss) (AOCI) as of and for the year ended December 31, 2014:
	(In thousands)	Unrealized investment gains (losses)				Currency translation adjustments			Net pension asset				Accumulated other comprehensive income (loss)
	Changes in AOCI
	Beginning of period	$	256,566			$	(60,524	)	$	(6,651	)		$	189,391
	Other comprehensive income (loss) before reclassifications	98,294				(62,125		)	—				36,169
	Amounts reclassified from AOCI	(48,628		)		—			6,651				(41,977		)
	Other comprehensive income (loss)	49,666				(62,125		)	6,651				(5,808		)
	Unrealized investment gain related to non-controlling interest	(33		)		—			—				(33		)
	Ending balance	$	306,199			$	(122,649	)	$	—			$	183,550
	Amounts reclassified from AOCI
	Pre-tax	$	(74,812	)	-1	$	—		$	10,232		-3	$	(64,580	)
	Tax effect	26,184			-2	—			(3,581		)	-2	22,603
	After-tax amounts reclassified	$	(48,628	)		$	—		$	6,651			$	(41,977	)
	Other comprehensive income (loss)
	Pre-tax	$	72,889			$	(62,125	)	$	10,232			$	20,996
	Tax effect	(23,223		)		—			(3,581		)		(26,804		)
	Other comprehensive income (loss)	$	49,666			$	(62,125	)	$	6,651			$	(5,808	)
	The following table presents the components of the changes in accumulated other comprehensive income (loss) (AOCI) as of and for the year ended December 31, 2013:
	(In thousands)	Unrealized investment gains (losses)				Currency translation adjustments			Net pension asset				Accumulated other comprehensive income (loss)
	Changes in AOCI
	Beginning of period	$	517,658			$	(36,676	)	$	(15,351	)		$	465,631
	Other comprehensive income (loss) before reclassifications	(193,188		)		(23,848		)	—				(217,036		)
	Amounts reclassified from AOCI	(67,876		)		—			8,700				(59,176		)
	Other comprehensive income (loss)	(261,064		)		(23,848		)	8,700				(276,212		)
	Unrealized investment gain related to non-controlling interest	(28		)		—			—				(28		)
	Ending balance	$	256,566			$	(60,524	)	$	(6,651	)		$	189,391
	Amounts reclassified from AOCI
	Pre-tax	$	(104,425	)	-1	$	—		$	13,387		-3	$	(91,038	)
	Tax effect	36,549			-2	—			(4,687		)	-2	31,862
	After-tax amounts reclassified	$	(67,876	)		$	—		$	8,700			$	(59,176	)
	Other comprehensive income (loss)
	Pre-tax	$	(401,637	)		$	(23,848	)	$	13,387			$	(412,098	)
	Tax effect	140,573				—			(4,687		)		135,886
	Other comprehensive income (loss)	$	(261,064	)		$	(23,848	)	$	8,700			$	(276,212	)
	_______________
	(1) Net investment gains in the consolidated statements of income.
	(2) Income tax expense in the consolidated statements of income.
	(3) Other operating costs and expenses in the consolidated statements of income.

Investments_In_Fixed_Maturity_1

Investments In Fixed Maturity Securities (Tables) (Debt Securities)	12 Months Ended
	Dec. 31, 2014												Dec. 31, 2012
Debt Securities
Schedule of Marketable Securities [Line Items]
Investments In Fixed Maturity Securities	At December 31, 2014 and 2013, investments in fixed maturity securities were as follows:
	(In thousands)	Amortized		Gross		Gross			Fair		Carrying
		Cost		Unrealized		Unrealized			Value		Value
				Gains		Losses
	December 31, 2014
	Held to maturity:
	State and municipal	$	72,901	$	17,501	$	—		$	90,402	$	72,901
	Residential mortgage-backed securities	23,278		2,854		—			26,132		23,278
	Corporate	4,998		291		—			5,289		4,998
	Total held to maturity	101,177		20,646		—			121,823		101,177
	Available for sale:
	U.S. government and government agency	773,192		33,353		(3,157		)	803,388		803,388
	State and municipal	4,137,866		229,150		(4,020		)	4,362,996		4,362,996
	Mortgage-backed securities:
	Residential(1)	1,201,924		27,124		(9,449		)	1,219,599		1,219,599
	Commercial	74,479		1,610		(52		)	76,037		76,037
	Corporate	5,036,958		187,960		(24,781		)	5,200,137		5,200,137
	Foreign government	897,668		62,223		(18,065		)	941,826		941,826
	Total available for sale	12,122,087		541,420		(59,524		)	12,603,983		12,603,983
	Total investment in fixed maturity securities	$	12,223,264	$	562,066	$	(59,524	)	$	12,725,806	$	12,705,160
	December 31, 2013
	Held to maturity:
	State and municipal	$	68,929	$	11,172	$	—		$	80,101	$	68,929
	Residential mortgage-backed securities	27,393		3,311		—			30,704		27,393
	Corporate	4,998		417		—			5,415		4,998
	Total held to maturity	101,320		14,900		—			116,220		101,320
	Available for sale:
	U.S. government and government agency	858,319		34,522		(7,982		)	884,859		884,859
	State and municipal	4,085,791		162,330		(29,837		)	4,218,284		4,218,284
	Mortgage-backed securities:
	Residential(1)	1,248,693		25,895		(25,941		)	1,248,647		1,248,647
	Commercial	76,454		5,670		(988		)	81,136		81,136
	Corporate	4,076,585		156,256		(30,100		)	4,202,741		4,202,741
	Foreign government	844,469		51,674		(16,286		)	879,857		879,857
	Total available for sale	11,190,311		436,347		(111,134		)	11,515,524		11,515,524
	Total investment in fixed maturity securities	$	11,291,631	$	451,247	$	(111,134	)	$	11,631,744	$	11,616,844
	_______________________________________
	-1	Gross unrealized losses for mortgage-backed securities include $1,095,671 and $1,961,247, as of December 31, 2014 and 2013, respectively, related to the non-credit portion of OTTI recognized in other comprehensive income.
The Amortized Cost And Fair Value of Fixed Maturity Securities													The amortized cost and fair value of fixed maturity securities at December 31, 2014, by contractual maturity, are shown below. Actual maturities may differ from contractual maturities because certain issuers may have the right to call or prepay obligations.
													(In thousands)	Amortized		Fair Value
														Cost
													Due in one year or less	$	884,831	$	895,004
													Due after one year through five years	3,953,003		4,119,946
													Due after five years through ten years	3,600,155		3,790,402
													Due after ten years	2,485,594		2,598,686
													Mortgage-backed securities	1,299,681		1,321,768
													Total	$	12,223,264	$	12,725,806

Investments_In_Equity_Securiti1

Investments In Equity Securities Available For Sale (Tables) (Equity securities available for sale)	12 Months Ended
	Dec. 31, 2014
Equity securities available for sale
Schedule of Available-for-sale Securities [Line Items]
Schedule of Investments in Equity Securities	At December 31, 2014 and 2013, investments in equity securities available for sale were as follows:
	(In thousands)	Cost		Gross		Gross			Fair		Carrying
				Unrealized		Unrealized			Value		Value
				Gains		Losses
	December 31, 2014
	Common stocks	$	69,870	$	11,929	$	(5,453	)	$	76,346	$	76,346
	Preferred stocks	90,425		8,385		(4,165		)	94,645		94,645
	Total	$	160,295	$	20,314	$	(9,618	)	$	170,991	$	170,991
	December 31, 2013
	Common stocks	$	118,536	$	42,239	$	—		$	160,775	$	160,775
	Preferred stocks	85,091		43,791		(6,319		)	122,563		122,563
	Total	$	203,627	$	86,030	$	(6,319	)	$	283,338	$	283,338

Net_Investment_Income_Tables

Net Investment Income (Tables)	12 Months Ended
	Dec. 31, 2014
Net Investment Income [Abstract]
Net Investment Income	Net investment income consists of the following:
	(In thousands)	2014			2013			2012
	Investment income earned on:
	Fixed maturity securities, including cash and cash equivalents and loans receivable	$	439,489		$	442,287		$	479,035
	Equity securities available for sale	6,726			11,380			16,419
	Investment funds	131,649			67,712			77,015
	Arbitrage trading account	22,438			20,431			8,286
	Real estate	10,228			12,498			12,097
	Gross investment income	610,530			554,308			592,852
	Investment expense	(9,645		)	(10,017		)	(6,089		)
	Net investment income	$	600,885		$	544,291		$	586,763

Investment_Funds_Tables

Investment Funds (Tables)	12 Months Ended
	Dec. 31, 2014
Equity Method Investments and Joint Ventures [Abstract]
Schedule of Investment Funds	Investment funds consist of the following:
		Carrying Value				Income
		as of December 31,
	(In thousands)	2014		2013		2014		2013		2012
	Real estate	$	466,703	$	378,435	$	26,233	$	9,315	$	30,196
	Energy	152,056		155,026		12,797		29,739		33,146
	Hedged equity	282,335		271,575		10,760		7,655		5,912
	Other funds	310,307		262,459		81,859		21,003		7,761
	Total	$	1,211,401	$	1,067,495	$	131,649	$	67,712	$	77,015
	Other funds include private equity investments carried on the equity method of accounting, which includes a publicly traded common stock investment in HealthEquity, Inc. (HQY). Our ownership interest in HQY as of December 31, 2014 is 28.1%, with a fair value of $392 million and a carrying value of $45 million.

Real_Estate_Tables

Real Estate (Tables)	12 Months Ended
	Dec. 31, 2014
Real Estate [Abstract]
Schedule of real estate properties	Investment in real estate represents directly owned property held for investment, as follows:
		As of December 31,
	(In thousands)	2014		2013
	Properties in operation	$	196,980	$	283,393
	Properties under development	534,632		431,849
	Total	$	731,612	$	715,242

Loans_Receivable_Tables

Loans Receivable (Tables)	12 Months Ended
	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable, Gross, Allowance, and Net [Abstract]
Schedule of Loans Receivable	Loans receivable are as follows:
		As of December 31,
	(In thousands)	2014		2013
	Amortized cost:
	Real estate loans	$	243,407	$	282,357
	Commercial loans	78,605		61,226
	Total	$	322,012	$	343,583
	Fair value:
	Real estate loans	$	245,112	$	284,017
	Commercial loans	80,107		62,729
	Total	$	325,219	$	346,746
	Valuation allowance:
	Specific	$	115	$	—
	General	2,371		2,087
	Total	$	2,486	$	2,087
		For the Year Ended December 31,
		2014		2013
	Increase in valuation allowance	$	398	$	308

Realized_And_Unrealized_Invest1

Realized And Unrealized Investment Gains and Losses (Tables)	12 Months Ended
	Dec. 31, 2014
Realized and Unrealized Investment Gains (Losses) [Abstract]
Realized and Unrealized Investment Gains (Losses)	Realized and unrealized investment gains and losses are as follows:
	(In thousands)	2014			2013			2012
	Realized investment gains and losses:
	Fixed maturity securities:
	Gains	$	39,113		$	48,860		$	34,295
	Losses	(4,420		)	(14,670		)	(6,436		)
	Equity securities available for sale	38,296			70,235			97,300
	Investment funds	96,204			10,976			74,777
	Real estate	85,659			—			—
	Other gains	—			12,185			1,515
	Net realized gains on investments sales	254,852			127,586			201,451
	Net other-than-temporary impairments:
	Other-than-temporary impairments	—			(6,042		)	(4,984		)
	Decrease in valuation allowance	—			—			13,998
	Net other-than-temporary impairments	—			(6,042		)	9,014
	Total net investment gains	254,852			121,544			210,465
	Income tax expense	(89,198		)	(47,426		)	(73,663		)
		$	165,654		$	74,118		$	136,802
Change In Unrealized Gains (Losses)
	Change in unrealized gains and losses of available for sales securities:
	Fixed maturity securities	$	155,765		$	(401,812	)	$	162,220
	Previously impaired fixed maturity securities	865			1,076			4,631
	Equity securities available for sale	(69,016		)	11,864			(33,199		)
	Investment funds	(14,725		)	(10,250		)	1,630
	Total change in unrealized gains	72,889			(399,122		)	135,282
	Income tax benefit (expense)	(23,223		)	138,058			(47,966		)
	Noncontrolling interests	(33		)	(28		)	(77		)
		$	49,633		$	(261,092	)	$	87,239

Securities_In_An_Unrealized_Lo1

Securities In An Unrealized Loss Position (Tables)	12 Months Ended
	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Securities In An Unrealized Loss Position	The following table summarizes all securities in an unrealized loss position at December 31, 2014 and 2013 by the length of time those securities have been continuously in an unrealized loss position.
		Less Than 12 Months						12 Months or Greater				Total
	(In thousands)	Fair			Gross			Fair		Gross		Fair		Gross
		Value			Unrealized			Value		Unrealized		Value		Unrealized
					Losses					Losses				Losses
	December 31, 2014
	U.S. government and government agency	$	84,750		$	522		$	84,850	$	2,635	$	169,600	$	3,157
	State and municipal	158,594			631			150,284		3,389		308,878		4,020
	Mortgage-backed securities	75,739			332			312,922		9,169		388,661		9,501
	Corporate	1,586,238			8,697			214,628		16,084		1,800,866		24,781
	Foreign government	76,471			3,907			85,025		14,158		161,496		18,065
	Fixed maturity securities	1,981,792			14,089			847,709		45,435		2,829,501		59,524
	Common stocks	15,929			5,453			—		—		15,929		5,453
	Preferred stocks	27,126			1,139			22,648		3,026		49,774		4,165
	Equity securities available for sale	43,055			6,592			22,648		3,026		65,703		9,618
	Total	$	2,024,847		$	20,681		$	870,357	$	48,461	$	2,895,204	$	69,142
	December 31, 2013
	U.S. government and government agency	$	260,882		$	7,927		$	2,163	$	55	$	263,045	$	7,982
	State and municipal	899,613			24,503			87,345		5,334		986,958		29,837
	Mortgage-backed securities	578,603			17,964			140,648		8,965		719,251		26,929
	Corporate	1,013,373			17,066			105,074		13,034		1,118,447		30,100
	Foreign government	320,215			16,286			—		—		320,215		16,286
	Fixed maturity securities	3,072,686			83,746			335,230		27,388		3,407,916		111,134
	Common stocks	—			—			—		—		—		—
	Preferred stocks	13,291			513			19,868		5,806		33,159		6,319
	Equity securities available for sale	13,291			513			19,868		5,806		33,159		6,319
	Total	$	3,085,977		$	84,259		$	355,098	$	33,194	$	3,441,075	$	117,453
Non-Investment Grade Fixed Maturity Securities	A summary of the Company’s non-investment grade fixed maturity securities that were in an unrealized loss position at December 31, 2014 is presented in the table below:
	(Dollars in thousands)	Number of		Aggregate			Gross
		Securities		Fair Value			Unrealized
							Loss
	Mortgage-backed securities	9		$	28,537		$	1,699
	Corporate	10		24,528			742
	Foreign government	2		11,177			247
	Total	21		$	64,242		$	2,688

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Assets And Liabilities Measured At Fair value, On A Recurring Basis	The following tables present the assets and liabilities measured at fair value on a recurring basis as of December 31, 2014 and 2013 by level:
	(In thousands)	Total		Level 1			Level 2			Level 3
	December 31, 2014
	Assets:
	Fixed maturity securities available for sale:
	U.S. government and government agency	$	803,388	$	—		$	803,388		$	—
	State and municipal	4,362,996		—			4,362,996			—
	Mortgage-backed securities	1,295,636		—			1,295,636			—
	Corporate	5,200,137		—			5,179,372			20,765
	Foreign government	941,826		—			941,826			—
	Total fixed maturity securities available for sale	12,603,983		—			12,583,218			20,765
	Equity securities available for sale:
	Common stocks	76,346		65,605			—			10,741
	Preferred stocks	94,645		—			90,932			3,713
	Total equity securities available for sale	170,991		65,605			90,932			14,454
	Arbitrage trading account	450,648		295,047			154,881			720
	Total	$	13,225,622	$	360,652		$	12,829,031		$	35,939
	Liabilities:
	Securities sold but not yet purchased	$	106,079	$	106,074		$	5		$	—
	December 31, 2013
	Assets:
	Fixed maturity securities available for sale:
	U.S. government and government agency	$	884,859	$	—		$	884,859		$	—
	State and municipal	4,218,284		—			4,218,284			—
	Mortgage-backed securities	1,329,783		—			1,329,783			—
	Corporate	4,202,741		—			4,159,877			42,864
	Foreign government	879,857		—			879,857			—
	Total fixed maturity securities available for sale	11,515,524		—			11,472,660			42,864
	Equity securities available for sale:
	Common stocks	160,775		159,537			—			1,238
	Preferred stocks	122,563		—			118,811			3,752
	Total equity securities available for sale	283,338		159,537			118,811			4,990
	Arbitrage trading account	522,128		192,281			328,067			1,780
	Total	$	12,320,990	$	351,818		$	11,919,538		$	49,634
	Liabilities:
	Securities sold but not yet purchased	$	162,278	$	162,126		$	152		$	—
Summarize Changes In Level 3 Assets and Liabilities	The following tables summarize changes in Level 3 assets and liabilities for the years ended December 31, 2014 and 2013:
		Gains (Losses) Included in:
	(In thousands)	Beginning Balance		Earnings			Other Comprehensive Income			Purchases		Sales			Paydowns/Maturities			In		Out			Ending Balance
	Year ended December 31, 2014
	Assets:
	Fixed maturity securities available for sale:
	Corporate	$	42,864	$	47		$	(3,711	)	$	238	$	(15,244	)	$	(3,429	)	$	—	$	—		$	20,765
	Total	42,864		47			(3,711		)	238		(15,244		)	(3,429		)	—		—			20,765
	Equity securities available for sale:
	Common stocks	1,238		—			(911		)	11,343		(929		)	—			—		—			10,741
	Preferred stocks	3,752		(17		)	—			3,430		(3,452		)	—			—		—			3,713
	Total	4,990		(17		)	(911		)	14,773		(4,381		)	—			—		—			14,454
	Arbitrage trading account	1,780		2,274			—			4,942		(14,073		)	—			9,064		(3,267		)	720
	Total	$	49,634	$	2,304		$	(4,622	)	$	19,953	$	(33,698	)	$	(3,429	)	$	9,064	$	(3,267	)	$	35,939
	Liabilities:
	Securities sold but not yet purchased	$	—	$	(20	)	$	—		$	31	$	(11	)	$	—		$	—	$	—		$	—
	Year ended December 31, 2013
	Assets:
	Fixed maturity securities available for sale:
	Corporate	$	59,065	$	677		$	309		$	170	$	(4,753	)	$	(12,604	)	$	—	$	—		$	42,864
	Total	59,065		677			309			170		(4,753		)	(12,604		)	—		—			42,864
	Equity securities available for sale:
	Common stocks	1,408		—			—			—		(170		)	—			—		—			1,238
	Preferred stocks	621		(299		)	—			3,430		—			—			—		—			3,752
	Total	2,029		(299		)	—			3,430		(170		)	—			—		—			4,990
	Arbitrage trading account	928		1,458			730			824		(853		)	—			22		(1,329		)	1,780
	Total	$	62,022	$	1,836		$	1,039		$	4,424	$	(5,776	)	$	(12,604	)	$	22	$	(1,329	)	$	49,634
	Liabilities:
	Securities sold but not yet purchased	$	20	$	(4	)	$	—		$	4	$	(20	)	$	—		$	—	$	—		$	—

Reserves_For_Losses_And_Loss_E1

Reserves For Losses And Loss Expenses (Tables)	12 Months Ended
	Dec. 31, 2013
Insurance [Abstract]
Schedule of Liability for Unpaid Claims and Claims Adjustment Expense	The table below provides a reconciliation of the beginning and ending reserve balances:
	(In thousands)	2014			2013			2012
	Net reserves at beginning of year	$	8,683,797		$	8,411,851		$	8,172,112
	Net provision for losses and loss expenses:
	Claims occuring during the current year(1)	3,495,825			3,221,393			2,997,995
	Decrease in estimates for claims occurring in prior years(2)(3)	(75,764		)	(78,810		)	(102,571		)
	Loss reserve discount accretion(4)	70,506			54,441			53,055
	Total	3,490,567			3,197,024			2,948,479
	Net payments for claims:
	Current year	898,944			822,787			698,834
	Prior year	2,216,283			2,055,284			2,010,101
	Total	3,115,227			2,878,071			2,708,935
	Foreign currency translation	(88,496		)	(47,007		)	195
	Net reserves at end of year	8,970,641			8,683,797			8,411,851
	Ceded reserve at end of year	1,399,060			1,397,144			1,339,235
	Gross reserves at end of year	$	10,369,701		$	10,080,941		$	9,751,086
	_______________________________________
	-1	Claims occurring during the current year are net of loss reserve discounts of $21,306,000, $22,680,000, and $26,078,000 in 2014, 2013 and 2012, respectively.
	-2	The decrease in estimates for claims occurring in prior years is net of loss reserve discount. On an undiscounted basis, the estimates for claims occurring in prior years decreased by $116,866,000, $77,430,000 and $100,667,000 in 2014, 2013 and 2012, respectively.
	-3	For certain retrospectively rated insurance polices and reinsurance agreements, reserve development is offset by additional or return premiums. Favorable reserve development, net of additional and return premiums, was $85 million, $98 million and $103 million in 2014, 2013 and 2012, respectively.

Reinsurance_Tables

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2014
Reinsurance Disclosures [Abstract]
Reinsurance Financial Information	The following is a summary of reinsurance financial information:
	(In thousands)	2014			2013			2012
	Written premiums:
	Direct	$	6,185,242		$	5,626,172		$	4,964,069
	Assumed	877,596			884,919			815,810
	Ceded	(1,065,891		)	(1,010,918		)	(881,340		)
	Total net written premiums	$	5,996,947		$	5,500,173		$	4,898,539
	Earned premiums:
	Direct	$	5,889,021		$	5,328,955		$	4,723,882
	Assumed	886,063			857,119			770,981
	Ceded	(1,030,666		)	(959,537		)	(821,347		)
	Total net earned premiums	$	5,744,418		$	5,226,537		$	4,673,516
	Ceded losses and loss expenses incurred	$	475,802		$	556,108		$	528,018
	Ceded commission earned	$	160,215		$	137,449		$	121,089
Schedule of Ceded Credit Risk by Reinsurer	The following table presents the amounts due from reinsurers as of December 31, 2014:
	(In thousands)
	Munich Re	$	141,489
	Allegany Grp	109,976
	Lloyd’s of London	101,308
	Swiss Re	97,300
	Partner Re	70,756
	Axis Capital	63,352
	Berkshire Hathaway	48,804
	Ace Group	44,215
	Everest Re	43,207
	Hannover Re Group	41,749
	Arch Capital Group	23,453
	Other reinsurers less than $20,000	212,270
	Subtotal	997,879
	Residual market pools	505,562
	Total	$	1,503,441

Indebtedness_Tables

Indebtedness (Tables) (Senior Notes and Other Debt)	12 Months Ended
	Dec. 31, 2013
Senior Notes and Other Debt
Debt Instrument [Line Items]
Schedule of Debt	consisted of the following as of December 31, 2014 (the difference between the face value and the carrying value is unamortized discount):
	(In thousands)	Interest Rate	Face Value		2014 Carrying Value		2013 Carrying Value
	Senior notes due on:
	May 15, 2015	5.60%	$	200,000	$	199,930	$	199,744
	August 15, 2019	6.15%	150,000		149,342		149,199
	September 15, 2019	7.38%	300,000		298,800		298,546
	September 15, 2020	5.38%	300,000		298,074		297,738
	January 1, 2022	8.70%	76,503		76,048		76,004
	15-Mar-22	4.63%	350,000		346,999		346,581
	February 15, 2037	6.25%	250,000		247,566		247,457
	1-Aug-44	4.75%	350,000		344,545		—
	Subsidiary debt (1)	Various	153,549		154,223		77,173
	Total senior notes and other debt		$	2,130,052	$	2,115,527	$	1,692,442
	Subordinated debentures	5.63%	$	350,000	$	340,060	$	339,800
	_____________
	(1) Subsidiary debt is due as follows: $76 million in 2015, $33 million in 2016, $42 million in 2017 and $3 million thereafter.
	In 2013, the Company issued $350 million aggregate principal amount of 5.625% Subordinated Debentures due April 2053. At December 31, 2014, the carrying value of the debentures, net of unamortized discount, was $340 million.

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	Income tax expense consists of:
	(In thousands)	Current			Deferred			Total
		Expense			Expense
	31-Dec-14
	Domestic	$	258,337		$	28,029		$	286,366
	Foreign	12,969			3,258			16,227
	Total expense	$	271,306		$	31,287		$	302,593
	31-Dec-13
	Domestic	$	116,802		$	47,370		$	164,172
	Foreign	22,362			7,053			29,415
	Total expense	$	139,164		$	54,423		$	193,587
	31-Dec-12
	Domestic	$	156,339		$	11,448		$	167,787
	Foreign	23,029			469			23,498
	Total expense	$	179,368		$	11,917		$	191,285
Schedule of Effective Income Tax Rate Reconciliation	A reconciliation of the income tax expense and the amounts computed by applying the Federal and foreign income tax rate of 35% to pre-tax income are as follows:
	(In thousands)	2014			2013			2012
	Computed “expected” tax expense	$	333,269		$	244,611		$	245,675
	Tax-exempt investment income	(38,757		)	(40,679		)	(50,665		)
	Change in valuation allowance	1,335			—			—
	Impact of foreign tax rates	6,239			(4,851		)	(5,234		)
	State and local taxes	2,375			2,906			(753		)
	Other, net	(1,868		)	(8,400		)	2,262
	Total expense	$	302,593		$	193,587		$	191,285
Schedule of Deferred Tax Assets and Liabilities
	(In thousands)	2014			2013			2012
	Computed “expected” tax expense	$	333,269		$	244,611		$	245,675
	Tax-exempt investment income	(38,757		)	(40,679		)	(50,665		)
	Change in valuation allowance	1,335			—			—
	Impact of foreign tax rates	6,239			(4,851		)	(5,234		)
	State and local taxes	2,375			2,906			(753		)
	Other, net	(1,868		)	(8,400		)	2,262
	Total expense	$	302,593		$	193,587		$	191,285
	At December 31, 2014 and 2013, the tax effects of differences that give rise to significant portions of the deferred tax asset and deferred tax liability are as follows:
	(In thousands)	2014			2013
	Deferred tax asset:
	Loss reserve discounting	$	77,216		$	87,394
	Unearned premiums	165,075			149,107
	Other-than-temporary impairments	45,367			49,483
	Restricted stock units	60,061			52,671
	Other	101,131			92,698
	Gross deferred tax asset	448,850			431,353
	Less valuation allowance	(1,335		)	—
	Deferred tax asset	447,515			431,353
	Deferred tax liability:
	Amortization of intangibles	22,747			11,886
	Deferred policy acquisition costs	152,001			136,635
	Unrealized investment gains	175,111			148,215
	Other	135,108			114,497
	Deferred tax liability	484,967			411,233
	Net deferred tax asset (liability)	$	(37,452	)	$	20,120

Dividends_From_Subsidiaries_An1

Dividends From Subsidiaries And Statutory Financial Information (Tables)	12 Months Ended
	Dec. 31, 2014
Insurance [Abstract]
Schedule of Combined Net Income and Policyholders' Surplus in Accordance with Statutory Accounting Practices	BIC’s net income and statutory capital and surplus, as determined in accordance with statutory accounting practices (SAP), are as follows:
	(In thousands)	2014		2013		2012
	Net income	$	753,260	$	469,354	$	482,457
	Statutory capital and surplus	$	5,438,064	$	4,908,010	$	4,671,979

Common_Stockholders_Equity_Tab

Common Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Weighted Average Number of Common Shares Used In the Computation of Basic and Diluted Earnings per Share	The weighted average number of shares used in the computation of net income per share was as follows:
		2014		2013		2012
	Basic	127,873,708		135,304,752		137,097,162
	Diluted	133,651,855		140,742,922		143,314,544
Schedule of Changes in Shares of Common Stock Outstanding	Changes in shares of common stock outstanding, net of treasury shares, are presented below. Shares of common stock issued and outstanding do not include shares related to unissued restricted stock units and unexercised stock options.
		2014		2013		2012
	Balance, beginning of year	132,233,167		136,017,732		137,520,019
	Shares issued	332,137		139,790		2,114,168
	Shares repurchased	(5,816,468	)	(3,924,355	)	-3,616,455
	Balance, end of year	126,748,836		132,233,167		136,017,732

Recovered_Sheet1

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Carrying Amounts and Estimated Fair Values of Financial Insruments	The following table presents the carrying amounts and estimated fair values of the Company’s financial instruments as of December 31, 2014 and 2013:
		2014				2013
	(In thousands)	Carrying Value		Fair Value		Carrying Value		Fair Value
	Assets:
	Fixed maturity securities	$	12,705,160	$	12,725,806	$	11,616,844	$	11,631,744
	Equity securities available for sale	170,991		170,991		283,338		283,338
	Arbitrage trading account	450,648		450,648		522,128		522,128
	Loans receivable	322,012		325,219		343,583		346,746
	Cash and cash equivalents	674,441		674,441		839,738		839,738
	Trading accounts receivable from brokers and clearing organizations	371,034		371,034		304,936		304,936
	Due from broker	—		—		17,735		17,735
	Liabilities:
	Due to broker	23,133		23,133		8,273		8,273
	Trading account securities sold but not yet purchased	106,079		106,079		162,278		162,278
	Subordinated debentures	340,060		332,640		339,800		288,540
	Senior notes and other debt	2,115,527		2,344,292		1,692,442		1,861,898

Stock_Incentive_Plan_Tables

Stock Incentive Plan (Tables)	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Share-based Compensation, Stock Options, Activity	The following table summarizes stock option information:
			2013							2012
			Shares			Price(1)				Shares			Price(1)
	Outstanding at beginning of year		3,375			$	15.17			1,314,057			$	11.04
	Exercised		3,375			15.17				1,310,682			11.03
	Canceled		—			—				—			—
	Outstanding at year end		—			$	—			3,375			$	15.17
	_______________________________________
	-1	Weighted average exercise price.
Schedule of Nonvested Restricted Stock Units Activity	The following table summarizes RSU information for the three years ended December 31, 2014:
		2014			2013			2012
	RSUs granted and unvested at beginning of period:	4,491,520			4,701,120			4,370,975
	Granted	1,154,950			108,400			2,161,220
	Vested	(81,500	)		(146,250	)		(1,704,625	)
	Cancelled	(234,525	)		(171,750	)		(126,450	)
	RSUs granted and unvested at end of period:	5,330,445			4,491,520			4,701,120
Schedule of Share-based Compensation, Unearned Compensation Related to RSU's	The fair value of RSUs at the date of grant are recorded as unearned compensation, a component of stockholders’ equity, and expensed over the vesting period. Following is a summary of changes in unearned compensation for the three years ended December 31, 2014:
	(In thousands)	2014				2013				2012
	Unearned compensation at beginning of year	$	73,205			$	93,653			$	57,315
	RSUs granted, net of cancellations	51,575				4,406				73,255
	RSUs expensed	(27,966		)		(22,881		)		(25,728		)
	RSUs forfeitures	(8,799		)		(1,973		)		(11,189		)
	Unearned compensation at end of year	$	88,015			$	73,205			$	93,653

Compensation_Plans_Tables

Compensation Plans (Tables)	12 Months Ended
	Dec. 31, 2014
Compensation Related Costs [Abstract]
Long-Term Incentive Compensation Plan Expense	The following table summarizes the LTIP expense for each of the three years ended December 31, 2014:
	(In thousands)	2014		2013		2012
	2008 grant	$	—	$	—	$	4,283
	2011 grant	9,855		6,939		6,822
	2013 grant	9,493		7,231		—
	2014 grant	3,663		—		—
	Total	$	23,011	$	14,170	$	11,105

Retirement_Benefits_Tables

Retirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]
Schedule of Changes in Projected Benefit Obligations	.
Schedule of Amounts Recognized in Other Comprehensive Income (Loss)	.
Schedule of Net Benefit Costs	.
Schedule of Defined Benefit Plan Amounts Recognized in Other Comprehensive Income (Loss)	.

Supplemental_Financial_Stateme1

Supplemental Financial Statement Information (Tables)	12 Months Ended
	Dec. 31, 2014
Other Income and Expenses [Abstract]
Schedule of Other Operating Cost and Expense, by Component	Other operating costs and expenses consist of the following:
	(In thousands)	2014			2013			2012
	Amortization of deferred policy acquisition costs	$	1,053,397		$	991,070		$	917,583
	Other underwriting expenses	843,133			780,058			675,163
	Service company expenses	102,726			88,662			84,986
	Net foreign currency gains	(27		)	(10,120		)	(6,092		)
	Other costs and expenses	158,227			151,014			127,983
	Total	$	2,157,456		$	2,000,684		$	1,799,623

Industry_Segments_Tables

Industry Segments (Tables)	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Financial Information Of Company Operating Segments	Summary financial information about the Company’s reporting segments is presented in the following table. Income (loss) before income taxes by segment includes allocated investment income. Identifiable assets by segment are those assets used in or allocated to the operation of each segment.
	Revenues
	(In thousands)	Earned		Investment		Other		Total		Pre-Tax			Net
		Premiums		Income						Income			Income
										(Loss)			(Loss)
	December 31, 2014:
	Insurance-Domestic	$	4,271,933	$	428,632	$	106,853	$	4,807,418	$	796,309		$	539,461
	Insurance-International	802,375		55,407		—		857,782		29,779			22,182
	Reinsurance-Global	670,110		88,821		—		758,931		115,677			79,720
	Corporate, other and eliminations(1)	—		28,025		421,920		449,945		(244,421		)	(158,133		)
	Net investment gains	—		—		254,852		254,852		254,852			165,654
	Consolidated	$	5,744,418	$	600,885	$	783,625	$	7,128,928	$	952,196		$	648,884
	December 31, 2013:
	Insurance-Domestic	$	3,782,416	$	404,280	$	107,517	$	4,294,213	$	648,740		$	449,981
	Insurance-International	723,151		47,039		—		770,190		56,922			40,292
	Reinsurance-Global	720,970		89,090		—		810,060		110,425			78,013
	Corporate, other and eliminations(1)	—		3,882		408,645		412,527		(238,743		)	(142,479		)
	Net investment gains	—		—		121,544		121,544		121,544			74,118
	Consolidated	$	5,226,537	$	544,291	$	637,706	$	6,408,534	$	698,888		$	499,925
	December 31, 2012:
	Insurance-Domestic	$	3,417,022	$	424,787	$	103,133	$	3,944,942	$	578,500		$	397,942
	Insurance-International	631,841		45,796		—		677,637		51,639			35,928
	Reinsurance-Global	624,653		106,932		—		731,585		103,690			72,916
	Corporate, other and eliminations(1)	—		9,248		249,677		258,925		(242,366		)	(132,996		)
	Net investment gains	—		—		210,465		210,465		210,465			136,802
	Consolidated	$	4,673,516	$	586,763	$	563,275	$	5,823,554	$	701,928		$	510,592
Identifiable Assets by Segments
	Identifiable Assets
	(In thousands)	31-Dec-14		31-Dec-13
	Insurance-Domestic	$	16,065,409	$	15,247,807
	Insurance-International	1,879,438		1,516,310
	Reinsurance-Global	2,713,554		3,103,193
	Corporate, other and eliminations(1)	1,058,290		684,486
	Consolidated	$	21,716,691	$	20,551,796
	_______________________________________
	-1	Corporate, other and eliminations represent corporate revenues and expenses and other items that are not allocated to business segments.
Net Premiums Earned By Major Line Of Business	Net premiums earned by major line of business are as follows:
	(In thousands)	2014		2013		2012
	Insurance-Domestic
	Other liability	$	1,449,425	$	1,259,376	$	1,104,369
	Workers' compensation	1,126,704		995,047		869,042
	Short-tail lines	875,898		774,809		733,239
	Commercial automobile	526,344		486,759		455,988
	Professional liability	293,562		266,425		254,384
	Total Insurance-Domestic	4,271,933		3,782,416		3,417,022
	Insurance-International
	Other liability	92,411		65,528		44,065
	Workers' compensation	71,997		84,637		82,066
	Short-tail lines	415,123		336,814		276,599
	Commercial automobile	116,369		130,020		125,927
	Professional liability	106,475		106,152		103,184
	Total Insurance-International	802,375		723,151		631,841
	Reinsurance-Global
	Casualty	487,264		507,790		456,376
	Property	182,846		213,180		168,277
	Total Reinsurance-Global	670,110		720,970		624,653
	Total	$	5,744,418	$	5,226,537	$	4,673,516

Quarterly_Financial_Informatio1

Quarterly Financial Information (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	The following is a summary of quarterly financial data:
	(In thousands. except per share data)	2014
	Three months ended	March 31		June 30		September 30		December 31
	Revenues	$	1,706,906	$	1,796,989	$	1,840,605	$	1,784,428
	Net income	169,673		179,961		188,539		110,711
	Net income per share(1)
	Basic	1.31		1.41		1.48		0.87
	Diluted	1.25		1.35		1.42		0.83
		2013
	Three months ended	March 31		June 30		September 30		December 31
	Revenues	$	1,506,769	$	1,570,962	$	1,634,124	$	1,696,679
	Net income	116,615		115,957		136,974		130,379
	Net income per share(1)
	Basic	0.86		0.85		1.01		0.97
	Diluted	0.83		0.82		0.97		0.93
	_______________________________________
	-1	Net income per share (“EPS”) in each quarter is computed using the weighted-average number of shares outstanding during that quarter, while EPS for the full year is computed using the weighted-average number of shares outstanding during the year. Thus, the sum of the four quarters EPS does not necessarily equal the full-year EPS.

Summary_of_Significant_Account3

Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Abstract]
Unbilled Audit Premiums	$9,000,000	$12,000,000	$7,000,000
Deposit contracts, liabilities	68,000,000	72,000,000
Depreciation	44,000,000	38,000,000	38,000,000
Goodwill and intangible asset impairment	0
Indefinite-lived Intangible Assets [Line Items]
Interest payments	120,000,000	125,000,000	119,000,000
Income taxes paid	314,000,000	186,000,000	133,000,000
Other Assets
Indefinite-lived Intangible Assets [Line Items]
Intangible assets, net (excluding goodwill)	$96,000,000	$72,000,000

Summary_of_Significant_Account4

Summary of Significant Accounting Policies (Recent accounting change) (Details) (USD $)	3 Months Ended												12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other operating costs and expenses													$2,157,456	$2,000,684	$1,799,623
Income before income taxes													952,196	698,888	701,928
Federal and foreign income taxes													-302,593	-193,587	-191,285
Net income	$110,711	$188,539	$179,961	$169,673	$130,379		$136,974		$115,957		$116,615		$648,884	$499,925	$510,592
Basic net income per share (dollars per share)	$0.87	$1.48	$1.41	$1.31	$0.97	[1]	$1.01	[1]	$0.85	[1]	$0.86	[1]	$5.07	$3.69	$3.72
Diluted net income per share (dollars per share)	$0.83	$1.42	$1.35	$1.25	$0.93	[1]	$0.97	[1]	$0.82	[1]	$0.83	[1]	$4.86	$3.55	$3.56
[1]	Net income per share (“EPS”) in each quarter is computed using the weighted-average number of shares outstanding during that quarter, while EPS for the full year is computed using the weighted-average number of shares outstanding during the year. Thus, the sum of the four quarters EPS does not necessarily equal the full-year EPS.

Acquisitions_Details

Acquisitions (Details) (USD $)	12 Months Ended					1 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Jan. 31, 2013
Business Acquisition [Line Items]
Accumulated other comprehensive income	$183,550,000		$189,391,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Premium and service fee receivable	150,944,000		110,146,000
Deferred federal and foreign income taxes	37,452,000		0
Proceeds from Sales of Business, Affiliate and Productive Assets	15,783,000
Assets of Disposal Group, Including Discontinued Operation	15,000,000
Disposal Group, Including Discontinued Operation, Property, Plant, and Equipment, Net	4,000,000
Disposal Group, Including Discontinued Operation, Goodwill	7,000,000
Disposal Group, Including Discontinued Operation, Other Assets	6,000,000
Disposal Group, Including Discontinued Operation, Liabilities of Disposal Group	2000
Other Comprehensive Income (Loss), Net of Tax	-5,808,000		-276,212,000		110,857,000
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	952,196,000		698,888,000		701,928,000
Other Cost and Expense, Operating	2,157,456,000		2,000,684,000		1,799,623,000
Income Tax expense	-302,593,000		-193,587,000		-191,285,000
Net income (loss)	649,603,000		505,301,000		510,643,000
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax	72,889,000		-401,637,000
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax	-62,125,000		-23,848,000
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	10,232,000		13,387,000		-1,575,000
Other Comprehensive Income (Loss), before Tax	20,996,000		-412,098,000
Other Comprehensive Income (Loss), Available-for-sale Securities, Tax	-23,223,000		140,573,000
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax	0		0
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Tax	-3,581,000		-4,687,000
Other Comprehensive Income (Loss), Tax	-26,804,000		135,886,000
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	49,666,000		-261,064,000
Net change in period	-62,125,000		-23,848,000		24,563,000
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	6,651,000		8,700,000
Worldwide Supplier of After-market (OEM) Parts [Member]
Business Acquisition [Line Items]
Business acquisition, cost of acquired entity, cash paid					43,000,000	43,000,000
Business Acquisition, Percentage of Voting Interests Acquired			100.00%		0.00%
Indefinite-lived Intangible Assets Acquired			3,000,000
London Acquisition, Inactive insurance Company, and Worldwide Supplier of After-market (OEM) Parts [Member]
Business Acquisition [Line Items]
Indefinite-lived Intangible Assets Acquired	10,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Cash and cash equivalents	17,457,000		3,911,000
Real estate, furniture and equipment	669,000		898,000
Goodwill and other intangibles assets	79,646,000		64,464,000
Premium and service fee receivable	24,432,000		0
Other assets	2,590,000		60,661,000
Total assets acquired	124,794,000		129,934,000
Deferred federal and foreign income taxes	-7,107,000		0
Debt	0		-27,612,000
Other liabilities assumed	-34,809,000		-17,076,000
Net assets acquired	-82,878,000		-85,246,000
Minimum | Worldwide Supplier of After-market (OEM) Parts [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	2 years
Maximum | Worldwide Supplier of After-market (OEM) Parts [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	15 years
Unrealized investment gains (losses)
Business Acquisition [Line Items]
Accumulated other comprehensive income	306,199,000		256,566,000		517,658,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Other comprehensive income (loss) before reclassifications	98,294,000		-193,188,000
Amounts reclassified from AOCI	-48,628,000		-67,876,000
Other Comprehensive Income (Loss), Net of Tax	49,666,000		-261,064,000
Unrealized investment gain related to non-controlling interest	-33,000		-28,000
Currency translation adjustments
Business Acquisition [Line Items]
Accumulated other comprehensive income	-122,649,000		-60,524,000		-36,676,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Other comprehensive income (loss) before reclassifications	-62,125,000		-23,848,000
Amounts reclassified from AOCI	0		0
Other Comprehensive Income (Loss), Net of Tax	-62,125,000		-23,848,000
Net change in period	-62,125,000		-23,848,000		24,563,000
Net pension asset
Business Acquisition [Line Items]
Accumulated other comprehensive income	0		-6,651,000		-15,351,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Other comprehensive income (loss) before reclassifications	0		0
Amounts reclassified from AOCI	6,651,000		8,700,000
Other Comprehensive Income (Loss), Net of Tax	6,651,000		8,700,000
Accumulated other comprehensive income (loss)
Business Acquisition [Line Items]
Accumulated other comprehensive income	183,550,000		189,391,000		465,631,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Other comprehensive income (loss) before reclassifications	36,169,000		-217,036,000
Amounts reclassified from AOCI	-41,977,000		-59,176,000
Other Comprehensive Income (Loss), Net of Tax	-5,808,000		-276,212,000
Unrealized investment gain related to non-controlling interest	-33,000		-28,000
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized investment gains (losses)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Marketable Securities, Realized Gain (Loss), Excluding Other than Temporary Impairments	-74,812,000	[1]	-104,425,000	[1]
Income Tax expense	26,184,000	[2]	36,549,000	[2]
Net income (loss)	-48,628,000		-67,876,000
Reclassification out of Accumulated Other Comprehensive Income [Member] | Currency translation adjustments
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	0		0
Income Tax expense	0		0
Net income (loss)	0		0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net pension asset
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Other Cost and Expense, Operating	10,232,000	[3]	13,387,000	[3]
Income Tax expense	-3,581,000	[2]	-4,687,000	[2]
Net income (loss)	6,651,000		8,700,000
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated other comprehensive income (loss)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	-64,580,000		-91,038,000
Income Tax expense	22,603,000		31,862,000
Net income (loss)	($41,977,000)		($59,176,000)
[1]	Net investment gains in the consolidated statements of income.
[2]	Income tax expense in the consolidated statements of income.
[3]	Other operating costs and expenses in the consolidated statements of income.

Consolidated_Statement_of_Comp2

Consolidated Statement of Comprehensive Income (Loss) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning of period	$189,391
Other comprehensive income (loss)	-5,808		-276,212		110,857
Ending balance	183,550		189,391
Income before income taxes	952,196		698,888		701,928
Other operating costs and expenses	2,157,456		2,000,684		1,799,623
Federal and foreign income taxes	-302,593		-193,587		-191,285
Net income before noncontrolling interests	649,603		505,301		510,643
Unrealized investment gains, before tax	72,889		-401,637
Currency translation adjustments, before tax	-62,125		-23,848
Net pension asset, before tax	10,232		13,387		-1,575
Other comprehensive income (loss), before tax	20,996		-412,098
Unrealized investment gains, tax	-23,223		140,573
Currency translation adjustments, tax	0		0
Net pension asset, tax	-3,581		-4,687
Other comprehensive income (loss), tax	-26,804		135,886
Unrealized investment gains, net of tax	49,666		-261,064
Change in unrealized translation adjustments	-62,125		-23,848		24,563
Net pension asset, net of tax	6,651		8,700
Unrealized investment gains (losses)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning of period	256,566		517,658
Other comprehensive income (loss) before reclassifications	98,294		-193,188
Amounts reclassified from AOCI	-48,628		-67,876
Other comprehensive income (loss)	49,666		-261,064
Unrealized investment gain related to non-controlling interest	-33		-28
Ending balance	306,199		256,566
Unrealized investment gains (losses) | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net investment gains	-74,812	[1]	-104,425	[1]
Federal and foreign income taxes	26,184	[2]	36,549	[2]
Net income before noncontrolling interests	-48,628		-67,876
Currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning of period	-60,524		-36,676
Other comprehensive income (loss) before reclassifications	-62,125		-23,848
Amounts reclassified from AOCI	0		0
Other comprehensive income (loss)	-62,125		-23,848
Ending balance	-122,649		-60,524		-36,676
Change in unrealized translation adjustments	-62,125		-23,848		24,563
Currency translation adjustments | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	0		0
Federal and foreign income taxes	0		0
Net income before noncontrolling interests	0		0
Net pension asset
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning of period	-6,651		-15,351
Other comprehensive income (loss) before reclassifications	0		0
Amounts reclassified from AOCI	6,651		8,700
Other comprehensive income (loss)	6,651		8,700
Ending balance	0		-6,651
Net pension asset | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other operating costs and expenses	10,232	[3]	13,387	[3]
Federal and foreign income taxes	-3,581	[2]	-4,687	[2]
Net income before noncontrolling interests	6,651		8,700
Accumulated other comprehensive income (loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning of period	189,391		465,631
Other comprehensive income (loss) before reclassifications	36,169		-217,036
Amounts reclassified from AOCI	-41,977		-59,176
Other comprehensive income (loss)	-5,808		-276,212
Unrealized investment gain related to non-controlling interest	-33		-28
Ending balance	183,550		189,391
Accumulated other comprehensive income (loss) | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	-64,580		-91,038
Federal and foreign income taxes	22,603		31,862
Net income before noncontrolling interests	($41,977)		($59,176)
[1]	Net investment gains in the consolidated statements of income.
[2]	Income tax expense in the consolidated statements of income.
[3]	Other operating costs and expenses in the consolidated statements of income.

Recovered_Sheet2

Investments in Fixed Maturity Securities (Investments in Fixed Maturity Securities) (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total held to maturity, Amortized Cost	$101,177,000		$101,320,000
Total held to maturity, Gross Unrealized Gains	20,646,000		14,900,000
Total held to maturity, Gross Unrealized Losses	0		0
Total held to maturity, Fair Value	121,823,000		116,220,000
Total held to maturity, Carrying Value	101,177,000		101,320,000
Total available for sale, Amortized Cost	12,122,087,000		11,190,311,000
Total available for sale, Gross Unrealized Gains	541,420,000		436,347,000
Total available for sale, Gross Unrealized Losses	-59,524,000		-111,134,000
Total available for sale, Fair Value	12,603,983,000		11,515,524,000
Total available for sale, Carrying Value	12,603,983,000		11,515,524,000
Total investment in fixed maturity securities, Amortized Cost	12,223,264,000		11,291,631,000
Total investments in fixed maturity securities, Gross Unrealized Gains	562,066,000		451,247,000
Total investments in fixed maturity securities, Gross Unrealized Losses	-59,524,000		-111,134,000
Total investments in fixed maturity securities, Fair Value	12,725,806,000		11,631,744,000
Total investments in fixed maturity securities, carrying value	12,705,160,000		11,616,844,000
U.S. government and government agency
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total available for sale, Amortized Cost	773,192,000		858,319,000
Total available for sale, Gross Unrealized Gains	33,353,000		34,522,000
Total available for sale, Gross Unrealized Losses	-3,157,000		-7,982,000
Total available for sale, Fair Value	803,388,000		884,859,000
Total available for sale, Carrying Value	803,388,000		884,859,000
State and municipal
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total available for sale, Amortized Cost	4,137,866,000		4,085,791,000
Total available for sale, Gross Unrealized Gains	229,150,000		162,330,000
Total available for sale, Gross Unrealized Losses	-4,020,000		-29,837,000
Total available for sale, Fair Value	4,362,996,000		4,218,284,000
Total available for sale, Carrying Value	4,362,996,000		4,218,284,000
Residential mortgage-backed securities
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total available for sale, Amortized Cost	1,201,924,000		1,248,693,000	[1]
Total available for sale, Gross Unrealized Gains	27,124,000		25,895,000	[1]
Total available for sale, Gross Unrealized Losses	-9,449,000		-25,941,000	[1]
Total available for sale, Fair Value	1,219,599,000	[1]	1,248,647,000	[1]
Total available for sale, Carrying Value	1,219,599,000		1,248,647,000	[1]
Non-credit portion of other-than-temporary impairments ("OTTI")	1,095,671		1,961,247
Commercial
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total available for sale, Amortized Cost	74,479,000		76,454,000
Total available for sale, Gross Unrealized Gains	1,610,000		5,670,000
Total available for sale, Gross Unrealized Losses	-52,000		-988,000
Total available for sale, Fair Value	76,037,000		81,136,000
Total available for sale, Carrying Value	76,037,000		81,136,000
Corporate
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total available for sale, Amortized Cost	5,036,958,000		4,076,585,000
Total available for sale, Gross Unrealized Gains	187,960,000		156,256,000
Total available for sale, Gross Unrealized Losses	-24,781,000		-30,100,000
Total available for sale, Fair Value	5,200,137,000		4,202,741,000
Total available for sale, Carrying Value	5,200,137,000		4,202,741,000
Foreign government
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total available for sale, Amortized Cost	897,668,000		844,469,000
Total available for sale, Gross Unrealized Gains	62,223,000		51,674,000
Total available for sale, Gross Unrealized Losses	-18,065,000		-16,286,000
Total available for sale, Fair Value	941,826,000		879,857,000
Total available for sale, Carrying Value	941,826,000		879,857,000
State and municipal
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total held to maturity, Amortized Cost	72,901,000		68,929,000
Total held to maturity, Gross Unrealized Gains	17,501,000		11,172,000
Total held to maturity, Gross Unrealized Losses	0		0
Total held to maturity, Fair Value	90,402,000		80,101,000
Total held to maturity, Carrying Value	72,901,000		68,929,000
Residential mortgage-backed securities
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total held to maturity, Amortized Cost	23,278,000		27,393,000
Total held to maturity, Gross Unrealized Gains	2,854,000		3,311,000
Total held to maturity, Gross Unrealized Losses	0		0
Total held to maturity, Fair Value	26,132,000		30,704,000
Total held to maturity, Carrying Value	23,278,000		27,393,000
Corporate
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total held to maturity, Amortized Cost	4,998,000		4,998,000
Total held to maturity, Gross Unrealized Gains	291,000		417,000
Total held to maturity, Gross Unrealized Losses	0		0
Total held to maturity, Fair Value	5,289,000		5,415,000
Total held to maturity, Carrying Value	$4,998,000		$4,998,000
[1]	Gross unrealized losses for mortgage-backed securities include $1,095,671 and $1,961,247, as of December 31, 2014 and 2013, respectively, related to the non-credit portion of OTTI recognized in other comprehensive income.

Recovered_Sheet3

Investments in Fixed Maturity Securities (The Amortized Cost and Fair Value of Fixed Maturity Securities) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Investments, Debt and Equity Securities [Abstract]
Amortized Cost, Due in one year or less	$884,831
Amortized Cost, Due after one year through five years	3,953,003
Amortized Cost, Due after five years through ten years	3,600,155
Amortized Cost, Due after ten years	2,485,594
Amortized Cost, Mortgage-backed securities	1,299,681
Total investment in fixed maturity securities, Amortized Cost	12,223,264	11,291,631
Fair Value, Due in one year or less	895,004
Fair Value, Due after one year through five years	4,119,946
Fair Value, Due after five years through ten years	3,790,402
Fair Value, Due after ten years	2,598,686
Fair Value, Mortgage-backed securities	1,321,768
Total investments in fixed maturity securities, Fair Value	$12,725,806	$11,631,744

Recovered_Sheet4

Investments in Equity Securities Available for Sale (Investments in Equity Securities Available for Sale) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]
Cost	$160,295	$203,627
Gross Unrealized, Gains	20,314	86,030
Gross Unrealized, Losses	-9,618	-6,319
Carrying value and fair value of equity securities	170,991	283,338
Common stocks
Schedule of Available-for-sale Securities [Line Items]
Cost	69,870	118,536
Gross Unrealized, Gains	11,929	42,239
Gross Unrealized, Losses	-5,453	0
Carrying value and fair value of equity securities	76,346	160,775
Preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Cost	90,425	85,091
Gross Unrealized, Gains	8,385	43,791
Gross Unrealized, Losses	-4,165	-6,319
Carrying value and fair value of equity securities	$94,645	$122,563

Arbitrage_Trading_Account_Deta

Arbitrage Trading Account (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Trading Securities and Derivative Instruments [Abstract]
Arbitrage trading account	$450,648,000	$522,128,000
Options Held | Long
Derivative [Line Items]
Other derivatives not designated as hedging instruments at fair value, net	8,000,000
Derivative, notional amount	133,000,000
Options Held | Short
Derivative [Line Items]
Other derivatives not designated as hedging instruments at fair value, net	2,000,000
Derivative, notional amount	$106,000,000

Net_Investment_Income_Net_Inve

Net Investment Income (Net Investment Income) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Investment Income [Line Items]
Gross investment income	$610,530	$554,308	$592,852
Investment expense	-9,645	-10,017	-6,089
Net investment income	600,885	544,291	586,763
Fixed maturity securities, including cash and cash equivalents and loans receivable
Net Investment Income [Line Items]
Gross investment income	439,489	442,287	479,035
Equity securities available for sale
Net Investment Income [Line Items]
Gross investment income	6,726	11,380	16,419
Investment funds
Net Investment Income [Line Items]
Gross investment income	131,649	67,712	77,015
Arbitrage trading account
Net Investment Income [Line Items]
Gross investment income	22,438	20,431	8,286
Real estate
Net Investment Income [Line Items]
Gross investment income	$10,228	$12,498	$12,097

Investment_Funds_Schedule_of_I

Investment Funds (Schedule of Investment Funds) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Equity Method Investments [Line Items]
Investment funds	$1,211,401	$1,067,495
Income	131,649	67,712	77,015
Real estate
Schedule of Equity Method Investments [Line Items]
Investment funds	466,703	378,435
Income	26,233	9,315	30,196
Energy
Schedule of Equity Method Investments [Line Items]
Investment funds	152,056	155,026
Income	12,797	29,739	33,146
Hedged equity
Schedule of Equity Method Investments [Line Items]
Investment funds	282,335	271,575
Income	10,760	7,655	5,912
Other funds
Schedule of Equity Method Investments [Line Items]
Investment funds	310,307	262,459
Income	$81,859	$21,003	$7,761

Real_Estate_Details

Real Estate (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Real Estate [Abstract]
Properties in operation	$196,980	$283,393
Properties under development	534,632	431,849
Total	$731,612	$715,242

Loans_Receivable_Details

Loans Receivable (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Loans Receivable [Line Items]
Loans and Leases Receivable, Gross	$322,012,000	$343,583,000
Loans receivable	325,219,000	346,746,000
Debt Instrument, Term	10 years
Total loans receivable	322,012,000	343,583,000
Valuation allowance, Specific	115,000	0
Valuation allowance, General	2,371,000	2,087,000
Valuation allowance	2,486,000	2,087,000
Increase (decrease) in valuation allowance	398,000	308,000
Loans in nonaccrual status	14,000,000
Real Estate
Loans Receivable [Line Items]
Loans and Leases Receivable, Gross	243,407,000	282,357,000
Loans receivable	245,112,000	284,017,000
Commercial
Loans Receivable [Line Items]
Loans and Leases Receivable, Gross	78,605,000	61,226,000
Loans receivable	$80,107,000	$62,729,000

Recovered_Sheet5

Realized and Unrealized Investment Gains and Losses (Realized and Unrealized Investment Gains (Losses) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Realized and Unrealized Investment Gains (Losses) [Abstract]
Fixed maturity securities, Gains	$39,113	$48,860	$34,295
Fixed maturity securities, Losses	-4,420	-14,670	-6,436
Equity securities available for sale	38,296	70,235	97,300
Investment funds	96,204	10,976	74,777
Gain (Loss) on Sale of Properties	85,659	0	0
Other gains	0	12,185	1,515
Net realized gains on investments sales	254,852	127,586	201,451
Other-than-temporary impairments	0	-6,042	-4,984
Decrease in valuation allowance	0	0	13,998
Net other-than-temporary impairments	0	-6,042	9,014
Net investment gains	254,852	121,544	210,465
Income tax expense	-89,198	-47,426	-73,663
Total after-tax investment gains	$165,654	$74,118	$136,802

Recovered_Sheet6

Realized and Unrealized Investment Gains and Losses (Change in Unrealized Gains (Losses) of Available For Sales Securities) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized gains (losses) before income taxes and noncontrolling interests	$72,889	($399,122)	$135,282
Income tax benefit (expense)	-23,223	138,058	-47,966
Noncontrolling interests	-33	-28	-77
Total change in unrealized gains and losses	49,633	-261,092	87,239
Debt Securities
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized gains (losses) before income taxes and noncontrolling interests	155,765	-401,812	162,220
Debt Securities Previously Impaired
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized gains (losses) before income taxes and noncontrolling interests	865	1,076	4,631
Equity securities available for sale
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized gains (losses) before income taxes and noncontrolling interests	-69,016	11,864	-33,199
Investment funds
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized gains (losses) before income taxes and noncontrolling interests	($14,725)	($10,250)	$1,630

Recovered_Sheet7

Securities in an Unrealized Loss Position (Securities in an Unrealized Loss Position) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale Securities, Less Than 12 Months, Fair Value	$2,024,847	$3,085,977
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	20,681	84,259
Available-for-sale Securities, 12 Months or Greater, Fair Value	870,357	355,098
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	48,461	33,194
Available-for-sale Securities, Fair Value	2,895,204	3,441,075
Available For Sale Securities, Gross Unrealized Losses	69,142	117,453
U.S. government and government agency
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale Securities, Less Than 12 Months, Fair Value	84,750	260,882
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	522	7,927
Available-for-sale Securities, 12 Months or Greater, Fair Value	84,850	2,163
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	2,635	55
Available-for-sale Securities, Fair Value	169,600	263,045
Available For Sale Securities, Gross Unrealized Losses	3,157	7,982
State and municipal
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale Securities, Less Than 12 Months, Fair Value	158,594	899,613
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	631	24,503
Available-for-sale Securities, 12 Months or Greater, Fair Value	150,284	87,345
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	3,389	5,334
Available-for-sale Securities, Fair Value	308,878	986,958
Available For Sale Securities, Gross Unrealized Losses	4,020	29,837
Mortgage-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale Securities, Less Than 12 Months, Fair Value	75,739	578,603
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	332	17,964
Available-for-sale Securities, 12 Months or Greater, Fair Value	312,922	140,648
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	9,169	8,965
Available-for-sale Securities, Fair Value	388,661	719,251
Available For Sale Securities, Gross Unrealized Losses	9,501	26,929
Corporate
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale Securities, Less Than 12 Months, Fair Value	1,586,238	1,013,373
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	8,697	17,066
Available-for-sale Securities, 12 Months or Greater, Fair Value	214,628	105,074
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	16,084	13,034
Available-for-sale Securities, Fair Value	1,800,866	1,118,447
Available For Sale Securities, Gross Unrealized Losses	24,781	30,100
Foreign government
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale Securities, Less Than 12 Months, Fair Value	76,471	320,215
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	3,907	16,286
Available-for-sale Securities, 12 Months or Greater, Fair Value	85,025	0
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	14,158	0
Available-for-sale Securities, Fair Value	161,496	320,215
Available For Sale Securities, Gross Unrealized Losses	18,065	16,286
Fixed maturity securities
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale Securities, Less Than 12 Months, Fair Value	1,981,792	3,072,686
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	14,089	83,746
Available-for-sale Securities, 12 Months or Greater, Fair Value	847,709	335,230
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	45,435	27,388
Available-for-sale Securities, Fair Value	2,829,501	3,407,916
Available For Sale Securities, Gross Unrealized Losses	59,524	111,134
Common stocks
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale Securities, Less Than 12 Months, Fair Value	15,929	0
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	5,453	0
Available-for-sale Securities, 12 Months or Greater, Fair Value	0	0
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	0	0
Available-for-sale Securities, Fair Value	15,929	0
Available For Sale Securities, Gross Unrealized Losses	5,453	0
Preferred stocks
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale Securities, Less Than 12 Months, Fair Value	27,126	13,291
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	1,139	513
Available-for-sale Securities, 12 Months or Greater, Fair Value	22,648	19,868
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	3,026	5,806
Available-for-sale Securities, Fair Value	49,774	33,159
Available For Sale Securities, Gross Unrealized Losses	4,165	6,319
Equity securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale Securities, Less Than 12 Months, Fair Value	43,055	13,291
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	6,592	513
Available-for-sale Securities, 12 Months or Greater, Fair Value	22,648	19,868
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	3,026	5,806
Available-for-sale Securities, Fair Value	65,703	33,159
Available For Sale Securities, Gross Unrealized Losses	$9,618	$6,319

Recovered_Sheet8

Securities in an Unrealized Loss Position (Non-Investment Grade Fixed Maturity Securities) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]
Aggregate Fair Value	$2,895,204	$3,441,075
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Aggregate Fair Value	388,661	719,251
Corporate
Schedule of Available-for-sale Securities [Line Items]
Aggregate Fair Value	1,800,866	1,118,447
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Aggregate Fair Value	2,829,501	3,407,916
Unrealized Loss Less than 5 Million | Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Number Of Securities	9
Aggregate Fair Value	28,537
Gross Unrealized Loss	1,699
Unrealized Loss Less than 5 Million | Corporate
Schedule of Available-for-sale Securities [Line Items]
Number Of Securities	10
Aggregate Fair Value	24,528
Gross Unrealized Loss	742
Unrealized Loss Less than 5 Million | State and Municipal
Schedule of Available-for-sale Securities [Line Items]
Number Of Securities	2
Aggregate Fair Value	11,177
Gross Unrealized Loss	247
Unrealized Loss Less than 5 Million | Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Number Of Securities	21
Aggregate Fair Value	64,242
Gross Unrealized Loss	$2,688

Securities_in_an_Unrealized_Lo2

Securities in an Unrealized Loss Position (Narrative) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Securities in continuous unrealized loss position fair value	$2,895,204,000	$3,441,075,000
Securities in continuous unrealized loss position, aggregate losses accumulated In AOCI	69,142,000	117,453,000
Loans and Leases Receivable, Other, Allowance	3,000,000	2,000,000
Preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Securities in unrealized loss positions	6
Securities in continuous unrealized loss position fair value	49,774,000	33,159,000
Securities in continuous unrealized loss position, aggregate losses accumulated In AOCI	4,165,000	6,319,000
Common stocks
Schedule of Available-for-sale Securities [Line Items]
Securities in unrealized loss positions	2
Securities in continuous unrealized loss position fair value	15,929,000	0
Securities in continuous unrealized loss position, aggregate losses accumulated In AOCI	$5,453,000	$0

Fair_Value_Measurements_Assets

Fair Value Measurements (Assets and Liabilities Measured At Fair Value, On a Recurring Basis) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	$12,603,983	$11,515,524
Equity securities available for sale	170,991	283,338
Arbitrage trading account	450,648	522,128
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	12,603,983	11,515,524
Equity securities available for sale	170,991	283,338
Arbitrage trading account	450,648	522,128
Total assets	13,225,622	12,320,990
Securities sold but not yet purchased	106,079	162,278
Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	0	0
Equity securities available for sale	65,605	159,537
Arbitrage trading account	295,047	192,281
Total assets	360,652	351,818
Securities sold but not yet purchased	106,074	162,126
Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	12,583,218	11,472,660
Equity securities available for sale	90,932	118,811
Arbitrage trading account	154,881	328,067
Total assets	12,829,031	11,919,538
Securities sold but not yet purchased	5	152
Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	20,765	42,864
Equity securities available for sale	14,454	4,990
Arbitrage trading account	720	1,780
Total assets	35,939	49,634
Securities sold but not yet purchased	0	0
Recurring | U.S. government and government agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	803,388	884,859
Recurring | U.S. government and government agency | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	0	0
Recurring | U.S. government and government agency | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	803,388	884,859
Recurring | U.S. government and government agency | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	0	0
Recurring | State and municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	4,362,996	4,218,284
Recurring | State and municipal | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	0	0
Recurring | State and municipal | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	4,362,996	4,218,284
Recurring | State and municipal | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	0	0
Recurring | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	1,295,636	1,329,783
Recurring | Mortgage-backed securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	0	0
Recurring | Mortgage-backed securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	1,295,636	1,329,783
Recurring | Mortgage-backed securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	0	0
Recurring | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	5,200,137	4,202,741
Recurring | Corporate | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	0	0
Recurring | Corporate | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	5,179,372	4,159,877
Recurring | Corporate | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	20,765	42,864
Recurring | Foreign government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	941,826	879,857
Recurring | Foreign government | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	0	0
Recurring | Foreign government | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	941,826	879,857
Recurring | Foreign government | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities available for sale	0	0
Recurring | Common stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities available for sale	76,346	160,775
Recurring | Common stocks | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities available for sale	65,605	159,537
Recurring | Common stocks | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities available for sale	0	0
Recurring | Common stocks | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities available for sale	10,741	1,238
Recurring | Preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities available for sale	94,645	122,563
Recurring | Preferred stocks | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities available for sale	0	0
Recurring | Preferred stocks | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities available for sale	90,932	118,811
Recurring | Preferred stocks | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities available for sale	$3,713	$3,752

Fair_Value_Measurements_Summar

Fair Value Measurements (Summarize Changes in Level 3 Assets and Liabilities) (Details) (Level 3, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$0	$20,000
Earnings	-20,000	-4,000
Other Comprehensive Income	0	0
Purchases	31,000	4,000
Sales	-11,000	-20,000
Paydown/Maturities	0	0
In	0	0
Out	0	0
Ending balance	0	0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	49,634,000	62,022,000
Earnings	2,304,000	1,836,000
Other Comprehensive Income	-4,622,000	1,039,000
Purchases	19,953,000	4,424,000
Sales	-33,698,000	-5,776,000
Paydowns / Maturities	-3,429,000	-12,604,000
In	9,064,000	22,000
Out	-3,267,000	-1,329,000
Ending Balance	35,939,000	49,634,000
Corporate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	42,864,000	59,065,000
Earnings	47,000	677,000
Other Comprehensive Income	-3,711,000	309,000
Purchases	238,000	170,000
Sales	-15,244,000	-4,753,000
Paydowns / Maturities	-3,429,000	-12,604,000
In	0	0
Out	0	0
Ending Balance	20,765,000	42,864,000
Fixed maturity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	42,864,000	59,065,000
Earnings	47,000	677,000
Other Comprehensive Income	-3,711,000	309,000
Purchases	238,000	170,000
Sales	-15,244,000	-4,753,000
Paydowns / Maturities	-3,429,000	-12,604,000
In	0	0
Out	0	0
Ending Balance	20,765,000	42,864,000
Common stocks
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,238,000	1,408,000
Earnings	0	0
Other Comprehensive Income	-911,000	0
Purchases	11,343,000	0
Sales	-929,000	-170,000
Paydowns / Maturities	0	0
In	0	0
Out	0	0
Ending Balance	10,741,000	1,238,000
Preferred stocks
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	3,752,000	621,000
Earnings	-17,000	-299,000
Other Comprehensive Income	0	0
Purchases	3,430,000	3,430,000
Sales	-3,452,000	0
Paydowns / Maturities	0	0
In	0	0
Out	0	0
Ending Balance	3,713,000	3,752,000
Equity securities available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	4,990,000	2,029,000
Earnings	-17,000	-299,000
Other Comprehensive Income	-911,000	0
Purchases	14,773,000	3,430,000
Sales	-4,381,000	-170,000
Paydowns / Maturities	0	0
In	0	0
Out	0	0
Ending Balance	14,454,000	4,990,000
Trading account
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,780,000	928,000
Earnings	2,274,000	1,458,000
Other Comprehensive Income	0	730,000
Purchases	4,942,000	824,000
Sales	-14,073,000	-853,000
Paydowns / Maturities	0	0
In	9,064,000	22,000
Out	3,267,000	-1,329,000
Ending Balance	$720,000	$1,780,000

Reserves_For_Losses_And_Loss_E2

Reserves For Losses And Loss Expenses (Schedule of Liability for Unpaid Claims and Claims Adjustment Expense) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Net reserves at beginning of year	$8,683,797,000	$8,411,851,000		$8,172,112,000
Net provision for losses and loss expenses:
Claims occuring during the current year	3,495,825,000	3,221,393,000	[1]	2,997,995,000	[1]
Decrease in estimates for claims occurring in prior years	-75,764,000	-78,810,000	[2],[3]	-102,571,000	[2],[3]
Loss reserve discount accretion(4)	70,506,000	54,441,000		53,055,000
Total	3,490,567,000	3,197,024,000		2,948,479,000
Net payments for claims:
Current year	898,944,000	822,787,000		698,834,000
Prior year	2,216,283,000	2,055,284,000		2,010,101,000
Total	3,115,227,000	2,878,071,000		2,708,935,000
Foreign currency translation	-88,496,000	-47,007,000		195,000
Net reserves at end of year	8,970,641,000	8,683,797,000		8,411,851,000
Ceded reserve at end of year	1,399,060,000	1,397,144,000		1,339,235,000
Gross reserves at end of year	10,369,701,000	10,080,941,000		9,751,086,000
Workers' Compensation Discount, Current Year Amount	21,306,000	22,680,000		26,078,000
Decrease in estimates for claims occurring in prior years, undiscounted basis	116,866,000	77,430,000		100,667,000
Favorable reserve development and return premiums	$85,000,000	$98,000,000		$103,000,000
[1]	Claims occurring during the current year are net of loss reserve discounts of $21,306,000, $22,680,000, and $26,078,000 in 2014, 2013 and 2012, respectively.
[2]	The decrease in estimates for claims occurring in prior years is net of loss reserve discount. On an undiscounted basis, the estimates for claims occurring in prior years decreased by $116,866,000, $77,430,000 and $100,667,000 in 2014, 2013 and 2012, respectively.
[3]	For certain retrospectively rated insurance polices and reinsurance agreements, reserve development is offset by additional or return premiums. Favorable reserve development, net of additional and return premiums, was $85 million, $98 million and $103 million in 2014, 2013 and 2012, respectively.

Reserves_For_Losses_And_Loss_E3

Reserves For Losses And Loss Expenses (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reserves For Losses And Loss Expenses [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims, Prior Years, Reserve Development, Net of Premiums, Favorable (Unfavorable)	$85,000,000	$98,000,000	$103,000,000
Prior year	2,216,283,000	2,055,284,000	2,010,101,000
Reserve for losses and loss adjustment expenses relating to asbestos and environmental claims, net		36,000,000
Reserve for losses and loss adjustment expenses relating to asbestos and environmental claims, gross	56,000,000	59,000,000
Increase (decrease) in net incurred losses and loss expenses relating to asbestos and environmental claims	4,000,000	5,000,000	2,000,000
Net paid losses and loss expenses for asbestos and environmental claims	3,000,000	3,000,000	2,000,000
Workers' compensation discount after effects of ceded reinsurance, amount	746,000,000	837,000,000	867,000,000
Non-Proportional Reinsurance
Reserves For Losses And Loss Expenses [Line Items]
Workers' compensation weighted average discount rate, percent	4.20%
Non-Proportional Reinsurance | Minimum
Reserves For Losses And Loss Expenses [Line Items]
Workers' compensation discount, percent	2.00%
Non-Proportional Reinsurance | Maximum
Reserves For Losses And Loss Expenses [Line Items]
Workers' compensation discount, percent	6.50%
Proportional Reinsurance
Reserves For Losses And Loss Expenses [Line Items]
Workers' compensation discount, percent	2.00%
Undiscounted [Member]
Reserves For Losses And Loss Expenses [Line Items]
Liability For Unpaid Claims And Claims Adjustment Expense Incurred Claims Undiscounted Basis Prior Years	30,000,000
Discounted [Member]
Reserves For Losses And Loss Expenses [Line Items]
Prior year	$12,000,000

Reinsurance_Reinsurance_Financ

Reinsurance (Reinsurance Financial Information) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reinsurance Disclosures [Abstract]
Written premiums, Direct	$6,185,242	$5,626,172	$4,964,069
Written premiums, Assumed	877,596	884,919	815,810
Written premiums, Ceded	-1,065,891	-1,010,918	-881,340
Total net premiums written	5,996,947	5,500,173	4,898,539
Earned premiums, Direct	5,889,021	5,328,955	4,723,882
Earned premiums, Assumed	886,063	857,119	770,981
Earned premiums, Ceded	-1,030,666	-959,537	-821,347
Net premiums earned	5,744,418	5,226,537	4,673,516
Ceded losses incurred	475,802	556,108	528,018
Uncollectible reinsurance	1,144	1,385	1,680
Fees and Commissions, Other	$160,215	$137,449	$121,089

Reinsurance_Schedule_Of_Ceded_

Reinsurance (Schedule Of Ceded Credit Risk by Reinsurer) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	$1,503,441	$1,533,103
Credit Risk Reinsurers, Subtotal, Excluding Residual Market Pools [Member]
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	997,879
Munich Re
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	141,489
Lloyds of London
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	109,976
Swiss Re
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	101,308
Alleghany Group
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	97,300
Partner Re
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	70,756
Axis Capital
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	63,352
Berkshire Hathaway
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	48,804
Ace Group
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	44,215
Hannover Re Group
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	43,207
Everest Re
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	41,749
Arch Capital Group
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	23,453
Other Reinsurers
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	212,270
Residual Market Pools
Ceded Credit Risk [Line Items]
Ceded reserve at end of year	$505,562

Indebtedness_Details

Indebtedness (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013
Subsidiary Debt
Debt Instrument [Line Items]
Face Value	$153,549,000
Carrying Value	154,223,000	[1]	77,173,000	[1]
Repayments in 2014			76,000,000
Repayments in 2015			33,000,000
Repayments in 2016			42,000,000
Repayments thereafter			3,000,000
Senior Notes and Other Debt
Debt Instrument [Line Items]
Face Value	2,130,052,000
Carrying Value	2,115,527,000		1,692,442,000
Senior Notes | Senior Notes due May 15, 2015
Debt Instrument [Line Items]
Rate			5.60%
Face Value	200,000,000
Carrying Value	199,930,000		199,744,000
Senior Notes | Senior Notes due August 15, 2019
Debt Instrument [Line Items]
Rate			6.15%
Face Value	150,000,000
Carrying Value	149,342,000		149,199,000
Senior Notes | Senior Notes due September 15, 2019
Debt Instrument [Line Items]
Rate			7.38%
Face Value	300,000,000
Carrying Value	298,800,000		298,546,000
Senior Notes | Senior Notes due September 15, 2020
Debt Instrument [Line Items]
Rate			5.38%
Face Value	300,000,000
Carrying Value	298,074,000		297,738,000
Senior Notes | Senior Notes due January 1, 2022
Debt Instrument [Line Items]
Rate			8.70%
Face Value	76,503,000
Carrying Value	76,048,000		76,004,000
Senior Notes | Senior Notes due March 15, 2022
Debt Instrument [Line Items]
Rate			4.63%
Face Value	350,000,000
Carrying Value	346,999,000		346,581,000
Senior Notes | Senior Notes due February 15, 2037
Debt Instrument [Line Items]
Rate			6.25%
Face Value	250,000,000
Carrying Value	247,566,000		247,457,000
Senior Notes | Senior Notes due August 1, 2044 [Member]
Debt Instrument [Line Items]
Rate			4.75%
Face Value	350,000,000
Carrying Value	344,545,000		0
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Face Value			350,000,000
Carrying Value	$340,060,000		$339,800,000
Junior Subordinated Debt [Member] | Five Point Six Two Five Percent Subordinated Debentures [Member]
Debt Instrument [Line Items]
Rate			5.63%
[1]	Subsidiary debt is due as follows: $76 million in 2015, $33 million in 2016, $42 million in 2017 and $3 million thereafter.

Income_Taxes_Schedule_of_Compo

Income Taxes (Schedule of Components of Income Tax Expense (Benefit)) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Current Expense, Domestic	$258,337,000	$116,802,000	$156,339,000
Deferred Expense (Benefit), Domestic	28,029,000	47,370,000	11,448,000
Domestic, Total	286,366,000	164,172,000	167,787,000
Current Expense, Foreign	12,969,000	22,362,000	23,029,000
Deferred Expense (Benefit), Foreign	3,258,000	7,053,000	469,000
Foreign, Total	16,227,000	29,415,000	23,498,000
Current Expense, Total	271,306,000	139,164,000	179,368,000
Deferred Expense (Benefit), Total	31,287,000	54,423,000	11,917,000
Total expense	302,593,000	193,587,000	191,285,000
Income (Loss) from Continuing Operations before Income Taxes, Domestic	910,000,000	598,000,000	624,000,000
Income (Loss) from Continuing Operations before Income Taxes, Foreign	$42,000,000	$101,000,000	$78,000,000

Income_Taxes_Schedule_of_Effec

Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Statutory federal income tax rate		35.00%
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Computed “expected” tax expense	$333,269	$244,611	$245,675
Tax-exempt investment income	-38,757	-40,679	-50,665
Change in valuation allowance	1,335	0	0
Impact of foreign tax rates	6,239	-4,851	-5,234
State and local taxes	2,375	2,906	-753
Other, net	-1,868	-8,400	2,262
Total expense	$302,593	$193,587	$191,285

Income_Taxes_Schedule_of_Defer

Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Deferred tax asset:
Loss reserve discounting	$77,216,000	$87,394,000
Unearned premiums	165,075,000	149,107,000
Other-than-temporary impairments	45,367,000	49,483,000
Restricted stock units	60,061,000	52,671,000
Other	101,131,000	92,698,000
Gross deferred tax asset	448,850,000	431,353,000
Less valuation allowance	-1,335,000	0
Deferred tax asset	447,515,000	431,353,000
Deferred tax liability:
Amortization of intangibles	22,747,000	11,886,000
Deferred policy acquisition costs	152,001,000	136,635,000
Unrealized investment gains	175,111,000	148,215,000
Other	135,108,000	114,497,000
Deferred tax liability	484,967,000	411,233,000
Net deferred tax asset (liability)	-37,452,000	20,120,000
Current Federal income taxes	67,623,000	24,737,000
Operating Loss Carryforwards [Line Items]
Taxes Payable, Current		24,737,000
Tax Credit Carryforward, Valuation Allowance	1,335,000
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	559,000
Foreign Tax Authority (expiration 2031) [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	6,000,000
Foreign Tax Authority (No expiration) [Member] [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$12,000,000

Dividends_From_Subsidiaries_An2

Dividends From Subsidiaries And Statutory Financial Information (Schedule of Combined Net Income and Policyholders' Surplus in Accordance with Statutory Accounting Practices) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Insurance [Abstract]
Amount available for dividend distribution without prior approval from regulatory authorities	$631,000,000
Net income	753,260,000	469,354,000	482,457,000
Policyholders' surplus	5,438,064,000	4,908,010,000	4,671,979,000
Increase in BIC's statutory capital and surplus	251,000,000
Total Adjusted Capital percentage threshold		200.00%
BIC's Total Adjusted Capital balance	$5,200,000,000
BIC's Total Adjusted Capital balance as percentage of RBC Authorized Control Level	465.00%

Common_Stockholders_Equity_Wei

Common Stockholders' Equity (Weighted Average Number of Common Shares Used In the Computation of Basic and Diluted Earnings per Share) (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity [Abstract]
Basic	127,873,708	135,304,752	137,097,162
Diluted	133,651,855	140,742,922	143,314,544

Common_Stockholders_Equity_Sch

Common Stockholders' Equity (Schedule of Changes in Shares of Common Stock Outstanding) (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Common Stock Shares Outstanding [Roll Forward]
Balance, beginning of year	132,233,167	136,017,732	137,520,019
Shares issued	332,137	139,790	2,114,168
Shares repurchased	-5,816,468	-3,924,355	-3,616,455
Balance, end of year	126,748,836	132,233,167	136,017,732

Fair_Value_of_Financial_Instru1

Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Assets:
Arbitrage trading account	$450,648	$522,128
Loans receivable	325,219	346,746
Due To Broker	23,133	8,273
Due To Broker Fair Value	23,133	8,273
Carrying Value
Assets:
Fixed maturity securities	12,705,160	11,616,844
Equity securities available for sale	170,991	283,338
Arbitrage trading account	450,648	522,128
Loans receivable	322,012	343,583
Cash and cash equivalents	674,441	839,738
Trading accounts receivable from brokers and clearing organizations	371,034	304,936
Due from broker	0	17,735
Liabilities:
Trading account securities sold but not yet purchased	106,079	162,278
Subordinated debentures	340,060	339,800
Senior notes and other debt	2,115,527	1,692,442
Fair Value
Assets:
Fixed maturity securities	12,725,806	11,631,744
Equity securities available for sale	170,991	283,338
Arbitrage trading account	450,648	522,128
Loans receivable	325,219	346,746
Cash and cash equivalents	674,441	839,738
Trading accounts receivable from brokers and clearing organizations	371,034	304,936
Due from broker	0	17,735
Liabilities:
Trading account securities sold but not yet purchased	106,079	162,278
Subordinated debentures	332,640	288,540
Senior notes and other debt	$2,344,292	$1,861,898

Lease_Obligations_Details

Lease Obligations (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Leases [Abstract]
Future minimum lease payment - due in 2014	$41,210,000
Future minimum lease payment - due in 2015	36,547,000
Future minimum lease payment - due in 2016	32,336,000
Future minimum lease payment - due in 2017	27,012,000
Operating Leases, Future Minimum Payments, Due in Five Years	23,344,000
Future minimum lease payment - due after 2017	78,517,000
Rental expense	$45,198,000	$44,752,000	$38,179,000

Commitments_Litigation_And_Con1

Commitments, Litigation And Contingent Liabilities (Details) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified
Commitments and Contingencies Disclosure [Abstract]
Maximum commitments to invest	$242

Stock_Incentive_Plan_Schedule_

Stock Incentive Plan (Schedule of Share-based Compensation, Stock Options, Activity) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of outstanding options - vested and exercisable	3,375		3,375		1,314,057
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding at beginning of year (in shares)	3,375		1,314,057
Exercised (in shares)	3,375		1,310,682
Canceled (in shares)	0		0
Outstanding at year end (in shares)	0		3,375
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Oustanding at beginning of year (Price) (in dollars per share)	$15.17	[1]	$11.04	[1]
Exercised (Price) (in dollars per share)	$15.17	[1]	$11.03	[1]
Canceled (Price) (in dollars per share)	$0	[1]	$0	[1]
Outstanding at end of year (Price) (in dollars per share)	$0	[1]	$15.17	[1]
[1]	Weighted average exercise price.

Stock_Incentive_Plan_Schedule_1

Stock Incentive Plan (Schedule of Nonvested Restricted Stock Units Activity) (Details) (Restricted Stock Units (RSUs))	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		5 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
RSUs granted and unvested at beginning of period:	4,491,520,000	4,701,120	4,370,975
Granted	1,154,950,000	108,400	2,161,220
Vested	-81,500,000	-146,250	-1,704,625
Cancelled	-234,525,000	-171,750	-126,450
RSUs granted and unvested at end of period:	5,330,445,000	4,491,520,000	4,701,120

Stock_Incentive_Plan_Schedule_2

Stock Incentive Plan (Schedule of Share-based Compensation, Unearned Compensation Related to RSU's) (Details) (Restricted Stock Units (RSUs), USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Changes In Unearned Compensation [Roll Forward]
Unearned compensation at beginning of year	$73,205	$93,653	$57,315
RSUs granted, net of cancellations	51,575	4,406	73,255
RSUs expensed	27,966	-22,881	-25,728
RSUs forfeitures	8,799	-1,973	-11,189
Unearned compensation at end of year	$88,015	$73,205	$93,653

Compensation_Plans_Details

Compensation Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
LTIP Expense	$23,011,000	$14,170,000	$11,105,000
Deferred Profit Sharing
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Profit Sharing Plan Minimum Contribution, Percent		5.00%
Profit Sharing Plan, Contributions Vesting Immediately, Percent		40.00%
Profit Sharing Plan, Contributions Vesting Based on Years of Service, Percent		60.00%
Profit sharing expense	38,000,000	34,000,000	31,000,000
2011 grant
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Long-Term Incentive Compensation Plan, Number of Units Oustanding	175,100
Long-Term Incentive Compensation Plan, Maximum Value	43,800,000
Long-Term Incentive Compensation Plan, Earned	27,300,000
LTIP Expense	9,855,000	6,939,000	6,822,000
2008 grant
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Long-Term Incentive Compensation Plan, Earned		23,000,000
LTIP Expense	0	0	4,283,000
2013 grant
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Long-Term Incentive Compensation Plan, Number of Units Oustanding	208,000
Long-Term Incentive Compensation Plan, Maximum Value	52,000,000
Long-Term Incentive Compensation Plan, Earned	16,700,000
LTIP Expense	9,493,000	7,231,000	0
Long-term Incentive Compensation Plan, 2014 [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Long-Term Incentive Compensation Plan, Number of Units Oustanding	220,000
Long-Term Incentive Compensation Plan, Maximum Value	22,000,000
Long-Term Incentive Compensation Plan, Earned	3,700,000
LTIP Expense	$3,663,000	$0	$0

Retirement_Benefits_Schedule_o

Retirement Benefits (Schedule of Changes in Projected Benefit Obligations) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of year	$64,632	$56,787	$59,400
Interest cost	2,191	2,476
Benefits paid	-285	-1,426
Actuarial loss	-2,221	6,795
Benefit obligation at end of year	$64,317	$64,632	$59,400

Retirement_Benefits_Schedule_o1

Retirement Benefits (Schedule of Amounts Recognized in Other Comprehensive Income (Loss)) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Compensation and Retirement Disclosure [Abstract]
Net actuarial loss	$4,242	$14,605
Prior service cost	5,988	9,012
Net pension asset	$10,230	$23,617

Retirement_Benefits_Schedule_o2

Retirement Benefits (Schedule of Net Benefit Costs) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Compensation and Retirement Disclosure [Abstract]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	($4,242)	($14,605)
Interest cost	2,191	2,476
Amortization of unrecognized:
Prior service costs	3,023	3,023
Net actuarial loss	8,143	2,197
Net periodic pension cost	13,357	7,696
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax	5,988	9,012
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	$10,230	$23,617

Retirement_Benefits_Schedule_o3

Retirement Benefits (Schedule of Defined Benefit Plan Amounts Recognized in Other Comprehensive Income (Loss)) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Amortization of:
Net actuarial (gain) loss		($2,221)	$6,795
Net actuarial loss		-8,143	-2,197
Prior service costs		-3,023	-3,023
Total recognized in other comprehensive income	-10,232	-13,387	1,575
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net after tax unamortized periodic pension cost	-4,624,134	-4,369,394
Net pension asset
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net after tax unamortized periodic pension cost	$0	$6,651	$15,351	$14,329

Retirement_Benefits_Retirement

Retirement Benefits Retirement Benefits (narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation	$59,400,000	$64,317,000	$64,632,000	$56,787,000
Defined Benefit Plan, Benefits Paid		285,000	1,426,000
Pension Expense	9,994,000	13,357,000	7,696,000
Supplemental Benefit Agreement (SBA) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefits Paid	$4,600,000	$300,000

Supplemental_Financial_Stateme2

Supplemental Financial Statement Information (Schedule of Other Operating Cost and Expense, by Component) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other Income and Expenses [Abstract]
Amortization of deferred policy acquisition costs	$1,053,397	$991,070	$917,583
Other underwriting expenses	843,133	780,058	675,163
Service company expenses	102,726	88,662	84,986
Net foreign currency gains	-27	-10,120	-6,092
Other costs and expenses	158,227	151,014	127,983
Total	$2,157,456	$2,000,684	$1,799,623

Industry_Segments_Financial_In

Industry Segments (Financial Information of Company Operating Segments) (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Segment Reporting Information [Line Items]
Earned Premiums									$5,744,418		$5,226,537		$4,673,516
Investment Income									600,885		544,291		586,763
Other Revenues									783,625		637,706		563,275
Total revenues	1,784,428	1,840,605	1,796,989	1,706,906	1,696,679	1,634,124	1,570,962	1,506,769	7,128,928		6,408,534		5,823,554
Pre-Tax Income (Loss)									952,196		698,888		701,928
Net income to common stockholders	110,711	188,539	179,961	169,673	130,379	136,974	115,957	116,615	648,884		499,925		510,592
Net investment gains, before tax									254,852		121,544		210,465
Net investment gains, net of tax									165,654		74,118		136,802
Insurance-Domestic
Segment Reporting Information [Line Items]
Earned Premiums									4,271,933		3,782,416		3,417,022
Insurance-International
Segment Reporting Information [Line Items]
Earned Premiums									802,375		723,151		631,841
Reinsurance-Global
Segment Reporting Information [Line Items]
Earned Premiums									670,110		720,970		624,653
Net Investment Gains Segment [Member]
Segment Reporting Information [Line Items]
Earned Premiums									0		0		0
Operating Segments | Insurance-Domestic
Segment Reporting Information [Line Items]
Earned Premiums									4,271,933		3,782,416		3,417,022
Investment Income									428,632		404,280		424,787
Other Revenues									106,853		107,517		103,133
Total revenues									4,807,418		4,294,213		3,944,942
Pre-Tax Income (Loss)									796,309		648,740		578,500
Net income to common stockholders									539,461		449,981		397,942
Operating Segments | Insurance-International
Segment Reporting Information [Line Items]
Earned Premiums									802,375		723,151		631,841
Investment Income									55,407		47,039		45,796
Other Revenues									0		0		0
Total revenues									857,782		770,190		677,637
Pre-Tax Income (Loss)									29,779		56,922		51,639
Net income to common stockholders									22,182		40,292		35,928
Operating Segments | Reinsurance-Global
Segment Reporting Information [Line Items]
Earned Premiums									670,110		720,970		624,653
Investment Income									88,821		89,090		106,932
Other Revenues									0		0		0
Total revenues									758,931		810,060		731,585
Pre-Tax Income (Loss)									115,677		110,425		103,690
Net income to common stockholders									79,720		78,013		72,916
Corporate, Other and Eliminations Segment
Segment Reporting Information [Line Items]
Earned Premiums									0		0	[1]	0	[1]
Investment Income									28,025		3,882	[1]	9,248	[1]
Other Revenues									421,920		408,645	[1]	249,677	[1]
Total revenues									449,945	[1]	412,527	[1]	258,925	[1]
Pre-Tax Income (Loss)									-244,421		-238,743	[1]	-242,366	[1]
Net income to common stockholders									($158,133)		($142,479)	[1]	($132,996)	[1]
[1]	Corporate, other and eliminations represent corporate revenues and expenses and other items that are not allocated to business segments.

Industry_Segments_Identifiable

Industry Segments (Identifiable Assets by Segment) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	$21,716,691	$20,551,796
Operating Segments | Insurance-Domestic
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	16,065,409	15,247,807
Operating Segments | Insurance-International
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	1,879,438	1,516,310
Operating Segments | Reinsurance-Global
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	2,713,554	3,103,193
Corporate, Other and Eliminations Segment
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	$1,058,290	$684,486	[1]
[1]	Corporate, other and eliminations represent corporate revenues and expenses and other items that are not allocated to business segments.

Industry_Segments_Net_Premiums

Industry Segments (Net Premiums Earned By Major Line of Business) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Net premiums earned	$5,744,418	$5,226,537	$4,673,516
Insurance-Domestic
Segment Reporting Information [Line Items]
Net premiums earned	4,271,933	3,782,416	3,417,022
Insurance-Domestic | Other Liability [Member]
Segment Reporting Information [Line Items]
Net premiums earned	1,449,425	1,259,376	1,104,369
Insurance-Domestic | Workers' Compensation [Member]
Segment Reporting Information [Line Items]
Net premiums earned	1,126,704	995,047	869,042
Insurance-Domestic | Short-tail Lines [Member]
Segment Reporting Information [Line Items]
Net premiums earned	875,898	774,809	733,239
Insurance-Domestic | Commercial Automobile [Member]
Segment Reporting Information [Line Items]
Net premiums earned	526,344	486,759	455,988
Insurance-Domestic | Professional Liability [Member]
Segment Reporting Information [Line Items]
Net premiums earned	293,562	266,425	254,384
Insurance-International
Segment Reporting Information [Line Items]
Net premiums earned	802,375	723,151	631,841
Insurance-International | Other Liability [Member]
Segment Reporting Information [Line Items]
Net premiums earned	92,411	65,528	44,065
Insurance-International | Workers' Compensation [Member]
Segment Reporting Information [Line Items]
Net premiums earned	71,997	84,637	82,066
Insurance-International | Short-tail Lines [Member]
Segment Reporting Information [Line Items]
Net premiums earned	415,123	336,814	276,599
Insurance-International | Commercial Automobile [Member]
Segment Reporting Information [Line Items]
Net premiums earned	116,369	130,020	125,927
Insurance-International | Professional Liability [Member]
Segment Reporting Information [Line Items]
Net premiums earned	106,475	106,152	103,184
Reinsurance-Global
Segment Reporting Information [Line Items]
Net premiums earned	670,110	720,970	624,653
Reinsurance-Global | Casualty [Member]
Segment Reporting Information [Line Items]
Net premiums earned	487,264	507,790	456,376
Reinsurance-Global | Property [Member]
Segment Reporting Information [Line Items]
Net premiums earned	$182,846	$213,180	$168,277

Quarterly_Financial_Informatio2

Quarterly Financial Information (Unaudited) (Schedule of Quarterly Financial Information) (Details) (USD $)	3 Months Ended												12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Revenues	$1,784,428	$1,840,605	$1,796,989	$1,706,906	$1,696,679		$1,634,124		$1,570,962		$1,506,769		$7,128,928	$6,408,534	$5,823,554
Net income	$110,711	$188,539	$179,961	$169,673	$130,379		$136,974		$115,957		$116,615		$648,884	$499,925	$510,592
Net income per share
Basic (dollars per share)	$0.87	$1.48	$1.41	$1.31	$0.97	[1]	$1.01	[1]	$0.85	[1]	$0.86	[1]	$5.07	$3.69	$3.72
Diluted (dollars per share)	$0.83	$1.42	$1.35	$1.25	$0.93	[1]	$0.97	[1]	$0.82	[1]	$0.83	[1]	$4.86	$3.55	$3.56
[1]	Net income per share (“EPS”) in each quarter is computed using the weighted-average number of shares outstanding during that quarter, while EPS for the full year is computed using the weighted-average number of shares outstanding during the year. Thus, the sum of the four quarters EPS does not necessarily equal the full-year EPS.

Schedule_II_Condensed_Financia1

Schedule II - Condensed Financial Information of Registrant (Balance Sheets (Parent Company)) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 30, 2011
In Thousands, unless otherwise specified
Assets:
Cash and cash equivalents	$674,441	$839,738	$905,670	$911,742
Fixed maturity securities available for sale at fair value (cost $272,283 and $61,084 at December 31, 2014 and 2013, respectively)	12,705,160	11,616,844
Equity securities available for sale, at fair value (cost $3,738 in 2014 and $4,668 in 2013)	170,991	283,338
Deferred Federal income taxes	0	20,120
Current Federal income taxes	67,623	24,737
Property, furniture and equipment at cost, less accumulated depreciation	332,098	339,448
Other assets	369,558	335,225
Total assets	21,716,691	20,551,796
Liabilities:
Other liabilities	859,736	848,749
Deferred Federal income taxes	37,452	0
Subordinated debentures	340,060	339,800
Total liabilities	17,092,557	16,182,402
Stockholders' equity:
Preferred stock	0	0
Common stock	47,024	47,024
Additional paid-in capital	991,512	967,440
Retained earnings (including accumulated undistributed net income of subsidiaries of $4,700,821 and $4,393,420 at December 31, 2014 and 2013, respectively)	5,732,410	5,265,015
Accumulated other comprehensive income	183,550	189,391
Treasury stock, at cost	-2,364,551	-2,132,835
Total common stockholders’ equity	4,589,945	4,336,035
Total liabilities and equity	21,716,691	20,551,796
Equity securities available for sale at cost	160,295	203,627
Parent Company
Assets:
Cash and cash equivalents	90,693	17,315	162,972		270,637
Fixed maturity securities available for sale at fair value (cost $272,283 and $61,084 at December 31, 2014 and 2013, respectively)	273,773	63,115
Equity securities available for sale, at fair value (cost $3,738 in 2014 and $4,668 in 2013)	3,738	11,240
Investment in subsidiaries	6,693,731	6,250,979
Due from subsidiaries	0	13,648
Deferred Federal income taxes	0	51,346
Current Federal income taxes	62,882	17,540
Property, furniture and equipment at cost, less accumulated depreciation	9,852	9,028
Other assets	6,978	5,795
Total assets	7,141,647	6,440,006
Liabilities:
Due to subsidiaries	87,540	0
Other liabilities	162,648	148,903
Current Federal income taxes	149
Deferred Federal income taxes		0
Subordinated debentures	340,060	339,800
Senior notes	1,961,305	1,615,268
Total liabilities	2,551,702	2,103,971
Stockholders' equity:
Preferred stock	0	0
Common stock	47,024	47,024
Additional paid-in capital	991,512	967,440
Retained earnings (including accumulated undistributed net income of subsidiaries of $4,700,821 and $4,393,420 at December 31, 2014 and 2013, respectively)	5,732,410	5,265,015
Accumulated other comprehensive income	183,550	189,391
Treasury stock, at cost	-2,364,551	-2,132,835
Total common stockholders’ equity	4,589,945	4,336,035
Total liabilities and equity	7,141,647	6,440,006
Fixed maturity securities available for sale at cost	272,283	61,084
Equity securities available for sale at cost	3,738	4,668
Accumulated undistributed net income of subsidiaries	$4,700,821	$4,393,420

Schedule_II_Condensed_Financia2

Schedule II - Condensed Financial Information of Registrant (Statements of Income (Parent Company)) (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Income Statements, Captions [Line Items]
Other income									$1,308	$1,026	$2,564
Total revenues	1,784,428	1,840,605	1,796,989	1,706,906	1,696,679	1,634,124	1,570,962	1,506,769	7,128,928	6,408,534	5,823,554
Operating costs and expense									6,176,732	5,709,646	5,121,626
Income before income taxes									952,196	698,888	701,928
Federal income taxes:
Net expense									-302,593	-193,587	-191,285
Net income to common stockholders	110,711	188,539	179,961	169,673	130,379	136,974	115,957	116,615	648,884	499,925	510,592
Dividends from subsidiaries									503,483	269,626	25,968
Parent Company
Condensed Income Statements, Captions [Line Items]
Management fees and investment income including dividends from subsidiaries of $503,483, $269,626, and $25,968 for the years ended December 31, 2014, 2013 and 2012, respectively									515,775	277,223	29,961
Net investment gains									5,487	24,550	71,130
Other income									450	223	271
Total revenues									521,712	301,996	101,362
Operating costs and expense									148,288	122,562	133,326
Interest expense									125,352	120,066	124,298
Income before income taxes									248,072	59,368	-156,262
Federal income taxes:
Federal income taxes provided by subsidiaries on a separate return basis									366,721	225,845	132,379
Federal income tax expense on a consolidated return basis									-273,310	-154,928	-160,226
Net expense									93,411	70,917	-27,847
Income (loss) before undistributed equity in net income of subsidiaries									341,483	130,285	-184,109
Equity in undistributed net income of subsidiaries									307,401	369,640	694,701
Net income to common stockholders									$648,884	$499,925	$510,592

Schedule_II_Condensed_Financia3

Schedule II - Condensed Financial Information of Registrant (Statements of Cash Flows (Parent Company)) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Cash Flow Statements, Captions [Line Items]
Fixed maturity securities available for sale at fair value (cost $272,283 and $61,084 at December 31, 2014 and 2013, respectively)	$12,705,160	$11,616,844
Cash flows from operating activities:
Net income	648,884	499,925	510,592
Adjustments to reconcile net income to net cash from operating activities:
Net investment gains	-254,852	-121,544	-210,465
Depreciation and amortization	88,836	103,090	103,419
Stock incentive plans	28,068	23,784	26,763
Change in:
Other liabilities	-58,254	42,787	102,014
Net cash from operating activities	734,847	819,798	675,458
Cash from (used in) investing activities:
Proceeds from sale of fixed maturity securities	633,459	1,344,707	838,576
Proceeds from maturities and prepayments of fixed maturity securities	2,605,839	2,718,156	2,291,105
Proceeds from sales of equity securities	113,251	267,554	409,610
Cost of purchases of fixed maturity securities	-4,292,165	-4,198,135	-3,617,002
Payments to Acquire Available-for-sale Securities, Equity	-31,207	-156,557	-284,991
Payments to Acquire Businesses, Net of Cash Acquired	-65,421	-56,878	-42,779
Change in balance due to security broker	32,617	-26,155	-25,799
Net additions to real estate, furniture & equipment	-41,958	-63,150	-40,556
Net cash used in investing activities	-808,311	-545,364	-775,068
Cash from (used in) financing activities:
Net proceeds from stock options exercised	0	53	7,660
Purchase of common treasury shares	-238,933	-166,473	-127,663
Cash dividends to common stockholders	-181,489	-52,717	-183,947
Net cash from (used in) financing activities	-69,773	-330,262	97,192
Net decrease in cash and cash equivalents	-165,297	-65,932	-6,072
Cash and cash equivalents at beginning of year	839,738	905,670	911,742
Cash and cash equivalents at end of year	674,441	839,738	905,670
Parent Company
Condensed Cash Flow Statements, Captions [Line Items]
Fixed maturity securities available for sale at fair value (cost $272,283 and $61,084 at December 31, 2014 and 2013, respectively)	273,773	63,115
Cash flows from operating activities:
Net income	648,884	499,925	510,592
Adjustments to reconcile net income to net cash from operating activities:
Net investment gains	-5,487	-24,550	-71,130
Depreciation and amortization	2,916	10,397	5,624
Equity in undistributed earnings of subsidiaries	-307,401	-369,640	-694,701
Tax payments received from subsidiaries	462,809	77,305	125,046
Federal income taxes provided by subsidiaries on a separate return basis	-366,721	-225,845	-132,379
Stock incentive plans	28,068	23,784	26,763
Change in:
Federal income taxes	-15,239	21,866	44,423
Other assets	-364	-821	911
Other liabilities	-39,780	-15,470	28,017
Accrued investment income	-820	967	97
Other, net	0	0	-13
Net cash from operating activities	406,865	-2,082	-156,750
Cash from (used in) investing activities:
Proceeds from sale of fixed maturity securities	289,683	230,854	93,354
Proceeds from maturities and prepayments of fixed maturity securities	103,646	68,918	121,191
Proceeds from sales of equity securities	7,356	23,395	72,565
Cost of purchases of fixed maturity securities	-605,768	-79,132	-255,885
Payments to Acquire Available-for-sale Securities, Equity	0	-4,668	0
Payments to Acquire Businesses, Net of Cash Acquired	-82,879	0	0
Investments in and advances to subsidiaries, net	34,191	-58,454	-16,480
Change in balance due to security broker	-2,151	6,918	-4,767
Net additions to real estate, furniture & equipment	-1,615	-1,896	-1,857
Net cash used in investing activities	-257,537	185,935	8,121
Cash from (used in) financing activities:
Net proceeds from issuance of senior notes	344,472	339,627	345,823
Net proceeds from stock options exercised	0	53	13,544
Repayment of senior notes	0	-450,000	0
Purchase of common treasury shares	-238,933	-166,473	-134,456
Cash dividends to common stockholders	-181,489	-52,717	-183,947
Net cash from (used in) financing activities	-75,950	-329,510	40,964
Net decrease in cash and cash equivalents	73,378	-145,657	-107,665
Cash and cash equivalents at beginning of year	17,315	162,972
Cash and cash equivalents at end of year	$90,693	$17,315	$162,972

Schedule_III_Supplementary_Ins1

Schedule III - Supplementary Insurance Information (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplementary Insurance Information, by Segment [Line Items]
Deferrred Policy Acquisition Cost	$488,525	$452,101	$404,047
Reserve for Losses and Loss Expenses	10,369,701	10,080,941	9,751,086
Unearned Premiums	3,026,732	2,781,437	2,474,847
Net Premiums Earned	5,744,418	5,226,537	4,673,516
Net Investment Income	600,885	544,291	586,763
Loss and Loss Expenses	3,490,567	3,197,024	2,948,479
Amortization of Deferred Policy Acquisition Cost	1,053,397	991,070	917,583
Other Operating Cost and Expenses	1,104,059	1,009,614	882,040
Net Premiums Written	5,996,947	5,500,173	4,898,539
Operating Segments | Insurance-Domestic
Supplementary Insurance Information, by Segment [Line Items]
Deferrred Policy Acquisition Cost	347,261	306,464	269,418
Reserve for Losses and Loss Expenses	8,000,863	7,715,124	7,466,538
Unearned Premiums	2,384,511	2,107,768	1,844,452
Net Premiums Earned	4,271,933	3,782,416	3,417,022
Net Investment Income	428,632	404,280	424,787
Loss and Loss Expenses	2,571,010	2,318,541	2,169,090
Amortization of Deferred Policy Acquisition Cost	710,141	651,524	613,252
Other Operating Cost and Expenses	729,958	671,096	584,100
Net Premiums Written	4,517,587	3,994,387	3,569,883
Operating Segments | Insurance-International
Supplementary Insurance Information, by Segment [Line Items]
Deferrred Policy Acquisition Cost	60,900	60,751	56,995
Reserve for Losses and Loss Expenses	855,852	672,009	622,202
Unearned Premiums	342,746	317,691	297,581
Net Premiums Earned	802,375	723,151	631,841
Net Investment Income	55,407	47,039	45,796
Loss and Loss Expenses	503,997	429,900	377,459
Amortization of Deferred Policy Acquisition Cost	173,877	152,843	136,412
Other Operating Cost and Expenses	150,129	124,497	112,128
Net Premiums Written	828,076	756,185	664,459
Operating Segments | Reinsurance-Global
Supplementary Insurance Information, by Segment [Line Items]
Deferrred Policy Acquisition Cost	80,364	84,886	77,634
Reserve for Losses and Loss Expenses	1,512,986	1,693,808	1,662,346
Unearned Premiums	299,475	355,978	332,814
Net Premiums Earned	670,110	720,970	624,653
Net Investment Income	88,821	89,090	106,932
Loss and Loss Expenses	415,560	448,583	401,930
Amortization of Deferred Policy Acquisition Cost	169,379	186,703	167,919
Other Operating Cost and Expenses	58,315	64,567	58,044
Net Premiums Written	651,284	749,601	664,197
Corporate and adjustments
Supplementary Insurance Information, by Segment [Line Items]
Deferrred Policy Acquisition Cost	0	0	0
Reserve for Losses and Loss Expenses	0	0	0
Unearned Premiums	0	0	0
Net Premiums Earned	0	0	0
Net Investment Income	28,025	3,882	9,248
Loss and Loss Expenses	0	0	0
Amortization of Deferred Policy Acquisition Cost	0	0	0
Other Operating Cost and Expenses	165,657	149,454	127,768
Net Premiums Written	$0

Schedule_IV_Reinsurance_Detail

Schedule IV - Reinsurance (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct Amount	$6,185,242	$5,626,172	$4,964,069
Ceded to Other Companies	1,065,891	1,010,918	881,340
Assumed from Other Companies	877,596	884,919	815,810
Total net premiums written	5,996,947	5,500,173	4,898,539
Percentage of Amount Assumed to Net	14.60%	16.10%	16.70%
Insurance-Domestic
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct Amount	5,214,849	4,699,348	4,133,960
Ceded to Other Companies	866,092	809,368	691,284
Assumed from Other Companies	168,830	104,407	127,207
Total net premiums written	4,517,587	3,994,387	3,569,883
Percentage of Amount Assumed to Net	3.70%	2.60%	3.60%
Insurance-International
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct Amount	927,799	887,027	798,750
Ceded to Other Companies	156,195	142,591	137,598
Assumed from Other Companies	56,472	11,749	3,307
Total net premiums written	828,076	756,185	664,459
Percentage of Amount Assumed to Net	6.80%	1.60%	0.50%
Reinsurance-Global
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct Amount	42,594	39,797	31,359
Ceded to Other Companies	43,604	58,959	52,458
Assumed from Other Companies	652,294	768,763	685,296
Total net premiums written	$651,284	$749,601	$664,197
Percentage of Amount Assumed to Net	100.20%	102.60%	103.20%

Schedule_V_Valuation_and_Quali1

Schedule V - Valuation and Qualifying Accounts (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Movement in Valuation Allowances and Reserves [Roll Forward]
Opening Balance	$24,423	$30,219	$40,640
Additions - Charged to Expense	7,979	3,627	-4,103
Deductions - Amounts Written Off	-5,991	-9,423	-6,318
Ending Balance	26,411	24,423	30,219
Premiums and fees receivable
Movement in Valuation Allowances and Reserves [Roll Forward]
Opening Balance	20,951	22,919	17,666
Additions - Charged to Expense	5,944	3,133	9,598
Deductions - Amounts Written Off	-5,449	-5,101	-4,345
Ending Balance	21,446	20,951	22,919
Due from reinsurers
Movement in Valuation Allowances and Reserves [Roll Forward]
Opening Balance	1,385	1,680	3,169
Additions - Charged to Expense	301	186	22
Deductions - Amounts Written Off	-542	-481	-1,511
Ending Balance	1,144	1,385	1,680
Deferred federal and foreign income taxes
Movement in Valuation Allowances and Reserves [Roll Forward]
Opening Balance	0
Additions - Charged to Expense	1,335
Deductions - Amounts Written Off	0
Ending Balance	1,335
Loan loss reserves
Movement in Valuation Allowances and Reserves [Roll Forward]
Opening Balance	2,087	5,620	19,805
Additions - Charged to Expense	399	308	-13,723
Deductions - Amounts Written Off	0	-3,841	-462
Ending Balance	$2,486	$2,087	$5,620

Schedule_VI_Supplementary_Info1

Schedule VI - Supplementary Information Concerning Property-Casualty Insurance Operations (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Supplemental Information for Property, Casualty Insurance Underwriters [Abstract]
Deferred policy acquisition costs	$488,525	$452,101	$404,047
Reserves for losses and loss expenses	10,369,701	10,080,941	9,751,086
Unearned premium	3,026,732	2,781,437	2,474,847
Net premiums earned	5,744,418	5,226,537	4,673,516
Net investment income	600,885	544,291	586,763
Losses and loss expenses incurred:
Current year	3,495,825	3,221,393	2,997,995
Prior years		-75,764	-78,810	-102,571
Loss reserve discount accretion	70,506	54,441	53,055
Amortization of deferred policy acquisition costs	1,053,397	991,070	917,583
Paid losses and loss expenses	3,115,227	2,878,071	2,708,935
Net premiums written	$5,996,947	$5,500,173	$4,898,539