Endurance Specialty (ENH) 10-Q 6 May 15 2015 Q1 Quarterly report Financial data

Document_And_Entity_Informatio

Document And Entity Information	3 Months Ended
	Mar. 31, 2015	1-May-15
Document and Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	FALSE
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Entity Registrant Name	Endurance Specialty Holdings Ltd.
Entity Central Index Key	1179755
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		45,133,456

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheets (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
ASSETS
Fixed maturity investments, available for sale at fair value (amortized cost: $4,866,862 and $5,032,506 at March 31, 2015 and December 31, 2014, respectively)	$4,953,893	$5,092,581
Short-term investments, available for sale at fair value (amortized cost: $2,822 and $9,015 at March 31, 2015 and December 31, 2014, respectively)	2,822	9,014
Equity securities, available for sale at fair value (cost: $342,597 and $303,922 at March 31, 2015 and December 31, 2014, respectively)	366,897	331,368
Other investments	575,974	541,454
Total investments	5,899,586	5,974,417
Cash and cash equivalents	657,194	745,472
Premiums receivable, net	1,446,205	883,450
Insurance and reinsurance balances receivable	109,545	122,214
Deferred acquisition costs	258,753	207,368
Prepaid reinsurance premiums	692,466	354,940
Reinsurance recoverable on unpaid losses	605,809	670,795
Reinsurance recoverable on paid losses	136,642	218,291
Accrued investment income	23,165	27,183
Goodwill and intangible assets	151,816	153,405
Deferred tax asset	43,105	48,995
Net receivable on sales of investments	86,367	38,877
Other assets	269,491	199,375
Total assets	10,380,144	9,644,782
LIABILITIES
Reserve for losses and loss expenses	3,621,728	3,846,859
Reserve for unearned premiums	1,964,307	1,254,519
Deposit liabilities	13,722	15,136
Reinsurance balances payable	502,339	375,711
Debt	527,781	527,715
Net payable on purchases of investments	163,891	151,682
Other liabilities	311,530	287,978
Total liabilities	7,105,298	6,459,600
Commitments and contingent liabilities
SHAREHOLDERS' EQUITY
Preferred shares, Series A and B, total liquidation preference $430,000 (2014 - $430,000)	17,200	17,200
Common shares, Ordinary - 45,120,686 issued and outstanding (2014 - 44,765,153)	45,121	44,765
Additional paid-in capital	601,986	598,226
Accumulated other comprehensive income	77,759	76,706
Retained earnings	2,532,780	2,448,285
Total shareholders' equity	3,274,846	3,185,182
Total liabilities and shareholders' equity	$10,380,144	$9,644,782

Condensed_Consolidated_Balance1

Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, except Share data, unless otherwise specified
Available-for-sale Securities [Abstract]
Fixed maturity investments, available for sale, amortized cost	$4,866,862	$5,032,506
Short-term investments, available for sale, amortized cost	2,822	9,015
Equity securities, available for sale, cost	342,597	303,922
Stockholders' Equity, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, aggregate liquidation preference	$430,000	$430,000
Common stock, shares issued	45,120,686	44,765,153
Common stock, shares outstanding	45,120,686	44,765,153

Condensed_Consolidated_Stateme

Condensed Consolidated Statements Of Income And Comprehensive Income (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Revenues
Gross premiums written	$1,301,432	$1,157,515
Ceded premiums written	-536,478	-358,810
Net premiums written	764,954	798,705
Change in unearned premiums	-375,095	-402,439
Net premiums earned	389,859	396,266
Net investment income	41,861	40,990
Net realized and unrealized gains	18,189	4,872
Total other-than-temporary impairment losses	-649	-111
Portion of loss recognized in other comprehensive income	0	0
Net impairment losses recognized in earnings	-649	-111
Other underwriting income (loss)	2,406	-1,238
Total revenues	451,666	440,779
Expenses
Net losses and loss expenses	171,936	176,896
Acquisition expenses	82,093	72,157
General and administrative expenses	67,158	73,206
Amortization of intangibles	1,599	1,617
Net foreign exchange losses	7,552	2,964
Interest expense	9,059	9,051
Total expenses	339,397	335,891
Income before income taxes	112,269	104,888
Income tax expense	-3,790	-408
Net income	108,479	104,480
Preferred dividends	-8,188	-8,188
Net income available to common and participating common shareholders	100,291	96,292
Comprehensive income
Net income	108,479	104,480
Other comprehensive income
Net unrealized holding gains on investments arising during the period (net of other-than-temporary impairment losses recognized in other comprehensive income, reclassification adjustment and applicable deferred income taxes of ($2,022) and ($2,435) for the three months ended March 31, 2015 and 2014, respectively)	24,489	23,380
Foreign currency translation adjustments	-23,458	3,225
Reclassification adjustment for net losses on derivative designated as cash flow hedge included in net income	22	23
Other comprehensive income	1,053	26,628
Comprehensive income	$109,532	$131,108
Per share data
Basic earnings per common share	$2.24	$2.17
Diluted earnings per common share	$2.23	$2.17
Dividend per common share	$0.35	$0.34

Condensed_Consolidated_Stateme1

Condensed Consolidated Statements Of Income And Comprehensive Income (Parenthetical) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Other comprehensive income, net unrealized holding gains on investments arising during the period, tax	($2,022)	($2,435)

Condensed_Consolidated_Stateme2

Condensed Consolidated Statements Of Changes In Shareholders' Equity (USD $)	Total	Preferred Shares [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Cumulative Foreign Currency Translation Adjustments [Member]	Unrealized Holding Gains On Investments, Net Of Deferred Taxes [Member]	Accumulated Derivative Loss On Cash Flow Hedging Instruments [Member]	Accumulated Other Comprehensive Income [Member]	Retained Earnings [Member]
In Thousands
Balance, beginning of period at Dec. 31, 2013		$17,200	$44,369	$569,116	$18,636	$45,950	($1,855)		$2,193,133
Issuance of common shares, net of forfeitures			232	131
Settlement of equity awards				-3,768
Stock-based compensation expense				10,205
Foreign currency translation adjustments	3,225				3,225
Net unrealized holding gains arising during the period, net of other-than-temporary impairment losses and reclassification adjustment	23,380					23,380
Net change from current period hedging transactions, net of reclassification adjustment							23
Net income	104,480								104,480
Dividends on preferred shares	-8,188								-8,188
Dividends on common shares									-15,160
Balance, end of period at Mar. 31, 2014	3,001,109	17,200	44,601	575,684	21,861	69,330	-1,832	89,359	2,274,265
Balance, beginning of period at Dec. 31, 2014	3,185,182	17,200	44,765	598,226	-7,628	86,100	-1,766		2,448,285
Issuance of common shares, net of forfeitures			356	79
Settlement of equity awards				-6,092
Stock-based compensation expense				9,773
Foreign currency translation adjustments	-23,458				-23,458
Net unrealized holding gains arising during the period, net of other-than-temporary impairment losses and reclassification adjustment	24,489					24,489
Net change from current period hedging transactions, net of reclassification adjustment							22
Net income	108,479								108,479
Dividends on preferred shares	-8,188								-8,188
Dividends on common shares									-15,796
Balance, end of period at Mar. 31, 2015	$3,274,846	$17,200	$45,121	$601,986	($31,086)	$110,589	($1,744)	$77,759	$2,532,780

Condensed_Consolidated_Stateme3

Condensed Consolidated Statements Of Cash Flows (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Cash flows used in operating activities
Net income	$108,479	$104,480
Adjustments to reconcile net income to net cash used in operating activities:
Amortization of net premium on investments	12,496	12,240
Amortization of other intangibles and depreciation	6,210	4,726
Net realized and unrealized investment gains	-18,189	-4,872
Net impairment losses recognized in earnings	649	111
Deferred taxes	3,868	772
Stock-based compensation expense	9,773	10,205
Equity in earnings of other investments	-12,388	-13,542
Premiums receivable, net	-562,755	-596,173
Insurance and reinsurance balances receivable	12,669	-9,011
Deferred acquisition costs	-51,385	-45,140
Prepaid reinsurance premiums	-337,526	-256,289
Reinsurance recoverable on unpaid losses	64,986	59,420
Reinsurance recoverable on paid losses	81,649	104,436
Accrued investment income	4,018	943
Other assets	8,417	417
Reserve for losses and loss expenses	-225,131	-154,485
Reserve for unearned premiums	709,788	659,382
Deposit liabilities	-1,414	-774
Reinsurance balances payable	126,628	126,508
Other liabilities	-33,144	-28,950
Net cash flows used in operating activities	-92,302	-25,596
Cash flows provided by investing activities
Proceeds from sales of available for sale investments	1,399,972	1,110,582
Proceeds from maturities and calls on available for sale investments	155,627	141,879
Proceeds from the redemption of other investments	17,189	13,780
Purchases of available for sale investments	-1,478,073	-1,151,127
Purchases of other investments	-39,321	-4,674
Net settlements of other assets	-456	17,099
Purchases of fixed assets	-3,526	-7,427
Net cash paid for subsidiary acquisition	-10	0
Net cash flows provided by investing activities	51,402	120,112
Cash flows used in financing activities
Issuance of common shares, net of forfeitures	370	309
Settlement of equity awards	-6,092	-3,768
Proceeds from issuance of debt	235	138
Repayments and repurchases of debt	-226	-130
Dividends on preferred shares	-8,188	-8,188
Dividends on common shares	-15,771	-15,159
Net cash flows used in financing activities	-29,672	-26,798
Effect of exchange rate changes on cash and cash equivalents	-17,706	3,096
Net (decrease) increase in cash and cash equivalents	-88,278	70,814
Cash and cash equivalents, beginning of period	745,472	845,851
Cash and cash equivalents, end of period	$657,194	$916,665

General

General	3 Months Ended
	Mar. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
General
	1	General
	Endurance Specialty Holdings Ltd. (“Endurance Holdings” or the “Company”) was organized as a Bermuda holding company on June 27, 2002. Endurance Holdings writes specialty lines of insurance and reinsurance on a global basis through its wholly-owned operating subsidiaries:
	Operating Subsidiaries		Domicile
	Endurance Specialty Insurance Ltd.		Bermuda
	Endurance Worldwide Insurance Limited		England
	Endurance Reinsurance Corporation of America		Delaware
	Endurance American Insurance Company		Delaware
	Endurance American Specialty Insurance Company		Delaware
	Endurance Risk Solutions Assurance Co.		Delaware
	American Agri-Business Insurance Company		Texas
	On March 31, 2015, the Company announced the signing of a definitive agreement and plan of merger (the “Merger Agreement”) with Montpelier Re Holdings Ltd. (“Montpelier”) and Millhill Holdings Ltd., a direct, wholly-owned subsidiary of the Company ("Merger Sub"), under which Endurance Holdings will, through Merger Sub, acquire Montpelier (the “Merger”). Montpelier, through its operating subsidiaries, is a provider of global property and casualty reinsurance and insurance products. The Merger is expected to close in the third quarter of 2015, subject to the satisfaction of customary closing conditions including, but not limited to, approval by the Company's shareholders of the Company's share issuance at the special general meeting of the Company's shareholders, approval of the Merger Agreement, the statutory merger agreement and the Merger by Montpelier shareholders at the special general meeting of Montpelier shareholders and regulatory approvals. The aggregate consideration for the Merger will consist of 0.472 of an Endurance Holdings ordinary share for each Montpelier common share and a pre-closing dividend of $9.89 per Montpelier common share payable, in cash, by Montpelier to its common shareholders. The Company will account for the Merger under the acquisition method of accounting in accordance with current accounting guidance under which the total consideration paid will be allocated among acquired assets and assumed liabilities based on the fair values of the assets acquired and liabilities assumed. The Company anticipates that the purchase price paid will exceed the fair value of the net assets acquired and the excess will be accounted for as goodwill. There can be no assurance that the Merger will occur. Refer to Note 10, Commitments and contingencies, for more information with respect to the Merger.

Summary_Of_Significant_Account

Summary Of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Summary Of Significant Accounting Policies
	2	Summary of significant accounting policies
	The accompanying unaudited condensed consolidated financial statements have been prepared on the basis of accounting principles generally accepted in the United States for interim financial information and with the instructions to the Quarterly Report on Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by accounting principles generally accepted in the United States for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation have been included. Results for the three months ended March 31, 2015 are not necessarily indicative of the results that may be expected for the year ending December 31, 2015. The unaudited condensed consolidated financial statements include the accounts of Endurance Holdings and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. Management is required to make estimates and assumptions that affect the amounts reported in the unaudited condensed consolidated financial statements and accompanying disclosures. Actual results could differ from those estimates. Among other matters, significant estimates and assumptions are used to record premiums written and ceded, to record the fair value of investments and to record reserves for losses and loss expenses and contingencies. Estimates and assumptions are periodically reviewed and the effects of revisions are recorded in the consolidated financial statements in the period that they are determined to be necessary.
	The balance sheet at December 31, 2014 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by accounting principles generally accepted in the United States for complete financial statements. These unaudited condensed consolidated financial statements and notes thereto should be read in conjunction with the consolidated financial statements and notes thereto for the year ended December 31, 2014 contained in Endurance Holdings’ Annual Report on Form 10-K for the fiscal year ended December 31, 2014 (the “2014 Form 10-K”).
	2	Summary of significant accounting policies, cont'd.
	Certain comparative information has been reclassified to conform to current year presentation.
	There were no material changes in the Company’s significant accounting and reporting policies subsequent to the filing of the 2014 Form 10-K.

Investments

Investments	3 Months Ended
	Mar. 31, 2015
Investments [Abstract]
Investments
	3	Investments
	Composition of Net Investment Income and of Invested Assets
	The components of net investment income for the three months ended March 31, 2015 and 2014 are as follows:
		Three Months Ended March 31,
		2015				2014
	Available for sale investments	$	32,217			$	30,327
	Other investments	12,388				13,542
	Cash and cash equivalents	630				786
		45,235				44,655
	Investment expenses	(3,374		)		(3,665		)
	Net investment income	$	41,861			$	40,990
	The following table summarizes the composition of the investment portfolio by investment type at March 31, 2015 and December 31, 2014:
			31-Mar-15						31-Dec-14
	Type of Investment		Fair Value				Percentage		Fair Value				Percentage
	Fixed maturity investments		$	4,953,893			76.5	%	$	5,092,581			77.1	%
	Cash and cash equivalents(1)		579,670				8.9	%	632,667				9.6	%
	Other investments(2)		575,974				8.9	%	541,454				8.2	%
	Short-term investments		2,822				—	%	9,014				0.1	%
	Equity securities		366,897				5.7	%	331,368				5	%
	Total		$	6,479,256			100	%	$	6,607,084			100	%
	-1	Includes net receivable on sales of investments and net payable on purchases of investments.
	-2	Consists of investments in alternative funds and specialty funds.
	The following table summarizes the composition by investment rating of the fixed maturity and short-term investments at March 31, 2015 and December 31, 2014. In some cases, where bonds are unrated, the rating of the issuer has been applied.
			31-Mar-15						31-Dec-14
	Ratings(1)		Fair Value				Percentage		Fair Value				Percentage
	U.S. government and agencies securities		$	439,276			8.9	%	$	587,411			11.5	%
	AAA / Aaa		1,196,188				24.1	%	1,206,252				23.6	%
	AA / Aa		1,647,963				33.2	%	1,717,343				33.7	%
	A / A		1,055,259				21.3	%	1,045,301				20.5	%
	BBB		494,065				10	%	427,018				8.4	%
	Below BBB		103,728				2.1	%	96,244				1.9	%
	Not rated		20,236				0.4	%	22,026				0.4	%
	Total		$	4,956,715			100	%	$	5,101,595			100	%
	-1	The credit rating for each security reflected above was determined based on the rating assigned to the individual security by Standard & Poor’s Financial Services LLC (“Standard & Poor’s”). If a rating is not supplied by Standard & Poor’s, the equivalent rating supplied by Moody’s Investors Service, Inc. (“Moody's”), Fitch Ratings, Inc., or DBRS, Inc. is used.
	3	Investments, cont'd.
	Contractual maturities of the Company’s fixed maturity and short-term investments are shown below as of March 31, 2015 and December 31, 2014. Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.
		31-Mar-15							31-Dec-14
		Amortized				Fair Value			Amortized				Fair Value
		Cost							Cost
	Due within one year	$	104,359			$	105,176		$	126,921			$	127,821
	Due after one year through five years	1,518,003				1,533,554			1,627,154				1,632,259
	Due after five years through ten years	406,967				417,073			474,959				479,138
	Due after ten years	54,453				58,324			43,314				46,720
	Residential mortgage-backed securities	1,098,830				1,127,954			1,149,536				1,175,006
	Commercial mortgage-backed securities	979,828				1,003,437			960,598				979,419
	Collateralized loan and debt obligations	302,842				304,512			247,510				248,011
	Asset-backed securities	404,402				406,685			411,529				413,221
	Total	$	4,869,684			$	4,956,715		$	5,041,521			$	5,101,595
	In addition to the Company’s fixed maturity, short-term and equity investments, the Company invests in (i) hedge funds and private investment funds that generally invest in senior secured bank debt, high yield credit, distressed debt, distressed real estate, derivatives, and equity long/short strategies (“alternative funds”) and (ii) high yield loan funds (“specialty funds”). The Company’s alternative funds and specialty funds are recorded on the Company’s balance sheet as “other investments.” At March 31, 2015 and December 31, 2014, the Company had invested, net of capital returned, a total of $413.1 million and $387.2 million, respectively, in other investments. At March 31, 2015 and December 31, 2014, the carrying value of other investments was $576.0 million and $541.5 million, respectively. The following table summarizes the composition and redemption restrictions of other investments as of March 31, 2015 and December 31, 2014:
	31-Mar-15		Market Value				Unfunded			Ineligible for
							Commitments			Redemption over
										next 12 months
	Alternative funds
	Hedge funds		$	443,307			$	—		$	58,099
	Private investment funds		76,305				56,956			76,305
	Total alternative funds		519,612				56,956			134,404
	Specialty funds
	High yield loan funds		56,362				—			—
	Total specialty funds		56,362				—			—
	Total other investments		$	575,974			$	56,956		$	134,404
	31-Dec-14		Market Value				Unfunded			Ineligible for
							Commitments			Redemption in 2015
	Alternative funds
Hedge funds		$	411,280			$	—		$	10,580
Private investment funds		74,664				70,542			74,664
Total alternative funds		485,944				70,542			85,244
Specialty funds
High yield loan funds		55,510				—			—
Total specialty funds		55,510				—			—
Total other investments		$	541,454			$	70,542		$	85,244
3	Investments, cont'd.
Hedge funds – The redemption frequency of the hedge funds range from monthly to biennially with notice periods from 30 to 90 days. Over one year, it is estimated that the Company can liquidate approximately 86.9% of the hedge fund portfolio, with the remainder over the following two years.
Private investment funds – The Company generally has no right to redeem its interest in any private investment funds in advance of dissolution of the applicable partnership. Instead, the nature of these investments is that distributions are received by the Company in connection with the liquidation of or distribution of earnings from the underlying assets of the applicable limited partnership. It is estimated that the majority of the underlying assets of the limited partnerships would liquidate over 5 to 10 years from inception of the limited partnership. A secondary market, with unpredictable liquidity, exists for limited partner interests in private equity funds.
High yield loan funds – There are generally no restrictions on the Company’s right to redeem its interest in high yield loan funds with the exception of certain redemption frequency and notice requirements. The redemption frequency of these funds ranges from monthly to quarterly with notice periods from 30 to 90 days.
Net Realized and Unrealized Gains
Realized and unrealized gains and losses are recognized in earnings using the first in, first out method. The analysis of net realized and unrealized gains and the change in the fair value of investment-related derivative financial instruments for the three months ended March 31, 2015 and 2014 is as follows:
	Three Months Ended March 31,
	2015				2014
Gross realized gains on investment sales	$	22,666			$	10,247
Gross realized losses on investment sales	(4,896		)		(5,984		)
Change in fair value of derivative financial instruments(1)	419				609
Net realized and unrealized gains	$	18,189			$	4,872
-1	For additional information on the Company’s derivative financial instruments, see Note 7.
3	Investments, cont'd.
Unrealized Gains and Losses and Other-Than-Temporary Impairments
The Company classifies its investments in fixed maturity investments, short-term investments and equities as available for sale. The amortized cost, fair value and related gross unrealized gains and losses and non-credit other-than-temporary impairment (“OTTI”) losses on the Company’s securities classified as available for sale at March 31, 2015 and December 31, 2014 are as follows:
31-Mar-15		Amortized				Gross			Gross				Fair Value		Non-Credit
		Cost				Unrealized			Unrealized						OTTI(2)
						Gains			Losses
Fixed maturity investments
U.S. government and agencies securities		$	430,517			$	9,470		$	(711	)		$	439,276	$	—
U.S. state and municipal securities		51,930				407			(206		)		52,131		—
Foreign government securities		169,866				2,971			(639		)		172,198		—
Government guaranteed corporate securities		39,431				635			(1		)		40,065		—
Corporate securities		1,389,216				20,131			(1,712		)		1,407,635		—
Residential mortgage-backed securities		1,098,830				30,485			(1,361		)		1,127,954		(3,098		)
Commercial mortgage-backed securities		979,828				25,162			(1,553		)		1,003,437		—
Collateralized loan and debt obligations(1)		302,842				1,980			(310		)		304,512		—
Asset-backed securities		404,402				2,652			(369		)		406,685		—
Total fixed maturity investments		4,866,862				93,893			(6,862		)		4,953,893		(3,098		)
Short-term investments		2,822				—			—				2,822		—
Total fixed income investments		$	4,869,684			$	93,893		$	(6,862	)		$	4,956,715	$	(3,098	)
Equity securities
Equity investments		$	217,035			$	22,837		$	(1,478	)		$	238,394	$	—
Emerging market debt funds		61,874				—			(1,407		)		60,467		—
Convertible funds		46,331				2,167			—				48,498		—
Preferred equity investments		13,715				2,194			(12		)		15,897		—
Short-term fixed income fund		3,642				—			(1		)		3,641		—
Total equity securities		$	342,597			$	27,198		$	(2,898	)		$	366,897	$	—
-1	Balances include amounts related to collateralized debt obligations held with total fair values of $13.1 million.
-2	Represents total OTTI recognized in accumulated other comprehensive income. It does not include the change in fair value subsequent to the impairment measurement date. At March 31, 2015, the gross unrealized loss related to fixed income investments for which a non-credit OTTI was recognized in accumulated other comprehensive income was nil.
3	Investments, cont'd.
31-Dec-14		Amortized				Gross			Gross				Fair Value		Non-Credit
		Cost				Unrealized			Unrealized						OTTI(2)
						Gains			Losses
Fixed maturity investments
U.S. government and agencies securities		$	582,970			$	6,471		$	(2,030	)		$	587,411	$	—
U.S. state and municipal securities		39,340				191			(118		)		39,413		—
Foreign government securities		239,217				2,983			(1,664		)		240,536		—
Government guaranteed corporate securities		47,436				675			(9		)		48,102		—
Corporate securities		1,354,370				12,742			(5,650		)		1,361,462		—
Residential mortgage-backed securities		1,149,536				27,542			(2,072		)		1,175,006		(3,233		)
Commercial mortgage-backed securities		960,598				21,374			(2,553		)		979,419		(5		)
Collateralized loan and debt obligations(1)		247,510				1,449			(948		)		248,011		—
Asset-backed securities		411,529				2,265			(573		)		413,221		—
Total fixed maturity investments		5,032,506				75,692			(15,617		)		5,092,581		(3,238		)
Short-term investments		9,015				—			(1		)		9,014		—
Total fixed income investments		$	5,041,521			$	75,692		$	(15,618	)		$	5,101,595	$	(3,238	)
Equity securities
Equity investments		$	176,167			$	29,660		$	(3,292	)		$	202,535	$	—
Emerging market debt funds		60,826				—			(676		)		60,150		—
Convertible funds		46,331				—			(220		)		46,111		—
Preferred equity investments		13,858				2,022			(44		)		15,836		—
Short-term fixed income funds		6,740				—			(4		)		6,736		—
Total equity securities		$	303,922			$	31,682		$	(4,236	)		$	331,368	$	—
-1	Balances include amounts related to collateralized debt obligations held with total fair values of $15.2 million.
-2	Represents total OTTI recognized in accumulated other comprehensive income. It does not include the change in fair value subsequent to the impairment measurement date. At December 31, 2014, the gross unrealized loss related to fixed income investments for which a non-credit OTTI was recognized in accumulated other comprehensive income was nil.
3	Investments, cont'd.
The following tables summarize, for all available for sale securities in an unrealized loss position at March 31, 2015 and December 31, 2014, the aggregate fair value and gross unrealized loss by length of time the security has continuously been in an unrealized loss position.
		Less than 12 months							12 months or greater						Total
31-Mar-15		Unrealized				Fair			Unrealized				Fair		Unrealized			Fair
		Losses(1)				Value			Losses(1)				Value		Losses(1)			Value
Fixed maturity investments
U.S. government and agencies securities		$	(177	)		$	27,378		$	(534	)		$	24,374	$	(711	)	$	51,752
U.S. state and municipal securities		(198		)		17,685			(8		)		3,003		(206		)	20,688
Foreign government securities		(450		)		14,770			(189		)		1,688		(639		)	16,458
Government guaranteed corporate securities		(1		)		1,286			—				—		(1		)	1,286
Corporate securities		(1,048		)		192,963			(664		)		35,725		(1,712		)	228,688
Residential mortgage-backed securities		(308		)		79,275			(1,053		)		86,646		(1,361		)	165,921
Commercial mortgage-backed securities		(939		)		139,745			(614		)		38,908		(1,553		)	178,653
Collateralized loan and debt obligations		(255		)		141,280			(55		)		17,557		(310		)	158,837
Asset-backed securities		(217		)		121,075			(152		)		17,231		(369		)	138,306
Total fixed income investments		$	(3,593	)		735,457			(3,269		)		225,132		(6,862		)	960,589
Equity securities
Equity investments		$	(1,478	)		$	87,056		$	—			$	—	$	(1,478	)	$	87,056
Emerging market debt funds		(1,407		)		60,467			—				—		(1,407		)	60,467
Preferred equity investments		(12		)		2,089			—				—		(12		)	2,089
Short-term fixed income fund		(1		)		2,919			—				—		(1		)	2,919
Total equity securities		$	(2,898	)		$	152,531		$	—			$	—	$	(2,898	)	$	152,531
-1	Gross unrealized losses include unrealized losses on non-OTTI and non-credit OTTI securities recognized in accumulated other comprehensive income at March 31, 2015.
As of March 31, 2015, 491 available for sale securities were in an unrealized loss position aggregating $9.8 million. Of those, 107 securities with aggregated unrealized losses of $3.3 million had been in a continuous unrealized loss position for twelve months or greater.
3	Investments, cont'd.
		Less than 12 months							12 months or greater						Total
31-Dec-14		Unrealized				Fair			Unrealized				Fair		Unrealized			Fair
		Losses(1)				Value			Losses(1)				Value		Losses(1)			Value
Fixed maturity investments
U.S. government and agencies securities		$	(481	)		$	155,350		$	(1,549	)		$	45,993	$	(2,030	)	$	201,343
U.S. state and municipal securities		(47		)		3,295			(71		)		6,841		(118		)	10,136
Foreign government securities		(1,378		)		37,904			(286		)		4,306		(1,664		)	42,210
Government guaranteed corporate securities		(9		)		4,598			—				—		(9		)	4,598
Corporate securities		(4,023		)		533,139			(1,627		)		84,278		(5,650		)	617,417
Residential mortgage-backed securities		(260		)		62,832			(1,812		)		108,899		(2,072		)	171,731
Commercial mortgage-backed securities		(1,068		)		180,222			(1,485		)		78,412		(2,553		)	258,634
Collateralized loan and debt obligations		(876		)		176,439			(72		)		6,491		(948		)	182,930
Asset-backed securities		(415		)		199,205			(158		)		19,095		(573		)	218,300
Total fixed maturity investments		(8,557		)		1,352,984			(7,060		)		354,315		(15,617		)	1,707,299
Short-term investments		(1		)		1,953			—				—		(1		)	1,953
Total fixed income investments		$	(8,558	)		$	1,354,937		$	(7,060	)		$	354,315	$	(15,618	)	$	1,709,252
Equity securities
Equity investments		$	(3,292	)		$	53,591		$	—			$	—	$	(3,292	)	$	53,591
Emerging market debt funds		(676		)		60,150			—				—		(676		)	60,150
Convertible funds		(220		)		46,111			—				—		(220		)	46,111
Preferred equity investments		(44		)		4,449			—				—		(44		)	4,449
Short-term fixed income fund		(4		)		6,736			—				—		(4		)	6,736
Total equity securities		$	(4,236	)		$	171,037		$	—			$	—	$	(4,236	)	$	171,037
-1	Gross unrealized losses include unrealized losses on non-OTTI and non-credit OTTI securities recognized in accumulated other comprehensive income at December 31, 2014.
As of December 31, 2014, 747 available for sale securities were in an unrealized loss position aggregating $19.9 million. Of those, 171 securities with aggregated unrealized losses of $7.1 million had been in a continuous unrealized loss position for twelve months or greater.
The analysis of OTTI for the three months ended March 31, 2015 and 2014 is as follows:
	Three Months Ended March 31,
	2015				2014
Total other-than-temporary impairment losses	$	(649	)		$	(111	)
Portion of loss recognized in other comprehensive income	—				—
Net impairment losses recognized in earnings	$	(649	)		$	(111	)
3	Investments, cont'd.
Of the $0.6 million (2014: $0.1 million) of OTTI losses recognized by the Company in the first quarter of 2015, the majority was related to an equity investment for which the Company has subsequently made a decision to sell. The decrease in gross unrealized losses on the Company’s fixed income investments at March 31, 2015 compared to December 31, 2014 was primarily due to a decrease in interest rates and tightening credit spreads during the quarter. At March 31, 2015, the Company did not have the intent to sell any of the remaining fixed income investments in an unrealized loss position and determined that it was unlikely that the Company would be required to sell those securities in an unrealized loss position. The Company has the ability and intent to hold its equity securities until recovery; therefore, the Company does not consider its fixed income investments or equity securities to be other-than-temporarily impaired at March 31, 2015.
The following table provides a roll-forward of the amount related to credit losses for the Company’s available for sale investments recognized in earnings for which a portion of an OTTI loss was recognized in accumulated other comprehensive income for the three months ended March 31, 2015 and 2014:
	Three Months Ended March 31,
	2015				2014
Beginning balance	$	(838	)		$	(1,553	)
Addition for the amount related to the credit loss for which an other-than-temporary impairment was not previously recognized	—				—
Addition for the amount related to the credit loss for which an other-than-temporary impairment was previously recognized	—				—
Reductions for increases in cash flows expected to be collected that are recognized over the remaining life of the security	—				—
Reductions for securities sold during the period	43				33
Ending balance	$	(795	)		$	(1,520	)
Variable Interest Entities
Entities that do not have sufficient equity at risk to allow the entity to finance its activities without additional financial support or in which the equity investors, as a group, do not have the characteristics of a controlling financial interest are referred to as variable interest entities (“VIE”). A VIE is consolidated by the variable interest holder that is determined to have the controlling financial interest (primary beneficiary) as a result of having both the power to direct the activities of a VIE that most significantly impact the VIE’s economic performance and the obligation to absorb losses or right to receive benefits from the VIE that could potentially be significant to the VIE. The Company determines whether it is the primary beneficiary of an entity subject to consolidation based on a qualitative assessment of the VIE’s capital structure, contractual terms, nature of the VIE’s operations and purpose and the Company’s relative exposure to the related risks of the VIE on the date it becomes initially involved in the VIE. The Company reassesses its VIE determination with respect to an entity on an ongoing basis.
The Company is involved in the normal course of business with VIEs primarily as a passive investor in residential and commercial mortgage-backed securities and through its interests in various other investments that are structured as limited partnerships considered to be third party VIEs. The Company determined that it was not the primary beneficiary for any of these investments as of March 31, 2015. The Company believes its exposure to loss with respect to these investments is generally limited to the investment carrying amounts reported in the Company’s Condensed Consolidated Balance Sheets and any unfunded investment commitments.

Fair_Value_Measurement

Fair Value Measurement	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurement
	4	Fair value measurement
	The Company determines the fair value of the fixed maturity investments, short-term investments, equity securities, other investments, debt, and other assets and liabilities in accordance with current accounting guidance, which defines fair value and establishes a fair value hierarchy based on inputs to the various valuation techniques used for each fair value measurement. The Company determines the estimated fair value of each individual security utilizing the highest level inputs available. Valuation inputs by security type may include the following:
	•	Government and agencies fixed maturity securities – These securities are generally priced by pricing services or index providers. The pricing services or index providers may use current market trades for securities with similar quality, maturity and coupon. If no such trades are available, the pricing service typically uses analytical models which may incorporate option adjusted spreads, daily interest rate data and market/sector news. The Company generally classifies the fair values of government and agencies securities in Level 2. Current issue U.S. government securities are generally valued based on Level 1 inputs, which use the market approach valuation technique.
	•	Government guaranteed corporate fixed maturity securities – These securities are generally priced by pricing services or index providers. The pricing service or index providers may use current market trades for securities with similar quality, maturity and coupon. If no such trades are available, the pricing service typically uses analytical spread models which may incorporate inputs from the U.S. treasury curve or LIBOR. The Company generally classifies the fair values of its government guaranteed corporate securities in Level 2.
	•	Corporate fixed maturity securities – These securities are generally priced by pricing services or index providers. The pricing services or index providers typically use discounted cash flow models that incorporate benchmark curves for treasury, swap and high issuance credits. Credit spreads are developed from current market observations for like or similar securities. The Company generally classifies the fair values of its corporate securities in Level 2.
	•	Equity securities – These securities are generally priced by pricing services or index providers. Depending on the type of underlying equity security or equity fund, the securities are priced by pricing services or index providers based on quoted market prices in active markets or through a discounted cash flow model that incorporates benchmark curves for treasury, swap and credits for like or similar securities. The Company generally classifies the fair values of its equity securities in Level 1 or 2.
	•	Other assets and liabilities – A portion of other assets and liabilities are composed of a variety of derivative instruments used to enhance the efficiency of the investment portfolio and economically hedge certain risks. These instruments are generally priced by pricing services, broker/dealers and/or recent trading activity. The market value approach valuation technique is used to estimate the fair value for these derivatives based on significant observable market inputs. Certain derivative instruments are priced by pricing services based on quoted market prices in active markets. These derivative instruments are generally classified in Level 1. Other derivative instruments are priced using industry valuation models and are considered Level 2, as the inputs to the valuation model are based on observable market inputs. Also included in this line item are proprietary, non-exchange traded derivative-based risk management products primarily used to address weather and energy risks. The trading market for these weather derivatives are generally linked to energy and agriculture commodities, weather and other natural phenomena. In instances where market prices are not available, the Company uses industry or internally developed valuation techniques such as spread option, Black Scholes, quanto and simulation modeling to determine fair value and classifies these in Level 3. These models may reference prices for similar instruments.
	•	Structured securities including agency and non-agency, residential and commercial, mortgage and asset-backed securities and collateralized loan and debt obligations – These securities are generally priced by broker/dealers. Broker/dealers may use current market trades for securities with similar qualities. If no such trades are available, inputs such as bid and offer, prepayment speeds, the U.S. treasury curve, swap curve and cash settlement may be used in a discounted cash flow model to determine the fair value of a security. The Company generally classifies the fair values of its structured securities in Level 2.
	4	Fair value measurement, cont'd.
	•	Other investments – Other investments are comprised of alternative funds and specialty funds and are generally priced on net asset values (“NAV”) received from the fund managers or administrators. Due to the timing of the delivery of the final NAV by certain of the fund managers, valuations of certain alternative funds and specialty funds are estimated based on the most recently available information, including period end NAVs, period end estimates, or, in some cases, prior month or prior quarter NAVs. As this valuation technique incorporates both observable and significant unobservable inputs, the Company generally classifies the fair value of its other investments in Level 3.
	•	Debt – Outstanding debt consists of the Company’s 6.15% Senior Notes due October 15, 2015 and the 7.0% Senior Notes due July 15, 2034 (the “Senior Notes”). The fair values of these securities were obtained from a third party pricing service and pricing was based on the spread above the risk-free yield curve. These spreads are generally obtained from the new issue market, secondary trading and broker-dealer quotes. As these spreads and the yields for the risk-free yield curve are observable market inputs, the fair values of the Senior Notes are classified in Level 2.
	The carrying values of cash and cash equivalents, accrued investment income, net receivable on sales of investments, net payable on purchases of investments and other financial instruments not described above approximated their fair values at March 31, 2015 and December 31, 2014.
	Transfers between levels are assumed to occur at the end of each period.
	4	Fair value measurement, cont'd.
	The following table sets forth the Company’s available for sale investments, other investments, other assets and liabilities and debt categorized by the level within the hierarchy in which the fair value measurements fall at March 31, 2015:
		Fair Value Measurements at March 31, 2015
		Total at			Quoted Prices in			Significant Other			Significant Unobservable
		March 31, 2015			Active Markets for			Observable Inputs			Inputs
					Identical Assets			(Level 2)			(Level 3)
					(Level 1)
	Assets
	Fixed maturity investments
	U.S. government and agencies securities	$	439,276		$	16,825		$	422,451		$	—
	U.S. state and municipal securities	52,131			—			52,131			—
	Foreign government securities	172,198			—			172,198			—
	Government guaranteed corporate securities	40,065			—			40,065			—
	Corporate securities	1,407,635			—			1,405,136			2,499
	Residential mortgage-backed securities	1,127,954			—			1,127,954			—
	Commercial mortgage-backed securities	1,003,437			—			1,002,868			569
	Collateralized loan and debt obligations	304,512			—			301,046			3,466
	Asset-backed securities	406,685			—			403,719			2,966
	Total fixed maturity investments	4,953,893			16,825			4,927,568			9,500
	Equity securities
	Equity investments	238,394			144,297			94,097			—
	Emerging market debt funds	60,467			—			60,467			—
	Convertible funds	48,498			—			48,498			—
	Preferred equity investments	15,897			—			15,897			—
	Short-term fixed income fund	3,641			3,641			—			—
	Total equity securities	366,897			147,938			218,959			—
	Short-term investments	2,822			—			2,822			—
	Other investments	575,974			—			—			575,974
	Other assets (see Note 7)	170,023			—			154,800			15,223
	Total assets	$	6,069,609		$	164,763		$	5,304,149		$	600,697
	Liabilities
	Other liabilities (see Note 7)	$	114,943		$	—		$	97,558		$	17,385
	Debt	635,154			—			635,154			—
	Total liabilities	$	750,097		$	—		$	732,712		$	17,385
	During the three months ended March 31, 2015, $1.7 million of collateralized debt and loan obligations were transferred into Level 3 as no observable inputs were available, and $4.3 million of primarily commercial mortgage-backed securities were transferred out of Level 3 to Level 2 during the period as market activity for these securities increased and observable inputs became available.
	4	Fair value measurement, cont'd.
	The following table sets forth the Company’s available for sale investments, other investments, other assets and liabilities and debt categorized by the level within the hierarchy in which the fair value measurements fall at December 31, 2014:
		Fair Value Measurements at December 31, 2014
		Total at			Quoted Prices in			Significant Other			Significant
		December 31, 2014			Active Markets for			Observable Inputs			Unobservable
					Identical Assets			(Level 2)			Inputs
					(Level 1)						(Level 3)
	Assets
	Fixed maturity investments
	U.S. government and agencies securities	$	587,411		$	105,121		$	482,290		$	—
	U.S. state and municipal securities	39,413			—			39,413			—
	Foreign government securities	240,536			—			240,536			—
	Government guaranteed corporate securities	48,102			—			48,102			—
	Corporate securities	1,361,462			—			1,358,960			2,502
	Residential mortgage-backed securities	1,175,006			—			1,174,997			9
Commercial mortgage-backed securities	979,419			—			974,602			4,817
Collateralized loan and debt obligations	248,011			—			246,042			1,969
Asset-backed securities	413,221			—			410,228			2,993
Total fixed maturity investments	5,092,581			105,121			4,975,170			12,290
Equity securities
Equity investments	202,535			138,463			64,072			—
Emerging market debt funds	60,150			—			60,150			—
Convertible funds	46,111			—			46,111			—
Preferred equity investments	15,836			—			15,836			—
Short-term fixed income fund	6,736			6,736			—			—
Total equity securities	331,368			145,199			186,169			—
Short-term investments	9,014			—			9,014			—
Other investments	541,454			—			—			541,454
Other assets (see Note 7)	99,504			—			73,889			25,615
Total assets	$	6,073,921		$	250,320		$	5,244,242		$	579,359
Liabilities
Other liabilities (see Note 7)	$	54,338		$	—		$	18,972		$	35,366
Debt	623,740			—			623,740			—
Total liabilities	$	678,078		$	—		$	642,712		$	35,366
Level 3 assets represented 9.9% and 9.5% of the Company’s total available for sale investments, other investments and derivative instruments at March 31, 2015 and December 31, 2014, respectively. Level 3 securities are primarily comprised of corporate securities, mortgage-backed securities, collateralized loan and debt obligations, asset-backed securities, investments in alternative and specialty funds, and weather derivatives. The NAV used to measure the fair value of the Company’s other investments are generally derived from the underlying investments held within the funds. Although the Company does not have direct access to detailed financial information related to the underlying investments of the funds, the Company obtains and reviews fund financial statements, internal control review reports, and industry benchmarking reports to determine the reasonability of the NAV of the funds. There were no material changes in the Company’s valuation techniques for the three months ended March 31, 2015.
4	Fair value measurement, cont'd.
Other assets and other liabilities measured at fair value at March 31, 2015 include assets of $15.2 million (2014 - $25.6 million) and liabilities of $17.4 million (2014 - $35.4 million) related to proprietary, non-exchange traded derivative-based risk management products used in the Company’s weather risk management business, and hedging and trading activities related to these risks. In instances where market prices are not available, the Company may use industry or internally developed valuation techniques such as historical analysis and simulation modeling to determine fair value and are considered Level 3.
Observable and unobservable inputs to these valuation techniques vary by contract requirements and commodity type, are validated using market-based or independently sourced parameters where applicable and may include the following:
•Observable inputs: contract price, notional, option strike, term to expiry, interest rate, contractual limits;
•Unobservable inputs: correlation; and
•Both observable and unobservable: forward commodity price, forward weather curve.
The Company’s weather curves are determined by taking the average payouts for each transaction within its portfolio utilizing detrended historical weather measurements. The Company’s commodity curves are determined using historical market data scaled to currently observed market prices. The range of each unobservable input could vary based on the specific commodity, including, but not limited to natural gas, electricity, crude, liquids, temperature or precipitation. Due to the diversity of the portfolio, the range of unobservable inputs could be wide-spread as reflected in the below table on quantitative information.
If a trade has one or more significant valuation inputs that are unobservable, such trades are initially valued at the transaction price, which is considered to be the best initial estimate of fair value. Subsequent to the initial valuation, the Company updates market observable inputs to reflect observable market changes. The unobservable inputs are validated at each reporting period and are only changed when corroborated by evidence such as similar market transactions, third-party pricing services and/or broker or dealer quotations or other empirical market data.
Changes in any or all of the unobservable inputs listed above may contribute positively or negatively to the overall portfolio fair value depending upon the underlying position. In general, movements in weather curves are the largest contributing factor that impacts fair value.
4	Fair value measurement, cont'd.
Below is a summary of quantitative information regarding the significant unobservable inputs used in determining the fair value of the net weather and energy related derivative liabilities classified in Level 3 that are measured at fair value on a recurring basis at March 31, 2015 and December 31, 2014:
	31-Mar-15
	Fair Value			Valuation		Unobservable	Low			High			Weighted Average
	(Level 3)			Techniques		Inputs							or Actual
	(U.S. dollars in thousands, except for correlation)
Net weather and energy related derivative liabilities	$	2,162		Historical		Correlation	0			1			Actual
				Analysis and Simulation
						Weather curve	$	2,200		$	2,700		Actual
						Commodity curve	$	—		$	14		Actual
	31-Dec-14
	Fair Value			Valuation		Unobservable	Low			High			Weighted Average
	(Level 3)			Techniques		Inputs							or Actual
	(U.S. dollars in thousands, except for correlation)
Net weather and energy related derivative liabilities	$	9,751		Historical		Correlation	0			1			Actual
				Analysis and Simulation
						Weather curve	$	(828	)	$	2,500		Actual
						Commodity curve	$	—		$	—		Actual
There were no impairment losses on Level 3 securities recognized in earnings for the three months ended March 31, 2015 or 2014.
4	Fair value measurement, cont'd.
The following tables present a reconciliation of the beginning and ending balances for all assets and liabilities measured at fair value on a recurring basis using Level 3 inputs during the three months ended March 31, 2015 and 2014:
	Three Months Ended March 31, 2015
	Fixed maturity			Other			Other assets			Total assets			Other
	investments			investments									liabilities
Level 3, beginning of period	$	12,290		$	541,454		$	25,615		$	579,359		$	(35,366	)
Total equity income and realized gains included in earnings	113			20,549			—			20,662			—
Total equity losses and losses included in earnings	(9		)	(8,161		)	—			(8,170		)	—
Total income included in other underwriting income (loss)	—			—			2,096			2,096			13,059
Total loss included in other underwriting income (loss)	—			—			(8,842		)	(8,842		)	(3,529		)
Change in unrealized gains included in other comprehensive income	6			—			—			6			—
Change in unrealized losses included in other comprehensive income	(129		)	—			—			(129		)	—
Purchases	—			39,321			—			39,321			—
Issues	—			—			3,212			3,212			(6,424		)
Sales	(214		)	(17,189		)	—			(17,403		)	—
Settlements	—			—			(6,858		)	(6,858		)	14,875
Transfers into Level 3	1,733			—			—			1,733			—
Transfers out of Level 3	(4,290		)	—			—			(4,290		)	—
Level 3, end of period	$	9,500		$	575,974		$	15,223		$	600,697		$	(17,385	)
	Three Months Ended March 31, 2014
	Fixed maturity			Other			Other assets			Total assets			Other
	investments			investments									liabilities
Level 3, beginning of period	$	7,328		$	617,478		$	14,038		$	638,844		$	(19,569	)
Total equity income and realized gains included in earnings	17			19,186			—			19,203			—
Total equity losses and losses included in earnings	(26		)	(5,645		)	—			(5,671		)	—
Total income included in other underwriting income (loss)	—			—			3,975			3,975			7,426
Total loss included in other underwriting income (loss)	—			—			(6,888		)	(6,888		)	(4,776		)
Change in unrealized gains included in other comprehensive income	111			—			—			111			—
Change in unrealized losses included in other comprehensive income	(115		)	—			—			(115		)	—
Purchases	—			4,674			—			4,674			—
Issues	—			—			640			640			(1,280		)
Sales	(184		)	(13,779		)	—			(13,963		)	—
Settlements	—			—			(3,233		)	(3,233		)	4,751
Transfers in to Level 3	2,117			—			—			2,117			—
Transfers out of Level 3	(263		)	—			—			(263		)	—
Level 3, end of period	$	8,985		$	621,914		$	8,532		$	639,431		$	(13,448	)

Earnings_Per_Share

Earnings Per Share	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Earnings Per Share	5.     Earnings per share
	The two-class method utilized by the Company is an earnings allocation formula that determines earnings per share for the holders of Endurance Holdings’ ordinary shares (also referred to as “common shares”) and participating common shares, which includes unvested restricted shares and restricted share units that receive cash dividends, according to dividends declared and participation rights in undistributed earnings. Net income available to common and participating common shareholders is reduced by the amount of dividends declared in the current period and by the contractual amount of dividends that must be paid for the current period related to the Company’s common and participating common shares. Any remaining undistributed earnings are allocated to the common and participating common shareholders to the extent that each security may share in earnings as if all of the earnings for the period had been distributed. In periods of loss, no losses are allocated to participating common shareholders. Instead, all such losses are allocated solely to the common shareholders.
	Basic earnings per common share are calculated by dividing net income available to common shareholders by the weighted average number of common shares outstanding. The weighted average number of common shares excludes any dilutive effect of outstanding options and convertible securities such as unvested restricted shares and restricted share units.
	Diluted earnings per common share are based on the weighted average number of common shares and assumes the exercise of all dilutive stock options and the vesting or conversion of all convertible securities such as unvested restricted shares and restricted share units using the two-class method described above.
	The following table sets forth the computation of basic and diluted earnings per share for the three months ended March 31, 2015 and 2014:
		Three Months Ended
		March 31,
		2015			2014
	Numerator:
	Net income available to common and participating common shareholders	$	100,291		$	96,292
	Less amount allocated to participating common	(2,959		)	(2,769		)
	shareholders(1)
	Net income allocated to common shareholders	97,332			93,523
	Denominator:
	Weighted average shares - basic	43,542,491			43,160,156
	Share equivalents:
	Options	146,792			—
	Restricted shares and restricted share units	7,028			286
	Weighted average shares - diluted	43,696,311			43,160,442
	Basic earnings per common share	$	2.24		$	2.17
	Diluted earnings per common share	$	2.23		$	2.17
	-1	Represents earnings attributable to holders of unvested restricted shares and restricted share units issued under the Company's equity compensation plan that are considered participating. In periods of loss, no losses are allocated to participating common shareholders (unvested restricted shares and restricted share units).
	5.     Earnings per share, cont'd.
	Endurance Holdings declared a dividend of $0.484375 per Series A preferred share and $0.468750 per Series B preferred share on February 22, 2015 (2014 - Series A: $0.484375, Series B: $0.468750). The Series A and Series B preferred share dividends were paid on March 16, 2015 to shareholders of record on March 2, 2015. Endurance Holdings also declared a dividend of $0.35 per common share on February 26, 2015 (2014 - $0.34). The dividend was paid on March 31, 2015 to shareholders of record on March 17, 2015.
		Three Months Ended
		March 31,
		2015			2014
	Dividends declared per Series A preferred share	$	0.484375		$	0.484375
	Dividends declared per Series B preferred share	$	0.46875		$	0.46875
	Dividends declared per common share	$	0.35		$	0.34

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Income	3 Months Ended
	Mar. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income
	6	Accumulated other comprehensive income
	The following tables present the changes in accumulated other comprehensive income balances by component for the three months ended March 31, 2015 and 2014:
		For the Three Months Ended March 31, 2015
		Losses on				Unrealized gains on available for sale securities			Foreign currency translation adjustments			Total
		cash flow hedges
	Beginning balance	$	(1,766	)		$	86,100		$	(7,628	)	$	76,706
	Other comprehensive income before reclassifications	—				40,734			(23,458		)	17,276
	Amounts reclassified from accumulated other comprehensive income(1)	22				(16,245		)	—			(16,223		)
	Net current period other comprehensive income	22				24,489			(23,458		)	1,053
	Ending balance	$	(1,744	)		$	110,589		$	(31,086	)	$	77,759
	(1)All amounts are net of tax.
		For the Three Months Ended March 31, 2014
		Losses on cash flow hedges				Unrealized gains on available for sale securities			Foreign currency translation adjustments			Total
	Beginning balance	$	(1,855	)		45,950			$	18,636		$	62,731
	Other comprehensive income before reclassifications	—				27,665			3,225			30,890
	Amounts reclassified from accumulated other comprehensive income(1)	23				(4,285		)	—			(4,262		)
	Net current period other comprehensive income	23				23,380			3,225			26,628
	Ending balance	$	(1,832	)		$	69,330		$	21,861		$	89,359
	(1)All amounts are net of tax.
	6	Accumulated other comprehensive income, cont'd.
	The following tables present the significant items reclassified out of accumulated other comprehensive income during the three months ended March 31, 2015 and 2014:
	Three Months Ended March 31, 2015
	Details about accumulated other comprehensive		Amount reclassified				Affected line item in the Unaudited
	income components		from accumulated other				Condensed Consolidated Statements of
			comprehensive income				Income and Comprehensive Income
	Losses on cash flow hedges - Debt		$	22			Interest expense
			22				Total before income taxes
			—				Income tax expense
			$	22			Total net of income taxes
	Unrealized gains on available for sale securities		$	(17,770	)		Net realized and unrealized gains
			649				Net impairment losses recognized in earnings
			(17,121		)		Total before income taxes
			876				Income tax expense
			$	(16,245	)		Total net of income taxes
	Three Months Ended March 31, 2014
	Details about accumulated other comprehensive		Amount reclassified				Affected line item in the Unaudited
	income components		from accumulated other				Condensed Consolidated Statements of
			comprehensive income				Income and Comprehensive Income
	Losses on cash flow hedges - Debt		$	23			Interest expense
			23				Total before income taxes
			—				Income tax expense
			$	23			Total net of income taxes
	Unrealized gains on available for sale securities		$	(4,263	)		Net realized and unrealized gains
			111				Net impairment losses recognized in earnings
			(4,152		)		Total before income taxes
			(133		)		Income tax benefit
			$	(4,285	)		Total net of income taxes

Derivatives

Derivatives	3 Months Ended
	Mar. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives
	7	Derivatives
	The Company regularly transacts in certain derivative-based weather risk management products primarily to address weather and energy risks on behalf of third parties. The markets for these derivatives are generally linked to energy and agriculture commodities, weather and other natural phenomena. Generally, the Company’s current portfolio of such derivative contracts is of short duration and such contracts are predominantly seasonal in nature. The Company also invests a portion of its fixed maturity assets with third party investment managers with investment guidelines that permit the use of derivative instruments. The Company may enter derivative transactions directly or as part of strategies employed by its external investment managers.
	The Company’s derivative instruments are recorded in the Condensed Consolidated Balance Sheets at fair value, with changes in fair value and gains and losses recognized in net realized and unrealized gains, net foreign exchange losses and other underwriting income (loss) in the Condensed Consolidated Statements of Income and Comprehensive Income.
	The Company’s derivatives are not designated as hedges under current accounting guidance.
	The Company’s objectives for holding these derivatives are as follows:
	Interest Rate Futures, Swaps, Swaptions and Options - to manage exposure to interest rate risk, which can include increasing or decreasing its exposure to this risk through modification of the portfolio composition and duration.
	Foreign Exchange Forwards, Futures and Options - as part of overall currency risk management and investment strategies.
	Credit Default Swaps - to manage market exposures. The Company may assume or economically hedge credit risk through credit default swaps to replicate or hedge investment positions. The original term of these credit default swaps is generally five years or less.
	To-Be-Announced Mortgage-backed Securities (“TBAs”) - to enhance investment performance and as part of overall investment strategy. TBAs represent commitments to purchase or sell a future issuance of agency mortgage-backed securities. For the period between purchase of a TBA and issuance of the underlying securities, the Company’s position is accounted for as a derivative.
	Energy and Weather Contracts – to address weather and energy risks. The Company may purchase or sell contracts with financial settlements based on the performance of an index linked to a quantifiable weather element, such as temperature, precipitation, snowfall or windspeed, and structures with multiple risk triggers indexed to a quantifiable weather element and a weather sensitive commodity price, such as temperature and electrical power or natural gas. Generally, the Company’s current portfolio of energy and weather derivative contracts is of comparably short duration and such contracts are predominantly seasonal in nature.
	7	Derivatives, cont'd.
	The fair values and the related notional values of derivatives at March 31, 2015 and December 31, 2014 are shown below.
		31-Mar-15						31-Dec-14
		Fair			Notional			Fair		Notional
		Value			Principal			Value		Principal
					Amount					Amount
	Derivatives recorded in other assets
	Foreign exchange forward contracts	$	1,021		$	37,927		$	651	$	42,694
	Interest rate futures	16			120,235			7		7,595
	TBAs	153,763			146,000			73,231		70,000
	Energy and weather contracts	15,223			59,012			25,615		81,624
	Total recorded in other assets	170,023						99,504
	Derivatives recorded in other liabilities
	Foreign exchange forward contracts	557			$	22,438		123		$	20,945
	Interest rate swaps	267			4,757			20		12,549
	Interest rate swaptions	—			10,500			9		13,100
	Interest rate futures	28			124,771			—		—
	TBAs	96,706			92,000			18,820		18,000
	Energy and weather contracts	17,385			117,999			35,366		135,050
	Total recorded in other liabilities	114,943						54,338
	Net derivative asset	$	55,080					$	45,166
	At March 31, 2015, the Company’s derivative assets of $170.0 million (December 31, 2014 - $99.5 million) and liabilities of $114.9 million (December 31, 2014 - $54.3 million) are subject to master netting agreements, which provide for the ability to settle the derivative asset and liability with each counterparty on a net basis. At March 31, 2015 and December 31, 2014, interest rate futures were not subject to a master netting agreement. At March 31, 2015 and December 31, 2014, none of the Company’s derivative instruments were recorded on a net basis in the Condensed Consolidated Balance Sheets.
	The gains and losses on the Condensed Consolidated Statements of Income and Comprehensive Income for derivatives for the three months ended March 31, 2015 and 2014 were as follows:
		Three Months Ended
		March 31,
		2015			2014
	Total included in net foreign exchange losses from foreign exchange forward contracts	$	1,469		$	(227	)
	Futures contracts	122			21
	Interest rate swaps	(555		)	(766		)
	Interest rate swaptions	28			429
	TBAs	824			925
	Total included in net realized and unrealized gains	419			609
	Total included in other underwriting income (loss) from energy and weather contracts	2,784			(258		)
	Total gains from derivatives	$	4,672		$	124

StockBased_Employee_Compensati

Stock-Based Employee Compensation And Other Stock Plans	3 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Employee Compensation And Other Stock Plans
	8	Stock-based employee compensation and other stock plans
	The Company has a stock-based employee compensation plan, which provides the Company with the ability to grant options to purchase the Company’s ordinary shares, share appreciation rights, restricted shares, restricted share units, share bonuses and other equity incentive awards to key employees.
	Options
	In 2013, the Company issued options to the current Chief Executive Officer as an inducement to his joining the Company. The options vest annually, in five equal tranches commencing on May 28, 2013, subject to the Chief Executive Officer's continued employment, or in the event of certain terminations of employment and other events. The Chief Executive Officer's options have a ten-year contractual life. The Company uses the Black-Scholes-Merton formula to estimate the value of stock options granted. For the quarter ended March 31, 2015, compensation costs recognized in earnings for all options totaled $0.6 million (2014 - $1.1 million). At March 31, 2015, compensation costs not yet recognized related to unvested stock options was $2.1 million (2014 - $4.6 million).
	Performance-Based Restricted Shares
	Commencing in March 2015, the Company issued performance-based restricted shares to certain of its senior executives. The performance-based restricted shares represent the right to receive a specified number of ordinary shares in the future, based upon the achievement of pre-established performance criteria during the applicable performance period. Performance-based restricted shares granted to employees cliff vest at the end of the three-year period. The number of performance-based restricted shares that will ultimately vest is subject to a periodic review and adjustment taking into account actual performance of the Company compared to the performance of a publicly-traded peer group of companies.
	Performance-based restricted shares are forfeited upon departure from the Company for any reason prior to the applicable vesting date other than in cases of death, disability, termination of employment in connection with a change in control and retirement. In the case of death, disability or change in control, 50% of the performance-based restricted shares will vest upon the date of death or disability or termination of employment in connection with a change in control. Where an employee meets certain retirement eligibility criteria, the performance-based restricted shares will continue to vest post-employment, subject to compliance with certain non-competition obligations.
	The fair value of the performance-based restricted shares is measured at the grant date using a Monte Carlo simulation based on pre-established targets relating to certain performance based measures achieved by the Company, with the associated expense recognized over the applicable performance and vesting period.
	Time-Based Restricted Shares
	The Company has issued time-based restricted shares to employees and non-employee directors. Restricted shares granted to employees generally vest pro rata over a four-year period. Restricted shares are forfeited upon departure from the Company for any reason prior to the applicable vesting date other than in cases where an employee meets certain retirement eligibility criteria which allow for continuing post-employment vesting of restricted shares, subject to compliance with certain non-competition obligations.
	Restricted shares granted to non-employee directors vest twelve months following the date of grant and are forfeited upon departure from the Board of Directors for any reason prior to the applicable vesting date.
	The fair value of the restricted shares granted is equal to the fair market value of the Company’s ordinary shares on the grant date. Compensation equal to the fair market value of the restricted shares at the measurement date is amortized and charged to income over the vesting period.
	Restricted Share Units
	The Company has issued restricted share units to employees in select jurisdictions where the issuance of restricted shares results in unfavorable tax treatment for employee recipients. Restricted share units granted to employees generally vest pro rata over a four-year period. Restricted share units are forfeited upon departure from the Company for any reason prior to the applicable vesting date.
	8	Stock-based employee compensation and other stock plans, cont'd.
	The fair value of the restricted share units granted is equal to the fair market value of the Company’s ordinary shares on the grant date. Compensation equal to the fair market value of the restricted share units at the measurement date is amortized and charged to income over the vesting period.
	Summary of Stock-Based Employee Compensation Activity
	No options were granted, expired, vested or exercised during the quarters ended March 31, 2015 and 2014.
	A summary of the restricted share and restricted share unit activity during the quarter ended March 31, 2015, is presented below:
			Number of		Aggregate
			Shares/Units		Intrinsic Value
	Unvested, beginning of year		1,290,894
	Granted		472,662
	Settled		(285,044	)
	Forfeited		—
	Unvested, end of year		1,478,512
	Outstanding, end of year		1,478,512		$	90,396
	During the quarter ended March 31, 2015, the Company granted an aggregate of 472,662 (2014 – 335,771) restricted shares and restricted share units under the 2007 Plan. The restricted shares and restricted share units granted had weighted average grant date fair values of $28.0 million (2014 - $17.6 million). During the quarter ended March 31, 2015, the aggregate fair value of restricted shares and restricted share units that vested was $13.8 million (2014 - $9.8 million). For the quarter ended March 31, 2015, compensation costs recognized in earnings for all restricted shares and restricted share units were $9.2 million (2014 - $9.1 million). At March 31, 2015, compensation costs not yet recognized related to unvested restricted shares and restricted share units was $38.7 million (2014 - $34.9 million).
	Employee Share Purchase Plan
	The Company also has an Employee Share Purchase Plan ("2005 Employee Share purchase Plan") under which employees of Endurance Holdings and certain of its subsidiaries may purchase Endurance Holdings’ ordinary shares. For the quarter ended March 31, 2015, total expenses related to the Company’s 2005 Employee Share Purchase Plan were approximately $65,000 (2014 - $54,000).
	The 2005 Employee Share Purchase Plan is scheduled to terminate in accordance with its terms on October 1, 2015. On February 26, 2015, the Compensation Committee of the Board of Directors of Endurance Holdings approved, subject to approval by the Company's shareholders, a new employee share purchase plan (“2015 Employee Share Purchase Plan”). If the 2015 Employee Share Purchase Plan is approved by the Company's shareholders, the Company will cease offering and issuing new shares under the 2005 Employee Share Purchase Plan on June 30, 2015 and offer and issue new shares under the 2015 Employee Share Purchase Plan beginning on or after July 1, 2015.

Segment_Reporting

Segment Reporting	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Segment Reporting
	9	Segment reporting
	The determination of the Company’s business segments is based on how the Company monitors the performance of its underwriting operations. The Company has two reportable business segments, Insurance and Reinsurance, which are comprised of the following lines of business:
	Insurance segment lines of business
	•Agriculture
	•Casualty and other specialty
	•Professional lines
	•Property, marine and energy
	Reinsurance segment lines of business
	•Catastrophe
	•Property
	•Casualty
	•Professional lines
	•Specialty
	Management measures segment results on the basis of the combined ratio, which is obtained by dividing the sum of the net losses and loss expenses, acquisition expenses and general and administrative expenses by net premiums earned. When purchased within a single line of business, ceded reinsurance and recoveries are accounted for within that line of business. When purchased across multiple lines of business, ceded reinsurance and recoveries are allocated to the lines of business in proportion to the related risks assumed. The Company does not manage its assets by segment; accordingly, investment income and total assets are not allocated to the individual business segments. General and administrative expenses incurred by the segments are allocated directly. Remaining general and administrative expenses not directly incurred by the segments are allocated primarily based on estimated consumption, headcount and other variables deemed relevant to the allocation of such expenses. Ceded reinsurance and recoveries are recorded within the business segment to which they apply.
	9	Segment reporting, cont'd.
	The following table provides a summary of segment revenues, results and reserves for losses and loss expenses for the three months ended March 31, 2015:
		Three Months Ended March 31, 2015
		Insurance			Reinsurance			Total
	Revenues
	Gross premiums written	$	736,218		$	565,214		$	1,301,432
	Ceded premiums written	(432,179		)	(104,299		)	(536,478		)
	Net premiums written	304,039			460,915			764,954
	Net premiums earned	135,864			253,995			389,859
	Other underwriting income	—			2,406			2,406
		135,864			256,401			392,265
	Expenses
	Net losses and loss expenses	74,512			97,424			171,936
	Acquisition expenses	15,883			66,210			82,093
	General and administrative expenses	32,684			34,474			67,158
		123,079			198,108			321,187
	Underwriting income	$	12,785		$	58,293		$	71,078
	Net loss ratio	54.8		%	38.3		%	44.1		%
	Acquisition expense ratio	11.7		%	26.1		%	21.1		%
	General and administrative expense ratio	24.1		%	13.6		%	17.2		%
	Combined ratio	90.6		%	78		%	82.4		%
	Reserve for losses and loss expenses	$	1,952,277		$	1,669,451		$	3,621,728
	9	Segment reporting, cont'd.
	The following table provides a summary of segment revenues, results and reserves for losses and loss expenses for the three months ended March 31, 2014:
		Three Months Ended March 31, 2014
		Insurance			Reinsurance			Total
	Revenues
	Gross premiums written	$	652,276		$	505,239		$	1,157,515
	Ceded premiums written	(309,249		)	(49,561		)	(358,810		)
	Net premiums written	343,027			455,678			798,705
	Net premiums earned	144,021			252,245			396,266
	Other underwriting loss	—			(1,238		)	(1,238		)
		144,021			251,007			395,028
	Expenses
	Net losses and loss expenses	88,533			88,363			176,896
	Acquisition expenses	12,261			59,896			72,157
	General and administrative expenses	41,736			31,470			73,206
		142,530			179,729			322,259
	Underwriting income	$	1,491		$	71,278		$	72,769
	Net loss ratio	61.5		%	35		%	44.6		%
	Acquisition expense ratio	8.5		%	23.7		%	18.2		%
	General and administrative expense ratio	29		%	12.6		%	18.5		%
	Combined ratio	99		%	71.3		%	81.3		%
	Reserve for losses and loss expenses	$	2,023,819		$	1,823,955		$	3,847,774
	The following table reconciles total segment results to income before income taxes for the three months ended March 31, 2015 and 2014:
		Three Months Ended March 31,
		2015			2014
	Total underwriting income	$	71,078		$	72,769
	Net investment income	41,861			40,990
Net foreign exchange losses	(7,552		)	(2,964		)
Net realized and unrealized gains	18,189			4,872
Net impairment losses recognized in earnings	(649		)	(111		)
Amortization of intangibles	(1,599		)	(1,617		)
Interest expense	(9,059		)	(9,051		)
Income before income taxes	$	112,269		$	104,888
9	Segment reporting, cont'd.
The following table provides gross and net premiums written by line of business for the three months ended March 31, 2015 and 2014:
	Gross			Net			Gross			Net
	premiums			premiums			premiums			premiums
	written			written			written			written
Business Segment	2015			2015			2014			2014
Insurance
Agriculture	$	516,916		$	202,460		$	527,894		$	281,645
Casualty and other specialty	100,682			45,058			67,653			36,813
Professional lines	54,760			24,231			38,780			14,570
Property, marine and energy	63,860			32,290			17,949			9,999
Total Insurance	736,218			304,039			652,276			343,027
Reinsurance
Catastrophe	124,407			53,460			126,648			78,963
Property	125,700			123,449			166,413			166,322
Casualty	58,098			58,098			84,982			83,392
Professional lines	43,857			43,857			25,619			25,619
Specialty	213,152			182,051			101,577			101,382
Total Reinsurance	565,214			460,915			505,239			455,678
Total	$	1,301,432		$	764,954		$	1,157,515		$	798,705

Commitments_And_Contingencies

Commitments And Contingencies	3 Months Ended
	Mar. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments And Contingencies
	10	Commitments and contingencies
	Concentrations of credit risk. The Company’s reinsurance recoverables on paid and unpaid losses at March 31, 2015 and December 31, 2014 amounted to $742.5 million and $889.1 million, respectively. At March 31, 2015, substantially all reinsurance recoverables on paid and unpaid losses were due from the U.S. government or from reinsurers rated A- or better by A.M. Best Company Inc. or Standard & Poor’s Corporation. At March 31, 2015 and December 31, 2014, the Company held collateral of $175.3 million and $199.7 million, respectively, related to its ceded reinsurance agreements.
	Major production sources. The following table shows the percentage of net premiums written generated through the Company’s largest brokers for the three months ended March 31, 2015 and 2014, respectively:
	Broker		2015		2014
	Marsh & McLennan Companies, Inc.		18.9	%	16.7	%
	Aon Benfield		17.7	%	15.1	%
	Willis Companies		11.5	%	12	%
	Total of largest brokers		48.1	%	43.8	%
	Letters of credit. As of March 31, 2015, the Company had issued letters of credit of $192.9 million (December 31, 2014 – $209.9 million) under its credit facilities and letter of credit reimbursement agreements in favor of certain ceding companies to collateralize obligations.
	10	Commitments and contingencies, cont'd.
	Investment commitments. As of March 31, 2015 and December 31, 2014, the Company had pledged cash and cash equivalents and fixed maturity investments of $130.7 million and $130.6 million, respectively, in favor of certain ceding companies to collateralize obligations. As of March 31, 2015 and December 31, 2014, the Company had also pledged $219.8 million and $240.0 million of its cash and fixed maturity investments as required to meet collateral obligations for $192.9 million and $209.9 million, respectively, in letters of credit outstanding under its credit facilities and letter of credit reimbursement agreements. In addition, as of March 31, 2015 and December 31, 2014, cash and fixed maturity investments with fair values of $205.4 million and $205.2 million were on deposit with U.S. state regulators, respectively.
	The Company is subject to certain commitments with respect to other investments at March 31, 2015 and December 31, 2014. See Note 3.
	Reinsurance commitments. In the ordinary course of business, the Company periodically enters into reinsurance agreements that include terms which could require the Company to collateralize certain of its obligations.
	Employment agreements. The Company has entered into employment agreements with certain officers that provide for equity incentive awards, executive benefits and severance payments under certain circumstances.
	Operating leases. The Company leases office space and office equipment under operating leases. Future minimum lease commitments at March 31, 2015 are as follows:
	Twelve months ended March 31,		Amount
	2016		$	14,928
	2017		14,123
	2018		13,739
	2019		13,204
	2020		13,859
	2021 and thereafter		31,728
			$	101,581
	Total net lease expense under operating leases for the three months ended March 31, 2015 was $3.1 million (2014 – $4.2 million).
	Legal proceedings. The Company is party to various legal proceedings generally arising in the normal course of its business. While any proceeding contains an element of uncertainty, the Company does not believe that the eventual outcome of any litigation or arbitration proceeding to which it is presently a party could have a material adverse effect on its financial condition or business. Pursuant to the Company’s insurance and reinsurance agreements, disputes are generally required to be settled by arbitration.
	Acquisition of Montpelier. On March 31, 2015, the Company announced the signing of the Merger Agreement with Montpelier and Merger Sub pursuant to which the Company will, through Merger Sub, acquire Montpelier for consideration per Montpelier common share of 0.472 of an Endurance Holdings ordinary share and a pre-closing dividend of $9.89 per each such Montpelier common share payable, in cash, by Montpelier to its common shareholders, which represented $40.24 per Montpelier common share based on the Company's closing price on March 30, 2015, the last trading day before the signing of the Merger Agreement. The Merger Agreement has been unanimously approved by both companies' Boards of Directors. The Merger is expected to be completed in the third quarter of 2015 and is subject to the satisfaction of customary closing conditions including, but not limited to, approval by the Company's shareholders of the Company's share issuance at the special general meeting of the Company's shareholders, approval of the Merger Agreement, the statutory merger agreement and the Merger by the Montpelier shareholders at the special general meeting of Montpelier shareholders and regulatory approvals. There can be no assurance that the Merger will occur.
	Under the terms of the Merger Agreement, the aggregate consideration for the Merger will consist of approximately $450.0 million in cash and 21.5 million Endurance Holdings ordinary shares, which were valued at approximately $1.4 billion based on the Company's closing price on March 30, 2015, the last trading day before the signing of the Merger Agreement. The cash portion of the consideration will be funded through a pre-closing dividend paid by Montpelier to its common shareholders. Following completion of the Merger, Montpelier's existing common shareholders will own approximately
	10	Commitments and contingencies, cont'd.
	32% of Endurance Holdings' common shares. Endurance Holdings has agreed to appoint three of Montpelier's current directors to its Board of Directors, such appointment being subject to a customary vetting process to ensure, among other things, that such three new directors qualify as “independent” under the rules of the New York Stock Exchange.
	In connection with the Merger, Montpelier will exercise its option to redeem all of its outstanding 8.875% non-cumulative preferred shares Series A for $156.0 million plus all declared and unpaid dividends, if any, without interest thereon in accordance with the certificate of designation governing such preferred shares, prior to the Montpelier shareholders meeting to approve the Merger.
	If the Merger is terminated because (a) (i) Montpelier's shareholders do not approve the Merger or (ii) Montpelier is in material breach of the Merger Agreement, then, in each case, Montpelier will pay Endurance Holdings' expenses relating to the Merger up to a cap of $9.15 million and (b) (i) Endurance Holdings' shareholders do not approve the issuance of new Endurance Holdings ordinary shares in connection with the Merger or (ii) Endurance Holdings is in material breach of the Merger Agreement, then Endurance Holdings, in each case, will pay Montpelier's expenses relating to the Merger up to a cap of $9.15 million. If a takeover proposal with respect to Endurance Holdings or Montpelier, as applicable, was outstanding at least thirty days prior to the applicable shareholder meeting in the case of a termination described in (a)(i) or (b)(i), as applicable, or the date on which a breach described in (a)(ii) or (b)(ii), as applicable, occurred, and Endurance Holdings or Montpelier consummates a takeover proposal within 12 months of the termination, such party would be required to pay a termination fee of $73.25 million to the other party in addition to paying the expenses relating to the Merger as noted above.
	The Company incurred $1.0 million of corporate expenses associated with the Merger during the three months ended March 31, 2015 and is contractually obligated to pay investment banking fees of $15.0 million upon closing of the Merger. The Company expects to incur additional costs and expenses associated with the Merger during 2015.

Investments_Policy

Investments (Policy)	3 Months Ended
	Mar. 31, 2015
Investments [Abstract]
Other Investments	In addition to the Company’s fixed maturity, short-term and equity investments, the Company invests in (i) hedge funds and private investment funds that generally invest in senior secured bank debt, high yield credit, distressed debt, distressed real estate, derivatives, and equity long/short strategies (“alternative funds”) and (ii) high yield loan funds (“specialty funds”). The Company’s alternative funds and specialty funds are recorded on the Company’s balance sheet as “other investments.”
Gain Loss On Investments	Realized and unrealized gains and losses are recognized in earnings using the first in, first out method.
Variable Interest Entities	Entities that do not have sufficient equity at risk to allow the entity to finance its activities without additional financial support or in which the equity investors, as a group, do not have the characteristics of a controlling financial interest are referred to as variable interest entities (“VIE”). A VIE is consolidated by the variable interest holder that is determined to have the controlling financial interest (primary beneficiary) as a result of having both the power to direct the activities of a VIE that most significantly impact the VIE’s economic performance and the obligation to absorb losses or right to receive benefits from the VIE that could potentially be significant to the VIE. The Company determines whether it is the primary beneficiary of an entity subject to consolidation based on a qualitative assessment of the VIE’s capital structure, contractual terms, nature of the VIE’s operations and purpose and the Company’s relative exposure to the related risks of the VIE on the date it becomes initially involved in the VIE. The Company reassesses its VIE determination with respect to an entity on an ongoing basis.
	The Company is involved in the normal course of business with VIEs primarily as a passive investor in residential and commercial mortgage-backed securities and through its interests in various other investments that are structured as limited partnerships considered to be third party VIEs. The Company determined that it was not the primary beneficiary for any of these investments as of March 31, 2015. The Company believes its exposure to loss with respect to these investments is generally limited to the investment carrying amounts reported in the Company’s Condensed Consolidated Balance Sheets and any unfunded investment commitments.

Fair_Value_Measurement_Policy

Fair Value Measurement (Policy)	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value Of Financial Instruments	The Company determines the fair value of the fixed maturity investments, short-term investments, equity securities, other investments, debt, and other assets and liabilities in accordance with current accounting guidance, which defines fair value and establishes a fair value hierarchy based on inputs to the various valuation techniques used for each fair value measurement. The Company determines the estimated fair value of each individual security utilizing the highest level inputs available. Valuation inputs by security type may include the following:
	•	Government and agencies fixed maturity securities – These securities are generally priced by pricing services or index providers. The pricing services or index providers may use current market trades for securities with similar quality, maturity and coupon. If no such trades are available, the pricing service typically uses analytical models which may incorporate option adjusted spreads, daily interest rate data and market/sector news. The Company generally classifies the fair values of government and agencies securities in Level 2. Current issue U.S. government securities are generally valued based on Level 1 inputs, which use the market approach valuation technique.
	•	Government guaranteed corporate fixed maturity securities – These securities are generally priced by pricing services or index providers. The pricing service or index providers may use current market trades for securities with similar quality, maturity and coupon. If no such trades are available, the pricing service typically uses analytical spread models which may incorporate inputs from the U.S. treasury curve or LIBOR. The Company generally classifies the fair values of its government guaranteed corporate securities in Level 2.
	•	Corporate fixed maturity securities – These securities are generally priced by pricing services or index providers. The pricing services or index providers typically use discounted cash flow models that incorporate benchmark curves for treasury, swap and high issuance credits. Credit spreads are developed from current market observations for like or similar securities. The Company generally classifies the fair values of its corporate securities in Level 2.
	•	Equity securities – These securities are generally priced by pricing services or index providers. Depending on the type of underlying equity security or equity fund, the securities are priced by pricing services or index providers based on quoted market prices in active markets or through a discounted cash flow model that incorporates benchmark curves for treasury, swap and credits for like or similar securities. The Company generally classifies the fair values of its equity securities in Level 1 or 2.
	•	Other assets and liabilities – A portion of other assets and liabilities are composed of a variety of derivative instruments used to enhance the efficiency of the investment portfolio and economically hedge certain risks. These instruments are generally priced by pricing services, broker/dealers and/or recent trading activity. The market value approach valuation technique is used to estimate the fair value for these derivatives based on significant observable market inputs. Certain derivative instruments are priced by pricing services based on quoted market prices in active markets. These derivative instruments are generally classified in Level 1. Other derivative instruments are priced using industry valuation models and are considered Level 2, as the inputs to the valuation model are based on observable market inputs. Also included in this line item are proprietary, non-exchange traded derivative-based risk management products primarily used to address weather and energy risks. The trading market for these weather derivatives are generally linked to energy and agriculture commodities, weather and other natural phenomena. In instances where market prices are not available, the Company uses industry or internally developed valuation techniques such as spread option, Black Scholes, quanto and simulation modeling to determine fair value and classifies these in Level 3. These models may reference prices for similar instruments.
	•	Structured securities including agency and non-agency, residential and commercial, mortgage and asset-backed securities and collateralized loan and debt obligations – These securities are generally priced by broker/dealers. Broker/dealers may use current market trades for securities with similar qualities. If no such trades are available, inputs such as bid and offer, prepayment speeds, the U.S. treasury curve, swap curve and cash settlement may be used in a discounted cash flow model to determine the fair value of a security. The Company generally classifies the fair values of its structured securities in Level 2.
	4	Fair value measurement, cont'd.
	•	Other investments – Other investments are comprised of alternative funds and specialty funds and are generally priced on net asset values (“NAV”) received from the fund managers or administrators. Due to the timing of the delivery of the final NAV by certain of the fund managers, valuations of certain alternative funds and specialty funds are estimated based on the most recently available information, including period end NAVs, period end estimates, or, in some cases, prior month or prior quarter NAVs. As this valuation technique incorporates both observable and significant unobservable inputs, the Company generally classifies the fair value of its other investments in Level 3.
	•	Debt – Outstanding debt consists of the Company’s 6.15% Senior Notes due October 15, 2015 and the 7.0% Senior Notes due July 15, 2034 (the “Senior Notes”). The fair values of these securities were obtained from a third party pricing service and pricing was based on the spread above the risk-free yield curve. These spreads are generally obtained from the new issue market, secondary trading and broker-dealer quotes. As these spreads and the yields for the risk-free yield curve are observable market inputs, the fair values of the Senior Notes are classified in Level 2.
	The carrying values of cash and cash equivalents, accrued investment income, net receivable on sales of investments, net payable on purchases of investments and other financial instruments not described above approximated their fair values at March 31, 2015 and December 31, 2014.
Fair Value Transfer Between Levels	Transfers between levels are assumed to occur at the end of each period.

Earnings_Per_Share_Policy

Earnings Per Share (Policy)	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Earnings Per Share	The two-class method utilized by the Company is an earnings allocation formula that determines earnings per share for the holders of Endurance Holdings’ ordinary shares (also referred to as “common shares”) and participating common shares, which includes unvested restricted shares and restricted share units that receive cash dividends, according to dividends declared and participation rights in undistributed earnings. Net income available to common and participating common shareholders is reduced by the amount of dividends declared in the current period and by the contractual amount of dividends that must be paid for the current period related to the Company’s common and participating common shares. Any remaining undistributed earnings are allocated to the common and participating common shareholders to the extent that each security may share in earnings as if all of the earnings for the period had been distributed. In periods of loss, no losses are allocated to participating common shareholders. Instead, all such losses are allocated solely to the common shareholders.
	Basic earnings per common share are calculated by dividing net income available to common shareholders by the weighted average number of common shares outstanding. The weighted average number of common shares excludes any dilutive effect of outstanding options and convertible securities such as unvested restricted shares and restricted share units.
	Diluted earnings per common share are based on the weighted average number of common shares and assumes the exercise of all dilutive stock options and the vesting or conversion of all convertible securities such as unvested restricted shares and restricted share units using the two-class method described above.

Derivatives_Policy

Derivatives (Policy)	3 Months Ended
	Mar. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Accounting policy for derivatives	The Company regularly transacts in certain derivative-based weather risk management products primarily to address weather and energy risks on behalf of third parties. The markets for these derivatives are generally linked to energy and agriculture commodities, weather and other natural phenomena. Generally, the Company’s current portfolio of such derivative contracts is of short duration and such contracts are predominantly seasonal in nature. The Company also invests a portion of its fixed maturity assets with third party investment managers with investment guidelines that permit the use of derivative instruments. The Company may enter derivative transactions directly or as part of strategies employed by its external investment managers.
	The Company’s derivative instruments are recorded in the Condensed Consolidated Balance Sheets at fair value, with changes in fair value and gains and losses recognized in net realized and unrealized gains, net foreign exchange losses and other underwriting income (loss) in the Condensed Consolidated Statements of Income and Comprehensive Income.
	The Company’s derivatives are not designated as hedges under current accounting guidance.
	The Company’s objectives for holding these derivatives are as follows:
	Interest Rate Futures, Swaps, Swaptions and Options - to manage exposure to interest rate risk, which can include increasing or decreasing its exposure to this risk through modification of the portfolio composition and duration.
	Foreign Exchange Forwards, Futures and Options - as part of overall currency risk management and investment strategies.
	Credit Default Swaps - to manage market exposures. The Company may assume or economically hedge credit risk through credit default swaps to replicate or hedge investment positions. The original term of these credit default swaps is generally five years or less.
	To-Be-Announced Mortgage-backed Securities (“TBAs”) - to enhance investment performance and as part of overall investment strategy. TBAs represent commitments to purchase or sell a future issuance of agency mortgage-backed securities. For the period between purchase of a TBA and issuance of the underlying securities, the Company’s position is accounted for as a derivative.
	Energy and Weather Contracts – to address weather and energy risks. The Company may purchase or sell contracts with financial settlements based on the performance of an index linked to a quantifiable weather element, such as temperature, precipitation, snowfall or windspeed, and structures with multiple risk triggers indexed to a quantifiable weather element and a weather sensitive commodity price, such as temperature and electrical power or natural gas. Generally, the Company’s current portfolio of energy and weather derivative contracts is of comparably short duration and such contracts are predominantly seasonal in nature.
Offsetting of derivatives policy	At March 31, 2015 and December 31, 2014, none of the Company’s derivative instruments were recorded on a net basis in the Condensed Consolidated Balance Sheets.

Segment_Reporting_Policy

Segment Reporting (Policy)	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Segment Reporting	The determination of the Company’s business segments is based on how the Company monitors the performance of its underwriting operations. The Company has two reportable business segments, Insurance and Reinsurance, which are comprised of the following lines of business:
	Insurance segment lines of business
	•Agriculture
	•Casualty and other specialty
	•Professional lines
	•Property, marine and energy
	Reinsurance segment lines of business
	•Catastrophe
	•Property
	•Casualty
	•Professional lines
	•Specialty
	Management measures segment results on the basis of the combined ratio, which is obtained by dividing the sum of the net losses and loss expenses, acquisition expenses and general and administrative expenses by net premiums earned. When purchased within a single line of business, ceded reinsurance and recoveries are accounted for within that line of business. When purchased across multiple lines of business, ceded reinsurance and recoveries are allocated to the lines of business in proportion to the related risks assumed. The Company does not manage its assets by segment; accordingly, investment income and total assets are not allocated to the individual business segments. General and administrative expenses incurred by the segments are allocated directly. Remaining general and administrative expenses not directly incurred by the segments are allocated primarily based on estimated consumption, headcount and other variables deemed relevant to the allocation of such expenses. Ceded reinsurance and recoveries are recorded within the business segment to which they apply.

Investments_Tables

Investments (Tables)	3 Months Ended
	Mar. 31, 2015
Investments [Abstract]
Composition Of Net Investment Income	The components of net investment income for the three months ended March 31, 2015 and 2014 are as follows:
		Three Months Ended March 31,
		2015				2014
	Available for sale investments	$	32,217			$	30,327
	Other investments	12,388				13,542
	Cash and cash equivalents	630				786
		45,235				44,655
	Investment expenses	(3,374		)		(3,665		)
	Net investment income	$	41,861			$	40,990
Composition of the Investment Portfolio by Investment Type	The following table summarizes the composition of the investment portfolio by investment type at March 31, 2015 and December 31, 2014:
			31-Mar-15						31-Dec-14
	Type of Investment		Fair Value				Percentage		Fair Value				Percentage
	Fixed maturity investments		$	4,953,893			76.5	%	$	5,092,581			77.1	%
	Cash and cash equivalents(1)		579,670				8.9	%	632,667				9.6	%
	Other investments(2)		575,974				8.9	%	541,454				8.2	%
	Short-term investments		2,822				—	%	9,014				0.1	%
	Equity securities		366,897				5.7	%	331,368				5	%
	Total		$	6,479,256			100	%	$	6,607,084			100	%
	-1	Includes net receivable on sales of investments and net payable on purchases of investments.
	-2	Consists of investments in alternative funds and specialty funds.
Composition Of Fixed Income Portfolio, Including Fixed Maturity Investments And Short-Term Investments, By Investment Ratings	The following table summarizes the composition by investment rating of the fixed maturity and short-term investments at March 31, 2015 and December 31, 2014. In some cases, where bonds are unrated, the rating of the issuer has been applied.
			31-Mar-15						31-Dec-14
	Ratings(1)		Fair Value				Percentage		Fair Value				Percentage
	U.S. government and agencies securities		$	439,276			8.9	%	$	587,411			11.5	%
	AAA / Aaa		1,196,188				24.1	%	1,206,252				23.6	%
	AA / Aa		1,647,963				33.2	%	1,717,343				33.7	%
	A / A		1,055,259				21.3	%	1,045,301				20.5	%
	BBB		494,065				10	%	427,018				8.4	%
	Below BBB		103,728				2.1	%	96,244				1.9	%
	Not rated		20,236				0.4	%	22,026				0.4	%
	Total		$	4,956,715			100	%	$	5,101,595			100	%
	-1	The credit rating for each security reflected above was determined based on the rating assigned to the individual security by Standard & Poor’s Financial Services LLC (“Standard & Poor’s”). If a rating is not supplied by Standard & Poor’s, the equivalent rating supplied by Moody’s Investors Service, Inc. (“Moody's”), Fitch Ratings, Inc., or DBRS, Inc. is used.
Contractual Maturities Of Fixed Maturity And Short-Term Investments	Contractual maturities of the Company’s fixed maturity and short-term investments are shown below as of March 31, 2015 and December 31, 2014. Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.
		31-Mar-15							31-Dec-14
		Amortized				Fair Value			Amortized				Fair Value
		Cost							Cost
	Due within one year	$	104,359			$	105,176		$	126,921			$	127,821
	Due after one year through five years	1,518,003				1,533,554			1,627,154				1,632,259
	Due after five years through ten years	406,967				417,073			474,959				479,138
	Due after ten years	54,453				58,324			43,314				46,720
	Residential mortgage-backed securities	1,098,830				1,127,954			1,149,536				1,175,006
	Commercial mortgage-backed securities	979,828				1,003,437			960,598				979,419
	Collateralized loan and debt obligations	302,842				304,512			247,510				248,011
	Asset-backed securities	404,402				406,685			411,529				413,221
	Total	$	4,869,684			$	4,956,715		$	5,041,521			$	5,101,595
Other Investments	The following table summarizes the composition and redemption restrictions of other investments as of March 31, 2015 and December 31, 2014:
	31-Mar-15		Market Value				Unfunded			Ineligible for
							Commitments			Redemption over
										next 12 months
	Alternative funds
	Hedge funds		$	443,307			$	—		$	58,099
	Private investment funds		76,305				56,956			76,305
	Total alternative funds		519,612				56,956			134,404
	Specialty funds
	High yield loan funds		56,362				—			—
	Total specialty funds		56,362				—			—
	Total other investments		$	575,974			$	56,956		$	134,404
	31-Dec-14		Market Value				Unfunded			Ineligible for
							Commitments			Redemption in 2015
	Alternative funds
	Hedge funds		$	411,280			$	—		$	10,580
	Private investment funds		74,664				70,542			74,664
	Total alternative funds		485,944				70,542			85,244
	Specialty funds
	High yield loan funds		55,510				—			—
	Total specialty funds		55,510				—			—
	Total other investments		$	541,454			$	70,542		$	85,244
Net Realized And Unrealized Investment Gains (Losses)	The analysis of net realized and unrealized gains and the change in the fair value of investment-related derivative financial instruments for the three months ended March 31, 2015 and 2014 is as follows:
		Three Months Ended March 31,
		2015				2014
	Gross realized gains on investment sales	$	22,666			$	10,247
	Gross realized losses on investment sales	(4,896		)		(5,984		)
	Change in fair value of derivative financial instruments(1)	419				609
	Net realized and unrealized gains	$	18,189			$	4,872
	-1	For additional information on the Company’s derivative financial instruments, see Note 7.
Amortized Cost, Fair Value, Unrealized Gains and Losses And Non-Credit Other-Then-Temporary Impairments	The amortized cost, fair value and related gross unrealized gains and losses and non-credit other-than-temporary impairment (“OTTI”) losses on the Company’s securities classified as available for sale at March 31, 2015 and December 31, 2014 are as follows:
	31-Mar-15		Amortized				Gross			Gross				Fair Value		Non-Credit
			Cost				Unrealized			Unrealized						OTTI(2)
							Gains			Losses
	Fixed maturity investments
	U.S. government and agencies securities		$	430,517			$	9,470		$	(711	)		$	439,276	$	—
	U.S. state and municipal securities		51,930				407			(206		)		52,131		—
	Foreign government securities		169,866				2,971			(639		)		172,198		—
	Government guaranteed corporate securities		39,431				635			(1		)		40,065		—
	Corporate securities		1,389,216				20,131			(1,712		)		1,407,635		—
	Residential mortgage-backed securities		1,098,830				30,485			(1,361		)		1,127,954		(3,098		)
	Commercial mortgage-backed securities		979,828				25,162			(1,553		)		1,003,437		—
	Collateralized loan and debt obligations(1)		302,842				1,980			(310		)		304,512		—
	Asset-backed securities		404,402				2,652			(369		)		406,685		—
	Total fixed maturity investments		4,866,862				93,893			(6,862		)		4,953,893		(3,098		)
	Short-term investments		2,822				—			—				2,822		—
	Total fixed income investments		$	4,869,684			$	93,893		$	(6,862	)		$	4,956,715	$	(3,098	)
	Equity securities
	Equity investments		$	217,035			$	22,837		$	(1,478	)		$	238,394	$	—
	Emerging market debt funds		61,874				—			(1,407		)		60,467		—
	Convertible funds		46,331				2,167			—				48,498		—
	Preferred equity investments		13,715				2,194			(12		)		15,897		—
	Short-term fixed income fund		3,642				—			(1		)		3,641		—
	Total equity securities		$	342,597			$	27,198		$	(2,898	)		$	366,897	$	—
	-1	Balances include amounts related to collateralized debt obligations held with total fair values of $13.1 million.
	-2	Represents total OTTI recognized in accumulated other comprehensive income. It does not include the change in fair value subsequent to the impairment measurement date. At March 31, 2015, the gross unrealized loss related to fixed income investments for which a non-credit OTTI was recognized in accumulated other comprehensive income was nil.
	31-Dec-14		Amortized				Gross			Gross				Fair Value		Non-Credit
			Cost				Unrealized			Unrealized						OTTI(2)
							Gains			Losses
	Fixed maturity investments
	U.S. government and agencies securities		$	582,970			$	6,471		$	(2,030	)		$	587,411	$	—
	U.S. state and municipal securities		39,340				191			(118		)		39,413		—
	Foreign government securities		239,217				2,983			(1,664		)		240,536		—
	Government guaranteed corporate securities		47,436				675			(9		)		48,102		—
	Corporate securities		1,354,370				12,742			(5,650		)		1,361,462		—
	Residential mortgage-backed securities		1,149,536				27,542			(2,072		)		1,175,006		(3,233		)
	Commercial mortgage-backed securities		960,598				21,374			(2,553		)		979,419		(5		)
	Collateralized loan and debt obligations(1)		247,510				1,449			(948		)		248,011		—
	Asset-backed securities		411,529				2,265			(573		)		413,221		—
	Total fixed maturity investments		5,032,506				75,692			(15,617		)		5,092,581		(3,238		)
	Short-term investments		9,015				—			(1		)		9,014		—
	Total fixed income investments		$	5,041,521			$	75,692		$	(15,618	)		$	5,101,595	$	(3,238	)
	Equity securities
	Equity investments		$	176,167			$	29,660		$	(3,292	)		$	202,535	$	—
	Emerging market debt funds		60,826				—			(676		)		60,150		—
	Convertible funds		46,331				—			(220		)		46,111		—
	Preferred equity investments		13,858				2,022			(44		)		15,836		—
	Short-term fixed income funds		6,740				—			(4		)		6,736		—
	Total equity securities		$	303,922			$	31,682		$	(4,236	)		$	331,368	$	—
	-1	Balances include amounts related to collateralized debt obligations held with total fair values of $15.2 million.
	-2	Represents total OTTI recognized in accumulated other comprehensive income. It does not include the change in fair value subsequent to the impairment measurement date. At December 31, 2014, the gross unrealized loss related to fixed income investments for which a non-credit OTTI was recognized in accumulated other comprehensive income was nil.
Available For Sale Securities In An Unrealized Loss Position
			Less than 12 months							12 months or greater						Total
	31-Dec-14		Unrealized				Fair			Unrealized				Fair		Unrealized			Fair
			Losses(1)				Value			Losses(1)				Value		Losses(1)			Value
	Fixed maturity investments
	U.S. government and agencies securities		$	(481	)		$	155,350		$	(1,549	)		$	45,993	$	(2,030	)	$	201,343
	U.S. state and municipal securities		(47		)		3,295			(71		)		6,841		(118		)	10,136
	Foreign government securities		(1,378		)		37,904			(286		)		4,306		(1,664		)	42,210
	Government guaranteed corporate securities		(9		)		4,598			—				—		(9		)	4,598
	Corporate securities		(4,023		)		533,139			(1,627		)		84,278		(5,650		)	617,417
	Residential mortgage-backed securities		(260		)		62,832			(1,812		)		108,899		(2,072		)	171,731
	Commercial mortgage-backed securities		(1,068		)		180,222			(1,485		)		78,412		(2,553		)	258,634
	Collateralized loan and debt obligations		(876		)		176,439			(72		)		6,491		(948		)	182,930
	Asset-backed securities		(415		)		199,205			(158		)		19,095		(573		)	218,300
	Total fixed maturity investments		(8,557		)		1,352,984			(7,060		)		354,315		(15,617		)	1,707,299
	Short-term investments		(1		)		1,953			—				—		(1		)	1,953
	Total fixed income investments		$	(8,558	)		$	1,354,937		$	(7,060	)		$	354,315	$	(15,618	)	$	1,709,252
	Equity securities
	Equity investments		$	(3,292	)		$	53,591		$	—			$	—	$	(3,292	)	$	53,591
	Emerging market debt funds		(676		)		60,150			—				—		(676		)	60,150
	Convertible funds		(220		)		46,111			—				—		(220		)	46,111
	Preferred equity investments		(44		)		4,449			—				—		(44		)	4,449
	Short-term fixed income fund		(4		)		6,736			—				—		(4		)	6,736
	Total equity securities		$	(4,236	)		$	171,037		$	—			$	—	$	(4,236	)	$	171,037
	-1	Gross unrealized losses include unrealized losses on non-OTTI and non-credit OTTI securities recognized in accumulated other comprehensive income at December 31, 2014.
	The following tables summarize, for all available for sale securities in an unrealized loss position at March 31, 2015 and December 31, 2014, the aggregate fair value and gross unrealized loss by length of time the security has continuously been in an unrealized loss position.
			Less than 12 months							12 months or greater						Total
	31-Mar-15		Unrealized				Fair			Unrealized				Fair		Unrealized			Fair
			Losses(1)				Value			Losses(1)				Value		Losses(1)			Value
	Fixed maturity investments
	U.S. government and agencies securities		$	(177	)		$	27,378		$	(534	)		$	24,374	$	(711	)	$	51,752
	U.S. state and municipal securities		(198		)		17,685			(8		)		3,003		(206		)	20,688
	Foreign government securities		(450		)		14,770			(189		)		1,688		(639		)	16,458
	Government guaranteed corporate securities		(1		)		1,286			—				—		(1		)	1,286
	Corporate securities		(1,048		)		192,963			(664		)		35,725		(1,712		)	228,688
	Residential mortgage-backed securities		(308		)		79,275			(1,053		)		86,646		(1,361		)	165,921
	Commercial mortgage-backed securities		(939		)		139,745			(614		)		38,908		(1,553		)	178,653
	Collateralized loan and debt obligations		(255		)		141,280			(55		)		17,557		(310		)	158,837
	Asset-backed securities		(217		)		121,075			(152		)		17,231		(369		)	138,306
	Total fixed income investments		$	(3,593	)		735,457			(3,269		)		225,132		(6,862		)	960,589
	Equity securities
	Equity investments		$	(1,478	)		$	87,056		$	—			$	—	$	(1,478	)	$	87,056
	Emerging market debt funds		(1,407		)		60,467			—				—		(1,407		)	60,467
	Preferred equity investments		(12		)		2,089			—				—		(12		)	2,089
	Short-term fixed income fund		(1		)		2,919			—				—		(1		)	2,919
	Total equity securities		$	(2,898	)		$	152,531		$	—			$	—	$	(2,898	)	$	152,531
	-1	Gross unrealized losses include unrealized losses on non-OTTI and non-credit OTTI securities recognized in accumulated other comprehensive income at March 31, 2015.
Analysis Of OTTI	The analysis of OTTI for the three months ended March 31, 2015 and 2014 is as follows:
		Three Months Ended March 31,
		2015				2014
	Total other-than-temporary impairment losses	$	(649	)		$	(111	)
	Portion of loss recognized in other comprehensive income	—				—
	Net impairment losses recognized in earnings	$	(649	)		$	(111	)
Credit Losses Recognized For Available For Sale Investments In Earnings, OTTI Loss Was Recognized In Accumulated Other Comprehensive Income	The following table provides a roll-forward of the amount related to credit losses for the Company’s available for sale investments recognized in earnings for which a portion of an OTTI loss was recognized in accumulated other comprehensive income for the three months ended March 31, 2015 and 2014:
		Three Months Ended March 31,
		2015				2014
	Beginning balance	$	(838	)		$	(1,553	)
	Addition for the amount related to the credit loss for which an other-than-temporary impairment was not previously recognized	—				—
	Addition for the amount related to the credit loss for which an other-than-temporary impairment was previously recognized	—				—
	Reductions for increases in cash flows expected to be collected that are recognized over the remaining life of the security	—				—
	Reductions for securities sold during the period	43				33
	Ending balance	$	(795	)		$	(1,520	)

Fair_Value_Measurement_Tables

Fair Value Measurement (Tables)	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Schedule Of Available For Sale Investments, Other Investments, Derivative Instruments And Debt Measured On A Recurring Basis	The following table sets forth the Company’s available for sale investments, other investments, other assets and liabilities and debt categorized by the level within the hierarchy in which the fair value measurements fall at March 31, 2015:
		Fair Value Measurements at March 31, 2015
		Total at			Quoted Prices in			Significant Other			Significant Unobservable
		March 31, 2015			Active Markets for			Observable Inputs			Inputs
					Identical Assets			(Level 2)			(Level 3)
					(Level 1)
	Assets
	Fixed maturity investments
	U.S. government and agencies securities	$	439,276		$	16,825		$	422,451		$	—
	U.S. state and municipal securities	52,131			—			52,131			—
	Foreign government securities	172,198			—			172,198			—
	Government guaranteed corporate securities	40,065			—			40,065			—
	Corporate securities	1,407,635			—			1,405,136			2,499
	Residential mortgage-backed securities	1,127,954			—			1,127,954			—
	Commercial mortgage-backed securities	1,003,437			—			1,002,868			569
	Collateralized loan and debt obligations	304,512			—			301,046			3,466
	Asset-backed securities	406,685			—			403,719			2,966
	Total fixed maturity investments	4,953,893			16,825			4,927,568			9,500
	Equity securities
	Equity investments	238,394			144,297			94,097			—
	Emerging market debt funds	60,467			—			60,467			—
	Convertible funds	48,498			—			48,498			—
	Preferred equity investments	15,897			—			15,897			—
	Short-term fixed income fund	3,641			3,641			—			—
	Total equity securities	366,897			147,938			218,959			—
	Short-term investments	2,822			—			2,822			—
	Other investments	575,974			—			—			575,974
	Other assets (see Note 7)	170,023			—			154,800			15,223
	Total assets	$	6,069,609		$	164,763		$	5,304,149		$	600,697
	Liabilities
	Other liabilities (see Note 7)	$	114,943		$	—		$	97,558		$	17,385
	Debt	635,154			—			635,154			—
	Total liabilities	$	750,097		$	—		$	732,712		$	17,385
	The following table sets forth the Company’s available for sale investments, other investments, other assets and liabilities and debt categorized by the level within the hierarchy in which the fair value measurements fall at December 31, 2014:
		Fair Value Measurements at December 31, 2014
		Total at			Quoted Prices in			Significant Other			Significant
		December 31, 2014			Active Markets for			Observable Inputs			Unobservable
					Identical Assets			(Level 2)			Inputs
					(Level 1)						(Level 3)
	Assets
	Fixed maturity investments
	U.S. government and agencies securities	$	587,411		$	105,121		$	482,290		$	—
	U.S. state and municipal securities	39,413			—			39,413			—
	Foreign government securities	240,536			—			240,536			—
	Government guaranteed corporate securities	48,102			—			48,102			—
	Corporate securities	1,361,462			—			1,358,960			2,502
	Residential mortgage-backed securities	1,175,006			—			1,174,997			9
	Commercial mortgage-backed securities	979,419			—			974,602			4,817
	Collateralized loan and debt obligations	248,011			—			246,042			1,969
	Asset-backed securities	413,221			—			410,228			2,993
	Total fixed maturity investments	5,092,581			105,121			4,975,170			12,290
	Equity securities
	Equity investments	202,535			138,463			64,072			—
	Emerging market debt funds	60,150			—			60,150			—
	Convertible funds	46,111			—			46,111			—
	Preferred equity investments	15,836			—			15,836			—
	Short-term fixed income fund	6,736			6,736			—			—
	Total equity securities	331,368			145,199			186,169			—
	Short-term investments	9,014			—			9,014			—
	Other investments	541,454			—			—			541,454
	Other assets (see Note 7)	99,504			—			73,889			25,615
	Total assets	$	6,073,921		$	250,320		$	5,244,242		$	579,359
	Liabilities
	Other liabilities (see Note 7)	$	54,338		$	—		$	18,972		$	35,366
Debt	623,740			—			623,740			—
Total liabilities	$	678,078		$	—		$	642,712		$	35,366
Fair Value Inputs Assets And Liabilities Quantitative Information [Table Text Block]	Below is a summary of quantitative information regarding the significant unobservable inputs used in determining the fair value of the net weather and energy related derivative liabilities classified in Level 3 that are measured at fair value on a recurring basis at March 31, 2015 and December 31, 2014:
		31-Mar-15
		Fair Value			Valuation		Unobservable	Low			High			Weighted Average
		(Level 3)			Techniques		Inputs							or Actual
		(U.S. dollars in thousands, except for correlation)
	Net weather and energy related derivative liabilities	$	2,162		Historical		Correlation	0			1			Actual
					Analysis and Simulation
							Weather curve	$	2,200		$	2,700		Actual
							Commodity curve	$	—		$	14		Actual
		31-Dec-14
		Fair Value			Valuation		Unobservable	Low			High			Weighted Average
		(Level 3)			Techniques		Inputs							or Actual
		(U.S. dollars in thousands, except for correlation)
	Net weather and energy related derivative liabilities	$	9,751		Historical		Correlation	0			1			Actual
					Analysis and Simulation
							Weather curve	$	(828	)	$	2,500		Actual
							Commodity curve	$	—		$	—		Actual
Reconciliation Of The Beginning And Ending Balances For All Available For Sale Investments, Other Investments And Derivative Instruments Measured At Fair Value On A Recurring Basis Using Level 3 Inputs	The following tables present a reconciliation of the beginning and ending balances for all assets and liabilities measured at fair value on a recurring basis using Level 3 inputs during the three months ended March 31, 2015 and 2014:
		Three Months Ended March 31, 2015
		Fixed maturity			Other			Other assets			Total assets			Other
		investments			investments									liabilities
	Level 3, beginning of period	$	12,290		$	541,454		$	25,615		$	579,359		$	(35,366	)
	Total equity income and realized gains included in earnings	113			20,549			—			20,662			—
	Total equity losses and losses included in earnings	(9		)	(8,161		)	—			(8,170		)	—
	Total income included in other underwriting income (loss)	—			—			2,096			2,096			13,059
	Total loss included in other underwriting income (loss)	—			—			(8,842		)	(8,842		)	(3,529		)
	Change in unrealized gains included in other comprehensive income	6			—			—			6			—
	Change in unrealized losses included in other comprehensive income	(129		)	—			—			(129		)	—
	Purchases	—			39,321			—			39,321			—
	Issues	—			—			3,212			3,212			(6,424		)
	Sales	(214		)	(17,189		)	—			(17,403		)	—
	Settlements	—			—			(6,858		)	(6,858		)	14,875
	Transfers into Level 3	1,733			—			—			1,733			—
	Transfers out of Level 3	(4,290		)	—			—			(4,290		)	—
	Level 3, end of period	$	9,500		$	575,974		$	15,223		$	600,697		$	(17,385	)
		Three Months Ended March 31, 2014
		Fixed maturity			Other			Other assets			Total assets			Other
		investments			investments									liabilities
	Level 3, beginning of period	$	7,328		$	617,478		$	14,038		$	638,844		$	(19,569	)
	Total equity income and realized gains included in earnings	17			19,186			—			19,203			—
	Total equity losses and losses included in earnings	(26		)	(5,645		)	—			(5,671		)	—
	Total income included in other underwriting income (loss)	—			—			3,975			3,975			7,426
	Total loss included in other underwriting income (loss)	—			—			(6,888		)	(6,888		)	(4,776		)
	Change in unrealized gains included in other comprehensive income	111			—			—			111			—
	Change in unrealized losses included in other comprehensive income	(115		)	—			—			(115		)	—
	Purchases	—			4,674			—			4,674			—
	Issues	—			—			640			640			(1,280		)
	Sales	(184		)	(13,779		)	—			(13,963		)	—
	Settlements	—			—			(3,233		)	(3,233		)	4,751
	Transfers in to Level 3	2,117			—			—			2,117			—
	Transfers out of Level 3	(263		)	—			—			(263		)	—
	Level 3, end of period	$	8,985		$	621,914		$	8,532		$	639,431		$	(13,448	)

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Schedule Of Computation Of Basic And Diluted Earnings Per Share	The following table sets forth the computation of basic and diluted earnings per share for the three months ended March 31, 2015 and 2014:
		Three Months Ended
		March 31,
		2015			2014
	Numerator:
	Net income available to common and participating common shareholders	$	100,291		$	96,292
	Less amount allocated to participating common	(2,959		)	(2,769		)
	shareholders(1)
	Net income allocated to common shareholders	97,332			93,523
	Denominator:
	Weighted average shares - basic	43,542,491			43,160,156
	Share equivalents:
	Options	146,792			—
	Restricted shares and restricted share units	7,028			286
	Weighted average shares - diluted	43,696,311			43,160,442
	Basic earnings per common share	$	2.24		$	2.17
	Diluted earnings per common share	$	2.23		$	2.17
	-1	Represents earnings attributable to holders of unvested restricted shares and restricted share units issued under the Company's equity compensation plan that are considered participating. In periods of loss, no losses are allocated to participating common shareholders (unvested restricted shares and restricted share units).
Schedule Of Dividends Declared
		Three Months Ended
		March 31,
		2015			2014
	Dividends declared per Series A preferred share	$	0.484375		$	0.484375
	Dividends declared per Series B preferred share	$	0.46875		$	0.46875
	Dividends declared per common share	$	0.35		$	0.34

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Income (Tables)	3 Months Ended
	Mar. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule Of Accumulated Other Comprehensive Income	The following tables present the changes in accumulated other comprehensive income balances by component for the three months ended March 31, 2015 and 2014:
		For the Three Months Ended March 31, 2015
		Losses on				Unrealized gains on available for sale securities			Foreign currency translation adjustments			Total
		cash flow hedges
	Beginning balance	$	(1,766	)		$	86,100		$	(7,628	)	$	76,706
	Other comprehensive income before reclassifications	—				40,734			(23,458		)	17,276
	Amounts reclassified from accumulated other comprehensive income(1)	22				(16,245		)	—			(16,223		)
	Net current period other comprehensive income	22				24,489			(23,458		)	1,053
	Ending balance	$	(1,744	)		$	110,589		$	(31,086	)	$	77,759
	(1)All amounts are net of tax.
		For the Three Months Ended March 31, 2014
		Losses on cash flow hedges				Unrealized gains on available for sale securities			Foreign currency translation adjustments			Total
	Beginning balance	$	(1,855	)		45,950			$	18,636		$	62,731
	Other comprehensive income before reclassifications	—				27,665			3,225			30,890
	Amounts reclassified from accumulated other comprehensive income(1)	23				(4,285		)	—			(4,262		)
	Net current period other comprehensive income	23				23,380			3,225			26,628
	Ending balance	$	(1,832	)		$	69,330		$	21,861		$	89,359
	(1)All amounts are net of tax.
Reclassification Out Of Accumulated Other Comprehensive Income	The following tables present the significant items reclassified out of accumulated other comprehensive income during the three months ended March 31, 2015 and 2014:
	Three Months Ended March 31, 2015
	Details about accumulated other comprehensive		Amount reclassified				Affected line item in the Unaudited
	income components		from accumulated other				Condensed Consolidated Statements of
			comprehensive income				Income and Comprehensive Income
	Losses on cash flow hedges - Debt		$	22			Interest expense
			22				Total before income taxes
			—				Income tax expense
			$	22			Total net of income taxes
	Unrealized gains on available for sale securities		$	(17,770	)		Net realized and unrealized gains
			649				Net impairment losses recognized in earnings
			(17,121		)		Total before income taxes
			876				Income tax expense
			$	(16,245	)		Total net of income taxes
	Three Months Ended March 31, 2014
	Details about accumulated other comprehensive		Amount reclassified				Affected line item in the Unaudited
	income components		from accumulated other				Condensed Consolidated Statements of
			comprehensive income				Income and Comprehensive Income
	Losses on cash flow hedges - Debt		$	23			Interest expense
			23				Total before income taxes
			—				Income tax expense
			$	23			Total net of income taxes
	Unrealized gains on available for sale securities		$	(4,263	)		Net realized and unrealized gains
			111				Net impairment losses recognized in earnings
			(4,152		)		Total before income taxes
			(133		)		Income tax benefit
			$	(4,285	)		Total net of income taxes

Derivatives_Tables

Derivatives (Tables)	3 Months Ended
	Mar. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule Of The Fair Value And Related Notional Amounts Of Derivatives Included In The Company's Consolidated Balance Sheet	The fair values and the related notional values of derivatives at March 31, 2015 and December 31, 2014 are shown below.
		31-Mar-15						31-Dec-14
		Fair			Notional			Fair		Notional
		Value			Principal			Value		Principal
					Amount					Amount
	Derivatives recorded in other assets
	Foreign exchange forward contracts	$	1,021		$	37,927		$	651	$	42,694
	Interest rate futures	16			120,235			7		7,595
	TBAs	153,763			146,000			73,231		70,000
	Energy and weather contracts	15,223			59,012			25,615		81,624
	Total recorded in other assets	170,023						99,504
	Derivatives recorded in other liabilities
	Foreign exchange forward contracts	557			$	22,438		123		$	20,945
	Interest rate swaps	267			4,757			20		12,549
	Interest rate swaptions	—			10,500			9		13,100
	Interest rate futures	28			124,771			—		—
	TBAs	96,706			92,000			18,820		18,000
	Energy and weather contracts	17,385			117,999			35,366		135,050
	Total recorded in other liabilities	114,943						54,338
	Net derivative asset	$	55,080					$	45,166
Schedule Of The Gains And Losses On The Consolidated Statements Of Income And Comprehensive Income From Derivatives	The gains and losses on the Condensed Consolidated Statements of Income and Comprehensive Income for derivatives for the three months ended March 31, 2015 and 2014 were as follows:
		Three Months Ended
		March 31,
		2015			2014
	Total included in net foreign exchange losses from foreign exchange forward contracts	$	1,469		$	(227	)
	Futures contracts	122			21
	Interest rate swaps	(555		)	(766		)
	Interest rate swaptions	28			429
	TBAs	824			925
	Total included in net realized and unrealized gains	419			609
	Total included in other underwriting income (loss) from energy and weather contracts	2,784			(258		)
	Total gains from derivatives	$	4,672		$	124

StockBased_Employee_Compensati1

Stock-Based Employee Compensation And Other Stock Plans Stock-Based Employee Compensation And Other Stock Plans (Tables)	3 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block]	A summary of the restricted share and restricted share unit activity during the quarter ended March 31, 2015, is presented below:
		Number of		Aggregate
		Shares/Units		Intrinsic Value
	Unvested, beginning of year	1,290,894
	Granted	472,662
	Settled	(285,044	)
	Forfeited	—
	Unvested, end of year	1,478,512
	Outstanding, end of year	1,478,512		$	90,396

Segment_Reporting_Tables

Segment Reporting (Tables)	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Summary Of The Segment Revenues, Results And Reserve For Losses And Loss Expenses	The following table provides a summary of segment revenues, results and reserves for losses and loss expenses for the three months ended March 31, 2015:
		Three Months Ended March 31, 2015
		Insurance			Reinsurance			Total
	Revenues
	Gross premiums written	$	736,218		$	565,214		$	1,301,432
	Ceded premiums written	(432,179		)	(104,299		)	(536,478		)
	Net premiums written	304,039			460,915			764,954
	Net premiums earned	135,864			253,995			389,859
	Other underwriting income	—			2,406			2,406
		135,864			256,401			392,265
	Expenses
	Net losses and loss expenses	74,512			97,424			171,936
	Acquisition expenses	15,883			66,210			82,093
	General and administrative expenses	32,684			34,474			67,158
		123,079			198,108			321,187
	Underwriting income	$	12,785		$	58,293		$	71,078
	Net loss ratio	54.8		%	38.3		%	44.1		%
	Acquisition expense ratio	11.7		%	26.1		%	21.1		%
	General and administrative expense ratio	24.1		%	13.6		%	17.2		%
	Combined ratio	90.6		%	78		%	82.4		%
	Reserve for losses and loss expenses	$	1,952,277		$	1,669,451		$	3,621,728
	The following table provides a summary of segment revenues, results and reserves for losses and loss expenses for the three months ended March 31, 2014:
		Three Months Ended March 31, 2014
		Insurance			Reinsurance			Total
	Revenues
	Gross premiums written	$	652,276		$	505,239		$	1,157,515
	Ceded premiums written	(309,249		)	(49,561		)	(358,810		)
	Net premiums written	343,027			455,678			798,705
	Net premiums earned	144,021			252,245			396,266
	Other underwriting loss	—			(1,238		)	(1,238		)
		144,021			251,007			395,028
	Expenses
	Net losses and loss expenses	88,533			88,363			176,896
	Acquisition expenses	12,261			59,896			72,157
	General and administrative expenses	41,736			31,470			73,206
		142,530			179,729			322,259
	Underwriting income	$	1,491		$	71,278		$	72,769
	Net loss ratio	61.5		%	35		%	44.6		%
	Acquisition expense ratio	8.5		%	23.7		%	18.2		%
	General and administrative expense ratio	29		%	12.6		%	18.5		%
	Combined ratio	99		%	71.3		%	81.3		%
	Reserve for losses and loss expenses	$	2,023,819		$	1,823,955		$	3,847,774
Schedule Of Segment Results To Income Before Income Taxes	The following table reconciles total segment results to income before income taxes for the three months ended March 31, 2015 and 2014:
		Three Months Ended March 31,
		2015			2014
	Total underwriting income	$	71,078		$	72,769
	Net investment income	41,861			40,990
	Net foreign exchange losses	(7,552		)	(2,964		)
	Net realized and unrealized gains	18,189			4,872
	Net impairment losses recognized in earnings	(649		)	(111		)
	Amortization of intangibles	(1,599		)	(1,617		)
	Interest expense	(9,059		)	(9,051		)
	Income before income taxes	$	112,269		$	104,888
Schedule Of Gross And Net Premiums By Line Of Business	The following table provides gross and net premiums written by line of business for the three months ended March 31, 2015 and 2014:
		Gross			Net			Gross			Net
		premiums			premiums			premiums			premiums
		written			written			written			written
	Business Segment	2015			2015			2014			2014
	Insurance
	Agriculture	$	516,916		$	202,460		$	527,894		$	281,645
	Casualty and other specialty	100,682			45,058			67,653			36,813
	Professional lines	54,760			24,231			38,780			14,570
	Property, marine and energy	63,860			32,290			17,949			9,999
	Total Insurance	736,218			304,039			652,276			343,027
	Reinsurance
	Catastrophe	124,407			53,460			126,648			78,963
	Property	125,700			123,449			166,413			166,322
	Casualty	58,098			58,098			84,982			83,392
	Professional lines	43,857			43,857			25,619			25,619
	Specialty	213,152			182,051			101,577			101,382
	Total Reinsurance	565,214			460,915			505,239			455,678
	Total	$	1,301,432		$	764,954		$	1,157,515		$	798,705

Commitments_And_Contingencies_

Commitments And Contingencies (Tables)	3 Months Ended
	Mar. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Schedule Of Percentage Of Net Premiums	The following table shows the percentage of net premiums written generated through the Company’s largest brokers for the three months ended March 31, 2015 and 2014, respectively:
	Broker	2015		2014
	Marsh & McLennan Companies, Inc.	18.9	%	16.7	%
	Aon Benfield	17.7	%	15.1	%
	Willis Companies	11.5	%	12	%
	Total of largest brokers	48.1	%	43.8	%
Schedule Of Future Minimum Lease Commitments	Future minimum lease commitments at March 31, 2015 are as follows:
	Twelve months ended March 31,	Amount
	2016	$	14,928
	2017	14,123
	2018	13,739
	2019	13,204
	2020	13,859
	2021 and thereafter	31,728
		$	101,581

General_Details

General (Details) (Scenario, Forecast [Member], USD $)	3 Months Ended
	Sep. 30, 2015
Scenario, Forecast [Member]
Business Acquisition [Line Items]
Number of Endurance shares per Montpelier share	0.472
Cash per share	$9.89

Investments_Narrative_Details

Investments (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014	Dec. 31, 2014
Investments [Abstract]
Number of available for sale securities in an unrealized loss position	491			747
Number of securities in a continuous unrealized loss position for twelve months or greater	107			171
Unrealized losses	($9,800,000)	[1]		($19,900,000)	[2]
Unrealized losses, 12 months or greater	-3,300,000	[1]		-7,100,000	[2]
OTTI losses recognized	$649,000		$111,000
[1]	Gross unrealized losses include unrealized losses on non-OTTI and non-credit OTTI securities recognized in accumulated other comprehensive income at MarchB 31, 2015.
[2]	Gross unrealized losses include unrealized losses on non-OTTI and non-credit OTTI securities recognized in accumulated other comprehensive income at DecemberB 31, 2014.

Investments_Composition_Of_Net

Investments (Composition Of Net Investment Income) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Investments [Abstract]
Available for sale investments	$32,217	$30,327
Other investments	12,388	13,542
Cash and cash equivalents	630	786
Gross investment income	45,235	44,655
Investment expenses	-3,374	-3,665
Net investment income	$41,861	$40,990

Investments_Summary_Of_Investm

Investments (Summary Of Investment Portfolio By Type) (Details) (USD $)	Mar. 31, 2015		Dec. 31, 2014
In Thousands, unless otherwise specified
Investment Holdings [Line Items]
Fair value	$6,479,256		$6,607,084
Percentage	100.00%		100.00%
Fixed Maturities [Member]
Investment Holdings [Line Items]
Fair value	4,953,893		5,092,581
Percentage	76.50%		77.10%
Cash and Cash Equivalents [Member]
Investment Holdings [Line Items]
Fair value	579,670	[1]	632,667	[1]
Percentage	8.90%	[1]	9.60%	[1]
Other Investments [Member]
Investment Holdings [Line Items]
Fair value	575,974	[2]	541,454	[2]
Percentage	8.90%	[2]	8.20%	[2]
Short-term Investments [Member]
Investment Holdings [Line Items]
Fair value	2,822		9,014
Percentage	0.00%		0.10%
Equity Securities [Member]
Investment Holdings [Line Items]
Fair value	$366,897		$331,368
Percentage	5.70%		5.00%
[1]	Includes net receivable on sales of investments and net payable on purchases of investments.
[2]	Consists of investments in alternative funds and specialty funds.

Investments_Composition_Of_The

Investments (Composition Of The Fixed Income Portfolio By Investment Ratings Assigned By Rating Agencies) (Details) (USD $)	Mar. 31, 2015		Dec. 31, 2014
In Thousands, unless otherwise specified
US Government and Agencies Securities [Member]
Investments By Rating [Line Items]
Fair Value of fixed income portfolio by investment ratings	$439,276	[1]	$587,411	[1]
Percentage of fixed income portfolio by investment ratings	8.90%	[1]	11.50%	[1]
Standard & Poor's, AAA Rating [Member]
Investments By Rating [Line Items]
Fair Value of fixed income portfolio by investment ratings	1,196,188	[1]	1,206,252	[1]
Percentage of fixed income portfolio by investment ratings	24.10%	[1]	23.60%	[1]
Standard & Poor's, AA Rating [Member]
Investments By Rating [Line Items]
Fair Value of fixed income portfolio by investment ratings	1,647,963	[1]	1,717,343	[1]
Percentage of fixed income portfolio by investment ratings	33.20%	[1]	33.70%	[1]
Standard & Poor's, A Rating [Member]
Investments By Rating [Line Items]
Fair Value of fixed income portfolio by investment ratings	1,055,259	[1]	1,045,301	[1]
Percentage of fixed income portfolio by investment ratings	21.30%	[1]	20.50%	[1]
Standard & Poor's, BBB Rating [Member]
Investments By Rating [Line Items]
Fair Value of fixed income portfolio by investment ratings	494,065	[1]	427,018	[1]
Percentage of fixed income portfolio by investment ratings	10.00%	[1]	8.40%	[1]
Standard & Poor's, Below BBB Rating [Member]
Investments By Rating [Line Items]
Fair Value of fixed income portfolio by investment ratings	103,728	[1]	96,244	[1]
Percentage of fixed income portfolio by investment ratings	2.10%	[1]	1.90%	[1]
Not Rated [Member]
Investments By Rating [Line Items]
Fair Value of fixed income portfolio by investment ratings	20,236	[1]	22,026	[1]
Percentage of fixed income portfolio by investment ratings	0.40%	[1]	0.40%	[1]
Fixed Income Investments [Member]
Investments By Rating [Line Items]
Fair Value of fixed income portfolio by investment ratings	$4,956,715	[1]	$5,101,595	[1]
Percentage of fixed income portfolio by investment ratings	100.00%	[1]	100.00%	[1]
[1]	The credit rating for each security reflected above was determined based on the rating assigned to the individual security by StandardB & Poorbs Financial Services LLC (bStandardB & Poorbsb). If a rating is not supplied by StandardB & Poorbs, the equivalent rating supplied by Moodybs Investors Service, Inc. (bMoody'sb), Fitch Ratings, Inc., or DBRS, Inc. is used.

Investments_Contractual_Maturi

Investments (Contractual Maturities Of Fixed Income Securities) (Details) (USD $)	Mar. 31, 2015		Dec. 31, 2014
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]
Due within one year, amortized cost	$104,359		$126,921
Due within one year, fair value	105,176		127,821
Due after one year through five years, amortized cost	1,518,003		1,627,154
Due after one year through five years, fair value	1,533,554		1,632,259
Due after five years through ten years, amortized cost	406,967		474,959
Due after five years through ten years, fair value	417,073		479,138
Due after ten years, amortized cost	54,453		43,314
Due after ten years, fair value	58,324		46,720
Fixed income investments, amortized cost	4,866,862		5,032,506
Fixed income investments, fair value	4,953,893		5,092,581
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
No single maturity date, amortized cost	1,098,830		1,149,536
No single maturity date, fair value	1,127,954		1,175,006
Fixed income investments, amortized cost	1,098,830		1,149,536
Fixed income investments, fair value	1,127,954		1,175,006
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
No single maturity date, amortized cost	979,828		960,598
No single maturity date, fair value	1,003,437		979,419
Fixed income investments, amortized cost	979,828		960,598
Fixed income investments, fair value	1,003,437		979,419
Collateralized Loan and Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
No single maturity date, amortized cost	302,842		247,510
No single maturity date, fair value	304,512		248,011
Fixed income investments, amortized cost	302,842	[1]	247,510	[2]
Fixed income investments, fair value	304,512	[1]	248,011	[2]
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
No single maturity date, amortized cost	404,402		411,529
No single maturity date, fair value	406,685		413,221
Fixed income investments, amortized cost	404,402		411,529
Fixed income investments, fair value	406,685		413,221
Fixed Income Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed income investments, amortized cost	4,869,684		5,041,521
Fixed income investments, fair value	$4,956,715		$5,101,595
[1]	Balances include amounts related to collateralized debt obligations held with total fair values of $13.1 million.
[2]	Balances include amounts related to collateralized debt obligations held with total fair values of $15.2 million.

Investments_Other_Investments_

Investments (Other Investments) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Schedule of Equity Method Investments [Line Items]
Other investments, market value	$575,974	$541,454
Commitments under investment fund classified within other investments	56,956	70,542
Prohibited amount under redemption requests over the next 12 months	134,404	85,244
Alternative Funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments, market value	519,612	485,944
Commitments under investment fund classified within other investments	56,956	70,542
Prohibited amount under redemption requests over the next 12 months	134,404	85,244
Hedge Funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments, market value	443,307	411,280
Commitments under investment fund classified within other investments	0	0
Prohibited amount under redemption requests over the next 12 months	58,099	10,580
Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments, market value	76,305	74,664
Commitments under investment fund classified within other investments	56,956	70,542
Prohibited amount under redemption requests over the next 12 months	76,305	74,664
Specialty Funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments, market value	56,362	55,510
Commitments under investment fund classified within other investments	0	0
Prohibited amount under redemption requests over the next 12 months	0	0
High Yield Loan Funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments, market value	56,362	55,510
Commitments under investment fund classified within other investments	0	0
Prohibited amount under redemption requests over the next 12 months	$0	$0

Investments_Other_Investments_1

Investments (Other Investments Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Other investments, invested amount	413,100,000	$387,200,000
Other investments, market value	575,974,000	541,454,000
Alternative Funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments, market value	519,612,000	485,944,000
Hedge Funds [Member]
Schedule of Equity Method Investments [Line Items]
Estimated liquidation, percentage in next 12 months	86.90%
Other investments, market value	443,307,000	411,280,000
Hedge Funds [Member] | Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Estimated notice period, in days	90 days
Hedge Funds [Member] | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Estimated notice period, in days	30 days
Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments, market value	76,305,000	74,664,000
Private Equity Funds [Member] | Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Estimated remaining liquidation period in years	10 years
Private Equity Funds [Member] | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Estimated remaining liquidation period in years	5 years
Specialty Funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments, market value	56,362,000	55,510,000
High Yield Loan Funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments, market value	56,362,000	$55,510,000
High Yield Loan Funds [Member] | Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Estimated notice period, in days	90 days
High Yield Loan Funds [Member] | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Estimated notice period, in days	30 days

Investments_Net_Realized_and_U

Investments (Net Realized and Unrealized Investment Gains) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Investments [Abstract]
Gross realized gains on investment sales	$22,666		$10,247
Gross realized losses on investment sales	-4,896		-5,984
Change in fair value of derivative financial instruments	419	[1]	609	[1]
Net realized and unrealized gains	$18,189		$4,872
[1]	For additional information on the Companybs derivative financial instruments, see Note 7.

Investments_Amortized_Cost_Fai

Investments (Amortized Cost, Fair Value, Unrealized Gains And Losses And Non-Credit Other-Than-Temporary Impairment) (Details) (USD $)	Mar. 31, 2015		Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Fixed income investments, amortized cost	$4,866,862,000		$5,032,506,000
Fixed income investments, fair value	4,953,893,000		5,092,581,000
Equity securities, cost	342,597,000		303,922,000
Equity securities, fair value	366,897,000		331,368,000
Gross unrealized loss related to securities, non-credit OTTI	0		0
US Government and Agencies Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed income investments, amortized cost	430,517,000		582,970,000
Fixed income investments, gross unrealized gains	9,470,000		6,471,000
Fixed income investments, gross unrealized losses	-711,000		-2,030,000
Fixed income investments, fair value	439,276,000		587,411,000
Non-Credit OTTI	0	[1]	0	[2]
US State and Municipal Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed income investments, amortized cost	51,930,000		39,340,000
Fixed income investments, gross unrealized gains	407,000		191,000
Fixed income investments, gross unrealized losses	-206,000		-118,000
Fixed income investments, fair value	52,131,000		39,413,000
Non-Credit OTTI	0	[1]	0	[2]
Foreign Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed income investments, amortized cost	169,866,000		239,217,000
Fixed income investments, gross unrealized gains	2,971,000		2,983,000
Fixed income investments, gross unrealized losses	-639,000		-1,664,000
Fixed income investments, fair value	172,198,000		240,536,000
Non-Credit OTTI	0	[1]	0	[2]
Government Guaranteed Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed income investments, amortized cost	39,431,000		47,436,000
Fixed income investments, gross unrealized gains	635,000		675,000
Fixed income investments, gross unrealized losses	-1,000		-9,000
Fixed income investments, fair value	40,065,000		48,102,000
Non-Credit OTTI	0	[1]	0	[2]
Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed income investments, amortized cost	1,389,216,000		1,354,370,000
Fixed income investments, gross unrealized gains	20,131,000		12,742,000
Fixed income investments, gross unrealized losses	-1,712,000		-5,650,000
Fixed income investments, fair value	1,407,635,000		1,361,462,000
Non-Credit OTTI	0	[1]	0	[2]
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed income investments, amortized cost	1,098,830,000		1,149,536,000
Fixed income investments, gross unrealized gains	30,485,000		27,542,000
Fixed income investments, gross unrealized losses	-1,361,000		-2,072,000
Fixed income investments, fair value	1,127,954,000		1,175,006,000
Non-Credit OTTI	-3,098,000	[1]	-3,233,000	[2]
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed income investments, amortized cost	979,828,000		960,598,000
Fixed income investments, gross unrealized gains	25,162,000		21,374,000
Fixed income investments, gross unrealized losses	-1,553,000		-2,553,000
Fixed income investments, fair value	1,003,437,000		979,419,000
Non-Credit OTTI	0	[1]	-5,000	[2]
Collateralized Loan and Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed income investments, amortized cost	302,842,000	[3]	247,510,000	[4]
Fixed income investments, gross unrealized gains	1,980,000	[3]	1,449,000	[4]
Fixed income investments, gross unrealized losses	-310,000	[3]	-948,000	[4]
Fixed income investments, fair value	304,512,000	[3]	248,011,000	[4]
Non-Credit OTTI	0	[1],[3]	0	[2],[4]
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed income investments, amortized cost	404,402,000		411,529,000
Fixed income investments, gross unrealized gains	2,652,000		2,265,000
Fixed income investments, gross unrealized losses	-369,000		-573,000
Fixed income investments, fair value	406,685,000		413,221,000
Non-Credit OTTI	0	[1]	0	[2]
Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed income investments, amortized cost	4,866,862,000		5,032,506,000
Fixed income investments, gross unrealized gains	93,893,000		75,692,000
Fixed income investments, gross unrealized losses	-6,862,000		-15,617,000
Fixed income investments, fair value	4,953,893,000		5,092,581,000
Non-Credit OTTI	-3,098,000	[1]	-3,238,000	[2]
Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed income investments, amortized cost	2,822,000		9,015,000
Fixed income investments, gross unrealized gains	0		0
Fixed income investments, gross unrealized losses	0		-1,000
Fixed income investments, fair value	2,822,000		9,014,000
Non-Credit OTTI	0	[1]	0	[2]
Fixed Income Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed income investments, amortized cost	4,869,684,000		5,041,521,000
Fixed income investments, gross unrealized gains	93,893,000		75,692,000
Fixed income investments, gross unrealized losses	-6,862,000		-15,618,000
Fixed income investments, fair value	4,956,715,000		5,101,595,000
Non-Credit OTTI	-3,098,000	[1]	-3,238,000	[2]
Equity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity securities, cost	217,035,000		176,167,000
Equity securities, gross unrealized gains	22,837,000		29,660,000
Equity securities, gross unrealized losses	-1,478,000		-3,292,000
Equity securities, fair value	238,394,000		202,535,000
Non-Credit OTTI	0	[1]	0	[2]
Emerging Market Debt Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity securities, cost	61,874,000		60,826,000
Equity securities, gross unrealized gains	0		0
Equity securities, gross unrealized losses	-1,407,000		-676,000
Equity securities, fair value	60,467,000		60,150,000
Non-Credit OTTI	0	[1]	0	[2]
Convertible Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity securities, cost	46,331,000		46,331,000
Equity securities, gross unrealized gains	2,167,000		0
Equity securities, gross unrealized losses	0		-220,000
Equity securities, fair value	48,498,000		46,111,000
Non-Credit OTTI	0	[1]	0	[2]
Preferred Equity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity securities, cost	13,715,000		13,858,000
Equity securities, gross unrealized gains	2,194,000		2,022,000
Equity securities, gross unrealized losses	-12,000		-44,000
Equity securities, fair value	15,897,000		15,836,000
Non-Credit OTTI	0	[1]	0	[2]
Short-term Fixed Income Fund [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity securities, cost	3,642,000		6,740,000
Equity securities, gross unrealized gains	0		0
Equity securities, gross unrealized losses	-1,000		-4,000
Equity securities, fair value	3,641,000		6,736,000
Non-Credit OTTI	0	[1]	0	[2]
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity securities, cost	342,597,000		303,922,000
Equity securities, gross unrealized gains	27,198,000		31,682,000
Equity securities, gross unrealized losses	-2,898,000		-4,236,000
Equity securities, fair value	366,897,000		331,368,000
Non-Credit OTTI	0	[1]	0	[2]
Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed income investments, fair value	$13,100,000		$15,200,000
[1]	Represents total OTTI recognized in accumulated other comprehensive income. It does not include the change in fair value subsequent to the impairment measurement date. At MarchB 31, 2015, the gross unrealized loss related to fixed income investments for which a non-credit OTTI was recognized in accumulated other comprehensive income was nil.
[2]	Represents total OTTI recognized in accumulated other comprehensive income. It does not include the change in fair value subsequent to the impairment measurement date. At DecemberB 31, 2014, the gross unrealized loss related to fixed income investments for which a non-credit OTTI was recognized in accumulated other comprehensive income was nil.
[3]	Balances include amounts related to collateralized debt obligations held with total fair values of $13.1 million.
[4]	Balances include amounts related to collateralized debt obligations held with total fair values of $15.2 million.

Investments_Available_For_Sale

Investments (Available For Sale Securities In An Unrealized Loss Position) (Details) (USD $)	Mar. 31, 2015		Dec. 31, 2014
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, 12 months or greater	($3,300)	[1]	($7,100)	[2]
Unrealized losses	-9,800	[1]	-19,900	[2]
US Government and Agencies Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	-177	[1]	-481	[2]
Fair value, less than 12 months	27,378		155,350
Unrealized losses, 12 months or greater	-534	[1]	-1,549	[2]
Fair value, 12 months or greater	24,374		45,993
Unrealized losses	-711	[1]	-2,030	[2]
Fair value	51,752		201,343
US State and Municipal Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	-198	[1]	-47	[2]
Fair value, less than 12 months	17,685		3,295
Unrealized losses, 12 months or greater	-8	[1]	-71	[2]
Fair value, 12 months or greater	3,003		6,841
Unrealized losses	-206	[1]	-118	[2]
Fair value	20,688		10,136
Foreign Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	-450	[1]	-1,378	[2]
Fair value, less than 12 months	14,770		37,904
Unrealized losses, 12 months or greater	-189	[1]	-286	[2]
Fair value, 12 months or greater	1,688		4,306
Unrealized losses	-639	[1]	-1,664	[2]
Fair value	16,458		42,210
Government Guaranteed Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	-1	[1]	-9	[2]
Fair value, less than 12 months	1,286		4,598
Unrealized losses, 12 months or greater	0	[1]	0	[2]
Fair value, 12 months or greater	0		0
Unrealized losses	-1	[1]	-9	[2]
Fair value	1,286		4,598
Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	-1,048	[1]	-4,023	[2]
Fair value, less than 12 months	192,963		533,139
Unrealized losses, 12 months or greater	-664	[1]	-1,627	[2]
Fair value, 12 months or greater	35,725		84,278
Unrealized losses	-1,712	[1]	-5,650	[2]
Fair value	228,688		617,417
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	-308	[1]	-260	[2]
Fair value, less than 12 months	79,275		62,832
Unrealized losses, 12 months or greater	-1,053	[1]	-1,812	[2]
Fair value, 12 months or greater	86,646		108,899
Unrealized losses	-1,361	[1]	-2,072	[2]
Fair value	165,921		171,731
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	-939	[1]	-1,068	[2]
Fair value, less than 12 months	139,745		180,222
Unrealized losses, 12 months or greater	-614	[1]	-1,485	[2]
Fair value, 12 months or greater	38,908		78,412
Unrealized losses	-1,553	[1]	-2,553	[2]
Fair value	178,653		258,634
Collateralized Loan and Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	-255	[1]	-876	[2]
Fair value, less than 12 months	141,280		176,439
Unrealized losses, 12 months or greater	-55	[1]	-72	[2]
Fair value, 12 months or greater	17,557		6,491
Unrealized losses	-310	[1]	-948	[2]
Fair value	158,837		182,930
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	-217	[1]	-415	[2]
Fair value, less than 12 months	121,075		199,205
Unrealized losses, 12 months or greater	-152	[1]	-158	[2]
Fair value, 12 months or greater	17,231		19,095
Unrealized losses	-369	[1]	-573	[2]
Fair value	138,306		218,300
Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months			-8,557	[2]
Fair value, less than 12 months			1,352,984
Unrealized losses, 12 months or greater			-7,060	[2]
Fair value, 12 months or greater			354,315
Unrealized losses			-15,617	[2]
Fair value			1,707,299
Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months			-1	[2]
Fair value, less than 12 months			1,953
Unrealized losses, 12 months or greater			0	[2]
Fair value, 12 months or greater			0
Unrealized losses			-1	[2]
Fair value			1,953
Fixed Income Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	-3,593	[1]	-8,558	[2]
Fair value, less than 12 months	735,457		1,354,937
Unrealized losses, 12 months or greater	-3,269	[1]	-7,060	[2]
Fair value, 12 months or greater	225,132		354,315
Unrealized losses	-6,862	[1]	-15,618	[2]
Fair value	960,589		1,709,252
Equity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	-1,478	[1]	-3,292	[2]
Fair value, less than 12 months	87,056		53,591
Unrealized losses, 12 months or greater	0	[1]	0	[2]
Fair value, 12 months or greater	0		0
Unrealized losses	-1,478	[1]	-3,292	[2]
Fair value	87,056		53,591
Emerging Market Debt Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	-1,407	[1]	-676	[2]
Fair value, less than 12 months	60,467		60,150
Unrealized losses, 12 months or greater	0	[1]	0	[2]
Fair value, 12 months or greater	0		0
Unrealized losses	-1,407	[1]	-676	[2]
Fair value	60,467		60,150
Convertible Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months			-220	[2]
Fair value, less than 12 months			46,111
Unrealized losses, 12 months or greater			0	[2]
Fair value, 12 months or greater			0
Unrealized losses			-220	[2]
Fair value			46,111
Preferred Equity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	-12	[1]	-44	[2]
Fair value, less than 12 months	2,089		4,449
Unrealized losses, 12 months or greater	0	[1]	0	[2]
Fair value, 12 months or greater	0		0
Unrealized losses	-12	[1]	-44	[2]
Fair value	2,089		4,449
Short-term Fixed Income Fund [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	-1	[1]	-4	[2]
Fair value, less than 12 months	2,919		6,736
Unrealized losses, 12 months or greater	0	[1]	0	[2]
Fair value, 12 months or greater	0		0
Unrealized losses	-1	[1]	-4	[2]
Fair value	2,919		6,736
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, less than 12 months	-2,898	[1]	-4,236	[2]
Fair value, less than 12 months	152,531		171,037
Unrealized losses, 12 months or greater	0	[1]	0	[2]
Fair value, 12 months or greater	0		0
Unrealized losses	-2,898	[1]	-4,236	[2]
Fair value	$152,531		$171,037
[1]	Gross unrealized losses include unrealized losses on non-OTTI and non-credit OTTI securities recognized in accumulated other comprehensive income at MarchB 31, 2015.
[2]	Gross unrealized losses include unrealized losses on non-OTTI and non-credit OTTI securities recognized in accumulated other comprehensive income at DecemberB 31, 2014.

Investments_Analysis_Of_OTTI_D

Investments (Analysis Of OTTI) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Investments [Abstract]
Total other-than-temporary impairment losses	($649)	($111)
Portion of loss recognized in other comprehensive income	0	0
Net impairment losses recognized in earnings	($649)	($111)

Investments_Credit_Losses_Roll

Investments (Credit Losses Rollforward) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Investments [Abstract]
Beginning balance	($838)	($1,553)
Addition for the amount related to the credit loss for which an other-than-temporary impairment was not previously recognized	0	0
Addition for the amount related to the credit loss for which an other-than-temporary impairment was previously recognized	0	0
Reductions for increases in cash flows expected to be collected that are recognized over the remaining life of the security	0	0
Reductions for securities sold during the period	43	33
Ending balance	($795)	($1,520)

Fair_Value_Measurement_Narrati

Fair Value Measurement (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers into Level 3	$1,733,000	$2,117,000
Transfers out of Level 3	-4,290,000	-263,000
Net impairment losses recognized in earnings	649,000	111,000
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of level 3 assets	9.90%		9.50%
Net impairment losses recognized in earnings	$0

Fair_Value_Measurement_Schedul

Fair Value Measurement (Schedule Of Available For Sale Investments, Other Investments, Derivative Instruments And Debt) (Details) (USD $)	Mar. 31, 2015		Dec. 31, 2014
In Thousands, unless otherwise specified
Assets
Fixed maturity investments	$4,953,893		$5,092,581
Short-term investments	2,822		9,014
Equity securities	366,897		331,368
Other investments	575,974		541,454
Other assets (see Note 7)	170,023		99,504
Total assets	6,069,609		6,073,921
Liabilities
Other liabilities (see Note 7)	114,943		54,338
Debt	635,154		623,740
Total liabilities	750,097		678,078
Fair Value, Inputs, Level 1 [Member]
Assets
Short-term investments	0		0
Other investments	0		0
Other assets (see Note 7)	0		0
Total assets	164,763		250,320
Liabilities
Other liabilities (see Note 7)	0		0
Debt	0		0
Total liabilities	0		0
Fair Value, Inputs, Level 2 [Member]
Assets
Short-term investments	2,822		9,014
Other investments	0		0
Other assets (see Note 7)	154,800		73,889
Total assets	5,304,149		5,244,242
Liabilities
Other liabilities (see Note 7)	97,558		18,972
Debt	635,154		623,740
Total liabilities	732,712		642,712
Fair Value, Inputs, Level 3 [Member]
Assets
Short-term investments	0		0
Other investments	575,974		541,454
Other assets (see Note 7)	15,223		25,615
Total assets	600,697		579,359
Liabilities
Other liabilities (see Note 7)	17,385		35,366
Debt	0		0
Total liabilities	17,385		35,366
US Government and Agencies Securities [Member]
Assets
Fixed maturity investments	439,276		587,411
US Government and Agencies Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Fixed maturity investments	16,825		105,121
US Government and Agencies Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Fixed maturity investments	422,451		482,290
US Government and Agencies Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Fixed maturity investments	0		0
US State and Municipal Debt Securities [Member]
Assets
Fixed maturity investments	52,131		39,413
US State and Municipal Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Fixed maturity investments	0		0
US State and Municipal Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Fixed maturity investments	52,131		39,413
US State and Municipal Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Fixed maturity investments	0		0
Foreign Government Securities [Member]
Assets
Fixed maturity investments	172,198		240,536
Foreign Government Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Fixed maturity investments	0		0
Foreign Government Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Fixed maturity investments	172,198		240,536
Foreign Government Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Fixed maturity investments	0		0
Government Guaranteed Corporate Securities [Member]
Assets
Fixed maturity investments	40,065		48,102
Government Guaranteed Corporate Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Fixed maturity investments	0		0
Government Guaranteed Corporate Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Fixed maturity investments	40,065		48,102
Government Guaranteed Corporate Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Fixed maturity investments	0		0
Corporate Securities [Member]
Assets
Fixed maturity investments	1,407,635		1,361,462
Corporate Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Fixed maturity investments	0		0
Corporate Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Fixed maturity investments	1,405,136		1,358,960
Corporate Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Fixed maturity investments	2,499		2,502
Residential Mortgage Backed Securities [Member]
Assets
Fixed maturity investments	1,127,954		1,175,006
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Fixed maturity investments	0		0
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Fixed maturity investments	1,127,954		1,174,997
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Fixed maturity investments	0		9
Commercial Mortgage Backed Securities [Member]
Assets
Fixed maturity investments	1,003,437		979,419
Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Fixed maturity investments	0		0
Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Fixed maturity investments	1,002,868		974,602
Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Fixed maturity investments	569		4,817
Collateralized Loan and Debt Obligations [Member]
Assets
Fixed maturity investments	304,512	[1]	248,011	[2]
Collateralized Loan and Debt Obligations [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Fixed maturity investments	0		0
Collateralized Loan and Debt Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Fixed maturity investments	301,046		246,042
Collateralized Loan and Debt Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Fixed maturity investments	3,466		1,969
Asset-backed Securities [Member]
Assets
Fixed maturity investments	406,685		413,221
Asset-backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Fixed maturity investments	0		0
Asset-backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Fixed maturity investments	403,719		410,228
Asset-backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Fixed maturity investments	2,966		2,993
Fixed Maturities [Member]
Assets
Fixed maturity investments	4,953,893		5,092,581
Fixed Maturities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Fixed maturity investments	16,825		105,121
Fixed Maturities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Fixed maturity investments	4,927,568		4,975,170
Fixed Maturities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Fixed maturity investments	9,500		12,290
Equity Investments [Member]
Assets
Equity securities	238,394		202,535
Equity Investments [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Equity securities	144,297		138,463
Equity Investments [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Equity securities	94,097		64,072
Equity Investments [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Equity securities	0		0
Emerging Market Debt Funds [Member]
Assets
Equity securities	60,467		60,150
Emerging Market Debt Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Equity securities	0		0
Emerging Market Debt Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Equity securities	60,467		60,150
Emerging Market Debt Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Equity securities	0		0
Convertible Funds [Member]
Assets
Equity securities	48,498		46,111
Convertible Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Equity securities	0		0
Convertible Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Equity securities	48,498		46,111
Convertible Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Equity securities	0		0
Preferred Equity Investments [Member]
Assets
Equity securities	15,897		15,836
Preferred Equity Investments [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Equity securities	0		0
Preferred Equity Investments [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Equity securities	15,897		15,836
Preferred Equity Investments [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Equity securities	0		0
Short-term Fixed Income Fund [Member]
Assets
Equity securities	3,641		6,736
Short-term Fixed Income Fund [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Equity securities	3,641		6,736
Short-term Fixed Income Fund [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Equity securities	0		0
Short-term Fixed Income Fund [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Equity securities	0		0
Equity Securities [Member]
Assets
Equity securities	366,897		331,368
Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Equity securities	147,938		145,199
Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Equity securities	218,959		186,169
Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Equity securities	$0		$0
[1]	Balances include amounts related to collateralized debt obligations held with total fair values of $13.1 million.
[2]	Balances include amounts related to collateralized debt obligations held with total fair values of $15.2 million.

Fair_Value_Measurement_Quantit

Fair Value Measurement (Quantitative Information Used As Level 3 Inputs) (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Net weather and energy related derivative liabilities	$55,080,000	$45,166,000
Derivatives recorded in other assets, fair value	170,023,000	99,504,000
Derivatives recorded in other liabilities, fair value	114,943,000	54,338,000
Energy Related Derivative [Member]
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Derivatives recorded in other assets, fair value	15,223,000	25,615,000
Derivatives recorded in other liabilities, fair value	17,385,000	35,366,000
Simulation Valuation Technique [Member] | Energy Related Derivative [Member]
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Net weather and energy related derivative liabilities	2,162,000	9,751,000
Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Derivatives recorded in other assets, fair value	15,223,000	25,615,000
Derivatives recorded in other liabilities, fair value	17,385,000	35,366,000
Fair Value, Inputs, Level 3 [Member] | Simulation Valuation Technique [Member] | Maximum [Member]
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Correlation	1	1
Weather curve	2,700,000	2,500,000
Commodity curve	14,000	0
Fair Value, Inputs, Level 3 [Member] | Simulation Valuation Technique [Member] | Minimum [Member]
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Correlation	0	0
Weather curve	2,200,000	-828,000
Commodity curve	$0	$0

Fair_Value_Measurement_Reconci

Fair Value Measurement (Reconciliation Of The Beginning And Ending Balances For Fixed Maturity Investments, Other Investments, Other Assets and Other Liabilities Measured At Fair Value On A Recurring Basis Using Level 3 Inputs) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Level 3, beginning of period	$579,359	$638,844
Total equity income and realized gains included in earnings	20,662	19,203
Total equity losses and losses included in earnings	-8,170	-5,671
Total income included in other underwriting income (loss)	2,096	3,975
Total loss included in other underwriting income (loss)	-8,842	-6,888
Change in unrealized gains included in other comprehensive income	6	111
Change in unrealized losses included in other comprehensive income	-129	-115
Purchases	39,321	4,674
Issues	3,212	640
Sales	-17,403	-13,963
Settlements	-6,858	-3,233
Transfers into Level 3	1,733	2,117
Transfers out of Level 3	-4,290	-263
Level 3, end of period	600,697	639,431
Fixed Maturity Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Level 3, beginning of period	12,290	7,328
Total equity income and realized gains included in earnings	113	17
Total equity losses and losses included in earnings	-9	-26
Total income included in other underwriting income (loss)	0	0
Total loss included in other underwriting income (loss)	0	0
Change in unrealized gains included in other comprehensive income	6	111
Change in unrealized losses included in other comprehensive income	-129	-115
Purchases	0	0
Issues	0	0
Sales	-214	-184
Settlements	0	0
Transfers into Level 3	1,733	2,117
Transfers out of Level 3	-4,290	-263
Level 3, end of period	9,500	8,985
Other Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Level 3, beginning of period	541,454	617,478
Total equity income and realized gains included in earnings	20,549	19,186
Total equity losses and losses included in earnings	-8,161	-5,645
Total income included in other underwriting income (loss)	0	0
Total loss included in other underwriting income (loss)	0	0
Change in unrealized gains included in other comprehensive income	0	0
Change in unrealized losses included in other comprehensive income	0	0
Purchases	39,321	4,674
Issues	0	0
Sales	-17,189	-13,779
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Level 3, end of period	575,974	621,914
Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Level 3, beginning of period	25,615	14,038
Total equity income and realized gains included in earnings	0	0
Total equity losses and losses included in earnings	0	0
Total income included in other underwriting income (loss)	2,096	3,975
Total loss included in other underwriting income (loss)	-8,842	-6,888
Change in unrealized gains included in other comprehensive income	0	0
Change in unrealized losses included in other comprehensive income	0	0
Purchases	0	0
Issues	3,212	640
Sales	0	0
Settlements	-6,858	-3,233
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Level 3, end of period	15,223	8,532
Other Liabilities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Level 3, beginning of period	-35,366	-19,569
Total equity income and realized gains included in earnings	0	0
Total equity losses and losses included in earnings	0	0
Total income included in other underwriting income (loss)	13,059	7,426
Total loss included in other underwriting income (loss)	-3,529	-4,776
Change in unrealized gains included in other comprehensive income	0	0
Change in unrealized losses included in other comprehensive income	0	0
Purchases	0	0
Issues	-6,424	-1,280
Sales	0	0
Settlements	14,875	4,751
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Level 3, end of period	($17,385)	($13,448)

Earnings_Per_Share_Schedule_Of

Earnings Per Share (Schedule Of Computing Basic And Diluted Earnings Per Share) (Details) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Net income available to common and participating common shareholders	$100,291		$96,292
Less amount allocated to participating common shareholders	-2,959	[1]	-2,769	[1]
Net income allocated to common shareholders	$97,332		$93,523
Weighted average shares - basic	43,542,491		43,160,156
Weighted average shares - diluted	43,696,311		43,160,442
Basic earnings per common share	$2.24		$2.17
Diluted earnings per common share	$2.23		$2.17
Employee Stock Option [Member]
Share equivalents	146,792		0
Restricted Stock [Member]
Share equivalents	7,028		286
[1]	Represents earnings attributable to holders of unvested restricted shares and restricted share units issued under the Company's equity compensation plan that are considered participating. In periods of loss, no losses are allocated to participating common shareholders (unvested restricted shares and restricted share units).

Earnings_Per_Share_Schedule_Of1

Earnings Per Share (Schedule Of Dividends Declared) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Dividends Declared [Line Items]
Dividends declared per common share	$0.35	$0.34
Series A Preferred Stock [Member]
Dividends Declared [Line Items]
Dividends declared per preferred share	$0.48	$0.48
Series B Preferred Stock [Member]
Dividends Declared [Line Items]
Dividends declared per preferred share	$0.47	$0.47

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Income (Schedule Of Changes In Accumulated Other Comprehensive Income By Component) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Accumulated Other Comprehensive Income [Line Items]
Beginning balance	$76,706		$62,731
Other comprehensive income before reclassifications	17,276		30,890
Amounts reclassified from accumulated other comprehensive income	-16,223	[1]	-4,262	[1]
Other comprehensive income	1,053		26,628
Ending balance	77,759		89,359
Gains and losses on cash flow hedges [Member]
Accumulated Other Comprehensive Income [Line Items]
Beginning balance	-1,766		-1,855
Other comprehensive income before reclassifications	0		0
Amounts reclassified from accumulated other comprehensive income	22	[1]	23	[1]
Other comprehensive income	22		23
Ending balance	-1,744		-1,832
Unrealized gains on available for sale securities [Member]
Accumulated Other Comprehensive Income [Line Items]
Beginning balance	86,100		45,950
Other comprehensive income before reclassifications	40,734		27,665
Amounts reclassified from accumulated other comprehensive income	-16,245	[1]	-4,285	[1]
Other comprehensive income	24,489		23,380
Ending balance	110,589		69,330
Foreign currency translation adjustments [Member]
Accumulated Other Comprehensive Income [Line Items]
Beginning balance	-7,628		18,636
Other comprehensive income before reclassifications	-23,458		3,225
Amounts reclassified from accumulated other comprehensive income	0	[1]	0	[1]
Other comprehensive income	-23,458		3,225
Ending balance	($31,086)		$21,861
[1]	All amounts are net of tax.

Accumulated_Other_Comprehensiv3

Accumulated Other Comprehensive Income (Schedule Of Reclassifications Out Of Accumulated Other Comprehensive Income) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	$9,059,000	$9,051,000
Net realized and unrealized investment gains	-18,189,000	-4,872,000
Net impairment losses recognized in earnings	649,000	111,000
Total before income taxes	-112,269,000	-104,888,000
Income tax expense	3,790,000	408,000
Total net of income taxes	-108,479,000	-104,480,000
Gains and losses on cash flow hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	22,000	23,000
Total before income taxes	-22,000	-23,000
Income tax expense	0	0
Total net of income taxes	-22,000	-23,000
Unrealized gains on available for sale securities [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized and unrealized investment gains	-17,770,000	-4,263,000
Net impairment losses recognized in earnings	649,000	111,000
Total before income taxes	-17,121,000	-4,152,000
Income tax expense	876,000	-133,000
Total net of income taxes	($16,245,000)	($4,285,000)

Derivatives_Schedule_Of_Deriva

Derivatives (Schedule Of Derivative Fair Value And Notional Amount) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Derivatives recorded in other assets, fair value	170,023,000	$99,504,000
Derivatives recorded in other liabilities, fair value	114,943,000	54,338,000
Net derivative asset, fair value	55,080,000	45,166,000
Derivative assets traded under master netting agreements	170,000,000	99,500,000
Derivative liabilities traded under master netting agreements	114,900,000	54,300,000
Maximum [Member]
Derivatives, Fair Value [Line Items]
Original term of credit default swap, in years	5 years
Foreign Exchange Forward [Member]
Derivatives, Fair Value [Line Items]
Derivatives recorded in other assets, fair value	1,021,000	651,000
Derivatives recorded in other liabilities, fair value	557,000	123,000
Derivatives recorded in other assets, notional principal amount	37,927,000	42,694,000
Derivatives recorded in other liabilities, notional principal amount	22,438,000	20,945,000
Interest Rate Future [Member]
Derivatives, Fair Value [Line Items]
Derivatives recorded in other assets, fair value	16,000	7,000
Derivatives recorded in other liabilities, fair value	28,000	0
Derivatives recorded in other assets, notional principal amount	120,235,000	7,595,000
Derivatives recorded in other liabilities, notional principal amount	124,771,000	0
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivatives recorded in other liabilities, fair value	267,000	20,000
Derivatives recorded in other liabilities, notional principal amount	4,757,000	12,549,000
Interest Rate Swaption [Member]
Derivatives, Fair Value [Line Items]
Derivatives recorded in other liabilities, fair value	0	9,000
Derivatives recorded in other liabilities, notional principal amount	10,500,000	13,100,000
TBA [Member]
Derivatives, Fair Value [Line Items]
Derivatives recorded in other assets, fair value	153,763,000	73,231,000
Derivatives recorded in other liabilities, fair value	96,706,000	18,820,000
Derivatives recorded in other assets, notional principal amount	146,000,000	70,000,000
Derivatives recorded in other liabilities, notional principal amount	92,000,000	18,000,000
Energy and weather contracts [Member]
Derivatives, Fair Value [Line Items]
Derivatives recorded in other assets, fair value	15,223,000	25,615,000
Derivatives recorded in other liabilities, fair value	17,385,000	35,366,000
Derivatives recorded in other assets, notional principal amount	59,012,000	81,624,000
Derivatives recorded in other liabilities, notional principal amount	117,999,000	$135,050,000

Derivatives_Schedule_Of_Deriva1

Derivatives (Schedule Of Derivative Gain (Loss)) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Derivative [Line Items]
Derivatives included in net realized and unrealized investment gains	$419	$609
Total gains from derivatives	4,672	124
Foreign Exchange Forward [Member]
Derivative [Line Items]
Derivatives included in net foreign exchange losses from foreign exchange forward contracts	1,469	-227
Interest Rate Future [Member]
Derivative [Line Items]
Derivatives included in net realized and unrealized investment gains	122	21
Interest Rate Swap [Member]
Derivative [Line Items]
Derivatives included in net realized and unrealized investment gains	-555	-766
Interest Rate Swaption [Member]
Derivative [Line Items]
Derivatives included in net realized and unrealized investment gains	28	429
TBA [Member]
Derivative [Line Items]
Derivatives included in net realized and unrealized investment gains	824	925
Energy and weather contracts [Member]
Derivative [Line Items]
Derivatives included in other underwriting income (loss) from energy and weather contracts	$2,784	($258)

StockBased_Employee_Compensati2

Stock-Based Employee Compensation And Other Stock Plans (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares and RSUs, grants in period	472,662	335,771
Restricted shares and RSUs weighted average grant date fair value	$28,000,000	$17,600,000
Aggregate fair value of restricted shares and RSUs vested	13,800,000	9,800,000
Expenses related to employee stock purchase plan	65,000	54,000
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting rate	20.00%
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate of restricted shares, percentage	50.00%
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for employee awards	4 years
Restricted share awards to non-employee directors, vesting period	12 months
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for employee awards	4 years
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual life of stock options	10 years
Number of options granted	0	0
Number of options expired	0	0
Number of options vested	0	0
Number of options exercised	0	0
Compensation costs recognized in earnings	600,000	1,100,000
Compensation costs not yet recognized - stock options	2,100,000	4,600,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation costs recognized in earnings	9,200,000	9,100,000
Compensation costs not yet recognized - restricted stock	$38,700,000	$34,900,000
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for employee awards	3 years

StockBased_Employee_Compensati3

Stock-Based Employee Compensation And Other Stock Plans Stock-Based Employee Compensation And Other Stock Plans (Restricted Share And Restricted Share Unit Activity) (Details) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested, beginning of year	1,290,894
Granted	472,662	335,771
Settled	-285,044
Forfeited	0
Unvested, end of year	1,478,512
Number of Shares/Units, Outstanding, end of year	1,478,512
Aggregate Intrinsic Value, Outstanding, end of year	$90,396

Segment_Reporting_Summary_Of_T

Segment Reporting (Summary Of The Segment Revenues, Results And Reserve For Losses And Loss Expenses) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Gross premiums written	$1,301,432	$1,157,515
Ceded premiums written	-536,478	-358,810
Net premiums written	764,954	798,705
Net premiums earned	389,859	396,266
Other underwriting income (loss)	2,406	-1,238
Total revenue	392,265	395,028
Net losses and loss expenses	171,936	176,896
Acquisition expenses	82,093	72,157
General and administrative expenses	67,158	73,206
Total expenses	321,187	322,259
Underwriting income	71,078	72,769
Net loss ratio	44.10%	44.60%
Acquisition expense ratio	21.10%	18.20%
General and administrative expense ratio	17.20%	18.50%
Combined ratio	82.40%	81.30%
Reserve for losses and loss expenses	3,621,728	3,847,774	3,846,859
Insurance [Member]
Segment Reporting Information [Line Items]
Gross premiums written	736,218	652,276
Ceded premiums written	-432,179	-309,249
Net premiums written	304,039	343,027
Net premiums earned	135,864	144,021
Other underwriting income (loss)	0	0
Total revenue	135,864	144,021
Net losses and loss expenses	74,512	88,533
Acquisition expenses	15,883	12,261
General and administrative expenses	32,684	41,736
Total expenses	123,079	142,530
Underwriting income	12,785	1,491
Net loss ratio	54.80%	61.50%
Acquisition expense ratio	11.70%	8.50%
General and administrative expense ratio	24.10%	29.00%
Combined ratio	90.60%	99.00%
Reserve for losses and loss expenses	1,952,277	2,023,819
Reinsurance [Member]
Segment Reporting Information [Line Items]
Gross premiums written	565,214	505,239
Ceded premiums written	-104,299	-49,561
Net premiums written	460,915	455,678
Net premiums earned	253,995	252,245
Other underwriting income (loss)	2,406	-1,238
Total revenue	256,401	251,007
Net losses and loss expenses	97,424	88,363
Acquisition expenses	66,210	59,896
General and administrative expenses	34,474	31,470
Total expenses	198,108	179,729
Underwriting income	58,293	71,278
Net loss ratio	38.30%	35.00%
Acquisition expense ratio	26.10%	23.70%
General and administrative expense ratio	13.60%	12.60%
Combined ratio	78.00%	71.30%
Reserve for losses and loss expenses	$1,669,451	$1,823,955

Segment_Reporting_Schedule_Of_

Segment Reporting (Schedule Of Segment Results To Income Before Income Taxes) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Segment Reporting [Abstract]
Total underwriting income	$71,078	$72,769
Net investment income	41,861	40,990
Net foreign exchange losses	-7,552	-2,964
Net realized and unrealized investment gains	18,189	4,872
Net impairment losses recognized in earnings	-649	-111
Amortization of intangibles	-1,599	-1,617
Interest expense	-9,059	-9,051
Income before income taxes	$112,269	$104,888

Segment_Reporting_Schedule_Of_1

Segment Reporting (Schedule Of Gross And Net Premiums By Line Of Business) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Revenue from External Customer [Line Items]
Gross premiums written	$1,301,432	$1,157,515
Net premiums written	764,954	798,705
Insurance [Member]
Revenue from External Customer [Line Items]
Gross premiums written	736,218	652,276
Net premiums written	304,039	343,027
Agriculture Insurance [Member]
Revenue from External Customer [Line Items]
Gross premiums written	516,916	527,894
Net premiums written	202,460	281,645
Casualty And Other Specialty Insurance [Member]
Revenue from External Customer [Line Items]
Gross premiums written	100,682	67,653
Net premiums written	45,058	36,813
Professional Lines Insurance [Member]
Revenue from External Customer [Line Items]
Gross premiums written	54,760	38,780
Net premiums written	24,231	14,570
Property, Marine And Energy Insurance [Member]
Revenue from External Customer [Line Items]
Gross premiums written	63,860	17,949
Net premiums written	32,290	9,999
Reinsurance [Member]
Revenue from External Customer [Line Items]
Gross premiums written	565,214	505,239
Net premiums written	460,915	455,678
Catastrophe Reinsurance [Member]
Revenue from External Customer [Line Items]
Gross premiums written	124,407	126,648
Net premiums written	53,460	78,963
Casualty Reinsurance [Member]
Revenue from External Customer [Line Items]
Gross premiums written	58,098	84,982
Net premiums written	58,098	83,392
Property Reinsurance [Member]
Revenue from External Customer [Line Items]
Gross premiums written	125,700	166,413
Net premiums written	123,449	166,322
Professional Lines Reinsurance [Member]
Revenue from External Customer [Line Items]
Gross premiums written	43,857	25,619
Net premiums written	43,857	25,619
Specialty Reinsurance [Member]
Revenue from External Customer [Line Items]
Gross premiums written	213,152	101,577
Net premiums written	$182,051	$101,382

Commitments_And_Contingencies_1

Commitments And Contingencies (Narrative) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Commitments and Contingencies Disclosure [Abstract]
Amount of letters of credit outstanding	$192.90	$209.90
Securities pledged as collateral obligation	130.7	130.6
Cash and investments pledged under letters of credit facility	219.8	240
Ceded Credit Risk [Line Items]
Reinsurance recoverables	742.5	889.1
Ceded Credit Risk, Secured [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	$175.30	$199.70

Commitments_And_Contingencies_2

Commitments And Contingencies (Schedule Of Percentage Of Net Premiums) (Details)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Revenue from External Customer [Line Items]
Percentage of net premium written	48.10%	43.80%
Aon Benfield [Member]
Revenue from External Customer [Line Items]
Percentage of net premium written	17.70%	15.10%
Willis Companies [Member]
Revenue from External Customer [Line Items]
Percentage of net premium written	11.50%	12.00%
Marsh & Mclennan Companies, Inc. [Member]
Revenue from External Customer [Line Items]
Percentage of net premium written	18.90%	16.70%

Commitments_And_Contingencies_3

Commitments And Contingencies (Deposits) (Details) (UNITED STATES [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
UNITED STATES [Member]
Statutory Accounting Practices [Line Items]
Assets Held by Insurance Regulators	$205.40	$205.20

Commitments_And_Contingencies_4

Commitments And Contingencies (Schedule Of Future Minimum Lease Commitments) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
2016	$14,928,000
2017	14,123,000
2018	13,739,000
2019	13,204,000
2020	13,859,000
2021 and thereafter	31,728,000
Total	101,581,000
Total lease expenses under operating leases	$3,100,000	$4,200,000

Commitments_And_Contingencies_5

Commitments And Contingencies Commitments And Contingencies (Merger Agreement) (Details) (USD $)	3 Months Ended
	Sep. 30, 2015	Mar. 31, 2015
Business Acquisition [Line Items]
Acquisition transaction costs		$1,000,000
Scenario, Forecast [Member]
Business Acquisition [Line Items]
Number of Endurance shares per Montpelier share	0.472
Cash per share	$9.89
Purchase price per Montpelier share	$40.24
Cash consideration	450,000,000
Number of Endurance shares to be issued	21,500,000
Value of Endurance shares to be issued	1,400,000,000
Montpelier shareholders ownership percentage of Endurance	32.00%
Number of Montpelier directors to be appointed	3
Acquisition transaction costs	15,000,000
Termination fee	73,250,000
Montpelier [Member] | Scenario, Forecast [Member]
Business Acquisition [Line Items]
Percentage dividend rate of Montpelier preferred shares	8.88%
Redemption amount of Montpelier preferred shares	156,000,000
Acquisition transaction costs	$9,150,000
Number of months, takeover proposal	12