Navigators (NAVG) 10-K 14 Feb 14 2013 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2013	Jan. 31, 2014	Jun. 30, 2013
Document Information [Line Items]	'	'	'
Document Type	'10-K	'	'
Amendment Flag	'false	'	'
Document Period End Date	31-Dec-13	'	'
Document Fiscal Year Focus	'2013	'	'
Document Fiscal Period Focus	'FY	'	'
Trading Symbol	'NAVG	'	'
Entity Registrant Name	'NAVIGATORS GROUP INC	'	'
Entity Central Index Key	'0000793547	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Well-known Seasoned Issuer	'No	'	'
Entity Current Reporting Status	'Yes	'	'
Entity Voluntary Filers	'No	'	'
Entity Filer Category	'Accelerated Filer	'	'
Entity Common Stock, Shares Outstanding	'	14,207,545	'
Entity Public Float	'	'	$612,115,085

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Investments and cash:	'	'
Fixed maturities, available-for-sale, at fair value (amortized cost: 2013, $2,036,999; 2012, $2,034,765)	$2,047,873	$2,121,833
Equity securities, available-for-sale, at fair value (cost: 2013, $118,804; 2012, $85,004)	143,954	101,297
Short-term investments, at cost which approximates fair value	296,250	153,788
Cash	86,509	45,336
Total investments and cash	2,574,586	2,422,254
Premiums receivable	325,025	320,182
Prepaid reinsurance premiums	247,822	221,015
Reinsurance recoverable on paid losses	38,384	49,282
Reinsurance recoverable on unpaid losses and loss adjustment expenses	822,438	880,139
Deferred policy acquisition costs	67,007	61,005
Accrued investment income	13,866	12,587
Goodwill and other intangible assets	7,177	7,093
Current income tax receivable, net	9,918	'
Deferred income tax, net	28,187	3,216
Receivable for investments sold	3	4,310
Other assets	35,039	26,587
Total assets	4,169,452	4,007,670
Liabilities:	'	'
Reserves for losses and loss adjustment expenses	2,045,071	2,097,048
Unearned premiums	714,606	642,407
Reinsurance balances payable	167,252	165,813
Senior Notes	263,308	114,424
Current income tax payable, net	'	2,133
Payable for investments purchased	7,624	58,345
Accounts payable and other liabilities	69,379	48,015
Total liabilities	3,267,240	3,128,185
Stockholders' equity:	'	'
Preferred stock, $.10 par value, authorized 1,000,000 shares, none issued	'	'
Common stock, $.10 par value, authorized 50,000,000 shares, issued 17,709,876 shares for 2013 and 17,558,046 shares for 2012	1,770	1,755
Additional paid-in capital	335,546	329,452
Treasury stock, at cost (3,511,380 shares for 2013 and 2012)	-155,801	-155,801
Retained earnings	692,337	628,871
Accumulated other comprehensive income	28,360	75,208
Total stockholders' equity	902,212	879,485
Total liabilities and stockholders' equity	$4,169,452	$4,007,670

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, except Share data, unless otherwise specified
Fixed maturities, available-for-sale, amortized cost	$2,036,999	$2,034,765
Equity securities, available-for-sale, cost	$118,804	$85,004
Preferred stock, par value	$0.10	$0.10
Preferred stock, authorized shares	1,000,000	1,000,000
Preferred stock, issued shares	'	'
Common stock, par value	$0.10	$0.10
Common stock, authorized shares	50,000,000	50,000,000
Common stock, issued shares	17,709,876	17,558,046
Treasury stock, shares	3,511,380	3,511,380

Consolidated_Statements_of_Inc

Consolidated Statements of Income (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Gross written premiums	$1,370,517	$1,286,465	$1,108,216
Revenues:	'	'	'
Net written premiums	887,922	833,655	753,798
Change in unearned premiums	-45,983	-51,691	-62,153
Net earned premiums	841,939	781,964	691,645
Net investment income	56,251	54,248	63,500
Total other-than-temporary impairment losses	-2,393	-902	-3,617
Portion of loss recognized in other comprehensive income (before tax)	'	44	1,632
Net other-than-temporary impairment losses recognized in earnings	-2,393	-858	-1,985
Net realized gains (losses)	22,939	41,074	11,996
Other income (expense)	-1,172	1,488	1,229
Total revenues	917,564	877,916	766,385
Expenses:	'	'	'
Net losses and loss adjustment expenses	518,961	497,433	476,997
Commission expenses	113,494	121,470	110,437
Other operating expenses	164,434	159,079	138,029
Call premium on Senior Notes	17,895	'	'
Interest expense	10,507	8,198	8,188
Total expenses	825,291	786,180	733,651
Income before income taxes	92,273	91,736	32,734
Income tax expense (benefit)	28,807	27,974	7,137
Net income	$63,466	$63,762	$25,597
Net income per common share:	'	'	'
Basic	$4.49	$4.54	$1.71
Diluted	$4.42	$4.45	$1.69
Average common shares outstanding:	'	'	'
Basic	14,133,925	14,052,311	14,980,429
Diluted	14,345,553	14,327,820	15,183,285

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net income	$63,466	$63,762	$25,597
Change in net unrealized gains (losses) on investments:	'	'	'
Unrealized gains (losses) on investments arising during the period, net of deferred tax of $17,521, $13,136 and $17,776 in 2013, 2012 and 2011, respectively	-32,546	24,350	34,276
Reclassification adjustment for net realized (gains) losses included in net income net of deferred tax of $6,218, $10,314 and $2,588 in 2013, 2012 and 2011, respectively	-11,548	-19,154	-4,807
Change in net unrealized gains (losses on investments)	-44,094	5,196	29,469
Change in other-than-temporary impairments:	'	'	'
Non credit other-than-temporary impairments arising during the period, net of deferred tax of $174, $612 and $39 in 2013, 2012 and 2011, respectively	320	1,135	72
Reclassification adjustment for non credit other-than-temporary impairment losses recognized in net income net of deferred tax of $16 and $84 in 2012 and 2011, respectively	'	-29	-155
Change in other-than-temporary impairments	320	1,106	-83
Change in foreign currency translation gains (losses), net of deferred tax of $1,650, $521 and $192 in 2013, 2012 and 2011, respectively	-3,074	-1,342	401
Other comprehensive income (loss)	-46,848	4,960	29,787
Comprehensive income (loss)	$16,618	$68,722	$55,384

Consolidated_Statements_of_Com1

Consolidated Statements of Comprehensive Income (Parenthetical) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Unrealized gains (losses) on investments arising during the period, deferred tax	$17,521	$13,136	$17,776
Reclassification adjustment for net realized (gains) losses included in net income, deferred tax	6,218	10,314	2,588
Non credit other-than-temporary impairments arising during the period, deferred tax	174	612	39
Reclassification adjustment for non credit other-than-temporary impairment losses recognized in net income, deferred tax	'	16	84
Change in foreign currency translation gains (losses), deferred tax	$1,650	$521	$192

Consolidated_Statements_of_Sto

Consolidated Statements of Stockholders' Equity (USD $)	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
In Thousands, except Share data, unless otherwise specified
Beginning balance at Dec. 31, 2010	$829,354	$1,728	$312,588	($64,935)	$539,512	$40,461
Beginning balance at Dec. 31, 2010	15,742,000	17,274,440	'	1,532,273	'	'
Net income	25,597	'	'	'	25,597	'
Changes in comprehensive income:	'	'	'	'	'	'
Change in net unrealized gain (loss) on investments	29,469	'	'	'	'	29,469
Change in net non-credit other- than-temporary impairment losses	-83	'	'	'	'	-83
Change in foreign currency translation gain (loss)	401	'	'	'	'	401
Total comprehensive income	29,787	'	'	'	'	29,787
Shares issued under stock plan (in shares)	'	193,175	'	'	'	'
Shares issued under stock plan	18	18	'	'	'	'
Share-based compensation	9,545	'	9,545	'	'	'
Treasury stock acquired (in shares)	1,979,107	'	'	1,979,107	'	'
Treasury stock acquired	-90,866	'	'	-90,866	'	'
Ending balance at Dec. 31, 2011	803,435	1,746	322,133	-155,801	565,109	70,248
Ending balance at Dec. 31, 2011	13,956,000	17,467,615	'	3,511,380	'	'
Net income	63,762	'	'	'	63,762	'
Changes in comprehensive income:	'	'	'	'	'	'
Change in net unrealized gain (loss) on investments	5,196	'	'	'	'	5,196
Change in net non-credit other- than-temporary impairment losses	1,106	'	'	'	'	1,106
Change in foreign currency translation gain (loss)	-1,342	'	'	'	'	-1,342
Total comprehensive income	4,960	'	'	'	'	4,960
Shares issued under stock plan (in shares)	'	90,431	'	'	'	'
Shares issued under stock plan	-52	9	-61	'	'	'
Share-based compensation	7,380	'	7,380	'	'	'
Ending balance at Dec. 31, 2012	879,485	1,755	329,452	-155,801	628,871	75,208
Ending balance at Dec. 31, 2012	14,047,000	17,558,046	'	3,511,380	'	'
Net income	63,466	'	'	'	63,466	'
Changes in comprehensive income:	'	'	'	'	'	'
Change in net unrealized gain (loss) on investments	-44,094	'	'	'	'	-44,094
Change in net non-credit other- than-temporary impairment losses	320	'	'	'	'	320
Change in foreign currency translation gain (loss)	-3,074	'	'	'	'	-3,074
Total comprehensive income	-46,848	'	'	'	'	-46,848
Shares issued under stock plan (in shares)	'	151,830	'	'	'	'
Shares issued under stock plan	2,740	15	2,725	'	'	'
Share-based compensation	3,369	'	3,369	'	'	'
Ending balance at Dec. 31, 2013	$902,212	$1,770	$335,546	($155,801)	$692,337	$28,360
Ending balance at Dec. 31, 2013	14,198,000	17,709,876	'	3,511,380	'	'

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating activities:	'	'	'
Net income	$63,466	$63,762	$25,597
Adjustments to reconcile net income to netcash provided by (used in) operating activities:	'	'	'
Depreciation & amortization	4,518	5,931	4,059
Deferred income taxes	277	-11,414	6,224
Net realized (gains) losses	-22,939	-41,074	-11,996
Net other-than-temporary losses recognized in earnings	2,393	858	1,985
Call premium on redemption of Senior Notes	17,895	'	'
Changes in assets and liabilities:	'	'	'
Reinsurance recoverable on paid and unpaid losses and loss adjustment expenses	68,599	-40,185	10,084
Reserves for losses and loss adjustment expenses	-51,977	14,369	98,879
Prepaid reinsurance premiums	-26,807	-56,853	-7,477
Unearned premiums	72,199	109,778	69,602
Premiums receivable	-4,843	-64,457	-75,973
Deferred policy acquisition costs	-6,002	2,979	-8,815
Accrued investment income	-1,279	1,905	961
Reinsurance balances payable	1,439	57,114	2,865
Current income taxes	-12,051	17,523	-17,226
Other	31,987	36,503	19,569
Net cash provided by (used in) operating activities	136,875	96,739	118,338
Fixed maturities	'	'	'
Redemptions and maturities	237,627	188,282	166,657
Sales	648,335	1,319,404	666,976
Purchases	-899,930	-1,711,080	-803,568
Equity securities	'	'	'
Sales	72,113	39,503	73,590
Purchases	-89,288	-37,587	-75,894
Change in payable for securities	-46,414	56,543	12,432
Net change in short-term investments	-142,214	-31,568	30,384
Purchase of property and equipment	-10,088	-3,336	-4,571
Net cash provided by (used in) investing activities	-229,859	-179,839	66,006
Financing activities:	'	'	'
Net Proceeds from Debt Offering	263,278	'	'
Redemption of 7.0% Senior Notes Due May 1, 2016	-132,437	'	'
Purchase of treasury stock	'	'	-90,866
Proceeds of stock issued from employee stock purchase plan	821	672	945
Proceeds of stock issued from exercise of stock options	2,495	404	1,169
Net cash provided by (used in) financing activities	134,157	1,076	-88,752
Increase (decrease) in cash	41,173	-82,024	95,592
Cash at beginning of year	45,336	127,360	31,768
Cash at end of period	86,509	45,336	127,360
Supplemental cash information:	'	'	'
Income taxes paid, net	41,094	19,602	14,145
Interest paid	8,050	8,050	8,050
Issuance of stock to directors	$400	$242	$210

Consolidated_Statements_of_Cas1

Consolidated Statements of Cash Flows (Parenthetical)	12 Months Ended
	Dec. 31, 2013
Interest rate stated on senior notes	7.00%
Senior notes due date	1-May-16

Organization_and_Summary_of_Si

Organization and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2013
Organization and Summary of Significant Accounting Policies	'
	Note 1. Organization and Summary of Significant Accounting Policies
	Organization
	The accompanying Consolidated Financial Statements, consisting of the accounts of The Navigators Group, Inc., a Delaware holding company established in 1982, and its wholly-owned subsidiaries, are prepared on the basis of U.S. generally accepted accounting principles (“GAAP” or “U.S. GAAP”). The terms “we”, “us”, “our” and “the Company” as used herein are used to mean The Navigators Group, Inc. and its wholly-owned subsidiaries, unless the context otherwise requires. The terms “Parent” or “Parent Company” are used to mean The Navigators Group, Inc. without its subsidiaries. All significant intercompany transactions and balances have been eliminated.
	We are an international insurance company focusing on specialty products within the overall property and casualty insurance market. Our largest product line and most long-standing area of specialization is ocean marine insurance. We have also developed other specialty insurance lines such as commercial primary and excess liability as well as specialty niches in professional liability, and have expanded our specialty reinsurance business since launching Navigators Re in the fourth quarter of 2010.
	Our revenue is primarily comprised of premiums and investment income. We derive our premiums primarily from business written by wholly-owned underwriting management companies which produce, manage and underwrite insurance and reinsurance for us. Our products are distributed through multiple channels, utilizing global, national and regional retail and wholesale insurance brokers.
	We conduct operations through our Insurance Companies and our Lloyd’s Operations underwriting segments. The Insurance Companies segment consists of Navigators Insurance Company, which includes a United Kingdom Branch (the “U.K. Branch”), and Navigators Specialty Insurance Company, which underwrites specialty and professional liability insurance on an excess and surplus lines basis. All of the insurance business written by Navigators Specialty Insurance Company is fully reinsured by Navigators Insurance Company pursuant to a 100% quota share reinsurance agreement. The insurance and reinsurance business written by our Insurance Companies is underwritten through our wholly-owned underwriting management Companies, Navigators Management Company, Inc. (“NMC”) and Navigators Management (UK) Ltd. (“NMUK”).
	Our Lloyd’s Operations segment includes Navigators Underwriting Agency Ltd. (“NUAL”), a Lloyd’s of London (“Lloyd’s”) underwriting agency which manages Lloyd’s Syndicate 1221 (“Syndicate 1221”). Our Lloyd’s Operations primarily underwrite marine and related lines of business along with offshore energy, construction coverages for onshore energy business and professional liability insurance at Lloyd’s through Syndicate 1221. We controlled 100% of Syndicate 1221’s stamp capacity for the 2013, 2012 and 2011 underwriting years through our wholly-owned subsidiary, Navigators Corporate Underwriters Ltd., which is referred to as a corporate name in the Lloyd’s market. We have also established underwriting agencies in Antwerp, Belgium, Stockholm, Sweden and Copenhagen, Denmark, which underwrite risks pursuant to binding authorities with NUAL into Syndicate 1221. For financial information by segment, refer to Note 3, Segment Information, to the Consolidated Financial Statements.
	Significant Accounting Policies
	Cash
	Cash includes cash on hand and demand deposits with banks, excluding such amounts held by Syndicate 1221 included as Funds at Lloyd’s.
	Investments
	As of December 31, 2013 and 2012, all fixed maturity and equity securities held by the Company were carried at fair value and classified as available-for-sale. Available-for-sale securities are debt and equity securities not classified as either held-to-maturity securities or trading securities and are reported at fair value, with unrealized gains and losses excluded from earnings and reported in accumulated other comprehensive income (“AOCI”) as a separate component of stockholders’ equity. Fixed maturity securities include bonds, mortgage-backed and asset-backed securities. Equity securities consist of common stock.
	Short-term investments are carried at cost, which approximates fair value. Short-term investments mature within one year from the purchase date.
	All prices for our fixed maturities, equity securities and short-term investments valued as Level 1, Level 2 or Level 3 in the fair value hierarchy, as defined in the Financial Accounts Standards Board (“FASB”) Accounting Standards Codification 820 (“ASC 820”), Fair Value Measurements, are received from independent pricing services utilized by one of our outside investment managers whom we employ to assist us with investment accounting services. This manager utilizes a pricing committee which approves the use of one or more independent pricing service vendors. The pricing committee consists of five or more members of the investment management firm, one from senior management and one from the accounting group with the remainder from the asset class specialists and client strategists. The pricing source of each security is determined in accordance with the pricing source procedures approved by the pricing committee. The investment manager uses supporting documentation received from the independent pricing service vendor detailing the inputs, models and processes used in the independent pricing service vendors’ evaluation process to determine the appropriate fair value hierarchy. Any pricing where the input is believed to be unobservable is deemed to be a Level 3 price. Management has reviewed this process by which the manager determines the prices and has obtained alternative pricing to validate a sample of the prices and assess their reasonableness.
	Premiums and discounts on fixed maturity securities are amortized into interest income over the life of the security under the interest method. For mortgage-backed and asset-backed securities, anticipated prepayments and expected maturities are utilized in applying the interest rate method to our mortgage-backed and asset-backed securities. An effective yield is calculated based on projected principal cash flows at the time of original purchase. The effective yield is used to amortize the purchase price of the security over the security’s expected life. Book values are adjusted to reflect the amortization of premium or accretion of discount on a monthly basis. The projected principal cash flows are based on certain prepayment assumptions which are generated using a prepayment model. The prepayment model uses a number of factors to estimate prepayment activity including the current levels of interest rates (refinancing incentive), time of year (seasonality), economic activity (including housing turnover) and term and age of the underlying collateral (burnout, seasoning). Prepayment assumptions associated with the mortgage-backed and asset-backed securities are reviewed on a periodic basis. When changes in prepayment assumptions are deemed necessary as the result of actual prepayments differing from anticipated prepayments, securities are revalued based upon the new prepayment assumptions utilizing the retrospective adjustment method, whereby the effective yield is recalculated to reflect actual payments to date and anticipated future payments. The investment in such securities is adjusted to the amount that would have existed had the new effective yield been applied since the acquisition of the security. Such adjustments, if any, are included in net investment income for the current period being reported.
	Realized gains and losses on sales of investments are recognized when the related trades are executed and are determined on the basis of the specific identification method.
	Impairment of Invested Assets
	Management regularly reviews our fixed maturity and equity securities portfolios to evaluate the necessity of recording impairment losses for other-than-temporary declines in the fair value of securities.
	For fixed maturity securities, we consider our intent to sell a security and whether it is more likely than not that we will be required to sell a security before the anticipated recovery as part of the process of evaluating whether a security’s unrealized loss represents an other-than-temporary decline. For fixed maturity securities that have a fair value below amortized cost and that we intend to sell or for which it is more likely than not that we would be required to sell, an other than temporary impairment (“OTTI”) loss is recognized in earnings by writing such security down to fair value. For fixed maturity securities we do not intend to sell or for which it is more likely that not we would not be required to sell, a decline in value below amortized cost is only recognized to the extent the present value of future cash flows expected to be collected is less than the amortized cost of the security. Such shortfall in the present value future cash flows is considered the credit loss and is recognized as an OTTI loss in earnings, with the non-credit portion of the impairment (i.e. the difference between the present value of future cash flows and fair value of the security) recognized as OTTI losses in other comprehensive income (“OCI”).
	In evaluating OTTI of equity securities, we consider our intent to hold the securities as part of the process of evaluating whether a decline in fair value below cost represents an other than temporary decline in value. For equity securities in an unrealized loss position that we do not intent to hold or that we do not expect to recover their value within a reasonable period of time, an OTTI loss is recognized in earnings by writing such security down to the fair value.
	Syndicate 1221
	Syndicate 1221 reports the amount of premiums, claims, and expenses recorded in an underwriting account for a particular year over a three year period. Traditionally, three years has been necessary to report substantially all premiums associated with an underwriting year and to report most of the related claims, although claims may remain unsettled after the underwriting year is closed. Syndicate 1221 typically closes an underwriting year by reinsuring outstanding claims in that underwriting year with the next underwriting year. Only profits from closed underwriting years of account are distributed to NCUL. Profits from open underwriting years of account are not available and therefore not distributed to NCUL until the end of the three year period.
	The Company’s financial statements include all of the assets, liabilities, revenues and expenses of Syndicate1221. Adjustments are recorded to recognize underwriting results as incurred in the specific year and not over a three year period. Syndicate 1221 is not a separate legal entity. Refer to Note 10, Lloyd’s Syndicate 1221, for additional information.
	Translation of Foreign Currencies
	Functional currency assets and liabilities are translated into U.S. dollars using period end rates of exchange and the related translation adjustments are recorded as a separate component of AOCI. Statement of income amounts expressed in functional currencies are translated using average exchange rates. Realized gains and losses resulting from foreign currency transactions are recorded in Other income (expense) in our Consolidated Statements of Income.
	Premium Revenues
	Written premium is recorded based on the insurance policies that have been reported to us and the policies that have been written by agents but not yet reported to us. We must estimate the amount of written premium not yet reported based on judgments relative to current and historical trends of the business being written. Such estimates are regularly reviewed and updated and any resulting adjustments are included in the current year’s results. An unearned premium reserve is established to reflect the unexpired portion of each policy at the financial reporting date.
	Substantially all of our business is placed through agents and brokers. We record estimates for both unreported direct and assumed premiums. We also record the ceded portion of the estimated gross written premium and related acquisition costs. The earned gross, ceded and net premiums are calculated based on our earning methodology which is generally pro-rata over the policy period or over the period of risk if the period of risk differs significantly from the contract period.
	A portion of our premium is estimated for unreported premium, mostly for the Marine business written by our U.K. Branch and Lloyd’s Operations as well as the Accident & Health and Latin American & Caribbean property casualty and surety reinsurance business written by NavRe. Such premium estimates are generally based on submission data received from brokers and agents and recorded when the insurance policy or reinsurance contract is written or bound. The estimates are regularly reviewed and updated taking into account the premium received to date versus the estimate and the age of the estimate. To the extent that the actual premium varies from the estimates, the difference, along with the related loss reserves and underwriting expenses, is recorded in current operations.
	Reinsurance Ceded
	In the normal course of business, reinsurance is purchased by us from insurers or reinsurers to reduce the amount of loss arising from claims. In order to determine the proper accounting for the reinsurance, management analyzes the reinsurance agreements to determine whether the reinsurance should be classified as prospective or retroactive based upon the terms of the reinsurance agreement and whether the reinsurer has assumed significant insurance risk to the extent that the reinsurer may realize a significant loss from the transaction.
	Prospective reinsurance is reinsurance in which an assuming company agrees to reimburse the ceding company for losses that may be incurred as a result of future insurable events covered under contracts subject to the reinsurance. Retroactive reinsurance is reinsurance in which an assuming company agrees to reimburse a ceding company for liabilities incurred as a result of past insurable events covered under contracts subject to the reinsurance.
	Ceded reinsurance premiums and any related ceding commission and ceded losses are reflected as reductions of the respective income or expense accounts over the terms of the reinsurance contracts. Prepaid reinsurance premiums represent the portion of premiums ceded to reinsurers applicable to the unexpired terms of the reinsurance contracts in force. Reinsurance reinstatement premiums are recognized in the same period as the loss event that gave rise to the reinstatement premiums. Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability associated with the reinsured policy. Unearned premiums ceded and estimates of amounts recoverable from reinsurers on paid and unpaid losses are reflected as assets. Provisions are made for estimated unrecoverable reinsurance.
	Deferred Policy Acquisition Costs
	Costs of acquiring business which vary with and are directly related to the production of new or renewal business are deferred and amortized ratably over the period that the related premiums are recognized as revenue. Such costs primarily include commission expense, other underwriting expenses and premium taxes are limited to the incremental direct costs related to the successful acquisition of new or renewal business. The method of computing deferred policy acquisition costs limits the deferral to their estimated net realizable value based on the related unearned premiums and takes into account anticipated losses and loss adjustment expenses, commission expense and operating expenses based on historical and current experience as well as anticipated investment income.
	Reserves for Losses and Loss Adjustment Expenses
	Unpaid losses and loss adjustment expenses are determined on an individual basis for claims reported on direct business for insureds, from reports received from ceding insurers for insurance assumed from such insurers and on estimates based on Company and industry experience for IBNR claims and loss adjustment expenses. Indicated IBNR loss reserves are calculated by our actuaries using several standard actuarial methodologies, including the paid and incurred loss development and the paid and incurred Bornheutter-Ferguson loss methods. Additional analyses, such as frequency/severity analyses, are performed for certain books of business. The provision for unpaid losses and loss adjustment expenses has been established to cover the estimated unpaid cost of claims incurred. Such estimates are regularly reviewed and updated and any resulting adjustments are included in the current year’s results. Management believes that the liability it has recognized for unpaid losses and loss adjustment expenses is a reasonable estimate of the ultimate unpaid claims incurred, however, such provisions are necessarily based on estimates and, accordingly, no representation is made that the ultimate liability will not differ materially from the amounts recorded in the accompanying consolidated financial statements. Losses and loss adjustment expenses are recorded on an undiscounted basis.
	Earnings per Share
	Basic earnings per share (“EPS”) is computed by dividing net income by the weighted average number of common shares outstanding for the period. Diluted earnings per share reflects the basic earnings per share adjusted for the potential dilution that would occur if all issued stock options were exercised and all stock grants were fully vested.
	Depreciation and Amortization
	Depreciation of furniture and fixtures, electronic data processing equipment and computer software is provided over the estimated useful lives of the respective assets, ranging from three to seven years, using the straight-line method. Amortization of leasehold improvements is provided over the shorter of the useful lives of those improvements or the contractual terms of the leases using the straight-line method.
	Goodwill and Other Intangible Assets
	Goodwill represents the excess of cost of acquiring a business enterprise over the fair value of the net assets acquired. The Company has also recorded indefinite lived intangible assets related to the acquisition of the remaining non-controlled stamp capacity of Lloyd’s Syndicate 1221. Goodwill and indefinite lived intangible assets are reported at carrying value and are tested for impairment at least annually. Goodwill and indefinite lived intangible assets are considered impaired if the estimated fair value is less than its carrying value. Any impairment loss is measured as the difference between the implied fair value and the carrying value. This Company did not recognize an impairment on goodwill or the indefinite lived intangible assets for any of the years ended December 31, 2013, 2012 and 2011.
	As of December 31, 2013, the carrying value of goodwill and indefinite lived intangible assets was $7.2 million, consisting of $2.5 million and $2.4 million of goodwill assigned to NMC and our Lloyd’s Operations, respectively, and $2.3 million of indefinite lived intangible assets assigned to our Lloyd’s Operations. As of December 31, 2012, the carrying value of goodwill and indefinite lived intangible assets was $7.1 million, consisting of $2.5 million and $2.4 million of goodwill assigned to NMC and our Lloyd’s Operations, respectively, and $2.2 million of indefinite lived intangible assets assigned to our Lloyd’s Operations. Changes in the carrying value of the goodwill and indefinite lived intangible assets are due to fluctuations in currency exchange rates between the U.S. dollar and the British pound.
	Income Taxes
	We apply the asset and liability method of accounting for income taxes. Under the asset and liability method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax basis. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. In assessing the realization of deferred tax assets, management considers whether it is more likely than not that the deferred tax assets will be realized.
	Use of Estimates
	The preparation of financial statements in conformity with GAAP requires the use of estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the period. The accounting estimates that are viewed by management as critical are those in connection with reserves for losses and loss adjustment expenses, reinsurance recoverables, written and unearned premiums, deferred tax assets, and impairment of invested assets.
	Recently Adopted Accounting Pronouncements
	In February 2013, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2013 -02 amending Codification topic 220 – Comprehensive Income. The amendments do not change the current requirements for reporting net income or other comprehensive income in the financial statements. The guidance requires an entity to present information about significant items reclassified out of AOCI by component and for items reclassified out of AOCI and into net income, the entity must disclose the effect of such items on the affected net income line item. The Company adopted this standard effective January 1, 2013, and presents this information on the consolidated statements of comprehensive income. Adoption of this standard did not have any impact on the Company’s consolidated balance sheets, results of operations or cash flows.
	In July 2012, the FASB issued ASU 2012-02 amending Codification topic 350 – Intangibles – Goodwill and Other. The amendment is intended to reduce cost and complexity, in addition to enhancing consistency of impairment testing guidance among long-lived asset categories by permitting entities to assess qualitative factors to determine whether it is necessary to calculate an asset’s fair value when testing an indefinite-lived asset for impairment. The amendment is effective for fiscal years beginning after September 15, 2012. The Company adopted this standard effective January 1, 2013. Adoption of this standard did not have any impact on the Company’s consolidated financial position, results of operating or cash flows.

Earnings_Per_Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2013
Earnings Per Share	'
	Note 2. Earnings Per Share
	The following is a reconciliation of the basic and diluted EPS computations for the years ended December 31, 2013, 2012 and 2011:
		Year Ended December 31,
	In thousands, except share and per share amounts	2013		2012		2011
	Net income	$	63,466	$	63,762	$	25,597
	Basic weighted average shares		14,133,925		14,052,311		14,980,429
	Effect of common stock equivalents:
	Assumed exercise of stock options and vesting of stock grants		211,628		275,509		202,856
	Diluted weighted average shares		14,345,553		14,327,820		15,183,285
	Net income per common share:
	Basic	$	4.49	$	4.54	$	1.71
	Diluted	$	4.42	$	4.45	$	1.69

Segment_Information

Segment Information	12 Months Ended
	Dec. 31, 2013
Segment Information	'
	Note 3. Segment Information
	The Company classifies its business into two underwriting segments consisting of the Insurance Companies segment (“Insurance Companies”) and the Lloyd’s Operations segment (“Lloyd’s Operations”), which are separately managed by division and aggregated into each underwriting segment, and a Corporate segment (“Corporate”). Segment data for each of the two underwriting segments include allocations of the operating expenses of the wholly-owned underwriting management companies and the Parent Company’s operating expenses and related income tax amounts. The Corporate segment consists of the Parent Company’s investment income, interest expense and the related tax effect.
	The Company evaluates the performance of each underwriting segment based on its underwriting and GAAP results. The Insurance Companies’ and the Lloyd’s Operations’ results are measured by taking into account net earned premiums, net losses and loss adjustment expenses (“LAE”), commission expenses, other operating expenses and other income (expense). Each segment maintains its own investments on which it earns income and realizes capital gains or losses. The Company’s underwriting performance is evaluated separately from the performance of its investment portfolios.
	The Insurance Companies consist of Navigators Insurance Company, including its U.K. Branch, and its wholly-owned subsidiary, Navigators Specialty Insurance Company (“Navigators Specialty”). They are primarily engaged in underwriting marine insurance and related lines of business, specialty insurance lines of business, including contractors general liability insurance, commercial umbrella and primary and excess casualty businesses, specialty assumed reinsurance business, and professional liability insurance. Navigators Specialty underwrites specialty and professional liability insurance on an excess and surplus lines basis. Navigators Specialty is 100% reinsured by Navigators Insurance Company.
	The Lloyd’s Operations primarily underwrite marine and related lines of business along with offshore energy, professional liability insurance and construction coverages for onshore energy business at Lloyd’s through Syndicate 1221. The Lloyd’s Operations includes NUAL, a Lloyd’s underwriting agency which manages Syndicate 1221.
	Navigators Management Company, Inc. (“NMC”) is a wholly-owned underwriting management company that produces, manages and underwrites insurance and reinsurance, and provides corporate services for the Company. The operating results for NMC are allocated to both the Insurance Companies and Lloyd’s Operations as appropriate.
	The Insurance Companies’ and the Lloyd’s Operations’ underwriting results are measured based on underwriting profit or loss and the related combined ratio, which are both non-GAAP measures of underwriting profitability. Underwriting profit or loss is calculated from net earned premiums, less the sum of net losses and LAE, commission expenses, other operating expenses and other income (expense). The combined ratio is derived by dividing the sum of net losses and LAE, commission expenses, other operating expenses and other income (expense) by net earned premiums. A combined ratio of less than 100% indicates an underwriting profit and greater than 100% indicates an underwriting loss.
	Financial data by segment for the years ended December 31, 2013, 2012, and 2011 were as follows:
			Year Ended December 31, 2013
			Insurance			Lloyd’s
	In thousands		Companies			Operations			Corporate(1)			Total
	Gross written premiums		$	1,002,275		$	368,242		$	—		$	1,370,517
	Net written premiums			680,008			207,914			—			887,922
	Net earned premiums			639,338			202,601			—			841,939
	Net losses and loss adjustment expenses			(415,413	)		(103,548	)		—			(518,961	)
	Commission expenses			(81,132	)		(34,710	)		2,348			(113,494	)
	Other operating expenses			(119,920	)		(44,514	)		—			(164,434	)
	Other income (expense)			2,764			(1,588	)		(2,348	)		(1,172	)
	Underwriting profit (loss)		$	25,637		$	18,241		$	—		$	43,878
	Net investment income			49,083			7,160			8			56,251
	Net realized gains (losses)			20,600			(58	)		4			20,546
	Call premium on Senior Notes			—			—			(17,895	)		(17,895	)
	Interest expense			—			—			(10,507	)		(10,507	)
	Income (loss) before income taxes		$	95,320		$	25,343		$	(28,390	)	$	92,273
	Income tax expense (benefit)			29,965			8,728			(9,886	)		28,807
	Net income (loss)		$	65,355		$	16,615		$	(18,504	)	$	63,466
	Identifiable assets		$	3,077,437		$	930,567		$	161,448		$	4,169,452
	Losses and loss adjustment expenses ratio			65	%		51.1	%					61.6	%
	Commission expense ratio			12.7	%		17.1	%					13.5	%
	Other operating expense ratio (2)			18.3	%		22.8	%					19.7	%
	Combined ratio			96	%		91	%					94.8	%
	-1	- Includes Corporate segment intercompany eliminations.
	-2	- Includes Other operating expenses and Other income.
			Year Ended December 31, 2012
			Insurance			Lloyd’s
	In thousands		Companies			Operations			Corporate(1)			Total
	Gross written premiums		$	921,325		$	365,140		$	—		$	1,286,465
	Net written premiums			622,956			210,699			—			833,655
	Net earned premiums			571,439			210,525			—			781,964
	Net losses and loss adjustment expenses			(417,082	)		(80,351	)		—			(497,433	)
	Commission expenses			(81,370	)		(42,449	)		2,349			(121,470	)
	Other operating expenses			(113,625	)		(45,454	)		—			(159,079	)
	Other income (expense)			3,790			47			(2,349	)		1,488
	Underwriting profit (loss)		$	(36,848	)	$	42,318		$	—		$	5,470
	Net investment income			46,549			7,551			148			54,248
	Net realized gains (losses)			36,468			3,555			193			40,216
	Interest expense			—			—			(8,198	)		(8,198	)
	Income (loss) before income taxes		$	46,169		$	53,424		$	(7,857	)	$	91,736
	Income tax expense (benefit)			12,686			18,620			(3,332	)		27,974
	Net income (loss)		$	33,483		$	34,804		$	(4,525	)	$	63,762
	Identifiable assets		$	3,036,489		$	928,448		$	42,733		$	4,007,670
	Losses and loss adjustment expenses ratio			73	%		38.2	%					63.6	%
	Commission expense ratio			14.2	%		20.2	%					15.5	%
	Other operating expense ratio (2)			19.2	%		21.5	%					20.2	%
	Combined ratio			106.4	%		79.9	%					99.3	%
	-1	- Includes Corporate segment intercompany eliminations.
	-2	- Includes Other operating expenses and Other income.
			Year Ended December 31, 2011
			Insurance			Lloyd’s
	In thousands		Companies			Operations			Corporate(1)			Total
	Gross written premiums		$	788,419		$	319,797		$	—		$	1,108,216
	Net written premiums			542,391			211,407			—			753,798
	Net earned premiums			472,463			219,182			—			691,645
Net losses and loss adjustment expenses			(341,625	)		(135,372	)		—			(476,997	)
Commission expenses			(64,165	)		(48,341	)		2,069			(110,437	)
Other operating expenses			(101,517	)		(36,512	)		—			(138,029	)
Other income (expense)			3,955			(657	)		(2,069	)		1,229
Underwriting profit (loss)		$	(30,889	)	$	(1,700	)	$	—		$	(32,589	)
Net investment income			54,164			8,955			381			63,500
Net realized gains (losses)			12,151			(2,354	)		214			10,011
Interest expense			—			—			(8,188	)		(8,188	)
Income (loss) before income taxes		$	35,426		$	4,901		$	(7,593	)	$	32,734
Income tax expense (benefit)			8,271			1,523			(2,657	)		7,137
Net income (loss)		$	27,155		$	3,378		$	(4,936	)	$	25,597
Identifiable assets		$	2,768,930		$	865,230		$	35,847		$	3,670,007
Losses and loss adjustment expenses ratio			72.3	%		61.8	%					69	%
Commission expense ratio			13.6	%		22.1	%					16	%
Other operating expense ratio (2)			20.6	%		16.9	%					19.7	%
Combined ratio			106.5	%		100.8	%					104.7	%
-1	- Includes Corporate segment intercompany eliminations.
-2	- Includes Other operating expenses and Other income.
The following tables provide additional financial data by segment for the years ended December 31, 2013, 2012 and 2011:
		Year Ended December 31, 2013
		Insurance			Lloyd’s
In thousands		Companies			Operations			Total
Gross written premiums:
Marine		$	171,822		$	181,046		$	352,868
Property casualty			700,087			129,522			829,609
Professional liability			130,366			57,674			188,040
Total		$	1,002,275		$	368,242		$	1,370,517
Net written premiums:
Marine		$	119,837		$	134,627		$	254,464
Property casualty			462,942			42,334			505,276
Professional liability			97,229			30,953			128,182
Total		$	680,008		$	207,914		$	887,922
Net earned premiums:
Marine		$	129,276		$	138,690		$	267,966
Property casualty			409,480			37,722			447,202
Professional liability			100,582			26,189			126,771
Total		$	639,338		$	202,601		$	841,939
		Year Ended December 31, 2012
		Insurance			Lloyd’s
In thousands		Companies			Operations			Total
Gross written premiums:
Marine		$	200,095		$	194,423		$	394,518
Property casualty			590,741			127,028			717,769
Professional liability			130,489			43,689			174,178
Total		$	921,325		$	365,140		$	1,286,465
Net written premiums:
Marine		$	133,210		$	143,600		$	276,810
Property casualty			390,168			43,824			433,992
Professional liability			99,578			23,275			122,853
Total		$	622,956		$	210,699		$	833,655
Net earned premiums:
Marine		$	142,181		$	136,898		$	279,079
Property casualty			332,782			52,951			385,733
Professional liability			96,476			20,676			117,152
Total		$	571,439		$	210,525		$	781,964
		Year Ended December 31, 2011
		Insurance			Lloyd’s
In thousands		Companies			Operations			Total
Gross written premiums:
Marine		$	228,500		$	167,562		$	396,062
Property casualty			445,287			115,138			560,425
Professional liability			114,632			37,097			151,729
Total		$	788,419		$	319,797		$	1,108,216
Net written premiums:
Marine		$	170,642		$	137,206		$	307,848
Property casualty			293,758			56,249			350,007
Professional liability			77,991			17,952			95,943
Total		$	542,391		$	211,407		$	753,798
Net earned premiums:
Marine		$	169,018		$	145,659		$	314,677
Property casualty			231,297			55,903			287,200
Professional liability			72,148			17,620			89,768
Total		$	472,463		$	219,182		$	691,645
The Insurance Companies net earned premiums include $44.6 million, $63.9 million and $88.3 million of net earned premiums from the U.K. Branch for 2013, 2012 and 2011, respectively.

Investments

Investments	12 Months Ended
	Dec. 31, 2013
Investments	'
	Note 4. Investments
	The following tables set forth the Company’s cash and investments as of December 31, 2013 and 2012. The tables below include OTTI securities recognized within AOCI.
		December 31, 2013
						Gross				Gross
						Unrealized				Unrealized			Amortized
	In thousands	Fair Value				Gains				Losses			Cost
	Fixed maturities:
	U.S. Treasury bonds, agency bonds and foreign government bonds	$	441,685			$	2,854			$	(8,855	)	$	447,686
	States, municipalities and political subdivisions		460,422				9,298				(13,651	)		464,775
	Mortgage-backed and asset-backed securities:
	Agency mortgage-backed securities		301,274				6,779				(6,016	)		300,511
	Residential mortgage obligations		41,755				1,212				(161	)		40,704
	Asset-backed securities		125,133				653				(480	)		124,960
	Commercial mortgage-backed securities		172,750				7,656				(374	)		165,468
	Subtotal	$	640,912			$	16,300			$	(7,031	)	$	631,643
	Corporate bonds		504,854				15,402				(3,443	)		492,895
	Total fixed maturities	$	2,047,873			$	43,854			$	(32,980	)	$	2,036,999
	Equity securities—common stocks		143,954				25,700				(550	)		118,804
	Short-term investments		296,250				—				—			296,250
	Cash		86,509				—				—			86,509
	Total	$	2,574,586			$	69,554			$	(33,530	)	$	2,538,562
		December 31, 2012
						Gross				Gross
						Unrealized				Unrealized			Amortized
	In thousands	Fair Value				Gains				Losses			Cost
	Fixed maturities:
	U.S. Treasury bonds, agency bonds and foreign government bonds	$	649,692			$	8,654			$	(36	)	$	641,074
	States, municipalities and political subdivisions		322,947				18,712				(380	)		304,615
	Mortgage-backed and asset-backed securities:
	Agency mortgage-backed securities		384,445				13,652				(204	)		370,997
	Residential mortgage obligations		38,692				1,053				(549	)		38,188
	Asset-backed securities		50,382				1,133				(49	)		49,298
	Commercial mortgage-backed securities		204,821				17,996				(18	)		186,843
	Subtotal	$	678,340			$	33,834			$	(820	)	$	645,326
	Corporate bonds		470,854				27,129				(25	)		443,750
	Total fixed maturities	$	2,121,833			$	88,329			$	(1,261	)	$	2,034,765
	Equity securities—common stocks		101,297				16,919				(626	)		85,004
	Short-term investments		153,788				—				—			153,788
	Cash		45,336				—				—			45,336
	Total	$	2,422,254			$	105,248			$	(1,887	)	$	2,318,893
	As of December 31, 2013 and 2012, debt securities for which non-credit OTTI was previously recognized and included in other comprehensive income are now in an unrealized gains position of $0.5 million and $20 thousand, respectively.
	The fair value of the Company’s investment portfolio may fluctuate significantly in response to various factors such as changes in interest rates, investment quality ratings, equity prices, foreign exchange rates and credit spreads. The Company does not have the intent to sell nor is it more likely than not that it will have to sell debt securities in unrealized loss positions that are not other-than-temporarily impaired before recovery. For structured securities, default probability and severity assumptions differ based on property type, vintage and the stress of the collateral. We do not intend to sell any of these securities and it is more likely than not that we will not be required to sell these securities before the recovery of the amortized cost basis. For equity securities, the Company also considers its intent to hold securities as part of the process of evaluating whether a decline in fair value represents an other-than-temporary decline in value. The Company may realize investment losses to the extent its liquidity needs require the disposition of fixed maturity securities in unfavorable interest rate, liquidity or credit spread environments. Significant changes in the factors the Company considers when evaluating investments for impairment losses could result in a significant change in impairment losses reported in the consolidated financial statements.
	The contractual maturity dates for fixed maturity securities categorized by the number of years until maturity as of December 31, 2013 are shown in the following table:
		December 31, 2013
						Amortized
	In thousands	Fair Value				Cost
	Due in one year or less	$	85,240			$	84,691
	Due after one year through five years		627,515				615,267
	Due after five years through ten years		443,197				446,918
	Due after ten years		251,009				258,480
	Mortgage- and asset-backed securities		640,912				631,643
	Total	$	2,047,873			$	2,036,999
	Expected maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties. Due to the periodic repayment of principal, the mortgage-backed and asset-backed securities are estimated to have an effective maturity of approximately 4.5 years.
	The following table shows the amount and percentage of the Company’s fixed maturities as of December 31, 2013 by Standard & Poor’s (“S&P”) credit rating or, if an S&P rating is not available, the equivalent Moody’s Investor Services (“Moody’s”) rating. The table includes fixed maturities at fair value, and the total rating is the weighted average quality rating.
		December 31, 2013
								Percent
	In thousands	Rating		Fair Value				of Total
	Rating description:
	Extremely strong	AAA		$	348,908				17	%
	Very strong	AA			1,047,155				51	%
	Strong	A			452,455				22	%
	Adequate	BBB			184,302				9	%
	Speculative	BB & Below			11,500				1	%
Not rated	NR			3,553				0	%
Total	AA		$	2,047,873				100	%
The following table summarizes all securities in a gross unrealized loss position as of December 31, 2013 and 2012, showing the aggregate fair value and gross unrealized loss by the length of time those securities had continuously been in a gross unrealized loss position as well as the relevant number of securities.
	December 31, 2013											December 31, 2012
									Gross									Gross
	Number of								Unrealized			Number of						Unrealized
In thousands, except # of securities	Securities				Fair Value				Loss			Securities			Fair Value			Loss
Fixed maturities:
U.S. Treasury bonds, agency bonds, and foreign government bonds
0-6 months		27			$	136,360			$	1,096			8		$	23,760		$	22
7-12 months		26				149,370				7,759			3			14,118			11
> 12 months		—				—				—			1			4,652			3
Subtotal		53			$	285,730			$	8,855			12		$	42,530		$	36
States, municipalities and political subdivisions
0-6 months		28			$	40,132			$	297			10		$	21,299		$	325
7-12 months		104				205,152				12,100			—			—			—
> 12 months		6				12,357				1,254			4			2,908			55
Subtotal		138			$	257,641			$	13,651			14		$	24,207		$	380
Agency mortgage-backed securities
0-6 months		39			$	39,458			$	434			10		$	62,516		$	174
7-12 months		64				77,860				3,768			2			1,671			30
> 12 months		9				22,784				1,814			—			—			—
Subtotal		112			$	140,102			$	6,016			12		$	64,187		$	204
Residential mortgage obligations
0-6 months		3			$	431			$	2			6		$	1,825		$	22
7-12 months		7				950				29			—			—			—
> 12 months		15				2,467				130			35			7,252			527
Subtotal		25			$	3,848			$	161			41		$	9,077		$	549
Asset-backed securities
0-6 months		14			$	75,887			$	479			—		$	—		$	—
7-12 months		1				203				1			—			—			—
> 12 months		—				—				—			2			2,369			49
Subtotal		15			$	76,090			$	480			2		$	2,369		$	49
Commercial mortgage-backed securities
0-6 months		4			$	6,712			$	31			7		$	2,639		$	7
7-12 months		2				15,098				322			—			—			—
> 12 months		4				774				21			5			845			11
Subtotal		10			$	22,584			$	374			12		$	3,484		$	18
Corporate bonds
0-6 months		34			$	93,591			$	717			2		$	3,528		$	6
7-12 months		18				55,021				2,726			—			—			—
> 12 months		—				—				—			4			6,689			19
Subtotal		52			$	148,612			$	3,443			6		$	10,217		$	25
Total fixed maturities		405			$	934,607			$	32,980			99		$	156,071		$	1,261
Equity securities—common stocks
0-6 months		5			$	7,387			$	422			13		$	23,345		$	522
7-12 months		2				3,538				128			1			1,943			104
> 12 months		—				—				—			—			—			—
Total equity securities		7			$	10,925			$	550			14		$	25,288		$	626
As of December 31, 2013 and 2012, the largest unrealized loss by a non-government backed issuer in the investment portfolio was $1.1 million and $0.2 million, respectively.
The company analyzes impaired securities quarterly to determine if any are other-than-temporary. The above securities with unrealized losses have been determined to be temporarily impaired based on our evaluation.
For debt securities, when assessing whether the amortized cost basis of the security will be recovered, the Company compares the present value of cash flows expected to be collected in relation to the current book value. Any shortfalls of the present value of the cash flows expected to be collected to the amortized cost basis is considered the credit loss portion of OTTI losses and is recognized in earnings. All non-credit losses are recognized as changes in OTTI losses within OCI.
To determine whether the unrealized loss on structured securities is other-than-temporary, the Company analyzes the projections provided by its investment managers with respect to an expected principal loss under a range of scenarios and utilizes the most likely outcomes. The analysis relies on actual collateral performance measures such as default rate, prepayment rate and loss severity. These assumptions are applied throughout the remaining term of the deal, incorporating the transaction structure and priority of payments, to generate loss adjusted cash flows. Results of the analysis will indicate whether the security is expected ultimately to incur a loss or whether there is a material impact on yield due to either a projected loss or a change in cash flow timing. A break even default rate is also calculated. A comparison of the break even default rate to the actual default rate provides an indication of the level of cushion or coverage to the first dollar principal loss. The analysis applies the stated assumptions throughout the remaining term of the transaction to forecast cash flows, which are then applied through the transaction structure to determine whether there is a loss to the security. For securities in which a tranche loss is present, and the net present value of loss adjusted cash flows is less than book value, impairment is recognized. The output data also includes a number of additional metrics such as average life remaining, original and current credit support, over 60 day delinquency and security rating.
The significant inputs used to measure the amount of credit loss recognized in earnings were actual delinquency rates, default probability assumptions, severity assumptions and prepayment assumptions. Projected losses are a function of both loss severity and probability of default. Default probability and severity assumptions differ based on property type, vintage and the stress of the collateral. The Company does not intend to sell any of these securities and it is more likely than not that it will not be required to sell these securities before the recovery of the amortized cost basis.
For equity securities, in general, the Company focuses its attention on those securities with a fair value less than 80% of their cost for six or more consecutive months. If warranted as the result of conditions relating to a particular security, the Company will focus on a significant decline in fair value regardless of the time period involved. Factors considered in evaluating potential impairment include, but are not limited to, the current fair value as compared to cost of the security, the length of time the investment has been below cost and by how much the investment is below cost. If an equity security is deemed to be other-than-temporarily impaired, the cost is written down to fair value with the loss recognized in earnings.
The Company’s ability to hold securities is supported by sufficient cash flow from its operations and from maturities within its investment portfolio in order to meet its claims payment and other disbursement obligations arising from its underwriting operations without selling such investments. With respect to securities where the decline in value is determined to be temporary and the security’s value is not written down, a subsequent decision may be made to sell that security and realize a loss. Subsequent decisions on security sales are made within the context of overall risk monitoring, changing information and market conditions.
As of December 31, 2013, there were no securities with a fair value that was less than 80% of amortized cost.
The table below summarizes the Company’s activity related to OTTI losses for the periods indicated:
	Year Ended December 31,
	2013								2012						2011
	Number of								Number of						Number of
In thousands, except # of securities	Securities				Amount				Securities			Amount			Securities			Amount
Total OTTI losses:
Corporate and other bonds		1			$	1,822				—		$	—			1		$	109
Commercial mortgage-backed securities		—				—				—			—			—			—
Residential mortgage-backed securities		—				—				1			55			19			2,616
Asset-backed securities		—				—				—			—			—			—
Equities		3				571				3			847			2			892
Total		4			$	2,393				4		$	902			22		$	3,617
Less: Portion of loss in accumulated other comprehensive income (loss):
Corporate and other bonds					$	—						$	—					$	—
Commercial mortgage-backed securities						—							—						—
Residential mortgage-backed securities						—							44						1,632
Asset-backed securities						—							—						—
Equities						—							—						—
Total					$	—						$	44					$	1,632
Impairment losses recognized in earnings:
Corporate and other bonds					$	1,822						$	—					$	109
Commercial mortgage-backed securities						—							—						—
Residential mortgage-backed securities						—							11						984
Asset-backed securities						—							—						—
Equities						571							847						892
Total					$	2,393						$	858					$	1,985
The following table summarizes the cumulative amounts related to the Company’s credit loss portion of the OTTI losses on debt securities for the years ended December 31, 2013, 2012 and 2011. The Company does not intend to sell and it is more likely than not that it will not be required to sell, the securities prior to recovery of the amortized cost basis for which the non-credit loss portion is included in OCI.
	Year Ended December 31,
In thousands	2013				2012				2011
Beginning balance	$	3,332			$	3,321			$	2,228
Additions for credit loss impairments recognized in the current period on securities not previously impaired		1,822								109
Additions for credit loss impairments recognized in the current period on securities previously impaired						11				984
Reductions for credit loss impairments previously recognized on securities sold during the period		—				—				—
Ending balance	$	5,154			$	3,332			$	3,321
The contractual maturity dates for fixed maturity securities categorized by the number of years until maturity, with a gross unrealized loss as of December 31, 2013 is presented in the following table:
	December 31, 2013
	Gross Unrealized Losses								Fair Value
					Percent							Percent
In thousands	Amount				of Total				Amount			of Total
Due in one year or less	$	1				0	%		$	7,687			1	%
Due after one year through five years		2,152				7	%			242,879			26	%
Due after five years through ten years		13,585				41	%			262,989			28	%
Due after ten years		10,211				31	%			178,428			19	%
Mortgage- and asset-backed securities		7,031				21	%			242,624			26	%
Total	$	32,980				100	%		$	934,607			100	%
The Company’s net investment income was derived from the following sources:
	Year Ended December 31,
In thousands	2013				2012				2011
Fixed maturities	$	53,898			$	58,995			$	65,060
Equity securities		4,835				3,945				5,071
Short-term investments		774				1,694				964
Total investment income		59,507				64,634				71,095
Investment expenses		(3,256	)			(10,386	)			(7,595	)
Net investment income	$	56,251			$	54,248			$	63,500
Investment expenses for the year ended December 31, 2012 and 2011 include $4.5 million and $4.7 million, respectively, for a total of $9.2 million, of interest expense related to the settlement of a dispute with Equitas over foregone interest on amounts that were due on certain reinsurance contracts. In the dispute Equitas alleged that we failed to make timely payments to them under certain reinsurance agreements in connection with subrogation recoveries received by the Company with respect to several catastrophe losses that occurred in the late 1980’s and early 1990’s. In addition, investment expenses for the year ended December 31, 2012 includes a $2.8 million investment performance fee.
The change in net unrealized gains and losses, inclusive of the change in the non-credit portion of OTTI losses, consisted of:
	Year Ended December 31,
In thousands	2013				2012				2011
Fixed maturities	$	(76,194	)		$	15,709			$	44,712
Equity securities		8,857				(5,989	)			(183	)
Gross unrealized gains (losses)		(67,337	)			9,720				44,529
Deferred income tax		(23,565	)			3,418				15,143
Change in net unrealized gains (losses), net	$	(43,772	)		$	6,302			$	29,386
Realized gains and losses, excluding net OTTI losses recognized in earnings, for the periods indicated were as follows:
	Year Ended December 31,
In thousands	2013				2012				2011
Fixed maturities:
Gains	$	8,539			$	28,789			$	11,678
Losses		(2,797	)			(1,915	)			(7,044	)
Fixed maturities, net	$	5,742			$	26,874			$	4,634
Equity securities:
Gains	$	17,955			$	14,673			$	9,319
Losses		(758	)			(473	)			(1,957	)
Equity securities, net	$	17,197			$	14,200			$	7,362
Net realized gains (losses)	$	22,939			$	41,074			$	11,996
The following tables present, for each of the fair value hierarchy levels as defined by the accounting guidance for fair value measurements and described below, the Company’s fixed maturities and equity securities by asset class that are measured at fair value on a recurring basis as of December 31, 2013 and 2012:
	December 31, 2013
In thousands	Level 1				Level 2				Level 3			Total
Fixed maturities:
U.S. Treasury bonds, agency bonds and foreign government bonds	$	242,379			$	199,306			$	—		$	441,685
States, municipalities and political subdivisions		—				460,422				—			460,422
Mortgage-backed and asset-backed securities:													—
Agency mortgage-backed securities		—				301,274				—			301,274
Residential mortgage obligations		—				41,755				—			41,755
Asset-backed securities		—				125,133				—			125,133
Commercial mortgage-backed securities		—				172,750				—			172,750
Subtotal	$	—			$	640,912			$	—		$	640,912
Corporate bonds		—				500,447				4,407			504,854
Total fixed maturities	$	242,379			$	1,801,087			$	4,407		$	2,047,873
Equity securities—common stocks		143,954				—				—			143,954
Total	$	386,333			$	1,801,087			$	4,407		$	2,191,827
	December 31, 2012
In thousands	Level 1				Level 2				Level 3			Total
Fixed maturities:
U.S. Treasury bonds, agency bonds and foreign government bonds	$	414,502			$	235,190			$	—		$	649,692
States, municipalities and political subdivisions		—				322,947				—			322,947
Mortgage-backed and asset-backed securities:													—
Agency mortgage-backed securities		—				384,445				—			384,445
Residential mortgage obligations		—				38,692				—			38,692
Asset-backed securities		—				50,382				—			50,382
Commercial mortgage-backed securities		—				204,821				—			204,821
Subtotal	$	—			$	678,340			$	—		$	678,340
Corporate bonds		—				470,854				—			470,854
Total fixed maturities	$	414,502			$	1,707,331			$	—		$	2,121,833
Equity securities—common stocks		101,297				—				—			101,297
Total	$	515,799			$	1,707,331			$	—		$	2,223,130
The fair value of financial instruments is determined based on the following fair value hierarchy:
Level 1 – Quoted prices for identical instruments in active markets. Examples are listed equity and fixed income securities traded on an exchange. U.S. Treasury securities are reported as level 1 and are valued based on unadjusted quoted prices for identical assets in active markets that the Company can access.
Level 2 – Quoted prices for similar instruments in active markets; quoted prices for identical or similar instruments in markets that are not active; and model-derived valuations in which all significant inputs and significant value drivers are observable in active markets. Examples are asset-backed and mortgage-backed securities that are similar to other asset-backed or mortgage-backed securities observed in the market. U.S. government agency securities are reported as level 2 and are valued using yields and spreads that are observable in active markets.
Level 3 – Valuations derived from valuation techniques in which one or more significant inputs or significant value drivers are unobservable. An example would be a private placement with minimal liquidity.
The Company did not have any significant transfers between Level 1 and 2 for the years ended December 31, 2013 and 2012.
The following tables present a reconciliation of the beginning and ending balances for all investments measured at fair value using Level 3 inputs for the years ended December 31, 2013 and 2011. As of December 31, 2012, the Company did not have any Level 3 assets.
	Year Ended December 31, 2013
					Realized				Unrealized											Transfers		Transfers
	Beginning				Gains				Gains											into		out of			Ending
In thousands	Balance				(Losses)				(Losses)			Purchases			Sales			Settlements		Level 3		Level 3			Balance
Assets:
Coporate Bond	$	—			$	—			$	(42	)	$	4,660		$	(211	)	$	—	$	—	$	—		$	4,407
Total assets	$	—			$	—			$	(42	)	$	4,660		$	(211	)	$	—	$	—	$	—		$	4,407
	Year Ended December 31, 2011
					Realized				Unrealized											Transfers		Transfers
	Beginning				Gains				Gains											into		out of			Ending
In thousands	Balance				(Losses)				(Losses)			Purchases			Sales			Settlements		Level 3		Level 3			Balance
Assets:
Commercial Mortgage Obligations	$	1,837			$	—			$	94		$	—		$	—		$	—	$	—	$	(1,931	)	$	—
Total assets	$	1,837			$	—			$	94		$	—		$	—		$	—	$	—	$	(1,931	)	$	—
The Level 3 security is valued using unobservable inputs based on a proxy of a security of similar duration in which market quotations are available.
As of December 31, 2013 and 2012, the Company’s restricted net assets in support of the underwriting activities of the Insurance Companies and Lloyd’s Operations were $520.9 and $519.2 million, respectively, consisting of fixed maturities, short term investments and cash. Refer to Note 13, Dividends and Statutory Financial Information, for additional information on the nature and type of restricted net assets.
As of December 31, 2013 and 2012, the Company did not have a concentration of greater than 5% of invested assets in a single non-U.S. government-backed issuer.

Reserves_for_Losses_and_Loss_A

Reserves for Losses and Loss Adjustment Expenses	12 Months Ended
	Dec. 31, 2013
Reserves for Losses and Loss Adjustment Expenses	'
	Note 5. Reserves for Losses and Loss Adjustment Expenses
	Insurance companies and Lloyd’s syndicates are required to maintain reserves for unpaid losses and unpaid loss adjustment expenses for all lines of business. These reserves are intended to cover the probable ultimate cost of settling all losses incurred and unpaid, including those incurred but not reported. The determination of reserves for losses and LAE for insurance companies such as Navigators Insurance Company and Navigators Specialty Insurance Company, and Lloyd’s corporate members such as Navigators Corporate Underwriters Ltd. is dependent upon the receipt of information from the agents and brokers which produce the insurance business for us. Generally, there is a lag between the time premiums are written and related losses and loss adjustment expenses are incurred, and the time such events are reported to the agents and brokers and, subsequently, to Navigators Insurance Company, Navigators Specialty Insurance Company, Navigators Corporate Underwriters Ltd.
	Case reserves are established by our Insurance Companies and Syndicate 1221 for reported claims when notice of the claim is first received. Reserves for such reported claims are established on a case-by-case basis by evaluating several factors, including the type of risk involved, knowledge of the circumstances surrounding such claim, severity of injury or damage, the potential for ultimate exposure, experience with the line of business, and the policy provisions relating to the type of claim. Reserves for IBNR are determined in part on the basis of statistical information, in part on industry experience and in part on the judgment of our senior corporate officers. Indicated reserves are calculated by our actuaries using several standard actuarial methodologies, including the paid and incurred loss development and the paid and incurred Bornheutter-Ferguson loss methods. Additional analyses, such as frequency/severity analyses, are performed for certain books of business.
	Total loss reserves are estimates of what the insurer or reinsurer expects to pay on claims, based on facts and circumstances then known. It is possible that the ultimate liability may exceed or be less than such estimates. In setting our loss reserve estimates, we review statistical data covering several years, analyze patterns by line of business and consider several factors including trends in claims frequency and severity, changes in operations, emerging economic and social trends, inflation and changes in the regulatory and litigation environment. Using the aforementioned actuarial methods and different underlying assumptions, our actuaries produce a number of point estimates for each class of business. After reviewing the appropriateness of the underlying assumptions, management selects the carried reserve for each class of business. We do not calculate a range of loss reserve estimates. We believe that ranges may not be a true reflection of the potential volatility between carried loss reserves and the ultimate settlement amount of losses incurred prior to the balance sheet date. The numerous factors that contribute to the inherent uncertainty in the process of establishing loss reserves include: interpreting loss development activity, emerging economic and social trends, inflation, changes in the regulatory and judicial environment and changes in our operations, including changes in underwriting standards and claims handling procedures. During the loss settlement period, which, in some cases, may last several years, additional facts regarding individual claims may become known and, accordingly, it often becomes necessary to refine and adjust the estimates of liability on a claim upward or downward. Such estimates are regularly reviewed and updated and any resulting adjustments are included in the current year’s income statement. Even then, the ultimate liability may exceed or be less than the revised estimates. The reserving process is intended to provide implicit recognition of the impact of inflation and other factors affecting loss payments by taking into account changes in historical payment patterns and perceived probable trends. There is generally no precise method for the subsequent evaluation of the adequacy of the consideration given to inflation, or to any other specific factor, because the eventual deficiency or redundancy of reserves is affected by many factors, some of which are interdependent. To the extent that reserves are deficient or redundant, the amount of such deficiency or redundancy is treated as a charge or credit to earnings in the period in which the deficiency or redundancy is recognized.
	The following table summarizes the Company’s reserves for losses and LAE activity for the years ended December 31, 2013, 2012 and 2011:
			Year Ended December 31,
	In thousands		2013			2012			2011
	Net reserves for losses and LAE at beginning of year		$	1,216,909		$	1,237,234		$	1,142,542
	Provision for losses and LAE for claims occurring in the current year			520,227			542,724			474,852
	Increase (decrease) in estimated losses and LAE for claims occurring in prior years			(1,266	)		(45,291	)		2,145
	Incurred losses and LAE			518,961			497,433			476,997
	Losses and LAE paid for claims occurring during:
	Current year			(147,758	)		(110,373	)		(73,242	)
	Prior years			(365,479	)		(407,385	)		(309,063	)
	Losses and LAE payments			(513,237	)		(517,758	)		(382,305	)
	Net reserves for losses and LAE at end of year			1,222,633			1,216,909			1,237,234
	Reinsurance recoverables on unpaid losses and LAE			822,438			880,139			845,445
	Gross reserves for losses and LAE at end of year		$	2,045,071		$	2,097,048		$	2,082,679
	The segment and line of business breakdowns of prior period net reserve deficiencies (redundancies) for the years ended December 31, 2013, 2012 and 2011 are as follows:
			Year Ended December 31,
	In thousands		2013			2012			2011
	Insurance Companies:
	Marine		$	(15,227	)	$	(10,010	)	$	1,348
	Property Casualty			18,466			4,293			(6,828	)
	Professional Liability			10,191			7,613			17,582
	Insurance Companies		$	13,430		$	1,896		$	12,102
	Lloyd’s Operations:
	Marine		$	(2,998	)	$	(30,735	)	$	(10,311	)
	Property Casualty			(14,574	)		(6,890	)		(5,434	)
	Professional Liability			2,876			(9,562	)		5,788
	Lloyd’s Operations		$	(14,696	)	$	(47,187	)	$	(9,957	)
	Total deficiencies (redundancies)		$	(1,266	)	$	(45,291	)	$	2,145
	The following is a discussion of relevant factors related to the $1.3 million prior period net reserve releases recorded for the year ended December 31, 2013:
	The Insurance Companies recorded $13.4 million of net strengthening primarily driven by our Property Casualty and Professional Liability businesses. Within the Property Casualty business, we reported net prior period reserve strengthening of $18.5 million, which includes $13.2 million of net strengthening from our Assumed Reinsurance division mostly attributable to our excess-of-loss A&H treaty business in connection with UYs 2012 and 2011, $10.4 million of strengthening from our Primary Casualty business related to our general liability coverage for general and artisan contractors, and a total of $2.1 million of strengthening for business in run-off. The aforementioned net prior period reserve strengthening was partially offset by $8.0 million of net prior period reserve releases from our Energy & Engineering division in connection with favorable emergence on our offshore energy lines written by our UK Branch.
	Our Insurance Companies Professional Liability business reported net prior period reserve strengthening of $10.2 million largely attributable to $6.1 million reserve strengthening from our D&O division related to specific large claims for UYs 2010 and prior, and $4.4 million reserve strengthening from our E&O division related to specific large claims from our insurance agents, miscellaneous professional liability, and small lawyer lines from UYs 2011 and prior.
	The aforementioned net strengthening from our Insurance Companies Property Casualty and Professional Liability were partially offset by $15.2 million of net reserve releases from our Insurance Companies Marine business in connection with favorable emergence from our Marine liability lines for UYs 2012 and prior.
	Our Lloyd’s Operations recorded $14.7 million of net reserve releases driven by our Property Casualty and Marine businesses partially offset by strengthening in our Professional Liability business. Within our Lloyd’s Property Casualty business we reported net prior period reserve releases of $14.6 million primarily from our Energy & Engineering division. Within our Lloyd’s Marine business we reported prior period reserve releases of $3.0 million driven by our marine liability business. Within our Lloyd’s Professional Liability business we reported strengthening of $2.9 million, inclusive of $6.1 million of strengthening in our Lloyd’s E&O business partially offset by $3.2 million of favorable emergence from our Lloyd’s D&O business.
	The following is a discussion of relevant factors related to the $45.3 million prior period net reserve releases recorded for the year ended December 31, 2012:
	The Insurance Companies recorded $1.9 million net strengthening. The Marine business had $10.0 million of net reserve releases, which were primarily driven by:
		•		an IBNR adjustment of 4.0 million to reflect the actual emergence of claims for underwriting year “(UY)” 2010, which was more favorable than the expected emergence.
		•		case reserve releases of $3.4 million due to the favorable settlement of several large losses; and
		•		a favorable IBNR adjustment of $2.6 million attributable to changes in our assumptions for salvage and subrogation from our short tail marine lines that was based on our observation of a consistent and persistent historical pattern of favorable savings attributable to salvage and subrogation.
	The Marine reserve releases were partially offset by net strengthening of $7.6 million from the small lawyer and accountants lines within our Professional Liability business. This strengthening was primarily driven by several large losses that caused the actual claims emergence for these lines to exceed the expected losses. We also incurred net reserve strengthening of $4.3 million within our Property Casualty segment, which were primarily attributable to two large hemophiliac claims from UY 2011 arising from our A&H business.
	Our Lloyd’s Operations recorded $47.2 million of net prior period reserve releases across all businesses and divisions. In connection with the Company’s implementation of the Solvency II technical provisions in its Lloyd’s operation, the Company’s actuaries undertook a comprehensive review during 2012 of the historical claims emergence patterns for all lines of business underwritten through Syndicate 1221. As a result of this review, the Company updated the loss emergence patterns used to project ultimate losses for all such lines of business, aligning these loss emergence factors with the historical median. This caused a reduction in ultimate loss estimates for all Lloyd’s segments other than certain lines of business in Property Casualty segment, which increased. The Lloyd’s Operations also experienced significant reserve redundancies in several large claims. The amount of reserve redundancies attributable to these settlements was $5.0 million, consisting of $4.1 million from the Lloyd’s Marine business and $0.9 million from Lloyd’s Professional Liability business. A summary of the resulting prior period redundancies for each business within our Lloyd’s Operations by prior UY is set forth below:
	In thousands		Marine			Property			Professional			Total
						Casualty			Liability
	2010			3,492			378			1,157			5,027
	2009			14,792			4,170			6,072			25,034
	2008 and Prior			12,451			2,342			2,333			17,126
	Total Redundancy		$	30,735		$	6,890		$	9,562		$	47,187
	The following is a discussion of relevant factors impacting our $2.1 million net reserve deficiencies for the year ended December 31, 2011:
	The adverse development of $1.3 million for our Insurance Companies Marine business was driven by $4.0 million of unfavorable loss emergence in Inland Marine in accident years 2009 and 2010 which was offset by $2.7 million favorable development in Ocean Marine. The Ocean Marine development was driven by $5.8 million of favorable development in accident years 2008 to 2010 and was partially offset by $3.2 million of adverse development for accident years 2007 and prior. Ocean Marine’s favorable development was driven by the Craft, protection and indemnity, and Transport classes with partial offsets from the Specie and Liability classes.
	Our Insurance Companies Property Casualty business experienced $6.8 million of favorable development overall which was driven by favorable development of $8.4 million from Offshore Energy across several accident years and was partially offset by adverse development from runoff Liquor Liability in accident years 2008 and 2009.
	Our Insurance Companies Professional Liability business had overall adverse development of $17.6 million, which consisted of adverse development of $14.5 million and $3.1 million from Management Liability and Errors and Omissions, respectively. The Management Liability development was primarily driven by coverage of Public companies for accident years 2009 and 2010. The Errors and Omissions development was driven by Small Lawyer Professional Liability and Miscellaneous Professional Liability classes for accident year 2010.
	Our Lloyd’s operations experienced $10.0 million of favorable development. This was driven by favorable development of $10.3 million and $5.5 million from the Marine and Nav Tech divisions respectively, which was partially offset by $5.8 million of unfavorable development from Professional Liability. The favorable development in Marine was primarily from the Cargo, Liability and Specie classes for accident years 2008 and prior. The favorable development in Nav Tech was from Offshore Energy primarily in accident years 2007 to 2009. The adverse development in Professional Liability was mostly from Errors and Omissions in accident years 2006 to 2008.
	Management believes that the reserves for losses and loss adjustment expenses are adequate to cover the ultimate cost of losses and loss adjustment expenses on reported and unreported claims. We continue to review our reserves on a regular basis.

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2013
Reinsurance	'
	Note 6. Reinsurance
	We utilize reinsurance principally to reduce our exposure on individual risks, to protect against catastrophic losses, and to stabilize loss ratios and underwriting results. Although reinsurance makes the reinsurer liable to us to the extent the risk is transferred or ceded to the reinsurer, ceded reinsurance arrangements do not eliminate our obligation to pay claims to our policyholders. Accordingly, we bear credit risk with respect to our reinsurers. Specifically, our reinsurers may not pay claims made by us on a timely basis, or they may not pay some or all of these claims. Either of these events would increase our costs and could have a material adverse effect on our business. We are required to pay the losses even if the reinsurer fails to meet its obligations under the reinsurance agreement.
	We have established a reserve for uncollectible reinsurance in the amount of $11.3 million and $11.5 million as of December 31, 2013 and 2012, respectively, which was determined by considering reinsurer specific default risk as indicated by their financial strength ratings. Actual uncollectible reinsurance could potentially exceed our estimate.
	We are protected by various treaty and facultative reinsurance agreements. Our exposure to credit risk from any one reinsurer is managed through diversification by reinsuring with a number of different reinsurers, principally in the United States and European reinsurance markets. To meet our standards of acceptability, when the reinsurance is placed, a reinsurer generally must have a rating from A.M. Best Company (“A.M. Best”) and/or S&P of “A” or better, or an equivalent financial strength if not rated, plus at least $500 million in policyholders’ surplus. Our Reinsurance Security Committee, which is part of our Enterprise Risk Management Finance and Credit Sub-Committee, monitors the financial strength of our reinsurers and the related reinsurance receivables and periodically reviews the list of acceptable reinsurers. The reinsurance is placed either directly by us or through reinsurance intermediaries. The reinsurance intermediaries are compensated by the reinsurers.
	The credit quality distribution of the Company’s reinsurance recoverables of $1.1 billion as of December 31, 2013 for ceded paid and unpaid losses and LAE and ceded unearned premiums based on insurer financial strength ratings from A.M. Best or S&P were as follows:
					Carrying				Percent
	In thousands		Rating		Value (2)				of Total (3)
	A.M. Best Rating description (1):
	Superior		A++, A+		$	536,325				49	%
	Excellent		A, A-			525,314				47	%
	Very good		B++, B+			12,295				1	%
	Fair		B, B-			23,283				2	%
	Not rated		NR			11,427				1	%
	Total				$	1,108,644				100	%
	(1) -	Equivalent S&P rating used for certain companies when an A.M. Best rating was unavailable.
	(2) -	Net of reserve for uncollectible reinsurance of approximately $11.3 million. The carrying value consists of reinsurance recoverables on paid losses due within 30-45 days and reinsurance on unpaid losses which by nature of our reserving process is our best estimate of the value as of December 31, 2013.
	(3) -	The Company holds offsetting collateral of approximately 20.2%, including 0.2% for B++, B+ and B companies and 46.7% from non rated companies which includes letters of credit, ceded balances payable and other balances held by our Insurance Companies and our Lloyd’s Operations.
	The Company’s ceded earned premiums were $456.0 million, $396.6 million and $346.2 million for the years ended December 31, 2013, 2012 and 2011, respectively.
	The Company’s ceded incurred losses were $188.7 million, $262.6 million and $213.4 million for the years ended December 31, 2013, 2012 and 2011, respectively.
	The following table lists the Company’s 20 largest reinsurers measured by the amount of reinsurance recoverable for ceded losses and LAE and ceded unearned premium (constituting 76.3% of the total recoverable), together with the reinsurance recoverable and collateral as of December 31, 2013, and the reinsurers’ ratings from A.M. Best and S&P:
			Reinsurance Recoverables
			Unearned				Paid/Unpaid							Collateral
	In thousands		Premium				Losses				Total (1)			Held (2)		A.M. Best	S&P
	National Indemnity Company			53,145				87,618				140,763			30,785	A++	AA+
	Transatlantic Reinsurance Company			21,411				74,069				95,480			8,506	A	A+
	Everest Reinsurance Company			21,581				68,566				90,147			7,704	A+	A+
	Munich Reinsurance America Inc.			5,067				70,233				75,300			4,352	A+	AA-
	Swiss Reinsurance America Corporation			5,800				68,157				73,957			9,609	A+	AA-
	Lloyd’s Syndicate #2003			8,832				43,167				51,999			10,299	A	A+
	Allied World Reinsurance			13,859				30,215				44,074			3,971	A	A
	Partner Reinsurance Europe			10,962				29,692				40,654			17,027	A+	A+
	Scor Global P&C SE			11,710				24,623				36,333			9,895	A	A+
	Tower Insurance Company			—				23,283				23,283			—	B	NR
	Atlantic Specialty Insurance			9,260				13,602				22,862			3,526	A	A-
	Employers Mutual Casualty Company			10,738				10,796				21,534			9,709	A	NR
	Validus Reinsurance Ltd.			2,403				17,308				19,711			14,501	A	A
	Lloyd’s Syndicate #4000			147				19,432				19,579			407	A	A+
	QBE Reinsurance Corp			7,131				11,292				18,423			1,781	A	A+
	Ace Property and Casualty Insurance Company			9,862				7,687				17,549			7,342	A+	AA-
	Odyssey American Reinsurance Corporation			3,550				11,997				15,547			2,175	A	A-
	Berkley Insurance Company			1,983				13,439				15,422			485	A+	A+
	Ironshore Indemnity Inc.			6,808				7,980				14,788			7,959	A	NR
	AXIS Re Europe			4,762				9,347				14,109			3,675	A+	A+
	Top 20 Reinsurers			209,011				642,503				851,514			153,708
	Others			38,811				218,319				257,130			69,769
	Total			247,822				860,822				1,108,644			223,477
	(1) -	Net of reserve for uncollectible reinsurance of approximately $11.3 million.
	(2) -	Collateral of $223.5 million consists of $167.3 million in ceded balances payable, $53.4 million in letters of credit, and $2.8 million of other balances held by the Company’s Insurance Companies and Lloyd’s Operations.
	Approximately 24% of the collateral held consists of letters of credit obtained from reinsurers in accordance with New York Insurance Regulation Nos. 20 and 133. Regulation 20 requires collateral to be held by the ceding company from reinsurers not licensed in New York State in order for the ceding company to take credit for the reinsurance recoverables on its statutory balance sheet. The specific requirements governing the letters of credit are contained in Regulation 133 and include a clean and unconditional letter of credit and an “evergreen” clause which prevents the expiration of the letter of credit without due notice to the Company. Only banks considered qualified by the National Association of Insurance Commissioners (“NAIC”) may be deemed acceptable issuers of letters. In addition, based on our credit assessment of the reinsurer, there are certain instances where we require collateral from a reinsurer even if the reinsurer is licensed in New York State, generally applying the requirements of Regulation No. 133. The contractual terms of the letters of credit require that access to the collateral is unrestricted. In the event that the counterparty to our collateral would be deemed not qualified by the NAIC, the reinsurer would be required by agreement to replace such collateral with acceptable security under the reinsurance agreement. There is no assurance, however, that the reinsurer would be able to replace the counterparty bank in the event such counterparty bank becomes unqualified and the reinsurer experiences significant financial deterioration. Under such circumstances, we could incur a substantial loss from uncollectible reinsurance from such reinsurer. In November 2010, Regulation No. 20 was amended to provide the New York Superintendent of Financial Services (the “New York Superintendent”) discretion to allow a reduction in collateral that qualifying reinsurers must post in order for New York domestic ceding insurers such as Navigators Insurance Company and Navigators Specialty Insurance Company to receive full financial statement credit. The “collateral required” percentages range from 0% – 100%, are based upon the New York Superintendent’s evaluation of a number of factors, including the reinsurer’s financial strength ratings, and apply to contracts entered into, renewed or having an anniversary date on or after January 1, 2011. In November 2011, the NAIC adopted similar amendments to its Credit for Reinsurance Model Act that would apply to certain non-U.S. reinsurers. States will have the option to retain a 100% funding requirement if they so choose and it remains to be seen whether and when states will amend their credit for reinsurance laws and regulations in accordance with such model act.
	As of December 31, 2013, the reinsurance recoverables for paid and unpaid losses due from reinsurers in connection with all catastrophic losses was $46.5 million. Included in this figure is $30.7 million for Superstorm Sandy and $3.3 million for the 2008 Hurricanes. As of December 31, 2012, the reinsurance recoverables for paid and unpaid losses due from reinsurers in connection with all catastrophic losses was $88.2 million. Included in this figure is $54.6 million for Superstorm Sandy and $15.2 million for the 2008 Hurricanes.
	The following table summarizes written premium:
			Year Ended December 31,
	In thousands		2013				2012				2011
	Direct		$	1,127,331			$	1,034,658			$	929,778
	Assumed			243,187				251,807				178,438
	Ceded			(482,596	)			(452,810	)			(354,418	)
	Net		$	887,922			$	833,655			$	753,798
	The following table summarizes earned premium:
			Year Ended December 31,
	In thousands		2013				2012				2011
	Direct		$	1,069,677			$	972,844			$	912,020
	Assumed			228,247				205,759				125,797
	Ceded			(455,985	)			(396,639	)			(346,172	)
Net		$	841,939			$	781,964			$	691,645
The following table summarizes losses and loss adjustment expenses incurred:
		Year Ended December 31,
In thousands		2013				2012				2011
Direct		$	552,381			$	608,945			$	608,445
Assumed			155,313				151,137				81,945
Ceded			(188,733	)			(262,649	)			(213,393	)
Net		$	518,961			$	497,433			$	476,997

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2013
Income Taxes	'
	Note 7. Income Taxes
	The Company is subject to the tax laws and regulations of the United States (“U.S.”) and the foreign countries in which it operates. The Company files a consolidated U.S. Federal tax return, which includes all domestic subsidiaries and the U.K. Branch. The income from the foreign operations is designated as either U.S. connected income or non-U.S. connected income. Lloyd’s is required to pay U.S. income tax on U.S. connected income written by Lloyd’s syndicates. Lloyd’s and the U.S. Internal Revenue Service (“IRS”) have entered into an agreement whereby the amount of tax due on U.S. connected income is calculated by Lloyd’s and remitted directly to the IRS. These amounts are then charged to the corporate member in proportion to its participation in the relevant syndicates. The Company’s corporate member is subject to this agreement and receives United Kingdom (“U.K.”) tax credits in the U.K. for any U.S. income tax incurred up to the U.K. income tax charged on the U.S. connected income. The non-U.S. connected insurance income would generally constitute taxable income under the Subpart F income section of the U.S. Internal Revenue Code (“Subpart F”) since less than 50% of Syndicate 1221’s premiums are derived within the U.K. and would therefore be subject to U.S. taxation when the Lloyd’s year of account closes. Taxes are accrued at a 35% rate on the Company’s foreign source insurance income and foreign tax credits, where available, are utilized to offset U.S. tax as permitted. The Company’s effective tax rate for Syndicate 1221 taxable income could substantially exceed 35% to the extent the Company is unable to offset U.S. taxes paid under Subpart F tax regulations with U.K. tax credits on future underwriting year distributions. U.S. taxes are not accrued on the earnings of the Company’s foreign agencies as these earnings are not includable as Subpart F income in the current year. These earnings were subject to taxes under U.K. tax regulations at a 26% rate through March 31, 2012. A finance bill was enacted in the U.K. that reduced the U.K. corporate tax rate from 26% to 24% effective April 2012 and from 24% to 23% effective April 2013.
	The components of current and deferred income tax expense (benefit) are as follows:
		Year Ended December 31,
	In thousands	2013			2012			2011
	Current income tax expense (benefit):
	Federal and foreign	$	28,084		$	39,242		$	573
	State and local		446			146			340
	Subtotal		28,530			39,388			913
	Deferred income tax expense (benefit):
	Federal and foreign		277			(11,414	)		6,224
	State and local		—			—			—
	Subtotal		277			(11,414	)		6,224
	Total income tax expense (benefit)	$	28,807		$	27,974		$	7,137
	A reconciliation of total income taxes applicable to pre-tax operating income and the amounts computed by applying the federal statutory income tax rate to the pre-tax operating income were as follows:
		Year Ended December 31,
	In thousands	2013						2012					2011
	Computed expected tax expense	$	32,299			35	%	$	32,109		35	%	$	11,457		35	%
	Tax-exempt interest		(3,839	)		-4.2	%		(4,443	)	-4.8	%		(4,437	)	-13.6	%
	Dividends received deduction		(897	)		-1	%		(799	)	-0.9	%		(1,065	)	-3.3	%
	Proration		710			0.8	%		786		0.9	%		825		2.5	%
	Current state and local income taxes, net of federal income tax		290			0.3	%		95		0.1	%		221		0.7	%
	Other		244			0.3	%		226		0.2	%		136		0.5	%
	Actual tax expense and rate	$	28,807			31.2	%	$	27,974		30.5	%	$	7,137		21.8	%
	The tax effects of temporary differences that give rise to federal, foreign, state and local deferred tax assets and deferred tax liabilities were as follows:
		December 31,
	In thousands	2013			2012
	Deferred tax assets:
	Loss reserve discount	$	27,822		$	29,687
	Unearned premiums		25,706			22,860
	Compensation related		6,782			5,285
	State and local net deferred tax assets		555			499
	Other		3,889			4,245
	Total gross deferred tax assets		64,754			62,576
	Less: Valuation allowance		(555	)		(499	)
	Total deferred tax assets	$	64,199		$	62,077
	Deferred tax liabilities:
	Deferred acquisition costs	$	(19,258	)	$	(16,903	)
	Net unrealized gains on securities		(12,635	)		(36,200	)
	Other		(4,119	)		(5,758	)
	Total deferred tax liabilities	$	(36,012	)	$	(58,861	)
	Net deferred income tax asset (liability)	$	28,187		$	3,216
	The Company has not provided for U.S. income taxes on approximately $20.3 million of undistributed earnings of its non-U.S. subsidiaries since it is intended that those earnings will be reinvested indefinitely in those subsidiaries. If a future determination is made that those earnings no longer are intended to be reinvested indefinitely in those subsidiaries, U.S. income taxes of approximately $2.1 million, assuming all foreign tax credits are realized, would be included in the tax provision at that time and would be payable if those earnings were distributed to the Company.
	Unrecognized tax benefits are differences between tax positions taken in the tax returns and benefits recognized in the financial statements. The Company has no unrecognized tax benefits as of December 31, 2013 and 2012. The Company did not incur any interest or penalties related to unrecognized tax benefits for the years ended December 31, 2013 and 2012. The Company currently is under examination by the Internal Revenue Service for taxable years 2010 and 2011, and generally is subject to U.S. Federal, state or local, or foreign tax examinations by tax authorities for 2009 and subsequent years.
	The Company had state and local deferred tax assets amounting to potential future tax benefits of $0.6 million and $0.5 million as of December 31, 2013 and 2012, respectively. Included in the deferred tax assets are state and local net operating loss carry-forwards of $0.1 million and $0.2 million for December 31, 2013 and 2012. A valuation allowance was established for the full amount of these potential future tax benefits due to the uncertainty associated with their realization. The Company’s state and local tax carry-forwards as of December 31, 2013 expire from 2023 to 2031.
	In assessing the realization of deferred tax assets, management considers whether it is more likely than not that the deferred tax assets will be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences become deductible. Management considers the scheduled reversal of deferred tax liabilities, tax planning strategies and anticipated future taxable income in making this assessment and believes it is more likely than not that the Company will realize the benefits of its deductible differences as of December 31, 2013, net of any valuation allowance.

Credit_Facility

Credit Facility	12 Months Ended
	Dec. 31, 2013
Credit Facility	'
	Note 8. Credit Facility
	On November 22, 2012, we entered into a $165 million credit facility agreement with ING Bank N.V., London Branch, individually and as Administrative Agent, and a syndicate of lenders. The new credit facility amended and restated a $165 million letter of credit facility entered into by the parties on March 28, 2011. The credit facility, which is denominated in U.S. dollars, is utilized to fund our participation in Syndicate 1221 through letters of credit for the 2013 and 2014 underwriting years, as well as open prior years. The letters of credit issued under the facility can be denominated in British pounds and their aggregate face amount will fluctuate based on exchange rates. If any letters of credit remain outstanding under the facility after December 31, 2014, we would be required to post additional collateral to secure the remaining letters of credit. As of December 31, 2013, letters of credit with an aggregate face amount of $151.9 million were outstanding under the credit facility.
	This credit facility contains customary covenants for facilities of this type, including restrictions on indebtedness and liens, limitations on mergers, dividends and the sale of assets, and requirements as to maintaining certain consolidated tangible net worth, statutory surplus and other financial ratios. The credit facility also provides for customary events of default, including failure to pay principal, interest or fees when due, failure to comply with covenants, any representation or warranty made by the Company being false in any material respect, default under certain other indebtedness, certain insolvency or receivership events affecting the Company and its subsidiaries, the occurrence of certain material judgments, or a change in control of the Company. The letter of credit facility is secured by a pledge of the stock of certain insurance subsidiaries of the Company. To the extent the aggregate face amount issued under the credit facility exceeds the commitment amount, the Company is required to post collateral with the lead bank of the consortium. The Company was in compliance with all covenants under the credit facility as of December 31, 2013.
	The applicable margin and applicable fee rate payable under the credit facility are based on a tiered schedule that is based on the Company’s then-current ratings issued by S&P and Moody’s with respect to the Company’s Senior Notes without third-party credit enhancement, and the amount of the Company’s own collateral utilized to fund its participation in Syndicate 1221.

Senior_Note

Senior Note	12 Months Ended
	Dec. 31, 2013
Senior Note	'
	Note 9. Senior Note
	On October 4, 2013, the Company completed a public debt offering of $265 million principal amount of 5.75% Senior Notes (“5.75% Senior Notes”) and received net proceeds of $263 million. The Principal amount of the Senior Notes is payable in one single installment on October 15, 2023. The Company used a portion of the proceeds of the 5.75% Senior Notes for the redemption of the 7.0% Senior Notes due May 1, 2016 (“7.0% Senior Notes). The Company incurred a charge of $17.9 million for the payment of call premium in connection with the redemption of the 7.0% Senior Notes. The Senior Notes liability as of December 31, 2013 was $263.3 million. The unamortized discount as of December 31, 2013 was $1.7 million.
	The fair value of the 5.75% Senior Notes as of December 31, 2013 was $277.6 million. The fair value of the 7.0% Senior Notes as of December 31, 2012 was $123.2 million. The fair values were determined using quoted prices for similar instruments in active markets and is classified as Level 2 within the fair value hierarchy as defined by the accounting guidance for fair value measurements.
	Interest is payable on the 5.75% Senior Notes each April 15 and October 15. The effective interest rate related to the 5.75% Senior Notes, based on the proceeds net of discount and all issuance costs, approximates 5.86%. Interest expense on the 5.75% and 7.0% Senior Notes totaled $10.5 million for the year ended December 31, 2013. Interest expense on the 7.0% Senior Notes was $8.2 million for the years ended December 31, 2012 and 2011, respectively.
	The interest rate payable on the 5.75% Senior Notes is subject to a tiered adjustment based on defined changes in the Company’s debt ratings. The Company may redeem the 5.75% Senior Notes in whole at any time or in part from time to time at a make-whole redemption price. The 5.75% Senior Notes are the Company’s only senior unsecured obligation and will rank equally with future senior unsecured indebtedness.
	The terms of the 5.75% Senior Notes contain various restrictive business and financial covenants, including a restriction on indebtness, and other restrictions typical for debt obligations of this type, including limitations on mergers, liens and dispositions of the common stock of certain subsidiaries. As of December 31, 2013, the Company was in compliance with all such covenants.

Lloyds_Syndicate_1221

Lloyd's Syndicate 1221	12 Months Ended
	Dec. 31, 2013
Lloyd's Syndicate 1221	'
	Note 10. Lloyd’s Syndicate 1221
	The Company’s Lloyd’s Operations included in the consolidated financial statements represents its participation in Syndicate 1221. Syndicate 1221’s stamp capacity is £195 million ($323.7 million) for the 2013 underwriting year compared to £184 million ($300 million) for the 2012 underwriting year. Stamp capacity is a measure of the amount of premiums a Lloyd’s syndicate is authorized to write based on a business plan approved by the Council of Lloyd’s. Syndicate 1221’s stamp capacity is expressed net of commission (as is standard at Lloyd’s). The Syndicate 1221 premiums recorded in the Company’s financial statements are gross of commission. The Company controlled 100% of Syndicate 1221’s stamp capacity for the 2013, 2012 and 2011 underwriting years through its wholly-owned Lloyd’s corporate member.
	The Company provides letters of credit and posts cash to Lloyd’s to support its participation in Syndicate 1221’s stamp capacity. As of December 31, 2013, the Company had provided letters of credit of $151.9 million and has $1.0 million of cash collateral posted. If Syndicate 1221 increases its stamp capacity and the Company participates in the additional stamp capacity, or if Lloyd’s changes the capital requirements, the Company may be required to supply additional collateral acceptable to Lloyd’s. If the Company is unwilling or unable to provide additional acceptable collateral, the Company will be required to reduce its participation in the stamp capacity of Syndicate 1221. The letters of credit are provided through a credit facility with a consortium of banks which provides the Company with the ability to have letters of credit issued to support Syndicate 1221’s stamp capacity at Lloyd’s for the 2013 and 2014 underwriting years, as well as open prior years. If any letters of credit remain outstanding under the facility after December 31, 2014, we would be required to post additional collateral to secure the remaining letters of credit. If the credit facility is not renewed prior to December 31, 2014, the Company will need to find internal and/or external sources to provide either letters of credit or other collateral in order to continue to participate in Syndicate 1221. The credit facility is collateralized by all of the common stock of Navigators Insurance Company. Refer to Note 8, Credit Facility, for additional information.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies	'
	Note 11. Commitments and Contingencies
	Future minimum annual rental commitments as of December 31, 2013 under various non-cancellable operating leases for our office facilities, which expire at various dates through 2023, are as follows:
		Year Ended
	In thousands	December 31,
	2014	$	11,061
	2015		11,092
	2016		9,228
	2017		7,990
	2018		6,884
	Thereafter		15,696
	Total minimum operating lease payments	$	61,951
	We are also liable for additional payments to the landlords for certain annual cost increases. Rent expense for the years ended December 31, 2013, 2012 and 2011 was $11.5 million, $10.5 million and $10.4 million, respectively.
	The State of Connecticut awarded the Company up to $11.5 million ($8.0 million in loans and $3.5 million in grants) as an incentive to move its corporate headquarters to Stamford Connecticut. The loan is non-interest bearing, has a term of 10 years and is subject to forgiveness under conditions of the agreement with the State. The amount of the assistance to be received is dependent on the Company reaching certain milestones for creation of new jobs over a five-year period, and the funds are to be used to offset certain equipment purchases, facility costs, training of employees and other eligible project-related costs. The Company completed the move to Stamford in September 2013 and received $7.5 million for reaching the first job milestone. Earning of the grant and forgiveness of the loan is subject to certain conditions, including maintaining the required jobs for an extended period of time. As of December 31, 2013, the length of time commitment has not been met, however, the Company expects to meet all the conditions to keep the amount of assistance received to date, and accordingly, is recognizing the assistance received over the period in which the Company recognizes the expenses for which the assistance is intended to compensate, and is recognized as a reduction of such expenses. During the year ended December 31, 2013, the Company recognized $0.3 million of the assistance and has deferred revenue of $7.2 million, which is included in other liabilities.
	In the ordinary course of conducting business, the Company’s subsidiaries are involved in various legal proceedings, either indirectly as insurers for parties or directly as defendants. Most of these proceedings consist of claims litigation involving the Company’s subsidiaries as either (a) liability insurers defending or providing indemnity for third party claims brought against insureds or (b) insurers defending first party coverage claims brought against them. The Company accounts for such activity through the establishment of unpaid loss and loss adjustment reserves. The Company’s management believes that the ultimate liability, if any, with respect to such ordinary-course claims litigation, after consideration of provisions made for potential losses and cost of defense, will not be material to the Company’s consolidated financial condition, results of operations, or cash flows.
	The Company’s subsidiaries are also from time to time involved with other legal actions, some of which assert claims for substantial amounts. These actions include claims asserting extra contractual obligations, such as claims involving allegations of bad faith in the handling of claims or the underwriting of policies. In general, the Company believes it has valid defenses to these cases. The Company’s management expects that the ultimate liability, if any, with respect to future extra-contractual matters will not be material to its consolidated financial position. Nonetheless, given the large or indeterminate amounts sought in certain of these matters, and the inherent unpredictability of litigation, an adverse outcome in such matters could, from time to time, have a material adverse outcome on the Company’s consolidated results of operations or cash flows in a particular fiscal quarter or year.

Share_Capital_and_Share_Repurc

Share Capital and Share Repurchases	12 Months Ended
	Dec. 31, 2013
Share Capital and Share Repurchases	'
	Note 12. Share Capital and Share Repurchases
	Our authorized share capital consists of 50,000,000 common shares with a par value of $0.10 per share and 1,000,000 preferred shares with a par value of $0.10 per share. The Company has not issued any preferred shares as of December 31, 2013.
	The following table represents changes in the Company’s issued and outstanding common shares for the periods indicated:
		Year Ended December 31,
	In thousands	2013		2012		2011
	Beginning balance		14,047		13,956		15,742
	Vested stock grants		50		60		122
	Employee stock purchase plan		17		16		19
	Stock options exercised		84		15		52
	Treasury shares purchased		—		—		(1,979	)
	Ending balance		14,198		14,047		13,956
	In May 2011, the Parent Company’s Board of Directors authorized an additional $50 million under the existing share repurchase program of the Company’s common stock, which increased the size of the program to $150 million. This repurchase program was initially authorized in November 2009. The share repurchase program as originally approved was scheduled to expire on December 31, 2010, however, prior to its expiration, the Parent Company’s Board of Directors approved an extension to December 31, 2011. The share repurchase program expired on December 31, 2011 and was not renewed.
	The following presents our share repurchases under the aforementioned programs for the periods indicated:
		Total		Average
		Number of		Cost Paid
		Shares		Per Share
		Purchased
	Fourth quarter 2009 activity		141,576	$	47.72
	Total 2009 activity		141,576	$	47.72
	First quarter 2010 activity		573,600	$	41.27
	Second quarter 2010 activity		558,003		40.32
	Third quarter 2010 activity		97,115		42.25
	Fourth quarter 2010 activity		35,566		48.04
	Total 2010 activity		1,264,284	$	41.11
	First quarter 2011 activity		256,094	$	50.96
	Second quarter 2011 activity		597,026		47.55
	Third quarter 2011 activity		749,076		43.03
	Fourth quarter 2011 activity		376,911		45.61
	Total 2011 activity		1,979,107	$	45.91

Dividends_and_Statutory_Financ

Dividends and Statutory Financial Information	12 Months Ended
	Dec. 31, 2013
Dividends and Statutory Financial Information	'
	Note 13. Dividends and Statutory Financial Information
	The Parent Company has not paid or declared any cash dividends on common stock. There are no regulatory restrictions on the ability of the Parent Company to pay dividends. While there is no intention to pay cash dividends on the common stock, future declarations, if any, are at the discretion of our Board of Directors. The amounts of such dividends will be dependent, upon other factors such as, our results of operations and cash flow, financial condition and business needs, restrictive covenants under our credit facility and senior notes that require us to maintain certain consolidated tangible net worth, the capital and surplus requirements of our subsidiaries, and applicable insurance regulations that limit the amount of dividends that may be paid by our regulated insurance subsidiaries. Refer to Note 8, Credit Facility, for additional information on the restrictions of our credit facility that limit the amount of dividends that may be paid by our subsidiaries.
	The amount and nature of net assets that are restricted from payment of dividends as of December 31, 2013 and 2012 are presented in the following table:
			As of December 31,
	In thousands		2013		2012
	Restricted Net Assets:
	Insurance Companies:
	Fixed maturities at fair value (amortized cost: 2013, $9,730; 2012, $9,607)		$	11,105	$	11,728
	Short term investments, at cost which approximates fair value			290		290
	Cash			1,210		5,208
	Total Insurance Companies (1)			12,605		17,226
	Lloyd’s Operations:
	Fixed maturities at fair value (amortized cost: 2013, $398,930; 2012, $419,271)			398,808		428,142
	Short term investments, at cost which approximates fair value			108,485		72,984
	Cash			988		849
	Total Lloyd’s Operations (2)			508,281		501,975
	Total Restricted Net Assets		$	520,886	$	519,201
	-1	- The restricted net assets for the Insurance Companies primarily consist of fixed maturities on deposit with various state insurance departments. The cash as of December 31, 2012 and 2011, as presented in the table above, was on deposit with a U.K. bank to comply with the regulatory requirements of the Prudential Regulation Authority for the underwriting activities of the U.K. Branch.
	(2)	- The restricted net assets for the Lloyd’s Operations consists of fixed maturities and cash held in trust for the benefit of syndicate policyholders and short term investments primarily consisting of overseas deposits in various countries with Lloyd’s to support underwriting activities in those countries.
	In addition to the Company’s restricted net assets provided in the table above, there are regulatory limitations on the payment of dividends by our subsidiaries, discussed below, and the Company’s letter of credit facility is secured by all of the common stock of Navigators Insurance Company.
	Insurance Companies
	Navigators Insurance Company may pay dividends to the Parent Company out of its statutory earned surplus pursuant to statutory restrictions imposed under the New York insurance law. As of December 31, 2013, the maximum amount available for the payment of dividends by Navigators Insurance Company in 2014 without prior regulatory approval is $80.4 million. Navigators Insurance Company did not pay any dividends to the Parent Company in 2013. In 2012 and 2011, Navigators Insurance Company paid $15.0 million and $45.0 million, respectively, in dividends to the Parent Company.
	The Insurance Companies’ statutory net income as filed with the regulatory authorities for 2013, 2012 and 2011 was $59.4 million, $28.6 million and $16.3 million, respectively. The statutory capital and surplus as filed with the regulatory authorities was $804.1 million and $682.9 million as of December 31, 2013 and 2012, respectively.
	The NAIC has codified Statutory Accounting Practices and Procedures (“SAP”) for insurance enterprises. We prepare our statutory basis financial statements in accordance with the most recently updated SAP manual subject to any deviations prescribed or permitted by the New York Insurance Commissioner. The significant differences between SAP and GAAP, as they relate to our operations, are as follows: (1) acquisition and commission costs are expensed when incurred, while under GAAP these costs are deferred and amortized as the related premium is earned; (2) bonds are stated at amortized cost, while under GAAP bonds are classified as available-for-sale and reported at fair value, with unrealized gains and losses recognized in other comprehensive income as a separate component of stockholders’ equity; (3) certain deferred tax assets are not permitted to be included in statutory surplus, while under GAAP deferred taxes are provided to reflect all temporary differences between the carrying values and tax basis of assets and liabilities; (4) unearned premiums and loss reserves are reflected net of ceded amounts, while under GAAP the unearned premiums and loss reserves are reflected gross of ceded amounts; (5) agents’ balances over ninety days due are excluded from the balance sheet, and uncollateralized amounts due from unauthorized reinsurers are deducted from surplus, while under GAAP they are restored to the balance sheet, subject to the usual tests regarding recoverability.
	The NAIC has adopted Risked Based Capital (“RBC”) requirements to elevate the adequacy of statutory capital and surplus in relation to risks associated with: (1) asset risk; (2) insurance risk; (3) interest rate and equity market risk; and (4) business risk. The RBC formula is designated as an early warning tool for the states to identify possible undercapitalized companies for the purpose of initiating regulatory action. In the course of operations, we periodically monitor the RBC level of the Navigators Insurance Company. As of December 31, 2013 and 2012, the Navigators Insurance Company exceeded the company action RBC levels. The RBC ratio of Navigators Insurance Company was 304.2% and 295.1% of the company action level as of December 31, 2013 and 2012, respectively.
	As part of its general regulatory oversight process, the New York State Department of Finance conducts detailed examinations of the books, records and accounts of New York insurance companies every three to five years. In 2011, the New York State Department of Finance conducted an examination of Navigators Insurance Company and Navigators Specialty Insurance Company for the years 2005 through 2009. The U.K. Branch is required to maintain certain capital requirements under U.K. regulations and is subject to examination by the U.K. Prudential Regulation Authority (PRA).
	Lloyd’s Operations
	Lloyd’s sets the corporate member’s required capital annually based on Syndicate 1221’s business plans, rating environment, reserving environment and input arising from Lloyd’s discussions with regulatory and rating agencies. The capital requirement of Syndicate 1221, known as Funds at Lloyd’s (the “FAL”), is currently calculated using the internal Lloyd’s risk-based capital model. The FAL may comprise cash, investments and undrawn letters of credit provided by various banks. As of December 31, 2013 and 2012, the FAL requirement set by Lloyd’s for Syndicate 1221 was $279.3 million (£168.3 million) and $223.4 million (£137.1 million), respectively, based on its business plans, approved in November 2013 and November 2012, respectively.
	The valuation of the assets and letters of credit posted for FAL for Syndicate 1221 as of December 31, 2013 and 2012 was $280.2 million (£168.8 million) and $227.3 million (£139.5 million), respectively.
	We prepare our Lloyd’s financial statements in accordance with U.K. GAAP basis. The significant differences between U.K. GAAP and GAAP, as they relate to our operations, are as follows: (1) investments are recorded at fair value with unrealized gains and losses being recorded in income while under GAAP the changes in unrealized gains and losses are recorded through AOCI as a separate component of stockholders’ equity; (2) realized foreign exchange on inter-currency conversions are recorded through the income statement, while under GAAP foreign exchange translation is recorded through AOCI as a separate component of stockholders’ equity; (3) Lloyd’s membership costs are not deferred for U.K. GAAP, while under GAAP a prepaid asset is established and amortized over each year of account.
	The primary source of income for NCUL, a corporate member of Lloyd’s and controller of 100% of Syndicate 1221’s stamp capacity, is generated through Syndicate 1221. Syndicate 1221 is subject to oversight by the Council of Lloyd’s. Lloyd’s as a whole is authorized and regulated by the PRA. Syndicate 1221’s income as filed with Lloyd’s for 2013, 2012 and 2011 was $21.0 million, $54.9 million and $5.3 million, respectively. The Syndicate’s capital and surplus as filed with Lloyd’s was $124.2 million (£74.8 million) and $110.0 million (£67.5 million) as of December 31, 2013 and 2012, respectively. The difference between our Syndicate’s capital and surplus and the FAL primarily consists of letters of credit and cash held by our corporate member.
	NCUL may pay dividends to the Parent Company up to the extent of available profits that have been distributed from Syndicate 1221. The Syndicate’s capital and surplus as filed with Lloyd’s consists of undistributed profits on closed and open years of account. In connection with the business plan approved in November 2013, NCUL posted all of the available undistributed profits on closed years of $127.4 million (£76.7 million) to support a portion of the FAL requirement and therefore that amount is not available for distribution to NCUL, which ultimately is not available to the Parent in the form of a dividend. As of December 31, 2013, NCUL has the ability to pay dividends of up to $11.6 million (£7.0 million), consisting of previously distributed profits from Syndicate 1221, to the Parent in the form of dividends.
	Refer to Note 1, Organization and Summary of Significant Accounting Policies, for additional disclosure on the accounting treatment for Syndicate 1221 as it relates to closed and open years of account.

Stock_Option_Plans_Stock_Grant

Stock Option Plans, Stock Grants, Stock Appreciation Rights and Employee Stock Purchase Plan	12 Months Ended
	Dec. 31, 2013
Stock Option Plans, Stock Grants, Stock Appreciation Rights and Employee Stock Purchase Plan	'
	Note 14. Stock Option Plans, Stock Grants, Stock Appreciation Rights and Employee Stock Purchase Plan
	At our May 2005 Annual Meeting, the stockholders approved the 2005 Stock Incentive Plan. The 2005 Stock Incentive Plan authorizes the issuance in the aggregate of 1,000,000 incentive stock options, non-incentive stock options, restricted shares and stock appreciation rights for our common stock. Upon the approval of the 2005 Amended and Restated Stock Incentive Plan, no further awards are being issued under any of our other stock plans or the stock appreciation rights plan. All stock options issued under the 2005 Amended and Restated Stock Incentive Plan are exercisable upon vesting for one share of our common stock and are granted at exercise prices no less than the fair market value of our common stock on the date of grant.
	In April 2009, the stockholders approved an amendment to the 2005 Stock Incentive Plan increasing the available number of restricted shares from 1,000,000 to 1,500,000. In April 2013, the stockholders further amended and restated the 2005 Stock Incentive Plan increasing the available number of restricted shares from 1,500,000 to 2,000,000. As of December 31, 2013, 1,340,885 of such awards were issued leaving 659,115 awards available to be issued in subsequent periods.
	Stock-based compensation granted under the Company’s stock plans is expensed in tranches over the vesting period. Options and non-performance based grants generally vest equally over a three or four year period and the options have a maximum term of ten years. Certain non-performance based grants vest over five years with one-third vesting in each of the third, fourth and fifth years. The Company’s performance based share grants generally consist of two types of awards. The restricted stock units issued in 2011 and after will cliff vest over a three year period, with 50% vesting in full, and 50% dependent on the rate of compound annual growth in book value per share for the three years immediately prior to the vesting date, with actual shares that vest ranging between 150% to 0% of that portion of the original award. Those performance based restricted stock units issued prior to 2011 generally vest over five years with one-third vesting in each of the third, fourth and fifth years, dependent on the rolling three-year average return on equity based on the three years prior to the year in which the vesting occurs, with actual shares that vest ranging between 150% to 0% of the original award.
	The amounts charged to expense for stock-based compensation for the years ended December 31, 2013, 2012 and 2011 are presented in the following table:
			Year Ended December 31,
	In thousands		2013			2012			2011
	Restricted stock units		$	3,369		$	7,380		$	139
	Directors restricted stock grants(1)			413			390			248
	Employee stock purchase plan			132			82			173
	Stock appreciation rights(2)			—			—			(100	)
	Total stock-based compensation		$	3,914		$	7,852		$	460
	-1	- Relates to non-employee directors serving on the Parent Company’s Board of Directors, all of whom have been elected by the Company’s stockholders, as well as non-employee directors serving on NUAL’s Board of Directors.
	-2	- All outstanding stock appreciation rights were exercised during 2011.
	Unvested restricted stock units outstanding as of December 31, 2013, 2012 and 2011, and changes during the years ended on those dates, are presented in the following table:
			December 31,
			2013			2012			2011
	Beginning balance			587,629			526,972			590,661
	Granted—Performance			114,463			97,145			86,118
	Granted—Non Performance			155,463			146,915			98,640
	Total Granted			269,926			244,060			184,758
	Vested—Performance Earned			(15,714	)		—			(22,993	)
	Vested—Performance Unearned			(57,585	)		(46,998	)		(42,334	)
	Vested—Non Performance			(60,183	)		(91,323	)		(149,738	)
	Total Vested			(133,482	)		(138,321	)		(215,065	)
	Forfeited			(97,261	)		(45,082	)		(33,382	)
	Ending balance			626,812			587,629			526,972
	As included in the table above, there were 15,714 and 22,933 performance based shares that vested during the years ended December 31, 2013 and 2011, respectively. There were no performance based shares that vested during the year ended December 31, 2012.
	The fair value of total vested shares for the years ended December 31, 2013, 2012 and 2011 was $3.5 million, $4.6 million and $8.6 million, respectively.
	The weighted average grant date fair value of all RSUs granted during the years ended December 31, 2013, 2012 and 2011 was $55.36, $48.21 and $50.06, respectively.
	As of December 31, 2013 and 2012, the total unrecognized compensation expense, net of estimated forfeitures, related to unvested RSUs was $10.6 million and $11.9 million, respectively, which is expected to be recognized as expense over weighted average periods of 2.2 years and 2.2 years, respectively. The aggregate fair value of all unvested RSUs as of December 31, 2013 and 2012 was $39.6 million and $30.0 million, respectively.
	Stock options outstanding as of December 31, 2013, 2012 and 2011 are as follows:
			December 31,
			2013						2012					2011
						Average						Average					Average
			# of Shares			Exercise Price			# of Shares			Exercise Price		# of Shares			Exercise Price
	Beginning balance			90,250		$	29.94			105,250		$	29.5		157,500		$	27.13
	Granted			—			—			—			—		—			—
	Exercised			(83,500	)	$	29.88			(15,000	)	$	26.9		(52,250	)	$	22.35
	Expired or forfeited			—			—			—			—		—		$	—
	Ending balance			6,750		$	30.65			90,250		$	29.94		105,250		$	29.5
	Number of options exercisable			6,750		$	30.65			90,250		$	29.94		105,250		$	29.5
	The following table summarizes information about stock options outstanding as of December 31, 2013:
						Average
			Outstanding			Remaining			Average			Average Aggregate		Exercisable			Average		Average Aggregate
	Price Range		Options			Contract Life			Exercise Price			Intrinsic Value		Options			Exercise Price		Intrinsic Value
	$21 to $30			5,250			0.2		$	29.11		$	34.05		5,250		$	29.11	$	34.05
	$31 to $37			1,500			1.7		$	36.03		$	27.13		1,500		$	36.03	$	27.13
	Total			6,750			1.9								6,750
	The Company has a Stock Appreciation Rights Plan which allows for the grant of up to 300,000 stock appreciation rights (“SARs”) at prices of no less than 90% of the fair market value of the common stock. As a result of the approval of the 2005 Amended and Restated Stock Incentive Plan, no further awards will be issued from the Stock Appreciation Rights Plan. SARs outstanding as of December 31, 2013, 2012 and 2011 were as follows:
			December 31,
			2013						2012					2011
						Average						Average					Average
						Exercise						Exercise					Exercise
			SARs			Prices			SARs			Prices		SARs			Prices
	Beginning balance			—		$	—			—		$	—		16,500		$	18.74
	Granted			—			—			—			—		—			—
	Exercised			—			—			—		$	—		(16,500	)	$	18.74
	Expired or forfeited			—			—			—			—		—			—
	Ending balance			—		$	—			—		$	—		—		$	—
	Number of SARs exercisable			—		$	—			—		$	—		—		$	—
	We offer an Employee Stock Purchase Plan (the “ESPP”) to all of our eligible employees. Employees are offered the opportunity to purchase the Company’s common stock at 90% of fair market value at the lower of the price at the beginning or the end of each six month offering period. Employees can invest up to 10% of their base compensation through payroll withholding towards the purchase of our common stock subject to the lesser of 1,000 shares or total market value of $25,000. There will be 8,738 shares purchased in 2014 from funds withheld during the July 1, 2013 to December 31, 2013 offering period. There were 17,640 shares purchased in 2013 in the aggregate from funds withheld during the offering periods of July 1, 2012 to December 31, 2012 and January 1, 2013 to June 30, 2013. We expense both the value of the 10% discount and the “look-back” option which provides for the more favorable price at either the beginning or end of the offering period.

Retirement_Plans

Retirement Plans	12 Months Ended
	Dec. 31, 2013
Retirement Plans	'
	Note 15. Retirement Plans
	We have a 401(k) Plan for all U.S. eligible employees. Each eligible employee can contribute a portion of their salary, limited by certain Federal regulations. Beginning in 2008, we matched 100% of employee contributions on eligible compensation, up to a maximum of 4% each pay period; our contribution vests immediately. For 2013 and 2012, eligible compensation consisted of gross base salary and annual bonus. For 2011, eligible compensation consisted solely of gross base salary. In addition, we have the discretion of contributing up to 4% of eligible compensation to each eligible employee’s 401(k) plan irrespective of the employees’ contribution amount, which also vests immediately. The Company will make a discretionary matching contribution of 2% or $0.8 million for the year ended December 31, 2013. There were no discretionary matching contributions for the years ended 2012 and 2011.
	We sponsored a standalone retirement savings defined contribution plan covering substantially all of the Company’s U.S. employees through December 31, 2011. The standalone retirement savings defined contribution plan was merged into the 401(k) Plan effective January 1, 2012. Company contributions were equal to 7.5% of each eligible employee’s eligible compensation up to the amount permitted by certain Federal regulations. For 2013 and 2012, eligible compensation consisted solely of gross base salary. For 2011, eligible compensation consisted of gross base salary and annual bonus, with the contribution on the bonus not to exceed $2,500. The Company’s contributions vest at 20% per year for six years with vesting beginning in an employee’s second year of service. For any employee hired prior to January 1, 2008, vesting is calculated based on hours of service and vesting commences on January 1 following an employee’s first full year of service. For employees hired after January 1, 2008, vesting is calculated based on elapsed time and vesting commences on the employees anniversary date.
	The expense recorded for all contributions to the 401(k) Plan for the year ended December 31, 2013 was $5.1 million, consisting of $2.7 million for the retirement savings contributions, $1.6 million for the non discretionary matching contributions, and $0.8 million for the discretionary matching contribution. The expense recorded for all contributions to the 401(k) Plan for the year ended December 31, 2012 was $4.6 million, consisting of $2.5 million for the retirement savings contributions and $2.1 million for the non discretionary matching contributions. The expense recorded for the 401(k) Plan for the year ended December 31, 2011 was $1.6 million. The expense recorded for the money purchase defined contribution plan for the year ended December 31, 2011 was $2.8 million.
	The Company sponsors a defined contribution plan for the Company’s U.K. employees under U.K. regulations. Contributions, which are fully vested when made, are equal to 15% of each eligible employee’s gross base salary. All U.K. employees are eligible on their date of hire. The expense recorded for the U.K. defined contribution plan was $2.2 million, $1.9 million and $1.7 million for 2013, 2012 and 2011, respectively. Such expenses are included in Other operating expenses.

Quarterly_Financial_Data_Unaud

Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2013
Quarterly Financial Data (Unaudited)	'
	Note 16. Quarterly Financial Data (Unaudited)
	The following is a summary of quarterly financial data for the periods indicated:
		March 31,			June 30,			September 30,			December 31,
	In thousands, except per share amounts	2013			2013			2013			2013
	Gross written premiums	$	393,222		$	332,128		$	312,076		$	333,091
	Revenues:
	Net written premiums	$	269,452		$	198,469		$	196,556		$	223,445
	Change in unearned premiums		(67,124	)		7,345			17,339			(3,543	)
	Net earned premiums		202,328			205,814			213,895			219,902
	Net investment income		13,657			14,246			14,094			14,254
	Total other-than-temporary impairment losses		(42	)		—			(1,821	)		(530	)
	Portion of loss recognized in other comprehensive income (before tax)		—			—			—			—
	Net other-than-temporary impairment losses recognized in earnings		(42	)		—			(1,821	)		(530	)
	Net realized gains (losses)		4,814			3,345			(988	)		15,768
	Other income (expense)		618			(915	)		(210	)		(665	)
	Total revenues	$	221,375		$	222,490		$	224,970		$	248,729
	Expenses:
	Net losses and loss adjustment expenses	$	131,342		$	131,148		$	125,086		$	131,385
	Commission expenses		26,555			28,391			27,685			30,863
	Other operating expenses		40,874			40,678			39,056			43,826
	Call premium on Senior Notes		—			—			—			17,895
	Interest expense		2,051			2,052			2,053			4,351
	Total expenses	$	200,822		$	202,269		$	193,880		$	228,320
	Income before income taxes		20,553			20,221			31,090			20,409
	Income tax expense	$	6,643		$	6,284		$	9,804		$	6,076
	Net income	$	13,910		$	13,937		$	21,286		$	14,333
	Comprehensive income (loss)	$	14,785		$	(24,829	)	$	25,462		$	1,200
	Combined ratio		97.9	%		97.7	%		89.8	%		94	%
	Net income (loss) per share:
	Basic	$	0.99		$	0.99		$	1.5		$	1.01
	Diluted	$	0.97		$	0.97		$	1.48		$	1
		March 31,			June 30,			September 30,			December 31,
	In thousands, except per share amounts	2012			2012			2012			2012
	Gross written premiums	$	343,149		$	322,987		$	298,742		$	321,587
	Revenues:
	Net written premiums	$	243,045		$	190,252		$	188,046		$	212,312
	Change in unearned premiums		(59,926	)		5,765			13,216			(10,746	)
	Net earned premiums		183,119			196,017			201,262			201,566
	Net investment income		11,258			15,777			13,597			13,616
	Total other-than-temporary impairment losses		(198	)		(496	)		—			(208	)
	Portion of loss recognized in other comprehensive income (before tax)		44			—			—			—
	Net other-than-temporary impairment losses recognized in earnings		(154	)		(496	)		—			(208	)
	Net realized gains		1,842			4,217			4,761			30,254
	Other income (expense)		911			387			789			(599	)
	Total revenues	$	196,976		$	215,902		$	220,409		$	244,629
	Expenses:
	Net losses and loss adjustment expenses	$	117,985		$	123,407		$	128,850		$	127,191
	Commission expenses		29,450			29,503			31,258			31,259
	Other operating expenses		36,307			39,819			40,112			42,841
	Interest expense		2,049			2,049			2,049			2,051
	Total expenses	$	185,791		$	194,778		$	202,269		$	203,342
	Income before income taxes		11,185			21,124			18,140			41,287
	Income tax expense	$	3,281		$	6,225		$	5,225		$	13,243
	Net income	$	7,904		$	14,899		$	12,915		$	28,044
	Comprehensive income	$	13,881		$	21,663		$	30,760		$	2,418
	Combined ratio		99.8	%		98.1	%		99.1	%		100.2	%
	Net income per share:
	Basic	$	0.57		$	1.06		$	0.92		$	2
	Diluted	$	0.56		$	1.05		$	0.9		$	1.96

Summary_of_Consolidated_Invest

Summary of Consolidated Investments-Other Than Investments in Related Parties	12 Months Ended
	Dec. 31, 2013
Summary of Consolidated Investments-Other Than Investments in Related Parties	'
	SCHEDULE I
	THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES
	Summary of Consolidated Investments-Other Than Investments in Related Parties
	December 31, 2013
		December 31, 2013
	In thousands	Fair Value		Gross		Gross			Amortized
				Unrealized		Unrealized			Cost
				Gains		Losses
	Fixed maturities:
	U.S. Treasury bonds, agency bonds and foreign government bonds	$	441,685	$	2,854	$	(8,855	)	$	447,686
	States, municipalities and political subdivisions		460,422		9,298		(13,651	)		464,775
	Mortgage-backed and asset-backed securities:
	Agency mortgage-backed securities		301,274		6,779		(6,016	)		300,511
	Residential mortgage obligations		41,755		1,212		(161	)		40,704
	Asset-backed securities		125,133		653		(480	)		124,960
	Commercial mortgage-backed securities		172,750		7,656		(374	)		165,468
	Subtotal	$	640,912	$	16,300	$	(7,031	)	$	631,643
	Corporate bonds		504,854		15,402		(3,443	)		492,895
	Total fixed maturities	$	2,047,873	$	43,854	$	(32,980	)	$	2,036,999
	Equity securities—common stocks		143,954		25,700		(550	)		118,804
	Short-term investments		296,250		—		—			296,250
	Cash		86,509		—		—			86,509
	Total	$	2,574,586	$	69,554	$	(33,530	)	$	2,538,562

Condensed_Financial_Informatio

Condensed Financial Information of Registrant	12 Months Ended
	Dec. 31, 2013
Condensed Financial Information of Registrant	'
	SCHEDULE II
	THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES
	Condensed Financial Information of Registrant
	The Navigators Group, Inc.
	Balance Sheets
	(Parent Company)
	(In thousands, except share amounts)
		December 31,
		2013			2012
	ASSETS
	Cash and investments	$	100,676		$	15,026
	Investments in subsidiaries		1,040,214			955,024
	Goodwill and other intangible assets		2,534			2,534
	Other assets		26,538			23,219
	Total assets	$	1,169,962		$	995,803
	LIABILITIES AND STOCKHOLDERS’ EQUITY
	Liabilities:
	Senior Notes	$	263,308		$	114,424
	Accounts payable and other liabilities		802			552
	Accrued interest payable		3,640			1,342
	Total liabilities	$	267,750		$	116,318
	Stockholders’ Equity:
	Preferred stock, $.10 par value, authorized 1,000,000 shares, none issued	$	—		$	—
	Common stock, $.10 par value, authorized 50,000,000 shares, issued 17,709,876 shares for 2013 and 17,558,046 shares for 2012		1,770			1,755
	Additional paid-in capital		335,546			329,452
	Treasury stock, at cost (3,511,380 shares for 2013 and 2012)		(155,801	)		(155,801	)
	Retained earnings		692,337			628,871
	Accumulated other comprehensive income:
	Net unrealized gains (losses) on securities available-for-sale, net of tax		23,387			67,161
	Foreign currency translation adjustment, net of tax		4,973			8,047
	Total stockholders’ equity	$	902,212		$	879,485
	Total liabilities and stockholders’ equity	$	1,169,962		$	995,803
	SCHEDULE II
	THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES
	Condensed Financial Information of Registrant (Continued)
	The Navigators Group, Inc.
	Statements of Income
	(Parent Company)
	(In thousands)
		Year Ended December 31,
		2013			2012			2011
	Revenues:
	Net investment income	$	13		$	341		$	595
	Dividends received from wholly-owned subsidiaries		—			15,000			45,000
	Total revenues	$	13		$	15,341		$	45,595
	Expenses:
	Call premium on Senior Notes	$	17,895		$	—		$	—
	Interest expense		10,507			8,198			8,188
	Other (income) expense		2			1,749			2,969
	Total expenses	$	28,404		$	9,947		$	11,157
	Income (loss) before income tax benefit	$	(28,391	)	$	5,394		$	34,438
	Income tax benefit		(9,886	)		(3,332	)		(3,635	)
	Income (loss) before equity in undistributed net income of wholly owned subsidiaries	$	(18,505	)	$	8,726		$	38,073
	Equity in undistributed net income of wholly-owned subsidiaries		81,971			55,036			(12,476	)
	Net income	$	63,466		$	63,762		$	25,597
	SCHEDULE II
	THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES
	Condensed Financial Information of Registrant (Continued)
	The Navigators Group, Inc.
	Statements of Cash Flows
	(Parent Company)
	(In thousands)
		Year Ended December 31,
	2013			2012			2011
Operating activities:
Net income	$	63,466		$	63,762		$	25,597
Adjustments to reconcile net income to net cash provided by (used in) operations:
Equity in undistributed net income of wholly-owned subsidiaries		(81,971	)		(70,036	)		(32,524	)
Dividends received from subsidiaries		—			15,000			45,000
Call premium on redemption of Senior Notes		17,895			—			—
Other		2,098			(3,265	)		5,831
Net cash provided by (used in) operating activities	$	1,488		$	5,461		$	43,904
Investing activities:
Fixed maturities, available-for-sale
Sales	$	8,754		$	7,986		$	45,716
Purchases		(1,249	)		(14,700	)		(9,253	)
Equity securities
Sales		—			—			—
Purchases		—			—			—
Net increase in short-term investments		(89,988	)		(167	)		10,064
Net cash provided by (used in) investing activities	$	(82,483	)	$	(6,881	)	$	46,527
Financing activities:
Capital contribution to subsidiary	$	(50,000	)	$	—		$	—
Net Proceeds from Debt Offering		263,278			—			—
Redemption of 7.0% Senior Notes Due May 1, 2016		(132,437	)		—			—
Purchase of treasury stock		—			—			(90,866	)
Proceeds of stock issued from employee stock purchase plan		821			672			945
Proceeds of stock issued from exercise of stock options		2,495			404			1,169
Net cash provided by (used in) financing activities	$	84,157		$	1,076		$	(88,752	)
Increase (decrease) in cash	$	3,162		$	(344	)	$	1,679
Cash at beginning of year		2,981			3,325			1,646
Cash at end of year	$	6,143		$	2,981		$	3,325

Supplementary_Insurance_Inform

Supplementary Insurance Information	12 Months Ended
	Dec. 31, 2013
Supplementary Insurance Information	'
	SCHEDULE III
	THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES
	Supplementary Insurance Information
	In thousands		Deferred		Reserve		Unearned		Other policy		Net		Net		Losses		Amortization		Other		Net
			policy		for losses		premiums		claims and		earned		investment		and loss		of deferred		operating		written
			acquisition		and loss				benefits		premiums		income (1)		adjustment		policy		expenses (1)		premiums
			costs		adjustment				payable						expenses		acquisition
					expenses										incurred		costs (2)
	Year ended December 31, 2013
	Insurance Companies		$	54,984	$	1,523,175	$	536,303	$	—	$	639,338	$	49,083	$	415,413	$	81,132	$	119,920	$	680,008
	Lloyd’s Operations			12,023		521,896		178,303		—		202,601		7,160		103,548		34,710		44,514		207,914
			$	67,007	$	2,045,071	$	714,606	$	—	$	841,939	$	56,243	$	518,961	$	115,842	$	164,434	$	887,922
	Year ended December 31, 2012
	Insurance Companies		$	48,294	$	1,567,045	$	470,425	$	—	$	571,439	$	46,549	$	417,082	$	81,370	$	113,625	$	622,956
	Lloyd’s Operations			12,711		530,003		171,982		—		210,525		7,551		80,351		42,449		45,454		210,699
			$	61,005	$	2,097,048	$	642,407	$	—	$	781,964	$	54,100	$	497,433	$	123,819	$	159,079	$	833,655
	Year ended December 31, 2011
	Insurance Companies		$	47,298	$	1,517,331	$	384,596	$	—	$	472,463	$	54,164	$	341,625	$	64,165	$	101,517	$	542,391
	Lloyd’s Operations			16,686		565,348		148,032		—		219,182		8,955		135,372		48,341		36,512		211,407
			$	63,984	$	2,082,679	$	532,628	$	—	$	691,645	$	63,119	$	476,997	$	112,506	$	138,029	$	753,798
	(1)  -	Net investment income and Other operating expenses reflect only such amounts attributable to the Company’s insurance operations.
	(2)  -	Amortization of deferred policy acquisition costs reflects only such amounts attributable to the Company’s insurance operations. A portion of these costs is eliminated in consolidation.

ReinsuranceWritten_Premium

Reinsurance-Written Premium	12 Months Ended
	Dec. 31, 2013
Reinsurance-Written Premium	'
	SCHEDULE IV
	THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES
	Reinsurance—Written Premium
				Ceded to		Assumed				Percentage
		Direct		other		from other		Net		of amount
	In thousands	Amount		companies		companies		amount		assumed to net
	Year ended December 31, 2013
	Property-Casualty	$	1,127,331	$	482,596	$	243,187	$	887,922		27	%
	Year ended December 31, 2012
	Property-Casualty	$	1,034,658	$	452,810	$	251,807	$	833,655		30	%
	Year ended December 31, 2011
	Property-Casualty	$	929,778	$	354,418	$	178,438	$	753,798		24	%

Valuation_and_Qualifying_Accou

Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2013
Valuation and Qualifying Accounts	'
	SCHEDULE V
	THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES
	Valuation and Qualifying Accounts
		Balance at		Charged (Credited) to			Charged to		Deductions		Balance at
	In thousands	January 1, 2013		Costs and Expenses			Other Accounts		(Describe)		December 31, 2013
	Description:
	Allowance for uncollectable reinsurance	$	11,520	$	(188	)	$	—	$	—	$	11,332
	Valuation allowance in deferred taxes	$	499	$	55		$	—	$	—	$	554

Supplementary_Information_Conc

Supplementary Information Concerning Property-Casualty Insurance Operations	12 Months Ended
	Dec. 31, 2013
Supplementary Information Concerning Property-Casualty Insurance Operations	'
	SCHEDULE VI
	THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES
	Supplementary Information Concerning Property-Casualty Insurance Operations
	($ in thousands)
			Deferred		Reserve										Losses and loss					Amortization
					for losses										adjustment					of deferred
			policy		and loss		Discount,				Net		Net		expenses incurred related to					policy		Other		Net
			acquisition		adjustment		if any,		Unearned		earned		investment		Current		Prior			acquisition		operating		written
	Affiliation with Registrant		costs		expenses		deducted		premiums		premiums		income (1)		year		years			costs (2)		expenses (1)		premiums
	Consolidated Subsidiaries:
	Year ended December 31, 2013		$	67,007	$	2,045,071	$	—	$	714,606	$	841,939	$	56,243	$	520,227	$	(1,266	)	$	115,842	$	164,434	$	887,922
	Year ended December 31, 2012		$	61,005	$	2,097,048	$	—	$	642,407	$	781,964	$	54,100	$	542,724	$	(45,291	)	$	123,819	$	159,079	$	833,655
	Year ended December 31, 2011		$	63,984	$	2,082,679	$	—	$	532,628	$	691,645	$	63,119	$	474,852	$	2,145		$	112,506	$	138,029	$	753,798
	-1	- Net investment income and Other operating expenses reflect only such amounts attributable to the Company’s insurance operations.
	-2	- Amortization of deferred policy acquisition costs reflects only such amounts attributable to the Company’s insurance operations. A portion of these costs is eliminated in consolidation.

Organization_and_Summary_of_Si1

Organization and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2013
Cash	'
	Cash
	Cash includes cash on hand and demand deposits with banks, excluding such amounts held by Syndicate 1221 included as Funds at Lloyd’s.
Investments	'
	Investments
	As of December 31, 2013 and 2012, all fixed maturity and equity securities held by the Company were carried at fair value and classified as available-for-sale. Available-for-sale securities are debt and equity securities not classified as either held-to-maturity securities or trading securities and are reported at fair value, with unrealized gains and losses excluded from earnings and reported in accumulated other comprehensive income (“AOCI”) as a separate component of stockholders’ equity. Fixed maturity securities include bonds, mortgage-backed and asset-backed securities. Equity securities consist of common stock.
	Short-term investments are carried at cost, which approximates fair value. Short-term investments mature within one year from the purchase date.
	All prices for our fixed maturities, equity securities and short-term investments valued as Level 1, Level 2 or Level 3 in the fair value hierarchy, as defined in the Financial Accounts Standards Board (“FASB”) Accounting Standards Codification 820 (“ASC 820”), Fair Value Measurements, are received from independent pricing services utilized by one of our outside investment managers whom we employ to assist us with investment accounting services. This manager utilizes a pricing committee which approves the use of one or more independent pricing service vendors. The pricing committee consists of five or more members of the investment management firm, one from senior management and one from the accounting group with the remainder from the asset class specialists and client strategists. The pricing source of each security is determined in accordance with the pricing source procedures approved by the pricing committee. The investment manager uses supporting documentation received from the independent pricing service vendor detailing the inputs, models and processes used in the independent pricing service vendors’ evaluation process to determine the appropriate fair value hierarchy. Any pricing where the input is believed to be unobservable is deemed to be a Level 3 price. Management has reviewed this process by which the manager determines the prices and has obtained alternative pricing to validate a sample of the prices and assess their reasonableness.
	Premiums and discounts on fixed maturity securities are amortized into interest income over the life of the security under the interest method. For mortgage-backed and asset-backed securities, anticipated prepayments and expected maturities are utilized in applying the interest rate method to our mortgage-backed and asset-backed securities. An effective yield is calculated based on projected principal cash flows at the time of original purchase. The effective yield is used to amortize the purchase price of the security over the security’s expected life. Book values are adjusted to reflect the amortization of premium or accretion of discount on a monthly basis. The projected principal cash flows are based on certain prepayment assumptions which are generated using a prepayment model. The prepayment model uses a number of factors to estimate prepayment activity including the current levels of interest rates (refinancing incentive), time of year (seasonality), economic activity (including housing turnover) and term and age of the underlying collateral (burnout, seasoning). Prepayment assumptions associated with the mortgage-backed and asset-backed securities are reviewed on a periodic basis. When changes in prepayment assumptions are deemed necessary as the result of actual prepayments differing from anticipated prepayments, securities are revalued based upon the new prepayment assumptions utilizing the retrospective adjustment method, whereby the effective yield is recalculated to reflect actual payments to date and anticipated future payments. The investment in such securities is adjusted to the amount that would have existed had the new effective yield been applied since the acquisition of the security. Such adjustments, if any, are included in net investment income for the current period being reported.
	Realized gains and losses on sales of investments are recognized when the related trades are executed and are determined on the basis of the specific identification method.
Impairment of Invested Assets	'
	Impairment of Invested Assets
	Management regularly reviews our fixed maturity and equity securities portfolios to evaluate the necessity of recording impairment losses for other-than-temporary declines in the fair value of securities.
	For fixed maturity securities, we consider our intent to sell a security and whether it is more likely than not that we will be required to sell a security before the anticipated recovery as part of the process of evaluating whether a security’s unrealized loss represents an other-than-temporary decline. For fixed maturity securities that have a fair value below amortized cost and that we intend to sell or for which it is more likely than not that we would be required to sell, an other than temporary impairment (“OTTI”) loss is recognized in earnings by writing such security down to fair value. For fixed maturity securities we do not intend to sell or for which it is more likely that not we would not be required to sell, a decline in value below amortized cost is only recognized to the extent the present value of future cash flows expected to be collected is less than the amortized cost of the security. Such shortfall in the present value future cash flows is considered the credit loss and is recognized as an OTTI loss in earnings, with the non-credit portion of the impairment (i.e. the difference between the present value of future cash flows and fair value of the security) recognized as OTTI losses in other comprehensive income (“OCI”).
	In evaluating OTTI of equity securities, we consider our intent to hold the securities as part of the process of evaluating whether a decline in fair value below cost represents an other than temporary decline in value. For equity securities in an unrealized loss position that we do not intent to hold or that we do not expect to recover their value within a reasonable period of time, an OTTI loss is recognized in earnings by writing such security down to the fair value.
Syndicate 1221	'
	Syndicate 1221
	Syndicate 1221 reports the amount of premiums, claims, and expenses recorded in an underwriting account for a particular year over a three year period. Traditionally, three years has been necessary to report substantially all premiums associated with an underwriting year and to report most of the related claims, although claims may remain unsettled after the underwriting year is closed. Syndicate 1221 typically closes an underwriting year by reinsuring outstanding claims in that underwriting year with the next underwriting year. Only profits from closed underwriting years of account are distributed to NCUL. Profits from open underwriting years of account are not available and therefore not distributed to NCUL until the end of the three year period.
	The Company’s financial statements include all of the assets, liabilities, revenues and expenses of Syndicate1221. Adjustments are recorded to recognize underwriting results as incurred in the specific year and not over a three year period. Syndicate 1221 is not a separate legal entity. Refer to Note 10, Lloyd’s Syndicate 1221, for additional information.
Translation of Foreign Currencies	'
	Translation of Foreign Currencies
	Functional currency assets and liabilities are translated into U.S. dollars using period end rates of exchange and the related translation adjustments are recorded as a separate component of AOCI. Statement of income amounts expressed in functional currencies are translated using average exchange rates. Realized gains and losses resulting from foreign currency transactions are recorded in Other income (expense) in our Consolidated Statements of Income.
Premium Revenues	'
	Premium Revenues
	Written premium is recorded based on the insurance policies that have been reported to us and the policies that have been written by agents but not yet reported to us. We must estimate the amount of written premium not yet reported based on judgments relative to current and historical trends of the business being written. Such estimates are regularly reviewed and updated and any resulting adjustments are included in the current year’s results. An unearned premium reserve is established to reflect the unexpired portion of each policy at the financial reporting date.
	Substantially all of our business is placed through agents and brokers. We record estimates for both unreported direct and assumed premiums. We also record the ceded portion of the estimated gross written premium and related acquisition costs. The earned gross, ceded and net premiums are calculated based on our earning methodology which is generally pro-rata over the policy period or over the period of risk if the period of risk differs significantly from the contract period.
	A portion of our premium is estimated for unreported premium, mostly for the Marine business written by our U.K. Branch and Lloyd’s Operations as well as the Accident & Health and Latin American & Caribbean property casualty and surety reinsurance business written by NavRe. Such premium estimates are generally based on submission data received from brokers and agents and recorded when the insurance policy or reinsurance contract is written or bound. The estimates are regularly reviewed and updated taking into account the premium received to date versus the estimate and the age of the estimate. To the extent that the actual premium varies from the estimates, the difference, along with the related loss reserves and underwriting expenses, is recorded in current operations.
Reinsurance Ceded	'
	Reinsurance Ceded
	In the normal course of business, reinsurance is purchased by us from insurers or reinsurers to reduce the amount of loss arising from claims. In order to determine the proper accounting for the reinsurance, management analyzes the reinsurance agreements to determine whether the reinsurance should be classified as prospective or retroactive based upon the terms of the reinsurance agreement and whether the reinsurer has assumed significant insurance risk to the extent that the reinsurer may realize a significant loss from the transaction.
	Prospective reinsurance is reinsurance in which an assuming company agrees to reimburse the ceding company for losses that may be incurred as a result of future insurable events covered under contracts subject to the reinsurance. Retroactive reinsurance is reinsurance in which an assuming company agrees to reimburse a ceding company for liabilities incurred as a result of past insurable events covered under contracts subject to the reinsurance.
	Ceded reinsurance premiums and any related ceding commission and ceded losses are reflected as reductions of the respective income or expense accounts over the terms of the reinsurance contracts. Prepaid reinsurance premiums represent the portion of premiums ceded to reinsurers applicable to the unexpired terms of the reinsurance contracts in force. Reinsurance reinstatement premiums are recognized in the same period as the loss event that gave rise to the reinstatement premiums. Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability associated with the reinsured policy. Unearned premiums ceded and estimates of amounts recoverable from reinsurers on paid and unpaid losses are reflected as assets. Provisions are made for estimated unrecoverable reinsurance.
Deferred Policy Acquisition Costs	'
	Deferred Policy Acquisition Costs
	Costs of acquiring business which vary with and are directly related to the production of new or renewal business are deferred and amortized ratably over the period that the related premiums are recognized as revenue. Such costs primarily include commission expense, other underwriting expenses and premium taxes are limited to the incremental direct costs related to the successful acquisition of new or renewal business. The method of computing deferred policy acquisition costs limits the deferral to their estimated net realizable value based on the related unearned premiums and takes into account anticipated losses and loss adjustment expenses, commission expense and operating expenses based on historical and current experience as well as anticipated investment income.
Reserves for Losses and Loss Adjustment Expenses	'
	Reserves for Losses and Loss Adjustment Expenses
	Unpaid losses and loss adjustment expenses are determined on an individual basis for claims reported on direct business for insureds, from reports received from ceding insurers for insurance assumed from such insurers and on estimates based on Company and industry experience for IBNR claims and loss adjustment expenses. Indicated IBNR loss reserves are calculated by our actuaries using several standard actuarial methodologies, including the paid and incurred loss development and the paid and incurred Bornheutter-Ferguson loss methods. Additional analyses, such as frequency/severity analyses, are performed for certain books of business. The provision for unpaid losses and loss adjustment expenses has been established to cover the estimated unpaid cost of claims incurred. Such estimates are regularly reviewed and updated and any resulting adjustments are included in the current year’s results. Management believes that the liability it has recognized for unpaid losses and loss adjustment expenses is a reasonable estimate of the ultimate unpaid claims incurred, however, such provisions are necessarily based on estimates and, accordingly, no representation is made that the ultimate liability will not differ materially from the amounts recorded in the accompanying consolidated financial statements. Losses and loss adjustment expenses are recorded on an undiscounted basis.
Earnings per Share	'
	Earnings per Share
	Basic earnings per share (“EPS”) is computed by dividing net income by the weighted average number of common shares outstanding for the period. Diluted earnings per share reflects the basic earnings per share adjusted for the potential dilution that would occur if all issued stock options were exercised and all stock grants were fully vested.
Depreciation and Amortization	'
	Depreciation and Amortization
	Depreciation of furniture and fixtures, electronic data processing equipment and computer software is provided over the estimated useful lives of the respective assets, ranging from three to seven years, using the straight-line method. Amortization of leasehold improvements is provided over the shorter of the useful lives of those improvements or the contractual terms of the leases using the straight-line method.
Goodwill and Other Intangible Assets	'
	Goodwill and Other Intangible Assets
	Goodwill represents the excess of cost of acquiring a business enterprise over the fair value of the net assets acquired. The Company has also recorded indefinite lived intangible assets related to the acquisition of the remaining non-controlled stamp capacity of Lloyd’s Syndicate 1221. Goodwill and indefinite lived intangible assets are reported at carrying value and are tested for impairment at least annually. Goodwill and indefinite lived intangible assets are considered impaired if the estimated fair value is less than its carrying value. Any impairment loss is measured as the difference between the implied fair value and the carrying value. This Company did not recognize an impairment on goodwill or the indefinite lived intangible assets for any of the years ended December 31, 2013, 2012 and 2011.
	As of December 31, 2013, the carrying value of goodwill and indefinite lived intangible assets was $7.2 million, consisting of $2.5 million and $2.4 million of goodwill assigned to NMC and our Lloyd’s Operations, respectively, and $2.3 million of indefinite lived intangible assets assigned to our Lloyd’s Operations. As of December 31, 2012, the carrying value of goodwill and indefinite lived intangible assets was $7.1 million, consisting of $2.5 million and $2.4 million of goodwill assigned to NMC and our Lloyd’s Operations, respectively, and $2.2 million of indefinite lived intangible assets assigned to our Lloyd’s Operations. Changes in the carrying value of the goodwill and indefinite lived intangible assets are due to fluctuations in currency exchange rates between the U.S. dollar and the British pound.
Income Taxes	'
	Income Taxes
	We apply the asset and liability method of accounting for income taxes. Under the asset and liability method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax basis. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. In assessing the realization of deferred tax assets, management considers whether it is more likely than not that the deferred tax assets will be realized.
Use of Estimates	'
	Use of Estimates
	The preparation of financial statements in conformity with GAAP requires the use of estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the period. The accounting estimates that are viewed by management as critical are those in connection with reserves for losses and loss adjustment expenses, reinsurance recoverables, written and unearned premiums, deferred tax assets, and impairment of invested assets.
Recently Adopted Accounting Pronouncements	'
	Recently Adopted Accounting Pronouncements
	In February 2013, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2013 -02 amending Codification topic 220 – Comprehensive Income. The amendments do not change the current requirements for reporting net income or other comprehensive income in the financial statements. The guidance requires an entity to present information about significant items reclassified out of AOCI by component and for items reclassified out of AOCI and into net income, the entity must disclose the effect of such items on the affected net income line item. The Company adopted this standard effective January 1, 2013, and presents this information on the consolidated statements of comprehensive income. Adoption of this standard did not have any impact on the Company’s consolidated balance sheets, results of operations or cash flows.
	In July 2012, the FASB issued ASU 2012-02 amending Codification topic 350 – Intangibles – Goodwill and Other. The amendment is intended to reduce cost and complexity, in addition to enhancing consistency of impairment testing guidance among long-lived asset categories by permitting entities to assess qualitative factors to determine whether it is necessary to calculate an asset’s fair value when testing an indefinite-lived asset for impairment. The amendment is effective for fiscal years beginning after September 15, 2012. The Company adopted this standard effective January 1, 2013. Adoption of this standard did not have any impact on the Company’s consolidated financial position, results of operating or cash flows.

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2013
Reconciliation of Basic and Diluted Earnings per Share Computations	'
	The following is a reconciliation of the basic and diluted EPS computations for the years ended December 31, 2013, 2012 and 2011:
		Year Ended December 31,
	In thousands, except share and per share amounts	2013		2012		2011
	Net income	$	63,466	$	63,762	$	25,597
	Basic weighted average shares		14,133,925		14,052,311		14,980,429
	Effect of common stock equivalents:
	Assumed exercise of stock options and vesting of stock grants		211,628		275,509		202,856
	Diluted weighted average shares		14,345,553		14,327,820		15,183,285
	Net income per common share:
	Basic	$	4.49	$	4.54	$	1.71
	Diluted	$	4.42	$	4.45	$	1.69

Segment_Information_Tables

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2013
Financial Data by Segment	'
	Financial data by segment for the years ended December 31, 2013, 2012, and 2011 were as follows:
			Year Ended December 31, 2013
			Insurance			Lloyd’s
	In thousands		Companies			Operations			Corporate(1)			Total
	Gross written premiums		$	1,002,275		$	368,242		$	—		$	1,370,517
	Net written premiums			680,008			207,914			—			887,922
	Net earned premiums			639,338			202,601			—			841,939
	Net losses and loss adjustment expenses			(415,413	)		(103,548	)		—			(518,961	)
	Commission expenses			(81,132	)		(34,710	)		2,348			(113,494	)
	Other operating expenses			(119,920	)		(44,514	)		—			(164,434	)
	Other income (expense)			2,764			(1,588	)		(2,348	)		(1,172	)
	Underwriting profit (loss)		$	25,637		$	18,241		$	—		$	43,878
	Net investment income			49,083			7,160			8			56,251
	Net realized gains (losses)			20,600			(58	)		4			20,546
	Call premium on Senior Notes			—			—			(17,895	)		(17,895	)
	Interest expense			—			—			(10,507	)		(10,507	)
	Income (loss) before income taxes		$	95,320		$	25,343		$	(28,390	)	$	92,273
	Income tax expense (benefit)			29,965			8,728			(9,886	)		28,807
	Net income (loss)		$	65,355		$	16,615		$	(18,504	)	$	63,466
	Identifiable assets		$	3,077,437		$	930,567		$	161,448		$	4,169,452
	Losses and loss adjustment expenses ratio			65	%		51.1	%					61.6	%
	Commission expense ratio			12.7	%		17.1	%					13.5	%
	Other operating expense ratio (2)			18.3	%		22.8	%					19.7	%
	Combined ratio			96	%		91	%					94.8	%
	-1	- Includes Corporate segment intercompany eliminations.
	-2	- Includes Other operating expenses and Other income.
			Year Ended December 31, 2012
			Insurance			Lloyd’s
	In thousands		Companies			Operations			Corporate(1)			Total
	Gross written premiums		$	921,325		$	365,140		$	—		$	1,286,465
	Net written premiums			622,956			210,699			—			833,655
	Net earned premiums			571,439			210,525			—			781,964
	Net losses and loss adjustment expenses			(417,082	)		(80,351	)		—			(497,433	)
	Commission expenses			(81,370	)		(42,449	)		2,349			(121,470	)
	Other operating expenses			(113,625	)		(45,454	)		—			(159,079	)
	Other income (expense)			3,790			47			(2,349	)		1,488
	Underwriting profit (loss)		$	(36,848	)	$	42,318		$	—		$	5,470
	Net investment income			46,549			7,551			148			54,248
	Net realized gains (losses)			36,468			3,555			193			40,216
	Interest expense			—			—			(8,198	)		(8,198	)
	Income (loss) before income taxes		$	46,169		$	53,424		$	(7,857	)	$	91,736
	Income tax expense (benefit)			12,686			18,620			(3,332	)		27,974
	Net income (loss)		$	33,483		$	34,804		$	(4,525	)	$	63,762
	Identifiable assets		$	3,036,489		$	928,448		$	42,733		$	4,007,670
	Losses and loss adjustment expenses ratio			73	%		38.2	%					63.6	%
	Commission expense ratio			14.2	%		20.2	%					15.5	%
	Other operating expense ratio (2)			19.2	%		21.5	%					20.2	%
	Combined ratio			106.4	%		79.9	%					99.3	%
	-1	- Includes Corporate segment intercompany eliminations.
	-2	- Includes Other operating expenses and Other income.
			Year Ended December 31, 2011
			Insurance			Lloyd’s
	In thousands		Companies			Operations			Corporate(1)			Total
	Gross written premiums		$	788,419		$	319,797		$	—		$	1,108,216
	Net written premiums			542,391			211,407			—			753,798
	Net earned premiums			472,463			219,182			—			691,645
	Net losses and loss adjustment expenses			(341,625	)		(135,372	)		—			(476,997	)
	Commission expenses			(64,165	)		(48,341	)		2,069			(110,437	)
	Other operating expenses			(101,517	)		(36,512	)		—			(138,029	)
	Other income (expense)			3,955			(657	)		(2,069	)		1,229
	Underwriting profit (loss)		$	(30,889	)	$	(1,700	)	$	—		$	(32,589	)
	Net investment income			54,164			8,955			381			63,500
	Net realized gains (losses)			12,151			(2,354	)		214			10,011
Interest expense			—			—			(8,188	)		(8,188	)
Income (loss) before income taxes		$	35,426		$	4,901		$	(7,593	)	$	32,734
Income tax expense (benefit)			8,271			1,523			(2,657	)		7,137
Net income (loss)		$	27,155		$	3,378		$	(4,936	)	$	25,597
Identifiable assets		$	2,768,930		$	865,230		$	35,847		$	3,670,007
Losses and loss adjustment expenses ratio			72.3	%		61.8	%					69	%
Commission expense ratio			13.6	%		22.1	%					16	%
Other operating expense ratio (2)			20.6	%		16.9	%					19.7	%
Combined ratio			106.5	%		100.8	%					104.7	%
-1	- Includes Corporate segment intercompany eliminations.
-2	- Includes Other operating expenses and Other income.
Additional Financial Data by Segment	'
	The following tables provide additional financial data by segment for the years ended December 31, 2013, 2012 and 2011:
			Year Ended December 31, 2013
			Insurance			Lloyd’s
	In thousands		Companies			Operations			Total
	Gross written premiums:
	Marine		$	171,822		$	181,046		$	352,868
	Property casualty			700,087			129,522			829,609
	Professional liability			130,366			57,674			188,040
	Total		$	1,002,275		$	368,242		$	1,370,517
	Net written premiums:
	Marine		$	119,837		$	134,627		$	254,464
	Property casualty			462,942			42,334			505,276
	Professional liability			97,229			30,953			128,182
	Total		$	680,008		$	207,914		$	887,922
	Net earned premiums:
	Marine		$	129,276		$	138,690		$	267,966
	Property casualty			409,480			37,722			447,202
	Professional liability			100,582			26,189			126,771
	Total		$	639,338		$	202,601		$	841,939
			Year Ended December 31, 2012
			Insurance			Lloyd’s
	In thousands		Companies			Operations			Total
	Gross written premiums:
	Marine		$	200,095		$	194,423		$	394,518
	Property casualty			590,741			127,028			717,769
	Professional liability			130,489			43,689			174,178
	Total		$	921,325		$	365,140		$	1,286,465
	Net written premiums:
	Marine		$	133,210		$	143,600		$	276,810
	Property casualty			390,168			43,824			433,992
	Professional liability			99,578			23,275			122,853
	Total		$	622,956		$	210,699		$	833,655
	Net earned premiums:
	Marine		$	142,181		$	136,898		$	279,079
	Property casualty			332,782			52,951			385,733
	Professional liability			96,476			20,676			117,152
	Total		$	571,439		$	210,525		$	781,964
			Year Ended December 31, 2011
			Insurance			Lloyd’s
	In thousands		Companies			Operations			Total
	Gross written premiums:
	Marine		$	228,500		$	167,562		$	396,062
	Property casualty			445,287			115,138			560,425
	Professional liability			114,632			37,097			151,729
	Total		$	788,419		$	319,797		$	1,108,216
	Net written premiums:
	Marine		$	170,642		$	137,206		$	307,848
	Property casualty			293,758			56,249			350,007
	Professional liability			77,991			17,952			95,943
	Total		$	542,391		$	211,407		$	753,798
	Net earned premiums:
	Marine		$	169,018		$	145,659		$	314,677
	Property casualty			231,297			55,903			287,200
	Professional liability			72,148			17,620			89,768
	Total		$	472,463		$	219,182		$	691,645

Investments_Tables

Investments (Tables)	12 Months Ended
	Dec. 31, 2013
Cash and Investments Including Other-Than-Temporarily Impaired Securities Recognized within Other Comprehensive Income	'
	The following tables set forth the Company’s cash and investments as of December 31, 2013 and 2012. The tables below include OTTI securities recognized within AOCI.
		December 31, 2013
						Gross				Gross
						Unrealized				Unrealized			Amortized
	In thousands	Fair Value				Gains				Losses			Cost
	Fixed maturities:
	U.S. Treasury bonds, agency bonds and foreign government bonds	$	441,685			$	2,854			$	(8,855	)	$	447,686
	States, municipalities and political subdivisions		460,422				9,298				(13,651	)		464,775
	Mortgage-backed and asset-backed securities:
	Agency mortgage-backed securities		301,274				6,779				(6,016	)		300,511
	Residential mortgage obligations		41,755				1,212				(161	)		40,704
	Asset-backed securities		125,133				653				(480	)		124,960
	Commercial mortgage-backed securities		172,750				7,656				(374	)		165,468
	Subtotal	$	640,912			$	16,300			$	(7,031	)	$	631,643
	Corporate bonds		504,854				15,402				(3,443	)		492,895
	Total fixed maturities	$	2,047,873			$	43,854			$	(32,980	)	$	2,036,999
	Equity securities—common stocks		143,954				25,700				(550	)		118,804
	Short-term investments		296,250				—				—			296,250
	Cash		86,509				—				—			86,509
	Total	$	2,574,586			$	69,554			$	(33,530	)	$	2,538,562
		December 31, 2012
						Gross				Gross
						Unrealized				Unrealized			Amortized
	In thousands	Fair Value				Gains				Losses			Cost
	Fixed maturities:
	U.S. Treasury bonds, agency bonds and foreign government bonds	$	649,692			$	8,654			$	(36	)	$	641,074
	States, municipalities and political subdivisions		322,947				18,712				(380	)		304,615
	Mortgage-backed and asset-backed securities:
	Agency mortgage-backed securities		384,445				13,652				(204	)		370,997
	Residential mortgage obligations		38,692				1,053				(549	)		38,188
	Asset-backed securities		50,382				1,133				(49	)		49,298
	Commercial mortgage-backed securities		204,821				17,996				(18	)		186,843
	Subtotal	$	678,340			$	33,834			$	(820	)	$	645,326
	Corporate bonds		470,854				27,129				(25	)		443,750
	Total fixed maturities	$	2,121,833			$	88,329			$	(1,261	)	$	2,034,765
	Equity securities—common stocks		101,297				16,919				(626	)		85,004
	Short-term investments		153,788				—				—			153,788
	Cash		45,336				—				—			45,336
	Total	$	2,422,254			$	105,248			$	(1,887	)	$	2,318,893
Scheduled Maturity Dates for Fixed Maturity Securities by Number of Years Until Maturity	'
	The contractual maturity dates for fixed maturity securities categorized by the number of years until maturity as of December 31, 2013 are shown in the following table:
		December 31, 2013
						Amortized
	In thousands	Fair Value				Cost
	Due in one year or less	$	85,240			$	84,691
	Due after one year through five years		627,515				615,267
	Due after five years through ten years		443,197				446,918
	Due after ten years		251,009				258,480
	Mortgage- and asset-backed securities		640,912				631,643
	Total	$	2,047,873			$	2,036,999
Amount and Percentage of Fixed Maturities by Rating	'
	The following table shows the amount and percentage of the Company’s fixed maturities as of December 31, 2013 by Standard & Poor’s (“S&P”) credit rating or, if an S&P rating is not available, the equivalent Moody’s Investor Services (“Moody’s”) rating. The table includes fixed maturities at fair value, and the total rating is the weighted average quality rating.
		December 31, 2013
								Percent
	In thousands	Rating		Fair Value				of Total
	Rating description:
	Extremely strong	AAA		$	348,908				17	%
	Very strong	AA			1,047,155				51	%
	Strong	A			452,455				22	%
	Adequate	BBB			184,302				9	%
	Speculative	BB & Below			11,500				1	%
	Not rated	NR			3,553				0	%
	Total	AA		$	2,047,873				100	%
Summary of Aggregate Fair Value and Gross Unrealized Loss by Length of Time Securities had Continuously been in Gross Unrealized Loss Position as Well as Number of Securities	'
	The following table summarizes all securities in a gross unrealized loss position as of December 31, 2013 and 2012, showing the aggregate fair value and gross unrealized loss by the length of time those securities had continuously been in a gross unrealized loss position as well as the relevant number of securities.
		December 31, 2013											December 31, 2012
										Gross									Gross
		Number of								Unrealized			Number of						Unrealized
	In thousands, except # of securities	Securities				Fair Value				Loss			Securities			Fair Value			Loss
	Fixed maturities:
	U.S. Treasury bonds, agency bonds, and foreign government bonds
	0-6 months		27			$	136,360			$	1,096			8		$	23,760		$	22
	7-12 months		26				149,370				7,759			3			14,118			11
	> 12 months		—				—				—			1			4,652			3
	Subtotal		53			$	285,730			$	8,855			12		$	42,530		$	36
	States, municipalities and political subdivisions
	0-6 months		28			$	40,132			$	297			10		$	21,299		$	325
	7-12 months		104				205,152				12,100			—			—			—
	> 12 months		6				12,357				1,254			4			2,908			55
	Subtotal		138			$	257,641			$	13,651			14		$	24,207		$	380
	Agency mortgage-backed securities
	0-6 months		39			$	39,458			$	434			10		$	62,516		$	174
	7-12 months		64				77,860				3,768			2			1,671			30
	> 12 months		9				22,784				1,814			—			—			—
	Subtotal		112			$	140,102			$	6,016			12		$	64,187		$	204
	Residential mortgage obligations
	0-6 months		3			$	431			$	2			6		$	1,825		$	22
	7-12 months		7				950				29			—			—			—
	> 12 months		15				2,467				130			35			7,252			527
	Subtotal		25			$	3,848			$	161			41		$	9,077		$	549
	Asset-backed securities
	0-6 months		14			$	75,887			$	479			—		$	—		$	—
	7-12 months		1				203				1			—			—			—
	> 12 months		—				—				—			2			2,369			49
	Subtotal		15			$	76,090			$	480			2		$	2,369		$	49
	Commercial mortgage-backed securities
	0-6 months		4			$	6,712			$	31			7		$	2,639		$	7
	7-12 months		2				15,098				322			—			—			—
	> 12 months		4				774				21			5			845			11
	Subtotal		10			$	22,584			$	374			12		$	3,484		$	18
	Corporate bonds
	0-6 months		34			$	93,591			$	717			2		$	3,528		$	6
	7-12 months		18				55,021				2,726			—			—			—
	> 12 months		—				—				—			4			6,689			19
	Subtotal		52			$	148,612			$	3,443			6		$	10,217		$	25
	Total fixed maturities		405			$	934,607			$	32,980			99		$	156,071		$	1,261
	Equity securities—common stocks
	0-6 months		5			$	7,387			$	422			13		$	23,345		$	522
	7-12 months		2				3,538				128			1			1,943			104
	> 12 months		—				—				—			—			—			—
	Total equity securities		7			$	10,925			$	550			14		$	25,288		$	626
Summary of Activity Related to Other-Than-Temporary Impairment Losses	'
	The table below summarizes the Company’s activity related to OTTI losses for the periods indicated:
		Year Ended December 31,
		2013								2012						2011
		Number of								Number of						Number of
	In thousands, except # of securities	Securities				Amount				Securities			Amount			Securities			Amount
	Total OTTI losses:
	Corporate and other bonds		1			$	1,822				—		$	—			1		$	109
	Commercial mortgage-backed securities		—				—				—			—			—			—
	Residential mortgage-backed securities		—				—				1			55			19			2,616
	Asset-backed securities		—				—				—			—			—			—
	Equities		3				571				3			847			2			892
	Total		4			$	2,393				4		$	902			22		$	3,617
	Less: Portion of loss in accumulated other comprehensive income (loss):
	Corporate and other bonds					$	—						$	—					$	—
	Commercial mortgage-backed securities						—							—						—
	Residential mortgage-backed securities						—							44						1,632
	Asset-backed securities						—							—						—
	Equities						—							—						—
	Total					$	—						$	44					$	1,632
	Impairment losses recognized in earnings:
	Corporate and other bonds					$	1,822						$	—					$	109
	Commercial mortgage-backed securities						—							—						—
	Residential mortgage-backed securities						—							11						984
	Asset-backed securities						—							—						—
	Equities						571							847						892
	Total					$	2,393						$	858					$	1,985
Summary of Cumulative Amounts Related to Credit Loss Portion of Other-Than-Temporary Impairment Losses on Debt Securities	'
	The following table summarizes the cumulative amounts related to the Company’s credit loss portion of the OTTI losses on debt securities for the years ended December 31, 2013, 2012 and 2011. The Company does not intend to sell and it is more likely than not that it will not be required to sell, the securities prior to recovery of the amortized cost basis for which the non-credit loss portion is included in OCI.
		Year Ended December 31,
	In thousands	2013				2012				2011
	Beginning balance	$	3,332			$	3,321			$	2,228
	Additions for credit loss impairments recognized in the current period on securities not previously impaired		1,822								109
	Additions for credit loss impairments recognized in the current period on securities previously impaired						11				984
	Reductions for credit loss impairments previously recognized on securities sold during the period		—				—				—
	Ending balance	$	5,154			$	3,332			$	3,321
Contractual Maturity by Number of Years Until Maturity for Fixed Maturity Securities with a Gross Unrealized Loss	'
	The contractual maturity dates for fixed maturity securities categorized by the number of years until maturity, with a gross unrealized loss as of December 31, 2013 is presented in the following table:
		December 31, 2013
		Gross Unrealized Losses								Fair Value
						Percent							Percent
	In thousands	Amount				of Total				Amount			of Total
	Due in one year or less	$	1				0	%		$	7,687			1	%
	Due after one year through five years		2,152				7	%			242,879			26	%
	Due after five years through ten years		13,585				41	%			262,989			28	%
	Due after ten years		10,211				31	%			178,428			19	%
	Mortgage- and asset-backed securities		7,031				21	%			242,624			26	%
	Total	$	32,980				100	%		$	934,607			100	%
Net Investment Income	'
	The Company’s net investment income was derived from the following sources:
		Year Ended December 31,
	In thousands	2013				2012				2011
	Fixed maturities	$	53,898			$	58,995			$	65,060
	Equity securities		4,835				3,945				5,071
	Short-term investments		774				1,694				964
	Total investment income		59,507				64,634				71,095
	Investment expenses		(3,256	)			(10,386	)			(7,595	)
	Net investment income	$	56,251			$	54,248			$	63,500
Change in Net Unrealized Gains/(Losses)	'
	The change in net unrealized gains and losses, inclusive of the change in the non-credit portion of OTTI losses, consisted of:
		Year Ended December 31,
	In thousands	2013				2012				2011
	Fixed maturities	$	(76,194	)		$	15,709			$	44,712
	Equity securities		8,857				(5,989	)			(183	)
	Gross unrealized gains (losses)		(67,337	)			9,720				44,529
	Deferred income tax		(23,565	)			3,418				15,143
	Change in net unrealized gains (losses), net	$	(43,772	)		$	6,302			$	29,386
Realized Gains and Losses Excluding Net Other-Than-Temporary Impairment Losses Recognized in Earnings	'
	Realized gains and losses, excluding net OTTI losses recognized in earnings, for the periods indicated were as follows:
		Year Ended December 31,
	In thousands	2013				2012				2011
	Fixed maturities:
	Gains	$	8,539			$	28,789			$	11,678
	Losses		(2,797	)			(1,915	)			(7,044	)
	Fixed maturities, net	$	5,742			$	26,874			$	4,634
	Equity securities:
	Gains	$	17,955			$	14,673			$	9,319
	Losses		(758	)			(473	)			(1,957	)
	Equity securities, net	$	17,197			$	14,200			$	7,362
	Net realized gains (losses)	$	22,939			$	41,074			$	11,996
Fixed Maturities and Equity Securities by Asset Class that are Measured at Fair Value	'
	The following tables present, for each of the fair value hierarchy levels as defined by the accounting guidance for fair value measurements and described below, the Company’s fixed maturities and equity securities by asset class that are measured at fair value on a recurring basis as of December 31, 2013 and 2012:
		December 31, 2013
	In thousands	Level 1				Level 2				Level 3			Total
	Fixed maturities:
	U.S. Treasury bonds, agency bonds and foreign government bonds	$	242,379			$	199,306			$	—		$	441,685
	States, municipalities and political subdivisions		—				460,422				—			460,422
	Mortgage-backed and asset-backed securities:													—
	Agency mortgage-backed securities		—				301,274				—			301,274
	Residential mortgage obligations		—				41,755				—			41,755
	Asset-backed securities		—				125,133				—			125,133
	Commercial mortgage-backed securities		—				172,750				—			172,750
	Subtotal	$	—			$	640,912			$	—		$	640,912
	Corporate bonds		—				500,447				4,407			504,854
	Total fixed maturities	$	242,379			$	1,801,087			$	4,407		$	2,047,873
	Equity securities—common stocks		143,954				—				—			143,954
	Total	$	386,333			$	1,801,087			$	4,407		$	2,191,827
		December 31, 2012
	In thousands	Level 1				Level 2				Level 3			Total
	Fixed maturities:
	U.S. Treasury bonds, agency bonds and foreign government bonds	$	414,502			$	235,190			$	—		$	649,692
	States, municipalities and political subdivisions		—				322,947				—			322,947
	Mortgage-backed and asset-backed securities:													—
	Agency mortgage-backed securities		—				384,445				—			384,445
	Residential mortgage obligations		—				38,692				—			38,692
	Asset-backed securities		—				50,382				—			50,382
	Commercial mortgage-backed securities		—				204,821				—			204,821
	Subtotal	$	—			$	678,340			$	—		$	678,340
	Corporate bonds		—				470,854				—			470,854
	Total fixed maturities	$	414,502			$	1,707,331			$	—		$	2,121,833
	Equity securities—common stocks		101,297				—				—			101,297
	Total	$	515,799			$	1,707,331			$	—		$	2,223,130
Reconciliation of Beginning and Ending Balances for All Investments Measured at Fair Value Using Level 3 Inputs	'
	The following tables present a reconciliation of the beginning and ending balances for all investments measured at fair value using Level 3 inputs for the years ended December 31, 2013 and 2011. As of December 31, 2012, the Company did not have any Level 3 assets.
		Year Ended December 31, 2013
						Realized				Unrealized											Transfers		Transfers
		Beginning				Gains				Gains											into		out of			Ending
	In thousands	Balance				(Losses)				(Losses)			Purchases			Sales			Settlements		Level 3		Level 3			Balance
	Assets:
	Coporate Bond	$	—			$	—			$	(42	)	$	4,660		$	(211	)	$	—	$	—	$	—		$	4,407
	Total assets	$	—			$	—			$	(42	)	$	4,660		$	(211	)	$	—	$	—	$	—		$	4,407
		Year Ended December 31, 2011
						Realized				Unrealized											Transfers		Transfers
		Beginning				Gains				Gains											into		out of			Ending
	In thousands	Balance				(Losses)				(Losses)			Purchases			Sales			Settlements		Level 3		Level 3			Balance
	Assets:
	Commercial Mortgage Obligations	$	1,837			$	—			$	94		$	—		$	—		$	—	$	—	$	(1,931	)	$	—
	Total assets	$	1,837			$	—			$	94		$	—		$	—		$	—	$	—	$	(1,931	)	$	—

Reserves_for_Losses_and_Loss_A1

Reserves for Losses and Loss Adjustment Expenses (Tables)	12 Months Ended
	Dec. 31, 2013
Summary of Activity in Reserve for Losses and Loss Adjustment Expenses	'
	The following table summarizes the Company’s reserves for losses and LAE activity for the years ended December 31, 2013, 2012 and 2011:
		Year Ended December 31,
	In thousands	2013			2012			2011
	Net reserves for losses and LAE at beginning of year	$	1,216,909		$	1,237,234		$	1,142,542
	Provision for losses and LAE for claims occurring in the current year		520,227			542,724			474,852
	Increase (decrease) in estimated losses and LAE for claims occurring in prior years		(1,266	)		(45,291	)		2,145
	Incurred losses and LAE		518,961			497,433			476,997
	Losses and LAE paid for claims occurring during:
	Current year		(147,758	)		(110,373	)		(73,242	)
	Prior years		(365,479	)		(407,385	)		(309,063	)
	Losses and LAE payments		(513,237	)		(517,758	)		(382,305	)
	Net reserves for losses and LAE at end of year		1,222,633			1,216,909			1,237,234
	Reinsurance recoverables on unpaid losses and LAE		822,438			880,139			845,445
	Gross reserves for losses and LAE at end of year	$	2,045,071		$	2,097,048		$	2,082,679
Segment Break Down of Prior Years' Net Reserve Deficiency (Redundancy)	'
	The segment and line of business breakdowns of prior period net reserve deficiencies (redundancies) for the years ended December 31, 2013, 2012 and 2011 are as follows:
		Year Ended December 31,
	In thousands	2013			2012			2011
	Insurance Companies:
	Marine	$	(15,227	)	$	(10,010	)	$	1,348
	Property Casualty		18,466			4,293			(6,828	)
	Professional Liability		10,191			7,613			17,582
	Insurance Companies	$	13,430		$	1,896		$	12,102
	Lloyd’s Operations:
	Marine	$	(2,998	)	$	(30,735	)	$	(10,311	)
	Property Casualty		(14,574	)		(6,890	)		(5,434	)
	Professional Liability		2,876			(9,562	)		5,788
	Lloyd’s Operations	$	(14,696	)	$	(47,187	)	$	(9,957	)
	Total deficiencies (redundancies)	$	(1,266	)	$	(45,291	)	$	2,145
Lloyd's	'
Segment Break Down of Prior Years' Net Reserve Deficiency (Redundancy)	'
	Liability business. A summary of the resulting prior period redundancies for each business within our Lloyd’s Operations by prior UY is set forth below:
	In thousands	Marine			Property			Professional			Total
					Casualty			Liability
	2010		3,492			378			1,157			5,027
	2009		14,792			4,170			6,072			25,034
	2008 and Prior		12,451			2,342			2,333			17,126
	Total Redundancy	$	30,735		$	6,890		$	9,562		$	47,187

Reinsurance_Tables

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2013
Credit Quality Distribution of Reinsurance Recoverables for Ceded Paid and Unpaid Losses and Loss Adjustment Expenses and Ceded Unearned Premiums Based On Insurer Financial Strength Ratings from A. M. Best or S&P	'
	The credit quality distribution of the Company’s reinsurance recoverables of $1.1 billion as of December 31, 2013 for ceded paid and unpaid losses and LAE and ceded unearned premiums based on insurer financial strength ratings from A.M. Best or S&P were as follows:
					Carrying				Percent
	In thousands		Rating		Value (2)				of Total (3)
	A.M. Best Rating description (1):
	Superior		A++, A+		$	536,325				49	%
	Excellent		A, A-			525,314				47	%
	Very good		B++, B+			12,295				1	%
	Fair		B, B-			23,283				2	%
	Not rated		NR			11,427				1	%
	Total				$	1,108,644				100	%
	(1) -	Equivalent S&P rating used for certain companies when an A.M. Best rating was unavailable.
	(2) -	Net of reserve for uncollectible reinsurance of approximately $11.3 million. The carrying value consists of reinsurance recoverables on paid losses due within 30-45 days and reinsurance on unpaid losses which by nature of our reserving process is our best estimate of the value as of December 31, 2013.
	(3) -	The Company holds offsetting collateral of approximately 20.2%, including 0.2% for B++, B+ and B companies and 46.7% from non rated companies which includes letters of credit, ceded balances payable and other balances held by our Insurance Companies and our Lloyd’s Operations.
Lists of 20 Largest Reinsurers Measured by Reinsurance Recoverable	'
	The following table lists the Company’s 20 largest reinsurers measured by the amount of reinsurance recoverable for ceded losses and LAE and ceded unearned premium (constituting 76.3% of the total recoverable), together with the reinsurance recoverable and collateral as of December 31, 2013, and the reinsurers’ ratings from A.M. Best and S&P:
			Reinsurance Recoverables
			Unearned				Paid/Unpaid							Collateral
	In thousands		Premium				Losses				Total (1)			Held (2)		A.M. Best	S&P
	National Indemnity Company			53,145				87,618				140,763			30,785	A++	AA+
	Transatlantic Reinsurance Company			21,411				74,069				95,480			8,506	A	A+
	Everest Reinsurance Company			21,581				68,566				90,147			7,704	A+	A+
	Munich Reinsurance America Inc.			5,067				70,233				75,300			4,352	A+	AA-
	Swiss Reinsurance America Corporation			5,800				68,157				73,957			9,609	A+	AA-
	Lloyd’s Syndicate #2003			8,832				43,167				51,999			10,299	A	A+
	Allied World Reinsurance			13,859				30,215				44,074			3,971	A	A
	Partner Reinsurance Europe			10,962				29,692				40,654			17,027	A+	A+
	Scor Global P&C SE			11,710				24,623				36,333			9,895	A	A+
	Tower Insurance Company			—				23,283				23,283			—	B	NR
	Atlantic Specialty Insurance			9,260				13,602				22,862			3,526	A	A-
	Employers Mutual Casualty Company			10,738				10,796				21,534			9,709	A	NR
	Validus Reinsurance Ltd.			2,403				17,308				19,711			14,501	A	A
	Lloyd’s Syndicate #4000			147				19,432				19,579			407	A	A+
	QBE Reinsurance Corp			7,131				11,292				18,423			1,781	A	A+
	Ace Property and Casualty Insurance Company			9,862				7,687				17,549			7,342	A+	AA-
	Odyssey American Reinsurance Corporation			3,550				11,997				15,547			2,175	A	A-
	Berkley Insurance Company			1,983				13,439				15,422			485	A+	A+
	Ironshore Indemnity Inc.			6,808				7,980				14,788			7,959	A	NR
	AXIS Re Europe			4,762				9,347				14,109			3,675	A+	A+
	Top 20 Reinsurers			209,011				642,503				851,514			153,708
	Others			38,811				218,319				257,130			69,769
	Total			247,822				860,822				1,108,644			223,477
	(1) -	Net of reserve for uncollectible reinsurance of approximately $11.3 million.
	(2) -	Collateral of $223.5 million consists of $167.3 million in ceded balances payable, $53.4 million in letters of credit, and $2.8 million of other balances held by the Company’s Insurance Companies and Lloyd’s Operations.
Summary of Written Premium	'
	The following table summarizes written premium:
			Year Ended December 31,
	In thousands		2013				2012				2011
	Direct		$	1,127,331			$	1,034,658			$	929,778
	Assumed			243,187				251,807				178,438
	Ceded			(482,596	)			(452,810	)			(354,418	)
	Net		$	887,922			$	833,655			$	753,798
Summary of Earned Premium	'
	The following table summarizes earned premium:
			Year Ended December 31,
	In thousands		2013				2012				2011
	Direct		$	1,069,677			$	972,844			$	912,020
	Assumed			228,247				205,759				125,797
	Ceded			(455,985	)			(396,639	)			(346,172	)
	Net		$	841,939			$	781,964			$	691,645
Summary of Losses and Loss Adjustment Expenses Incurred	'
	The following table summarizes losses and loss adjustment expenses incurred:
			Year Ended December 31,
	In thousands		2013				2012				2011
	Direct		$	552,381			$	608,945			$	608,445
	Assumed			155,313				151,137				81,945
	Ceded			(188,733	)			(262,649	)			(213,393	)
	Net		$	518,961			$	497,433			$	476,997

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2013
Components of Current and Deferred Income Tax Expense (Benefit)	'
	The components of current and deferred income tax expense (benefit) are as follows:
		Year Ended December 31,
	In thousands	2013			2012			2011
	Current income tax expense (benefit):
	Federal and foreign	$	28,084		$	39,242		$	573
	State and local		446			146			340
	Subtotal		28,530			39,388			913
	Deferred income tax expense (benefit):
	Federal and foreign		277			(11,414	)		6,224
	State and local		—			—			—
	Subtotal		277			(11,414	)		6,224
	Total income tax expense (benefit)	$	28,807		$	27,974		$	7,137
Reconciliation of Total Income Taxes Applicable to Pre-Tax Operating Income and Amounts Computed by Applying Federal Statutory Income Tax Rate to Pre-Tax Operating Income	'
	A reconciliation of total income taxes applicable to pre-tax operating income and the amounts computed by applying the federal statutory income tax rate to the pre-tax operating income were as follows:
		Year Ended December 31,
	In thousands	2013						2012					2011
	Computed expected tax expense	$	32,299			35	%	$	32,109		35	%	$	11,457		35	%
	Tax-exempt interest		(3,839	)		-4.2	%		(4,443	)	-4.8	%		(4,437	)	-13.6	%
	Dividends received deduction		(897	)		-1	%		(799	)	-0.9	%		(1,065	)	-3.3	%
	Proration		710			0.8	%		786		0.9	%		825		2.5	%
	Current state and local income taxes, net of federal income tax		290			0.3	%		95		0.1	%		221		0.7	%
	Other		244			0.3	%		226		0.2	%		136		0.5	%
	Actual tax expense and rate	$	28,807			31.2	%	$	27,974		30.5	%	$	7,137		21.8	%
Tax Effects of Temporary Differences That Give Rise to Federal, Foreign, State and Local Deferred Tax Assets and Deferred Tax Liabilities	'
	The tax effects of temporary differences that give rise to federal, foreign, state and local deferred tax assets and deferred tax liabilities were as follows:
		December 31,
	In thousands	2013			2012
	Deferred tax assets:
	Loss reserve discount	$	27,822		$	29,687
	Unearned premiums		25,706			22,860
	Compensation related		6,782			5,285
	State and local net deferred tax assets		555			499
	Other		3,889			4,245
	Total gross deferred tax assets		64,754			62,576
	Less: Valuation allowance		(555	)		(499	)
	Total deferred tax assets	$	64,199		$	62,077
	Deferred tax liabilities:
	Deferred acquisition costs	$	(19,258	)	$	(16,903	)
	Net unrealized gains on securities		(12,635	)		(36,200	)
	Other		(4,119	)		(5,758	)
	Total deferred tax liabilities	$	(36,012	)	$	(58,861	)
	Net deferred income tax asset (liability)	$	28,187		$	3,216

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2013
Future Minimum Annual Rental Commitments under Various Noncancellable Operating Leases	'
	Future minimum annual rental commitments as of December 31, 2013 under various non-cancellable operating leases for our office facilities, which expire at various dates through 2023, are as follows:
		Year Ended
	In thousands	December 31,
	2014	$	11,061
	2015		11,092
	2016		9,228
	2017		7,990
	2018		6,884
	Thereafter		15,696
	Total minimum operating lease payments	$	61,951

Share_Capital_and_Share_Repurc1

Share Capital and Share Repurchases (Tables)	12 Months Ended
	Dec. 31, 2013
Changes in Company's Issued and Outstanding Common Shares	'
	The following table represents changes in the Company’s issued and outstanding common shares for the periods indicated:
		Year Ended December 31,
	In thousands	2013		2012		2011
	Beginning balance		14,047		13,956		15,742
	Vested stock grants		50		60		122
	Employee stock purchase plan		17		16		19
	Stock options exercised		84		15		52
	Treasury shares purchased		—		—		(1,979	)
	Ending balance		14,198		14,047		13,956
Share Repurchases	'
	The following presents our share repurchases under the aforementioned programs for the periods indicated:
		Total		Average
		Number of		Cost Paid
		Shares		Per Share
		Purchased
	Fourth quarter 2009 activity		141,576	$	47.72
	Total 2009 activity		141,576	$	47.72
	First quarter 2010 activity		573,600	$	41.27
	Second quarter 2010 activity		558,003		40.32
	Third quarter 2010 activity		97,115		42.25
	Fourth quarter 2010 activity		35,566		48.04
	Total 2010 activity		1,264,284	$	41.11
	First quarter 2011 activity		256,094	$	50.96
	Second quarter 2011 activity		597,026		47.55
	Third quarter 2011 activity		749,076		43.03
	Fourth quarter 2011 activity		376,911		45.61
	Total 2011 activity		1,979,107	$	45.91

Dividends_and_Statutory_Financ1

Dividends and Statutory Financial Information (Tables)	12 Months Ended
	Dec. 31, 2013
Amount and Nature of Net Assets Restricted from Payment of Dividends	'
	The amount and nature of net assets that are restricted from payment of dividends as of December 31, 2013 and 2012 are presented in the following table:
			As of December 31,
	In thousands		2013		2012
	Restricted Net Assets:
	Insurance Companies:
	Fixed maturities at fair value (amortized cost: 2013, $9,730; 2012, $9,607)		$	11,105	$	11,728
	Short term investments, at cost which approximates fair value			290		290
	Cash			1,210		5,208
	Total Insurance Companies (1)			12,605		17,226
	Lloyd’s Operations:
	Fixed maturities at fair value (amortized cost: 2013, $398,930; 2012, $419,271)			398,808		428,142
	Short term investments, at cost which approximates fair value			108,485		72,984
	Cash			988		849
	Total Lloyd’s Operations (2)			508,281		501,975
	Total Restricted Net Assets		$	520,886	$	519,201
	-1	- The restricted net assets for the Insurance Companies primarily consist of fixed maturities on deposit with various state insurance departments. The cash as of December 31, 2012 and 2011, as presented in the table above, was on deposit with a U.K. bank to comply with the regulatory requirements of the Prudential Regulation Authority for the underwriting activities of the U.K. Branch.
	(2)	- The restricted net assets for the Lloyd’s Operations consists of fixed maturities and cash held in trust for the benefit of syndicate policyholders and short term investments primarily consisting of overseas deposits in various countries with Lloyd’s to support underwriting activities in those countries.

Stock_Option_Plans_Stock_Grant1

Stock Option Plans, Stock Grants, Stock Appreciation Rights and Employee Stock Purchase Plan (Tables)	12 Months Ended
	Dec. 31, 2013
Amounts Charged to Expense for Stock-based Compensation	'
	The amounts charged to expense for stock-based compensation for the years ended December 31, 2013, 2012 and 2011 are presented in the following table:
			Year Ended December 31,
	In thousands		2013			2012			2011
	Restricted stock units		$	3,369		$	7,380		$	139
	Directors restricted stock grants(1)			413			390			248
	Employee stock purchase plan			132			82			173
	Stock appreciation rights(2)			—			—			(100	)
	Total stock-based compensation		$	3,914		$	7,852		$	460
	-1	- Relates to non-employee directors serving on the Parent Company’s Board of Directors, all of whom have been elected by the Company’s stockholders, as well as non-employee directors serving on NUAL’s Board of Directors.
	-2	- All outstanding stock appreciation rights were exercised during 2011.
Unvested Restricted Stock Grants Outstanding	'
	Unvested restricted stock units outstanding as of December 31, 2013, 2012 and 2011, and changes during the years ended on those dates, are presented in the following table:
			December 31,
			2013			2012			2011
	Beginning balance			587,629			526,972			590,661
	Granted—Performance			114,463			97,145			86,118
	Granted—Non Performance			155,463			146,915			98,640
	Total Granted			269,926			244,060			184,758
	Vested—Performance Earned			(15,714	)		—			(22,993	)
	Vested—Performance Unearned			(57,585	)		(46,998	)		(42,334	)
	Vested—Non Performance			(60,183	)		(91,323	)		(149,738	)
	Total Vested			(133,482	)		(138,321	)		(215,065	)
	Forfeited			(97,261	)		(45,082	)		(33,382	)
	Ending balance			626,812			587,629			526,972
Stock Options Outstanding	'
	Stock options outstanding as of December 31, 2013, 2012 and 2011 are as follows:
			December 31,
			2013						2012					2011
						Average						Average					Average
			# of Shares			Exercise Price			# of Shares			Exercise Price		# of Shares			Exercise Price
	Beginning balance			90,250		$	29.94			105,250		$	29.5		157,500		$	27.13
	Granted			—			—			—			—		—			—
	Exercised			(83,500	)	$	29.88			(15,000	)	$	26.9		(52,250	)	$	22.35
	Expired or forfeited			—			—			—			—		—		$	—
	Ending balance			6,750		$	30.65			90,250		$	29.94		105,250		$	29.5
	Number of options exercisable			6,750		$	30.65			90,250		$	29.94		105,250		$	29.5
Summarized Information about Options Outstanding	'
	The following table summarizes information about stock options outstanding as of December 31, 2013:
						Average
			Outstanding			Remaining			Average			Average Aggregate		Exercisable			Average		Average Aggregate
	Price Range		Options			Contract Life			Exercise Price			Intrinsic Value		Options			Exercise Price		Intrinsic Value
	$21 to $30			5,250			0.2		$	29.11		$	34.05		5,250		$	29.11	$	34.05
	$31 to $37			1,500			1.7		$	36.03		$	27.13		1,500		$	36.03	$	27.13
	Total			6,750			1.9								6,750
SARs Outstanding	'
	SARs outstanding as of December 31, 2013, 2012 and 2011 were as follows:
			December 31,
			2013						2012					2011
						Average						Average					Average
						Exercise						Exercise					Exercise
			SARs			Prices			SARs			Prices		SARs			Prices
	Beginning balance			—		$	—			—		$	—		16,500		$	18.74
	Granted			—			—			—			—		—			—
	Exercised			—			—			—		$	—		(16,500	)	$	18.74
	Expired or forfeited			—			—			—			—		—			—
	Ending balance			—		$	—			—		$	—		—		$	—
	Number of SARs exercisable			—		$	—			—		$	—		—		$	—

Quarterly_Financial_Data_Unaud1

Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2013
Summary of Quarterly Financial Data	'
	The following is a summary of quarterly financial data for the periods indicated:
		March 31,			June 30,			September 30,			December 31,
	In thousands, except per share amounts	2013			2013			2013			2013
	Gross written premiums	$	393,222		$	332,128		$	312,076		$	333,091
	Revenues:
	Net written premiums	$	269,452		$	198,469		$	196,556		$	223,445
	Change in unearned premiums		(67,124	)		7,345			17,339			(3,543	)
	Net earned premiums		202,328			205,814			213,895			219,902
	Net investment income		13,657			14,246			14,094			14,254
	Total other-than-temporary impairment losses		(42	)		—			(1,821	)		(530	)
	Portion of loss recognized in other comprehensive income (before tax)		—			—			—			—
	Net other-than-temporary impairment losses recognized in earnings		(42	)		—			(1,821	)		(530	)
	Net realized gains (losses)		4,814			3,345			(988	)		15,768
	Other income (expense)		618			(915	)		(210	)		(665	)
	Total revenues	$	221,375		$	222,490		$	224,970		$	248,729
	Expenses:
	Net losses and loss adjustment expenses	$	131,342		$	131,148		$	125,086		$	131,385
	Commission expenses		26,555			28,391			27,685			30,863
	Other operating expenses		40,874			40,678			39,056			43,826
	Call premium on Senior Notes		—			—			—			17,895
	Interest expense		2,051			2,052			2,053			4,351
	Total expenses	$	200,822		$	202,269		$	193,880		$	228,320
	Income before income taxes		20,553			20,221			31,090			20,409
	Income tax expense	$	6,643		$	6,284		$	9,804		$	6,076
	Net income	$	13,910		$	13,937		$	21,286		$	14,333
	Comprehensive income (loss)	$	14,785		$	(24,829	)	$	25,462		$	1,200
	Combined ratio		97.9	%		97.7	%		89.8	%		94	%
	Net income (loss) per share:
	Basic	$	0.99		$	0.99		$	1.5		$	1.01
	Diluted	$	0.97		$	0.97		$	1.48		$	1
		March 31,			June 30,			September 30,			December 31,
	In thousands, except per share amounts	2012			2012			2012			2012
	Gross written premiums	$	343,149		$	322,987		$	298,742		$	321,587
	Revenues:
	Net written premiums	$	243,045		$	190,252		$	188,046		$	212,312
	Change in unearned premiums		(59,926	)		5,765			13,216			(10,746	)
	Net earned premiums		183,119			196,017			201,262			201,566
	Net investment income		11,258			15,777			13,597			13,616
	Total other-than-temporary impairment losses		(198	)		(496	)		—			(208	)
	Portion of loss recognized in other comprehensive income (before tax)		44			—			—			—
	Net other-than-temporary impairment losses recognized in earnings		(154	)		(496	)		—			(208	)
	Net realized gains		1,842			4,217			4,761			30,254
	Other income (expense)		911			387			789			(599	)
	Total revenues	$	196,976		$	215,902		$	220,409		$	244,629
	Expenses:
	Net losses and loss adjustment expenses	$	117,985		$	123,407		$	128,850		$	127,191
	Commission expenses		29,450			29,503			31,258			31,259
	Other operating expenses		36,307			39,819			40,112			42,841
	Interest expense		2,049			2,049			2,049			2,051
	Total expenses	$	185,791		$	194,778		$	202,269		$	203,342
	Income before income taxes		11,185			21,124			18,140			41,287
	Income tax expense	$	3,281		$	6,225		$	5,225		$	13,243
	Net income	$	7,904		$	14,899		$	12,915		$	28,044
	Comprehensive income	$	13,881		$	21,663		$	30,760		$	2,418
	Combined ratio		99.8	%		98.1	%		99.1	%		100.2	%
	Net income per share:
	Basic	$	0.57		$	1.06		$	0.92		$	2
	Diluted	$	0.56		$	1.05		$	0.9		$	1.96

Organization_and_Summary_of_Si2

Organization and Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Minimum

Maximum

Navigators Insurance Company

Lloyd's

Lloyd's

Lloyd's

Lloyd's

Lloyd's

NMC Operations

NMC Operations

Syndicate 1221

Syndicate 1221

Syndicate 1221

Organization And Summary Of Significant Accounting Policies [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of Navigators Specialty Insurance Company reinsured by Navigators Insurance Company

'

'

'

'

100.00%

'

'

'

'

'

'

'

Percentage control of stamp capacity

'

'

'

'

'

'

'

100.00%

100.00%

100.00%

'

'

Property, Plant and Equipment, Useful Life

'

'

'3 years

'7 years

'

'

'

'

'

'

'

'

Goodwill and other intangible assets

$7,177,000

$7,093,000

'

'

'

'

'

'

'

'

'

'

Goodwill

'

'

'

'

'

2,400,000

2,400,000

'

'

'

2,500,000

2,500,000

Other intangible assets

'

'

'

'

'

$2,300,000

$2,200,000

'

'

'

'

'

Reconciliation_of_Basic_and_Di

Reconciliation of Basic and Diluted Earnings Per Share Computations (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Share Disclosure [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net income	$14,333	$21,286	$13,937	$13,910	$28,044	$12,915	$14,899	$7,904	$63,466	$63,762	$25,597
Basic weighted average shares	'	'	'	'	'	'	'	'	14,133,925	14,052,311	14,980,429
Effect of common stock equivalents:	'	'	'	'	'	'	'	'	'	'	'
Assumed exercise of stock options and vesting of stock grants	'	'	'	'	'	'	'	'	211,628	275,509	202,856
Diluted weighted average shares	'	'	'	'	'	'	'	'	14,345,553	14,327,820	15,183,285
Net income per common share:	'	'	'	'	'	'	'	'	'	'	'
Basic	$1.01	$1.50	$0.99	$0.99	$2	$0.92	$1.06	$0.57	$4.49	$4.54	$1.71
Diluted	$1	$1.48	$0.97	$0.97	$1.96	$0.90	$1.05	$0.56	$4.42	$4.45	$1.69

Segment_Information_Additional

Segment Information - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
									Segment
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Number of business segments	'	'	'	'	'	'	'	'	2	'	'
Combined ratio indicating underwriting profit	'	'	'	'	'	'	'	'	100.00%	'	'
Combined ratio indicating underwriting loss	'	'	'	'	'	'	'	'	100.00%	'	'
Net earned premiums	$219,902	$213,895	$205,814	$202,328	$201,566	$201,262	$196,017	$183,119	$841,939	$781,964	$691,645
Navigators Insurance Company	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Percentage of Navigators Specialty Insurance Company reinsured by Navigators Insurance Company	100.00%	'	'	'	'	'	'	'	100.00%	'	'
Insurance	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net earned premiums	'	'	'	'	'	'	'	'	639,338	571,439	472,463
Insurance | UK Branch	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net earned premiums	'	'	'	'	'	'	'	'	$44,600	$63,900	$88,300

Financial_Data_by_Segment_Deta

Financial Data by Segment (Detail) (USD $)

3 Months Ended

12 Months Ended

In Thousands, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Gross written premiums

$333,091

$312,076

$332,128

$393,222

$321,587

$298,742

$322,987

$343,149

$1,370,517

$1,286,465

$1,108,216

Net written premiums

223,445

196,556

198,469

269,452

212,312

188,046

190,252

243,045

887,922

833,655

753,798

Net earned premiums

219,902

213,895

205,814

202,328

201,566

201,262

196,017

183,119

841,939

781,964

691,645

Net losses and loss adjustment expenses

-131,385

-125,086

-131,148

-131,342

-127,191

-128,850

-123,407

-117,985

-518,961

-497,433

-476,997

Commission expenses

-30,863

-27,685

-28,391

-26,555

-31,259

-31,258

-29,503

-29,450

-113,494

-121,470

-110,437

Other operating expenses

-43,826

-39,056

-40,678

-40,874

-42,841

-40,112

-39,819

-36,307

-164,434

-159,079

-138,029

Other income (expense)

-665

-210

-915

618

-599

789

387

911

-1,172

1,488

1,229

Underwriting profit (loss)

'

'

'

'

'

'

'

'

43,878

5,470

-32,589

Net investment income

14,254

14,094

14,246

13,657

13,616

13,597

15,777

11,258

56,251

54,248

63,500

Net realized gains (losses)

'

'

'

'

'

'

'

'

20,546

40,216

10,011

Call premium on Senior Notes

-17,895

'

'

'

'

'

'

'

-17,895

'

'

Interest expense

-4,351

-2,053

-2,052

-2,051

-2,051

-2,049

-2,049

-2,049

-10,507

-8,198

-8,188

Income before income taxes

20,409

31,090

20,221

20,553

41,287

18,140

21,124

11,185

92,273

91,736

32,734

Income tax expense (benefit)

6,076

9,804

6,284

6,643

13,243

5,225

6,225

3,281

28,807

27,974

7,137

Net income (loss)

14,333

21,286

13,937

13,910

28,044

12,915

14,899

7,904

63,466

63,762

25,597

Identifiable assets

4,169,452

'

'

'

4,007,670

'

'

'

4,169,452

4,007,670

3,670,007

Losses and loss adjustment expenses ratio

'

'

'

'

'

'

'

'

61.60%

63.60%

69.00%

Commission expense ratio

'

'

'

'

'

'

'

'

13.50%

15.50%

16.00%

Other operating expense ratio

'

'

'

'

'

'

'

'

19.70%

[1]

20.20%

[1]

19.70%

[1]

Combined ratio

94.00%

89.80%

97.70%

97.90%

100.20%

99.10%

98.10%

99.80%

94.80%

99.30%

104.70%

Insurance

'

'

'

'

'

'

'

'

'

'

'

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Gross written premiums

'

'

'

'

'

'

'

'

1,002,275

921,325

788,419

Net written premiums

'

'

'

'

'

'

'

'

680,008

622,956

542,391

Net earned premiums

'

'

'

'

'

'

'

'

639,338

571,439

472,463

Net losses and loss adjustment expenses

'

'

'

'

'

'

'

'

-415,413

-417,082

-341,625

Commission expenses

'

'

'

'

'

'

'

'

-81,132

-81,370

-64,165

Other operating expenses

'

'

'

'

'

'

'

'

-119,920

-113,625

-101,517

Other income (expense)

'

'

'

'

'

'

'

'

2,764

3,790

3,955

Underwriting profit (loss)

'

'

'

'

'

'

'

'

25,637

-36,848

-30,889

Net investment income

'

'

'

'

'

'

'

'

49,083

46,549

54,164

Net realized gains (losses)

'

'

'

'

'

'

'

'

20,600

36,468

12,151

Income before income taxes

'

'

'

'

'

'

'

'

95,320

46,169

35,426

Income tax expense (benefit)

'

'

'

'

'

'

'

'

29,965

12,686

8,271

Net income (loss)

'

'

'

'

'

'

'

'

65,355

33,483

27,155

Identifiable assets

3,077,437

'

'

'

3,036,489

'

'

'

3,077,437

3,036,489

2,768,930

Losses and loss adjustment expenses ratio

'

'

'

'

'

'

'

'

65.00%

73.00%

72.30%

Commission expense ratio

'

'

'

'

'

'

'

'

12.70%

14.20%

13.60%

Other operating expense ratio

'

'

'

'

'

'

'

'

18.30%

[1]

19.20%

[1]

20.60%

[1]

Combined ratio

'

'

'

'

'

'

'

'

96.00%

106.40%

106.50%

Lloyd's

'

'

'

'

'

'

'

'

'

'

'

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Gross written premiums

'

'

'

'

'

'

'

'

368,242

365,140

319,797

Net written premiums

'

'

'

'

'

'

'

'

207,914

210,699

211,407

Net earned premiums

'

'

'

'

'

'

'

'

202,601

210,525

219,182

Net losses and loss adjustment expenses

'

'

'

'

'

'

'

'

-103,548

-80,351

-135,372

Commission expenses

'

'

'

'

'

'

'

'

-34,710

-42,449

-48,341

Other operating expenses

'

'

'

'

'

'

'

'

-44,514

-45,454

-36,512

Other income (expense)

'

'

'

'

'

'

'

'

-1,588

47

-657

Underwriting profit (loss)

'

'

'

'

'

'

'

'

18,241

42,318

-1,700

Net investment income

'

'

'

'

'

'

'

'

7,160

7,551

8,955

Net realized gains (losses)

'

'

'

'

'

'

'

'

-58

3,555

-2,354

Income before income taxes

'

'

'

'

'

'

'

'

25,343

53,424

4,901

Income tax expense (benefit)

'

'

'

'

'

'

'

'

8,728

18,620

1,523

Net income (loss)

'

'

'

'

'

'

'

'

16,615

34,804

3,378

Identifiable assets

930,567

'

'

'

928,448

'

'

'

930,567

928,448

865,230

Losses and loss adjustment expenses ratio

'

'

'

'

'

'

'

'

51.10%

38.20%

61.80%

Commission expense ratio

'

'

'

'

'

'

'

'

17.10%

20.20%

22.10%

Other operating expense ratio

'

'

'

'

'

'

'

'

22.80%

[1]

21.50%

[1]

16.90%

[1]

Combined ratio

'

'

'

'

'

'

'

'

91.00%

79.90%

100.80%

Corporate

'

'

'

'

'

'

'

'

'

'

'

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Commission expenses

'

'

'

'

'

'

'

'

2,348

[2]

2,349

[2]

2,069

[2]

Other income (expense)

'

'

'

'

'

'

'

'

-2,348

[2]

-2,349

[2]

-2,069

[2]

Net investment income

'

'

'

'

'

'

'

'

8

[2]

148

[2]

381

[2]

Net realized gains (losses)

'

'

'

'

'

'

'

'

4

[2]

193

[2]

214

[2]

Call premium on Senior Notes

'

'

'

'

'

'

'

'

-17,895

[2]

'

'

Interest expense

'

'

'

'

'

'

'

'

-10,507

[2]

-8,198

[2]

-8,188

[2]

Income before income taxes

'

'

'

'

'

'

'

'

-28,390

[2]

-7,857

[2]

-7,593

[2]

Income tax expense (benefit)

'

'

'

'

'

'

'

'

-9,886

[2]

-3,332

[2]

-2,657

[2]

Net income (loss)

'

'

'

'

'

'

'

'

-18,504

[2]

-4,525

[2]

-4,936

[2]

Identifiable assets

$161,448

[2]

'

'

'

$42,733

[2]

'

'

'

$161,448

[2]

$42,733

[2]

$35,847

[2]

[1]

Includes Other operating expenses and Other income.

[2]

Includes Corporate segment intercompany eliminations.

Additional_Financial_Data_by_S

Additional Financial Data by Segment (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Gross written premiums	$333,091	$312,076	$332,128	$393,222	$321,587	$298,742	$322,987	$343,149	$1,370,517	$1,286,465	$1,108,216
Net written premiums	223,445	196,556	198,469	269,452	212,312	188,046	190,252	243,045	887,922	833,655	753,798
Net earned premiums	219,902	213,895	205,814	202,328	201,566	201,262	196,017	183,119	841,939	781,964	691,645
Marine	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Gross written premiums	'	'	'	'	'	'	'	'	352,868	394,518	396,062
Net written premiums	'	'	'	'	'	'	'	'	254,464	276,810	307,848
Net earned premiums	'	'	'	'	'	'	'	'	267,966	279,079	314,677
Property Casualty	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Gross written premiums	'	'	'	'	'	'	'	'	829,609	717,769	560,425
Net written premiums	'	'	'	'	'	'	'	'	505,276	433,992	350,007
Net earned premiums	'	'	'	'	'	'	'	'	447,202	385,733	287,200
Professional Liability	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Gross written premiums	'	'	'	'	'	'	'	'	188,040	174,178	151,729
Net written premiums	'	'	'	'	'	'	'	'	128,182	122,853	95,943
Net earned premiums	'	'	'	'	'	'	'	'	126,771	117,152	89,768
Insurance	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Gross written premiums	'	'	'	'	'	'	'	'	1,002,275	921,325	788,419
Net written premiums	'	'	'	'	'	'	'	'	680,008	622,956	542,391
Net earned premiums	'	'	'	'	'	'	'	'	639,338	571,439	472,463
Insurance | Marine	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Gross written premiums	'	'	'	'	'	'	'	'	171,822	200,095	228,500
Net written premiums	'	'	'	'	'	'	'	'	119,837	133,210	170,642
Net earned premiums	'	'	'	'	'	'	'	'	129,276	142,181	169,018
Insurance | Property Casualty	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Gross written premiums	'	'	'	'	'	'	'	'	700,087	590,741	445,287
Net written premiums	'	'	'	'	'	'	'	'	462,942	390,168	293,758
Net earned premiums	'	'	'	'	'	'	'	'	409,480	332,782	231,297
Insurance | Professional Liability	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Gross written premiums	'	'	'	'	'	'	'	'	130,366	130,489	114,632
Net written premiums	'	'	'	'	'	'	'	'	97,229	99,578	77,991
Net earned premiums	'	'	'	'	'	'	'	'	100,582	96,476	72,148
Lloyd's	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Gross written premiums	'	'	'	'	'	'	'	'	368,242	365,140	319,797
Net written premiums	'	'	'	'	'	'	'	'	207,914	210,699	211,407
Net earned premiums	'	'	'	'	'	'	'	'	202,601	210,525	219,182
Lloyd's | Marine	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Gross written premiums	'	'	'	'	'	'	'	'	181,046	194,423	167,562
Net written premiums	'	'	'	'	'	'	'	'	134,627	143,600	137,206
Net earned premiums	'	'	'	'	'	'	'	'	138,690	136,898	145,659
Lloyd's | Property Casualty	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Gross written premiums	'	'	'	'	'	'	'	'	129,522	127,028	115,138
Net written premiums	'	'	'	'	'	'	'	'	42,334	43,824	56,249
Net earned premiums	'	'	'	'	'	'	'	'	37,722	52,951	55,903
Lloyd's | Professional Liability	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Gross written premiums	'	'	'	'	'	'	'	'	57,674	43,689	37,097
Net written premiums	'	'	'	'	'	'	'	'	30,953	23,275	17,952
Net earned premiums	'	'	'	'	'	'	'	'	$26,189	$20,676	$17,620

Cash_and_Investments_Including

Cash and Investments Including Other-Than-Temporarily Impaired Securities Recognized within Other Comprehensive Income (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Gain (Loss) on Investments [Line Items]	'	'
Total investments	$2,191,827	$2,223,130
Total investments and cash	2,574,586	2,422,254
Gross Unrealized Gains	69,554	105,248
Gross Unrealized Losses	-33,530	-1,887
Amortized Cost	2,538,562	2,318,893
Short-term investments	'	'
Gain (Loss) on Investments [Line Items]	'	'
Total investments and cash	296,250	153,788
Amortized Cost	296,250	153,788
Cash	'	'
Gain (Loss) on Investments [Line Items]	'	'
Total investments and cash	86,509	45,336
Amortized Cost	86,509	45,336
Fixed maturities	'	'
Gain (Loss) on Investments [Line Items]	'	'
Total investments	2,047,873	2,121,833
Gross Unrealized Gains	43,854	88,329
Gross Unrealized Losses	-32,980	-1,261
Amortized Cost	2,036,999	2,034,765
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign	'	'
Gain (Loss) on Investments [Line Items]	'	'
Total investments	441,685	649,692
Gross Unrealized Gains	2,854	8,654
Gross Unrealized Losses	-8,855	-36
Amortized Cost	447,686	641,074
Fixed maturities | States, municipalities and political subdivisions	'	'
Gain (Loss) on Investments [Line Items]	'	'
Total investments	460,422	322,947
Gross Unrealized Gains	9,298	18,712
Gross Unrealized Losses	-13,651	-380
Amortized Cost	464,775	304,615
Fixed maturities | Agency mortgage-backed securities	'	'
Gain (Loss) on Investments [Line Items]	'	'
Total investments	301,274	384,445
Gross Unrealized Gains	6,779	13,652
Gross Unrealized Losses	-6,016	-204
Amortized Cost	300,511	370,997
Fixed maturities | Residential Mortgage Backed Securities	'	'
Gain (Loss) on Investments [Line Items]	'	'
Total investments	41,755	38,692
Gross Unrealized Gains	1,212	1,053
Gross Unrealized Losses	-161	-549
Amortized Cost	40,704	38,188
Fixed maturities | Asset-backed securities	'	'
Gain (Loss) on Investments [Line Items]	'	'
Total investments	125,133	50,382
Gross Unrealized Gains	653	1,133
Gross Unrealized Losses	-480	-49
Amortized Cost	124,960	49,298
Fixed maturities | Commercial mortgage-backed securities	'	'
Gain (Loss) on Investments [Line Items]	'	'
Total investments	172,750	204,821
Gross Unrealized Gains	7,656	17,996
Gross Unrealized Losses	-374	-18
Amortized Cost	165,468	186,843
Fixed maturities | Mortgage-backed and asset-backed securities	'	'
Gain (Loss) on Investments [Line Items]	'	'
Total investments	640,912	678,340
Gross Unrealized Gains	16,300	33,834
Gross Unrealized Losses	-7,031	-820
Amortized Cost	631,643	645,326
Fixed maturities | Corporate bonds	'	'
Gain (Loss) on Investments [Line Items]	'	'
Total investments	504,854	470,854
Gross Unrealized Gains	15,402	27,129
Gross Unrealized Losses	-3,443	-25
Amortized Cost	492,895	443,750
Equity Securities | Common Stock	'	'
Gain (Loss) on Investments [Line Items]	'	'
Total investments	143,954	101,297
Gross Unrealized Gains	25,700	16,919
Gross Unrealized Losses	-550	-626
Amortized Cost	$118,804	$85,004

Investments_Additional_Informa

Investments - Additional Information (Detail) (USD $)

12 Months Ended

24 Months Ended

12 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Settlement Agreement

Settlement Agreement

Settlement Agreement

Mortgage-backed and asset-backed securities

Non-government backed securities

Non-government backed securities

Non-government backed securities

Non-government backed securities

Equity Securities

Y

Maximum

Maximum

Investments

Investments

Maximum

Schedule of Investments [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Non-credit OTTI on debt securities in an unrealized gain position

$500,000

$20,000

'

'

'

'

'

'

'

'

'

'

Securities, effective maturities

'

'

'

'

'

'

4.5

'

'

'

'

'

Gross Unrealized Loss

'

'

'

'

'

'

'

'

'

1,100,000

200,000

'

Percentage of fair value under carrying value

'

'

'

'

'

'

'

'

'

'

'

80.00%

Investment Expenses

3,256,000

10,386,000

7,595,000

4,500,000

4,700,000

9,200,000

'

'

'

'

'

'

Investment performance fee

'

2,800,000

'

'

'

'

'

'

'

'

'

'

Total Restricted Net Assets

$520,886,000

$519,201,000

'

'

'

'

'

'

'

'

'

'

Percentage of investment

'

'

'

'

'

'

'

5.00%

5.00%

'

'

'

Scheduled_Maturity_Dates_for_F

Scheduled Maturity Dates for Fixed Maturity Securities by Number of Years Until Maturity (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Fair Value	'	'
Due in one year or less	$85,240	'
Due after one year through five years	627,515	'
Due after five years through ten years	443,197	'
Due after ten years	251,009	'
Mortgage- and asset-backed securities	640,912	'
Total	2,047,873	2,121,833
Amortized Cost	'	'
Due in one year or less	84,691	'
Due after one year through five years	615,267	'
Due after five years through ten years	446,918	'
Due after ten years	258,480	'
Mortgage- and asset-backed securities	631,643	'
Total	$2,036,999	$2,034,765

Amount_and_Percentage_of_Fixed

Amount and Percentage of Fixed Maturities by Rating (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Investment Securities [Line Items]	'	'
Rating	'AA	'
Fair Value	$2,047,873	$2,121,833
Percent of Total	100.00%	'
Extremely strong	'	'
Investment Securities [Line Items]	'	'
Rating	'AAA	'
Fair Value	348,908	'
Percent of Total	17.00%	'
Very strong	'	'
Investment Securities [Line Items]	'	'
Rating	'AA	'
Fair Value	1,047,155	'
Percent of Total	51.00%	'
Strong	'	'
Investment Securities [Line Items]	'	'
Rating	'A	'
Fair Value	452,455	'
Percent of Total	22.00%	'
Adequate	'	'
Investment Securities [Line Items]	'	'
Rating	'BBB	'
Fair Value	184,302	'
Percent of Total	9.00%	'
Speculative	'	'
Investment Securities [Line Items]	'	'
Rating	'BB & Below	'
Fair Value	11,500	'
Percent of Total	1.00%	'
Not rated	'	'
Investment Securities [Line Items]	'	'
Rating	'NR	'
Fair Value	$3,553	'
Percent of Total	0.00%	'

Summary_of_Aggregate_Fair_Valu

Summary of Aggregate Fair Value and Gross Unrealized Loss by Length of Time Securities had Continuously been in Gross Unrealized Loss Position as Well as Number of Securities (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Investment	Investment
Fixed maturities	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	405	99
Fair Value	$934,607	$156,071
Gross Unrealized Loss	32,980	1,261
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	53	12
Fair Value	285,730	42,530
Gross Unrealized Loss	8,855	36
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign | 0-6 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	27	8
Fair Value	136,360	23,760
Gross Unrealized Loss	1,096	22
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign | 7-12 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	26	3
Fair Value	149,370	14,118
Gross Unrealized Loss	7,759	11
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign | > 12 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	'	1
Fair Value	'	4,652
Gross Unrealized Loss	'	3
Fixed maturities | States, municipalities and political subdivisions	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	138	14
Fair Value	257,641	24,207
Gross Unrealized Loss	13,651	380
Fixed maturities | States, municipalities and political subdivisions | 0-6 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	28	10
Fair Value	40,132	21,299
Gross Unrealized Loss	297	325
Fixed maturities | States, municipalities and political subdivisions | 7-12 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	104	'
Fair Value	205,152	'
Gross Unrealized Loss	12,100	'
Fixed maturities | States, municipalities and political subdivisions | > 12 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	6	4
Fair Value	12,357	2,908
Gross Unrealized Loss	1,254	55
Fixed maturities | Agency mortgage-backed securities	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	112	12
Fair Value	140,102	64,187
Gross Unrealized Loss	6,016	204
Fixed maturities | Agency mortgage-backed securities | 0-6 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	39	10
Fair Value	39,458	62,516
Gross Unrealized Loss	434	174
Fixed maturities | Agency mortgage-backed securities | 7-12 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	64	2
Fair Value	77,860	1,671
Gross Unrealized Loss	3,768	30
Fixed maturities | Agency mortgage-backed securities | > 12 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	9	'
Fair Value	22,784	'
Gross Unrealized Loss	1,814	'
Fixed maturities | Residential Mortgage Backed Securities	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	25	41
Fair Value	3,848	9,077
Gross Unrealized Loss	161	549
Fixed maturities | Residential Mortgage Backed Securities | 0-6 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	3	6
Fair Value	431	1,825
Gross Unrealized Loss	2	22
Fixed maturities | Residential Mortgage Backed Securities | 7-12 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	7	'
Fair Value	950	'
Gross Unrealized Loss	29	'
Fixed maturities | Residential Mortgage Backed Securities | > 12 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	15	35
Fair Value	2,467	7,252
Gross Unrealized Loss	130	527
Fixed maturities | Asset-backed securities	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	15	2
Fair Value	76,090	2,369
Gross Unrealized Loss	480	49
Fixed maturities | Asset-backed securities | 0-6 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	14	'
Fair Value	75,887	'
Gross Unrealized Loss	479	'
Fixed maturities | Asset-backed securities | 7-12 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	1	'
Fair Value	203	'
Gross Unrealized Loss	1	'
Fixed maturities | Asset-backed securities | > 12 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	'	2
Fair Value	'	2,369
Gross Unrealized Loss	'	49
Fixed maturities | Commercial mortgage-backed securities	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	10	12
Fair Value	22,584	3,484
Gross Unrealized Loss	374	18
Fixed maturities | Commercial mortgage-backed securities | 0-6 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	4	7
Fair Value	6,712	2,639
Gross Unrealized Loss	31	7
Fixed maturities | Commercial mortgage-backed securities | 7-12 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	2	'
Fair Value	15,098	'
Gross Unrealized Loss	322	'
Fixed maturities | Commercial mortgage-backed securities | > 12 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	4	5
Fair Value	774	845
Gross Unrealized Loss	21	11
Fixed maturities | Corporate bonds	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	52	6
Fair Value	148,612	10,217
Gross Unrealized Loss	3,443	25
Fixed maturities | Corporate bonds | 0-6 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	34	2
Fair Value	93,591	3,528
Gross Unrealized Loss	717	6
Fixed maturities | Corporate bonds | 7-12 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	18	'
Fair Value	55,021	'
Gross Unrealized Loss	2,726	'
Fixed maturities | Corporate bonds | > 12 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	'	4
Fair Value	'	6,689
Gross Unrealized Loss	'	19
Common Stock	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	7	14
Fair Value	10,925	25,288
Gross Unrealized Loss	550	626
Common Stock | 0-6 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	5	13
Fair Value	7,387	23,345
Gross Unrealized Loss	422	522
Common Stock | 7-12 months	'	'
Gain (Loss) on Investments [Line Items]	'	'
Number of Securities	2	1
Fair Value	3,538	1,943
Gross Unrealized Loss	$128	$104

Summary_of_Activity_Related_to

Summary of Activity Related to Other-Than-Temporary Impairment Losses (Detail) (USD $)	3 Months Ended						12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
							Investment	Investment	Investment
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'	'	'	'	'	'	'
Number of Securities	'	'	'	'	'	'	4	4	22
Total other-than-temporary impairment losses	$530	$1,821	$42	$208	$496	$198	$2,393	$902	$3,617
Portion of loss recognized in other comprehensive income	'	'	'	'	'	44	'	44	1,632
Net other-than-temporary impairment losses recognized in earnings	530	1,821	42	208	496	154	2,393	858	1,985
Corporate And Other Bonds	'	'	'	'	'	'	'	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'	'	'	'	'	'	'
Number of Securities	'	'	'	'	'	'	1	'	1
Total other-than-temporary impairment losses	'	'	'	'	'	'	1,822	'	109
Net other-than-temporary impairment losses recognized in earnings	'	'	'	'	'	'	1,822	'	109
Residential Mortgage Backed Securities	'	'	'	'	'	'	'	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'	'	'	'	'	'	'
Number of Securities	'	'	'	'	'	'	'	1	19
Total other-than-temporary impairment losses	'	'	'	'	'	'	'	55	2,616
Portion of loss recognized in other comprehensive income	'	'	'	'	'	'	'	44	1,632
Net other-than-temporary impairment losses recognized in earnings	'	'	'	'	'	'	'	11	984
Equity Securities	'	'	'	'	'	'	'	'	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'	'	'	'	'	'	'
Number of Securities	'	'	'	'	'	'	3	3	2
Total other-than-temporary impairment losses	'	'	'	'	'	'	571	847	892
Net other-than-temporary impairment losses recognized in earnings	'	'	'	'	'	'	$571	$847	$892

Summary_of_Cumulative_Amounts_

Summary of Cumulative Amounts Related to Credit Loss Portion of Other-Than-Temporary Impairment Losses on Debt Securities (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'
Beginning balance	$3,332	$3,321	$2,228
Additions for credit loss impairments recognized in the current period on securities not previously impaired	1,822	'	109
Additions for credit loss impairments recognized in the current period on securities previously impaired	'	11	984
Reductions for credit loss impairments previously recognized on securities sold during the period	'	'	'
Ending balance	$5,154	$3,332	$3,321

Contractual_Maturity_by_Number

Contractual Maturity by Number of Years Until Maturity for Fixed Maturity Securities with Gross Unrealized Loss (Detail) (Fixed maturities, USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]	'	'
Gross Unrealized Loss Amount	$32,980	$1,261
Percent of Total Gross Unrealized Loss	100.00%	'
Fair Value Amount	934,607	156,071
Percent of Total Fair Value	100.00%	'
Due in one year or less	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Gross Unrealized Loss Amount	1	'
Percent of Total Gross Unrealized Loss	0.00%	'
Fair Value Amount	7,687	'
Percent of Total Fair Value	1.00%	'
Due After One Year Through Five Years	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Gross Unrealized Loss Amount	2,152	'
Percent of Total Gross Unrealized Loss	7.00%	'
Fair Value Amount	242,879	'
Percent of Total Fair Value	26.00%	'
Due After Five Years Through Ten Years	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Gross Unrealized Loss Amount	13,585	'
Percent of Total Gross Unrealized Loss	41.00%	'
Fair Value Amount	262,989	'
Percent of Total Fair Value	28.00%	'
Due After Ten Years	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Gross Unrealized Loss Amount	10,211	'
Percent of Total Gross Unrealized Loss	31.00%	'
Fair Value Amount	178,428	'
Percent of Total Fair Value	19.00%	'
Mortgage- and asset-backed securities	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Gross Unrealized Loss Amount	7,031	'
Percent of Total Gross Unrealized Loss	21.00%	'
Fair Value Amount	$242,624	'
Percent of Total Fair Value	26.00%	'

Net_Investment_Income_Detail

Net Investment Income (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net Investment Income [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Investment Income	'	'	'	'	'	'	'	'	$59,507	$64,634	$71,095
Investment expenses	'	'	'	'	'	'	'	'	-3,256	-10,386	-7,595
Net investment income	14,254	14,094	14,246	13,657	13,616	13,597	15,777	11,258	56,251	54,248	63,500
Fixed maturities	'	'	'	'	'	'	'	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Investment Income	'	'	'	'	'	'	'	'	53,898	58,995	65,060
Equity Securities	'	'	'	'	'	'	'	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Investment Income	'	'	'	'	'	'	'	'	4,835	3,945	5,071
Short-term investments	'	'	'	'	'	'	'	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Investment Income	'	'	'	'	'	'	'	'	$774	$1,694	$964

Change_in_Net_Unrealized_Gains

Change in Net Unrealized Gains and Losses (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Gross unrealized gains (losses)	($67,337)	$9,720	$44,529
Deferred income tax	-23,565	3,418	15,143
Change in net unrealized gains (losses), net	-43,772	6,302	29,386
Fixed maturities	'	'	'
Gross unrealized gains (losses)	-76,194	15,709	44,712
Equity Securities	'	'	'
Gross unrealized gains (losses)	$8,857	($5,989)	($183)

Realized_Gains_and_Losses_Excl

Realized Gains and Losses Excluding Net Other-Than-Temporary Impairment Losses Recognized in Earnings (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Gain (Loss) on Investments [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Net realized gains (losses)	$15,768	($988)	$3,345	$4,814	$30,254	$4,761	$4,217	$1,842	$22,939	$41,074	$11,996
Fixed maturities	'	'	'	'	'	'	'	'	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Gains	'	'	'	'	'	'	'	'	8,539	28,789	11,678
Losses	'	'	'	'	'	'	'	'	-2,797	-1,915	-7,044
Net realized gains (losses)	'	'	'	'	'	'	'	'	5,742	26,874	4,634
Equity Securities	'	'	'	'	'	'	'	'	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Gains	'	'	'	'	'	'	'	'	17,955	14,673	9,319
Losses	'	'	'	'	'	'	'	'	-758	-473	-1,957
Net realized gains (losses)	'	'	'	'	'	'	'	'	$17,197	$14,200	$7,362

Fixed_Maturities_and_Equity_Se

Fixed Maturities and Equity Securities by Asset Class that are Measured at Fair Value (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	$2,191,827	$2,223,130
Fixed maturities	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	2,047,873	2,121,833
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	441,685	649,692
Fixed maturities | States, municipalities and political subdivisions	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	460,422	322,947
Fixed maturities | Agency mortgage-backed securities	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	301,274	384,445
Fixed maturities | Residential Mortgage Backed Securities	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	41,755	38,692
Fixed maturities | Asset-backed securities	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	125,133	50,382
Fixed maturities | Commercial mortgage-backed securities	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	172,750	204,821
Fixed maturities | Mortgage-backed and asset-backed securities	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	640,912	678,340
Fixed maturities | Corporate bonds	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	504,854	470,854
Equity Securities | Common Stock	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	143,954	101,297
Level 1	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	386,333	515,799
Level 1 | Fixed maturities	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	242,379	414,502
Level 1 | Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	242,379	414,502
Level 1 | Equity Securities | Common Stock	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	143,954	101,297
Level 2	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	1,801,087	1,707,331
Level 2 | Fixed maturities	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	1,801,087	1,707,331
Level 2 | Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	199,306	235,190
Level 2 | Fixed maturities | States, municipalities and political subdivisions	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	460,422	322,947
Level 2 | Fixed maturities | Agency mortgage-backed securities	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	301,274	384,445
Level 2 | Fixed maturities | Residential Mortgage Backed Securities	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	41,755	38,692
Level 2 | Fixed maturities | Asset-backed securities	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	125,133	50,382
Level 2 | Fixed maturities | Commercial mortgage-backed securities	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	172,750	204,821
Level 2 | Fixed maturities | Mortgage-backed and asset-backed securities	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	640,912	678,340
Level 2 | Fixed maturities | Corporate bonds	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	500,447	470,854
Level 3	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	4,407	'
Level 3 | Fixed maturities	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	4,407	'
Level 3 | Fixed maturities | Corporate bonds	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Fixed maturities and equity securities, at fair Value	$4,407	'

Reconciliation_of_Beginning_an

Reconciliation of Beginning and Ending Balances for all Investments Measured at Fair Value Using Level 3 Inputs (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'
Beginning Balance	'	$1,837
Realized Gains (Losses)	'	'
Unrealized Gains (Losses)	-42	94
Purchases	4,660	'
Sales	-211	'
Settlements	'	'
Transfers into Level 3	'	'
Transfers out of Level 3	'	-1,931
Ending Balance	4,407	'
Corporate bonds	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'
Realized Gains (Losses)	'	'
Unrealized Gains (Losses)	-42	'
Purchases	4,660	'
Sales	-211	'
Settlements	'	'
Transfers into Level 3	'	'
Ending Balance	4,407	'
Commercial mortgage-backed securities	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'
Beginning Balance	'	1,837
Realized Gains (Losses)	'	'
Unrealized Gains (Losses)	'	94
Settlements	'	'
Transfers into Level 3	'	'
Transfers out of Level 3	'	($1,931)

Summary_of_Activity_in_Reserve

Summary of Activity in Reserve for Losses and Loss Adjustment Expenses (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserves for losses and LAE at beginning of year	$1,216,909	$1,237,234	$1,142,542
Provision for losses and LAE for claims occurring in the current year	520,227	542,724	474,852
Increase (decrease) in estimated losses and LAE for claims occurring in prior years	-1,266	-45,291	2,145
Incurred losses and LAE	518,961	497,433	476,997
Losses and LAE paid for claims occurring during:	'	'	'
Current year	-147,758	-110,373	-73,242
Prior years	-365,479	-407,385	-309,063
Losses and LAE payments	-513,237	-517,758	-382,305
Net reserves for losses and LAE at end of year	1,222,633	1,216,909	1,237,234
Reinsurance recoverables on unpaid losses and LAE	822,438	880,139	845,445
Gross reserves for losses and LAE at end of year	$2,045,071	$2,097,048	$2,082,679

Segment_And_Line_of_Business_B

Segment And Line of Business Breakdowns of Prior Period Net Reserve Deficiency (Redundancy) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	($1,266)	($45,291)	$2,145
Insurance	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	13,430	1,896	12,102
Insurance | Marine	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	-15,227	-10,010	1,348
Insurance | Property Casualty	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	18,466	4,293	-6,828
Insurance | Professional Liability	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	10,191	7,613	17,582
Lloyd's	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	-14,696	-47,187	-9,957
Lloyd's | Marine	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	-2,998	-30,735	-10,311
Lloyd's | Property Casualty	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	-14,574	-6,890	-5,434
Lloyd's | Professional Liability	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	$2,876	($9,562)	$5,788

Reserves_for_Losses_and_Loss_A2

Reserves for Losses and Loss Adjustment Expenses - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	($1,266,000)	($45,291,000)	$2,145,000
Marine | Short Tail Marine Lines	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	2,600,000	'
Marine | Case Reserves	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	3,400,000	'
Marine | Claims Emergence	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	4,000,000	'
Insurance	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	13,430,000	1,896,000	12,102,000
Insurance | Offshore Energy	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	8,000,000	'	'
Insurance | Marine	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	-15,227,000	-10,010,000	1,348,000
Insurance | Professional Liability	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	10,191,000	7,613,000	17,582,000
Insurance | Professional Liability | Management Liability	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	6,100,000	'	14,500,000
Insurance | Professional Liability | Errors and Omissions	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	4,400,000	'	3,100,000
Insurance | Property Casualty	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	18,466,000	4,293,000	-6,828,000
Insurance | Property Casualty | Accident and Health	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	13,200,000	4,300,000	'
Insurance | Property Casualty | Offshore Energy	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	'	8,400,000
Insurance | Property Casualty | Small general and artisan contractors	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	10,400,000	'	'
Insurance | Property Casualty | Business in run-off	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	2,100,000	'	'
Insurance | Inland Marine	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	'	4,000,000
Insurance | Ocean Marine	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	'	-2,700,000
Insurance | Ocean Marine | Craft, P&I, and Transport classes	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	'	-5,800,000
Insurance | Ocean Marine | Specie and Liability classes	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	'	3,200,000
Lloyd's	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	-14,696,000	-47,187,000	-9,957,000
Impact of settlement of unpaid claims and claim adjustments	'	5,000,000	'
Lloyd's | NavTech	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	'	-5,500,000
Lloyd's | Marine	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	-2,998,000	-30,735,000	-10,311,000
Impact of settlement of unpaid claims and claim adjustments	'	4,100,000	'
Lloyd's | Professional Liability	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	2,876,000	-9,562,000	5,788,000
Impact of settlement of unpaid claims and claim adjustments	'	900,000	'
Lloyd's | Professional Liability | Management Liability	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	3,200,000	'	'
Lloyd's | Professional Liability | Errors and Omissions	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	6,100,000	'	'
Lloyd's | Property Casualty	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	($14,574,000)	($6,890,000)	($5,434,000)

Net_Prior_Period_Reserve_Redun

Net Prior Period Reserve Redundancies (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	$1,266	$45,291	($2,145)
Lloyd's	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	14,696	47,187	9,957
Lloyd's | 2010	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	5,027	'
Lloyd's | 2009	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	25,034	'
Lloyd's | 2008 and Prior	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	17,126	'
Marine | Lloyd's	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	2,998	30,735	10,311
Marine | Lloyd's | 2010	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	3,492	'
Marine | Lloyd's | 2009	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	14,792	'
Marine | Lloyd's | 2008 and Prior	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	12,451	'
Property And Casualty | Lloyd's	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	6,890	'
Property And Casualty | Lloyd's | 2010	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	378	'
Property And Casualty | Lloyd's | 2009	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	4,170	'
Property And Casualty | Lloyd's | 2008 and Prior	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	2,342	'
Professional Liability | Lloyd's	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	9,562	'
Professional Liability | Lloyd's | 2010	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	1,157	'
Professional Liability | Lloyd's | 2009	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	6,072	'
Professional Liability | Lloyd's | 2008 and Prior	'	'	'
Liability for Unpaid Claims and Claims Adjustment Expense, Adjustment of Opening Balance [Line Items]	'	'	'
Net reserve deficiencies (redundancies) in prior years	'	$2,333	'

Reinsurance_Additional_Informa

Reinsurance - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
	Entity
Effects of Reinsurance [Line Items]	'		'	'
Reserve for uncollectible reinsurance amount	$11,300,000		$11,500,000	'
Reinsurance rating description	'To meet our standards of acceptability, when the reinsurance is placed, a reinsurer generally must have a rating from A.M. Best Company ("A.M. Best") and/or S&P of "A" or better, or an equivalent financial strength if not rated, plus at least $500 million in policyholders' surplus.		'	'
Reinsurance recoverables	1,108,644,000	[1],[2],[3]	'	'
Ceded premiums earned	455,985,000		396,639,000	346,172,000
Ceded losses incurred	188,733,000		262,649,000	213,393,000
Percentage of reinsurance recoverable of 20 largest reinsurers	76.30%		'	'
Number of largest reinsurers	20		'	'
Percentage of funding requirement to retain	100.00%		'	'
Reinsurance recoverables for paid and unpaid losses	860,822,000		'	'
Catastrophic	'		'	'
Effects of Reinsurance [Line Items]	'		'	'
Reinsurance recoverables for paid and unpaid losses	46,500,000		88,200,000	'
Superstorm Sandy	'		'	'
Effects of Reinsurance [Line Items]	'		'	'
Reinsurance recoverables for paid and unpaid losses	30,700,000		54,600,000	'
Hurricane Gustav and Ike	'		'	'
Effects of Reinsurance [Line Items]	'		'	'
Reinsurance recoverables for paid and unpaid losses	3,300,000		15,200,000	'
Letter of Credit	'		'	'
Effects of Reinsurance [Line Items]	'		'	'
Percentage of collateral held	24.00%		'	'
Minimum	'		'	'
Effects of Reinsurance [Line Items]	'		'	'
Policyholders' surplus for reinsurance	$500,000,000		'	'
Percentage of collateral required of qualifying reinsurers	0.00%		'	'
Maximum	'		'	'
Effects of Reinsurance [Line Items]	'		'	'
Percentage of collateral required of qualifying reinsurers	100.00%		'	'
[1]	Equivalent S&P rating used for certain companies when an A.M. Best rating was unavailable.
[2]	Net of reserve for uncollectible reinsurance of approximately $11.3 million. The carrying value consists of reinsurance recoverables on paid losses due within 30-45 days and reinsurance on unpaid losses which by nature of our reserving process is our best estimate of the value as of December 31, 2013.
[3]	Net of reserve for uncollectible reinsurance of approximately $11.3 million.

Credit_Quality_Distribution_of

Credit Quality Distribution of Reinsurance Recoverables for Ceded Paid and Unpaid Losses and Loss Adjustment Expenses and Ceded Unearned Premiums Based On Insurer Financial Strength Ratings from A. M. Best or S&P (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013
Ceded Credit Risk [Line Items]	'
Rating	'AA
Fair Value	$1,108,644	[1],[2],[3]
Percent of Total	100.00%	[1],[4]
Superior	'
Ceded Credit Risk [Line Items]	'
Rating	'A++, A+	[1]
Fair Value	536,325	[1],[2]
Percent of Total	49.00%	[1],[4]
Excellent	'
Ceded Credit Risk [Line Items]	'
Rating	'A, A-	[1]
Fair Value	525,314	[1],[2]
Percent of Total	47.00%	[1],[4]
Very Good	'
Ceded Credit Risk [Line Items]	'
Rating	'B++, B+	[1]
Fair Value	12,295	[1],[2]
Percent of Total	1.00%	[1],[4]
Fair	'
Ceded Credit Risk [Line Items]	'
Rating	'B, B-	[1]
Fair Value	23,283	[1],[2]
Percent of Total	2.00%	[1],[4]
Not rated	'
Ceded Credit Risk [Line Items]	'
Rating	'NR	[1]
Fair Value	$11,427	[1],[2]
Percent of Total	1.00%	[1],[4]
[1]	Equivalent S&P rating used for certain companies when an A.M. Best rating was unavailable.
[2]	Net of reserve for uncollectible reinsurance of approximately $11.3 million. The carrying value consists of reinsurance recoverables on paid losses due within 30-45 days and reinsurance on unpaid losses which by nature of our reserving process is our best estimate of the value as of December 31, 2013.
[3]	Net of reserve for uncollectible reinsurance of approximately $11.3 million.
[4]	The Company holds offsetting collateral of approximately 20.2%, including 0.2% for B++, B+ and B companies and 46.7% from non rated companies which includes letters of credit, ceded balances payable and other balances held by our Insurance Companies and our Lloyd's Operations.

Credit_Quality_Distribution_of1

Credit Quality Distribution of Reinsurance Recoverables for Ceded Paid and Unpaid Losses and Loss Adjustment Expenses and Ceded Unearned Premiums Based On Insurer Financial Strength Ratings from A. M. Best or S&P (Parenthetical) (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2012
In Millions, unless otherwise specified			Minimum	Maximum	Very Good	Not rated
Ceded Credit Risk [Line Items]	'	'	'	'	'	'
Reserve for uncollectible reinsurance amount	$11.30	$11.50	'	'	'	'
Reinsurance recoverable due date	'	'	'30 days	'45 days	'	'
Percentage of offsetting collateral held	'	20.20%	'	'	0.20%	46.70%

Lists_of_20_Largest_Reinsurers

Lists of 20 Largest Reinsurers Measured by Reinsurance Recoverable (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	$247,822		$221,015
Reinsurance Recoverables Paid/Unpaid Losses	860,822		'
Reinsurance Recoverables Total	1,108,644	[1],[2],[3]	'
Collateral Held	223,477	[4]	'
Rating	'AA		'
National Indemnity Company | AM Best, A++ Rating | Standard & Poor's, AA+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	53,145		'
Reinsurance Recoverables Paid/Unpaid Losses	87,618		'
Reinsurance Recoverables Total	140,763	[3]	'
Collateral Held	30,785	[4]	'
Transatlantic Reinsurance Company | AM Best, A Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	21,411		'
Reinsurance Recoverables Paid/Unpaid Losses	74,069		'
Reinsurance Recoverables Total	95,480	[3]	'
Collateral Held	8,506	[4]	'
Everest Reinsurance Company | AM Best, A+ Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	21,581		'
Reinsurance Recoverables Paid/Unpaid Losses	68,566		'
Reinsurance Recoverables Total	90,147	[3]	'
Collateral Held	7,704	[4]	'
Munich Reinsurance America Inc. | AM Best, A+ Rating | Standard & Poor's, AA- Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	5,067		'
Reinsurance Recoverables Paid/Unpaid Losses	70,233		'
Reinsurance Recoverables Total	75,300	[3]	'
Collateral Held	4,352	[4]	'
Swiss Reinsurance America Corporation | AM Best, A+ Rating | Standard & Poor's, AA- Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	5,800		'
Reinsurance Recoverables Paid/Unpaid Losses	68,157		'
Reinsurance Recoverables Total	73,957	[3]	'
Collateral Held	9,609	[4]	'
Lloyd Syndicate #2003 | AM Best, A Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	8,832		'
Reinsurance Recoverables Paid/Unpaid Losses	43,167		'
Reinsurance Recoverables Total	51,999	[3]	'
Collateral Held	10,299	[4]	'
Allied World Reinsurance | AM Best, A Rating | Standard & Poor's, A Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	13,859		'
Reinsurance Recoverables Paid/Unpaid Losses	30,215		'
Reinsurance Recoverables Total	44,074	[3]	'
Collateral Held	3,971	[4]	'
Partner Reinsurance Europe | AM Best, A+ Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	10,962		'
Reinsurance Recoverables Paid/Unpaid Losses	29,692		'
Reinsurance Recoverables Total	40,654	[3]	'
Collateral Held	17,027	[4]	'
Scor Global P&C SE | AM Best, A Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	11,710		'
Reinsurance Recoverables Paid/Unpaid Losses	24,623		'
Reinsurance Recoverables Total	36,333	[3]	'
Collateral Held	9,895	[4]	'
Tower Insurance Company | AM Best, B Rating | Standard & Poor's, Not Rated	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Paid/Unpaid Losses	23,283		'
Reinsurance Recoverables Total	23,283	[3]	'
Atlantic Specialty Insurance | AM Best, A Rating | Standard & Poor's, A- Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	9,260		'
Reinsurance Recoverables Paid/Unpaid Losses	13,602		'
Reinsurance Recoverables Total	22,862	[3]	'
Collateral Held	3,526	[4]	'
Employers Mutual Casualty Company | AM Best, A Rating | Standard & Poor's, Not Rated	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	10,738		'
Reinsurance Recoverables Paid/Unpaid Losses	10,796		'
Reinsurance Recoverables Total	21,534	[3]	'
Collateral Held	9,709	[4]	'
Validus Reinsurance Ltd | AM Best, A Rating | Standard & Poor's, A Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	2,403		'
Reinsurance Recoverables Paid/Unpaid Losses	17,308		'
Reinsurance Recoverables Total	19,711	[3]	'
Collateral Held	14,501	[4]	'
Lloyd Syndicate #4000 | AM Best, A Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	147		'
Reinsurance Recoverables Paid/Unpaid Losses	19,432		'
Reinsurance Recoverables Total	19,579	[3]	'
Collateral Held	407	[4]	'
QBE Reinsurance Corp | AM Best, A Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	7,131		'
Reinsurance Recoverables Paid/Unpaid Losses	11,292		'
Reinsurance Recoverables Total	18,423	[3]	'
Collateral Held	1,781	[4]	'
Ace Property and Casualty Insurance Company | AM Best, A+ Rating | Standard & Poor's, AA- Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	9,862		'
Reinsurance Recoverables Paid/Unpaid Losses	7,687		'
Reinsurance Recoverables Total	17,549	[3]	'
Collateral Held	7,342	[4]	'
Odyssey American Reinsurance Corporation | AM Best, A Rating | Standard & Poor's, A- Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	3,550		'
Reinsurance Recoverables Paid/Unpaid Losses	11,997		'
Reinsurance Recoverables Total	15,547	[3]	'
Collateral Held	2,175	[4]	'
Berkley Insurance Company | AM Best, A+ Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	1,983		'
Reinsurance Recoverables Paid/Unpaid Losses	13,439		'
Reinsurance Recoverables Total	15,422	[3]	'
Collateral Held	485	[4]	'
Ironshore Indemnity Inc. | AM Best, A Rating | Standard & Poor's, Not Rated	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	6,808		'
Reinsurance Recoverables Paid/Unpaid Losses	7,980		'
Reinsurance Recoverables Total	14,788	[3]	'
Collateral Held	7,959	[4]	'
AXIS Re Europe | AM Best, A+ Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	4,762		'
Reinsurance Recoverables Paid/Unpaid Losses	9,347		'
Reinsurance Recoverables Total	14,109	[3]	'
Collateral Held	3,675	[4]	'
Insurance	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	209,011		'
Reinsurance Recoverables Paid/Unpaid Losses	642,503		'
Reinsurance Recoverables Total	851,514	[3]	'
Collateral Held	153,708	[4]	'
All Other	'		'
Ceded Credit Risk [Line Items]	'		'
Reinsurance Recoverables Unearned Premium	38,811		'
Reinsurance Recoverables Paid/Unpaid Losses	218,319		'
Reinsurance Recoverables Total	257,130	[3]	'
Collateral Held	$69,769	[4]	'
AM Best | National Indemnity Company | AM Best, A++ Rating | Standard & Poor's, AA+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A++		'
AM Best | Transatlantic Reinsurance Company | AM Best, A Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A		'
AM Best | Everest Reinsurance Company | AM Best, A+ Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A+		'
AM Best | Munich Reinsurance America Inc. | AM Best, A+ Rating | Standard & Poor's, AA- Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A+		'
AM Best | Swiss Reinsurance America Corporation | AM Best, A+ Rating | Standard & Poor's, AA- Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A+		'
AM Best | Lloyd Syndicate #2003 | AM Best, A Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A		'
AM Best | Allied World Reinsurance | AM Best, A Rating | Standard & Poor's, A Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A		'
AM Best | Partner Reinsurance Europe | AM Best, A+ Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A+		'
AM Best | Scor Global P&C SE | AM Best, A Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A		'
AM Best | Tower Insurance Company | AM Best, B Rating | Standard & Poor's, Not Rated	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'B		'
AM Best | Atlantic Specialty Insurance | AM Best, A Rating | Standard & Poor's, A- Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A		'
AM Best | Employers Mutual Casualty Company | AM Best, A Rating | Standard & Poor's, Not Rated	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A		'
AM Best | Validus Reinsurance Ltd | AM Best, A Rating | Standard & Poor's, A Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A		'
AM Best | Lloyd Syndicate #4000 | AM Best, A Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A		'
AM Best | QBE Reinsurance Corp | AM Best, A Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A		'
AM Best | Ace Property and Casualty Insurance Company | AM Best, A+ Rating | Standard & Poor's, AA- Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A+		'
AM Best | Odyssey American Reinsurance Corporation | AM Best, A Rating | Standard & Poor's, A- Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A		'
AM Best | Berkley Insurance Company | AM Best, A+ Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A+		'
AM Best | Ironshore Indemnity Inc. | AM Best, A Rating | Standard & Poor's, Not Rated	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A		'
AM Best | AXIS Re Europe | AM Best, A+ Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A+		'
Standard & Poor's | National Indemnity Company | AM Best, A++ Rating | Standard & Poor's, AA+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'AA+		'
Standard & Poor's | Transatlantic Reinsurance Company | AM Best, A Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A+		'
Standard & Poor's | Everest Reinsurance Company | AM Best, A+ Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A+		'
Standard & Poor's | Munich Reinsurance America Inc. | AM Best, A+ Rating | Standard & Poor's, AA- Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'AA-		'
Standard & Poor's | Swiss Reinsurance America Corporation | AM Best, A+ Rating | Standard & Poor's, AA- Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'AA-		'
Standard & Poor's | Lloyd Syndicate #2003 | AM Best, A Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A+		'
Standard & Poor's | Allied World Reinsurance | AM Best, A Rating | Standard & Poor's, A Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A		'
Standard & Poor's | Partner Reinsurance Europe | AM Best, A+ Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A+		'
Standard & Poor's | Scor Global P&C SE | AM Best, A Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A+		'
Standard & Poor's | Tower Insurance Company | AM Best, B Rating | Standard & Poor's, Not Rated	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'NR		'
Standard & Poor's | Atlantic Specialty Insurance | AM Best, A Rating | Standard & Poor's, A- Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A-		'
Standard & Poor's | Employers Mutual Casualty Company | AM Best, A Rating | Standard & Poor's, Not Rated	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'NR		'
Standard & Poor's | Validus Reinsurance Ltd | AM Best, A Rating | Standard & Poor's, A Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A		'
Standard & Poor's | Lloyd Syndicate #4000 | AM Best, A Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A+		'
Standard & Poor's | QBE Reinsurance Corp | AM Best, A Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A+		'
Standard & Poor's | Ace Property and Casualty Insurance Company | AM Best, A+ Rating | Standard & Poor's, AA- Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'AA-		'
Standard & Poor's | Odyssey American Reinsurance Corporation | AM Best, A Rating | Standard & Poor's, A- Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A-		'
Standard & Poor's | Berkley Insurance Company | AM Best, A+ Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A+		'
Standard & Poor's | Ironshore Indemnity Inc. | AM Best, A Rating | Standard & Poor's, Not Rated	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'NR		'
Standard & Poor's | AXIS Re Europe | AM Best, A+ Rating | Standard & Poor's, A+ Rating	'		'
Ceded Credit Risk [Line Items]	'		'
Rating	'A+		'
[1]	Equivalent S&P rating used for certain companies when an A.M. Best rating was unavailable.
[2]	Net of reserve for uncollectible reinsurance of approximately $11.3 million. The carrying value consists of reinsurance recoverables on paid losses due within 30-45 days and reinsurance on unpaid losses which by nature of our reserving process is our best estimate of the value as of December 31, 2013.
[3]	Net of reserve for uncollectible reinsurance of approximately $11.3 million.
[4]	Collateral of $223.5 million consists of $167.3 million in ceded balances payable, $53.4 million in letters of credit, and $2.8 million of other balances held by the Company's Insurance Companies and Lloyd's Operations.

Lists_of_20_Largest_Reinsurers1

Lists of 20 Largest Reinsurers Measured by Reinsurance Recoverable (Parenthetical) (Detail) (USD $)	Dec. 31, 2013		Dec. 31, 2012
Ceded Credit Risk [Line Items]	'		'
Reserve for uncollectible reinsurance amount	$11,300,000		$11,500,000
Collateral Held	223,477,000	[1]	'
Ceded Balances Payable	'		'
Ceded Credit Risk [Line Items]	'		'
Collateral Held	167,300,000		'
Letter of Credit	'		'
Ceded Credit Risk [Line Items]	'		'
Collateral Held	53,400,000		'
All Other	'		'
Ceded Credit Risk [Line Items]	'		'
Collateral Held	$2,800,000		'
[1]	Collateral of $223.5 million consists of $167.3 million in ceded balances payable, $53.4 million in letters of credit, and $2.8 million of other balances held by the Company's Insurance Companies and Lloyd's Operations.

Summary_of_Written_Premium_Det

Summary of Written Premium (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Direct	'	'	'	'	'	'	'	'	$1,127,331	$1,034,658	$929,778
Assumed	'	'	'	'	'	'	'	'	243,187	251,807	178,438
Ceded	'	'	'	'	'	'	'	'	-482,596	-452,810	-354,418
Net	223,445	196,556	198,469	269,452	212,312	188,046	190,252	243,045	887,922	833,655	753,798
Direct	'	'	'	'	'	'	'	'	1,069,677	972,844	912,020
Assumed	'	'	'	'	'	'	'	'	228,247	205,759	125,797
Ceded	'	'	'	'	'	'	'	'	-455,985	-396,639	-346,172
Net earned premiums	219,902	213,895	205,814	202,328	201,566	201,262	196,017	183,119	841,939	781,964	691,645
Direct	'	'	'	'	'	'	'	'	552,381	608,945	608,445
Assumed	'	'	'	'	'	'	'	'	155,313	151,137	81,945
Ceded	'	'	'	'	'	'	'	'	-188,733	-262,649	-213,393
Net	$131,385	$125,086	$131,148	$131,342	$127,191	$128,850	$123,407	$117,985	$518,961	$497,433	$476,997

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Apr. 30, 2013	Apr. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013
In Millions, unless otherwise specified			United Kingdom	United Kingdom	United Kingdom	United Kingdom	United Kingdom	United Kingdom	State and Local Jurisdiction	State and Local Jurisdiction
							Syndicate 1221	Syndicate 1221	Maximum	Minimum
							Maximum	Minimum
Income Taxes [Line Items]	'	'	'	'	'	'	'	'	'	'
Foreign effective income tax rate	'	'	'	'	'	35.00%	'	35.00%	'	'
Percentage of premiums	'	'	'	'	'	'	50.00%	'	'	'
Corporate tax rate	'	'	23.00%	24.00%	26.00%	'	'	'	'	'
Undistributed earnings of non-U.S. subsidiaries	$20.30	'	'	'	'	'	'	'	'	'
Taxes payable on undistributed earnings	2.1	'	'	'	'	'	'	'	'	'
Deferred Tax Assets: State and Local	0.6	0.5	'	'	'	'	'	'	'	'
State and local net operating loss carry-forwards	$0.10	$0.20	'	'	'	'	'	'	'	'
State and local tax carry-forwards expiration year	'	'	'	'	'	'	'	'	'2031	'2023

Components_of_Current_and_Defe

Components of Current and Deferred Income Tax Expense (Benefit) (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Current income tax expense (benefit):	'	'	'	'	'	'	'	'	'	'	'
Federal and foreign	'	'	'	'	'	'	'	'	$28,084	$39,242	$573
State and local	'	'	'	'	'	'	'	'	446	146	340
Subtotal	'	'	'	'	'	'	'	'	28,530	39,388	913
Deferred income tax expense (benefit):	'	'	'	'	'	'	'	'	'	'	'
Federal and foreign	'	'	'	'	'	'	'	'	277	-11,414	6,224
State and local	'	'	'	'	'	'	'	'	'	'	'
Subtotal	'	'	'	'	'	'	'	'	277	-11,414	6,224
Income tax expense (benefit)	$6,076	$9,804	$6,284	$6,643	$13,243	$5,225	$6,225	$3,281	$28,807	$27,974	$7,137

Reconciliation_of_Total_Income

Reconciliation of Total Income Taxes Applicable to Pre-Tax Operating Income and Amounts Computed by Applying Federal Statutory Income Tax Rate to Pre-Tax Operating Income (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation	'	'	'	'	'	'	'	'	'	'	'
Computed expected tax expense	'	'	'	'	'	'	'	'	$32,299	$32,109	$11,457
Tax-exempt interest	'	'	'	'	'	'	'	'	-3,839	-4,443	-4,437
Dividends received deduction	'	'	'	'	'	'	'	'	-897	-799	-1,065
Proration	'	'	'	'	'	'	'	'	710	786	825
Current state and local income taxes, net of federal income tax	'	'	'	'	'	'	'	'	290	95	221
Other	'	'	'	'	'	'	'	'	244	226	136
Income tax expense (benefit)	$6,076	$9,804	$6,284	$6,643	$13,243	$5,225	$6,225	$3,281	$28,807	$27,974	$7,137
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation	'	'	'	'	'	'	'	'	'	'	'
Computed expected tax expense	'	'	'	'	'	'	'	'	35.00%	35.00%	35.00%
Tax-exempt interest	'	'	'	'	'	'	'	'	-4.20%	-4.80%	-13.60%
Dividends received deduction	'	'	'	'	'	'	'	'	-1.00%	-0.90%	-3.30%
Proration	'	'	'	'	'	'	'	'	0.80%	0.90%	2.50%
Current state and local income taxes, net of federal income tax	'	'	'	'	'	'	'	'	0.30%	0.10%	0.70%
Other	'	'	'	'	'	'	'	'	0.30%	0.20%	0.50%
Actual tax expense and rate	'	'	'	'	'	'	'	'	31.20%	30.50%	21.80%

Tax_Effects_of_Temporary_Diffe

Tax Effects of Temporary Differences That Give Rise to Federal, Foreign, State and Local Deferred Tax Assets and Deferred Tax Liabilities (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Deferred tax assets:	'	'
Loss reserve discount	$27,822	$29,687
Unearned premiums	25,706	22,860
Compensation related	6,782	5,285
State and local net deferred tax assets	555	499
Other	3,889	4,245
Total gross deferred tax assets	64,754	62,576
Less: Valuation allowance	-555	-499
Total deferred tax assets	64,199	62,077
Deferred tax liabilities:	'	'
Deferred acquisition costs	-19,258	-16,903
Net unrealized gains on securities	-12,635	-36,200
Other	-4,119	-5,758
Total deferred tax liabilities	-36,012	-58,861
Net deferred income tax asset (liability)	$28,187	$3,216

Credit_Facility_Additional_Inf

Credit Facility - Additional Information (Detail) (USD $)	12 Months Ended			0 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Mar. 28, 2011	Dec. 31, 2013	Nov. 22, 2012
			Lloyd's	Amended and Restated Credit Agreement
			Syndicate 1221
Line of Credit Facility [Line Items]	'	'	'	'
Line of credit facility	'	$165	'	$165
Issuance of new letters of credit, expiry date	'	'	'	31-Dec-14
Aggregate face amount of letters of credit outstanding	'	'	$151.90	'
Line of credit facility, covenant terms	'This credit facility contains customary covenants for facilities of this type, including restrictions on indebtedness and liens, limitations on mergers, dividends and the sale of assets, and requirements as to maintaining certain consolidated tangible net worth, statutory surplus and other financial ratios. The credit facility also provides for customary events of default, including failure to pay principal, interest or fees when due, failure to comply with covenants, any representation or warranty made by the Company being false in any material respect, default under certain other indebtedness, certain insolvency or receivership events affecting the Company and its subsidiaries, the occurrence of certain material judgments, or a change in control of the Company.	'	'	'
Line of credit facility, covenant compliance	'The Company was in compliance with all covenants under the credit facility as of December 31, 2013.	'	'	'

Senior_Note_Additional_Informa

Senior Note - Additional Information (Detail) (USD $)

3 Months Ended

12 Months Ended

0 Months Ended

1 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Oct. 04, 2013

Oct. 04, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Oct. 04, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Senior Notes

Senior Notes

Senior Notes

Senior Notes

Senior Notes

Senior Notes

Senior Notes

Senior Notes

Senior Notes

Senior Notes

5.75% Senior Notes

5.75% Senior Notes

5.75% Senior Notes

5.75% Senior Notes

5.75% Senior Notes

7.0 % Senior Notes

7.0 % Senior Notes

7.0 % Senior Notes

7.0 % Senior Notes

Semi Annual Payment, First Payment

Semi Annual Payment, Second Payment

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Principal amount of senior notes

'

'

'

'

'

'

'

'

'

'

'

'

$265,000,000

$265,000,000

'

'

'

'

'

'

'

Interest rate stated on senior notes

7.00%

'

'

'

'

'

'

'

7.00%

'

'

'

5.75%

5.75%

'

'

'

'

7.00%

'

'

Senior notes due date

'

'

'

'

'

'

'

'

1-May-16

'

'

'

15-Oct-23

'

'

'

'

'

1-May-16

'

'

Net proceeds from issuance of senior notes

'

'

'

'

'

'

'

'

'

'

'

'

'

263,000,000

'

'

'

'

'

'

'

Unamortized discount

'

'

'

'

'

'

'

'

'

'

'

1,700,000

'

'

'

'

'

'

'

'

'

Outstanding principal amount of senior notes

'

'

'

'

'

'

'

'

'

'

'

263,300,000

'

'

'

'

'

'

'

'

'

Call premium on redemption of Senior Notes

-17,895,000

'

'

'

'

'

'

'

-17,895,000

'

'

'

'

'

'

'

'

17,900,000

'

'

'

Fair value of senior notes

'

'

'

'

'

'

'

'

'

'

'

'

'

'

277,600,000

'

'

'

'

123,200,000

'

Interest expense on senior notes

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

8,200,000

8,200,000

Effective interest rate related to senior notes

'

'

'

'

'

'

'

'

'

'

'

'

'

'

5.86%

'

'

'

'

'

'

Interest payment date on senior notes

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'--04-15

'--10-15

'

'

'

'

Interest expense

$4,351,000

$2,053,000

$2,052,000

$2,051,000

$2,051,000

$2,049,000

$2,049,000

$2,049,000

$10,507,000

$8,198,000

$8,188,000

$10,500,000

'

'

'

'

'

'

'

'

'

Debt instrument, covenant compliance

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'As of December 31, 2013, the Company was in compliance with all such covenants.

'

'

'

'

'

'

Lloyds_Syndicate_1221_Addition

Lloyd's Syndicate 1221 - Additional Information (Detail) (Lloyd's, Syndicate 1221)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2011
	USD ($)	GBP (£)	USD ($)	GBP (£)
Supplementary Insurance Information, by Segment [Line Items]	'	'	'	'	'
Syndicate 1221's stamp capacity	$323.70	£ 195	$300	£ 184	'
Percentage control of stamp capacity	100.00%	100.00%	100.00%	100.00%	100.00%
Letters of credit	151.9	'	'	'	'
Cash collateral posted	$1	'	'	'	'

Commitment_and_Contingencies_A

Commitment and Contingencies - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2013
Loss Contingencies [Line Items]	'	'	'	'
Rent expense	$11.50	$10.50	$10.40	'
Incentive awarded to the company by the State of Connecticut, total	11.5	'	'	'
Incentive awarded to the company by the State of Connecticut, non-interest bearing loans	8	'	'	'
Incentive awarded to the company by the State of Connecticut, grants	3.5	'	'	'
Non-interest bearing incentive loan term	'10 years	'	'	'
Incentive awarded to the company by the State of Connecticut, revenue recognized	0.3	'	'	'
Incentive awarded to the company by the State of Connecticut, deferred revenue	$7.20	'	'	$7.50
Maximum	'	'	'	'
Loss Contingencies [Line Items]	'	'	'	'
Noncancellable operating leases expiration year	'2023	'	'	'

Future_Minimum_Annual_Rental_C

Future Minimum Annual Rental Commitments Under Various Noncancellable Operating Leases (Detail) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Operating Leased Assets [Line Items]	'
2014	$11,061
2015	11,092
2016	9,228
2017	7,990
2018	6,884
Thereafter	15,696
Total minimum operating lease payments	$61,951

Share_Capital_and_Share_Repurc2

Share Capital and Share Repurchases - Additional Information (Detail) (USD $)	0 Months Ended	26 Months Ended
In Millions, except Share data, unless otherwise specified	31-May-11	Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2012
Equity, Class of Treasury Stock [Line Items]	'	'	'	'
Common stock, authorized shares	'	'	50,000,000	50,000,000
Common stock, par value	'	'	$0.10	$0.10
Preferred stock, authorized shares	'	'	1,000,000	1,000,000
Preferred stock, par value	'	'	$0.10	$0.10
Share repurchase program, authorized amount	$50	$150	'	'

Changes_in_Issued_and_Outstand

Changes in Issued and Outstanding Common Shares (Detail)

3 Months Ended

12 Months Ended

Dec. 31, 2011

Sep. 30, 2011

Jun. 30, 2011

Mar. 31, 2011

Dec. 31, 2010

Sep. 30, 2010

Jun. 30, 2010

Mar. 31, 2010

Dec. 31, 2009

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2009

Beginning balance

'

'

'

15,742,000

'

'

'

'

'

14,047,000

13,956,000

15,742,000

'

'

Vested stock grants

'

'

'

'

'

'

'

'

'

50,000

60,000

122,000

'

'

Employee stock purchase plan

'

'

'

'

'

'

'

'

'

17,640

16,000

19,000

'

'

Stock options exercised

'

'

'

'

'

'

'

'

'

83,500

15,000

52,250

'

'

Treasury shares purchased

-376,911

-749,076

-597,026

-256,094

-35,566

-97,115

-558,003

-573,600

-141,576

'

'

-1,979,107

-1,264,284

-141,576

Ending balance

13,956,000

'

'

'

15,742,000

'

'

'

'

14,198,000

14,047,000

13,956,000

15,742,000

'

Share_Repurchases_Detail

Share Repurchases (Detail) (USD $)	3 Months Ended									12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Equity, Class of Treasury Stock [Line Items]	'	'	'	'	'	'	'	'	'	'	'	'
Total Number of Shares Purchased	376,911	749,076	597,026	256,094	35,566	97,115	558,003	573,600	141,576	1,979,107	1,264,284	141,576
Average Cost Paid Per Share	$45.61	$43.03	$47.55	$50.96	$48.04	$42.25	$40.32	$41.27	$47.72	$45.91	$41.11	$47.72

Amount_and_Nature_of_Net_Asset

Amount and Nature of Net Assets Restricted from Payment of Dividends (Detail) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Thousands, unless otherwise specified
Restricted Assets And Liabilities Relating To Securitization [Line Items]	'		'
Total Restricted Net Assets	$520,886		$519,201
Insurance	'		'
Restricted Assets And Liabilities Relating To Securitization [Line Items]	'		'
Total Restricted Net Assets	12,605	[1]	17,226	[1]
Insurance | Fixed maturities	'		'
Restricted Assets And Liabilities Relating To Securitization [Line Items]	'		'
Total Restricted Net Assets	11,105		11,728
Insurance | Short-term investments	'		'
Restricted Assets And Liabilities Relating To Securitization [Line Items]	'		'
Total Restricted Net Assets	290		290
Insurance | Cash	'		'
Restricted Assets And Liabilities Relating To Securitization [Line Items]	'		'
Total Restricted Net Assets	1,210		5,208
Lloyd's	'		'
Restricted Assets And Liabilities Relating To Securitization [Line Items]	'		'
Total Restricted Net Assets	508,281	[2]	501,975	[2]
Lloyd's | Fixed maturities	'		'
Restricted Assets And Liabilities Relating To Securitization [Line Items]	'		'
Total Restricted Net Assets	398,808		428,142
Lloyd's | Short-term investments	'		'
Restricted Assets And Liabilities Relating To Securitization [Line Items]	'		'
Total Restricted Net Assets	108,485		72,984
Lloyd's | Cash	'		'
Restricted Assets And Liabilities Relating To Securitization [Line Items]	'		'
Total Restricted Net Assets	$988		$849
[1]	The restricted net assets for the Insurance Companies primarily consist of fixed maturities on deposit with various state insurance departments. The cash as of December 31, 2012 and 2011, as presented in the table above, was on deposit with a U.K. bank to comply with the regulatory requirements of the Prudential Regulation Authority for the underwriting activities of the U.K. Branch.
[2]	The restricted net assets for the Lloyd's Operations consists of fixed maturities and cash held in trust for the benefit of syndicate policyholders and short term investments primarily consisting of overseas deposits in various countries with Lloyd's to support underwriting activities in those countries.

Amount_and_Nature_of_Net_Asset1

Amount and Nature of Net Assets Restricted from Payment of Dividends (Parenthetical) (Detail) (Fixed maturities, USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Insurance	'	'
Restricted Assets And Liabilities Relating To Securitization [Line Items]	'	'
Restricted net assets, amortized cost	$9,730	$9,607
Lloyd's	'	'
Restricted Assets And Liabilities Relating To Securitization [Line Items]	'	'
Restricted net assets, amortized cost	$398,930	$419,271

Dividends_and_Statutory_Financ2

Dividends and Statutory Financial Information - Additional Information (Detail)

0 Months Ended

12 Months Ended

12 Months Ended

Nov. 30, 2013

Nov. 30, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 21, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2012

Dec. 31, 2011

USD ($)

GBP (£)

USD ($)

GBP (£)

Navigators Insurance Company

Navigators Insurance Company

Navigators Insurance Company

Insurance

Insurance

Insurance

Insurance

Insurance

Lloyd's

Lloyd's

Lloyd's

Lloyd's

Lloyd's

Lloyd's

Lloyd's

Lloyd's

Lloyd's

Lloyd's

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

Minimum

Maximum

USD ($)

USD ($)

USD ($)

GBP (£)

GBP (£)

Syndicate 1221

Syndicate 1221

Syndicate 1221

Syndicate 1221

Syndicate 1221

USD ($)

GBP (£)

USD ($)

GBP (£)

Statutory Accounting Practices [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Maximum amount available for payment of dividends without prior regulatory approval

'

'

'

'

'

'

$80,400,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Dividends paid to Parent Company

'

'

'

'

15,000,000

45,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Statutory net income

'

'

'

'

'

'

'

59,400,000

28,600,000

16,300,000

'

'

'

'

'

'

'

'

'

'

'

'

Statutory capital and surplus

'

'

'

'

'

'

'

804,100,000

682,900,000

'

'

'

124,200,000

110,000,000

'

74,800,000

67,500,000

'

'

'

'

'

Risk based capital ratio

'

'

'

'

295.10%

'

304.20%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Insurance examinations period

'

'

'

'

'

'

'

'

'

'

'3 years

'5 years

'

'

'

'

'

'

'

'

'

'

FAL requirement set by Lloyd's for Syndicate 1221 based on its business plan, approved in November 2012 and 2011

'

'

'

'

'

'

'

'

'

'

'

'

279,300,000

223,400,000

'

168,300,000

137,100,000

'

'

'

'

'

Valuation of assets and letters of credit posted

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

280,200,000

168,800,000

227,300,000

139,500,000

'

Pre-tax regulatory income

'

'

'

'

'

'

'

'

'

'

'

'

21,000,000

54,900,000

5,300,000

'

'

'

'

'

'

'

Percentage control of stamp capacity

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

100.00%

100.00%

100.00%

100.00%

100.00%

Undistributed Profit

127,400,000

76,700,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Dividend Capacity

'

'

$11,600,000

£ 7,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Stock_Option_Plans_Stock_Grant2

Stock Option Plans, Stock Grants, Stock Appreciation Rights and Employee Stock Purchase Plan - Additional Information (Detail) (USD $)

12 Months Ended

12 Months Ended

12 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2005

Dec. 31, 2013

Apr. 30, 2013

Apr. 30, 2009

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Performance Based Shares

Performance Based Shares

Performance Based Shares

Maximum

2005 Stock Incentive Plan

Amended And Restated 2005 Stock Incentive Plan

Amended And Restated 2005 Stock Incentive Plan

Amended And Restated 2005 Stock Incentive Plan

Options and Non Performance Based Grants

Options and Non Performance Based Grants

Non Performance Based Shares

Non Performance Based Shares

Non Performance Based Shares

Non Performance Based Shares

Performance Based Shares Issued in 2011

Restricted stock units

Restricted stock units

Performance Based Shares Issued Prior to 2011

Performance Based Shares Issued Prior to 2011

Performance Based Shares Issued Prior to 2011

Performance Based Shares Issued Prior to 2011

Performance Based Shares Issued Prior to 2011

Performance Based Shares Issued Prior to 2011

Stock appreciation rights

Stock appreciation rights

Stock appreciation rights

Stock appreciation rights

Restricted stock units

Restricted stock units

Restricted stock units

Employee stock purchase plan

Minimum

Maximum

Year Three

Year Four

Year Five

Minimum

Maximum

Year Three

Year Four

Year Five

Minimum

Maximum

Minimum

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of stock authorized for issuance

'

'

'

'

'

'

'

1,000,000

'

2,000,000

1,500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

300,000

'

'

'

'

'

'

'

Stock issued during period under incentive plan

'

'

'

'

'

'

'

'

1,340,885

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of stock available to be issued

'

'

'

'

'

'

'

'

659,115

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Share based payment award, award vesting period

'

'

'

'

'

'

'

'

'

'

'

'3 years

'4 years

'5 years

'

'

'

'3 years

'

'

'5 years

'

'

'

'

'

'

'

'

'

'

'

'

'

Options expiration term (in years)

'

'

'

'

'

'

'10 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of shares vesting over the period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

33.33%

33.33%

33.33%

50.00%

0.00%

150.00%

'

33.33%

33.33%

33.33%

0.00%

150.00%

'

'

'

'

'

'

'

'

Percentage of remaining shares vesting over the period dependent on compound annual growth book value per share immediately prior to vesting date

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

50.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Performance based shares that vested

133,482

138,321

215,065

15,714

0

22,933

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fair value of total vested shares

$3,500,000

$4,600,000

$8,600,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Weighted average grant date fair value of all RSU granted

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$55.36

$48.21

$50.06

'

Unrecognized compensation expense, net of estimated forfeitures

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

10,600,000

11,900,000

'

'

Weighted Average Periods

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'2 years 2 months 12 days

'2 years 2 months 12 days

'

'

Aggregate fair value of all unvested RSU

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

39,600,000

30,000,000

'

'

Exercise price as percentage of fair market value

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

90.00%

'

'

'

90.00%

Percentage of employees base compensation through payroll that can be invested for the purchase of common stock, maximum

10.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of shares which can be acquired by employee, maximum

1,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total market value of shares that can be acquired by employee

$25,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Employee Stock Purchase Plan, shares to be purchased in following period

8,738

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Employee Stock Purchase Plan, shares purchased by employees

17,640

16,000

19,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Discount on employee stock purchase plan

10.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Amounts_Charged_to_Expense_for

Amounts Charged to Expense for Stock-based Compensation (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'		'
Stock based compensation	$3,914		$7,852		$460
Restricted stock units	'		'		'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'		'
Stock based compensation	3,369		7,380		139
Directors restricted stock grants	'		'		'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'		'
Stock based compensation	413	[1]	390	[1]	248	[1]
Employee stock purchase plan	'		'		'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'		'
Stock based compensation	132		82		173
Stock appreciation rights	'		'		'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'		'
Stock based compensation	'		'		($100)	[2]
[1]	Relates to non-employee directors serving on the Parent Company's Board of Directors, all of whom have been elected by the Company's stockholders, as well as non-employee directors serving on NUAL's Board of Directors.
[2]	All outstanding stock appreciation rights were exercised during 2011.

Unvested_Restricted_Stock_Gran

Unvested Restricted Stock Grants Outstanding (Detail)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Beginning balance	587,629	526,972	590,661
Granted	269,926	244,060	184,758
Vested	-133,482	-138,321	-215,065
Forfeited	-97,261	-45,082	-33,382
Ending balance	626,812	587,629	526,972
Performance Based Shares	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Granted	114,463	97,145	86,118
Vested	-15,714	0	-22,933
Performance Based Shares | Earned	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Vested	-15,714	'	-22,993
Performance Based Shares | Unearned	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Vested	-57,585	-46,998	-42,334
Non Performance Based Shares	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Granted	155,463	146,915	98,640
Vested	-60,183	-91,323	-149,738

Stock_Options_Outstanding_Deta

Stock Options Outstanding (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Number of Shares	'	'	'
Beginning balance	90,250	105,250	157,500
Exercised	-83,500	-15,000	-52,250
Ending balance	6,750	90,250	105,250
Number of options exercisable	6,750	90,250	105,250
Granted	'	'	'
Expired or forfeited	'	'	'
Average Exercise Price	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Beginning of Period	$29.94	$29.50	$27.13
Granted	'	'	'
Exercised	$29.88	$26.90	$22.35
Expired or forfeited	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, End of Period	$30.65	$29.94	$29.50
Number of options exercisable	$30.65	$29.94	$29.50

Summarized_Information_about_O

Summarized Information about Options Outstanding (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'
Outstanding Options	6,750
Average Remaining Contract Life	'1 year 10 months 24 days
Exercisable Options	6,750
Price Range $21 to $30	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'
Price Range, Lower Range	21
Price Range, Upper Range	30
Outstanding Options	5,250
Average Remaining Contract Life	'2 months 12 days
Average Exercise Price	29.11
Average Aggregate Intrinsic Value	34.05
Exercisable Options	5,250
Average Exercise Price	29.11
Average Aggregate Intrinsic Value of Exercisable Options	34.05
Price Range $31 to $37	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'
Price Range, Lower Range	31
Price Range, Upper Range	37
Outstanding Options	1,500
Average Remaining Contract Life	'1 year 8 months 12 days
Average Exercise Price	36.03
Average Aggregate Intrinsic Value	27.13
Exercisable Options	1,500
Average Exercise Price	36.03
Average Aggregate Intrinsic Value of Exercisable Options	27.13

Stock_Appreciation_Rights_Outs

Stock Appreciation Rights Outstanding (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
SARs	'	'	'
Beginning balance	587,629	526,972	590,661
Granted	269,926	244,060	184,758
Expired or forfeited	97,261	45,082	33,382
Ending balance	626,812	587,629	526,972
Stock appreciation rights	'	'	'
SARs	'	'	'
Beginning balance	'	'	16,500
Granted	'	'	'
Exercised	'	'	-16,500
Expired or forfeited	'	'	'
Number of SARs exercisable	'	'	'
Average Exercise Prices	'	'	'
Beginning balance	'	'	18.74
Granted	'	'	'
Exercised	'	'	18.74
Expired or forfeited	'	'	'
Number of SARs exercisable	'	'	'

Retirement_Plans_Additional_In

Retirement Plans - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Employee Benefits Disclosure [Line Items]	'	'	'
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	100.00%	100.00%	100.00%
Employees contribution to 401(k) plan that is 100 % matched by employer	4.00%	4.00%	4.00%
Defined Contribution Plan, employer discretionary matching contribution percent	2.00%	0.00%	0.00%
Defined Contribution Plan, employer discretionary matching contribution amount	$800,000	$0	$0
401(k) plan expense	5,100,000	4,600,000	1,600,000
Retirement Savings Contributions	'	'	'
Employee Benefits Disclosure [Line Items]	'	'	'
401(k) plan expense	2,700,000	2,500,000	'
Non Discretionary Matching Contributions	'	'	'
Employee Benefits Disclosure [Line Items]	'	'	'
401(k) plan expense	1,600,000	2,100,000	'
Money Purchase Defined Contribution Plan	'	'	'
Employee Benefits Disclosure [Line Items]	'	'	'
401(k) plan expense	'	'	2,800,000
Maximum	'	'	'
Employee Benefits Disclosure [Line Items]	'	'	'
Discretion of contribution to each eligible employee's 401(k) plan irrespective of the employees' contribution	4.00%	'	'
United States	'	'	'
Employee Benefits Disclosure [Line Items]	'	'	'
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	7.50%	'	'
Defined contribution plan employees vesting percentage beginning at the end of their second year	20.00%	'	'
Defined contribution plan additional employees vesting percentage being fully vested	'6 years	'	'
United States | Maximum	'	'	'
Employee Benefits Disclosure [Line Items]	'	'	'
Bonus to employees	'	'	2,500
United Kingdom	'	'	'
Employee Benefits Disclosure [Line Items]	'	'	'
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	15.00%	'	'
401(k) plan expense	$2,200,000	$1,900,000	$1,700,000

Summary_of_Quarterly_Financial

Summary of Quarterly Financial Data (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Gross written premiums	$333,091	$312,076	$332,128	$393,222	$321,587	$298,742	$322,987	$343,149	$1,370,517	$1,286,465	$1,108,216
Revenues:	'	'	'	'	'	'	'	'	'	'	'
Net written premiums	223,445	196,556	198,469	269,452	212,312	188,046	190,252	243,045	887,922	833,655	753,798
Change in unearned premiums	-3,543	17,339	7,345	-67,124	-10,746	13,216	5,765	-59,926	-45,983	-51,691	-62,153
Net earned premiums	219,902	213,895	205,814	202,328	201,566	201,262	196,017	183,119	841,939	781,964	691,645
Net investment income	14,254	14,094	14,246	13,657	13,616	13,597	15,777	11,258	56,251	54,248	63,500
Total other-than-temporary impairment losses	-530	-1,821	'	-42	-208	'	-496	-198	-2,393	-902	-3,617
Portion of loss recognized in other comprehensive income (before tax)	'	'	'	'	'	'	'	44	'	44	1,632
Net other-than-temporary impairment losses recognized in earnings	-530	-1,821	'	-42	-208	'	-496	-154	-2,393	-858	-1,985
Net realized gains (losses)	15,768	-988	3,345	4,814	30,254	4,761	4,217	1,842	22,939	41,074	11,996
Other income (expense)	-665	-210	-915	618	-599	789	387	911	-1,172	1,488	1,229
Total revenues	248,729	224,970	222,490	221,375	244,629	220,409	215,902	196,976	917,564	877,916	766,385
Expenses:	'	'	'	'	'	'	'	'	'	'	'
Net losses and loss adjustment expenses	131,385	125,086	131,148	131,342	127,191	128,850	123,407	117,985	518,961	497,433	476,997
Commission expenses	30,863	27,685	28,391	26,555	31,259	31,258	29,503	29,450	113,494	121,470	110,437
Other operating expenses	43,826	39,056	40,678	40,874	42,841	40,112	39,819	36,307	164,434	159,079	138,029
Call premium on Senior Notes	17,895	'	'	'	'	'	'	'	17,895	'	'
Interest expense	4,351	2,053	2,052	2,051	2,051	2,049	2,049	2,049	10,507	8,198	8,188
Total expenses	228,320	193,880	202,269	200,822	203,342	202,269	194,778	185,791	825,291	786,180	733,651
Income before income taxes	20,409	31,090	20,221	20,553	41,287	18,140	21,124	11,185	92,273	91,736	32,734
Income tax expense	6,076	9,804	6,284	6,643	13,243	5,225	6,225	3,281	28,807	27,974	7,137
Net income	14,333	21,286	13,937	13,910	28,044	12,915	14,899	7,904	63,466	63,762	25,597
Comprehensive income (loss)	$1,200	$25,462	($24,829)	$14,785	$2,418	$30,760	$21,663	$13,881	$16,618	$68,722	$55,384
Combined ratio	94.00%	89.80%	97.70%	97.90%	100.20%	99.10%	98.10%	99.80%	94.80%	99.30%	104.70%
Net income (loss) per share:	'	'	'	'	'	'	'	'	'	'	'
Basic	$1.01	$1.50	$0.99	$0.99	$2	$0.92	$1.06	$0.57	$4.49	$4.54	$1.71
Diluted	$1	$1.48	$0.97	$0.97	$1.96	$0.90	$1.05	$0.56	$4.42	$4.45	$1.69

Summary_of_Consolidated_Invest1

Summary of Consolidated Investments-Other Than Investments in Related Parties (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'	'
Total investments and cash	$2,191,827	$2,223,130
Total investments and cash	2,574,586	2,422,254
Gross Unrealized Gains	69,554	105,248
Gross Unrealized Losses	-33,530	-1,887
Amortized Cost	2,538,562	2,318,893
Short-term investments	'	'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'	'
Total investments and cash	296,250	153,788
Amortized Cost	296,250	153,788
Cash	'	'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'	'
Total investments and cash	86,509	45,336
Amortized Cost	86,509	45,336
Fixed maturities	'	'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'	'
Total investments and cash	2,047,873	2,121,833
Gross Unrealized Gains	43,854	88,329
Gross Unrealized Losses	-32,980	-1,261
Amortized Cost	2,036,999	2,034,765
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign	'	'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'	'
Total investments and cash	441,685	649,692
Gross Unrealized Gains	2,854	8,654
Gross Unrealized Losses	-8,855	-36
Amortized Cost	447,686	641,074
Fixed maturities | States, municipalities and political subdivisions	'	'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'	'
Total investments and cash	460,422	322,947
Gross Unrealized Gains	9,298	18,712
Gross Unrealized Losses	-13,651	-380
Amortized Cost	464,775	304,615
Fixed maturities | Agency mortgage-backed securities	'	'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'	'
Total investments and cash	301,274	384,445
Gross Unrealized Gains	6,779	13,652
Gross Unrealized Losses	-6,016	-204
Amortized Cost	300,511	370,997
Fixed maturities | Residential Mortgage Backed Securities	'	'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'	'
Total investments and cash	41,755	38,692
Gross Unrealized Gains	1,212	1,053
Gross Unrealized Losses	-161	-549
Amortized Cost	40,704	38,188
Fixed maturities | Asset-backed securities	'	'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'	'
Total investments and cash	125,133	50,382
Gross Unrealized Gains	653	1,133
Gross Unrealized Losses	-480	-49
Amortized Cost	124,960	49,298
Fixed maturities | Commercial mortgage-backed securities	'	'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'	'
Total investments and cash	172,750	204,821
Gross Unrealized Gains	7,656	17,996
Gross Unrealized Losses	-374	-18
Amortized Cost	165,468	186,843
Fixed maturities | Mortgage-backed and asset-backed securities	'	'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'	'
Total investments and cash	640,912	678,340
Gross Unrealized Gains	16,300	33,834
Gross Unrealized Losses	-7,031	-820
Amortized Cost	631,643	645,326
Fixed maturities | Corporate bonds	'	'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'	'
Total investments and cash	504,854	470,854
Gross Unrealized Gains	15,402	27,129
Gross Unrealized Losses	-3,443	-25
Amortized Cost	492,895	443,750
Equity Securities | Common Stock	'	'
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]	'	'
Total investments and cash	143,954	101,297
Gross Unrealized Gains	25,700	16,919
Gross Unrealized Losses	-550	-626
Amortized Cost	$118,804	$85,004

Condensed_Financial_Informatio1

Condensed Financial Information - Balance Sheets (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
In Thousands, unless otherwise specified
ASSETS	'	'	'	'
Cash and investments	$2,574,586	$2,422,254	'	'
Goodwill and other intangible assets	7,177	7,093	'	'
Other assets	35,039	26,587	'	'
Total assets	4,169,452	4,007,670	3,670,007	'
LIABILITIES AND STOCKHOLDERS' EQUITY	'	'	'	'
Senior Notes	263,308	114,424	'	'
Accounts payable and other liabilities	69,379	48,015	'	'
Total liabilities	3,267,240	3,128,185	'	'
Preferred stock, $.10 par value, authorized 1,000,000 shares, none issued	'	'	'	'
Common stock, $.10 par value, authorized 50,000,000 shares, issued 17,709,876 shares for 2013 and 17,558,046 shares for 2012	1,770	1,755	'	'
Additional paid-in capital	335,546	329,452	'	'
Treasury stock, at cost (3,511,380 shares for 2013 and 2012)	-155,801	-155,801	'	'
Retained earnings	692,337	628,871	'	'
Accumulated other comprehensive income:	'	'	'	'
Total stockholders' equity	902,212	879,485	803,435	829,354
Total liabilities and stockholders' equity	4,169,452	4,007,670	'	'
Parent Company	'	'	'	'
ASSETS	'	'	'	'
Cash and investments	100,676	15,026	'	'
Investments in subsidiaries	1,040,214	955,024	'	'
Goodwill and other intangible assets	2,534	2,534	'	'
Other assets	26,538	23,219	'	'
Total assets	1,169,962	995,803	'	'
LIABILITIES AND STOCKHOLDERS' EQUITY	'	'	'	'
Senior Notes	263,308	114,424	'	'
Accounts payable and other liabilities	802	552	'	'
Accrued interest payable	3,640	1,342	'	'
Total liabilities	267,750	116,318	'	'
Preferred stock, $.10 par value, authorized 1,000,000 shares, none issued	'	'	'	'
Common stock, $.10 par value, authorized 50,000,000 shares, issued 17,709,876 shares for 2013 and 17,558,046 shares for 2012	1,770	1,755	'	'
Additional paid-in capital	335,546	329,452	'	'
Treasury stock, at cost (3,511,380 shares for 2013 and 2012)	-155,801	-155,801	'	'
Retained earnings	692,337	628,871	'	'
Accumulated other comprehensive income:	'	'	'	'
Net unrealized gains (losses) on securities available-for-sale, net of tax	23,387	67,161	'	'
Foreign currency translation adjustment, net of tax	4,973	8,047	'	'
Total stockholders' equity	902,212	879,485	'	'
Total liabilities and stockholders' equity	$1,169,962	$995,803	'	'

Condensed_Financial_Informatio2

Condensed Financial Information - Balance Sheets (Parenthetical) (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]	'	'
Preferred stock, par value	$0.10	$0.10
Preferred stock, authorized shares	1,000,000	1,000,000
Preferred stock, issued shares	'	'
Common stock, par value	$0.10	$0.10
Common stock, authorized shares	50,000,000	50,000,000
Common stock, issued shares	17,709,876	17,558,046
Treasury stock, shares	3,511,380	3,511,380
Parent Company	'	'
Condensed Financial Statements, Captions [Line Items]	'	'
Preferred stock, par value	$0.10	$0.10
Preferred stock, authorized shares	1,000,000	1,000,000
Preferred stock, issued shares	0	0
Common stock, par value	$0.10	$0.10
Common stock, authorized shares	50,000,000	50,000,000
Common stock, issued shares	17,709,876	17,558,046
Treasury stock, shares	3,511,380	3,511,380

Condensed_Financial_Informatio3

Condensed Financial Information - Statement of Income (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues:	'	'	'	'	'	'	'	'	'	'	'
Net investment income	$14,254	$14,094	$14,246	$13,657	$13,616	$13,597	$15,777	$11,258	$56,251	$54,248	$63,500
Total revenues	248,729	224,970	222,490	221,375	244,629	220,409	215,902	196,976	917,564	877,916	766,385
Expenses:	'	'	'	'	'	'	'	'	'	'	'
Call premium on Senior Notes	17,895	'	'	'	'	'	'	'	17,895	'	'
Interest expense	4,351	2,053	2,052	2,051	2,051	2,049	2,049	2,049	10,507	8,198	8,188
Other (income) expense	665	210	915	-618	599	-789	-387	-911	1,172	-1,488	-1,229
Total expenses	228,320	193,880	202,269	200,822	203,342	202,269	194,778	185,791	825,291	786,180	733,651
Income before income taxes	20,409	31,090	20,221	20,553	41,287	18,140	21,124	11,185	92,273	91,736	32,734
Income tax benefit	6,076	9,804	6,284	6,643	13,243	5,225	6,225	3,281	28,807	27,974	7,137
Net income	14,333	21,286	13,937	13,910	28,044	12,915	14,899	7,904	63,466	63,762	25,597
Parent Company	'	'	'	'	'	'	'	'	'	'	'
Revenues:	'	'	'	'	'	'	'	'	'	'	'
Net investment income	'	'	'	'	'	'	'	'	13	341	595
Dividends received from wholly-owned subsidiaries	'	'	'	'	'	'	'	'	'	15,000	45,000
Total revenues	'	'	'	'	'	'	'	'	13	15,341	45,595
Expenses:	'	'	'	'	'	'	'	'	'	'	'
Call premium on Senior Notes	'	'	'	'	'	'	'	'	17,895	'	'
Interest expense	'	'	'	'	'	'	'	'	10,507	8,198	8,188
Other (income) expense	'	'	'	'	'	'	'	'	2	1,749	2,969
Total expenses	'	'	'	'	'	'	'	'	28,404	9,947	11,157
Income before income taxes	'	'	'	'	'	'	'	'	-28,391	5,394	34,438
Income tax benefit	'	'	'	'	'	'	'	'	-9,886	-3,332	-3,635
Income (loss) before equity in undistributed net income of wholly owned subsidiaries	'	'	'	'	'	'	'	'	-18,505	8,726	38,073
Equity in undistributed net income of wholly-owned subsidiaries	'	'	'	'	'	'	'	'	81,971	55,036	-12,476
Net income	'	'	'	'	'	'	'	'	$63,466	$63,762	$25,597

Condensed_Financial_Informatio4

Condensed Financial Information - Statement of Cash Flows (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating activities:	'	'	'
Net income	$63,466	$63,762	$25,597
Adjustments to reconcile net income to net cash provided by (used in) operations:	'	'	'
Call premium on redemption of Senior Notes	17,895	'	'
Other	31,987	36,503	19,569
Net cash provided by (used in) operating activities	136,875	96,739	118,338
Fixed maturities, available-for-sale	'	'	'
Sales	648,335	1,319,404	666,976
Purchases	-899,930	-1,711,080	-803,568
Equity securities	'	'	'
Sales	72,113	39,503	73,590
Net increase in short-term investments	-142,214	-31,568	30,384
Net cash provided by (used in) investing activities	-229,859	-179,839	66,006
Financing activities:	'	'	'
Net Proceeds from Debt Offering	263,278	'	'
Redemption of 7.0% Senior Notes Due May 1, 2016	-132,437	'	'
Purchase of treasury stock	'	'	-90,866
Proceeds of stock issued from employee stock purchase plan	821	672	945
Proceeds of stock issued from exercise of stock options	2,495	404	1,169
Net cash provided by (used in) financing activities	134,157	1,076	-88,752
Cash at beginning of year	45,336	127,360	31,768
Cash at end of period	86,509	45,336	127,360
Parent Company	'	'	'
Operating activities:	'	'	'
Net income	63,466	63,762	25,597
Adjustments to reconcile net income to net cash provided by (used in) operations:	'	'	'
Equity in undistributed net income of wholly-owned subsidiaries	-81,971	-70,036	-32,524
Dividends received from subsidiaries	'	15,000	45,000
Call premium on redemption of Senior Notes	17,895	'	'
Other	2,098	-3,265	5,831
Net cash provided by (used in) operating activities	1,488	5,461	43,904
Fixed maturities, available-for-sale	'	'	'
Sales	8,754	7,986	45,716
Purchases	-1,249	-14,700	-9,253
Equity securities	'	'	'
Sales	'	'	'
Purchases	'	'	'
Net increase in short-term investments	-89,988	-167	10,064
Net cash provided by (used in) investing activities	-82,483	-6,881	46,527
Financing activities:	'	'	'
Capital contribution to subsidiary	-50,000	'	'
Net Proceeds from Debt Offering	263,278	'	'
Redemption of 7.0% Senior Notes Due May 1, 2016	-132,437	'	'
Purchase of treasury stock	'	'	-90,866
Proceeds of stock issued from employee stock purchase plan	821	672	945
Proceeds of stock issued from exercise of stock options	2,495	404	1,169
Net cash provided by (used in) financing activities	84,157	1,076	-88,752
Increase (decrease) in cash	3,162	-344	1,679
Cash at beginning of year	2,981	3,325	1,646
Cash at end of period	$6,143	$2,981	$3,325

Condensed_Financial_Informatio5

Condensed Financial Information - Statement of Cash Flows (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]	'
Interest rate stated on senior notes	7.00%
Senior notes due date	1-May-16
Parent Company	'
Condensed Financial Statements, Captions [Line Items]	'
Interest rate stated on senior notes	7.00%
Senior notes due date	1-May-16

Supplementary_Insurance_Inform1

Supplementary Insurance Information (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Supplementary Insurance Information, by Segment [Line Items]	'		'		'
Deferred policy acquisition costs	$67,007		$61,005		$63,984
Reserve for losses and loss adjustment expenses	2,045,071		2,097,048		2,082,679
Unearned premiums	714,606		642,407		532,628
Other policy claims and benefits payable	'		'		'
Net earned premiums	841,939		781,964		691,645
Net investment income	56,243	[1]	54,100	[1]	63,119	[1]
Losses and loss adjustment expenses incurred	518,961		497,433		476,997
Amortization of deferred policy acquisition costs	115,842	[2]	123,819	[2]	112,506	[2]
Other operating expenses	164,434	[1]	159,079	[1]	138,029	[1]
Net written premiums	887,922		833,655		753,798
Insurance	'		'		'
Supplementary Insurance Information, by Segment [Line Items]	'		'		'
Deferred policy acquisition costs	54,984		48,294		47,298
Reserve for losses and loss adjustment expenses	1,523,175		1,567,045		1,517,331
Unearned premiums	536,303		470,425		384,596
Other policy claims and benefits payable	'		'		'
Net earned premiums	639,338		571,439		472,463
Net investment income	49,083	[1]	46,549	[1]	54,164	[1]
Losses and loss adjustment expenses incurred	415,413		417,082		341,625
Amortization of deferred policy acquisition costs	81,132	[2]	81,370	[2]	64,165	[2]
Other operating expenses	119,920	[1]	113,625	[1]	101,517	[1]
Net written premiums	680,008		622,956		542,391
Lloyd's	'		'		'
Supplementary Insurance Information, by Segment [Line Items]	'		'		'
Deferred policy acquisition costs	12,023		12,711		16,686
Reserve for losses and loss adjustment expenses	521,896		530,003		565,348
Unearned premiums	178,303		171,982		148,032
Other policy claims and benefits payable	'		'		'
Net earned premiums	202,601		210,525		219,182
Net investment income	7,160	[1]	7,551	[1]	8,955	[1]
Losses and loss adjustment expenses incurred	103,548		80,351		135,372
Amortization of deferred policy acquisition costs	34,710	[2]	42,449	[2]	48,341	[2]
Other operating expenses	44,514	[1]	45,454	[1]	36,512	[1]
Net written premiums	$207,914		$210,699		$211,407
[1]	Net investment income and Other operating expenses reflect only such amounts attributable to the Company's insurance operations.
[2]	Amortization of deferred policy acquisition costs reflects only such amounts attributable to the Company's insurance operations. A portion of these costs is eliminated in consolidation.

Reinsurance_Detail

Reinsurance (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Supplementary Insurance Information, by Segment [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Direct Amount	'	'	'	'	'	'	'	'	$1,069,677	$972,844	$912,020
Ceded to other companies	'	'	'	'	'	'	'	'	455,985	396,639	346,172
Assumed from other companies	'	'	'	'	'	'	'	'	228,247	205,759	125,797
Net earned premiums	219,902	213,895	205,814	202,328	201,566	201,262	196,017	183,119	841,939	781,964	691,645
Property Casualty	'	'	'	'	'	'	'	'	'	'	'
Supplementary Insurance Information, by Segment [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Direct Amount	'	'	'	'	'	'	'	'	1,127,331	1,034,658	929,778
Ceded to other companies	'	'	'	'	'	'	'	'	482,596	452,810	354,418
Assumed from other companies	'	'	'	'	'	'	'	'	243,187	251,807	178,438
Net earned premiums	'	'	'	'	'	'	'	'	$887,922	$833,655	$753,798
Percentage of amount assumed to net	'	'	'	'	'	'	'	'	27.00%	30.00%	24.00%

Valuation_and_Qualifying_Accou1

Valuation and Qualifying Accounts (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013
Allowance for uncollectable reinsurance	'
Valuation and Qualifying Accounts Disclosure [Line Items]	'
Balance at January 1, 2013	$11,520
Charged (Credited) to Costs and Expenses	-188
Charged to Other Accounts	'
Deductions (Describe)	'
Balance at December 31, 2013	11,332
Valuation allowance in deferred taxes	'
Valuation and Qualifying Accounts Disclosure [Line Items]	'
Balance at January 1, 2013	499
Charged (Credited) to Costs and Expenses	55
Charged to Other Accounts	'
Deductions (Describe)	'
Balance at December 31, 2013	$554

Supplementary_Information_Conc1

Supplementary Information Concerning Property-Casualty Insurance Operations (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]	'		'		'
Deferred policy acquisition costs	$67,007		$61,005		$63,984
Reserve for losses and loss adjustment expenses	2,045,071		2,097,048		2,082,679
Discount, if any, deducted	'		'		'
Unearned premiums	714,606		642,407		532,628
Net earned premiums	841,939		781,964		691,645
Net investment income	56,243	[1]	54,100	[1]	63,119	[1]
Losses and loss adjustment expenses incurred related to Current year	520,227		542,724		474,852
Losses and loss adjustment expenses incurred related to Prior year	-1,266		-45,291		2,145
Amortization of deferred policy acquisition costs	115,842	[2]	123,819	[2]	112,506	[2]
Other operating expenses	164,434	[1]	159,079	[1]	138,029	[1]
Net written premiums	$887,922		$833,655		$753,798
[1]	Net investment income and Other operating expenses reflect only such amounts attributable to the Company's insurance operations.
[2]	Amortization of deferred policy acquisition costs reflects only such amounts attributable to the Company's insurance operations. A portion of these costs is eliminated in consolidation.