Navigators (NAVG) 10-K 17 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Jan. 31, 2015	Jun. 30, 2014
Document Information [Line Items]
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Trading Symbol	NAVG
Entity Registrant Name	NAVIGATORS GROUP INC
Entity Central Index Key	793547
Current Fiscal Year End Date	-19
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		14,289,970
Entity Public Float			$723,657,575

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Investments and cash:
Fixed maturities, available-for-sale, at fair value (amortized cost: 2014, $2,323,959; 2013, $2,036,999)	$2,365,934	$2,047,873
Equity securities, available-for-sale, at fair value (cost: 2014, $154,843; 2013, $118,804)	184,295	143,954
Short-term investments, at fair value (amortized cost: 2014: $179,527; 2013: $296,250)	179,506	296,250
Cash	90,751	86,509
Total investments and cash	2,820,486	2,574,586
Premiums receivable	342,479	325,025
Prepaid reinsurance premiums	237,851	247,822
Reinsurance recoverable on paid losses	51,347	38,384
Reinsurance recoverable on unpaid losses and loss adjustment expenses	851,498	822,438
Deferred policy acquisition costs	79,452	67,007
Accrued investment income	14,791	13,866
Goodwill and other intangible assets	7,013	7,177
Current income tax receivable, net	14,549	14,299
Deferred income tax, net		23,806
Receivable for investments sold	326	3
Other assets	44,384	35,039
Total assets	4,464,176	4,169,452
Liabilities:
Reserves for losses and loss adjustment expenses	2,159,634	2,045,071
Unearned premiums	766,167	714,606
Reinsurance balances payable	152,774	167,252
Senior Notes	263,440	263,308
Deferred income tax, net	1,467
Payable for investments purchased	134	7,624
Accounts payable and other liabilities	93,336	69,379
Total liabilities	3,436,952	3,267,240
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 17,792,846 shares for 2014 and 17,709,876 shares for 2013	1,778	1,770
Additional paid-in capital	347,022	335,546
Treasury stock, at cost (3,511,380 shares for 2014 and 2013)	-155,801	-155,801
Retained earnings	787,666	692,337
Accumulated other comprehensive income	46,559	28,360
Total stockholders' equity	1,027,224	902,212
Total liabilities and stockholders' equity	$4,464,176	$4,169,452

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Fixed maturities, available-for-sale, amortized cost	$2,323,959	$2,036,999
Equity securities, available-for-sale, cost	154,843	118,804
Short-term investments, amortized cost	$179,527	$296,250
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	17,792,846	17,709,876
Treasury stock, shares	3,511,380	3,511,380

Consolidated_Statements_of_Inc

Consolidated Statements of Income (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Gross written premiums	$333,299	$327,469	$348,795	$422,790	$333,091	$312,076	$332,128	$393,222	$1,432,353	$1,370,517	$1,286,465
Revenues:
Net written premiums	228,007	228,417	231,864	311,850	223,445	196,556	198,469	269,452	1,000,138	887,922	833,655
Change in unearned premiums	6,165	16,950	-780	-86,578	-3,543	17,339	7,345	-67,124	-64,243	-45,983	-51,691
Net earned premiums	234,172	245,367	231,084	225,272	219,902	213,895	205,814	202,328	935,895	841,939	781,964
Net investment income	16,071	15,839	15,648	16,610	14,254	14,094	14,246	13,657	64,168	56,251	54,248
Total other-than-temporary impairment losses	-21	158			-530	-1,821		-42	137	-2,393	-902
Portion of loss recognized in other comprehensive income (before tax)	21	-158							-137		44
Net other-than-temporary impairment losses recognized in earnings					-530	-1,821		-42		-2,393	-858
Net realized gains (losses)	788	6,718	4,473	833	15,768	-988	3,345	4,814	12,812	22,939	41,074
Other income (expense)	586	1,336	-1,665	10,399	-665	-210	-915	618	10,656	-1,172	1,488
Total revenues	251,617	269,260	249,540	253,114	248,729	224,970	222,490	221,375	1,023,531	917,564	877,916
Expenses:
Net losses and loss adjustment expenses	134,658	135,284	140,220	135,067	131,385	125,086	131,148	131,342	545,229	518,961	497,433
Commission expenses	33,708	33,943	32,150	25,727	30,863	27,685	28,391	26,555	125,528	113,494	121,470
Other operating expenses	51,299	50,388	47,992	47,146	43,826	39,056	40,678	40,874	196,825	164,434	159,079
Call premium on Senior Notes					17,895					17,895
Interest expense	3,854	3,388	4,319	3,852	4,351	2,053	2,052	2,051	15,413	10,507	8,198
Total expenses	223,519	223,003	224,681	211,792	228,320	193,880	202,269	200,822	882,995	825,291	786,180
Income (loss) before income taxes	28,098	46,257	24,859	41,322	20,409	31,090	20,221	20,553	140,536	92,273	91,736
Income tax expense (benefit)	8,823	15,032	7,998	13,354	6,076	9,804	6,284	6,643	45,207	28,807	27,974
Net income	$19,275	$31,225	$16,861	$27,968	$14,333	$21,286	$13,937	$13,910	$95,329	$63,466	$63,762
Net income per common share:
Basic	$1.35	$2.19	$1.18	$1.96	$1.01	$1.50	$0.99	$0.99	$6.69	$4.49	$4.54
Diluted	$1.31	$2.14	$1.17	$1.94	$1	$1.48	$0.97	$0.97	$6.51	$4.42	$4.45
Average common shares outstanding:
Basic									14,259,768	14,133,925	14,052,311
Diluted									14,646,369	14,345,553	14,327,820

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net income	$95,329	$63,466	$63,762
Change in net unrealized gains (losses) on investments:
Unrealized gains (losses) on investments arising during the period, net of deferred tax of $14,925, $17,521 and $13,136 in 2014, 2013 and 2012 respectively	28,252	-32,546	24,350
Reclassification adjustment for net realized (gains) losses included in net income net of deferred tax of $2,776, $6,218 and $10,314 in 2014, 2013 and 2012 respectively	-5,156	-11,548	-19,154
Change in net unrealized gains (losses on investments)	23,096	-44,094	5,196
Change in other-than-temporary impairments:
Non credit other-than-temporary impairments arising during the period, net of deferred tax of $48, $174 and $612 in 2014, 2013 and 2012 respectively	89	320	1,135
Reclassification adjustment for non credit other-than-temporary impairment losses recognized in net income net of deferred tax of $0, $0 and $16 in 2014, 2013 and 2012 respectively			-29
Change in other-than-temporary impairments	89	320	1,106
Change in foreign currency translation gains (losses), net of deferred tax of $2,800, $1,650, and $521 in 2014, 2013 and 2012 respectively	-4,986	-3,074	-1,342
Other comprehensive income (loss)	18,199	-46,848	4,960
Comprehensive income (loss)	$113,528	$16,618	$68,722

Consolidated_Statements_of_Com1

Consolidated Statements of Comprehensive Income (Parenthetical) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Unrealized gains (losses) on investments arising during the period, deferred tax	$14,925	$17,521	$13,136
Reclassification adjustment for net realized (gains) losses included in net income, deferred tax	2,776	6,218	10,314
Non credit other-than-temporary impairments arising during the period, deferred tax	48	174	612
Reclassification adjustment for non credit other-than-temporary impairment losses recognized in net income, deferred tax	0	0	16
Change in foreign currency translation gains (losses), deferred tax	$2,800	$1,650	$521

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, 2011	$803,435	$1,746	$322,133	($155,801)	$565,109	$70,248
Beginning balance (in shares) at Dec. 31, 2011		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 (in shares) at Dec. 31, 2012		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 (in shares) at Dec. 31, 2013		17,709,876		3,511,380
Net income	95,329				95,329
Changes in comprehensive income:
Change in net unrealized gain (loss) on investments	23,096					23,096
Change in net non-credit other- than-temporary impairment losses	89					89
Change in foreign currency translation gain (loss)	-4,986					-4,986
Total comprehensive income	18,199					18,199
Shares issued under stock plan (in shares)		82,970
Shares issued under stock plan	-23	8	-31
Share-based compensation	11,507		11,507
Ending balance at Dec. 31, 2014	$1,027,224	$1,778	$347,022	($155,801)	$787,666	$46,559
Ending balance (in shares) at Dec. 31, 2014		17,792,846		3,511,380

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating activities:
Net income	$95,329	$63,466	$63,762
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation & amortization	4,915	4,518	5,931
Deferred income taxes	16,881	4,658	-11,414
Net realized (gains) losses	-12,812	-22,939	-41,074
Net other-than-temporary losses recognized in earnings		2,393	858
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	-42,024	68,599	-40,185
Reserves for losses and loss adjustment expenses	114,563	-51,977	14,369
Prepaid reinsurance premiums	10,344	-26,807	-56,853
Unearned premiums	52,380	72,199	109,778
Premiums receivable	-17,455	-4,843	-64,457
Deferred policy acquisition costs	-12,445	-6,002	2,979
Accrued investment income	-925	-1,279	1,905
Reinsurance balances payable	-14,716	1,439	57,114
Current income taxes	-582	-16,432	17,523
Other	29,039	31,987	36,503
Net cash provided by (used in) operating activities	222,492	136,875	96,739
Fixed maturities
Redemptions and maturities	210,674	237,627	188,282
Sales	362,136	648,335	1,319,404
Purchases	-864,902	-899,930	-1,711,080
Equity securities
Sales	54,900	72,113	39,503
Purchases	-83,845	-89,288	-37,587
Change in payable for securities	-7,814	-46,414	56,543
Net change in short-term investments	117,740	-142,214	-31,568
Purchase of property and equipment	-8,359	-10,088	-3,336
Net cash provided by (used in) investing activities	-219,470	-229,859	-179,839
Financing activities:
Net Proceeds from Debt Offering		263,278
Redemption of 7.0% Senior Notes Due May 1, 2016		-132,437
Proceeds of stock issued from employee stock purchase plan	1,067	821	672
Proceeds of stock issued from exercise of stock options	153	2,495	404
Net cash provided by (used in) financing activities	1,220	134,157	1,076
Increase (decrease) in cash	4,242	41,173	-82,024
Cash at beginning of year	86,509	45,336	127,360
Cash at end of period	90,751	86,509	45,336
Supplemental cash information:
Income taxes paid, net	27,066	41,094	19,602
Interest paid	15,703	8,050	8,050
Issuance of stock to directors	$438	$400	$242

Consolidated_Statements_of_Cas1

Consolidated Statements of Cash Flows (Parenthetical)	12 Months Ended
	Dec. 31, 2014
Interest rate stated on senior notes	7.00%
Senior notes due date	1-May-16

Organization_Summary_of_Signif

Organization & Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2014
Organization & Summary of Significant Accounting Policies	Note 1.	Organization & Summary of Significant Accounting Policies
	Organization
	The accompanying Consolidated Financial Statements, consisting of the results of The Navigators Group, Inc., a Delaware holding company established in 1982, and its subsidiaries are prepared on the basis of United States (“U.S.”) generally accepted accounting principles (“GAAP” or “U.S. GAAP”). All significant intercompany transactions and balances have been eliminated. The preparation of these consolidated financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the consolidated financial statements and the reported revenues and expenses during the reporting periods. The results of operations for any interim period are not necessarily indicative of results for the full year. The terms “we,” “us,” “our” or “our Company” as used herein are used to mean The Navigators Group, Inc. and its subsidiaries, unless the context otherwise requires. The terms “Parent” or “Parent Company” are used to mean The Navigators Group, Inc. without its subsidiaries. Certain amounts for the prior year have been reclassified to conform to the current year’s presentation.
	Our Company is an international insurance company focusing on specialty products within the overall property and casualty insurance market. Our long-standing area of specialization is Marine insurance. We have also developed niches in Professional Liability insurance and Property Casualty lines of insurance, such as Primary and Excess casualty coverages offered to commercial enterprises and Assumed Reinsurance.
	We classify its business into one Corporate segment (“Corporate”) and two underwriting segments, the Insurance Companies segment (“Insurance Companies”) and the Lloyd’s Operations segment (“Lloyd’s Operations”) which are separately managed by business line divisions. The Insurance Companies are primarily engaged in underwriting Marine insurance, Primary Casualty insurance with a concentration in contractors’ general liability products, Excess Casualty insurance with a concentration in commercial umbrella products, Assumed Reinsurance, Management Liability insurance and Errors & Omissions (“E&O”) insurance. This segment is comprised of Navigators Insurance Company (“NIC”), which includes a United Kingdom (“UK”) branch (“UK Branch”), and Navigators Specialty Insurance Company (“NSIC”), which underwrites business on an excess and surplus lines basis. All of the business underwritten by NSIC is fully reinsured by NIC pursuant to a 100% quota share reinsurance agreement.
	The Lloyd’s Operations are primarily engaged in underwriting Marine insurance; Energy & Engineering insurance with a concentration in offshore energy products and onshore energy construction products, Assumed Reinsurance, Management Liability insurance and E&O insurance at Lloyd’s of London (“Lloyd’s”) through Lloyd’s Syndicate 1221 (“Syndicate 1221”). The Corporate segment consists of the Parent Company’s investment income, interest expense and related income tax.
	Our revenue is primarily comprised of premiums and investment income. We derive our premiums predominantly from business written by wholly-owned underwriting management companies, Navigators Management Company (“NMC”) and Navigators Management (UK) Ltd. (“NMUK”) that manage and service insurance and reinsurance business written by the Insurance Companies. Our products are distributed through multiple channels, utilizing global, national and regional retail and wholesale insurance brokers.
	Navigators Underwriting Agency Ltd. (“NUAL”) is a Lloyd’s underwriting agency that manages Syndicate 1221. We control 100% of Syndicate 1221’s stamp capacity through our wholly-owned subsidiary, Navigators Corporate Underwriters Ltd. (“NCUL”), which is referred to as a corporate name in the Lloyd’s market. In addition, we have also established underwriting agencies in Antwerp, Belgium; Stockholm, Sweden; and Copenhagen, Denmark, as well as branches of the appointed representative, Navigators Underwriting Ltd. (“NUL”), in the European Economic Area (“EEA”), in Milan, Italy; Rotterdam, The Netherlands; and Paris, France, which underwrite risks pursuant to binding authorities with NUAL into Syndicate 1221. We have also established a presence in Brazil and China through contractual arrangements with local affiliates of Lloyd’s.
	For financial information by segment, refer to Note 3, Segment Information, in the Notes to Consolidated Financial Statements, included herein.
	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, 2014 and 2013, all fixed maturity and equity securities held by our 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 and preferred stock.
	Short-term investments are carried at 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. 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 than not our Company 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 of 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, a net 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 have 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.
	Our 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.
	Foreign Currency Remeasurement and Translation
	The functional currency in each of our operations is generally the currency of the local operating environment, except for our Lloyd’s Operations which is the U.S. dollar. Transactions in currencies other than an operation’s functional currency are remeasured into the functional currency and the resulting foreign exchange gains and losses are reflected in net Other Income (Expense) in the Consolidated Statements of Income. 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.
	During the first quarter, Syndicate 1221 revised its foreign exchange accounting methodology from reporting its financial position and results using three functional currencies (GBP, USD and CAD) to one functional currency (USD). The USD was chosen as the single functional currency as the majority of the Syndicate’s insurance business has been and continues to be transacted in USD. This cumulative change in re-measurement has resulted in an immaterial correction of $10.0 million ($6.6 million, after-tax) reducing Accumulated Other Comprehensive Income in the consolidated balance sheet, offset by a gain in Other Income in the consolidated statement of income. The impact of the correction is not material to the previously issued annual financial statements for 2013 and 2012.
	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 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 (“A&H”) 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 are deferred and amortized ratably over the period that the related premiums are recognized as revenue. Such costs (e.g., 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 incurred but not reported (“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. Our 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, and when permitted by the applicable accounting guidance, qualitative factors are assessed to determine whether it is necessary to calculate an asset’s fair value when testing an asset with an indefinite life for impairment. Goodwill and indefinite lived intangible assets are considered impaired if the estimated fair value is less than its carrying value and 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, 2014, 2013 and 2012.
	As of December 31, 2014, the carrying value of goodwill and indefinite lived intangible assets was $7.0 million, consisting of $2.5 million and $2.4 million of goodwill assigned to NMC and our Lloyd’s Operations, respectively, and $2.1 million of indefinite lived intangible assets assigned to our Lloyd’s Operations. 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. 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 whereby deferred 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. 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. These reviews include, among other factors, the nature and amount of the taxable income and expense items, the expected timing of when assets will be used or liabilities will be required to be reported, as well as the reliability of historical profitability of businesses expected to provide future earnings. After review, if management determines that the realization of the tax asset does not meet the more likely than not criterion an offsetting valuation allowance is recorded, which reduces net earnings and the deferred tax asset in that period. Additional information regarding our deferred tax assets can be found in Note 7, Income Taxes, in the Notes to Consolidated Financial Statements, included herein.
	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, the recoverability of deferred tax assets, and impairment of invested assets.

Earnings_Per_Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2014
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, 2014, 2013 and 2012:
			Year Ended December 31,
	In thousands, except share and per share amounts		2014		2013		2012
	Net income		$	95,329	$	63,466	$	63,762
	Basic weighted average shares			14,259,768		14,133,925		14,052,311
	Effect of common stock equivalents:
	Assumed exercise of stock options and vesting of stock grants			386,601		211,628		275,509
	Diluted weighted average shares			14,646,369		14,345,553		14,327,820
	Net income per common share:
	Basic		$	6.69	$	4.49	$	4.54
	Diluted		$	6.51	$	4.42	$	4.45

Segment_Information

Segment Information	12 Months Ended
	Dec. 31, 2014
Segment Information	Note 3.	Segment Information
	We classify our business into one corporate segment and two underwriting segments, Insurance Companies and Lloyd’s Operations. Management takes into consideration a wide range of factors in planning the business strategy of the Company and evaluating the results of its operations. The performance of each underwriting segment is based on their underwriting and GAAP results. 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 or expense. The combined ratio is derived by dividing the sum of net losses and LAE, commission expenses, other operating expenses and other underwriting (expense) by net earned premiums. A combined ratio of less than 100% indicates an underwriting profit and greater than 100% indicates an underwriting loss. Each segment maintains its own investments on which it earns income and realizes capital gains or losses. Each segment’s underwriting performance is evaluated separately from the performance of its investment portfolio. The Corporate segment’s results consist of the Parent Company’s investment income, interest expense and related income taxes.
	Access to capital also has a significant impact on management’s outlook for the operations. The Insurance Companies’ operations and ability to grow their business and take advantage of market opportunities are constrained by regulatory capital requirements and rating agency assessments of capital adequacy. Similarly, the ability to grow the Lloyd’s Operations is subject to capital and operating requirements of the Lloyd’s and UK regulatory authorities.
	The accounting policies used to prepare the segment reporting data for the Company’s segments are the same as those described in the Summary of Significant Accounting Policies in Footnote 1.
	Financial data by segment for the years ended December 31, 2014, 2013, and 2012 were as follows:
			Year Ended December 31, 2014
	In thousands		Insurance			Lloyd’s			Corporate(1)			Total
			Companies			Operations
	Gross written premiums		$	1,045,454		$	386,899		$	—		$	1,432,353
	Net written premiums			752,773			247,365			—			1,000,138
	Net earned premiums			704,574			231,321			—			935,895
	Net losses and loss adjustment expenses			(434,396	)		(110,833	)		—			(545,229	)
	Commission expenses			(85,137	)		(42,558	)		2,167			(125,528	)
	Other operating expenses			(138,675	)		(58,150	)		—			(196,825	)
	Other underwriting income (expense)			2,727			35			(2,167	)		595
	Underwriting profit (loss)		$	49,093		$	19,815		$	—		$	68,908
	Net investment income			56,714			7,378			76			64,168
	Net realized gains (losses)			12,715			97			—			12,812
	Call premium on Senior Notes			—			—			—			—
	Interest expense			—			—			(15,413	)		(15,413	)
	Other income (expense)			(2,182	)		12,243			—			10,061
	Income (loss) before income taxes		$	116,340		$	39,533		$	(15,337	)	$	140,536
	Income tax expense (benefit)			36,609			13,885			(5,287	)		45,207
	Net income (loss)		$	79,731		$	25,648		$	(10,050	)	$	95,329
	Identifiable assets		$	3,344,084		$	957,795		$	162,297		$	4,464,176
	Losses and loss adjustment expenses ratio			61.7	%		47.9	%					58.3	%
	Commission expense ratio			12.1	%		18.4	%					13.4	%
	Other operating expense ratio (2)			19.2	%		25.1	%					20.9	%
	Combined ratio			93	%		91.4	%					92.6	%
	(1) - Includes Corporate segment intercompany eliminations.
	(2) - Includes Other operating expenses and Other underwriting income (expenses).
			Year Ended December 31, 2013
	In thousands		Insurance			Lloyd’s			Corporate(1)			Total
			Companies			Operations
	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
	In thousands		Insurance			Lloyd’s			Corporate(1)			Total
			Companies			Operations
	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.
The following tables provide additional financial data by segment for the years ended December 31, 2014, 2013 and 2012:
		Year Ended December 31, 2014
In thousands		Insurance			Lloyd’s			Total
		Companies			Operations
Gross written premiums:
Marine		$	177,363		$	188,107		$	365,470
Property casualty			755,059			126,016			881,075
Professional liability			113,032			72,776			185,808
Total		$	1,045,454		$	386,899		$	1,432,353
Net written premiums:
Marine		$	123,617		$	144,327		$	267,944
Property casualty			554,844			55,917			610,761
Professional liability			74,312			47,121			121,433
Total		$	752,773		$	247,365		$	1,000,138
Net earned premiums:
Marine		$	123,203		$	141,471		$	264,674
Property casualty			496,209			51,338			547,547
Professional liability			85,162			38,512			123,674
Total		$	704,574		$	231,321		$	935,895
		Year Ended December 31, 2013
In thousands		Insurance			Lloyd’s			Total
		Companies			Operations
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
In thousands		Insurance			Lloyd’s			Total
		Companies			Operations
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
The Insurance Companies net earned premiums include $37.7 million, $44.6 million and $63.9 million of net earned premiums from the U.K. Branch for 2014, 2013 and 2012, respectively.

Investments

Investments	12 Months Ended
	Dec. 31, 2014
Investments	Note 4.	Investments
	The following tables set forth our Company’s cash and investments as of December 31, 2014 and 2013. The tables below include OTTI securities recognized within AOCI.
			December 31, 2014
	In thousands		Fair Value				Gross				Gross			Amortized
							Unrealized				Unrealized			Cost
							Gains				Losses
	Fixed maturities:
	U.S. Treasury bonds, agency bonds and foreign government bonds		$	397,923			$	3,431			$	(5,965	)	$	400,457
	States, municipalities and political subdivisions			541,007				19,204				(558	)		522,361
	Mortgage-backed and asset-backed securities:
	Agency mortgage-backed securities			364,622				8,476				(998	)		357,144
	Residential mortgage obligations			34,087				1,153				(138	)		33,072
	Asset-backed securities			206,413				380				(964	)		206,997
	Commercial mortgage-backed securities			206,318				6,630				(98	)		199,786
	Subtotal		$	811,440			$	16,639			$	(2,198	)	$	796,999
	Corporate bonds			615,564				13,048				(1,626	)		604,142
	Total fixed maturities		$	2,365,934			$	52,322			$	(10,347	)	$	2,323,959
	Equity securities - common stocks			127,183				28,520				(1,254	)		99,917
	Equity securities - preferred stocks			57,112				2,236				(50	)		54,926
	Short-term investments			179,506				—				(21	)		179,527
	Cash			90,751				—				—			90,751
	Total		$	2,820,486			$	83,078			$	(11,672	)	$	2,749,080
			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
	As of December 31, 2014 and 2013, fixed maturities for which non-credit OTTI was previously recognized and included in accumulated other comprehensive income are now in an unrealized gains position of $0.7 million and $0.5 million, respectively.
	The fair value of our 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. Our Company does not have the intent to sell nor is it more likely than not that it will have to sell fixed maturities 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. Our Company does not intend to sell any of these securities and it is more likely than not that, our Company will not be required to sell these securities before the recovery of the amortized cost basis. For equity securities, our 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. Our 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 our 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 maturities categorized by the number of years until maturity as of December 31, 2014 are shown in the following table:
			December 31, 2014
	In thousands		Fair Value				Amortized
							Cost
	Due in one year or less		$	63,670			$	65,643
	Due after one year through five years			765,084				758,064
	Due after five years through ten years			356,929				348,195
	Due after ten years			368,811				355,058
	Mortgage- and asset-backed securities			811,440				796,999
	Total		$	2,365,934			$	2,323,959
	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 4.4 years.
	The following table shows the amount and percentage of our Company’s fixed maturities as of December 31, 2014 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, 2014
	In thousands		Rating		Fair Value				Percent
									of Total
	Rating description:
	Extremely strong		AAA		$	462,603				20	%
	Very strong		AA			1,090,505				45	%
	Strong		A			612,131				26	%
	Adequate		BBB			185,372				8	%
	Speculative		BB & Below			14,852				1	%
Not rated		NR			471				0	%
Total		AA		$	2,365,934				100	%
The following table summarizes all securities in a gross unrealized loss position as of December 31, 2014 and 2013, 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, 2014											December 31, 2013
In thousands, except # of securities		Number of				Fair Value				Gross			Number of			Fair Value			Gross
		Securities								Unrealized			Securities						Unrealized
										Loss									Loss
Fixed maturities:
U.S. Treasury bonds, agency bonds, and foreign government bonds
0-6 months			19			$	87,915			$	1,061			27		$	136,360		$	1,096
7-12 months			—				—				—			26			149,370			7,759
> 12 months			31				117,683				4,904			—			—			—
Subtotal			50			$	205,598			$	5,965			53		$	285,730		$	8,855
States, municipalities and political subdivisions
0-6 months			13			$	14,242			$	41			28		$	40,132		$	297
7-12 months			2				2,107				19			104			205,152			12,100
> 12 months			17				37,340				498			6			12,357			1,254
Subtotal			32			$	53,689			$	558			138		$	257,641		$	13,651
Agency mortgage-backed securities
0-6 months			4			$	14,743			$	52			39		$	39,458		$	434
7-12 months			2				4,138				28			64			77,860			3,768
> 12 months			46				58,301				918			9			22,784			1,814
Subtotal			52			$	77,182			$	998			112		$	140,102		$	6,016
Residential mortgage obligations
0-6 months			6			$	4,966			$	43			3		$	431		$	2
7-12 months			2				659				7			7			950			29
> 12 months			14				1,728				88			15			2,467			130
Subtotal			22			$	7,353			$	138			25		$	3,848		$	161
Asset-backed securities
0-6 months			19			$	96,123			$	354			14		$	75,887		$	479
7-12 months			3				14,152				185			1			203			1
> 12 months			3				34,530				425			—			—			—
Subtotal			25			$	144,805			$	964			15		$	76,090		$	480
Commercial mortgage-backed securities
0-6 months			4			$	18,665			$	65			4		$	6,712		$	31
7-12 months			1				1,076				6			2			15,098			322
> 12 months			3				1,391				27			4			774			21
Subtotal			8			$	21,132			$	98			10		$	22,584		$	374
Corporate bonds
0-6 months			52			$	179,390			$	797			34		$	93,591		$	717
7-12 months			4				11,071				74			18			55,021			2,726
> 12 months			14				31,126				755			—			—			—
Subtotal			70			$	221,587			$	1,626			52		$	148,612		$	3,443
Total fixed maturities			259			$	731,346			$	10,347			405		$	934,607		$	32,980
Equity securities - common stocks
0-6 months			6			$	9,152			$	761			5		$	7,387		$	422
7-12 months			1				3,887				486			2			3,538			128
> 12 months			1				238				7			—			—			—
			8			$	13,277			$	1,254			7		$	10,925		$	550
Equity securities - preferred stocks
0-6 months			7			$	6,651			$	50			—		$	—		$	—
7-12 months			—				—				—			—			—			—
> 12 months			—				—				—			—			—			—
			7			$	6,651			$	50			—		$	—		$	—
Total equity securities			15			$	19,928			$	1,304			7		$	10,925		$	550
As of December 31, 2014 and 2013, the largest unrealized loss by a non-government backed issuer in the investment portfolio was $0.5 million and $1.1 million, respectively.
Our 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 fixed maturities, when assessing whether the amortized cost basis of the security will be recovered, our 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 AOCI.
To determine whether the unrealized loss on structured securities is other-than-temporary, our 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. Our 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, our 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, our 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.
Our 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, 2014, there were no securities with a fair value that was less than 80% of amortized cost.
The table below summarizes our Company’s activity related to OTTI losses for the periods indicated:
		Year Ended December 31,
		2014								2013						2012
In thousands, except # of securities		Number of				Amount				Number of			Amount			Number of			Amount
		Securities								Securities						Securities
Total OTTI losses:
Corporate and other bonds			—			$	—				1		$	1,822			—		$	—
Commercial mortgage-backed securities			—				—				—			—			—			—
Residential mortgage-backed securities			31				(137	)			—			—			1			55
Asset-backed securities			—				—				—			—			—			—
Equities			—				—				3			571			3			847
Total			31			$	(137	)			4		$	2,393			4		$	902
Less: Portion of loss in accumulated other comprehensive income (loss):
Corporate and other bonds						$	—						$	—					$	—
Commercial mortgage-backed securities							—							—						—
Residential mortgage-backed securities							(137	)						—						44
Asset-backed securities							—							—						—
Equities							—							—						—
Total						$	(137	)					$	—					$	44
Impairment losses recognized in earnings:
Corporate and other bonds						$	—						$	1,822					$	—
Commercial mortgage-backed securities							—							—						—
Residential mortgage-backed securities							—							—						11
Asset-backed securities							—							—						—
Equities							—							571						847
Total						$	—						$	2,393					$	858
The following table summarizes the cumulative amounts related to our Company’s credit loss portion of the OTTI losses on fixed maturities for the years ended December 31, 2014, 2013 and 2012. Our 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 and for which the non-credit loss portion is included in AOCI.
		Year Ended December 31,
In thousands		2014				2013				2012
Beginning balance		$	5,154			$	3,332			$	3,321
Additions for credit loss impairments recognized in the current period on securities not previously impaired			—				1,822				—
Additions for credit loss impairments recognized in the current period on securities previously impaired			—				—				11
Reductions for credit loss impairments previously recognized on securities sold during the period			(2,793	)			—				—
Ending balance		$	2,361			$	5,154			$	3,332
The contractual maturity dates for fixed maturities categorized by the number of years until maturity, with a gross unrealized loss as of December 31, 2014 is presented in the following table:
		December 31, 2014
		Gross Unrealized Losses								Fair Value
In thousands		Amount				Percent				Amount			Percent
						of Total							of Total
Due in one year or less		$	2,638				25	%		$	21,919			3	%
Due after one year through five years			3,791				37	%			334,046			46	%
Due after five years through ten years			1,562				15	%			103,376			14	%
Due after ten years			158				2	%			21,533			3	%
Mortgage- and asset-backed securities			2,198				21	%			250,472			34	%
Total		$	10,347				100	%		$	731,346			100	%
Our Company’s net investment income was derived from the following sources:
		Year Ended December 31,
In thousands		2014				2013				2012
Fixed maturities		$	57,219			$	53,898			$	58,995
Equity securities			9,036				4,835				3,945
Short-term investments			911				774				1,694
Total investment income			67,166				59,507				64,634
Investment expenses			(2,998	)			(3,256	)			(10,386	)
Net investment income		$	64,168			$	56,251			$	54,248
Investment expenses for the year ended December 31, 2012 include $4.5 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 our 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		2014				2013				2012
Fixed maturities		$	31,080			$	(76,194	)		$	15,709
Equity securities			4,302				8,857				(5,989	)
Gross unrealized gains (losses)			35,382				(67,337	)			9,720
Deferred income tax			12,197				(23,565	)			3,418
Change in net unrealized gains (losses), net		$	23,185			$	(43,772	)		$	6,302
Realized gains and losses, excluding net OTTI losses recognized in earnings, for the periods indicated, were as follows:
		Year Ended December 31,
In thousands		2014				2013				2012
Fixed maturities:
Gains		$	8,326			$	8,539			$	28,789
Losses			(2,610	)			(2,797	)			(1,915	)
Fixed maturities, net		$	5,716			$	5,742			$	26,874
Equity securities:
Gains		$	9,447			$	17,955			$	14,673
Losses			(2,351	)			(758	)			(473	)
Equity securities, net		$	7,096			$	17,197			$	14,200
Net realized gains (losses)		$	12,812			$	22,939			$	41,074
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, our Company’s fixed maturities and equity securities by asset class that are measured at fair value on a recurring basis as of December 31, 2014 and 2013:
		December 31, 2014
In thousands		Level 1				Level 2				Level 3			Total
Fixed maturities:
U.S. Treasury bonds, agency bonds and foreign government bonds		$	146,904			$	251,019			$	—		$	397,923
States, municipalities and political subdivisions			—				541,007				—			541,007
Mortgage-backed and asset-backed securities:														—
Agency mortgage-backed securities			—				364,622				—			364,622
Residential mortgage obligations			—				34,087				—			34,087
Asset-backed securities			—				206,413				—			206,413
Commercial mortgage-backed securities			—				206,318				—			206,318
Subtotal		$	—			$	811,440			$	—		$	811,440
Corporate bonds			—				615,564				—			615,564
Total fixed maturities		$	146,904			$	2,219,030			$	—		$	2,365,934
Equity securities - common stocks			127,183								—			127,183
Equity securities - preferred stocks			—				57,112				—			57,112
Total		$	274,087			$	2,276,142			$	—		$	2,550,229
		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
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 our 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.
Our Company did not have any significant transfers between Level 1 and 2 for the years ended December 31, 2014 and 2013.
Our Company did not have any Level 3 assets for the year ended December 31, 2014.
During 2014, one security was transferred from Level 3 to Level 2 as our Company was able to obtain a price from a vendor, in which all significant inputs to the model are observable in active markets.
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, 2014 and 2013. For the year ended December 31, 2012, our Company did not have any Level 3 assets.
		Year Ended December 31, 2014
In thousands		Beginning				Realized				Unrealized			Purchase			Sales			Settlements		Transfers		Transfers			Ending
		Balance				Gains				Gains											into		out of
						(Losses)				(Losses)											Level 3		Level 3
Assets:
Corporate Bond		$	4,407			$	—			$	—		$	—		$	—		$	—	$	—	$	(4,407	)	$	—
Total assets		$	4,407			$	—			$	—		$	—		$	—		$	—	$	—	$	(4,407	)	$	—
		Year Ended December 31, 2013
In thousands		Beginning				Realized				Unrealized			Purchase			Sales			Settlements		Transfers		Transfers			Ending
		Balance				Gains				Gains											into		out of
						(Losses)				(Losses)											Level 3		Level 3
Assets:
Commercial
Mortgage		$	—			$	—			$	(42	)	$	4,660		$	(211	)	$	—	$	—	$	—		$	4,407
Total assets		$	—			$	—			$	(42	)	$	4,660		$	(211	)	$	—	$	—	$	—		$	4,407
In 2013 the Level 3 security was valued using unobservable inputs based on a proxy of a security of similar duration in which market quotations are available.
As of December 31, 2014 and 2013, our Company’s restricted net assets in support of the underwriting activities of the Insurance Companies and Lloyd’s Operations were $523.4 million and $520.9 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, 2014 and 2013, our 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, 2014
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 the Insurance Companies and the Lloyd’s Operations 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, the Insurance Companies and the Lloyd’s Operations.
	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. 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 strengthening or release of reserves is affected by many factors, some of which are interdependent. To the extent that reserves are strengthened or released, the amount of such strengthening or release is treated as a charge or credit to earnings in the period in which the strengthening or release is recognized.
	The following table summarizes our Company’s reserves for losses and LAE activity for the years ended December 31, 2014, 2013 and 2012:
			Year Ended December 31,
	In thousands		2014			2013			2012
	Net reserves for losses and LAE at beginning of year		$	1,222,633		$	1,216,909		$	1,237,234
	Provision for losses and LAE for claims occurring in the current year			601,041			520,227			542,724
	Increase (decrease) in estimated losses and LAE for claims occurring in prior years			(55,812	)		(1,266	)		(45,291	)
	Incurred losses and LAE			545,229			518,961			497,433
	Losses and LAE paid for claims occurring during:
	Current year			(164,199	)		(147,758	)		(110,373	)
	Prior years			(295,527	)		(365,479	)		(407,385	)
	Losses and LAE payments			(459,726	)		(513,237	)		(517,758	)
	Net reserves for losses and LAE at end of year			1,308,136			1,222,633			1,216,909
	Reinsurance recoverables on unpaid losses and LAE			851,498			822,438			880,139
	Gross reserves for losses and LAE at end of year		$	2,159,634		$	2,045,071		$	2,097,048
	The segment and line of business breakdowns of prior period net reserve strengthening (releases) for the years ended December 31, 2014, 2013 and 2012 are as follows:
			Year Ended December 31,
	In thousands		2014			2013			2012
	Insurance Companies:
	Marine		$	(41,388	)	$	(15,227	)	$	(10,010	)
	Property Casualty			14,612			18,466			4,293
	Professional Liability			(3,536	)		10,191			7,613
	Insurance Companies		$	(30,312	)	$	13,430		$	1,896
	Lloyd’s Operations:
	Marine		$	(21,336	)	$	(2,998	)	$	(30,735	)
	Property Casualty			(1,500	)		(14,574	)		(6,890	)
	Professional Liability			(2,664	)		2,876			(9,562	)
	Lloyd’s Operations		$	(25,500	)	$	(14,696	)	$	(47,187	)
	Total strengthening (releases)		$	(55,812	)	$	(1,266	)	$	(45,291	)
	The following is a discussion of relevant factors related to the $55.8 million prior period net reserve releases recorded for the year ended December 31, 2014:
	The Insurance Companies recorded $30.3 million of net prior year reserve releases, primarily driven by our Marine business, in connection with $41.4 million of net favorable loss emergence due to a lesser amount of large losses and improved underwriting over the past couple of years across all core product lines, inclusive of $13.4 million from Marine Liability, $7.2 million from Craft/Fishing vessels, $6.4 million from P&I, $4.7 million from Inland Marine, $1.1 million from Bluewater Hull and $0.7 million from Cargo.
	The Insurance Companies’ Marine reserve releases were partially offset by $14.6 million of net reserve strengthening from our Property Casualty business which is driven by $23.2 million of prior year reserve strengthening from our Primary Casualty division resulting entirely from unfavorable activity on pre-2010 California construction defect liability claims, partially offset by $6.1 million of reserve releases due to favorable loss emergence from our Excess Casualty division.
	The Insurance Companies’ Professional Liability business recorded $3.5 million of net prior year reserve releases primarily driven by $4.5 million of favorable loss emergence from our Management Liability division due to a cash settlement of a contract dispute with a former third party administrator, partially offset by unfavorable loss emergence from our Errors and Omissions (“E&O”) division due to our small lawyers’ product lines, which are in runoff.
	The Lloyds Operations recorded $25.5 million of net prior year reserve releases primarily driven by $21.3 million of Marine releases in connection with favorable loss emergence across all core product lines, inclusive of $11.0 million from Marine Liability, $3.7 million from Specie, $1.3 million from Transport, $1.0 million from Cargo, $2.3 million from Energy Liability and $2.0 million from Marine Assumed.
	The Lloyd’s Operations Property Casualty line recorded prior year releases of $1.5 million due to favorable loss emergence on our Onshore Energy book. Additionally, the Professional Liability business reserve releases on older underwriting years (“UWYs”) was due to favorable loss emergence on both our E&O book by $1.0 million and Excess D&O by $1.7 million.
	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 lines in connection with UWYs 2012 and 2011, $10.4 million of strengthening from our Primary Casualty division 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 Management Liability division related to specific large claims for UWYs 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 UWYs 2011 and prior.
	The aforementioned net prior period reserve 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 UWYs 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 Operations Property Casualty business, we reported net prior period reserve releases of $14.6 million primarily from our Energy & Engineering division. Within our Lloyd’s Operations Marine business, we reported prior period reserve releases of $3.0 million driven by our Marine Liability product. Within our Lloyd’s Operations Professional Liability business, we reported strengthening of $2.9 million, inclusive of $6.1 million of strengthening in our E&O division partially offset by $3.2 million of favorable emergence from our Management Liability division.
	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 UWY 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 UWY 2011 arising from our A&H product lines.
	Our Lloyd’s Operations recorded $47.2 million of net prior period reserve releases across all businesses and divisions. In connection with our Company’s implementation of the Solvency II technical provisions in its Lloyd’s Operations, our 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, our 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 Operations 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 Marine business and $0.9 million from Professional Liability business. A summary of the resulting prior period redundancies for each business within our Lloyd’s Operations by prior UWY 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
	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.

Ceded_Reinsurance

Ceded Reinsurance	12 Months Ended
	Dec. 31, 2014
Ceded Reinsurance	Note 6.	Ceded 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.
	Our Company’s ceded earned premiums were $440.7 million, $456.0 million and $396.6 million for the years ended December 31, 2014, 2013 and 2012, respectively.
	Our Company’s ceded incurred losses were $230.2 million, $188.7 million and $262.6 million for the years ended December 31, 2014, 2013 and 2012, respectively.
	We have established a reserve for uncollectible reinsurance in the amount of $11.3 million as of December 31, 2014 and 2013, which was determined by considering reinsurer specific default risk as indicated by their financial strength ratings as well as additional default risk for Asbestos and Environmental related recoverables. Actual uncollectible reinsurance could exceed or be less than 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 our Company’s reinsurance recoverables of $1.1 billion as of December 31, 2014 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:
	In thousands		Rating		Carrying				Percent
					Value (2)				of Total
	A.M. Best Rating description (1):
	Superior		A++, A+		$	575,205				50	%
	Excellent		A, A-			547,314				48	%
	Very good		B++, B+			8,483				1	%
	Fair		B, B-			—				0	%
	Not rated		NR			9,694				1	%
	Total				$	1,140,696				100	%
	-1		-		When an A.M. Best rating is unavailable, the equivalent S&P rating is used.
	-2		-		The carrying value is comprised of prepaid reinsurance premium as well as reinsurance recoverables on paid and unpaid losses which are net of the reserve for uncollectible reinsurance.
	Our Company holds collateral of $202.0 million, which consists of $152.8 million in ceded balances payable, $43.1 million in letters of credit and $6.1 million of funds held and trust account balances, all of which are held by our Insurance Companies and Lloyd’s Operations. In total, the collateral represents 17.7% of the carrying value of the reinsurance recoverables. Collateral of $5.2 million or 53.6% of the carrying value is held for NR rated reinsurance recoverables.
	The following table lists our Company’s 20 largest reinsurers measured by the amount of reinsurance recoverable for ceded losses and LAE and ceded unearned premium (constituting 75.7% of the total recoverable), together with the reinsurance recoverable and collateral as of December 31, 2014, and the reinsurers’ ratings from A.M. Best or S&P:
	In thousands		Unearned				Paid/Unpaid				Total (1)			Collateral		A.M. Best	S&P
			Premium				Losses							Held
	National Indemnity Company		$	25,202			$	117,562			$	142,764		$	22,069	A++	AA+
	Everest Reinsurance Company			21,573				75,063				96,636			7,326	A+	A+
	Swiss Reinsurance America Corporation			22,815				73,305				96,120			14,587	A+	AA-
	Transatlantic Reinsurance Company			11,916				74,072				85,988			4,038	A	A+
	Munich Reinsurance America Inc.			11,366				58,768				70,134			5,539	A+	AA-
	Allied World Reinsurance			9,048				37,088				46,136			1,666	A	A
	Lloyd’s Syndicate #2003			4,399				35,123				39,522			5,191	A	A+
	Partner Reinsurance Europe			10,986				25,409				36,395			16,052	A+	A+
	Employers Mutual Casualty Company			11,928				21,851				33,779			10,935	A	NR
	Scor Global P&C SE			10,190				17,572				27,762			5,558	A	A+
	Ace Property and Casualty Insurance Company			11,165				12,741				23,906			2,907	A++	AA
	Tower Insurance Company			—				21,509				21,509			2,455	A-	NR
	Aspen Insurance UK Ltd.			8,928				11,227				20,155			4,869	A	A
	Ironshore Indemnity Inc.			6,234				13,395				19,629			8,645	A	NR
	Validus Reinsurance Ltd.			2,020				16,873				18,893			10,975	A	A
	Atlantic Specialty Insurance			2,542				15,812				18,354			—	A	A-
	QBE Reinsurance Corp			2,636				15,539				18,175			—	A	A+
	National Union Fire Ins.			8,067				8,459				16,526			6,158	A	A+
	Endurance Reinsurance Corporation			5,695				9,936				15,631			1,337	A	A
	Odyssey American Reinsurance Corporation			3,506				11,650				15,156			1,604	A	A-
	Top 20		$	190,216			$	672,954			$	863,170		$	131,911
	Others			47,635				229,891				277,526			70,065
	Total		$	237,851			$	902,845			$	1,140,696		$	201,976
	(1) - Net of reserve for uncollectible reinsurance of approximately $11.3 million.
	Approximately 21% 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 our 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, 2014, the reinsurance recoverables for paid and unpaid losses due from reinsurers in connection with all catastrophic losses was $43.3 million. Included in this figure is $25.4 million for Superstorm Sandy and $7.3 million for the 2008 Hurricanes. 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.
	The following table summarizes the components of Net Written Premium:
			Year Ended December 31,
	In thousands		2014				2013				2012
	Direct		$	1,184,538			$	1,127,331			$	1,034,658
	Assumed			247,815				243,187				251,807
	Ceded			(432,215	)			(482,596	)			(452,810	)
	Net Written Premiums		$	1,000,138			$	887,922			$	833,655
	The following table summarizes the components of Net Earned Premium:
			Year Ended December 31,
	In thousands		2014				2013				2012
	Direct		$	1,133,336			$	1,069,677			$	972,844
	Assumed			243,215				228,247				205,759
	Ceded			(440,656	)			(455,985	)			(396,639	)
	Net Earned Premiums		$	935,895			$	841,939			$	781,964
	The following table summarizes the components of Net Losses and LAE incurred:
			Year Ended December 31,
In thousands		2014				2013				2012
Direct		$	631,730			$	552,381			$	608,945
Assumed			143,681				155,313				151,137
Ceded			(230,182	)			(188,733	)			(262,649	)
Net Losses and LAE		$	545,229			$	518,961			$	497,433

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Taxes	Note 7.	Income Taxes
	Our Company is subject to the tax laws and regulations of the United States (“U.S.”) and the foreign countries in which it operates. Our 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 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. Our Company’s corporate member is subject to this agreement and receives 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 our Company’s foreign source insurance income and foreign tax credits, where available, are utilized to offset U.S. tax as permitted. Our Company’s effective tax rate for Syndicate 1221 taxable income could substantially exceed 35% to the extent our 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 our Company’s foreign agencies as these earnings are subject to the active financing exception and are not includable as Subpart F income. Certain provisions of Subpart F expired for years after December 31, 2014; therefore, these earnings will be taxable in the U.S. at the 35% tax rate beginning January 1, 2015.
	The components of current and deferred income tax expense (benefit) are as follows:
			Year Ended December 31,
	In thousands		2014			2013			2012
	Current income tax expense (benefit):
	Federal and foreign		$	27,290		$	23,703		$	39,242
	State and local			1,036			446			146
	Subtotal			28,326			24,149			39,388
	Deferred income tax expense (benefit):
	Federal and foreign			16,881			4,658			(11,414	)
	State and local			—			—			—
	Subtotal			16,881			4,658			(11,414	)
	Total income tax expense (benefit)		$	45,207		$	28,807		$	27,974
	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		2014						2013					2012
	Computed expected tax expense		$	49,187			35	%	$	32,299		35	%	$	32,109		35	%
	Tax-exempt interest			(4,771	)		-3.4	%		(3,839	)	-4.2	%		(4,443	)	-4.8	%
	Dividends received deduction			(1,257	)		-0.9	%		(897	)	-1	%		(799	)	-0.9	%
	Proration of DRD and Tax-exempt interest			904			0.6	%		710		0.8	%		786		0.9	%
	Current state and local income taxes, net of federal income tax deduction			674			0.5	%		290		0.3	%		95		0.1	%
	Other			470			0.3	%		244		0.3	%		226		0.2	%
	Actual tax expense and rate		$	45,207			32.2	%	$	28,807		31.2	%	$	27,974		30.5	%
	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		2014			2013
	Deferred tax assets:
	Loss reserve discount		$	24,820		$	27,822
	Unearned premiums			29,080			25,706
	Compensation related			10,586			6,782
	State and local net deferred tax assets			777			555
	Other			1,834			3,889
	Total gross deferred tax assets			67,097			64,754
	Less: Valuation allowance			(777	)		(555	)
	Total deferred tax assets		$	66,320		$	64,199
	Deferred tax liabilities:
	Net unrealized gains/losses on securities			(24,832	)		(9,119	)
	Deferred acquisition costs			(22,120	)		(19,258	)
	Lloyd’s year of account deferral			(13,578	)		(4,381	)
	Net unrealized foreign exchange			(4,470	)		(3,516	)
	Other			(2,787	)		(4,119	)
	Total deferred tax liabilities		$	(67,787	)	$	(40,393	)
	Net deferred income tax asset (liability)		$	(1,467	)	$	23,806
	Our Company has not provided for U.S. income taxes on approximately $22.6 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 $2.3 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 our Company.
	Unrecognized tax benefits are differences between tax positions taken in the tax returns and benefits recognized in the financial statements. Our Company has no unrecognized tax benefits as of December 31, 2014 and 2013. Our Company did not incur any interest or penalties related to unrecognized tax benefits for the years ended December 31, 2014 and 2013. Our Company currently is under examination by the IRS for taxable years 2010, 2011, and 2012 and generally is subject to U.S. Federal, state or local or foreign tax examinations by tax authorities for 2009 and subsequent years.
	Our Company recorded income tax expense of $45.2 million for the year ended December 31, 2014 compared to $28.8 million for the same period in 2013, resulting in an effective tax rate of 32.2% for the year ended December 31, 2014 and 31.2% for the comparable periods in 2013.
	Our Company had state and local deferred tax assets amounting to potential future tax benefits of $0.8 million and $0.6 million as of December 31, 2014 and 2013, respectively. Included in the deferred tax assets are state and local net operating loss carry-forwards of $0.0 million as of December 31, 2014 and $0.1 million for December 31, 2013. A valuation allowance was established for the full amount of these potential future tax benefits due to the uncertainty associated with their realization. Our Company’s state and local tax carry-forwards as of December 31, 2014 expire from 2024 to 2032.
	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 our Company will realize the benefits of its deductible differences as of December 31, 2014, net of any valuation allowance.

Credit_Facilities

Credit Facilities	12 Months Ended
	Dec. 31, 2014
Credit Facilities	Note 8.	Credit Facilities
	On November 6, 2014 NUAL entered into a credit facility for $8.0 million Australian Dollars with Barclays Bank PLC to fund its participation in Syndicate 1221. The facility is used to fund Australian underwriting obligations for the 2014 and prior underwriting years. The facility contains customary covenants for facilities of this type, including a restriction on future encumbrances that are outside the ordinary course of business, and a requirement to maintain at least £75 million of Funds at Lloyd’s. Interest is payable on the facility at a rate of 2% per annum above a floating rate tied to the average mid-rate for Australian bills of exchange administered by the Australian Financial Markets Association. The facility may be cancelled by either party after providing written notice. As of December 31, 2014, our Company was in compliance with all covenants.
	On November 24, 2014, our Company entered into a $175 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 November 22, 2012. The credit facility, which is denominated in U.S. dollars, is utilized to fund participation in Syndicate 1221 through letters of credit for the 2015 and 2016 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, 2016, our Company would be required to post additional collateral to secure the remaining letters of credit. As of December 31, 2014, letters of credit with an aggregate face amount of $149.4 million were outstanding under the credit facility and our Company had $1.0 million of cash collateral posted.
	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 our Company being false in any material respect, default under certain other indebtedness, certain insolvency or receivership events affecting our Company and its subsidiaries, the occurrence of certain material judgments, or a change in control of our Company. The letter of credit facility is secured by a pledge of the stock of certain insurance subsidiaries of our Company. To the extent, the aggregate face amount issued under the credit facility exceeds the commitment amount; our Company is required to post collateral with the lead bank of the consortium. Our Company was in compliance with all covenants under the credit facility as of December 31, 2014 and our Company had $1.0 million of cash collateral posted.
	The applicable fee rate payable under the credit facility are based on a tiered schedule that is based on our Company’s then-current financial strength ratings issued by S&P and A.M. Best and the amount of our Company’s own collateral utilized to fund its participation in Syndicate 1221.

Senior_Notes

Senior Notes	12 Months Ended
	Dec. 31, 2014
Senior Notes	Note 9.	Senior Notes
	On October 4, 2013, our 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 5.75% Senior Notes is payable in one single installment on October 15, 2023. Our 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”). Our 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 5.75% Senior Notes Liability as of December 31, 2014 and 2013 was $263.4 million and $263.3 million, respectively. The unamortized discount as of December 31, 2014 and 2013 was $1.6 million and $1.7 million, respectively.
	The fair value of the 5.75% Senior Notes was $285.7 million and $277.6 million as of December 31, 2014 and December 31, 2013, respectively. 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% was $15.4 million for the year ended December 31, 2014. Interest expense on the 5.75% Senior Notes 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 year ended December 31, 2012.
	The interest rate payable on the 5.75% Senior Note is subject to a tiered adjustment based on defined changes in our Company’s debt ratings. Our 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 our 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 indebtedness, 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, 2014, our Company was in compliance with all such covenants.

Lloyds_Syndicate_1221

Lloyd's Syndicate 1221	12 Months Ended
	Dec. 31, 2014
Lloyd's Syndicate 1221	Note 10.	Lloyd’s Syndicate 1221
	The Lloyd’s Operations included in the consolidated financial statements represents its participation in Syndicate 1221. Syndicate 1221’s stamp capacity is £215 million ($336.9 million) for the 2014 underwriting year compared to £195 million ($323.7 million) for the 2013 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 our Company’s financial statements are gross of commission. Our Company controlled 100% of Syndicate 1221’s stamp capacity for the 2014, 2013 and 2012 underwriting years through its wholly-owned Lloyd’s corporate member.
	During the first quarter, Syndicate 1221 revised its foreign exchange accounting methodology from reporting its financial position and results using three functional currencies (GBP, USD and CAD) to one functional currency (USD). The USD was chosen as the single functional currency as the majority of the Syndicate’s insurance business has been and continues to be transacted in USD. This cumulative change in re-measurement has resulted in an immaterial correction of $10.0 million ($6.6 million, after-tax) reducing Accumulated Other Comprehensive Income in the consolidated balance sheet, offset by a gain in Other Income in the consolidated statement of income. The impact of the correction is not material to the previously issued annual financial statements for 2013 and 2012.
	Our Company provides letters of credit and posts cash to Lloyd’s to support its participation in Syndicate 1221’s stamp capacity. If Syndicate 1221 increases its stamp capacity and our Company participates in the additional stamp capacity, or if Lloyd’s changes the capital requirements, our Company may be required to supply additional collateral acceptable to Lloyd’s. If our Company is unwilling or unable to provide additional acceptable collateral, our Company will be required to reduce its participation in the stamp capacity of Syndicate 1221. Refer to Note 8, Credit Facilities, for additional information.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies	Note 11.	Commitments and Contingencies
	Future minimum annual rental commitments as of December 31, 2014 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,
	2015		$	11,245
	2016			9,234
	2017			7,942
	2018			6,907
	2019			4,258
	Thereafter			12,811
	Total minimum operating lease payments		$	52,397
	We are also liable for additional payments to the landlords for certain annual cost increases. Rent expense for the years ended December 31, 2014, 2013 and 2012 was $13.2 million, $11.5 million and $10.5 million, respectively.
	The State of Connecticut (“the State”) awarded our 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 our 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. Our 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, 2014, the length of time commitment has not been met, however, our 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 our Company recognizes the expenses for which the assistance is intended to compensate, and is recognized as a reduction of such expenses. For the years ended December 31, 2014 and 2013, our Company recognized $1.1 million and $0.3 million of the assistance and as of December 31, 2014 has deferred revenue of $6.1 million, which is included in other liabilities.
	In the ordinary course of conducting business, our 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 our 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. Our Company accounts for such activity through the establishment of unpaid loss and loss adjustment reserves. Our 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 our Company’s consolidated financial condition, results of operations, or cash flows.
	Our Company’s subsidiaries are also occasionally 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, our Company believes it has valid defenses to these cases. Our 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 our Company’s consolidated results of operations or cash flows in a particular fiscal quarter or year.

Share_Capital

Share Capital	12 Months Ended
	Dec. 31, 2014
Share Capital	Note 12.	Share Capital
	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. Our Company has not issued any preferred shares as of December 31, 2014.
	The following table represents changes in our Company’s issued and outstanding common shares for the periods indicated:
			Year Ended December 31,
	In thousands		2014		2013		2012
	Beginning balance			14,198		14,047		13,956
	Vested stock grants			59		50		60
	Employee stock purchase plan			19		17		16
	Stock options exercised			5		84		15
	Treasury shares purchased			—		—		—
	Ending balance			14,281		14,198		14,047

Dividends_and_Statutory_Financ

Dividends and Statutory Financial Information	12 Months Ended
	Dec. 31, 2014
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 Facilities, for additional information on the restrictions of our credit facilities 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, 2014 and 2013 are presented in the following table:
			As of December 31,
	In thousands		2014		2013
	Restricted Net Assets:
	Insurance Companies:
	Fixed maturities at fair value (amortized cost: 2014, $10,086; 2013, $9,730)		$	11,732	$	11,105
	Short term investments, at cost which approximates fair value			290		290
	Cash			1,212		1,210
	Total Insurance Companies (1)		$	13,234	$	12,605
	Lloyd’s Operations:
	Fixed maturities at fair value (amortized cost: 2014, $445,504; 2013, $398,930)			447,679		398,808
	Short term investments, at cost which approximates fair value			61,549		108,485
	Cash			963		988
	Total Lloyd’s Operations (2)		$	510,191	$	508,281
	Total Restricted Net Assets		$	523,425	$	520,886
	(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, 2014 and 2013, 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 our 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 our Company’s letter of credit facility with ING Bank N.V., London Branch, as administrative agent, is secured by all of the common stock of NIC.
	Insurance Companies
	NIC 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, 2014, the maximum amount available for the payment of dividends by NIC in 2015 without prior regulatory approval is $89.4 million. NIC did not pay any dividends to the Parent Company in 2014 or 2013. In 2012, NIC paid $15.0 million in dividends to the Parent Company.
	The Insurance Companies’ statutory net income as filed with the regulatory authorities for 2014, 2013 and 2012 was $75.7 million, $59.4 million and $28.6 million, respectively. The statutory capital and surplus as filed with the regulatory authorities was $893.9 million and $804.1 million as of December 31, 2014 and 2013, 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 NIC. As of December 31, 2014 and 2013, NIC exceeded our company action RBC levels. The RBC ratio of NIC was 314.8% and 304.2% of our company action level as of December 31, 2014 and 2013, 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 NIC and NSIC for the years 2005 through 2009. Our Company has received notice that the New York Department intends to commence an examination of the years 2010 through 2014 on February 17, 2015.
	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, 2014 and 2013, the FAL requirement set by Lloyd’s for Syndicate 1221 was $268.1 million (£171.1 million) and $279.3 million (£168.3 million), respectively, based on its business plans, approved in November 2014 and November 2013, respectively.
	The valuation of the assets and letters of credit posted for FAL for Syndicate 1221 as of December 31, 2014 and 2013 was $290.1 million (£185.1 million) and $280.2 million (£168.8 million), respectively.
	We prepare our Lloyd’s financial statements in accordance with U.K. GAAP basis. The significant differences between U.K. GAAP and U.S. 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 U.S. 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 U.S. 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 U.S. 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 2014, 2013 and 2012 was $33.8 million, $21.0 million and $54.9 million, respectively. The Syndicate’s capital and surplus as filed with Lloyd’s was $140.1 million (£89.4 million) and $124.2 million (£74.8 million) as of December 31, 2014 and 2013, 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 2014, NCUL posted all of the available undistributed profits on closed years of $139.9 million (£89.3 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, 2014, NCUL has the ability to pay dividends of up to $9.9 million (£6.3 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, 2014
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, 2014, 1,523,228 of such awards were issued leaving 476,772 awards available to be issued in subsequent periods.
	Stock-based compensation granted under our 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. Our Company’s performance based share grants generally consist of three types of awards. The restricted stock units issued in 2014 and after will cliff vest on the third anniversary of the date of the grant with 100% dependent on the rate of cumulative annual growth in tangible book value for the three years immediately prior to the vesting date, with actual shares that vest ranging between 150% to 50% of that portion of the original award. The restricted stock units issued between 2011 – 2013 will cliff vest on the third anniversary of the date of grant, 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. The 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, with 100% 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, 2014, 2013 and 2012 are presented in the following table:
			Year Ended December 31,
	In thousands		2014			2013			2012
	Restricted stock units		$	11,507		$	3,369		$	7,380
	Directors restricted stock grants (1)			420			413			390
	Employee stock purchase plan			194			132			82
	Total stock-based compensation		$	12,121		$	3,914		$	7,852
	(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.
	Unvested restricted stock units outstanding as of December 31, 2014, 2013 and 2012, and changes during the years ended on those dates, are presented in the following table:
			December 31,
			2014			2013			2012
	Beginning balance			626,812			587,629			526,972
	Granted - Performance			228,607			114,463			97,145
	Granted - Non Performance			59,523			155,463			146,915
	Total Granted			288,130			269,926			244,060
	Vested - Performance Earned			—			(15,714	)		—
	Vested - Performance Unearned			(93,453	)		(57,585	)		(46,998	)
	Vested - Non Performance			(90,263	)		(60,183	)		(91,323	)
	Total Vested			(183,716	)		(133,482	)		(138,321	)
	Forfeited			(12,334	)		(97,261	)		(45,082	)
	Ending balance			718,892			626,812			587,629
	As included in the table above, there were 15,714 performance based shares that vested during the year ended December 31, 2013. There were no performance based shares that vested during the years ended December 31, 2014 and 2012.
	The fair value of total vested shares for the years ended December 31, 2014, 2013 and 2012 was $5.1 million, $3.5 million and $4.6 million, respectively.
	The weighted average grant date fair value per share of all RSUs granted during the years ended December 31, 2014, 2013 and 2012 was $60.75, $55.36 and $48.21, respectively.
	As of December 31, 2014 and 2013, the total unrecognized compensation expense, net of estimated forfeitures, related to unvested RSUs was $16.3 million and $10.6 million, respectively, which is expected to be recognized as expense over weighted average periods of 2.3 years and 2.2 years, respectively. The aggregate fair value of all unvested RSUs as of December 31, 2014 and 2013 was $46.1 million and $39.6 million, respectively.
	Stock options outstanding as of December 31, 2014, 2013 and 2012 are as follows:
			December 31,
			2014						2013					2012
			# of Shares			Average			# of Shares			Average		# of Shares			Average
						Exercise Price						Exercise Price					Exercise Price
	Beginning balance			6,750		$	30.65			90,250		$	29.94		105,250		$	29.5
	Granted			—			—			—			—		—			—
	Exercised			(5,250	)	$	29.11			(83,500	)	$	29.88		(15,000	)	$	26.9
	Expired or forfeited			—			—			—			—		—		$	—
	Ending balance			1,500		$	36.03			6,750		$	30.65		90,250		$	29.94
	Number of options exercisable			1,500		$	36.03			6,750		$	30.65		90,250		$	29.94
	The following table summarizes information about stock options outstanding as of December 31, 2014:
	Price Range		Outstanding			Average			Average			Average Aggregate		Exercisable			Average		Average Aggregate
			Options			Remaining			Exercise Price			Intrinsic Value		Options			Exercise Price		Intrinsic Value
						Contract Life
	$31 to $37			1,500			0.7		$	36.03		$	27.13		1,500		$	36.03	$	27.13
	Total			1,500			0.7								1,500
	We offer an Employee Stock Purchase Plan (the “ESPP”) to all of our eligible employees. Employees are offered the opportunity to purchase our 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 9,509 shares purchased in 2015 from funds withheld during the July 1, 2014 to December 31, 2014 offering period. There were 19,386 shares purchased in 2014 in the aggregate from funds withheld during the offering periods of July 1, 2013 to December 31, 2013 and January 1, 2014 to June 30, 2014. 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, 2014
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. Eligible compensation consisted of gross base salary and annual bonus. 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. Our Company will make a discretionary matching contribution of 3% or $1.6 million for the year ended December 31, 2014. Our Company made a discretionary matching contribution of 2% or $0.8 million for the year ended December 31, 2013. There was no discretionary matching contributions for the year ended 2012.
	We sponsored a standalone retirement savings defined contribution plan covering substantially all of our 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 2014, 2013 and 2012 eligible compensation consisted solely of gross base salary. Our 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, 2014 was $7.5 million, consisting of $3.8 million for the retirement savings contributions, $2.1 million for the non-discretionary matching contributions, and $1.6 million for the discretionary matching contribution. 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.
	Our Company sponsors a defined contribution plan for our 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 for all U.K. employees hired prior to November 2014 and 12% for all employees hired after November 2014. All U.K. employees are eligible on their date of hire. The expense recorded for the U.K. defined contribution plan was $2.6 million, $2.2 million and $1.9 million for the years ended December 31, 2014, 2013 and 2012, respectively. Such expenses are included in Other operating expenses.

Quarterly_Financial_Data_Unaud

Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Data (Unaudited)	Note 16.	Quarterly Financial Data (Unaudited)
	The following is a summary of quarterly financial data for the periods indicated:
	In thousands, except per share amounts		March 31,			June 30,			September 30,			December 31,
			2014			2014			2014			2014
	Gross written premiums		$	422,790		$	348,795		$	327,469		$	333,299
	Revenues:
	Net written premiums		$	311,850		$	231,864		$	228,417		$	228,007
	Change in unearned premiums			(86,578	)		(780	)		16,950			6,165
	Net earned premiums			225,272			231,084			245,367			234,172
	Net investment income			16,610			15,648			15,839			16,071
	Total other-than-temporary impairment losses						—			158			(21	)
	Portion of loss recognized in other comprehensive income (before tax)			—			—			(158	)		21
	Net other-than-temporary impairment losses recognized in earnings						—			—			—
	Net realized gains (losses)			833			4,473			6,718			788
	Other income (expense)			10,399			(1,665	)		1,336			586
	Total revenues		$	253,114		$	249,540		$	269,260		$	251,617
	Expenses:
	Net losses and loss adjustment expenses		$	135,067		$	140,220		$	135,284		$	134,658
	Commission expenses			25,727			32,150			33,943			33,708
	Other operating expenses			47,146			47,992			50,388			51,299
	Call premium on Senior Notes						—			—			—
	Interest expense			3,852			4,319			3,388			3,854
	Total expenses		$	211,792		$	224,681		$	223,003		$	223,519
	Income before income taxes			41,322			24,859			46,257			28,098
	Income tax expense		$	13,354		$	7,998		$	15,032		$	8,823
	Net income		$	27,968		$	16,861		$	31,225		$	19,275
	Comprehensive income (loss)		$	32,920		$	32,965		$	20,628		$	27,015
	Combined ratio			92.2	%		95.3	%		89.5	%		93.8	%
	Net income (loss) per share:
	Basic		$	1.96		$	1.18		$	2.19		$	1.35
	Diluted		$	1.94		$	1.17		$	2.14		$	1.31
	In thousands, except per share amounts		March 31,			June 30,			September 30,			December 31,
			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			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		$	14,785		$	(24,829	)	$	25,462		$	1,200
	Combined ratio			97.9	%		97.7	%		89.8	%		94	%
	Net income per share:
	Basic		$	0.99		$	0.99		$	1.5		$	1.01
	Diluted		$	0.97		$	0.97		$	1.48		$	1

Summary_of_Consolidated_Invest

Summary of Consolidated Investments-Other Than Investments in Related Parties	12 Months Ended
	Dec. 31, 2014
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, 2014
		December 31, 2014
	In thousands	Fair Value		Gross		Gross			Amortized
				Unrealized		Unrealized			Cost
				Gains		Losses
	Fixed maturities:
	U.S. Treasury bonds, agency bonds and foreign government bonds	$	397,923	$	3,431	$	(5,965	)	$	400,457
	States, municipalities and political subdivisions		541,007		19,204		(558	)		522,361
	Mortgage-backed and asset-backed securities:
	Agency mortgage-backed securities		364,622		8,476		(998	)		357,144
	Residential mortgage obligations		34,087		1,153		(138	)		33,072
	Asset-backed securities		206,413		380		(964	)		206,997
	Commercial mortgage-backed securities		206,318		6,630		(98	)		199,786
	Subtotal	$	811,440	$	16,639	$	(2,198	)	$	796,999
	Corporate bonds		615,564		13,048		(1,626	)		604,142
	Total fixed maturities	$	2,365,934	$	52,322	$	(10,347	)	$	2,323,959
	Equity securities - common stocks		127,183		28,520		(1,254	)		99,917
	Equity securities - preferred stocks		57,112		2,236		(50	)		54,926
	Short-term investments		179,506		—		(21	)		179,527
	Cash		90,751		—		—			90,751
	Total	$	2,820,486	$	83,078	$	(11,672	)	$	2,749,080

Condensed_Financial_Informatio

Condensed Financial Information of Registrant	12 Months Ended
	Dec. 31, 2014
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,
		2014			2013
	ASSETS
	Cash and investments	$	101,032		$	100,676
	Investments in subsidiaries		1,163,822			1,040,214
	Goodwill and other intangible assets		2,534			2,534
	Other assets		27,531			26,538
	Total assets	$	1,294,919		$	1,169,962
	LIABILITIES AND STOCKHOLDERS’ EQUITY
	Liabilities:
	Senior Notes	$	263,440		$	263,308
	Accounts payable and other liabilities		1,081			802
	Accrued interest payable		3,174			3,640
	Total liabilities	$	267,695		$	267,750
	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 17,792,846 shares for 2014 and 17,709,876 shares for 2013		1,778			1,770
	Additional paid-in capital		347,022			335,546
	Treasury stock, at cost (3,511,380 shares for 2014 and 2013)		(155,801	)		(155,801	)
	Retained earnings		787,666			692,337
	Accumulated other comprehensive income:
	Net unrealized gains (losses) on securities available-for-sale, net of tax		46,573			23,387
	Foreign currency translation adjustment, net of tax		(14	)		4,973
	Total stockholders’ equity	$	1,027,224		$	902,212
	Total liabilities and stockholders’ equity	$	1,294,919		$	1,169,962
	The Navigators Group, Inc.
	Statements of Income
	(Parent Company)
	(In thousands)
		Year Ended December 31,
		2014			2013			2012
	Revenues:
	Net investment income	$	76		$	13		$	341
	Dividends received from wholly-owned subsidiaries		—			—			15,000
	Total revenues	$	76		$	13		$	15,341
	Expenses:
	Call premium on Senior Notes	$	—		$	17,895		$	—
	Interest expense		15,413			10,507			8,198
	Other (income) expense		—			2			1,749
	Total expenses	$	15,413		$	28,404		$	9,947
	Income (loss) before income tax benefit	$	(15,337	)	$	(28,391	)	$	5,394
	Income tax benefit		(5,287	)		(9,886	)		(3,332	)
	Income (loss) before equity in undistributed net income of wholly owned subsidiaries	$	(10,050	)	$	(18,505	)	$	8,726
	Equity in undistributed net income of wholly-owned subsidiaries		105,379			81,971			55,036
	Net income	$	95,329		$	63,466		$	63,762
	The Navigators Group, Inc.
	Statements of Cash Flows
	(Parent Company)
	(In thousands)
		Year Ended December 31,
		2014			2013			2012
	Operating activities:
	Net income	$	95,329		$	63,466		$	63,762
	Adjustments to reconcile net income to net cash provided by (used in) operations:
	Equity in undistributed net income of wholly-owned subsidiaries		(105,379	)		(81,971	)		(70,036	)
	Dividends received from subsidiaries		—			—			15,000
	Call premium on redemption of Senior Notes		—			17,895			—
Other		9,211			2,098			(3,265	)
Net cash provided by (used in) operating activities	$	(839	)	$	1,488		$	5,461
Investing activities:
Fixed maturities, available-for-sale
Sales	$	3,200		$	8,754		$	7,986
Purchases		—			(1,249	)		(14,700	)
Equity securities
Sales		—			—			—
Purchases		—			—			—
Net increase in short-term investments		(3,424	)		(89,988	)		(167	)
Net cash provided by (used in) investing activities	$	(224	)	$	(82,483	)	$	(6,881	)
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		—			—			—
Proceeds of stock issued from employee stock purchase plan		1,067			821			672
Proceeds of stock issued from exercise of stock options		153			2,495			404
Net cash provided by (used in) financing activities	$	1,220		$	84,157		$	1,076
Increase (decrease) in cash	$	157		$	3,162		$	(344	)
Cash at beginning of year		6,143			2,981			3,325
Cash at end of year	$	6,300		$	6,143		$	2,981

Supplementary_Insurance_Inform

Supplementary Insurance Information	12 Months Ended
	Dec. 31, 2014
Supplementary Insurance Information	SCHEDULE III
	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, 2014
	Insurance Companies	$	63,200	$	1,645,984	$	579,331	$	—	$	704,574	$	56,714	$	434,396	$	85,137	$	138,675	$	752,773
	Lloyd’s Operations		16,252		513,650		186,836		—		231,321		7,378		110,833		42,558		58,150		247,365
		$	79,452	$	2,159,634	$	766,167	$	—	$	935,895	$	64,092		545,229	$	127,695		196,825		1,000,138
	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
	(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_Written_Premium

Reinsurance - Written Premium	12 Months Ended
	Dec. 31, 2014
Reinsurance - Written Premium	SCHEDULE IV
	THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES
	Reinsurance - Written Premium
	In thousands	Direct		Ceded to		Assumed		Net amount		Percentage of
		Amount		other		from other				amount
				companies		companies				assumed to net
	Year ended December 31, 2014
	Property-Casualty	$	1,184,538	$	432,214	$	247,814	$	1,000,138		25	%
	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	%

Valuation_and_Qualifying_Accou

Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2014
Valuation and Qualifying Accounts	SCHEDULE V
	THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES
	Valuation and Qualifying Accounts
	In thousands	Balance at		Charged (Credited) to		Charged to		Deductions		Balance at
		January 1, 2014		Costs and Expenses		Other Accounts		(Describe)		December 31, 2014
	Description:
	Allowance for uncollectable reinsurance	$	11,332	$	—	$	—	$	—	$	11,332
	Valuation allowance in deferred taxes	$	554	$	222	$	—	$	—	$	776

Supplementary_Information_Conc

Supplementary Information Concerning Property-Casualty Insurance Operations	12 Months Ended
	Dec. 31, 2014
Supplementary Information Concerning Property-Casualty Insurance Operations	SCHEDULE VI
	THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES
	Supplementary Information Concerning Property-Casualty Insurance Operations
	($ in thousands)
	Affiliation with	Deferred		Reserve		Discount,		Unearned		Net		Net							Amortization		Other		Net
	Registrant	policy		for losses		if any,		premiums		earned		investment		Losses and loss adjustment					of deferred		operating		written
		acquisition		and loss		deducted				premiums		income (1)		expenses incurred related to					Policy		expenses (1)		premiums
		costs		adjustment															acquisition
				expenses										Current		Prior			costs (2)
														year		years
	Consolidated Subsidiaries:
	Year ended December 31, 2014	$	79,452	$	2,159,634	$	—	$	766,167	$	935,895	$	64,092	$	601,041	$	(55,812	)	$	127,695	$	196,825	$	1,000,138
	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
	(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_Summary_of_Signif1

Organization & Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
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, 2014 and 2013, all fixed maturity and equity securities held by our 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 and preferred stock.
	Short-term investments are carried at 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. 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 than not our Company 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 of 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, a net 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 have 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.
	Our 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.
Foreign Currency Remeasurement and Translation	Foreign Currency Remeasurement and Translation
	The functional currency in each of our operations is generally the currency of the local operating environment, except for our Lloyd’s Operations which is the U.S. dollar. Transactions in currencies other than an operation’s functional currency are remeasured into the functional currency and the resulting foreign exchange gains and losses are reflected in net Other Income (Expense) in the Consolidated Statements of Income. 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.
	During the first quarter, Syndicate 1221 revised its foreign exchange accounting methodology from reporting its financial position and results using three functional currencies (GBP, USD and CAD) to one functional currency (USD). The USD was chosen as the single functional currency as the majority of the Syndicate’s insurance business has been and continues to be transacted in USD. This cumulative change in re-measurement has resulted in an immaterial correction of $10.0 million ($6.6 million, after-tax) reducing Accumulated Other Comprehensive Income in the consolidated balance sheet, offset by a gain in Other Income in the consolidated statement of income. The impact of the correction is not material to the previously issued annual financial statements for 2013 and 2012.
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 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 (“A&H”) 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 are deferred and amortized ratably over the period that the related premiums are recognized as revenue. Such costs (e.g., 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 incurred but not reported (“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. Our 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, and when permitted by the applicable accounting guidance, qualitative factors are assessed to determine whether it is necessary to calculate an asset’s fair value when testing an asset with an indefinite life for impairment. Goodwill and indefinite lived intangible assets are considered impaired if the estimated fair value is less than its carrying value and 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, 2014, 2013 and 2012.
	As of December 31, 2014, the carrying value of goodwill and indefinite lived intangible assets was $7.0 million, consisting of $2.5 million and $2.4 million of goodwill assigned to NMC and our Lloyd’s Operations, respectively, and $2.1 million of indefinite lived intangible assets assigned to our Lloyd’s Operations. 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. 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 whereby deferred 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. 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. These reviews include, among other factors, the nature and amount of the taxable income and expense items, the expected timing of when assets will be used or liabilities will be required to be reported, as well as the reliability of historical profitability of businesses expected to provide future earnings. After review, if management determines that the realization of the tax asset does not meet the more likely than not criterion an offsetting valuation allowance is recorded, which reduces net earnings and the deferred tax asset in that period. Additional information regarding our deferred tax assets can be found in Note 7, Income Taxes, in the Notes to Consolidated Financial Statements, included herein.
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, the recoverability of deferred tax assets, and impairment of invested assets.

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2014
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, 2014, 2013 and 2012:
		Year Ended December 31,
	In thousands, except share and per share amounts	2014		2013		2012
	Net income	$	95,329	$	63,466	$	63,762
	Basic weighted average shares		14,259,768		14,133,925		14,052,311
	Effect of common stock equivalents:
	Assumed exercise of stock options and vesting of stock grants		386,601		211,628		275,509
	Diluted weighted average shares		14,646,369		14,345,553		14,327,820
	Net income per common share:
	Basic	$	6.69	$	4.49	$	4.54
	Diluted	$	6.51	$	4.42	$	4.45

Segment_Information_Tables

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2014
Financial Data by Segment	Financial data by segment for the years ended December 31, 2014, 2013, and 2012 were as follows:
		Year Ended December 31, 2014
	In thousands	Insurance			Lloyd’s			Corporate(1)			Total
		Companies			Operations
	Gross written premiums	$	1,045,454		$	386,899		$	—		$	1,432,353
	Net written premiums		752,773			247,365			—			1,000,138
	Net earned premiums		704,574			231,321			—			935,895
	Net losses and loss adjustment expenses		(434,396	)		(110,833	)		—			(545,229	)
	Commission expenses		(85,137	)		(42,558	)		2,167			(125,528	)
	Other operating expenses		(138,675	)		(58,150	)		—			(196,825	)
	Other underwriting income (expense)		2,727			35			(2,167	)		595
	Underwriting profit (loss)	$	49,093		$	19,815		$	—		$	68,908
	Net investment income		56,714			7,378			76			64,168
	Net realized gains (losses)		12,715			97			—			12,812
	Call premium on Senior Notes		—			—			—			—
	Interest expense		—			—			(15,413	)		(15,413	)
	Other income (expense)		(2,182	)		12,243			—			10,061
	Income (loss) before income taxes	$	116,340		$	39,533		$	(15,337	)	$	140,536
	Income tax expense (benefit)		36,609			13,885			(5,287	)		45,207
	Net income (loss)	$	79,731		$	25,648		$	(10,050	)	$	95,329
	Identifiable assets	$	3,344,084		$	957,795		$	162,297		$	4,464,176
	Losses and loss adjustment expenses ratio		61.7	%		47.9	%					58.3	%
	Commission expense ratio		12.1	%		18.4	%					13.4	%
	Other operating expense ratio (2)		19.2	%		25.1	%					20.9	%
	Combined ratio		93	%		91.4	%					92.6	%
	(1) - Includes Corporate segment intercompany eliminations.
	(2) - Includes Other operating expenses and Other underwriting income (expenses).
		Year Ended December 31, 2013
	In thousands	Insurance			Lloyd’s			Corporate(1)			Total
		Companies			Operations
	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
	In thousands	Insurance			Lloyd’s			Corporate(1)			Total
		Companies			Operations
	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.
Additional Financial Data by Segment	The following tables provide additional financial data by segment for the years ended December 31, 2014, 2013 and 2012:
		Year Ended December 31, 2014
	In thousands	Insurance			Lloyd’s			Total
		Companies			Operations
	Gross written premiums:
	Marine	$	177,363		$	188,107		$	365,470
	Property casualty		755,059			126,016			881,075
	Professional liability		113,032			72,776			185,808
	Total	$	1,045,454		$	386,899		$	1,432,353
	Net written premiums:
	Marine	$	123,617		$	144,327		$	267,944
	Property casualty		554,844			55,917			610,761
	Professional liability		74,312			47,121			121,433
	Total	$	752,773		$	247,365		$	1,000,138
	Net earned premiums:
	Marine	$	123,203		$	141,471		$	264,674
	Property casualty		496,209			51,338			547,547
	Professional liability		85,162			38,512			123,674
	Total	$	704,574		$	231,321		$	935,895
		Year Ended December 31, 2013
	In thousands	Insurance			Lloyd’s			Total
		Companies			Operations
	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
	In thousands	Insurance			Lloyd’s			Total
		Companies			Operations
	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

Investments_Tables

Investments (Tables)	12 Months Ended
	Dec. 31, 2014
Cash and Investments Including Other-Than-Temporarily Impaired Securities Recognized within Other Comprehensive Income	The following tables set forth our Company’s cash and investments as of December 31, 2014 and 2013. The tables below include OTTI securities recognized within AOCI.
		December 31, 2014
	In thousands	Fair Value				Gross				Gross			Amortized
						Unrealized				Unrealized			Cost
						Gains				Losses
	Fixed maturities:
	U.S. Treasury bonds, agency bonds and foreign government bonds	$	397,923			$	3,431			$	(5,965	)	$	400,457
	States, municipalities and political subdivisions		541,007				19,204				(558	)		522,361
	Mortgage-backed and asset-backed securities:
	Agency mortgage-backed securities		364,622				8,476				(998	)		357,144
	Residential mortgage obligations		34,087				1,153				(138	)		33,072
	Asset-backed securities		206,413				380				(964	)		206,997
	Commercial mortgage-backed securities		206,318				6,630				(98	)		199,786
	Subtotal	$	811,440			$	16,639			$	(2,198	)	$	796,999
	Corporate bonds		615,564				13,048				(1,626	)		604,142
	Total fixed maturities	$	2,365,934			$	52,322			$	(10,347	)	$	2,323,959
	Equity securities - common stocks		127,183				28,520				(1,254	)		99,917
	Equity securities - preferred stocks		57,112				2,236				(50	)		54,926
	Short-term investments		179,506				—				(21	)		179,527
	Cash		90,751				—				—			90,751
	Total	$	2,820,486			$	83,078			$	(11,672	)	$	2,749,080
		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
Scheduled Maturity Dates for Fixed Maturity Securities by Number of Years Until Maturity	The contractual maturity dates for fixed maturities categorized by the number of years until maturity as of December 31, 2014 are shown in the following table:
		December 31, 2014
	In thousands	Fair Value				Amortized
						Cost
	Due in one year or less	$	63,670			$	65,643
	Due after one year through five years		765,084				758,064
	Due after five years through ten years		356,929				348,195
	Due after ten years		368,811				355,058
	Mortgage- and asset-backed securities		811,440				796,999
	Total	$	2,365,934			$	2,323,959
Amount and Percentage of Fixed Maturities by Rating	The following table shows the amount and percentage of our Company’s fixed maturities as of December 31, 2014 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, 2014
	In thousands	Rating		Fair Value				Percent
								of Total
	Rating description:
	Extremely strong	AAA		$	462,603				20	%
	Very strong	AA			1,090,505				45	%
	Strong	A			612,131				26	%
	Adequate	BBB			185,372				8	%
	Speculative	BB & Below			14,852				1	%
	Not rated	NR			471				0	%
	Total	AA		$	2,365,934				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, 2014 and 2013, 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, 2014											December 31, 2013
	In thousands, except # of securities	Number of				Fair Value				Gross			Number of			Fair Value			Gross
		Securities								Unrealized			Securities						Unrealized
										Loss									Loss
	Fixed maturities:
	U.S. Treasury bonds, agency bonds, and foreign government bonds
	0-6 months		19			$	87,915			$	1,061			27		$	136,360		$	1,096
	7-12 months		—				—				—			26			149,370			7,759
	> 12 months		31				117,683				4,904			—			—			—
	Subtotal		50			$	205,598			$	5,965			53		$	285,730		$	8,855
	States, municipalities and political subdivisions
	0-6 months		13			$	14,242			$	41			28		$	40,132		$	297
	7-12 months		2				2,107				19			104			205,152			12,100
	> 12 months		17				37,340				498			6			12,357			1,254
	Subtotal		32			$	53,689			$	558			138		$	257,641		$	13,651
	Agency mortgage-backed securities
	0-6 months		4			$	14,743			$	52			39		$	39,458		$	434
	7-12 months		2				4,138				28			64			77,860			3,768
	> 12 months		46				58,301				918			9			22,784			1,814
	Subtotal		52			$	77,182			$	998			112		$	140,102		$	6,016
	Residential mortgage obligations
	0-6 months		6			$	4,966			$	43			3		$	431		$	2
	7-12 months		2				659				7			7			950			29
	> 12 months		14				1,728				88			15			2,467			130
	Subtotal		22			$	7,353			$	138			25		$	3,848		$	161
	Asset-backed securities
	0-6 months		19			$	96,123			$	354			14		$	75,887		$	479
	7-12 months		3				14,152				185			1			203			1
	> 12 months		3				34,530				425			—			—			—
	Subtotal		25			$	144,805			$	964			15		$	76,090		$	480
	Commercial mortgage-backed securities
	0-6 months		4			$	18,665			$	65			4		$	6,712		$	31
	7-12 months		1				1,076				6			2			15,098			322
	> 12 months		3				1,391				27			4			774			21
	Subtotal		8			$	21,132			$	98			10		$	22,584		$	374
	Corporate bonds
	0-6 months		52			$	179,390			$	797			34		$	93,591		$	717
	7-12 months		4				11,071				74			18			55,021			2,726
	> 12 months		14				31,126				755			—			—			—
	Subtotal		70			$	221,587			$	1,626			52		$	148,612		$	3,443
	Total fixed maturities		259			$	731,346			$	10,347			405		$	934,607		$	32,980
	Equity securities - common stocks
	0-6 months		6			$	9,152			$	761			5		$	7,387		$	422
	7-12 months		1				3,887				486			2			3,538			128
	> 12 months		1				238				7			—			—			—
			8			$	13,277			$	1,254			7		$	10,925		$	550
	Equity securities - preferred stocks
	0-6 months		7			$	6,651			$	50			—		$	—		$	—
	7-12 months		—				—				—			—			—			—
	> 12 months		—				—				—			—			—			—
			7			$	6,651			$	50			—		$	—		$	—
	Total equity securities		15			$	19,928			$	1,304			7		$	10,925		$	550
Summary of Activity Related to Other-Than-Temporary Impairment Losses	The table below summarizes our Company’s activity related to OTTI losses for the periods indicated:
		Year Ended December 31,
		2014								2013						2012
	In thousands, except # of securities	Number of				Amount				Number of			Amount			Number of			Amount
		Securities								Securities						Securities
	Total OTTI losses:
	Corporate and other bonds		—			$	—				1		$	1,822			—		$	—
	Commercial mortgage-backed securities		—				—				—			—			—			—
	Residential mortgage-backed securities		31				(137	)			—			—			1			55
	Asset-backed securities		—				—				—			—			—			—
	Equities		—				—				3			571			3			847
	Total		31			$	(137	)			4		$	2,393			4		$	902
	Less: Portion of loss in accumulated other comprehensive income (loss):
	Corporate and other bonds					$	—						$	—					$	—
	Commercial mortgage-backed securities						—							—						—
	Residential mortgage-backed securities						(137	)						—						44
	Asset-backed securities						—							—						—
	Equities						—							—						—
	Total					$	(137	)					$	—					$	44
	Impairment losses recognized in earnings:
	Corporate and other bonds					$	—						$	1,822					$	—
	Commercial mortgage-backed securities						—							—						—
	Residential mortgage-backed securities						—							—						11
	Asset-backed securities						—							—						—
	Equities						—							571						847
	Total					$	—						$	2,393					$	858
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 our Company’s credit loss portion of the OTTI losses on fixed maturities for the years ended December 31, 2014, 2013 and 2012. Our 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 and for which the non-credit loss portion is included in AOCI.
		Year Ended December 31,
	In thousands	2014				2013				2012
	Beginning balance	$	5,154			$	3,332			$	3,321
	Additions for credit loss impairments recognized in the current period on securities not previously impaired		—				1,822				—
	Additions for credit loss impairments recognized in the current period on securities previously impaired		—				—				11
	Reductions for credit loss impairments previously recognized on securities sold during the period		(2,793	)			—				—
	Ending balance	$	2,361			$	5,154			$	3,332
Contractual Maturity by Number of Years Until Maturity for Fixed Maturity Securities with a Gross Unrealized Loss	The contractual maturity dates for fixed maturities categorized by the number of years until maturity, with a gross unrealized loss as of December 31, 2014 is presented in the following table:
		December 31, 2014
		Gross Unrealized Losses								Fair Value
	In thousands	Amount				Percent				Amount			Percent
						of Total							of Total
	Due in one year or less	$	2,638				25	%		$	21,919			3	%
	Due after one year through five years		3,791				37	%			334,046			46	%
	Due after five years through ten years		1,562				15	%			103,376			14	%
	Due after ten years		158				2	%			21,533			3	%
	Mortgage- and asset-backed securities		2,198				21	%			250,472			34	%
	Total	$	10,347				100	%		$	731,346			100	%
Net Investment Income	Our Company’s net investment income was derived from the following sources:
		Year Ended December 31,
	In thousands	2014				2013				2012
	Fixed maturities	$	57,219			$	53,898			$	58,995
	Equity securities		9,036				4,835				3,945
	Short-term investments		911				774				1,694
	Total investment income		67,166				59,507				64,634
	Investment expenses		(2,998	)			(3,256	)			(10,386	)
	Net investment income	$	64,168			$	56,251			$	54,248
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	2014				2013				2012
	Fixed maturities	$	31,080			$	(76,194	)		$	15,709
	Equity securities		4,302				8,857				(5,989	)
	Gross unrealized gains (losses)		35,382				(67,337	)			9,720
	Deferred income tax		12,197				(23,565	)			3,418
	Change in net unrealized gains (losses), net	$	23,185			$	(43,772	)		$	6,302
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	2014				2013				2012
	Fixed maturities:
	Gains	$	8,326			$	8,539			$	28,789
	Losses		(2,610	)			(2,797	)			(1,915	)
	Fixed maturities, net	$	5,716			$	5,742			$	26,874
	Equity securities:
	Gains	$	9,447			$	17,955			$	14,673
	Losses		(2,351	)			(758	)			(473	)
	Equity securities, net	$	7,096			$	17,197			$	14,200
	Net realized gains (losses)	$	12,812			$	22,939			$	41,074
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, our Company’s fixed maturities and equity securities by asset class that are measured at fair value on a recurring basis as of December 31, 2014 and 2013:
		December 31, 2014
	In thousands	Level 1				Level 2				Level 3			Total
	Fixed maturities:
	U.S. Treasury bonds, agency bonds and foreign government bonds	$	146,904			$	251,019			$	—		$	397,923
	States, municipalities and political subdivisions		—				541,007				—			541,007
	Mortgage-backed and asset-backed securities:													—
	Agency mortgage-backed securities		—				364,622				—			364,622
	Residential mortgage obligations		—				34,087				—			34,087
	Asset-backed securities		—				206,413				—			206,413
	Commercial mortgage-backed securities		—				206,318				—			206,318
	Subtotal	$	—			$	811,440			$	—		$	811,440
	Corporate bonds		—				615,564				—			615,564
	Total fixed maturities	$	146,904			$	2,219,030			$	—		$	2,365,934
	Equity securities - common stocks		127,183								—			127,183
	Equity securities - preferred stocks		—				57,112				—			57,112
	Total	$	274,087			$	2,276,142			$	—		$	2,550,229
		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
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, 2014 and 2013. For the year ended December 31, 2012, our Company did not have any Level 3 assets.
		Year Ended December 31, 2014
	In thousands	Beginning				Realized				Unrealized			Purchase			Sales			Settlements		Transfers		Transfers			Ending
		Balance				Gains				Gains											into		out of
						(Losses)				(Losses)											Level 3		Level 3
	Assets:
	Corporate Bond	$	4,407			$	—			$	—		$	—		$	—		$	—	$	—	$	(4,407	)	$	—
	Total assets	$	4,407			$	—			$	—		$	—		$	—		$	—	$	—	$	(4,407	)	$	—
		Year Ended December 31, 2013
	In thousands	Beginning				Realized				Unrealized			Purchase			Sales			Settlements		Transfers		Transfers			Ending
		Balance				Gains				Gains											into		out of
						(Losses)				(Losses)											Level 3		Level 3
	Assets:
	Commercial
	Mortgage	$	—			$	—			$	(42	)	$	4,660		$	(211	)	$	—	$	—	$	—		$	4,407
	Total assets	$	—			$	—			$	(42	)	$	4,660		$	(211	)	$	—	$	—	$	—		$	4,407

Reserves_for_Losses_and_Loss_A1

Reserves for Losses and Loss Adjustment Expenses (Tables)	12 Months Ended
	Dec. 31, 2014
Summary of Activity in Reserve for Losses and Loss Adjustment Expenses	The following table summarizes our Company’s reserves for losses and LAE activity for the years ended December 31, 2014, 2013 and 2012:
		Year Ended December 31,
	In thousands	2014			2013			2012
	Net reserves for losses and LAE at beginning of year	$	1,222,633		$	1,216,909		$	1,237,234
	Provision for losses and LAE for claims occurring in the current year		601,041			520,227			542,724
	Increase (decrease) in estimated losses and LAE for claims occurring in prior years		(55,812	)		(1,266	)		(45,291	)
	Incurred losses and LAE		545,229			518,961			497,433
	Losses and LAE paid for claims occurring during:
	Current year		(164,199	)		(147,758	)		(110,373	)
	Prior years		(295,527	)		(365,479	)		(407,385	)
	Losses and LAE payments		(459,726	)		(513,237	)		(517,758	)
	Net reserves for losses and LAE at end of year		1,308,136			1,222,633			1,216,909
	Reinsurance recoverables on unpaid losses and LAE		851,498			822,438			880,139
	Gross reserves for losses and LAE at end of year	$	2,159,634		$	2,045,071		$	2,097,048
Segment Break Down of Prior Years' Net Reserve Deficiency (Redundancy)	The segment and line of business breakdowns of prior period net reserve strengthening (releases) for the years ended December 31, 2014, 2013 and 2012 are as follows:
		Year Ended December 31,
	In thousands	2014			2013			2012
	Insurance Companies:
	Marine	$	(41,388	)	$	(15,227	)	$	(10,010	)
	Property Casualty		14,612			18,466			4,293
	Professional Liability		(3,536	)		10,191			7,613
	Insurance Companies	$	(30,312	)	$	13,430		$	1,896
	Lloyd’s Operations:
	Marine	$	(21,336	)	$	(2,998	)	$	(30,735	)
	Property Casualty		(1,500	)		(14,574	)		(6,890	)
	Professional Liability		(2,664	)		2,876			(9,562	)
	Lloyd’s Operations	$	(25,500	)	$	(14,696	)	$	(47,187	)
	Total strengthening (releases)	$	(55,812	)	$	(1,266	)	$	(45,291	)
Lloyd's
Segment Break Down of Prior Years' Net Reserve Deficiency (Redundancy)	A summary of the resulting prior period redundancies for each business within our Lloyd’s Operations by prior UWY 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

Ceded_Reinsurance_Tables

Ceded Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2014
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 our Company’s reinsurance recoverables of $1.1 billion as of December 31, 2014 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:
	In thousands	Rating		Carrying				Percent
				Value (2)				of Total
	A.M. Best Rating description (1):
	Superior	A++, A+		$	575,205				50	%
	Excellent	A, A-			547,314				48	%
	Very good	B++, B+			8,483				1	%
	Fair	B, B-			—				0	%
	Not rated	NR			9,694				1	%
	Total			$	1,140,696				100	%
	-1	-		When an A.M. Best rating is unavailable, the equivalent S&P rating is used.
	-2	-		The carrying value is comprised of prepaid reinsurance premium as well as reinsurance recoverables on paid and unpaid losses which are net of the reserve for uncollectible reinsurance.
Lists of 20 Largest Reinsurers Measured by Reinsurance Recoverable	The following table lists our Company’s 20 largest reinsurers measured by the amount of reinsurance recoverable for ceded losses and LAE and ceded unearned premium (constituting 75.7% of the total recoverable), together with the reinsurance recoverable and collateral as of December 31, 2014, and the reinsurers’ ratings from A.M. Best or S&P:
	In thousands	Unearned				Paid/Unpaid				Total (1)			Collateral		A.M. Best	S&P
		Premium				Losses							Held
	National Indemnity Company	$	25,202			$	117,562			$	142,764		$	22,069	A++	AA+
	Everest Reinsurance Company		21,573				75,063				96,636			7,326	A+	A+
	Swiss Reinsurance America Corporation		22,815				73,305				96,120			14,587	A+	AA-
	Transatlantic Reinsurance Company		11,916				74,072				85,988			4,038	A	A+
	Munich Reinsurance America Inc.		11,366				58,768				70,134			5,539	A+	AA-
	Allied World Reinsurance		9,048				37,088				46,136			1,666	A	A
	Lloyd’s Syndicate #2003		4,399				35,123				39,522			5,191	A	A+
	Partner Reinsurance Europe		10,986				25,409				36,395			16,052	A+	A+
	Employers Mutual Casualty Company		11,928				21,851				33,779			10,935	A	NR
	Scor Global P&C SE		10,190				17,572				27,762			5,558	A	A+
	Ace Property and Casualty Insurance Company		11,165				12,741				23,906			2,907	A++	AA
	Tower Insurance Company		—				21,509				21,509			2,455	A-	NR
	Aspen Insurance UK Ltd.		8,928				11,227				20,155			4,869	A	A
	Ironshore Indemnity Inc.		6,234				13,395				19,629			8,645	A	NR
	Validus Reinsurance Ltd.		2,020				16,873				18,893			10,975	A	A
	Atlantic Specialty Insurance		2,542				15,812				18,354			—	A	A-
	QBE Reinsurance Corp		2,636				15,539				18,175			—	A	A+
	National Union Fire Ins.		8,067				8,459				16,526			6,158	A	A+
	Endurance Reinsurance Corporation		5,695				9,936				15,631			1,337	A	A
	Odyssey American Reinsurance Corporation		3,506				11,650				15,156			1,604	A	A-
	Top 20	$	190,216			$	672,954			$	863,170		$	131,911
	Others		47,635				229,891				277,526			70,065
	Total	$	237,851			$	902,845			$	1,140,696		$	201,976
	(1) - Net of reserve for uncollectible reinsurance of approximately $11.3 million.
Summary of Written Premium	The following table summarizes the components of Net Written Premium:
		Year Ended December 31,
	In thousands	2014				2013				2012
	Direct	$	1,184,538			$	1,127,331			$	1,034,658
	Assumed		247,815				243,187				251,807
	Ceded		(432,215	)			(482,596	)			(452,810	)
	Net Written Premiums	$	1,000,138			$	887,922			$	833,655
Summary of Earned Premium	The following table summarizes the components of Net Earned Premium:
		Year Ended December 31,
	In thousands	2014				2013				2012
	Direct	$	1,133,336			$	1,069,677			$	972,844
	Assumed		243,215				228,247				205,759
	Ceded		(440,656	)			(455,985	)			(396,639	)
	Net Earned Premiums	$	935,895			$	841,939			$	781,964
Summary of Losses and Loss Adjustment Expenses Incurred	The following table summarizes the components of Net Losses and LAE incurred:
		Year Ended December 31,
	In thousands	2014				2013				2012
	Direct	$	631,730			$	552,381			$	608,945
	Assumed		143,681				155,313				151,137
	Ceded		(230,182	)			(188,733	)			(262,649	)
	Net Losses and LAE	$	545,229			$	518,961			$	497,433

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
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	2014			2013			2012
	Current income tax expense (benefit):
	Federal and foreign	$	27,290		$	23,703		$	39,242
	State and local		1,036			446			146
	Subtotal		28,326			24,149			39,388
	Deferred income tax expense (benefit):
	Federal and foreign		16,881			4,658			(11,414	)
	State and local		—			—			—
	Subtotal		16,881			4,658			(11,414	)
	Total income tax expense (benefit)	$	45,207		$	28,807		$	27,974
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	2014						2013					2012
	Computed expected tax expense	$	49,187			35	%	$	32,299		35	%	$	32,109		35	%
	Tax-exempt interest		(4,771	)		-3.4	%		(3,839	)	-4.2	%		(4,443	)	-4.8	%
	Dividends received deduction		(1,257	)		-0.9	%		(897	)	-1	%		(799	)	-0.9	%
	Proration of DRD and Tax-exempt interest		904			0.6	%		710		0.8	%		786		0.9	%
	Current state and local income taxes, net of federal income tax deduction		674			0.5	%		290		0.3	%		95		0.1	%
	Other		470			0.3	%		244		0.3	%		226		0.2	%
	Actual tax expense and rate	$	45,207			32.2	%	$	28,807		31.2	%	$	27,974		30.5	%
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	2014			2013
	Deferred tax assets:
	Loss reserve discount	$	24,820		$	27,822
	Unearned premiums		29,080			25,706
	Compensation related		10,586			6,782
	State and local net deferred tax assets		777			555
	Other		1,834			3,889
	Total gross deferred tax assets		67,097			64,754
	Less: Valuation allowance		(777	)		(555	)
	Total deferred tax assets	$	66,320		$	64,199
	Deferred tax liabilities:
	Net unrealized gains/losses on securities		(24,832	)		(9,119	)
	Deferred acquisition costs		(22,120	)		(19,258	)
	Lloyd’s year of account deferral		(13,578	)		(4,381	)
	Net unrealized foreign exchange		(4,470	)		(3,516	)
	Other		(2,787	)		(4,119	)
	Total deferred tax liabilities	$	(67,787	)	$	(40,393	)
	Net deferred income tax asset (liability)	$	(1,467	)	$	23,806

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Future Minimum Annual Rental Commitments under Various Noncancellable Operating Leases	Future minimum annual rental commitments as of December 31, 2014 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,
	2015	$	11,245
	2016		9,234
	2017		7,942
	2018		6,907
	2019		4,258
	Thereafter		12,811
	Total minimum operating lease payments	$	52,397

Share_Capital_Tables

Share Capital (Tables)	12 Months Ended
	Dec. 31, 2014
Changes in Company's Issued and Outstanding Common Shares	The following table represents changes in our Company’s issued and outstanding common shares for the periods indicated:
		Year Ended December 31,
	In thousands	2014		2013		2012
	Beginning balance		14,198		14,047		13,956
	Vested stock grants		59		50		60
	Employee stock purchase plan		19		17		16
	Stock options exercised		5		84		15
	Treasury shares purchased		—		—		—
	Ending balance		14,281		14,198		14,047

Dividends_and_Statutory_Financ1

Dividends and Statutory Financial Information (Tables)	12 Months Ended
	Dec. 31, 2014
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, 2014 and 2013 are presented in the following table:
		As of December 31,
	In thousands	2014		2013
	Restricted Net Assets:
	Insurance Companies:
	Fixed maturities at fair value (amortized cost: 2014, $10,086; 2013, $9,730)	$	11,732	$	11,105
	Short term investments, at cost which approximates fair value		290		290
	Cash		1,212		1,210
	Total Insurance Companies (1)	$	13,234	$	12,605
	Lloyd’s Operations:
	Fixed maturities at fair value (amortized cost: 2014, $445,504; 2013, $398,930)		447,679		398,808
	Short term investments, at cost which approximates fair value		61,549		108,485
	Cash		963		988
	Total Lloyd’s Operations (2)	$	510,191	$	508,281
	Total Restricted Net Assets	$	523,425	$	520,886
	(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, 2014 and 2013, 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, 2014
Amounts Charged to Expense for Stock-based Compensation	The amounts charged to expense for stock-based compensation for the years ended December 31, 2014, 2013 and 2012 are presented in the following table:
		Year Ended December 31,
	In thousands	2014			2013			2012
	Restricted stock units	$	11,507		$	3,369		$	7,380
	Directors restricted stock grants (1)		420			413			390
	Employee stock purchase plan		194			132			82
	Total stock-based compensation	$	12,121		$	3,914		$	7,852
	(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.
Unvested Restricted Stock Grants Outstanding	Unvested restricted stock units outstanding as of December 31, 2014, 2013 and 2012, and changes during the years ended on those dates, are presented in the following table:
		December 31,
		2014			2013			2012
	Beginning balance		626,812			587,629			526,972
	Granted - Performance		228,607			114,463			97,145
	Granted - Non Performance		59,523			155,463			146,915
	Total Granted		288,130			269,926			244,060
	Vested - Performance Earned		—			(15,714	)		—
	Vested - Performance Unearned		(93,453	)		(57,585	)		(46,998	)
	Vested - Non Performance		(90,263	)		(60,183	)		(91,323	)
	Total Vested		(183,716	)		(133,482	)		(138,321	)
	Forfeited		(12,334	)		(97,261	)		(45,082	)
	Ending balance		718,892			626,812			587,629
Stock Options Outstanding	Stock options outstanding as of December 31, 2014, 2013 and 2012 are as follows:
		December 31,
		2014						2013					2012
		# of Shares			Average			# of Shares			Average		# of Shares			Average
					Exercise Price						Exercise Price					Exercise Price
	Beginning balance		6,750		$	30.65			90,250		$	29.94		105,250		$	29.5
	Granted		—			—			—			—		—			—
	Exercised		(5,250	)	$	29.11			(83,500	)	$	29.88		(15,000	)	$	26.9
	Expired or forfeited		—			—			—			—		—		$	—
	Ending balance		1,500		$	36.03			6,750		$	30.65		90,250		$	29.94
	Number of options exercisable		1,500		$	36.03			6,750		$	30.65		90,250		$	29.94
Summarized Information about Options Outstanding	The following table summarizes information about stock options outstanding as of December 31, 2014:
	Price Range	Outstanding			Average			Average			Average Aggregate		Exercisable			Average		Average Aggregate
		Options			Remaining			Exercise Price			Intrinsic Value		Options			Exercise Price		Intrinsic Value
					Contract Life
	$31 to $37		1,500			0.7		$	36.03		$	27.13		1,500		$	36.03	$	27.13
	Total		1,500			0.7								1,500

Quarterly_Financial_Data_Unaud1

Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
Summary of Quarterly Financial Data	The following is a summary of quarterly financial data for the periods indicated:
	In thousands, except per share amounts	March 31,			June 30,			September 30,			December 31,
		2014			2014			2014			2014
	Gross written premiums	$	422,790		$	348,795		$	327,469		$	333,299
	Revenues:
	Net written premiums	$	311,850		$	231,864		$	228,417		$	228,007
	Change in unearned premiums		(86,578	)		(780	)		16,950			6,165
	Net earned premiums		225,272			231,084			245,367			234,172
	Net investment income		16,610			15,648			15,839			16,071
	Total other-than-temporary impairment losses					—			158			(21	)
	Portion of loss recognized in other comprehensive income (before tax)		—			—			(158	)		21
	Net other-than-temporary impairment losses recognized in earnings					—			—			—
	Net realized gains (losses)		833			4,473			6,718			788
	Other income (expense)		10,399			(1,665	)		1,336			586
	Total revenues	$	253,114		$	249,540		$	269,260		$	251,617
	Expenses:
	Net losses and loss adjustment expenses	$	135,067		$	140,220		$	135,284		$	134,658
	Commission expenses		25,727			32,150			33,943			33,708
	Other operating expenses		47,146			47,992			50,388			51,299
	Call premium on Senior Notes					—			—			—
	Interest expense		3,852			4,319			3,388			3,854
	Total expenses	$	211,792		$	224,681		$	223,003		$	223,519
	Income before income taxes		41,322			24,859			46,257			28,098
	Income tax expense	$	13,354		$	7,998		$	15,032		$	8,823
	Net income	$	27,968		$	16,861		$	31,225		$	19,275
	Comprehensive income (loss)	$	32,920		$	32,965		$	20,628		$	27,015
	Combined ratio		92.2	%		95.3	%		89.5	%		93.8	%
	Net income (loss) per share:
	Basic	$	1.96		$	1.18		$	2.19		$	1.35
	Diluted	$	1.94		$	1.17		$	2.14		$	1.31
	In thousands, except per share amounts	March 31,			June 30,			September 30,			December 31,
		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		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	$	14,785		$	(24,829	)	$	25,462		$	1,200
	Combined ratio		97.9	%		97.7	%		89.8	%		94	%
	Net income per share:
	Basic	$	0.99		$	0.99		$	1.5		$	1.01
	Diluted	$	0.97		$	0.97		$	1.48		$	1

Organization_and_Summary_of_Si

Organization and Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	Segment
Organization And Summary Of Significant Accounting Policies [Line Items]
Number of underwriting segments	2
Number of corporate segment	1
Remeasurement of Foreign Currecy	$10,000,000
Remeasurement of Foreign currency, After tax	6,600,000
Goodwill and other intangible assets	7,013,000	7,177,000
Minimum
Organization And Summary Of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Maximum
Organization And Summary Of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	7 years
Navigators Insurance Company
Organization And Summary Of Significant Accounting Policies [Line Items]
Percentage of Navigators Specialty Insurance Company reinsured by Navigators Insurance Company	100.00%
Lloyd's
Organization And Summary Of Significant Accounting Policies [Line Items]
Goodwill	2,400,000	2,400,000
Other intangible assets	2,100,000	2,300,000
Lloyd's | Syndicate 1221
Organization And Summary Of Significant Accounting Policies [Line Items]
Percentage control of stamp capacity	100.00%	100.00%	100.00%
Underwriting Segments
Organization And Summary Of Significant Accounting Policies [Line Items]
Goodwill	$2,500,000	$2,500,000

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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share Disclosure [Line Items]
Net income	$19,275	$31,225	$16,861	$27,968	$14,333	$21,286	$13,937	$13,910	$95,329	$63,466	$63,762
Basic weighted average shares									14,259,768	14,133,925	14,052,311
Effect of common stock equivalents:
Assumed exercise of stock options and vesting of stock grants									386,601	211,628	275,509
Diluted weighted average shares									14,646,369	14,345,553	14,327,820
Net income per common share:
Basic	$1.35	$2.19	$1.18	$1.96	$1.01	$1.50	$0.99	$0.99	$6.69	$4.49	$4.54
Diluted	$1.31	$2.14	$1.17	$1.94	$1	$1.48	$0.97	$0.97	$6.51	$4.42	$4.45

Segment_Information_Additional

Segment Information - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
									Segment
Segment Reporting Information [Line Items]
Number of underwriting segments									2
Number of corporate segment									1
Combined ratio indicating underwriting profit									100.00%
Combined ratio indicating underwriting loss									100.00%
Net earned premiums	$234,172	$245,367	$231,084	$225,272	$219,902	$213,895	$205,814	$202,328	$935,895	$841,939	$781,964
Insurance Companies
Segment Reporting Information [Line Items]
Net earned premiums									704,574	639,338	571,439
Insurance Companies | UK Branch
Segment Reporting Information [Line Items]
Net earned premiums									$37,700	$44,600	$63,900

Financial_Data_by_Segment_Deta

Financial Data by Segment (Detail) (USD $)	3 Months Ended										12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Segment Reporting Information [Line Items]
Gross written premiums	$333,299		$327,469	$348,795	$422,790	$333,091		$312,076	$332,128	$393,222	$1,432,353		$1,370,517		$1,286,465
Net written premiums	228,007		228,417	231,864	311,850	223,445		196,556	198,469	269,452	1,000,138		887,922		833,655
Net earned premiums	234,172		245,367	231,084	225,272	219,902		213,895	205,814	202,328	935,895		841,939		781,964
Net losses and loss adjustment expenses	-134,658		-135,284	-140,220	-135,067	-131,385		-125,086	-131,148	-131,342	-545,229		-518,961		-497,433
Commission expenses	-33,708		-33,943	-32,150	-25,727	-30,863		-27,685	-28,391	-26,555	-125,528		-113,494		-121,470
Other operating expenses	-51,299		-50,388	-47,992	-47,146	-43,826		-39,056	-40,678	-40,874	-196,825		-164,434		-159,079
Other underwriting income (expense)											595
Other income (expense)	586		1,336	-1,665	10,399	-665		-210	-915	618	10,656		-1,172		1,488
Underwriting profit (loss)											68,908		43,878		5,470
Net investment income	16,071		15,839	15,648	16,610	14,254		14,094	14,246	13,657	64,168		56,251		54,248
Net realized gains (losses)											12,812		20,546		40,216
Call premium on Senior Notes						-17,895							-17,895
Interest expense	-3,854		-3,388	-4,319	-3,852	-4,351		-2,053	-2,052	-2,051	-15,413		-10,507		-8,198
Other income (expense)											10,061
Income (loss) before income taxes	28,098		46,257	24,859	41,322	20,409		31,090	20,221	20,553	140,536		92,273		91,736
Income tax expense (benefit)	8,823		15,032	7,998	13,354	6,076		9,804	6,284	6,643	45,207		28,807		27,974
Net income (loss)	19,275		31,225	16,861	27,968	14,333		21,286	13,937	13,910	95,329		63,466		63,762
Identifiable assets	4,464,176					4,169,452					4,464,176		4,169,452		4,007,670
Losses and loss adjustment expenses ratio											58.30%		61.60%		63.60%
Commission expense ratio											13.40%		13.50%		15.50%
Other operating expense ratio											20.90%	[1]	19.70%	[2]	20.20%	[2]
Combined ratio	93.80%		89.50%	95.30%	92.20%	94.00%		89.80%	97.70%	97.90%	92.60%		94.80%		99.30%
Insurance Companies
Segment Reporting Information [Line Items]
Gross written premiums											1,045,454		1,002,275		921,325
Net written premiums											752,773		680,008		622,956
Net earned premiums											704,574		639,338		571,439
Net losses and loss adjustment expenses											-434,396		-415,413		-417,082
Commission expenses											-85,137		-81,132		-81,370
Other operating expenses											-138,675		-119,920		-113,625
Other underwriting income (expense)											2,727
Other income (expense)													2,764		3,790
Underwriting profit (loss)											49,093		25,637		-36,848
Net investment income											56,714		49,083		46,549
Net realized gains (losses)											12,715		20,600		36,468
Other income (expense)											-2,182
Income (loss) before income taxes											116,340		95,320		46,169
Income tax expense (benefit)											36,609		29,965		12,686
Net income (loss)											79,731		65,355		33,483
Identifiable assets	3,344,084					3,077,437					3,344,084		3,077,437		3,036,489
Losses and loss adjustment expenses ratio											61.70%		65.00%		73.00%
Commission expense ratio											12.10%		12.70%		14.20%
Other operating expense ratio											19.20%	[1]	18.30%	[2]	19.20%	[2]
Combined ratio											93.00%		96.00%		106.40%
Lloyd's
Segment Reporting Information [Line Items]
Gross written premiums											386,899		368,242		365,140
Net written premiums											247,365		207,914		210,699
Net earned premiums											231,321		202,601		210,525
Net losses and loss adjustment expenses											-110,833		-103,548		-80,351
Commission expenses											-42,558		-34,710		-42,449
Other operating expenses											-58,150		-44,514		-45,454
Other underwriting income (expense)											35
Other income (expense)													-1,588		47
Underwriting profit (loss)											19,815		18,241		42,318
Net investment income											7,378		7,160		7,551
Net realized gains (losses)											97		-58		3,555
Other income (expense)											12,243
Income (loss) before income taxes											39,533		25,343		53,424
Income tax expense (benefit)											13,885		8,728		18,620
Net income (loss)											25,648		16,615		34,804
Identifiable assets	957,795					930,567					957,795		930,567		928,448
Losses and loss adjustment expenses ratio											47.90%		51.10%		38.20%
Commission expense ratio											18.40%		17.10%		20.20%
Other operating expense ratio											25.10%	[1]	22.80%	[2]	21.50%	[2]
Combined ratio											91.40%		91.00%		79.90%
Corporate
Segment Reporting Information [Line Items]
Commission expenses											2,167	[3]	2,348	[3]	2,349	[3]
Other underwriting income (expense)											-2,167	[3]
Other income (expense)													-2,348	[3]	-2,349	[3]
Net investment income											76	[3]	8	[3]	148	[3]
Net realized gains (losses)													4	[3]	193	[3]
Call premium on Senior Notes													-17,895	[3]
Interest expense											-15,413	[3]	-10,507	[3]	-8,198	[3]
Income (loss) before income taxes											-15,337	[3]	-28,390	[3]	-7,857	[3]
Income tax expense (benefit)											-5,287	[3]	-9,886	[3]	-3,332	[3]
Net income (loss)											-10,050	[3]	-18,504	[3]	-4,525	[3]
Identifiable assets	$162,297	[3]				$161,448	[3]				$162,297	[3]	$161,448	[3]	$42,733	[3]
[1]	Includes Other operating expenses and Other underwriting income (expenses).
[2]	Includes Other operating expenses and Other income.
[3]	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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Gross written premiums	$333,299	$327,469	$348,795	$422,790	$333,091	$312,076	$332,128	$393,222	$1,432,353	$1,370,517	$1,286,465
Net written premiums	228,007	228,417	231,864	311,850	223,445	196,556	198,469	269,452	1,000,138	887,922	833,655
Net earned premiums	234,172	245,367	231,084	225,272	219,902	213,895	205,814	202,328	935,895	841,939	781,964
Marine
Segment Reporting Information [Line Items]
Gross written premiums									365,470	352,868	394,518
Net written premiums									267,944	254,464	276,810
Net earned premiums									264,674	267,966	279,079
Property Casualty
Segment Reporting Information [Line Items]
Gross written premiums									881,075	829,609	717,769
Net written premiums									610,761	505,276	433,992
Net earned premiums									547,547	447,202	385,733
Professional Liability
Segment Reporting Information [Line Items]
Gross written premiums									185,808	188,040	174,178
Net written premiums									121,433	128,182	122,853
Net earned premiums									123,674	126,771	117,152
Insurance Companies
Segment Reporting Information [Line Items]
Gross written premiums									1,045,454	1,002,275	921,325
Net written premiums									752,773	680,008	622,956
Net earned premiums									704,574	639,338	571,439
Insurance Companies | Marine
Segment Reporting Information [Line Items]
Gross written premiums									177,363	171,822	200,095
Net written premiums									123,617	119,837	133,210
Net earned premiums									123,203	129,276	142,181
Insurance Companies | Property Casualty
Segment Reporting Information [Line Items]
Gross written premiums									755,059	700,087	590,741
Net written premiums									554,844	462,942	390,168
Net earned premiums									496,209	409,480	332,782
Insurance Companies | Professional Liability
Segment Reporting Information [Line Items]
Gross written premiums									113,032	130,366	130,489
Net written premiums									74,312	97,229	99,578
Net earned premiums									85,162	100,582	96,476
Lloyd's
Segment Reporting Information [Line Items]
Gross written premiums									386,899	368,242	365,140
Net written premiums									247,365	207,914	210,699
Net earned premiums									231,321	202,601	210,525
Lloyd's | Marine
Segment Reporting Information [Line Items]
Gross written premiums									188,107	181,046	194,423
Net written premiums									144,327	134,627	143,600
Net earned premiums									141,471	138,690	136,898
Lloyd's | Property Casualty
Segment Reporting Information [Line Items]
Gross written premiums									126,016	129,522	127,028
Net written premiums									55,917	42,334	43,824
Net earned premiums									51,338	37,722	52,951
Lloyd's | Professional Liability
Segment Reporting Information [Line Items]
Gross written premiums									72,776	57,674	43,689
Net written premiums									47,121	30,953	23,275
Net earned premiums									$38,512	$26,189	$20,676

Cash_and_Investments_Including

Cash and Investments Including Other-Than-Temporarily Impaired Securities Recognized within Accumulated Other Comprehensive Income (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Gain (Loss) on Investments [Line Items]
Total investments	$2,550,229	$2,191,827
Total investments and cash	2,820,486	2,574,586
Gross Unrealized Gains	83,078	69,554
Gross Unrealized Losses	-11,672	-33,530
Amortized Cost	2,749,080	2,538,562
Short-term investments
Gain (Loss) on Investments [Line Items]
Total investments and cash	179,506	296,250
Gross Unrealized Losses	-21
Amortized Cost	179,527	296,250
Cash
Gain (Loss) on Investments [Line Items]
Total investments and cash	90,751	86,509
Amortized Cost	90,751	86,509
Fixed maturities
Gain (Loss) on Investments [Line Items]
Total investments	2,365,934	2,047,873
Gross Unrealized Gains	52,322	43,854
Gross Unrealized Losses	-10,347	-32,980
Amortized Cost	2,323,959	2,036,999
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign
Gain (Loss) on Investments [Line Items]
Total investments	397,923	441,685
Gross Unrealized Gains	3,431	2,854
Gross Unrealized Losses	-5,965	-8,855
Amortized Cost	400,457	447,686
Fixed maturities | States, municipalities and political subdivisions
Gain (Loss) on Investments [Line Items]
Total investments	541,007	460,422
Gross Unrealized Gains	19,204	9,298
Gross Unrealized Losses	-558	-13,651
Amortized Cost	522,361	464,775
Fixed maturities | Agency mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Total investments	364,622	301,274
Gross Unrealized Gains	8,476	6,779
Gross Unrealized Losses	-998	-6,016
Amortized Cost	357,144	300,511
Fixed maturities | Residential Mortgage Backed Securities
Gain (Loss) on Investments [Line Items]
Total investments	34,087	41,755
Gross Unrealized Gains	1,153	1,212
Gross Unrealized Losses	-138	-161
Amortized Cost	33,072	40,704
Fixed maturities | Asset-backed securities
Gain (Loss) on Investments [Line Items]
Total investments	206,413	125,133
Gross Unrealized Gains	380	653
Gross Unrealized Losses	-964	-480
Amortized Cost	206,997	124,960
Fixed maturities | Commercial mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Total investments	206,318	172,750
Gross Unrealized Gains	6,630	7,656
Gross Unrealized Losses	-98	-374
Amortized Cost	199,786	165,468
Fixed maturities | Mortgage-backed and asset-backed securities
Gain (Loss) on Investments [Line Items]
Total investments	811,440	640,912
Gross Unrealized Gains	16,639	16,300
Gross Unrealized Losses	-2,198	-7,031
Amortized Cost	796,999	631,643
Fixed maturities | Corporate bonds
Gain (Loss) on Investments [Line Items]
Total investments	615,564	504,854
Gross Unrealized Gains	13,048	15,402
Gross Unrealized Losses	-1,626	-3,443
Amortized Cost	604,142	492,895
Equity Securities | Common Stock
Gain (Loss) on Investments [Line Items]
Total investments	127,183	143,954
Gross Unrealized Gains	28,520	25,700
Gross Unrealized Losses	-1,254	-550
Amortized Cost	99,917	118,804
Equity Securities | Preferred Stock
Gain (Loss) on Investments [Line Items]
Total investments	57,112
Gross Unrealized Gains	2,236
Gross Unrealized Losses	-50
Amortized Cost	$54,926

Investments_Additional_Informa

Investments - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	Securities
Schedule of Investments [Line Items]
Non-credit OTTI on fixed maturities in an unrealized gain position	$700,000	$500,000
Gross Unrealized Loss	1,304,000	550,000
Investment Expenses	2,998,000	3,256,000	10,386,000
Investment performance fee			2,800,000
Number of securities transferred from Level 3 to Level 2	1
Level 3 assets		4,407,000	0
Total Restricted Net Assets	523,425,000	520,886,000
Settlement Agreement
Schedule of Investments [Line Items]
Investment Expenses			4,500,000
Mortgage-backed and asset-backed securities
Schedule of Investments [Line Items]
Securities, effective maturities	4 years 4 months 24 days
Equity Securities | Maximum
Schedule of Investments [Line Items]
Percentage of fair value under carrying value	80.00%
Non-government-backed securities
Schedule of Investments [Line Items]
Gross Unrealized Loss	$500,000	$1,100,000
Non-government-backed securities | Maximum
Schedule of Investments [Line Items]
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, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair Value
Due in one year or less	$63,670
Due after one year through five years	765,084
Due after five years through ten years	356,929
Due after ten years	368,811
Mortgage- and asset-backed securities	811,440
Total	2,365,934	2,047,873
Amortized Cost
Due in one year or less	65,643
Due after one year through five years	758,064
Due after five years through ten years	348,195
Due after ten years	355,058
Mortgage- and asset-backed securities	796,999
Total	$2,323,959	$2,036,999

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, 2014	Dec. 31, 2013
Investment Securities [Line Items]
Rating	AA
Fair Value	$2,365,934	$2,047,873
Percent of Total	100.00%
Extremely strong
Investment Securities [Line Items]
Rating	AAA
Fair Value	462,603
Percent of Total	20.00%
Very strong
Investment Securities [Line Items]
Rating	AA
Fair Value	1,090,505
Percent of Total	45.00%
Strong
Investment Securities [Line Items]
Rating	A
Fair Value	612,131
Percent of Total	26.00%
Adequate
Investment Securities [Line Items]
Rating	BBB
Fair Value	185,372
Percent of Total	8.00%
Speculative
Investment Securities [Line Items]
Rating	BB & Below
Fair Value	14,852
Percent of Total	1.00%
Not rated
Investment Securities [Line Items]
Rating	NR
Fair Value	$471
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, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Investment	Investment
Gain (Loss) on Investments [Line Items]
Number of Securities	15	7
Fair Value	$19,928	$10,925
Gross Unrealized Loss	1,304	550
Fixed maturities
Gain (Loss) on Investments [Line Items]
Number of Securities	259	405
Fair Value	731,346	934,607
Gross Unrealized Loss	10,347	32,980
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign
Gain (Loss) on Investments [Line Items]
Number of Securities	50	53
Fair Value	205,598	285,730
Gross Unrealized Loss	5,965	8,855
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	19	27
Fair Value	87,915	136,360
Gross Unrealized Loss	1,061	1,096
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities		26
Fair Value		149,370
Gross Unrealized Loss		7,759
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	31
Fair Value	117,683
Gross Unrealized Loss	4,904
Fixed maturities | States, municipalities and political subdivisions
Gain (Loss) on Investments [Line Items]
Number of Securities	32	138
Fair Value	53,689	257,641
Gross Unrealized Loss	558	13,651
Fixed maturities | States, municipalities and political subdivisions | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	13	28
Fair Value	14,242	40,132
Gross Unrealized Loss	41	297
Fixed maturities | States, municipalities and political subdivisions | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2	104
Fair Value	2,107	205,152
Gross Unrealized Loss	19	12,100
Fixed maturities | States, municipalities and political subdivisions | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	17	6
Fair Value	37,340	12,357
Gross Unrealized Loss	498	1,254
Fixed maturities | Agency mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Number of Securities	52	112
Fair Value	77,182	140,102
Gross Unrealized Loss	998	6,016
Fixed maturities | Agency mortgage-backed securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	4	39
Fair Value	14,743	39,458
Gross Unrealized Loss	52	434
Fixed maturities | Agency mortgage-backed securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2	64
Fair Value	4,138	77,860
Gross Unrealized Loss	28	3,768
Fixed maturities | Agency mortgage-backed securities | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	46	9
Fair Value	58,301	22,784
Gross Unrealized Loss	918	1,814
Fixed maturities | Residential Mortgage Backed Securities
Gain (Loss) on Investments [Line Items]
Number of Securities	22	25
Fair Value	7,353	3,848
Gross Unrealized Loss	138	161
Fixed maturities | Residential Mortgage Backed Securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	6	3
Fair Value	4,966	431
Gross Unrealized Loss	43	2
Fixed maturities | Residential Mortgage Backed Securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2	7
Fair Value	659	950
Gross Unrealized Loss	7	29
Fixed maturities | Residential Mortgage Backed Securities | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	14	15
Fair Value	1,728	2,467
Gross Unrealized Loss	88	130
Fixed maturities | Asset-backed securities
Gain (Loss) on Investments [Line Items]
Number of Securities	25	15
Fair Value	144,805	76,090
Gross Unrealized Loss	964	480
Fixed maturities | Asset-backed securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	19	14
Fair Value	96,123	75,887
Gross Unrealized Loss	354	479
Fixed maturities | Asset-backed securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	3	1
Fair Value	14,152	203
Gross Unrealized Loss	185	1
Fixed maturities | Asset-backed securities | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	3
Fair Value	34,530
Gross Unrealized Loss	425
Fixed maturities | Commercial mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Number of Securities	8	10
Fair Value	21,132	22,584
Gross Unrealized Loss	98	374
Fixed maturities | Commercial mortgage-backed securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	4	4
Fair Value	18,665	6,712
Gross Unrealized Loss	65	31
Fixed maturities | Commercial mortgage-backed securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	1	2
Fair Value	1,076	15,098
Gross Unrealized Loss	6	322
Fixed maturities | Commercial mortgage-backed securities | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	3	4
Fair Value	1,391	774
Gross Unrealized Loss	27	21
Fixed maturities | Corporate bonds
Gain (Loss) on Investments [Line Items]
Number of Securities	70	52
Fair Value	221,587	148,612
Gross Unrealized Loss	1,626	3,443
Fixed maturities | Corporate bonds | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	52	34
Fair Value	179,390	93,591
Gross Unrealized Loss	797	717
Fixed maturities | Corporate bonds | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	4	18
Fair Value	11,071	55,021
Gross Unrealized Loss	74	2,726
Fixed maturities | Corporate bonds | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	14
Fair Value	31,126
Gross Unrealized Loss	755
Common Stock
Gain (Loss) on Investments [Line Items]
Number of Securities	8	7
Fair Value	13,277	10,925
Gross Unrealized Loss	1,254	550
Common Stock | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	6	5
Fair Value	9,152	7,387
Gross Unrealized Loss	761	422
Common Stock | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	1	2
Fair Value	3,887	3,538
Gross Unrealized Loss	486	128
Common Stock | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	1
Fair Value	238
Gross Unrealized Loss	7
Preferred Stock
Gain (Loss) on Investments [Line Items]
Number of Securities	7
Fair Value	6,651
Gross Unrealized Loss	50
Preferred Stock | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	7
Fair Value	6,651
Gross Unrealized Loss	$50

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, 2014	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
						Investment	Investment	Investment
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Number of Securities						31	4	4
Total other-than-temporary impairment losses	$21	($158)	$530	$1,821	$42	($137)	$2,393	$902
Portion of loss recognized in other comprehensive income	21	-158				-137		44
Net other-than-temporary impairment losses recognized in earnings			530	1,821	42		2,393	858
Corporate And Other Bonds
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Number of Securities							1
Total other-than-temporary impairment losses							1,822
Net other-than-temporary impairment losses recognized in earnings							1,822
Residential Mortgage Backed Securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Number of Securities						31		1
Total other-than-temporary impairment losses						-137		55
Portion of loss recognized in other comprehensive income						-137		44
Net other-than-temporary impairment losses recognized in earnings								11
Equity Securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Number of Securities							3	3
Total other-than-temporary impairment losses							571	847
Net other-than-temporary impairment losses recognized in earnings							$571	$847

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, 2014	Dec. 31, 2013	Dec. 31, 2012
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Beginning balance	$5,154	$3,332	$3,321
Additions for credit loss impairments recognized in the current period on securities not previously impaired		1,822
Additions for credit loss impairments recognized in the current period on securities previously impaired			11
Reductions for credit loss impairments previously recognized on securities sold during the period	-2,793
Ending balance	$2,361	$5,154	$3,332

Contractual_Maturity_by_Number

Contractual Maturity by Number of Years Until Maturity for Fixed Maturity Securities with Gross Unrealized Loss (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	$1,304	$550
Fair Value Amount	19,928	10,925
Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	10,347	32,980
Percent of Total Gross Unrealized Loss	100.00%
Fair Value Amount	731,346	934,607
Percent of Total Fair Value	100.00%
Fixed maturities | Due in one year or less
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	2,638
Percent of Total Gross Unrealized Loss	25.00%
Fair Value Amount	21,919
Percent of Total Fair Value	3.00%
Fixed maturities | Due After One Year Through Five Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	3,791
Percent of Total Gross Unrealized Loss	37.00%
Fair Value Amount	334,046
Percent of Total Fair Value	46.00%
Fixed maturities | Due After Five Years Through Ten Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	1,562
Percent of Total Gross Unrealized Loss	15.00%
Fair Value Amount	103,376
Percent of Total Fair Value	14.00%
Fixed maturities | Due After Ten Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	158
Percent of Total Gross Unrealized Loss	2.00%
Fair Value Amount	21,533
Percent of Total Fair Value	3.00%
Fixed maturities | Mortgage- and asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	2,198
Percent of Total Gross Unrealized Loss	21.00%
Fair Value Amount	$250,472
Percent of Total Fair Value	34.00%

Net_Investment_Income_Detail

Net Investment Income (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Investment Income [Line Items]
Investment Income									$67,166	$59,507	$64,634
Investment expenses									-2,998	-3,256	-10,386
Net investment income	16,071	15,839	15,648	16,610	14,254	14,094	14,246	13,657	64,168	56,251	54,248
Fixed maturities
Net Investment Income [Line Items]
Investment Income									57,219	53,898	58,995
Equity Securities
Net Investment Income [Line Items]
Investment Income									9,036	4,835	3,945
Short-term investments
Net Investment Income [Line Items]
Investment Income									$911	$774	$1,694

Change_in_Net_Unrealized_Gains

Change in Net Unrealized Gains and Losses (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Gross unrealized gains (losses)	$35,382	($67,337)	$9,720
Deferred income tax	12,197	-23,565	3,418
Change in net unrealized gains (losses), net	23,185	-43,772	6,302
Fixed maturities
Gross unrealized gains (losses)	31,080	-76,194	15,709
Equity Securities
Gross unrealized gains (losses)	$4,302	$8,857	($5,989)

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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Gain (Loss) on Investments [Line Items]
Net realized gains (losses)	$788	$6,718	$4,473	$833	$15,768	($988)	$3,345	$4,814	$12,812	$22,939	$41,074
Fixed maturities
Gain (Loss) on Investments [Line Items]
Gains									8,326	8,539	28,789
Losses									-2,610	-2,797	-1,915
Net realized gains (losses)									5,716	5,742	26,874
Equity Securities
Gain (Loss) on Investments [Line Items]
Gains									9,447	17,955	14,673
Losses									-2,351	-758	-473
Net realized gains (losses)									$7,096	$17,197	$14,200

Fixed_Maturities_and_Equity_Se

Fixed Maturities and Equity Securities by Asset Class that are Measured at Fair Value (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	$2,550,229	$2,191,827
Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	2,365,934	2,047,873
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	397,923	441,685
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	541,007	460,422
Fixed maturities | Agency mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	364,622	301,274
Fixed maturities | Residential Mortgage Backed Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	34,087	41,755
Fixed maturities | Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	206,413	125,133
Fixed maturities | Commercial mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	206,318	172,750
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	811,440	640,912
Fixed maturities | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	615,564	504,854
Equity Securities | Common Stock
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	127,183	143,954
Equity Securities | Preferred Stock
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	57,112
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	274,087	386,333
Level 1 | Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	146,904	242,379
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	146,904	242,379
Level 1 | Equity Securities | Common Stock
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	127,183	143,954
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	2,276,142	1,801,087
Level 2 | Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	2,219,030	1,801,087
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	251,019	199,306
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	541,007	460,422
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	364,622	301,274
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	34,087	41,755
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	206,413	125,133
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	206,318	172,750
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	811,440	640,912
Level 2 | Fixed maturities | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	615,564	500,447
Level 2 | Equity Securities | Preferred Stock
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	57,112
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, 2014	Dec. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$4,407	$0
Realized Gains (Losses)	0	0
Unrealized Gains (Losses)		-42
Purchase		4,660
Sales		-211
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	-4,407
Ending Balance		4,407
Corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	4,407
Realized Gains (Losses)	0
Settlements	0
Transfers into Level 3	0
Transfers out of Level 3	-4,407
Commercial mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Realized Gains (Losses)		0
Unrealized Gains (Losses)		-42
Purchase		4,660
Sales		-211
Settlements		0
Transfers into Level 3		0
Ending Balance		$4,407

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, 2014	Dec. 31, 2013	Dec. 31, 2012
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserves for losses and LAE at beginning of year	$1,222,633	$1,216,909	$1,237,234
Provision for losses and LAE for claims occurring in the current year	601,041	520,227	542,724
Increase (decrease) in estimated losses and LAE for claims occurring in prior years	-55,812	-1,266	-45,291
Incurred losses and LAE	545,229	518,961	497,433
Losses and LAE paid for claims occurring during:
Current year	-164,199	-147,758	-110,373
Prior years	-295,527	-365,479	-407,385
Losses and LAE payments	-459,726	-513,237	-517,758
Net reserves for losses and LAE at end of year	1,308,136	1,222,633	1,216,909
Reinsurance recoverables on unpaid losses and LAE	851,498	822,438	880,139
Gross reserves for losses and LAE at end of year	$2,159,634	$2,045,071	$2,097,048

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, 2014	Dec. 31, 2013	Dec. 31, 2012
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	$55,812	$1,266	$45,291
Insurance Companies
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	-30,312	13,430	1,896
Insurance Companies | Marine
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	-41,388	-15,227	-10,010
Insurance Companies | Property Casualty
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	14,612	18,466	4,293
Insurance Companies | Professional Liability
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	-3,536	10,191	7,613
Lloyd's
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	-25,500	-14,696	-47,187
Lloyd's | Marine
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	-21,336	-2,998	-30,735
Lloyd's | Property Casualty
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	-1,500	-14,574	-6,890
Lloyd's | Professional Liability
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	($2,664)	$2,876	($9,562)

Reserves_for_Losses_and_Loss_A2

Reserves for Losses and Loss Adjustment Expenses - Additional Information (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	$55,812	$1,266	$45,291
Marine | Short Tail Marine Lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years			2,600
Marine | Claims Emergence
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years			4,000
Marine | Case Reserves
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years			3,400
Insurance Companies
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	-30,312	13,430	1,896
Insurance Companies | Offshore Energy
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years		8,000
Insurance Companies | Marine
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	-41,388	-15,227	-10,010
Insurance Companies | Marine | Marine Liability
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	13,400
Insurance Companies | Marine | Craft/Fishing Vassels
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	7,200
Insurance Companies | Marine | P&I
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	6,400
Insurance Companies | Marine | Inland Marine
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	4,700
Insurance Companies | Marine | Bluewater Hull
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	1,100
Insurance Companies | Marine | Cargo
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	700
Insurance Companies | Property Casualty
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	14,612	18,466	4,293
Insurance Companies | Property Casualty | Contractors
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	23,200	10,400
Insurance Companies | Property Casualty | Claims Emergence
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	6,100
Insurance Companies | Property Casualty | Accident and Health
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years		13,200	4,300
Insurance Companies | Property Casualty | Business in run-off
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years		2,100
Insurance Companies | Professional Liability
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	-3,536	10,191	7,613
Insurance Companies | Professional Liability | Errors and Omissions
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years		4,400
Insurance Companies | Professional Liability | Management Liability
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years		6,100
Insurance Companies | Professional Liability | Settlement
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	4,500
Lloyd's
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	-25,500	-14,696	-47,187
Lloyd's | Syndicate 1221
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years			5,000
Lloyd's | Marine
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	-21,336	-2,998	-30,735
Lloyd's | Marine | Marine Liability
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	11,000
Lloyd's | Marine | Cargo
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	1,000
Lloyd's | Marine | Specie
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	3,700
Lloyd's | Marine | Transport
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	1,300
Lloyd's | Marine | Energy Liability
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	2,300
Lloyd's | Marine | Marine Assumed
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	2,000
Lloyd's | Marine | Syndicate 1221
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years			4,100
Lloyd's | Property Casualty
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	-1,500	-14,574	-6,890
Lloyd's | Professional Liability
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	-2,664	2,876	-9,562
Lloyd's | Professional Liability | Errors and Omissions
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	1,000	6,100
Lloyd's | Professional Liability | Management Liability
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	1,700	3,200
Lloyd's | Professional Liability | Syndicate 1221
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years			$900

Net_Prior_Period_Reserve_Redun

Net Prior Period Reserve Redundancies (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	($55,812)	($1,266)	($45,291)
Lloyd's
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	25,500	14,696	47,187
Lloyd's | 2010
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years			5,027
Lloyd's | 2009
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years			25,034
Lloyd's | 2008 and Prior
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years			17,126
Marine | Lloyd's
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	21,336	2,998	30,735
Marine | Lloyd's | 2010
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years			3,492
Marine | Lloyd's | 2009
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years			14,792
Marine | Lloyd's | 2008 and Prior
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years			12,451
Property Casualty | Lloyd's
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	1,500	14,574	6,890
Property Casualty | Lloyd's | 2010
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years			378
Property Casualty | Lloyd's | 2009
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years			4,170
Property Casualty | Lloyd's | 2008 and Prior
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years			2,342
Professional Liability | Lloyd's
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	2,664	-2,876	9,562
Professional Liability | Lloyd's | 2010
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years			1,157
Professional Liability | Lloyd's | 2009
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years			6,072
Professional Liability | Lloyd's | 2008 and Prior
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years			$2,333

Ceded_Reinsurance_Additional_I

Ceded Reinsurance - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
	Entity
Effects of Reinsurance [Line Items]
Ceded premiums earned	$440,656,000		$455,985,000	$396,639,000
Ceded losses incurred	230,182,000		188,733,000	262,649,000
Reserve for uncollectible reinsurance amount	11,300,000		11,300,000
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	1,140,696,000	[1],[2],[3]
Collateral Held	201,976,000
Percentage of offsetting collateral held	17.70%
Percentage of reinsurance recoverable of 20 largest reinsurers	75.70%
Number of largest reinsurers	20
Percentage of funding requirement to retain	100.00%
Reinsurance recoverables for paid and unpaid losses	902,845,000
Not rated
Effects of Reinsurance [Line Items]
Reinsurance recoverables	5,200,000
Percentage of offsetting collateral held	53.60%
Ceded Balances Payable
Effects of Reinsurance [Line Items]
Collateral Held	152,800,000
Letter of Credit
Effects of Reinsurance [Line Items]
Collateral Held	43,100,000
Percentage of collateral held	21.00%
All Other
Effects of Reinsurance [Line Items]
Collateral Held	6,100,000
Catastrophic
Effects of Reinsurance [Line Items]
Reinsurance recoverables for paid and unpaid losses	43,300,000		46,500,000
Superstorm Sandy
Effects of Reinsurance [Line Items]
Reinsurance recoverables for paid and unpaid losses	25,400,000		30,700,000
Hurricane Gustav and Ike
Effects of Reinsurance [Line Items]
Reinsurance recoverables for paid and unpaid losses	7,300,000		3,300,000
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]	Net of reserve for uncollectible reinsurance of approximately $11.3 million.
[2]	When an A.M. Best rating is unavailable, the equivalent S&P rating is used.
[3]	The carrying value is comprised of prepaid reinsurance premium as well as reinsurance recoverables on paid and unpaid losses which are net of the reserve for uncollectible reinsurance.

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, 2014
Ceded Credit Risk [Line Items]
Rating	AA
Fair Value	$1,140,696	[1],[2],[3]
Percent of Total	100.00%	[1]
Superior
Ceded Credit Risk [Line Items]
Rating	A++, A+	[1]
Fair Value	575,205	[1],[3]
Percent of Total	50.00%	[1]
Excellent
Ceded Credit Risk [Line Items]
Rating	A, A-	[1]
Fair Value	547,314	[1],[3]
Percent of Total	48.00%	[1]
Very Good
Ceded Credit Risk [Line Items]
Rating	B++, B+	[1]
Fair Value	8,483	[1],[3]
Percent of Total	1.00%	[1]
Fair
Ceded Credit Risk [Line Items]
Rating	B, B-	[1]
Percent of Total	0.00%	[1]
Not rated
Ceded Credit Risk [Line Items]
Rating	NR	[1]
Fair Value	$9,695	[1],[3]
Percent of Total	1.00%	[1]
[1]	When an A.M. Best rating is unavailable, the equivalent S&P rating is used.
[2]	Net of reserve for uncollectible reinsurance of approximately $11.3 million.
[3]	The carrying value is comprised of prepaid reinsurance premium as well as reinsurance recoverables on paid and unpaid losses which are net of the reserve for uncollectible reinsurance.

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, 2014		Dec. 31, 2013
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	$237,851		$247,822
Reinsurance Recoverables Paid/Unpaid Losses	902,845
Reinsurance Recoverables Total	1,140,696	[1],[2],[3]
Collateral Held	201,976
Rating	AA
National Indemnity Company | AM Best, A++ Rating | Standard & Poor's, AA+ Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	25,202
Reinsurance Recoverables Paid/Unpaid Losses	117,562
Reinsurance Recoverables Total	142,764	[1]
Collateral Held	22,069
Everest Reinsurance Company | AM Best, A+ Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	21,573
Reinsurance Recoverables Paid/Unpaid Losses	75,063
Reinsurance Recoverables Total	96,636	[1]
Collateral Held	7,326
Swiss Reinsurance America Corporation | AM Best, A+ Rating | Standard & Poor's, AA- Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	22,815
Reinsurance Recoverables Paid/Unpaid Losses	73,305
Reinsurance Recoverables Total	96,120	[1]
Collateral Held	14,587
Transatlantic Reinsurance Company | AM Best, A Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	11,916
Reinsurance Recoverables Paid/Unpaid Losses	74,072
Reinsurance Recoverables Total	85,988	[1]
Collateral Held	4,038
Munich Reinsurance America Inc. | AM Best, A+ Rating | Standard & Poor's, AA- Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	11,366
Reinsurance Recoverables Paid/Unpaid Losses	58,768
Reinsurance Recoverables Total	70,134	[1]
Collateral Held	5,539
Allied World Reinsurance | AM Best, A Rating | Standard & Poor's, A Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	9,048
Reinsurance Recoverables Paid/Unpaid Losses	37,088
Reinsurance Recoverables Total	46,136	[1]
Collateral Held	1,666
Lloyd Syndicate #2003 | AM Best, A Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	4,399
Reinsurance Recoverables Paid/Unpaid Losses	35,123
Reinsurance Recoverables Total	39,522	[1]
Collateral Held	5,191
Partner Reinsurance Europe | AM Best, A+ Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	10,986
Reinsurance Recoverables Paid/Unpaid Losses	25,409
Reinsurance Recoverables Total	36,395	[1]
Collateral Held	16,052
Employers Mutual Casualty Company | AM Best, A Rating | Standard & Poor's, Not Rated
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	11,928
Reinsurance Recoverables Paid/Unpaid Losses	21,851
Reinsurance Recoverables Total	33,779	[1]
Collateral Held	10,935
Scor Global P&C SE | AM Best, A Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	10,190
Reinsurance Recoverables Paid/Unpaid Losses	17,572
Reinsurance Recoverables Total	27,762	[1]
Collateral Held	5,558
Ace Property and Casualty Insurance Company | AM Best, A++ Rating | Standard & Poor's, AA Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	11,165
Reinsurance Recoverables Paid/Unpaid Losses	12,741
Reinsurance Recoverables Total	23,906	[1]
Collateral Held	2,907
Tower Insurance Company | AM Best, A- Rating | Standard & Poor's, Not Rated
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Paid/Unpaid Losses	21,509
Reinsurance Recoverables Total	21,509	[1]
Collateral Held	2,455
Aspen Insurance UK Ltd. | AM Best, A Rating | Standard & Poor's, A Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	8,928
Reinsurance Recoverables Paid/Unpaid Losses	11,227
Reinsurance Recoverables Total	20,155	[1]
Collateral Held	4,869
Ironshore Indemnity Inc. | AM Best, A Rating | Standard & Poor's, Not Rated
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	6,234
Reinsurance Recoverables Paid/Unpaid Losses	13,395
Reinsurance Recoverables Total	19,629	[1]
Collateral Held	8,645
Validus Reinsurance Ltd | AM Best, A Rating | Standard & Poor's, A Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	2,020
Reinsurance Recoverables Paid/Unpaid Losses	16,873
Reinsurance Recoverables Total	18,893	[1]
Collateral Held	10,975
Atlantic Specialty Insurance | AM Best, A Rating | Standard & Poor's, A- Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	2,542
Reinsurance Recoverables Paid/Unpaid Losses	15,812
Reinsurance Recoverables Total	18,354	[1]
QBE Reinsurance Corp | AM Best, A Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	2,636
Reinsurance Recoverables Paid/Unpaid Losses	15,539
Reinsurance Recoverables Total	18,175	[1]
National Union Fire Ins. | AM Best, A Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	8,067
Reinsurance Recoverables Paid/Unpaid Losses	8,459
Reinsurance Recoverables Total	16,526	[1]
Collateral Held	6,158
Endurance Reinsurance Corporation | AM Best, A Rating | Standard & Poor's, A Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	5,695
Reinsurance Recoverables Paid/Unpaid Losses	9,936
Reinsurance Recoverables Total	15,631	[1]
Collateral Held	1,337
Odyssey American Reinsurance Corporation | AM Best, A Rating | Standard & Poor's, A- Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	3,506
Reinsurance Recoverables Paid/Unpaid Losses	11,650
Reinsurance Recoverables Total	15,156	[1]
Collateral Held	1,604
Insurance Companies
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	190,216
Reinsurance Recoverables Paid/Unpaid Losses	672,954
Reinsurance Recoverables Total	863,170	[1]
Collateral Held	131,911
All Other
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium	47,635
Reinsurance Recoverables Paid/Unpaid Losses	229,891
Reinsurance Recoverables Total	277,526	[1]
Collateral Held	$70,065
AM Best | National Indemnity Company | AM Best, A++ Rating | Standard & Poor's, AA+ 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 | Swiss Reinsurance America Corporation | 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 | Munich Reinsurance America Inc. | AM Best, A+ Rating | Standard & Poor's, AA- 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 | Lloyd Syndicate #2003 | 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 | Employers Mutual Casualty Company | AM Best, A Rating | Standard & Poor's, Not Rated
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 | Ace Property and Casualty Insurance Company | AM Best, A++ Rating | Standard & Poor's, AA Rating
Ceded Credit Risk [Line Items]
Rating	A++
AM Best | Tower Insurance Company | AM Best, A- Rating | Standard & Poor's, Not Rated
Ceded Credit Risk [Line Items]
Rating	A-
AM Best | Aspen Insurance UK Ltd. | 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 | Validus Reinsurance Ltd | AM Best, A Rating | Standard & Poor's, A Rating
Ceded Credit Risk [Line Items]
Rating	A
AM Best | Atlantic Specialty Insurance | 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 | National Union Fire Ins. | AM Best, A Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Rating	A
AM Best | Endurance Reinsurance Corporation | AM Best, A Rating | Standard & Poor's, A 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
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 | Everest Reinsurance Company | AM Best, A+ Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Rating	A+
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 | Transatlantic 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 | Allied World Reinsurance | AM Best, A Rating | Standard & Poor's, A Rating
Ceded Credit Risk [Line Items]
Rating	A
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 | Partner Reinsurance Europe | 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 | Scor Global P&C SE | 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 | Tower Insurance Company | AM Best, A- Rating | Standard & Poor's, Not Rated
Ceded Credit Risk [Line Items]
Rating	NR
Standard & Poor's | Aspen Insurance UK Ltd. | 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 | Validus Reinsurance Ltd | AM Best, A Rating | Standard & Poor's, A Rating
Ceded Credit Risk [Line Items]
Rating	A
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 | QBE Reinsurance Corp | AM Best, A Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Rating	A+
Standard & Poor's | National Union Fire Ins. | AM Best, A Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Rating	A+
Standard & Poor's | Endurance Reinsurance Corporation | AM Best, A Rating | Standard & Poor's, A Rating
Ceded Credit Risk [Line Items]
Rating	A
Standard & Poor's | Odyssey American Reinsurance Corporation | AM Best, A Rating | Standard & Poor's, A- Rating
Ceded Credit Risk [Line Items]
Rating	A-
[1]	Net of reserve for uncollectible reinsurance of approximately $11.3 million.
[2]	When an A.M. Best rating is unavailable, the equivalent S&P rating is used.
[3]	The carrying value is comprised of prepaid reinsurance premium as well as reinsurance recoverables on paid and unpaid losses which are net of the reserve for uncollectible reinsurance.

Lists_of_20_Largest_Reinsurers1

Lists of 20 Largest Reinsurers Measured by Reinsurance Recoverable (Parenthetical) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Ceded Credit Risk [Line Items]
Reserve for uncollectible reinsurance amount	$11.30	$11.30

Summary_of_Written_Premium_Det

Summary of Written Premium (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct									$1,184,538	$1,127,331	$1,034,658
Assumed									247,815	243,187	251,807
Ceded									-432,215	-482,596	-452,810
Net Written Premiums	228,007	228,417	231,864	311,850	223,445	196,556	198,469	269,452	1,000,138	887,922	833,655
Direct									1,133,336	1,069,677	972,844
Assumed									243,215	228,247	205,759
Ceded									-440,656	-455,985	-396,639
Net earned premiums	234,172	245,367	231,084	225,272	219,902	213,895	205,814	202,328	935,895	841,939	781,964
Direct									631,730	552,381	608,945
Assumed									143,681	155,313	151,137
Ceded									-230,182	-188,733	-262,649
Net Losses and LAE	$134,658	$135,284	$140,220	$135,067	$131,385	$125,086	$131,148	$131,342	$545,229	$518,961	$497,433

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended			0 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 01, 2015
Income Taxes [Line Items]
Domestic effective income tax rate									35.00%	35.00%	35.00%
Undistributed earnings of non-U.S. subsidiaries	$22,600,000								$22,600,000
Taxes payable on undistributed earnings	2,300,000								2,300,000
Unrecognized tax benefits	0				0				0	0
Interest or penalties related to unrecognized tax benefits									0	0
Income tax (benefit) expense	8,823,000	15,032,000	7,998,000	13,354,000	6,076,000	9,804,000	6,284,000	6,643,000	45,207,000	28,807,000	27,974,000
Effective income tax rate									32.20%	31.20%	30.50%
Deferred Tax Assets: State and Local	777,000				555,000				777,000	555,000
State and local net operating loss carry-forwards	$0				$100,000				$0	$100,000
Syndicate 1221 | Subsequent Event
Income Taxes [Line Items]
Domestic effective income tax rate												35.00%
United Kingdom
Income Taxes [Line Items]
Foreign effective income tax rate									35.00%
United Kingdom | Syndicate 1221 | Maximum
Income Taxes [Line Items]
Percentage of premiums	50.00%								50.00%
United Kingdom | Syndicate 1221 | Minimum
Income Taxes [Line Items]
Foreign effective income tax rate									35.00%
State and Local Jurisdiction | Maximum
Income Taxes [Line Items]
State and local tax carry-forwards expiration year									2032
State and Local Jurisdiction | Minimum
Income Taxes [Line Items]
State and local tax carry-forwards expiration year									2024

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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current income tax expense (benefit):
Federal and foreign									$27,290	$23,703	$39,242
State and local									1,036	446	146
Subtotal									28,326	24,149	39,388
Deferred income tax expense (benefit):
Federal and foreign									16,881	4,658	-11,414
State and local									0	0	0
Subtotal									16,881	4,658	-11,414
Actual tax expense and rate	$8,823	$15,032	$7,998	$13,354	$6,076	$9,804	$6,284	$6,643	$45,207	$28,807	$27,974

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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation
Computed expected tax expense									$49,187	$32,299	$32,109
Tax-exempt interest									-4,771	-3,839	-4,443
Dividends received deduction									-1,257	-897	-799
Proration of DRD and Tax-exempt interest									904	710	786
Current state and local income taxes, net of federal income tax deduction									674	290	95
Other									470	244	226
Actual tax expense and rate	$8,823	$15,032	$7,998	$13,354	$6,076	$9,804	$6,284	$6,643	$45,207	$28,807	$27,974
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation
Computed expected tax expense									35.00%	35.00%	35.00%
Tax-exempt interest									-3.40%	-4.20%	-4.80%
Dividends received deduction									-0.90%	-1.00%	-0.90%
Proration of DRD and Tax-exempt interest									0.60%	0.80%	0.90%
Current state and local income taxes, net of federal income tax deduction									0.50%	0.30%	0.10%
Other									0.30%	0.30%	0.20%
Actual tax expense and rate									32.20%	31.20%	30.50%

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, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Deferred tax assets:
Loss reserve discount	$24,820	$27,822
Unearned premiums	29,080	25,706
Compensation related	10,586	6,782
State and local net deferred tax assets	777	555
Other	1,834	3,889
Total gross deferred tax assets	67,097	64,754
Less: Valuation allowance	-777	-555
Total deferred tax assets	66,320	64,199
Deferred tax liabilities:
Net unrealized gains/losses on securities	-24,832	-9,119
Deferred acquisition costs	-22,120	-19,258
Net unrealized foreign exchange	-4,470	-3,516
Other	-2,787	-4,119
Total deferred tax liabilities	-67,787	-40,393
Net deferred income tax (liability)	-1,467
Net deferred income tax asset		23,806
Lloyd's
Deferred tax liabilities:
Lloyd's year of account deferral	($13,578)	($4,381)

Credit_Facilities_Additional_I

Credit Facilities - Additional Information (Detail)	12 Months Ended			12 Months Ended			0 Months Ended		0 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Mar. 28, 2011	Dec. 31, 2014	Dec. 31, 2014	Nov. 06, 2014	Nov. 06, 2014	Nov. 06, 2014	Dec. 31, 2014	Nov. 22, 2012	Nov. 22, 2012
		USD ($)	Line of Credit	Syndicate 1221	Syndicate 1221	Syndicate 1221	Syndicate 1221	Syndicate 1221	Amended and Restated Credit Agreement	Amended and Restated Credit Agreement
			USD ($)		AUD	GBP (£)	Above Floating Rate	Lloyd's		USD ($)
							Line of Credit	USD ($)
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing amount					8
Line of credit facility, underwriting reserve required						75
Line of credit facility, covenant compliance	The Company was in compliance with all covenants under the credit facility as of December 31, 2014 and the Company had $1.0 million of cash collateral posted.			As of December 31, 2014, our Company was in compliance with all covenants.
Line of credit facility, interest rate							2.00%
Line of credit facility		175								165
Issuance of new letters of credit, expiry date									31-Dec-16
Aggregate face amount of letters of credit outstanding								149.4
Cash collateral posted			$1					$1
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.

Senior_Notes_Additional_Inform

Senior Notes - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended			0 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 04, 2013
Debt Instrument [Line Items]
Interest rate stated on senior notes	7.00%								7.00%
Senior notes due date									1-May-16
Call premium on redemption of Senior Notes					($17,895,000)					($17,895,000)
Interest expense	3,854,000	3,388,000	4,319,000	3,852,000	4,351,000	2,053,000	2,052,000	2,051,000	15,413,000	10,507,000	8,198,000
Senior Notes
Debt Instrument [Line Items]
Unamortized discount	1,600,000				1,700,000				1,600,000	1,700,000
Interest expense										10,500,000
Senior Notes | 5.75% Senior Notes
Debt Instrument [Line Items]
Principal amount of senior notes												265,000,000
Interest rate stated on senior notes												5.75%
Senior notes due date									15-Oct-23
Net proceeds from issuance of senior notes												263,000,000
Outstanding principal amount of senior notes	263,400,000				263,300,000				263,400,000	263,300,000
Fair value of senior notes	285,700,000				277,600,000				285,700,000	277,600,000
Effective interest rate related to senior notes	5.86%								5.86%
Interest expense									15,400,000
Debt instrument, covenant compliance									As of December 31, 2014, our Company was in compliance with all such covenants.
Senior Notes | 5.75% Senior Notes | Semi Annual Payment, First Payment
Debt Instrument [Line Items]
Interest payment date on senior notes									-11
Senior Notes | 5.75% Senior Notes | Semi Annual Payment, Second Payment
Debt Instrument [Line Items]
Interest payment date on senior notes									-5
Senior Notes | 7.0% Senior Notes
Debt Instrument [Line Items]
Interest rate stated on senior notes	7.00%								7.00%
Senior notes due date									1-May-16
Call premium on redemption of Senior Notes												17,900,000
Interest expense on senior notes											$8,200,000

Lloyds_Syndicate_1221_Addition

Lloyd's Syndicate 1221 - Additional Information (Detail) (Lloyd's, Syndicate 1221)	3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012
	USD ($)	USD ($)	GBP (£)	USD ($)	GBP (£)
Supplementary Insurance Information, by Segment [Line Items]
Syndicate 1221's stamp capacity		$336.90	£ 215	$323.70	£ 195
Percentage control of stamp capacity		100.00%	100.00%	100.00%	100.00%	100.00%
Pre-tax gain in connection with a change in functional currency	10
After-tax gain in connection with a change in functional currency	$6.60

Commitments_and_Contingencies_1

Commitments and Contingencies - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Loss Contingencies [Line Items]
Rent expense	$13.20	$11.50	$10.50
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	1.1	0.3
Incentive awarded to the company by the State of Connecticut, deferred revenue	$6.10	$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, 2014
In Thousands, unless otherwise specified
Operating Leased Assets [Line Items]
2015	$11,245
2016	9,234
2017	7,942
2018	6,907
2019	4,258
Thereafter	12,811
Total minimum operating lease payments	$52,397

Share_Capital_and_Share_Repurc

Share Capital and Share Repurchases - Additional Information (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
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

Changes_in_Issued_and_Outstand

Changes in Issued and Outstanding Common Shares (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Beginning balance	14,198,000	14,047,000	13,956,000
Vested stock grants	59,000	50,000	60,000
Employee stock purchase plan	19,386	17,000	16,000
Stock options exercised	5,250	83,500	15,000
Treasury shares purchased	0	0	0
Ending balance	14,281,000	14,198,000	14,047,000

Amount_and_Nature_of_Net_Asset

Amount and Nature of Net Assets Restricted from Payment of Dividends (Detail) (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Thousands, unless otherwise specified
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	$523,425		$520,886
Insurance Companies
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	13,234	[1]	12,605	[1]
Insurance Companies | Fixed maturities
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	11,732		11,105
Insurance Companies | Short-term investments
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	290		290
Insurance Companies | Cash
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	1,212		1,210
Lloyd's
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	510,191	[2]	508,281	[2]
Lloyd's | Fixed maturities
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	447,679		398,808
Lloyd's | Short-term investments
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	61,549		108,485
Lloyd's | Cash
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	$963		$988
[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, 2014 and 2013, 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, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Insurance Companies
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Restricted net assets, amortized cost	$10,086	$9,730
Lloyd's
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Restricted net assets, amortized cost	$445,504	$398,930

Dividends_and_Statutory_Financ2

Dividends and Statutory Financial Information - Additional Information (Detail)

1 Months Ended

12 Months Ended

12 Months Ended

Nov. 30, 2013

Nov. 30, 2013

Dec. 31, 2014

Dec. 31, 2014

Dec. 31, 2012

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2014

Dec. 31, 2014

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2014

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

USD ($)

GBP (£)

USD ($)

GBP (£)

Navigators Insurance Company

Navigators Insurance Company

Navigators Insurance Company

Insurance Companies

Insurance Companies

Insurance Companies

Insurance Companies

Insurance Companies

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 ($)

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

$89,400,000

Dividends paid to Parent Company

15,000,000

Statutory net income

75,700,000

59,400,000

28,600,000

Statutory capital and surplus

893,900,000

804,100,000

140,100,000

124,200,000

89,400,000

74,800,000

Risk based capital ratio

314.80%

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 2014 and 2013

268,100,000

279,300,000

171,100,000

168,300,000

Valuation of assets and letters of credit posted

290,100,000

185,100,000

280,200,000

168,800,000

Pre-tax regulatory income

33,800,000

21,000,000

54,900,000

Percentage control of stamp capacity

100.00%

100.00%

100.00%

100.00%

100.00%

Undistributed Profit

139,900,000

89,300,000

Dividend Capacity

$9,900,000

£ 6,300,000

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
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2005	Apr. 30, 2013	Apr. 30, 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance based shares that vested	183,716	133,482	138,321
Fair value of total vested shares	$5,100,000	$3,500,000	$4,600,000
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	9,509
Employee Stock Purchase Plan, shares purchased by employees	19,386	17,000	16,000
Discount on employee stock purchase plan	10.00%
Performance Based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance based shares that vested	0	15,714	0
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options expiration term (in years)	10 years
Options and Non Performance Based Grants | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award, award vesting period	3 years
Options and Non Performance Based Grants | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award, award vesting period	4 years
Non Performance Based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award, award vesting period	5 years
Performance based shares that vested	90,263	60,183	91,323
Non Performance Based Shares | Year Three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	33.33%
Non Performance Based Shares | Year Four
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	33.33%
Non Performance Based Shares | Year Five
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	33.33%
Performance Based Shares Issued in 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of remaining shares vesting over the period dependent on compound annual growth book value per share immediately prior to vesting date	100.00%
Performance Based Shares Issued in 2014 | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	50.00%
Performance Based Shares Issued in 2014 | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	150.00%
Performance Based Shares Issued Between 2011-2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	50.00%
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 Issued Between 2011-2013 | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	0.00%
Performance Based Shares Issued Between 2011-2013 | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	150.00%
Performance Based Shares Issued Prior to 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award, award vesting period	5 years
Performance Based Shares Issued Prior to 2011 | Year Three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	33.33%
Performance Based Shares Issued Prior to 2011 | Year Four
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	33.33%
Performance Based Shares Issued Prior to 2011 | Year Five
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	33.33%
Performance Based Shares Issued Prior to 2011 | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	0.00%
Performance Based Shares Issued Prior to 2011 | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	150.00%
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value of all RSU granted	$60.75	$55.36	$48.21
Unrecognized compensation expense, net of estimated forfeitures	16,300,000	10,600,000
Weighted Average Periods	2 years 3 months 18 days	2 years 3 months 12 days
Aggregate fair value of all unvested RSU	$46,100,000	$39,600,000
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price as percentage of fair market value	90.00%
2005 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock authorized for issuance				1,000,000
Amended And Restated 2005 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock authorized for issuance					2,000,000	1,500,000
Stock issued during period under incentive plan	1,523,228
Number of stock available to be issued	476,772

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, 2014		Dec. 31, 2013		Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation	$12,121		$3,914		$7,852
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation	11,507		3,369		7,380
Directors restricted stock grants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation	420	[1]	413	[1]	390	[1]
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation	$194		$132		$82
[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.

Unvested_Restricted_Stock_Gran

Unvested Restricted Stock Grants Outstanding (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance	626,812	587,629	526,972
Granted	288,130	269,926	244,060
Vested	-183,716	-133,482	-138,321
Forfeited	-12,334	-97,261	-45,082
Ending balance	718,892	626,812	587,629
Performance Based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	228,607	114,463	97,145
Performance Based Shares | Earned
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested		-15,714
Performance Based Shares | Unearned
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested	-93,453	-57,585	-46,998
Non Performance Based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	59,523	155,463	146,915
Vested	-90,263	-60,183	-91,323

Stock_Options_Outstanding_Deta

Stock Options Outstanding (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Number of Shares
Beginning balance	6,750	90,250	105,250
Granted	0	0	0
Exercised	-5,250	-83,500	-15,000
Expired or forfeited	0	0	0
Ending balance	1,500	6,750	90,250
Number of options exercisable	1,500	6,750	90,250
Average Exercise Price
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Beginning of Period	$30.65	$29.94	$29.50
Granted	$0	$0	$0
Exercised	$29.11	$29.88	$26.90
Expired or forfeited	$0	$0	$0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, End of Period	$36.03	$30.65	$29.94
Number of options exercisable	$36.03	$30.65	$29.94

Summarized_Information_about_O

Summarized Information about Options Outstanding (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding Options	1,500
Average Remaining Contract Life	8 months 12 days
Exercisable Options	1,500
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	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

Retirement_Plans_Additional_In

Retirement Plans - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
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	3.00%	2.00%	0.00%
Defined Contribution Plan, employer discretionary matching contribution amount	$1.60	$0.80	$0
401(k) plan expense	7.5	5.1	4.6
Retirement Savings Contributions
Employee Benefits Disclosure [Line Items]
401(k) plan expense	3.8	2.7	2.5
Non Discretionary Matching Contributions
Employee Benefits Disclosure [Line Items]
401(k) plan expense	2.1	1.6	2.1
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 Kingdom
Employee Benefits Disclosure [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	15.00%
401(k) plan expense	$2.60	$2.20	$1.90

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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Gross written premiums	$333,299	$327,469	$348,795	$422,790	$333,091	$312,076	$332,128	$393,222	$1,432,353	$1,370,517	$1,286,465
Revenues:
Net written premiums	228,007	228,417	231,864	311,850	223,445	196,556	198,469	269,452	1,000,138	887,922	833,655
Change in unearned premiums	6,165	16,950	-780	-86,578	-3,543	17,339	7,345	-67,124	-64,243	-45,983	-51,691
Net earned premiums	234,172	245,367	231,084	225,272	219,902	213,895	205,814	202,328	935,895	841,939	781,964
Net investment income	16,071	15,839	15,648	16,610	14,254	14,094	14,246	13,657	64,168	56,251	54,248
Total other-than-temporary impairment losses	-21	158			-530	-1,821		-42	137	-2,393	-902
Portion of loss recognized in other comprehensive income (before tax)	21	-158							-137		44
Net other-than-temporary impairment losses recognized in earnings					-530	-1,821		-42		-2,393	-858
Net realized gains (losses)	788	6,718	4,473	833	15,768	-988	3,345	4,814	12,812	22,939	41,074
Other income (expense)	586	1,336	-1,665	10,399	-665	-210	-915	618	10,656	-1,172	1,488
Total revenues	251,617	269,260	249,540	253,114	248,729	224,970	222,490	221,375	1,023,531	917,564	877,916
Expenses:
Net losses and loss adjustment expenses	134,658	135,284	140,220	135,067	131,385	125,086	131,148	131,342	545,229	518,961	497,433
Commission expenses	33,708	33,943	32,150	25,727	30,863	27,685	28,391	26,555	125,528	113,494	121,470
Other operating expenses	51,299	50,388	47,992	47,146	43,826	39,056	40,678	40,874	196,825	164,434	159,079
Call premium on Senior Notes					17,895					17,895
Interest expense	3,854	3,388	4,319	3,852	4,351	2,053	2,052	2,051	15,413	10,507	8,198
Total expenses	223,519	223,003	224,681	211,792	228,320	193,880	202,269	200,822	882,995	825,291	786,180
Income before income taxes	28,098	46,257	24,859	41,322	20,409	31,090	20,221	20,553	140,536	92,273	91,736
Income tax expense	8,823	15,032	7,998	13,354	6,076	9,804	6,284	6,643	45,207	28,807	27,974
Net income	19,275	31,225	16,861	27,968	14,333	21,286	13,937	13,910	95,329	63,466	63,762
Comprehensive income (loss)	$27,015	$20,628	$32,965	$32,920	$1,200	$25,462	($24,829)	$14,785	$113,528	$16,618	$68,722
Combined ratio	93.80%	89.50%	95.30%	92.20%	94.00%	89.80%	97.70%	97.90%	92.60%	94.80%	99.30%
Net income (loss) per share:
Basic	$1.35	$2.19	$1.18	$1.96	$1.01	$1.50	$0.99	$0.99	$6.69	$4.49	$4.54
Diluted	$1.31	$2.14	$1.17	$1.94	$1	$1.48	$0.97	$0.97	$6.51	$4.42	$4.45

Summary_of_Consolidated_Invest1

Summary of Consolidated Investments-Other Than Investments in Related Parties (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash	$2,550,229	$2,191,827
Total investments and cash	2,820,486
Gross Unrealized Gains	83,078	69,554
Gross Unrealized Losses	-11,672	-33,530
Amortized Cost	2,749,080	2,538,562
Short-term investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash	179,506
Gross Unrealized Losses	-21
Amortized Cost	179,527	296,250
Cash
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash	90,751
Amortized Cost	90,751	86,509
Fixed maturities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash	2,365,934	2,047,873
Gross Unrealized Gains	52,322	43,854
Gross Unrealized Losses	-10,347	-32,980
Amortized Cost	2,323,959	2,036,999
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	397,923	441,685
Gross Unrealized Gains	3,431	2,854
Gross Unrealized Losses	-5,965	-8,855
Amortized Cost	400,457	447,686
Fixed maturities | States, municipalities and political subdivisions
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash	541,007	460,422
Gross Unrealized Gains	19,204	9,298
Gross Unrealized Losses	-558	-13,651
Amortized Cost	522,361	464,775
Fixed maturities | Agency mortgage-backed securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash	364,622	301,274
Gross Unrealized Gains	8,476	6,779
Gross Unrealized Losses	-998	-6,016
Amortized Cost	357,144	300,511
Fixed maturities | Residential Mortgage Backed Securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash	34,087	41,755
Gross Unrealized Gains	1,153	1,212
Gross Unrealized Losses	-138	-161
Amortized Cost	33,072	40,704
Fixed maturities | Asset-backed securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash	206,413	125,133
Gross Unrealized Gains	380	653
Gross Unrealized Losses	-964	-480
Amortized Cost	206,997	124,960
Fixed maturities | Commercial mortgage-backed securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash	206,318	172,750
Gross Unrealized Gains	6,630	7,656
Gross Unrealized Losses	-98	-374
Amortized Cost	199,786	165,468
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	811,440	640,912
Gross Unrealized Gains	16,639	16,300
Gross Unrealized Losses	-2,198	-7,031
Amortized Cost	796,999	631,643
Fixed maturities | Corporate bonds
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash	615,564	504,854
Gross Unrealized Gains	13,048	15,402
Gross Unrealized Losses	-1,626	-3,443
Amortized Cost	604,142	492,895
Equity Securities | Common Stock
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash	127,183	143,954
Gross Unrealized Gains	28,520	25,700
Gross Unrealized Losses	-1,254	-550
Amortized Cost	99,917	118,804
Equity Securities | Preferred Stock
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash	57,112
Gross Unrealized Gains	2,236
Gross Unrealized Losses	-50
Amortized Cost	$54,926

Condensed_Financial_Informatio1

Condensed Financial Information - Balance Sheets (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
ASSETS
Cash and investments	$2,820,486	$2,574,586
Goodwill and other intangible assets	7,013	7,177
Other assets	44,384	35,039
Total assets	4,464,176	4,169,452	4,007,670
LIABILITIES AND STOCKHOLDERS' EQUITY
Senior Notes	263,440	263,308
Accounts payable and other liabilities	93,336	69,379
Total liabilities	3,436,952	3,267,240
Preferred stock, $.10 par value, authorized 1,000,000 shares, none issued
Common stock, $.10 par value, authorized 50,000,000 shares, issued 17,792,846 shares for 2014 and 17,709,876 shares for 2013	1,778	1,770
Additional paid-in capital	347,022	335,546
Treasury stock, at cost (3,511,380 shares for 2014 and 2013)	-155,801	-155,801
Retained earnings	787,666	692,337
Accumulated other comprehensive income:
Total stockholders' equity	1,027,224	902,212	879,485	803,435
Total liabilities and stockholders' equity	4,464,176	4,169,452
Parent Company
ASSETS
Cash and investments	101,032	100,676
Investments in subsidiaries	1,163,822	1,040,214
Goodwill and other intangible assets	2,534	2,534
Other assets	27,531	26,538
Total assets	1,294,919	1,169,962
LIABILITIES AND STOCKHOLDERS' EQUITY
Senior Notes	263,440	263,308
Accounts payable and other liabilities	1,081	802
Accrued interest payable	3,174	3,640
Total liabilities	267,695	267,750
Preferred stock, $.10 par value, authorized 1,000,000 shares, none issued
Common stock, $.10 par value, authorized 50,000,000 shares, issued 17,792,846 shares for 2014 and 17,709,876 shares for 2013	1,778	1,770
Additional paid-in capital	347,022	335,546
Treasury stock, at cost (3,511,380 shares for 2014 and 2013)	-155,801	-155,801
Retained earnings	787,666	692,337
Accumulated other comprehensive income:
Net unrealized gains (losses) on securities available-for-sale, net of tax	46,573	23,387
Foreign currency translation adjustment, net of tax	-14	4,973
Total stockholders' equity	1,027,224	902,212
Total liabilities and stockholders' equity	$1,294,919	$1,169,962

Condensed_Financial_Informatio2

Condensed Financial Information - Balance Sheets (Parenthetical) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
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	17,792,846	17,709,876
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	17,792,846	17,709,876
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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues:
Net investment income	$16,071	$15,839	$15,648	$16,610	$14,254	$14,094	$14,246	$13,657	$64,168	$56,251	$54,248
Total revenues	251,617	269,260	249,540	253,114	248,729	224,970	222,490	221,375	1,023,531	917,564	877,916
Expenses:
Call premium on Senior Notes					17,895					17,895
Interest expense	3,854	3,388	4,319	3,852	4,351	2,053	2,052	2,051	15,413	10,507	8,198
Other (income) expense	-586	-1,336	1,665	-10,399	665	210	915	-618	-10,656	1,172	-1,488
Total expenses	223,519	223,003	224,681	211,792	228,320	193,880	202,269	200,822	882,995	825,291	786,180
Income (loss) before income tax benefit	28,098	46,257	24,859	41,322	20,409	31,090	20,221	20,553	140,536	92,273	91,736
Income tax benefit	8,823	15,032	7,998	13,354	6,076	9,804	6,284	6,643	45,207	28,807	27,974
Net income	19,275	31,225	16,861	27,968	14,333	21,286	13,937	13,910	95,329	63,466	63,762
Parent Company
Revenues:
Net investment income									76	13	341
Dividends received from wholly-owned subsidiaries											15,000
Total revenues									76	13	15,341
Expenses:
Call premium on Senior Notes										17,895
Interest expense									15,413	10,507	8,198
Other (income) expense										2	1,749
Total expenses									15,413	28,404	9,947
Income (loss) before income tax benefit									-15,337	-28,391	5,394
Income tax benefit									-5,287	-9,886	-3,332
Income (loss) before equity in undistributed net income of wholly owned subsidiaries									-10,050	-18,505	8,726
Equity in undistributed net income of wholly-owned subsidiaries									105,379	81,971	55,036
Net income									$95,329	$63,466	$63,762

Condensed_Financial_Informatio4

Condensed Financial Information - Statement of Cash Flows (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating activities:
Net income	$95,329	$63,466	$63,762
Adjustments to reconcile net income to net cash provided by (used in) operations:
Call premium on redemption of Senior Notes		17,895
Other	29,039	31,987	36,503
Net cash provided by (used in) operating activities	222,492	136,875	96,739
Fixed maturities, available-for-sale
Sales	362,136	648,335	1,319,404
Purchases	-864,902	-899,930	-1,711,080
Equity securities
Sales	54,900	72,113	39,503
Purchases	-83,845	-89,288	-37,587
Net increase in short-term investments	117,740	-142,214	-31,568
Net cash provided by (used in) investing activities	-219,470	-229,859	-179,839
Financing activities:
Net Proceeds from Debt Offering		263,278
Redemption of 7.0% Senior Notes Due May 1, 2016		-132,437
Proceeds of stock issued from employee stock purchase plan	1,067	821	672
Proceeds of stock issued from exercise of stock options	153	2,495	404
Net cash provided by (used in) financing activities	1,220	134,157	1,076
Cash at beginning of year	86,509	45,336	127,360
Cash at end of period	90,751	86,509	45,336
Parent Company
Operating activities:
Net income	95,329	63,466	63,762
Adjustments to reconcile net income to net cash provided by (used in) operations:
Equity in undistributed net income of wholly-owned subsidiaries	-105,379	-81,971	-70,036
Dividends received from subsidiaries			15,000
Call premium on redemption of Senior Notes		17,895
Other	9,211	2,098	-3,265
Net cash provided by (used in) operating activities	-839	1,488	5,461
Fixed maturities, available-for-sale
Sales	3,200	8,754	7,986
Purchases		-1,249	-14,700
Equity securities
Sales	0	0	0
Purchases	0	0	0
Net increase in short-term investments	-3,424	-89,988	-167
Net cash provided by (used in) investing activities	-224	-82,483	-6,881
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	0	0	0
Proceeds of stock issued from employee stock purchase plan	1,067	821	672
Proceeds of stock issued from exercise of stock options	153	2,495	404
Net cash provided by (used in) financing activities	1,220	84,157	1,076
Increase (decrease) in cash	157	3,162	-344
Cash at beginning of year	6,143	2,981	3,325
Cash at end of period	$6,300	$6,143	$2,981

Condensed_Financial_Informatio5

Condensed Financial Information - Statement of Cash Flows (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2014
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, 2014		Dec. 31, 2013		Dec. 31, 2012
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	$79,452		$67,007		$61,005
Reserve for losses and loss adjustment expenses	2,159,634		2,045,071		2,097,048
Unearned Premiums	766,167		714,606		642,407
Other policy claims and benefits payable	0		0		0
Net earned premiums	935,895		841,939		781,964
Net investment income	64,092	[1]	56,243	[1]	54,100	[1]
Losses and loss adjustment expenses incurred	545,229		518,961		497,433
Amortization of deferred policy acquisition costs	127,695	[2]	115,842	[2]	123,819	[2]
Other operating expenses	196,825	[1]	164,434	[1]	159,079	[1]
Net written premiums	1,000,138		887,922		833,655
Insurance Companies
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	63,200		54,984		48,294
Reserve for losses and loss adjustment expenses	1,645,984		1,523,175		1,567,045
Unearned Premiums	579,331		536,303		470,425
Other policy claims and benefits payable	0		0		0
Net earned premiums	704,574		639,338		571,439
Net investment income	56,714	[1]	49,083	[1]	46,549	[1]
Losses and loss adjustment expenses incurred	434,396		415,413		417,082
Amortization of deferred policy acquisition costs	85,137	[2]	81,132	[2]	81,370	[2]
Other operating expenses	138,675	[1]	119,920	[1]	113,625	[1]
Net written premiums	752,773		680,008		622,956
Lloyd's
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	16,252		12,023		12,711
Reserve for losses and loss adjustment expenses	513,650		521,896		530,003
Unearned Premiums	186,836		178,303		171,982
Other policy claims and benefits payable	0		0		0
Net earned premiums	231,321		202,601		210,525
Net investment income	7,378	[1]	7,160	[1]	7,551	[1]
Losses and loss adjustment expenses incurred	110,833		103,548		80,351
Amortization of deferred policy acquisition costs	42,558	[2]	34,710	[2]	42,449	[2]
Other operating expenses	58,150	[1]	44,514	[1]	45,454	[1]
Net written premiums	$247,365		$207,914		$210,699
[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_Written_Premium_De

Reinsurance Written Premium (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplementary Insurance Information, by Segment [Line Items]
Direct Amount									$1,133,336	$1,069,677	$972,844
Ceded to other companies									440,656	455,985	396,639
Assumed from other companies									243,215	228,247	205,759
Net earned premiums	234,172	245,367	231,084	225,272	219,902	213,895	205,814	202,328	935,895	841,939	781,964
Property Casualty
Supplementary Insurance Information, by Segment [Line Items]
Direct Amount									1,184,538	1,127,331	1,034,658
Ceded to other companies									432,214	482,596	452,810
Assumed from other companies									247,814	243,187	251,807
Net earned premiums									$1,000,138	$887,922	$833,655
Percentage of amount assumed to net									25.00%	27.00%	30.00%

Valuation_and_Qualifying_Accou1

Valuation and Qualifying Accounts (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
Allowance for uncollectable reinsurance
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at January 1, 2014	$11,332
Charged to Other Accounts	0
Deductions (Describe)	0
Balance at December 31, 2014	11,332
Valuation allowance in deferred taxes
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at January 1, 2014	554
Charged (Credited) to Costs and Expenses	222
Charged to Other Accounts	0
Deductions (Describe)	0
Balance at December 31, 2014	$776

Supplementary_Information_Conc1

Supplementary Information Concerning Property-Casualty Insurance Operations (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred policy acquisition costs	$79,452		$67,007		$61,005
Reserve for losses and loss adjustment expenses	2,159,634		2,045,071		2,097,048
Discount, if any, deducted	0		0		0
Unearned premiums	766,167		714,606		642,407
Net earned premiums	935,895		841,939		781,964
Net investment income	64,092	[1]	56,243	[1]	54,100	[1]
Losses and loss adjustment expenses incurred related to Current year	601,041		520,227		542,724
Increase (decrease) in estimated losses and LAE for claims occurring in prior years	-55,812		-1,266		-45,291
Amortization of deferred policy acquisition costs	127,695	[2]	115,842	[2]	123,819	[2]
Other operating expenses	196,825	[1]	164,434	[1]	159,079	[1]
Net written premiums	$1,000,138		$887,922		$833,655
[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.