Navigators (NAVG) 10-Q 8 May 15 2015 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2015	1-May-15
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	FALSE
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Trading Symbol	NAVG
Entity Registrant Name	NAVIGATORS GROUP INC
Entity Central Index Key	793547
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		14,394,985

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Investments and cash:
Fixed maturities, available-for-sale, at fair value (amortized cost: 2015, $2,294,763; 2014, $2,323,959)	$2,345,225	$2,365,934
Equity securities, available-for-sale, at fair value (cost: 2015, $133,968; 2014, $154,843)	159,044	184,295
Short-term investments, at fair value (amortized cost: 2015: $243,730; 2014: $179,527)	242,553	179,506
Cash	90,016	90,751
Total investments and cash	2,836,838	2,820,486
Premiums receivable	396,357	342,479
Prepaid reinsurance premiums	244,599	237,851
Reinsurance recoverable on paid losses	55,990	51,347
Reinsurance recoverable on unpaid losses and loss adjustment expenses	828,799	851,498
Deferred policy acquisition costs	86,221	79,452
Accrued investment income	14,685	14,791
Goodwill and other intangible assets	6,785	7,013
Current income tax receivable, net	5,869	14,549
Receivable for investments sold	19	326
Other assets	42,663	44,384
Total assets	4,518,825	4,464,176
Liabilities:
Reserves for losses and loss adjustment expenses	2,141,705	2,159,634
Unearned premiums	825,740	766,167
Reinsurance balances payable	153,980	152,774
Senior notes	263,474	263,440
Deferred income tax, net	2,325	1,467
Payable for investments purchased	15,392	134
Accounts payable and other liabilities	62,606	93,336
Total liabilities	3,465,222	3,436,952
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 17,903,198 shares for 2015 and 17,792,846 shares for 2014	1,789	1,778
Additional paid-in capital	346,338	347,022
Treasury stock, at cost (3,511,380 shares for 2015 and 2014)	-155,801	-155,801
Retained earnings	813,595	787,666
Accumulated other comprehensive income	47,682	46,559
Total stockholders' equity	1,053,603	1,027,224
Total liabilities and stockholders' equity	$4,518,825	$4,464,176

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, except Share data, unless otherwise specified
Fixed maturities, available-for-sale, amortized cost	$2,294,763	$2,323,959
Equity securities, available-for-sale, cost	133,968	154,843
Short-term investments, amortized cost	$243,730	$179,527
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	17,903,198	17,792,846
Treasury stock, shares	3,511,380	3,511,380

Consolidated_Statements_of_Inc

Consolidated Statements of Income (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Gross written premiums	$396,460	$422,790
Revenues:
Net written premiums	288,958	311,850
Change in unearned premiums	-52,826	-86,578
Net earned premiums	236,132	225,272
Net investment income	16,253	16,610
Net realized gains (losses)	5,596	833
Other income (expense)	2,242	10,399
Total revenues	260,223	253,114
Expenses:
Net losses and loss adjustment expenses	130,198	135,067
Commission expenses	32,905	25,727
Other operating expenses	54,909	47,146
Interest expense	3,855	3,852
Total expenses	221,867	211,792
Income before income taxes	38,356	41,322
Income tax expense	12,427	13,354
Net income	$25,929	$27,968
Net income per common share:
Basic	$1.81	$1.96
Diluted	$1.77	$1.94
Average common shares outstanding:
Basic	14,327,606	14,233,504
Diluted	14,637,837	14,408,416

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Net income (loss)	$25,929	$27,968
Change in net unrealized gains (losses) on investments:
Unrealized gains (losses) on investments arising during the period, net of deferred tax of $1,723 and $7,010 in 2015 and 2014, respectively	3,201	13,314
Reclassification adjustment for net realized (gains) losses included in net income net of deferred tax of $698 and $366 in 2015 and 2014, respectively	-1,297	-679
Change in net unrealized gains (losses) on investments	1,904	12,635
Change in other-than-temporary impairments:
Non credit other-than-temporary impairments arising during the period, net of deferred tax of $8 and $31 in 2015 and 2014, respectively	15	56
Reclassification adjustment for non credit other-than-temporary impairment losses recognized in net income net of deferred tax of $0 in 2015 and 2014, respectively	0	0
Change in other-than-temporary impairments	15	56
Change in foreign currency translation gains (losses), net of deferred tax of $429 and $3,584 in 2015 and 2014, respectively	-796	-7,739
Other comprehensive income	1,123	4,952
Comprehensive income	$27,052	$32,920

Consolidated_Statements_of_Com1

Consolidated Statements of Comprehensive Income (Parenthetical) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Unrealized gains (losses) on investments arising during the period, deferred tax	$1,723	$7,010
Reclassification adjustment for net realized (gains) losses included in net income, deferred tax	698	366
Non credit other-than-temporary impairments arising during the period, deferred tax	8	-31
Reclassification adjustment for non credit other-than-temporary impairment losses recognized in net income, deferred tax	0	0
Change in foreign currency translation gains (losses), deferred tax	$429	$3,584

Consolidated_Statement_of_Stoc

Consolidated Statement 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, 2014	$1,027,224	$1,778	$347,022	($155,801)	$787,666	$46,559
Beginning balance (in shares) at Dec. 31, 2014		17,792,846		3,511,380
Net income	25,929				25,929
Changes in other comprehensive income:
Change in net unrealized gain (loss) on investments	1,904					1,904
Change in net non-credit other- than-temporary impairment losses	15					15
Change in foreign currency translation gain (loss)	-796					-796
Total other comprehensive income	1,123					1,123
Shares issued under stock plan (in shares)		110,352
Shares issued under stock plan	-4,147	11	-4,158
Share-based compensation	3,474		3,474
Ending balance at Mar. 31, 2015	$1,053,603	$1,789	$346,338	($155,801)	$813,595	$47,682
Ending balance (in shares) at Mar. 31, 2015		17,903,198		3,511,380

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Operating activities:
Net income	$25,929	$27,968
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation & amortization	1,051	1,184
Deferred income taxes	865	-106
Net realized (gains) losses	-5,596	-833
Changes in assets and liabilities:
Reinsurance recoverable on paid and unpaid losses and loss adjustment expenses	18,056	-11,869
Reserves for losses and loss adjustment expenses	-17,930	42,400
Prepaid reinsurance premiums	-6,374	2,051
Unearned premiums	60,393	86,063
Premiums receivable	-53,878	-91,650
Deferred policy acquisition costs	-6,769	-12,327
Accrued investment income	106	-355
Reinsurance balances payable	1,445	-22,476
Current income tax payable, net	9,388	6,714
Accounts payable	-31,229	-11,224
Other	-372	-6,698
Net cash provided by (used in) operating activities	-4,915	8,842
Fixed maturities
Redemptions and maturities	37,241	50,542
Sales	119,505	107,681
Purchases	-130,196	-259,494
Equity securities
Sales	38,343	7,935
Purchases	-12,320	-25,473
Change in payable for securities	15,565	-7,469
Net change in short-term investments	-63,168	88,353
Purchase of property and equipment	-790	-2,991
Net cash provided by (used in) investing activities	4,180	-40,916
Financing activities:
Proceeds of stock issued from employee stock purchase plan		453
Proceeds of stock issued from exercise of stock options		153
Net cash provided by financing activities		606
Decrease in cash	-735	-31,468
Cash at beginning of year	90,751	86,509
Cash at end of period	90,016	55,041
Supplemental cash information:
Income taxes paid, net	1,793	3,628
Issuance of stock to directors	$563	$438

Organization_and_Summary_of_Si

Organization and Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2015
Organization and Summary of Significant Accounting Policies	Note 1.	Organization and Summary of Significant Accounting Policies
	Basis of Presentation
	The accompanying interim consolidated financial statements are unaudited and reflect all adjustments which, in the opinion of management, are necessary to fairly present the results of The Navigators Group, Inc. and its subsidiaries for the interim periods presented on the basis of United States generally accepted accounting principles (“GAAP” or “U.S. GAAP”). All significant intercompany transactions and balances have been eliminated in consolidation. The preparation of these 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 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 interim consolidated financial statements should be read in conjunction with our Annual Report on Form 10-K for the year ended December 31, 2014. Certain amounts for the prior year have been reclassified to conform with the current period presentation. Unless the context requires otherwise, the terms “we,” “us,” “our,” or “our Company” are used to mean The Navigators Group, Inc., a Delaware holding company established in 1982, and its subsidiaries. The terms “Parent” or “Parent Company” are used to mean The Navigators Group, Inc. without its subsidiaries.
	Organization
	We are an international insurance company with a long-standing area of specialization in Marine insurance. Our Property and Casualty (“P&C”) insurance business primarily offers General Liability coverage and Umbrella & Excess Liability coverage to commercial enterprises through our Primary and Excess Casualty divisions. We have also developed niches in Professional Liability insurance, through our Management Liability and Errors and Omissions divisions. Beginning in 2010, we added reinsurance products through our Assumed Reinsurance division.
	We operate through various wholly-owned subsidiaries, including Navigators Insurance Company, inclusive of its United Kingdom Branch (“U.K. Branch”), and Navigators Specialty Insurance Company, both of which are U.S. insurance companies, and Navigators Underwriting Agency Ltd., a Lloyd’s of London (“Lloyd’s”) underwriting agency that manages Lloyd’s Syndicate 1221 (“the Syndicate”) in the U.K. The Company controls 100% of the Syndicate’s stamp capacity.
	Foreign Exchange Remeasurement and Translation
	During the first quarter of 2014, the Syndicate 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 remeasurement has resulted in an immaterial correction of $10.0 million ($6.6 million after-tax) in Accumulated other comprehensive income (“AOCI”), on the Consolidated Balance Sheets, offset by a gain in Other income in the Consolidated Statements of Income.
	Catastrophe Risk Management
	We have exposure to losses caused by hurricanes, earthquakes, and other natural and man-made catastrophic events. The frequency and severity of catastrophic events is unpredictable. The extent of covered losses from a catastrophe is a function of both the total amount of insured exposure in an area affected by the event and the severity of the event. We had no material catastrophic events occur in the first quarter 2015.
	Income Taxes
	The income tax provision has been computed based on our estimated annual effective tax rate. Our effective tax rate for the quarter differs from the federal tax rate of 35% principally because of tax-exempt investment income and dividends received deduction.
	Current and Pending Accounting Pronouncements
	As of January 1, 2015, we did not adopt any new accounting pronouncements. In April 2015, the Financial Accounting Standards Board issued a new pronouncement, Accounting Standards Update 2015-03 – Interest – Imputation of Interest (Subtopic 835-30) – Simplifying the Presentation of Debt Issuance Costs, which will be effective for fiscal years beginning after December 15, 2015. The new pronouncement was issued to simplify presentation of debt issuance costs. We are assessing the future impact of this update to our Consolidated Financial Statements. There were no additional pending accounting pronouncements that are expected to have a significant impact on the consolidated financial statements upon adoption.

Segment_Information

Segment Information	3 Months Ended
	Mar. 31, 2015
Segment Information	Note 2.	Segment Information
	During the first quarter of 2015, we realigned our reporting segments from Insurance Companies, Lloyd’s Operations and Corporate to U.S. Insurance, International Insurance (“Int’l Insurance”), Global Reinsurance (“GlobalRe”) and Corporate. The new segment presentation reflects an increase in the level of importance that the Chief Operating Decision Maker now places on the results of the underlying operating segments when aggregated and reported in alignment with the products and services offered to the marketplace versus when aggregated and reported in alignment with our legal entity structure. Over the past few years, we have been monitoring the growth and stability of our reinsurance business and in 2015 determined that reinsurance has become a stable and significant component of our Company. We are also increasing our focus on additional international insurance markets by establishing underwriting offices in Continental Europe. The offices were fully operational during our January renewal season. We considered these changes in conjunction with operating and reportable segments.
	Our previously reported segments were consistent with our legal entity structure; however, our new reporting segments are now primarily reflective of where our business is written. We reclassified our international business from our previously reported Lloyd’s Operations segment to the Int’l Insurance segment. We also reclassified our non-Lloyd’s business written internationally (primarily business written by the U.K. Branch) into this segment and have excluded Assumed Reinsurance. Our new GlobalRe segment was previously reported within our U.S. Insurance and Lloyd’s Operations segments as Assumed Reinsurance. Our U.S. Insurance segment now excludes the U.K. Branch and Assumed Reinsurance. Our Corporate segment now includes investment income (loss), interest income (loss), foreign exchange gain (loss) and income tax benefit (expense), which are not allocated to the U.S. Insurance, Int’l Insurance and GlobalRe segments (together “underwriting segments”). We do not allocate assets under the new reporting segments, as it is impracticable to do so.
	As noted above, we classify our business into three underwriting segments (U.S. Insurance, Int’l Insurance and GlobalRe) and a Corporate Segment. Both the U.S. Insurance and Int’l Insurance reporting segments are each comprised of three operating segments: Marine, Professional Liability and P&C. These operating segments have been aggregated into the aforementioned reporting segments based upon the criteria specified in Accounting Standards Codification 280, Segment Reporting. Consistent with the guidance, these operating segments; (a) engage in business activities from which they may earn revenues and incur expenses, (b) are regularly reviewed by our management to assess the performance of the segments and make decisions about resources to be allocated to the segments and (c) have discrete financial information.
	We evaluate the performance of each of the underwriting segments based on underwriting 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 loss adjustment expenses (“LAE”), commission expenses, other operating expenses, and other underwriting income (expense). The combined ratio is derived by dividing the sum of net loss and LAE, commission expenses, other operating expenses and other underwriting income (expense) by net earned premiums. A combined ratio of less than 100% indicates an underwriting profit and greater than 100% indicates an underwriting loss. Our underwriting performance is evaluated separately from the rest of our operations. The performance of our investment portfolios, our liquidity and capital resource needs, our foreign currency exposure and our tax planning strategies are evaluated on a consolidated basis within our Corporate reporting segment.
	The accounting policies used to prepare the segment reporting data for our reporting segments are the same as those described in Note 1 and Note 3 of our Annual Report on Form 10-K for the year ended December 31, 2014. In addition, 2014 data presented in this Quarterly Report has been recast to align with the new segment reporting described above.
	Financial data by segment for the three months ended March 31, 2015 and 2014 were as follows:
			Three Months Ended March 31, 2015
	amounts in thousands		U.S.			Int’l			GlobalRe			Corporate (1)			Total
			Insurance			Insurance
	Gross written premiums		$	199,327		$	122,427		$	74,706		$	—		$	396,460
	Ceded written premiums			(68,730	)		(34,256	)		(4,516	)		—			(107,502	)
	Net written premiums			130,597			88,171			70,190			—			288,958
	Net earned premiums			131,091			65,525			39,516			—			236,132
	Net losses and LAE			(77,799	)		(29,691	)		(22,708	)		—			(130,198	)
	Commission expenses			(14,345	)		(11,413	)		(7,298	)		151			(32,905	)
	Other operating expenses			(33,688	)		(17,009	)		(4,212	)		—			(54,909	)
	Other underwriting income (expense)			196			—			10			(151	)		55
	Underwriting profit (loss)		$	5,455		$	7,412		$	5,308		$	—		$	18,175
	Net investment income												16,253			16,253
	Net realized gains (losses)												5,596			5,596
	Interest expense												(3,855	)		(3,855	)
	Other income												2,187			2,187
	Income before income taxes		$	5,455		$	7,412		$	5,308		$	20,181		$	38,356
	Income tax (expense) benefit												(12,427	)		(12,427	)
	Net income (loss)														$	25,929
	Losses and LAE ratio			59.3	%		45.3	%		57.5	%					55.1	%
	Commission expense ratio			10.9	%		17.4	%		18.5	%					13.9	%
	Other operating expense ratio (2)			25.6	%		26	%		10.6	%					23.3	%
	Combined ratio			95.8	%		88.7	%		86.6	%					92.3	%
	(1) - Includes Corporate segment intercompany eliminations.
	(2) - Includes Other operating expenses and Other underwriting income.
			Three Months Ended March 31, 2014
	amounts in thousands		U.S.			Int’l			GlobalRe			Corporate (1)			Total
			Insurance			Insurance
	Gross written premiums		$	198,348		$	119,192		$	105,250		$	—		$	422,790
	Ceded written premiums			(65,066	)		(42,582	)		(3,292	)		—			(110,940	)
	Net written premiums			133,282			76,610			101,958			—			311,850
	Net earned premiums			115,190			62,054			48,028			—			225,272
	Net losses and LAE			(72,964	)		(31,220	)		(30,883	)		—			(135,067	)
	Commission expenses			(9,509	)		(8,855	)		(7,872	)		509			(25,727	)
	Other operating expenses			(27,993	)		(15,059	)		(4,094	)		—			(47,146	)
	Other underwriting income (expense)			513			6			145			(509	)		155
	Underwriting profit (loss)		$	5,237		$	6,926		$	5,324		$	—		$	17,487
	Net investment income												16,610			16,610
	Net realized gains (losses)												833			833
	Interest expense												(3,852	)		(3,852	)
	Other income												10,244			10,244
	Income before income taxes		$	5,237		$	6,926		$	5,324		$	23,835		$	41,322
	Income tax (expense) benefit												(13,354	)		(13,354	)
	Net income (loss)														$	27,968
	Losses and LAE ratio			63.3	%		50.3	%		64.3	%					60	%
	Commission expense ratio			8.3	%		14.3	%		16.4	%					11.4	%
	Other operating expense ratio (2)			23.9	%		24.2	%		8.2	%					20.8	%
	Combined ratio			95.5	%		88.8	%		88.9	%					92.2	%
	(1) - Includes Corporate segment intercompany eliminations.
	(2) - Includes Other operating expenses and Other underwriting income.
	Revenue by operating segment for the three months ended March 31, 2015 and 2014 was as follows:
			Q1 2015												Q1 2014										% Change
	amounts in thousands		Gross			Ceded			Net			Net			Gross			Ceded			Net		Net		Gross			Ceded			Net			Net
			written			written			written			earned			written			written			written		earned		written			written			written			earned
			premiums			premiums			premiums			premiums			premiums			premiums			premiums		premiums		premiums			premiums			premiums			premiums
	U.S. Insurance
	Marine		$	40,835		$	(16,286	)	$	24,549		$	23,924		$	43,025		$	(9,170	)	$	33,855	$	27,986		-5.1	%		77.6	%		-27.5	%		-14.5	%
P&C			134,146			(39,558	)		94,588			90,735			125,119			(46,156	)		78,963		64,931		7.2	%		-14.3	%		19.8	%		39.7	%
Professional Liability			24,346			(12,886	)		11,460			16,432			30,204			(9,740	)		20,464		22,273		-19.4	%		32.3	%		-44	%		-26.2	%
Total			199,327			(68,730	)		130,597			131,091			198,348			(65,066	)		133,282		115,190		0.5	%		5.6	%		-2	%		13.8	%
Int’l Insurance
Marine		$	67,410		$	(10,822	)	$	56,588		$	37,792		$	61,982		$	(12,394	)	$	49,588	$	38,044		8.8	%		-12.7	%		14.1	%		-0.7	%
P&C			32,950			(16,129	)		16,821			16,034			42,250			(24,464	)		17,786		16,441		-22	%		-34.1	%		-5.4	%		-2.5	%
Professional Liability			22,067			(7,305	)		14,762			11,699			14,960			(5,724	)		9,236		7,569		47.5	%		27.6	%		59.8	%		54.6	%
Total			122,427			(34,256	)		88,171			65,525			119,192			(42,582	)		76,610		62,054		2.7	%		-19.6	%		15.1	%		5.6	%
GlobalRe		$	74,706		$	(4,516	)	$	70,190		$	39,516		$	105,250		$	(3,292	)	$	101,958	$	48,028		-29	%		37.2	%		-31.2	%		-17.7	%
Total		$	396,460		$	(107,502	)	$	288,958		$	236,132		$	422,790		$	(110,940	)	$	311,850	$	225,272		-6.2	%		-3.1	%		-7.3	%		4.8	%

Investments

Investments	3 Months Ended
	Mar. 31, 2015
Investments	Note 3.	Investments
	The following tables set forth our Company’s investments as of March 31, 2015 and December 31, 2014 and include Other-than-temporary-impairment (“OTTI”) securities recognized within AOCI.
			March 31, 2015
	amounts in thousands		Fair			Gross			Gross			Cost or
			Value			Unrealized			Unrealized			Amortized
						Gains			(Losses)			Cost
	Fixed maturities:
	U.S. Treasury bonds, agency bonds and foreign government bonds		$	310,389		$	4,858		$	(8,732	)	$	314,263
	States, municipalities and political subdivisions			547,664			19,989			(321	)		527,996
	Mortgage-backed and asset-backed securities:
	Agency mortgage-backed securities			364,468			9,975			(589	)		355,082
	Residential mortgage obligations			33,116			1,079			(117	)		32,154
	Asset-backed securities			216,475			814			(554	)		216,215
	Commercial mortgage-backed securities			231,703			7,789			(28	)		223,942
	Subtotal		$	845,762		$	19,657		$	(1,288	)	$	827,393
	Corporate bonds			641,410			17,231			(932	)		625,111
	Total fixed maturities		$	2,345,225		$	61,735		$	(11,273	)	$	2,294,763
	Equity securities			159,044			26,113			(1,037	)		133,968
	Short-term investments			242,553			20			(1,197	)		243,730
	Total Investments		$	2,746,822		$	87,868		$	(13,507	)	$	2,672,461
			December 31, 2014
	amounts in thousands		Fair			Gross			Gross			Cost or
			Value			Unrealized			Unrealized			Amortized
						Gains			(Losses)			Cost
	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			184,295			30,756			(1,304	)		154,843
	Short-term investments			179,506			—			(21	)		179,527
	Total Investments		$	2,729,735		$	83,078		$	(11,672	)	$	2,658,329
	As of March 31, 2015 and December 31, 2014, our Company did not have a concentration of greater than 5% of invested assets in a single non-U.S. government-backed issuer.
	As of March 31, 2015 and December 31, 2014, fixed maturities for which non-credit OTTI was previously recognized and included in AOCI are now in an unrealized gains position of $0.7 million.
	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, 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 our 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 our 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 March 31, 2015 are shown in the following table:
			March 31, 2015
	amounts in thousands		Fair			Amortized
			Value			Cos t
	Due in one year or less		$	55,121		$	59,300
	Due after one year through five years			756,593			746,400
	Due after five years through ten years			326,731			315,462
	Due after ten years			361,018			346,208
	Mortgage- and asset-backed securities			845,762			827,393
	Total		$	2,345,225		$	2,294,763
	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. 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 accounting method. Due to the periodic repayment of principal, the mortgage-backed and asset-backed securities are estimated to have an effective maturity of approximately 4.5 years.
	The following tables summarize all securities in a gross unrealized loss position as of March 31, 2015 and December 31, 2014, showing the aggregate fair value and gross unrealized loss by the length of time those securities have continuously been in a gross unrealized loss position:
			Less than 12 months						Greater than 12 months						Total
	March 31, 2015					Gross						Gross					Gross
	amounts in thousands		Fair			Unrealized			Fair			Unrealized			Fair		Unrealized
			Value			(Losses)			Value			(Losses)			Value		(Losses)
	Fixed maturities:
	U.S. Treasury bonds, agency bonds and foreign government bonds		$	38,187		$	(2,879	)	$	27,210		$	(5,853	)	$	65,397	$	(8,732	)
	States, municipalities and political subdivisions			23,698			(127	)		3,514			(194	)		27,212		(321	)
	Mortgage-backed and asset-backed securities:
	Agency mortgage-backed securities			25,824			(78	)		22,530			(511	)		48,354		(589	)
	Residential mortgage obligations			2,002			(22	)		1,623			(95	)		3,625		(117	)
	Asset-backed securities			61,801			(209	)		41,475			(345	)		103,276		(554	)
Commercial mortgage-backed securities			4,088			(9	)		1,369			(19	)		5,457		(28	)
Subtotal		$	93,715		$	(318	)	$	66,997		$	(970	)	$	160,712	$	(1,288	)
Corporate bonds			86,144			(386	)		3,954			(546	)		90,098		(932	)
Total fixed maturities		$	241,744		$	(3,710	)	$	101,675		$	(7,563	)	$	343,419	$	(11,273	)
Equity securities			10,770			(628	)		1,803			(409	)		12,573		(1,037	)
Total fixed maturities and equity securities		$	252,514		$	(4,338	)	$	103,478		$	(7,972	)	$	355,992	$	(12,310	)
		Less than 12 months						Greater than 12 months						Total
December 31, 2014					Gross						Gross					Gross
amounts in thousands		Fair			Unrealized			Fair			Unrealized			Fair		Unrealized
		Value			(Losses)			Value			(Losses)			Value		(Losses)
Fixed maturities:
U.S. Treasury bonds, agency bonds and foreign government bonds		$	87,915		$	(1,061	)	$	117,683		$	(4,904	)	$	205,598	$	(5,965	)
States, municipalities and political subdivisions			16,349			(60	)		37,340			(498	)		53,689		(558	)
Mortgage-backed and asset-backed securities:
Agency mortgage-backed securities			18,881			(80	)		58,301			(918	)		77,182		(998	)
Residential mortgage obligations			5,625			(50	)		1,728			(88	)		7,353		(138	)
Asset-backed securities			110,275			(539	)		34,530			(425	)		144,805		(964	)
Commercial mortgage-backed securities			19,741			(71	)		1,391			(27	)		21,132		(98	)
Subtotal		$	154,522		$	(740	)	$	95,950		$	(1,458	)	$	250,472	$	(2,198	)
Corporate bonds			190,461			(871	)		31,126			(755	)		221,587		(1,626	)
Total fixed maturities		$	449,247		$	(2,732	)	$	282,099		$	(7,615	)	$	731,346	$	(10,347	)
Equity securities			19,690			(1,297	)		238			(7	)		19,928		(1,304	)
Total fixed maturities and equity securities		$	468,937		$	(4,029	)	$	282,337		$	(7,622	)	$	751,274	$	(11,651	)
At March 31, 2015, there were 147 fixed maturities in an unrealized loss position, and there were six equity securities in an unrealized loss position. In the above table, the gross unrealized loss for the greater than 12 months category consists primarily of agency and foreign government bonds primarily due to an unfavorable foreign exchange movement. At December 31, 2014, there were 259 fixed maturities in an unrealized loss position, and there were 15 equity securities in an unrealized loss position. The gross unrealized loss for the greater than 12 months category consists primarily of Treasury and agency bonds, due to an increase in interest rates and unfavorable foreign exchange movement.
As of March 31, 2015 and December 31, 2014, the largest unrealized loss by a non-government backed issuer in the investment portfolio was $0.4 million and $0.5 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 our 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, 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 our 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 our operations and from maturities within our investment portfolio in order to meet our claims payment and other disbursement obligations arising from our 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.
Our Company did not have any credit related OTTI losses during the three months ended March 31, 2015 and 2014.
The following table summarizes the cumulative amounts related to our Company’s credit loss portion of the OTTI losses on fixed maturities for the three months ended March 31, 2015 and 2014. 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.
		Three Months Ended March 31,
amounts in thousands		2015			2014
Beginning balance		$	2,361		$	5,154
Additions for credit loss impairments recognized in the current period on securities not previously impaired			—			—
Additions for credit loss impairments recognized in the current period on securities previously impaired			—			—
Reductions for credit loss impairments previously recognized on securities sold during the period			—			—
Ending balance		$	2,361		$	5,154
Our Company’s net investment income was derived from the following sources:
		Three Months Ended March 31,
amounts in thousands		2015			2014
Fixed maturities		$	15,047		$	13,953
Equity securities			1,968			3,233
Short-term investments			183			218
Total investment income		$	17,198		$	17,404
Investment expenses			(945	)		(794	)
Net investment income		$	16,253		$	16,610
Realized gains and losses, excluding net OTTI losses recognized in earnings, for the periods indicated, were as follows:
		Three Months Ended March 31,
amounts in thousands		2015			2014
Fixed maturities:
Gains		$	1,174		$	1,867
Losses			(572	)		(2,051	)
Fixed maturities, net		$	602		$	(184	)
Short-term:
Gains		$	8		$	—
Losses			(162	)		—
Short-term, net		$	(154	)	$	—
Equity securities:
Gains		$	6,325		$	1,920
Losses			(1,177	)		(903	)
Equity securities, net		$	5,148		$	1,017
Net realized gains (losses)		$	5,596		$	833

Fair_Value_Measurement

Fair Value Measurement	3 Months Ended
	Mar. 31, 2015
Fair Value Measurement	Note 4.	Fair Value Measurement
	The fair value of our 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.
	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 well as the fair value of the 5.75% Senior notes due October 15, 2023 (the “Senior notes”) carried at amortized cost as of March 31, 2015 and December 31, 2014:
			March 31, 2015
	amounts in thousands		Level 1		Level 2		Level 3		Total
	Fixed maturities:
	U.S. Treasury bonds, agency bonds and foreign government bonds		$	80,823	$	229,566	$	—	$	310,389
	States, municipalities and political subdivisions			—		547,664		—		547,664
	Mortgage-backed and asset-backed securities:
	Agency mortgage-backed securities			—		364,468		—		364,468
	Residential mortgage obligations			—		33,116		—		33,116
	Asset-backed securities			—		216,475		—		216,475
	Commercial mortgage-backed securities			—		231,703		—		231,703
	Subtotal		$	—	$	845,762	$	—	$	845,762
	Corporate bonds			—		641,410		—		641,410
	Total fixed maturities		$	80,823	$	2,264,402	$	—	$	2,345,225
	Equity securities			87,701		71,343		—		159,044
	Short-term investments			242,553		—		—		242,553
	Total assets measured at fair value		$	411,077	$	2,335,745	$	—	$	2,746,822
	Senior notes		$	—	$	290,524	$	—	$	290,524
	Total liabilities measured at fair value		$	—	$	290,524	$	—	$	290,524
			December 31, 2014
	amounts 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			127,183		57,112		—		184,295
	Short-term investments			179,506		—		—		179,506
	Total assets measured at fair value		$	453,593	$	2,276,142	$	—	$	2,729,735
	Senior notes		$	—	$	285,710	$	—	$	285,710
	Total liabilities measured at fair value		$	—	$	285,710	$	—	$	285,710
	All other financial assets and liabilities including cash, premium receivables, reinsurance recoverables and reinsurance balance payables are carried at cost, which approximates fair value.
	Our Company did not have any significant transfers between the Level 1 and Level 2 classifications for the three months ended March 31, 2015 and 2014.
	As of March 31, 2015, our Company did not have any Level 3 assets. For the three months ended March 31, 2014, our Company had one corporate bond for $4.4 million which transferred from Level 3 to Level 2. Our Company was able to obtain a valuation in which all significant inputs to the model are observable in active markets.

Ceded_Reinsurance

Ceded Reinsurance	3 Months Ended
	Mar. 31, 2015
Ceded Reinsurance	Note 5.	Ceded Reinsurance
	As of March 31, 2015, the credit quality distribution of our Company’s reinsurance recoverables of $1.1 billion for ceded paid losses, ceded unpaid losses and LAE, and ceded unearned premiums based on insurer financial strength ratings from A.M. Best or S&P was not significantly different from the credit quality distribution as of December 31, 2014.
	Our allowance for uncollectible reinsurance was $8.2 million and $11.3 million as of March 31, 2015 and December 31, 2014, respectively. The reduction in our allowance for uncollectible reinsurance was the result of payments of outstanding balances from one of our large reinsurers.
	As of March 31, 2015, our 20 largest reinsurers measured by the amount of Reinsurance recoverable for ceded losses and LAE and ceded unearned premium, together with the Reinsurance recoverable and collateral, were not significantly different from December 31, 2014.

Debt

Debt	3 Months Ended
	Mar. 31, 2015
Debt	Note 6.	Debt
	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 the Syndicate. The facility is used to fund Australian underwriting obligations for the 2015 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 March 31, 2015, 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 our participation in the Syndicate by posting Funds at Lloyd’s 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 March 31, 2015, letters of credit with an aggregate face amount of $145.1 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 syndicate of lenders.
	The applicable fee rate payable under the credit facility is 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 the Syndicate.
	Senior notes
	The Senior notes had no material changes in the first quarter 2015.

Commitments_and_Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2015
Commitments and Contingencies	Note 7.	Commitments and Contingencies
	In 2013, 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) to move our corporate headquarters to Stamford, Connecticut. The loan is non-interest bearing, has a term of 10 years and is subject to forgiveness based on our compliance with certain conditions set forth in the agreement with the State. The amount of the loan 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 of the award, which is comprised of $6.0 million of the loan and $1.5 million of the grant 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 March 31, 2015, the length of time commitment has not been met. However, our Company expects to meet all the conditions for the state to forgive the amount of the loan received to date, and accordingly, is recognizing the amount of loan and grants received over the period in which our Company recognizes the expenses for which the assistance is intended to compensate as a reduction of such expenses. Our Company recognized $0.2 million of the incentive for each of the three months ended March 31, 2015 and 2014, respectively. As of March 31, 2015 and December 31, 2014, our Company has deferred revenue of $5.9 million and $6.1 million, respectively, which is included in Other liabilities on the Consolidated Balance Sheets.
	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 the Company’s subsidiaries as either: (a) liability insurers defending or providing indemnity for third party claims brought against insureds or (b) insurers defending first party coverage claims brought against them. Our Company accounts for such activity through the establishment of unpaid loss and LAE 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 Balance Sheets, Consolidated Statements of Income or Consolidated Statements of Cash Flows.
	Our Company’s subsidiaries are also from time to time involved with other legal actions, some of which assert claims for substantial amounts. These actions include claims asserting extra contractual obligations, such as claims involving allegations of bad faith in the handling of claims or the underwriting of policies. In general, 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 our Consolidated Balance Sheets, Consolidated Statements of Income or Consolidated Statements of Cash Flows. 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 Statements of Income or Consolidated Statements of Cash Flows in a particular fiscal quarter or year.

Stock_Options_Stock_Grants_SAR

Stock Options, Stock Grants, SARs and ESPP	3 Months Ended
	Mar. 31, 2015
Stock Options, Stock Grants, SARs and ESPP	Note 8.	Stock Options, Stock Grants, SARs and ESPP
	Stock-based compensation granted under the Company’s stock plans is expensed in tranches over the vesting period. Options and non-performance based grants generally vest equally over a three or four-year period and the options have a maximum term of ten years. Pursuant to the provisions of the Second Amended and Restated 2005 Stock Incentive Plan (“the Plan”), shares that are subject to an award and are forfeited or otherwise terminate without the delivery of the full number of shares may, to the extent of such forfeiture or termination, again be available for grant under the Plan. The Compensation Committee has adopted a policy that shares that are forfeited to satisfy the withholding tax obligations of a grantee, and which have not otherwise been issued or outstanding, will, pursuant to this provision, again be available for grant under the Plan. This policy has been applied effective January 1, 2010.
	Restricted stock units and performance units are granted at the market closing price on the grant date. On February 10, 2015, we granted 4,658 restricted stock units and on March 5, 2015, we granted 185,050 performance units to employees and officers with a grant date fair market value of $77.31 and $74.49, respectively. Each performance unit and restricted stock unit represents a contingent right to receive of one share of common stock as of the vesting date.

Organization_and_Summary_of_Si1

Organization and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2015
Basis of Presentation	Basis of Presentation
	The accompanying interim consolidated financial statements are unaudited and reflect all adjustments which, in the opinion of management, are necessary to fairly present the results of The Navigators Group, Inc. and its subsidiaries for the interim periods presented on the basis of United States generally accepted accounting principles (“GAAP” or “U.S. GAAP”). All significant intercompany transactions and balances have been eliminated in consolidation. The preparation of these 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 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 interim consolidated financial statements should be read in conjunction with our Annual Report on Form 10-K for the year ended December 31, 2014. Certain amounts for the prior year have been reclassified to conform with the current period presentation. Unless the context requires otherwise, the terms “we,” “us,” “our,” or “our Company” are used to mean The Navigators Group, Inc., a Delaware holding company established in 1982, and its subsidiaries. The terms “Parent” or “Parent Company” are used to mean The Navigators Group, Inc. without its subsidiaries.
Organization	Organization
	We are an international insurance company with a long-standing area of specialization in Marine insurance. Our Property and Casualty (“P&C”) insurance business primarily offers General Liability coverage and Umbrella & Excess Liability coverage to commercial enterprises through our Primary and Excess Casualty divisions. We have also developed niches in Professional Liability insurance, through our Management Liability and Errors and Omissions divisions. Beginning in 2010, we added reinsurance products through our Assumed Reinsurance division.
	We operate through various wholly-owned subsidiaries, including Navigators Insurance Company, inclusive of its United Kingdom Branch (“U.K. Branch”), and Navigators Specialty Insurance Company, both of which are U.S. insurance companies, and Navigators Underwriting Agency Ltd., a Lloyd’s of London (“Lloyd’s”) underwriting agency that manages Lloyd’s Syndicate 1221 (“the Syndicate”) in the U.K. The Company controls 100% of the Syndicate’s stamp capacity.
Foreign Exchange Remeasurement and Translation	Foreign Exchange Remeasurement and Translation
	During the first quarter of 2014, the Syndicate 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 remeasurement has resulted in an immaterial correction of $10.0 million ($6.6 million after-tax) in Accumulated other comprehensive income (“AOCI”), on the Consolidated Balance Sheets, offset by a gain in Other income in the Consolidated Statements of Income.
Catastrophe Risk Management	Catastrophe Risk Management
	We have exposure to losses caused by hurricanes, earthquakes, and other natural and man-made catastrophic events. The frequency and severity of catastrophic events is unpredictable. The extent of covered losses from a catastrophe is a function of both the total amount of insured exposure in an area affected by the event and the severity of the event. We had no material catastrophic events occur in the first quarter 2015.
Income Taxes	Income Taxes
	The income tax provision has been computed based on our estimated annual effective tax rate. Our effective tax rate for the quarter differs from the federal tax rate of 35% principally because of tax-exempt investment income and dividends received deduction.
Current and Pending Accounting Pronouncements	Current and Pending Accounting Pronouncements
	As of January 1, 2015, we did not adopt any new accounting pronouncements. In April 2015, the Financial Accounting Standards Board issued a new pronouncement, Accounting Standards Update 2015-03 – Interest – Imputation of Interest (Subtopic 835-30) – Simplifying the Presentation of Debt Issuance Costs, which will be effective for fiscal years beginning after December 15, 2015. The new pronouncement was issued to simplify presentation of debt issuance costs. We are assessing the future impact of this update to our Consolidated Financial Statements. There were no additional pending accounting pronouncements that are expected to have a significant impact on the consolidated financial statements upon adoption.

Segment_Information_Tables

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2015
Financial Data by Segment	Financial data by segment for the three months ended March 31, 2015 and 2014 were as follows:
		Three Months Ended March 31, 2015
	amounts in thousands	U.S.			Int’l			GlobalRe			Corporate (1)			Total
		Insurance			Insurance
	Gross written premiums	$	199,327		$	122,427		$	74,706		$	—		$	396,460
	Ceded written premiums		(68,730	)		(34,256	)		(4,516	)		—			(107,502	)
	Net written premiums		130,597			88,171			70,190			—			288,958
	Net earned premiums		131,091			65,525			39,516			—			236,132
	Net losses and LAE		(77,799	)		(29,691	)		(22,708	)		—			(130,198	)
	Commission expenses		(14,345	)		(11,413	)		(7,298	)		151			(32,905	)
	Other operating expenses		(33,688	)		(17,009	)		(4,212	)		—			(54,909	)
	Other underwriting income (expense)		196			—			10			(151	)		55
	Underwriting profit (loss)	$	5,455		$	7,412		$	5,308		$	—		$	18,175
	Net investment income											16,253			16,253
	Net realized gains (losses)											5,596			5,596
	Interest expense											(3,855	)		(3,855	)
	Other income											2,187			2,187
	Income before income taxes	$	5,455		$	7,412		$	5,308		$	20,181		$	38,356
	Income tax (expense) benefit											(12,427	)		(12,427	)
	Net income (loss)													$	25,929
	Losses and LAE ratio		59.3	%		45.3	%		57.5	%					55.1	%
	Commission expense ratio		10.9	%		17.4	%		18.5	%					13.9	%
	Other operating expense ratio (2)		25.6	%		26	%		10.6	%					23.3	%
	Combined ratio		95.8	%		88.7	%		86.6	%					92.3	%
	(1) - Includes Corporate segment intercompany eliminations.
	(2) - Includes Other operating expenses and Other underwriting income.
		Three Months Ended March 31, 2014
	amounts in thousands	U.S.			Int’l			GlobalRe			Corporate (1)			Total
		Insurance			Insurance
	Gross written premiums	$	198,348		$	119,192		$	105,250		$	—		$	422,790
	Ceded written premiums		(65,066	)		(42,582	)		(3,292	)		—			(110,940	)
	Net written premiums		133,282			76,610			101,958			—			311,850
	Net earned premiums		115,190			62,054			48,028			—			225,272
	Net losses and LAE		(72,964	)		(31,220	)		(30,883	)		—			(135,067	)
	Commission expenses		(9,509	)		(8,855	)		(7,872	)		509			(25,727	)
	Other operating expenses		(27,993	)		(15,059	)		(4,094	)		—			(47,146	)
	Other underwriting income (expense)		513			6			145			(509	)		155
	Underwriting profit (loss)	$	5,237		$	6,926		$	5,324		$	—		$	17,487
	Net investment income											16,610			16,610
	Net realized gains (losses)											833			833
	Interest expense											(3,852	)		(3,852	)
	Other income											10,244			10,244
	Income before income taxes	$	5,237		$	6,926		$	5,324		$	23,835		$	41,322
	Income tax (expense) benefit											(13,354	)		(13,354	)
	Net income (loss)													$	27,968
	Losses and LAE ratio		63.3	%		50.3	%		64.3	%					60	%
	Commission expense ratio		8.3	%		14.3	%		16.4	%					11.4	%
	Other operating expense ratio (2)		23.9	%		24.2	%		8.2	%					20.8	%
	Combined ratio		95.5	%		88.8	%		88.9	%					92.2	%
	(1) - Includes Corporate segment intercompany eliminations.
	(2) - Includes Other operating expenses and Other underwriting income.
Additional Financial Data by Segment	Revenue by operating segment for the three months ended March 31, 2015 and 2014 was as follows:
		Q1 2015												Q1 2014										% Change
	amounts in thousands	Gross			Ceded			Net			Net			Gross			Ceded			Net		Net		Gross			Ceded			Net			Net
		written			written			written			earned			written			written			written		earned		written			written			written			earned
		premiums			premiums			premiums			premiums			premiums			premiums			premiums		premiums		premiums			premiums			premiums			premiums
	U.S. Insurance
	Marine	$	40,835		$	(16,286	)	$	24,549		$	23,924		$	43,025		$	(9,170	)	$	33,855	$	27,986		-5.1	%		77.6	%		-27.5	%		-14.5	%
	P&C		134,146			(39,558	)		94,588			90,735			125,119			(46,156	)		78,963		64,931		7.2	%		-14.3	%		19.8	%		39.7	%
	Professional Liability		24,346			(12,886	)		11,460			16,432			30,204			(9,740	)		20,464		22,273		-19.4	%		32.3	%		-44	%		-26.2	%
	Total		199,327			(68,730	)		130,597			131,091			198,348			(65,066	)		133,282		115,190		0.5	%		5.6	%		-2	%		13.8	%
	Int’l Insurance
	Marine	$	67,410		$	(10,822	)	$	56,588		$	37,792		$	61,982		$	(12,394	)	$	49,588	$	38,044		8.8	%		-12.7	%		14.1	%		-0.7	%
	P&C		32,950			(16,129	)		16,821			16,034			42,250			(24,464	)		17,786		16,441		-22	%		-34.1	%		-5.4	%		-2.5	%
	Professional Liability		22,067			(7,305	)		14,762			11,699			14,960			(5,724	)		9,236		7,569		47.5	%		27.6	%		59.8	%		54.6	%
	Total		122,427			(34,256	)		88,171			65,525			119,192			(42,582	)		76,610		62,054		2.7	%		-19.6	%		15.1	%		5.6	%
	GlobalRe	$	74,706		$	(4,516	)	$	70,190		$	39,516		$	105,250		$	(3,292	)	$	101,958	$	48,028		-29	%		37.2	%		-31.2	%		-17.7	%
	Total	$	396,460		$	(107,502	)	$	288,958		$	236,132		$	422,790		$	(110,940	)	$	311,850	$	225,272		-6.2	%		-3.1	%		-7.3	%		4.8	%

Investments_Tables

Investments (Tables)	3 Months Ended
	Mar. 31, 2015
Investments Including Other-Than-Temporarily Impaired Securities Recognized within Other Comprehensive Income	The following tables set forth our Company’s investments as of March 31, 2015 and December 31, 2014 and include Other-than-temporary-impairment (“OTTI”) securities recognized within AOCI.
		March 31, 2015
	amounts in thousands	Fair			Gross			Gross			Cost or
		Value			Unrealized			Unrealized			Amortized
					Gains			(Losses)			Cost
	Fixed maturities:
	U.S. Treasury bonds, agency bonds and foreign government bonds	$	310,389		$	4,858		$	(8,732	)	$	314,263
	States, municipalities and political subdivisions		547,664			19,989			(321	)		527,996
	Mortgage-backed and asset-backed securities:
	Agency mortgage-backed securities		364,468			9,975			(589	)		355,082
	Residential mortgage obligations		33,116			1,079			(117	)		32,154
	Asset-backed securities		216,475			814			(554	)		216,215
	Commercial mortgage-backed securities		231,703			7,789			(28	)		223,942
	Subtotal	$	845,762		$	19,657		$	(1,288	)	$	827,393
	Corporate bonds		641,410			17,231			(932	)		625,111
	Total fixed maturities	$	2,345,225		$	61,735		$	(11,273	)	$	2,294,763
	Equity securities		159,044			26,113			(1,037	)		133,968
	Short-term investments		242,553			20			(1,197	)		243,730
	Total Investments	$	2,746,822		$	87,868		$	(13,507	)	$	2,672,461
		December 31, 2014
	amounts in thousands	Fair			Gross			Gross			Cost or
		Value			Unrealized			Unrealized			Amortized
					Gains			(Losses)			Cost
	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		184,295			30,756			(1,304	)		154,843
	Short-term investments		179,506			—			(21	)		179,527
	Total Investments	$	2,729,735		$	83,078		$	(11,672	)	$	2,658,329
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 March 31, 2015 are shown in the following table:
		March 31, 2015
	amounts in thousands	Fair			Amortized
		Value			Cos t
	Due in one year or less	$	55,121		$	59,300
	Due after one year through five years		756,593			746,400
	Due after five years through ten years		326,731			315,462
	Due after ten years		361,018			346,208
	Mortgage- and asset-backed securities		845,762			827,393
	Total	$	2,345,225		$	2,294,763
Summary of Aggregate Fair Value and Gross Unrealized Loss by Length of Time Securities had Continuously been in Gross Unrealized Loss Position	The following tables summarize all securities in a gross unrealized loss position as of March 31, 2015 and December 31, 2014, showing the aggregate fair value and gross unrealized loss by the length of time those securities have continuously been in a gross unrealized loss position:
		Less than 12 months						Greater than 12 months						Total
	March 31, 2015				Gross						Gross					Gross
	amounts in thousands	Fair			Unrealized			Fair			Unrealized			Fair		Unrealized
		Value			(Losses)			Value			(Losses)			Value		(Losses)
	Fixed maturities:
	U.S. Treasury bonds, agency bonds and foreign government bonds	$	38,187		$	(2,879	)	$	27,210		$	(5,853	)	$	65,397	$	(8,732	)
	States, municipalities and political subdivisions		23,698			(127	)		3,514			(194	)		27,212		(321	)
	Mortgage-backed and asset-backed securities:
	Agency mortgage-backed securities		25,824			(78	)		22,530			(511	)		48,354		(589	)
	Residential mortgage obligations		2,002			(22	)		1,623			(95	)		3,625		(117	)
	Asset-backed securities		61,801			(209	)		41,475			(345	)		103,276		(554	)
	Commercial mortgage-backed securities		4,088			(9	)		1,369			(19	)		5,457		(28	)
	Subtotal	$	93,715		$	(318	)	$	66,997		$	(970	)	$	160,712	$	(1,288	)
	Corporate bonds		86,144			(386	)		3,954			(546	)		90,098		(932	)
	Total fixed maturities	$	241,744		$	(3,710	)	$	101,675		$	(7,563	)	$	343,419	$	(11,273	)
	Equity securities		10,770			(628	)		1,803			(409	)		12,573		(1,037	)
	Total fixed maturities and equity securities	$	252,514		$	(4,338	)	$	103,478		$	(7,972	)	$	355,992	$	(12,310	)
		Less than 12 months						Greater than 12 months						Total
	December 31, 2014				Gross						Gross					Gross
	amounts in thousands	Fair			Unrealized			Fair			Unrealized			Fair		Unrealized
		Value			(Losses)			Value			(Losses)			Value		(Losses)
	Fixed maturities:
	U.S. Treasury bonds, agency bonds and foreign government bonds	$	87,915		$	(1,061	)	$	117,683		$	(4,904	)	$	205,598	$	(5,965	)
	States, municipalities and political subdivisions		16,349			(60	)		37,340			(498	)		53,689		(558	)
	Mortgage-backed and asset-backed securities:
	Agency mortgage-backed securities		18,881			(80	)		58,301			(918	)		77,182		(998	)
	Residential mortgage obligations		5,625			(50	)		1,728			(88	)		7,353		(138	)
	Asset-backed securities		110,275			(539	)		34,530			(425	)		144,805		(964	)
	Commercial mortgage-backed securities		19,741			(71	)		1,391			(27	)		21,132		(98	)
	Subtotal	$	154,522		$	(740	)	$	95,950		$	(1,458	)	$	250,472	$	(2,198	)
	Corporate bonds		190,461			(871	)		31,126			(755	)		221,587		(1,626	)
	Total fixed maturities	$	449,247		$	(2,732	)	$	282,099		$	(7,615	)	$	731,346	$	(10,347	)
	Equity securities		19,690			(1,297	)		238			(7	)		19,928		(1,304	)
	Total fixed maturities and equity securities	$	468,937		$	(4,029	)	$	282,337		$	(7,622	)	$	751,274	$	(11,651	)
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 three months ended March 31, 2015 and 2014. 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.
		Three Months Ended March 31,
	amounts in thousands	2015			2014
	Beginning balance	$	2,361		$	5,154
	Additions for credit loss impairments recognized in the current period on securities not previously impaired		—			—
	Additions for credit loss impairments recognized in the current period on securities previously impaired		—			—
	Reductions for credit loss impairments previously recognized on securities sold during the period		—			—
	Ending balance	$	2,361		$	5,154
Net Investment Income	Our Company’s net investment income was derived from the following sources:
		Three Months Ended March 31,
	amounts in thousands	2015			2014
	Fixed maturities	$	15,047		$	13,953
	Equity securities		1,968			3,233
	Short-term investments		183			218
	Total investment income	$	17,198		$	17,404
	Investment expenses		(945	)		(794	)
	Net investment income	$	16,253		$	16,610
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:
		Three Months Ended March 31,
	amounts in thousands	2015			2014
	Fixed maturities:
	Gains	$	1,174		$	1,867
	Losses		(572	)		(2,051	)
	Fixed maturities, net	$	602		$	(184	)
	Short-term:
	Gains	$	8		$	—
	Losses		(162	)		—
	Short-term, net	$	(154	)	$	—
	Equity securities:
	Gains	$	6,325		$	1,920
	Losses		(1,177	)		(903	)
	Equity securities, net	$	5,148		$	1,017
	Net realized gains (losses)	$	5,596		$	833

Fair_Value_Measurement_Tables

Fair Value Measurement (Tables)	3 Months Ended
	Mar. 31, 2015
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 well as the fair value of the 5.75% Senior notes due October 15, 2023 (the “Senior notes”) carried at amortized cost as of March 31, 2015 and December 31, 2014:
		March 31, 2015
	amounts in thousands	Level 1		Level 2		Level 3		Total
	Fixed maturities:
	U.S. Treasury bonds, agency bonds and foreign government bonds	$	80,823	$	229,566	$	—	$	310,389
	States, municipalities and political subdivisions		—		547,664		—		547,664
	Mortgage-backed and asset-backed securities:
	Agency mortgage-backed securities		—		364,468		—		364,468
	Residential mortgage obligations		—		33,116		—		33,116
	Asset-backed securities		—		216,475		—		216,475
	Commercial mortgage-backed securities		—		231,703		—		231,703
	Subtotal	$	—	$	845,762	$	—	$	845,762
	Corporate bonds		—		641,410		—		641,410
	Total fixed maturities	$	80,823	$	2,264,402	$	—	$	2,345,225
	Equity securities		87,701		71,343		—		159,044
	Short-term investments		242,553		—		—		242,553
	Total assets measured at fair value	$	411,077	$	2,335,745	$	—	$	2,746,822
	Senior notes	$	—	$	290,524	$	—	$	290,524
	Total liabilities measured at fair value	$	—	$	290,524	$	—	$	290,524
		December 31, 2014
	amounts 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		127,183		57,112		—		184,295
	Short-term investments		179,506		—		—		179,506
	Total assets measured at fair value	$	453,593	$	2,276,142	$	—	$	2,729,735
	Senior notes	$	—	$	285,710	$	—	$	285,710
	Total liabilities measured at fair value	$	—	$	285,710	$	—	$	285,710

Organization_and_Summary_of_Si2

Organization and Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015
Organization And Summary Of Significant Accounting Policies [Line Items]
Remeasurement of Foreign Currency	$10
Remeasurement of Foreign currency, After tax	$6.60
Effective Tax Rate	35.00%
Syndicate 1221
Organization And Summary Of Significant Accounting Policies [Line Items]
Equity Method Investment, Ownership Percentage	100.00%

Segment_Information_Additional

Segment Information - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2015
	Segment
Segment Reporting Information [Line Items]
Number of underwriting Segments	3
Number of Operating Segments	3

Financial_Data_by_Segment_Deta

Financial Data by Segment (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Segment Reporting Information [Line Items]
Gross written premiums	$396,460		$422,790
Ceded written premiums	-107,502		-110,940
Net written premiums	288,958		311,850
Net earned premiums	236,132		225,272
Net losses and LAE	-130,198		-135,067
Commission expenses	-32,905		-25,727
Other operating expenses	-54,909		-47,146
Other underwriting income (expense)	55		155
Underwriting profit (loss)	18,175		17,487
Net investment income	16,253		16,610
Net realized gains (losses)	5,596		833
Interest expense	-3,855		-3,852
Other income	2,187		10,244
Income before income taxes	38,356		41,322
Income tax (expense) benefit	-12,427		-13,354
Net income (loss)	25,929		27,968
Losses and LAE ratio	55.10%		60.00%
Commission expense ratio	13.90%		11.40%
Other operating expense ratio	23.30%	[1]	20.80%	[1]
Combined ratio	92.30%		92.20%
U.S.Insurance
Segment Reporting Information [Line Items]
Gross written premiums	199,327		198,348
Ceded written premiums	-68,730		-65,066
Net written premiums	130,597		133,282
Net earned premiums	131,091		115,190
Net losses and LAE	-77,799		-72,964
Commission expenses	-14,345		-9,509
Other operating expenses	-33,688		-27,993
Other underwriting income (expense)	196		513
Underwriting profit (loss)	5,455		5,237
Income before income taxes	5,455		5,237
Losses and LAE ratio	59.30%		63.30%
Commission expense ratio	10.90%		8.30%
Other operating expense ratio	25.60%	[1]	23.90%	[1]
Combined ratio	95.80%		95.50%
International Insurance
Segment Reporting Information [Line Items]
Gross written premiums	122,427		119,192
Ceded written premiums	-34,256		-42,582
Net written premiums	88,171		76,610
Net earned premiums	65,525		62,054
Net losses and LAE	-29,691		-31,220
Commission expenses	-11,413		-8,855
Other operating expenses	-17,009		-15,059
Other underwriting income (expense)			6
Underwriting profit (loss)	7,412		6,926
Income before income taxes	7,412		6,926
Losses and LAE ratio	45.30%		50.30%
Commission expense ratio	17.40%		14.30%
Other operating expense ratio	26.00%	[1]	24.20%	[1]
Combined ratio	88.70%		88.80%
Global Reinsurance
Segment Reporting Information [Line Items]
Gross written premiums	74,706		105,250
Ceded written premiums	-4,516		-3,292
Net written premiums	70,190		101,958
Net earned premiums	39,516		48,028
Net losses and LAE	-22,708		-30,883
Commission expenses	-7,298		-7,872
Other operating expenses	-4,212		-4,094
Other underwriting income (expense)	10		145
Underwriting profit (loss)	5,308		5,324
Income before income taxes	5,308		5,324
Losses and LAE ratio	57.50%		64.30%
Commission expense ratio	18.50%		16.40%
Other operating expense ratio	10.60%	[1]	8.20%	[1]
Combined ratio	86.60%		88.90%
Corporate
Segment Reporting Information [Line Items]
Commission expenses	151	[2]	509	[2]
Other underwriting income (expense)	-151	[2]	-509	[2]
Net investment income	16,253	[2]	16,610	[2]
Net realized gains (losses)	5,596	[2]	833	[2]
Interest expense	-3,855	[2]	-3,852	[2]
Other income	2,187	[2]	10,244	[2]
Income before income taxes	20,181	[2]	23,835	[2]
Income tax (expense) benefit	($12,427)	[2]	($13,354)	[2]
[1]	Includes Other operating expenses and Other underwriting income.
[2]	Includes Corporate segment intercompany eliminations.

Additional_Financial_Data_by_S

Additional Financial Data by Segment (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information [Line Items]
Gross written premiums	$396,460	$422,790
Ceded written premiums	-107,502	-110,940
Net written premiums	288,958	311,850
Net earned premiums	236,132	225,272
% Change Gross written premiums	-6.20%
% Change Ceded written premiums	-3.10%
% Change Net written premiums	-7.30%
% Change Net earned premiums	4.80%
U.S.Insurance
Segment Reporting Information [Line Items]
Gross written premiums	199,327	198,348
Ceded written premiums	-68,730	-65,066
Net written premiums	130,597	133,282
Net earned premiums	131,091	115,190
% Change Gross written premiums	0.50%
% Change Ceded written premiums	5.60%
% Change Net written premiums	-2.00%
% Change Net earned premiums	13.80%
U.S.Insurance | Marine
Segment Reporting Information [Line Items]
Gross written premiums	40,835	43,025
Ceded written premiums	-16,286	-9,170
Net written premiums	24,549	33,855
Net earned premiums	23,924	27,986
% Change Gross written premiums	-5.10%
% Change Ceded written premiums	77.60%
% Change Net written premiums	-27.50%
% Change Net earned premiums	-14.50%
U.S.Insurance | Property Casualty
Segment Reporting Information [Line Items]
Gross written premiums	134,146	125,119
Ceded written premiums	-39,558	-46,156
Net written premiums	94,588	78,963
Net earned premiums	90,735	64,931
% Change Gross written premiums	7.20%
% Change Ceded written premiums	-14.30%
% Change Net written premiums	19.80%
% Change Net earned premiums	39.70%
U.S.Insurance | Professional Liability
Segment Reporting Information [Line Items]
Gross written premiums	24,346	30,204
Ceded written premiums	-12,886	-9,740
Net written premiums	11,460	20,464
Net earned premiums	16,432	22,273
% Change Gross written premiums	-19.40%
% Change Ceded written premiums	32.30%
% Change Net written premiums	-44.00%
% Change Net earned premiums	-26.20%
International Insurance
Segment Reporting Information [Line Items]
Gross written premiums	122,427	119,192
Ceded written premiums	-34,256	-42,582
Net written premiums	88,171	76,610
Net earned premiums	65,525	62,054
% Change Gross written premiums	2.70%
% Change Ceded written premiums	-19.60%
% Change Net written premiums	15.10%
% Change Net earned premiums	5.60%
International Insurance | Marine
Segment Reporting Information [Line Items]
Gross written premiums	67,410	61,982
Ceded written premiums	-10,822	-12,394
Net written premiums	56,588	49,588
Net earned premiums	37,792	38,044
% Change Gross written premiums	8.80%
% Change Ceded written premiums	-12.70%
% Change Net written premiums	14.10%
% Change Net earned premiums	-0.70%
International Insurance | Property Casualty
Segment Reporting Information [Line Items]
Gross written premiums	32,950	42,250
Ceded written premiums	-16,129	-24,464
Net written premiums	16,821	17,786
Net earned premiums	16,034	16,441
% Change Gross written premiums	-22.00%
% Change Ceded written premiums	-34.10%
% Change Net written premiums	-5.40%
% Change Net earned premiums	-2.50%
International Insurance | Professional Liability
Segment Reporting Information [Line Items]
Gross written premiums	22,067	14,960
Ceded written premiums	-7,305	-5,724
Net written premiums	14,762	9,236
Net earned premiums	11,699	7,569
% Change Gross written premiums	47.50%
% Change Ceded written premiums	27.60%
% Change Net written premiums	59.80%
% Change Net earned premiums	54.60%
Global Reinsurance
Segment Reporting Information [Line Items]
Gross written premiums	74,706	105,250
Ceded written premiums	-4,516	-3,292
Net written premiums	70,190	101,958
Net earned premiums	$39,516	$48,028
% Change Gross written premiums	-29.00%
% Change Ceded written premiums	37.20%
% Change Net written premiums	-31.20%
% Change Net earned premiums	-17.70%

Investments_Including_OtherTha

Investments Including Other-Than-Temporarily Impaired Securities Recognized within Accumulated Other Comprehensive Income (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Gain (Loss) on Investments [Line Items]
Total investments	$2,746,822	$2,729,735
Gross Unrealized Gains	87,868	83,078
Gross Unrealized Losses	-13,507	-11,672
Amortized Cost	2,672,461	2,658,329
Fixed maturities
Gain (Loss) on Investments [Line Items]
Total investments	2,345,225	2,365,934
Gross Unrealized Gains	61,735	52,322
Gross Unrealized Losses	-11,273	-10,347
Amortized Cost	2,294,763	2,323,959
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign
Gain (Loss) on Investments [Line Items]
Total investments	310,389	397,923
Gross Unrealized Gains	4,858	3,431
Gross Unrealized Losses	-8,732	-5,965
Amortized Cost	314,263	400,457
Fixed maturities | States, municipalities and political subdivisions
Gain (Loss) on Investments [Line Items]
Total investments	547,664	541,007
Gross Unrealized Gains	19,989	19,204
Gross Unrealized Losses	-321	-558
Amortized Cost	527,996	522,361
Fixed maturities | Agency mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Total investments	364,468	364,622
Gross Unrealized Gains	9,975	8,476
Gross Unrealized Losses	-589	-998
Amortized Cost	355,082	357,144
Fixed maturities | Residential Mortgage Backed Securities
Gain (Loss) on Investments [Line Items]
Total investments	33,116	34,087
Gross Unrealized Gains	1,079	1,153
Gross Unrealized Losses	-117	-138
Amortized Cost	32,154	33,072
Fixed maturities | Asset-backed securities
Gain (Loss) on Investments [Line Items]
Total investments	216,475	206,413
Gross Unrealized Gains	814	380
Gross Unrealized Losses	-554	-964
Amortized Cost	216,215	206,997
Fixed maturities | Commercial mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Total investments	231,703	206,318
Gross Unrealized Gains	7,789	6,630
Gross Unrealized Losses	-28	-98
Amortized Cost	223,942	199,786
Fixed maturities | Mortgage-backed and asset-backed securities
Gain (Loss) on Investments [Line Items]
Total investments	845,762	811,440
Gross Unrealized Gains	19,657	16,639
Gross Unrealized Losses	-1,288	-2,198
Amortized Cost	827,393	796,999
Fixed maturities | Corporate bonds
Gain (Loss) on Investments [Line Items]
Total investments	641,410	615,564
Gross Unrealized Gains	17,231	13,048
Gross Unrealized Losses	-932	-1,626
Amortized Cost	625,111	604,142
Equity Securities
Gain (Loss) on Investments [Line Items]
Total investments	159,044	184,295
Gross Unrealized Gains	26,113	30,756
Gross Unrealized Losses	-1,037	-1,304
Amortized Cost	133,968	154,843
Short-term investments
Gain (Loss) on Investments [Line Items]
Total investments	242,553	179,506
Gross Unrealized Gains	20
Gross Unrealized Losses	-1,197	-21
Amortized Cost	$243,730	$179,527

Investments_Additional_Informa

Investments - Additional Information (Detail) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Schedule of Investments [Line Items]
Non-credit OTTI on fixed maturities in an unrealized gain position	$700,000		$700,000
Gross Unrealized Loss	12,310,000		11,651,000
OTTI losses	0	0
Equity Securities
Schedule of Investments [Line Items]
Number of unrealized loss position	6		15
Gross Unrealized Loss	1,037,000		1,304,000
Equity Securities | Maximum
Schedule of Investments [Line Items]
Percentage of fair value under carrying value	80.00%
Fixed maturities
Schedule of Investments [Line Items]
Number of unrealized loss position	147		259
Gross Unrealized Loss	11,273,000		10,347,000
Mortgage-backed and asset-backed securities
Schedule of Investments [Line Items]
Securities, effective maturities	4 years 6 months
Mortgage-backed and asset-backed securities | Fixed maturities
Schedule of Investments [Line Items]
Gross Unrealized Loss	1,288,000		2,198,000
Non-government-backed securities
Schedule of Investments [Line Items]
Gross Unrealized Loss	$400,000		$500,000
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 $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Fair Value
Due in one year or less	$55,121
Due after one year through five years	756,593
Due after five years through ten years	326,731
Due after ten years	361,018
Mortgage- and asset-backed securities	845,762
Total	2,345,225	2,365,934
Amortized Cost
Due in one year or less	59,300
Due after one year through five years	746,400
Due after five years through ten years	315,462
Due after ten years	346,208
Mortgage- and asset-backed securities	827,393
Total	$2,294,763	$2,323,959

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 $)	3 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	$252,514	$468,937
Less than 12 months Gross Unrealized Losses	-4,338	-4,029
Greater than 12 months Fair Value	103,478	282,337
Greater than 12 months Gross Unrealized Losses	-7,972	-7,622
Fair Value	355,992	751,274
Gross Unrealized Losses	-12,310	-11,651
Fixed maturities
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	241,744	449,247
Less than 12 months Gross Unrealized Losses	-3,710	-2,732
Greater than 12 months Fair Value	101,675	282,099
Greater than 12 months Gross Unrealized Losses	-7,563	-7,615
Fair Value	343,419	731,346
Gross Unrealized Losses	-11,273	-10,347
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	38,187	87,915
Less than 12 months Gross Unrealized Losses	-2,879	-1,061
Greater than 12 months Fair Value	27,210	117,683
Greater than 12 months Gross Unrealized Losses	-5,853	-4,904
Fair Value	65,397	205,598
Gross Unrealized Losses	-8,732	-5,965
Fixed maturities | States, municipalities and political subdivisions
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	23,698	16,349
Less than 12 months Gross Unrealized Losses	-127	-60
Greater than 12 months Fair Value	3,514	37,340
Greater than 12 months Gross Unrealized Losses	-194	-498
Fair Value	27,212	53,689
Gross Unrealized Losses	-321	-558
Fixed maturities | Agency mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	25,824	18,881
Less than 12 months Gross Unrealized Losses	-78	-80
Greater than 12 months Fair Value	22,530	58,301
Greater than 12 months Gross Unrealized Losses	-511	-918
Fair Value	48,354	77,182
Gross Unrealized Losses	-589	-998
Fixed maturities | Residential Mortgage Backed Securities
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	2,002	5,625
Less than 12 months Gross Unrealized Losses	-22	-50
Greater than 12 months Fair Value	1,623	1,728
Greater than 12 months Gross Unrealized Losses	-95	-88
Fair Value	3,625	7,353
Gross Unrealized Losses	-117	-138
Fixed maturities | Asset-backed securities
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	61,801	110,275
Less than 12 months Gross Unrealized Losses	-209	-539
Greater than 12 months Fair Value	41,475	34,530
Greater than 12 months Gross Unrealized Losses	-345	-425
Fair Value	103,276	144,805
Gross Unrealized Losses	-554	-964
Fixed maturities | Commercial mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	4,088	19,741
Less than 12 months Gross Unrealized Losses	-9	-71
Greater than 12 months Fair Value	1,369	1,391
Greater than 12 months Gross Unrealized Losses	-19	-27
Fair Value	5,457	21,132
Gross Unrealized Losses	-28	-98
Fixed maturities | Corporate bonds
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	86,144	190,461
Less than 12 months Gross Unrealized Losses	-386	-871
Greater than 12 months Fair Value	3,954	31,126
Greater than 12 months Gross Unrealized Losses	-546	-755
Fair Value	90,098	221,587
Gross Unrealized Losses	-932	-1,626
Fixed maturities | Mortgage-backed and asset-backed securities
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	93,715	154,522
Less than 12 months Gross Unrealized Losses	-318	-740
Greater than 12 months Fair Value	66,997	95,950
Greater than 12 months Gross Unrealized Losses	-970	-1,458
Fair Value	160,712	250,472
Gross Unrealized Losses	-1,288	-2,198
Equity Securities
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	10,770	19,690
Less than 12 months Gross Unrealized Losses	-628	-1,297
Greater than 12 months Fair Value	1,803	238
Greater than 12 months Gross Unrealized Losses	-409	-7
Fair Value	12,573	19,928
Gross Unrealized Losses	($1,037)	($1,304)

Summary_of_Cumulative_Amounts_

Summary of Cumulative Amounts Related to Credit Loss Portion of Other-Than-Temporary Impairment Losses on Debt Securities (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Beginning balance	$2,361	$5,154
Additions for credit loss impairments recognized in the current period on securities not previously impaired	0	0
Additions for credit loss impairments recognized in the current period on securities previously impaired	0	0
Reductions for credit loss impairments previously recognized on securities sold during the period	0	0
Ending balance	$2,361	$5,154

Net_Investment_Income_Detail

Net Investment Income (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Net Investment Income [Line Items]
Investment Income	$17,198	$17,404
Investment expenses	-945	-794
Net investment income	16,253	16,610
Fixed maturities
Net Investment Income [Line Items]
Investment Income	15,047	13,953
Equity Securities
Net Investment Income [Line Items]
Investment Income	1,968	3,233
Short-term investments
Net Investment Income [Line Items]
Investment Income	$183	$218

Realized_Gains_and_Losses_Excl

Realized Gains and Losses, Excluding Net Other-Than-Temporary Impairment Losses Recognized in Earnings (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Gain (Loss) on Investments [Line Items]
Net realized gains (losses)	$5,596	$833
Fixed maturities
Gain (Loss) on Investments [Line Items]
Gains	1,174	1,867
Losses	-572	-2,051
Net realized gains (losses)	602	-184
Short-term investments
Gain (Loss) on Investments [Line Items]
Gains	8
Losses	-162
Net realized gains (losses)	-154
Equity Securities
Gain (Loss) on Investments [Line Items]
Gains	6,325	1,920
Losses	-1,177	-903
Net realized gains (losses)	$5,148	$1,017

Fair_Value_Measurement_Additio

Fair Value Measurement - Additional Information (Detail) (USD $)	12 Months Ended	3 Months Ended
	Dec. 31, 2014	Mar. 31, 2014	Mar. 31, 2015
5.75% Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate stated on senior notes			5.75%
Senior notes due date	15-Oct-23
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Level 3 assets			0
Transfers from Level 3 to Level 2		$4,400,000

Fixed_Maturities_and_Equity_Se

Fixed Maturities and Equity Securities by Asset Class that are Measured at Fair Value (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	$2,746,822	$2,729,735
Liabilities, at fair Value	290,524	285,710
Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	2,345,225	2,365,934
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	310,389	397,923
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	547,664	541,007
Fixed maturities | Agency mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	364,468	364,622
Fixed maturities | Residential Mortgage Backed Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	33,116	34,087
Fixed maturities | Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	216,475	206,413
Fixed maturities | Commercial mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	231,703	206,318
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	845,762	811,440
Fixed maturities | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	641,410	615,564
Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	159,044	184,295
Short-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	242,553	179,506
Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities, at fair Value	290,524	285,710
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	411,077	453,593
Level 1 | Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	80,823	146,904
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	80,823	146,904
Level 1 | Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	87,701	127,183
Level 1 | Short-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	242,553	179,506
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	2,335,745	2,276,142
Liabilities, at fair Value	290,524	285,710
Level 2 | Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	2,264,402	2,219,030
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	229,566	251,019
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	547,664	541,007
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	364,468	364,622
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	33,116	34,087
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	216,475	206,413
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	231,703	206,318
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	845,762	811,440
Level 2 | Fixed maturities | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	641,410	615,564
Level 2 | Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	71,343	57,112
Level 2 | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities, at fair Value	$290,524	$285,710

Ceded_Reinsurance_Additional_I

Ceded Reinsurance - Additional Information (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Effects of Reinsurance [Line Items]
Reinsurance recoverables	$1,100,000,000
Reserve for uncollectible reinsurance amount	$8,200,000	$11,300,000

Debt_Additional_Information_De

Debt - Additional Information (Detail)	3 Months Ended			3 Months Ended				0 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Nov. 24, 2014	Nov. 22, 2012	Mar. 31, 2015	Nov. 06, 2014	Nov. 06, 2014	Mar. 31, 2015	Nov. 06, 2014
		USD ($)	USD ($)	Syndicate 1221	Syndicate 1221	Syndicate 1221	Syndicate 1221	Syndicate 1221
					AUD	GBP (£)	Lloyd's	Above Floating Rate
							USD ($)	Line of Credit
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				As of March 31, 2015, 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							145.1
Cash collateral posted							$1

Commitments_Contingencies_Guar

Commitments, Contingencies & Guarantees - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Loss Contingencies [Line Items]
Incentive awarded to the company by the State of Connecticut, total		$11.50
Incentive awarded to the company by the State of Connecticut, non-interest bearing loans	6	8
Incentive awarded to the company by the State of Connecticut, grants	1.5	3.5
Non-interest bearing incentive loan term		10 years
Incentive awarded to the company by the State of Connecticut, revenue recognized		0.2	0.2
Incentive awarded to the company by the State of Connecticut, deferred revenue	$7.50	$5.90		$6.10

Stock_Options_Stock_Grants_SAR1

Stock Options, Stock Grants, SARs and ESPP - Additional Information (Detail) (USD $)	3 Months Ended	0 Months Ended
	Mar. 31, 2015	Feb. 10, 2015	Mar. 05, 2015
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
Options expiration term (in years)	10 years
Restricted stock awards | Employee And Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock granted		4,658
Restricted stock grant date fair value		$77.31
Performance Based Shares | Employee And Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock granted			185,050
Restricted stock grant date fair value			$74.49