Navigators (NAVG) 10-K 17 Feb 17 2016 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2016	Jan. 27, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Trading Symbol	NAVG
Entity Registrant Name	NAVIGATORS GROUP INC
Entity Central Index Key	793,547
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		29,155,547
Entity Public Float			$ 1,014,101,687

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Investments:
Fixed maturities, available-for-sale, at fair value (amortized cost: 2016: $2,628,225; 2015: $2,400,245)		$ 2,635,882	$ 2,414,210
Equity securities, available-for-sale, at fair value (cost: 2016: $327,911; 2015: $281,943)		349,142	305,271
Short-term investments, at fair value (amortized cost: 2016: $143,451; 2015: $217,743)		143,539	217,745
Total investments		3,130,523	2,937,226
Cash		64,643	69,901
Premiums receivable		306,686	276,616
Prepaid reinsurance premiums		213,377	232,588
Reinsurance recoverable on paid losses		82,582	49,506
Reinsurance recoverable on unpaid losses and loss adjustment expenses		779,276	809,518
Deferred policy acquisition costs		119,660	91,983
Accrued investment income		17,315	16,001
Goodwill and other intangible assets		6,451	6,807
Current income tax receivable, net		20,556	22,323
Deferred income tax, net		20,938	3,900
Other assets		52,030	67,643
Total assets		4,814,037	4,584,012
Other invested assets		1,960
Liabilities:
Reserves for losses and loss adjustment expenses		2,289,727	2,202,644
Unearned premiums		887,344	820,676
Reinsurance balances payable		108,980	107,411
Senior notes		263,728	263,580
Accounts payable and other liabilities		86,070	93,553
Total liabilities		3,635,849	3,487,864
Stockholders' equity:
Preferred stock, $.10 par value, authorized 1,000,000 shares, none issued	[1]
Common stock, $.10 par value, authorized 50,000,000 shares, issued 36,146,899 shares for 2016 and 35,884,538 shares for 2015	[1]	3,612	3,586
Additional paid-in capital	[1]	373,983	356,036
Treasury stock, at cost (7,022,760 shares for 2016 and 2015)	[1]	(155,801)	(155,801)
Retained earnings	[1]	947,519	868,723
Accumulated other comprehensive income	[1]	8,875	23,604
Total stockholders' equity	[1]	1,178,188	1,096,148
Total liabilities and stockholders' equity		$ 4,814,037	$ 4,584,012
[1]	We completed a two-for-one stock split on January 20, 2017. All per share data has been retroactively restated on a post-split basis.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) $ in Thousands	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)$ / sharesshares
Fixed maturities, available-for-sale, amortized cost | $	$ 2,628,225	$ 2,400,245
Equity securities, available-for-sale, cost | $	327,911	281,943
Short-term investments, amortized cost | $	$ 143,451	$ 217,743
Preferred stock, par value | $ / shares	$ 0.10	$ 0.10
Preferred stock, authorized shares	1,000,000	1,000,000
Preferred stock, issued shares	0	0
Common stock, par value | $ / shares	$ 0.10	$ 0.10
Common stock, authorized shares	50,000,000	50,000,000
Common stock, issued shares	36,146,899	35,884,538
Treasury stock, shares	7,022,760	7,022,760

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands		3 Months Ended																12 Months Ended
		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Income Statement [Abstract]
Gross written premiums		$ 367,539		$ 374,930		$ 412,565		$ 413,877		$ 323,509		$ 354,062		$ 379,471		$ 396,460		$ 1,568,911		$ 1,453,502		$ 1,432,353
Revenues:
Net written premiums		282,868		277,001		306,535		319,820		244,719		251,939		258,244		288,958		1,186,224		1,043,860		1,000,138
Change in unearned premiums		1,117		7,009		(38,543)		(55,462)		6,826		2,143		(15,916)		(52,826)		(85,879)		(59,773)		(64,243)
Net earned premiums		283,985		284,010		267,992		264,358		251,545		254,082		242,328		236,132		1,100,345		984,087		935,895
Net investment income		20,107		19,875		19,875		19,594		18,499		17,371		16,595		16,253		79,451		68,718		64,168
Total other-than-temporary impairment losses		21		23		(162)		(109)		(123)		(1,298)		(423)				(227)		(1,870)		137
Portion of loss recognized in other comprehensive income (before tax)		(21)		(23)		12		109		123		23						77		172		(137)
Net other-than-temporary impairment losses recognized in earnings						(150)						(1,275)		(423)				(150)		(1,698)		0
Net realized gains (losses)																		9,186		8,373		12,812
Other income (expense)		1,905		(183)		4,430		2,549		4,147		(2,518)		(4,362)		2,242		8,701		(491)		10,656
Total revenues		310,040		305,288		294,107		288,098		272,111		268,178		258,477		260,223		1,197,533		1,058,989		1,023,531
Expenses:
Net losses and loss adjustment expenses		172,493		172,793		167,206		152,956		153,881		146,546		141,973		130,198		665,448		572,598		545,229
Commission expenses		44,154		42,611		40,726		37,554		31,339		34,253		31,480		32,905		165,045		129,977		125,528
Other operating expenses																		234,096		223,516		196,825
Interest expense		3,860		3,859		3,858		3,858		3,857		3,856		3,856		3,855		15,435		15,424		15,413
Total expenses		278,583		275,400		270,864		255,177		248,296		241,254		230,098		221,867		1,080,024		941,515		882,995
Income before income taxes		31,457		29,888		23,243		32,921		23,815		26,924		28,379		38,356		117,509		117,474		140,536
Income tax expense (benefit)		9,866		7,875		7,053		9,989		6,072		8,723		9,195		12,427		34,783		36,417		45,207
Net income		$ 21,591		$ 22,013		$ 16,190		$ 22,932		$ 17,743		$ 18,201		$ 19,184		$ 25,929		$ 82,726		$ 81,057		$ 95,329
Net income per common share:
Basic		$ 0.74	[1]	$ 0.76	[1]	$ 0.56	[1]	$ 0.79	[1]	$ 0.62	[2]	$ 0.63	[2]	$ 0.67	[2]	$ 0.90	[2]	$ 2.85	[1]	$ 2.82	[1]	$ 3.34	[1]
Diluted		$ 0.71	[1]	$ 0.73	[1]	$ 0.54	[1]	$ 0.77	[1]	$ 0.59	[2]	$ 0.61	[2]	$ 0.65	[2]	$ 0.89	[2]	$ 2.75	[1]	$ 2.73	[1]	$ 3.25	[1]
Average common shares outstanding:
Basic	[1]																	29,073,803		28,785,044		28,519,536
Diluted																		30,031,609		29,651,490		29,292,738
[1]	We completed a two-for-one stock split on January 20, 2017. All share and per share data has been retroactively restated on a post-split basis.
[2]	We completed a two-for-one stock split on January 20, 2017. All per share data has been retroactively restated on a post-split basis.

Consolidated Statements of Inc5

Consolidated Statements of Income (Parenthetical)	Jan. 20, 2017	Dec. 06, 2016
Stock split ratio		2
Stockholders equity, stock split		On December 6, 2016, our Board of Directors declared a two-for-one stock split of The Navigators Group, Inc. Common stock, to be effected in the form of a stock dividend.
Subsequent Event [Member]
Stock split ratio	2
Stockholders equity, stock split	We completed a two-for-one stock split on January 20, 2017.

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 82,726	$ 81,057	$ 95,329
Change in net unrealized gains (losses) on investments:
Unrealized gains (losses) on investments arising during the period, net of deferred tax of $3,730, $2,624, and $(14,925) in 2016, 2015 and 2014 respectively	(6,927)	(5,331)	28,252
Reclassification adjustment for net realized (gains) losses included in net income net of deferred tax of $(846), $9,185, and $2,776 in 2016, 2015 and 2014 respectively	1,572	(17,058)	(5,156)
Change in net unrealized gains (losses on investments)	(5,355)	(22,389)	23,096
Change in other-than-temporary impairments:
Non credit other-than-temporary impairments arising during the period, net of deferred tax of $27, $60, and $(48) in 2016, 2015 and 2014 respectively	(50)	(112)	89
Reclassification adjustment for other-than-temporary impairment credit losses recognized in net income net of deferred tax of $0, $(90), and $0 in 2016, 2015 and 2014 respectively		168
Change in other-than-temporary impairments	(50)	56	89
Change in foreign currency translation gains (losses), net of deferred tax of $5,017, $351, and $2,800 in 2016, 2015 and 2014 respectively	(9,324)	(622)	(4,986)
Other comprehensive income (loss)	(14,729)	(22,955)	18,199
Comprehensive income (loss)	$ 67,997	$ 58,102	$ 113,528

Consolidated Statements of Com7

Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Unrealized gains (losses) on investments arising during the period, deferred tax	$ 3,730	$ 2,624	$ (14,925)
Reclassification adjustment for net realized (gains) losses included in net income, deferred tax	(846)	9,185	2,776
Non credit other-than-temporary impairments arising during the period, deferred tax	27	60	(48)
Reclassification adjustment for other-than-temporary impairment credit losses recognized in net income, deferred tax	0	(90)	0
Change in foreign currency translation gains (losses), deferred tax	$ 5,017	$ 351	$ 2,800

Consolidated Statement of Stock

Consolidated Statement of Stockholders' Equity - USD ($) $ in Thousands		Total		Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2013		$ 902,212		$ 3,540	$ 333,776	$ (155,801)	$ 692,337	$ 28,360
Beginning balance (in shares) at Dec. 31, 2013				35,419,752		7,022,760
Net income		95,329					95,329
Changes in comprehensive income:
Change in net unrealized gain (loss) on investments		23,096						23,096
Change in net non-credit other-than-temporary impairment losses		89						89
Change in foreign currency translation gain (loss)		(4,986)						(4,986)
Other comprehensive income (loss)		18,199						18,199
Shares issued	[1]	(23)		$ 16	(39)
Shares issued (in shares)	[1]			165,940
Share-based compensation		11,507			11,507
Ending balance at Dec. 31, 2014		1,027,224		$ 3,556	345,244	$ (155,801)	787,666	46,559
Ending balance (in shares) at Dec. 31, 2014				35,585,692		7,022,760
Net income		81,057					81,057
Changes in comprehensive income:
Change in net unrealized gain (loss) on investments		(22,389)						(22,389)
Change in net non-credit other-than-temporary impairment losses		56						56
Change in foreign currency translation gain (loss)		(622)						(622)
Other comprehensive income (loss)		(22,955)						(22,955)
Shares issued	[1]	(4,175)		$ 30	(4,205)
Shares issued (in shares)	[1]			298,846
Share-based compensation		14,997			14,997
Ending balance at Dec. 31, 2015		$ 1,096,148	[2]	$ 3,586	356,036	$ (155,801)	868,723	23,604
Ending balance (in shares) at Dec. 31, 2015		35,884,538		35,884,538		7,022,760
Net income		$ 82,726					82,726
Dividends paid		(3,930)					(3,930)
Changes in comprehensive income:
Change in net unrealized gain (loss) on investments		(5,355)						(5,355)
Change in net non-credit other-than-temporary impairment losses		(50)						(50)
Change in foreign currency translation gain (loss)		(9,324)						(9,324)
Other comprehensive income (loss)		(14,729)						(14,729)
Shares issued	[1]	349		$ 26	323
Shares issued (in shares)	[1]			262,361
Share-based compensation		17,624			17,624
Ending balance at Dec. 31, 2016		$ 1,178,188	[2]	$ 3,612	$ 373,983	$ (155,801)	$ 947,519	$ 8,875
Ending balance (in shares) at Dec. 31, 2016		36,146,899		36,146,899		7,022,760
[1]	Includes shares issued under the stock plan, to directors and ESPP
[2]	We completed a two-for-one stock split on January 20, 2017. All per share data has been retroactively restated on a post-split basis.

Consolidated Statement of Stoc9

Consolidated Statement of Stockholders' Equity (Parenthetical)	Jan. 20, 2017	Dec. 06, 2016
Stockholders equity, stock split		On December 6, 2016, our Board of Directors declared a two-for-one stock split of The Navigators Group, Inc. Common stock, to be effected in the form of a stock dividend.
Stock split ratio		2
Subsequent Event [Member]
Stockholders equity, stock split	We completed a two-for-one stock split on January 20, 2017.
Stock split ratio	2

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities:
Net income	$ 82,726	$ 81,057	$ 95,329
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation & amortization	5,429	5,386	4,915
Share-based compensation	17,624	14,997	11,507
Deferred income taxes	(5,755)	7,004	16,881
Net realized (gains) losses	(9,186)	(8,373)	(12,812)
Net other-than-temporary losses recognized in earnings	150	1,698	0
Changes in assets and liabilities:
Reinsurance recoverable on paid and unpaid losses and loss adjustment expenses	(2,835)	43,822	(42,024)
Reserves for losses and loss adjustment expenses	87,083	43,010	114,563
Prepaid reinsurance premiums	19,211	5,264	10,344
Unearned premiums	66,668	54,509	52,380
Premiums receivable	(30,070)	65,863	(17,455)
Deferred policy acquisition costs	(27,677)	(12,531)	(12,445)
Accrued investment income	(1,314)	(1,210)	(925)
Reinsurance balances payable	1,568	(45,124)	(14,716)
Current income taxes	(1,988)	(8,072)	(582)
Other	22,593	(19,676)	17,532
Net cash provided by (used in) operating activities	224,227	227,624	222,492
Fixed maturities
Redemptions and maturities	275,706	180,876	210,674
Sales	446,666	376,522	362,136
Purchases	(962,419)	(648,059)	(864,902)
Equity securities
Sales	54,798	96,405	54,900
Purchases	(92,329)	(215,405)	(83,845)
Change in payable for securities	(1,517)	1,851	(7,814)
Purchase of other invested assets	(1,960)
Net change in short-term investments	73,541	(38,468)	117,740
Purchase of property and equipment	(3,918)	(3,577)	(8,359)
Net cash provided by (used in) investing activities	(211,432)	(249,855)	(219,470)
Financing activities:
Proceeds of stock issued from employee stock purchase plan	1,840	1,352	1,067
Proceeds of stock issued from exercise of stock options		29	153
Dividends paid	(3,930)
Net cash provided by (used in) financing activities	(2,090)	1,381	1,220
Effect of exchange rate on cash	(15,963)
Change in cash	(5,258)	(20,850)	4,242
Cash at beginning of year	69,901	90,751	86,509
Cash at end of period	64,643	69,901	90,751
Supplemental cash information:
Income taxes paid, net	34,830	35,447	27,066
Interest paid	15,238	15,238	15,703
Issuance of stock to directors	$ 633	$ 563	$ 438

Organization and Summary of Sig

Organization and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Organization and Summary of Significant Accounting Policies	NOTE 1. ORGANIZATION & SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation The accompanying consolidated financial statements of The Navigators Group, Inc. and its subsidiaries have been prepared in conformity with accounting principles generally accepted in the United States of America (“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, disclosure of contingent assets and liabilities at the date of the financial statements and the reported revenues and expenses during the reporting periods. 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 term “Parent Company” is 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 U.S. and Int’l Insurance reporting segments. We have also developed niches in Professional Liability insurance, through our Directors & Officers (“D&O”) and Errors & Omissions (“E&O”) divisions. We also provide reinsurance products through our Global Reinsurance (“GlobalRe”) business. We operate through various wholly-owned subsidiaries, including Navigators Insurance Company (“NIC”), inclusive of its United Kingdom Branch (“U.K. Branch”), and Navigators Specialty Insurance Company (“NSIC”), both of which are U.S. insurance companies, and Navigators Underwriting Agency Ltd. (“NUAL”), a Lloyd’s of London (“Lloyd’s”) underwriting agency that manages Lloyd’s Syndicate 1221 (“the Syndicate”) in the U.K. and is the underwriting company of Navigators Holdings (U.K.) Ltd. (“NHUK”). Our Company controls 100% of the Syndicate’s stamp capacity. In May 2016, our Company received authorization from the Prudential Regulation Authority (“PRA”) and the Financial Conduct Authority (“FCA”) for a new U.K. based insurance company, Navigators International Insurance Company Ltd (“NIIC”), which is a wholly-owned direct subsidiary of our Parent Company, and has been fully capitalized in compliance with the terms of the authorization from the PRA. Significant Accounting Policies Cash Cash includes cash on hand and demand deposits with banks, excluding such amounts held by the Syndicate included as Funds at Lloyd’s (“FAL”), which are classified as short term investments. Investments As of December 31, 2016 and 2015, all fixed maturity and equity securities held by our Company were carried at fair value and classified as available-for-sale. Available-for-sale securities are debt and equity securities not classified as either held-to-maturity securities or trading securities and are reported at fair value, with unrealized gains and losses excluded from earnings and reported in accumulated other comprehensive income (“AOCI”) as a separate component of stockholders’ equity. Fixed maturity securities include bonds, mortgage-backed and asset-backed securities. Equity securities consist of common stock, exchange traded funds and preferred stock. Other invested assets consist of investments our Company made in certain strategic companies which are accounted for using the equity method of accounting. In applying the equity method, these investments are initially recorded at cost and are subsequently adjusted based on our Company’s proportionate share of the net income or loss of the companies. Changes in the carrying value of such investments are recorded in Other income. In applying the equity method, we use the most recently available financial information provided by the companies which is generally three months prior to the end of the reporting period. Short-term investments are carried at fair value. Short-term investments mature within one year from the purchase date. All prices for our fixed maturities, equity securities and short-term investments are classified as Level 1, Level 2 or Level 3 under the fair value hierarchy, as defined in the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification 820 (“ASC 820”). Premiums and discounts on fixed maturity securities are amortized into interest income over the life of the security using the interest method. For mortgage-backed and asset-backed securities, anticipated prepayments and expected maturities are utilized in applying the interest rate method. An effective yield is calculated based on projected principal cash flows at the time of original purchase. The effective yield is used to amortize the purchase price of the security over the security’s expected life. Book values are adjusted to reflect the amortization of premium or accretion of discount on a monthly basis. The projected principal cash flows are based on certain prepayment assumptions, which are generated using a prepayment model. The prepayment model uses a number of factors to estimate prepayment activity including the current levels of interest rates (refinancing incentive), time of year (seasonality), economic activity (including housing turnover) and term and age of the underlying collateral (burnout, seasoning). Prepayment assumptions associated with the mortgage-backed and asset-backed securities are reviewed on a periodic basis. When changes in prepayment assumptions are deemed necessary as the result of actual prepayments differing from anticipated prepayments, securities are revalued based upon the new prepayment assumptions utilizing the retrospective adjustment method, whereby the effective yield is recalculated to reflect actual payments to date and anticipated future payments. The investment in such securities is adjusted to the amount that would have existed had the new effective yield been applied since the acquisition of the security. Such adjustments, if any, are included in Net investment income for the current period. Realized gains and losses on sales of investments are recognized when the related trades are executed and are determined on the basis of the specific identification method. Impairment of Invested Assets Management regularly reviews our fixed maturity and equity securities portfolios to evaluate the necessity of recording impairment losses for other-than-temporary declines in the fair value of securities. Our Company reviews the magnitude of a security’s unrealized loss compared to its cost/amortized cost and the length of time that the security has been impaired to determine if an unrealized loss is other-than-temporary. If warranted as a result of conditions relating to a particular security, our Company will also review securities with declines in fair value resulting from a headline news event involving the issuer, a headline news event involving the asset class, the advice of our external asset managers, or economic events that may impact the issuer to determine if an unrealized loss is other-than-temporary. The depth of analysis performed is dependent upon the nature and magnitude of the indicators of other-than-temporary impairment present in regards to each impaired security. For Equity securities, our Company performs a fundamental analysis of the issuer, including an evaluation of the mean analysts’ target price, to assess the likelihood of recovery of our cost basis in the security. Management also assesses the likelihood of future cash flows, dividends and increases to dividends, all of which affect the securities eligible for our equity strategy and therefore our intent to hold the security. 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. For Fixed maturities, our Company assesses the underlying fundamentals of each issuer to determine if there is a change in the amount or timing of expected cash flows. Management compares the amortized cost basis to the present value of the revised cash flows using the historical book yield to determine the credit loss portion of impairment which is recognized in earnings. All non-credit losses where we have the intent and ability to hold the security until recovery are recognized as changes in OTTI losses within AOCI. Specifically for structured Fixed maturities, our Company analyzes 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. For securities in which a tranche loss is present and the net present value of loss adjusted cash flows is less than book value, credit impairment is recognized in earnings. 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, severity and prepayment assumptions. Projected losses are a function of both loss severity and probability of default, which differ based on property type, vintage and the stress of the collateral . Foreign Currency Remeasurement and Translation The functional currency of each of our operations is generally the currency of the local operating environment, except for our Lloyd’s business which is United States Dollar (“USD”). Transactions in currencies other than an operation’s functional currency are remeasured into the functional currency and the resulting foreign exchange gains and losses are reflected in net Other income (expense) in the Consolidated Statements of Income. Functional currency assets and liabilities of foreign operations are translated into USD using period end rates of exchange and the related translation adjustments are recorded as a separate component of AOCI. Consolidated Statements of Income amounts expressed in functional currencies are translated using average exchange rates. 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 British Pound Sterling (“GBP”), U.S. Dollars (“USD”) and Canadian Dollars (“CAD”) to one functional currency, the 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 resulted in a 2014 immaterial correction of $10.0 million ($6.6 million after-tax) in AOCI, on the Consolidated Balance Sheets, offset by a gain in Other income in the Consolidated Statements of Income. Premium Revenues Written premium is based on the insurance policies that have been reported to us and the policies that have been written by agents but not yet reported to us. We estimate the amount of written premium not yet reported based on judgments relative to current and historical trends of the business being written. Such estimates are regularly reviewed and updated and any resulting adjustments are included in the current year’s results. An Unearned premium reserve is established to reflect the unexpired portion of each policy at the financial reporting date. Substantially all of our business is placed through agents and brokers. We record estimates for both unreported direct and assumed premiums. We also record the ceded portion of the estimated Gross written premiums and related acquisition costs. These estimates are mostly for our Marine and Energy & Engineering products written by our International Insurance (“Int’l Insurance”) reporting segment as well as our Accident & Health (“A&H”) and Latin American (“LatAm”) business written by our GlobalRe reporting segment. Such premium estimates are generally based on submission data received from brokers and agents and recorded when the insurance policy or reinsurance contract is written or bound. The earned gross, ceded and net premiums are calculated based on our earning methodology, which is generally pro-rata over the policy period or over the period of risk if the period of risk differs significantly from the contract period. Reinsurance Ceded In the normal course of business, we purchase reinsurance from insurers or reinsurers to reduce the amount of loss arising from claims. Management analyzes the reinsurance agreements to determine whether the reinsurance should be classified as prospective or retroactive based upon the terms of the reinsurance agreement and whether the reinsurer has assumed significant insurance risk to the extent that the reinsurer may realize a significant loss from the transaction. Prospective reinsurance is reinsurance in which an assuming company agrees to reimburse the ceding company for losses that may be incurred as a result of future insurable events covered under contracts subject to the reinsurance. Retroactive reinsurance is reinsurance in which an assuming company agrees to reimburse a ceding company for liabilities incurred as a result of past insurable events covered under contracts subject to the reinsurance. Ceded reinsurance premiums net of ceding commissions and ceded losses are reflected as reductions of the respective income or expense accounts over the terms of the reinsurance contracts. Prepaid reinsurance premiums represent the portion of premiums ceded to reinsurers applicable to the unexpired terms of the reinsurance contracts in force. Reinsurance reinstatement premiums (“RRPs”) are recognized in the same period as the loss event that gave rise to the reinstatement premiums. Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability associated with the reinsured policy. Ceded Unearned premiums and estimates of amounts recoverable from reinsurers on paid and unpaid losses are reflected as assets. Provisions are made for estimated unrecoverable reinsurance. Deferred Policy Acquisition Costs Costs of acquiring business are deferred and amortized over the period that the related premiums are recognized as revenue. Such costs (e.g., Commission expenses, Other underwriting expenses and Premium taxes) are limited to the incremental direct costs related to the successful acquisition of new or renewal business. The method of computing deferred policy acquisition costs limits the deferral to their estimated net realizable value based on the related Unearned premiums and takes into account anticipated losses, loss adjustment expense (“LAE”), Commission expenses and Operating expenses based on historical and current experience, as well as anticipated investment income. Reserves for Losses and Loss Adjustment Expenses Unpaid losses and LAE are determined on: (a) individual claims reported on direct business for insureds, (b) from reports received from ceding insurers for assumed business and (c) on estimates based on Company and industry experience for incurred but not reported (“IBNR”) claims and LAE. Indicated IBNR reserves for losses and LAE are calculated by our actuaries using several standard actuarial methodologies, including the paid and incurred loss development and the paid and incurred Bornheutter-Ferguson loss methods. Frequency/severity analyses are performed for certain books of business. The Reserve for losses and LAE has been established to cover the estimated unpaid cost of claims incurred. Such estimates are regularly compared to indicated reserves and updated and any resulting adjustments are included in the current year’s results. Management believes that the liability recognized for unpaid losses and LAE is a reasonable estimate of the ultimate unpaid claims incurred, however, no representation is made that the ultimate liability will not differ materially from the amounts recorded in the accompanying Consolidated Financial Statements. Losses and LAE are recorded on an undiscounted basis. Earnings per Share Basic earnings per share (“EPS”) is computed by dividing Net income by the weighted average number of common shares outstanding for the period. Diluted EPS reflects the basic EPS adjusted for the potential dilution that would occur if all issued stock options were exercised and all stock grants were fully vested. Depreciation and Amortization Depreciation of furniture and fixtures, electronic data processing equipment and computer software is provided over the estimated useful lives of the respective assets, ranging from three to seven years, using the straight-line method. Amortization of leasehold improvements are provided over the shorter of the useful lives of those improvements or the contractual terms of the leases, ranging from five to ten years, using the straight-line method. Goodwill and Other Intangible Assets Goodwill represents the excess of the cost of acquiring a business enterprise over the fair value of the net assets acquired. Our Company’s recorded indefinite lived intangible assets represent acquired stamp capacity in the Syndicate. Goodwill and indefinite lived intangible assets are reported at carrying value and are tested for impairment at least annually, and when permitted by the applicable accounting guidance, qualitative factors are assessed to determine whether it is necessary to calculate an asset’s fair value when testing an asset with an indefinite life for impairment. Goodwill and indefinite lived intangible assets are considered impaired if the estimated fair value is less than its carrying value and any impairment loss is measured as the difference between the implied fair value and the carrying value. Our Company did not recognize an impairment of goodwill or the indefinite lived intangible assets for any of the years ended December 31, 2016, 2015 and 2014. As of December 31, 2016, the carrying value of goodwill and indefinite lived intangible assets was $6.5 million, which is $0.3 million less than the carrying value as of December 31, 2015, $6.8 million. Changes in the carrying value of the goodwill and indefinite lived intangible assets are due to amortization and fluctuations in currency exchange rates between the USD and the GBP. Income Taxes We recognize deferred tax assets and liabilities based on the differences between the financial statement carrying amounts and the tax bases of assets and liabilities. Deferred tax assets are reduced by a valuation allowance if, based on the weight of available evidence, it is more likely than not that some portion or all of the deferred tax assets will not be realized. All available evidence, both positive and negative, is considered to determine whether, based on the weight of that evidence, a valuation allowance is needed. Future realization of the tax benefit of an existing deferred tax asset ultimately depends on the existence of sufficient taxable income of the appropriate character within the carryback/carryforward period available under the tax law. In determining whether a valuation allowance is needed, management considers the timing of the reversal of each deferred tax asset as well as expected future levels of taxable income, amounts of taxable income in carryback years, and tax planning strategies. Additional information regarding our deferred tax assets can be found in Note 9, Income Taxes. Current and Pending Accounting Pronouncements As of January 1, 2016, we adopted the following accounting pronouncements, which did not have a material effect, singly or in the aggregate, on our Consolidated Financial Statements: • Accounting Standards Update 2015-03 – Interest – Imputation of Interest (Subtopic 835-30) – Simplifying the Presentation of Debt Issuance Costs, which is effective for fiscal years beginning after December 15, 2015. The new pronouncement was issued to simplify presentation of debt issuance costs. • Accounting Standards Update 2015-05 – Intangibles – Goodwill and Other – Internal Use Software (Subtopic 350-40) Customer’s Accounting for Fees Paid in a Cloud Computing Arrangement, which is effective for fiscal years beginning after December 15, 2015. The new pronouncement was issued to provide guidance to customers about whether a cloud computing arrangement includes a software license. • Accounting Standards Update 2015-07 – Fair Value Measurement – (Topic 820) Disclosures for Investments in Certain Entities that Calculate Net Asset Value per Share (or its equivalent) (a consensus of the Emerging Issues Task Force), which is effective for fiscal years beginning after December 15, 2015. The new pronouncement was issued to ensure that all investments categorized in the fair value hierarchy are classified using a consistent approach. The Financial Accounting Standards Board has issued the following new pronouncements that may have an impact on our Company and we are assessing the future impact of these updates on our Consolidated Financial Statements: • Accounting Standards Update 2016-01 – Financial Instruments (Subtopic 825-10) – Recognition and Measurement of Financial Assets and Financial Liabilities, which will be effective for fiscal years beginning after December 15, 2017. The new pronouncement was issued to make targeted improvements to the presentation of financial instruments. We expect the adoption of this pronouncement to have limited impact to our financial statements. • Accounting Standards Update 2016-02 – Leases (Topic 842) – Amends the recognition of a right-to-use asset and lease liability on the statement of financial position of those leases previously classified as operating leases under the previous guidance, which will be effective for fiscal years beginning after December 15, 2018. The new pronouncement was issued to improve transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. We expect the adoption of this pronouncement to result in limited changes to our total assets and total liabilities. • Accounting Standards Update 2016-09 – Compensation – Stock Compensation – (Topic 718) – Improvements to Employee Share-Based Accounting, which will be effective for fiscal years beginning after December 15, 2016. The new pronouncement was issued to simplify employee share-based accounting. We expect the adoption of this pronouncement to simplify our reporting but not have a material effect to our financial statements. • Accounting Standards Update 2016-13 – Financial Instruments – Credit Losses (Topic 326) – amends the measurement of credit losses on financial instruments not accounted for at fair value including loans, debt securities, reinsurance receivables and any other financial assets, which will be effective for the fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. We expect the adoption of this pronouncement to have limited impact to our financial statements. • Accounting Standards Update 2016-15 – Statements of Cash Flows (Topic 230) – Classification of Certain Cash Receipts and Cash Payments amends how certain cash receipts and cash payments are presented in the statement of cash flows to reduce existing diversity in practice. We expect that the adoption of this pronouncement will not have a material effect on our financial statements. • Accounting Standards Update 2016-16 - Income Taxes (Topic 740) - Amends current guidance by eliminating the exception for an intra-entity transfer of an asset other than inventory. Under the new standard, an entity should recognize the income tax consequences when the transfer occurs. The guidance prescribed is effective beginning fiscal year 2018, including interim periods. We expect that the adoption of this pronouncement will not have a material effect on our financial statements. • Accounting Standards Update 2016-17 - Consolidation (Topic 810) - Amends the consolidation guidance concerning the evaluation of interests in variable interest entities. The accounting standards update requires a reporting entity to include interests held by related parties under common control proportionally when assessing whether it holds a variable interest in a VIE. The prescribed guidance is effective beginning in fiscal year 2017, including interim periods. We expect that the adoption of this pronouncement will not have a material effect on our financial statements. • Accounting Standards Updated 2016-18 - Statement of Cash Flows (Topic 230) - Requires that amounts generally described as restricted cash and cash equivalents be included within total cash and cash equivalents in the Statement of Cash Flows. The guidance prescribed is effective beginning in fiscal year 2018, including interim periods. We expect the adoption of this pronouncement to have limited impact to our financial statements. There were no additional accounting pronouncements that are expected to have an impact on the Consolidated Financial Statements upon adoption.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Segment Information	NOTE 2. SEGMENT INFORMATION We report our results of operations consistent with the manner in which our Chief Operating Decision Maker reviews the business to assess performance through our reporting segments: U.S. Insurance, International Insurance (“Int’l Insurance”), GlobalRe and Corporate. We classify our business into three underwriting segments: U.S. Insurance, Int’l Insurance and GlobalRe. Both the U.S. Insurance and Int’l Insurance reporting segments are each comprised of three operating segments: Marine, P&C and Professional Liability. 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 (loss) is calculated from Net earned premiums less the sum of Net losses and LAE, Commission expenses, Other operating expenses and Other underwriting income (expense). The Combined ratio is derived by dividing the sum of Net losses 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 segment. The following tables set forth the financial data by segment for the years ended December 31, 2016, 2015 and 2014: Year Ended December 31, 2016 U.S. Int'l amounts in thousands Insurance Insurance GlobalRe Corporate (1) Total Net earned premiums $ 629,308 $ 307,416 $ 163,621 $ — $ 1,100,345 Net losses and LAE (397,860 ) (178,284 ) (89,304 ) — (665,448 ) Commission expenses (70,812 ) (61,703 ) (34,008 ) 1,478 (165,045 ) Other operating expenses (128,108 ) (86,395 ) (19,593 ) — (234,096 ) Other underwriting income (expense) 1,092 — 522 (1,478 ) 136 Underwriting profit (loss) $ 33,620 $ (18,966 ) $ 21,238 $ — $ 35,892 Net investment income 79,451 79,451 Net realized gains (losses) 9,036 9,036 Interest expense (15,435 ) (15,435 ) Other income (loss) 8,565 8,565 Income before income taxes $ 33,620 $ (18,966 ) $ 21,238 $ 81,617 $ 117,509 Income tax (expense) benefit (34,783 ) (34,783 ) Net income (loss) $ 82,726 Losses and LAE ratio 63.2 % 58.0 % 54.6 % 60.5 % Commission expense ratio 11.3 % 20.1 % 20.8 % 15.0 % Other operating expense ratio (2) 20.2 % 28.1 % 11.6 % 21.2 % Combined ratio 94.7 % 106.2 % 87.0 % 96.7 % ( 1) - Includes Corporate segment intercompany eliminations. (2) - Includes Other operating expenses and Other underwriting income (expense). Year Ended December 31, 2015 U.S. Int'l amounts in thousands Insurance Insurance GlobalRe Corporate (1) Total Net earned premiums $ 555,836 $ 259,960 $ 168,291 $ — $ 984,087 Net losses and LAE (343,497 ) (134,702 ) (94,399 ) — (572,598 ) Commission expenses (56,319 ) (43,676 ) (32,240 ) 2,258 (129,977 ) Other operating expenses (131,407 ) (75,867 ) (16,242 ) — (223,516 ) Other underwriting income (expense) 1,690 — 690 (2,258 ) 122 Underwriting profit (loss) $ 26,303 $ 5,715 $ 26,100 $ — $ 58,118 Net investment income 68,718 68,718 Net realized gains (losses) 6,675 6,675 Interest expense (15,424 ) (15,424 ) Other income (loss) (613 ) (613 ) Income before income taxes $ 26,303 $ 5,715 $ 26,100 $ 59,356 $ 117,474 Income tax (expense) benefit (36,417 ) (36,417 ) Net income (loss) $ 81,057 Losses and LAE ratio 61.8 % 51.8 % 56.1 % 58.2 % Commission expense ratio 10.1 % 16.8 % 19.2 % 13.2 % Other operating expense ratio (2) 23.4 % 29.2 % 9.2 % 22.7 % Combined ratio 95.3 % 97.8 % 84.5 % 94.1 % (1) - Includes Corporate segment intercompany eliminations. (2) - Includes Other operating expenses and Other underwriting income (expense ). Year Ended December 31, 2014 U.S. Int'l amounts in thousands Insurance Insurance GlobalRe Corporate (1) Total Net earned premiums $ 504,289 $ 243,485 $ 188,121 $ — $ 935,895 Net losses and LAE (311,839 ) (115,079 ) (118,311 ) — (545,229 ) Commission expenses (49,840 ) (44,426 ) (33,429 ) 2,167 (125,528 ) Other operating expenses (115,817 ) (65,275 ) (15,733 ) — (196,825 ) Other underwriting income (expense) 2,241 32 489 (2,167 ) 595 Underwriting profit (loss) $ 29,034 $ 18,737 $ 21,137 $ — $ 68,908 Net investment income 64,168 64,168 Net realized gains (losses) 12,812 12,812 Interest expense (15,413 ) (15,413 ) Other income (loss) 10,061 10,061 Income (loss) before income taxes $ 29,034 $ 18,737 $ 21,137 $ 71,628 $ 140,536 Income tax (expense) benefit (45,207 ) (45,207 ) Net income (loss) $ 95,329 Losses and LAE ratio 61.8 % 47.3 % 62.9 % 58.3 % Commission expense ratio 9.9 % 18.2 % 17.8 % 13.4 % Other operating expense ratio (2) 22.5 % 26.8 % 8.1 % 20.9 % Combined ratio 94.2 % 92.3 % 88.8 % 92.6 % (1) - Includes Corporate segment intercompany eliminations. (2) - Includes Other operating expenses and Other underwriting income (expense ). The following tables provide additional financial data by operating segment for the years ended December 31, 2016, 2015 and 2014: Year Ended December 31, 2016 amounts in thousands Gross written premiums Ceded premiums Net written premiums Net earned premiums U.S. Insurance Marine $ 169,405 $ (70,858 ) $ 98,547 $ 100,132 P&C 631,562 (135,888 ) 495,674 453,673 Professional Liability 118,428 (29,081 ) 89,347 75,503 Total $ 919,395 $ (235,827 ) $ 683,568 $ 629,308 Int'l Insurance Marine $ 183,228 $ (40,092 ) $ 143,136 $ 141,593 P&C 181,094 (69,606 ) 111,488 89,455 Professional Liability 120,149 (28,806 ) 91,343 76,368 Total $ 484,471 $ (138,504 ) $ 345,967 $ 307,416 GlobalRe $ 165,045 $ (8,356 ) $ 156,689 $ 163,621 Total $ 1,568,911 $ (382,687 ) $ 1,186,224 $ 1,100,345 Year Ended December 31, 2015 amounts in thousands Gross written premiums Ceded written premiums Net written premiums Net earned premiums U.S. Insurance Marine $ 158,124 $ (61,916 ) $ 96,208 $ 96,082 P&C 596,673 (152,168 ) 444,505 401,408 Professional Liability 110,984 (54,691 ) 56,293 58,346 Total $ 865,781 $ (268,775 ) $ 597,006 $ 555,836 Int'l Insurance Marine $ 183,707 $ (36,515 ) $ 147,192 $ 149,256 P&C 130,729 (67,722 ) 63,007 55,320 Professional Liability 97,511 (29,768 ) 67,743 55,384 Total $ 411,947 $ (134,005 ) $ 277,942 $ 259,960 GlobalRe $ 175,774 $ (6,862 ) $ 168,912 $ 168,291 Total $ 1,453,502 $ (409,642 ) $ 1,043,860 $ 984,087 Year Ended December 31, 2014 amounts in thousands Gross written premiums Ceded written premiums Net written premiums Net earned premiums U.S. Insurance Marine $ 154,233 $ (46,685 ) $ 107,548 $ 105,650 P&C 543,045 (169,953 ) 373,092 314,833 Professional Liability 109,830 (38,345 ) 71,485 83,806 Total $ 807,108 $ (254,983 ) $ 552,125 $ 504,289 Int'l Insurance Marine $ 190,787 $ (47,805 ) $ 142,982 $ 141,097 P&C 158,139 (98,087 ) 60,052 62,520 Professional Liability 75,978 (26,029 ) 49,949 39,868 Total $ 424,904 $ (171,921 ) $ 252,983 $ 243,485 GlobalRe $ 200,341 $ (5,311 ) $ 195,030 $ 188,121 Total $ 1,432,353 $ (432,215 ) $ 1,000,138 $ 935,895 The assets of the Company are reviewed in total by management for purposes of decision making.

Investments

Investments	12 Months Ended
	Dec. 31, 2016
Investments Debt And Equity Securities [Abstract]
Investments	NOTE 3. INVESTMENTS The following tables set forth our Company’s available- for- sale investments as of December 31, 2016 and 2015 and include OTTI securities recognized within AOCI: December 31, 2016 Gross Gross Unrealized Unrealized Amortized amounts in thousands Fair Value Gains Losses Cost Fixed maturities: U.S. Treasury bonds, agency bonds and foreign government bonds $ 273,776 $ 2,192 $ (5,128 ) $ 276,712 States, municipalities and political subdivisions 547,415 11,542 (4,036 ) 539,909 Mortgage-backed and asset-backed securities: Agency mortgage-backed securities 487,364 4,016 (6,585 ) 489,933 Residential mortgage obligations 20,530 453 (55 ) 20,132 Asset-backed securities 314,601 824 (1,178 ) 314,955 Commercial mortgage-backed securities 154,139 2,859 (1,904 ) 153,184 Subtotal $ 976,634 $ 8,152 $ (9,722 ) $ 978,204 Corporate bonds 838,057 10,185 (5,528 ) 833,400 Total fixed maturities $ 2,635,882 $ 32,071 $ (24,414 ) $ 2,628,225 Equity securities 349,142 27,016 (5,785 ) 327,911 Short-term investments 143,539 88 — 143,451 Total investments $ 3,128,563 $ 59,175 $ (30,199 ) $ 3,099,587 December 31, 2015 Gross Gross Unrealized Unrealized Amortized amounts in thousands Fair Value Gains Losses Cost Fixed maturities: U.S. Treasury bonds, agency bonds and foreign government bonds $ 252,882 $ 2,273 $ (9,214 ) $ 259,823 States, municipalities and political subdivisions 576,859 21,233 (781 ) 556,407 Mortgage-backed and asset-backed securities: Agency mortgage-backed securities 379,269 5,573 (2,082 ) 375,778 Residential mortgage obligations 30,465 694 (82 ) 29,853 Asset-backed securities 225,012 85 (1,624 ) 226,551 Commercial mortgage-backed securities 189,713 3,119 (1,864 ) 188,458 Subtotal $ 824,459 $ 9,471 $ (5,652 ) $ 820,640 Corporate bonds 760,010 7,373 (10,738 ) 763,375 Total fixed maturities $ 2,414,210 $ 40,350 $ (26,385 ) $ 2,400,245 Equity securities 305,271 26,341 (3,013 ) 281,943 Short-term investments 217,745 2 — 217,743 Total investments $ 2,937,226 $ 66,693 $ (29,398 ) $ 2,899,931 During 2016 our Company made strategic investments in certain companies which are reported as Other invested assets on the Consolidated Balance Sheet and accounted for using the equity method. In applying the equity method, these investments are initially recorded at cost and are subsequently adjusted based on our Company’s proportionate share of the net income or loss of the companies. Our initial purchase price of $2.0 million is reflected in our December 31, 2016 Consolidated Balance Sheet at $2.0 million. As of December 31, 2016 and 2015, 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 December 31, 2016 and 2015, fixed maturities for which non-credit OTTI was previously recognized and included in AOCI are now in a net unrealized net gains position of $0.4 million and $0.5 million, respectively. The fair value of our Company’s investment portfolio may fluctuate significantly in response to various factors such as changes in interest rates, investment quality ratings, equity prices, foreign exchange rates and credit spreads. Our Company does not have the intent to sell nor is it more likely than not that it will have to sell fixed maturities in unrealized loss positions that are not other-than-temporarily impaired before recovery. For structured securities, default probability and severity assumptions differ based on property type, vintage and the stress of the collateral. Our Company does not intend to sell, 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 December 31, 2016 are shown in the following table: December 31, 2016 Amortized amounts in thousands Fair Value Cost Due in one year or less $ 133,644 $ 134,931 Due after one year through five years 778,875 778,511 Due after five years through ten years 295,742 291,811 Due after ten years 450,987 444,768 Mortgage-backed and asset-backed securities 976,634 978,204 Total $ 2,635,882 $ 2,628,225 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 4.9 years. The following tables summarize all securities in a gross unrealized loss position as of December 31, 2016 and 2015, 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: December 31, 2016 Less than 12 months Greater than 12 months Total Gross Gross Gross Fair Unrealized Fair Unrealized Fair Unrealized amounts in thousands Value (Losses) Value (Losses) Value (Losses) Fixed maturities: U.S. Treasury bonds, agency bonds and foreign government bonds $ 150,891 $ (2,570 ) $ 16,819 $ (2,558 ) $ 167,710 $ (5,128 ) States, municipalities and political subdivisions 137,731 (3,111 ) 13,255 (925 ) 150,986 (4,036 ) Mortgage-backed and asset-backed securities: Agency mortgage-backed securities 349,119 (6,155 ) 12,401 (430 ) 361,520 (6,585 ) Residential mortgage obligations 953 (18 ) 926 (37 ) 1,879 (55 ) Asset-backed securities 95,514 (970 ) 48,093 (208 ) 143,607 (1,178 ) Commercial mortgage-backed securities 51,932 (1,164 ) 7,910 (740 ) 59,842 (1,904 ) Subtotal $ 497,518 $ (8,307 ) $ 69,330 $ (1,415 ) $ 566,848 $ (9,722 ) Corporate bonds 325,733 (5,086 ) 26,005 (442 ) 351,738 (5,528 ) Total fixed maturities $ 1,111,873 $ (19,074 ) $ 125,409 $ (5,340 ) $ 1,237,282 $ (24,414 ) Equity securities 145,014 (5,419 ) 1,994 (366 ) 147,008 (5,785 ) Total fixed maturities and equity securities $ 1,256,887 $ (24,493 ) $ 127,403 $ (5,706 ) $ 1,384,290 $ (30,199 ) December 31, 2015 Less than 12 months Greater than 12 months Total Gross Gross Gross Fair Unrealized Fair Unrealized Fair Unrealized amounts in thousands Value (Losses) Value (Losses) Value (Losses) Fixed maturities: U.S. Treasury bonds, agency bonds and foreign government bonds $ 142,233 $ (3,032 ) $ 22,230 $ (6,182 ) $ 164,463 $ (9,214 ) States, municipalities and political subdivisions 50,577 (549 ) 4,808 (232 ) 55,385 (781 ) Mortgage-backed and asset-backed securities: Agency mortgage-backed securities 164,817 (1,315 ) 29,862 (767 ) 194,679 (2,082 ) Residential mortgage obligations 3,910 (5 ) 1,684 (77 ) 5,594 (82 ) Asset-backed securities 112,479 (663 ) 81,477 (961 ) 193,956 (1,624 ) Commercial mortgage-backed securities 83,024 (1,826 ) 3,065 (38 ) 86,089 (1,864 ) Subtotal $ 364,230 $ (3,809 ) $ 116,088 $ (1,843 ) $ 480,318 $ (5,652 ) Corporate bonds 395,399 (10,114 ) 13,849 (624 ) 409,248 (10,738 ) Total fixed maturities $ 952,439 $ (17,504 ) $ 156,975 $ (8,881 ) $ 1,109,414 $ (26,385 ) Equity securities 58,531 (3,013 ) — — 58,531 (3,013 ) Total fixed maturities and equity securities $ 1,010,970 $ (20,517 ) $ 156,975 $ (8,881 ) $ 1,167,945 $ (29,398 ) Our Company analyzes impaired securities quarterly to determine if any impairments are other-than-temporary. The above securities with unrealized losses have been determined to be temporarily impaired based on our evaluation. At December 31, 2016, there were 413 Fixed maturities and 75 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 and is mostly due to an unfavorable foreign exchange movement in our Canadian portfolio. To a lesser extent the gross unrealized loss for the greater than 12 months category is driven by unrealized losses on our longer dated municipal securities which were impacted by rising interest rates and credit spreads widening. The gross unrealized loss for the less than 12 months category consists primarily of agency mortgage backed securities, corporate bonds and preferred stocks, which are reported in equity securities, due to an increase in interest rates. At December 31, 2015, there were 368 fixed maturities and 57 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 mostly due to an unfavorable foreign exchange movement in our Canadian portfolio. The gross unrealized loss for the less than 12 months category consists primarily of corporate bonds in the energy sector which have been impacted by recent declines in oil prices. To a lesser extent, losses on equity securities in the less than 12 month category were impacted by volatility in the equity markets coupled with the timing of the purchases of certain equity securities. As of December 31, 2016 and 2015, the largest unrealized loss by a non-government backed issuer in the investment portfolio was $1.0 million and $2.6 million, respectively. 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 payments 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 had one credit related OTTI loss totaling $0.2 million during the year ended December 31, 2016 from our fixed maturities portfolio. Our Company had three credit related OTTI losses totaling $1.7 million during the year ended December 31, 2015 from our equity portfolio. Our Company did not have any credit related OTTI losses during the year ended December 31, 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 years ended December 31, 2016, 2015 and 2014. Years Ended December 31, amounts in thousands 2016 2015 2014 Beginning balance $ 2,361 $ 2,361 $ 5,154 Additions for credit loss impairments recognized in the current period on securities not previously impaired 150 — — 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 (150 ) — (2,793 ) Ending balance $ 2,361 $ 2,361 $ 2,361 Our Company’s Net investment income was derived from the following sources: Years Ended December 31, amounts in thousands 2016 2015 2014 Fixed maturities $ 67,772 $ 61,572 $ 57,219 Equity securities 14,271 9,813 9,036 Short-term investments 727 683 911 Total investment income $ 82,770 $ 72,068 $ 67,166 Investment expenses (3,319 ) (3,350 ) (2,998 ) Net investment income $ 79,451 $ 68,718 $ 64,168 Realized gains and losses, excluding net OTTI losses recognized in earnings, for the periods indicated, were as follows: Years Ended December 31, amounts in thousands 2016 2015 2014 Fixed maturities: Gains $ 5,681 $ 4,756 $ 8,326 Losses (4,271 ) (5,926 ) (2,610 ) Fixed maturities, net $ 1,410 $ (1,170 ) $ 5,716 Short-term: Gains $ 890 $ 130 $ — Losses (1,552 ) (383 ) — Short-term, net $ (662 ) $ (253 ) $ — Equity securities: Gains $ 9,096 $ 14,331 $ 9,447 Losses (658 ) (4,535 ) (2,351 ) Equity securities, net $ 8,438 $ 9,796 $ 7,096 Net realized gains (losses) $ 9,186 $ 8,373 $ 12,812

Fair Value Measurement

Fair Value Measurement	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value Measurement	NOTE 4. FAIR VALUE MEASUREMENT Fair value measurements are received from independent pricing service vendors, utilized by our outside investment manager whom we employ to assist us with investment accounting services. This manager utilizes a pricing committee, which oversees the use of one or more independent pricing service vendors. The pricing committee consists of five or more members of the investment management firm, one from senior management and one from the accounting group, with the remainder representing asset class specialists and client strategists. The pricing source for each security is determined in accordance with the pricing source procedures approved by the pricing committee. The investment manager receives supporting documentation from the independent pricing service vendor detailing the inputs, models and processes used in the vendors’ evaluation process to determine the appropriate fair value hierarchy. It is ultimately our responsibility to determine whether the values obtained from these service providers are representative of fair value. To validate the techniques or models used by pricing sources, our review process includes, but is not limited to: (i) A review of the validity of the fair market valuation of individual securities deemed as outliers (i.e., vendor price differed significantly from other vendor prices), securities with significant price movements from previous months, securities with stale prices and securities with negative yields. (ii) A comparison of the count of securities priced by certain vendors for significant movements in vendor CUSIP counts. (iii) A review of the results of back-testing, including the comparison of executed prices to the historical fair value estimates from the pricing service and documentation to support trades above certain variance thresholds. (iv) A review of the Statement on Standards for Attestation Engagements (“SSAE”) No.16 report of our outside investment managers for any exceptions. (v) Management also periodically independently prices the portfolio using alternative pricing vendors and investigates variances outside of the established thresholds. 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 “5.75% Senior notes”) carried at amortized cost as of December 31, 2016 and 2015: December 31, 2016 amounts in thousands Level 1 Level 2 Level 3 Total Fixed maturities: U.S. Treasury bonds, agency bonds and foreign government bonds $ 47,704 $ 226,072 $ — $ 273,776 States, municipalities and political subdivisions — 547,415 — 547,415 Mortgage-backed and asset-backed securities: Agency mortgage-backed securities — 487,364 — 487,364 Residential mortgage obligations — 20,530 — 20,530 Asset-backed securities — 314,601 — 314,601 Commercial mortgage-backed securities — 154,139 — 154,139 Subtotal $ — $ 976,634 $ — $ 976,634 Corporate bonds — 838,057 — 838,057 Total fixed maturities $ 47,704 $ 2,588,178 $ — $ 2,635,882 Equity securities 164,088 185,054 — 349,142 Short-term investments 143,539 — — 143,539 Total assets measured at fair value $ 355,331 $ 2,773,232 $ — $ 3,128,563 Senior notes $ — $ 280,316 $ — $ 280,316 Total liabilities measured at fair value $ — $ 280,316 $ — $ 280,316 December 31, 2015 amounts in thousands Level 1 Level 2 Level 3 Total Fixed maturities: U.S. Treasury bonds, agency bonds and foreign government bonds $ 67,394 $ 185,488 $ — $ 252,882 States, municipalities and political subdivisions — 576,859 — 576,859 Mortgage-backed and asset-backed securities: Agency mortgage-backed securities — 379,269 — 379,269 Residential mortgage obligations — 30,465 — 30,465 Asset-backed securities — 225,012 — 225,012 Commercial mortgage-backed securities — 189,713 — 189,713 Subtotal $ — $ 824,459 $ — $ 824,459 Corporate bonds — 760,010 — 760,010 Total fixed maturities $ 67,394 $ 2,346,816 $ — $ 2,414,210 Equity securities 126,455 178,816 — 305,271 Short-term investments 217,745 — — 217,745 Total assets measured at fair value $ 411,594 $ 2,525,632 $ — $ 2,937,226 Senior notes $ — $ 282,486 $ — $ 282,486 Total liabilities measured at fair value $ — $ 282,486 $ — $ 282,486 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 years ended December 31, 2016 and 2015. As of December 31, 2016 and 2015, our Company did not have any Level 3 assets.

Reserves for Losses and LAE

Reserves for Losses and LAE	12 Months Ended
	Dec. 31, 2016
Insurance [Abstract]
Reserves for Losses and LAE	NOTE 5. RESERVES FOR LOSSES AND LAE We establish reserves for the estimated unpaid ultimate liability for losses and LAE under the terms of our policies and agreements. The determination of reserves for losses and LAE is partially dependent upon the receipt of information from agents and brokers. Reserves include estimates for both claims that have been reported and for IBNR, and include estimates of expenses associated with processing and settling these claims. Reserves are recorded in Reserves for losses and LAE in the Consolidated Balance Sheets. Our estimates and judgments may be revised as additional experience and other data become available and are reviewed, as new or improved methodologies are developed, or as laws change. Frequency/severity analyses are also performed for certain books of business. To the extent that reserves are found deficient or redundant, a strengthening or release is recognized as a charge or credit to earnings. The following table summarizes activity for our Company’s Reserves for losses and LAE for the years ended December 31, 2016, 2015 and 2014: Years Ended December 31, amounts in thousands 2016 2015 2014 Net reserves for losses and LAE at beginning of year $ 1,393,126 $ 1,308,136 $ 1,222,633 Provision for losses and LAE for claims occurring in the current year 693,976 637,267 601,041 Increase (decrease) in estimated losses and LAE for claims occurring in prior years (28,528 ) (64,669 ) (55,812 ) Incurred losses and LAE $ 665,448 $ 572,598 $ 545,229 Losses and LAE paid for claims occurring during: Current year (119,485 ) (159,802 ) (158,806 ) Prior years (412,544 ) (320,863 ) (295,527 ) Losses and LAE payments $ (532,029 ) $ (480,665 ) $ (454,333 ) Foreign Currency Adjustment (16,094 ) (6,943 ) (5,393 ) Net reserves for losses and LAE at end of year 1,510,451 1,393,126 1,308,136 Reinsurance recoverables on unpaid losses and LAE 779,276 809,518 851,498 Gross reserves for losses and LAE at end of year $ 2,289,727 $ 2,202,644 $ 2,159,634 The reporting and operating segments breakdowns of prior period net reserve strengthening (releases) for the years ended December 31, 2016, 2015 and 2014 are as follows: Years Ended December 31, amounts in thousands 2016 2015 2014 U.S. Insurance Marine $ (10,122 ) $ (24,825 ) $ (29,047 ) P&C 2,790 (706 ) 17,081 Professional Liability 5,984 (3,788 ) (3,454 ) Total $ (1,348 ) $ (29,319 ) $ (15,420 ) Int'l Insurance Marine (22,068 ) (21,914 ) (31,677 ) P&C (7,051 ) (8,458 ) (3,829 ) Professional Liability 4,100 4,156 (2,746 ) Total $ (25,019 ) $ (26,216 ) $ (38,252 ) GlobalRe $ (2,161 ) $ (9,134 ) $ (2,140 ) Total strengthening (releases) $ (28,528 ) $ (64,669 ) $ (55,812 ) The following is a discussion of the relevant factors related to the prior period net reserve releases of $28.5 million recorded for the year ended December 31, 2016: U.S. Insurance reporting segment recorded prior period net reserve releases of $1.3 million. The drivers are as follows: • Marine operating segment recorded prior period net reserve releases of $10.1 million driven by favorable claims development in the Craft, Marine Liability, Customs Bonds and Inland Marine products. • P&C operating segment recorded prior period net reserve strengthening of $2.8 million driven by large loss activity within our Primary Casualty division, partially offset by ongoing favorable performance within our Excess Casualty, Environmental and Other P&C divisions. • Professional Liability operating segment recorded prior period net reserve strengthening of $6.0 million driven by unfavorable development on a few large D&O claims. Int’l Insurance reporting segment recorded prior period net reserve releases of $25.0 million. The drivers are as follows: • Marine operating segment recorded prior period net reserve releases of $22.1 million due to favorable claims development predominately from our Marine Liability product. • P&C operating segment recorded prior period net reserve releases of $7.1 million primarily due to favorable claims development in our Energy & Engineering division, partially offset by large loss activity within our Property division. • Professional Liability operating segment recorded prior period net reserve strengthening of $4.1 million primarily due to a decline in expected recoveries from a large reinsurer resulting in an increase in bad debt reserve within our D&O division. GlobalRe reporting segment recorded prior period net reserve releases of $2.2 million primarily driven by favorable loss development in our A&H, P&C and Professional Liability products, partially offset by large loss activity in our Marine product. The following is a discussion of the relevant factors related to the prior period net reserve releases of $64.7 million recorded for the year ended December 31, 2015: U.S. Insurance reporting segment recorded prior period net reserve releases of $29.3 million. The drivers are as follows: • Marine operating segment recorded prior period net reserve releases of $24.8 million driven by favorable claims development in the Marine Liability, Inland Marine and Cargo products. • P&C operating segment recorded prior period net reserve releases of $0.7 million driven by ongoing favorable performance within our Excess Casualty, Environmental and Other P&C divisions, mostly offset by large loss activity within our Primary Casualty division. • Professional Liability operating segment recorded prior period net reserve releases of $3.8 million driven by favorable emergence in our E&O division, partially offset by unfavorable development in several large D&O claims Int’l Insurance reporting segment recorded prior period net reserve releases of $26.2 million. The drivers are as follows: • Marine operating segment recorded prior period net reserve releases of $21.9 million driven primarily due to favorable claims development on the Marine Liability, Protection and Indemnity and Specie products. • P&C operating segment recorded prior period net reserve releases of $8.5 million due to favorable claims development on the Offshore Energy product within the Energy & Engineering division. • Professional Liability operating segment recorded prior period net reserve strengthening of $4.2 million driven by adverse development in our D&O division related to two large losses, partially offset by favorable claims development on our E&O division. GlobalRe reporting segment recorded prior period net reserve releases of $9.1 million primarily driven by favorable loss development in our Marine, P&C and A&H products. The following is a discussion of relevant factors related to the prior period net reserve releases of $55.8 million recorded for the year ended December 31, 2014: U.S. Insurance reporting segment recorded prior period net reserve releases of $15.4 million. The drivers of these prior period net reserve releases by operating segment are as follows. • Marine operating segment recorded prior period net reserve releases of $29.0 million driven by favorable claims development on our Marine Liability, Craft, Fishing Vessels, Inland Marine, Hull and Cargo products. • P&C operating segment recorded prior period net reserve strengthening of $17.1 million driven by unfavorable activity on pre-2010 California construction defect liability claims in our Primary Casualty division, partially offset by reserve releases due to favorable loss emergence from our Excess Casualty division. • Professional Liability operating segment recorded prior period net reserve releases of $3.5 million driven primarily by favorable loss emergence from our D&O division due to a cash settlement of a contract dispute with a former third party administrator. Int’l Insurance reporting segment recorded prior period net reserve releases of $38.3 million. The drivers are as follows: • Marine operating segment recorded prior period net reserve releases of $31.7 million driven by favorable loss emergence across various products. • P&C operating segment recorded prior period net reserve releases of $3.8 million driven primarily by favorable claims development in our Energy & Engineering division. • Professional Liability operating segment recorded prior period net reserve releases of $2.7 million due to favorable loss emergence in our E&O and D&O divisions. GlobalRe reporting segment recorded prior period net reserve releases of $2.1 million driven by favorable claim development in our Marine product. Supplemental tables related to Short Duration Contracts Effectively all property and casualty insurance contracts are described as “Short Duration Contracts” as opposed to life insurance, by the Securities and Exchange Commission. Our Company only issues short duration contracts. Below are two tables with reserve data for each reporting and operating segment. These tables are presented net of reinsurance. The first table reflects incurred claims development as of December 31, 2016, as well as the cumulative claims frequency and the total of Incurred But Not Reported (“IBNR”) liabilities and expected development on reported claims included within the net incurred claims amounts. The second table reflects the cumulative paid claims development as of December 31, 2016. The conversion of all non USD currencies amounts, for all Accident Years (“AY”), is in USD as of December 31, 2016. Records for Syndicate 1221 are not available by AY for reporting periods prior to 2012 since data was compiled only on a year-of- account basis prior to 2012, and as such the tables below for our Int’l Insurance reporting segment begin with the 2012 reporting year. Our GlobalRe Segment reserve tables do not have data prior to 2010, as we began writing assumed reinsurance in that year. Claims frequency is based on claims posted in our Company’s data system as reported. Generally, for most direct insurance and excess-of-loss assumed reinsurance, one claim count is posted for each claim. For assumed bordereau business and business written on binders, one claim count is posted for each bordereau received, which could account for multiple claims. Additionally, if the insured is covered for multiple years, a claim may be initially established in all potentially impacted policy years until the appropriate policy year is determined. The information about incurred claims development and cumulative paid claims and Allocated Loss Adjustment Expense (“ALAE”), net of reinsurance, for the years ended December 31, 2007 through 2015, is presented as unaudited supplementary information. Note that asbestos reserves are included in the U.S. Marine operating segment in years prior to 2007. IBNR values shown in the following tables are the difference between the case reserves for reported losses and the estimated future payments for claims arising from the specific accident period. Our Company has always applied prudent claim reserving practices. For a number of segments, this has resulted in case reserves for more mature accident years exceeding the future payments consistently. IBNR estimates will be negative where our history indicates such favorable future emergence is the best estimate. U.S. Marine Loss and ALAE, Net of Reinsurance amounts in thousands For the Years Ended December 31, As of December 31, 2016 AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Total IBNR # of Reported Claims 2007 $ 52,974 $ 60,645 $ 61,216 $ 59,148 $ 65,020 $ 66,090 $ 66,024 $ 65,909 $ 66,297 $ 66,846 $ 60 2,737 2008 56,923 67,710 72,580 73,970 73,731 68,703 68,873 67,024 67,238 348 3,202 2009 63,769 60,813 57,266 51,804 49,762 50,905 53,091 52,169 (186 ) 2,404 2010 66,336 66,187 63,172 57,063 54,815 59,143 58,557 (263 ) 2,164 2011 71,575 72,232 70,019 65,514 64,196 62,571 1,204 2,012 2012 87,905 91,118 73,940 70,421 71,868 (7 ) 1,968 2013 65,132 61,289 55,494 58,148 (619 ) 1,910 2014 67,610 49,889 48,355 1,509 1,962 2015 64,575 54,121 13,317 2,155 2016 56,209 32,884 1,824 Total $ 596,082 U.S. Marine Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance amounts in thousands For the Years Ended December 31, AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ 9,294 $ 28,937 $ 40,256 $ 49,214 $ 58,772 $ 62,002 $ 62,767 $ 63,384 $ 64,450 $ 64,570 2008 7,554 36,499 54,408 56,695 62,633 62,989 63,316 63,429 64,317 2009 12,975 30,012 36,593 42,846 44,760 47,347 48,209 50,888 2010 17,211 33,821 41,941 45,032 50,271 54,044 57,254 2011 16,007 41,322 50,841 54,471 59,224 60,198 2012 27,546 47,639 56,040 62,104 68,556 2013 19,565 38,487 44,606 50,410 2014 15,702 29,916 41,609 2015 17,169 32,439 2016 12,665 Total $ 502,906 Net reserves < 2007 13,112 Total Net reserves $ 106,288 U.S. Marine Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 U.S. Marine 26.4 % 32.4 % 16.5 % 8.3 % 8.7 % 3.7 % 2.2 % 2.1 % 1.5 % 0.2 % U.S. P&C Loss and ALAE, Net of Reinsurance amounts in thousands For the Years Ended December 31, As of December 31, 2016 AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Total IBNR # of Reported Claims 2007 $ 139,377 $ 139,570 $ 140,551 $ 130,501 $ 133,050 $ 128,087 $ 134,310 $ 139,870 $ 145,472 $ 148,609 $ 3,753 11,703 2008 158,337 158,336 144,164 140,818 141,332 143,219 147,434 152,416 157,519 3,971 10,818 2009 133,394 135,984 136,700 142,416 149,975 155,156 155,682 159,110 7,717 8,434 2010 101,527 100,529 98,675 104,709 107,602 109,323 112,080 10,106 7,804 2011 86,056 85,238 92,266 95,292 95,958 105,149 15,964 6,346 2012 111,479 96,618 98,060 103,716 111,746 24,895 4,481 2013 141,728 130,314 133,068 141,817 29,961 3,533 2014 193,897 164,364 152,447 76,085 3,356 2015 251,752 224,532 134,029 3,123 2016 274,692 258,449 2,106 Total $ 1,587,701 U.S. P&C Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance amounts in thousands For the Years Ended December 31, AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ 7,127 $ 24,521 $ 49,616 $ 72,462 $ 92,840 $ 104,841 $ 114,160 $ 122,568 $ 130,279 $ 136,896 2008 12,178 36,713 58,491 82,028 103,804 115,526 123,945 133,064 146,463 2009 14,619 36,641 59,933 92,033 119,360 132,695 138,227 145,407 2010 12,682 27,542 49,109 69,027 81,262 89,873 94,766 2011 3,925 19,548 35,551 51,868 63,800 75,806 2012 10,013 23,019 33,477 51,980 72,495 2013 7,317 21,500 49,562 85,719 2014 5,272 13,762 45,324 2015 3,641 24,291 2016 7,706 Total $ 834,873 Net reserves < 2007 16,571 Total Net reserves $ 769,399 U.S. P&C Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 U.S. P&C 5.9 % 11.7 % 16.2 % 18.0 % 14.2 % 8.6 % 4.9 % 5.3 % 6.8 % 4.5 % U.S. Professional Liability Loss and ALAE, Net of Reinsurance amounts in thousands For the Years Ended December 31, As of December 31, 2016 AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Total IBNR # of Reported Claims 2007 $ 38,000 $ 38,553 $ 55,491 $ 57,643 $ 62,630 $ 61,935 $ 60,445 $ 60,447 $ 59,936 $ 59,574 $ (70 ) 634 2008 34,346 38,449 39,130 35,844 37,603 37,939 37,497 37,620 41,766 (382 ) 770 2009 47,473 53,273 61,023 58,600 60,789 58,487 58,660 58,143 (563 ) 1,370 2010 52,302 64,020 68,375 75,619 74,535 86,787 85,348 83 1,429 2011 58,116 62,087 70,240 73,028 79,181 79,136 622 1,724 2012 61,196 54,480 57,097 55,917 58,344 3,214 2,180 2013 60,899 54,982 49,104 48,298 4,989 2,226 2014 50,020 35,870 39,826 6,504 2,278 2015 31,659 30,764 15,870 1,709 2016 41,672 36,356 1,739 Total $ 542,871 U.S. Professional Liability Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance amounts in thousands For the Years Ended December 31, AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ 1,861 $ 10,365 $ 32,621 $ 47,980 $ 52,941 $ 58,515 $ 59,280 $ 59,332 $ 59,565 $ 59,570 2008 1,880 15,288 25,042 30,581 34,902 35,206 35,598 37,175 42,056 2009 3,837 21,742 41,675 51,642 55,378 53,859 57,744 58,095 2010 2,981 23,147 46,868 54,019 59,765 82,013 84,511 2011 3,204 23,878 43,551 59,576 65,710 75,641 2012 3,855 22,635 35,681 44,028 49,675 2013 4,677 22,167 32,904 38,876 2014 2,304 14,371 29,392 2015 2,257 11,249 2016 2,383 Total $ 451,448 Net reserves < 2007 (386 ) Total Net reserves $ 91,037 U.S. Professional Liability Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 U.S. Professional Liability 5.7 % 28.3 % 28.7 % 15.9 % 8.2 % 9.2 % 3.0 % 1.5 % 6.0 % 0.0 % Int'l Marine Loss and ALAE, Net of Reinsurance amounts in thousands For the Years Ended December 31, As of December 31, 2016 AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Total IBNR # of Reported Claims 2007 $ — $ — $ — $ — $ — $ 70,633 $ 67,148 $ 66,951 $ 66,883 $ 66,239 $ (35 ) 5,585 2008 — — — — 88,720 85,285 84,131 84,191 82,752 98 5,809 2009 — — — 89,057 86,914 84,497 82,096 79,526 111 4,969 2010 — — 123,719 119,021 114,188 111,468 108,405 282 5,317 2011 — 91,347 86,795 78,872 75,873 70,751 25 4,824 2012 93,696 115,935 99,683 94,886 90,523 (216 ) 5,201 2013 68,587 82,313 80,713 77,239 747 5,075 2014 85,512 105,072 107,789 (1,500 ) 4,928 2015 70,675 91,371 5,194 6,967 2016 84,156 26,285 5,577 Total $ 858,751 Int'l Marine Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance amounts in thousands For the Years Ended December 31, AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ — $ — $ — $ — $ — $ 59,831 $ 60,702 $ 61,956 $ 62,729 $ 63,281 2008 — — — — 69,959 72,309 73,746 77,535 78,683 2009 — — — 64,058 68,085 70,834 74,311 75,006 2010 — — 74,920 87,186 93,167 97,132 99,416 2011 — 43,740 56,569 60,879 65,580 66,538 2012 22,777 52,968 68,498 76,572 79,205 2013 21,703 42,953 54,826 60,828 2014 24,445 50,168 73,921 2015 22,323 52,356 2016 22,192 Total $ 671,426 Net reserves < 2007 9,207 Total Net reserves $ 196,532 Int'l Marine Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 Int'l Marine 24.5 % 28.1 % 18.2 % 7.6 % 5.0 % 2.8 % 2.7 % 2.4 % 1.3 % 0.8 % Int'l P&C Loss and ALAE, Net of Reinsurance amounts in thousands For the Years Ended December 31, As of December 31, 2016 AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Total IBNR # of Reported Claims 2007 $ — $ — $ — $ — $ — $ 26,084 $ 25,817 $ 25,740 $ 25,855 $ 25,778 $ (60 ) 584 2008 — — — — 39,504 37,884 37,867 37,296 36,729 (75 ) 891 2009 — — — 26,499 25,804 25,910 25,418 25,113 13 743 2010 — — 39,082 39,409 39,050 39,031 38,198 58 836 2011 — 57,463 53,654 52,093 52,666 52,202 (198 ) 833 2012 34,479 30,643 30,347 28,626 27,828 (353 ) 877 2013 29,496 33,720 31,050 29,684 (308 ) 1,229 2014 20,234 16,987 17,006 173 1,167 2015 26,414 30,932 2,106 1,678 2016 75,571 13,006 2,646 Total $ 359,041 Int'l P&C Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance amounts in thousands For the Years Ended December 31, AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ — $ — $ — $ — $ — $ 23,885 $ 24,681 $ 25,150 $ 25,292 $ 25,289 2008 — — — — 34,084 35,161 35,463 35,975 35,826 2009 — — — 23,371 24,257 24,713 24,286 24,369 2010 — — 32,156 36,499 39,017 36,509 36,601 2011 — 33,316 42,280 45,125 47,591 48,502 2012 7,884 15,648 20,850 24,871 26,049 2013 6,829 17,613 24,735 27,180 2014 3,813 8,458 12,304 2015 6,739 18,096 2016 24,255 Total $ 278,471 Net reserves < 2007 619 Total Net reserves $ 81,189 Int'l P&C Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 Int'l P&C 25.4 % 33.5 % 21.8 % 9.4 % 5.2 % -1.0 % -0.2 % 1.2 % 0.1 % 0.0 % Int'l Professional Liability Loss and ALAE, Net of Reinsurance amounts in thousands For the Years Ended December 31, As of December 31, 2016 AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Total IBNR # of Reported Claims 2007 $ — $ — $ — $ — $ — $ 12,901 $ 12,587 $ 12,445 $ 12,378 $ 12,381 $ (64 ) 235 2008 — — — — 15,511 15,302 14,816 14,010 14,023 (175 ) 365 2009 — — — 14,809 15,367 14,972 16,289 15,780 629 445 2010 — — 18,603 16,159 15,661 17,451 15,619 1,409 653 2011 — 9,686 7,648 7,125 7,050 6,835 356 681 2012 8,204 9,753 9,106 11,175 16,891 490 718 2013 15,096 17,628 16,272 15,402 4,255 1,053 2014 18,835 24,070 23,457 12,421 1,276 2015 22,760 30,104 17,379 1,939 2016 36,006 31,814 2,554 Total $ 186,498 Int'l Professional Liability Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance amounts in thousands For the Years Ended December 31, AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ — $ — $ — $ — $ — $ 11,293 $ 11,704 $ 12,269 $ 12,277 $ 12,382 2008 — — — — 12,150 13,306 13,702 13,732 14,019 2009 — — — 8,805 10,716 12,783 13,803 14,118 2010 — — 5,801 7,169 10,460 12,632 13,366 2011 — 1,197 2,002 2,950 4,007 4,576 2012 2,133 3,219 4,253 5,483 7,365 2013 725 2,196 2,952 9,230 2014 1,368 2,421 5,068 2015 3,355 5,765 2016 2,012 Total $ 87,901 Net reserves < 2007 92 Total Net reserves $ 98,689 Int'l Professional Liability Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 Int'l Professional 7.5 % 7.3 % 7.4 % 20.6 % 15.9 % 11.8 % 4.7 % 2.3 % 1.1 % 0.8 % GlobalRe Loss and ALAE, Net of Reinsurance amounts in thousands For the Years Ended December 31, As of December 31, 2016 AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Total IBNR # of Reported Claims 2007 $ — $ — $ — $ — $ — $ 6,215 $ 6,190 $ 6,173 $ 5,889 $ 5,883 $ (141 ) 254 2008 — — — — 13,863 14,024 13,530 13,304 13,298 672 294 2009 4,970 3,734 3,752 11,186 11,380 10,745 10,390 10,475 204 202 2010 3,743 3,500 13,455 13,661 12,899 11,597 12,330 (1,000 ) 195 2011 39,678 50,832 74,131 73,511 73,042 72,667 (461 ) 766 2012 108,790 103,183 94,766 89,053 114,728 531 1,419 2013 112,735 119,012 101,703 104,913 3,973 1,185 2014 120,479 141,108 121,535 9,825 920 2015 99,874 91,098 11,623 680 2016 88,192 38,785 335 Total $ 635,119 GlobalRe Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance amounts in thousands For the Years Ended December 31, AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ — $ — $ — $ — $ — $ 5,225 $ 5,275 $ 5,345 $ 5,357 $ 5,350 2008 — — — — 11,629 11,650 11,510 11,488 11,546 2009 — 3,734 3,752 8,620 8,853 8,974 9,932 10,045 2010 0 3,490 9,875 10,213 10,387 11,009 11,062 2011 4,160 43,342 71,010 71,677 71,954 72,094 2012 37,644 77,077 83,183 84,533 111,681 2013 53,375 82,558 90,567 98,271 2014 66,249 119,136 105,505 2015 41,620 64,316 2016 36,253 Total $ 526,123 Net reserves < 2007 2,598 Total Net reserves $ 111,594 GlobalRe Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 GlobalRe 47.1 % 32.1 % 0.6 % 3.1 % 8.5 % 2.1 % 2.8 % 0.7 % 0.3 % -0.1 % The reconciliation of the net incurred and paid claims development tables to the Reserve for losses and LAE in the consolidated statement of financial position is as follows: Carried Reserves Reconciliation amounts in thousands For the Year Ended December 31, 2016 Total Net reserves Reinsurance recoverables on unpaid claims Total Gross reserves U.S. Marine $ 106,288 $ 83,988 $ 190,276 U.S. P&C 769,399 409,648 1,179,047 U.S. Professional Liability 91,037 59,938 150,975 Int'l Marine 196,532 88,900 285,432 Int'l P&C 81,189 79,548 160,737 Int'l Professional Liability 98,689 52,518 151,207 GlobalRe 111,594 4,736 116,330 Liabilities for unpaid claims and claim adjustment expenses $ 1,454,728 779,276 $ 2,234,004 Unallocated claims adjustment expenses 55,444 Other 279 Total gross liability for unpaid claims and claim adjustment expense $ 2,289,727 F-1

Ceded Reinsurance

Ceded Reinsurance	12 Months Ended
	Dec. 31, 2016
Insurance [Abstract]
Ceded Reinsurance	NOTE 6. CEDED REINSURANCE We utilize reinsurance principally to reduce our exposure on individual risks, to protect against catastrophic losses and to stabilize loss ratios and net underwriting results. Reinsurers are liable to us to the extent the risk is transferred or ceded to them. However, ceded reinsurance arrangements do not eliminate our obligation to pay claims to our policyholders. Accordingly, we bear credit risk with respect to our reinsurers. We are protected by various treaty and facultative reinsurance agreements. Our exposure to credit risk from any one reinsurer is managed through diversification of reinsurers, principally in the U.S. and European reinsurance markets. A reinsurer generally must have a rating from A.M. Best and/or S&P of “A” or better, or an equivalent financial strength if not rated, plus at least $500 million in policyholders’ surplus to meet our standards of acceptability. Our Reinsurance Security Committee, which is part of our Enterprise Risk Management Finance and Credit Sub-Committee of our Board of Directors, monitors the financial strength of our reinsurers and the related reinsurance recoverables and periodically reviews the list of acceptable reinsurers. The following table lists our Company’s 10 largest reinsurers measured by the amount of total reinsurance recoverables as of December 31, 2016, and the reinsurers’ ratings from A.M. Best and S&P: Reinsurance Recoverables Unearned Paid/Unpaid Collateral amounts in thousands Premium Losses (1) Total Held A.M. Best S&P Everest Reinsurance Company $ 25,321 $ 82,154 $ 107,475 $ 6,571 A+ A+ National Indemnity Company 7,467 98,759 106,226 3,183 A++ AA+ Swiss Reinsurance America Corporation 22,442 77,199 99,641 6,440 A+ AA- Transatlantic Reinsurance Company 7,669 53,347 61,016 2,494 A+ A+ Munich Reinsurance America Inc. 8,959 50,612 59,571 3,477 A+ AA- Allied World Reinsurance 6,319 35,931 42,250 1,575 A A Employers Mutual Casualty Company 8,856 32,687 41,543 5,551 A NR Aspen Insurance UK Ltd. 11,281 22,737 34,018 5,452 A A Ace Property and Casualty Insurance Company 10,192 22,352 32,544 2,722 A++ AA Partner Reinsurance Europe 6,868 20,681 27,549 25,045 A A+ Top 10 $ 115,374 $ 496,459 $ 611,833 $ 62,510 All Others 98,003 365,399 463,402 89,198 Total $ 213,377 $ 861,858 $ 1,075,235 $ 151,708 (1) - Net of reserve for uncollectible reinsurance of approximately $12.1 million. Our Company holds reserves for uncollectible reinsurance in the amounts of $12.1 million and $6.9 million as of December 31, 2016 and 2015, respectively. This reserve is determined by reinsurer specific default risk as indicated by their financial strength ratings as well as additional default risk for asbestos and environmental related recoverables. Actual uncollectible reinsurance could exceed or be less than our reserve balance. The increase in our reserves for uncollectible reinsurance as compared to 2015 is driven primarily by one of our reinsurers having been placed under supervision of a conservator by the State of California. We will continue to monitor the conservation process and assess our potential exposure. Our Company holds collateral of $151.7 million, which consists of $109.0 million in ceded balances payable, $39.7 million in letters of credit and $3.0 million of funds held. NIC and NSIC are required to collateralize reinsurance obligations due to us from reinsurers not authorized by their respective states of domicile. The following table summarizes the components of Net written premium: Years Ended December 31, amounts in thousands 2016 2015 2014 Direct $ 1,403,865 $ 1,277,728 $ 1,232,012 Assumed 165,046 175,774 200,341 Ceded (382,687 ) (409,642 ) (432,215 ) Net written premiums $ 1,186,224 $ 1,043,860 $ 1,000,138 The following table summarizes the components of Net earned premium: Years Ended December 31, amounts in thousands 2016 2015 2014 Direct $ 1,330,265 $ 1,223,840 $ 1,183,120 Assumed 171,978 175,153 193,431 Ceded (401,898 ) (414,906 ) (440,656 ) Net earned premiums $ 1,100,345 $ 984,087 $ 935,895 The following table summarizes the components of Net losses and LAE incurred: Years Ended December 31, amounts in thousands 2016 2015 2014 Direct $ 795,414 $ 703,361 $ 657,059 Assumed 87,995 97,947 118,352 Ceded (217,961 ) (228,710 ) (230,182 ) Net losses and LAE $ 665,448 $ 572,598 $ 545,229

Debt

Debt	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Debt	NOTE 7. DEBT Credit Facilities On November 4, 2016, NUAL entered into a credit facility for 14.0 million Australian Dollars with Barclays Bank PLC. Interest is payable under this facility at a rate of 1.25% per annum. The facility may be cancelled by either party after providing written notice. This credit 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 £75.0 million of Funds at Lloyd’s. As of December 31, 2016, letters of credit with an aggregate face amount of 14.0 million Australian Dollars were outstanding under the credit facility, and our Company was in compliance with all covenants. On November 7, 2016, we entered into a credit facility agreement with ING Bank N.V., London Branch, individually and as Administrative Agent and a syndicate of lenders (the “Club Facility”), which is secured by all the common stock of NIC and requires us to maintain at least forty percent of the outstanding amounts under such facility as Funds at Lloyd’s. The Club Facility has two tranches with one tranche extending a $140.0 million commitment and the other tranche extending a £60.0 million commitment. In addition, in order to support the increased underwriting capacity of the Syndicate for the 2017 UWY, we amended that certain $25.0 million credit facility with ING Bank N.V., London Branch, dated November 20, 2015, on November 7, 2016, to extend the term for an additional two years (the “Bilateral Facility”). Both of these facilities, as well as the November 4, 2016 facility, are used to fund underwriting obligations at Lloyd’s for the 2017 UWY, as well as open prior UWYs. The Bilateral Facility is a non-committed facility which has an applicable fee rate ranging from 0.85% to 1.20% per annum based upon the Company’s S&P rating. For the Club Facility the applicable fee rate payable ranges from 0.95% to 1.60% per annum based on a tiered schedule that is based on our then-current financial strength ratings issued by S&P and A.M. Best and the amount of our own collateral utilized to fund our participation in the Syndicate. If any letters of credit remain outstanding under these facilities after December 31, 2018, we would be required to post additional collateral to secure the remaining letters of credit. As of December 31, 2016, letters of credit with an aggregate face amount of $125.0 million and £60.0 million were outstanding under the Club Facility and we had an aggregate of $1.1 million of cash collateral posted. As of December 31, 2016 there were no letters of credit outstanding under the Bilateral Facility. The Bilateral and Club Facilities contain 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. These credit facilities also provide 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 our subsidiaries, the occurrence of certain material judgments, or a change in control of our Company. As of December 31, 2016, our Company was in compliance with all covenants. Senior notes On October 4, 2013, our Company completed a public debt offering of $265.0 million principal amount of the 5.75% Senior notes and received net proceeds of $263.3 million. Our Company used a portion of the proceeds for the redemption of the 7.0% Senior notes due May 1, 2016 (“7.0% Senior notes”), as well as a $17.9 million call premium in connection with the redemption of the 7.0% Senior notes. The unamortized discount as of December 31, 2016 and 2015 was $1.3 million and $1.4 million, respectively. The interest rate payable on the 5.75% Senior notes is subject to a tiered adjustment based on defined changes in our Company’s debt ratings. Our Company may redeem the 5.75% Senior notes in whole at any time or in part from time to time at a make-whole redemption price. The 5.75% Senior notes are our Company’s only senior unsecured obligation and will rank equally with future senior unsecured indebtedness. The terms of the 5.75% Senior notes contain various restrictive business and financial covenants, including a restriction on indebtedness, and other restrictions typical for debt obligations of this type, including limitations on mergers, liens and dispositions of the Common stock of certain subsidiaries. As of December 31, 2016, our Company was in compliance with all such covenants.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	NOTE 8. COMMITMENT AND CONTINGENCIES Future minimum annual rental commitments as of December 31, 2016 under various non-cancellable operating leases for our office facilities, which expire at various dates through 2030, are as follows: Rental Commitments for Years Ended December 31, amounts in thousands 2017 $ 13,024 2018 11,843 2019 9,107 2020 8,945 2021 7,684 2022-2030 38,267 Total minimum operating lease payments $ 88,870 We are also liable for additional payments to the landlords for certain annual cost increases. Rent expense for the years ended December 31, 2016, 2015 and 2014 was $13.2 million, $12.9 million and $13.2 million, respectively. 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. As of December 31, 2016, our Company received $9.0 million of the award ($7.0 million in loans and $2.0 million of the grant) and earned a loan forgiveness credit of $6.0 million with the State . On February 16, 2017, our Company entered into a Guarantee, pursuant to which it guaranteed all of the liabilities and obligations of NIIC (the “Guarantee”), to facilitate the issuance of a financial strength rating to NIIC by A.M. Best. The Guarantee would remain effective until all of such liabilities and obligations are discharged, and in the event that our Company does not meet its obligations under the Guarantee, any person who is covered by an insurance policy, certificate of coverage or reinsurance contract issued by NIIC would be a third party beneficiary under the Guarantee. Our Company’s obligations under the Guarantee may be terminated by providing twelve months prior written notice to NIIC. However the obligations of our Company under the Guarantee terminate immediately in the event that (i) the majority of the outstanding voting capital stock in NIIC is sold to any non-affiliated entity; (ii) A.M. Best confirms that NIIC would receive the same financial strength rating as NIC or NSIC, without the benefit of the Guarantee; or (iii) NIIC withdraws its request to be rated by A.M. Best, provided that NIIC has not been downgraded within the prior twelve months. In the ordinary course of conducting business, our Parent Company’s subsidiaries are involved in various legal proceedings. Most of these proceedings consist of claims litigation involving our Parent 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. In general, our Company believes we have valid defenses to these cases. Our Company’s management believes that the ultimate liability, if any, with respect to these legal proceedings, after consideration of provisions made for potential losses and cost of defense, will not be material to our Company’s Consolidated Balance Sheets, Statements of Income and Statements of Cash Flows.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	NOTE 9. INCOME TAXES Our Company is subject to the tax laws and regulations of the U.S. and the foreign countries in which it operates. Our Company files a consolidated U.S. Federal tax return, which includes all domestic subsidiaries and the U.K. Branch. The income from the foreign operations is designated as either U.S. connected income or non-U.S. connected income. Lloyd’s is required to pay U.S. income tax on U.S. connected income written by Lloyd’s syndicates. Lloyd’s and the Internal Revenue Service (“IRS”) have entered into an agreement whereby the amount of tax due on U.S. connected income is calculated by Lloyd’s and remitted directly to the IRS. These amounts are then charged to the corporate member in proportion to its participation in the relevant syndicates. Our Company’s corporate member is subject to this agreement and receives U.K. tax credits in the U.K. for any U.S. income tax incurred up to the U.K. income tax charged on the U.S. connected income. The non-U.S. connected insurance income would generally constitute taxable income under the Subpart F income section of the U.S. Internal Revenue Code (“Subpart F”) since less than 50% of the Syndicate’s premiums are derived within the U.K. and would therefore be subject to U.S. taxation when the Lloyd’s year of account closes. Taxes are accrued at a 35% rate on our Company’s foreign source insurance income and foreign tax credits, where available, are utilized to offset U.S. tax as permitted. Our Company’s effective tax rate for the Syndicate taxable income could substantially exceed 35% to the extent our Company is unable to offset U.S. taxes paid under Subpart F tax regulations with U.K. tax credits on future underwriting year distributions. U.S. taxes are not accrued on the earnings of our Company’s foreign agencies as these earnings are subject to the active financing exception and are not includable as Subpart F income. The components of current and deferred income tax expense (benefit) are as follows: Years Ended December 31, amounts in thousands 2016 2015 2014 Current income tax expense (benefit): Federal and foreign $ 39,900 $ 27,937 $ 27,290 State and local 638 1,476 1,036 Subtotal $ 40,538 $ 29,413 $ 28,326 Deferred income tax expense (benefit): Federal and foreign $ (5,755 ) $ 7,004 $ 16,881 State and local — — — Subtotal $ (5,755 ) $ 7,004 $ 16,881 Total income tax expense (benefit) $ 34,783 $ 36,417 $ 45,207 A reconciliation of total income taxes applicable to pre‑tax operating income and the amounts computed by applying the federal statutory income tax rate to the pre‑tax operating income were as follows: Years Ended December 31, amounts in thousands 2016 2015 2014 Computed expected tax expense $ 41,128 35.0 % $ 41,116 35.0 % $ 49,187 35.0 % Tax-exempt interest (4,559 ) -3.9 % (4,987 ) -4.2 % (4,771 ) -3.4 % Dividends received deduction (3,812 ) -3.2 % (2,086 ) -1.8 % (1,257 ) -0.9 % Proration of DRD and Tax-exempt interest 1,256 1.1 % 1,061 0.9 % 904 0.6 % Current state and local income taxes, net of federal income tax deduction 415 0.4 % 959 0.8 % 674 0.5 % Other 355 0.2 % 354 0.3 % 470 0.4 % Actual tax expense and rate $ 34,783 29.6 % $ 36,417 31.0 % $ 45,207 32.2 % The tax effects of cumulative temporary differences that give rise to federal, foreign, state and local deferred tax assets and deferred tax liabilities were as follows: December 31, amounts in thousands 2016 2015 Deferred tax assets: Loss reserve discount $ 25,420 $ 25,353 Unearned premiums 33,886 31,486 Compensation related 15,288 11,175 State and local net deferred tax assets 699 721 Net currency translation adjustments 5,363 346 Other 3,618 3,969 Total gross deferred tax assets 84,274 73,050 Less: Valuation allowance (699 ) (721 ) Total deferred tax assets $ 83,575 $ 72,329 Deferred tax liabilities: Net unrealized gains/losses on securities $ (10,142 ) $ (13,053 ) Deferred acquisition costs (29,401 ) (24,037 ) Lloyd's year of account deferral (15,471 ) (24,466 ) Net unrealized foreign exchange (3,575 ) (4,164 ) Other (4,048 ) (2,709 ) Total deferred tax liabilities $ (62,637 ) $ (68,429 ) Net deferred income tax asset (liability) $ 20,938 $ 3,900 Our Company has not provided for U.S. income taxes on approximately $156.6 million of undistributed earnings of our non-U.S. subsidiaries since it is intended that those earnings will be reinvested indefinitely in those subsidiaries. If a future determination is made that those earnings no longer are intended to be reinvested indefinitely in those subsidiaries, U.S. income taxes of approximately $2.7 million, assuming all foreign tax credits are realized, would be included in the tax provision at that time and would be payable if those earnings were distributed to our Company. Unrecognized tax benefits are differences between tax positions taken in the tax returns and benefits recognized in the financial statements. Our Company has no unrecognized tax benefits as of December 31, 2016, 2015 and 2014. Our Company did not incur any interest or penalties related to unrecognized tax benefits for the years ended December 31, 2016, 2015 and 2014. Our Company is not currently under examination by the IRS; however is generally subject to U.S. Federal, state or local or foreign tax examinations by tax authorities for 2009 and subsequent years. Our Company had state and local deferred tax assets amounting to potential future tax benefits of $0.7 million as of December 31, 2016 and 2015. Included in the deferred tax assets are minimal state and local net operating loss carry-forwards. A valuation allowance was established for the full amount of these potential future tax benefits due to the uncertainty associated with their realization. Our Company’s state and local tax carry-forwards as of December 31, 2016 expire from 2026 to 2034. In assessing the realization of deferred tax assets, management considers whether it is more likely than not that, the deferred tax assets will be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences become deductible. Management considers the scheduled reversal of deferred tax liabilities, tax planning strategies and anticipated future taxable income in making this assessment and believes it is more likely than not that our Company will realize the benefits of its deductible differences as of December 31, 2016, net of any valuation allowance.

Stockholders Equity

Stockholders Equity	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Stockholders' Equity	NOTE 10. STOCKHOLDERS’ EQUITY Our authorized share capital consists of 50,000,000 common shares with a par value of $0.10 per share and 1,000,000 preferred shares with a par value of $0.10 per share. Our Company has not issued any preferred shares as of December 31, 2016. The following table represents changes in our Company’s issued and outstanding common shares for the periods indicated. We completed a two-for-one stock split on January 20, 2017. All share and per share data has been retroactively restated on a post-split basis. Years Ended December 31, amounts in thousands 2016 2015 2014 Beginning balance 28,862 28,562 28,396 Vested stock grants 220 254 118 Employee stock purchase plan 42 42 38 Stock options exercised — 4 10 Ending balance 29,124 28,862 28,562 On December 6, 2016, our Board of Directors declared a two-for-one stock split of The Navigators Group, Inc. Common stock, to be effected in the form of a stock dividend. Stockholders of record at the close of business on December 30, 2016 received one additional share of Common stock for every share of Common stock held. All disclosures of shares and per share data have been retroactively adjusted to reflect the stock split for all periods presented. On July 15, September 30, and December 29, 2016, our Company paid dividends of $0.045 per share to stockholders of record of our Company’s Common stock as of June 20, August 19, and November 18, 2016, respectively. The declaration and amount of any future dividend will be at the discretion of the Board of Directors, and will depend upon our Company’s financial condition, results of operations, business requirements, regulatory and legal constraints and any other factors the Board of Directors deems relevant. Refer to Footnote 16 – Subsequent Events. NIC may pay dividends to our Parent Company out of its statutory earned surplus pursuant to statutory restrictions imposed under the New York insurance law. As of December 31, 2016, the maximum amount available for the payment of dividends by NIC without prior regulatory approval is $102.7 million. NIC paid a dividend to our Parent Company of $5.0 million in 2016. NIC did not pay any dividends to our Parent Company in 2015. NCUL may pay dividends to our Parent Company up to the extent of available profits that have been distributed from the Syndicate. The Syndicate’s capital and surplus as filed with Lloyd’s consists of undistributed profits on closed and open UWYs. In connection with the business plan approved in November 2015, NCUL posted all of the available undistributed profits on closed years of $141.9 million to support a portion of the FAL requirement and therefore that amount is not available for distribution to NCUL, which ultimately is not available to our Parent Company in the form of a dividend. As of December 31, 2016, NCUL has the ability to pay up to $3.0 million, consisting of distributed profits on closed UWYs from the Syndicate, to the Parent Company in the form of dividends. The amount and nature of net assets that are restricted from payment of dividends as of December 31, 2016 and 2015 are presented in the following table: As of December 31, amounts in thousands 2016 2015 Restricted net assets: NIC and NSIC: Fixed maturities at fair value (amortized cost: 2016, $9,820; 2015, $9,950) $ 10,690 $ 11,277 Short term investments, at fair value 290 290 Cash 7,168 6,208 Total NIC and NSIC (1) $ 18,148 $ 17,775 NHUK: Fixed maturities at fair value (amortized cost: 2016, $457,225; 2015, $458,558) $ 452,053 $ 448,666 Short term investments, at fair value 63,729 71,320 Cash — 3,262 Total NHUK (2) $ 515,782 $ 523,248 Total Restricted Net Assets $ 533,930 $ 541,023 (1) - The restricted net assets for NIC and NSIC primarily consist of fixed maturities on deposit with various state insurance departments. The cash as of December 31, 2016 and 2015, as presented in the table above, was on deposit with a U.K. bank to comply with the regulatory requirements of the Prudential Regulation Authority for the underwriting activities of the U.K. Branch. (2) - The restricted net assets for NHUK consists of fixed maturities and cash held in trust for the benefit of syndicate policyholders and short term investments primarily consisting of overseas deposits in various countries with Lloyd's to support underwriting activities in those countries.

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Earnings Per Share	NOTE 11. EARNINGS PER SHARE The following is a reconciliation of the basic and diluted EPS computations for the years ended December 31, 2016, 2015 and 2014: Years Ended December 31, amounts in thousands, except share and per share amounts 2016 2015 2014 Net income $ 82,726 $ 81,057 $ 95,329 Basic weighted average shares (1) 29,073,803 28,785,044 28,519,536 Effect of common stock equivalents: Assumed exercise of stock options and vesting of stock 957,806 866,446 773,202 Diluted weighted average shares 30,031,609 29,651,490 29,292,738 Net income per common share: Basic $ 2.85 $ 2.82 $ 3.34 Diluted $ 2.75 $ 2.73 $ 3.25 (1) - We completed a two-for-one stock split on January 20, 2017. All share and per share data has been retroactively restated on a post-split basis.

Statutory Financial Information

Statutory Financial Information	12 Months Ended
	Dec. 31, 2016
Text Block [Abstract]
Statutory Financial Information	NOTE 12. STATUTORY FINANCIAL INFORMATION The following table presents statutory Net income and capital and surplus in accordance with statutory accounting practices: Years Ended December 31, amounts in millions 2016 2015 2014 NIC & NSIC: Statutory net income $ 84.2 $ 60.8 $ 75.7 Statutory capital and surplus $ 1,027.3 $ 949.1 $ 893.9 The Syndicate: Syndicate's net income $ 46.3 $ 41.0 $ 33.8 Syndicate's capital and surplus $ 180.7 $ 177.5 $ 140.1 Our insurance subsidiaries file financial statements prepared in accordance with statutory accounting practices prescribed or permitted by domestic and foreign insurance regulatory authorities. The differences between statutory financial statements and financial statements prepared in accordance with U.S. GAAP vary between domestic and foreign jurisdictions. For NIC and NSIC, the National Association of Insurance Commissioners (“NAIC”) has codified Statutory Accounting Practices and Procedures (“SAP”) for insurance enterprises. We prepare our statutory basis financial statements in accordance with the most recently updated NAIC SAP manual subject to any deviations prescribed or permitted by the New York Insurance Commissioner. The following table represents some of the significant differences between SAP and U.S. GAAP as they relate to our operations: Differences SAP U.S. GAAP Acquisition and Commission Costs Expensed when incurred Costs are generally deferred Bonds Generally stated at amortized cost Stated at fair value Deferred tax assets Certain temporary differences are not admitted All temporary differences recognized Receivables over 90 days outstanding and other intangible assets Not recognized Generally recognized (subject to valuation allowances) Unearned premiums and loss reserves Net of ceded amounts Gross of ceded amounts The Syndicate is subject to oversight by the Council of Lloyd’s. Lloyd’s as a whole is authorized and regulated by the PRA. Our other international businesses are also regulated by the PRA. The following table represents some of the significant differences between U.K. GAAP and U.S. GAAP as they relate to our operations: Differences U.K. GAAP U.S. GAAP Unrealized gains/losses Recognized in income Recognized in AOCI Foreign exchange gains/losses on translation Recognized in income Recognized in AOCI Lloyd’s membership costs Expensed when incurred Amortized over each UWY Refer to Note 1, Organization and Summary of Significant Accounting Policies For NIC and NSIC, aggregate minimum required statutory capital and surplus is based on the greater of the risk-based capital level that would trigger regulatory action or minimum requirements per state insurance regulation. Capital and surplus requirements of our foreign subsidiaries differ from those prescribed in the U.S. and vary by jurisdiction. The capital requirement of the Syndicate, known as FAL, is currently calculated using the internal Lloyd’s risk-based capital model. The FAL may be comprised of cash, investments and undrawn letters of credit provided by various banks. Lloyd’s sets the corporate member’s required capital annually based on the Syndicate business plans, rating environment, reserving environment and input arising from Lloyd’s discussions with regulatory and rating agencies. As of December 31, 2016 and 2015, all insurance subsidiaries individually exceed the minimum required statutory capital and surplus requirements and all U.S. domestic insurance subsidiaries individually exceeded risk-based capital minimum requirements.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	NOTE 13. STOCK-BASED COMPENSATION As of December 31, 2016, there were 2,000,000 available restricted shares in the Second Amended and Restated 2005 Stock Incentive Plan. As of December 31, 2016, 1,531,058 of such awards were issued leaving 468,942 awards available to be issued in subsequent periods. Stock-based compensation granted under our Company’s stock plans is expensed in tranches over the vesting period. Options and non-performance based grants generally vest equally over a three or four year period and the options have a maximum term of ten years. Our Company’s performance based share grants generally consist of three types of awards. The performance units issued in 2016, 2015 and 2014 will cliff vest on the third anniversary of the date of the grant in an amount as determined by the rate of cumulative annual growth in tangible book value for the three years immediately prior to the vesting date, with actual shares that vest ranging between 150% to 50% of that portion of the original award. Unvested restricted stock units and performance units outstanding as of December 31, 2016, 2015 and 2014, and changes during the years ended on those dates, are presented in the following table: December 31, 2016 2015 2014 Beginning balance 1,393,030 1,437,784 1,253,624 Granted - Performance 404,946 370,100 457,214 Granted - Non Performance 84,000 64,316 119,046 Total Granted 488,946 434,416 576,260 Vested - Performance (285,208 ) (136,160 ) (186,906 ) Vested - Non Performance (55,000 ) (271,200 ) (180,526 ) Total Vested (340,208 ) (407,360 ) (367,432 ) Forfeited (167,604 ) (71,810 ) (24,668 ) Ending balance 1,374,164 1,393,030 1,437,784 As of December 31, 2016 and 2015, the total unrecognized compensation expense, net of estimated forfeitures, related to unvested stock units was $22.3 million and $17.3 million, respectively, which is expected to be recognized as expense over weighted average periods of 1.8 years and 2.0 years, respectively. The aggregate fair value of all unvested restricted stock units as of December 31, 2016 and 2015 was $87.2 million and $55.2 million, respectively. The aggregate fair value will not change after the stock split, as shares will be doubled and the price per share will be halved. Stock options outstanding as of December 31, 2016, 2015 and 2014 are as follows: December 31, 2016 (1) 2015 2014 Average Average Average # of Shares Exercise Price # of Shares Exercise Price # of Shares Exercise Price Beginning balance — $ — 1,500 $ 36.03 6,750 $ 30.65 Granted — — — — — — Exercised — $ — (1,500 ) $ 36.03 (5,250 ) $ 29.11 Expired or forfeited — — — — — — Ending balance — $ — — $ — 1,500 $ 36.03 Number of options exercisable — $ — — $ — 1,500 $ 36.03 (1) – Our company has not recently issued stock options and does not currently have any options outstanding. We offer an Employee Stock Purchase Plan (the “ESPP”) to all of our eligible employees. Employees are offered the opportunity to purchase our Company’s Common stock at 90% of fair market value at the lower of the price at the beginning or the end of each six month offering period. Each employee can invest up to 10% of their base compensation subject to the lesser of 1,000 common stock shares or total market value of $25,000. There were 41,224 shares purchased in 2016 from funds withheld during the July 1, 2015 to December 31, 2015 and January 1, 2016 to June 30, 2016 offering periods. There were 41,714 shares purchased in 2015 in the aggregate from funds withheld during the offering periods of July 1, 2014 to December 31, 2014 and January 1, 2015 to June 30, 2015. We expense both the value of the 10% discount and the “look-back” option, which provides for the more favorable price at either the beginning or end of the offering period.

Retirement Plans

Retirement Plans	12 Months Ended
	Dec. 31, 2016
Compensation And Retirement Disclosure [Abstract]
Retirement Plans	NOTE 14. RETIREMENT PLANS We have a 401(k) Plan for all U.S. eligible employees. Each eligible employee can contribute a portion of their salary, limited by certain Federal regulations. The expense recorded for all contributions to the 401(k) Plan for the year ended December 31, 2016 was $7.4 million, consisting of $4.2 million for the retirement savings contributions and $3.2 million for the non-discretionary matching contributions. The expense recorded for all contributions to the 401(k) Plan for the year ended December 31, 2015 was $6.3 million, consisting of $3.8 million for the retirement savings contributions and $2.5 million for the non-discretionary matching contributions. The expense recorded for all contributions to the 401(k) Plan for the year ended December 31, 2014 was $7.5 million, consisting of $3.8 million for the retirement savings contributions, $2.1 million for the non-discretionary matching contributions and $1.6 million for the discretionary matching contribution. Our Company sponsors a defined contribution plan for all of our Company’s U.K. employees under U.K. regulations. Contributions, which are fully vested when made, are equal to 15.0% of each eligible employee’s gross base salary for all U.K. employees hired prior to November 2014 and 12.0% for all employees hired after November 2014. The expense recorded for the U.K. defined contribution plan was $2.9 million, $2.9 million and $2.6 million for the years ended December 31, 2016, 2015 and 2014, respectively. Our Company sponsors defined contribution plans for employees in several of our other European offices, outside of the U.K., under each countries’ regulations. Contributions, which are fully vested when made, range by European office between 2.1% and 26.0% of each eligible employee’s gross base salary. The expense recorded for the other European offices defined contribution plans was $0.5 million, $0.5 million and $0.2 million for the years ended December 31, 2016, 2015 and 2014, respectively. Such expenses are included in Other operating expenses.

Condensed (Unaudited) Quarterly

Condensed (Unaudited) Quarterly Financial Data	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Condensed (Unaudited) Quarterly Financial Data	NOTE 15. CONDENSED (Unaudited) QUARTERLY FINANCIAL DATA The following is a summary of quarterly financial data for the periods indicated: March 31, June 30, September December 31, amounts in thousands, except per share amounts 2016 2016 2016 2016 Gross written premiums $ 413,877 $ 412,565 $ 374,930 $ 367,539 Revenues: Net written premiums $ 319,820 $ 306,535 $ 277,001 $ 282,868 Change in unearned premiums (55,462 ) (38,543 ) 7,009 1,117 Net earned premiums $ 264,358 $ 267,992 $ 284,010 $ 283,985 Net investment income 19,594 19,875 19,875 20,107 Total other-than-temporary impairment losses (109 ) (162 ) 23 21 Portion of loss recognized in other comprehensive income (before tax) 109 12 (23 ) (21 ) Net other-than-temporary impairment losses recognized in earnings — (150 ) — — Net realized gains (losses) 1,597 1,960 1,586 4,043 Other income (expense) 2,549 4,430 (183 ) 1,905 Total revenues $ 288,098 $ 294,107 $ 305,288 $ 310,040 Expenses: Net losses and LAE $ 152,956 $ 167,206 $ 172,793 $ 172,493 Commission expenses 37,554 40,726 42,611 44,154 Other operating expenses 60,809 59,074 56,137 58,076 Interest expense 3,858 3,858 3,859 3,860 Total expenses $ 255,177 $ 270,864 $ 275,400 $ 278,583 Income before income taxes 32,921 23,243 29,888 31,457 Income tax expense $ 9,989 $ 7,053 $ 7,875 $ 9,866 Net income $ 22,932 $ 16,190 $ 22,013 $ 21,591 Comprehensive income (loss) $ 45,721 $ 35,228 $ 18,760 $ (31,712 ) Combined ratio 95.1 % 99.6 % 95.6 % 96.7 % Net income per share: (1) Basic $ 0.79 $ 0.56 $ 0.76 $ 0.74 Diluted $ 0.77 $ 0.54 $ 0.73 $ 0.71 (1) - We completed a two-for-one stock split on January 20, 2017. All share and per share data has been retroactively restated on a post-split basis. March 31, June 30, September 30, December 31, amounts in thousands, except per share amounts 2015 2015 2015 2015 Gross written premiums $ 396,460 $ 379,471 $ 354,062 $ 323,509 Revenues: Net written premiums $ 288,958 $ 258,244 $ 251,939 $ 244,719 Change in unearned premiums (52,826 ) (15,916 ) 2,143 6,826 Net earned premiums $ 236,132 $ 242,328 $ 254,082 $ 251,545 Net investment income 16,253 16,595 17,371 18,499 Total other-than-temporary impairment losses — (423 ) (1,298 ) (123 ) Portion of loss recognized in other comprehensive income (before tax) — — 23 123 Net other-than-temporary impairment losses recognized in earnings — (423 ) (1,275 ) — Net realized gains 5,596 4,339 518 (2,080 ) Other income (expense) 2,242 (4,362 ) (2,518 ) 4,147 Total revenues $ 260,223 $ 258,477 $ 268,178 $ 272,111 Expenses: Net losses and LAE $ 130,198 $ 141,973 $ 146,546 $ 153,881 Commission expenses 32,905 31,480 34,253 31,339 Other operating expenses 54,909 52,789 56,599 59,219 Interest expense 3,855 3,856 3,856 3,857 Total expenses $ 221,867 $ 230,098 $ 241,254 $ 248,296 Income before income taxes 38,356 28,379 26,924 23,815 Income tax expense $ 12,427 $ 9,195 $ 8,723 $ 6,072 Net income $ 25,929 $ 19,184 $ 18,201 $ 17,743 Comprehensive income $ 27,052 $ (3,789 ) $ 18,849 $ 15,990 Combined ratio 92.3 % 93.4 % 93.4 % 97.2 % Net income per share: (1) Basic $ 0.90 $ 0.67 $ 0.63 $ 0.62 Diluted $ 0.89 $ 0.65 $ 0.61 $ 0.59 (1) - We completed a two-for-one stock split on January 20, 2017. All per share data has been retroactively restated on a post-split basis.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2016
Subsequent Events [Abstract]
Subsequent Events	NOTE 16. SUBSEQUENT EVENTS On December 6, 2016, our Board of Directors declared a two-for-one stock split of The Navigators Group, Inc. Common stock, to be effected in the form of a stock dividend. Stockholders of record at the close of business on December 30, 2016 received one additional share of Common stock for every share of Common stock held. The additional shares of Common stock were issued on January 20, 2017. . , o n February 16, 2017, our Board of Directors declared a cash dividend on The Navigators Group, Inc. Common stock of $0.045 per share, payable on March 24, 2017 to stockholders of record on March 3, 2017. Effective January 1, 2017, we entered into a reinsurance arrangement to cede 100% of the unearned premium as of such date on the North American exposures of our Property business underwritten at Lloyd’s to Vibe Syndicate Management Limited (“Vibe”). All losses occurring after the effective date on this business will be covered by Vibe. Also, effective January 1, 2017, the Parent Company sold its insurance agency operations in Sweden and Denmark to Ryan Specialty Group, LLC (“RSG”). The transaction represents a 100% acquisition of its Sweden and Denmark corporations, NUAL AB and Navigators A/S, respectively. This transaction also included the transfer of the operating lease for the Stockholm office to RSG. We do not expect these transactions to have a material effect on our financial statements. On February 16, 2017, our Company entered into that certain Guarantee, pursuant to which it guaranteed all of the liabilities and obligations of NIIC. The Guarantee would remain effective until all of such liabilities and obligations are discharged, and in the event that our Company does not meets its obligations under the Guarantee, any person who is covered by an insurance policy, certificate of coverage or reinsurance contract issued by NIIC would be a third party beneficiary under the Guarantee. Refer to Note 8, Commitment and Contingencies

Summary of Consolidated Investm

Summary of Consolidated Investments-Other Than Investments in Related Parties	12 Months Ended
	Dec. 31, 2016
Summary Of Investments Other Than Investments In Related Parties [Abstract]
Disclosure - Summary of Consolidated Investments-Other Than Investments in Related Parties	THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES Summary of Consolidated Investments - Other than Investments in Related Parties December 31, 2016 Gross Gross Unrealized Unrealized Amortized amounts in thousands Fair Value (1) Gains Losses Cost Fixed maturities: U.S. Treasury bonds, agency bonds and foreign government bonds $ 273,776 $ 2,192 $ (5,128 ) $ 276,712 States, municipalities and political subdivisions 547,415 11,542 (4,036 ) 539,909 Mortgage-backed and asset-backed securities: — — — — Agency mortgage-backed securities 487,364 4,016 (6,585 ) 489,933 Residential mortgage obligations 20,530 453 (55 ) 20,132 Asset-backed securities 314,601 824 (1,178 ) 314,955 Commercial mortgage-backed securities 154,139 2,859 (1,904 ) 153,184 Subtotal $ 976,634 $ 8,152 $ (9,722 ) $ 978,204 Corporate bonds 838,057 10,185 (5,528 ) 833,400 Total fixed maturities $ 2,635,882 $ 32,071 $ (24,414 ) $ 2,628,225 Equity securities 349,142 27,016 (5,785 ) 327,911 Other invested assets 1,960 — — 1,960 Short-term investments 143,539 88 — 143,451 Total investments $ 3,130,523 $ 59,175 $ (30,199 ) $ 3,101,547 (1) Other invested assets are accounted for using the equity method of accounting. All other investments are shown at fair value.

Condensed Financial Information

Condensed Financial Information of Registrant	12 Months Ended
	Dec. 31, 2016
Condensed Financial Information Of Parent Company Only Disclosure [Abstract]
Condensed Financial Information of Registrant	THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES Condensed Financial Information of Registrant The Navigators Group, Inc. Balance Sheets (Parent Company) December 31, amounts in thousands except share amounts 2016 2015 ASSETS Investments $ 1,660 $ 89,586 Cash 11,003 6,417 Investments in subsidiaries 1,381,652 1,232,012 Goodwill and other intangible assets 2,534 2,534 Other assets 49,588 33,647 Total assets $ 1,446,437 $ 1,364,196 LIABILITIES AND STOCKHOLDERS' EQUITY Liabilities: Senior notes $ 263,728 $ 263,580 Accounts payable and other liabilities 1,347 1,294 Accrued interest payable 3,174 3,174 Total liabilities $ 268,249 $ 268,048 Stockholders' Equity: (1) Preferred stock, $.10 par value, authorized 1,000,000 shares, none issued $ — $ — Common stock, $.10 par value, authorized 50,000,000 shares, issued 36,146,899 shares for 2016 and 35,884,538 shares for 2015 3,612 3,586 Additional paid-in capital 373,983 356,036 Treasury stock, at cost (7,022,760 shares for 2016 and 2015) (155,801 ) (155,801 ) Retained earnings 947,519 868,723 Accumulated other comprehensive income: Net unrealized gains (losses) on securities available-for-sale, net of tax 8,882 23,611 Foreign currency translation adjustment, net of tax (7 ) (7 ) Total stockholders' equity $ 1,178,188 $ 1,096,148 Total liabilities and stockholders' equity $ 1,446,437 $ 1,364,196 (1) - We completed a two-for-one stock split on January 20, 2017. All share and per share data has been retroactively restated on a post-split basis. SCHEDULE II THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES Condensed Financial Information of Registrant (Continued) The Navigators Group, Inc. Statements of Income (Parent Company) Years Ended December 31, amounts in thousands 2016 2015 2014 Revenues: Net investment income $ 53 $ 147 $ 76 Total revenues $ 53 $ 147 $ 76 Expenses: Interest expense 15,435 15,424 15,413 Other (income) expense 22 — — Total expenses $ 15,457 $ 15,424 $ 15,413 Income (loss) before income tax benefit $ (15,404 ) $ (15,277 ) $ (15,337 ) Income tax benefit (8,009 ) (5,472 ) (5,287 ) Income (loss) before equity in undistributed net income of wholly owned subsidiaries $ (7,395 ) $ (9,805 ) $ (10,050 ) Equity in undistributed net income of wholly-owned subsidiaries 90,121 90,862 105,379 Net income $ 82,726 $ 81,057 $ 95,329 SCHEDULE II THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES Condensed Financial Information of Registrant (Continued) The Navigators Group, Inc. Statements of Cash Flows (Parent Company) Years Ended December 31, amounts in thousands 2016 2015 2014 Operating activities: Net income $ 82,726 $ 81,057 $ 95,329 Adjustments to reconcile net income to net cash provided by (used in) operations: Equity in undistributed net income of wholly-owned subsidiaries (90,121 ) (90,862 ) (105,379 ) Dividends received from subsidiaries 5,000 — — Other 379 3,373 9,211 Net cash provided by (used in) operating activities $ (2,016 ) $ (6,432 ) $ (839 ) Investing activities: Fixed maturities, available-for-sale Sales $ — $ 1,250 $ 3,200 Purchases — — — Equity securities Sales — — — Purchases — — — Net (increase) decrease in short-term investments 87,942 3,918 (3,424 ) Net cash provided by (used in) investing activities $ 87,942 $ 5,168 $ (224 ) Financing activities: Capital contribution to subsidiary $ (79,250 ) $ — $ — Proceeds of stock issued from employee stock purchase plan 1,840 1,352 1,067 Proceeds of stock issued from exercise of stock options — 29 153 Dividends paid (3,930 ) — — Net cash provided by (used in) financing activities $ (81,340 ) $ 1,381 $ 1,220 Increase (decrease) in cash $ 4,586 $ 117 $ 157 Cash at beginning of year 6,417 6,300 6,143 Cash at end of year $ 11,003 $ 6,417 $ 6,300

Supplementary Insurance Informa

Supplementary Insurance Information	12 Months Ended
	Dec. 31, 2016
Supplementary Insurance Information [Abstract]
Supplementary Insurance Information	SCHEDULE III THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES Supplementary Insurance Information Amortization Deferred Other policy of deferred policy Reserve claims and Net Net Losses policy Other Net acquisition for losses Unearned benefits earned investment and LAE acquisition operating written amounts in thousands costs and LAE premiums payable premiums income (1) incurred costs (2) expenses (1) premiums Year ended December 31, 2016 NIC, NSIC and Navigators Management Company, Inc. $ 83,060 $ 1,753,630 $ 640,210 $ — $ 798,151 $ 71,044 $ 482,789 $ 108,809 $ 162,387 $ 844,987 NHUK 36,600 536,097 247,134 — 302,194 8,344 182,659 56,236 68,152 341,237 NIIC — — — — — 25 — — 44 — $ 119,660 $ 2,289,727 $ 887,344 $ — $ 1,100,345 $ 79,413 $ 665,448 $ 165,045 $ 230,583 $ 1,186,224 Year ended December 31, 2015 NIC, NSIC and Navigators Management Company, Inc. $ 67,144 $ 1,692,886 $ 607,062 $ — $ 722,749 $ 61,863 $ 451,296 $ 88,597 $ 153,194 $ 757,117 NHUK 24,839 509,758 213,614 — 261,338 6,708 121,302 41,380 67,449 286,743 $ 91,983 $ 2,202,644 $ 820,676 $ — $ 984,087 $ 68,571 $ 572,598 $ 129,977 $ 220,643 $ 1,043,860 Year ended December 31, 2014 NIC, NSIC and Navigators Management Company, Inc. $ 63,200 $ 1,645,984 $ 579,331 $ — $ 704,574 $ 56,714 $ 434,396 $ 85,137 $ 138,675 $ 752,773 NHUK 16,252 513,650 186,836 — 231,321 7,378 110,833 42,558 58,150 247,365 $ 79,452 $ 2,159,634 $ 766,167 $ — $ 935,895 $ 64,092 $ 545,229 $ 127,695 $ 196,825 $ 1,000,138 (1) - Net investment income and Other operating expenses reflect only such amounts attributable to our Company's insurance operations. (2) - Amortization of deferred policy acquisition costs reflects only such amounts attributable to our Company's insurance operations. A portion of these costs is eliminated in consolidation.

Reinsurance - Written Premium

Reinsurance - Written Premium	12 Months Ended
	Dec. 31, 2016
Supplemental Schedule Of Reinsurance Premiums For Insurance Companies [Abstract]
Reinsurance - Written Premium	SCHEDULE IV THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES Reinsurance - Written Premium Ceded to Assumed Percentage Direct other from other Net of amount amounts in thousands Amount companies companies amount assumed Year ended December 31, 2016 P&C $ 1,403,865 $ 382,687 $ 165,046 $ 1,186,224 14 % Year ended December 31, 2015 P&C $ 1,277,728 $ 409,642 $ 175,774 $ 1,043,860 17 % Year ended December 31, 2014 P&C $ 1,232,012 $ 432,215 $ 200,341 $ 1,000,138 20 %

Valuation and Qualifying Accoun

Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2016
Valuation And Qualifying Accounts [Abstract]
Valuation and Qualifying Accounts	SCHEDULE V THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES Valuation and Qualifying Accounts Balance at Charged (Credited) to Charged to Deductions Balance at amounts in thousands January 1 Costs and Expenses Other Accounts (Describe) December 31 Year ended December 31, 2016 Allowance for uncollectable reinsurance $ 6,921 $ 5,157 $ — $ — $ 12,078 Valuation allowance in deferred taxes $ 721 $ (22 ) $ — $ — $ 699 Year ended December 31, 2015 Allowance for uncollectable reinsurance $ 11,332 $ (4,411 ) $ — $ — $ 6,921 Valuation allowance in deferred taxes $ 776 $ (55 ) $ — $ — $ 721 Year ended December 31, 2014 Allowance for uncollectable reinsurance $ 11,332 $ — $ — $ — $ 11,332 Valuation allowance in deferred taxes $ 554 $ 222 $ — $ — $ 776

Supplementary Information Conce

Supplementary Information Concerning Property-Casualty Insurance Operations	12 Months Ended
	Dec. 31, 2016
Supplemental Information For Property Casualty Insurance Underwriters [Abstract]
Supplementary Information Concerning Property-Casualty Insurance Operations	SCHEDULE VI THE NAVIGATORS GROUP, INC. AND SUBSIDIARIES Supplementary Information Concerning P&C Insurance Operations Losses and LAE Amortization Deferred policy Reserve Net Net expenses incurred related to of deferred policy Other Net amounts in thousands acquisition for losses Unearned earned investment Current Prior acquisition operating written Affiliation with Registrant costs and LAE premiums premiums income (1) year years costs (2) expenses (1) premiums Consolidated Subsidiaries: Year ended December 31, $ 119,660 $ 2,289,727 $ 887,344 $ 1,100,345 $ 79,413 $ 693,976 $ (28,528 ) $ 165,045 $ 230,583 $ 1,186,224 Year ended December 31, 2015 $ 91,983 $ 2,202,644 $ 820,676 $ 984,087 $ 68,571 $ 637,267 $ (64,669 ) $ 129,977 $ 220,643 $ 1,043,860 Year ended December 31, 2014 $ 79,452 $ 2,159,634 $ 766,167 $ 935,895 $ 64,092 $ 601,041 $ (55,812 ) $ 127,695 $ 196,825 $ 1,000,138 (1) - Net investment income and Other operating expenses reflect only such amounts attributable to our Company's insurance operations. (2) - Amortization of deferred policy acquisition costs reflects only such amounts attributable to our Company's insurance operations. A portion of these costs is eliminated in consolidation.

Organization and Summary of S33

Organization and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements of The Navigators Group, Inc. and its subsidiaries have been prepared in conformity with accounting principles generally accepted in the United States of America (“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, disclosure of contingent assets and liabilities at the date of the financial statements and the reported revenues and expenses during the reporting periods. 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 term “Parent Company” is 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 U.S. and Int’l Insurance reporting segments. We have also developed niches in Professional Liability insurance, through our Directors & Officers (“D&O”) and Errors & Omissions (“E&O”) divisions. We also provide reinsurance products through our Global Reinsurance (“GlobalRe”) business. We operate through various wholly-owned subsidiaries, including Navigators Insurance Company (“NIC”), inclusive of its United Kingdom Branch (“U.K. Branch”), and Navigators Specialty Insurance Company (“NSIC”), both of which are U.S. insurance companies, and Navigators Underwriting Agency Ltd. (“NUAL”), a Lloyd’s of London (“Lloyd’s”) underwriting agency that manages Lloyd’s Syndicate 1221 (“the Syndicate”) in the U.K. and is the underwriting company of Navigators Holdings (U.K.) Ltd. (“NHUK”). Our Company controls 100% of the Syndicate’s stamp capacity. In May 2016, our Company received authorization from the Prudential Regulation Authority (“PRA”) and the Financial Conduct Authority (“FCA”) for a new U.K. based insurance company, Navigators International Insurance Company Ltd (“NIIC”), which is a wholly-owned direct subsidiary of our Parent Company, and has been fully capitalized in compliance with the terms of the authorization from the PRA.
Cash	Cash Cash includes cash on hand and demand deposits with banks, excluding such amounts held by the Syndicate included as Funds at Lloyd’s (“FAL”), which are classified as short term investments.
Investments	Investments As of December 31, 2016 and 2015, all fixed maturity and equity securities held by our Company were carried at fair value and classified as available-for-sale. Available-for-sale securities are debt and equity securities not classified as either held-to-maturity securities or trading securities and are reported at fair value, with unrealized gains and losses excluded from earnings and reported in accumulated other comprehensive income (“AOCI”) as a separate component of stockholders’ equity. Fixed maturity securities include bonds, mortgage-backed and asset-backed securities. Equity securities consist of common stock, exchange traded funds and preferred stock. Other invested assets consist of investments our Company made in certain strategic companies which are accounted for using the equity method of accounting. In applying the equity method, these investments are initially recorded at cost and are subsequently adjusted based on our Company’s proportionate share of the net income or loss of the companies. Changes in the carrying value of such investments are recorded in Other income. In applying the equity method, we use the most recently available financial information provided by the companies which is generally three months prior to the end of the reporting period. Short-term investments are carried at fair value. Short-term investments mature within one year from the purchase date. All prices for our fixed maturities, equity securities and short-term investments are classified as Level 1, Level 2 or Level 3 under the fair value hierarchy, as defined in the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification 820 (“ASC 820”). Premiums and discounts on fixed maturity securities are amortized into interest income over the life of the security using the interest method. For mortgage-backed and asset-backed securities, anticipated prepayments and expected maturities are utilized in applying the interest rate method. An effective yield is calculated based on projected principal cash flows at the time of original purchase. The effective yield is used to amortize the purchase price of the security over the security’s expected life. Book values are adjusted to reflect the amortization of premium or accretion of discount on a monthly basis. The projected principal cash flows are based on certain prepayment assumptions, which are generated using a prepayment model. The prepayment model uses a number of factors to estimate prepayment activity including the current levels of interest rates (refinancing incentive), time of year (seasonality), economic activity (including housing turnover) and term and age of the underlying collateral (burnout, seasoning). Prepayment assumptions associated with the mortgage-backed and asset-backed securities are reviewed on a periodic basis. When changes in prepayment assumptions are deemed necessary as the result of actual prepayments differing from anticipated prepayments, securities are revalued based upon the new prepayment assumptions utilizing the retrospective adjustment method, whereby the effective yield is recalculated to reflect actual payments to date and anticipated future payments. The investment in such securities is adjusted to the amount that would have existed had the new effective yield been applied since the acquisition of the security. Such adjustments, if any, are included in Net investment income for the current period. Realized gains and losses on sales of investments are recognized when the related trades are executed and are determined on the basis of the specific identification method.
Impairment of Invested Assets	Impairment of Invested Assets Management regularly reviews our fixed maturity and equity securities portfolios to evaluate the necessity of recording impairment losses for other-than-temporary declines in the fair value of securities. Our Company reviews the magnitude of a security’s unrealized loss compared to its cost/amortized cost and the length of time that the security has been impaired to determine if an unrealized loss is other-than-temporary. If warranted as a result of conditions relating to a particular security, our Company will also review securities with declines in fair value resulting from a headline news event involving the issuer, a headline news event involving the asset class, the advice of our external asset managers, or economic events that may impact the issuer to determine if an unrealized loss is other-than-temporary. The depth of analysis performed is dependent upon the nature and magnitude of the indicators of other-than-temporary impairment present in regards to each impaired security. For Equity securities, our Company performs a fundamental analysis of the issuer, including an evaluation of the mean analysts’ target price, to assess the likelihood of recovery of our cost basis in the security. Management also assesses the likelihood of future cash flows, dividends and increases to dividends, all of which affect the securities eligible for our equity strategy and therefore our intent to hold the security. 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. For Fixed maturities, our Company assesses the underlying fundamentals of each issuer to determine if there is a change in the amount or timing of expected cash flows. Management compares the amortized cost basis to the present value of the revised cash flows using the historical book yield to determine the credit loss portion of impairment which is recognized in earnings. All non-credit losses where we have the intent and ability to hold the security until recovery are recognized as changes in OTTI losses within AOCI. Specifically for structured Fixed maturities, our Company analyzes 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. For securities in which a tranche loss is present and the net present value of loss adjusted cash flows is less than book value, credit impairment is recognized in earnings. 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, severity and prepayment assumptions. Projected losses are a function of both loss severity and probability of default, which differ based on property type, vintage and the stress of the collateral .
Foreign Currency Remeasurement and Translation	Foreign Currency Remeasurement and Translation The functional currency of each of our operations is generally the currency of the local operating environment, except for our Lloyd’s business which is United States Dollar (“USD”). Transactions in currencies other than an operation’s functional currency are remeasured into the functional currency and the resulting foreign exchange gains and losses are reflected in net Other income (expense) in the Consolidated Statements of Income. Functional currency assets and liabilities of foreign operations are translated into USD using period end rates of exchange and the related translation adjustments are recorded as a separate component of AOCI. Consolidated Statements of Income amounts expressed in functional currencies are translated using average exchange rates. 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 British Pound Sterling (“GBP”), U.S. Dollars (“USD”) and Canadian Dollars (“CAD”) to one functional currency, the 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 resulted in a 2014 immaterial correction of $10.0 million ($6.6 million after-tax) in AOCI, on the Consolidated Balance Sheets, offset by a gain in Other income in the Consolidated Statements of Income.
Premium Revenues	Premium Revenues Written premium is based on the insurance policies that have been reported to us and the policies that have been written by agents but not yet reported to us. We estimate the amount of written premium not yet reported based on judgments relative to current and historical trends of the business being written. Such estimates are regularly reviewed and updated and any resulting adjustments are included in the current year’s results. An Unearned premium reserve is established to reflect the unexpired portion of each policy at the financial reporting date. Substantially all of our business is placed through agents and brokers. We record estimates for both unreported direct and assumed premiums. We also record the ceded portion of the estimated Gross written premiums and related acquisition costs. These estimates are mostly for our Marine and Energy & Engineering products written by our International Insurance (“Int’l Insurance”) reporting segment as well as our Accident & Health (“A&H”) and Latin American (“LatAm”) business written by our GlobalRe reporting segment. Such premium estimates are generally based on submission data received from brokers and agents and recorded when the insurance policy or reinsurance contract is written or bound. The earned gross, ceded and net premiums are calculated based on our earning methodology, which is generally pro-rata over the policy period or over the period of risk if the period of risk differs significantly from the contract period.
Reinsurance Ceded	Reinsurance Ceded In the normal course of business, we purchase reinsurance from insurers or reinsurers to reduce the amount of loss arising from claims. Management analyzes the reinsurance agreements to determine whether the reinsurance should be classified as prospective or retroactive based upon the terms of the reinsurance agreement and whether the reinsurer has assumed significant insurance risk to the extent that the reinsurer may realize a significant loss from the transaction. Prospective reinsurance is reinsurance in which an assuming company agrees to reimburse the ceding company for losses that may be incurred as a result of future insurable events covered under contracts subject to the reinsurance. Retroactive reinsurance is reinsurance in which an assuming company agrees to reimburse a ceding company for liabilities incurred as a result of past insurable events covered under contracts subject to the reinsurance. Ceded reinsurance premiums net of ceding commissions and ceded losses are reflected as reductions of the respective income or expense accounts over the terms of the reinsurance contracts. Prepaid reinsurance premiums represent the portion of premiums ceded to reinsurers applicable to the unexpired terms of the reinsurance contracts in force. Reinsurance reinstatement premiums (“RRPs”) are recognized in the same period as the loss event that gave rise to the reinstatement premiums. Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability associated with the reinsured policy. Ceded Unearned premiums and estimates of amounts recoverable from reinsurers on paid and unpaid losses are reflected as assets. Provisions are made for estimated unrecoverable reinsurance.
Deferred Policy Acquisition Costs	Deferred Policy Acquisition Costs Costs of acquiring business are deferred and amortized over the period that the related premiums are recognized as revenue. Such costs (e.g., Commission expenses, Other underwriting expenses and Premium taxes) are limited to the incremental direct costs related to the successful acquisition of new or renewal business. The method of computing deferred policy acquisition costs limits the deferral to their estimated net realizable value based on the related Unearned premiums and takes into account anticipated losses, loss adjustment expense (“LAE”), Commission expenses and Operating expenses based on historical and current experience, as well as anticipated investment income.
Reserves for Losses and Loss Adjustment Expenses	Reserves for Losses and Loss Adjustment Expenses Unpaid losses and LAE are determined on: (a) individual claims reported on direct business for insureds, (b) from reports received from ceding insurers for assumed business and (c) on estimates based on Company and industry experience for incurred but not reported (“IBNR”) claims and LAE. Indicated IBNR reserves for losses and LAE are calculated by our actuaries using several standard actuarial methodologies, including the paid and incurred loss development and the paid and incurred Bornheutter-Ferguson loss methods. Frequency/severity analyses are performed for certain books of business. The Reserve for losses and LAE has been established to cover the estimated unpaid cost of claims incurred. Such estimates are regularly compared to indicated reserves and updated and any resulting adjustments are included in the current year’s results. Management believes that the liability recognized for unpaid losses and LAE is a reasonable estimate of the ultimate unpaid claims incurred, however, no representation is made that the ultimate liability will not differ materially from the amounts recorded in the accompanying Consolidated Financial Statements. Losses and LAE are recorded on an undiscounted basis.
Earnings per Share	Earnings per Share Basic earnings per share (“EPS”) is computed by dividing Net income by the weighted average number of common shares outstanding for the period. Diluted EPS reflects the basic EPS adjusted for the potential dilution that would occur if all issued stock options were exercised and all stock grants were fully vested.
Depreciation and Amortization	Depreciation and Amortization Depreciation of furniture and fixtures, electronic data processing equipment and computer software is provided over the estimated useful lives of the respective assets, ranging from three to seven years, using the straight-line method. Amortization of leasehold improvements are provided over the shorter of the useful lives of those improvements or the contractual terms of the leases, ranging from five to ten years, using the straight-line method.
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets Goodwill represents the excess of the cost of acquiring a business enterprise over the fair value of the net assets acquired. Our Company’s recorded indefinite lived intangible assets represent acquired stamp capacity in the Syndicate. Goodwill and indefinite lived intangible assets are reported at carrying value and are tested for impairment at least annually, and when permitted by the applicable accounting guidance, qualitative factors are assessed to determine whether it is necessary to calculate an asset’s fair value when testing an asset with an indefinite life for impairment. Goodwill and indefinite lived intangible assets are considered impaired if the estimated fair value is less than its carrying value and any impairment loss is measured as the difference between the implied fair value and the carrying value. Our Company did not recognize an impairment of goodwill or the indefinite lived intangible assets for any of the years ended December 31, 2016, 2015 and 2014. As of December 31, 2016, the carrying value of goodwill and indefinite lived intangible assets was $6.5 million, which is $0.3 million less than the carrying value as of December 31, 2015, $6.8 million. Changes in the carrying value of the goodwill and indefinite lived intangible assets are due to amortization and fluctuations in currency exchange rates between the USD and the GBP.
Income Taxes	Income Taxes We recognize deferred tax assets and liabilities based on the differences between the financial statement carrying amounts and the tax bases of assets and liabilities. Deferred tax assets are reduced by a valuation allowance if, based on the weight of available evidence, it is more likely than not that some portion or all of the deferred tax assets will not be realized. All available evidence, both positive and negative, is considered to determine whether, based on the weight of that evidence, a valuation allowance is needed. Future realization of the tax benefit of an existing deferred tax asset ultimately depends on the existence of sufficient taxable income of the appropriate character within the carryback/carryforward period available under the tax law. In determining whether a valuation allowance is needed, management considers the timing of the reversal of each deferred tax asset as well as expected future levels of taxable income, amounts of taxable income in carryback years, and tax planning strategies. Additional information regarding our deferred tax assets can be found in Note 9, Income Taxes.
Current and Pending Accounting Pronouncements	Current and Pending Accounting Pronouncements As of January 1, 2016, we adopted the following accounting pronouncements, which did not have a material effect, singly or in the aggregate, on our Consolidated Financial Statements: • Accounting Standards Update 2015-03 – Interest – Imputation of Interest (Subtopic 835-30) – Simplifying the Presentation of Debt Issuance Costs, which is effective for fiscal years beginning after December 15, 2015. The new pronouncement was issued to simplify presentation of debt issuance costs. • Accounting Standards Update 2015-05 – Intangibles – Goodwill and Other – Internal Use Software (Subtopic 350-40) Customer’s Accounting for Fees Paid in a Cloud Computing Arrangement, which is effective for fiscal years beginning after December 15, 2015. The new pronouncement was issued to provide guidance to customers about whether a cloud computing arrangement includes a software license. • Accounting Standards Update 2015-07 – Fair Value Measurement – (Topic 820) Disclosures for Investments in Certain Entities that Calculate Net Asset Value per Share (or its equivalent) (a consensus of the Emerging Issues Task Force), which is effective for fiscal years beginning after December 15, 2015. The new pronouncement was issued to ensure that all investments categorized in the fair value hierarchy are classified using a consistent approach. The Financial Accounting Standards Board has issued the following new pronouncements that may have an impact on our Company and we are assessing the future impact of these updates on our Consolidated Financial Statements: • Accounting Standards Update 2016-01 – Financial Instruments (Subtopic 825-10) – Recognition and Measurement of Financial Assets and Financial Liabilities, which will be effective for fiscal years beginning after December 15, 2017. The new pronouncement was issued to make targeted improvements to the presentation of financial instruments. We expect the adoption of this pronouncement to have limited impact to our financial statements. • Accounting Standards Update 2016-02 – Leases (Topic 842) – Amends the recognition of a right-to-use asset and lease liability on the statement of financial position of those leases previously classified as operating leases under the previous guidance, which will be effective for fiscal years beginning after December 15, 2018. The new pronouncement was issued to improve transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. We expect the adoption of this pronouncement to result in limited changes to our total assets and total liabilities. • Accounting Standards Update 2016-09 – Compensation – Stock Compensation – (Topic 718) – Improvements to Employee Share-Based Accounting, which will be effective for fiscal years beginning after December 15, 2016. The new pronouncement was issued to simplify employee share-based accounting. We expect the adoption of this pronouncement to simplify our reporting but not have a material effect to our financial statements. • Accounting Standards Update 2016-13 – Financial Instruments – Credit Losses (Topic 326) – amends the measurement of credit losses on financial instruments not accounted for at fair value including loans, debt securities, reinsurance receivables and any other financial assets, which will be effective for the fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. We expect the adoption of this pronouncement to have limited impact to our financial statements. • Accounting Standards Update 2016-15 – Statements of Cash Flows (Topic 230) – Classification of Certain Cash Receipts and Cash Payments amends how certain cash receipts and cash payments are presented in the statement of cash flows to reduce existing diversity in practice. We expect that the adoption of this pronouncement will not have a material effect on our financial statements. • Accounting Standards Update 2016-16 - Income Taxes (Topic 740) - Amends current guidance by eliminating the exception for an intra-entity transfer of an asset other than inventory. Under the new standard, an entity should recognize the income tax consequences when the transfer occurs. The guidance prescribed is effective beginning fiscal year 2018, including interim periods. We expect that the adoption of this pronouncement will not have a material effect on our financial statements. • Accounting Standards Update 2016-17 - Consolidation (Topic 810) - Amends the consolidation guidance concerning the evaluation of interests in variable interest entities. The accounting standards update requires a reporting entity to include interests held by related parties under common control proportionally when assessing whether it holds a variable interest in a VIE. The prescribed guidance is effective beginning in fiscal year 2017, including interim periods. We expect that the adoption of this pronouncement will not have a material effect on our financial statements. • Accounting Standards Updated 2016-18 - Statement of Cash Flows (Topic 230) - Requires that amounts generally described as restricted cash and cash equivalents be included within total cash and cash equivalents in the Statement of Cash Flows. The guidance prescribed is effective beginning in fiscal year 2018, including interim periods. We expect the adoption of this pronouncement to have limited impact to our financial statements. There were no additional accounting pronouncements that are expected to have an impact on the Consolidated Financial Statements upon adoption.

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Financial Data by Segment	The following tables set forth the financial data by segment for the years ended December 31, 2016, 2015 and 2014: Year Ended December 31, 2016 U.S. Int'l amounts in thousands Insurance Insurance GlobalRe Corporate (1) Total Net earned premiums $ 629,308 $ 307,416 $ 163,621 $ — $ 1,100,345 Net losses and LAE (397,860 ) (178,284 ) (89,304 ) — (665,448 ) Commission expenses (70,812 ) (61,703 ) (34,008 ) 1,478 (165,045 ) Other operating expenses (128,108 ) (86,395 ) (19,593 ) — (234,096 ) Other underwriting income (expense) 1,092 — 522 (1,478 ) 136 Underwriting profit (loss) $ 33,620 $ (18,966 ) $ 21,238 $ — $ 35,892 Net investment income 79,451 79,451 Net realized gains (losses) 9,036 9,036 Interest expense (15,435 ) (15,435 ) Other income (loss) 8,565 8,565 Income before income taxes $ 33,620 $ (18,966 ) $ 21,238 $ 81,617 $ 117,509 Income tax (expense) benefit (34,783 ) (34,783 ) Net income (loss) $ 82,726 Losses and LAE ratio 63.2 % 58.0 % 54.6 % 60.5 % Commission expense ratio 11.3 % 20.1 % 20.8 % 15.0 % Other operating expense ratio (2) 20.2 % 28.1 % 11.6 % 21.2 % Combined ratio 94.7 % 106.2 % 87.0 % 96.7 % ( 1) - Includes Corporate segment intercompany eliminations. (2) - Includes Other operating expenses and Other underwriting income (expense). Year Ended December 31, 2015 U.S. Int'l amounts in thousands Insurance Insurance GlobalRe Corporate (1) Total Net earned premiums $ 555,836 $ 259,960 $ 168,291 $ — $ 984,087 Net losses and LAE (343,497 ) (134,702 ) (94,399 ) — (572,598 ) Commission expenses (56,319 ) (43,676 ) (32,240 ) 2,258 (129,977 ) Other operating expenses (131,407 ) (75,867 ) (16,242 ) — (223,516 ) Other underwriting income (expense) 1,690 — 690 (2,258 ) 122 Underwriting profit (loss) $ 26,303 $ 5,715 $ 26,100 $ — $ 58,118 Net investment income 68,718 68,718 Net realized gains (losses) 6,675 6,675 Interest expense (15,424 ) (15,424 ) Other income (loss) (613 ) (613 ) Income before income taxes $ 26,303 $ 5,715 $ 26,100 $ 59,356 $ 117,474 Income tax (expense) benefit (36,417 ) (36,417 ) Net income (loss) $ 81,057 Losses and LAE ratio 61.8 % 51.8 % 56.1 % 58.2 % Commission expense ratio 10.1 % 16.8 % 19.2 % 13.2 % Other operating expense ratio (2) 23.4 % 29.2 % 9.2 % 22.7 % Combined ratio 95.3 % 97.8 % 84.5 % 94.1 % (1) - Includes Corporate segment intercompany eliminations. (2) - Includes Other operating expenses and Other underwriting income (expense ). Year Ended December 31, 2014 U.S. Int'l amounts in thousands Insurance Insurance GlobalRe Corporate (1) Total Net earned premiums $ 504,289 $ 243,485 $ 188,121 $ — $ 935,895 Net losses and LAE (311,839 ) (115,079 ) (118,311 ) — (545,229 ) Commission expenses (49,840 ) (44,426 ) (33,429 ) 2,167 (125,528 ) Other operating expenses (115,817 ) (65,275 ) (15,733 ) — (196,825 ) Other underwriting income (expense) 2,241 32 489 (2,167 ) 595 Underwriting profit (loss) $ 29,034 $ 18,737 $ 21,137 $ — $ 68,908 Net investment income 64,168 64,168 Net realized gains (losses) 12,812 12,812 Interest expense (15,413 ) (15,413 ) Other income (loss) 10,061 10,061 Income (loss) before income taxes $ 29,034 $ 18,737 $ 21,137 $ 71,628 $ 140,536 Income tax (expense) benefit (45,207 ) (45,207 ) Net income (loss) $ 95,329 Losses and LAE ratio 61.8 % 47.3 % 62.9 % 58.3 % Commission expense ratio 9.9 % 18.2 % 17.8 % 13.4 % Other operating expense ratio (2) 22.5 % 26.8 % 8.1 % 20.9 % Combined ratio 94.2 % 92.3 % 88.8 % 92.6 % (1) - Includes Corporate segment intercompany eliminations. (2) - Includes Other operating expenses and Other underwriting income (expense ).
Additional Financial Data by Segment	The following tables provide additional financial data by operating segment for the years ended December 31, 2016, 2015 and 2014: Year Ended December 31, 2016 amounts in thousands Gross written premiums Ceded premiums Net written premiums Net earned premiums U.S. Insurance Marine $ 169,405 $ (70,858 ) $ 98,547 $ 100,132 P&C 631,562 (135,888 ) 495,674 453,673 Professional Liability 118,428 (29,081 ) 89,347 75,503 Total $ 919,395 $ (235,827 ) $ 683,568 $ 629,308 Int'l Insurance Marine $ 183,228 $ (40,092 ) $ 143,136 $ 141,593 P&C 181,094 (69,606 ) 111,488 89,455 Professional Liability 120,149 (28,806 ) 91,343 76,368 Total $ 484,471 $ (138,504 ) $ 345,967 $ 307,416 GlobalRe $ 165,045 $ (8,356 ) $ 156,689 $ 163,621 Total $ 1,568,911 $ (382,687 ) $ 1,186,224 $ 1,100,345 Year Ended December 31, 2015 amounts in thousands Gross written premiums Ceded written premiums Net written premiums Net earned premiums U.S. Insurance Marine $ 158,124 $ (61,916 ) $ 96,208 $ 96,082 P&C 596,673 (152,168 ) 444,505 401,408 Professional Liability 110,984 (54,691 ) 56,293 58,346 Total $ 865,781 $ (268,775 ) $ 597,006 $ 555,836 Int'l Insurance Marine $ 183,707 $ (36,515 ) $ 147,192 $ 149,256 P&C 130,729 (67,722 ) 63,007 55,320 Professional Liability 97,511 (29,768 ) 67,743 55,384 Total $ 411,947 $ (134,005 ) $ 277,942 $ 259,960 GlobalRe $ 175,774 $ (6,862 ) $ 168,912 $ 168,291 Total $ 1,453,502 $ (409,642 ) $ 1,043,860 $ 984,087 Year Ended December 31, 2014 amounts in thousands Gross written premiums Ceded written premiums Net written premiums Net earned premiums U.S. Insurance Marine $ 154,233 $ (46,685 ) $ 107,548 $ 105,650 P&C 543,045 (169,953 ) 373,092 314,833 Professional Liability 109,830 (38,345 ) 71,485 83,806 Total $ 807,108 $ (254,983 ) $ 552,125 $ 504,289 Int'l Insurance Marine $ 190,787 $ (47,805 ) $ 142,982 $ 141,097 P&C 158,139 (98,087 ) 60,052 62,520 Professional Liability 75,978 (26,029 ) 49,949 39,868 Total $ 424,904 $ (171,921 ) $ 252,983 $ 243,485 GlobalRe $ 200,341 $ (5,311 ) $ 195,030 $ 188,121 Total $ 1,432,353 $ (432,215 ) $ 1,000,138 $ 935,895

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2016
Investments Debt And Equity Securities [Abstract]
Available-for-Sale Investments Including Other-Than-Temporarily Impaired Securities Recognized within Accumulated Other Comprehensive Income	The following tables set forth our Company’s available- for- sale investments as of December 31, 2016 and 2015 and include OTTI securities recognized within AOCI: December 31, 2016 Gross Gross Unrealized Unrealized Amortized amounts in thousands Fair Value Gains Losses Cost Fixed maturities: U.S. Treasury bonds, agency bonds and foreign government bonds $ 273,776 $ 2,192 $ (5,128 ) $ 276,712 States, municipalities and political subdivisions 547,415 11,542 (4,036 ) 539,909 Mortgage-backed and asset-backed securities: Agency mortgage-backed securities 487,364 4,016 (6,585 ) 489,933 Residential mortgage obligations 20,530 453 (55 ) 20,132 Asset-backed securities 314,601 824 (1,178 ) 314,955 Commercial mortgage-backed securities 154,139 2,859 (1,904 ) 153,184 Subtotal $ 976,634 $ 8,152 $ (9,722 ) $ 978,204 Corporate bonds 838,057 10,185 (5,528 ) 833,400 Total fixed maturities $ 2,635,882 $ 32,071 $ (24,414 ) $ 2,628,225 Equity securities 349,142 27,016 (5,785 ) 327,911 Short-term investments 143,539 88 — 143,451 Total investments $ 3,128,563 $ 59,175 $ (30,199 ) $ 3,099,587 December 31, 2015 Gross Gross Unrealized Unrealized Amortized amounts in thousands Fair Value Gains Losses Cost Fixed maturities: U.S. Treasury bonds, agency bonds and foreign government bonds $ 252,882 $ 2,273 $ (9,214 ) $ 259,823 States, municipalities and political subdivisions 576,859 21,233 (781 ) 556,407 Mortgage-backed and asset-backed securities: Agency mortgage-backed securities 379,269 5,573 (2,082 ) 375,778 Residential mortgage obligations 30,465 694 (82 ) 29,853 Asset-backed securities 225,012 85 (1,624 ) 226,551 Commercial mortgage-backed securities 189,713 3,119 (1,864 ) 188,458 Subtotal $ 824,459 $ 9,471 $ (5,652 ) $ 820,640 Corporate bonds 760,010 7,373 (10,738 ) 763,375 Total fixed maturities $ 2,414,210 $ 40,350 $ (26,385 ) $ 2,400,245 Equity securities 305,271 26,341 (3,013 ) 281,943 Short-term investments 217,745 2 — 217,743 Total investments $ 2,937,226 $ 66,693 $ (29,398 ) $ 2,899,931
Scheduled Maturity Dates for Fixed Maturity Securities by Number of Years Until Maturity	The contractual maturity dates for Fixed maturities categorized by the number of years until maturity as of December 31, 2016 are shown in the following table: December 31, 2016 Amortized amounts in thousands Fair Value Cost Due in one year or less $ 133,644 $ 134,931 Due after one year through five years 778,875 778,511 Due after five years through ten years 295,742 291,811 Due after ten years 450,987 444,768 Mortgage-backed and asset-backed securities 976,634 978,204 Total $ 2,635,882 $ 2,628,225
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 December 31, 2016 and 2015, 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: December 31, 2016 Less than 12 months Greater than 12 months Total Gross Gross Gross Fair Unrealized Fair Unrealized Fair Unrealized amounts in thousands Value (Losses) Value (Losses) Value (Losses) Fixed maturities: U.S. Treasury bonds, agency bonds and foreign government bonds $ 150,891 $ (2,570 ) $ 16,819 $ (2,558 ) $ 167,710 $ (5,128 ) States, municipalities and political subdivisions 137,731 (3,111 ) 13,255 (925 ) 150,986 (4,036 ) Mortgage-backed and asset-backed securities: Agency mortgage-backed securities 349,119 (6,155 ) 12,401 (430 ) 361,520 (6,585 ) Residential mortgage obligations 953 (18 ) 926 (37 ) 1,879 (55 ) Asset-backed securities 95,514 (970 ) 48,093 (208 ) 143,607 (1,178 ) Commercial mortgage-backed securities 51,932 (1,164 ) 7,910 (740 ) 59,842 (1,904 ) Subtotal $ 497,518 $ (8,307 ) $ 69,330 $ (1,415 ) $ 566,848 $ (9,722 ) Corporate bonds 325,733 (5,086 ) 26,005 (442 ) 351,738 (5,528 ) Total fixed maturities $ 1,111,873 $ (19,074 ) $ 125,409 $ (5,340 ) $ 1,237,282 $ (24,414 ) Equity securities 145,014 (5,419 ) 1,994 (366 ) 147,008 (5,785 ) Total fixed maturities and equity securities $ 1,256,887 $ (24,493 ) $ 127,403 $ (5,706 ) $ 1,384,290 $ (30,199 ) December 31, 2015 Less than 12 months Greater than 12 months Total Gross Gross Gross Fair Unrealized Fair Unrealized Fair Unrealized amounts in thousands Value (Losses) Value (Losses) Value (Losses) Fixed maturities: U.S. Treasury bonds, agency bonds and foreign government bonds $ 142,233 $ (3,032 ) $ 22,230 $ (6,182 ) $ 164,463 $ (9,214 ) States, municipalities and political subdivisions 50,577 (549 ) 4,808 (232 ) 55,385 (781 ) Mortgage-backed and asset-backed securities: Agency mortgage-backed securities 164,817 (1,315 ) 29,862 (767 ) 194,679 (2,082 ) Residential mortgage obligations 3,910 (5 ) 1,684 (77 ) 5,594 (82 ) Asset-backed securities 112,479 (663 ) 81,477 (961 ) 193,956 (1,624 ) Commercial mortgage-backed securities 83,024 (1,826 ) 3,065 (38 ) 86,089 (1,864 ) Subtotal $ 364,230 $ (3,809 ) $ 116,088 $ (1,843 ) $ 480,318 $ (5,652 ) Corporate bonds 395,399 (10,114 ) 13,849 (624 ) 409,248 (10,738 ) Total fixed maturities $ 952,439 $ (17,504 ) $ 156,975 $ (8,881 ) $ 1,109,414 $ (26,385 ) Equity securities 58,531 (3,013 ) — — 58,531 (3,013 ) Total fixed maturities and equity securities $ 1,010,970 $ (20,517 ) $ 156,975 $ (8,881 ) $ 1,167,945 $ (29,398 )
Summary of Cumulative Amounts Related to Credit Loss Portion of Other-Than-Temporary Impairment Losses on Debt Securities	The following table summarizes the cumulative amounts related to our Company’s credit loss portion of the OTTI losses on fixed maturities for the years ended December 31, 2016, 2015 and 2014. Years Ended December 31, amounts in thousands 2016 2015 2014 Beginning balance $ 2,361 $ 2,361 $ 5,154 Additions for credit loss impairments recognized in the current period on securities not previously impaired 150 — — 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 (150 ) — (2,793 ) Ending balance $ 2,361 $ 2,361 $ 2,361
Net Investment Income	Our Company’s Net investment income was derived from the following sources: Years Ended December 31, amounts in thousands 2016 2015 2014 Fixed maturities $ 67,772 $ 61,572 $ 57,219 Equity securities 14,271 9,813 9,036 Short-term investments 727 683 911 Total investment income $ 82,770 $ 72,068 $ 67,166 Investment expenses (3,319 ) (3,350 ) (2,998 ) Net investment income $ 79,451 $ 68,718 $ 64,168
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: Years Ended December 31, amounts in thousands 2016 2015 2014 Fixed maturities: Gains $ 5,681 $ 4,756 $ 8,326 Losses (4,271 ) (5,926 ) (2,610 ) Fixed maturities, net $ 1,410 $ (1,170 ) $ 5,716 Short-term: Gains $ 890 $ 130 $ — Losses (1,552 ) (383 ) — Short-term, net $ (662 ) $ (253 ) $ — Equity securities: Gains $ 9,096 $ 14,331 $ 9,447 Losses (658 ) (4,535 ) (2,351 ) Equity securities, net $ 8,438 $ 9,796 $ 7,096 Net realized gains (losses) $ 9,186 $ 8,373 $ 12,812

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
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 “5.75% Senior notes”) carried at amortized cost as of December 31, 2016 and 2015: December 31, 2016 amounts in thousands Level 1 Level 2 Level 3 Total Fixed maturities: U.S. Treasury bonds, agency bonds and foreign government bonds $ 47,704 $ 226,072 $ — $ 273,776 States, municipalities and political subdivisions — 547,415 — 547,415 Mortgage-backed and asset-backed securities: Agency mortgage-backed securities — 487,364 — 487,364 Residential mortgage obligations — 20,530 — 20,530 Asset-backed securities — 314,601 — 314,601 Commercial mortgage-backed securities — 154,139 — 154,139 Subtotal $ — $ 976,634 $ — $ 976,634 Corporate bonds — 838,057 — 838,057 Total fixed maturities $ 47,704 $ 2,588,178 $ — $ 2,635,882 Equity securities 164,088 185,054 — 349,142 Short-term investments 143,539 — — 143,539 Total assets measured at fair value $ 355,331 $ 2,773,232 $ — $ 3,128,563 Senior notes $ — $ 280,316 $ — $ 280,316 Total liabilities measured at fair value $ — $ 280,316 $ — $ 280,316 December 31, 2015 amounts in thousands Level 1 Level 2 Level 3 Total Fixed maturities: U.S. Treasury bonds, agency bonds and foreign government bonds $ 67,394 $ 185,488 $ — $ 252,882 States, municipalities and political subdivisions — 576,859 — 576,859 Mortgage-backed and asset-backed securities: Agency mortgage-backed securities — 379,269 — 379,269 Residential mortgage obligations — 30,465 — 30,465 Asset-backed securities — 225,012 — 225,012 Commercial mortgage-backed securities — 189,713 — 189,713 Subtotal $ — $ 824,459 $ — $ 824,459 Corporate bonds — 760,010 — 760,010 Total fixed maturities $ 67,394 $ 2,346,816 $ — $ 2,414,210 Equity securities 126,455 178,816 — 305,271 Short-term investments 217,745 — — 217,745 Total assets measured at fair value $ 411,594 $ 2,525,632 $ — $ 2,937,226 Senior notes $ — $ 282,486 $ — $ 282,486 Total liabilities measured at fair value $ — $ 282,486 $ — $ 282,486

Reserves for Losses and LAE (Ta

Reserves for Losses and LAE (Tables)	12 Months Ended
	Dec. 31, 2016
Summary of Activity in Reserve for Losses and LAE	The following table summarizes activity for our Company’s Reserves for losses and LAE for the years ended December 31, 2016, 2015 and 2014: Years Ended December 31, amounts in thousands 2016 2015 2014 Net reserves for losses and LAE at beginning of year $ 1,393,126 $ 1,308,136 $ 1,222,633 Provision for losses and LAE for claims occurring in the current year 693,976 637,267 601,041 Increase (decrease) in estimated losses and LAE for claims occurring in prior years (28,528 ) (64,669 ) (55,812 ) Incurred losses and LAE $ 665,448 $ 572,598 $ 545,229 Losses and LAE paid for claims occurring during: Current year (119,485 ) (159,802 ) (158,806 ) Prior years (412,544 ) (320,863 ) (295,527 ) Losses and LAE payments $ (532,029 ) $ (480,665 ) $ (454,333 ) Foreign Currency Adjustment (16,094 ) (6,943 ) (5,393 ) Net reserves for losses and LAE at end of year 1,510,451 1,393,126 1,308,136 Reinsurance recoverables on unpaid losses and LAE 779,276 809,518 851,498 Gross reserves for losses and LAE at end of year $ 2,289,727 $ 2,202,644 $ 2,159,634
Reporting and Operating Segments Break Down of Prior Years' Net Reserve Deficiency (Redundancy)	The reporting and operating segments breakdowns of prior period net reserve strengthening (releases) for the years ended December 31, 2016, 2015 and 2014 are as follows: Years Ended December 31, amounts in thousands 2016 2015 2014 U.S. Insurance Marine $ (10,122 ) $ (24,825 ) $ (29,047 ) P&C 2,790 (706 ) 17,081 Professional Liability 5,984 (3,788 ) (3,454 ) Total $ (1,348 ) $ (29,319 ) $ (15,420 ) Int'l Insurance Marine (22,068 ) (21,914 ) (31,677 ) P&C (7,051 ) (8,458 ) (3,829 ) Professional Liability 4,100 4,156 (2,746 ) Total $ (25,019 ) $ (26,216 ) $ (38,252 ) GlobalRe $ (2,161 ) $ (9,134 ) $ (2,140 ) Total strengthening (releases) $ (28,528 ) $ (64,669 ) $ (55,812 )
Summary of Reconciliation of Net Incurred and Paid Claims Development to the Reserve for Losses and LAE	The reconciliation of the net incurred and paid claims development tables to the Reserve for losses and LAE in the consolidated statement of financial position is as follows: Carried Reserves Reconciliation amounts in thousands For the Year Ended December 31, 2016 Total Net reserves Reinsurance recoverables on unpaid claims Total Gross reserves U.S. Marine $ 106,288 $ 83,988 $ 190,276 U.S. P&C 769,399 409,648 1,179,047 U.S. Professional Liability 91,037 59,938 150,975 Int'l Marine 196,532 88,900 285,432 Int'l P&C 81,189 79,548 160,737 Int'l Professional Liability 98,689 52,518 151,207 GlobalRe 111,594 4,736 116,330 Liabilities for unpaid claims and claim adjustment expenses $ 1,454,728 779,276 $ 2,234,004 Unallocated claims adjustment expenses 55,444 Other 279 Total gross liability for unpaid claims and claim adjustment expense $ 2,289,727
U.S.Insurance | Marine
Summary of Information about Incurred Claims Development and Cumulative Paid Claims and Allocated Loss Adjustment Expense (ALAE), Net of Reinsurance	U.S. Marine Loss and ALAE, Net of Reinsurance amounts in thousands For the Years Ended December 31, As of December 31, 2016 AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Total IBNR # of Reported Claims 2007 $ 52,974 $ 60,645 $ 61,216 $ 59,148 $ 65,020 $ 66,090 $ 66,024 $ 65,909 $ 66,297 $ 66,846 $ 60 2,737 2008 56,923 67,710 72,580 73,970 73,731 68,703 68,873 67,024 67,238 348 3,202 2009 63,769 60,813 57,266 51,804 49,762 50,905 53,091 52,169 (186 ) 2,404 2010 66,336 66,187 63,172 57,063 54,815 59,143 58,557 (263 ) 2,164 2011 71,575 72,232 70,019 65,514 64,196 62,571 1,204 2,012 2012 87,905 91,118 73,940 70,421 71,868 (7 ) 1,968 2013 65,132 61,289 55,494 58,148 (619 ) 1,910 2014 67,610 49,889 48,355 1,509 1,962 2015 64,575 54,121 13,317 2,155 2016 56,209 32,884 1,824 Total $ 596,082 U.S. Marine Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance amounts in thousands For the Years Ended December 31, AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ 9,294 $ 28,937 $ 40,256 $ 49,214 $ 58,772 $ 62,002 $ 62,767 $ 63,384 $ 64,450 $ 64,570 2008 7,554 36,499 54,408 56,695 62,633 62,989 63,316 63,429 64,317 2009 12,975 30,012 36,593 42,846 44,760 47,347 48,209 50,888 2010 17,211 33,821 41,941 45,032 50,271 54,044 57,254 2011 16,007 41,322 50,841 54,471 59,224 60,198 2012 27,546 47,639 56,040 62,104 68,556 2013 19,565 38,487 44,606 50,410 2014 15,702 29,916 41,609 2015 17,169 32,439 2016 12,665 Total $ 502,906 Net reserves < 2007 13,112 Total Net reserves $ 106,288 U.S. Marine Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 U.S. Marine 26.4 % 32.4 % 16.5 % 8.3 % 8.7 % 3.7 % 2.2 % 2.1 % 1.5 % 0.2 %
U.S.Insurance | Property Casualty
Summary of Information about Incurred Claims Development and Cumulative Paid Claims and Allocated Loss Adjustment Expense (ALAE), Net of Reinsurance	U.S. P&C Loss and ALAE, Net of Reinsurance amounts in thousands For the Years Ended December 31, As of December 31, 2016 AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Total IBNR # of Reported Claims 2007 $ 139,377 $ 139,570 $ 140,551 $ 130,501 $ 133,050 $ 128,087 $ 134,310 $ 139,870 $ 145,472 $ 148,609 $ 3,753 11,703 2008 158,337 158,336 144,164 140,818 141,332 143,219 147,434 152,416 157,519 3,971 10,818 2009 133,394 135,984 136,700 142,416 149,975 155,156 155,682 159,110 7,717 8,434 2010 101,527 100,529 98,675 104,709 107,602 109,323 112,080 10,106 7,804 2011 86,056 85,238 92,266 95,292 95,958 105,149 15,964 6,346 2012 111,479 96,618 98,060 103,716 111,746 24,895 4,481 2013 141,728 130,314 133,068 141,817 29,961 3,533 2014 193,897 164,364 152,447 76,085 3,356 2015 251,752 224,532 134,029 3,123 2016 274,692 258,449 2,106 Total $ 1,587,701 U.S. P&C Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance amounts in thousands For the Years Ended December 31, AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ 7,127 $ 24,521 $ 49,616 $ 72,462 $ 92,840 $ 104,841 $ 114,160 $ 122,568 $ 130,279 $ 136,896 2008 12,178 36,713 58,491 82,028 103,804 115,526 123,945 133,064 146,463 2009 14,619 36,641 59,933 92,033 119,360 132,695 138,227 145,407 2010 12,682 27,542 49,109 69,027 81,262 89,873 94,766 2011 3,925 19,548 35,551 51,868 63,800 75,806 2012 10,013 23,019 33,477 51,980 72,495 2013 7,317 21,500 49,562 85,719 2014 5,272 13,762 45,324 2015 3,641 24,291 2016 7,706 Total $ 834,873 Net reserves < 2007 16,571 Total Net reserves $ 769,399 U.S. P&C Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 U.S. P&C 5.9 % 11.7 % 16.2 % 18.0 % 14.2 % 8.6 % 4.9 % 5.3 % 6.8 % 4.5 %
U.S.Insurance | Professional Liability
Summary of Information about Incurred Claims Development and Cumulative Paid Claims and Allocated Loss Adjustment Expense (ALAE), Net of Reinsurance	U.S. Professional Liability Loss and ALAE, Net of Reinsurance amounts in thousands For the Years Ended December 31, As of December 31, 2016 AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Total IBNR # of Reported Claims 2007 $ 38,000 $ 38,553 $ 55,491 $ 57,643 $ 62,630 $ 61,935 $ 60,445 $ 60,447 $ 59,936 $ 59,574 $ (70 ) 634 2008 34,346 38,449 39,130 35,844 37,603 37,939 37,497 37,620 41,766 (382 ) 770 2009 47,473 53,273 61,023 58,600 60,789 58,487 58,660 58,143 (563 ) 1,370 2010 52,302 64,020 68,375 75,619 74,535 86,787 85,348 83 1,429 2011 58,116 62,087 70,240 73,028 79,181 79,136 622 1,724 2012 61,196 54,480 57,097 55,917 58,344 3,214 2,180 2013 60,899 54,982 49,104 48,298 4,989 2,226 2014 50,020 35,870 39,826 6,504 2,278 2015 31,659 30,764 15,870 1,709 2016 41,672 36,356 1,739 Total $ 542,871 U.S. Professional Liability Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance amounts in thousands For the Years Ended December 31, AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ 1,861 $ 10,365 $ 32,621 $ 47,980 $ 52,941 $ 58,515 $ 59,280 $ 59,332 $ 59,565 $ 59,570 2008 1,880 15,288 25,042 30,581 34,902 35,206 35,598 37,175 42,056 2009 3,837 21,742 41,675 51,642 55,378 53,859 57,744 58,095 2010 2,981 23,147 46,868 54,019 59,765 82,013 84,511 2011 3,204 23,878 43,551 59,576 65,710 75,641 2012 3,855 22,635 35,681 44,028 49,675 2013 4,677 22,167 32,904 38,876 2014 2,304 14,371 29,392 2015 2,257 11,249 2016 2,383 Total $ 451,448 Net reserves < 2007 (386 ) Total Net reserves $ 91,037 U.S. Professional Liability Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 U.S. Professional Liability 5.7 % 28.3 % 28.7 % 15.9 % 8.2 % 9.2 % 3.0 % 1.5 % 6.0 % 0.0 %
International Insurance | Marine
Summary of Information about Incurred Claims Development and Cumulative Paid Claims and Allocated Loss Adjustment Expense (ALAE), Net of Reinsurance	Int'l Marine Loss and ALAE, Net of Reinsurance amounts in thousands For the Years Ended December 31, As of December 31, 2016 AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Total IBNR # of Reported Claims 2007 $ — $ — $ — $ — $ — $ 70,633 $ 67,148 $ 66,951 $ 66,883 $ 66,239 $ (35 ) 5,585 2008 — — — — 88,720 85,285 84,131 84,191 82,752 98 5,809 2009 — — — 89,057 86,914 84,497 82,096 79,526 111 4,969 2010 — — 123,719 119,021 114,188 111,468 108,405 282 5,317 2011 — 91,347 86,795 78,872 75,873 70,751 25 4,824 2012 93,696 115,935 99,683 94,886 90,523 (216 ) 5,201 2013 68,587 82,313 80,713 77,239 747 5,075 2014 85,512 105,072 107,789 (1,500 ) 4,928 2015 70,675 91,371 5,194 6,967 2016 84,156 26,285 5,577 Total $ 858,751 Int'l Marine Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance amounts in thousands For the Years Ended December 31, AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ — $ — $ — $ — $ — $ 59,831 $ 60,702 $ 61,956 $ 62,729 $ 63,281 2008 — — — — 69,959 72,309 73,746 77,535 78,683 2009 — — — 64,058 68,085 70,834 74,311 75,006 2010 — — 74,920 87,186 93,167 97,132 99,416 2011 — 43,740 56,569 60,879 65,580 66,538 2012 22,777 52,968 68,498 76,572 79,205 2013 21,703 42,953 54,826 60,828 2014 24,445 50,168 73,921 2015 22,323 52,356 2016 22,192 Total $ 671,426 Net reserves < 2007 9,207 Total Net reserves $ 196,532 Int'l Marine Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 Int'l Marine 24.5 % 28.1 % 18.2 % 7.6 % 5.0 % 2.8 % 2.7 % 2.4 % 1.3 % 0.8 %
International Insurance | Property Casualty
Summary of Information about Incurred Claims Development and Cumulative Paid Claims and Allocated Loss Adjustment Expense (ALAE), Net of Reinsurance	Int'l P&C Loss and ALAE, Net of Reinsurance amounts in thousands For the Years Ended December 31, As of December 31, 2016 AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Total IBNR # of Reported Claims 2007 $ — $ — $ — $ — $ — $ 26,084 $ 25,817 $ 25,740 $ 25,855 $ 25,778 $ (60 ) 584 2008 — — — — 39,504 37,884 37,867 37,296 36,729 (75 ) 891 2009 — — — 26,499 25,804 25,910 25,418 25,113 13 743 2010 — — 39,082 39,409 39,050 39,031 38,198 58 836 2011 — 57,463 53,654 52,093 52,666 52,202 (198 ) 833 2012 34,479 30,643 30,347 28,626 27,828 (353 ) 877 2013 29,496 33,720 31,050 29,684 (308 ) 1,229 2014 20,234 16,987 17,006 173 1,167 2015 26,414 30,932 2,106 1,678 2016 75,571 13,006 2,646 Total $ 359,041 Int'l P&C Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance amounts in thousands For the Years Ended December 31, AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ — $ — $ — $ — $ — $ 23,885 $ 24,681 $ 25,150 $ 25,292 $ 25,289 2008 — — — — 34,084 35,161 35,463 35,975 35,826 2009 — — — 23,371 24,257 24,713 24,286 24,369 2010 — — 32,156 36,499 39,017 36,509 36,601 2011 — 33,316 42,280 45,125 47,591 48,502 2012 7,884 15,648 20,850 24,871 26,049 2013 6,829 17,613 24,735 27,180 2014 3,813 8,458 12,304 2015 6,739 18,096 2016 24,255 Total $ 278,471 Net reserves < 2007 619 Total Net reserves $ 81,189 Int'l P&C Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 Int'l P&C 25.4 % 33.5 % 21.8 % 9.4 % 5.2 % -1.0 % -0.2 % 1.2 % 0.1 % 0.0 %
International Insurance | Professional Liability
Summary of Information about Incurred Claims Development and Cumulative Paid Claims and Allocated Loss Adjustment Expense (ALAE), Net of Reinsurance	Int'l Professional Liability Loss and ALAE, Net of Reinsurance amounts in thousands For the Years Ended December 31, As of December 31, 2016 AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Total IBNR # of Reported Claims 2007 $ — $ — $ — $ — $ — $ 12,901 $ 12,587 $ 12,445 $ 12,378 $ 12,381 $ (64 ) 235 2008 — — — — 15,511 15,302 14,816 14,010 14,023 (175 ) 365 2009 — — — 14,809 15,367 14,972 16,289 15,780 629 445 2010 — — 18,603 16,159 15,661 17,451 15,619 1,409 653 2011 — 9,686 7,648 7,125 7,050 6,835 356 681 2012 8,204 9,753 9,106 11,175 16,891 490 718 2013 15,096 17,628 16,272 15,402 4,255 1,053 2014 18,835 24,070 23,457 12,421 1,276 2015 22,760 30,104 17,379 1,939 2016 36,006 31,814 2,554 Total $ 186,498 Int'l Professional Liability Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance amounts in thousands For the Years Ended December 31, AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ — $ — $ — $ — $ — $ 11,293 $ 11,704 $ 12,269 $ 12,277 $ 12,382 2008 — — — — 12,150 13,306 13,702 13,732 14,019 2009 — — — 8,805 10,716 12,783 13,803 14,118 2010 — — 5,801 7,169 10,460 12,632 13,366 2011 — 1,197 2,002 2,950 4,007 4,576 2012 2,133 3,219 4,253 5,483 7,365 2013 725 2,196 2,952 9,230 2014 1,368 2,421 5,068 2015 3,355 5,765 2016 2,012 Total $ 87,901 Net reserves < 2007 92 Total Net reserves $ 98,689 Int'l Professional Liability Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 Int'l Professional 7.5 % 7.3 % 7.4 % 20.6 % 15.9 % 11.8 % 4.7 % 2.3 % 1.1 % 0.8 %
Global Reinsurance
Summary of Information about Incurred Claims Development and Cumulative Paid Claims and Allocated Loss Adjustment Expense (ALAE), Net of Reinsurance	GlobalRe Loss and ALAE, Net of Reinsurance amounts in thousands For the Years Ended December 31, As of December 31, 2016 AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Total IBNR # of Reported Claims 2007 $ — $ — $ — $ — $ — $ 6,215 $ 6,190 $ 6,173 $ 5,889 $ 5,883 $ (141 ) 254 2008 — — — — 13,863 14,024 13,530 13,304 13,298 672 294 2009 4,970 3,734 3,752 11,186 11,380 10,745 10,390 10,475 204 202 2010 3,743 3,500 13,455 13,661 12,899 11,597 12,330 (1,000 ) 195 2011 39,678 50,832 74,131 73,511 73,042 72,667 (461 ) 766 2012 108,790 103,183 94,766 89,053 114,728 531 1,419 2013 112,735 119,012 101,703 104,913 3,973 1,185 2014 120,479 141,108 121,535 9,825 920 2015 99,874 91,098 11,623 680 2016 88,192 38,785 335 Total $ 635,119 GlobalRe Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance amounts in thousands For the Years Ended December 31, AY 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ — $ — $ — $ — $ — $ 5,225 $ 5,275 $ 5,345 $ 5,357 $ 5,350 2008 — — — — 11,629 11,650 11,510 11,488 11,546 2009 — 3,734 3,752 8,620 8,853 8,974 9,932 10,045 2010 0 3,490 9,875 10,213 10,387 11,009 11,062 2011 4,160 43,342 71,010 71,677 71,954 72,094 2012 37,644 77,077 83,183 84,533 111,681 2013 53,375 82,558 90,567 98,271 2014 66,249 119,136 105,505 2015 41,620 64,316 2016 36,253 Total $ 526,123 Net reserves < 2007 2,598 Total Net reserves $ 111,594 GlobalRe Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 GlobalRe 47.1 % 32.1 % 0.6 % 3.1 % 8.5 % 2.1 % 2.8 % 0.7 % 0.3 % -0.1 %

Ceded Reinsurance (Tables)

Ceded Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2016
Insurance [Abstract]
Lists of 10 Largest Reinsurers Measured by Reinsurance Recoverable	The following table lists our Company’s 10 largest reinsurers measured by the amount of total reinsurance recoverables as of December 31, 2016, and the reinsurers’ ratings from A.M. Best and S&P: Reinsurance Recoverables Unearned Paid/Unpaid Collateral amounts in thousands Premium Losses (1) Total Held A.M. Best S&P Everest Reinsurance Company $ 25,321 $ 82,154 $ 107,475 $ 6,571 A+ A+ National Indemnity Company 7,467 98,759 106,226 3,183 A++ AA+ Swiss Reinsurance America Corporation 22,442 77,199 99,641 6,440 A+ AA- Transatlantic Reinsurance Company 7,669 53,347 61,016 2,494 A+ A+ Munich Reinsurance America Inc. 8,959 50,612 59,571 3,477 A+ AA- Allied World Reinsurance 6,319 35,931 42,250 1,575 A A Employers Mutual Casualty Company 8,856 32,687 41,543 5,551 A NR Aspen Insurance UK Ltd. 11,281 22,737 34,018 5,452 A A Ace Property and Casualty Insurance Company 10,192 22,352 32,544 2,722 A++ AA Partner Reinsurance Europe 6,868 20,681 27,549 25,045 A A+ Top 10 $ 115,374 $ 496,459 $ 611,833 $ 62,510 All Others 98,003 365,399 463,402 89,198 Total $ 213,377 $ 861,858 $ 1,075,235 $ 151,708 (1) - Net of reserve for uncollectible reinsurance of approximately $12.1 million.
Summary of Components of Net Written Premium	The following table summarizes the components of Net written premium: Years Ended December 31, amounts in thousands 2016 2015 2014 Direct $ 1,403,865 $ 1,277,728 $ 1,232,012 Assumed 165,046 175,774 200,341 Ceded (382,687 ) (409,642 ) (432,215 ) Net written premiums $ 1,186,224 $ 1,043,860 $ 1,000,138
Summary of Components of Net Earned Premium	The following table summarizes the components of Net earned premium: Years Ended December 31, amounts in thousands 2016 2015 2014 Direct $ 1,330,265 $ 1,223,840 $ 1,183,120 Assumed 171,978 175,153 193,431 Ceded (401,898 ) (414,906 ) (440,656 ) Net earned premiums $ 1,100,345 $ 984,087 $ 935,895
Summary of Components of Net Losses and Loss Adjustment Expenses Incurred	The following table summarizes the components of Net losses and LAE incurred: Years Ended December 31, amounts in thousands 2016 2015 2014 Direct $ 795,414 $ 703,361 $ 657,059 Assumed 87,995 97,947 118,352 Ceded (217,961 ) (228,710 ) (230,182 ) Net losses and LAE $ 665,448 $ 572,598 $ 545,229

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Future Minimum Annual Rental Commitments under Various Non-cancellable Operating Leases	Future minimum annual rental commitments as of December 31, 2016 under various non-cancellable operating leases for our office facilities, which expire at various dates through 2030, are as follows: Rental Commitments for Years Ended December 31, amounts in thousands 2017 $ 13,024 2018 11,843 2019 9,107 2020 8,945 2021 7,684 2022-2030 38,267 Total minimum operating lease payments $ 88,870

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Components of Current and Deferred Income Tax Expense (Benefit)	The components of current and deferred income tax expense (benefit) are as follows: Years Ended December 31, amounts in thousands 2016 2015 2014 Current income tax expense (benefit): Federal and foreign $ 39,900 $ 27,937 $ 27,290 State and local 638 1,476 1,036 Subtotal $ 40,538 $ 29,413 $ 28,326 Deferred income tax expense (benefit): Federal and foreign $ (5,755 ) $ 7,004 $ 16,881 State and local — — — Subtotal $ (5,755 ) $ 7,004 $ 16,881 Total income tax expense (benefit) $ 34,783 $ 36,417 $ 45,207
Reconciliation of Total Income Taxes Applicable to Pre-Tax Operating Income and Amounts Computed by Applying Federal Statutory Income Tax Rate to Pre-Tax Operating Income	A reconciliation of total income taxes applicable to pre‑tax operating income and the amounts computed by applying the federal statutory income tax rate to the pre‑tax operating income were as follows: Years Ended December 31, amounts in thousands 2016 2015 2014 Computed expected tax expense $ 41,128 35.0 % $ 41,116 35.0 % $ 49,187 35.0 % Tax-exempt interest (4,559 ) -3.9 % (4,987 ) -4.2 % (4,771 ) -3.4 % Dividends received deduction (3,812 ) -3.2 % (2,086 ) -1.8 % (1,257 ) -0.9 % Proration of DRD and Tax-exempt interest 1,256 1.1 % 1,061 0.9 % 904 0.6 % Current state and local income taxes, net of federal income tax deduction 415 0.4 % 959 0.8 % 674 0.5 % Other 355 0.2 % 354 0.3 % 470 0.4 % Actual tax expense and rate $ 34,783 29.6 % $ 36,417 31.0 % $ 45,207 32.2 %
Tax Effects of Temporary Differences That Give Rise to Federal, Foreign, State and Local Deferred Tax Assets and Deferred Tax Liabilities	The tax effects of cumulative temporary differences that give rise to federal, foreign, state and local deferred tax assets and deferred tax liabilities were as follows: December 31, amounts in thousands 2016 2015 Deferred tax assets: Loss reserve discount $ 25,420 $ 25,353 Unearned premiums 33,886 31,486 Compensation related 15,288 11,175 State and local net deferred tax assets 699 721 Net currency translation adjustments 5,363 346 Other 3,618 3,969 Total gross deferred tax assets 84,274 73,050 Less: Valuation allowance (699 ) (721 ) Total deferred tax assets $ 83,575 $ 72,329 Deferred tax liabilities: Net unrealized gains/losses on securities $ (10,142 ) $ (13,053 ) Deferred acquisition costs (29,401 ) (24,037 ) Lloyd's year of account deferral (15,471 ) (24,466 ) Net unrealized foreign exchange (3,575 ) (4,164 ) Other (4,048 ) (2,709 ) Total deferred tax liabilities $ (62,637 ) $ (68,429 ) Net deferred income tax asset (liability) $ 20,938 $ 3,900

Stockholders Equity (Tables)

Stockholders Equity (Tables)	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Changes in Company's Issued and Outstanding Common Shares	The following table represents changes in our Company’s issued and outstanding common shares for the periods indicated. We completed a two-for-one stock split on January 20, 2017. All share and per share data has been retroactively restated on a post-split basis. Years Ended December 31, amounts in thousands 2016 2015 2014 Beginning balance 28,862 28,562 28,396 Vested stock grants 220 254 118 Employee stock purchase plan 42 42 38 Stock options exercised — 4 10 Ending balance 29,124 28,862 28,562
Amount and Nature of Net Assets Restricted from Payment of Dividends	The amount and nature of net assets that are restricted from payment of dividends as of December 31, 2016 and 2015 are presented in the following table: As of December 31, amounts in thousands 2016 2015 Restricted net assets: NIC and NSIC: Fixed maturities at fair value (amortized cost: 2016, $9,820; 2015, $9,950) $ 10,690 $ 11,277 Short term investments, at fair value 290 290 Cash 7,168 6,208 Total NIC and NSIC (1) $ 18,148 $ 17,775 NHUK: Fixed maturities at fair value (amortized cost: 2016, $457,225; 2015, $458,558) $ 452,053 $ 448,666 Short term investments, at fair value 63,729 71,320 Cash — 3,262 Total NHUK (2) $ 515,782 $ 523,248 Total Restricted Net Assets $ 533,930 $ 541,023 (1) - The restricted net assets for NIC and NSIC primarily consist of fixed maturities on deposit with various state insurance departments. The cash as of December 31, 2016 and 2015, as presented in the table above, was on deposit with a U.K. bank to comply with the regulatory requirements of the Prudential Regulation Authority for the underwriting activities of the U.K. Branch. (2) - The restricted net assets for NHUK consists of fixed maturities and cash held in trust for the benefit of syndicate policyholders and short term investments primarily consisting of overseas deposits in various countries with Lloyd's to support underwriting activities in those countries.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Reconciliation of Basic and Diluted Earnings per Share Computations	The following is a reconciliation of the basic and diluted EPS computations for the years ended December 31, 2016, 2015 and 2014: Years Ended December 31, amounts in thousands, except share and per share amounts 2016 2015 2014 Net income $ 82,726 $ 81,057 $ 95,329 Basic weighted average shares (1) 29,073,803 28,785,044 28,519,536 Effect of common stock equivalents: Assumed exercise of stock options and vesting of stock 957,806 866,446 773,202 Diluted weighted average shares 30,031,609 29,651,490 29,292,738 Net income per common share: Basic $ 2.85 $ 2.82 $ 3.34 Diluted $ 2.75 $ 2.73 $ 3.25 (1) - We completed a two-for-one stock split on January 20, 2017. All share and per share data has been retroactively restated on a post-split basis.

Statutory Financial Informati43

Statutory Financial Information (Tables)	12 Months Ended
	Dec. 31, 2016
Insurance [Abstract]
Summary of Statutory Net Income (Loss) and Capital and Surplus	The following table presents statutory Net income and capital and surplus in accordance with statutory accounting practices: Years Ended December 31, amounts in millions 2016 2015 2014 NIC & NSIC: Statutory net income $ 84.2 $ 60.8 $ 75.7 Statutory capital and surplus $ 1,027.3 $ 949.1 $ 893.9 The Syndicate: Syndicate's net income $ 46.3 $ 41.0 $ 33.8 Syndicate's capital and surplus $ 180.7 $ 177.5 $ 140.1

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Unvested Restricted Stock Units and Performance Units Grants Outstanding	Unvested restricted stock units and performance units outstanding as of December 31, 2016, 2015 and 2014, and changes during the years ended on those dates, are presented in the following table: December 31, 2016 2015 2014 Beginning balance 1,393,030 1,437,784 1,253,624 Granted - Performance 404,946 370,100 457,214 Granted - Non Performance 84,000 64,316 119,046 Total Granted 488,946 434,416 576,260 Vested - Performance (285,208 ) (136,160 ) (186,906 ) Vested - Non Performance (55,000 ) (271,200 ) (180,526 ) Total Vested (340,208 ) (407,360 ) (367,432 ) Forfeited (167,604 ) (71,810 ) (24,668 ) Ending balance 1,374,164 1,393,030 1,437,784
Stock Options Outstanding	Stock options outstanding as of December 31, 2016, 2015 and 2014 are as follows: December 31, 2016 (1) 2015 2014 Average Average Average # of Shares Exercise Price # of Shares Exercise Price # of Shares Exercise Price Beginning balance — $ — 1,500 $ 36.03 6,750 $ 30.65 Granted — — — — — — Exercised — $ — (1,500 ) $ 36.03 (5,250 ) $ 29.11 Expired or forfeited — — — — — — Ending balance — $ — — $ — 1,500 $ 36.03 Number of options exercisable — $ — — $ — 1,500 $ 36.03 (1) – Our company has not recently issued stock options and does not currently have any options outstanding.

Condensed (Unaudited) Quarter45

Condensed (Unaudited) Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Summary of Condensed Quarterly Financial Data	The following is a summary of quarterly financial data for the periods indicated: March 31, June 30, September December 31, amounts in thousands, except per share amounts 2016 2016 2016 2016 Gross written premiums $ 413,877 $ 412,565 $ 374,930 $ 367,539 Revenues: Net written premiums $ 319,820 $ 306,535 $ 277,001 $ 282,868 Change in unearned premiums (55,462 ) (38,543 ) 7,009 1,117 Net earned premiums $ 264,358 $ 267,992 $ 284,010 $ 283,985 Net investment income 19,594 19,875 19,875 20,107 Total other-than-temporary impairment losses (109 ) (162 ) 23 21 Portion of loss recognized in other comprehensive income (before tax) 109 12 (23 ) (21 ) Net other-than-temporary impairment losses recognized in earnings — (150 ) — — Net realized gains (losses) 1,597 1,960 1,586 4,043 Other income (expense) 2,549 4,430 (183 ) 1,905 Total revenues $ 288,098 $ 294,107 $ 305,288 $ 310,040 Expenses: Net losses and LAE $ 152,956 $ 167,206 $ 172,793 $ 172,493 Commission expenses 37,554 40,726 42,611 44,154 Other operating expenses 60,809 59,074 56,137 58,076 Interest expense 3,858 3,858 3,859 3,860 Total expenses $ 255,177 $ 270,864 $ 275,400 $ 278,583 Income before income taxes 32,921 23,243 29,888 31,457 Income tax expense $ 9,989 $ 7,053 $ 7,875 $ 9,866 Net income $ 22,932 $ 16,190 $ 22,013 $ 21,591 Comprehensive income (loss) $ 45,721 $ 35,228 $ 18,760 $ (31,712 ) Combined ratio 95.1 % 99.6 % 95.6 % 96.7 % Net income per share: (1) Basic $ 0.79 $ 0.56 $ 0.76 $ 0.74 Diluted $ 0.77 $ 0.54 $ 0.73 $ 0.71 (1) - We completed a two-for-one stock split on January 20, 2017. All share and per share data has been retroactively restated on a post-split basis. March 31, June 30, September 30, December 31, amounts in thousands, except per share amounts 2015 2015 2015 2015 Gross written premiums $ 396,460 $ 379,471 $ 354,062 $ 323,509 Revenues: Net written premiums $ 288,958 $ 258,244 $ 251,939 $ 244,719 Change in unearned premiums (52,826 ) (15,916 ) 2,143 6,826 Net earned premiums $ 236,132 $ 242,328 $ 254,082 $ 251,545 Net investment income 16,253 16,595 17,371 18,499 Total other-than-temporary impairment losses — (423 ) (1,298 ) (123 ) Portion of loss recognized in other comprehensive income (before tax) — — 23 123 Net other-than-temporary impairment losses recognized in earnings — (423 ) (1,275 ) — Net realized gains 5,596 4,339 518 (2,080 ) Other income (expense) 2,242 (4,362 ) (2,518 ) 4,147 Total revenues $ 260,223 $ 258,477 $ 268,178 $ 272,111 Expenses: Net losses and LAE $ 130,198 $ 141,973 $ 146,546 $ 153,881 Commission expenses 32,905 31,480 34,253 31,339 Other operating expenses 54,909 52,789 56,599 59,219 Interest expense 3,855 3,856 3,856 3,857 Total expenses $ 221,867 $ 230,098 $ 241,254 $ 248,296 Income before income taxes 38,356 28,379 26,924 23,815 Income tax expense $ 12,427 $ 9,195 $ 8,723 $ 6,072 Net income $ 25,929 $ 19,184 $ 18,201 $ 17,743 Comprehensive income $ 27,052 $ (3,789 ) $ 18,849 $ 15,990 Combined ratio 92.3 % 93.4 % 93.4 % 97.2 % Net income per share: (1) Basic $ 0.90 $ 0.67 $ 0.63 $ 0.62 Diluted $ 0.89 $ 0.65 $ 0.61 $ 0.59 (1) - We completed a two-for-one stock split on January 20, 2017. All per share data has been retroactively restated on a post-split basis.

Organization and Summary of S46

Organization and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Organization And Summary Of Significant Accounting Policies [Line Items]
Remeasurement of Foreign Currency			$ 10,000,000
Remeasurement of Foreign currency, After tax			6,600,000
Impairment of goodwill and indefinite lived intangible assets	$ 0	$ 0	$ 0
Goodwill and other intangible assets	6,451,000	$ 6,807,000
Changes in the carrying value of the goodwill and indefinite lived intangible assets	$ 300,000
Minimum
Organization And Summary Of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Maximum
Organization And Summary Of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	7 years
Leasehold Improvements | Minimum
Organization And Summary Of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Leasehold Improvements | Maximum
Organization And Summary Of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Syndicate 1,221
Organization And Summary Of Significant Accounting Policies [Line Items]
Percentage control of stamp capacity	100.00%

Segment Information - Additiona

Segment Information - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016Segment
Segment Reporting [Abstract]
Number of underwriting Segments	3
Number of Operating Segments	3

Financial Data by Segment (Deta

Financial Data by Segment (Detail) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net earned premiums		$ 283,985	$ 284,010	$ 267,992	$ 264,358	$ 251,545	$ 254,082	$ 242,328	$ 236,132	$ 1,100,345	$ 984,087	$ 935,895
Net losses and LAE		(172,493)	(172,793)	(167,206)	(152,956)	(153,881)	(146,546)	(141,973)	(130,198)	(665,448)	(572,598)	(545,229)
Commission expenses		(44,154)	(42,611)	(40,726)	(37,554)	(31,339)	(34,253)	(31,480)	(32,905)	(165,045)	(129,977)	(125,528)
Other operating expenses										(234,096)	(223,516)	(196,825)
Other underwriting income (expense)										136	122	595
Underwriting profit (loss)										35,892	58,118	68,908
Net investment income		20,107	19,875	19,875	19,594	18,499	17,371	16,595	16,253	79,451	68,718	64,168
Net realized gains (losses)										9,036	6,675	12,812
Interest expense		(3,860)	(3,859)	(3,858)	(3,858)	(3,857)	(3,856)	(3,856)	(3,855)	(15,435)	(15,424)	(15,413)
Other income (loss)										8,565	(613)	10,061
Income before income taxes		31,457	29,888	23,243	32,921	23,815	26,924	28,379	38,356	117,509	117,474	140,536
Income tax (expense) benefit		(9,866)	(7,875)	(7,053)	(9,989)	(6,072)	(8,723)	(9,195)	(12,427)	(34,783)	(36,417)	(45,207)
Net income		$ 21,591	$ 22,013	$ 16,190	$ 22,932	$ 17,743	$ 18,201	$ 19,184	$ 25,929	$ 82,726	$ 81,057	$ 95,329
Losses and LAE ratio										60.50%	58.20%	58.30%
Commission expense ratio										15.00%	13.20%	13.40%
Other operating expense ratio	[1]									21.20%	22.70%	20.90%
Combined ratio		96.70%	95.60%	99.60%	95.10%	97.20%	93.40%	93.40%	92.30%	96.70%	94.10%	92.60%
U.S.Insurance
Segment Reporting Information [Line Items]
Net earned premiums										$ 629,308	$ 555,836	$ 504,289
Net losses and LAE										(397,860)	(343,497)	(311,839)
Commission expenses										(70,812)	(56,319)	(49,840)
Other operating expenses										(128,108)	(131,407)	(115,817)
Other underwriting income (expense)										1,092	1,690	2,241
Underwriting profit (loss)										33,620	26,303	29,034
Income before income taxes										$ 33,620	$ 26,303	$ 29,034
Losses and LAE ratio										63.20%	61.80%	61.80%
Commission expense ratio										11.30%	10.10%	9.90%
Other operating expense ratio	[1]									20.20%	23.40%	22.50%
Combined ratio										94.70%	95.30%	94.20%
International Insurance
Segment Reporting Information [Line Items]
Net earned premiums										$ 307,416	$ 259,960	$ 243,485
Net losses and LAE										(178,284)	(134,702)	(115,079)
Commission expenses										(61,703)	(43,676)	(44,426)
Other operating expenses										(86,395)	(75,867)	(65,275)
Other underwriting income (expense)												32
Underwriting profit (loss)										(18,966)	5,715	18,737
Income before income taxes										$ (18,966)	$ 5,715	$ 18,737
Losses and LAE ratio										58.00%	51.80%	47.30%
Commission expense ratio										20.10%	16.80%	18.20%
Other operating expense ratio	[1]									28.10%	29.20%	26.80%
Combined ratio										106.20%	97.80%	92.30%
Global Reinsurance
Segment Reporting Information [Line Items]
Net earned premiums										$ 163,621	$ 168,291	$ 188,121
Net losses and LAE										(89,304)	(94,399)	(118,311)
Commission expenses										(34,008)	(32,240)	(33,429)
Other operating expenses										(19,593)	(16,242)	(15,733)
Other underwriting income (expense)										522	690	489
Underwriting profit (loss)										21,238	26,100	21,137
Income before income taxes										$ 21,238	$ 26,100	$ 21,137
Losses and LAE ratio										54.60%	56.10%	62.90%
Commission expense ratio										20.80%	19.20%	17.80%
Other operating expense ratio	[1]									11.60%	9.20%	8.10%
Combined ratio										87.00%	84.50%	88.80%
Corporate
Segment Reporting Information [Line Items]
Commission expenses	[2]									$ 1,478	$ 2,258	$ 2,167
Other underwriting income (expense)	[2]									(1,478)	(2,258)	(2,167)
Net investment income	[2]									79,451	68,718	64,168
Net realized gains (losses)	[2]									9,036	6,675	12,812
Interest expense	[2]									(15,435)	(15,424)	(15,413)
Other income (loss)	[2]									8,565	(613)	10,061
Income before income taxes	[2]									81,617	59,356	71,628
Income tax (expense) benefit	[2]									$ (34,783)	$ (36,417)	$ (45,207)
[1]	Includes Other operating expenses and Other underwriting income (expense).
[2]	Includes Corporate segment intercompany eliminations.

Additional Financial Data by Se

Additional Financial Data by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Gross written premiums	$ 367,539	$ 374,930	$ 412,565	$ 413,877	$ 323,509	$ 354,062	$ 379,471	$ 396,460	$ 1,568,911	$ 1,453,502	$ 1,432,353
Ceded written premiums									(382,687)	(409,642)	(432,215)
Net written premiums	282,868	277,001	306,535	319,820	244,719	251,939	258,244	288,958	1,186,224	1,043,860	1,000,138
Net earned premiums	$ 283,985	$ 284,010	$ 267,992	$ 264,358	$ 251,545	$ 254,082	$ 242,328	$ 236,132	1,100,345	984,087	935,895
Property Casualty
Segment Reporting Information [Line Items]
Net earned premiums									1,186,224	1,043,860	1,000,138
U.S.Insurance
Segment Reporting Information [Line Items]
Gross written premiums									919,395	865,781	807,108
Ceded written premiums									(235,827)	(268,775)	(254,983)
Net written premiums									683,568	597,006	552,125
Net earned premiums									629,308	555,836	504,289
U.S.Insurance | Marine
Segment Reporting Information [Line Items]
Gross written premiums									169,405	158,124	154,233
Ceded written premiums									(70,858)	(61,916)	(46,685)
Net written premiums									98,547	96,208	107,548
Net earned premiums									100,132	96,082	105,650
U.S.Insurance | Property Casualty
Segment Reporting Information [Line Items]
Gross written premiums									631,562	596,673	543,045
Ceded written premiums									(135,888)	(152,168)	(169,953)
Net written premiums									495,674	444,505	373,092
Net earned premiums									453,673	401,408	314,833
U.S.Insurance | Professional Liability
Segment Reporting Information [Line Items]
Gross written premiums									118,428	110,984	109,830
Ceded written premiums									(29,081)	(54,691)	(38,345)
Net written premiums									89,347	56,293	71,485
Net earned premiums									75,503	58,346	83,806
International Insurance
Segment Reporting Information [Line Items]
Gross written premiums									484,471	411,947	424,904
Ceded written premiums									(138,504)	(134,005)	(171,921)
Net written premiums									345,967	277,942	252,983
Net earned premiums									307,416	259,960	243,485
International Insurance | Marine
Segment Reporting Information [Line Items]
Gross written premiums									183,228	183,707	190,787
Ceded written premiums									(40,092)	(36,515)	(47,805)
Net written premiums									143,136	147,192	142,982
Net earned premiums									141,593	149,256	141,097
International Insurance | Property Casualty
Segment Reporting Information [Line Items]
Gross written premiums									181,094	130,729	158,139
Ceded written premiums									(69,606)	(67,722)	(98,087)
Net written premiums									111,488	63,007	60,052
Net earned premiums									89,455	55,320	62,520
International Insurance | Professional Liability
Segment Reporting Information [Line Items]
Gross written premiums									120,149	97,511	75,978
Ceded written premiums									(28,806)	(29,768)	(26,029)
Net written premiums									91,343	67,743	49,949
Net earned premiums									76,368	55,384	39,868
Global Reinsurance
Segment Reporting Information [Line Items]
Gross written premiums									165,045	175,774	200,341
Ceded written premiums									(8,356)	(6,862)	(5,311)
Net written premiums									156,689	168,912	195,030
Net earned premiums									$ 163,621	$ 168,291	$ 188,121

Available-for-Sale Investments

Available-for-Sale Investments Including Other-Than-Temporarily Impaired Securities Recognized within Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	Dec. 31, 2016		Dec. 31, 2015
Gain (Loss) on Investments [Line Items]
Total investments	$ 3,128,563		$ 2,937,226
Gross Unrealized Gains	59,175		66,693
Gross Unrealized Losses	(30,199)		(29,398)
Amortized Cost	3,099,587		2,899,931
Fixed maturities
Gain (Loss) on Investments [Line Items]
Total investments	2,635,882	[1]	2,414,210
Gross Unrealized Gains	32,071		40,350
Gross Unrealized Losses	(24,414)		(26,385)
Amortized Cost	2,628,225		2,400,245
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign
Gain (Loss) on Investments [Line Items]
Total investments	273,776	[1]	252,882
Gross Unrealized Gains	2,192		2,273
Gross Unrealized Losses	(5,128)		(9,214)
Amortized Cost	276,712		259,823
Fixed maturities | States, municipalities and political subdivisions
Gain (Loss) on Investments [Line Items]
Total investments	547,415	[1]	576,859
Gross Unrealized Gains	11,542		21,233
Gross Unrealized Losses	(4,036)		(781)
Amortized Cost	539,909		556,407
Fixed maturities | Agency mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Total investments	487,364	[1]	379,269
Gross Unrealized Gains	4,016		5,573
Gross Unrealized Losses	(6,585)		(2,082)
Amortized Cost	489,933		375,778
Fixed maturities | Residential Mortgage Backed Securities
Gain (Loss) on Investments [Line Items]
Total investments	20,530	[1]	30,465
Gross Unrealized Gains	453		694
Gross Unrealized Losses	(55)		(82)
Amortized Cost	20,132		29,853
Fixed maturities | Asset-backed securities
Gain (Loss) on Investments [Line Items]
Total investments	314,601	[1]	225,012
Gross Unrealized Gains	824		85
Gross Unrealized Losses	(1,178)		(1,624)
Amortized Cost	314,955		226,551
Fixed maturities | Commercial mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Total investments	154,139	[1]	189,713
Gross Unrealized Gains	2,859		3,119
Gross Unrealized Losses	(1,904)		(1,864)
Amortized Cost	153,184		188,458
Fixed maturities | Mortgage-backed and asset-backed securities
Gain (Loss) on Investments [Line Items]
Total investments	976,634	[1]	824,459
Gross Unrealized Gains	8,152		9,471
Gross Unrealized Losses	(9,722)		(5,652)
Amortized Cost	978,204		820,640
Fixed maturities | Corporate bonds
Gain (Loss) on Investments [Line Items]
Total investments	838,057	[1]	760,010
Gross Unrealized Gains	10,185		7,373
Gross Unrealized Losses	(5,528)		(10,738)
Amortized Cost	833,400		763,375
Equity Securities
Gain (Loss) on Investments [Line Items]
Total investments	349,142	[1]	305,271
Gross Unrealized Gains	27,016		26,341
Gross Unrealized Losses	(5,785)		(3,013)
Amortized Cost	327,911		281,943
Short-term investments
Gain (Loss) on Investments [Line Items]
Total investments	143,539	[1]	217,745
Gross Unrealized Gains	88		2
Amortized Cost	$ 143,451		$ 217,743
[1]	Other invested assets are accounted for using the equity method of accounting. All other investments are shown at fair value.

Investments - Additional Inform

Investments - Additional Information (Detail) $ in Thousands	3 Months Ended			12 Months Ended
	Jun. 30, 2016USD ($)	Sep. 30, 2015USD ($)	Jun. 30, 2015USD ($)	Dec. 31, 2016USD ($)Security	Dec. 31, 2015USD ($)Security	Dec. 31, 2014USD ($)
Schedule of Investments [Line Items]
Other invested assets				$ 1,960
Non-credit OTTI on fixed maturities in a net unrealized net gain position				400	$ 500
Gross Unrealized Loss				30,199	29,398
OTTI losses	$ 150	$ 1,275	$ 423	$ 150	$ 1,698	$ 0
Equity Securities
Schedule of Investments [Line Items]
Number of securities in unrealized loss position | Security				75	57
Gross Unrealized Loss				$ 5,785	$ 3,013
Fixed maturities
Schedule of Investments [Line Items]
Number of securities in unrealized loss position | Security				413	368
Gross Unrealized Loss				$ 24,414	$ 26,385
OTTI losses				200
Equity Portfolio
Schedule of Investments [Line Items]
OTTI losses					1,700
Non-government-backed securities
Schedule of Investments [Line Items]
Gross Unrealized Loss				$ 1,000	$ 2,600
Non-government-backed securities | Maximum
Schedule of Investments [Line Items]
Percentage of investment				5.00%	5.00%
Mortgage-backed and asset-backed securities
Schedule of Investments [Line Items]
Securities, effective maturities				4 years 10 months 24 days
Mortgage-backed and asset-backed securities | Fixed maturities
Schedule of Investments [Line Items]
Gross Unrealized Loss				$ 9,722	$ 5,652

Scheduled Maturity Dates for Fi

Scheduled Maturity Dates for Fixed Maturity Securities by Number of Years Until Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value
Due in one year or less	$ 133,644
Due after one year through five years	778,875
Due after five years through ten years	295,742
Due after ten years	450,987
Mortgage-backed and asset-backed securities	976,634
Total	2,635,882	$ 2,414,210
Amortized Cost
Due in one year or less	134,931
Due after one year through five years	778,511
Due after five years through ten years	291,811
Due after ten years	444,768
Mortgage-backed and asset-backed securities	978,204
Total	$ 2,628,225	$ 2,400,245

Summary of Aggregate Fair Value

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 ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	$ 1,256,887	$ 1,010,970
Less than 12 months Gross Unrealized Losses	(24,493)	(20,517)
Greater than 12 months Fair Value	127,403	156,975
Greater than 12 months Gross Unrealized Losses	(5,706)	(8,881)
Fair Value	1,384,290	1,167,945
Gross Unrealized Losses	(30,199)	(29,398)
Fixed maturities
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	1,111,873	952,439
Less than 12 months Gross Unrealized Losses	(19,074)	(17,504)
Greater than 12 months Fair Value	125,409	156,975
Greater than 12 months Gross Unrealized Losses	(5,340)	(8,881)
Fair Value	1,237,282	1,109,414
Gross Unrealized Losses	(24,414)	(26,385)
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	150,891	142,233
Less than 12 months Gross Unrealized Losses	(2,570)	(3,032)
Greater than 12 months Fair Value	16,819	22,230
Greater than 12 months Gross Unrealized Losses	(2,558)	(6,182)
Fair Value	167,710	164,463
Gross Unrealized Losses	(5,128)	(9,214)
Fixed maturities | States, municipalities and political subdivisions
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	137,731	50,577
Less than 12 months Gross Unrealized Losses	(3,111)	(549)
Greater than 12 months Fair Value	13,255	4,808
Greater than 12 months Gross Unrealized Losses	(925)	(232)
Fair Value	150,986	55,385
Gross Unrealized Losses	(4,036)	(781)
Fixed maturities | Agency mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	349,119	164,817
Less than 12 months Gross Unrealized Losses	(6,155)	(1,315)
Greater than 12 months Fair Value	12,401	29,862
Greater than 12 months Gross Unrealized Losses	(430)	(767)
Fair Value	361,520	194,679
Gross Unrealized Losses	(6,585)	(2,082)
Fixed maturities | Residential Mortgage Backed Securities
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	953	3,910
Less than 12 months Gross Unrealized Losses	(18)	(5)
Greater than 12 months Fair Value	926	1,684
Greater than 12 months Gross Unrealized Losses	(37)	(77)
Fair Value	1,879	5,594
Gross Unrealized Losses	(55)	(82)
Fixed maturities | Asset-backed securities
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	95,514	112,479
Less than 12 months Gross Unrealized Losses	(970)	(663)
Greater than 12 months Fair Value	48,093	81,477
Greater than 12 months Gross Unrealized Losses	(208)	(961)
Fair Value	143,607	193,956
Gross Unrealized Losses	(1,178)	(1,624)
Fixed maturities | Commercial mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	51,932	83,024
Less than 12 months Gross Unrealized Losses	(1,164)	(1,826)
Greater than 12 months Fair Value	7,910	3,065
Greater than 12 months Gross Unrealized Losses	(740)	(38)
Fair Value	59,842	86,089
Gross Unrealized Losses	(1,904)	(1,864)
Fixed maturities | Mortgage-backed and asset-backed securities
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	497,518	364,230
Less than 12 months Gross Unrealized Losses	(8,307)	(3,809)
Greater than 12 months Fair Value	69,330	116,088
Greater than 12 months Gross Unrealized Losses	(1,415)	(1,843)
Fair Value	566,848	480,318
Gross Unrealized Losses	(9,722)	(5,652)
Fixed maturities | Corporate bonds
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	325,733	395,399
Less than 12 months Gross Unrealized Losses	(5,086)	(10,114)
Greater than 12 months Fair Value	26,005	13,849
Greater than 12 months Gross Unrealized Losses	(442)	(624)
Fair Value	351,738	409,248
Gross Unrealized Losses	(5,528)	(10,738)
Equity Securities
Gain (Loss) on Investments [Line Items]
Less than 12 months Fair Value	145,014	58,531
Less than 12 months Gross Unrealized Losses	(5,419)	(3,013)
Greater than 12 months Fair Value	1,994
Greater than 12 months Gross Unrealized Losses	(366)
Fair Value	147,008	58,531
Gross Unrealized Losses	$ (5,785)	$ (3,013)

Summary of Cumulative Amounts R

Summary of Cumulative Amounts Related to Credit Loss Portion of Other-Than-Temporary Impairment Losses on Debt Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investments Debt And Equity Securities [Abstract]
Beginning balance	$ 2,361	$ 2,361	$ 5,154
Additions for credit loss impairments recognized in the current period on securities not previously impaired	150	0	0
Additions for credit loss impairments recognized in the current period on securities previously impaired	0	0	0
Reductions for credit loss impairments previously recognized on securities sold during the period	(150)	0	(2,793)
Ending balance	$ 2,361	$ 2,361	$ 2,361

Net Investment Income (Detail)

Net Investment Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Investment Income [Line Items]
Investment Income									$ 82,770	$ 72,068	$ 67,166
Investment expenses									(3,319)	(3,350)	(2,998)
Net investment income	$ 20,107	$ 19,875	$ 19,875	$ 19,594	$ 18,499	$ 17,371	$ 16,595	$ 16,253	79,451	68,718	64,168
Fixed maturities
Net Investment Income [Line Items]
Investment Income									67,772	61,572	57,219
Equity Securities
Net Investment Income [Line Items]
Investment Income									14,271	9,813	9,036
Short-term investments
Net Investment Income [Line Items]
Investment Income									$ 727	$ 683	$ 911

Realized Gains and Losses, Excl

Realized Gains and Losses, Excluding Net Other-Than-Temporary Impairment Losses Recognized in Earnings (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Gain (Loss) on Investments [Line Items]
Net realized gains (losses)	$ 9,186	$ 8,373	$ 12,812
Fixed maturities
Gain (Loss) on Investments [Line Items]
Gains	5,681	4,756	8,326
Losses	(4,271)	(5,926)	(2,610)
Net realized gains (losses)	1,410	(1,170)	5,716
Short-term investments
Gain (Loss) on Investments [Line Items]
Gains	890	130
Losses	(1,552)	(383)
Net realized gains (losses)	(662)	(253)
Equity Securities
Gain (Loss) on Investments [Line Items]
Gains	9,096	14,331	9,447
Losses	(658)	(4,535)	(2,351)
Net realized gains (losses)	$ 8,438	$ 9,796	$ 7,096

Fair Value Measurement - Additi

Fair Value Measurement - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Significant transfers between Level 1 and Level 2	$ 0	$ 0
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Level 3 assets	$ 0	$ 0
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	Oct. 15, 2023

Fixed Maturities and Equity Sec

Fixed Maturities and Equity Securities by Asset Class that are Measured at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2016		Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	$ 3,128,563		$ 2,937,226
Total liabilities measured at fair value	280,316		282,486
Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	2,635,882	[1]	2,414,210
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	273,776	[1]	252,882
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	547,415	[1]	576,859
Fixed maturities | Agency mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	487,364	[1]	379,269
Fixed maturities | Residential Mortgage Backed Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	20,530	[1]	30,465
Fixed maturities | Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	314,601	[1]	225,012
Fixed maturities | Commercial mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	154,139	[1]	189,713
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	976,634	[1]	824,459
Fixed maturities | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	838,057	[1]	760,010
Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	349,142	[1]	305,271
Short-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	143,539	[1]	217,745
Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes, at fair value	280,316		282,486
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	355,331		411,594
Level 1 | Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	47,704		67,394
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	47,704		67,394
Level 1 | Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	164,088		126,455
Level 1 | Short-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	143,539		217,745
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	2,773,232		2,525,632
Total liabilities measured at fair value	280,316		282,486
Level 2 | Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	2,588,178		2,346,816
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	226,072		185,488
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	547,415		576,859
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	487,364		379,269
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	20,530		30,465
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	314,601		225,012
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	154,139		189,713
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	976,634		824,459
Level 2 | Fixed maturities | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	838,057		760,010
Level 2 | Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	185,054		178,816
Level 2 | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes, at fair value	$ 280,316		$ 282,486
[1]	Other invested assets are accounted for using the equity method of accounting. All other investments are shown at fair value.

Summary of Activity in Reserve

Summary of Activity in Reserve for Losses and LAE (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Insurance [Abstract]
Net reserves for losses and LAE at beginning of year	$ 1,393,126	$ 1,308,136	$ 1,222,633
Provision for losses and LAE for claims occurring in the current year	693,976	637,267	601,041
Increase (decrease) in estimated losses and LAE for claims occurring in prior years	(28,528)	(64,669)	(55,812)
Incurred losses and LAE	665,448	572,598	545,229
Losses and LAE paid for claims occurring during:
Current year	(119,485)	(159,802)	(158,806)
Prior years	(412,544)	(320,863)	(295,527)
Losses and LAE payments	(532,029)	(480,665)	(454,333)
Foreign Currency Adjustment	(16,094)	(6,943)	(5,393)
Net reserves for losses and LAE at end of year	1,510,451	1,393,126	1,308,136
Reinsurance recoverables on unpaid losses and LAE	779,276	809,518	851,498
Gross reserves for losses and LAE at end of year	$ 2,289,727	$ 2,202,644	$ 2,159,634

Reporting and Operating Segment

Reporting and Operating Segments Breakdowns of Prior Period Net Reserve Deficiency (Redundancy) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	$ (28,528)	$ (64,669)	$ (55,812)
U.S.Insurance
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	(1,348)	(29,319)	(15,420)
U.S.Insurance | Marine
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	(10,122)	(24,825)	(29,047)
U.S.Insurance | Property Casualty
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	2,790	(706)	17,081
U.S.Insurance | Professional Liability
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	5,984	(3,788)	(3,454)
International Insurance
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	(25,019)	(26,216)	(38,252)
International Insurance | Marine
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	(22,068)	(21,914)	(31,677)
International Insurance | Property Casualty
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	(7,051)	(8,458)	(3,829)
International Insurance | Professional Liability
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	4,100	4,156	(2,746)
Global Reinsurance
Liability for Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	$ (2,161)	$ (9,134)	$ (2,140)

Reserves for Losses and LAE - A

Reserves for Losses and LAE - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)Claim	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	$ (28,528)	$ (64,669)	$ (55,812)
Number of reported claim | Claim	1
U.S.Insurance
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	$ (1,348)	(29,319)	(15,420)
U.S.Insurance | Marine
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	(10,122)	(24,825)	(29,047)
U.S.Insurance | Property Casualty
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	2,790	(706)	17,081
U.S.Insurance | Professional Liability
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	5,984	(3,788)	(3,454)
U.S.Insurance | Professional Liability | Directors and Officers
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	6,000		(3,500)
U.S.Insurance | Professional Liability | Errors and Omissions
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years		(3,800)
International Insurance
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	(25,019)	(26,216)	(38,252)
International Insurance | Marine
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	(22,068)	(21,914)	(31,677)
International Insurance | Property Casualty
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	(7,051)	(8,458)	(3,829)
International Insurance | Professional Liability
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	4,100	4,156	(2,746)
Global Reinsurance
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net reserve deficiencies (redundancies) in prior years	$ (2,161)	$ (9,134)	$ (2,140)

Summary of Information about In

Summary of Information about Incurred Claims Development and Cumulative Paid Claims and Allocated Loss Adjustment Expense (ALAE), Net of Reinsurance (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)Claim	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)	Dec. 31, 2010USD ($)	Dec. 31, 2009USD ($)	Dec. 31, 2008USD ($)	Dec. 31, 2007USD ($)
Claims Development [Line Items]
Number of Reported Claims | Claim	1
U.S.Insurance | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	$ 596,082
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	502,906
Net reserves lesser than 2007	13,112
Total Net reserves	$ 106,288
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 1	26.40%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 2	32.40%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 3	16.50%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 4	8.30%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 5	8.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 6	3.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 7	2.20%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 8	2.10%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 9	1.50%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 10	0.20%
U.S.Insurance | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	$ 1,587,701
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	834,873
Net reserves lesser than 2007	16,571
Total Net reserves	$ 769,399
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 1	5.90%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 2	11.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 3	16.20%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 4	18.00%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 5	14.20%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 6	8.60%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 7	4.90%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 8	5.30%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 9	6.80%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 10	4.50%
U.S.Insurance | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	$ 542,871
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	451,448
Net reserves lesser than 2007	(386)
Total Net reserves	$ 91,037
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 1	5.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 2	28.30%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 3	28.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 4	15.90%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 5	8.20%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 6	9.20%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 7	3.00%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 8	1.50%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 9	6.00%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 10	0.00%
U.S.Insurance | 2007 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	$ 66,846	$ 66,297	$ 65,909	$ 66,024	$ 66,090	$ 65,020	$ 59,148	$ 61,216	$ 60,645	$ 52,974
Total IBNR	$ 60
Number of Reported Claims | Claim	2,737
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 64,570	64,450	63,384	62,767	62,002	58,772	49,214	40,256	28,937	9,294
U.S.Insurance | 2007 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	148,609	145,472	139,870	134,310	128,087	133,050	130,501	140,551	139,570	139,377
Total IBNR	$ 3,753
Number of Reported Claims | Claim	11,703
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 136,896	130,279	122,568	114,160	104,841	92,840	72,462	49,616	24,521	7,127
U.S.Insurance | 2007 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	59,574	59,936	60,447	60,445	61,935	62,630	57,643	55,491	38,553	38,000
Total IBNR	$ (70)
Number of Reported Claims | Claim	634
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 59,570	59,565	59,332	59,280	58,515	52,941	47,980	32,621	10,365	$ 1,861
U.S.Insurance | 2008 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	67,238	67,024	68,873	68,703	73,731	73,970	72,580	67,710	56,923
Total IBNR	$ 348
Number of Reported Claims | Claim	3,202
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 64,317	63,429	63,316	62,989	62,633	56,695	54,408	36,499	7,554
U.S.Insurance | 2008 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	157,519	152,416	147,434	143,219	141,332	140,818	144,164	158,336	158,337
Total IBNR	$ 3,971
Number of Reported Claims | Claim	10,818
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 146,463	133,064	123,945	115,526	103,804	82,028	58,491	36,713	12,178
U.S.Insurance | 2008 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	41,766	37,620	37,497	37,939	37,603	35,844	39,130	38,449	34,346
Total IBNR	$ (382)
Number of Reported Claims | Claim	770
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 42,056	37,175	35,598	35,206	34,902	30,581	25,042	15,288	$ 1,880
U.S.Insurance | 2009 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	52,169	53,091	50,905	49,762	51,804	57,266	60,813	63,769
Total IBNR	$ (186)
Number of Reported Claims | Claim	2,404
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 50,888	48,209	47,347	44,760	42,846	36,593	30,012	12,975
U.S.Insurance | 2009 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	159,110	155,682	155,156	149,975	142,416	136,700	135,984	133,394
Total IBNR	$ 7,717
Number of Reported Claims | Claim	8,434
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 145,407	138,227	132,695	119,360	92,033	59,933	36,641	14,619
U.S.Insurance | 2009 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	58,143	58,660	58,487	60,789	58,600	61,023	53,273	47,473
Total IBNR	$ (563)
Number of Reported Claims | Claim	1,370
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 58,095	57,744	53,859	55,378	51,642	41,675	21,742	3,837
U.S.Insurance | 2010 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	58,557	59,143	54,815	57,063	63,172	66,187	66,336
Total IBNR	$ (263)
Number of Reported Claims | Claim	2,164
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 57,254	54,044	50,271	45,032	41,941	33,821	17,211
U.S.Insurance | 2010 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	112,080	109,323	107,602	104,709	98,675	100,529	101,527
Total IBNR	$ 10,106
Number of Reported Claims | Claim	7,804
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 94,766	89,873	81,262	69,027	49,109	27,542	12,682
U.S.Insurance | 2010 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	85,348	86,787	74,535	75,619	68,375	64,020	52,302
Total IBNR	$ 83
Number of Reported Claims | Claim	1,429
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 84,511	82,013	59,765	54,019	46,868	23,147	2,981
U.S.Insurance | 2011 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	62,571	64,196	65,514	70,019	72,232	71,575
Total IBNR	$ 1,204
Number of Reported Claims | Claim	2,012
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 60,198	59,224	54,471	50,841	41,322	16,007
U.S.Insurance | 2011 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	105,149	95,958	95,292	92,266	85,238	86,056
Total IBNR	$ 15,964
Number of Reported Claims | Claim	6,346
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 75,806	63,800	51,868	35,551	19,548	3,925
U.S.Insurance | 2011 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	79,136	79,181	73,028	70,240	62,087	58,116
Total IBNR	$ 622
Number of Reported Claims | Claim	1,724
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 75,641	65,710	59,576	43,551	23,878	3,204
U.S.Insurance | 2012 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	71,868	70,421	73,940	91,118	87,905
Total IBNR	$ (7)
Number of Reported Claims | Claim	1,968
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 68,556	62,104	56,040	47,639	27,546
U.S.Insurance | 2012 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	111,746	103,716	98,060	96,618	111,479
Total IBNR	$ 24,895
Number of Reported Claims | Claim	4,481
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 72,495	51,980	33,477	23,019	10,013
U.S.Insurance | 2012 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	58,344	55,917	57,097	54,480	61,196
Total IBNR	$ 3,214
Number of Reported Claims | Claim	2,180
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 49,675	44,028	35,681	22,635	3,855
U.S.Insurance | 2013 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	58,148	55,494	61,289	65,132
Total IBNR	$ (619)
Number of Reported Claims | Claim	1,910
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 50,410	44,606	38,487	19,565
U.S.Insurance | 2013 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	141,817	133,068	130,314	141,728
Total IBNR	$ 29,961
Number of Reported Claims | Claim	3,533
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 85,719	49,562	21,500	7,317
U.S.Insurance | 2013 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	48,298	49,104	54,982	60,899
Total IBNR	$ 4,989
Number of Reported Claims | Claim	2,226
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 38,876	32,904	22,167	4,677
U.S.Insurance | 2014 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	48,355	49,889	67,610
Total IBNR	$ 1,509
Number of Reported Claims | Claim	1,962
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 41,609	29,916	15,702
U.S.Insurance | 2014 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	152,447	164,364	193,897
Total IBNR	$ 76,085
Number of Reported Claims | Claim	3,356
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 45,324	13,762	5,272
U.S.Insurance | 2014 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	39,826	35,870	50,020
Total IBNR	$ 6,504
Number of Reported Claims | Claim	2,278
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 29,392	14,371	2,304
U.S.Insurance | 2015 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	54,121	64,575
Total IBNR	$ 13,317
Number of Reported Claims | Claim	2,155
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 32,439	17,169
U.S.Insurance | 2015 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	224,532	251,752
Total IBNR	$ 134,029
Number of Reported Claims | Claim	3,123
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 24,291	3,641
U.S.Insurance | 2015 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	30,764	31,659
Total IBNR	$ 15,870
Number of Reported Claims | Claim	1,709
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 11,249	2,257
U.S.Insurance | 2016 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	56,209
Total IBNR	$ 32,884
Number of Reported Claims | Claim	1,824
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 12,665
U.S.Insurance | 2016 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	274,692
Total IBNR	$ 258,449
Number of Reported Claims | Claim	2,106
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 7,706
U.S.Insurance | 2016 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	41,672
Total IBNR	$ 36,356
Number of Reported Claims | Claim	1,739
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,383
International Insurance | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	858,751
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	671,426
Net reserves lesser than 2007	9,207
Total Net reserves	$ 196,532
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 1	24.50%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 2	28.10%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 3	18.20%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 4	7.60%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 5	5.00%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 6	2.80%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 7	2.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 8	2.40%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 9	1.30%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 10	0.80%
International Insurance | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	$ 359,041
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	278,471
Net reserves lesser than 2007	619
Total Net reserves	$ 81,189
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 1	25.40%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 2	33.50%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 3	21.80%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 4	9.40%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 5	5.20%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 6	(1.00%)
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 7	(0.20%)
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 8	1.20%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 9	0.10%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 10	0.00%
International Insurance | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	$ 186,498
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	87,901
Net reserves lesser than 2007	92
Total Net reserves	$ 98,689
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 1	7.50%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 2	7.30%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 3	7.40%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 4	20.60%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 5	15.90%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 6	11.80%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 7	4.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 8	2.30%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 9	1.10%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 10	0.80%
International Insurance | 2007 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	$ 66,239	66,883	66,951	67,148	70,633
Total IBNR	$ (35)
Number of Reported Claims | Claim	5,585
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 63,281	62,729	61,956	60,702	59,831
International Insurance | 2007 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	25,778	25,855	25,740	25,817	26,084
Total IBNR	$ (60)
Number of Reported Claims | Claim	584
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 25,289	25,292	25,150	24,681	23,885
International Insurance | 2007 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	12,381	12,378	12,445	12,587	12,901
Total IBNR	$ (64)
Number of Reported Claims | Claim	235
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 12,382	12,277	12,269	11,704	11,293
International Insurance | 2008 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	82,752	84,191	84,131	85,285	88,720
Total IBNR	$ 98
Number of Reported Claims | Claim	5,809
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 78,683	77,535	73,746	72,309	69,959
International Insurance | 2008 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	36,729	37,296	37,867	37,884	39,504
Total IBNR	$ (75)
Number of Reported Claims | Claim	891
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 35,826	35,975	35,463	35,161	34,084
International Insurance | 2008 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	14,023	14,010	14,816	15,302	15,511
Total IBNR	$ (175)
Number of Reported Claims | Claim	365
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 14,019	13,732	13,702	13,306	12,150
International Insurance | 2009 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	79,526	82,096	84,497	86,914	89,057
Total IBNR	$ 111
Number of Reported Claims | Claim	4,969
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 75,006	74,311	70,834	68,085	64,058
International Insurance | 2009 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	25,113	25,418	25,910	25,804	26,499
Total IBNR	$ 13
Number of Reported Claims | Claim	743
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 24,369	24,286	24,713	24,257	23,371
International Insurance | 2009 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	15,780	16,289	14,972	15,367	14,809
Total IBNR	$ 629
Number of Reported Claims | Claim	445
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 14,118	13,803	12,783	10,716	8,805
International Insurance | 2010 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	108,405	111,468	114,188	119,021	123,719
Total IBNR	$ 282
Number of Reported Claims | Claim	5,317
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 99,416	97,132	93,167	87,186	74,920
International Insurance | 2010 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	38,198	39,031	39,050	39,409	39,082
Total IBNR	$ 58
Number of Reported Claims | Claim	836
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 36,601	36,509	39,017	36,499	32,156
International Insurance | 2010 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	15,619	17,451	15,661	16,159	18,603
Total IBNR	$ 1,409
Number of Reported Claims | Claim	653
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 13,366	12,632	10,460	7,169	5,801
International Insurance | 2011 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	70,751	75,873	78,872	86,795	91,347
Total IBNR	$ 25
Number of Reported Claims | Claim	4,824
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 66,538	65,580	60,879	56,569	43,740
International Insurance | 2011 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	52,202	52,666	52,093	53,654	57,463
Total IBNR	$ (198)
Number of Reported Claims | Claim	833
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 48,502	47,591	45,125	42,280	33,316
International Insurance | 2011 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	6,835	7,050	7,125	7,648	9,686
Total IBNR	$ 356
Number of Reported Claims | Claim	681
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 4,576	4,007	2,950	2,002	1,197
International Insurance | 2012 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	90,523	94,886	99,683	115,935	93,696
Total IBNR	$ (216)
Number of Reported Claims | Claim	5,201
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 79,205	76,572	68,498	52,968	22,777
International Insurance | 2012 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	27,828	28,626	30,347	30,643	34,479
Total IBNR	$ (353)
Number of Reported Claims | Claim	877
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 26,049	24,871	20,850	15,648	7,884
International Insurance | 2012 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	16,891	11,175	9,106	9,753	8,204
Total IBNR	$ 490
Number of Reported Claims | Claim	718
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 7,365	5,483	4,253	3,219	2,133
International Insurance | 2013 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	77,239	80,713	82,313	68,587
Total IBNR	$ 747
Number of Reported Claims | Claim	5,075
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 60,828	54,826	42,953	21,703
International Insurance | 2013 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	29,684	31,050	33,720	29,496
Total IBNR	$ (308)
Number of Reported Claims | Claim	1,229
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 27,180	24,735	17,613	6,829
International Insurance | 2013 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	15,402	16,272	17,628	15,096
Total IBNR	$ 4,255
Number of Reported Claims | Claim	1,053
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 9,230	2,952	2,196	725
International Insurance | 2014 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	107,789	105,072	85,512
Total IBNR	$ (1,500)
Number of Reported Claims | Claim	4,928
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 73,921	50,168	24,445
International Insurance | 2014 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	17,006	16,987	20,234
Total IBNR	$ 173
Number of Reported Claims | Claim	1,167
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 12,304	8,458	3,813
International Insurance | 2014 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	23,457	24,070	18,835
Total IBNR	$ 12,421
Number of Reported Claims | Claim	1,276
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 5,068	2,421	1,368
International Insurance | 2015 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	91,371	70,675
Total IBNR	$ 5,194
Number of Reported Claims | Claim	6,967
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 52,356	22,323
International Insurance | 2015 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	30,932	26,414
Total IBNR	$ 2,106
Number of Reported Claims | Claim	1,678
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 18,096	6,739
International Insurance | 2015 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	30,104	22,760
Total IBNR	$ 17,379
Number of Reported Claims | Claim	1,939
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 5,765	3,355
International Insurance | 2016 | Marine
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	84,156
Total IBNR	$ 26,285
Number of Reported Claims | Claim	5,577
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 22,192
International Insurance | 2016 | Property Casualty
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	75,571
Total IBNR	$ 13,006
Number of Reported Claims | Claim	2,646
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 24,255
International Insurance | 2016 | Professional Liability
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	36,006
Total IBNR	$ 31,814
Number of Reported Claims | Claim	2,554
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,012
Global Reinsurance
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	635,119
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	526,123
Net reserves lesser than 2007	2,598
Total Net reserves	$ 111,594
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 1	47.10%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 2	32.10%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 3	0.60%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 4	3.10%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 5	8.50%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 6	2.10%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 7	2.80%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 8	0.70%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 9	0.30%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance 10	(0.10%)
Global Reinsurance | 2007
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	$ 5,883	5,889	6,173	6,190	6,215
Total IBNR	$ (141)
Number of Reported Claims | Claim	254
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 5,350	5,357	5,345	5,275	5,225
Global Reinsurance | 2008
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	13,298	13,304	13,530	14,024	13,863
Total IBNR	$ 672
Number of Reported Claims | Claim	294
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 11,546	11,488	11,510	11,650	11,629
Global Reinsurance | 2009
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	10,475	10,390	10,745	11,380	11,186	3,752	3,734	$ 4,970
Total IBNR	$ 204
Number of Reported Claims | Claim	202
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 10,045	9,932	8,974	8,853	8,620	3,752	3,734
Global Reinsurance | 2010
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	12,330	11,597	12,899	13,661	13,455	3,500	3,743
Total IBNR	$ (1,000)
Number of Reported Claims | Claim	195
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 11,062	11,009	10,387	10,213	9,875	3,490	$ 0
Global Reinsurance | 2011
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	72,667	73,042	73,511	74,131	50,832	39,678
Total IBNR	$ (461)
Number of Reported Claims | Claim	766
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 72,094	71,954	71,677	71,010	43,342	$ 4,160
Global Reinsurance | 2012
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	114,728	89,053	94,766	103,183	108,790
Total IBNR	$ 531
Number of Reported Claims | Claim	1,419
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 111,681	84,533	83,183	77,077	$ 37,644
Global Reinsurance | 2013
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	104,913	101,703	119,012	112,735
Total IBNR	$ 3,973
Number of Reported Claims | Claim	1,185
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 98,271	90,567	82,558	$ 53,375
Global Reinsurance | 2014
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	121,535	141,108	120,479
Total IBNR	$ 9,825
Number of Reported Claims | Claim	920
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 105,505	119,136	$ 66,249
Global Reinsurance | 2015
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	91,098	99,874
Total IBNR	$ 11,623
Number of Reported Claims | Claim	680
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 64,316	$ 41,620
Global Reinsurance | 2016
Claims Development [Line Items]
Loss and ALAE, Net of Reinsurance	88,192
Total IBNR	$ 38,785
Number of Reported Claims | Claim	335
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 36,253

Summary of Reconciliation of Ne

Summary of Reconciliation of Net Incurred and Paid Claims Development to the Reserve for Losses and LAE (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total Net reserves	$ 1,454,728
Reinsurance recoverables on unpaid claims	779,276
Total Gross reserves	2,234,004
Unallocated claims adjustment expenses	55,444
Other	279
Total gross liability for unpaid claims and claim adjustment expense	2,289,727	$ 2,202,644	$ 2,159,634
U.S.Insurance | Marine
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total Net reserves	106,288
Reinsurance recoverables on unpaid claims	83,988
Total Gross reserves	190,276
U.S.Insurance | Property Casualty
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total Net reserves	769,399
Reinsurance recoverables on unpaid claims	409,648
Total Gross reserves	1,179,047
U.S.Insurance | Professional Liability
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total Net reserves	91,037
Reinsurance recoverables on unpaid claims	59,938
Total Gross reserves	150,975
International Insurance | Marine
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total Net reserves	196,532
Reinsurance recoverables on unpaid claims	88,900
Total Gross reserves	285,432
International Insurance | Property Casualty
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total Net reserves	81,189
Reinsurance recoverables on unpaid claims	79,548
Total Gross reserves	160,737
International Insurance | Professional Liability
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total Net reserves	98,689
Reinsurance recoverables on unpaid claims	52,518
Total Gross reserves	151,207
Global Reinsurance
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items]
Total Net reserves	111,594
Reinsurance recoverables on unpaid claims	4,736
Total Gross reserves	$ 116,330

Ceded Reinsurance - Additional

Ceded Reinsurance - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Effects of Reinsurance [Line Items]
Policyholders' surplus for reinsurance	$ 500,000
Reinsurance rating description	A reinsurer generally must have a rating from A.M. Best and/or S&P of “A” or better, or an equivalent financial strength if not rated, plus at least $500 million in policyholders’ surplus to meet our standards of acceptability.
Reserve for uncollectible reinsurance amount	$ 12,100	$ 6,900
Collateral Held	151,708
Ceded Balances Payable
Effects of Reinsurance [Line Items]
Collateral Held	109,000
Letter of Credit
Effects of Reinsurance [Line Items]
Collateral Held	39,700
All Others
Effects of Reinsurance [Line Items]
Collateral Held	$ 3,000

Lists of 10 Largest Reinsurers

Lists of 10 Largest Reinsurers Measured by Reinsurance Recoverable (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		$ 213,377	$ 232,588
Reinsurance Recoverables Paid/Unpaid Losses	[1]	861,858
Reinsurance Recoverables Total		1,075,235
Collateral Held		151,708
National Indemnity Company | AM Best, A++ Rating | Standard & Poor's, AA+ Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		7,467
Reinsurance Recoverables Paid/Unpaid Losses	[1]	98,759
Reinsurance Recoverables Total		106,226
Collateral Held		$ 3,183
National Indemnity Company | AM Best, A++ Rating | AM Best | Standard & Poor's, AA+ Rating
Ceded Credit Risk [Line Items]
Rating		A++
National Indemnity Company | AM Best, A++ Rating | Standard & Poor's | Standard & Poor's, AA+ Rating
Ceded Credit Risk [Line Items]
Rating		AA+
Everest Reinsurance Company | AM Best, A+ Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		$ 25,321
Reinsurance Recoverables Paid/Unpaid Losses	[1]	82,154
Reinsurance Recoverables Total		107,475
Collateral Held		$ 6,571
Everest Reinsurance Company | AM Best, A+ Rating | AM Best | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Rating		A+
Everest Reinsurance Company | AM Best, A+ Rating | Standard & Poor's | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Rating		A+
Swiss Reinsurance America Corporation | AM Best, A+ Rating | Standard & Poor's, AA- Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		$ 22,442
Reinsurance Recoverables Paid/Unpaid Losses	[1]	77,199
Reinsurance Recoverables Total		99,641
Collateral Held		$ 6,440
Swiss Reinsurance America Corporation | AM Best, A+ Rating | AM Best | Standard & Poor's, AA- Rating
Ceded Credit Risk [Line Items]
Rating		A+
Swiss Reinsurance America Corporation | AM Best, A+ Rating | Standard & Poor's | Standard & Poor's, AA- Rating
Ceded Credit Risk [Line Items]
Rating		AA-
Transatlantic Reinsurance Company | AM Best, A+ Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		$ 7,669
Reinsurance Recoverables Paid/Unpaid Losses	[1]	53,347
Reinsurance Recoverables Total		61,016
Collateral Held		$ 2,494
Transatlantic Reinsurance Company | AM Best, A+ Rating | AM Best | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Rating		A+
Transatlantic Reinsurance Company | AM Best, A+ Rating | Standard & Poor's | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Rating		A+
Munich Reinsurance America Inc | AM Best, A+ Rating | Standard & Poor's, AA- Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		$ 8,959
Reinsurance Recoverables Paid/Unpaid Losses	[1]	50,612
Reinsurance Recoverables Total		59,571
Collateral Held		$ 3,477
Munich Reinsurance America Inc | AM Best, A+ Rating | AM Best | Standard & Poor's, AA- Rating
Ceded Credit Risk [Line Items]
Rating		A+
Munich Reinsurance America Inc | AM Best, A+ Rating | Standard & Poor's | Standard & Poor's, AA- Rating
Ceded Credit Risk [Line Items]
Rating		AA-
Allied World Reinsurance | AM Best, A Rating | Standard & Poor's, A Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		$ 6,319
Reinsurance Recoverables Paid/Unpaid Losses	[1]	35,931
Reinsurance Recoverables Total		42,250
Collateral Held		$ 1,575
Allied World Reinsurance | AM Best, A Rating | AM Best | Standard & Poor's, A Rating
Ceded Credit Risk [Line Items]
Rating		A
Allied World Reinsurance | AM Best, A Rating | Standard & Poor's | Standard & Poor's, A Rating
Ceded Credit Risk [Line Items]
Rating		A
Employers Mutual Casualty Company | AM Best, A Rating | Standard & Poor's, Not Rated
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		$ 8,856
Reinsurance Recoverables Paid/Unpaid Losses	[1]	32,687
Reinsurance Recoverables Total		41,543
Collateral Held		$ 5,551
Employers Mutual Casualty Company | AM Best, A Rating | AM Best | Standard & Poor's, Not Rated
Ceded Credit Risk [Line Items]
Rating		A
Employers Mutual Casualty Company | AM Best, A Rating | Standard & Poor's | Standard & Poor's, Not Rated
Ceded Credit Risk [Line Items]
Rating		NR
Aspen Insurance UK Ltd. | AM Best, A Rating | Standard & Poor's, A Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		$ 11,281
Reinsurance Recoverables Paid/Unpaid Losses	[1]	22,737
Reinsurance Recoverables Total		34,018
Collateral Held		$ 5,452
Aspen Insurance UK Ltd. | AM Best, A Rating | AM Best | Standard & Poor's, A Rating
Ceded Credit Risk [Line Items]
Rating		A
Aspen Insurance UK Ltd. | AM Best, A Rating | Standard & Poor's | Standard & Poor's, A Rating
Ceded Credit Risk [Line Items]
Rating		A
Ace Property and Casualty Insurance Company | AM Best, A++ Rating | Standard & Poor's, AA Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		$ 10,192
Reinsurance Recoverables Paid/Unpaid Losses	[1]	22,352
Reinsurance Recoverables Total		32,544
Collateral Held		$ 2,722
Ace Property and Casualty Insurance Company | AM Best, A++ Rating | AM Best | Standard & Poor's, AA Rating
Ceded Credit Risk [Line Items]
Rating		A++
Ace Property and Casualty Insurance Company | AM Best, A++ Rating | Standard & Poor's | Standard & Poor's, AA Rating
Ceded Credit Risk [Line Items]
Rating		AA
Partner Reinsurance Europe | AM Best, A Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		$ 6,868
Reinsurance Recoverables Paid/Unpaid Losses	[1]	20,681
Reinsurance Recoverables Total		27,549
Collateral Held		$ 25,045
Partner Reinsurance Europe | AM Best, A Rating | AM Best | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Rating		A
Partner Reinsurance Europe | AM Best, A Rating | Standard & Poor's | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Rating		A+
Insurance Companies
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		$ 115,374
Reinsurance Recoverables Paid/Unpaid Losses	[1]	496,459
Reinsurance Recoverables Total		611,833
Collateral Held		62,510
All Others
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		98,003
Reinsurance Recoverables Paid/Unpaid Losses	[1]	365,399
Reinsurance Recoverables Total		463,402
Collateral Held		$ 89,198
[1]	Net of reserve for uncollectible reinsurance of approximately $12.1 million.

Lists of 10 Largest Reinsurer66

Lists of 10 Largest Reinsurers Measured by Reinsurance Recoverable (Parenthetical) (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Insurance [Abstract]
Reserve for uncollectible reinsurance amount	$ 12.1	$ 6.9

Summary of Components of Net Wr

Summary of Components of Net Written Premium (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Insurance [Abstract]
Direct									$ 1,403,865	$ 1,277,728	$ 1,232,012
Assumed									165,046	175,774	200,341
Ceded written premiums									(382,687)	(409,642)	(432,215)
Net written premiums	$ 282,868	$ 277,001	$ 306,535	$ 319,820	$ 244,719	$ 251,939	$ 258,244	$ 288,958	$ 1,186,224	$ 1,043,860	$ 1,000,138

Summary of Components of Net Ea

Summary of Components of Net Earned Premium (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Insurance [Abstract]
Direct									$ 1,330,265	$ 1,223,840	$ 1,183,120
Assumed									171,978	175,153	193,431
Ceded									(401,898)	(414,906)	(440,656)
Net earned premiums	$ 283,985	$ 284,010	$ 267,992	$ 264,358	$ 251,545	$ 254,082	$ 242,328	$ 236,132	$ 1,100,345	$ 984,087	$ 935,895

Summary of Components of Net Lo

Summary of Components of Net Losses and Loss Adjustment Expenses Incurred (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Insurance [Abstract]
Direct									$ 795,414	$ 703,361	$ 657,059
Assumed									87,995	97,947	118,352
Ceded									(217,961)	(228,710)	(230,182)
Net losses and LAE	$ 172,493	$ 172,793	$ 167,206	$ 152,956	$ 153,881	$ 146,546	$ 141,973	$ 130,198	$ 665,448	$ 572,598	$ 545,229

Debt - Additional Information (

Debt - Additional Information (Detail) £ in Millions	Nov. 07, 2016USD ($)Tranche	Nov. 04, 2016AUD	Oct. 04, 2013USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2016AUD	Dec. 31, 2016GBP (£)	Nov. 07, 2016GBP (£)Tranche	Nov. 04, 2016GBP (£)	Dec. 31, 2015USD ($)
Line of Credit Facility [Line Items]
Issuance of new letters of credit, expiry date				Dec. 31, 2018
Line of credit facility, covenant terms				The Bilateral and Club Facilities contain 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. These credit facilities also provide 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 our subsidiaries, the occurrence of certain material judgments, or a change in control of our Company. As of December 31, 2016, our Company was in compliance with all covenants.
Senior Notes
Line of Credit Facility [Line Items]
Unamortized discount				$ 1,300,000					$ 1,400,000
Club Facility
Line of Credit Facility [Line Items]
Number of tranches | Tranche	2						2
Club Facility | Minimum
Line of Credit Facility [Line Items]
Credit facility fee rate	0.95%
Club Facility | Maximum
Line of Credit Facility [Line Items]
Credit facility fee rate	1.60%
Bilateral Facility
Line of Credit Facility [Line Items]
Line of credit facility	$ 25,000,000
Additional extended term	2 years
Bilateral Facility | Minimum
Line of Credit Facility [Line Items]
Credit facility fee rate	0.85%
Bilateral Facility | Maximum
Line of Credit Facility [Line Items]
Credit facility fee rate	1.20%
Syndicate 1,221
Line of Credit Facility [Line Items]
Aggregate face amount of letters of credit outstanding | AUD					AUD 14,000,000
Line of credit facility, covenant compliance				As of December 31, 2016, our Company was in compliance with all covenants.
Syndicate 1221 | Line of Credit
Line of Credit Facility [Line Items]
Line of credit facility, interest rate		1.25%
Lloyd's | Syndicate 1221
Line of Credit Facility [Line Items]
Line of credit facility, underwriting reserve required | £								£ 75
Lloyd's | Syndicate 1221 | Club Facility
Line of Credit Facility [Line Items]
Aggregate face amount of letters of credit outstanding				$ 125,000,000		£ 60
Cash collateral posted				1,100,000
Lloyd's | Syndicate 1221 | Bilateral Facility
Line of Credit Facility [Line Items]
Aggregate face amount of letters of credit outstanding				$ 0
Credit Facility | Syndicate 1221
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing amount | AUD		AUD 14,000,000
Tranche One Extending | Club Facility
Line of Credit Facility [Line Items]
Line of credit, commitment	$ 140,000,000
Tranche Two Extending | Club Facility
Line of Credit Facility [Line Items]
Line of credit, commitment | £							£ 60
5.75% Senior Notes
Line of Credit Facility [Line Items]
Interest rate stated on senior notes				5.75%	5.75%	5.75%
Senior notes due date				Oct. 15, 2023
5.75% Senior Notes | Senior Notes
Line of Credit Facility [Line Items]
Principal amount of senior notes			$ 265,000,000
Interest rate stated on senior notes			5.75%
Net proceeds from issuance of senior notes			$ 263,300,000
Debt instrument, covenant compliance				As of December 31, 2016, our Company was in compliance with all such covenants
7.0% Senior Notes | Senior Notes
Line of Credit Facility [Line Items]
Interest rate stated on senior notes				7.00%	7.00%	7.00%
Senior notes due date				May 1, 2016
Call premium on redemption of Senior notes				$ 17,900,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loss Contingencies [Line Items]
Rent expense		$ 13.2	$ 12.9	$ 13.2
Incentive awarded to the company by the State of Connecticut, total	$ 9				$ 11.5
Incentive awarded to the company by the State of Connecticut, non-interest bearing loans	7				8
Incentive awarded to the company by the State of Connecticut, grants	2				$ 3.5
Non-interest bearing incentive loan term		10 years
Forgiveness awarded to the company by the state of Connecticut	6
Incentive awarded to the company by the State of Connecticut, revenue recognized		$ 1.4	1.4	$ 1.1
Incentive awarded to the company by the State of Connecticut, deferred revenue	$ 4.8	$ 4.8	$ 6.3
Maximum
Loss Contingencies [Line Items]
Non-cancellable operating leases expiration year		2,030

Future Minimum Annual Rental Co

Future Minimum Annual Rental Commitments Under Various Non-cancellable Operating Leases (Detail) $ in Thousands	Dec. 31, 2016USD ($)
Leases [Abstract]
2,017	$ 13,024
2,018	11,843
2,019	9,107
2,020	8,945
2,021	7,684
2022-2030	38,267
Total minimum operating lease payments	$ 88,870

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Undistributed earnings of non-U.S. subsidiaries	$ 156,600,000
Taxes payable on undistributed earnings	2,700,000
Unrecognized tax benefits	0	$ 0	$ 0
Interest or penalties related to unrecognized tax benefits	0	0	$ 0
Deferred Tax Assets: State and Local	$ 699,000	$ 721,000
United Kingdom
Income Taxes [Line Items]
Foreign effective income tax rate	35.00%
United Kingdom | Syndicate 1221 | Maximum
Income Taxes [Line Items]
Percentage of premiums	50.00%
United Kingdom | Syndicate 1221 | Minimum
Income Taxes [Line Items]
Foreign effective income tax rate	35.00%
State and Local Jurisdiction | Maximum
Income Taxes [Line Items]
State and local tax carry-forwards expiration year	2,034
State and Local Jurisdiction | Minimum
Income Taxes [Line Items]
State and local tax carry-forwards expiration year	2,026

Components of Current and Defer

Components of Current and Deferred Income Tax Expense (Benefit) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current income tax expense (benefit):
Federal and foreign									$ 39,900	$ 27,937	$ 27,290
State and local									638	1,476	1,036
Subtotal									40,538	29,413	28,326
Deferred income tax expense (benefit):
Federal and foreign									(5,755)	7,004	16,881
State and local									0	0	0
Subtotal									(5,755)	7,004	16,881
Actual tax expense and rate	$ 9,866	$ 7,875	$ 7,053	$ 9,989	$ 6,072	$ 8,723	$ 9,195	$ 12,427	$ 34,783	$ 36,417	$ 45,207

Reconciliation of Total Income

Reconciliation of Total Income Taxes Applicable to Pre-Tax Operating Income and Amounts Computed by Applying Federal Statutory Income Tax Rate to Pre-Tax Operating Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation
Computed expected tax expense									$ 41,128	$ 41,116	$ 49,187
Tax-exempt interest									(4,559)	(4,987)	(4,771)
Dividends received deduction									(3,812)	(2,086)	(1,257)
Proration of DRD and Tax-exempt interest									1,256	1,061	904
Current state and local income taxes, net of federal income tax deduction									415	959	674
Other									355	354	470
Actual tax expense and rate	$ 9,866	$ 7,875	$ 7,053	$ 9,989	$ 6,072	$ 8,723	$ 9,195	$ 12,427	$ 34,783	$ 36,417	$ 45,207
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation
Computed expected tax expense									35.00%	35.00%	35.00%
Tax-exempt interest									(3.90%)	(4.20%)	(3.40%)
Dividends received deduction									(3.20%)	(1.80%)	(0.90%)
Proration of DRD and Tax-exempt interest									1.10%	0.90%	0.60%
Current state and local income taxes, net of federal income tax deduction									0.40%	0.80%	0.50%
Other									0.20%	0.30%	0.40%
Actual tax expense and rate									29.60%	31.00%	32.20%

Tax Effects of Temporary Differ

Tax Effects of Temporary Differences That Give Rise to Federal, Foreign, State and Local Deferred Tax Assets and Deferred Tax Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Loss reserve discount	$ 25,420	$ 25,353
Unearned premiums	33,886	31,486
Compensation related	15,288	11,175
State and local net deferred tax assets	699	721
Net currency translation adjustments	5,363	346
Other	3,618	3,969
Total gross deferred tax assets	84,274	73,050
Less: Valuation allowance	(699)	(721)
Total deferred tax assets	83,575	72,329
Deferred tax liabilities:
Net unrealized gains/losses on securities	(10,142)	(13,053)
Deferred acquisition costs	(29,401)	(24,037)
Net unrealized foreign exchange	(3,575)	(4,164)
Other	(4,048)	(2,709)
Total deferred tax liabilities	(62,637)	(68,429)
Net deferred income tax asset (liability)	20,938	3,900
Lloyd's
Deferred tax liabilities:
Lloyd's year of account deferral	$ (15,471)	$ (24,466)

Stockholders Equity - Additiona

Stockholders Equity - Additional Information (Detail) $ / shares in Units, $ in Millions	Feb. 16, 2017	Jan. 20, 2017	Dec. 30, 2016shares	Dec. 29, 2016$ / shares	Dec. 06, 2016	Sep. 30, 2016$ / shares	Jul. 15, 2016$ / shares	Nov. 30, 2015USD ($)	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)$ / sharesshares
Stockholders Equity [Line Items]
Common stock, authorized shares | shares									50,000,000	50,000,000
Common stock, par value									$ 0.10	$ 0.10
Preferred stock, authorized shares | shares									1,000,000	1,000,000
Preferred stock, par value									$ 0.10	$ 0.10
Stock split ratio					2
Stockholders equity, stock split					On December 6, 2016, our Board of Directors declared a two-for-one stock split of The Navigators Group, Inc. Common stock, to be effected in the form of a stock dividend.
Number of additional shares for every share held | shares			1
Undistributed Profit | $								$ 141.9
Dividend Capacity | $									$ 3
Navigators Insurance Company
Stockholders Equity [Line Items]
Maximum amount available for payment of dividends without prior regulatory approval | $									102.7
Dividend paid | $									$ 5	$ 0
Installment 1 - FY 2016
Stockholders Equity [Line Items]
Common stock dividend paid per share							$ 0.045
Cash Dividend Paid Date									Jul. 15, 2016
Dividend payable record date									Jun. 20, 2016
Installment 2 - FY 2016
Stockholders Equity [Line Items]
Common stock dividend paid per share						$ 0.045
Cash Dividend Paid Date									Sep. 30, 2016
Dividend payable record date									Aug. 19, 2016
Installment 3 - FY 2016
Stockholders Equity [Line Items]
Common stock dividend paid per share				$ 0.045
Cash Dividend Paid Date									Dec. 29, 2016
Dividend payable record date									Nov. 18, 2016
Subsequent Event [Member]
Stockholders Equity [Line Items]
Stock split ratio		2
Stockholders equity, stock split		We completed a two-for-one stock split on January 20, 2017.
Dividend payable record date	Mar. 3, 2017

Changes in Issued and Outstandi

Changes in Issued and Outstanding Common Shares (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity [Abstract]
Beginning balance	28,862,000	28,562,000	28,396,000
Vested stock grants	220,000	254,000	118,000
Employee stock purchase plan	41,224	41,714	38,000
Stock options exercised		1,500	5,250
Ending balance	29,124,000	28,862,000	28,562,000

Amount and Nature of Net Assets

Amount and Nature of Net Assets Restricted from Payment of Dividends (Detail) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets		$ 533,930	$ 541,023
NIC and NSIC
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	[1]	18,148	17,775
NIC and NSIC | Fixed maturities
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets		10,690	11,277
NIC and NSIC | Short-term investments
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets		290	290
NIC and NSIC | Cash
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets		7,168	6,208
NHUK
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	[2]	515,782	523,248
NHUK | Fixed maturities
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets		452,053	448,666
NHUK | Short-term investments
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets		$ 63,729	71,320
NHUK | Cash
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets			$ 3,262
[1]	The restricted net assets for NIC and NSIC primarily consist of fixed maturities on deposit with various state insurance departments. The cash as of December 31, 2016 and 2015, as presented in the table above, was on deposit with a U.K. bank to comply with the regulatory requirements of the Prudential Regulation Authority for the underwriting activities of the U.K. Branch.
[2]	The restricted net assets for NHUK consists of fixed maturities and cash held in trust for the benefit of syndicate policyholders and short term investments primarily consisting of overseas deposits in various countries with Lloyd's to support underwriting activities in those countries.

Amount and Nature of Net Asse80

Amount and Nature of Net Assets Restricted from Payment of Dividends (Parenthetical) (Detail) - Fixed maturities - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
NIC and NSIC
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Restricted net assets, amortized cost	$ 9,820	$ 9,950
NHUK
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Restricted net assets, amortized cost	$ 457,225	$ 458,558

Reconciliation of Basic and Dil

Reconciliation of Basic and Diluted Earnings per Share Computations (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended																12 Months Ended
		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Earning Per Share Basic And Diluted [Abstract]
Net income		$ 21,591		$ 22,013		$ 16,190		$ 22,932		$ 17,743		$ 18,201		$ 19,184		$ 25,929		$ 82,726		$ 81,057		$ 95,329
Basic weighted average shares	[1]																	29,073,803		28,785,044		28,519,536
Effect of common stock equivalents:
Assumed exercise of stock options and vesting of stock grants																		957,806		866,446		773,202
Diluted weighted average shares																		30,031,609		29,651,490		29,292,738
Net income per common share:
Basic		$ 0.74	[1]	$ 0.76	[1]	$ 0.56	[1]	$ 0.79	[1]	$ 0.62	[2]	$ 0.63	[2]	$ 0.67	[2]	$ 0.90	[2]	$ 2.85	[1]	$ 2.82	[1]	$ 3.34	[1]
Diluted		$ 0.71	[1]	$ 0.73	[1]	$ 0.54	[1]	$ 0.77	[1]	$ 0.59	[2]	$ 0.61	[2]	$ 0.65	[2]	$ 0.89	[2]	$ 2.75	[1]	$ 2.73	[1]	$ 3.25	[1]
[1]	We completed a two-for-one stock split on January 20, 2017. All share and per share data has been retroactively restated on a post-split basis.
[2]	We completed a two-for-one stock split on January 20, 2017. All per share data has been retroactively restated on a post-split basis.

Reconciliation of Basic and D82

Reconciliation of Basic and Diluted Earnings per Share Computations (Parenthetical) (Detail)	Jan. 20, 2017	Dec. 06, 2016
Earnings Per Share Disclosure [Line Items]
Stock split ratio		2
Stockholders equity, stock split		On December 6, 2016, our Board of Directors declared a two-for-one stock split of The Navigators Group, Inc. Common stock, to be effected in the form of a stock dividend.
Subsequent Event [Member]
Earnings Per Share Disclosure [Line Items]
Stock split ratio	2
Stockholders equity, stock split	We completed a two-for-one stock split on January 20, 2017.

Summary of Statutory Net Income

Summary of Statutory Net Income (Loss) and Capital and Surplus (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
NIC and NSIC
Statutory Accounting Practices [Line Items]
Net income	$ 84.2	$ 60.8	$ 75.7
Capital and surplus	1,027.3	949.1	893.9
Syndicate
Statutory Accounting Practices [Line Items]
Net income	46.3	41	33.8
Capital and surplus	$ 180.7	$ 177.5	$ 140.1

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of employees base compensation that can be invested for the purchase of common stock, maximum	10.00%
Number of shares which can be acquired by employee, maximum	1,000
Total market value of shares that can be acquired by employee	$ 25,000
Employee Stock Purchase Plan, shares purchased by employees	41,224	41,714	38,000
Discount on employee stock purchase plan	10.00%
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price as percentage of fair market value	90.00%
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, net of estimated forfeitures	$ 22,300,000	$ 17,300,000
Weighted Average Periods	1 year 9 months 18 days	2 years
Aggregate fair value of all unvested RSU	$ 87,200,000	$ 55,200,000
Minimum | Options and Non Performance Based Grants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award, award vesting period	3 years
Minimum | Performance Based Shares Issued in 2016, 2015 and 2014 | Third Anniversary of Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	50.00%
Maximum | Options and Non Performance Based Grants
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
Maximum | Performance Based Shares Issued in 2016, 2015 and 2014 | Third Anniversary of Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	150.00%
Second Amended and Restated 2005 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock authorized for issuance	2,000,000
Stock issued during period under incentive plan	1,531,058
Number of stock available to be issued	468,942

Unvested Restricted Stock Units

Unvested Restricted Stock Units and Performance Units Grants Outstanding (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance	1,393,030	1,437,784	1,253,624
Granted	488,946	434,416	576,260
Vested	(340,208)	(407,360)	(367,432)
Forfeited	(167,604)	(71,810)	(24,668)
Ending balance	1,374,164	1,393,030	1,437,784
Performance Based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	404,946	370,100	457,214
Vested	(285,208)	(136,160)	(186,906)
Non Performance Based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	84,000	64,316	119,046
Vested	(55,000)	(271,200)	(180,526)

Stock Options Outstanding (Deta

Stock Options Outstanding (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Number of Shares
Beginning balance	1,500	6,750
Granted	0	0
Exercised	(1,500)	(5,250)
Expired or forfeited	0	0
Ending balance		1,500
Number of options exercisable		1,500
Average Exercise Price
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Beginning of Period	$ 36.03	$ 30.65
Granted	0	0
Exercised	36.03	29.11
Expired or forfeited	$ 0	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, End of Period		36.03
Number of options exercisable		$ 36.03

Retirement Plans - Additional I

Retirement Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
401(k) plan expense	$ 7.4	$ 6.3	$ 7.5
Defined Contribution Plan, employer discretionary matching contribution amount			1.6
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
401(k) plan expense	2.9	$ 2.9	2.6
United Kingdom | Employees hired prior to November 2014
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay		15.00%
United Kingdom | Employees hired after November 2014
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay		12.00%
European Offices
Defined Benefit Plan Disclosure [Line Items]
401(k) plan expense	$ 0.5	$ 0.5	0.2
European Offices | Minimum
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	2.10%
European Offices | Maximum
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	26.00%
Retirement Savings Contributions
Defined Benefit Plan Disclosure [Line Items]
401(k) plan expense	$ 4.2	3.8	3.8
Non Discretionary Matching Contributions
Defined Benefit Plan Disclosure [Line Items]
401(k) plan expense	$ 3.2	$ 2.5	$ 2.1

Summary of Condensed Quarterly

Summary of Condensed Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Income Statement [Abstract]
Gross written premiums	$ 367,539		$ 374,930		$ 412,565		$ 413,877		$ 323,509		$ 354,062		$ 379,471		$ 396,460		$ 1,568,911		$ 1,453,502		$ 1,432,353
Revenues:
Net written premiums	282,868		277,001		306,535		319,820		244,719		251,939		258,244		288,958		1,186,224		1,043,860		1,000,138
Change in unearned premiums	1,117		7,009		(38,543)		(55,462)		6,826		2,143		(15,916)		(52,826)		(85,879)		(59,773)		(64,243)
Net earned premiums	283,985		284,010		267,992		264,358		251,545		254,082		242,328		236,132		1,100,345		984,087		935,895
Net investment income	20,107		19,875		19,875		19,594		18,499		17,371		16,595		16,253		79,451		68,718		64,168
Total other-than-temporary impairment losses	21		23		(162)		(109)		(123)		(1,298)		(423)				(227)		(1,870)		137
Portion of loss recognized in other comprehensive income (before tax)	(21)		(23)		12		109		123		23						77		172		(137)
Net other-than-temporary impairment losses recognized in earnings					(150)						(1,275)		(423)				(150)		(1,698)		0
Net realized gains (losses)	4,043		1,586		1,960		1,597		(2,080)		518		4,339		5,596
Other income (expense)	1,905		(183)		4,430		2,549		4,147		(2,518)		(4,362)		2,242		8,701		(491)		10,656
Total revenues	310,040		305,288		294,107		288,098		272,111		268,178		258,477		260,223		1,197,533		1,058,989		1,023,531
Expenses:
Net losses and LAE	172,493		172,793		167,206		152,956		153,881		146,546		141,973		130,198		665,448		572,598		545,229
Commission expenses	44,154		42,611		40,726		37,554		31,339		34,253		31,480		32,905		165,045		129,977		125,528
Other operating expenses	58,076		56,137		59,074		60,809		59,219		56,599		52,789		54,909
Interest expense	3,860		3,859		3,858		3,858		3,857		3,856		3,856		3,855		15,435		15,424		15,413
Total expenses	278,583		275,400		270,864		255,177		248,296		241,254		230,098		221,867		1,080,024		941,515		882,995
Income before income taxes	31,457		29,888		23,243		32,921		23,815		26,924		28,379		38,356		117,509		117,474		140,536
Income tax expense	9,866		7,875		7,053		9,989		6,072		8,723		9,195		12,427		34,783		36,417		45,207
Net income	21,591		22,013		16,190		22,932		17,743		18,201		19,184		25,929		82,726		81,057		95,329
Comprehensive income (loss)	$ (31,712)		$ 18,760		$ 35,228		$ 45,721		$ 15,990		$ 18,849		$ (3,789)		$ 27,052		$ 67,997		$ 58,102		$ 113,528
Combined ratio	96.70%		95.60%		99.60%		95.10%		97.20%		93.40%		93.40%		92.30%		96.70%		94.10%		92.60%
Net income per share:
Basic	$ 0.74	[1]	$ 0.76	[1]	$ 0.56	[1]	$ 0.79	[1]	$ 0.62	[2]	$ 0.63	[2]	$ 0.67	[2]	$ 0.90	[2]	$ 2.85	[1]	$ 2.82	[1]	$ 3.34	[1]
Diluted	$ 0.71	[1]	$ 0.73	[1]	$ 0.54	[1]	$ 0.77	[1]	$ 0.59	[2]	$ 0.61	[2]	$ 0.65	[2]	$ 0.89	[2]	$ 2.75	[1]	$ 2.73	[1]	$ 3.25	[1]
[1]	We completed a two-for-one stock split on January 20, 2017. All share and per share data has been retroactively restated on a post-split basis.
[2]	We completed a two-for-one stock split on January 20, 2017. All per share data has been retroactively restated on a post-split basis.

Summary of Condensed Quarterl89

Summary of Condensed Quarterly Financial Data (Parenthetical) (Detail)	Jan. 20, 2017	Dec. 06, 2016
Stockholders equity, stock split		On December 6, 2016, our Board of Directors declared a two-for-one stock split of The Navigators Group, Inc. Common stock, to be effected in the form of a stock dividend.
Stock split ratio		2
Subsequent Event [Member]
Stockholders equity, stock split	We completed a two-for-one stock split on January 20, 2017.
Stock split ratio	2

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail)	Feb. 16, 2017$ / shares	Jan. 20, 2017	Jan. 01, 2017	Dec. 30, 2016shares	Dec. 06, 2016
Subsequent Event [Line Items]
Stock split ratio					2
Stockholders equity, stock split					On December 6, 2016, our Board of Directors declared a two-for-one stock split of The Navigators Group, Inc. Common stock, to be effected in the form of a stock dividend.
Number of additional shares for every share held | shares				1
Subsequent Event [Member]
Subsequent Event [Line Items]
Stock split ratio		2
Stockholders equity, stock split		We completed a two-for-one stock split on January 20, 2017.
Dividend declaration date	Feb. 16, 2017
Common stock dividend declared per share | $ / shares	$ 0.045
Dividend payable date	Mar. 24, 2017
Dividend payable record date	Mar. 3, 2017
Percentage of ownership interest sold			100.00%
Subsequent Event [Member] | North American Property Business
Subsequent Event [Line Items]
Reinsurance arrangement			100.00%

Summary of Consolidated Inves91

Summary of Consolidated Investments-Other Than Investments in Related Parties (Detail) - USD ($) $ in Thousands		Dec. 31, 2016		Dec. 31, 2015
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments		$ 3,128,563		$ 2,937,226
Gross Unrealized Gains		59,175		66,693
Gross Unrealized Losses		(30,199)		(29,398)
Amortized Cost		3,099,587		2,899,931
Fixed maturities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments		2,635,882	[1]	2,414,210
Gross Unrealized Gains		32,071		40,350
Gross Unrealized Losses		(24,414)		(26,385)
Amortized Cost		2,628,225		2,400,245
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments		273,776	[1]	252,882
Gross Unrealized Gains		2,192		2,273
Gross Unrealized Losses		(5,128)		(9,214)
Amortized Cost		276,712		259,823
Fixed maturities | States, municipalities and political subdivisions
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments		547,415	[1]	576,859
Gross Unrealized Gains		11,542		21,233
Gross Unrealized Losses		(4,036)		(781)
Amortized Cost		539,909		556,407
Fixed maturities | Agency mortgage-backed securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments		487,364	[1]	379,269
Gross Unrealized Gains		4,016		5,573
Gross Unrealized Losses		(6,585)		(2,082)
Amortized Cost		489,933		375,778
Fixed maturities | Residential Mortgage Backed Securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments		20,530	[1]	30,465
Gross Unrealized Gains		453		694
Gross Unrealized Losses		(55)		(82)
Amortized Cost		20,132		29,853
Fixed maturities | Asset-backed securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments		314,601	[1]	225,012
Gross Unrealized Gains		824		85
Gross Unrealized Losses		(1,178)		(1,624)
Amortized Cost		314,955		226,551
Fixed maturities | Commercial mortgage-backed securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments		154,139	[1]	189,713
Gross Unrealized Gains		2,859		3,119
Gross Unrealized Losses		(1,904)		(1,864)
Amortized Cost		153,184		188,458
Fixed maturities | Mortgage-backed and asset-backed securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments		976,634	[1]	824,459
Gross Unrealized Gains		8,152		9,471
Gross Unrealized Losses		(9,722)		(5,652)
Amortized Cost		978,204		820,640
Fixed maturities | Corporate bonds
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments		838,057	[1]	760,010
Gross Unrealized Gains		10,185		7,373
Gross Unrealized Losses		(5,528)		(10,738)
Amortized Cost		833,400		763,375
Equity Securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments		349,142	[1]	305,271
Gross Unrealized Gains		27,016		26,341
Gross Unrealized Losses		(5,785)		(3,013)
Amortized Cost		327,911		281,943
Short-term investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments		143,539	[1]	217,745
Gross Unrealized Gains		88		2
Amortized Cost		143,451		$ 217,743
Investment Including Other Invested Assets
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments	[1]	3,130,523
Gross Unrealized Gains		59,175
Gross Unrealized Losses		(30,199)
Amortized Cost		3,101,547
Other Invested Assets
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments	[1]	1,960
Amortized Cost		$ 1,960
[1]	Other invested assets are accounted for using the equity method of accounting. All other investments are shown at fair value.

Condensed Financial Informati92

Condensed Financial Information - Balance Sheets (Detail) - USD ($) $ in Thousands		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2013
ASSETS
Investments		$ 3,130,523		$ 2,937,226
Cash		64,643		69,901		$ 90,751	$ 86,509
Investments in subsidiaries		1,960
Goodwill and other intangible assets		6,451		6,807
Other assets		52,030		67,643
Total assets		4,814,037		4,584,012
Liabilities:
Reserves for losses and loss adjustment expenses		2,289,727		2,202,644		2,159,634
Unearned premiums		887,344		820,676
Reinsurance balances payable		108,980		107,411
Senior notes		263,728		263,580
Accounts payable and other liabilities		86,070		93,553
Total liabilities		3,635,849		3,487,864
Stockholders' equity:
Preferred stock, $.10 par value, authorized 1,000,000 shares, none issued	[1]
Common stock, $.10 par value, authorized 50,000,000 shares, issued 36,146,899 shares for 2016 and 35,884,538 shares for 2015	[1]	3,612		3,586
Additional paid-in capital	[1]	373,983		356,036
Treasury stock, at cost (7,022,760 shares for 2016 and 2015)	[1]	(155,801)		(155,801)
Retained earnings	[1]	947,519		868,723
Accumulated other comprehensive income:
Total stockholders' equity		1,178,188	[1]	1,096,148	[1]	1,027,224	902,212
Total liabilities and stockholders' equity		4,814,037		4,584,012
Parent Company
ASSETS
Investments		1,660		89,586
Cash		11,003		6,417		$ 6,300	$ 6,143
Investments in subsidiaries		1,381,652		1,232,012
Goodwill and other intangible assets		2,534		2,534
Other assets		49,588		33,647
Total assets		1,446,437		1,364,196
Liabilities:
Senior notes		263,728		263,580
Accounts payable and other liabilities		1,347		1,294
Accrued interest payable		3,174		3,174
Total liabilities		268,249		268,048
Stockholders' equity:
Preferred stock, $.10 par value, authorized 1,000,000 shares, none issued	[2]
Common stock, $.10 par value, authorized 50,000,000 shares, issued 36,146,899 shares for 2016 and 35,884,538 shares for 2015	[2]	3,612		3,586
Additional paid-in capital	[2]	373,983		356,036
Treasury stock, at cost (7,022,760 shares for 2016 and 2015)	[2]	(155,801)		(155,801)
Retained earnings	[2]	947,519		868,723
Accumulated other comprehensive income:
Net unrealized gains (losses) on securities available-for-sale, net of tax	[2]	8,882		23,611
Foreign currency translation adjustment, net of tax	[2]	(7)		(7)
Total stockholders' equity	[2]	1,178,188		1,096,148
Total liabilities and stockholders' equity		$ 1,446,437		$ 1,364,196
[1]	We completed a two-for-one stock split on January 20, 2017. All per share data has been retroactively restated on a post-split basis.
[2]	We completed a two-for-one stock split on January 20, 2017. All share and per share data has been retroactively restated on a post-split basis.

Condensed Financial Informati93

Condensed Financial Information - Balance Sheets (Parenthetical) (Detail)	Jan. 20, 2017	Dec. 06, 2016	Dec. 31, 2016$ / sharesshares	Dec. 31, 2015$ / sharesshares
Condensed Financial Statements Captions [Line Items]
Preferred stock, par value | $ / shares			$ 0.10	$ 0.10
Preferred stock, authorized shares			1,000,000	1,000,000
Preferred stock, issued shares			0	0
Common stock, par value | $ / shares			$ 0.10	$ 0.10
Common stock, authorized shares			50,000,000	50,000,000
Common stock, issued shares			36,146,899	35,884,538
Treasury stock, shares			7,022,760	7,022,760
Stock split ratio		2
Stockholders equity, stock split		On December 6, 2016, our Board of Directors declared a two-for-one stock split of The Navigators Group, Inc. Common stock, to be effected in the form of a stock dividend.
Subsequent Event [Member]
Condensed Financial Statements Captions [Line Items]
Stock split ratio	2
Stockholders equity, stock split	We completed a two-for-one stock split on January 20, 2017.
Parent Company
Condensed Financial Statements Captions [Line Items]
Preferred stock, par value | $ / shares			$ 10	$ 10
Preferred stock, authorized shares			1,000,000	1,000,000
Preferred stock, issued shares			0	0
Common stock, par value | $ / shares			$ 10	$ 10
Common stock, authorized shares			50,000,000	50,000,000
Common stock, issued shares			36,146,899	35,884,538
Treasury stock, shares			7,022,760	7,022,760
Parent Company | Subsequent Event [Member]
Condensed Financial Statements Captions [Line Items]
Stock split ratio	2
Stockholders equity, stock split	We completed a two-for-one stock split on January 20, 2017.

Condensed Financial Informati94

Condensed Financial Information - Statement of Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues:
Net investment income	$ 20,107	$ 19,875	$ 19,875	$ 19,594	$ 18,499	$ 17,371	$ 16,595	$ 16,253	$ 79,451	$ 68,718	$ 64,168
Total revenues	310,040	305,288	294,107	288,098	272,111	268,178	258,477	260,223	1,197,533	1,058,989	1,023,531
Expenses:
Interest expense	3,860	3,859	3,858	3,858	3,857	3,856	3,856	3,855	15,435	15,424	15,413
Other (income) expense	(1,905)	183	(4,430)	(2,549)	(4,147)	2,518	4,362	(2,242)	(8,701)	491	(10,656)
Total expenses	278,583	275,400	270,864	255,177	248,296	241,254	230,098	221,867	1,080,024	941,515	882,995
Income before income taxes	31,457	29,888	23,243	32,921	23,815	26,924	28,379	38,356	117,509	117,474	140,536
Income tax benefit	9,866	7,875	7,053	9,989	6,072	8,723	9,195	12,427	34,783	36,417	45,207
Net income	$ 21,591	$ 22,013	$ 16,190	$ 22,932	$ 17,743	$ 18,201	$ 19,184	$ 25,929	82,726	81,057	95,329
Parent Company
Revenues:
Net investment income									53	147	76
Total revenues									53	147	76
Expenses:
Interest expense									15,435	15,424	15,413
Other (income) expense									22
Total expenses									15,457	15,424	15,413
Income before income taxes									(15,404)	(15,277)	(15,337)
Income tax benefit									(8,009)	(5,472)	(5,287)
Income (loss) before equity in undistributed net income of wholly owned subsidiaries									(7,395)	(9,805)	(10,050)
Equity in undistributed net income of wholly-owned subsidiaries									$ 90,121	$ 90,862	$ 105,379

Condensed Financial Informati95

Condensed Financial Information - Statement of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities:
Net income	$ 21,591	$ 22,013	$ 16,190	$ 22,932	$ 17,743	$ 18,201	$ 19,184	$ 25,929	$ 82,726	$ 81,057	$ 95,329
Adjustments to reconcile net income to net cash provided by (used in) operations:
Other									22,593	(19,676)	17,532
Net cash provided by (used in) operating activities									224,227	227,624	222,492
Fixed maturities, available-for-sale
Sales									446,666	376,522	362,136
Purchases									(962,419)	(648,059)	(864,902)
Equity securities
Sales									54,798	96,405	54,900
Purchases									(92,329)	(215,405)	(83,845)
Net (increase) decrease in short-term investments									73,541	(38,468)	117,740
Net cash provided by (used in) investing activities									(211,432)	(249,855)	(219,470)
Financing activities:
Proceeds of stock issued from employee stock purchase plan									1,840	1,352	1,067
Proceeds of stock issued from exercise of stock options										29	153
Dividends paid									(3,930)
Net cash provided by (used in) financing activities									(2,090)	1,381	1,220
Change in cash									(5,258)	(20,850)	4,242
Cash at beginning of year				69,901				90,751	69,901	90,751	86,509
Cash at end of period	64,643				69,901				64,643	69,901	90,751
Parent Company
Adjustments to reconcile net income to net cash provided by (used in) operations:
Equity in undistributed net income of wholly-owned subsidiaries									(90,121)	(90,862)	(105,379)
Dividends received from subsidiaries									5,000
Other									379	3,373	9,211
Net cash provided by (used in) operating activities									(2,016)	(6,432)	(839)
Fixed maturities, available-for-sale
Sales										1,250	3,200
Equity securities
Sales									0	0	0
Purchases									0	0	0
Net (increase) decrease in short-term investments									87,942	3,918	(3,424)
Net cash provided by (used in) investing activities									87,942	5,168	(224)
Financing activities:
Capital contribution to subsidiary									(79,250)
Proceeds of stock issued from employee stock purchase plan									1,840	1,352	1,067
Proceeds of stock issued from exercise of stock options										29	153
Dividends paid									(3,930)
Net cash provided by (used in) financing activities									(81,340)	1,381	1,220
Change in cash									4,586	117	157
Cash at beginning of year				$ 6,417				$ 6,300	6,417	6,300	6,143
Cash at end of period	$ 11,003				$ 6,417				$ 11,003	$ 6,417	$ 6,300

Supplementary Insurance Infor96

Supplementary Insurance Information (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs		$ 119,660	$ 91,983	$ 79,452
Reserve for losses and LAE		2,289,727	2,202,644	2,159,634
Unearned premiums		887,344	820,676	766,167
Net earned premiums		1,100,345	984,087	935,895
Net investment income	[1]	79,413	68,571	64,092
Losses and LAE incurred		665,448	572,598	545,229
Amortization of deferred policy acquisition costs	[2]	165,045	129,977	127,695
Other operating expenses	[1]	230,583	220,643	196,825
Net written premiums		1,186,224	1,043,860	1,000,138
NIC, NSIC and Navigators Management Company, Inc.
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs		83,060	67,144	63,200
Reserve for losses and LAE		1,753,630	1,692,886	1,645,984
Unearned premiums		640,210	607,062	579,331
Net earned premiums		798,151	722,749	704,574
Net investment income	[1]	71,044	61,863	56,714
Losses and LAE incurred		482,789	451,296	434,396
Amortization of deferred policy acquisition costs	[2]	108,809	88,597	85,137
Other operating expenses	[1]	162,387	153,194	138,675
Net written premiums		844,987	757,117	752,773
NHUK
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs		36,600	24,839	16,252
Reserve for losses and LAE		536,097	509,758	513,650
Unearned premiums		247,134	213,614	186,836
Net earned premiums		302,194	261,338	231,321
Net investment income	[1]	8,344	6,708	7,378
Losses and LAE incurred		182,659	121,302	110,833
Amortization of deferred policy acquisition costs	[2]	56,236	41,380	42,558
Other operating expenses	[1]	68,152	67,449	58,150
Net written premiums		341,237	$ 286,743	$ 247,365
NIIC
Supplementary Insurance Information, by Segment [Line Items]
Net investment income	[1]	25
Other operating expenses	[1]	$ 44
[1]	Net investment income and Other operating expenses reflect only such amounts attributable to our Company's insurance operations.
[2]	Amortization of deferred policy acquisition costs reflects only such amounts attributable to our Company's insurance operations. A portion of these costs is eliminated in consolidation.

Reinsurance Written Premium (De

Reinsurance Written Premium (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplementary Insurance Information, by Segment [Line Items]
Direct Amount									$ 1,330,265	$ 1,223,840	$ 1,183,120
Ceded to other companies									401,898	414,906	440,656
Assumed from other companies									171,978	175,153	193,431
Net earned premiums	$ 283,985	$ 284,010	$ 267,992	$ 264,358	$ 251,545	$ 254,082	$ 242,328	$ 236,132	1,100,345	984,087	935,895
P&C
Supplementary Insurance Information, by Segment [Line Items]
Direct Amount									1,403,865	1,277,728	1,232,012
Ceded to other companies									382,687	409,642	432,215
Assumed from other companies									165,046	175,774	200,341
Net earned premiums									$ 1,186,224	$ 1,043,860	$ 1,000,138
Percentage of amount assumed to net									14.00%	17.00%	20.00%

Valuation and Qualifying Acco98

Valuation and Qualifying Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for uncollectable reinsurance
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	$ 6,921	$ 11,332	$ 11,332
Charged (Credited) to Costs and Expenses	5,157	(4,411)
Charged to Other Accounts	0	0	0
Deductions (Describe)	0	0	0
Ending Balance	12,078	6,921	11,332
Valuation allowance in deferred taxes
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	721	776	554
Charged (Credited) to Costs and Expenses	(22)	(55)	222
Charged to Other Accounts	0	0	0
Deductions (Describe)	0	0	0
Ending Balance	$ 699	$ 721	$ 776

Supplementary Information Con99

Supplementary Information Concerning P&C Insurance Operations (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Information For Property Casualty Insurance Underwriters [Abstract]
Deferred policy acquisition costs		$ 119,660	$ 91,983	$ 79,452
Reserve for losses and LAE		2,289,727	2,202,644	2,159,634
Unearned premiums		887,344	820,676	766,167
Net earned premiums		1,100,345	984,087	935,895
Net investment income	[1]	79,413	68,571	64,092
Losses and LAE expenses incurred related to Current year		693,976	637,267	601,041
Losses and LAE expenses incurred related to Prior years		(28,528)	(64,669)	(55,812)
Amortization of deferred policy acquisition costs	[2]	165,045	129,977	127,695
Other operating expenses	[1]	230,583	220,643	196,825
Net written premiums		$ 1,186,224	$ 1,043,860	$ 1,000,138
[1]	Net investment income and Other operating expenses reflect only such amounts attributable to our Company's insurance operations.
[2]	Amortization of deferred policy acquisition costs reflects only such amounts attributable to our Company's insurance operations. A portion of these costs is eliminated in consolidation.