Fixed Maturities and Equity Securities by Asset Class that are Measured at Fair Value (Detail) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	$ 1,975,767	$ 1,969,503
Fixed maturities \| U.S. Government Treasury bonds, agency bonds and foreign government bonds \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	100,325	212,933
Fixed maturities \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	100,325	212,933
Equity Securities \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	147,794	87,258
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	248,119	300,191
Fixed maturities \| U.S. Government Treasury bonds, agency bonds and foreign government bonds \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	201,432	111,212
Fixed maturities \| States, municipalities and political subdivisions \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	386,167	392,250
Fixed maturities \| Agency mortgage-backed securities \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	377,465	382,628
Fixed maturities \| Residential Mortgage Backed Securities \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	24,525	20,463
Fixed maturities \| Asset-backed securities \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	49,915	46,093
Fixed maturities \| Commercial mortgage-backed securities \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	215,033	188,178
Fixed maturities \| Mortgage- and asset-backed securities \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	666,938	637,362
Fixed maturities \| Corporate bonds \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	473,111	526,651
Fixed maturities \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	1,727,648	1,667,475
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	1,727,648	1,667,475
Fixed maturities \| Commercial mortgage-backed securities \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value		1,837
Fixed maturities \| Mortgage- and asset-backed securities \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value		1,837
Fixed maturities \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value		1,837
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value		1,837
Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	1,827,973	1,882,245
Fixed maturities \| U.S. Government Treasury bonds, agency bonds and foreign government bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	301,757	324,145
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	386,167	392,250
Fixed maturities \| Agency mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	377,465	382,628
Fixed maturities \| Residential Mortgage Backed Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	24,525	20,463
Fixed maturities \| Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	49,915	46,093
Fixed maturities \| Commercial mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	215,033	190,015
Fixed maturities \| Mortgage- and asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	666,938	639,199
Fixed maturities \| Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	473,111	526,651
Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities and equity securities, at fair Value	$ 147,794	$ 87,258

Fixed Maturities and Equity Securities by Asset Class that are Measured at Fair Value (Detail) (USD $)
In Thousands

Sep. 30, 2011

Dec. 31, 2010

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

$ 1,975,767

$ 1,969,503

Fixed maturities | U.S. Government Treasury bonds, agency bonds and foreign government bonds | Level 1

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

100,325

212,933

Fixed maturities | Level 1

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

100,325

212,933

Equity Securities | Level 1

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

147,794

87,258

Level 1

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

248,119

300,191

Fixed maturities | U.S. Government Treasury bonds, agency bonds and foreign government bonds | Level 2

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

201,432

111,212

Fixed maturities | States, municipalities and political subdivisions | Level 2

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

386,167

392,250

Fixed maturities | Agency mortgage-backed securities | Level 2

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

377,465

382,628

Fixed maturities | Residential Mortgage Backed Securities | Level 2

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

24,525

20,463

Fixed maturities | Asset-backed securities | Level 2

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

49,915

46,093

Fixed maturities | Commercial mortgage-backed securities | Level 2

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

215,033

188,178

Fixed maturities | Mortgage- and asset-backed securities | Level 2

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

666,938

637,362

Fixed maturities | Corporate bonds | Level 2

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

473,111

526,651

Fixed maturities | Level 2

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

1,727,648

1,667,475

Level 2

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

1,727,648

1,667,475

Fixed maturities | Commercial mortgage-backed securities | Level 3

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

1,837

Fixed maturities | Mortgage- and asset-backed securities | Level 3

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

1,837

Fixed maturities | Level 3

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

1,837

Level 3

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

1,837

Fixed maturities

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

1,827,973

1,882,245

Fixed maturities | U.S. Government Treasury bonds, agency bonds and foreign government bonds

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

301,757

324,145

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

386,167

392,250

Fixed maturities | Agency mortgage-backed securities

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

377,465

382,628

Fixed maturities | Residential Mortgage Backed Securities

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

24,525

20,463

Fixed maturities | Asset-backed securities

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

49,915

46,093

Fixed maturities | Commercial mortgage-backed securities

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

215,033

190,015

Fixed maturities | Mortgage- and asset-backed securities

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

666,938

639,199

Fixed maturities | Corporate bonds

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

473,111

526,651

Equity Securities

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Fixed maturities and equity securities, at fair Value

$ 147,794

$ 87,258

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

+ References+ Details