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

[1] Equivalent S&P rating used for certain companies when an A.M. Best rating was unavailable.

[2] Net of reserve for uncollectible reinsurance of approximately $11.3 million. The carrying value consists of reinsurance recoverables on paid losses due within 30-45 days and reinsurance on unpaid losses which by nature of our reserving process is our best estimate of the value as of December 31, 2013.

[3] Net of reserve for uncollectible reinsurance of approximately $11.3 million.

[4] Collateral of $223.5 million consists of $167.3 million in ceded balances payable, $53.4 million in letters of credit, and $2.8 million of other balances held by the Company's Insurance Companies and Lloyd's Operations.