Lists of 10 Largest Reinsurers Measured by Reinsurance Recoverable (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		$ 232,588	$ 237,851
Reinsurance Recoverables Paid/Unpaid Losses		859,024
Reinsurance Recoverables Total	[1]	1,091,612
Collateral Held		159,570
National Indemnity Company | AM Best, A++ Rating | Standard & Poor's, AA+ Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		14,854
Reinsurance Recoverables Paid/Unpaid Losses		118,337
Reinsurance Recoverables Total	[1]	133,191
Collateral Held		$ 7,198
National Indemnity Company | AM Best | AM Best, A++ Rating | Standard & Poor's, AA+ Rating
Ceded Credit Risk [Line Items]
Rating		A++
National Indemnity Company | Standard & Poor's | AM Best, A++ Rating | 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		$ 21,097
Reinsurance Recoverables Paid/Unpaid Losses		77,702
Reinsurance Recoverables Total	[1]	98,799
Collateral Held		$ 3,933
Everest Reinsurance Company | AM Best | AM Best, A+ Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Rating		A+
Everest Reinsurance Company | Standard & Poor's | AM Best, A+ Rating | 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		$ 25,564
Reinsurance Recoverables Paid/Unpaid Losses		63,081
Reinsurance Recoverables Total	[1]	88,645
Collateral Held		$ 7,814
Swiss Reinsurance America Corporation | AM Best | AM Best, A+ Rating | Standard & Poor's, AA- Rating
Ceded Credit Risk [Line Items]
Rating		A+
Swiss Reinsurance America Corporation | Standard & Poor's | AM Best, A+ Rating | 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		$ 9,267
Reinsurance Recoverables Paid/Unpaid Losses		62,402
Reinsurance Recoverables Total	[1]	71,669
Collateral Held		$ 1,783
Transatlantic Reinsurance Company | AM Best | AM Best, A Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Rating		A
Transatlantic Reinsurance Company | Standard & Poor's | AM Best, A Rating | 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		$ 9,051
Reinsurance Recoverables Paid/Unpaid Losses		51,795
Reinsurance Recoverables Total	[1]	60,846
Collateral Held		$ 1,577
Munich Reinsurance America Inc | AM Best | AM Best, A+ Rating | Standard & Poor's, AA- Rating
Ceded Credit Risk [Line Items]
Rating		A+
Munich Reinsurance America Inc | Standard & Poor's | AM Best, A+ Rating | 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		$ 7,177
Reinsurance Recoverables Paid/Unpaid Losses		38,343
Reinsurance Recoverables Total	[1]	45,520
Collateral Held		$ 1,012
Allied World Reinsurance | AM Best | AM Best, A Rating | Standard & Poor's, A Rating
Ceded Credit Risk [Line Items]
Rating		A
Allied World Reinsurance | Standard & Poor's | AM Best, A Rating | 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		$ 10,775
Reinsurance Recoverables Paid/Unpaid Losses		28,321
Reinsurance Recoverables Total	[1]	39,096
Collateral Held		$ 4,015
Employers Mutual Casualty Company | AM Best | AM Best, A Rating | Standard & Poor's, Not Rated
Ceded Credit Risk [Line Items]
Rating		A
Employers Mutual Casualty Company | Standard & Poor's | AM Best, A Rating | Standard & Poor's, Not Rated
Ceded Credit Risk [Line Items]
Rating		NR
Ace Property and Casualty Insurance Company | AM Best, A++ Rating | Standard & Poor's, AA Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		$ 12,577
Reinsurance Recoverables Paid/Unpaid Losses		21,470
Reinsurance Recoverables Total	[1]	34,047
Collateral Held		$ 3,284
Ace Property and Casualty Insurance Company | AM Best | AM Best, A++ Rating | Standard & Poor's, AA Rating
Ceded Credit Risk [Line Items]
Rating		A++
Ace Property and Casualty Insurance Company | Standard & Poor's | AM Best, A++ Rating | 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		$ 11,231
Reinsurance Recoverables Paid/Unpaid Losses		21,728
Reinsurance Recoverables Total	[1]	32,959
Collateral Held		$ 17,619
Partner Reinsurance Europe | AM Best | AM Best, A Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Rating		A
Partner Reinsurance Europe | Standard & Poor's | AM Best, A Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Rating		A+
National Union Fire Ins | AM Best, A Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		$ 7,478
Reinsurance Recoverables Paid/Unpaid Losses		22,288
Reinsurance Recoverables Total	[1]	29,766
Collateral Held		$ 5,717
National Union Fire Ins | AM Best | AM Best, A Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Rating		A
National Union Fire Ins | Standard & Poor's | AM Best, A Rating | Standard & Poor's, A+ Rating
Ceded Credit Risk [Line Items]
Rating		A+
Insurance Companies
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		$ 129,071
Reinsurance Recoverables Paid/Unpaid Losses		505,467
Reinsurance Recoverables Total	[1]	634,538
Collateral Held		53,952
All Other
Ceded Credit Risk [Line Items]
Reinsurance Recoverables Unearned Premium		103,517
Reinsurance Recoverables Paid/Unpaid Losses		353,557
Reinsurance Recoverables Total	[1]	457,074
Collateral Held		$ 105,618

[1] Net of reserve for uncollectible reinsurance of approximately $6.9 million.