Tax Effects of Temporary Differences that Give Rise to Significant Portions of Deferred Tax Assets and Deferred Tax Liabilities (Detail) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Deferred tax assets
State net operating loss carry forward	$ 15,200,000	$ 15,200,000
Reserves for capitalized real estate	4,000,000	3,700,000
Expenses deducted for tax purposes when paid	1,800,000	1,900,000
Other than temporary impairment	10,500,000	21,700,000
Property and casualty loss reserves	58,900,000	62,600,000
Unearned premium reserves	28,800,000	26,800,000
Compensation accruals	71,700,000	70,400,000
Other	30,400,000	14,200,000
Gross deferred tax assets before valuation allowance	221,300,000	216,500,000
Valuation allowance	(15,200,000)	(15,000,000)
Gross deferred tax assets	206,100,000	201,500,000
Deferred tax liabilities
Unrealized gain on investments	81,900,000	84,800,000
Tax over book depreciation	4,100,000	1,100,000
Deferred gains	2,400,000	2,500,000
Deferred acquisition costs	25,100,000	24,000,000
Purchase accounting adjustments	3,800,000	4,100,000
Other	7,800,000	7,900,000
Gross deferred tax liabilities	125,100,000	124,400,000
Net deferred tax assets	$ 80,975,000	$ 77,147,000