Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Deferred tax asset:
Loss reserve discounting	$ 119,725,000	$ 152,189,000
Unearned premiums	118,837,000	106,162,000
Other-than-temporary impairments	68,559,000	69,057,000
Restricted stock units	43,207,000	39,514,000
Other	82,734,000	26,813,000
Gross deferred tax asset	433,062,000	393,735,000
Less valuation allowance	0	(2,328,000)
Deferred tax asset	433,062,000	391,407,000
Deferred tax liability:
Amortization of intangibles	12,186,000	11,780,000
Deferred policy acquisition costs	136,349,000	124,141,000
Unrealized investment gains	223,024,000	169,106,000
Other	93,126,000	20,888,000
Deferred tax liabilities	464,685,000	325,915,000
Net deferred tax asset	(31,623,000)	65,492,000
Income Taxes Receivable	9,670,000	23,605,000
Deferred Tax Assets, Operating Loss Carryforwards, Foreign	$ 420,000