Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Deferred tax asset:
Loss reserve discounting	$ 119,547,000	$ 119,725,000
Unearned premiums	132,014,000	118,837,000
Other-than-temporary impairments	62,187,000	68,559,000
Restricted stock units	49,553,000	43,207,000
Other	83,740,000	82,734,000
Gross deferred tax asset	447,041,000	433,062,000
Less valuation allowance	0	0
Deferred tax asset	447,041,000	433,062,000
Deferred tax liability:
Amortization of intangibles	12,458,000	12,186,000
Deferred policy acquisition costs	120,532,000	107,561,000
Unrealized investment gains	274,497,000	223,024,000
Other	99,809,000	93,126,000
Deferred tax liabilities	507,296,000	435,897,000
Net deferred tax asset	(60,255,000)	(2,835,000)
Income Taxes Receivable	22,546,000	9,670,000
Deferred Tax Assets, Operating Loss Carryforwards, Foreign	$ 171,000