Adoption of Accounting Pronouncements (Balance Sheet Information) (Details) (USD $)	3 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Deferred policy acquisition costs	$ 161,505,000	$ 135,761,000
Deferred federal income tax recoverable	91,916,000	119,486,000	[1]
Retained earnings	1,131,115,000	1,116,319,000
Adjustment of deferred tax assets	600,000	600,000
As Previously Reported [Member]
Deferred policy acquisition costs		214,069,000
Deferred federal income tax recoverable		92,078,000	[1]
Retained earnings		1,167,219,000
Add: Adjustment for the cumulative effect on prior years of applying retroactively the new method of accounting for deferred policy acquisition costs [Member]
Deferred policy acquisition costs		(78,308,000)
Deferred federal income tax recoverable		27,408,000	[1]
Retained earnings		$ (50,900,000)

[1] 1 Included in the deferred federal income tax recoverable amount is an adjustment of $0.6 million reflecting the revaluation of a deferred tax asset acquired as part of the purchase of Mesa Underwriters Specialty Insurance Company ("MUSIC" ). For additional information, see Footnote 14, "Federal Income Taxes"