Investments Other Than Temporary Impairments by Asset Type (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012 Securities	Dec. 31, 2011 Securities	Dec. 31, 2010 Securities
Investment Holdings [Line Items]
Other Than Temporary Impairment, Number of Securities									41	67	32
Other than Temporary Impairment Losses, Investments									$ (5,411)	$ (20,180)	$ (19,544)
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent									9,521	13,796	4,323
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	9,387	1,686	978	2,881	16,285	8,891	2,229	6,571	14,932	33,976	23,867
Corporate Debt Securities, Finance [Member]
Investment Holdings [Line Items]
Other Than Temporary Impairment, Number of Securities									1		1
Other than Temporary Impairment Losses, Investments									(1,765)		(822)
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent									0		0
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net									1,765		822
Corporate Debt Securities, Wholesale and Retail Trade Sectors [Member]
Investment Holdings [Line Items]
Other Than Temporary Impairment, Number of Securities									1		1
Other than Temporary Impairment Losses, Investments									(622)		(1,576)
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent									0		0
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net									622		1,576
Residential Mortgage Backed Securities [Member]
Investment Holdings [Line Items]
Other Than Temporary Impairment, Number of Securities									39	66	30
Other than Temporary Impairment Losses, Investments									(3,024)	(19,420)	(17,146)
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent									9,521	13,796	4,323
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net									12,545	33,216	21,469
Equity Securities, Finance [Member]
Investment Holdings [Line Items]
Other Than Temporary Impairment, Number of Securities										1
Other than Temporary Impairment Losses, Investments										(760)
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent										0
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net										$ 760