Rollforward of Credit-Related Other-than-temporary Impairment Recognized in Earnings (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Beginning Balance	$ 75,228	$ 76,131
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment	0	113
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, Additional Credit Losses	247	3,609
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold	0	(7,796)
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Ending Balance	$ 75,475	$ 72,057