Rollforward of Credit-Related Other-than-temporary Impairment Recognized in Earnings (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Beginning Balance	$ 75,475	$ 72,057	$ 75,228	$ 76,131
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment	552	135	552	248
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, Additional Credit Losses	0	723	247	4,332
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold	0	0	0	(7,796)
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Ending Balance	$ 76,027	$ 72,915	$ 76,027	$ 72,915