Other-than-temporary Impairment (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended			48 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held	$ 75,228	$ 76,131	$ 52,624	$ 75,228
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment	113	3,368
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, Additional Credit Losses	6,780	20,139
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold	(7,796)	0
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	(5,882)	21,900	26,500	(71,640)
US States and Political Subdivisions Debt Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	1,000	1,600	1,000
Equity Securities And Mutual Funds [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	$ 457	$ 0	$ 327