Impairment of Investment Securities (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Cumulative Roll Forward of Credit Losses Recognized in Earnings for Debt Securities Held and Not Intended to be Sold
Balance, beginning	$ 44,501	$ 44,850	$ 44,736	$ 44,850
Credit losses on debt securities for which other-than-temporary impairment was not previously recognized	0	0	0	0
Additional credit losses on debt securities for which other-than-temporary impairment was previously recognized	0	0	0	0
Increases in cash flows expected to be collected, recognized over the remaining life of the security (b)	(271)	0	(506)	0
Balance, ending	$ 44,230	$ 44,850	$ 44,230	$ 44,850