Investment Securities (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Credit loss portion of other than temporary impairment
Credit-related other-than-temporary impairment	$ (7,210)	$ (28,393)	$ (27,575)
Credit losses on newly identified impairment		(818)
Reduction due to credit impaired securities sold	21,183
Non-agency Mortgage-Related Securities [Member]
Credit loss portion of other than temporary impairment
Credit-related other-than-temporary impairment	(532)	(17,558)	(17,556)
Credit losses on newly identified impairment		(2)
Reduction due to credit impaired securities sold	17,026
Trust Preferred Debt Securities [Member]
Credit loss portion of other than temporary impairment
Credit-related other-than-temporary impairment	(6,678)	(10,835)	(10,019)
Credit losses on newly identified impairment		(816)
Reduction due to credit impaired securities sold	$ 4,157