Investment Securities credit losses (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Mar. 31, 2013	Dec. 31, 2011
Credit loss portion of other than temporary impairment
Credit-related other-than-temporary impairment	$ (6,868)	$ (6,868)	$ (28,393)
Reduction due to credit impaired securities sold	21,525
Collateralized Mortgage Backed Securities [Member]
Credit loss portion of other than temporary impairment
Credit-related other-than-temporary impairment	(532)	(532)	(17,558)
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	(6,336)	(6,336)	(10,835)
Reduction due to credit impaired securities sold	$ 4,499