Investment Securities Summary of Cumulative Other-than-Temporary Impairment Charges Recognized in Earnings for Pooled Trust Preferred Securities Held (Details) (Pooled trust preferred securities, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pooled trust preferred securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Balance of cumulative credit losses on debt securities, beginning of year	$ (20,691)	$ (23,079)	$ (22,781)
Additions for credit losses recorded which were not previously recognized as components of earnings	(18)	(97)	(453)
Reductions for securities sold during the period	4,460	2,468	0
Reductions for increases in cash flows expected to be collected that are recognized over the remaining life of the security	7	17	155
Balance of cumulative credit losses on debt securities, end of year	$ (16,242)	$ (20,691)	$ (23,079)