Investment Securities - Investments in Debt and Equity Securities Reported Less than Historical Cost (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule of Investments [Line Items]
Fair value	$ 251,046	$ 17,038
Investments reported at less than historical cost
Schedule of Investments [Line Items]
Historical cost	264,454	22,999
Fair value	$ 251,046	$ 17,038
Percent of the Corporation's available for sale and held to maturity portfolio	27.60%	1.90%