Investment Securities - Investments in Debt and Equity Securities Reported Less than Historical Cost (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Investments [Line Items]
Fair value	$ 337,436	$ 477,132
Investments reported at less than historical cost:
Schedule of Investments [Line Items]
Historical cost	343,258	490,488
Fair value	$ 337,436	$ 477,132
Percent of the Corporation's available for sale and held to maturity portfolio	29.30%	43.60%