Investment Securities - Investments in Debt and Equity Securities Reported Less than Historical Cost (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Investments [Line Items]
Fair value	$ 151,316	$ 477,132
Investments reported at less than historical cost:
Schedule of Investments [Line Items]
Historical cost	153,642	490,488
Fair value	$ 151,316	$ 477,132
Percent of the Corporation's available for sale and held to maturity portfolio	12.50%	43.60%