Investment Securities - Investments in Debt and Equity Securities Reported Less than Historical Cost (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Fair value	$ 460,957	$ 510,297
Investments reported at less than historical cost
Schedule of Investments [Line Items]
Historical cost	471,434	523,773
Fair value	$ 460,957	$ 510,297
Percent of the Corporation's available for sale and held to maturity portfolio	34.70%	39.10%