Investment Securities (Maturities of Debt Securities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Investment Securities Available-for-Sale:
Due in one year or less, Amortized Cost	$ 160,093
Due after one year through five years, Amortized Cost	403,039
Due after five years through ten years, Amortized Cost	90,096
Due after ten years, Amortized Cost	4,566
Preferred stock, Amortized Cost	1,389
Total Available-for-sale Securities, Debt Maturities, Amortized Cost	659,183
Due in one year or less , Fair Value	159,861
Due after one year through five years, Fair Value	402,251
Due after five years through ten years, Fair Value	89,721
Due after ten years, Fair Value	4,426
Preferred stock, Fair Value	1,559
Total Available-for-sale securities, Debt maturities, Fair Value	657,818
Investment Securities Held-to-Maturity:
Due in one year or less, Amortized Cost	38,060
Due after one year through five years, Amortized Cost	104,588
Due after five years through ten years, Amortized Cost	79,077
Due after ten years, Amortized Cost	56,374
Total Held-to-maturity securities, Debt maturities, Amortized Cost	278,099	273,905	257,749
Due in one year or less , Fair Value	38,096
Due after one year through five years, Fair Value	105,892
Due after five years through ten years, Fair Value	79,653
Due after ten years, Fair Value	48,766
Total Held-to-maturity securities, Debt maturities, Fair Value	$ 272,407	$ 268,271	$ 261,405