Investment Securities (Maturities of Debt Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Investment Securities Available-for-Sale:
Due in one year or less, Amortized Cost	$ 198,939
Due after one year through five years, Amortized Cost	411,399
Due after five years through ten years, Amortized Cost	68,583
Due after ten years, Amortized Cost	5,818
Preferred stock, Amortized Cost	1,389
Total Available-for-sale Securities, Debt Maturities, Amortized Cost	686,128
Due in one year or less , Fair Value	198,680
Due after one year through five years, Fair Value	411,247
Due after five years through ten years, Fair Value	68,295
Due after ten years, Fair Value	5,823
Preferred stock, Fair Value	1,661
Total Available-for-sale securities, Debt maturities, Fair Value	685,706
Investment Securities Held-to-Maturity:
Due in one year or less, Amortized Cost	55,922
Due after one year through five years, Amortized Cost	209,886
Due after five years through ten years, Amortized Cost	127,398
Due after ten years, Amortized Cost	76,631
Total Held-to-maturity securities, Debt maturities, Amortized Cost	469,837	$ 316,413	$ 308,130
Due in one year or less , Fair Value	56,043
Due after one year through five years, Fair Value	209,768
Due after five years through ten years, Fair Value	125,775
Due after ten years, Fair Value	74,992
Total Held-to-maturity securities, Debt maturities, Fair Value	$ 466,578	$ 315,740	$ 303,961