Investment Securities (Summary of the Amortized Cost and Fair Value of Investment Securities by Maturity) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Investment Securities Available-for-Sale:
Due in one year or less, Amortized Cost	$ 194,598
Due after one year through five years, Amortized Cost	487,952
Due after five years through ten years, Amortized Cost	61,825
Due after ten years, Amortized Cost	3,423
Preferred stock, Amortized Cost	1,389
Total Available-for-sale Securities, Amortized Cost	749,187
Due in one year or less , Fair Value	194,475
Due after one year through five years, Fair Value	487,511
Due after five years through ten years, Fair Value	61,887
Due after ten years, Fair Value	3,401
Preferred stock, Fair Value	1,590
Total Available-for-sale securities, Fair Value	748,864
Investment Securities Held-to-Maturity:
Due in one year or less, Amortized Cost	37,069
Due after one year through five years, Amortized Cost	131,711
Due after five years through ten years, Amortized Cost	96,736
Due after ten years, Amortized Cost	50,897
Total Held-to-maturity securities, Amortized Cost	316,413	273,905
Due in one year or less , Fair Value	37,222
Due after one year through five years, Fair Value	134,918
Due after five years through ten years, Fair Value	98,774
Due after ten years, Fair Value	44,826
Total Held-to-maturity securities, Fair Value	$ 315,740	$ 268,271