Investment Securities (Summary of the Amortized Cost and Fair Value of Investment Securities by Maturity) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Investment Securities Available-for-Sale:
Due in one year or less, Amortized Cost	$ 268,608
Due after one year through five years, Amortized Cost	250,615
Due after five years through ten years, Amortized Cost	47,488
Due after ten years, Amortized Cost	7,379
Preferred stock, Amortized Cost	6,144
Total Available-for-sale Securities, Amortized Cost	580,234
Due in one year or less , Fair Value	270,737
Due after one year through five years, Fair Value	252,835
Due after five years through ten years, Fair Value	49,260
Due after ten years, Fair Value	7,488
Preferred stock, Fair Value	6,489
Total Available-for-sale securities, Fair Value	586,809
Investment Securities Held-to-Maturity:
Due in one year or less, Amortized Cost	38,311
Due after one year through five years, Amortized Cost	92,915
Due after five years through ten years, Amortized Cost	64,915
Due after ten years, Amortized Cost	33,836
Total Held-to-maturity securities, Amortized Cost	229,977
Due in one year or less , Fair Value	38,371
Due after one year through five years, Fair Value	94,790
Due after five years through ten years, Fair Value	67,129
Due after ten years, Fair Value	29,632
Total Held-to-maturity securities, Fair Value	$ 229,922