Investment Securities (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012
Investment Securities Available-for-Sale:
Due in one year or less, Amortized Cost	$ 171,593
Due after one year through five years, Amortized Cost	326,357
Due after five years through ten years, Amortized Cost	66,831
Due after ten years, Amortized Cost	68,390
Preferred stock, Amortized Cost	6,144
Total Available-for-sale Securities, Debt Maturities, Amortized Cost	639,315
Due in one year or less , Fair Value	173,000
Due after one year through five years, Fair Value	328,800
Due after five years through ten years, Fair Value	69,093
Due after ten years, Fair Value	69,257
Preferred stock, Fair Value	6,428
Total Available-for-sale securities, Debt maturities, Fair Value	646,578
Investment Securities Held-to-Maturity:
Due in one year or less, Amortized Cost	38,910
Due after one year through five years, Amortized Cost	94,392
Due after five years through ten years, Amortized Cost	57,290
Due after ten years, Amortized Cost	30,944
Total Held-to-maturity securities, Debt maturities, Amortized Cost	221,536
Due in one year or less , Fair Value	41,225
Due after one year through five years, Fair Value	96,740
Due after five years through ten years, Fair Value	59,023
Due after ten years, Fair Value	26,197
Total Held-to-maturity securities, Debt maturities, Fair Value	$ 223,185