Investment Securities (Maturities of Debt Securities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013
Investment Securities Available-for-Sale:
Due in one year or less, Amortized Cost	$ 111,238
Due after one year through five years, Amortized Cost	110,514
Due after five years through ten years, Amortized Cost	351,441
Due after ten years, Amortized Cost	117,910
Preferred stock, Amortized Cost	6,144
Total Available-for-sale Securities, Debt Maturities, Amortized Cost	697,247
Due in one year or less , Fair Value	112,000
Due after one year through five years, Fair Value	112,051
Due after five years through ten years, Fair Value	353,879
Due after ten years, Fair Value	119,106
Preferred stock, Fair Value	6,586
Total Available-for-sale securities, Debt maturities, Fair Value	703,622
Investment Securities Held-to-Maturity:
Due in one year or less, Amortized Cost	37,103
Due after one year through five years, Amortized Cost	103,486
Due after five years through ten years, Amortized Cost	78,048
Due after ten years, Amortized Cost	39,112
Total Held-to-maturity securities, Debt maturities, Amortized Cost	257,749
Due in one year or less , Fair Value	37,168
Due after one year through five years, Fair Value	106,000
Due after five years through ten years, Fair Value	82,248
Due after ten years, Fair Value	35,989
Total Held-to-maturity securities, Debt maturities, Fair Value	$ 261,405