Investment Securities (Maturities of Debt Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Investment Securities Available-for-Sale:
Due in one year or less, Amortized Cost	$ 167,082
Due after one year through five years, Amortized Cost	293,731
Due after five years through ten years, Amortized Cost	45,820
Due after ten years, Amortized Cost	4,719
Preferred stock, Amortized Cost	1,388
Total Available-for-sale Securities, Debt Maturities, Amortized Cost	512,740
Due in one year or less , Fair Value	167,114
Due after one year through five years, Fair Value	294,443
Due after five years through ten years, Fair Value	45,935
Due after ten years, Fair Value	4,757
Preferred stock, Fair Value	1,766
Total Available-for-sale securities, Debt maturities, Fair Value	514,015
Investment Securities Held-to-Maturity:
Due in one year or less, Amortized Cost	57,074
Due after one year through five years, Amortized Cost	239,496
Due after five years through ten years, Amortized Cost	142,968
Due after ten years, Amortized Cost	78,762
Total Held-to-maturity securities, Debt maturities, Amortized Cost	518,300	$ 509,971	$ 381,450
Due in one year or less , Fair Value	57,148
Due after one year through five years, Fair Value	241,445
Due after five years through ten years, Fair Value	145,988
Due after ten years, Fair Value	81,012
Total Held-to-maturity securities, Debt maturities, Fair Value	$ 525,593	$ 512,705	$ 380,176