Investment Securities (Maturities of Debt Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Investment Securities Available-for-Sale:
Due in one year or less, Amortized Cost	$ 200,319
Due after one year through five years, Amortized Cost	367,920
Due after five years through ten years, Amortized Cost	59,327
Due after ten years, Amortized Cost	5,244
Preferred stock, Amortized Cost	1,389
Total Available-for-sale Securities, Debt Maturities, Amortized Cost	634,199
Due in one year or less , Fair Value	200,435
Due after one year through five years, Fair Value	368,761
Due after five years through ten years, Fair Value	59,521
Due after ten years, Fair Value	5,270
Preferred stock, Fair Value	1,654
Total Available-for-sale securities, Debt maturities, Fair Value	635,641
Investment Securities Held-to-Maturity:
Due in one year or less, Amortized Cost	56,508
Due after one year through five years, Amortized Cost	229,324
Due after five years through ten years, Amortized Cost	135,569
Due after ten years, Amortized Cost	79,682
Total Held-to-maturity securities, Debt maturities, Amortized Cost	501,083	$ 316,413	$ 318,562
Due in one year or less , Fair Value	56,614
Due after one year through five years, Fair Value	229,045
Due after five years through ten years, Fair Value	134,841
Due after ten years, Fair Value	79,404
Total Held-to-maturity securities, Debt maturities, Fair Value	$ 499,904	$ 315,740	$ 314,275