Investment Securities (Maturities of Debt Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Securities with amortized cost pledged to secure borrowings and deposits	$ 838,000	$ 530,800
Investment Securities Available-for-Sale:
Due in one year or less, Amortized Cost	303,733
Due after one year through five years, Amortized Cost	563,948
Due after five years through ten years, Amortized Cost	266,242
Due after ten years, Amortized Cost	165,946
Preferred stock, Amortized Cost	1,388
Total Available-for-sale Securities, Debt Maturities, Amortized Cost	1,301,257
Due in one year or less , Fair Value	304,279
Due after one year through five years, Fair Value	565,258
Due after five years through ten years, Fair Value	266,463
Due after ten years, Fair Value	165,576
Preferred stock, Fair Value	1,805
Total Available-for-sale securities, Debt maturities, Fair Value	1,303,381
Investment Securities Held-to-Maturity:
Due in one year or less, Amortized Cost	60,391
Due after one year through five years, Amortized Cost	276,065
Due after five years through ten years, Amortized Cost	138,202
Due after ten years, Amortized Cost	89,063
Total Held-to-maturity securities, Debt maturities, Amortized Cost	563,721	509,971
Due in one year or less , Fair Value	60,508
Due after one year through five years, Fair Value	279,172
Due after five years through ten years, Fair Value	143,257
Due after ten years, Fair Value	92,207
Total Held-to-maturity securities, Debt maturities, Fair Value	$ 575,144	$ 512,705