Investment Securities (Summary Of Debt Securities By Contractual Maturity) (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Available-for-sale, Amortized Cost - Due in one year or less	$ 984
Available-for-sale, Amortized Cost - Due after one year through five years	97,780
Available-for-sale, Amortized Cost - Due after five through ten years	516,512
Available-for-sale, Amortized Cost - Due after ten years	2,287,201
Available-for-sale, Amortized Cost - Total debt securities	2,902,477
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale, Fair Value - Due in one year or less	984
Available-for-sale, Fair Value - Due after one year through five years	100,381
Available-for-sale, Fair Value - Due after five through ten years	516,139
Available-for-sale, Fair Value - Due after ten years	2,304,446
Available-for-sale, Fair Value - Total debt securities	2,921,950
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]
Held-to-maturity, Amortized Cost - Due in one year or less	20,725
Held-to-maturity, Amortized Cost - Due after one year through five years	25,989
Held-to-maturity, Amortized Cost - Due after five through ten years	39,146
Held-to-maturity, Amortized Cost - Due after ten years	3,835,114
Amortized Cost	3,920,974	$ 3,923,052
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Held to Maturity, Fair Value - Due in one year or less	20,838
Held-to-maturity, Fair Value - Due after one year through five years	26,508
Held to Maturity, Fair Value - Due after five through ten years	40,512
Held to Maturity, Fair Value - Due after ten years	3,939,896
Fair Value	$ 4,027,754	$ 3,961,534