Investment Securities (Summary Of Debt Securities By Contractual Maturity) (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Available-for-sale, Amortized Cost - Due in one year or less	$ 77,641
Available-for-sale, Amortized Cost - Due after one year through five years	21,426
Available-for-sale, Amortized Cost - Due after five through ten years	491,037
Available-for-sale, Amortized Cost - Due after ten years	2,240,987
Available-for-sale, Amortized Cost - Total debt securities	2,831,091
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale, Fair Value - Due in one year or less	77,882
Available-for-sale, Fair Value - Due after one year through five years	21,745
Available-for-sale, Fair Value - Due after five through ten years	493,662
Available-for-sale, Fair Value - Due after ten years	2,214,677
Available-for-sale, Fair Value - Total debt securities	2,807,966
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]
Held-to-maturity, Amortized Cost - Due in one year or less	16,289
Held-to-maturity, Amortized Cost - Due after one year through five years	7,849
Held-to-maturity, Amortized Cost - Due after five through ten years	44,759
Held-to-maturity, Amortized Cost - Due after ten years	4,150,301
Amortized Cost	4,219,198	$ 4,160,658
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Held to maturity, Fair Value - Due in one year or less	16,403
Held-to-maturity, Fair Value - Due after one year through five years	7,943
Held to maturity, Fair Value - Due after five through ten years	45,623
Held to maturity, Fair Value - Due after ten years	4,127,409
Fair Value	$ 4,197,378	$ 4,125,125