Investment Securities (Summary Of Debt Securities By Contractual Maturity) (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Available for Sale, Amortized Cost - Due in one year or less	$ 15,522
Available for Sale, Amortized Cost - Due after one year through five years	126,521
Available for Sale, Amortized Cost - Due after five through ten years	297,718
Available for Sale, Amortized Cost - Due after ten years	2,324,706
Available for Sale, Amortized Cost - Total debt securities	2,764,467
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Available for Sale, Fair Value - Due in one year or less	15,533
Available for Sale, Fair Value - Due after one year through five years	130,307
Available for Sale, Fair Value - Due after five through ten years	298,342
Available for Sale, Fair Value - Due after ten years	2,343,788
Available for Sale, Fair Value - Total debt securities	2,787,970
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]
Held to Maturity, Amortized Cost - Due in one year or less	15
Held to Maturity, Amortized Cost - Due after one year through five years	63,419
Held to Maturity, Amortized Cost - Due after five through ten years	65,509
Held to Maturity, Amortized Cost - Due after ten years	3,744,012
Held to Maturity, Amortized Cost - Total debt securities	3,872,955	3,358,721
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Held to Maturity, Fair Value - Due in one year or less	15
Held-to-maturity, Fair Value, Due after one year through five years	65,863
Held to Maturity, Fair Value - Due after five through ten years	68,037
Held to Maturity, Fair Value - Due after ten years	3,814,791
Held to Maturity, Fair Value - Total debt securities	$ 3,948,706	$ 3,370,912