Investment Securities (Summary Of Debt Securities By Contractual Maturity) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis	$ 35,941
Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis	99,028
Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Amortized Cost Basis	435,444
Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis	2,421,012
Available-for-sale Debt Securities, Amortized Cost Basis	2,991,425
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value	35,660
Available-for-sale Securities, Debt Maturities, Year Two Through Five, Fair Value	101,313
Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Fair Value	433,733
Available-for-sale Securities, Debt Maturities, after Ten Years, Fair Value	2,411,347
Available for Sale, Fair Value - Total debt securities	2,982,053
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]
Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount	320
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	33,940
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	48,818
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount	3,839,974
Amortized Cost	3,923,052	$ 3,872,955
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Held-to-maturity Securities, Debt Maturities, Next Twelve Months, Fair Value	323
Held-to-maturity Securities, Debt Maturities, Year Two Through Five, Fair Value	34,880
Held-to-maturity Securities, Debt Maturities, Year Six Through Ten, Fair Value	50,534
Held-to-maturity Securities, Debt Maturities, after Ten Years, Fair Value	3,875,797
Held-to-maturity Securities, Fair Value	$ 3,961,534	$ 3,948,706