Investment Securities (Summary Of Debt Securities By Contractual Maturity) (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
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	$ 75,466
Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis	21,781
Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Amortized Cost Basis	529,247
Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis	2,389,269
Available-for-sale Debt Securities, Amortized Cost Basis	3,015,763
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value	76,383
Available-for-sale Securities, Debt Maturities, Year Two Through Five, Fair Value	22,190
Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Fair Value	532,352
Available-for-sale Securities, Debt Maturities, after Ten Years, Fair Value	2,360,166
Available for Sale, Fair Value - Total debt securities	2,991,091
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	13,612
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	17,313
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	46,835
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount	4,082,898
Amortized Cost	4,160,658	$ 3,923,052
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Held-to-maturity Securities, Debt Maturities, Next Twelve Months, Fair Value	13,721
Held-to-maturity Securities, Debt Maturities, Year Two Through Five, Fair Value	17,611
Held-to-maturity Securities, Debt Maturities, Year Six Through Ten, Fair Value	47,780
Held-to-maturity Securities, Debt Maturities, after Ten Years, Fair Value	4,046,013
Held-to-maturity Securities, Fair Value	$ 4,125,125	$ 3,961,534