Securities (Remaining Contractual Maturity Of Securities) (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Investment [Line Items]
Available-For Sale Securities, One year or less, Amortized Cost	$ 1,793
Available-For Sale Securities, One year to five years, Amortized Cost	134,704
Available-For Sale Securities, Five years to ten years, Amortized Cost	124,966
Available-For Sale Securities, After ten years, Amortized Cost	12,352
Available-For-Sale Securities, Total Amortized Cost	1,549,803
Available-For Sale Securities, One year or less, Fair Value	1,813
Available-For Sale Securities, One year to five years, Fair Value	138,164
Available-For Sale Securities, Five years to ten years, Fair Value	132,892
Available-For Sale Securities, After ten years, Fair value	13,399
Total	1,625,649	1,783,465
Held-To-Maturity Securities and Non-Marketable Equity Investments, One year or less, Amortized Cost	523
Held-To-Maturity Securities and Non-Marketable Equity Investments, One year to five years, Amortized Cost	48
Held-To-Maturity Securities and Non-Marketable Equity Investments, Five years to ten years, Amortized Cost
Held-To-Maturity Securities and Non-Marketable Equity Investments, Ten years or more, Amortized Cost
Total	740,979
Held-To-Maturity Securities and Non-Marketable Equity Investments, One year or less, Fair Value	523
Held-To-Maturity Securities and Non-Marketable Equity Investments, One year to five years, Fair Value	48
Held-To-Maturity Securities and Non-Marketable Equity Investments, five years to ten years, Fair Value
Held-To-Maturity Securities and Non-Marketable Equity Investments, after ten years, Fair Value
Total	754,450
Collateralized Mortgage Obligations [Member]
Investment [Line Items]
Available-For Sale Securities, Debt Maturities, Without Single Maturity Date, Amortized Cost	292,177
Available-For Sale Securities, Debt Maturities, Without Single Maturity Date, Fair Value	305,268
Total	305,268	356,000
Residential Mortgage Backed Securities [Member]
Investment [Line Items]
Available-For Sale Securities, Debt Maturities, Without Single Maturity Date, Amortized Cost	983,811
Available-For Sale Securities, Debt Maturities, Without Single Maturity Date, Fair Value	1,034,113
Total	1,034,113	1,189,213
Held-To-Maturity Securities and Non-Marketable Equity Investments, Debt Maturities, Without Single Maturity Date, Amortized Cost	675,211
Held-To-Maturity Securities and Non-Marketable Equity Investments, Debt Maturities, Without Single Maturity Date, Fair Value	688,497
Commercial Mortgage Backed Securities [Member]
Investment [Line Items]
Held-To-Maturity Securities and Non-Marketable Equity Investments, Debt Maturities, Without Single Maturity Date, Amortized Cost	17,495
Held-To-Maturity Securities and Non-Marketable Equity Investments, Debt Maturities, Without Single Maturity Date, Fair Value	17,680
Non-Marketable Equity Investment [Member]
Investment [Line Items]
Held-To-Maturity Securities and Non-Marketable Equity Investments, Debt Maturities, Without Single Maturity Date, Amortized Cost	47,702
Held-To-Maturity Securities and Non-Marketable Equity Investments, Debt Maturities, Without Single Maturity Date, Fair Value	$ 47,702