Regulatory Matters (Information On The Capital Ratios) (Detail) $ in Thousands	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital	$ 2,543,131	$ 2,516,361
Common Equity Tier One Capital Required for Capital Adequacy	$ 1,008,512	$ 979,739
Common Equity Tier One Capital Ratio	0.1135	0.1156
Common Equity Tier One Capital Required to be Well-Capitalized	$ 1,456,739	$ 1,415,179
Total risk-based capital, Actual Amount	$ 3,045,652	$ 2,950,181
Total risk-based capital, Actual Ratio	0.1359	0.1355
Total risk-based capital, Capital Requirements, Minimum Amount	$ 1,792,910	$ 1,741,758
Total risk-based capital, Capital Requirements, Minimum Ratio	0.080	0.080
Total risk-based capital, Capital Requirements, Well Capitalized Amount	$ 2,241,137	$ 2,177,198
Total risk-based capital, Capital Requirements, Well Capitalized Ratio	0.100	0.100
Tier 1 risk-based capital, Actual Amount	$ 2,688,168	$ 2,661,398
Tier 1 risk-based capital, Actual Ratio	0.1199	0.1222
Tier 1 risk-based capital, Capital Requirements, Minimum Amount	$ 1,344,682	$ 1,306,319
Tier 1 risk-based capital, Capital Requirements, Minimum Ratio	0.060	0.060
Tier 1 risk-based capital, Capital Requirements, Well Capitalized Amount	$ 1,792,910	$ 1,741,758
Tier 1 risk-based capital, Capital Requirements, Well Capitalized Ratio	0.080	0.080
Tier 1 leverage capital, Actual Amount	$ 2,688,168	$ 2,661,398
Tier 1 leverage capital, Actual Ratio	0.0832	0.0896
Tier 1 leverage capital, Capital Requirements, Minimum Amount	$ 1,291,980	$ 1,188,507
Tier 1 leverage capital, Capital Requirements, Minimum Ratio	0.040	0.040
Tier 1 leverage capital, Capital Requirements, Well Capitalized Amount	$ 1,614,975	$ 1,485,634
Tier 1 leverage capital, Capital Requirements, Well Capitalized Ratio	0.050	0.050
Subsidiaries [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital	$ 2,791,474	$ 2,527,645
Common Equity Tier One Capital Required for Capital Adequacy	$ 1,008,027	$ 979,497
Common Equity Tier One Capital Ratio	0.1246	0.1161
Common Equity Tier One Capital Required to be Well-Capitalized	$ 1,456,039	$ 1,414,829
Total risk-based capital, Actual Amount	$ 3,071,505	$ 2,739,108
Total risk-based capital, Actual Ratio	0.1371	0.1258
Total risk-based capital, Capital Requirements, Minimum Amount	$ 1,792,048	$ 1,741,328
Total risk-based capital, Capital Requirements, Minimum Ratio	0.080	0.080
Total risk-based capital, Capital Requirements, Well Capitalized Amount	$ 2,240,060	$ 2,176,660
Total risk-based capital, Capital Requirements, Well Capitalized Ratio	0.100	0.100
Tier 1 risk-based capital, Actual Amount	$ 2,791,474	$ 2,527,645
Tier 1 risk-based capital, Actual Ratio	0.1246	0.1161
Tier 1 risk-based capital, Capital Requirements, Minimum Amount	$ 1,344,036	$ 1,305,996
Tier 1 risk-based capital, Capital Requirements, Minimum Ratio	0.060	0.060
Tier 1 risk-based capital, Capital Requirements, Well Capitalized Amount	$ 1,792,048	$ 1,741,328
Tier 1 risk-based capital, Capital Requirements, Well Capitalized Ratio	0.080	0.080
Tier 1 leverage capital, Actual Amount	$ 2,791,474	$ 2,527,645
Tier 1 leverage capital, Actual Ratio	0.0865	0.0851
Tier 1 leverage capital, Capital Requirements, Minimum Amount	$ 1,291,415	$ 1,187,953
Tier 1 leverage capital, Capital Requirements, Minimum Ratio	0.040	0.040
Tier 1 leverage capital, Capital Requirements, Well Capitalized Amount	$ 1,614,268	$ 1,484,941
Tier 1 leverage capital, Capital Requirements, Well Capitalized Ratio	0.050	0.050
Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital Ratio	0.045	0.045
Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets [Member] | Subsidiaries [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital Ratio	0.045	0.045
Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital Ratio	0.065	0.065
Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets [Member] | Subsidiaries [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital Ratio	0.065	0.065