Regulatory Matters (Information On The Capital Ratios) (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity tier 1, Actual Amount	$ 1,932,171	$ 1,824,106
Common equity tier 1, Actual Ratio	10.50%	10.70%
Common equity tier 1, Capital Requirements, Minimum Amount	$ 826,504	$ 766,848
Common equity tier 1, Capital Requirements, Minimum Ratio	4.50%	4.50%
Common equity tier 1, Capital Requirements, Well Capitalized Amount	$ 1,193,840	$ 1,107,670
Common equity tier 1, Capital Requirements, Well Capitalized Ratio	6.50%	6.50%
Total risk-based capital, Actual Amount	$ 2,328,808	$ 2,201,245
Total risk-based capital, Actual Ratio	12.70%	12.90%
Total risk-based capital, Capital Requirements, Minimum Amount	$ 1,469,341	$ 1,363,286
Total risk-based capital, Capital Requirements, Minimum Ratio	8.00%	8.00%
Total risk-based capital, Capital Requirements, Well Capitalized Amount	$ 1,836,677	$ 1,704,107
Total risk-based capital, Capital Requirements, Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital, Actual Amount	$ 2,054,881	$ 1,966,146
Tier 1 risk-based capital, Actual Ratio	11.20%	11.50%
Tier 1 risk-based capital, Capital Requirements, Minimum Amount	$ 1,102,006	$ 1,022,464
Tier 1 risk-based capital, Capital Requirements, Minimum Ratio	6.00%	6.00%
Tier 1 risk-based capital, Capital Requirements, Well Capitalized Amount	$ 1,469,341	$ 1,363,286
Tier 1 risk-based capital, Capital Requirements, Well Capitalized Ratio	8.00%	8.00%
Tier 1 leverage capital, Actual Amount	$ 2,054,881	$ 1,966,146
Tier 1 leverage capital, Actual Ratio	8.10%	8.20%
Tier 1 leverage capital, Capital Requirements, Minimum Amount	$ 1,010,857	$ 954,369
Tier 1 leverage capital, Capital Requirements, Minimum Ratio	4.00%	4.00%
Tier 1 leverage capital, Capital Requirements, Well Capitalized Amount	$ 1,263,571	$ 1,192,962
Tier 1 leverage capital, Capital Requirements, Well Capitalized Ratio	5.00%	5.00%
Subsidiaries [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity tier 1, Actual Amount	$ 1,945,332	$ 1,869,241
Common equity tier 1, Actual Ratio	10.60%	11.00%
Common equity tier 1, Capital Requirements, Minimum Amount	$ 825,228	$ 765,152
Common equity tier 1, Capital Requirements, Minimum Ratio	4.50%	4.50%
Common equity tier 1, Capital Requirements, Well Capitalized Amount	$ 1,191,995	$ 1,105,220
Common equity tier 1, Capital Requirements, Well Capitalized Ratio	6.50%	6.50%
Total risk-based capital, Actual Amount	$ 2,141,939	$ 2,046,350
Total risk-based capital, Actual Ratio	11.70%	12.00%
Total risk-based capital, Capital Requirements, Minimum Amount	$ 1,467,071	$ 1,360,271
Total risk-based capital, Capital Requirements, Minimum Ratio	8.00%	8.00%
Total risk-based capital, Capital Requirements, Well Capitalized Amount	$ 1,833,839	$ 1,700,338
Total risk-based capital, Capital Requirements, Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital, Actual Amount	$ 1,945,332	$ 1,869,241
Tier 1 risk-based capital, Actual Ratio	10.60%	11.00%
Tier 1 risk-based capital, Capital Requirements, Minimum Amount	$ 1,100,304	$ 1,020,203
Tier 1 risk-based capital, Capital Requirements, Minimum Ratio	6.00%	6.00%
Tier 1 risk-based capital, Capital Requirements, Well Capitalized Amount	$ 1,467,071	$ 1,360,271
Tier 1 risk-based capital, Capital Requirements, Well Capitalized Ratio	8.00%	8.00%
Tier 1 leverage capital, Actual Amount	$ 1,945,332	$ 1,869,241
Tier 1 leverage capital, Actual Ratio	7.70%	7.80%
Tier 1 leverage capital, Capital Requirements, Minimum Amount	$ 1,010,005	$ 953,300
Tier 1 leverage capital, Capital Requirements, Minimum Ratio	4.00%	4.00%
Tier 1 leverage capital, Capital Requirements, Well Capitalized Amount	$ 1,262,507	$ 1,191,626
Tier 1 leverage capital, Capital Requirements, Well Capitalized Ratio	5.00%	5.00%