Loans (Age Analysis Of Past Due Loans, Segregated By Class Of Loans) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	$ 43,181
Loans 90 or More Days Past Due	33,080
Total Past Due Loans	76,261
Current Loans	8,734,779
Total	8,811,040	7,995,129	8,089,577
Accruing Loans 90 or More Days Past Due	8,450
Commercial And Industrial, Energy [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	63
Total Past Due Loans	63
Current Loans	1,130,840
Total	1,130,903
Commercial And Industrial, Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	16,378
Loans 90 or More Days Past Due	17,792
Total Past Due Loans	34,170
Current Loans	3,321,228
Total	3,355,398
Accruing Loans 90 or More Days Past Due	5,793
Commercial Real Estate, Buildings, Land And Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	14,668
Loans 90 or More Days Past Due	11,547
Total Past Due Loans	26,215
Current Loans	2,639,713
Total	2,665,928
Accruing Loans 90 or More Days Past Due	400
Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	467
Total Past Due Loans	467
Current Loans	583,740
Total	584,207
Consumer Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	7,458
Loans 90 or More Days Past Due	3,162
Total Past Due Loans	10,620
Current Loans	757,862
Total	768,482
Accruing Loans 90 or More Days Past Due	1,720
Consumer And Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	4,147
Loans 90 or More Days Past Due	579
Total Past Due Loans	4,726
Current Loans	320,866
Total	325,592
Accruing Loans 90 or More Days Past Due	537
Unearned Discounts [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current Loans	(19,470)
Total	$ (19,470)