Loans (Age Analysis of Past Due Loans, Segregated by Class of Loans) (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	$ 41,207
Loans 90 or More Days Past Due	32,080
Total Past Due Loans	73,287
Current Loans	9,442,413
Total loans	9,515,700	9,223,848
Accruing Loans 90 or More Days Past Due	7,635
Commercial and Industrial, Energy [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	892
Loans 90 or More Days Past Due	559
Total Past Due Loans	1,451
Current Loans	1,113,958
Total loans	1,115,409
Accruing Loans 90 or More Days Past Due	500
Commercial and Industrial, Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	16,090
Loans 90 or More Days Past Due	8,069
Total Past Due Loans	24,159
Current Loans	3,767,508
Total loans	3,791,667
Accruing Loans 90 or More Days Past Due	2,223
Commercial Real Estate, Buildings, Land and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	14,492
Loans 90 or More Days Past Due	19,246
Total Past Due Loans	33,738
Current Loans	3,006,959
Total loans	3,040,697
Accruing Loans 90 or More Days Past Due	1,223
Commercial Real Estate, Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	679
Total Past Due Loans	679
Current Loans	425,960
Total loans	426,639
Consumer Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	4,978
Loans 90 or More Days Past Due	2,738
Total Past Due Loans	7,716
Current Loans	800,488
Total loans	808,204
Accruing Loans 90 or More Days Past Due	2,391
Consumer and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	4,076
Loans 90 or More Days Past Due	1,468
Total Past Due Loans	5,544
Current Loans	352,572
Total loans	358,116
Accruing Loans 90 or More Days Past Due	1,298
Unearned Discounts [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current Loans	(25,032)
Total loans	$ (25,032)