Loans (Weighted Average Risk Grades for All Commercial Loans b Class) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 Grade	Dec. 31, 2012 Grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 4,907,076	$ 4,828,612
Loans	3,467,336	3,319,795
Loans	426,639	608,306
Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	5.40	5.25
Loans	1,115,409	1,083,186
Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	6.27	6.21
Loans	3,791,667	3,745,426
Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	6.83	6.97
Loans	3,040,697	2,711,489
Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	7.10	6.94
Loans	426,639	608,306
Risk Grade One To Eight [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	5.37	5.24
Loans	1,106,348	1,081,725
Risk Grade One To Eight [Member] | Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	5.95	5.81
Loans	3,507,963	3,367,443
Risk Grade One To Eight [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	6.59	6.63
Loans	2,844,665	2,460,448
Risk Grade One To Eight [Member] | Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	7.05	6.82
Loans	418,999	579,108
Risk Grade Nine [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	9.00	9.00
Loans	7,726	392
Risk Grade Nine [Member] | Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	9.00	9.00
Loans	74,766	250,508
Risk Grade Nine [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	9.00	9.00
Loans	65,770	92,041
Risk Grade Nine [Member] | Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	9.00	9.00
Loans	1,301	23,046
Risk Grade Ten [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	10.00	10.00
Loans	245	0
Risk Grade Ten [Member] | Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	10.00	10.00
Loans	89,878	28,440
Risk Grade Ten [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	10.00	10.00
Loans	49,881	42,603
Risk Grade Ten [Member] | Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	10.00	10.00
Loans	5,931	4,435
Risk Grade Eleven [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	11.00	11.00
Loans	500	0
Risk Grade Eleven [Member] | Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	11.00	11.00
Loans	92,917	53,797
Risk Grade Eleven [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	11.00	11.00
Loans	53,208	77,658
Risk Grade Eleven [Member] | Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	11.00	11.00
Loans	408	617
Risk Grade Twelve [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	12.00	12.00
Loans	590	169
Risk Grade Twelve [Member] | Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	12.00	12.00
Loans	21,389	40,603
Risk Grade Twelve [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	12.00	12.00
Loans	24,387	35,602
Risk Grade Twelve [Member] | Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	12.00	12.00
Loans	0	1,100
Risk Grade Thirteen [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	13.00	13.00
Loans	0	900
Risk Grade Thirteen [Member] | Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	13.00	13.00
Loans	4,754	4,635
Risk Grade Thirteen [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	13.00	13.00
Loans	2,786	3,137
Risk Grade Thirteen [Member] | Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	13.00	13.00
Loans	$ 0	$ 0
Minimum [Member] | Risk Grade One To Eight [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	1.00	1.00
Maximum [Member] | Risk Grade One To Eight [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	8.00	8.00