Loans (Impaired Loans) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	$ 105,577	$ 113,515
Recorded Investment With No Allowance	43,083	76,952
Recorded Investment With Allowance	37,314	7,613
Total Recorded Investment	80,397	84,565
Related Allowance	8,237	3,904
Average Recorded Investment	86,580	108,914
Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	1,255
Recorded Investment With Allowance	1,069
Total Recorded Investment	1,069
Related Allowance	900
Average Recorded Investment	214
Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	56,784	57,723
Recorded Investment With No Allowance	21,709	34,712
Recorded Investment With Allowance	19,096	4,619
Total Recorded Investment	40,805	39,331
Related Allowance	4,200	2,696
Average Recorded Investment	42,630	53,830
Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	44,652	51,163
Recorded Investment With No Allowance	19,010	38,686
Recorded Investment With Allowance	17,149	2,243
Total Recorded Investment	36,159	40,929
Related Allowance	3,137	1,113
Average Recorded Investment	40,258	48,635
Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	1,497	1,568
Recorded Investment With No Allowance	1,100	1,281
Total Recorded Investment	1,100	1,281
Average Recorded Investment	1,392	4,339
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	961	2,499
Recorded Investment With No Allowance	864	1,719
Recorded Investment With Allowance		751
Total Recorded Investment	864	2,470
Related Allowance		95
Average Recorded Investment	1,617	1,845
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	428	562
Recorded Investment With No Allowance	400	554
Total Recorded Investment	400	554
Average Recorded Investment	$ 469	$ 265