Loans - Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	$ 89,258	$ 105,577
Recorded Investment With No Allowance	44,270	43,083
Recorded Investment With Allowance	25,506	37,314
Total Recorded Investment	69,776	80,397
Related Allowance	8,949	8,237
Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	545	1,255
Recorded Investment With No Allowance	538	0
Recorded Investment With Allowance	0	1,069
Total Recorded Investment	538	1,069
Related Allowance	0	900
Commercial and industrial, Other commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	41,214	56,784
Recorded Investment With No Allowance	19,134	21,709
Recorded Investment With Allowance	11,528	19,096
Total Recorded Investment	30,662	40,805
Related Allowance	6,607	4,200
Commercial real estate, Buildings, land and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	46,227	44,652
Recorded Investment With No Allowance	23,514	19,010
Recorded Investment With Allowance	13,978	17,149
Total Recorded Investment	37,492	36,159
Related Allowance	2,342	3,137
Commercial real estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	0	1,497
Recorded Investment With No Allowance	0	1,100
Recorded Investment With Allowance	0	0
Total Recorded Investment	0	1,100
Related Allowance	0	0
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	920	961
Recorded Investment With No Allowance	773	864
Recorded Investment With Allowance	0	0
Total Recorded Investment	773	864
Related Allowance	0	0
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	352	428
Recorded Investment With No Allowance	311	400
Recorded Investment With Allowance	0	0
Total Recorded Investment	311	400
Related Allowance	$ 0	$ 0