Loans - Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	$ 96,592	$ 105,577
Recorded Investment With No Allowance	53,751	43,083
Recorded Investment With Allowance	23,423	37,314
Total Recorded Investment	77,174	80,397
Related Allowance	7,494	8,237
Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance		1,255
Recorded Investment With No Allowance
Recorded Investment With Allowance		1,069
Total Recorded Investment		1,069
Related Allowance		900
Commercial and industrial, Other commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	47,024	56,784
Recorded Investment With No Allowance	28,127	21,709
Recorded Investment With Allowance	8,437	19,096
Total Recorded Investment	36,564	40,805
Related Allowance	4,150	4,200
Commercial real estate, Buildings, land and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	46,772	44,652
Recorded Investment With No Allowance	23,442	19,010
Recorded Investment With Allowance	14,986	17,149
Total Recorded Investment	38,428	36,159
Related Allowance	3,344	3,137
Commercial real estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	1,460	1,497
Recorded Investment With No Allowance	1,015	1,100
Recorded Investment With Allowance
Total Recorded Investment	1,015	1,100
Related Allowance
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	933	961
Recorded Investment With No Allowance	802	864
Recorded Investment With Allowance
Total Recorded Investment	802	864
Related Allowance
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	403	428
Recorded Investment With No Allowance	365	400
Recorded Investment With Allowance
Total Recorded Investment	365	400
Related Allowance