Loans (Impaired Loans) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	$ 69,656	$ 61,007	$ 105,577
Recorded Investment With No Allowance	50,473	32,588	43,083
Recorded Investment With Allowance	3,118	15,874	37,314
Total Recorded Investment	53,591	48,462	80,397
Related Allowance	1,680	6,926	8,237
Average Recorded Investment	49,636	71,741	86,580
Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	706	545	1,255
Recorded Investment With No Allowance	636	531	0
Recorded Investment With Allowance	0	0	1,069
Total Recorded Investment	636	531	1,069
Related Allowance	0	0	900
Average Recorded Investment	571	428	214
Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	42,212	31,429	56,784
Recorded Investment With No Allowance	29,007	15,337	21,709
Recorded Investment With Allowance	2,853	7,004	19,096
Total Recorded Investment	31,860	22,341	40,805
Related Allowance	1,613	4,140	4,200
Average Recorded Investment	27,154	34,894	42,630
Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	22,919	27,792	44,652
Recorded Investment With No Allowance	17,441	15,697	19,010
Recorded Investment With Allowance	265	8,870	17,149
Total Recorded Investment	17,706	24,567	36,159
Related Allowance	67	2,786	3,137
Average Recorded Investment	20,339	34,633	40,258
Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	3,007	0	1,497
Recorded Investment With No Allowance	2,793	0	1,100
Total Recorded Investment	2,793	0	1,100
Average Recorded Investment	739	634	1,392
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	812	907	961
Recorded Investment With No Allowance	596	745	864
Total Recorded Investment	596	745	864
Average Recorded Investment	674	804	1,617
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	0	334	428
Recorded Investment With No Allowance	0	278	400
Total Recorded Investment	0	278	400
Average Recorded Investment	$ 159	$ 348	$ 469

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Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 17

-URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5258-111524

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Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 14A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953550-111524

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