Loans and Allowance for Loan Losses - Loans Outstanding by Impairment Methodology (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	$ 80,588	$ 63,295
Collectively evaluated for impairment	4,179,784	4,153,770
Receivables Acquired with Deteriorated Credit Quality [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired with deteriorated credit quality	14,740	14,983
Non-residential Real Estate Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	11,843	8,619
Collectively evaluated for impairment	500,245	494,278
Non-residential Real Estate Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	9,363	8,608
Collectively evaluated for impairment	1,130,045	1,102,152
Residential Real Estate Permanent Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	8,337	7,543
Collectively evaluated for impairment	321,481	325,058
Residential Real Estate All Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	12,453	10,803
Collectively evaluated for impairment	687,420	665,886
Non-consumer Non-real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	33,780	22,983
Collectively evaluated for impairment	945,147	961,779
Consumer Non-real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	2,596	2,416
Collectively evaluated for impairment	261,851	266,453
Other Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	2,216	2,323
Collectively evaluated for impairment	160,655	160,293
Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively evaluated for impairment	172,940	177,871
Acquired Loans [Member] \| Receivables Acquired with Deteriorated Credit Quality [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired with deteriorated credit quality	$ 14,740	$ 14,983

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No definition available.

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- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524

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The balance of financing receivables that were individually evaluated for impairment.

+ References

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Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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