Loans and Allowance for Loan Losses - Loans Outstanding by Impairment Methodology (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	$ 118,356	$ 104,623
Collectively evaluated for impairment	4,850,240	4,611,915
Loans Acquired with Deteriorated Credit Quality [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired with deteriorated credit quality	7,380	5,457
Real Estate [Member] \| Non-residential Real Estate Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	17,846	15,281
Collectively evaluated for impairment	608,775	626,337
Real Estate [Member] \| Non-residential Real Estate Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	25,333	17,013
Collectively evaluated for impairment	1,120,795	1,109,578
Real Estate [Member] \| Residential Real Estate Permanent Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	9,026	8,100
Collectively evaluated for impairment	319,676	322,234
Real Estate [Member] \| Residential Real Estate All Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	21,285	15,052
Collectively evaluated for impairment	806,219	770,603
Commercial and Financial [Member] \| Non-consumer Non-real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	19,432	31,349
Collectively evaluated for impairment	1,264,222	1,253,056
Consumer Non-real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	3,093	2,600
Collectively evaluated for impairment	323,769	286,320
Other Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	209	764
Collectively evaluated for impairment	141,700	143,681
Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	22,132	14,464
Collectively evaluated for impairment	265,084	100,106
Acquired Loans [Member] \| Loans Acquired with Deteriorated Credit Quality [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired with deteriorated credit quality	$ 7,380	$ 5,457

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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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