Loans and Allowance for Loan Losses - Loans Outstanding by Impairment Methodology (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	$ 129,244	$ 118,356
Collectively evaluated for impairment	4,906,338	4,850,240
Loans Acquired with Deteriorated Credit Quality [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired with deteriorated credit quality	6,920	7,380
Real Estate [Member] \| Non-residential Real Estate Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	26,281	17,846
Collectively evaluated for impairment	612,738	608,775
Real Estate [Member] \| Non-residential Real Estate Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	26,695	25,333
Collectively evaluated for impairment	1,163,074	1,120,795
Real Estate [Member] \| Residential Real Estate Permanent Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	8,705	9,026
Collectively evaluated for impairment	324,961	319,676
Real Estate [Member] \| Residential Real Estate All Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	21,883	21,285
Collectively evaluated for impairment	819,550	806,219
Commercial and Financial [Member] \| Non-consumer Non-real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	28,722	19,432
Collectively evaluated for impairment	1,297,882	1,264,222
Consumer Non-real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	2,875	3,093
Collectively evaluated for impairment	324,131	323,769
Other Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	26	209
Collectively evaluated for impairment	142,394	141,700
Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	14,057	22,132
Collectively evaluated for impairment	221,608	265,084
Acquired Loans [Member] \| Loans Acquired with Deteriorated Credit Quality [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired with deteriorated credit quality	$ 6,920	$ 7,380

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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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