Loans and Allowance for Loan Losses - Schedule of Average Balance (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment, Total	$ 111,359	$ 100,772	$ 106,638
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	21,295	24,780	34,708
Average Recorded Investment with an allowance recorded	9,546	7,002	16,669
Commercial Real Estate - Other [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	39,902	34,632	28,793
Average Recorded Investment with an allowance recorded	27,317	26,562	20,465
Residential [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	2,305	2,415	1,355
Average Recorded Investment with an allowance recorded	840	1,012	1,074
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	832	1,761	855
Average Recorded Investment with an allowance recorded	1,957	2,155	2,367
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with an allowance recorded	$ 7,365	$ 453	$ 352

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

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Amount of average investment of impaired financing receivables for which there is no related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

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