Loans and Allowance for Loan Losses - Schedule of Average Balance (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment, Total	$ 108,923	$ 99,172	$ 107,820	$ 102,230
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	20,228	25,817	20,073	26,038
Average Recorded Investment with an allowance recorded	11,846	8,448	10,091	7,996
Commercial Real Estate - Other [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with an allowance recorded	21,439	22,916	24,246	28,911
Residential [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	2,189	2,376	2,274	2,121
Average Recorded Investment with an allowance recorded	942	1,147	918	1,125
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	1,741	1,717	1,722	1,420
Average Recorded Investment with an allowance recorded	1,970	2,069	2,050	2,021
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	43,893	$ 34,682	41,771	$ 32,598
Average Recorded Investment with an allowance recorded	$ 4,675		$ 4,675

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
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-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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

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