Loans and Allowance for Loan Losses - Schedule of Average Balance (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment, Total	$ 122,112	$ 103,551	$ 113,927	$ 102,507
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	19,960	24,234	20,445	27,197
Average Recorded Investment with an allowance recorded	14,771	7,792	10,393	8,086
Commercial Real Estate - Other [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	45,302	33,268	42,209	31,258
Average Recorded Investment with an allowance recorded	24,305	30,846	26,537	28,580
Residential [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	2,303	2,482	2,289	2,405
Average Recorded Investment with an allowance recorded	863	1,011	887	1,059
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	1,392	1,755	1,617	1,786
Average Recorded Investment with an allowance recorded	1,909	$ 2,163	2,013	$ 2,136
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with an allowance recorded	$ 11,307		$ 7,537

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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+ 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
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-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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+ 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
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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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