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Intangible Assets - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
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Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount | $ 32,009 | $ 23,585
Accumulated Amortization | (14,752) | (12,503)
Net Carrying Amount | 17,257 | 11,082
Core Deposit Intangibles [Member] |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount | 25,907 | 17,447
Accumulated Amortization | (10,423) | (8,451)
Net Carrying Amount | 15,484 | 8,996
Customer Relationship Intangibles [Member] |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount | 5,699 | 5,699
Accumulated Amortization | (4,028) | (3,767)
Net Carrying Amount | 1,671 | 1,932
Mortgage Servicing Intangibles [Member] |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount | 403 | 439
Accumulated Amortization | (301) | (285)
Net Carrying Amount | $ 102 | $ 154

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- Definition Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 + Details
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- Definition Sum of the carrying amounts of all intangible assets, excluding goodwill, as of the balance sheet date, net of accumulated amortization and impairment charges. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16212-109274 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph ((a)(1),(b)) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 + Details
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