Securities - Additional Information (Detail) - USD ($) |
3 Months Ended | 9 Months Ended | |||
|---|---|---|---|---|---|
Sep. 30, 2017 |
Sep. 30, 2016 |
Sep. 30, 2017 |
Sep. 30, 2016 |
Dec. 31, 2016 |
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| Investment Securities [Line Items] | |||||
| Impairment charges on securities in continuous unrealized loss position for 12 months or longer | $ 0 | $ 0 | $ 0 | ||
| Net realized gains (losses) on sales of securities | 267,000 | $ 46,000 | 1,473,000 | $ 46,000 | |
| Net unrealized gains (losses) recorded in comprehensive income | 227,000 | $ 321,000 | 971,000 | $ 314,000 | |
| Securities available for sale | 598,440,000 | 598,440,000 | 516,964,000 | ||
| Securities Pledged as Collateral [Member] | |||||
| Investment Securities [Line Items] | |||||
| Securities available for sale | $ 130,700,000 | $ 130,700,000 | $ 133,000,000 | ||
| X | ||||||||||
- Definition Amount of accumulated pre-tax unrealized loss on investments in available-for-sale securities that have been in a loss position for twelve months or longer. No definition available.
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| X | ||||||||||
- Definition Investment Securities [Line Items] No definition available.
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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
- Definition This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
- Definition Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities and unrealized holding gain (loss) related to transfers of securities into the available-for-sale classification and out of the held-to-maturity classification. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
- Details
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