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Securities - Narrative (Detail) |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jan. 01, 2019 USD ($) | Mar. 31, 2019 USD ($) Security | Mar. 31, 2018 USD ($) | Dec. 31, 2018 USD ($) Security
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Percentage of investment portfolio |  | 100.00% |  | 100.00% |
Weighted-average period of re-pricing of portfolio |  | 4 years 2 months 12 days |  | 4 years 7 months 12 days |
Fair value of securities transferred from held to maturity to available for sale |  | $ (19,190,000) |  | $ (42,394,000) | [1]
Fair value of securities transferred from held-to-maturity to available-for-sale |  | 121,202,000 |  | $ 99,857,000 |
Unrealized losses on securities transferred from held to maturity to available for sale |  | 431,000 | $ 0 |  |
Impairment recognized |  | $ 0 |  |  |
U.S. agency and mortgage-backed securities |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Number of securities in an unrealized loss position | Security |  | 66 |  | 83 |
Total number of securities | Security |  | 90 |  | 90 |
Fair value of securities transferred from held to maturity to available for sale |  | $ (13,861,000) |  | $ (26,551,000) |
Fair value of securities transferred from held-to-maturity to available-for-sale |  | $ 95,566,000 |  | $ 84,922,000 |
Obligations of states and political subdivisions |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Number of securities in an unrealized loss position | Security |  | 26 |  | 56 |
Total number of securities | Security |  | 82 |  | 82 |
Fair value of securities transferred from held to maturity to available for sale |  | $ (3,816,000) |  | $ (14,334,000) |
Fair value of securities transferred from held-to-maturity to available-for-sale |  | 25,636,000 |  | 14,935,000 |
Corporate debt securities |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair value of securities transferred from held to maturity to available for sale |  | (1,513,000) |  | $ (1,509,000) |
Accounting Standards Update 2017-12 |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair value of securities transferred from held to maturity to available for sale | $ 23,000,000 |  |  |  |
Fair value of securities transferred from held-to-maturity to available-for-sale | 23,000,000 |  |  |  |
Unrealized losses on securities transferred from held to maturity to available for sale | $ 431,000 | $ 431,000 |  |  |
[1] | Derived from audited consolidated financial statements.

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