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Impairment of Investment Securities - Additional Information (Detail) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2018 USD ($) | Sep. 30, 2017 USD ($) | Sep. 30, 2018 USD ($) | Sep. 30, 2017 USD ($) | Dec. 31, 2017 USD ($)
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |  |
Other than temporary impairment charges recognized |  |  | $ 0 | $ 0 |
Amortized Cost | $ 915,350,000 |  | 915,350,000 |  | $ 740,846,000
Securities available for sale, at fair value | 889,056,000 |  | 889,056,000 |  | 731,358,000
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss | 43,987,000 |  | $ 43,987,000 |  | 18,534,000
Probability of default |  |  | 100.00% |  |
Federal Home Loan Bank Stock | $ 25,029,000 |  | $ 25,029,000 |  | 29,837,000
Investment Securities in Unrealized Loss Position, Qualitative Disclosure, Number of Positions, Total | 183 |  | 183 |  |
Pooled Trust Preferred Collateralized Debt Obligations [Member] |  |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |  |
Securities available for sale, at fair value |  |  |  |  | 23,646,000
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss |  |  |  |  | 4,379,000
Trust preferred collateralized debt obligations [Member] |  |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |  |
Other than temporary impairment charges recognized |  |  |  | $ 0 |
Corporate Debt Securities [Member] |  |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |  |
Securities available for sale, at fair value | $ 21,101,000 |  | $ 21,101,000 |  | 16,493,000
Pooled Trust Preferred Securities [Member] |  |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |  |
Other than temporary impairment charges recognized |  | $ 0 |  |  |
Equity Securities [Member] |  |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |  |
Other than temporary impairment charges recognized | 0 | $ 0 |  |  |
Continuous Unrealized Loss Position, Fair Value | $ 0 |  | $ 0 |  | 0
Obligations of U.S. Government-Sponsored Enterprises - Other Government-Sponsored Enterprises [Member] |  |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |  |
Percent of Unrealized Losses | 84.00% |  | 84.00% |  |
Reported Value Measurement [Member] |  |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |  |
Securities available for sale, at fair value | $ 889,056,000 |  | $ 889,056,000 |  | 731,358,000
Federal Home Loan Bank Stock | 25,029,000 |  | 25,029,000 |  |
Pooled Trust Preferred Collateralized Debt Obligations [Member] |  |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |  |
Amortized Cost | 0 |  | 0 |  | 27,499,000
Securities available for sale, at fair value | $ 0 |  | $ 0 |  | $ 23,646,000

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- Definition Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss + References No definition available. + Details
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- Definition Investment Securities in Unrealized Loss Position, Qualitative Disclosure, Number of Positions, Total + References No definition available. + Details
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- Definition This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References No definition available. + Details
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- Definition Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 325 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=75031641&loc=d3e63345-112809 + Details
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- Definition The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting. + References No definition available. + Details
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