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Impairment of Investment Securities - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2018 USD ($) Security | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($)
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Number of securities in an unrealized loss positions | Security |  | 132 |  |
Corporate/Mortgage-Backed Securities, Amortized cost |  | $ 924,054,000 | $ 740,846,000 |
Securities available for sale |  | 909,247,000 | 731,358,000 |
Other than-temporary impairment charge | [1] | 9,164,000 | 0 | $ 0
Other investments |  | 30,456,000 | 29,837,000 |
Equity Securities, FV-NI |  | 1,670,000 |  |
Equity Securities, FV-NI, Gain (Loss) |  | 0 |  |
Threshold Percentage of Value Decline in Equity Securities to be considered Other than Temporary Impairment |  |  | 0 | 0
Debt Securities [Member] |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Corporate/Mortgage-Backed Securities, Amortized cost |  | 924,054,000 | 739,176,000 |
Securities available for sale |  | 909,247,000 | 729,688,000 |
Pooled Trust Preferred Collateralized Debt Obligations [Member] |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Corporate/Mortgage-Backed Securities, Amortized cost |  | 0 | 27,499,000 |
Securities available for sale |  | 0 | 23,646,000 |
Other than-temporary impairment charge |  | $ 0 | 0 | $ 0
Obligations of U.S. Government-Sponsored Enterprises [Member] |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Total unrealized losses |  | 82.00% |  |
Corporate Securities [Member] |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Corporate/Mortgage-Backed Securities, Amortized cost |  | $ 20,912,000 | 15,907,000 |
Securities available for sale |  | $ 21,012,000 | 16,493,000 |
Debt Securities [Member] |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Securities available for sale |  |  | 729,688,000 |
US States and Political Subdivisions Debt Securities [Member] | Other Government - Sponsored Enterprises [Member] |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Total unrealized losses |  | 16.00% |  |
Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage - Backed Securities - Residential [Member] |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Number of securities in an unrealized loss positions |  | 0 |  |
Corporate/Mortgage-Backed Securities, Amortized cost |  | $ 686,906,000 | 632,422,000 |
Securities available for sale |  | 673,361,000 | 625,555,000 |
Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government - Sponsored Enterprises [Member] |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Corporate/Mortgage-Backed Securities, Amortized cost |  | 10,000,000 | 1,098,000 |
Securities available for sale |  | $ 10,012,000 | $ 1,097,000 |
[1] | Represents the increase in cash flows recognized either as principal payments or interest income during the period.

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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 This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the equity method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value subject to the equity accounting method. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 35 -Paragraph 32 -URI http://asc.fasb.org/extlink&oid=114001220&loc=d3e32787-111569 + Details
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