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Income Taxes - Additional Information (Detail) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Income Taxes [Line Items] |  |  |
Securities transactions income tax expense | $ 171,000 | $ 10,000 | $ 1,400,000
Change in income tax expense (benefit) due to write down of net deferred tax asset resulting from federal tax rate change |  |  | $ 4,300,000
Federal tax rate, percentage | 21.00% | 21.00% | 35.00%
Recognition of interest and penalties related to unrecognized tax benefits | $ 0 | $ 0 | $ 0
Earliest Tax Year [Member] |  |  |
Income Taxes [Line Items] |  |  |
Year under examination | 2016 | 2013 |
Latest Tax Year [Member] |  |  |
Income Taxes [Line Items] |  |  |
Year under examination | 2018 | 2015 |

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- Definition Amount of income tax expense (benefit) for remeasurement of deferred tax from change in tax rate pursuant to Tax Cuts and Jobs Act. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32639-109319 + Details
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