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Interim Financial Data (Unaudited) - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017
Interim Reporting [Line Items] |  |
Tax benefit due to change in tax rate on the deferred tax assets and deferred tax liabilities |  | $ 1.9
Scenario, Forecast [Member] |  |
Interim Reporting [Line Items] |  |
Federal statutory tax rate, percentage | 21.00% |

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