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Divestitures - Additional Information (Detail) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |
Gain (loss) on divestiture and sale of investments | $ 18,421,000 |  | $ 561,000
Other Sales [Member] |  |  |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |  |  |
Gain (loss) on divestiture and sale of investments | $ 18,400,000 | $ 0 | $ 0

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