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Equity Investment - Narrative (Detail) - USD ($) $ in Thousands | 1 Months Ended | 3 Months Ended | 9 Months Ended
--- | --- | --- | ---
Jun. 30, 2020 | Mar. 31, 2020 | Oct. 31, 2016 | Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |
Non-cash impairment charge |  |  |  | $ 0 | $ 0 | $ 76,800 | $ 0
Proceeds from sale of equity investment |  |  |  |  |  | 10,000 | $ 0
October 2016 Investment | Variable Interest Entity, Not Primary Beneficiary |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |
Percentage of equity interest held | 10.00% |  | 10.00% |  |  |  |
Equity investments |  |  | $ 10,000 |  |  |  |
Non-cash impairment charge |  | $ 5,300 |  |  |  |  |
Proceeds from sale of equity investment | $ 10,000 |  |  |  |  |  |
Gain on sale of investment |  |  |  |  |  | $ 5,300 |

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