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Non-Marketable Investments - Additional Information (Detail) - USD ($) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2017
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items] |  |  |
Carrying value of the Company's non-marketable investments | $ 1,800,000 |  | $ 1,900,000
Losses from non-marketable investments |  | $ (200,000) |
Distributions received from funds | $ 0 | $ 400,000 |
Limited Partnerships Investments [Member] | Minimum [Member] |  |  |
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items] |  |  |
Ownership interest of Company | 5.00% |  |

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