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Non-Marketable Investments - Additional Information (Detail) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2018
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]          
Carrying value of the Company's non-marketable investments $ 2,400,000   $ 2,400,000   $ 2,500,000
Distributions received from funds $ 0 $ 0 $ 0 $ 0  
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%