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Related Party Transactions - Additional Information (Detail) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018 | Dec. 31, 2018
Related Party Transaction [Line Items] |  |  |  |  |
Gain (Loss) on Investments | $ (205) | $ (67) | $ 148 | $ (58) |
WisdomTree ETF [Member] |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Investment | $ 3,193 |  | $ 3,193 |  | $ 7,117

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- Definition Sum of the carrying amounts as of the balance sheet date of all investments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.1(h)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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