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Stock Transactions and Unit Redemptions - Schedule of Share Repurchase Activity (Detail) - Class A Common Stock [Member] - USD ($) | 3 Months Ended | 6 Months Ended | 12 Months Ended
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Jun. 30, 2019 | Jun. 30, 2019 | Dec. 31, 2018
Class Of Stock [Line Items] |  |  |
Balance at beginning of period, Total Number of Shares Repurchased |  | 50,000 |
Repurchase of common stock, shares | 1,613,032 | 1,613,032 |
Balance at Ending of period, Total Number of Shares Repurchased | 1,663,032 | 1,663,032 | 50,000
Repurchase, Average Price Paid per Unit | $ 8.61 | $ 8.65 | $ 9.73
Total Number of Shares Purchased as Part of Publicly Announced Program | 1,613,032 | 1,663,032 | 50,000
Approximate Dollar Value of Units and Shares That May Yet Be Redeemed/Purchased Under the Plan | $ 186,104 | $ 185,618 | $ 199,514

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- Definition Total cost of shares repurchased divided by the total number of shares repurchased. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655 + Details
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