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Related-Party Transactions - Additional Information (Detail) - USD ($) |  | 1 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Jul. 01, 2015 | Jul. 31, 2015 | Dec. 31, 2015 | Jun. 30, 2015 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |
Number of executive officers |  |  |  |  |  | 2 |  |
Due to adviser and administrator | [1] |  |  |  |  | $ 2,289,000 | $ 2,075,000 |
Annual base management fee, in percentage of stockholders' equity, adjusted to unrealized gains or losses (as percent) |  | 1.50% |  |  |  |  |  |
Quarterly base management fee, in percentage of stockholders' equity, adjusted to unrealized gains or losses (as percent) |  | 0.375% |  |  |  |  |  |
Annual base management fee, in percentage of stockholders' equity, in excess of recorded value of preferred stock (as percent) |  |  |  |  | 2.00% |  |  |
Base management fee | [2] |  |  |  |  | $ 4,959,000 | 3,930,000 | $ 3,474,000
Pre-incentive quarterly fee FFO in percentage of common stockholders' equity that will reward the adviser (as percent) |  | 2.00% |  |  | 1.75% |  |  |
Pre-incentive annual fee FFO in percentage of common stockholders' equity that will reward the adviser (as percent) |  | 8.00% |  |  | 7.00% |  |  |
Amount to be paid to adviser in percentage of pre-incentive fee condition one (as percent) |  | 15.00% |  |  | 100.00% |  |  |
Incentive fee description |  |  |  |  |  | However, in no event shall the incentive fee for a particular quarter exceed by 15.0% (the cap) the average quarterly incentive fee paid by us for the previous four quarters (excluding quarters for which no incentive fee was paid). |  |
Pre-incentive fee in percentage of common stockholders' equity that awards adviser hundred percent of amount of pre-incentive fee, maximum percentage |  |  |  |  | 2.1875% |  |  |
Amount to be paid to adviser in percentage of pre-incentive fee condition two (as percent) |  |  |  |  |  | 20.00% |  |
Pre-incentive fee in percentage of common stockholders' equity that awards the adviser 20% of the amount of the pre-incentive fee, minimum percentage |  |  |  |  |  | 2.1875% |  |
Incentive fee | [2] |  |  |  |  | $ 2,422,000 | 2,381,000 | 4,650,000
Credits related to unconditional and irrevocable voluntary waivers issued by the adviser | [2] |  |  |  |  |  | 0 | 2,500,000
Related-party transactions incentive fee, net |  |  |  |  |  | 2,400,000 | 2,400,000 | 2,200,000
Capital gains-based incentive fee percentage (as percent) |  | 15.00% |  |  |  |  |  |
Capital gain fee |  |  |  |  |  | 0 | 0 | 0
Notice period for termination of agreement without cause along with the two-thirds vote |  |  | 120 days |  |  |  |  |
Notice period for termination of agreement with cause |  |  | 30 days |  |  |  |  |
Multiple to compute the termination fee payable (as percent) |  |  | 200.00% |  |  |  |  |
Administration fee | [2] |  |  |  |  | 1,272,000 | 1,474,000 | 1,419,000
Fees paid |  |  |  |  |  | $ 200,000 | $ 300,000 | $ 200,000
Financing fee on total secured mortgages (as percent) |  |  |  |  |  | 0.24% | 0.32% | 0.29%
Minimum |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |
Percentage of the amount of the mortgage (as percent) |  |  |  |  |  | 0.15% |  |
Maximum |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |
Percentage of the amount of the mortgage (as percent) |  |  |  |  |  | 1.00% |  |
Amended Advisory Agreement |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |
Credits related to unconditional and irrevocable voluntary waivers issued by the adviser |  |  |  | $ 0 |  | $ 0 | $ 0 |
Adviser and Administrator |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |
Credits related to unconditional and irrevocable voluntary waivers issued by the adviser | [2] |  |  |  |  | $ 0 |  |
Dealer Manager |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |
Agreement termination date |  |  |  |  |  | Mar. 28, 2015 |  |
Write-off of deferred offering costs |  |  |  |  |  | $ 100,000 |  |
Dealer manager fee in percentage of gross proceeds of shares of senior common stock sold (as percent) |  |  |  |  |  | 7.00% |  |
Sales commission fee in percentage of gross proceeds of shares of senior common stock sold (as percent) |  |  |  |  |  | 3.00% |  |
Payments made to the dealer manager pursuant to dealer manager agreement |  |  |  |  |  |  |  | $ 300,000
[1] | Refer to Note 2 “Related-Party Transactions”
[2] | Refer to Note 2 “Related-Party Transactions”

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