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Equity (Details) - USD ($) |  |  |  |  |  |  | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Nov. 01, 2017 | Aug. 02, 2017 | May 03, 2017 | Mar. 01, 2017 | Feb. 03, 2017 | Jul. 14, 2016 | Aug. 31, 2017 | May 31, 2017 | Mar. 31, 2017 | Sep. 30, 2017 | Mar. 31, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016 | Dec. 31, 2016 | Dec. 31, 2015
Common stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of shares under public offering |  |  |  |  |  |  |  |  |  |  |  |  | $ 76,225,000 |  |  |
Payment to internalize the management team and terminate the existing management agreement using the proceed from public offering |  |  |  |  |  |  |  |  |  |  |  |  | 25,000,000 |  |  |
Accumulated Other Comprehensive Income |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss), Net of Tax |  |  |  |  |  |  |  |  |  | $ 205,761 |  |  | 205,761 |  | $ 320,917 |
Unrealized gain related to available-for-sale securities |  |  |  |  |  |  |  |  |  | $ 200,000 |  |  | $ 200,000 |  | 600,000 |
Net unrealized losses on derivatives designated as cash flow hedges, net of deferred losses on terminated interest swaps |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 200,000 |
Deferred losses on terminated interest swaps |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 100,000 |
Noncontrolling Interest |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, par value (in dollars per share) |  |  |  |  |  |  |  |  |  | $ 0.01 |  |  | $ 0.01 |  | $ 0.01 |
Distributions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash dividend declared (in dollars per share) |  |  |  |  |  |  |  |  |  | $ 0.18 |  | $ 0.16 | $ 0.53 | $ 0.46 |  |
Performance |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Vesting period (in years) |  |  |  |  |  |  |  |  |  |  |  |  | 3 years |  |  |
Restricted stock units eligible to receive annually |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,000,000 |  |  |
Chief executive officer | Restricted common stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of fully vested shares issued |  |  |  |  |  |  |  |  |  |  | 74,830 |  |  |  |  |
Total grant date fair value |  |  |  |  |  |  |  |  |  |  | $ 600,000 |  |  |  |  |
Vesting percentage |  |  |  |  |  |  |  |  |  |  | 25.00% |  |  |  |  |
Chief executive officer | Restricted common stock | First Anniversaries |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  |  |  |  |  |  |  |  | 25.00% |  |  |  |  |
Chief executive officer | Restricted common stock | Second Anniversaries |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  |  |  |  |  |  |  |  | 25.00% |  |  |  |  |
Chief executive officer | Restricted common stock | Third Anniversaries |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  |  |  |  |  |  |  |  | 25.00% |  |  |  |  |
Chief executive officer | Performance |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Granted of restricted stock units that vest at the end of four-year performance period (in shares) |  |  |  |  |  |  | 357,569 |  |  |  | 448,980 |  |  |  |  |
Vesting period (in years) |  |  |  |  |  |  |  |  |  |  |  |  | 4 years |  | 4 years | 4 years
Total grant date fair value |  |  |  |  |  |  | $ 2,700,000 |  |  |  | $ 1,000,000 |  |  |  |  |
Percentage increased in long-term equity awards due to equity capitalization growth goals |  |  |  |  |  |  |  |  |  |  |  |  | 10.00% |  |  |
Restricted stock units eligible to receive annually |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,000,000 |  |  |
Expiration period (in years) |  |  |  |  |  |  |  |  |  |  |  |  | 5 years |  |  |
Chief executive officer | Employee compensation and benefits | Restricted common stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based compensation expense |  |  |  |  |  |  |  |  |  |  | 100,000 |  |  |  |  |
Chief executive officer | Employee compensation and benefits | Performance |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based compensation expense |  |  |  |  |  |  | $ 100,000 |  |  |  |  |  |  |  |  |
Chief executive officer | Employee compensation and benefits | Performance | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based compensation expense |  |  |  |  |  |  |  |  |  |  | $ 100,000 |  |  |  |  |
Employees of the company and a related party | Restricted common stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of fully vested shares issued |  |  |  |  |  |  |  |  | 299,750 |  |  |  |  |  |  |
Total grant date fair value |  |  |  |  |  |  |  |  | $ 2,400,000 |  |  |  |  |  |  |
Vesting percentage |  |  |  |  |  |  |  |  | 33.00% |  |  |  |  |  |  |
Employees of the company and a related party | Restricted common stock | March, 2018 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  |  |  |  |  |  | 33.00% |  |  |  |  |  |  |
Employees of the company and a related party | Restricted common stock | March, 2019 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  |  |  |  |  |  | 33.00% |  |  |  |  |  |  |
Employees of the company and a related party | Employee compensation and benefits | Restricted common stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based compensation expense |  |  |  |  |  |  |  |  | $ 400,000 |  |  |  |  |  |  |
Employees of the company and a related party | Selling and administrative expense | Restricted common stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based compensation expense |  |  |  |  |  |  |  |  | $ 500,000 |  |  |  |  |  |  |
8.25% Series A preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Return on the preferred shares issued to third parties by its subsidiary REIT (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  | 8.25% | 8.25% | 8.25% |
7.75% Series B preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Return on the preferred shares issued to third parties by its subsidiary REIT (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  | 7.75% | 7.75% | 7.75% |
8.50% Series C preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Return on the preferred shares issued to third parties by its subsidiary REIT (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  | 8.50% | 8.50% | 8.50% |
Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of common stock sold under public offering (in shares) |  |  |  |  |  |  |  | 9,500,000 |  |  |  |  | 9,500,000 |  |  |
Issued price per share (in dollars per share) |  |  |  |  |  |  |  | $ 8.05 |  |  |  |  |  |  |  |
Proceeds from issuance of shares under public offering |  |  |  |  |  |  |  | $ 76,200,000 |  |  |  |  |  |  |  |
Payment to internalize the management team and terminate the existing management agreement using the proceed from public offering |  |  |  |  |  |  |  | $ 25,000,000 |  |  |  |  |  |  |  |
Number of shares available under an "At-The-Market" equity offering with JMP Securities LLC |  |  |  |  |  |  |  |  |  | 7,500,000 |  |  | 7,500,000 |  |  |
Value of common stock available under shelf registration statement |  |  |  |  |  |  |  |  |  | $ 323,500,000 |  |  | $ 323,500,000 |  |  |
Aggregate amount of securities filed under shelf registration statement |  |  |  |  |  |  |  |  |  | $ 500,000,000 |  |  | $ 500,000,000 |  |  |
Distributions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash dividend declared (in dollars per share) | $ 0.19 | $ 0.18 | $ 0.18 | $ 0.17 |  |  |  |  |  |  |  |  |  |  |  |
Common Stock | Non-management members of the Board of Directors |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of fully vested shares issued |  |  |  |  |  |  |  |  | 74,375 |  |  |  |  |  |  |
Common Stock | Non-management members of the Board of Directors | Selling and administrative expense |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based compensation expense |  |  |  |  |  |  |  |  | $ 600,000 |  |  |  |  |  |  |
Preferred Stock | 8.25% Series A preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Distributions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash dividend declared on redeemable preferred stock (in dollars per share) | $ 0.515625 | 0.515625 | 0.515625 |  | $ 0.515625 |  |  |  |  |  |  |  |  |  |  |
Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Return on the preferred shares issued to third parties by its subsidiary REIT (as a percent) | 8.25% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock | 7.75% Series B preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Distributions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash dividend declared on redeemable preferred stock (in dollars per share) | $ 0.484375 | 0.484375 | 0.484375 |  | 0.484375 |  |  |  |  |  |  |  |  |  |  |
Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Return on the preferred shares issued to third parties by its subsidiary REIT (as a percent) | 7.75% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock | 8.50% Series C preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Distributions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash dividend declared on redeemable preferred stock (in dollars per share) | $ 0.53125 | $ 0.53125 | $ 0.53125 |  | $ 0.53125 |  |  |  |  |  |  |  |  |  |  |
Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Return on the preferred shares issued to third parties by its subsidiary REIT (as a percent) | 8.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ACM Acquisition | ACM / Our "Former Manager" |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Noncontrolling Interest |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Consideration in stock to be paid with operating partnership units (in shares) |  |  |  |  |  | 21,230,769 |  |  |  |  |  |  |  |  |  |
Number of preferred stock shares paired with each operating partnership units |  |  |  |  |  | 1 |  |  |  |  |  |  |  |  |  |
Operating Partnership |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Noncontrolling Interest |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Conversion ratio for operating partnership units to common stock shares |  |  |  |  |  |  |  |  |  |  |  |  | 1 |  |  |
Operating Partnership | Special voting preferred shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Noncontrolling Interest |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of preferred stock shares paired with each operating partnership units |  |  |  |  |  |  |  |  |  |  |  |  | 1 |  |  |
Preferred stock, par value (in dollars per share) |  |  |  |  |  |  |  |  |  | $ 0.01 |  |  | $ 0.01 |  |  |
Voting power of outstanding stock (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  | 25.60% |  |  |
Operating Partnership | ACM Acquisition |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Noncontrolling Interest |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Consideration in stock to be paid with operating partnership units (in shares) |  |  |  |  |  | 21,230,769 |  |  |  |  |  |  |  |  |  |
Value of operating partnership units issues as consideration |  |  |  |  |  | $ 154,800,000 |  |  |  |  |  |  |  |  |  |

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