Annual report pursuant to Section 13 and 15(d)

Stockholder's Equity - Shelf Registration (Details)

v3.8.0.1
Stockholder's Equity - Shelf Registration (Details) - USD ($)
 3 Months Ended 12 Months Ended 22 Months Ended
Jan. 27, 2015
Jun. 30, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2017
Feb. 18, 2016
Class of Stock [Line Items]              
Aggregate offering price of shelf registration             $ 600,000,000
Reinvestment of dividends paid to common stockholders     $ 962,308 $ 815,889 $ 817,915    
Shelf registration after dividend reinvestment plan reduction     $ 524,500,000     $ 524,500,000  
Series A Cumulative Redeemable Preferred Stock [Member]              
Class of Stock [Line Items]              
Preferred stock interest rate     7.375%        
Dividend Reinvestment Plan [Member]              
Class of Stock [Line Items]              
Reinvestment of distributions to stockholders (in shares)           62,215  
Reinvestment of dividends paid to common stockholders           $ 1,800,000  
Depositary Shares [Member] | Underwritten Public Offering [Member]              
Class of Stock [Line Items]              
Reduction in shelf availability   $ 73,800,000          
Preferred Stock [Member] | Series A Cumulative Redeemable Preferred Stock [Member]              
Class of Stock [Line Items]              
Preferred stock interest rate 7.375%   7.375%