Quarterly report pursuant to Section 13 or 15(d)

Equity - Additional Information (Details)

v3.10.0.1
Equity - Additional Information (Details)
 5 Months Ended 9 Months Ended 15 Months Ended
May 31, 2018
USD ($)
$ / shares
shares
Apr. 04, 2018
USD ($)
shares
Mar. 27, 2018
USD ($)
$ / shares
shares
Apr. 12, 2017
USD ($)
security
May 31, 2018
USD ($)
$ / shares
shares
Sep. 30, 2018
USD ($)
$ / shares
shares
Sep. 30, 2017
USD ($)
shares
Jun. 30, 2018
USD ($)
shares
Jan. 10, 2018
shares
Jan. 09, 2018
shares
Dec. 31, 2017
$ / shares
shares
Dec. 31, 2016
shares
Aug. 07, 2015
USD ($)
Subsidiary, Sale of Stock [Line Items]                          
Stock authorized and unissued (in shares)                 6,500,000        
Common stock, shares authorized (in shares)           91,500,000       98,000,000 98,000,000    
Preferred stock, shares authorized (in shares)           6,500,000              
Preferred stock, par value (in dollars per share) | $ / shares           $ 0.001              
Preferred stock, liquidation value | $           $ 9,826,000              
Common stock, par value (in dollars per share) | $ / shares           $ 0.001         $ 0.001    
Common stock, shares issued (in shares)           16,070,616         13,791,574    
Common stock, shares outstanding (in shares)           16,070,616         13,791,574    
Maximum number of securities that can be sold (in securities) | security       2                  
Proceeds from issuance of preferred and common equity | $           $ 34,397,000 $ 40,421,000            
Average sales price of common stock sold (in dollars per share) | $ / shares     $ 12.15                    
Discounts and offering expenses | $     $ 12,700,000     $ 1,894,000 $ 1,962,000            
2017 Registration Statement                          
Subsidiary, Sale of Stock [Line Items]                          
Proceeds from issuance of preferred and common equity | $               $ 45,800,000          
Secondary Public Stock Offering                          
Subsidiary, Sale of Stock [Line Items]                          
Net proceeds from issuance of stock | $     $ 13,400,000                    
Sale of common stock sold under sale agreement (in shares)     1,100,000                    
Over-allotment option                          
Subsidiary, Sale of Stock [Line Items]                          
Discounts and offering expenses | $   $ 1,900,000                      
Net proceeds from issuance of stock | $   $ 2,000,000                      
Sale of common stock sold under sale agreement (in shares)   165,000                      
ATM Program                          
Subsidiary, Sale of Stock [Line Items]                          
Common stock, shares issued (in shares)           1,324,867              
Common stock, value authorized | $                         $ 30,000,000.0
Sale of common stock sold under sale agreement (in shares)           716,231              
Average sales price price (in dollars per share) | $ / shares           $ 12.83              
Common stock, value, outstanding | $           $ 17,000,000              
Common stock, value, issued | $           16,700,000              
At Market Program 2017 Issuances                          
Subsidiary, Sale of Stock [Line Items]                          
Discounts and offering expenses | $           9,100,000              
Net proceeds from issuance of stock | $           $ 9,200,000              
Average sales price price (in dollars per share) | $ / shares           $ 12.90              
Common Stock                          
Subsidiary, Sale of Stock [Line Items]                          
Common stock, shares outstanding (in shares)           16,070,616 13,485,025       13,791,574 10,024,875  
Common Stock | 2017 Registration Statement                          
Subsidiary, Sale of Stock [Line Items]                          
Common stock, shares issued (in shares)           3,675,306              
Common stock issued (in shares)               544,686          
Securities allowed for issuance (amount up to) | $       $ 300,000,000                  
Preferred Stock | 2017 Registration Statement                          
Subsidiary, Sale of Stock [Line Items]                          
Preferred stock, shares outstanding (in shares)           20,280              
Series B Preferred Stock                          
Subsidiary, Sale of Stock [Line Items]                          
Preferred stock, shares authorized (in shares)           6,500,000         0    
Preferred stock, par value (in dollars per share) | $ / shares           $ 0.001         $ 0    
Preferred stock, shares outstanding (in shares)           393,048         0    
Preferred stock, shares issued (in shares)           393,048         0    
Series B Preferred Stock | Preferred Stock                          
Subsidiary, Sale of Stock [Line Items]                          
Common stock, shares outstanding (in shares)           393,048 0       0 0  
Securities allowed for issuance (amount up to) | $ $ 150,000,000       $ 150,000,000                
Maximum amount authorized in Primary Offering (in shares) 6,000,000                        
Dividend rate (as percent) 6.00%                        
Average sales price of common stock sold (in dollars per share) | $ / shares $ 25       $ 25                
Proceeds from issuance of preferred stock | $ $ 131,300,000         $ 9,800,000              
Discounts and offering expenses | $           576,000              
Net proceeds from issuance of stock | $           $ 8,800,000              
Sale of common stock sold under sale agreement (in shares)         0 393,048              
OP Unit Holder                          
Subsidiary, Sale of Stock [Line Items]                          
Minimum period required to exercise, in months           12 months