Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity At-the-Market Offering (Details)

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Stockholders' Equity At-the-Market Offering (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2021
Mar. 31, 2021
Jun. 30, 2020
Mar. 31, 2020
Jun. 30, 2021
Jun. 30, 2020
Subsidiary, Sale of Stock [Line Items]            
Number of shares authorized to be sold under equity distribution agreement (in shares) 35,000,000       35,000,000  
Number of common shares issued under equity distribution agreement and outstanding as of period-end (in shares) 7,490,235       7,490,235  
Accumulated proceeds from issuance of common shares under equity distribution agreement $ 128,600       $ 128,600  
Issuance of stock, net of offering costs $ 93 $ 99 $ 95 $ 142    
At the Market Offering [Member]            
Subsidiary, Sale of Stock [Line Items]            
Number of shares of stock issued during period (in shares) 0   0   0 0
Issuance of stock, net of offering costs $ 0   $ 0   $ 0 $ 0