Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements (Warrants Outstanding) (Details)

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Fair Value Measurements (Warrants Outstanding) (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Jan. 12, 2018
Class of Warrant or Right [Line Items]        
Change in fair value $ 357 $ 36    
Class of Warrant or Right, Outstanding 338,583      
ESW Holdings, Inc.        
Class of Warrant or Right [Line Items]        
Class of Warrant or Right, Outstanding       925,000
Hale Capital, LLP        
Class of Warrant or Right [Line Items]        
Class of Warrant or Right, Outstanding 238,583   314,286  
Class of Warrant or Right, Exercise Price of Warrants or Rights $ 2.80      
Warrants and Rights Outstanding, Maturity Date Oct. 21, 2026      
iStudy Co., Ltd.        
Class of Warrant or Right [Line Items]        
Class of Warrant or Right, Outstanding 100,000      
Class of Warrant or Right, Exercise Price of Warrants or Rights $ 2.43      
Warrants and Rights Outstanding, Maturity Date Aug. 31, 2028