Related Parties (Details)
$ in Thousands
 1 Months Ended 12 Months Ended
Jun. 21, 2018
USD ($)
May 31, 2017
USD ($)
Apr. 30, 2017
USD ($)
item
Jan. 31, 2017
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Related Parties              
Due to related parties           $ 0  
Maturity term from issuance date of the notes   7 years 7 years        
Maturity date of termination   60 days 60 days        
Interest rate (as a percent)     2.05%        
Aggregate principal balance           0  
Amount from related party           0  
Amount due to related party           0  
January 2017 promissory note              
Related Parties              
Due to related parties           0  
Interest rate (as a percent)       1.97%      
Aggregate principal balance           0  
Amount from related party           0  
Amount due to related party           0  
May 2017 promissory note              
Related Parties              
Interest rate (as a percent)   2.04%          
Aggregate principal balance           0  
Amount from related party           0  
Flagship | Services agreement              
Related Parties              
Payment of general and administrative expenses         $ 1,300 900 $ 800
Cash payments         $ 1,300 $ 900 $ 800
Board of Directors Chairman              
Related Parties              
Amount loaned or remitted to related parties   $ 1,800   $ 700      
Principal amount of promissory note forgiven $ 2,500            
Interest on promissory note forgiven 100            
Executive officer              
Related Parties              
Amount loaned or remitted to related parties     $ 200        
Number of promissory notes | item     2        
Number of restricted stock agreements | item     2        
Aggregate principal balance 200            
Interest income form related parties 100            
Amount from related party $ 200