Quarterly report pursuant to Section 13 or 15(d)

Presentation and Summary of Significant Accounting Policies - Additional Information (Details)

v3.19.2
Presentation and Summary of Significant Accounting Policies - Additional Information (Details)
$ in Thousands
1 Months Ended 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2018
USD ($)
Jun. 30, 2019
USD ($)
Customer
Jun. 30, 2018
USD ($)
Customer
Jun. 30, 2019
USD ($)
Customer
Jun. 30, 2018
USD ($)
Customer
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Significant Accounting Policies [Line Items]              
Negative cash flows from operations       $ 16,606 $ 21,341 $ 42,227 $ 31,911
Net loss   $ 16,691 $ 14,330 32,997 27,379 61,104 $ 59,601
Accumulated deficit   203,408   203,408   $ 170,411  
Proceeds from common stock offerings, net $ 32,780     11,778 $ 32,536    
Cash, cash equivalents and marketable securities   $ 45,273   $ 45,273      
Sales Revenue, Net [Member] | Customer Concentration Risk [Member]              
Significant Accounting Policies [Line Items]              
Number of major customers | Customer   10 10 10 10    
Concentration risk percentage   25.90% 49.70% 24.90% 52.10%    
Equity Distribution Agreement [Member]              
Significant Accounting Policies [Line Items]              
Proceeds from common stock offerings, net       $ 12,215      
Equity Distribution Agreement [Member] | Maximum [Member]              
Significant Accounting Policies [Line Items]              
Aggregate available offering price, common stock       $ 35,468