Quarterly report pursuant to Section 13 or 15(d)

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

v3.19.1
Presentation and Summary of Significant Accounting Policies - Additional Information (Details)
$ in Thousands
1 Months Ended 3 Months Ended 12 Months Ended
Jun. 30, 2018
USD ($)
Mar. 31, 2019
USD ($)
Customer
Mar. 31, 2018
USD ($)
Customer
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Significant Accounting Policies [Line Items]          
Negative cash flows from operations   $ 4,632 $ 13,248 $ 42,227 $ 31,911
Net loss   16,306 13,049 61,104 $ 59,601
Accumulated deficit   186,717   $ 170,411  
Proceeds from common stock offerings, net $ 32,780 4,160 $ (64)    
Cash, cash equivalents and marketable securities   $ 50,923      
Sales Revenue, Net [Member] | Customer Concentration Risk [Member]          
Significant Accounting Policies [Line Items]          
Number of major customers | Customer   10 10    
Concentration risk percentage   28.00% 58.70%    
Equity Distribution Agreement [Member]          
Significant Accounting Policies [Line Items]          
Proceeds from common stock offerings, net   $ 4,160      
Equity Distribution Agreement [Member] | Maximum [Member]          
Significant Accounting Policies [Line Items]          
Aggregate available offering price, common stock   $ 44,904