XML 141 R57.htm IDEA: XBRL DOCUMENT v3.19.2
Long-term Debt - Series C Narrative (Details) - $ / shares
1 Months Ended
Jul. 31, 2017
Oct. 31, 2015
Mar. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Apr. 30, 2016
Dec. 31, 2015
Preferred Stock Warrants              
Class of Stock [Line Items]              
Warrants outstanding (in shares)   163,877 2,667,587 2,672,502 2,672,502    
Warrant exercise price (in USD per share)   $ 6.11 $ 6.11 $ 6.11   $ 6.11 $ 6.11
Series C              
Class of Stock [Line Items]              
Temporary equity, shares issued (in shares) 163,877 327,759          
Stock issued, price per share (in USD per share) $ 6.11 $ 6.11