Quarterly report pursuant to Section 13 or 15(d)

Revenues - Narrative (Details)

v3.19.2
Revenues - Narrative (Details) - USD ($)
$ in Thousands
 6 Months Ended 12 Months Ended
Jun. 30, 2019
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2018
Dec. 31, 2017
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]          
Deferred revenue $ 1,296 $ 1,296   $ 4,304 $ 15,000
Revenue   2,054   $ 15,000  
Shortfall Payments          
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]          
Deferred revenue $ 1,100 1,100      
Revenue   $ 1,000 $ 300    
Practical expedients          
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]          
Contract term (greater than) P1Y