Annual report pursuant to Section 13 and 15(d)

Revenues Revenues - Narrative (Details)

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Revenues Revenues - Narrative (Details) - USD ($)
12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jan. 01, 2018
Disaggregation of Revenue [Line Items]      
Increase for deferral of shortfall payments $ 4,246,000    
Recognized revenue 15,000,000    
Contract assets   $ 0 $ 0
Shortfall Payments      
Disaggregation of Revenue [Line Items]      
Recognized revenue $ 1,500,000