Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Deferred Revenue (Details)

v3.19.3
Summary of Significant Accounting Policies - Deferred Revenue (Details) - USD ($)
$ in Thousands
Sep. 30, 2019
Dec. 31, 2018
Dec. 31, 2017
Deferred Revenue Arrangement [Line Items]      
Deferred revenue $ 713,063 $ 591,625 $ 564,900
Customer agreements      
Deferred Revenue Arrangement [Line Items]      
Deferred revenue 601,976 576,727  
Customer agreements | Payments received      
Deferred Revenue Arrangement [Line Items]      
Deferred revenue 558,875 538,926  
Customer agreements | Financing component balance      
Deferred Revenue Arrangement [Line Items]      
Deferred revenue 43,101 37,801  
SREC contracts      
Deferred Revenue Arrangement [Line Items]      
Deferred revenue 111,087 14,898  
SREC contracts | Payments received      
Deferred Revenue Arrangement [Line Items]      
Deferred revenue 107,846 12,977  
SREC contracts | Financing component balance      
Deferred Revenue Arrangement [Line Items]      
Deferred revenue $ 3,241 $ 1,921