Quarterly report pursuant to Section 13 or 15(d)

Accounts Receivable and Revenues from Contracts with Customers - Additional Information (Details)

v3.19.2
Accounts Receivable and Revenues from Contracts with Customers - Additional Information (Details) - Accounts Receivable
$ in Millions
6 Months Ended 12 Months Ended
Jun. 30, 2019
USD ($)
Customer
Jun. 30, 2018
USD ($)
Customer
Dec. 31, 2018
USD ($)
Credit Concentration Risk      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Concentration risk, percentage 67.00%   59.00%
Accounts receivable, major customers $ 32.4   $ 34.8
Customer Concentration Risk [Member]      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Number of major customers | Customer 3 3  
Revenues, major customers $ 150.0 $ (157.8)  
Concentration risk, percentage 66.00% 84.00%  
Customer Concentration Risk [Member] | Major Customer 1      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Revenues, major customers $ (85.6)    
Concentration risk, percentage 38.00%    
Customer Concentration Risk [Member] | Major Customer 2      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Revenues, major customers $ (37.5)    
Concentration risk, percentage 16.00%    
Customer Concentration Risk [Member] | Major Customer 3      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Revenues, major customers $ (26.9)    
Concentration risk, percentage 12.00%