Accounts Receivable and Revenues from Contracts with Customers - Additional Information (Details) - Accounts Receivable $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) Customer	Sep. 30, 2018 USD ($) Customer	Dec. 31, 2018 USD ($)
Credit Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk, percentage	60.00%		63.00%
Accounts receivable, major customers	$ 32.9		$ 37.3
Customer Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of major customers | Customer	4	3
Revenues, major customers	$ 261.4	$ (254.5)
Concentration risk, percentage	76.00%	81.00%
Customer Concentration Risk [Member] | Major Customer 1
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	$ (127.1)
Concentration risk, percentage	37.00%
Customer Concentration Risk [Member] | Major Customer 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	$ (62.4)
Concentration risk, percentage	18.00%
Customer Concentration Risk [Member] | Major Customer 3
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	$ (37.3)
Concentration risk, percentage	11.00%
Customer Concentration Risk [Member] | Major Customer Four [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	$ (34.6)
Concentration risk, percentage	10.00%