Accounts Receivable and Revenues from Contracts with Customers - Additional Information (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($) Customer	Mar. 31, 2018 USD ($) Customer	Dec. 31, 2018 USD ($)
Sales Revenue | Customer Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of major customers | Customer	3	3
Revenues, major customers	$ 69.0	$ (70.6)
Concentration risk, percentage	66.00%	91.00%
Sales Revenue | Customer Concentration Risk [Member] | Major Customer 1
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	$ (39.9)
Concentration risk, percentage	38.00%
Sales Revenue | Customer Concentration Risk [Member] | Major Customer 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	$ (14.5)
Concentration risk, percentage	14.00%
Sales Revenue | Customer Concentration Risk [Member] | Major Customer 3
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues, major customers	$ (14.6)
Concentration risk, percentage	14.00%
Accounts Receivable | Credit Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk, percentage	70.00%		59.00%
Accounts receivable, major customers	$ 42.9		$ 34.8