Transactions with Major Customers and Concentration of Credit Risk - Schedule of Revenues from Third Party Customers (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Concentration Risk [Line Items]
Total revenue	$ 142.3	$ 153.5	$ 129.3	$ 99.6	$ 126.8	$ 121.8	$ 112.4	$ 109.1	$ 524.7	$ 470.1	$ 452.9
Customer C
Concentration Risk [Line Items]
Total revenue									$ 64.5	$ 70.3	$ 72.9