Investments - Summary of Selected Financial Information for Epic Gas (Details) - Epic Gas - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Schedule of Equity Method Investments [Line Items]
Total assets				$ 599.2	$ 579.0
Total liabilities				340.2	315.0
Total equity				259.0	264.0
Net earnings (loss)	$ (15.9)	$ (11.4)	$ (16.1)	$ (14.5)	$ (7.4)	$ (4.6)