Equity Method Investments - Summary of Income Statement Data for Equity Method Investments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Mars
Schedule of Equity Method Investments [Line Items]
Total revenues	$ 54.0	$ 56.8	$ 175.5	$ 148.7
Total operating expenses	23.1	19.2	62.1	63.0
Operating income	30.9	37.6	113.4	85.7
Net income	30.9	37.6	113.4	85.8
Bengal
Schedule of Equity Method Investments [Line Items]
Total revenues	17.3	18.6	52.3	52.2
Total operating expenses	7.2	7.2	20.7	20.3
Operating income	10.1	11.4	31.6	31.9
Net income	10.3	11.3	31.7	31.8
Poseidon
Schedule of Equity Method Investments [Line Items]
Total revenues	31.3	30.8	90.7	92.7
Total operating expenses	8.2	7.0	22.5	21.6
Operating income	23.1	23.8	68.2	71.1
Net income	$ 22.0	$ 22.9	$ 64.7	$ 67.8