Related Party Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Aug. 12, 2015	Jan. 13, 2015	May. 09, 2014	May. 08, 2014
Related Party Transaction [Line Items]
Interest in partnership (as a percent)	53.90%			53.40%	56.10%	54.10%	55.90%
Revenues	$ 1,362.7	$ 1,503.8	$ 1,647.7
Coal Logistics | Affiliated Entity | The Cline Group
Related Party Transaction [Line Items]
Revenues	22.0
Accounts receivable	$ 7.2
Coal Logistics | Affiliated Entity | The Cline Group | Sales Revenue, Net
Related Party Transaction [Line Items]
Sales to customers (as a percent)	1.60%
The Cline Group | Coal Logistics | Affiliated Entity
Related Party Transaction [Line Items]
Interest in partnership (as a percent)	10.30%