Partnership Initial Public Offering and Dropdown Transactions - Initial Public Offering (Details) - USD ($) $ in Millions					12 Months Ended
	Aug. 12, 2015	Jan. 13, 2015	May. 09, 2014	Jan. 23, 2013	Dec. 31, 2015	Dec. 31, 2012	May. 08, 2014	Jan. 24, 2013
Class of Stock [Line Items]
Ownership interest of general partnership (as a percent)					2.00%
Interest in partnership (as a percent)	53.40%	56.10%	54.10%		53.90%		55.90%
Ownership percentage held by public unitholders	44.60%	41.90%	43.90%		44.10%
IPO
Class of Stock [Line Items]
Proceeds from issuance of stock, net				$ 231.8
Offering costs				$ 24.7		$ 6.0
IPO | Public
Class of Stock [Line Items]
Stock issued (in shares)				13,500,000
Ownership percentage held by public unitholders				42.10%
IPO | General Partner
Class of Stock [Line Items]
Ownership interest of general partnership (as a percent)				2.00%
IPO | Haverhill Coke Company LLC and Middletown Coke Company LLC
Class of Stock [Line Items]
Funds retained fro environmental remediation project				$ 67.0
Interest in partnership (as a percent)								65.00%
IPO | Haverhill
Class of Stock [Line Items]
Sales discounts related to tax credits				$ 12.4