Guarantee of Securities of Subsidiaries Guarantee of Securities of Subsidiaries Statements of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Cash Flows
Net cash provided by (used in) operating activities	$ 166.4	$ 151.9
Investing Activities:
Capital expenditures	(74.0)	(110.9)
Proceeds from sale of operating assets	0.1	0.5
Advances to affiliates, net	0.0	0.0
Net cash provided by (used in) investing activities	(73.9)	(110.4)
Financing Activities:
Proceeds from borrowings on revolving credit agreement	125.0	145.0
Repayment of borrowings on revolving credit agreement	(180.0)	(145.0)
Principal payment of finance lease obligation	(0.2)	(0.1)
Advances from affiliates, net	0.0	0.0
Distributions paid	(25.6)	(25.6)
Net cash (used in) provided by financing activities	(80.8)	(25.7)
(Decrease) increase in cash and cash equivalents	11.7	15.8
Cash and cash equivalents at beginning of period	3.6	17.6
Cash and cash equivalents at end of period	15.3	33.4
Reportable Legal Entities | Parent Guarantor
Statement of Cash Flows
Net cash provided by (used in) operating activities	18.8	14.1
Investing Activities:
Capital expenditures	0.0	0.0
Proceeds from sale of operating assets	0.0	0.0
Advances to affiliates, net	6.6	11.5
Net cash provided by (used in) investing activities	6.6	11.5
Financing Activities:
Proceeds from borrowings on revolving credit agreement	0.0	0.0
Repayment of borrowings on revolving credit agreement	0.0	0.0
Principal payment of finance lease obligation	0.0	0.0
Advances from affiliates, net	0.0	0.0
Distributions paid	(25.6)	(25.6)
Net cash (used in) provided by financing activities	(25.6)	(25.6)
(Decrease) increase in cash and cash equivalents	(0.2)	0.0
Cash and cash equivalents at beginning of period	0.3	0.3
Cash and cash equivalents at end of period	0.1	0.3
Reportable Legal Entities | Subsidiary Issuer
Statement of Cash Flows
Net cash provided by (used in) operating activities	(44.9)	(36.3)
Investing Activities:
Capital expenditures	0.0	0.0
Proceeds from sale of operating assets	0.0	0.0
Advances to affiliates, net	(30.2)	(53.7)
Net cash provided by (used in) investing activities	(30.2)	(53.7)
Financing Activities:
Proceeds from borrowings on revolving credit agreement	0.0	0.0
Repayment of borrowings on revolving credit agreement	0.0	0.0
Principal payment of finance lease obligation	0.0	0.0
Advances from affiliates, net	75.9	104.2
Distributions paid	0.0	0.0
Net cash (used in) provided by financing activities	75.9	104.2
(Decrease) increase in cash and cash equivalents	0.8	14.2
Cash and cash equivalents at beginning of period	1.6	4.6
Cash and cash equivalents at end of period	2.4	18.8
Reportable Legal Entities | Non-Guarantor Subsidiaries
Statement of Cash Flows
Net cash provided by (used in) operating activities	192.5	174.1
Investing Activities:
Capital expenditures	(74.0)	(110.9)
Proceeds from sale of operating assets	0.1	0.5
Advances to affiliates, net	(82.5)	(115.7)
Net cash provided by (used in) investing activities	(156.4)	(226.1)
Financing Activities:
Proceeds from borrowings on revolving credit agreement	125.0	145.0
Repayment of borrowings on revolving credit agreement	(180.0)	(145.0)
Principal payment of finance lease obligation	(0.2)	(0.1)
Advances from affiliates, net	30.2	53.7
Distributions paid	0.0	0.0
Net cash (used in) provided by financing activities	(25.0)	53.6
(Decrease) increase in cash and cash equivalents	11.1	1.6
Cash and cash equivalents at beginning of period	1.7	12.7
Cash and cash equivalents at end of period	12.8	14.3
Eliminations
Statement of Cash Flows
Net cash provided by (used in) operating activities	0.0	0.0
Investing Activities:
Capital expenditures	0.0	0.0
Proceeds from sale of operating assets	0.0	0.0
Advances to affiliates, net	106.1	157.9
Net cash provided by (used in) investing activities	106.1	157.9
Financing Activities:
Proceeds from borrowings on revolving credit agreement	0.0	0.0
Repayment of borrowings on revolving credit agreement	0.0	0.0
Principal payment of finance lease obligation	0.0	0.0
Advances from affiliates, net	(106.1)	(157.9)
Distributions paid	0.0	0.0
Net cash (used in) provided by financing activities	(106.1)	(157.9)
(Decrease) increase in cash and cash equivalents	0.0	0.0
Cash and cash equivalents at beginning of period	0.0	0.0
Cash and cash equivalents at end of period	$ 0.0	$ 0.0