Business Segment Information Business Segment Information - Legacy Costs (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2016	Mar. 31, 2015
Segment Reporting Information [Line Items]
Operating income	$ 9.5	$ 25.5
Other Segments
Segment Reporting Information [Line Items]
Black lung charges	(1.7)	(0.9)
Postretirement benefit plan (expense) benefit	(0.2)	3.9
Defined benefit plan expense	0.0	(0.2)
Workers compensation expense	(0.3)	(0.9)
Operating income	$ (2.2)	$ 1.9

Increase (Decrease) in Estimated Black Lung Liability

No definition available.

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- Definition

The increase (decrease) during the reporting period in the amount due for insurance (or actual expenses) to cover the medical expenses and lost income for employees that are injured during the course of doing work-related activities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585

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- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

+ Details

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- Definition

The amount of costs recognized during the period for non-pension postretirement benefits, such as medical, dental and life insurance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (q)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

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- Definition

The amount of pension benefit costs recognized during the period for (1) defined benefit plans and (2) defined contribution plans. For defined benefit plans, pension expense includes the following components: service cost, interest cost, expected return on plan assets, gain (loss) on plan assets, prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments. For defined contribution plans, the pension expense generally equals the firm's contribution to employees' accounts (if the firm contributes) during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585

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-Paragraph 1
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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