Supplemental Guarantor/Non-Guarantor Financial Information (Details 2) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Cash Flows From Operating Activities
Net cash (used in) provided by continuing operations		$ 157,100,000	$ 365,900,000
Net cash (used in) provided by discontinued operations		(81,800,000)	(34,500,000)
Net cash (used in) provided by operating activities		75,300,000	331,400,000
Cash Flows From Investing Activities
Additions to property, plant, equipment and mine development		(64,700,000)	(166,500,000)
Changes in accrued expenses related to capital expenditures		(17,500,000)	(102,600,000)
Proceeds from disposal of assets, net of notes receivable		139,200,000	123,900,000
Purchases of debt securities		(4,200,000)	(9,700,000)
Proceeds from sales and maturities of debt securities		5,000,000	17,000,000
Proceeds from the maturity of short-term investments	4,800,000	0	4,800,000
Contributions to joint ventures		(271,300,000)	(323,800,000)
Distributions from joint ventures		269,000,000	372,100,000
Advances to related parties		(12,300,000)	(35,700,000)
Repayments of loans from related parties		2,200,000	18,200,000
Other, net		(2,000,000)	(3,600,000)
Net cash provided by (used in) continuing operations		43,400,000	(105,900,000)
Net cash provided by (used in) discontinued operations		5,000,000	(300,000)
Net cash provided by (used in) investing activities		48,400,000	(106,200,000)
Cash Flows From Financing Activities
Repayments of long-term debt		(10,400,000)	(215,600,000)
Payment of debt issuance costs		(10,100,000)	0
Dividends paid		(46,100,000)	(45,900,000)
Other, net		(2,700,000)	(4,600,000)
Transactions with affiliates, net		0	0
Net cash provided by (used in) financing activities		(69,300,000)	(266,100,000)
Net change in cash and cash equivalents		54,400,000	(40,900,000)
Cash and cash equivalents at beginning of period		444,000,000	558,800,000
Cash and cash equivalents at end of period	517,900,000	498,400,000	517,900,000
Parent Company [Member]
Cash Flows From Operating Activities
Net cash (used in) provided by continuing operations		(112,400,000)	114,500,000
Net cash (used in) provided by discontinued operations		(72,900,000)	(8,100,000)
Net cash (used in) provided by operating activities		(185,300,000)	106,400,000
Cash Flows From Investing Activities
Additions to property, plant, equipment and mine development		0	0
Changes in accrued expenses related to capital expenditures		0	0
Proceeds from disposal of assets, net of notes receivable		0	0
Purchases of debt securities		0	0
Proceeds from sales and maturities of debt securities		0	0
Proceeds from the maturity of short-term investments			0
Contributions to joint ventures		0	0
Distributions from joint ventures		0	0
Advances to related parties		0	0
Repayments of loans from related parties		0	0
Other, net		0	0
Net cash provided by (used in) continuing operations		0	0
Net cash provided by (used in) discontinued operations		0	0
Net cash provided by (used in) investing activities		0	0
Cash Flows From Financing Activities
Repayments of long-term debt		(6,000,000)	(167,000,000)
Payment of debt issuance costs		(10,100,000)
Dividends paid		(46,100,000)	(45,900,000)
Other, net		1,000,000	900,000
Transactions with affiliates, net		269,400,000	169,800,000
Net cash provided by (used in) financing activities		208,200,000	(42,200,000)
Net change in cash and cash equivalents		22,900,000	64,200,000
Cash and cash equivalents at beginning of period		300,700,000	269,600,000
Cash and cash equivalents at end of period	333,800,000	323,600,000	333,800,000
Guarantor Subsidiaries [Member]
Cash Flows From Operating Activities
Net cash (used in) provided by continuing operations		330,300,000	496,500,000
Net cash (used in) provided by discontinued operations		(1,400,000)	500,000
Net cash (used in) provided by operating activities		328,900,000	497,000,000
Cash Flows From Investing Activities
Additions to property, plant, equipment and mine development		(32,100,000)	(45,100,000)
Changes in accrued expenses related to capital expenditures		(1,300,000)	(2,400,000)
Proceeds from disposal of assets, net of notes receivable		50,900,000	42,100,000
Purchases of debt securities		0	0
Proceeds from sales and maturities of debt securities		0	0
Proceeds from the maturity of short-term investments			0
Contributions to joint ventures		0	0
Distributions from joint ventures		0	0
Advances to related parties		0	0
Repayments of loans from related parties		0	0
Other, net		(1,700,000)	(3,400,000)
Net cash provided by (used in) continuing operations		15,800,000	(8,800,000)
Net cash provided by (used in) discontinued operations		0	0
Net cash provided by (used in) investing activities		15,800,000	(8,800,000)
Cash Flows From Financing Activities
Repayments of long-term debt		0	(100,000)
Payment of debt issuance costs		0
Dividends paid		0	0
Other, net		(1,700,000)	(5,200,000)
Transactions with affiliates, net		(343,100,000)	(483,000,000)
Net cash provided by (used in) financing activities		(344,800,000)	(488,300,000)
Net change in cash and cash equivalents		(100,000)	(100,000)
Cash and cash equivalents at beginning of period		300,000	300,000
Cash and cash equivalents at end of period	200,000	200,000	200,000
Non-Guarantor Subsidiaries [Member]
Cash Flows From Operating Activities
Net cash (used in) provided by continuing operations		(60,800,000)	(245,100,000)
Net cash (used in) provided by discontinued operations		(7,500,000)	(26,900,000)
Net cash (used in) provided by operating activities		(68,300,000)	(272,000,000)
Cash Flows From Investing Activities
Additions to property, plant, equipment and mine development		(32,600,000)	(121,400,000)
Changes in accrued expenses related to capital expenditures		(16,200,000)	(100,200,000)
Proceeds from disposal of assets, net of notes receivable		88,300,000	81,800,000
Purchases of debt securities		(4,200,000)	(9,700,000)
Proceeds from sales and maturities of debt securities		5,000,000	17,000,000
Proceeds from the maturity of short-term investments			4,800,000
Contributions to joint ventures		(271,300,000)	(323,800,000)
Distributions from joint ventures		269,000,000	372,100,000
Advances to related parties		(12,300,000)	(35,700,000)
Repayments of loans from related parties		2,200,000	18,200,000
Other, net		(300,000)	(200,000)
Net cash provided by (used in) continuing operations		27,600,000	(97,100,000)
Net cash provided by (used in) discontinued operations		5,000,000	(300,000)
Net cash provided by (used in) investing activities		32,600,000	(97,400,000)
Cash Flows From Financing Activities
Repayments of long-term debt		(4,400,000)	(48,500,000)
Payment of debt issuance costs		0
Dividends paid		0	0
Other, net		(2,000,000)	(300,000)
Transactions with affiliates, net		73,700,000	313,200,000
Net cash provided by (used in) financing activities		67,300,000	264,400,000
Net change in cash and cash equivalents		31,600,000	(105,000,000)
Cash and cash equivalents at beginning of period		143,000,000	288,900,000
Cash and cash equivalents at end of period	$ 183,900,000	$ 174,600,000	$ 183,900,000