Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data in Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Property, equipment and mine development costs, accumulated depreciation and amortization	$ 2,242,382	$ 1,910,058
Owned and leased mineral rights, accumulated depletion (in dollars)	1,100,281	908,416
Other acquired intangibles, accumulated amortization (in dollars)	$ 404,597	$ 655,047
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	400.0	400.0
Common stock, shares issued	232.8	232.2
Common stock, shares outstanding	220.9	220.6
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10.0	10.0
Preferred stock, shares issued	0	0
Treasury stock, at cost	11.9	11.6