Inventories (Inventories) (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Inventory Disclosure [Abstract]
Coal	$ 180,917,000	$ 206,517,000
Repair parts and supplies	172,139,000	163,527,000
Work-in-process	12,368,000	7,446,000
Inventories	365,424,000	377,490,000
Allowance for slow-moving and obsolete inventories	$ 13,600,000	$ 13,100,000