Major Customers (Details) (USD $) In Thousands, unless otherwise specified			3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 NRG Energy, Inc. (fka GenOn Energy, Inc.) [Member]	Mar. 31, 2012 NRG Energy, Inc. (fka GenOn Energy, Inc.) [Member]	Mar. 31, 2013 Indiana Harbor Coke Company, L.P. [Member]	Mar. 31, 2012 Indiana Harbor Coke Company, L.P. [Member]	Mar. 31, 2012 PPL Corporation [Member]	Mar. 31, 2013 American Electric Power Company, Inc. [Member]
Revenue, Major Customer [Line Items]
Receivable balance	$ 34,221	$ 33,560	$ 4,011		$ 4,891			$ 3,427
Sales			$ 12,431	$ 10,523	$ 7,981	$ 9,328	$ 10,527	$ 9,598