Leases (Narrative) (Details) (USD $)	0 Months Ended	5 Months Ended	7 Months Ended	12 Months Ended
	Jan. 14, 2011	May 25, 2010	Dec. 31, 2010	Dec. 31, 2011	Dec. 31, 2009
Operating Leased Assets [Line Items]
Future annual rent expense				$ 10,297,000
Payment for early buyout option to purchase leased equipment	9,000,000
Operating Leases, Rent Expense		2,400,000	2,700,000	3,200,000	5,500,000
CDM and Caterpillar Financial Services Corporation [Member]
Operating Leased Assets [Line Items]
Future annual rent expense				$ 1,200,000