Receivables (Details) (USD $)	12 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2011 Allowance for Doubtful Accounts, Current [Member]	Dec. 31, 2010 Allowance for Doubtful Accounts, Current [Member]	Dec. 31, 2012 Accounts receivable [Member]	Dec. 31, 2011 Accounts receivable [Member]	Dec. 31, 2012 Notes receivable [Member]	Dec. 31, 2011 Notes receivable [Member]	Dec. 31, 2012 Other receivables [Member]	Dec. 31, 2011 Other receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross receivables	$ 254,036,000	$ 216,732,000			$ 252,413,000	$ 214,608,000	$ 0	$ 16,000	$ 1,623,000	$ 2,108,000
Allowance for doubtful accounts receivable	(767,000)	(125,000)
Net receivables	253,269,000	216,607,000
Bad debt expense	100,000
Valuation and Qualifying Accounts Disclosure [Line Items]
Collections on previous bad debts			$ 100,000	$ 100,000