Notes Receivable and Allowance for Doubtful Accounts - Allowance for Credit Losses on Notes Receivable (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2010
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of period	$ 1,054	$ 1,047	$ 1,054	$ 1,047	$ 1,054	$ 0	$ 1,047	$ 1,047
Provision for credit losses	0	0	1,054	0
Balance, end of period	$ 1,054	$ 1,047	$ 1,054	$ 1,047	$ 1,054	$ 0	$ 1,047	$ 1,047