Fair Value Measurements - Inputs (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Fair Value Disclosures [Abstract]
Rate reflecting our nonperformance risk	1.75%	1.75%
Weighted-average rate reflecting our counterparties' nonperformance risk	0.89%	3.38%