Stock-Based Compensation (Details 5) (Restricted Stock Units [Member], USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Dec. 31, 2010
Restricted Stock Units [Member]
Schedule of Information Regarding Restricted Stock Units Outstanding
RSUs outstanding, Number of Shares	676,755	407,765	417,923
RSUs outstanding, Weighted Average Remaining Contractual Life (years)	1 year 2 months 27 days	11 months 12 days
RSUs outstanding, Aggregate Intrinsic Value	$ 3.7	$ 2.1
RSUs outstanding, Fair Value	3.7	2.1
RSUs vested and expected to vest using estimated forfeiture rates, Number of Shares	551,319	336,454
RSUs vested and expected to vest, using estimated forfeiture rates, Weighted Average Remaining Contractual Life (years)	1 year 2 months 16 days	11 months 1 day
RSUs vested and expected to vest, using estimated forfeiture rates, Aggregate Intrinsic Value	$ 3.0	$ 1.7