Equity-Based Compensation (Fair Value Of Performance Share Awards) (Details) (Performance shares [Member], USD $)	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Performance shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	85,028	77,767
Stock price as of valuation date (in dollars per share)	$ 31.11	$ 39.10
Risk-free rate	0.40%	1.26%
Fair value of a performance share (in dollars per share)	$ 34.24	$ 55.84