Equity-Based Compensation (Summary Of Outstanding Performance Share Awards / Restricted Stock Units) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Performance shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Unvested shares outstanding at January 1, Shares	154,594
Granted (in shares)	85,028	77,767
Forfeited (in shares)	(2,596)
Unvested shares outstanding at June 30, Shares	237,026
Unvested shares outstanding at January 1, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 50.54
Granted, Weighted Av.g Exercise Price (in dollars per share)	$ 34.24	$ 55.84
Forfeited, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 44.99
Unvested shares outstanding at June 30, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 44.76
Aggregate Intrinsic Value	$ 7,399
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Unvested shares outstanding at January 1, Shares	36,359
Granted (in shares)	18,725
Vested (in shares)	(450)
Forfeited (in shares)	(1,504)
Unvested shares outstanding at June 30, Shares	53,130
Unvested shares outstanding at January 1, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 35.60
Granted, Weighted Av.g Exercise Price (in dollars per share)	$ 31.14
Vested, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 30.17
Forfeited, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 33.36
Unvested shares outstanding at June 30, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 34.14
Aggregate Intrinsic Value	$ 1,697