Equity-Based Compensation (Summary Of Outstanding Performance Share Awards / Restricted Stock Units) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Performance shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested shares outstanding at January 1, Shares	160,214
Granted (in shares)	83,111	85,028
Forfeited (in shares)	(5,407)
Unvested shares outstanding at March 31, Shares	237,918
Unvested shares outstanding at January 1, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 44.50
Granted, Weighted Av.g Exercise Price (in dollars per share)	$ 62.78	$ 34.24
Forfeited, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 41.02
Unvested shares outstanding at March 31, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 50.96
Aggregate Intrinsic Value	$ 10,521
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested shares outstanding at January 1, Shares	40,219
Granted (in shares)	14,949
Vested (in shares)	(2,650)
Forfeited (in shares)	(1,802)
Unvested shares outstanding at March 31, Shares	50,716
Unvested shares outstanding at January 1, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 34.82
Granted, Weighted Av.g Exercise Price (in dollars per share)	$ 45.42
Vested, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 36.22
Forfeited, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 33.62
Unvested shares outstanding at March 31, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 37.91
Aggregate Intrinsic Value	$ 2,326