Equity-Based Compensation (Summary Of Outstanding Performance Share Awards / Restricted Stock Units) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
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	184,601	171,595
Granted (in shares)	85,028	77,767	81,162
Vested (in shares)	(76,812)	(103,960)	(57,291)
Forfeited (in shares)	(2,596)	(3,814)	(10,865)
Unvested shares outstanding at December 31, Shares	160,214	154,594	184,601
Unvested shares outstanding at January 1, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 50.54	$ 38.45	$ 40.04
Granted, Weighted Av.g Exercise Price (in dollars per share)	$ 34.24	$ 55.84	$ 45.30
Vested, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 45.30	$ 33.32	$ 52.75
Forfeited, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 44.99	$ 42.77	$ 39.24
Unvested shares outstanding at December 31, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 44.50	$ 50.54	$ 38.45
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value	$ 3,480	$ 3,464	$ 3,022
Aggregate Intrinsic Value	6,019	4,747	5,752
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	41,715	41,559
Granted (in shares)	20,225	18,053	21,559
Vested (in shares)	(14,861)	(21,510)	(16,639)
Forfeited (in shares)	(1,504)	(1,899)	(4,764)
Unvested shares outstanding at December 31, Shares	40,219	36,359	41,715
Unvested shares outstanding at January 1, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 35.60	$ 29.37	$ 32.57
Granted, Weighted Av.g Exercise Price (in dollars per share)	$ 31.53	$ 38.57	$ 33.17
Vested, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 32.41	$ 26.26	$ 42.23
Forfeited, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 33.36	$ 32.78	$ 29.56
Unvested shares outstanding at December 31, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 34.82	$ 35.60	$ 29.37
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value	482	565	703
Aggregate Intrinsic Value	$ 1,575	$ 1,131	$ 1,395