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, 2011	Dec. 31, 2010	Dec. 31, 2009
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	184,601	171,595	131,108
Granted (in shares)	77,767	81,162	112,269
Vested (in shares)	(103,960)	(57,291)	(71,719)
Forfeited (in shares)	(3,814)	(10,865)	(63)
Unvested shares outstanding at September 30, Shares	154,594	184,601	171,595
Unvested shares outstanding at January 1, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 38.45	$ 40.04	$ 50.51
Granted, Weighted Av.g Exercise Price (in dollars per share)	$ 55.84	$ 45.30	$ 33.32
Vested, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 33.32	$ 52.75	$ 48.66
Forfeited, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 42.77	$ 39.24	$ 47.90
Unvested shares outstanding at September 30, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 50.54	$ 38.45	$ 40.04
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value	$ 3,464	$ 3,022	$ 3,490
Aggregate Intrinsic Value	4,747	5,752	4,890
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	41,715	41,559	39,711
Granted (in shares)	18,053	21,559	21,720
Vested (in shares)	(21,510)	(16,639)	(19,872)
Forfeited (in shares)	(1,899)	(4,764)	0
Unvested shares outstanding at September 30, Shares	36,359	41,715	41,559
Unvested shares outstanding at January 1, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 29.37	$ 32.57	$ 45.38
Granted, Weighted Av.g Exercise Price (in dollars per share)	$ 38.57	$ 33.17	$ 24.34
Vested, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 26.26	$ 42.23	$ 49.18
Forfeited, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 32.78	$ 29.56	$ 0.00
Unvested shares outstanding at September 30, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 35.60	$ 29.37	$ 32.57
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value	565	703	977
Aggregate Intrinsic Value	$ 1,131	$ 1,395	$ 1,325