Share-Based Compensation (Schedule Of Share-Based Compensation Activity Other Than Stock Option) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Service Award Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted during the period		18,434
Weighted average grant date fair value per share granted during the period		$ 42.72
Fair value of shares vested during the period	$ 448	$ 683
Performance Award Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted during the period	34,229	22,511
Weighted average grant date fair value per share granted during the period	$ 33.87	$ 44.44
Fair value of shares vested during the period	522	389
Board DSUs And Dividend Equivalents Granted To Board [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted during the period	1,286	1,420
Weighted average grant date fair value per share granted during the period	$ 36.74	$ 39.43
Fair value of shares vested during the period	102	116
Chief Executive Officer [Member] | DSU Service Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted during the period	1,283	900
Weighted average grant date fair value per share granted during the period	$ 34.03	$ 44.44
Fair value of shares vested during the period	572	704
Chief Executive Officer [Member] | DSU Performance Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted during the period	59,049	24,122
Weighted average grant date fair value per share granted during the period	$ 33.87	$ 44.44
Fair value of shares vested during the period	$ 396	$ 227