Share-Based Compensation and Capital Stock Summary Of Activity Related To PVRSU Grants (Details) (Performance Vested Restricted Stock Units [Member], USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Performance vested restricted stock units granted at target	58,902	38,476
Weighted average grant date fair value per share	$ 36.76	$ 35.60
Aggregate grant date fair value ($000)	$ 2,165	$ 1,370
Stock units forfeited	0	0
Requisite service period		3 years
Minimum [Member]
Requisite service period	22 months
Maximum [Member]
Requisite service period	36 months