Share-Based Compensation and Capital Stock Summary Of Activity Related To Restricted Stock Grants (Details) (Restricted Stock [Member], USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Granted - shares	194,541	238,019
Weighted average grant date fair value per share	$ 36.76	$ 35.70
Aggregate grant date fair value ($000)	$ 7,151	$ 8,497
Restricted shares forfeited	21,499	4,328
Grant date fair value of shares vested ($000)	$ 6,999	$ 5,013
Minimum [Member]
Vesting service period of shares granted	3 years	36 months
Maximum [Member]
Vesting service period of shares granted	4 years	68 months