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	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance vested restricted stock units granted at target	24,678	80,184	117,523
Weighted average grant date fair value (in dollars per share)	$ 45.59	$ 39.48	$ 35.27
Aggregate grant date fair value	$ 1,125	$ 3,165	$ 4,145
Stock units forfeited (in shares)	22,099	3,334	57,176
Requisite service period	36 months
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Requisite service period		22 months	24 months
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Requisite service period		38 months	60 months