Retirement Plans and Postretirement Medical Benefits (Effect of Change in the Assumed Health Care Cost Trend Rates) (Details) (Nonpension postretirement benefit plans, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Nonpension postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Effect of 1% increase on total of service and interest cost components	$ 548
Effect of 1% decrease on total of service and interest cost components	431
Effect of 1% increase on postretirement benefit obligation	9,512
Effect of 1% decrease on postretirement benefit obligation	$ 8,829