Pension Benefit and Retirement Health and Life Insurance Benefits (Summary of Changes in Fair Value of Guaranteed Deposit Account's Level 3 Assets) (Details) (Pension Benefits [Member], Guaranteed deposit account [Member], Level 3 [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Pension Benefits [Member] | Guaranteed deposit account [Member] | Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of year	$ 13,357
Realized gains (losses)	0
Unrealized gains relating to instruments still held at the reporting date	785
Purchases, sales, issuances and settlements (net)	(2,378)
Transfers in and/or out of Level 3	0
Balance at end of year	$ 11,764