Retirement Plans and Postretirement Medical Benefits (Level 3 Gains and Losses) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at	$ 158,021	$ 158,164
Realized (losses) gains	11,471	348
Unrealized gains	8,085	7,577
Net purchases, sales and settlements	(19,482)	(8,068)
Balance at	158,095	158,021
Mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at	2,634	3,191
Realized (losses) gains	12	0
Unrealized gains	59	205
Net purchases, sales and settlements	(603)	(762)
Balance at	2,102	2,634
Private equity
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at	87,470	91,805
Realized (losses) gains	11,174	(1,591)
Unrealized gains	1,886	2,190
Net purchases, sales and settlements	(19,284)	(4,934)
Balance at	81,246	87,470
Real estate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at	67,917	63,168
Realized (losses) gains	285	1,939
Unrealized gains	6,140	5,182
Net purchases, sales and settlements	405	(2,372)
Balance at	$ 74,747	$ 67,917