Retirement Plans and Postretirement Medical Benefits (Fair Value Measurements of Plan Assets) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	$ 1,114,543		$ 1,024,033
Cash	1,079,145		907,806		913,276	856,238
Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	619,617		526,489
Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	494,926		497,544
Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
United States
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	1,719,936		1,524,759
Securities lending payable	(131,901)	[1]	(6,602)	[1]
Cash	4,621		634
Other	807		4,888
Fair value of plan assets available for benefits	1,593,463		1,523,679		1,583,932
United States | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	364,278		323,378
United States | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	1,197,563		1,043,360
United States | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	158,095		158,021
United States | Money market funds
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	10,758		30,374
United States | Money market funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
United States | Money market funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	10,758		30,374
United States | Money market funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
United States | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	326,785		445,291
United States | Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	180,069		279,988
United States | Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	146,716		165,303
United States | Equity securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
United States | Commingled fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	261,571		209,674
United States | Commingled fixed income securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
United States | Commingled fixed income securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	261,571		209,674
United States | Commingled fixed income securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
United States | Debt securities - U.S. and foreign governments, agencies and municipalities
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	209,340		73,867
United States | Debt securities - U.S. and foreign governments, agencies and municipalities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	184,209		43,390
United States | Debt securities - U.S. and foreign governments, agencies and municipalities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	25,131		30,477
United States | Debt securities - U.S. and foreign governments, agencies and municipalities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
United States | Debt securities - corporate
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	598,927		568,567
United States | Debt securities - corporate | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
United States | Debt securities - corporate | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	598,927		568,567
United States | Debt securities - corporate | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
United States | Mortgage-backed securities
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	22,503		34,372
United States | Mortgage-backed securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
United States | Mortgage-backed securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	20,401		31,738
United States | Mortgage-backed securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	2,102		2,634
United States | Asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	2,158		625
United States | Asset-backed securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
United States | Asset-backed securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	2,158		625
United States | Asset-backed securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
United States | Private equity
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	81,246		87,470
United States | Private equity | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
United States | Private equity | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
United States | Private equity | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	81,246		87,470
United States | Real estate
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	74,747		67,917
United States | Real estate | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
United States | Real estate | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
United States | Real estate | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	74,747		67,917
United States | Securities lending collateral
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	131,901	[1]	6,602	[1]
United States | Securities lending collateral | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0	[1]	0	[1]
United States | Securities lending collateral | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	131,901	[1]	6,602	[1]
United States | Securities lending collateral | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0	[1]	0	[1]
Foreign
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	560,060		554,725
Cash	10,859		5,285
Other	4,073		1,068
Fair value of plan assets available for benefits	574,992		561,078		509,331
Foreign | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	99,570		109,403
Foreign | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	460,490		445,322
Foreign | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
Foreign | Money market funds
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	6,684		6,058
Foreign | Money market funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
Foreign | Money market funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	6,684		6,058
Foreign | Money market funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
Foreign | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	290,494		366,449
Foreign | Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	99,570		109,403
Foreign | Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	190,924		257,046
Foreign | Equity securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
Foreign | Commingled fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	151,017		104,070
Foreign | Commingled fixed income securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
Foreign | Commingled fixed income securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	151,017		104,070
Foreign | Commingled fixed income securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
Foreign | Debt securities - U.S. and foreign governments, agencies and municipalities
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	85,711		60,204
Foreign | Debt securities - U.S. and foreign governments, agencies and municipalities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
Foreign | Debt securities - U.S. and foreign governments, agencies and municipalities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	85,711		60,204
Foreign | Debt securities - U.S. and foreign governments, agencies and municipalities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
Foreign | Debt securities - corporate
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	26,154		17,944
Foreign | Debt securities - corporate | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0		0
Foreign | Debt securities - corporate | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	26,154		17,944
Foreign | Debt securities - corporate | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	$ 0		$ 0

[1] Securities lending collateral is offset by a corresponding securities lending payable amount.