Retirement Plans and Postretirement Medical Benefits (Fair Value Measurements of Plan Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	$ 747,177	$ 748,738
Cash	764,522	640,190	$ 1,043,439	$ 880,738
Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	232,829	143,450
Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	514,348	605,288
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	1,622,945	1,604,430
Securities lending payable	(174,651)	(154,690)
Cash	18,164	4,072
Other	(2,376)	6,978
Fair value of plan assets available for benefits	1,464,082	1,460,790	1,593,463
United States | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	400,926	318,113
United States | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	1,083,294	1,138,579
United States | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	138,725	147,738
United States | Money market funds
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	9,213	7,493
United States | Money market funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	2,604	0
United States | Money market funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	6,609	7,493
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	324,945	314,934
United States | Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	184,254	174,664
United States | Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	140,691	140,270
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	358,776	205,246
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	358,776	205,246
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	235,194	164,873
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	214,068	143,449
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	21,126	21,424
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	367,369	592,111
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	367,369	592,111
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	13,872	16,402
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	12,636	14,810
United States | Mortgage-backed securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	1,236	1,592
United States | Asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	1,436	2,535
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	1,436	2,535
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	49,637	63,577
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	49,637	63,577
United States | Real estate
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	87,852	82,569
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	87,852	82,569
United States | Securities lending collateral
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	174,651	154,690
United States | Securities lending collateral | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0	0
United States | Securities lending collateral | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	174,651	154,690
United States | Securities lending collateral | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0	0
Foreign
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	541,463	523,323
Cash	4,262	6,376
Other	1,565	413
Fair value of plan assets available for benefits	547,290	530,112	$ 574,992
Foreign | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	32,295	33,855
Foreign | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	437,906	429,778
Foreign | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	71,262	59,690
Foreign | Money market funds
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	6,811	7,596
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	6,811	7,596
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	214,238	216,965
Foreign | Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	32,295	33,855
Foreign | Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	181,943	183,110
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	69,022	138,220
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	69,022	138,220
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	29,363	73,573
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	29,363	73,573
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	150,767	27,279
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	150,767	27,279
Foreign | Debt securities - corporate | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0	0
Foreign | Real estate
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	34,483	39,177
Foreign | Real estate | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0	0
Foreign | Real estate | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0	0
Foreign | Real estate | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	34,483	39,177
Foreign | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0	20,513
Foreign | Derivatives | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0	0
Foreign | Derivatives | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0	0
Foreign | Derivatives | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0	$ 20,513
Foreign | Diversified growth funds
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	36,779
Foreign | Diversified growth funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0
Foreign | Diversified growth funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	0
Foreign | Diversified growth funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	$ 36,779