Retirement Plans and Postretirement Medical Benefits (Fair Value Measurements of Plan Assets) (Details) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		$ 738,371	$ 1,114,543
Cash		650,557	1,054,118	$ 886,788	$ 901,843
Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		143,450	619,617
Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		594,921	494,926
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		1,604,430	1,719,936
Securities lending payable	[1]	(154,690)	(131,901)
Cash		4,072	4,621
Other		6,978	807
Fair value of plan assets available for benefits		1,460,790	1,593,463	1,523,679
United States | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		318,113	364,278
United States | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		1,138,579	1,197,563
United States | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		147,738	158,095
United States | Money market funds
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		7,493	10,758
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		7,493	10,758
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		314,934	326,785
United States | Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		174,664	180,069
United States | Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		140,270	146,716
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		205,246	261,571
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		205,246	261,571
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		164,873	209,340
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		143,449	184,209
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		21,424	25,131
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		592,111	598,927
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		592,111	598,927
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		16,402	22,503
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		14,810	20,401
United States | Mortgage-backed securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		1,592	2,102
United States | Asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		2,535	2,158
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		2,535	2,158
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		63,577	81,246
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		63,577	81,246
United States | Real estate
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		82,569	74,747
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		82,569	74,747
United States | Securities lending collateral
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	[1]	154,690	131,901
United States | Securities lending collateral | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	[1]	0	0
United States | Securities lending collateral | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	[1]	154,690	131,901
United States | Securities lending collateral | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value	[1]	0	0
Foreign
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		523,323	560,060
Cash		6,376	10,859
Other		413	4,073
Fair value of plan assets available for benefits		530,112	574,992	$ 561,078
Foreign | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		33,855	99,570
Foreign | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		429,778	460,490
Foreign | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		59,690	0
Foreign | Money market funds
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		7,596	6,684
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		7,596	6,684
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		216,965	290,494
Foreign | Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		33,855	99,570
Foreign | Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		183,110	190,924
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		138,220	151,017
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		138,220	151,017
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		73,573	85,711
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		73,573	85,711
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		27,279	26,154
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		27,279	26,154
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		39,177
Foreign | Real estate | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		0
Foreign | Real estate | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		0
Foreign | Real estate | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		39,177
Foreign | Diversified growth funds
Defined Benefit Plan Disclosure [Line Items]
Total plan assets at fair value		20,513
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		$ 20,513

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