Unaudited Quarterly Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Unaudited Quarterly Data [Line Items]
Revenues									$ 3,278,420	$ 3,157,796	$ 3,094,018
Gross Profit									2,118,109	2,184,363	2,153,493
Operating profit									(1,007,888)	193,462	247,009
Net earnings									$ (866,628)	$ 96,422	$ 128,757
Basic earnings per common share									$ (16.34)	$ 1.82	$ 2.35
Diluted earnings per common share									(16.34)	1.81	2.33
Cash dividends declared per common share									$ 0.96	$ 0.93	$ 0.86
First Quarter [Member]
Unaudited Quarterly Data [Line Items]
Revenues				$ 877,639				$ 828,473
Gross Profit				564,593				562,550
Operating profit				56,598				59,458
Net earnings				$ 27,298				$ 27,266
Basic earnings per common share				$ 0.51				$ 0.52
Diluted earnings per common share				0.51				0.51
Cash dividends declared per common share				$ 0.24				$ 0.23
Second Quarter [Member]
Unaudited Quarterly Data [Line Items]
Revenues			$ 815,343				$ 768,426
Gross Profit			538,529				537,024
Operating profit			49,701				40,390
Net earnings			$ 23,147				$ 17,681
Basic earnings per common share			$ 0.44				$ 0.33
Diluted earnings per common share			0.43				0.33
Cash dividends declared per common share			$ 0.24				$ 0.23
Third Quarter [Member]
Unaudited Quarterly Data [Line Items]
Revenues		$ 791,605				$ 764,363
Gross Profit		488,612				539,758
Operating profit		6,565				45,920
Net earnings		$ (4,092)				$ 25,925
Basic earnings per common share		$ (0.08)				$ 0.49
Diluted earnings per common share		(0.08)				0.49
Cash dividends declared per common share		$ 0.24				$ 0.23
Fourth Quarter [Member]
Unaudited Quarterly Data [Line Items]
Revenues	$ 793,833				$ 796,534
Gross Profit	526,375				545,031
Operating profit	(1,120,752)				47,694
Net earnings	$ (912,981)				$ 25,550
Basic earnings per common share	$ (17.20)				$ 0.48
Diluted earnings per common share	(17.20)				0.48
Cash dividends declared per common share	$ 0.24				$ 0.24