Segment Information Analysis of Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2010
Segment Reporting Information [Line Items]
Sales and other operating revenues	$ 780,784	$ 493,888	$ 514,531	$ 361,564	$ 521,713	$ 522,144	$ 559,249	$ 490,956	$ 2,150,767	$ 2,094,062	$ 2,308,299
Operating income									154,813	132,874	223,814
Debt retirement expense									0	4,584	40,353
Interest expense									106,804	102,696	113,819
Interest income									6,149	7,255	4,550
Income before income taxes and other items									54,158	32,849	74,192
Segment assets	1,949,845				1,808,330				1,949,845	1,808,330	1,911,199
Trade and other receivables, net	303,090				279,904				303,090	279,904	207,387
Goodwill	2,794				2,794				2,794	2,794	2,794
Depreciation and amortization									33,143	28,216	29,113
Capital expenditures									42,347	70,608	17,452
South America [Member]
Segment Reporting Information [Line Items]
Sales and other operating revenues									622,923	714,371	828,572
Operating income									47,630	62,577	84,191
Segment assets	534,169				690,428				534,169	690,428	806,088
Trade and other receivables, net	57,223				72,926				57,223	72,926	41,920
Depreciation and amortization									11,242	8,933	9,206
Capital expenditures									15,655	49,289	6,380
Other Regions [Member]
Segment Reporting Information [Line Items]
Sales and other operating revenues									1,527,844	1,379,691	1,479,727
Operating income									107,183	70,297	139,623
Segment assets	1,415,676				1,117,902				1,415,676	1,117,902	1,105,111
Trade and other receivables, net	245,867				206,978				245,867	206,978	165,467
Goodwill	2,794				2,794				2,794	2,794	2,794
Equity in net assets of investee companies:	23,346				24,753				23,346	24,753	22,290
Depreciation and amortization									21,901	19,283	19,907
Capital expenditures									$ 26,692	$ 21,319	$ 11,072